Co-reporter:Yuan Li, Jennifer G. DiStefano, Akshay A. Murthy, Jeffrey D. Cain, Eve D. Hanson, Qianqian Li, Fernando C. Castro, Xinqi Chen, and Vinayak P. Dravid
ACS Nano October 24, 2017 Volume 11(Issue 10) pp:10321-10321
Publication Date(Web):September 21, 2017
DOI:10.1021/acsnano.7b05071
Integrating plasmonic materials into semiconductor media provides a promising approach for applications such as photosensing and solar energy conversion. The resulting structures introduce enhanced light–matter interactions, additional charge trap states, and efficient charge-transfer pathways for light-harvesting devices, especially when an intimate interface is built between the plasmonic nanostructure and semiconductor. Herein, we report the development of plasmonic photodetectors using Au@MoS2 heterostructures—an Au nanoparticle core that is encapsulated by a CVD-grown multilayer MoS2 shell, which perfectly realizes the intimate and direct interfacing of Au and MoS2. We explored their favorable applications in different types of photosensing devices. The first involves the development of a large-area interdigitated field-effect phototransistor, which shows a photoresponsivity ∼10 times higher than that of planar MoS2 transistors. The other type of device geometry is a Si-supported Au@MoS2 heterojunction gateless photodiode. We demonstrated its superior photoresponse and recovery ability, with a photoresponsivity as high as 22.3 A/W, which is beyond the most distinguished values of previously reported similar gateless photodetectors. The improvement of photosensing performance can be a combined result of multiple factors, including enhanced light absorption, creation of more trap states, and, possibly, the formation of interfacial charge-transfer transition, benefiting from the intimate connection of Au and MoS2.Keywords: Au@MoS2; core−shell; heterostructures; photodetectors; plasmonic enhancement;
Co-reporter:Heemin Kang, Dexter Siu Hong Wong, Xiaohui Yan, Hee Joon Jung, Sungkyu Kim, Sien Lin, Kongchang Wei, Gang Li, Vinayak P. Dravid, and Liming Bian
ACS Nano October 24, 2017 Volume 11(Issue 10) pp:9636-9636
Publication Date(Web):August 25, 2017
DOI:10.1021/acsnano.7b02857
Cellular adhesion is regulated by the dynamic ligation process of surface receptors, such as integrin, to adhesive motifs, such as Arg-Gly-Asp (RGD). Remote control of adhesive ligand presentation using external stimuli is an appealing strategy for the temporal regulation of cell–implant interactions in vivo and was recently demonstrated using photochemical reaction. However, the limited tissue penetration of light potentially hampers the widespread applications of this method in vivo. Here, we present a strategy for modulating the nanoscale oscillations of an integrin ligand simply and solely by adjusting the frequency of an oscillating magnetic field to regulate the adhesion and differentiation of stem cells. A superparamagnetic iron oxide nanoparticle (SPION) was conjugated with the RGD ligand and anchored to a glass substrate by a long flexible poly(ethylene glycol) linker to allow the oscillatory motion of the ligand to be magnetically tuned. In situ magnetic scanning transmission electron microscopy and atomic force microscopy imaging confirmed the nanoscale motion of the substrate-tethered RGD-grafted SPION. Our findings show that ligand oscillations under a low oscillation frequency (0.1 Hz) of the magnetic field promoted integrin–ligand binding and the formation and maturation of focal adhesions and therefore the substrate adhesion of stem cells, while ligands oscillating under high frequency (2 Hz) inhibited integrin ligation and stem cell adhesion, both in vitro and in vivo. Temporal switching of the multimodal ligand oscillations between low- and high-frequency modes reversibly regulated stem cell adhesion. The ligand oscillations further induced the stem cell differentiation and mechanosensing in the same frequency-dependent manner. Our study demonstrates a noninvasive, penetrative, and tunable approach to regulate cellular responses to biomaterials in vivo. Our work not only provides additional insight into the design considerations of biomaterials to control cellular adhesion in vivo but also offers a platform to elucidate the fundamental understanding of the dynamic integrin–ligand binding that regulates the adhesion, differentiation, and mechanotransduction of stem cells.Keywords: in vivo cell adhesion; integrin ligand oscillations; mesenchymal stem cells; multimodal control; SPION; stem cell differentiation;
Co-reporter:Heemin Kang, Sungkyu Kim, Dexter Siu Hong Wong, Hee Joon Jung, Sien Lin, Kaijie Zou, Rui Li, Gang Li, Vinayak P. Dravid, and Liming Bian
Nano Letters October 11, 2017 Volume 17(Issue 10) pp:6415-6415
Publication Date(Web):September 6, 2017
DOI:10.1021/acs.nanolett.7b03405
