Co-reporter:Haogang Zhu, Shancheng Yan, Shijie Xiong, and Xinglong Wu
Crystal Growth & Design November 1, 2017 Volume 17(Issue 11) pp:5608-5608
Publication Date(Web):October 5, 2017
DOI:10.1021/acs.cgd.7b00961
Sonication and centrifugation of two-dimensional nanosheets have been widely used to produce various layer-structured nanocrystals (LSNCs), but the formation mechanism is not yet clear. A general understanding is that the formation of LSNCs is due to the splitting of crystalline sheets under sonication/centrifugation. However, this has not been supported by experimental evidence. Here we experimentally show that high-speed rotation of amorphous black phosphorus ultrathin film can lead to the regulated formation of massive LSNCs confined in the spatial region of the original film. The probable sizes of these LSNCs are several nanometers depending on the rotation speed. Their volumes show a clear log-normal distribution having a line-width increase with rotation speed. This phenomenon can be explained based on the two-dimensional continuity and momentum equations. Our findings provide insight into formation and mechanisms of ultrathin amorphous films and LSNCs under sonication and centrifugation generally used.
Co-reporter:Lun Yang, Xiaobin Zhu, Shijie Xiong, Xinglong Wu, Yun Shan, and Paul K. Chu
ACS Applied Materials & Interfaces 2016 Volume 8(Issue 22) pp:13966-13972
Publication Date(Web):May 23, 2016
DOI:10.1021/acsami.6b04045
Tungsten trioxide dihydrate (WO3·2H2O) nanoplates are prepared by in situ anodic oxidation of tungsten disulfide (WS2) film on carbon fiber paper (CFP). The WO3·2H2O/WS2 hybrid catalyst exhibits excellent synergistic effects which facilitate the kinetics of the hydrogen evolution reaction (HER). The electrochromatic effect takes place via hydrogen intercalation into WO3·2H2O. This process is accelerated by the desirable proton diffusion coefficient in the layered WO3·2H2O. Hydrogen spillover from WO3·2H2O to WS2 occurs via atomic polarization caused by the electric field of the charges on the planar defect or edge active sites of WS2. The optimized hybrid catalyst presents a geometrical current density of 100 mA cm–2 at 152 mV overpotential with a Tafel slope of ∼54 mV per decade, making the materials one of the most active nonprecious metal HER catalysts.
Co-reporter:Xiaobin Zhu, Yun Shan, Shijie Xiong, Jiancang Shen, and Xinglong Wu
ACS Applied Materials & Interfaces 2016 Volume 8(Issue 24) pp:15848-15854
Publication Date(Web):June 3, 2016
DOI:10.1021/acsami.6b05464
Graphene oxide (GO) is a good adsorbent for heavy-metal ions because the oxygen functional groups offer active adsorption sites, but a small-size GO with dense oxygen-containing groups has high water solubility causing difficulty in separation. Herein, GO is bound to large brianyoungite (BY) by Zn–O coordination via a hydrothermal reaction that produces BY-GO composites with hollow spherical and flakelike morphologies that are easy to remove. By producing abundant oxygen-containing groups on GO, the Cu2+ adsorption capacity increases to 1724.1 mg/g, which is the highest value in graphene-related materials. The experimental and theoretical analysis clearly shows that the infrared spectral shifts toward the low-frequency side of C–O–H and O═C–O bending vibrations in the BY-GO composites stem from the Zn2+ (or Cu2+) coordination with O atoms in GO. The BY-GO also exhibits tunable deep-red photoluminescence up to 750 nm with a quantum yield of about 1%, which may be useful in infrared optoelectronic devices and solar energy exploitation. The photoluminescence which is different from that previously reported from chemically derived GO can be attributed to the optical transition in the disorder-induced localized states of the carbon–oxygen functional groups.
Co-reporter:Shuyi Wu, Xinglong Wu, Paul K. Chu
Journal of Materials Science & Technology 2016 Volume 32(Issue 2) pp:182-188
Publication Date(Web):February 2016
DOI:10.1016/j.jmst.2015.12.014
Qianlong Xuan paper, lost two hundred years ago, was reproduced by engineers in Red-Star Xuan Paper Limited Liability Company of China. Its remarkable performance and profound historical value are highly regarded by artists and the paper commands very high price in the commercial market. Ink penetrates and spreads optimally in the paper and the words exhibit clear edges with small fluctuations because of the desirable wettability and wicking. These characteristics make it stand out from three Xuan paper samples. The good wettability, verified by contact angle measurements, is an essential prerequisite to strong wicking. Attenuated total reflectance Fourier-transform infrared spectroscopy is performed to determine the chemical structure of Qianlong Xuan paper and the relatively large hydrogen bonding ratio contributes to the hydrophilicity. The microstructure investigated by scanning electron microscopy and atomic force microscopy reveals wide fibers and a uniform fiber arrangement with good connectivity, dense network, as well as rough fiber surface. These unique properties endow Qianlong Xuan paper with strong wicking to improve the ink expression.
Co-reporter:Xiaoxu Liu, Lizhe Liu, Lun Yang, Xinglong Wu, and Paul K. Chu
The Journal of Physical Chemistry C 2016 Volume 120(Issue 43) pp:24917-24924
Publication Date(Web):October 13, 2016
DOI:10.1021/acs.jpcc.6b10303
Recent theoretical research has demonstrated that a new two-dimensional material, the monolayer of gray arsenic (arsenene), can respond to the blue and ultraviolet light leading to possible optoelectronic applications. However, some topological defects often affect various properties of arsenene. Here we theoretically investigate the arsenene with monovacancy (MV), divacancy (DV), and Stone–Wales (SW) defects. Three kinds of MVs are identified and the reconstructed structures of DV and SW defects are confirmed. The dynamical stability, rearrangement, and migration for these defects are investigated in detail. Optical spectral calculations indicate that the MVs enhance optical transitions in the forbidden bands of arsenene and two new characteristic peaks appear in the dielectric and absorption spectra. However, there is only one new peak in the spectrum induced by DV and SW defects. Calculations of band structures indicate that the MV induces two defect bands in the forbidden bands of pristine arsenene, which are responsible for the two new peaks in the dielectric and absorption spectra. Our findings suggest that the optical dielectric and absorption spectra can help identify the types of topological defects in arsenene.
