Co-reporter:Yi Yu, Dandan Zhang, and Peidong Yang
Nano Letters September 13, 2017 Volume 17(Issue 9) pp:5489-5489
Publication Date(Web):August 10, 2017
DOI:10.1021/acs.nanolett.7b02146
A Ruddlesden–Popper (RP) type structure is well-known in oxide perovskites and is related to many interesting properties such as superconductivity and ferroelectricity. However, the RP phase has not yet been discovered in inorganic halide perovskites. Here, we report the direct observation of unusual structure in two-dimensional CsPbBr3 nanosheets which could be interpreted as the RP phase based on model simulations. Structural details of the plausible RP domains and domain boundaries between the RP and conventional perovskite phases have been revealed on the atomic level using aberration-corrected scanning transmission electron microscopy. The finding marks a major advance toward future inorganic halide RP phase synthesis and theoretical modeling, as well as unraveling their structure–property relationship.Keywords: aberration-corrected scanning transmission electron microscopy; domain; inorganic halide perovskite; Ruddlesden−Popper phase; two-dimensional;
Co-reporter:Zhiqiang Niu, Fan Cui, Yi Yu, Nigel Becknell, Yuchun Sun, Garo Khanarian, Dohyung Kim, Letian Dou, Ahmad Dehestani, Kerstin Schierle-Arndt, and Peidong Yang
Journal of the American Chemical Society May 31, 2017 Volume 139(Issue 21) pp:7348-7348
Publication Date(Web):May 8, 2017
DOI:10.1021/jacs.7b02884
Copper nanowire networks are considered a promising alternative to indium tin oxide as transparent conductors. The fast degradation of copper in ambient conditions, however, largely overshadows their practical applications. Here, we develop the synthesis of ultrathin Cu@Au core–shell nanowires using trioctylphosphine as a strong binding ligand to prevent galvanic replacement reactions. The epitaxial overgrowth of a gold shell with a few atomic layers on the surface of copper nanowires can greatly enhance their resistance to heat (80 °C), humidity (80%) and air for at least 700 h, while their optical and electrical performance remained similar to the original high-performance copper (e.g., sheet resistance 35 Ω sq–1 at transmittance of ∼89% with a haze factor <3%). The precise engineering of core–shell nanostructures demonstrated in this study offers huge potential to further explore the applications of copper nanowires in flexible and stretchable electronic and optoelectronic devices.
Co-reporter:Fan Cui, Letian Dou, Qin Yang, Yi Yu, Zhiqiang Niu, Yuchun Sun, Hao Liu, Ahmad Dehestani, Kerstin Schierle-Arndt, and Peidong Yang
Journal of the American Chemical Society March 1, 2017 Volume 139(Issue 8) pp:3027-3027
Publication Date(Web):January 31, 2017
DOI:10.1021/jacs.6b11900
In this work, we report a new, general synthetic approach that uses heat driven benzoin radicals to grow ultrathin copper nanowires with tunable diameters. This is the first time carbon organic radicals have been used as a reducing agent in metal nanowire synthesis. In-situ temperature dependent electron paramagnetic resonance (EPR) spectroscopic studies show that the active reducing agent is the free radicals produced by benzoins under elevated temperature. Furthermore, the reducing power of benzoin can be readily tuned by symmetrically decorating functional groups on the two benzene rings. When the aromatic rings are modified with electron donating (withdrawing) groups, the reducing power is promoted (suppressed). The controllable reactivity gives the carbon organic radical great potential as a versatile reducing agent that can be generalized in other metallic nanowire syntheses.
Co-reporter:Dohyung Kim, Chenlu Xie, Nigel Becknell, Yi Yu, Mohammadreza Karamad, Karen Chan, Ethan J. Crumlin, Jens K. Nørskov, and Peidong Yang
Journal of the American Chemical Society June 21, 2017 Volume 139(Issue 24) pp:8329-8329
Publication Date(Web):May 29, 2017
DOI:10.1021/jacs.7b03516
Precise control of elemental configurations within multimetallic nanoparticles (NPs) could enable access to functional nanomaterials with significant performance benefits. This can be achieved down to the atomic level by the disorder-to-order transformation of individual NPs. Here, by systematically controlling the ordering degree, we show that the atomic ordering transformation, applied to AuCu NPs, activates them to perform as selective electrocatalysts for CO2 reduction. In contrast to the disordered alloy NP, which is catalytically active for hydrogen evolution, ordered AuCu NPs selectively converted CO2 to CO at faradaic efficiency reaching 80%. CO formation could be achieved with a reduction in overpotential of ∼200 mV, and catalytic turnover was enhanced by 3.2-fold. In comparison to those obtained with a pure gold catalyst, mass activities could be improved as well. Atomic-level structural investigations revealed three atomic gold layers over the intermetallic core to be sufficient for enhanced catalytic behavior, which is further supported by DFT analysis.
Co-reporter:Chenlu Xie, Chen Chen, Yi Yu, Ji Su, Yifan Li, Gabor A. Somorjai, and Peidong Yang
Nano Letters June 14, 2017 Volume 17(Issue 6) pp:3798-3798
Publication Date(Web):May 11, 2017
DOI:10.1021/acs.nanolett.7b01139
Conversion of carbon dioxide to C2–C4 hydrocarbons is a major pursuit in clean energy research. Despite tremendous efforts, the lack of well-defined catalysts in which the spatial arrangement of interfaces is precisely controlled hinders the development of more efficient catalysts and in-depth understanding of reaction mechanisms. Herein, we utilized the strategy of tandem catalysis to develop a well-defined nanostructured catalyst CeO2–Pt@mSiO2–Co for converting CO2 to C2–C4 hydrocarbons using two metal-oxide interfaces. C2–C4 hydrocarbons are found to be produced with high (60%) selectivity, which is speculated to be the result of the two-step tandem process uniquely allowed by this catalyst. Namely, the Pt/CeO2 interface converts CO2 and H2 to CO, and on the neighboring Co/mSiO2 interface yields C2–C4 hydrocarbons through a subsequent Fischer–Tropsch process. In addition, the catalysts show no obvious deactivation over 40 h. The successful production of C2–C4 hydrocarbons via a tandem process on a rationally designed, structurally well-defined catalyst demonstrates the power of sophisticated structure control in designing nanostructured catalysts for multiple-step chemical conversions.Keywords: C2−C4 hydrocarbons; CO2 hydrogenation; interfaces; tandem catalysis;
Co-reporter:Michael B. Ross, Cao Thang Dinh, Yifan Li, Dohyung Kim, Phil De Luna, Edward H. Sargent, and Peidong Yang
Journal of the American Chemical Society July 12, 2017 Volume 139(Issue 27) pp:9359-9359
Publication Date(Web):June 29, 2017
DOI:10.1021/jacs.7b04892
Using renewable energy to recycle CO2 provides an opportunity to both reduce net CO2 emissions and synthesize fuels and chemical feedstocks. It is of central importance to design electrocatalysts that both are efficient and can access a tunable spectrum of products. Syngas, a mixture of carbon monoxide (CO) and hydrogen (H2), is an important chemical precursor that can be converted downstream into small molecules or larger hydrocarbons by fermentation or thermochemistry. Many processes that utilize syngas require different syngas compositions: we therefore pursued the rational design of a family of electrocatalysts that can be programmed to synthesize different designer syngas ratios. We utilize in situ surface-enhanced Raman spectroscopy and first-principles density functional theory calculations to develop a systematic picture of CO* binding on Cu-enriched Au surface model systems. Insights from these model systems are then translated to nanostructured electrocatalysts, whereby controlled Cu enrichment enables tunable syngas production while maintaining current densities greater than 20 mA/cm2.
Co-reporter:Nigel Becknell, Yoonkook Son, Dohyung Kim, Dongguo Li, Yi Yu, Zhiqiang Niu, Teng Lei, Brian T. Sneed, Karren L. More, Nenad M. Markovic, Vojislav R. Stamenkovic, and Peidong Yang
Journal of the American Chemical Society August 30, 2017 Volume 139(Issue 34) pp:11678-11678
Publication Date(Web):August 8, 2017
DOI:10.1021/jacs.7b05584
Platinum-based alloys are known to demonstrate advanced properties in electrochemical reactions that are relevant for proton exchange membrane fuel cells and electrolyzers. Further development of Pt alloy electrocatalysts relies on the design of architectures with highly active surfaces and optimized utilization of the expensive element, Pt. Here, we show that the three-dimensional Pt anisotropy of Pt–Ni rhombic dodecahedra can be tuned by controlling the ratio between Pt and Ni precursors such that either a completely hollow nanoframe or a new architecture, the excavated nanoframe, can be obtained. The excavated nanoframe showed ∼10 times higher specific and ∼6 times higher mass activity for the oxygen reduction reaction than Pt/C, and twice the mass activity of the hollow nanoframe. The high activity is attributed to enhanced Ni content in the near-surface region and the extended two-dimensional sheet structure within the nanoframe that minimizes the number of buried Pt sites.
Co-reporter:Minliang Lai;Qiao Kong;Connor G. Bischak;Yi Yu;Letian Dou
Nano Research 2017 Volume 10( Issue 4) pp:1107-1114
Publication Date(Web):2017 April
DOI:10.1007/s12274-016-1415-0
Cesium lead iodide (CsPbI3), in its black perovskite phase, has a suitable bandgap and high quantum efficiency for photovoltaic applications. However, CsPbI3 tends to crystalize into a yellow non-perovskite phase, which has poor optoelectronic properties, at room temperature. Therefore, controlling the phase transition in CsPbI3 is critical for practical application of this material. Here we report a systematic study of the phase transition of one-dimensional CsPbI3 nanowires and their corresponding structural, optical, and electrical properties. We show the formation of perovskite black phase CsPbI3 nanowires from the non-perovskite yellow phase through rapid thermal quenching. Post-transformed black phase CsPbI3 nanowires exhibit increased photoluminescence emission intensity with a shrinking of the bandgap from 2.78 to 1.76 eV. The perovskite nanowires were photoconductive and showed a fast photoresponse and excellent stability at room temperature. These promising optical and electrical properties make the perovskite CsPbI3 nanowires attractive for a variety of nanoscale optoelectronic devices.
Co-reporter:Yifan LiFan Cui, Michael B. RossDohyung Kim, Yuchun Sun, Peidong Yang
Nano Letters 2017 Volume 17(Issue 2) pp:
Publication Date(Web):January 17, 2017
DOI:10.1021/acs.nanolett.6b05287
Copper is uniquely active for the electrocatalytic reduction of carbon dioxide (CO2) to products beyond carbon monoxide, such as methane (CH4) and ethylene (C2H4). Therefore, understanding selectivity trends for CO2 electrocatalysis on copper surfaces is critical for developing more efficient catalysts for CO2 conversion to higher order products. Herein, we investigate the electrocatalytic activity of ultrathin (diameter ∼20 nm) 5-fold twinned copper nanowires (Cu NWs) for CO2 reduction. These Cu NW catalysts were found to exhibit high CH4 selectivity over other carbon products, reaching 55% Faradaic efficiency (FE) at −1.25 V versus reversible hydrogen electrode while other products were produced with less than 5% FE. This selectivity was found to be sensitive to morphological changes in the nanowire catalyst observed over the course of electrolysis. Wrapping the wires with graphene oxide was found to be a successful strategy for preserving both the morphology and reaction selectivity of the Cu NWs. These results suggest that product selectivity on Cu NWs is highly dependent on morphological features and that hydrocarbon selectivity can be manipulated by structural evolution or the prevention thereof.Keywords: 5-fold twinned nanowires; carbon dioxide reduction; electrocatalysis; graphene oxide; morphological evolution; selectivity;
Co-reporter:Qiao Kong, Dohyung Kim, Chong Liu, Yi Yu, Yude Su, Yifan Li, and Peidong Yang
Nano Letters 2016 Volume 16(Issue 9) pp:5675-5680
Publication Date(Web):August 5, 2016
DOI:10.1021/acs.nanolett.6b02321
Reducing carbon dioxide with a multicomponent artificial photosynthetic system, closely mimicking nature, represents a promising approach for energy storage. Previous works have focused on exploiting light-harvesting semiconductor nanowires (NW) for photoelectrochemical water splitting. With the newly developed CO2 reduction nanoparticle (NP) catalysts, direct interfacing of these nanocatalysts with NW light absorbers for photoelectrochemical reduction of CO2 becomes feasible. Here, we demonstrate a directed assembly of NP catalysts on vertical NW substrates for CO2-to-CO conversion under illumination. Guided by the one-dimensional geometry, well-dispersed assembly of Au3Cu NPs on the surface of Si NW arrays was achieved with facile coverage tunability. Such Au3Cu NP decorated Si NW arrays can readily serve as effective CO2 reduction photoelectrodes, exhibiting high CO2-to-CO selectivity close to 80% at −0.20 V vs RHE with suppressed hydrogen evolution. A reduction of 120 mV overpotential compared to the planar (PL) counterpart was observed resulting from the optimized spatial arrangement of NP catalysts on the high surface area NW arrays. In addition, this system showed consistent photoelectrochemical CO2 reduction capability up to 18 h. This simple photoelectrode assembly process will lead to further progress in artificial photosynthesis, by allowing the combination of developments in each subfield to create an efficient light-driven system generating carbon-based fuels.Keywords: artificial photosynthesis; carbon dioxide reduction; nanoparticle assembly; nanoparticle catalyst; nanowires;
Co-reporter:Yi Yu, Fan Cui, Jianwei Sun, and Peidong Yang
Nano Letters 2016 Volume 16(Issue 5) pp:3078-3084
Publication Date(Web):April 12, 2016
DOI:10.1021/acs.nanolett.6b00233
Understanding of the atomic structure and stability of nanowires (NWs) is critical for their applications in nanotechnology, especially when the diameter of NWs reduces to ultrathin scale (1–2 nm). Here, using aberration-corrected high-resolution transmission electron microscopy (AC-HRTEM), we report a detailed atomic structure study of the ultrathin Au NWs, which are synthesized using a silane-mediated approach. The NWs contain large amounts of generalized stacking fault defects. These defects evolve upon sustained electron exposure, and simultaneously the NWs undergo necking and breaking. Quantitative strain analysis reveals the key role of strain in the breakdown process. Besides, ligand-like morphology is observed at the surface of the NWs, indicating the possibility of using AC-HRTEM for surface ligand imaging. Moreover, the coalescence dynamic of ultrathin Au NWs is demonstrated by in situ observations. This work provides a comprehensive understanding of the structure of ultrathin metal NWs at atomic-scale and could have important implications for their applications.