Macrophages play crucial roles in various immune-related responses, such as host defense, wound healing, disease progression, and tissue regeneration. Macrophages perform distinct and dynamic functions in vivo, depending on their polarization states, such as the pro-inflammatory M1 phenotype and pro-healing M2 phenotype. Remote manipulation of the adhesion of host macrophages to the implants and their subsequent polarization in vivo can be an attractive strategy to control macrophage polarization-specific functions but has rarely been achieved. In this study, we grafted RGD ligand-bearing superparamagnetic iron oxide nanoparticles (SPIONs) to a planar matrix via a long flexible linker. We characterized the nanoscale motion of the RGD-bearing SPIONs grafted to the matrix, in real time by in situ magnetic scanning transmission electron microscopy (STEM) and in situ atomic force microscopy. The magnetic field was applied at various oscillation frequencies to manipulate the frequency-dependent ligand nano-oscillation speeds of the RGD-bearing SPIONs. We demonstrate that a low oscillation frequency of the magnetic field stimulated the adhesion and M2 polarization of macrophages, whereas a high oscillation frequency suppressed the adhesion of macrophages but promoted their M1 polarization, both in vitro and in vivo. Macrophage adhesion was also temporally regulated by switching between the low and high frequencies of the oscillating magnetic field. To the best of our knowledge, this is the first demonstration of the remote manipulation of the adhesion and polarization phenotype of macrophages, both in vitro and in vivo. Our system offers the promising potential to manipulate host immune responses to implanted biomaterials, including inflammation or tissue reparative processes, by regulating macrophage adhesion and polarization.Keywords: Ligand nano-oscillations; macrophage adhesion; macrophage polarization; remote manipulation; SPION;
Co-reporter:Xing Liao, Yi-kai Huang, Chad A. Mirkin, and Vinayak P. Dravid
ACS Nano May 23, 2017 Volume 11(Issue 5) pp:4439-4439
Publication Date(Web):March 13, 2017
DOI:10.1021/acsnano.7b00124
Reliably obtaining nanostructures of complex oxides over large area with nanoscale resolution and well-controlled shape, spacing, and pattern symmetry remains a major challenge. In this article, millions of nanowells have been routinely generated by beam pen lithography. Each attoliter volume nanowell functions as a “nanoreactor”, inside which oxide nanostructures are synthesized from their sol–gel precursors. Importantly, these nanometer scale entities are in single crystalline or textured forms and epitaxial to the underlying substrates, which promises functionalities including ferroelectricity, ferromagnetism, and multiferroicity. This method provides a general solution which allows one to rapidly screen structural parameters of oxide nanostructures comprising of three or more elements for prominent properties.Keywords: beam pen lithography; ferrimagnetism; ferroelectricity; multiferroics; nanofabrication; oxide nanostructures; sol−gel synthesis;
Co-reporter:Eve D. Hanson;Luc Lajaunie;Shiqiang Hao;Benjamin D. Myers;Fengyuan Shi;Akshay A. Murthy;Chris Wolverton;Raul Arenal
Advanced Functional Materials 2017 Volume 27(Issue 17) pp:
Publication Date(Web):2017/05/01
DOI:10.1002/adfm.201605380
Bulk and nanoscale molybdenum trioxide (MoO3) has shown impressive technologically relevant properties, but deeper investigation into 2D MoO3 has been prevented by the lack of reliable vapor-based synthesis and doping techniques. Herein, the successful synthesis of high-quality, few-layer MoO3 down to bilayer thickness via physical vapor deposition is reported. The electronic structure of MoO3 can be strongly modified by introducing oxygen substoichiometry (MoO3−x), which introduces gap states and increases conductivity. A dose-controlled electron irradiation technique to introduce oxygen vacancies into the few-layer MoO3 structure is presented, thereby adding n-type doping. By combining in situ transport with core-loss and monochromated low-loss scanning transmission electron microscopy–electron energy-loss spectroscopy studies, a detailed structure–property relationship is developed between Mo-oxidation state and resistance. Transport properties are reported for MoO3−x down to three layers thick, the most 2D-like MoO3−x transport hitherto reported. Combining these results with density functional theory calculations, a radiolysis-based mechanism for the irradiation-induced oxygen vacancy introduction is developed, including insights into favorable configurations of oxygen defects. These systematic studies represent an important step forward in bringing few-layer MoO3 and MoO3−x into the 2D family, as well as highlight the promise of MoO3−x as a functional, tunable electronic material.