Co-reporter:Jiarui Chen, Shuyu Qin, Xinglong Wu, and and Paul K. Chu
ACS Nano 2016 Volume 10(Issue 1) pp:832
Publication Date(Web):December 11, 2015
DOI:10.1021/acsnano.5b05936
Self-assembled peptide nanostructures have unique physical and biological properties and promising applications in electrical devices and functional molecular recognition. Although solution-based peptide molecules can self-assemble into different morphologies, it is challenging to control the self-assembly process. Herein, controllable self-assembly of diphenylalanine (FF) in an evaporative dewetting solution is reported. The fluid mechanical dimensionless numbers, namely Rayleigh, Marangoni, and capillary numbers, are introduced to control the interaction between the solution and FF molecules in the self-assembly process. The difference in the film thickness reflects the effects of Rayleigh and Marangoni convection, and the water vapor flow rate reveals the role of viscous fingering in the emergence of aligned FF flakes. By employing dewetting, various FF self-assembled patterns, like concentric and spokelike, and morphologies, like strips and hexagonal tubes/rods, can be produced, and there are no significant lattice structural changes in the FF nanostructures.Keywords: diphenylalanine self-assembly; evaporative dewetting; morphology and pattern control;
Co-reporter:Yun Shan;Hongyi Wu; Shijie Xiong; Xinglong Wu; Paul K. Chu
Angewandte Chemie International Edition 2016 Volume 55( Issue 6) pp:2017-2021
Publication Date(Web):
DOI:10.1002/anie.201508801
Co-reporter:Yun Shan;Hongyi Wu; Shijie Xiong; Xinglong Wu; Paul K. Chu
Angewandte Chemie 2016 Volume 128( Issue 6) pp:2057-2061
Publication Date(Web):
DOI:10.1002/ange.201508801
Co-reporter:J.Q. Xu, S.J. Xiong, X.L. Wu, L.Z. Liu, T.H. Li, Paul K. Chu
Acta Materialia 2015 Volume 83() pp:113-119
Publication Date(Web):15 January 2015
DOI:10.1016/j.actamat.2014.09.046
Abstract
A series of composites composed of 3C–SiC nanoparticles and metal oxide is fabricated by direct dispersion. Some vibrational modes observed from the 3C–SiC nanoparticle-based nanocomposites exhibit significant red shifts whereas other modes exhibit blue shifts, accompanied by increased line widths and asymmetry. However, these types of Raman shifts are not observed from composites containing only metal oxide nanoparticles, indicating that there are strong interfacial effects associated with the 3C–SiC nanoparticles causing electron buildup at the interface to produce surface plasmons. Our theoretical studies reveal that modification of the surface plasmon frequency caused by the larger electron population at the interface between the different materials produces the strong phonon–plasmon coupling, which shifts the Raman peaks around. The red shifts observed from some phonon modes and blue shifts from others can be explained if the interaction between the two longitudinal optical modes with first- and second-order strengths and plasmons is considered. Our results provide insights into the mechanism and fundamental understanding of the interactions between phonon modes and plasmons.
Co-reporter:L.Z. Liu, X.L. Wu, X.X. Liu, Paul K. Chu
Applied Surface Science 2015 Volume 356() pp:626-630
Publication Date(Web):30 November 2015
DOI:10.1016/j.apsusc.2015.08.125
Highlights
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Symmetry breaking is achieved by strain that modulates the band structure and carrier population.
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Compressed deformation transforms blue phosphorus into an in-plane structure.
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Superfluous electrons reduce the band gap causing a semiconductor–metal transition.
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Strain engineering is a useful method to design the related electronic devices.
Co-reporter:Lun Yang, Xinglong Wu, Xiaoshu Zhu, Chengyu He, Ming Meng, Zhixing Gan, Paul K. Chu
Applied Surface Science 2015 Volume 341() pp:149-156
Publication Date(Web):30 June 2015
DOI:10.1016/j.apsusc.2015.03.018
Highlights
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Amorphous nickel/cobalt tungsten sulfides were synthesized by a thermolytic process.
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Amorphous NiWS and CoWS could realize hydrogen evolution efficiently.
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Ni/Co promotion and annealing alter the porous structure and chemical bonding states.
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Active sites on the surface of amorphous WSx are increased with Ni or Co doping.
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Amorphous NiWS and CoWS have immense potentials in water splitting devices.
Co-reporter:L.Z. Liu, X.L. Wu, T.H. Li, J.C. Shen
Applied Surface Science 2015 Volume 347() pp:265-268
Publication Date(Web):30 August 2015
DOI:10.1016/j.apsusc.2015.04.085
Highlights
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SnO2 nanocrystals with bridging oxygen vacancies were prepared by laser ablation method.
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Bridging oxygen vacancies make the B2g mode redshift and occupy Eu(LO) position.
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Exact identification of both OV concentration and type can be realized by Raman scattering.
Co-reporter:Yanling Hao
The Journal of Physical Chemistry C 2015 Volume 119(Issue 6) pp:2956-2962
Publication Date(Web):January 22, 2015
DOI:10.1021/jp5114569
The photoluminescence (PL) spectra acquired from 1 to 6 nm large carbon quantum dots (CQDs) prepared by refluxing activated carbon in HNO3 show blue emission independent of the excitation wavelength as well as long-wavelength emission depending on the excitation wavelength. The dependence of the two emissions on pH is investigated, and the experimental results show that the peak position of the long-wavelength emission does not change with pH; however, the blue emission becomes more asymmetrical, and obvious shoulder peaks emerge as the pH increases. A model based on defect-bound trions in the CQDs is proposed to explain the shoulder peaks in the blue emission at high pH, and the calculated results agree well with experimental data concerning the integral intensity ratio of the trion to exciton emissions versus pH. Our experimental and theoretical results demonstrate for the first time emission from trions in CQDs.
Co-reporter:Ming Meng, Xinglong Wu, Xiaobin Zhu, Xiaoshu Zhu, and Paul K. Chu
ACS Applied Materials & Interfaces 2014 Volume 6(Issue 6) pp:4081
Publication Date(Web):February 25, 2014
DOI:10.1021/am4056358
Semiconductor nanowires (NWs) are useful building blocks in optoelectronic, sensing, and energy devices and one-dimensional NWs have been used in photoelectrochemical (PEC) water splitting because of the enhanced light absorption and charge transport. It has been theoretically predicted that the {001} facets of body center cubic (bcc) In2O3 nanocrystals can effectively accumulate photogenerated holes under illumination, but it is unclear whether facet cutting of NWs can enhance the efficiency of PEC water splitting. In this work, the photocurrent of square In2O3 NWs with four {001} facets is observed to be an order of magnitude larger than that of cylindrical In2O3 NWs under the same conditions and subsequent hydrogen treatment further promotes the PEC water splitting performance of the NWs. The optimized hydrogenated In2O3 NWs yield a photocurrent density of 1.2 mA/cm2 at 0.22 V versus Ag/AgCl with a Faradaic efficiency of about 84.4%. The enhanced PEC properties can be attributed to the reduced band gap due to merging of the disordered layer-induced band tail states with the valence band as well as improved separation of the photogenerated electrons/holes between the In2O3 crystal core and disordered layer interface. The results provide experimental evidence of the important role of facet cutting, which is promising in the design and fabrication of NW-based photoelectric devices.Keywords: facet cutting; hydrogen treatment; In2O3 nanowires; water splitting;
Co-reporter:Zhixing Gan, Xinglong Wu and Yanling Hao
CrystEngComm 2014 vol. 16(Issue 23) pp:4981-4986
Publication Date(Web):21 Mar 2014
DOI:10.1039/C4CE00200H
The blue photoluminescence from carbon nanodots (CNDs) weakens gradually and the most intense peak red-shifts slightly as the hydrothermal reaction time increases. The 890 cm−1 infrared vibration band, which is associated with carbon defects, decreases with the reaction time being consistent with the blue emission tendency. Based on the growth model of CNDs and understanding of photoluminescence from other carbon nanomaterials, carbon defects are believed to be responsible for the blue emission.
Co-reporter:Yanling Hao, Zhixing Gan, Jiaqing Xu, Xinglong Wu, Paul K. Chu
Applied Surface Science 2014 Volume 311() pp:490-497
Publication Date(Web):30 August 2014
DOI:10.1016/j.apsusc.2014.05.095
Highlights
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Poly(ethylene glycol)/carbon quantum dots (PEG/CQDs) composite solid films exhibiting strong and tunable blue–red emission were prepared. Successful preparation of tunable emitting CQDs solid films can extend the application of carbon quantum dots in photoelectric devices.
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The mechanism of the tunable emission from the PEG/CQDs composite solid films was discussed.
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On the basis of the characteristics of the PL from solid films in this work, the complex PL origins of CQDs were further defined. The PL mechanism provides insights into the fluorescence mechanism of CQDs and may promotes their applications.
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Poly(ethylene glycol); carbon quantum dots; Strong and tunable blue-red emission; The fluorescent quantum yield of 12.6%.