Co-reporter:Kelsey K. Sakimoto, Stephanie J. Zhang, and Peidong Yang
Nano Letters 2016 Volume 16(Issue 9) pp:5883-5887
Publication Date(Web):August 18, 2016
DOI:10.1021/acs.nanolett.6b02740
Tandem “Z-scheme” approaches to solar-to-chemical production afford the ability to independently develop and optimize reductive photocatalysts for CO2 reduction to multicarbon compounds and oxidative photocatalysts for O2 evolution. To connect the two redox processes, molecular redox shuttles, reminiscent of biological electron transfer, offer an additional level of facile chemical tunability that eliminates the need for solid-state semiconductor junction engineering. In this work, we report a tandem inorganic–biological hybrid system capable of oxygenic photosynthesis of acetic acid from CO2. The photoreductive catalyst consists of the bacterium Moorella thermoacetica self-photosensitized with CdS nanoparticles at the expense of the thiol amino acid cysteine (Cys) oxidation to the disulfide form cystine (CySS). To regenerate the CySS/Cys redox shuttle, the photooxidative catalyst, TiO2 loaded with cocatalyst Mn(II) phthalocyanine (MnPc), couples water oxidation to CySS reduction. The combined system M. thermoacetica–CdS + TiO2–MnPc demonstrates a potential biomimetic approach to complete oxygenic solar-to-chemical production.Keywords: artificial photosynthesis; Cadmium sulfide; Moorella thermoacetica; phthalocyanine; solar-to-chemical production; titanium dioxide;
Co-reporter:Yi Yu, Dandan Zhang, Christian Kisielowski, Letian Dou, Nikolay Kornienko, Yehonadav Bekenstein, Andrew B. Wong, A. Paul Alivisatos, and Peidong Yang
Nano Letters 2016 Volume 16(Issue 12) pp:7530-7535
Publication Date(Web):November 7, 2016
DOI:10.1021/acs.nanolett.6b03331
The radiation-sensitive nature of halide perovskites has hindered structural studies at the atomic scale. We overcome this obstacle by applying low dose-rate in-line holography, which combines aberration-corrected high-resolution transmission electron microscopy with exit-wave reconstruction. This technique successfully yields the genuine atomic structure of ultrathin two-dimensional CsPbBr3 halide perovskites, and a quantitative structure determination was achieved atom column by atom column using the phase information of the reconstructed exit-wave function without causing electron beam-induced sample alterations. An extraordinarily high image quality enables an unambiguous structural analysis of coexisting high-temperature and low-temperature phases of CsPbBr3 in single particles. On a broader level, our approach offers unprecedented opportunities to better understand halide perovskites at the atomic level as well as other radiation-sensitive materials.Keywords: Atomic resolution; halide perovskites; in-line holography; low dose-rate; radiation-sensitive materials;
Co-reporter:Jaeho Lee, Woochul Lee, Jongwoo Lim, Yi Yu, Qiao Kong, Jeffrey J. Urban, and Peidong Yang
Nano Letters 2016 Volume 16(Issue 7) pp:4133-4140
Publication Date(Web):May 31, 2016
DOI:10.1021/acs.nanolett.6b00956
Thermal transport in silicon nanowires has captured the attention of scientists for understanding phonon transport at the nanoscale, and the thermoelectric figure-of-merit (ZT) reported in rough nanowires has inspired engineers to develop cost-effective waste heat recovery systems. Thermoelectric generators composed of silicon target high-temperature applications due to improved efficiency beyond 550 K. However, there have been no studies of thermal transport in silicon nanowires beyond room temperature. High-temperature measurements also enable studies of unanswered questions regarding the impact of surface boundaries and varying mode contributions as the highest vibrational modes are activated (Debye temperature of silicon is 645 K). Here, we develop a technique to investigate thermal transport in nanowires up to 700 K. Our thermal conductivity measurements on smooth silicon nanowires show the classical diameter dependence from 40 to 120 nm. In conjunction with Boltzmann transport equation, we also probe an increasing contribution of high-frequency phonons (optical phonons) in smooth silicon nanowires as the diameter decreases and the temperature increases. Thermal conductivity of rough silicon nanowires is significantly reduced throughout the temperature range, demonstrating a potential for efficient thermoelectric generation (e.g., ZT = 1 at 700 K).
Co-reporter:Kyung Min Choi, Dohyung Kim, Bunyarat Rungtaweevoranit, Christopher A. Trickett, Jesika Trese Deniz Barmanbek, Ahmad S. Alshammari, Peidong Yang, and Omar M. Yaghi
Journal of the American Chemical Society 2016 Volume 139(Issue 1) pp:356-362
Publication Date(Web):November 26, 2016
DOI:10.1021/jacs.6b11027
Materials development for artificial photosynthesis, in particular, CO2 reduction, has been under extensive efforts, ranging from inorganic semiconductors to molecular complexes. In this report, we demonstrate a metal–organic framework (MOF)-coated nanoparticle photocatalyst with enhanced CO2 reduction activity and stability, which stems from having two different functional units for activity enhancement and catalytic stability combined together as a single construct. Covalently attaching a CO2-to-CO conversion photocatalyst ReI(CO)3(BPYDC)Cl, BPYDC = 2,2′-bipyridine-5,5′-dicarboxylate, to a zirconium MOF, UiO-67 (Ren-MOF), prevents dimerization leading to deactivation. By systematically controlling its density in the framework (n = 0, 1, 2, 3, 5, 11, 16, and 24 complexes per unit cell), the highest photocatalytic activity was found for Re3-MOF. Structural analysis of Ren-MOFs suggests that a fine balance of proximity between photoactive centers is needed for cooperatively enhanced photocatalytic activity, where an optimum number of Re complexes per unit cell should reach the highest activity. Based on the structure–activity correlation of Ren-MOFs, Re3-MOF was coated onto Ag nanocubes (Ag⊂Re3-MOF), which spatially confined photoactive Re centers to the intensified near-surface electric fields at the surface of Ag nanocubes, resulting in a 7-fold enhancement of CO2-to-CO conversion under visible light with long-term stability maintained up to 48 h.
Co-reporter:Ji Su, Chenlu Xie, Chen Chen, Yi Yu, Griffin Kennedy, Gabor A. Somorjai, and Peidong Yang
Journal of the American Chemical Society 2016 Volume 138(Issue 36) pp:11568-11574
Publication Date(Web):September 2, 2016
DOI:10.1021/jacs.6b03915
The concept of tandem catalysis, where sequential reactions catalyzed by different interfaces in single nanostructure give desirable product selectively, has previously been applied effectively in the production of propanal from methanol (via carbon monoxide and hydrogen) and ethylene via tandem hydroformylation. However, the underlying mechanism leading to enhanced product selectivity has remained elusive due to the lack of stable, well-defined catalyst suitable for in-depth comprehensive study. Accordingly, we present the design and synthesis of a three-dimensional (3D) catalyst CeO2–Pt@mSiO2 with well-defined metal–oxide interfaces and stable architecture and investigate the selective conversion of ethylene to propanal via tandem hydroformylation. The effective production of aldehyde through the tandem hydroformylation was also observed on propylene and 1-butene. A thorough study of the CeO2–Pt@mSiO2 under different reaction and control conditions reveals that the ethylene present for the hydroformylation step slows down initial methanol decomposition, preventing the accumulation of hydrogen (H2) and favoring propanal formation to achieve up to 80% selectivity. The selectivity is also promoted by the fact that the reaction intermediates produced from methanol decomposition are poised to directly undergo hydroformylation upon migration from one catalytic interface to another. This synergistic effect between the two sequential reactions and the corresponding altered reaction pathway, compared to the single-step reaction, constitute the key advantages of this tandem catalysis. Ultimately, this in-depth study unravels the principles of tandem catalysis related to hydroformylation and represents a key step toward the rational design of new heterogeneous catalysts.
Co-reporter:Dandan Zhang, Yi Yu, Yehonadav Bekenstein, Andrew B. Wong, A. Paul Alivisatos, and Peidong Yang
Journal of the American Chemical Society 2016 Volume 138(Issue 40) pp:13155-13158
Publication Date(Web):September 27, 2016
DOI:10.1021/jacs.6b08373
Highly uniform single crystal ultrathin CsPbBr3 nanowires (NWs) with diameter of 2.2 ± 0.2 nm and length up to several microns were successfully synthesized and purified using a catalyst-free colloidal synthesis method followed by a stepwise purification strategy. The NWs have bright photoluminescence (PL) with a photoluminescence quantum yield (PLQY) of about 30% after surface treatment. Large blue-shifted UV–vis absorption and PL spectra have been observed due to strong two-dimensional quantum confinement effects. A small angle X-ray scattering (SAXS) pattern shows the periodic packing of the ultrathin NWs along the radial direction, demonstrates the narrow radial distribution of the wires, and emphasizes the deep intercalation of the surfactants. Despite the extreme aspect ratios of the ultrathin NWs, their composition and the resulting optical properties can be readily tuned by an anion-exchange reaction with good morphology preservation. These bright ultrathin NWs may be used as a model system to study strong quantum confinement effects in a one-dimensional halide perovskite system.
Co-reporter:Zhi Cao; Dohyung Kim; Dachao Hong; Yi Yu; Jun Xu; Song Lin; Xiaodong Wen; Eva M. Nichols; Keunhong Jeong; Jeffrey A. Reimer; Peidong Yang◆;Christopher J. Chang
Journal of the American Chemical Society 2016 Volume 138(Issue 26) pp:8120-8125
Publication Date(Web):June 20, 2016
DOI:10.1021/jacs.6b02878
Conversion of the greenhouse gas carbon dioxide (CO2) to value-added products is an important challenge for sustainable energy research, and nanomaterials offer a broad class of heterogeneous catalysts for such transformations. Here we report a molecular surface functionalization approach to tuning gold nanoparticle (Au NP) electrocatalysts for reduction of CO2 to CO. The N-heterocyclic (NHC) carbene-functionalized Au NP catalyst exhibits improved faradaic efficiency (FE = 83%) for reduction of CO2 to CO in water at neutral pH at an overpotential of 0.46 V with a 7.6-fold increase in current density compared to that of the parent Au NP (FE = 53%). Tafel plots of the NHC carbene-functionalized Au NP (72 mV/decade) vs parent Au NP (138 mV/decade) systems further show that the molecular ligand influences mechanistic pathways for CO2 reduction. The results establish molecular surface functionalization as a complementary approach to size, shape, composition, and defect control for nanoparticle catalyst design.
Co-reporter:Dandan Zhang; Yiming Yang; Yehonadav Bekenstein; Yi Yu; Natalie A. Gibson; Andrew B. Wong; Samuel W. Eaton; Nikolay Kornienko; Qiao Kong; Minliang Lai; A. Paul Alivisatos; Stephen R. Leone;Peidong Yang
Journal of the American Chemical Society 2016 Volume 138(Issue 23) pp:7236-7239
Publication Date(Web):May 23, 2016
DOI:10.1021/jacs.6b03134
Here, we demonstrate the successful synthesis of brightly emitting colloidal cesium lead halide (CsPbX3, X = Cl, Br, I) nanowires (NWs) with uniform diameters and tunable compositions. By using highly monodisperse CsPbBr3 NWs as templates, the NW composition can be independently controlled through anion-exchange reactions. CsPbX3 alloy NWs with a wide range of alloy compositions can be achieved with well-preserved morphology and crystal structure. The NWs are highly luminescent with photoluminescence quantum yields (PLQY) ranging from 20% to 80%. The bright photoluminescence can be tuned over nearly the entire visible spectrum. The high PLQYs together with charge transport measurements exemplify the efficient alloying of the anionic sublattice in a one-dimensional CsPbX3 system. The wires increased functionality in the form of fast photoresponse rates and the low defect density suggest CsPbX3 NWs as prospective materials for optoelectronic applications.
Co-reporter:Nigel Becknell, Cindy Zheng, Chen Chen, Yi Yu, Peidong Yang
Surface Science 2016 Volume 648() pp:328-332
Publication Date(Web):June 2016
DOI:10.1016/j.susc.2015.09.024
•PtCo3 polyhedral nanoparticles were synthesized.•Polyhedral nanoparticle demonstrates segregation of platinum to its edges.•PtCo3 nanoparticle was evolved to Pt3Co nanoframe with hollow interior.Bimetallic nanoframes have great potential for achieving new levels of catalytic activity in various heterogeneous reactions due to their high surface area dispersion of expensive noble metals on the exterior and interior surfaces of the structure. PtCo3 nanoparticles with polyhedral shapes were synthesized by a hot-injection method. Scanning transmission electron microscopy combined with energy dispersive X-ray spectroscopy (EDS) showed that these nanoparticles demonstrated elemental segregation of platinum to the edges of the polyhedron, forming the basis for a framework nanostructure. The process of preferential oxidative leaching which removed cobalt from the interior of the framework was tracked by EDS and inductively coupled plasma optical emission spectroscopy. This evolution procedure left the platinum-rich edges intact to form a Pt3Co nanoframe. This is the first reported synthesis of a platinum–cobalt nanoframe and could have potential applications in catalytic reactions such as oxygen reduction.
Co-reporter:Kelsey K. Sakimoto;Andrew Barnabas Wong;Peidong Yang
Science 2016 Volume 351(Issue 6268) pp:74-77
Publication Date(Web):01 Jan 2016
DOI:10.1126/science.aad3317
Using light in the darkness
Solid-state devices can efficiently capture solar energy to produce chemicals and fuels from carbon dioxide. Yet biology has already developed a high-specificity, low-cost system to do just that through photosynthesis. Sakimoto et al. developed a biological-inorganic hybrid that combines the best of both worlds (see the Perspective by Müller). They precipitated semiconductor nanoparticles on the surface of a nonphotosynthetic bacterium to serve as a light harvester. The captured energy sustained cellular metabolism, producing acetic acid: a natural waste product of respiration.
Science, this issue p. 74; see also p. 34
Co-reporter:Jianwei Sun, Fan Cui, Christian Kisielowski, Yi Yu, Nikolay Kornienko, and Peidong Yang
The Journal of Physical Chemistry C 2016 Volume 120(Issue 37) pp:20525-20529
Publication Date(Web):November 30, 2015
DOI:10.1021/acs.jpcc.5b08289
Low-temperature synthesis of crystalline silicon and silicon-containing nanowires remains a challenge in synthetic chemistry due to the lack of sufficiently reactive Si precursors. We report that colloidal Si nanowires can be grown using tris(trimethylsilyl)silane or trisilane as the Si precursor by a Ga-mediated solution–liquid–solid (SLS) approach at temperatures of about 200 °C, which is more than 200 °C lower than that reported in the previous literature. We further demonstrate that the new Si chemistry can be adopted to incorporate Si atoms into III–V semiconductor lattices, which holds promise to produce a new Si-containing alloy semiconductor nanowire. This development represents an important step toward low-temperature fabrication of Si nanowire-based devices for broad applications.
Co-reporter:Jongwoo Lim, Hung-Ta Wang, Jinyao Tang, Sean C. Andrews, Hongyun So, Jaeho Lee, Dong Hyun Lee, Thomas P. Russell, and Peidong Yang
ACS Nano 2016 Volume 10(Issue 1) pp:124
Publication Date(Web):December 9, 2015
DOI:10.1021/acsnano.5b05385
Block copolymer patterned holey silicon (HS) was successfully integrated into a microdevice for simultaneous measurements of Seebeck coefficient, electrical conductivity, and thermal conductivity of the same HS microribbon. These fully integrated HS microdevices provided excellent platforms for the systematic investigation of thermoelectric transport properties tailored by the dimensions of the periodic hole array, that is, neck and pitch size, and the doping concentrations. Specifically, thermoelectric transport properties of HS with a neck size in the range of 16–34 nm and a fixed pitch size of 60 nm were characterized, and a clear neck size dependency was shown in the doping range of 3.1 × 1018 to 6.5 × 1019 cm–3. At 300 K, thermal conductivity as low as 1.8 ± 0.2 W/mK was found in HS with a neck size of 16 nm, while optimized zT values were shown in HS with a neck size of 24 nm. The controllable effects of holey array dimensions and doping concentrations on HS thermoelectric performance could aid in improving the understanding of the phonon scattering process in a holey structure and also in facilitating the development of silicon-based thermoelectric devices.Keywords: holey silicon; phonon transport; silicon nanostructure; thermal conductivity; thermoelectrics;
Co-reporter:Joaquin Resasco, Hao Zhang, Nikolay Kornienko, Nigel Becknell, Hyunbok Lee, Jinghua Guo, Alejandro L. Briseno, and Peidong Yang
ACS Central Science 2016 Volume 2(Issue 2) pp:80
Publication Date(Web):February 3, 2016
DOI:10.1021/acscentsci.5b00402
Metal oxides that absorb visible light are attractive for use as photoanodes in photoelectrosynthetic cells. However, their performance is often limited by poor charge carrier transport. We show that this problem can be addressed by using separate materials for light absorption and carrier transport. Here, we report a Ta:TiO2|BiVO4 nanowire photoanode, in which BiVO4 acts as a visible light-absorber and Ta:TiO2 acts as a high surface area electron conductor. Electrochemical and spectroscopic measurements provide experimental evidence for the type II band alignment necessary for favorable electron transfer from BiVO4 to TiO2. The host–guest nanowire architecture presented here allows for simultaneously high light absorption and carrier collection efficiency, with an onset of anodic photocurrent near 0.2 V vs RHE, and a photocurrent density of 2.1 mA/cm2 at 1.23 V vs RHE.