Co-reporter:Jingshan S. Du;Peng-Cheng Chen;Dr. Brian Meckes;Dr. Zhuang Xie;Jinghan Zhu;Yuan Liu; Vinayak P. Dravid; Chad A. Mirkin
Angewandte Chemie International Edition 2017 Volume 56(Issue 26) pp:7625-7629
Publication Date(Web):2017/06/19
DOI:10.1002/anie.201703296
AbstractMulticomponent nanoparticles can be synthesized with either homogeneous or phase-segregated architectures depending on the synthesis conditions and elements incorporated. To understand the parameters that determine their structural fate, multicomponent metal-oxide nanoparticles consisting of combinations of Co, Ni, and Cu were synthesized by using scanning probe block copolymer lithography and characterized using correlated electron microscopy. These studies revealed that the miscibility, ratio of the metallic components, and the synthesis temperature determine the crystal structure and architecture of the nanoparticles. A Co-Ni-O system forms a rock salt structure largely owing to the miscibility of CoO and NiO, while Cu-Ni-O, which has large miscibility gaps, forms either homogeneous oxides, heterojunctions, or alloys depending on the annealing temperature and composition. Moreover, a higher-ordered structure, Co-Ni-Cu-O, was found to follow the behavior of lower ordered systems.
Co-reporter:Mahyar M. MoghadamRan Li, D. Bruce Buchholz, Qianqian Li, Peter W. Voorhees, Vinayak P. Dravid
Crystal Growth & Design 2017 Volume 17(Issue 3) pp:
Publication Date(Web):January 30, 2017
DOI:10.1021/acs.cgd.6b01849
The crystallization kinetics of Zn0.3In1.4Sn0.3O3 (ZITO-30) thin films is investigated via isothermal in situ transmission electron microscopy measurements. Extensive analysis is conducted to reveal the nucleation mechanism and growth rate at four different temperatures. The results show that the nucleation rate in this system is time-dependent and continuously decelerates following a power law decay. The crystal growth rate is constant at a given temperature, and interface-limited growth is the controlling mechanism in the kinetics of amorphous ZITO-30 crystallization. The activation energy for the overall process and interface growth are derived from the experimental data. A morphological study of the grains shows that the {100} interfaces have low mobility and are responsible for the anisotropic crystal shapes. It is found that the {111} and {100} planes of the crystal form parallel to the film–vapor interface during the nucleation process. The results demonstrate a rather complex yet tractable correlation between the experimental results and theoretical underpinning in complex multicomponent oxide thin films.
Co-reporter:Qianqian Li, Zhenpeng Yao, Jinsong Wu, Sagar Mitra, Shiqiang Hao, Tuhin Subhra Sahu, Yuan Li, Chris Wolverton, Vinayak P. Dravid
Nano Energy 2017 Volume 38(Volume 38) pp:
Publication Date(Web):1 August 2017
DOI:10.1016/j.nanoen.2017.05.055
•A detailed understanding of the sodiation mechanism has the potential for further optimization and thus, improvements in sodium ion-based battery systems.•We present real-time and real-space account of the dynamics of intercalation and then conversion reactions in MoS2 electrodes with sodium, via in-situ electron diffraction and DFT calculation to reveal the atomistic mechanisms.•The critical Na-contents for 2H-NaxMoS2 to 1T-NaxMoS2 phase transformation and for intercalation to conversion reactions have been identified, respectively.•Several thermodynamically stable/metastable phases have also been found in the intercalation reactions.•Our contribution not only has broad scientific appeal, but also has critical and timely implications for new technological developments in sodium-ion storage, which has many potential advantages than lithium-ion battery.Alkali metal ion intercalation into layered transition-metal dichalcogenide structures is a promising approach to make next generation rechargeable batteries for energy storage. It has been noted that the number of Na-ions which can be reversibly intercalated and extracted per MoS2 is limited, and the chemical and electrochemical processes/mechanisms remain largely unknown, especially for nano-sized materials. Here, sodiation of MoS2 nanosheets are studied by in-situ electron diffraction