Co-reporter:Jing Wang, Xinglong Wu, Tinghui Li, Paul K. Chu
Scripta Materialia 2014 Volume 76() pp:17-20
Publication Date(Web):April 2014
DOI:10.1016/j.scriptamat.2013.12.004
Co-reporter:Ming Meng, Xinglong Wu, Xiaobin Zhu, Lun Yang, Zhixing Gan, Xiaoshu Zhu, Lizhe Liu, and Paul K. Chu
The Journal of Physical Chemistry Letters 2014 Volume 5(Issue 24) pp:4298-4304
Publication Date(Web):November 30, 2014
DOI:10.1021/jz502316h
Cubic In2O3 microparticles with exposed {001} facets as well as single morphology and size are produced on a large scale on silicon with a high yield. The morphological evolution during chemical vapor deposition is investigated and the new knowledge enables precise facet cutting. The synthesized Cubic In2O3 microparticles possess superior photoelectrocatalytic activity and excellent chemical and structural stability in oxygen evolution reaction on account of the unique surface structure and electronic band structure of the {001} facets. Our results reveal that it is feasible to promote the photolectrochemical water splitting efficiency of photoanode materials by controlling the growth on specific crystal facets. The technique and concept can be extended to other facet-specific materials in applications such as sensors, solar cells, and lithium batteries.Keywords: chemical vapor deposition; crystal facet cutting; cubic In2O3 microparticles; photoelectrochemical water splitting;
Co-reporter:Zhixing Gan, Xinglong Wu, Ming Meng, Xiaobin Zhu, Lun Yang, and Paul K. Chu
ACS Nano 2014 Volume 8(Issue 9) pp:9304
Publication Date(Web):August 25, 2014
DOI:10.1021/nn503249c
Photocatalysts possessing high efficiency in degrading aquatic organic pollutants are highly desirable. Although graphene-based nanocomposites exhibit excellent photocatalytic properties, the role of graphene has been largely underestimated. Herein, the photothermal effect of graphene-based nanocomposites is demonstrated to play an important role in the enhanced photocatalytic performance, which has not been considered previously. In our study on degradation of organic pollutants (methylene blue), the contribution of the photothermal effect caused by a nanocomposite consisting of P25 and reduced graphene oxide can be as high as ∼38% in addition to trapping and shuttling photogenerated electrons and increasing both light absorption and pollutant adsorptivity. The result reveals that the photothermal characteristic of graphene-based nanocomposite is vital to photocatalysis. It implies that designing graphene-based nanocomposites with the improved photothermal performance is a promising strategy to acquire highly efficient photocatalytic activity.Keywords: graphene; P25; photocatalyst; photothermal effect;
Co-reporter:Jinlei Zhang;Zhixing Gan;Xiaobin Zhu;Yamin Jin
Nano Research 2014 Volume 7( Issue 6) pp:929-937
Publication Date(Web):2014 June
DOI:10.1007/s12274-014-0455-6
High-temperature (150–220 °C) growth leads to the formation of some peptide nanotube/microtube (NT/MT) arrays but the NTs/MTs exhibit closed ends, irreversible phase modification and eliminations of piezoelectric and hydrophilic properties. Here we demonstrate the fabrication of unidirectionally aligned and stable diphenylalanine NT/MT arrays with centimeter scale area at room temperature by utilizing an external electric field. The interactions between the applied electric field and dipolar electric field on the NTs and surface positive charges are responsible for the formation. The unidirectionally aligned MT array exhibits a supercapacitance of 1,000 μF·cm−2 at a scanning rate of 50 mV·s−1; this is much larger than the values reported previously in peptide NT/MT arrays.
Co-reporter:Chengyu He ; Xinglong Wu ;Zhiqiang He
The Journal of Physical Chemistry C 2014 Volume 118(Issue 9) pp:4578-4584
Publication Date(Web):February 12, 2014
DOI:10.1021/jp408153b
Hydrogen generated by water splitting provides a renewable energy source, but development of materials with efficient electrocatalytic water splitting capability is challenging. Thin-film electrocatalytic material (H2–NiCat) with robust water reduction properties, which can be readily prepared by a reduction-induced electrodeposition method from nickel salts in a borate-buffered electrolyte (pH 9.2), is reported. The material consists of nanoparticles with nickel oxide or hydroxide species located at the surface and metallic nickel in the bulk. The catalyst mediates H2 evolution in a near-neutral aqueous buffer at low overpotential. The catalyst requires a subsequent oxidative pretreatment in order to attain a well-defined hydrogen evolution reaction (HER) activity, and the 1.5 h anodized catalyst film exhibits a HER current density of about 1.50 mA cm–2 at 0.452 V overpotential over a period of 24 h with no observable corrosion. In addition, it can be converted by anodic equilibration into an amorphous Ni-based oxide film (O2–NiCat) to catalyze O2 evolution, and the switch between the two catalytic forms is fully reversible. The robust, bifunctional, switchable, and noble-metal-free catalytic material has immense potential in artificial solar water-splitting devices.
Co-reporter:Yun Shan ; Xinglong Wu ; Xiao Gan ; Xiaobin Zhu ; Jiancang Shen ;Paul K. Chu
The Journal of Physical Chemistry C 2014 Volume 118(Issue 20) pp:11085-11092
Publication Date(Web):May 4, 2014
DOI:10.1021/jp500376u
Hydrogen peroxide (H2O2) is a potent oxidant that influences the growth and well-being of living organisms, and development of a probe to monitor H2O2 in biological media is of broad interest to chemistry, biology, and medicine. Herein, CdS:Mn–polysulfido nanoclusters (NCs) are demonstrated to be chromogenic probes that can monitor H2O2 in a fast and site-specific way. The NC complex is formed by a reaction between manganese ions and both polysulfido chains and small CdS nanoparticles. The NCs exhibit two color changes from beige to bright yellow and then colorless in the presence of H2O2. The bright yellow color appears within 15 s after the NCs come in contact with H2O2 and fades at a rate that is positively related to the H2O2 concentration. The appearance of the bright yellow color is accompanied by the production of a strong absorption peak at 387 nm related to free Mn-bonded polysulfido chains. Our results demonstrate potential applications of inorganic chromogenic nanomaterials to the monitoring of chemical and biological reactions.
Co-reporter:L. Z. Liu ; X. L. Wu ; X. X. Liu ; S. J. Xiong ;Paul K. Chu
The Journal of Physical Chemistry C 2014 Volume 118(Issue 44) pp:25429-25433
Publication Date(Web):October 10, 2014
DOI:10.1021/jp507221d
First-principles calculation discloses local magnetism on the β-SiC (110) and (001) surfaces due to nonmetallic dopants. The spontaneously polarized β-SiC (111) surface without dopants also exhibits strong magnetism which can be reduced significantly by dopant incorporation. The magnetic values depend on the arrangement of superfluous p electrons and location of dopants. If the dopants reach the third and seventh layers, the dopant-induced magnetism on the (001) and (110) surfaces disappears and the nonmagnetic bulk behavior is reverted. Our results suggest that surface magnetism can be tailored by facet engineering and dopant incorporation.