Co-reporter:Jie Ma;Letian Dou;Natalie A. Gibson;Minliang Lai;Lin-Wang Wang;Andrew B. Wong;Stephen R. Leone;Peidong Yang;Samuel W. Eaton
PNAS 2016 Volume 113 (Issue 8 ) pp:1993-1998
Publication Date(Web):2016-02-23
DOI:10.1073/pnas.1600789113
The rapidly growing field of nanoscale lasers can be advanced through the discovery of new, tunable light sources. The emission
wavelength tunability demonstrated in perovskite materials is an attractive property for nanoscale lasers. Whereas organic–inorganic
lead halide perovskite materials are known for their instability, cesium lead halides offer a robust alternative without sacrificing
emission tunability or ease of synthesis. Here, we report the low-temperature, solution-phase growth of cesium lead halide
nanowires exhibiting low-threshold lasing and high stability. The as-grown nanowires are single crystalline with well-formed
facets, and act as high-quality laser cavities. The nanowires display excellent stability while stored and handled under ambient
conditions over the course of weeks. Upon optical excitation, Fabry–Pérot lasing occurs in CsPbBr3 nanowires with an onset of 5 μJ cm−2 with the nanowire cavity displaying a maximum quality factor of 1,009 ± 5. Lasing under constant, pulsed excitation can be
maintained for over 1 h, the equivalent of 109 excitation cycles, and lasing persists upon exposure to ambient atmosphere. Wavelength tunability in the green and blue regions
of the spectrum in conjunction with excellent stability makes these nanowire lasers attractive for device fabrication.
Co-reporter:Kelsey K. Sakimoto;Nikolay Kornienko;Adam Schwartzberg;Charles. B. Harris;David M. Herlihy;Peidong Yang;A. Paul Alivisatos;Son C. Nguyen
PNAS 2016 Volume 113 (Issue 42 ) pp:11750-11755
Publication Date(Web):2016-10-18
DOI:10.1073/pnas.1610554113
The rise of inorganic–biological hybrid organisms for solar-to-chemical production has spurred mechanistic investigations
into the dynamics of the biotic–abiotic interface to drive the development of next-generation systems. The model system, Moorella thermoacetica–cadmium sulfide (CdS), combines an inorganic semiconductor nanoparticle light harvester with an acetogenic bacterium to drive
the photosynthetic reduction of CO2 to acetic acid with high efficiency. In this work, we report insights into this unique electrotrophic behavior and propose
a charge-transfer mechanism from CdS to M. thermoacetica. Transient absorption (TA) spectroscopy revealed that photoexcited electron transfer rates increase with increasing hydrogenase
(H2ase) enzyme activity. On the same time scale as the TA spectroscopy, time-resolved infrared (TRIR) spectroscopy showed spectral
changes in the 1,700–1,900-cm−1 spectral region. The quantum efficiency of this system for photosynthetic acetic acid generation also increased with increasing
H2ase activity and shorter carrier lifetimes when averaged over the first 24 h of photosynthesis. However, within the initial
3 h of photosynthesis, the rate followed an opposite trend: The bacteria with the lowest H2ase activity photosynthesized acetic acid the fastest. These results suggest a two-pathway mechanism: a high quantum efficiency
charge-transfer pathway to H2ase generating H2 as a molecular intermediate that dominates at long time scales (24 h), and a direct energy-transducing enzymatic pathway
responsible for acetic acid production at short time scales (3 h). This work represents a promising platform to utilize conventional
spectroscopic methodology to extract insights from more complex biotic–abiotic hybrid systems.
Co-reporter:Nikolay Kornienko, Natalie A. Gibson, Hao Zhang, Samuel W. Eaton, Yi Yu, Shaul Aloni, Stephen R. Leone, and Peidong Yang
ACS Nano 2016 Volume 10(Issue 5) pp:5525
Publication Date(Web):April 28, 2016
DOI:10.1021/acsnano.6b02083
Photoelectrochemical (PEC) water splitting into hydrogen and oxygen is a promising strategy to absorb solar energy and directly convert it into a dense storage medium in the form of chemical bonds. The continual development and improvement of individual components of PEC systems is critical toward increasing the solar to fuel efficiency of prototype devices. Within this context, we describe a study on the growth of wurtzite indium phosphide (InP) nanowire (NW) arrays on silicon substrates and their subsequent implementation as light-absorbing photocathodes in PEC cells. The high onset potential (0.6 V vs the reversible hydrogen electrode) and photocurrent (18 mA/cm2) of the InP photocathodes render them as promising building blocks for high performance PEC cells. As a proof of concept for overall system integration, InP photocathodes were combined with a nanoporous bismuth vanadate (BiVO4) photoanode to generate an unassisted solar water splitting efficiency of 0.5%.Keywords: catalysis; chemical vapor deposition; energy conversion; nanowire synthesis; photoelectrochemistry
Co-reporter:Letian Dou, Fan Cui, Yi Yu, Garo Khanarian, Samuel W. Eaton, Qin Yang, Joaquin Resasco, Christian Schildknecht, Kerstin Schierle-Arndt, and Peidong Yang
ACS Nano 2016 Volume 10(Issue 2) pp:2600
Publication Date(Web):January 28, 2016
DOI:10.1021/acsnano.5b07651
Copper nanowire (Cu NW) based transparent conductors are promising candidates to replace ITO (indium–tin-oxide) owing to the high electrical conductivity and low-cost of copper. However, the relatively low performance and poor stability of Cu NWs under ambient conditions limit the practical application of these devices. Here, we report a solution-based approach to wrap graphene oxide (GO) nanosheets on the surface of ultrathin copper nanowires. By mild thermal annealing, GO can be reduced and high quality Cu r-GO core–shell NWs can be obtained. High performance transparent conducting films were fabricated with these ultrathin core–shell nanowires and excellent optical and electric performance was achieved. The core–shell NW structure enables the production of highly stable conducting films (over 200 days stored in air), which have comparable performance to ITO and silver NW thin films (sheet resistance ∼28 Ω/sq, haze ∼2% at transmittance of ∼90%).Keywords: Cu nanowires; graphene oxide wrapping; high stability; low haze; solution-process; transparent conductors;
Co-reporter:Jaeho Lee, Jongwoo Lim, and Peidong Yang
Nano Letters 2015 Volume 15(Issue 5) pp:3273-3279
Publication Date(Web):April 10, 2015
DOI:10.1021/acs.nanolett.5b00495
When the size of semiconductors is smaller than the phonon mean free path, phonons can carry heat with no internal scattering. Ballistic phonon transport has received attention for both theoretical and practical aspects because Fourier’s law of heat conduction breaks down and the heat dissipation in nanoscale transistors becomes unpredictable in the ballistic regime. While recent experiments demonstrate room-temperature evidence of ballistic phonon transport in various nanomaterials, the thermal conductivity data for silicon in the length scale of 10–100 nm is still not available due to experimental challenges. Here we show ballistic phonon transport prevails in the cross-plane direction of holey silicon from 35 to 200 nm. The thermal conductivity scales linearly with the length (thickness) even though the lateral dimension (neck) is as narrow as 20 nm. We assess the impact of long-wavelength phonons and predict a transition from ballistic to diffusive regime using scaling models. Our results support strong persistence of long-wavelength phonons in nanostructures and are useful for controlling phonon transport for thermoelectrics and potential phononic applications.
Co-reporter:Andrew Barnabas Wong, Sarah Brittman, Yi Yu, Neil P. Dasgupta, and Peidong Yang
Nano Letters 2015 Volume 15(Issue 6) pp:4096-4101
Publication Date(Web):May 20, 2015
DOI:10.1021/acs.nanolett.5b01203
As an earth-abundant p-type semiconductor, copper sulfide (Cu2S) is an attractive material for application in photovoltaic devices. However, it suffers from a minority carrier diffusion length that is less than the length required for complete light absorption. Core–shell nanowires and nanorods have the potential to alleviate this difficulty because they decouple the length scales of light absorption and charge collection. To achieve this geometry using Cu2S, cation exchange was applied to an array of CdS nanorods to produce well-defined CdS–Cu2S core–shell nanorods. Previous work has demonstrated single-nanowire photovoltaic devices from this material system, but in this work, the cation exchange chemistry has been applied to nanorod arrays to produce ensemble-level devices with microscale sizes. The core–shell nanorod array devices show power conversion efficiencies of up to 3.8%. In addition, these devices are stable when measured in air after nearly one month of storage in a desiccator. These results are a first step in the development of large-area nanostructured Cu2S-based photovoltaics that can be processed from solution.
Co-reporter:Andrew Barnabas Wong, Minliang Lai, Samuel Wilson Eaton, Yi Yu, Elbert Lin, Letian Dou, Anthony Fu, and Peidong Yang
Nano Letters 2015 Volume 15(Issue 8) pp:5519-5524
Publication Date(Web):July 20, 2015
DOI:10.1021/acs.nanolett.5b02082
The nanowire and nanorod morphology offers great advantages for application in a range of optoelectronic devices, but these high-quality nanorod arrays are typically based on high temperature growth techniques. Here, we demonstrate the successful room temperature growth of a hybrid perovskite (CH3NH3PbBr3) nanorod array, and we also introduce a new low temperature anion exchange technique to convert the CH3NH3PbBr3 nanorod array into a CH3NH3PbI3 nanorod array while preserving morphology. We demonstrate the application of both these hybrid perovskite nanorod arrays for LEDs. This work highlights the potential utility of postsynthetic interconversion of hybrid perovskites for nanostructured optoelectronic devices such as LEDs, which enables new strategies for the application of hybrid perovskites.
Co-reporter:Chong Liu, Joseph J. Gallagher, Kelsey K. Sakimoto, Eva M. Nichols, Christopher J. Chang, Michelle C. Y. Chang, and Peidong Yang
Nano Letters 2015 Volume 15(Issue 5) pp:3634-3639
Publication Date(Web):April 7, 2015
DOI:10.1021/acs.nanolett.5b01254
Direct solar-powered production of value-added chemicals from CO2 and H2O, a process that mimics natural photosynthesis, is of fundamental and practical interest. In natural photosynthesis, CO2 is first reduced to common biochemical building blocks using solar energy, which are subsequently used for the synthesis of the complex mixture of molecular products that form biomass. Here we report an artificial photosynthetic scheme that functions via a similar two-step process by developing a biocompatible light-capturing nanowire array that enables a direct interface with microbial systems. As a proof of principle, we demonstrate that a hybrid semiconductor nanowire–bacteria system can reduce CO2 at neutral pH to a wide array of chemical targets, such as fuels, polymers, and complex pharmaceutical precursors, using only solar energy input. The high-surface-area silicon nanowire array harvests light energy to provide reducing equivalents to the anaerobic bacterium, Sporomusa ovata, for the photoelectrochemical production of acetic acid under aerobic conditions (21% O2) with low overpotential (η < 200 mV), high Faradaic efficiency (up to 90%), and long-term stability (up to 200 h). The resulting acetate (∼6 g/L) can be activated to acetyl coenzyme A (acetyl-CoA) by genetically engineered Escherichia coli and used as a building block for a variety of value-added chemicals, such as n-butanol, polyhydroxybutyrate (PHB) polymer, and three different isoprenoid natural products. As such, interfacing biocompatible solid-state nanodevices with living systems provides a starting point for developing a programmable system of chemical synthesis entirely powered by sunlight.
Co-reporter:Anthony Fu, Hanwei Gao, Petar Petrov, and Peidong Yang
Nano Letters 2015 Volume 15(Issue 10) pp:6909-6913
Publication Date(Web):September 17, 2015
DOI:10.1021/acs.nanolett.5b02839
Periodic structures with dimensions on the order of the wavelength of light can tailor and improve the performance of optical components, and they can enable the creation of devices with new functionalities. For example, distributed Bragg reflectors (DBRs), which are created by periodic modulations in a structure’s dielectric medium, are essential in dielectric mirrors, vertical cavity surface emitting lasers, fiber Bragg gratings, and single-frequency laser diodes. This work introduces nanoscale DBRs integrated directly into gallium nitride (GaN) nanowire waveguides. Photonic band gaps that are tunable across the visible spectrum are demonstrated by precisely controlling the grating’s parameters. Numerical simulations indicate that in-wire DBRs have significantly larger reflection coefficients in comparison with the nanowire’s end facet. By comparing the measured spectra with the simulated spectra, the index of refraction of the GaN nanowire waveguides was extracted to facilitate the design of photonic coupling structures that are sensitive to phase-matching conditions. This work indicates the potential to design nanowire-based devices with improved performance for optical resonators and optical routing.
Co-reporter:Fan Cui, Yi Yu, Letian Dou, Jianwei Sun, Qin Yang, Christian Schildknecht, Kerstin Schierle-Arndt, and Peidong Yang
Nano Letters 2015 Volume 15(Issue 11) pp:7610-7615
Publication Date(Web):October 23, 2015
DOI:10.1021/acs.nanolett.5b03422
Colloidal metal nanowire based transparent conductors are excellent candidates to replace indium–tin–oxide (ITO) owing to their outstanding balance between transparency and conductivity, flexibility, and solution-processability. Copper stands out as a promising material candidate due to its high intrinsic conductivity and earth abundance. Here, we report a new synthetic approach, using tris(trimethylsilyl)silane as a mild reducing reagent, for synthesizing high-quality, ultrathin, and monodispersed copper nanowires, with an average diameter of 17.5 nm and a mean length of 17 μm. A study of the growth mechanism using high-resolution transmission electron microscopy reveals that the copper nanowires adopt a five-fold twinned structure and evolve from decahedral nanoseeds. Fabricated transparent conducting films exhibit excellent transparency and conductivity. An additional advantage of our nanowire transparent conductors is highlighted through reduced optical haze factors (forward light scattering) due to the small nanowire diameter.
Co-reporter:Nikolay Kornienko; Yingbo Zhao; Christopher S. Kley; Chenhui Zhu; Dohyung Kim; Song Lin; Christopher J. Chang; Omar M. Yaghi◆;Peidong Yang◆
Journal of the American Chemical Society 2015 Volume 137(Issue 44) pp:14129-14135
Publication Date(Web):October 28, 2015
DOI:10.1021/jacs.5b08212
A key challenge in the field of electrochemical carbon dioxide reduction is the design of catalytic materials featuring high product selectivity, stability, and a composition of earth-abundant elements. In this work, we introduce thin films of nanosized metal–organic frameworks (MOFs) as atomically defined and nanoscopic materials that function as catalysts for the efficient and selective reduction of carbon dioxide to carbon monoxide in aqueous electrolytes. Detailed examination of a cobalt–porphyrin MOF, Al2(OH)2TCPP-Co (TCPP-H2 = 4,4′,4″,4‴-(porphyrin-5,10,15,20-tetrayl)tetrabenzoate) revealed a selectivity for CO production in excess of 76% and stability over 7 h with a per-site turnover number (TON) of 1400. In situ spectroelectrochemical measurements provided insights into the cobalt oxidation state during the course of reaction and showed that the majority of catalytic centers in this MOF are redox-accessible where Co(II) is reduced to Co(I) during catalysis.
Co-reporter:Nikolay Kornienko; Joaquin Resasco; Nigel Becknell; Chang-Ming Jiang; Yi-Sheng Liu; Kaiqi Nie; Xuhui Sun; Jinghua Guo; Stephen R. Leone;Peidong Yang
Journal of the American Chemical Society 2015 Volume 137(Issue 23) pp:7448-7455
Publication Date(Web):June 8, 2015
DOI:10.1021/jacs.5b03545
The generation of chemical fuel in the form of molecular H2 via the electrolysis of water is regarded to be a promising approach to convert incident solar power into an energy storage medium. Highly efficient and cost-effective catalysts are required to make such an approach practical on a large scale. Recently, a number of amorphous hydrogen evolution reaction (HER) catalysts have emerged that show promise in terms of scalability and reactivity, yet remain poorly understood. In this work, we utilize Raman spectroscopy and X-ray absorption spectroscopy (XAS) as a tool to elucidate the structure and function of an amorphous cobalt sulfide (CoSx) catalyst. Ex situ measurements reveal that the as-deposited CoSx catalyst is composed of small clusters in which the cobalt is surrounded by both sulfur and oxygen. Operando experiments, performed while the CoSx is catalyzing the HER, yield a molecular model in which cobalt is in an octahedral CoS2-like state where the cobalt center is predominantly surrounded by a first shell of sulfur atoms, which, in turn, are preferentially exposed to electrolyte relative to bulk CoS2. We surmise that these CoS2-like clusters form under cathodic polarization and expose a high density of catalytically active sulfur sites for the HER.