and the phase transformations in sodiation are identified with the aid of DFT calculations to reveal the reaction mechanism. Several thermodynamically stable/metastable structures are identified in the sodiation pathway of MoS2 nanosheets, previously unnoticed in bulk MoS2. The gradual reduction of Mo4+ upon Na-ion intercalation leads to a transition of the Mo-S polyhedron from a trigonal prism to an octahedron around 0.375 Na per MoS2 inserted (i.e. Na0.375MoS2). When the intercalated Na-content is larger than 1.75 per MoS2 structural unit (i.e. Na1.75MoS2), the MoS2 layered structure collapses and the intercalation reaction is replaced by an irreversible conversion reaction with the formation of Na2S and metal Mo nanoparticles. The calculated sodiation pathways reproduce the experimental sodiation voltages. The current observations provide useful insights in developing sodium-ion batteries with high cycling stability.In sodiation of MoS2 nanocrystals, several intermediate and metastable phases have been discovered via in-situ electron diffraction and DFT calculation.Download high-res image (193KB)Download full-size image
Co-reporter:V. Nandwana;S.-R. Ryoo;S. Kanthala;A. Kumar;A. Sharma;F. C. Castro;Y. Li;B. Hoffman;S. Lim;V. P. Dravid
RSC Advances (2011-Present) 2017 vol. 7(Issue 55) pp:34892-34900
Publication Date(Web):2017/07/07
DOI:10.1039/C7RA05681H
We report the development of a self-assembling protein nanocage as a contrast agent for magnetic resonance imaging (MRI). The protein nanocage is derived from genetically engineered ferritin from Archaeoglobus fulgidus (AfFtnAA). Iron (Fe) was loaded in a controlled manner within the core of the ferritin nanocage, resulting in the formation of iron oxide magnetic nanostructures (MNS). Using a variety of structural and magnetic characterization methods, we have demonstrated the magnetic and domain structures of the MNS formed within the protein nanocage and their contribution on water proton relaxation in MRI. With the primary focus on cardiac imaging for identification of atherosclerotic lesion, macrophage cell line was chosen for in vitro studies. The cytocompatibility of Fe-loaded engineered ferritin nanocages ((Fe)AfFtnAA) was confirmed by cell viability and oxidative stress measurements. The ferritin nanocages were successfully internalized by macrophage cells in a dose dependent manner and visualized under MRI. The drop in relaxation time with increasing concentration validated their potential as a contrast agent in MRI. Enhanced uptake and diagnostic capability in MRI of Fe-loaded ferritin nanocages imply their use as a “natural” probe for targeting and imaging plaque macrophages.
Co-reporter:Tuhin Subhra Sahu;Qianqian Li;Jinsong Wu;Sagar Mitra
Journal of Materials Chemistry A 2017 vol. 5(Issue 1) pp:355-363
Publication Date(Web):2016/12/20
DOI:10.1039/C6TA07390E
Sodium-ion batteries (SIBs) have undergone extensive research efforts as compatible successors of Li-ion batteries (LIBs) for grid-scale energy storage owing to the abundance of sodium resources. However, the poor cycling stability and low rate capability of existing anodes has prevented the practical application of SIBs. To mitigate the situation we have created a 3D heterostructure electrode based on alternative layers of 2D (MoS2–graphene) and 1D (CNTs) materials via a hydrothermal route that is fundamentally different from the usual composites. For comparison, composites were prepared using the same experimental conditions with either rGO or MWCNTs. While discharging at 100 mA g−1 and 500 mA g−1, the MoS2–MWCNT@rGO could deliver a high discharge capacity of 664 mA h g−1 and 551 mA h g−1, and retained 100% and 98.4% capacity after 80 and 250 discharge–charge cycles, respectively. At 2 A g−1, it can yield an initial discharge capacity of 375 mA h g−1, maintaining 81.3% and 67% capacity after 250 and 500 cycles, respectively. The excellent performance of the MoS2–MWCNT@rGO hybrid is mainly attributed to the robust MWCNT@rGO framework with improved 3D electrical conductivity, additional porosity and excellent buffering capability. Furthermore, an in situ TEM technique was employed to explore the sodiation mechanism of the MoS2 nanosheets.