Co-reporter:Liangliang Sun ; Xinglong Wu ; Ming Meng ; Xiaobin Zhu ;Paul K. Chu
The Journal of Physical Chemistry C 2014 Volume 118(Issue 48) pp:28063-28068
Publication Date(Web):November 11, 2014
DOI:10.1021/jp510772u
By performing precise facet cutting during hydrothermal synthesis, single-morphological and uniform-sized octahedral and cubic Cu2O microcrystals respectively with {111} and {100} facets are synthesized and subsequently encapsulated with reduced graphene oxide (rGO). Electrochemical impedance spectroscopy shows that the rGO/Cu2O polyhedral composite has excellent conductivity, indicating that rGO can serve as a flexible electrically conducting channel. On account of the accumulation of a large amount of photoexcited electrons on the {111} facets of the octahedrons and efficient electron transfer to the rGO sheet, photodegradation of methyl orange by the rGO/Cu2O octahedral composite is enhanced by a factor of 4 compared to both bare Cu2O octahedrons and rGO-encapsulated cubes with hole accumulation on the {100} facets, and the stability of the rGO/Cu2O octahedrons is obviously improved due to no direct touch with water molecules in comparison with Cu2O microcrystals without rGO wrap reported previously. This work shows that the combination of crystal facet cutting and conducting channels is an effective strategy to design new composites with enhanced photocatalytic properties.
Co-reporter:Xiang Wang, Zhiqiang He, Shijie Xiong, and Xinglong Wu
The Journal of Physical Chemistry C 2014 Volume 118(Issue 4) pp:2222-2228
Publication Date(Web):January 14, 2014
DOI:10.1021/jp410813z
Crystalline pyramidal ε-FeSi particles smaller than 1 μm in size with {111} lateral facets are synthesized by a spontaneous chemical vapor deposition method. The nanocrystals initially nucleate from the amorphous film via self-clustering forming a rectangular ε-FeSi (001) terrace as a result of the cubic crystalline structure and subsequent anisotropic accumulation on the terrace produces the pyramidal morphology. Room-temperature ferromagnetism is observed from ε-FeSi particles larger than 250 nm and having the {111} facets. A model is postulated to explain the morphology- and size-dependent ferromagnetism based on the nonuniform Fe atomic arrangement that forms atomic-scale islands on the surface and dipole interaction among these islands in the large enough particles. The morphology- and size-dependent ferromagnetism allows control of the magnetic moments of mesostructures and is important to spintronics and other applications.
Co-reporter:Min Sun;Shijie Xiong;Chengyu He;Tinghui Li;Paul K. Chu
Advanced Materials 2013 Volume 25( Issue 14) pp:2035-2039
Publication Date(Web):
DOI:10.1002/adma.201203864
Co-reporter:Zhixing Gan;Shijie Xiong;Tao Xu;Xiaobin Zhu;Xiao Gan;Junhong Guo;Jiancang Shen;Litao Sun;Paul K. Chu
Advanced Optical Materials 2013 Volume 1( Issue 12) pp:926-932
Publication Date(Web):
DOI:10.1002/adom.201300368
Co-reporter:Zhixing Gan;Gengxia Zhou;Jiancang Shen;Paul K. Chu
Advanced Optical Materials 2013 Volume 1( Issue 8) pp:554-558
Publication Date(Web):
DOI:10.1002/adom.201300152
Co-reporter:G.X. Zhou, S.J. Xiong, X.L. Wu, L.Z. Liu, T.H. Li, Paul K. Chu
Acta Materialia 2013 Volume 61(Issue 19) pp:7342-7347
Publication Date(Web):November 2013
DOI:10.1016/j.actamat.2013.08.040
Abstract
A facile and economical chemical route was used to synthesize nitrogen-doped tin oxide (SnO2) nanocrystals (NCs). Infrared and Raman spectral examinations reveal the existence of oxygen vacancies and local disorder. Temperature-dependent photoluminescence (PL) measurements display a broad band at 640 nm at room temperature that shifts to a higher energy at lower measurement temperature. Excitation wavelength-dependent PL spectra show that the band blue-shifts and its line width decreases as the excitation wavelength is reduced. The PL peak also blue-shifts when the annealing temperature is increased. Spectral analysis and theoretical calculation suggest that the PL band stems from the mutual effects of oxygen vacancies and nitrogen dopants. This PL investigation on N-doped SnO2 NCs provides more insights about the optical properties and will promote further applications of SnO2 NCs.
Co-reporter:Zhixing Gan; Xinglong Wu;Xiaobin Zhu ;Jiancang Shen
Angewandte Chemie 2013 Volume 125( Issue 7) pp:2109-2113
Publication Date(Web):
DOI:10.1002/ange.201207992
Co-reporter:Zhixing Gan, Xinglong Wu, Jinlei Zhang, Xiaobin Zhu, and Paul K. Chu
Biomacromolecules 2013 Volume 14(Issue 6) pp:
Publication Date(Web):May 16, 2013
DOI:10.1021/bm400562c
The temperature sensing capability of diphenylalanine nanotubes is investigated. The materials can detect local rapid temperature changes and measure the absolute temperature in situ with a precision of 1 °C by monitoring the temperature-dependent photoluminescence (PL) intensity and lifetime, respectively. The PL lifetime is independent of ion concentrations in the medium as well as pH in the physiological range. This biocompatible thermal sensing platform has immense potential in the in situ mapping of microenvironmental temperature fluctuations in biological systems for disease diagnosis and therapeutics.
Co-reporter:Junhong Guo, Shijie Xiong, Xinglong Wu, Jiancang Shen, Paul K. Chu
Biomaterials 2013 34(36) pp: 9183-9189
Publication Date(Web):
DOI:10.1016/j.biomaterials.2013.08.023
Co-reporter:Zhixing Gan; Xinglong Wu;Xiaobin Zhu ;Jiancang Shen
Angewandte Chemie International Edition 2013 Volume 52( Issue 7) pp:2055-2059
Publication Date(Web):
DOI:10.1002/anie.201207992
Co-reporter:Chengyu He, Xinglong Wu, Jiancang Shen, and Paul K. Chu
Nano Letters 2012 Volume 12(Issue 3) pp:1545-1548
Publication Date(Web):March 2, 2012
DOI:10.1021/nl3006947
Good understanding of the reaction mechanism in the electrochemical reduction of water to hydrogen is crucial to renewable energy technologies. Although previous studies have revealed that the surface properties of materials affect the catalytic reactivity, the effects of a catalytic surface on the hydrogen evolution reaction (HER) on the molecular level are still not well understood. Contrary to general belief, water molecules do not adsorb onto the surfaces of 3C-SiC nanocrystals (NCs), but rather spontaneously dissociate via a surface autocatalytic process forming a complex consisting of −H and −OH fragments. In this study, we show that ultrathin 3C-SiC NCs possess superior electrocatalytic activity in the HER. This arises from the large reduction in the activation barrier on the NC surface enabling efficient dissociation of H2O molecules. Furthermore, the ultrathin 3C-SiC NCs show enhanced HER activity in photoelectrochemical cells and are very promising to the water splitting based on the synergistic electrocatalytic and photoelectrochemical actions. This study provides a molecular-level understanding of the HER mechanism and reveals that NCs with surface autocatalytic effects can be used to split water with high efficiency thereby enabling renewable and economical production of hydrogen.
Co-reporter:J. Y. He, X. Wang, X. L Wu and Paul K. Chu
RSC Advances 2012 vol. 2(Issue 8) pp:3254-3256
Publication Date(Web):02 Mar 2012
DOI:10.1039/C2RA00893A
Needle-shaped β-FeSi2 nanowhiskers with diameters of 1–5 nm and lengths of 20–100 nm are produced by chemical etching of β-FeSi2 powders with microscale particles. The nanowhiskers mainly exhibit a <400> growth direction due to the anisotropic etching following the lowest etching rate of the Fe atomic facets. The absorbance spectra show that the energy gap of the β-FeSi2 nanowhiskers increases from 0.81 (bulk) to 0.94 eV, demonstrating distinct quantum size effect.