Co-reporter:Nigel Becknell; Yijin Kang; Chen Chen; Joaquin Resasco; Nikolay Kornienko; Jinghua Guo; Nenad M. Markovic; Gabor A. Somorjai; Vojislav R. Stamenkovic;Peidong Yang
Journal of the American Chemical Society 2015 Volume 137(Issue 50) pp:15817-15824
Publication Date(Web):December 10, 2015
DOI:10.1021/jacs.5b09639
Understanding the atomic structure of a catalyst is crucial to exposing the source of its performance characteristics. It is highly unlikely that a catalyst remains the same under reaction conditions when compared to as-synthesized. Hence, the ideal experiment to study the catalyst structure should be performed in situ. Here, we use X-ray absorption spectroscopy (XAS) as an in situ technique to study Pt3Ni nanoframe particles which have been proven to be an excellent electrocatalyst for the oxygen reduction reaction (ORR). The surface characteristics of the nanoframes were probed through electrochemical hydrogen underpotential deposition and carbon monoxide electrooxidation, which showed that nanoframe surfaces with different structure exhibit varying levels of binding strength to adsorbate molecules. It is well-known that Pt-skin formation on Pt–Ni catalysts will enhance ORR activity by weakening the binding energy between the surface and adsorbates. Ex situ and in situ XAS results reveal that nanoframes which bind adsorbates more strongly have a rougher Pt surface caused by insufficient segregation of Pt to the surface and consequent Ni dissolution. In contrast, nanoframes which exhibit extremely high ORR activity simultaneously demonstrate more significant segregation of Pt over Ni-rich subsurface layers, allowing better formation of the critical Pt-skin. This work demonstrates that the high ORR activity of the Pt3Ni hollow nanoframes depends on successful formation of the Pt-skin surface structure.
Co-reporter:Yingbo Zhao; Nikolay Kornienko; Zheng Liu; Chenhui Zhu; Shunsuke Asahina; Tsung-Rong Kuo; Wei Bao; Chenlu Xie; Alexander Hexemer; Osamu Terasaki; Peidong Yang;Omar M. Yaghi
Journal of the American Chemical Society 2015 Volume 137(Issue 6) pp:2199-2202
Publication Date(Web):January 26, 2015
DOI:10.1021/ja512951e
We enclose octahedral silver nanocrystals (Ag NCs) in metal–organic frameworks (MOFs) to make mesoscopic constructs Oh-nano-Ag⊂MOF in which the interface between the Ag and the MOF is pristine and the MOF is ordered (crystalline) and oriented on the Ag NCs. This is achieved by atomic layer deposition of aluminum oxide on Ag NCs and addition of a tetra-topic porphyrin-based linker, 4,4′,4″,4‴-(porphyrin-5,10,15,20-tetrayl)tetrabenzoic acid (H4TCPP), to react with alumina and make MOF [Al2(OH)2TCPP] enclosures around Ag NCs. Alumina thickness is precisely controlled from 0.1 to 3 nm, thus allowing control of the MOF thickness from 10 to 50 nm. Electron microscopy and grazing angle X-ray diffraction confirm the order and orientation of the MOF by virtue of the porphyrin units being perpendicular to the planes of the Ag. We use surface-enhanced Raman spectroscopy to directly track the metalation process on the porphyrin and map the distribution of the metalated and unmetalated linkers on a single-nanoparticle level.
Co-reporter:Dandan Zhang; Samuel W. Eaton; Yi Yu; Letian Dou;Peidong Yang
Journal of the American Chemical Society 2015 Volume 137(Issue 29) pp:9230-9233
Publication Date(Web):July 16, 2015
DOI:10.1021/jacs.5b05404
Halide perovskites have attracted much attention over the past 5 years as a promising class of materials for optoelectronic applications. However, compared to hybrid organic–inorganic perovskites, the study of their pure inorganic counterparts, like cesium lead halides (CsPbX3), lags far behind. Here, a catalyst-free, solution-phase synthesis of CsPbX3 nanowires (NWs) is reported. These NWs are single-crystalline, with uniform growth direction, and crystallize in the orthorhombic phase. Both CsPbBr3 and CsPbI3 are photoluminescence active, with composition-dependent temperature and self-trapping behavior. These NWs with a well-defined morphology could serve as an ideal platform for the investigation of fundamental properties and the development of future applications in nanoscale optoelectronic devices based on all-inorganic perovskites.
Co-reporter:Eva M. Nichols;Joseph J. Gallagher;Chong Liu;Yude Su;Joaquin Resasco;Yi Yu;Yujie Sun;Peidong Yang;Michelle C. Y. Chang;Christopher J. Chang
PNAS 2015 112 (37 ) pp:11461-11466
Publication Date(Web):2015-09-15
DOI:10.1073/pnas.1508075112
Natural photosynthesis harnesses solar energy to convert CO2 and water to value-added chemical products for sustaining life. We present a hybrid bioinorganic approach to solar-to-chemical
conversion in which sustainable electrical and/or solar input drives production of hydrogen from water splitting using biocompatible
inorganic catalysts. The hydrogen is then used by living cells as a source of reducing equivalents for conversion of CO2 to the value-added chemical product methane. Using platinum or an earth-abundant substitute, α-NiS, as biocompatible hydrogen
evolution reaction (HER) electrocatalysts and Methanosarcina barkeri as a biocatalyst for CO2 fixation, we demonstrate robust and efficient electrochemical CO2 to CH4 conversion at up to 86% overall Faradaic efficiency for ≥7 d. Introduction of indium phosphide photocathodes and titanium
dioxide photoanodes affords a fully solar-driven system for methane generation from water and CO2, establishing that compatible inorganic and biological components can synergistically couple light-harvesting and catalytic
functions for solar-to-chemical conversion.
Co-reporter:Dohyung Kim;Kelsey K. Sakimoto;Dr. Dachao Hong; Peidong Yang
Angewandte Chemie 2015 Volume 127( Issue 11) pp:3309-3316
Publication Date(Web):
DOI:10.1002/ange.201409116
Abstract
Angesichts der Unvereinbarkeit eines zunehmenden Verbrauchs von Kraftstoffen und chemischen Produkten und einer nur endlichen Menge an Ressourcen versuchen wir Möglichkeiten zu finden, wie wir unsere Gesellschaft auf Dauer nachhaltig gestalten können. Die künstliche Photosynthese nutzt das Sonnenlicht, um reichlich vorhandene Ressourcen in hochwertige Chemikalien umzuwandeln. Deshalb gilt sie als die aussichtsreichste Methode. Hier werden Entwicklungen und neueste Fortschritte sowie noch bestehende Herausforderungen für ihre Schlüsselprozesse, die photoelektrochemische Wasserspaltung und die elektrochemische CO2-Reduktion, beschrieben. Ein Überblick über die Fortschritte in der Katalyse, um den erneuerbaren Wasserstoff als Grundstoff für die Produktion von Chemikalien einzusetzen, soll verdeutlichen, welche Rolle die künstliche Photosynthese in einer nachhaltigen Chemie spielen wird.
Co-reporter:Dohyung Kim;Kelsey K. Sakimoto;Dr. Dachao Hong; Peidong Yang
Angewandte Chemie International Edition 2015 Volume 54( Issue 11) pp:3259-3266
Publication Date(Web):
DOI:10.1002/anie.201409116
Abstract
The apparent incongruity between the increasing consumption of fuels and chemicals and the finite amount of resources has led us to seek means to maintain the sustainability of our society. Artificial photosynthesis, which utilizes sunlight to create high-value chemicals from abundant resources, is considered as the most promising and viable method. This Minireview describes the progress and challenges in the field of artificial photosynthesis in terms of its key components: developments in photoelectrochemical water splitting and recent progress in electrochemical CO2 reduction. Advances in catalysis, concerning the use of renewable hydrogen as a feedstock for major chemical production, are outlined to shed light on the ultimate role of artificial photosynthesis in achieving sustainable chemistry.
Co-reporter:Letian Dou;Andrew B. Wong;Yi Yu;Minliang Lai;Nikolay Kornienko;Samuel W. Eaton;Anthony Fu;Connor G. Bischak;Jie Ma;Tina Ding;Naomi S. Ginsberg;Lin-Wang Wang;A. Paul Alivisatos;Peidong Yang
Science 2015 Vol 349(6255) pp:1518-1521
Publication Date(Web):25 Sep 2015
DOI:10.1126/science.aac7660
Flat perovskite crystals
Bulk crystals and thick films of inorganic-organic perovskite materials such as CH3NH3PbI3 have shown promise as active material for solar cells. Dou et al. show that thin films—a single unit cell or a few unit cells thick—of a related composition, (C4H9NH3)2PbBr4, form squares with edges several micrometers long. These materials exhibit strong and tunable blue photoluminescence.
Science, this issue p. 1518
Co-reporter:Nikolay Kornienko, Desiré D. Whitmore, Yi Yu, Stephen R. Leone, and Peidong Yang
ACS Nano 2015 Volume 9(Issue 4) pp:3951
Publication Date(Web):April 3, 2015
DOI:10.1021/nn507335j
The tunable physical and electronic structure of III–V semiconductor alloys renders them uniquely useful for a variety of applications, including biological imaging, transistors, and solar energy conversion. However, their fabrication typically requires complex gas phase instrumentation or growth from high-temperature melts, which consequently limits their prospects for widespread implementation. Furthermore, the need for lattice matched growth substrates in many cases confines the composition of the materials to a narrow range that can be epitaxially grown. In this work, we present a solution phase synthesis for indium gallium phosphide (InxGa1–xP) alloy nanowires, whose indium/gallium ratio, and consequently, physical and electronic structure, can be tuned across the entire x = 0 to x = 1 composition range. We demonstrate the evolution of structural and optical properties of the nanowires, notably the direct to indirect band gap transition, as the composition is varied from InP to GaP. Our scalable, low-temperature synthesis affords compositional, structural, and electronic tunability and can provide a route for realization of broader InxGa1–xP applications.Keywords: alloy; nanowire; solution phase synthesis;
Co-reporter:Neil P. Dasgupta;Jianwei Sun;Chong Liu;Sarah Brittman;Sean C. Andrews;Jongwoo Lim;Hanwei Gao;Ruoxue Yan;Peidong Yang
Advanced Materials 2014 Volume 26( Issue 14) pp:2137-2184
Publication Date(Web):
DOI:10.1002/adma.201305929
Semiconductor nanowires (NWs) have been studied extensively for over two decades for their novel electronic, photonic, thermal, electrochemical and mechanical properties. This comprehensive review article summarizes major advances in the synthesis, characterization, and application of these materials in the past decade. Developments in the understanding of the fundamental principles of “bottom-up” growth mechanisms are presented, with an emphasis on rational control of the morphology, stoichiometry, and crystal structure of the materials. This is followed by a discussion of the application of nanowires in i) electronic, ii) sensor, iii) photonic, iv) thermoelectric, v) photovoltaic, vi) photoelectrochemical, vii) battery, viii) mechanical, and ix) biological applications. Throughout the discussion, a detailed explanation of the unique properties associated with the one-dimensional nanowire geometry will be presented, and the benefits of these properties for the various applications will be highlighted. The review concludes with a brief perspective on future research directions, and remaining barriers which must be overcome for the successful commercial application of these technologies.
Co-reporter:Liming Zhang, Kaihui Liu, Andrew Barnabas Wong, Jonghwan Kim, Xiaoping Hong, Chong Liu, Ting Cao, Steven G. Louie, Feng Wang, and Peidong Yang
Nano Letters 2014 Volume 14(Issue 11) pp:6418-6423
Publication Date(Web):October 24, 2014
DOI:10.1021/nl502961e
Atomically thin two-dimensional (2D) layered materials, including graphene, boron nitride, and transition metal dichalcogenides (TMDs), can exhibit novel phenomena distinct from their bulk counterparts and hold great promise for novel electronic and optoelectronic applications. Controlled growth of such 2D materials with different thickness, composition, and symmetry are of central importance to realize their potential. In particular, the ability to control the symmetry of TMD layers is highly desirable because breaking the inversion symmetry can lead to intriguing valley physics, nonlinear optical properties, and piezoelectric responses. Here we report the first chemical vapor deposition (CVD) growth of spirals of layered MoS2 with atomically thin helical periodicity, which exhibits a chiral structure and breaks the three-dimensional (3D) inversion symmetry explicitly. The spirals composed of tens of connected MoS2 layers with decreasing areas: each basal plane has a triangular shape and shrinks gradually to the summit when spiraling up. All the layers in the spiral assume an AA lattice stacking, which is in contrast to the centrosymmetric AB stacking in natural MoS2 crystals. We show that the noncentrosymmetric MoS2 spiral leads to a strong bulk second-order optical nonlinearity. In addition, we found that the growth of spirals involves a dislocation mechanism, which can be generally applicable to other 2D TMD materials.
Co-reporter:Sarah Brittman, Youngdong Yoo, Neil P. Dasgupta, Si-in Kim, Bongsoo Kim, and Peidong Yang
Nano Letters 2014 Volume 14(Issue 8) pp:4665-4670
Publication Date(Web):July 11, 2014
DOI:10.1021/nl501750h
As a p-type semiconducting oxide that can absorb visible light, cuprous oxide (Cu2O) is an attractive material for solar energy conversion. This work introduces a high-temperature, vapor-phase synthesis that produces faceted Cu2O nanowires that grow epitaxially along the surface of a lattice-matched, single-crystal MgO substrate. Individual wires were then fabricated into single-wire, all-oxide diodes and solar cells using low-temperature atomic layer deposition (ALD) of TiO2 and ZnO films to form the heterojunction. The performance of devices made from pristine Cu2O wires and chlorine-exposed Cu2O wires was investigated under one-sun and laser illumination. These faceted wires allow the fabrication of well-controlled heterojunctions that can be used to investigate the interfacial properties of all-oxide solar cells.
Co-reporter:Kelsey K. Sakimoto, Chong Liu, Jongwoo Lim, and Peidong Yang
Nano Letters 2014 Volume 14(Issue 9) pp:5471-5476
Publication Date(Web):August 12, 2014
DOI:10.1021/nl502946j
Studying bacteria–nanostructure interactions is crucial to gaining controllable interfacing of biotic and abiotic components in advanced biotechnologies. For bioelectrochemical systems, tunable cell–electrode architectures offer a path toward improving performance and discovering emergent properties. As such, Sporomusa ovata cells cultured on vertical silicon nanowire arrays formed filamentous cells and aligned parallel to the nanowires when grown in increasing ionic concentrations. Here, we propose a model describing the kinetic and the thermodynamic driving forces of bacteria–nanowire interactions.
Co-reporter:Dandan Zhang ; Andrew B. Wong ; Yi Yu ; Sarah Brittman ; Jianwei Sun ; Anthony Fu ; Brandon Beberwyck ; A. Paul Alivisatos ;Peidong Yang
Journal of the American Chemical Society 2014 Volume 136(Issue 50) pp:17430-17433
Publication Date(Web):December 3, 2014
DOI:10.1021/ja511010q
As a cation-deficient, p-type semiconductor, copper sulfide (Cu2–xS) shows promise for applications such as photovoltaics, memristors, and plasmonics. However, these applications demand precise tuning of the crystal phase as well as the stoichiometry of Cu2–xS, an ongoing challenge in the synthesis of Cu2–xS materials for a specific application. Here, a detailed transformation diagram of cation-exchange (CE) chemistry from cadmium sulfide (CdS) into Cu2–xS nanowires (NWs) is reported. By varying the reaction time and the reactants’ concentration ratio, the progression of the CE process was captured, and tunable crystal phases of the Cu2–xS were achieved. It is proposed that the evolution of Cu2–xS phases in a NW system is dependent on both kinetic and thermodynamic factors. The reported data demonstrate that CE can be used to precisely control the structure, composition, and crystal phases of NWs, and such control may be generalized to other material systems for a variety of practical applications.