Co-reporter:Xinglong Wu ; Shijie Xiong ; Junhong Guo ; Lingli Wang ; Chunyan Hua ; Yayi Hou ;Paul K. Chu
The Journal of Physical Chemistry C 2012 Volume 116(Issue 3) pp:2356-2362
Publication Date(Web):December 27, 2011
DOI:10.1021/jp210599z
Ultrathin alumina nanoparticles (NPs) with an average size of less than 4 nm are produced from porous anodic alumina membranes. The alumina NPs in a suspension produce strong blue tunable photoluminescence (PL) with a high quantum efficiency of ∼15% and Stokes shift as large as 1.0 eV. An obvious blue-shift and diminished line width are observed after storing the suspension in air. The tunable blue PL which is closely related to the oxygen vacancy (OV) defect centers at different depths beneath the surface depends on the NP size. The experimental observations are corroborated by theoretical derivation demonstrating that the electron wave functions of the OV-induced defect levels are extended in space, and quantum confinement takes place when the alumina NP is smaller than the spread of the wave functions. It is thus possible to control the PL behavior by changing the NP size and OV depth distribution and the alumina NPs are experimentally demonstrated to be robust and nontoxic biological probes.
Co-reporter:Xinglong Wu, Shijie Xiong, Minjie Wang, Jiancang Shen, and Paul K. Chu
The Journal of Physical Chemistry C 2012 Volume 116(Issue 17) pp:9793-9799
Publication Date(Web):April 10, 2012
DOI:10.1021/jp212087h
High-frequency molecular vibrations in bioinspired peptide nanostructures provide insight into the important interactions between peptides and water molecules. Raman spectra acquired from diphenylalanine (FF) nanotubes show that water bonded weakly to FF molecules in the nanochannel cores leads to splitting of the molecular vibrational mode of benzene rings at 1034 cm–1 into a doublet with the separation diminishing with decreasing water content. X-ray diffraction discloses that loss of water results in noticeable lattice expansion in the subnanometer crystalline structure comprising hexagonal unit cells, and derivation based on the density functional theory shows that the Raman-active phonon modes often appear in pairs due to the duality of the major components in the FF molecules. Without water, the two typical peaks in the vicinity of 1034 cm–1 from the vibrations of two benzene rings in the FF molecule are very close and usually cannot be distinguished experimentally, but with the addition of water, the two peaks are gradually separated and the relative intensities change. Our results demonstrate that Raman scattering can be used to probe the quantity of water molecules in FF NTs via the linear dependence of the Raman mode position at the low-frequency side of the double-peak mode at 1034 cm–1 on water molecule number bonded to each FF molecule. This knowledge is important to the fundamental understanding of the interactions between FF nanotubes and water, device design, as well as applications to biochemistry, medicine, and molecular sensing.
Co-reporter:Z. X. Gan, S. J. Xiong, X. L. Wu, C. Y. He, J. C. Shen, and Paul K. Chu
Nano Letters 2011 Volume 11(Issue 9) pp:3951-3956
Publication Date(Web):August 17, 2011
DOI:10.1021/nl202240s
The photoluminescence (PL) characteristics of Mn2+-bonded reduced graphene oxide (rGO) are studied in details. The Mn2+-bonded rGO is synthesized using MnO2-decorated GO as the intermediate products and ideal tunable PL is obtained by enhancing the long-wavelength (450–550 nm) emission. The PL spectra excited by different wavelengths are analyzed to elucidate the mechanism, and the resonant energy transfer between Mn2+ and sp2 clusters of the rGO appears to be responsible for the enhanced long-wavelength emission. To examine the effect of Mn2+ on the long-wavelength emission from the Mn2+-bonded rGO, the PL characteristics of Mn2+-bonded rGO with smaller Mn concentrations are studied and weaker emission is observed. Our theoretical calculation corroborates the experimental results.
Co-reporter:Min Sun, Xinglong Wu, Chengyu He and Paul K. Chu
CrystEngComm 2011 vol. 13(Issue 21) pp:6337-6341
Publication Date(Web):19 Sep 2011
DOI:10.1039/C1CE05833A
One-dimensional hierarchical AlN nanostructures comprising a thin nanowire on top of a nanocolumn were synthesized via a vapor–liquid–solid growth mechanism. The abrupt change in the gas flow rate in the growth chamber is responsible for the observed nanostructures. The dynamic equilibrium between absorption and evaporation of the catalyst droplet plays a key role in forming the multilevel nanostructures.
Co-reporter:W.N. Su, X.L. Wu, X.S. Wu, D.H. Wang, Y.W. Du, Paul K. Chu
Solid State Communications 2011 Volume 151(Issue 1) pp:5-8
Publication Date(Web):January 2011
DOI:10.1016/j.ssc.2010.10.039
Co-reporter:L.Z. Liu, X.L. Wu, F. Gao, J.C. Shen, T.H. Li, Paul K. Chu
Solid State Communications 2011 Volume 151(Issue 11) pp:811-814
Publication Date(Web):June 2011
DOI:10.1016/j.ssc.2011.03.029
Raman spectra acquired from SnO2 nanocrystals with different sizes show a size-independent Raman mode at ∼574 cm−1. The intensity increases as the nanocrystal size decreases and this tendency is contrary to that of the normal bulk Raman modes. By considering the existence of oxygen vacancies at the nanocrystal surface, we adopt the density functional theory to calculate the Raman spectra with different oxygen vacancy positions and concentrations. The results clearly demonstrate that the in-plane oxygen vacancy is responsible for the 574 cm−1 mode and the intensity enhancement is a result of the higher in-plane oxygen vacancy concentration.HighlightsThe position of the 574 cm−1 Raman mode is independent of SnO2 nanocrystal sizes.► Its intensity increases with decreasing SnO2 nanocrystal sizes. ► The calculation indicates that the in-plane oxygen vacancy is responsible for the 574 cm−1 mode.► Its intensity enhancement is a result of the higher in-plane oxygen vacancy concentration.
Co-reporter:Minjie Wang, Lingjie Du, Xinglong Wu, Shijie Xiong, and Paul K. Chu
ACS Nano 2011 Volume 5(Issue 6) pp:4448
Publication Date(Web):May 18, 2011
DOI:10.1021/nn2016524
Hexagonal hierarchical microtubular structures are produced by diphenylalanine self-assembly and the ratio of the relative humidity in the growth chamber to the diphenylalanine concentration (defined as the RH–FF ratio) determines the microtubular morphology. The hexagonal arrangement of the diphenylalanine molecules first induces the hexagonal nanotubes with opposite charges on the two ends, and the dipolar electric field on the nanotubes serves as the driving force. Side-by-side hexagonal aggregation and end-to-end arrangement ensue finally producing a hexagonal hierarchical microtubular structure. Staining experiments and the external electric field-induced parallel arrangement provide evidence of the existence of opposite charges and dipolar electric field. In this self-assembly, the different RH–FF ratios induce different contents of crystalline phases. This leads to different initial nanotube numbers finally yielding different microtubular morphologies. Our calculation based on the dipole model supports the dipole-field mechanism that leads to the different microtubular morphologies.Keywords: diphenylalanine nanotubes; dipolar electric field; hexagonal hierarchical structures; self-assembly
Co-reporter:J. Wang, S. J. Xiong, X. L. Wu, T. H. Li and Paul K. Chu
Nano Letters 2010 Volume 10(Issue 4) pp:1466-1471
Publication Date(Web):March 8, 2010
DOI:10.1021/nl100407d
We have produced glycerol-bonded 3C-SiC nanocrystal (NC) films, which when excited by photons of different wavelengths, produce strong and tunable violet to blue-green (360−540 nm) emission as a result of the quantum confinement effects rendered by the 3C-SiC NCs. The emission is so intense that the emission spots are visible to the naked eyes. The light emission is very stable and even after storing in air for more than six months, no intensity degradation can be observed. X-ray photoelectron spectroscopy and absorption fine structure measurements indicate that the Si-terminated NC surfaces are completely bonded to glycerol molecules. Calculations of geometry optimization and electron structures based on the density functional theory for 3C-SiC NCs with attached glycerol molecules show that these molecules are bonded on the NCs causing strong surface structural change, while the isolated levels in the conduction band of the bare 3C-SiC NCs are replaced with quasi-continuous bands that provide continuous tunability of the emitted light by changing the frequencies of exciting laser. As an application, we demonstrate the potential of using 3C-SiC NCs to fabricate full-color emitting solid films by incorporating porous silicon.
Co-reporter:L. Z. Liu, X. L. Wu, J. C. Shen, T. H. Li, F. Gao and Paul K. Chu
Chemical Communications 2010 vol. 46(Issue 30) pp:5539-5541
Publication Date(Web):24 Jun 2010
DOI:10.1039/C0CC01277G
By experimentally examining and theoretically analyzing the Raman spectra of SixGe1−x nanocrystal-embedded silica films, we show that the 430 cm−1 Si–Si optical phonon mode can be used as a fingerprint to identify the existence of local silicon cluster nanostructures inside SixGe1−x nanocrystals with high silicon content.
Co-reporter:H. T. Chen, S. J. Xiong, X. L. Wu, J. Zhu and J. C. Shen and Paul K. Chu
Nano Letters 2009 Volume 9(Issue 5) pp:1926-1931
Publication Date(Web):March 30, 2009
DOI:10.1021/nl900075f
Vacancy structures in tin oxide nanoribbons fabricated via thermal evaporation and post-processing are probed by luminescence spectroscopy, and interesting properties that bode well for oxygen sensing are observed. Besides a broad 620-nm band, the fabricated tin oxide nanoribbons show a photoluminescence band at 480 nm when the measurement temperature is <100 K. The blue band appears from nanoribbons synthesized under high oxygen pressure or annealed under oxygen. The dependence suggests that the oxygen interstitial and vacancy densities determine the electronic states that produce the blue band. Calculation of the electron structures based on the density functional theory shows that decreased oxygen vacancies or increased oxygen interstitials enhance the 480-nm band but suppress the 620-nm band. The results reported here indicate that the tin oxide nanoribbons with vacancy structures have potential applications in luminescence-sensitive oxygen sensing.
Co-reporter:X. L. Wu, S. J. Xiong, J. Zhu, J. Wang, J. C. Shen and Paul K. Chu
Nano Letters 2009 Volume 9(Issue 12) pp:4053-4060
Publication Date(Web):November 6, 2009
DOI:10.1021/nl902226u
SiC nanocrystals (NCs) exhibit unique surface chemistry and possess special properties. This provides the opportunity to design suitable surface structures by terminating the surface dangling bonds with different atoms thereby boding well for practical applications. In this article, we report the photoluminescence properties of 3C-SiC NCs in water suspensions with different pH values. Besides a blue band stemming from the quantum confinement effect, the 3C-SiC NCs show an additional photoluminescence band at 510 nm when the excitation wavelengths are longer than 350 nm. Its intensity relative to the blue band increases with the excitation wavelength. The 510 nm band appears only in acidic suspensions but not in alkaline ones. Fourier transform infrared, X-ray photoelectron spectroscopy, and X-ray absorption near-edge structure analyses clearly reveal that the 3C-SiC NCs in the water suspension have Si−H and Si−OH bonds on their surface, implying that water molecules only react with a Si-terminated surface. First-principle calculations suggest that the additional 510 nm band arises from structures induced by H+ and OH− dissociated from water and attached to Si dimers on the modified (001) Si-terminated portion of the NCs. The size requirement is consistent with the observation that the 510 nm band can only be observed when the excitation wavelengths are relatively large, that is, excitation of bigger NCs.
Co-reporter:Z. Liu ; X. D. Wen ; X. L. Wu ; Y. J. Gao ; H. T. Chen ; J. Zhu ;P. K. Chu
Journal of the American Chemical Society 2009 Volume 131(Issue 26) pp:9405-9412
Publication Date(Web):June 11, 2009
DOI:10.1021/ja9039136
Novel uniform-sized, core−shell ZnO mesocrystal microspheres have been synthesized on a large scale using a facile one-pot hydrothermal method in the presence of the water-soluble polymer poly(sodium 4-styrenesulfonate). The mesocrystal forms via a nonclassical crystallization process. The intrinsic dipole field introduced by the nanoplatelets as a result of selective adsorption of the polyelectrolyte on some polar surfaces of the nanoparticles acts as the driving force. In addition, it plays an important role throughout the mesoscale assembly process from the creation of the bimesocrystalline core to the apple-like structure and finally the microsphere. Our calculation based on a dipole model confirms the dipole-field-driven mechanism forming the apple-like structure.
Co-reporter:W.C. Zhang, X.L. Wu, H.T. Chen, Y.J. Gao, J. Zhu, G.S. Huang, Paul K. Chu
Acta Materialia 2008 Volume 56(Issue 11) pp:2508-2513
Publication Date(Web):June 2008
DOI:10.1016/j.actamat.2008.01.043
Abstract
Three kinds of silver nanostructures – nanowires, nanocubes and bipyramids – were synthesized via a simple solvothermal method by reducing silver nitrate with ethylene glycol using poly(vinylpyrrolidone) as an adsorption agent and adding different concentrations of sodium chloride (NaCl) into the solution. When a low-concentration NaCl solution is used, trace amounts of silver chloride (AgCl) appear and act as the seeds to facilitate the formation of the silver nanowires. However, when a high-concentration NaCl solution is used, large amounts of AgCl appear and mainly act as the controlling agent leading to the formation of silver nanocubes and bipyramids. Electron microscopy, X-ray diffraction and absorption spectra have been used to investigate the products, and a mechanism is proposed to interpret the morphological control of these structures. Our work provides a strategy to fabricate silver nanostructures with different shapes.
Co-reporter:Y.J. Gao, W.C. Zhang, X.L. Wu, Y. Xia, G.S. Huang, L.L. Xu, J.C. Shen, G.G. Siu, Paul K. Chu
Applied Surface Science 2008 Volume 255(Issue 5) pp:1982-1987
Publication Date(Web):30 December 2008
DOI:10.1016/j.apsusc.2008.06.137
Abstract
Self-assembled zinc oxide (ZnO) nanostructures consisting of nanorods were synthesized at low temperature by means of a one-step hydrothermal method using a mixture of hexamethylenetetramine, zinc nitrate [Zn(NO3)2·6H2O], and sodium hydroxide (NaOH). Freestanding single-crystalline ZnO nanorods with polar surfaces on the sharp ends are congregated by the long-range electrostatic force resulting in the formation of ordered nanorod-based structures. The weak Van der Waals interaction causes random aggregation of some tiny nanostructures on the surfaces of the ordered nanostructures. As a result, sphere-like superstructures revealed by X-ray powder diffraction, scanning electron microscopy and transmission electron microscopy are formed due to energy minimization. In addition, some interesting Raman and photoluminescence properties of the composite ZnO nanorod structures are also discussed in detail. Our results are beneficial to a better understanding of the formation mechanism of some ZnO superstructures.
Co-reporter:T. Qiu, X.L. Wu, J.C. Shen, Y. Xia, P.N. Shen, Paul K. Chu
Applied Surface Science 2008 Volume 254(Issue 17) pp:5399-5402
Publication Date(Web):30 June 2008
DOI:10.1016/j.apsusc.2008.02.060
Abstract
Based on diffusion-limited aggregation process, a convenient nanotechnique is demonstrated to obtain large silver fractal networks for a surface-enhanced Raman scattering (SERS)-active substrate. The silver fractal networks are of high SERS enhancement factor, large dynamical range. The observed SERS efficiency can be explained in terms of strongly localized plasmon modes relative to the single particle plasmon resonance.