Co-reporter:Joaquin Resasco, Neil P. Dasgupta, Josep Roque Rosell, Jinghua Guo, and Peidong Yang
Journal of the American Chemical Society 2014 Volume 136(Issue 29) pp:10521-10526
Publication Date(Web):July 15, 2014
DOI:10.1021/ja505734s
The synthesis of one-dimensional nanostructures with specific properties is often hindered by difficulty in tuning the material composition without sacrificing morphology and material quality. Here, we present a simple solid state diffusion method utilizing atomic layer deposition to controllably alter the composition of metal oxide nanowires. This compositional control allows for modification of the optical, electronic, and electrochemical properties of the semiconductor nanowires. Using this method and a novel process for manganese oxide atomic layer deposition, we produced manganese-doped rutile TiO2 nanowires and investigated their structural and photoelectrochemical properties. A homogeneous incorporation of the Mn dopant into the rutile lattice was observed, and the local chemical environment of the Mn was determined using X-ray absorption spectroscopy. The doping process resulted in a tunable enhancement in the electrocatalytic activity for water oxidation, demonstrating that this simple and general method can be used to control the properties of one-dimensional nanostructures for use in a variety of applications including solar-to-fuel generation.
Co-reporter:Chong Liu, Neil P. Dasgupta, and Peidong Yang
Chemistry of Materials 2014 Volume 26(Issue 1) pp:415
Publication Date(Web):October 2, 2013
DOI:10.1021/cm4023198
In this Perspective, we discuss current challenges in artificial photosynthesis research, with a focus on the benefits of a nanowire morphology. Matching the flux between electrocatalysts and light-absorbers, and between individual semiconducting light-absorbers, are two major issues to design economically viable devices for artificial photosynthesis. With the knowledge that natural photosynthesis is an integrated nanosystem, individual building blocks of biomimetic artificial photosynthesis are discussed. Possible research directions are presented under an integrated device design scheme, with examples of our current progress in these areas. Coupling all of the components together, including electrocatalysts, light-absorbers, and charge transport units, is crucial due to both fundamental and practical considerations. Given the advantages of one-dimensional nanostructures, it is evident that semiconductor nanowires can function as essential building blocks and help to solve many of the issues in artificial photosynthesis.Keywords: artificial photosynthesis; nanowire; solar water splitting;
Co-reporter:Bin Liu, Cheng-Hao Wu, Jianwei Miao, and Peidong Yang
ACS Nano 2014 Volume 8(Issue 11) pp:11739
Publication Date(Web):November 3, 2014
DOI:10.1021/nn5051954
The generation of chemical fuels via direct solar-to-fuel conversion from a fully integrated artificial photosynthetic system is an attractive approach for clean and sustainable energy, but so far there has yet to be a system that would have the acceptable efficiency, durability and can be manufactured at a reasonable cost. Here, we show that a semiconductor mesh made from all inorganic nanowires can achieve unassisted solar-driven, overall water-splitting without using any electron mediators. Free-standing nanowire mesh networks could be made in large scales using solution synthesis and vacuum filtration, making this approach attractive for low cost implementation.Keywords: artificial photosynthesis; BiVO4; Rh-SrTiO3; semiconductor nanowire; solar water splitting;
Co-reporter:Xing Yi Ling;Ruoxue Yan;Sylvia Lo;Dat Tien Hoang;Chong Liu
Nano Research 2014 Volume 7( Issue 1) pp:132-143
Publication Date(Web):2014 January
DOI:10.1007/s12274-013-0380-0
A novel Ag-alumina hybrid surface-enhanced Raman spectroscopy (SERS) platform has been designed for the spectroscopic detection of surface reactions in the steady state. Single crystalline and faceted silver (Ag) nanoparticles with strong light scattering were prepared in large quantity, which enables their reproducible self-assembly into large scale monolayers of Raman sensor arrays by the Langmuir-Blodgett technique. The close packed sensor film contains high density of sub-nm gaps between sharp edges of Ag nanoparticles, which created large local electromagnetic fields that serve as “hot spots” for SERS enhancement. The SERS substrate was then coated with a thin layer of alumina by atomic layer deposition to prevent charge transfer between Ag and the reaction system. The photocatalytic water splitting reaction on a monolayer of anatase TiO2 nanoplates decorated with Pt co-catalyst nanoparticles was employed as a model reaction system. Reaction intermediates of water photo-oxidation were observed at the TiO2/solution interface under UV irradiation. The surface-enhanced Raman vibrations corresponding to peroxo, hydroperoxo and hydroxo surface intermediate species were observed on the TiO2 surface, suggesting that the photo-oxidation of water on these anatase TiO2 nanosheets may be initiated by a nucleophilic attack mechanism.
Co-reporter:Chen Chen;Yijin Kang;Ziyang Huo;Zhongwei Zhu;Wenyu Huang;Huolin L. Xin;Joshua D. Snyder;Dongguo Li;Jeffrey A. Herron;Manos Mavrikakis;Miaofang Chi;Karren L. More;Yadong Li;Nenad M. Markovic;Gabor A. Somorjai;Peidong Yang;Vojislav R. Stamenkovic
Science 2014 Volume 343(Issue 6177) pp:
Publication Date(Web):
DOI:10.1126/science.1249061
Giving Electrocatalysts an Edge
Platinum (Pt) is an excellent catalyst for the oxygen-reduction reaction (ORR) in fuel cells and electrolyzers, but it is too expensive and scarce for widespread deployment, even when dispersed as Pt nanoparticles on carbon electrode supports (Pt/C). Alternatively, Chen et al. (p. 1339, published online 27 February; see the Perspective by Greer) made highly active ORR catalysts by dissolving away the interior of rhombic dodecahedral PtNi3 nanocrystals to leave Pt-rich Pt3Ni edges. These nanoframe catalysts are durable—remaining active after 10,000 rounds of voltage cycling—and are far more active than Pt/C.
Co-reporter:Chong Liu, Jinyao Tang, Hao Ming Chen, Bin Liu, and Peidong Yang
Nano Letters 2013 Volume 13(Issue 6) pp:2989-2992
Publication Date(Web):May 6, 2013
DOI:10.1021/nl401615t
Artificial photosynthesis, the biomimetic approach to converting sunlight’s energy directly into chemical fuels, aims to imitate nature by using an integrated system of nanostructures, each of which plays a specific role in the sunlight-to-fuel conversion process. Here we describe a fully integrated system of nanoscale photoelectrodes assembled from inorganic nanowires for direct solar water splitting. Similar to the photosynthetic system in a chloroplast, the artificial photosynthetic system comprises two semiconductor light absorbers with large surface area, an interfacial layer for charge transport, and spatially separated cocatalysts to facilitate the water reduction and oxidation. Under simulated sunlight, a 0.12% solar-to-fuel conversion efficiency is achieved, which is comparable to that of natural photosynthesis. The result demonstrates the possibility of integrating material components into a functional system that mimics the nanoscopic integration in chloroplasts. It also provides a conceptual blueprint of modular design that allows incorporation of newly discovered components for improved performance.
Co-reporter:Hoon Eui Jeong, Ilsoo Kim, Pierre Karam, Heon-Jin Choi, and Peidong Yang
Nano Letters 2013 Volume 13(Issue 6) pp:2864-2869
Publication Date(Web):May 17, 2013
DOI:10.1021/nl401205b
Understanding how living cells interact with nanostructures is integral to a better understanding of the fundamental principles of biology and the development of next-generation biomedical/bioenergy devices. Recent studies have demonstrated that mammalian cells can recognize nanoscale topographies and respond to these structures. From this perspective, there is a growing recognition that nanostructures, along with their specific physicochemical properties, can also be used to regulate the responses and motions of bacterial cells. Here, by utilizing a well-defined silicon nanowire array platform and single-cell imaging, we present direct evidence that Shewanella oneidensis MR-1 can recognize nanoscale structures and that their swimming patterns and initial attachment locations are strongly influenced by the presence of nanowires on a surface. Analyses of bacterial trajectories revealed that MR-1 cells exhibited a confined diffusion mode in the presence of nanowires and showed preferential attachment to the nanowires, whereas a superdiffusion mode was observed in the absence of nanowires. These results demonstrate that nanoscale topography can affect bacterial movement and attachment and play an important role during the early stages of biofilm formation.
Co-reporter:Neil P. Dasgupta ; Chong Liu ; Sean Andrews ; Fritz B. Prinz ;Peidong Yang
Journal of the American Chemical Society 2013 Volume 135(Issue 35) pp:12932-12935
Publication Date(Web):August 20, 2013
DOI:10.1021/ja405680p
The photocathodic hydrogen evolution reaction (HER) from p-type Si nanowire (NW) arrays was evaluated using platinum deposited by atomic layer deposition (ALD) as a HER cocatalyst. ALD of Pt on the NW surface led to a highly conformal coating of nanoparticles with sizes ranging from 0.5 to 3 nm, allowing for precise control of the Pt loading in deep submonolayer quantities. The catalytic performance was measured using as little as 1 cycle of Pt ALD, which corresponded to a surface mass loading of ∼10 ng/cm2. The quantitative exploration of the lower limits of Pt cocatalyst loading reported here, and its application to high-surface-area NW photoelectrodes, establish a general approach for minimizing the cost of precious-metal cocatalysts for efficient and affordable solar-to-fuel applications.
Co-reporter:Yujie Sun ; Chong Liu ; David C. Grauer ; Junko Yano ⊗; Jeffrey R. Long ; Peidong Yang ;Christopher J. Chang
Journal of the American Chemical Society 2013 Volume 135(Issue 47) pp:17699-17702
Publication Date(Web):November 13, 2013
DOI:10.1021/ja4094764
A cobalt-sulfide (Co–S) film prepared via electrochemical deposition on conductive substrates is shown to behave as an efficient and robust catalyst for electrochemical and photoelectrochemical hydrogen generation from neutral pH water. Electrochemical experiments demonstrate that the film exhibits a low catalytic onset overpotential (η) of 43 mV, a Tafel slope of 93 mV/dec, and near 100% Faradaic efficiency in pH 7 phosphate buffer. Catalytic current densities can approach 50 mA/cm2 and activity is maintained for at least 40 h. The catalyst can also be electrochemically coated on silicon, rendering a water-compatible photoelectrochemical system for hydrogen production under simulated 1 sun illumination. The facile preparation of this Co–S film, along with its low overpotential, high activity, and long-term aqueous stability, offer promising features for potential use in solar energy applications.
Co-reporter:Bin Liu ; Hao Ming Chen ; Chong Liu ; Sean C. Andrews ; Chris Hahn ;Peidong Yang
Journal of the American Chemical Society 2013 Volume 135(Issue 27) pp:9995-9998
Publication Date(Web):July 1, 2013
DOI:10.1021/ja403761s
Practical implementation of one-dimensional semiconductors into devices capable of exploiting their novel properties is often hindered by low product yields, poor material quality, high production cost, or overall lack of synthetic control. Here, we show that a molten-salt flux scheme can be used to synthesize large quantities of high-quality, single-crystalline TiO2 nanowires with controllable dimensions. Furthermore, in situ dopant incorporation of various transition metals allows for the tuning of optical, electrical, and catalytic properties. With this combination of control, robustness, and scalability, the molten-salt flux scheme can provide high-quality TiO2 nanowires to satisfy a broad range of application needs from photovoltaics to photocatalysis.
Co-reporter:Yujie Sun, Jianwei Sun, Jeffrey R. Long, Peidong Yang and Christopher J. Chang
Chemical Science 2013 vol. 4(Issue 1) pp:118-124
Publication Date(Web):06 Sep 2012
DOI:10.1039/C2SC21163G
Recently, a family of cobalt pentapyridine complexes of the type [(R-PY5Me2)Co(H2O)])(CF3SO3)2, (R = CF3, H, or NMe2; PY5Me2 = 2,6-bis(1,1-di(pyridin-2-yl)ethyl)pyridine) were shown to catalyze the electrochemical generation of hydrogen from neutral aqueous solutions using a mercury electrode. We now report that the CF3 derivative of this series, [(CF3PY5Me2)Co(H2O)](CF3SO3)2 (1), can also operate in neutral water as an electrocatalyst for hydrogen generation under soluble, diffusion-limited conditions on a glassy carbon electrode, as well as a photocatalyst for hydrogen production using either molecular or semiconductor nanowire photosensitizers. Owing to its relatively low overpotential compared to other members of the PY5 family, complex 1 exhibits multiple redox features on glassy carbon, including a one-proton, one-electron coupled oxidative wave. Further, rotating disk electrode voltammetry measurements reveal the efficacy of 1 as a competent hydrogen evolution catalyst under soluble, diffusion-limited conditions. In addition, we establish that 1 can also generate hydrogen from neutral water under photocatalytic conditions with visible light irradiation (λirr ≥ 455 nm), using [Ru(bpy)3]2+ as a molecular inorganic chromophore and ascorbic acid as a sacrificial donor. Dynamic light scattering measurements show no evidence for nanoparticle formation for the duration of the photolytic hydrogen evolution experiments. Finally, we demonstrate that 1 is also able to enhance the hydrogen photolysis yield of GaP nanowires in water, showing that this catalyst is compatible with solid-state photosensitizers. Taken together, these data establish that the well-defined cobalt pentapyridine complex [(CF3PY5Me2)Co(H2O)]2+ is a versatile catalyst for hydrogen production from pure aqueous solutions using either solar or electrical input, providing a starting point for integrating molecular systems into sustainable energy generation devices.
Co-reporter:Cheng Hao Wu;Dr. Christopher Hahn;Sher Bahadar Khan;Abdullah M. Asiri;Salem M. Bawaked;Dr. Peidong Yang
Chemistry – An Asian Journal 2013 Volume 8( Issue 10) pp:2354-2357
Publication Date(Web):
DOI:10.1002/asia.201300717
Co-reporter:Christopher Hahn, Amy A. Cordones, Sean C. Andrews, Hanwei Gao, Anthony Fu, Stephen R. Leone, and Peidong Yang
The Journal of Physical Chemistry C 2013 Volume 117(Issue 7) pp:3627-3634
Publication Date(Web):January 31, 2013
DOI:10.1021/jp311685x
The utility of an annealing procedure in ammonia ambient is investigated for improving the optical characteristics of InxGa1–xN nanowires (0.07 ≤ x ≤ 0.42) grown on c-Al2O3 using a halide chemical vapor deposition method. Morphological studies using scanning electron microscopy confirm that the nanowire morphology is retained after annealing in ammonia at temperatures up to 800 °C. However, significant indium etching and composition inhomogeneities are observed for higher indium composition nanowires (x = 0.28, 0.42), as measured by energy-dispersive X-ray spectroscopy and Z-contrast scanning transmission electron microscopy. Structural analyses, using X-ray diffraction and high-resolution transmission electron microscopy, indicate that this is a result of the greater thermal instability of higher indium composition nanowires. The effect of these structural changes on the optical quality of InGaN nanowires is examined using steady-state and time-resolved photoluminescence measurements. Annealing in ammonia enhances the integrated photoluminescence intensity of InxGa1–xN nanowires by up to a factor of 4.11 ± 0.03 (for x = 0.42) by increasing the rate of radiative recombination. Fitting of photoluminescence decay curves to a Kohlrausch stretched exponential indicates that this increase is directly related to a larger distribution of recombination rates from composition inhomogeneities caused by annealing. The results demonstrate the role of thermal instability on the improved optical properties of InGaN nanowires annealed in ammonia.
Co-reporter:Joel Henzie;Xing Yi Ling;Peidong Yang;Sean C. Andrews;Zhiyong Li
PNAS 2013 Volume 110 (Issue 17 ) pp:6640-6645
Publication Date(Web):2013-04-23
DOI:10.1073/pnas.1218616110
Shaped colloids can be used as nanoscale building blocks for the construction of composite, functional materials that are
completely assembled from the bottom up. Assemblies of noble metal nanostructures have unique optical properties that depend
on key structural features requiring precise control of both position and connectivity spanning nanometer to micrometer length
scales. Identifying and optimizing structures that strongly couple to light is important for understanding the behavior of
surface plasmons in small nanoparticle clusters, and can result in highly sensitive chemical and biochemical sensors using
surface-enhanced Raman spectroscopy (SERS). We use experiment and simulation to examine the local surface plasmon resonances
of different arrangements of Ag polyhedral clusters. High-resolution transmission electron microscopy shows that monodisperse,
atomically smooth Ag polyhedra can self-assemble into uniform interparticle gaps that result in reproducible SERS enhancement
factors from assembly to assembly. We introduce a large-scale, gravity-driven assembly method that can generate arbitrary
nanoparticle clusters based on the size and shape of a patterned template. These templates enable the systematic examination
of different cluster arrangements and provide a means of constructing scalable and reliable SERS sensors.