Co-reporter:Y. Xiong, X.L. Wu, S.J. Xiong, Z.Y. Zhang, G.G. Siu, Paul K. Chu
Solid State Communications 2008 Volume 148(5–6) pp:182-185
Publication Date(Web):November 2008
DOI:10.1016/j.ssc.2008.08.023
A broad photoluminescence band centered at 745 nm was observed from Si nanowires (SiNWs) smaller than 4 nm in diameter with an oxide sheath. This emission band mainly originates from SiNWs grown along the [111] direction and its intensity increases with decreasing diameter and larger length. It becomes unobservable when the crystalline core of the SiNW is completely oxidized. Our theoretical calculations reveal electronic states in the band gap of the small diameter SiNWs when Si–O bands are formed and the results agree with experiments. This result provides insight into the electronic states of small-diameter SiNWs with surface oxide.
Co-reporter:Y.C. Cheng, X.L. Wu, S.H. Li, Paul K. Chu
Solid State Communications 2008 Volume 146(1–2) pp:69-72
Publication Date(Web):April 2008
DOI:10.1016/j.ssc.2008.01.017
Using the pseudopotential density functional method, an ab initio study has been performed to determine the lattice dynamics and thermodynamics of β-BC2N, including phonon dispersion, phonon density of states, and thermodynamic properties. A considerable energetic overlap between the LO-, TO-, and LA-phonons is revealed in the phonon dispersion. The total phonon density of states shows four main regions arising from different relative motions among the B, C1, C2, and N atoms. The calculation shows that β-BC2N has more vibration states in the low frequency region than diamond and hence, its heat capacity CvCv is greater than that of diamond. The Debye temperature ΘDΘD of β-BC2N, which determines the Debye stiffness, is found to be smaller and larger than those of diamond and cc-BN, respectively.
Co-reporter:F. Kong, X.L. Wu, G.S. Huang, R.K. Yuan, Paul K. Chu
Thin Solid Films 2008 Volume 516(Issue 18) pp:6287-6292
Publication Date(Web):31 July 2008
DOI:10.1016/j.tsf.2007.12.055
We have fabricated semiconducting polymer nanoparticles from poly[2-methoxy-5-(2'-ethyl-hexyloxy)-p-phenylene vinylene] (MEH-PPV), poly(N-vinylcarbazole) (PVK), and their blends via a reprecipitation method. When excited by the peak wavelength of the PVK absorption band, the polymer nanoparticles show enhanced emission from the MEH-PPV component. The emission color can be tuned from blue to orange–red by varying the content of the MEH-PPV component in the composite nanoparticles. Since the PVK nanoparticles have a wide photoluminescence (PL) spectrum, which overlaps well with the absorption band of the MEH-PPV nanoparticles, the PL enhancement is considered to be due to Förster energy transfer from PVK to MEH-PPV in the composite nanoparticles. Time-resolved fluorescence examinations confirm our assignment. These polymer nanoparticles are expected to have potential applications in future nano-optoelectronics.
Co-reporter:T. Qiu, X.L. Wu, F.Y. Jin, A.P. Huang, Paul K. Chu
Applied Surface Science 2007 Volume 253(Issue 8) pp:3987-3990
Publication Date(Web):15 February 2007
DOI:10.1016/j.apsusc.2006.08.034
Abstract
Unique magnesia (MgO) nanosheet arrays were fabricated via a promising micro-arc oxidation (MAO) technique on the surface of magnesium alloy. The non-uniform patterning of oxygen evolution on the sample surface and trapping of gas bubbles in the growing film are associated with the formations of the sheet and flower-like structures. These MgO structures may be useful in reinforcing composite materials or in further modifying other nanostructures.
Co-reporter:J.Y. Fan, X.L. Wu, Paul K. Chu
Progress in Materials Science 2006 Volume 51(Issue 8) pp:983-1031
Publication Date(Web):November 2006
DOI:10.1016/j.pmatsci.2006.02.001
Nanostructured silicon carbide has unique properties that make it useful in microelectronics, optoelectronics, and biomedical engineering. In this paper, the fabrication methods as well as optical and electrical characteristics of silicon carbide nanocrystals, nanowires, nanotubes, and nanosized films are reviewed. Silicon carbide nanocrystals are generally produced using two techniques, electrochemical etching of bulk materials to form porous SiC or embedding SiC crystallites in a matrix such as Si. Luminescence from SiC crystallites prepared by these two methods is generally believed to stem from surface or defect states. Stable colloidal 3C-SiC nanocrystals which exhibit intense visible photoluminescence arising from the quantum confinement effects have recently be produced. The field electron emission and photoluminescence characteristics of silicon carbide nanostructures as well as theoretical studies of the structural and electronic properties of the materials are described.
Co-reporter:P.Q. Zhao, X.L. Wu, J.Y. Fan, Paul K. Chu, G.G. Siu
Scripta Materialia 2006 Volume 55(Issue 12) pp:1123-1126
Publication Date(Web):December 2006
DOI:10.1016/j.scriptamat.2006.08.046
CdS nanocrystals were synthesized by a hydrothermal procedure and dispersed in an aqueous solution. CdS nanocrystal–polystyrene composites were produced by adding the CdS colloids into a toluene solution that contains dissolved polystyrene and casting the mixed solution onto a Si wafer. The photoluminescence from the composites was wavelength-tunable in the blue and its intensity was enhanced sixfold compared to that from the original solution. Raman results give unequivocal information about the origin of the intensity enhancement.
Co-reporter:D.S. Hu, X.L. Wu, M.X. Liao, N.C. Cheng, Paul K. Chu
Materials Chemistry and Physics 2006 Volume 97(2–3) pp:379-383
Publication Date(Web):10 June 2006
DOI:10.1016/j.matchemphys.2005.08.030
Electron beam irradiation was carried out to change the surface structure of Si nanocrystals in C60-coupled porous silicon with blue light emission at 460 nm. It was found that the photoluminescence (PL) intensities of the coupled system irradiated with an electron dose of 1015 cm−2 and energy of 0.5 MeV more than doubled compared to the untreated materials and then the intensities diminished with storage time in air. After 13 days, the PL intensities reached stable values that were higher than those observed from the untreated sample. Spectral analysis and ultraviolet ozone irradiation experiments on the coupled systems suggest that the formation of self-trapped excitons at the surfaces of the silicon nanocrystals with a higher density is responsible for the enhanced blue PL. Our technique provides an efficient way to improve the efficiency of blue light emission from these silicon nanostructures.
Co-reporter:T. Qiu, X.L. Wu, G.S. Huang, G.G. Siu, Y.F. Mei, F. Kong, M. Jiang
Thin Solid Films 2005 Volume 478(1–2) pp:56-60
Publication Date(Web):1 May 2005
DOI:10.1016/j.tsf.2004.10.002
Al-based anodic porous alumina membranes with ordered nanopore arrays are fabricated for exploring the template synthesis of carbon nanotubes and nanowires. Via the polymerization of acrylonitrile in the ordered nanopores of the membranes and subsequent heating, the polymer structure was converted into a quasi-graphitic structure. Atomic force microscopy observations revealed that the quasi-graphitic nanostructures are located in the pores of the porous alumina membrane, displaying a hexagonal symmetry. Raman scattering investigation confirmed the formation of carbon nanotubes in the nanopores. With further mild, controlled treatment in aqueous alkali and acidic solution, individual alumina nanotubes (ANTs) coaxially wrapping the carbon nanotubes and nanowires are obtained, as evidenced by transmission electron microscopy observations.