Co-reporter:Hanwei Gao;Peidong Yang;Sean C. Andrews;Anthony Fu
PNAS 2013 Volume 110 (Issue 3 ) pp:865-869
Publication Date(Web):2013-01-15
DOI:10.1073/pnas.1217335110
The miniaturization of optoelectronic devices is essential for the continued success of photonic technologies. Nanowires have
been identified as potential building blocks that mimic conventional photonic components such as interconnects, waveguides,
and optical cavities at the nanoscale. Semiconductor nanowires with high optical gain offer promising solutions for lasers
with small footprints and low power consumption. Although much effort has been directed toward controlling their size, shape,
and composition, most nanowire lasers currently suffer from emitting at multiple frequencies simultaneously, arising from
the longitudinal modes native to simple Fabry–Pérot cavities. Cleaved-coupled cavities, two Fabry–Pérot cavities that are
axially coupled through an air gap, are a promising architecture to produce single-frequency emission. The miniaturization
of this concept, however, imposes a restriction on the dimensions of the intercavity gaps because severe optical losses are
incurred when the cross-sectional dimensions of cavities become comparable to the lasing wavelength. Here we theoretically
investigate and experimentally demonstrate spectral manipulation of lasing modes by creating cleaved-coupled cavities in gallium
nitride (GaN) nanowires. Lasing operation at a single UV wavelength at room temperature was achieved using nanoscale gaps
to create the smallest cleaved-coupled cavities to date. Besides the reduced number of lasing modes, the cleaved-coupled nanowires
also operate with a lower threshold gain than that of the individual component nanowires. Good agreement was found between
the measured lasing spectra and the predicted spectral modes obtained by simulating optical coupling properties. This agreement
between theory and experiment presents design principles to rationally control the lasing modes in cleaved-coupled nanowire
lasers.
Co-reporter:Anna P. Goldstein, Sean C. Andrews, Robert F. Berger, Velimir R. Radmilovic, Jeffrey B. Neaton, and Peidong Yang
ACS Nano 2013 Volume 7(Issue 12) pp:10747
Publication Date(Web):November 15, 2013
DOI:10.1021/nn403836d
Existing models for the crystal structure of indium zinc oxide (IZO) and indium iron zinc oxide (IFZO) conflict with electron microscopy data. We propose a model based on imaging and spectroscopy of IZO and IFZO nanowires and verify it using density functional theory. The model features a {12̅1} “zigzag” layer, which is an inversion domain boundary containing 5-coordinate indium and/or iron atoms. Higher values are observed for greater proportion of iron. We suggest a mechanism of formation in which the basal inclusion and the zigzag diffuse inward together from the surface of the nanowire.Keywords: crystal structure; EELS; indium diffusion; nanowires; zinc oxide
Co-reporter:Chong Liu, Jianwei Sun, Jinyao Tang, and Peidong Yang
Nano Letters 2012 Volume 12(Issue 10) pp:5407-5411
Publication Date(Web):October 1, 2012
DOI:10.1021/nl3028729
Gallium phosphide (GaP) nanowire photocathodes synthesized using a surfactant-free solution–liquid–solid (SLS) method were investigated for their photoelectrochemical evolution of hydrogen. Zinc as a p-type dopant was introduced into the nanowires during synthesis to optimize the photocathode’s response. Investigation of the electrical properties of Zn-doped GaP nanowires confirmed their p-type conductivity. After optimization of the nanowire diameter and Zn doping concentration, higher absorbed photon-to-current efficiency (APCE) over the spectrum was achieved. The versatility of the SLS synthesis and the capability to control the electrical properties suggest that our approach could be generalized to other III–V and II–VI semiconductors.
Co-reporter:Yun Jeong Hwang, Cheng Hao Wu, Chris Hahn, Hoon Eui Jeong, and Peidong Yang
Nano Letters 2012 Volume 12(Issue 3) pp:1678-1682
Publication Date(Web):February 27, 2012
DOI:10.1021/nl3001138
Three-dimensional hierarchical nanostructures were synthesized by the halide chemical vapor deposition of InGaN nanowires on Si wire arrays. Single phase InGaN nanowires grew vertically on the sidewalls of Si wires and acted as a high surface area photoanode for solar water splitting. Electrochemical measurements showed that the photocurrent density with hierarchical Si/InGaN nanowire arrays increased by 5 times compared to the photocurrent density with InGaN nanowire arrays grown on planar Si (1.23 V vs RHE). High-resolution transmission electron microscopy showed that InGaN nanowires are stable after 15 h of illumination. These measurements show that Si/InGaN hierarchical nanostructures are a viable high surface area electrode geometry for solar water splitting.
Co-reporter:Jongwoo Lim, Kedar Hippalgaonkar, Sean C. Andrews, Arun Majumdar, and Peidong Yang
Nano Letters 2012 Volume 12(Issue 5) pp:2475-2482
Publication Date(Web):April 23, 2012
DOI:10.1021/nl3005868
Although it has been qualitatively demonstrated that surface roughness can reduce the thermal conductivity of crystalline Si nanowires (SiNWs), the underlying reasons remain unknown and warrant quantitative studies and analysis. In this work, vapor–liquid–solid (VLS) grown SiNWs were controllably roughened and then thoroughly characterized with transmission electron microscopy to obtain detailed surface profiles. Once the roughness information (root-mean-square, σ, correlation length, L, and power spectra) was extracted from the surface profile of a specific SiNW, the thermal conductivity of the same SiNW was measured. The thermal conductivity correlated well with the power spectra of surface roughness, which varies as a power law in the 1–100 nm length scale range. These results suggest a new realm of phonon scattering from rough interfaces, which restricts phonon transport below the Casimir limit. Insights gained from this study can help develop a more concrete theoretical understanding of phonon–surface roughness interactions as well as aid the design of next generation thermoelectric devices.
Co-reporter:Christopher Hahn;Melissa A. Fardy;Catherine Nguyen;Michelle Natera-Comte;Sean C. Andrews;Peidong Yang
Israel Journal of Chemistry 2012 Volume 52( Issue 11-12) pp:1111-1117
Publication Date(Web):
DOI:10.1002/ijch.201200067
Abstract
Recently, (Ga1-xZnx)(N1-xOx) has gained widespread attention as a comparatively high efficiency photocatalyst for visible-light-driven overall water splitting. Despite significant gains in efficiency over the past several years, a majority of the photogenerated carriers recombine within bulk powders. To improve the photocatalytic activity, we used an epitaxial casting method to synthesize single-crystalline, high surface area (Ga1-xZnx)(N1-xOx) nanotubes with ZnO compositions up to x=0.10. Individual nanotubes showed improved homogeneity over powder samples due to a well defined epitaxial interface for ZnO diffusion into GaN. Absorption measurements showed that the ZnO incorporation shifts the absorption into the visible region with a tail out to 500 nm. Gas chromatography (GC) was used to compare the solar water splitting activity of (Ga1-xZnx)(N1-xOx) nanotubes (x=0.05–0.10) with similar composition powders. Cocatalyst decorated samples were dispersed in aqueous solutions of CH3OH and AgO2CCH3 to monitor the H+ reduction and H2O oxidation half reactions, respectively. The nanotubes were found to have approximately 1.5–2 times higher photocatalytic activity than similar composition powders for the rate limiting H+ reduction half reaction. These results demonstrate that improvements in homogeneity and surface area using the nanotube geometry can enhance the photocatalytic activity of GaN:ZnO for solar water splitting.
Co-reporter:Hanwei Gao, Chong Liu, Hoon Eui Jeong, and Peidong Yang
ACS Nano 2012 Volume 6(Issue 1) pp:234
Publication Date(Web):December 6, 2011
DOI:10.1021/nn203457a
Photocatalytic water splitting represents a promising way to produce renewable hydrogen fuel from solar energy. Ultrathin semiconductor electrodes for water splitting are of particular interest because the optical absorption occurs in the region where photogenerated charge carriers can effectively contribute to the chemical reactions on the surface. It is therefore important to manipulate and concentrate the incident light so that more photons can be absorbed within the thin film. Here we show an enhanced photocurrent in a thin-film iron oxide photoanode coated on arrays of Au nanopillars. The enhancement can be attributed primarily to the increased optical absorption originating from both surface plasmon resonances and photonic-mode light trapping in the nanostructured topography. The resonances can be tuned to a desirable wavelength by varying the thickness of the iron oxide layer. A net enhancement as high as 50% was observed over the solar spectrum.Keywords: iron oxide; nanograting; photoanode; photocurrent; plasmonic
Co-reporter:Yun Jeong Hwang, Chris Hahn, Bin Liu, and Peidong Yang
ACS Nano 2012 Volume 6(Issue 6) pp:5060
Publication Date(Web):May 23, 2012
DOI:10.1021/nn300679d
We report that the length and surface properties of TiO2 nanowires can have a dramatic effect on their photoelectrochemical properties. To study the length dependence, rutile TiO2 nanowires (0.28–1.8 μm) were grown on FTO substrates with different reaction times (50–180 min) using a hydrothermal method. Nanowires show an increase in photocurrent with length, and a maximum photocurrent of 0.73 mA/cm2 was measured (1.5 V vs RHE) for 1.8 μm long nanowires under AM 1.5G simulated sunlight illumination. While the incident photon to current conversion efficiency (IPCE) increases linearly with photon absorptance (1–10–α×length) with near band gap illumination (λ = 410 nm), it decreases severely at shorter wavelengths of light for longer nanowires due to poor electron mobility. Atomic layer deposition (ALD) was used to deposit an epitaxial rutile TiO2 shell on nanowire electrodes which enhanced the photocatalytic activity by 1.5 times (1.5 V vs RHE) with 1.8 μm long nanowires, reaching a current density of 1.1 mA/cm2 (61% of the maximum photocurrent for rutile TiO2). Additionally, by fixing the epitaxial rutile shell thickness and studying photoelectrochemical (PEC) properties of different nanowire lengths (0.28–1.8 μm), we found that the enhancement of current increases with length. These results demonstrate that ALD coating improves the charge collection efficiency from TiO2 nanowires due to the passivation of surface states and an increase in surface area. Therefore, we propose that epitaxial coating on materials is a viable approach to improving their energy conversion efficiency.Keywords: atomic layer deposition; charge collection efficiency; length dependence; photoanode; photoelectrochemical water splitting; TiO2 nanowire
Co-reporter:Chong Liu, Yun Jeong Hwang, Hoon Eui Jeong, and Peidong Yang
Nano Letters 2011 Volume 11(Issue 9) pp:3755-3758
Publication Date(Web):July 18, 2011
DOI:10.1021/nl201798e
Artificial photosynthetic systems using semiconductor materials have been explored for more than three decades in order to store solar energy in chemical fuels such as hydrogen. By mimicking biological photosynthesis with two light-absorbing centers that relay excited electrons in a nanoscopic space, a dual-band gap photoelectrochemical (PEC) system is expected to have higher theoretical energy conversion efficiency than a single band gap system. This work demonstrates the vectorial charge transport of photogenerated electrons and holes within a single asymmetric Si/TiO2 nanowire using Kelvin probe force microscopy. Under UV illumination, higher surface potential was observed on the n-TiO2 side, relative to the potential of the p-Si side, as a result of majority carriers’ recombination at the Si/TiO2 interface. These results demonstrate a new approach to investigate charge separation and transport in a PEC system. This asymmetric nanowire heterostructure with a dual band gap configuration and simultaneously exposed anode and cathode surfaces represents an ideal platform for the development of technologies for the generation of solar fuels, although better photoanode materials remain to be discovered.
Co-reporter:Sarah Brittman, Hanwei Gao, Erik C. Garnett, and Peidong Yang
Nano Letters 2011 Volume 11(Issue 12) pp:5189-5195
Publication Date(Web):November 14, 2011
DOI:10.1021/nl2023806
In recent photovoltaic research, nanomaterials have offered two new approaches for trapping light within solar cells to increase their absorption: nanostructuring the absorbing semiconductor and using metallic nanostructures to couple light into the absorbing layer. This work combines these two approaches by decorating a single-nanowire silicon solar cell with an octahedral silver nanocrystal. Wavelength-dependent photocurrent measurements and finite-difference time domain simulations show that increases in photocurrent arise at wavelengths corresponding to the nanocrystal’s surface plasmon resonances, while decreases occur at wavelengths corresponding to optical resonances of the nanowire. Scanning photocurrent mapping with submicrometer spatial resolution experimentally confirms that changes in the device’s photocurrent come from the silver nanocrystal. These results demonstrate that understanding the interactions between nanoscale absorbers and plasmonic nanostructures is essential to optimizing the efficiency of nanostructured solar cells.
Co-reporter:Akram Boukai, Paul Haney, Aaron Katzenmeyer, Gregg M. Gallatin, A. Alec Talin, Peidong Yang
Chemical Physics Letters 2011 Volume 501(4–6) pp:153-158
Publication Date(Web):7 January 2011
DOI:10.1016/j.cplett.2010.11.069
Abstract
Radial p–n junction solar cells have been predicted theoretically to have better efficiencies than their planar counterparts due to a decrease in the distance required to collect minority carriers relative to carrier diffusion length. This advantage is also significantly enhanced when the diffusion length is much smaller than the absorption length. The radial p–n junctions studied here consist of micron-scale to nano-scale diameter holes etched into a copper contaminated silicon wafer. Radial p–n junctions contaminated with copper impurities show roughly a twofold increase in efficiency than similarly contaminated planar p–n junction solar cells; however the enhancement is a strong function of the radial junction pitch, with maximum enhancement occurring for a pitch that is twice the carrier diffusion length.
Co-reporter:Feng Lin;Dat Tien Hoang;Chia-Kuang Tsung;Wenyu Huang
Nano Research 2011 Volume 4( Issue 1) pp:61-71
Publication Date(Web):2011 January
DOI:10.1007/s12274-010-0042-4
Uniform clusters of Pt have been deposited on the surface of capping-agent-free CeO2 nanooctahedra and nanorods using electron beam (e-beam) evaporation. The coverage of the Pt nanocluster layer can be controlled by adjusting the e-beam evaporation time. The resulting e-beam evaporated Pt nanocluster layers on the CeO2 surfaces have a clean surface and clean interface between Pt and CeO2. Different growth behaviors of Pt on the two types of CeO2 nanocrystals were observed, with epitaxial growth of Pt on CeO2 nanooctahedra and random growth of Pt on CeO2 nanorods. The structures of the Pt clusters on the two different types of CeO2 nanocrystals have been studied and compared by using them as catalysts for model reactions. The results of hydrogenation reactions clearly showed the clean and similar chemical surface of the Pt clusters in both catalysts. The support-dependent activity of these catalysts was demonstrated by CO oxidation. The Pt/CeO2 nanorods showed much higher activity compared with Pt/CeO2 nanooctahedra because of the higher concentration of oxygen vacancies in the CeO2 nanorods. The structure-dependent selectivity of dehydrogenation reactions indicates that the structures of the Pt on CeO2 nanorods and nanooctahedra are different. Thes differences arise because the metal deposition behaviors are modulated by the strong metal-metal oxide interactions.
Co-reporter:Christopher Hahn, Zhaoyu Zhang, Anthony Fu, Cheng Hao Wu, Yun Jeong Hwang, Daniel J. Gargas, and Peidong Yang
ACS Nano 2011 Volume 5(Issue 5) pp:3970
Publication Date(Web):April 15, 2011
DOI:10.1021/nn200521r
Significant synthetic challenges remain for the epitaxial growth of high-quality InGaN across the entire compositional range. One strategy to address these challenges has been to use the nanowire geometry because of its strain relieving properties. Here, we demonstrate the heteroepitaxial growth of InxGa1–xN nanowire arrays (0.06 ≤ x ≤ 0.43) on c-plane sapphire (Al2O3(001)) using a halide chemical vapor deposition (HCVD) technique. Scanning electron microscopy and X-ray diffraction characterization confirmed the long-range order and epitaxy of vertically oriented nanowires. Structural characterization by transmission electron microscopy showed that single crystalline nanowires were grown in the ⟨002⟩ direction. Optical properties of InGaN nanowire arrays were investigated by absorption and photoluminescence measurements. These measurements show the tunable direct band gap properties of InGaN nanowires into the yellow-orange region of the visible spectrum. To demonstrate the utility of our HCVD method for implementation into devices, LEDs were fabricated from InxGa1–xN nanowires epitaxially grown on p-GaN(001). Devices showed blue (x = 0.06), green (x = 0.28), and orange (x = 0.43) electroluminescence, demonstrating electrically driven color tunable emission from this p–n junction.Keywords: epitaxy; halide chemical vapor deposition; InGaN nanowires; light-emitting diode; tunable emission
Co-reporter:Allon I. Hochbaum and Peidong Yang
Chemical Reviews 2010 Volume 110(Issue 1) pp:527
Publication Date(Web):October 9, 2009
DOI:10.1021/cr900075v
Co-reporter:Ling-I Hung;Chia-Kuang Tsung;Wenyu Huang;Peidong Yang
Advanced Materials 2010 Volume 22( Issue 17) pp:1910-1914
Publication Date(Web):
DOI:10.1002/adma.200903947
Co-reporter:Erik Garnett and Peidong Yang
Nano Letters 2010 Volume 10(Issue 3) pp:1082-1087
Publication Date(Web):January 28, 2010
DOI:10.1021/nl100161z
Thin-film structures can reduce the cost of solar power by using inexpensive substrates and a lower quantity and quality of semiconductor material. However, the resulting short optical path length and minority carrier diffusion length necessitates either a high absorption coefficient or excellent light trapping. Semiconducting nanowire arrays have already been shown to have low reflective losses compared to planar semiconductors, but their light-trapping properties have not been measured. Using optical transmission and photocurrent measurements on thin silicon films, we demonstrate that ordered arrays of silicon nanowires increase the path length of incident solar radiation by up to a factor of 73. This extraordinary light-trapping path length enhancement factor is above the randomized scattering (Lambertian) limit (2n2 ∼ 25 without a back reflector) and is superior to other light-trapping methods. By changing the silicon film thickness and nanowire length, we show that there is a competition between improved absorption and increased surface recombination; for nanowire arrays fabricated from 8 μm thick silicon films, the enhanced absorption can dominate over surface recombination, even without any surface passivation. These nanowire devices give efficiencies above 5%, with short-circuit photocurrents higher than planar control samples.
Co-reporter:Peidong Yang, Ruoxue Yan and Melissa Fardy
Nano Letters 2010 Volume 10(Issue 5) pp:1529-1536
Publication Date(Web):April 15, 2010
DOI:10.1021/nl100665r
In this perspective, we take a critical look at the research progress within the nanowire community for the past decade. We discuss issues on the discovery of fundamentally new phenomena versus performance benchmarking for many of the nanowire applications. We also notice that both the bottom-up and top-down approaches have played important roles in advancing our fundamental understanding of this new class of nanostructures. Finally we attempt to look into the future and offer our personal opinions on what the future trends will be in nanowire research.
Co-reporter:Jinyao Tang, Hung-Ta Wang, Dong Hyun Lee, Melissa Fardy, Ziyang Huo, Thomas P. Russell, and Peidong Yang
Nano Letters 2010 Volume 10(Issue 10) pp:4279-4283
Publication Date(Web):September 14, 2010
DOI:10.1021/nl102931z
This work investigated the thermoelectric properties of thin silicon membranes that have been decorated with high density of nanoscopic holes. These “holey silicon” (HS) structures were fabricated by either nanosphere or block-copolymer lithography, both of which are scalable for practical device application. By reducing the pitch of the hexagonal holey pattern down to 55 nm with 35% porosity, the thermal conductivity of HS is consistently reduced by 2 orders of magnitude and approaches the amorphous limit. With a ZT value of ∼0.4 at room temperature, the thermoelectric performance of HS is comparable with the best value recorded in silicon nanowire system.
Co-reporter:Alejandro L. Briseno, Thomas W. Holcombe, Akram I. Boukai, Erik C. Garnett, Steve W. Shelton, Jean J. M. Fréchet and Peidong Yang
Nano Letters 2010 Volume 10(Issue 1) pp:334-340
Publication Date(Web):December 15, 2009
DOI:10.1021/nl9036752
We demonstrate the basic operation of an organic/inorganic hybrid single nanowire solar cell. End-functionalized oligo- and polythiophenes were grafted onto ZnO nanowires to produce p−n heterojunction nanowires. The hybrid nanostructures were characterized via absorption and electron microscopy to determine the optoelectronic properties and to probe the morphology at the organic/inorganic interface. Individual nanowire solar cell devices exhibited well-resolved characteristics with efficiencies as high as 0.036%, Jsc = 0.32 mA/cm2, Voc = 0.4 V, and a FF = 0.28 under AM 1.5 illumination with 100 mW/cm2 light intensity. These individual test structures will enable detailed analysis to be carried out in areas that have been difficult to study in bulk heterojunction devices.
Co-reporter:Daniel J. Gargas, Michael C. Moore, Adrian Ni, Shu-Wei Chang, Zhaoyu Zhang, Shun-Lien Chuang and Peidong Yang
ACS Nano 2010 Volume 4(Issue 6) pp:3270
Publication Date(Web):April 23, 2010
DOI:10.1021/nn9018174
Disk-shaped semiconductor nanostructures provide enhanced architectures for low-threshold whispering gallery mode (WGM) lasing with the potential for on-chip nanophotonic integration. Unlike cavities that lase via Fabry−Perot modes, WGM structures utilize low-loss, total internal reflection of the optical mode along the circumference of the structure, which effectively reduces the volume of gain material required for lasing. As a result, circularly resonant cavities provide much higher quality (Q) factors than lower reflection linear cavities, which makes nanodisks an ideal platform to investigate lasing nanostructures smaller than the free-space wavelength of light (i.e., subwavelength laser). Here we report the bottom-up synthesis and single-mode lasing properties of individual ZnO disks with diameters from 280 to 900 nm and show finite difference time domain (FDTD) simulations of the whispering gallery mode inside subwavelength diameter disks. These results demonstrate ultraviolet WGM lasing in chemically synthesized, isolated nanostructures with subwavelength diameters.Keywords: disk; lasing; mode simulation; whispering gallery; ZnO
Co-reporter:
Nature Photonics 2009 3(10) pp:
Publication Date(Web):2009-10-01
DOI:10.1038/nphoton.2009.184
Semiconductor nanowires, by definition, typically have cross-sectional dimensions that can be tuned from 2–200 nm, with lengths spanning from hundreds of nanometres to millimetres. These subwavelength structures represent a new class of semiconductor materials for investigating light generation, propagation, detection, amplification and modulation. After more than a decade of research, nanowires can now be synthesized and assembled with specific compositions, heterojunctions and architectures. This has led to a host of nanowire photonic devices including photodetectors, chemical and gas sensors, waveguides, LEDs, microcavity lasers, solar cells and nonlinear optical converters. A fully integrated photonic platform using nanowire building blocks promises advanced functionalities at dimensions compatible with on-chip technologies.
Co-reporter:Yun Jeong Hwang, Akram Boukai and Peidong Yang
Nano Letters 2009 Volume 9(Issue 1) pp:410-415
Publication Date(Web):December 1, 2008
DOI:10.1021/nl8032763
There are currently great needs to develop low-cost inorganic materials that can efficiently perform solar water splitting as photoelectrolysis of water into hydrogen and oxygen has significant potential to provide clean energy. We investigate the Si/TiO2 nanowire heterostructures to determine their potential for the photooxidation of water. We observed that highly dense Si/TiO2 core/shell nanowire arrays enhanced the photocurrent by 2.5 times compared to planar Si/TiO2 structure due to their low reflectance and high surface area. We also showed that n-Si/n-TiO2 nanowire arrays exhibited a larger photocurrent and open circuit voltage than p-Si/n-TiO2 nanowires due to a barrier at the heterojunction.
Co-reporter:Ziyang Huo, Chia-Kuang Tsung, Wenyu Huang, Melissa Fardy, Ruoxue Yan, Xiaofeng Zhang, Yadong Li and Peidong Yang
Nano Letters 2009 Volume 9(Issue 3) pp:1260-1264
Publication Date(Web):February 10, 2009
DOI:10.1021/nl900209w
Sub-2-nm (down to one-unit cell) uniform oxide nanocrystals and highly ordered superstructures were obtained in one step using oleylamine and oleic acid as capping and structure directing agents. The cooperative nature of the nanocrystal growth and assembly resulted in mesoscopic one-dimensional ribbon-like superstructures made of these ultrathin nanocrystals. The process reported here is general and can be readily extended to the production of many other transition metal (TiO2, ZnO, Nb2O5) and rare earth oxide (Eu2O3, Sm2O3, Er2O3, Y2O3, Tb2O3, and Yb2O3) systems.
Co-reporter:Martin J. Mulvihill ; Xing Yi Ling ; Joel Henzie ;Peidong Yang
Journal of the American Chemical Society 2009 Volume 132(Issue 1) pp:268-274
Publication Date(Web):December 10, 2009
DOI:10.1021/ja906954f
The understanding of the localized surface plasmons (LSPs) that occur at the geometrically bounded surface of metal nanoparticles continues to advance as new and more complex nanostructures are found. It has been shown that the oscillation of electrons at the metal dielectric interface is strongly dependent on the size, symmetry, and proximity of nanoparticles. Here, we present a new method to chemically control the shape of silver nanocrystals by using a highly anisotropic etching process. Tuning of the etchant strength and reaction conditions allows the preparation of new nanoparticle shapes in high yield and purity, which cannot be synthesized with conventional nanocrystal growth methods. The etching process produces intraparticle gaps, which introduce modified plasmonic characteristics and significant scattering intensity in the near-infrared. These new silver particles serve as excellent substrates for wavelength-tunable, single-particle surface enhanced Raman spectroscopy (spSERS).
Co-reporter:Wenjie Liang;Oded Rabin;Allon I. Hochbaum;Melissa Fardy;Minjuan Zhang
Nano Research 2009 Volume 2( Issue 5) pp:394-399
Publication Date(Web):2009 May
DOI:10.1007/s12274-009-9039-2
The thermoelectric properties of individual solution-phase synthesized p-type PbSe nanowires have been examined. The nanowires showed near degenerately doped charge carrier concentrations. Compared to the bulk, the PbSe nanowires exhibited a similar Seebeck coefficient and a significant reduction in thermal conductivity in the temperature range 20 K to 300 K. Thermal annealing of the PbSe nanowires allowed their thermoelectric properties to be controllably tuned by increasing their carrier concentration or hole mobility. After optimal annealing, single PbSe nanowires exhibited a thermoelectric figure of merit (ZT) of 0.12 at room temperature.
Co-reporter:Ruoxue Yan;Peter Pausauskie;Jiaxing Huang;Peidong Yang
PNAS 2009 Volume 106 (Issue 50 ) pp:21045-21050
Publication Date(Web):2009-12-15
DOI:10.1073/pnas.0902064106
Metallic nanoscale structures are capable of supporting surface plasmon polaritons (SPPs), propagating collective electron
oscillations with tight spatial confinement at the metal surface. SPPs represent one of the most promising structures to beat
the diffraction limit imposed by conventional dielectric optics. Ag nano wires have drawn increasing research attention due
to 2D sub-100 nm mode confinement and lower losses as compared with fabricated metal structures. However, rational and versatile
integration of Ag nanowires with other active and passive optical components, as well as Ag nanowire based optical routing
networks, has yet to be achieved. Here, we demonstrate that SPPs can be excited simply by contacting a silver nanowire with
a SnO2 nanoribbon that serves both as an unpolarized light source and a dielectric waveguide. The efficient coupling makes it possible
to measure the propagation-distance-dependent waveguide spectra and frequency-dependent propagation length on a single Ag
nanowire. Furthermore, we have demonstrated prototypical photonic-plasmonic routing devices, which are essential for incorporating
low-loss Ag nanowire waveguides as practical components into high-capacity photonic circuits.
Co-reporter:Andrea R. Tao, Jiaxing Huang and Peidong Yang
Accounts of Chemical Research 2008 Volume 41(Issue 12) pp:1662
Publication Date(Web):August 7, 2008
DOI:10.1021/ar8000525
Although nanocrystals and nanowires have proliferated new scientific avenues in the study of their physics and chemistries, the bottom-up assembly of these small-scale building blocks remains a formidable challenge for device fabrication and processing. An attractive nanoscale assembly strategy should be cheap, fast, defect tolerant, compatible with a variety of materials, and parallel in nature, ideally utilizing the self-assembly to generate the core of a device, such as a memory chip or optical display. Langmuir−Blodgett (LB) assembly is a good candidate for arranging vast numbers of nanostructures on solid surfaces. In the LB technique, uniaxial compression of a nanocrystal or nanowire monolayer floating on an aqueous subphase causes the nanostructures to assemble and pack over a large area. The ordered monolayer can then be transferred to a solid surface en masse and with fidelity. In this Account, we present the Langmuir−Blodgett technique as a low-cost method for the massively parallel, controlled organization of nanostructures. The isothermal compression of fluid-supported nanoparticles or nanowires is unique in its ability to achieve control over nanoscale assembly by tuning a macroscopic property such as surface pressure. Under optimized conditions (e.g., surface pressure, substrate hydrophobicity, and pulling speed), it allows continuous variation of particle density, spacing, and even arrangement. For practical application and device fabrication, LB compression is ideal for forming highly dense assemblies of nanowires and nanocrystals over unprecedented surface areas. In addition, the dewetting properties of LB monolayers can be used to further achieve patterning within the range of micrometers to tens of nanometers without a predefined template. The LB method should allow for easy integration of nanomaterials into current manufacturing schemes, in addition to fast device prototyping and multiplexing capability.
Co-reporter:Rongrui He, X. L. Feng, M. L. Roukes and Peidong Yang
Nano Letters 2008 Volume 8(Issue 6) pp:1756-1761
Publication Date(Web):May 16, 2008
DOI:10.1021/nl801071w
Electronic readout of the motions of genuinely nanoscale mechanical devices at room temperature imposes an important challenge for the integration and application of nanoelectromechanical systems (NEMS). Here, we report the first experiments on piezoresistively transduced very high frequency Si nanowire (SiNW) resonators with on-chip electronic actuation at room temperature. We have demonstrated that, for very thin (∼90 nm down to ∼30 nm) SiNWs, their time-varying strain can be exploited for self-transducing the devices’ resonant motions at frequencies as high as ∼100 MHz. The strain of wire elongation, which is only second-order in doubly clamped structures, enables efficient displacement transducer because of the enhanced piezoresistance effect in these SiNWs. This intrinsically integrated transducer is uniquely suited for a class of very thin wires and beams where metallization and multilayer complex patterning on devices become impractical. The 30 nm thin SiNW NEMS offer exceptional mass sensitivities in the subzeptogram range. This demonstration makes it promising to advance toward NEMS sensors based on ultrathin and even molecular-scale SiNWs, and their monolithic integration with microelectronics on the same chip.
Co-reporter:Ziyang Huo, Chia-kuang Tsung, Wenyu Huang, Xiaofeng Zhang and Peidong Yang
Nano Letters 2008 Volume 8(Issue 7) pp:2041-2044
Publication Date(Web):June 7, 2008
DOI:10.1021/nl8013549
Ultrathin single crystal Au nanowires with diameter of ∼1.6 nm and length of few micrometers were synthesized with high yield by simply mixing HAuCl4 and oleylamine at room temperature. High resolution transmission electron microscopy studies revealed that all of these nanowires are single crystalline and grew along the [111] direction. The valency evolution of the gold species during the synthesis was studied by X-ray photoelectron spectroscopy, which showed a clear Au3+ → Au+ → Au stepwise reduction at different reaction stages. Small angle X-ray scattering and small-angle X-ray diffraction suggest mesostructure formation upon HAuCl4 and oleylamine mixing. The slow in situ reduction of this mesostructure leads to the formation of ultrathin nanowires in solution. This novel nanowire growth mechanism relies on cooperative interaction, organization, and reaction between inorganic precursor salts and oleylamine.