Co-reporter:Y.F. Mei, X.L. Wu, T. Qiu, X.F. Shao, G.G. Siu, Paul K. Chu
Thin Solid Films 2005 Volume 492(1–2) pp:66-70
Publication Date(Web):1 December 2005
DOI:10.1016/j.tsf.2005.06.044
Porous alumina templates with short-distance ordered 25 nm nanopores were fabricated by controlling anodizing progress of Al films on Si substrates in sulfuric acid solution. The ordering of nanopore arrangement with a hexagonal symmetry was found to be closely related to thickness of the deposited Al film, growth temperature, applied voltage, and solution concentration. These parameters were explored in detail and proper experimental conditions were obtained to be 0.44 μm, 5 °C, 20 V, and 15 wt.% for the formation of a relatively ordered nanopore array. Anodizing progress of the Al film was monitored through the current–time (I–t) curve. Infrared transmittance spectral characterization and microstructural observations disclose that a SiO2 island array has been formed on the surface of Si substrate under our experimental conditions. This kind of SiO2 island array can be expected to have applications in nanoelectronics and optoelectronics.
Co-reporter:Y. Gu, X.L. Wu, G.G. Siu, Z.Y. Zhang
Thin Solid Films 2005 Volume 476(Issue 1) pp:210-214
Publication Date(Web):1 April 2005
DOI:10.1016/j.tsf.2004.09.041
Using pulsed laser deposition, a layer of LiNbO3(:Fe) film with a thickness of 180 nm was coated onto porous Si (PS) stored in air for 1 year. A photoluminescence (PL) band enhanced about three times was observed at ∼625 nm with a same peak position as that of the stored PS. It is revealed that a new PL excitation band occurs at ∼363 nm, which is nearly equal to the fundamental optical absorption edge position of LiNbO3. The X-ray diffraction results disclose that the enhancement of the PL intensity is closely related to formation of a textured LiNbO3 film. Based on spectral analysis, we attribute the enhanced PL to optical transition in the E′ defect centers localized at the surfaces of PS nanocrystals, whereas the photoexcited carriers mainly come from the coated LiNbO3 film. This kind of LiNbO3(:Fe)/PS structures is expected to have important applications in modern ferroelectric optoelectronics.
Co-reporter:S.S. Deng, X.L. Wu, S.H. Yang
Acta Materialia 2004 Volume 52(Issue 7) pp:1953-1957
Publication Date(Web):19 April 2004
DOI:10.1016/j.actamat.2003.12.036
Abstract
Higher fullerenes (C70, C76, C84, C94) were covalently coupled on porous Si (PS) to form fullerene-coupled PS systems. After stored in air for 3–13 months, a blue photoluminescence (PL) was observed in the range of 430–480 nm. PL excitation spectral examinations reveal that the photoexcited carriers are generated in the quantum confined nanocrystalline Si (nc-Si ) cores, whereas radiative recombination occurs at the coupled nc-Si surface. Fourier-transform infrared absorption data disclose that the blue PL energy has a dependence on the oxygen content of nc-Si surface, indicating that the luminescent centers should be some oxygen-related defect states. Based on the annealing behavior of the blue PL peak in O2 and N2, we attribute the luminescent center to a pair of an oxygen vacancy and an interstitial oxygen, which also forms a peroxy linkage with an lattice oxygen.
Co-reporter:J Li, X.L Wu, D.S Hu, Y.M Yang, T Qiu, J.C Shen
Solid State Communications 2004 Volume 131(Issue 1) pp:21-25
Publication Date(Web):July 2004
DOI:10.1016/j.ssc.2004.04.026
(Ge:SiO2)/SiO2 multilayers were fabricated for exploring the influence of the stress on the structure of Ge nanocrystals. When annealed at 800 °C, the multilayers show a clear splitting (fine structure) of the Ge (220) X-ray diffraction peak and have a preferred orientation. Similar effects cannot take place in the multilayers annealed at higher or lower temperature. Analyses of Raman scattering, X-ray diffraction spectroscopy, and transmission electron microscope observations suggest that the observed phenomena arise from compressive stress exerted on Ge nanocrystals, which is induced by the confinement of both the SiO2 matrix in the cosputtered layer and neighboring SiO2 layers. The stress may cause an orthorhombic distortion of the diamond structure of bulk Ge. This will lead to the disappearance of the (111) and (311) diffraction peaks and the splitting of the (220) peak. This kind of (Ge:SiO2)/SiO2 multilayers enables us to control the sizes of the Ge crystallites and enhance the stress, and is thus promising in forming new nanocrystal structures.
Co-reporter:Z.H. Zhou, B.C. Wei, C.Y. He, Y.M. Min, C.H. Chen, L.Z. Liu, X.L. Wu
Applied Surface Science (15 May 2017) Volume 404() pp:
Publication Date(Web):15 May 2017
DOI:10.1016/j.apsusc.2017.01.305
•Symmetry breaking is achieved by strain that modulates the band structure and carrier population.•Mobility cunt-on rate can be enhanced by structural transformation.•The angle-dependent Raman spectrum of Ag-like, Eg-like and Cp models are used to discriminate and analysis structural anisotropy.•Strain engineering is a useful method to design the anisotropic Raman scattering and mobility.Regulation of electronic structure and mobility cut-on rate in two-dimensional transition metal dichalcogenides (TMDs) has attracted much attention because of its potential in electronic device design. The anisotropic Raman scattering and mobility cut-on rate of monolayer unique distorted-1T (1Td) ReS2 with external strain are determined theoretically based on the density function theory. The angle-dependent Raman spectrum of Ag-like, Eg-like and Cp models are used to discriminate and analysis structural anisotropy; the strain is exploited to adjust the structural symmetry and electronic structure of ReS2 so as to enhance mobility cut-on rate to almost 6 times of the original value. Our results suggest the use of the strain engineering in high-quality semiconductor switch device.
Co-reporter:Zhiqiang He; Shijie Xiong; Shuyi Wu; Xiaobin Zhu; Ming Meng
Journal of the American Chemical Society () pp:
Publication Date(Web):August 24, 2015
DOI:10.1021/jacs.5b06507
Crystalline β-FeSi2 nanocubes with two {100} facets and four {011} lateral facets synthesized by spontaneous one-step chemical vapor deposition exhibit strong room-temperature ferromagnetism with saturation magnetization of 15 emu/g. The room-temperature ferromagnetism is observed from the β-FeSi2 nanocubes larger than 150 nm with both the {100} and {011} facets. The ferromagnetism is tentatively explained with a simplified model including both the itinerant electrons in surface states and the local moments on Fe atoms near the surfaces. The work demonstrates the transformation from a nonmagnetic semiconductor to a magnetic one by exposing specific facets and the room-temperature ferromagnetism can be manipulated under light irradiation. The semiconducting β-FeSi2 nanocubes may have large potential in silicon-based spintronic applications.
Co-reporter:L. Z. Liu, X. L. Wu, J. C. Shen, T. H. Li, F. Gao and Paul K. Chu
Chemical Communications 2010 - vol. 46(Issue 30) pp:NaN5541-5541
Publication Date(Web):2010/06/24
DOI:10.1039/C0CC01277G
By experimentally examining and theoretically analyzing the Raman spectra of SixGe1−x nanocrystal-embedded silica films, we show that the 430 cm−1 Si–Si optical phonon mode can be used as a fingerprint to identify the existence of local silicon cluster nanostructures inside SixGe1−x nanocrystals with high silicon content.