Co-reporter:Elaine Lai;Woong Kim;Peidong Yang
Nano Research 2008 Volume 1( Issue 2) pp:123-128
Publication Date(Web):2008 August
DOI:10.1007/s12274-008-8017-4
Electroluminescence from a nanowire array-based light emitting diode is reported. The junction consists of a p-type GaN thin film grown by metal organic chemical vapor deposition (MOCVD) and a vertical n-type ZnO nanowire array grown epitaxially from the thin film through a simple low temperature solution method. The fabricated devices exhibit diode like current voltage behavior. Electroluminescence is visible to the human eye at a forward bias of 10 V and spectroscopy reveals that emission is dominated by acceptor to band transitions in the p-GaN thin film. It is suggested that the vertical nanowire architecture of the device leads to waveguided emission from the thin film through the nanowire array.
Co-reporter:Taleb Mokari Dr.;SusanE. Habas;Minjuan Zhang Dr.;Peidong Yang
Angewandte Chemie 2008 Volume 120( Issue 30) pp:5687-5690
Publication Date(Web):
DOI:10.1002/ange.200801162
Co-reporter:Taleb Mokari Dr.;SusanE. Habas;Minjuan Zhang Dr.;Peidong Yang
Angewandte Chemie International Edition 2008 Volume 47( Issue 30) pp:5605-5608
Publication Date(Web):
DOI:10.1002/anie.200801162
Co-reporter:Martin Mulvihill;Andrea Tao Dr.;Kanokraj Benjauthrit;John Arnold ;Peidong Yang
Angewandte Chemie International Edition 2008 Volume 47( Issue 34) pp:6456-6460
Publication Date(Web):
DOI:10.1002/anie.200800776
Co-reporter:Martin Mulvihill;Andrea Tao Dr.;Kanokraj Benjauthrit;John Arnold ;Peidong Yang
Angewandte Chemie 2008 Volume 120( Issue 34) pp:6556-6560
Publication Date(Web):
DOI:10.1002/ange.200800776
Co-reporter:Allon I. Hochbaum,
Renkun Chen,
Raul Diaz Delgado,
Wenjie Liang,
Erik C. Garnett,
Mark Najarian,
Arun Majumdar
&
Peidong Yang
Nature 2008 451(7175) pp:163
Publication Date(Web):2008-01-10
DOI:10.1038/nature06381
Approximately 90 per cent of the world’s power is generated by heat engines that use fossil fuel combustion as a heat source and typically operate at 30–40 per cent efficiency, such that roughly 15 terawatts of heat is lost to the environment. Thermoelectric modules could potentially convert part of this low-grade waste heat to electricity. Their efficiency depends on the thermoelectric figure of merit ZT of their material components, which is a function of the Seebeck coefficient, electrical resistivity, thermal conductivity and absolute temperature. Over the past five decades it has been challenging to increase ZT > 1, since the parameters of ZT are generally interdependent1. While nanostructured thermoelectric materials can increase ZT > 1 (refs 2–4), the materials (Bi, Te, Pb, Sb, and Ag) and processes used are not often easy to scale to practically useful dimensions. Here we report the electrochemical synthesis of large-area, wafer-scale arrays of rough Si nanowires that are 20–300 nm in diameter. These nanowires have Seebeck coefficient and electrical resistivity values that are the same as doped bulk Si, but those with diameters of about 50 nm exhibit 100-fold reduction in thermal conductivity, yielding ZT = 0.6 at room temperature. For such nanowires, the lattice contribution to thermal conductivity approaches the amorphous limit for Si, which cannot be explained by current theories. Although bulk Si is a poor thermoelectric material, by greatly reducing thermal conductivity without much affecting the Seebeck coefficient and electrical resistivity, Si nanowire arrays show promise as high-performance, scalable thermoelectric materials.
Co-reporter:M. Fardy;M. M. Zhang;A. I. Hochbaum;P. Yang;J. Goldberger
Advanced Materials 2007 Volume 19(Issue 19) pp:3047-3051
Publication Date(Web):11 SEP 2007
DOI:10.1002/adma.200602674
Single-crystalline arrays of PbS, PbSe, and PbTe nanowires (Figure: PbS) with diameters ranging from 40-200 nm and lengths up to 100 μm have been synthesized by a chemical vapor transport approach. Electrical and thermal characterization was performed to investigate their potential as thermoelectric materials. Compared to bulk, the nanowires exhibit reduced thermal conductivity below 100 K by up to 3 orders of magnitude, suggesting that they may be promising thermoelectric materials.
Co-reporter:W. Liang;E. C. Garnett;P. Yang
Advanced Materials 2007 Volume 19(Issue 19) pp:2946-2950
Publication Date(Web):31 AUG 2007
DOI:10.1002/adma.200700288
Pt nanoparticle catalysts are used to synthesize Si nanowires. The standard deviations of the starting colloid and the resulting wire diameters are essentially the same, whereas the wires were 22 % larger than the particles. The figure shows current–voltage plots of a silicon nanowire different gate voltages.
Co-reporter:D. J. Sirbuly;M. Law;P. Yang;A. Tao;R. Fan
Advanced Materials 2007 Volume 19(Issue 1) pp:61-66
Publication Date(Web):5 DEC 2006
DOI:10.1002/adma.200601995
A photonic sensing platform that utilizes the evanescent field of a subwavelength nanowire waveguide to perform optical spectroscopy on femtoliter probe volumes is demonstrated. Each evanescent sensor is capable of carrying out absorbance, fluorescence, and surface-enhanced Raman spectroscopy measurements on the same analyte while operating within a microfluidic flow cell (see figure).
Co-reporter:Jiaxing Huang Dr.;Rong Fan Dr.;Stephen Connor;Peidong Yang
Angewandte Chemie International Edition 2007 Volume 46(Issue 14) pp:
Publication Date(Web):27 FEB 2007
DOI:10.1002/anie.200604789
Dip, stick, slip: Dip coating, a widely used industrial process for making thin films, is used to align and position nanowires by means of the stick–slip motion of the solvent meniscus. Nanowire arrays with predefined spacing can be readily “printed” on a large substrate with tunable wire density (see picture), thus providing a facile method for producing nanowire-based devices.
Co-reporter:Jiaxing Huang Dr.;Rong Fan Dr.;Stephen Connor;Peidong Yang
Angewandte Chemie 2007 Volume 119(Issue 14) pp:
Publication Date(Web):27 FEB 2007
DOI:10.1002/ange.200604789
Eintauchen, haften, rutschen: Die Tauchbeschichtung, ein gängiger industrieller Prozess zur Herstellung dünner Filme, wurde verwendet, um Nanodrähte mithilfe der Haft-Rutsch-Bewegung des Lösungsmittelmeniskus auszurichten. Nanodrähte können so in vorgegebenem Abstand auf ein großes Substrat „gedruckt“ werden (siehe Bild), was entsprechende Funktionseinheiten einfach zugänglich macht.
Co-reporter:Yuri Nakayama,
Peter J. Pauzauskie,
Aleksandra Radenovic,
Robert M. Onorato,
Richard J. Saykally,
Jan Liphardt
&
Peidong Yang
Nature 2007 447(7148) pp:1098
Publication Date(Web):2007-06-28
DOI:10.1038/nature05921
One crucial challenge for subwavelength optics has been the development of a tunable source of coherent laser radiation for use in the physical, information and biological sciences that is stable at room temperature and physiological conditions. Current advanced near-field imaging techniques using fibre-optic scattering probes1, 2 have already achieved spatial resolution down to the 20-nm range. Recently reported far-field approaches for optical microscopy, including stimulated emission depletion3, structured illumination4, and photoactivated localization microscopy5, have enabled impressive, theoretically unlimited spatial resolution of fluorescent biomolecular complexes. Previous work with laser tweezers6, 7, 8 has suggested that optical traps could be used to create novel spatial probes and sensors. Inorganic nanowires have diameters substantially below the wavelength of visible light and have electronic and optical properties9, 10 that make them ideal for subwavelength laser and imaging technology. Here we report the development of an electrode-free, continuously tunable coherent visible light source compatible with physiological environments, from individual potassium niobate (KNbO3) nanowires. These wires exhibit efficient second harmonic generation, and act as frequency converters, allowing the local synthesis of a wide range of colours via sum and difference frequency generation. We use this tunable nanometric light source to implement a novel form of subwavelength microscopy, in which an infrared laser is used to optically trap and scan a nanowire over a sample, suggesting a wide range of potential applications in physics, chemistry, materials science and biology.
Co-reporter:
Nature Nanotechnology 2006 1(1) pp:
Publication Date(Web):
DOI:10.1038/nnano.2006.53
The piezoresistance effect of silicon1 has been widely used in mechanical sensors2, 3, 4, and is now being actively explored in order to improve the performance of silicon transistors5, 6. In fact, strain engineering is now considered to be one of the most promising strategies for developing high-performance sub-10-nm silicon devices7. Interesting electromechanical properties have been observed in carbon nanotubes8, 9. In this paper we report that Si nanowires possess an unusually large piezoresistance effect compared with bulk. For example, the longitudinal piezoresistance coefficient along the 111 direction increases with decreasing diameter for p-type Si nanowires, reaching as high as −3,550 × 10−11 Pa–1, in comparison with a bulk value of −94 × 10−11 Pa−1. Strain-induced carrier mobility change and surface modifications have been shown to have clear influence on piezoresistance coefficients. This giant piezoresistance effect in Si nanowires may have significant implications in nanowire-based flexible electronics, as well as in nanoelectromechanical systems.
Co-reporter:Benjamin D. Yuhas Dr.;Peter J. Pauzauskie;Rongrui He;Peidong Yang
Angewandte Chemie 2006 Volume 118(Issue 3) pp:
Publication Date(Web):12 DEC 2005
DOI:10.1002/ange.200503172
Gut gemischt! Zn1−xCoxO-Nanodrähte wurden mit einem lösungsbasierten Syntheseverfahren erhalten. Gemäß struktureller, optischer und spektroskopischer Charakterisierung ersetzen bei der Cobaltdotierung die Cobaltatome die Zinkkationen im Wirtsgitter (im Bild sind Co-dotierte ZnO-Nanodrähte zu sehen).
Co-reporter:Benjamin D. Yuhas, David O. Zitoun, Peter J. Pauzauskie, Rongrui He,Peidong Yang
Angewandte Chemie International Edition 2006 45(3) pp:420-423
Publication Date(Web):
DOI:10.1002/anie.200503172
Co-reporter:Andrea Tao;Prasert Sinsermsuksakul;Peidong Yang
Angewandte Chemie International Edition 2006 Volume 45(Issue 28) pp:
Publication Date(Web):22 JUN 2006
DOI:10.1002/anie.200601277
A scattering of silver: Polyhedral silver nanocrystals display complex and distinct scattering signatures dictated by their shape and size (see picture). The ability to engineer specific plasmon modes should have profound consequences for surface-enhanced Raman spectroscopy, subwavelength optics, and plasmonic transport.
Co-reporter:H.-J. Choi;H.-K. Seong;J. Chang;K.-I. Lee;Y.-J. Park;J.-J. Kim;S.-K. Lee;R. He;T. Kuykendall;P. Yang
Advanced Materials 2005 Volume 17(Issue 11) pp:
Publication Date(Web):24 MAR 2005
DOI:10.1002/adma.200401706
Single-crystalline diluted magnetic semiconductor GaN:Mn nanowires with controlled Mn concentrations have been successfully synthesized and incorporated into devices (see Figure). These nanowires exhibit Curie temperatures above room temperature, magnetoresistances near room temperature, and spin-dependent transport. The nanowires are used as building blocks for the fabrication of GaN:Mn/n-SiC based light-emitting diodes.
Co-reporter:Donald J. Sirbuly;Matt Law;Peter Pauzauskie;Haoquan Yan;Alex V. Maslov;Kelly Knutsen;Cun-Zheng Ning;Richard J. Saykally;Peidong Yang
PNAS 2005 102 (22 ) pp:7800-7805
Publication Date(Web):2005-05-31
DOI:10.1073/pnas.0408641102
The manipulation of photons in structures smaller than the wavelength of light is central to the development of nanoscale
integrated photonic systems for computing, communications, and sensing. We assemble small groups of freestanding, chemically
synthesized nanoribbons and nanowires into model structures that illustrate how light is exchanged between subwavelength cavities
made of three different semiconductors. The coupling strength of the optical linkages formed when nanowires are brought into
contact depends both on their volume of interaction and angle of intersection. With simple coupling schemes, lasing nanowires
can launch coherent pulses of light through ribbon waveguides that are up to a millimeter in length. Also, interwire coupling
losses are low enough to allow light to propagate across several right-angle bends in a grid of crossed ribbons. The fraction
of the guided wave traveling outside the wire/ribbon cavities is used to link nanowires through space and to separate colors
within multiribbon networks. In addition, we find that nanoribbons function efficiently as waveguides in liquid media and
provide a unique means for probing molecules in solution or in proximity to the waveguide surface. Our results lay the spadework
for photonic devices based on assemblies of active and passive nanowire elements and presage the use of nanowire waveguides
in microfluidics and biology.
Co-reporter:Andrea R. Tao ; Daniel P. Ceperley ; Prasert Sinsermsuksakul ; Andrew R. Neureuther ;Peidong Yang
Nano Letter () pp:
Publication Date(Web):October 17, 2008
DOI:10.1021/nl802877h
Metal nanostructures that support surface plasmons are compelling as plasmonic circuit elements and as the building blocks for metamaterials. We demonstrate here the spontaneous self-assembly of shaped silver nanoparticles into three-dimensional plasmonic crystals that display a frequency-selective response in the visible wavelengths. Extensive long-range order mediated by exceptional colloid monodispersity gives rise to optical passbands that can be tuned by particle volume fraction. These metallic supercrystals present a new paradigm for the fabrication of plasmonic materials, delivering a functional, tunable, completely bottom-up optical element that can be constructed on a massively parallel scale without lithography.
Co-reporter:Yujie Sun, Jianwei Sun, Jeffrey R. Long, Peidong Yang and Christopher J. Chang
Chemical Science (2010-Present) 2013 - vol. 4(Issue 1) pp:NaN124-124
Publication Date(Web):2012/09/06
DOI:10.1039/C2SC21163G
Recently, a family of cobalt pentapyridine complexes of the type [(R-PY5Me2)Co(H2O)])(CF3SO3)2, (R = CF3, H, or NMe2; PY5Me2 = 2,6-bis(1,1-di(pyridin-2-yl)ethyl)pyridine) were shown to catalyze the electrochemical generation of hydrogen from neutral aqueous solutions using a mercury electrode. We now report that the CF3 derivative of this series, [(CF3PY5Me2)Co(H2O)](CF3SO3)2 (1), can also operate in neutral water as an electrocatalyst for hydrogen generation under soluble, diffusion-limited conditions on a glassy carbon electrode, as well as a photocatalyst for hydrogen production using either molecular or semiconductor nanowire photosensitizers. Owing to its relatively low overpotential compared to other members of the PY5 family, complex 1 exhibits multiple redox features on glassy carbon, including a one-proton, one-electron coupled oxidative wave. Further, rotating disk electrode voltammetry measurements reveal the efficacy of 1 as a competent hydrogen evolution catalyst under soluble, diffusion-limited conditions. In addition, we establish that 1 can also generate hydrogen from neutral water under photocatalytic conditions with visible light irradiation (λirr ≥ 455 nm), using [Ru(bpy)3]2+ as a molecular inorganic chromophore and ascorbic acid as a sacrificial donor. Dynamic light scattering measurements show no evidence for nanoparticle formation for the duration of the photolytic hydrogen evolution experiments. Finally, we demonstrate that 1 is also able to enhance the hydrogen photolysis yield of GaP nanowires in water, showing that this catalyst is compatible with solid-state photosensitizers. Taken together, these data establish that the well-defined cobalt pentapyridine complex [(CF3PY5Me2)Co(H2O)]2+ is a versatile catalyst for hydrogen production from pure aqueous solutions using either solar or electrical input, providing a starting point for integrating molecular systems into sustainable energy generation devices.
![Hexanoic acid,6-[[5-[(3aS,4S,6aR)-hexahydro-2-oxo-1H-thieno[3,4-d]imidazol-4-yl]-1-oxopentyl]amino]-,2,5-dioxo-3-sulfo-1-pyrrolidinyl ester, sodium salt (1:1)](http://img.cochemist.com/ccimg/191700/191671-46-2.png)
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