Co-reporter:Yuan Li, Jeffrey D. Cain, Eve D. Hanson, Akshay A. Murthy, Shiqiang Hao, Fengyuan Shi, Qianqian Li, Chris Wolverton, Xinqi Chen, and Vinayak P. Dravid
Nano Letters 2016 Volume 16(Issue 12) pp:7696-7702
Publication Date(Web):October 26, 2016
DOI:10.1021/acs.nanolett.6b03764
There are emerging opportunities to harness diverse and complex geometric architectures based on nominal two-dimensional atomically layered structures. Herein we report synthesis and properties of a new core–shell heterostructure, termed Au@MoS2, where the Au nanoparticle is snugly and contiguously encapsulated by few shells of MoS2 atomic layers. The heterostructures were synthesized by direct growth of multilayer fullerene-like MoS2 shell on Au nanoparticle cores. The Au@MoS2 heterostructures exhibit interesting light–matter interactions due to the structural curvature of MoS2 shell and the plasmonic effect from the underlying Au nanoparticle core. We observed significantly enhanced Raman scattering and photoluminescence emission on these heterostructures. We attribute these enhancements to the surface plasmon-induced electric field, which simulations show to mainly localize within the MoS2 shell. We also found potential evidence for the charge transfer-induced doping effect on the MoS2 shell. The DFT calculations further reveal that the structural curvature of MoS2 shell results in a modification of its electronic structure, which may facilitate the charge transfer from MoS2 to Au. Such Au@MoS2 core–shell heterostructures have the potential for future optoelectronic devices, optical imaging, and other energy-environmental applications.Keywords: Au@MoS2 core−shell heterostructures; CVD; patterning; photoluminescence; Raman enhancement;
Co-reporter:Qianqian Li, Jinsong Wu, Junming Xu and Vinayak P. Dravid
Journal of Materials Chemistry A 2016 vol. 4(Issue 22) pp:8669-8675
Publication Date(Web):09 May 2016
DOI:10.1039/C6TA02051H
Replacing lithium with sodium-ion batteries for energy storage is of enormous interest, especially from practical and economic considerations. However, it has proved difficult to achieve competitive figures of merit for sodium-ion batteries due to the lack of a detailed understanding of the reaction mechanism(s). Herein, we report a sodium electrochemical conversion reaction with Co3O4 nanoparticles decorated on carbon nanotubes (Co3O4/CNTs) utilizing in situ TEM, down to the atomic-scale. We observe synergetic effects of the two nanoscale components, which provide insights into a new sodiation mechanism, facilitated by Na-diffusion along a CNT backbone and CNT–Co3O4 interfaces. A thin layer of amorphous low conductivity Na2O forms on the CNT surfaces at the beginning of sodiation. The conversion reaction results in the formation of ultrafine metallic Co nanoparticles and polycrystalline Na2O, and fast diffusion of the reaction products which might be due to the quick migration of Na2O under an electron beam. In the desodiation process, the dissociation of Na2O and formation of Co3O4 due to the de-conversion reaction are observed.
Co-reporter:Vikas Nandwana, Soo-Ryoon Ryoo, Shanthi Kanthala, Mrinmoy De, Stanley S. Chou, Pottumarthi V. Prasad, and Vinayak P. Dravid
ACS Applied Materials & Interfaces 2016 Volume 8(Issue 11) pp:6953
Publication Date(Web):March 3, 2016
DOI:10.1021/acsami.6b01377
Magnetic nanostructures (MNS) have emerged as promising functional probes for simultaneous diagnostics and therapeutics (theranostic) applications due to their ability to enhance localized contrast in magnetic resonance imaging (MRI) and heat under external radio frequency (RF) field, respectively. We show that the “theranostic” potential of the MNS can be significantly enhanced by tuning their core composition and architecture of surface coating. Metal ferrite (e.g., MFe2O4) nanoparticles of ∼8 nm size and nitrodopamine conjugated polyethylene glycol (NDOPA-PEG) were used as the core and surface coating of the MNS, respectively. The composition was controlled by tuning the stoichiometry of MFe2O4 nanoparticles (M = Fe, Mn, Zn, ZnxMn1–x) while the architecture of surface coating was tuned by changing the molecular weight of PEG, such that larger weight is expected to result in longer length extended away from the MNS surface. Our results suggest that both core as well as surface coating are important factors to take into consideration during the design of MNS as theranostic agents which is illustrated by relaxivity and thermal activation plots of MNS with different core composition and surface coating thickness. After optimization of these parameters, the r2 relaxivity and specific absorption rate (SAR) up to 552 mM–1 s–1 and 385 W/g were obtained, respectively, which are among the highest values reported for MNS with core magnetic nanoparticles of size below 10 nm. In addition, NDOPA-PEG coated MFe2O4 nanostructures showed enhanced biocompatibility (up to [Fe] = 200 μg/mL) and reduced nonspecific uptake in macrophage cells in comparison to other well established FDA approved Fe based MR contrast agents.Keywords: biomedical applications; hyperthermia; magnetic nanoparticles; magnetic nanostructures; magnetic resonance imaging contrast; nanomedicine; theranostics; thermal activation;
Co-reporter:Benjamin D. Myers, Qing-Yuan Lin, Huanxin Wu, Erik Luijten, Chad A. Mirkin, and Vinayak P. Dravid
ACS Nano 2016 Volume 10(Issue 6) pp:5679
Publication Date(Web):May 18, 2016
DOI:10.1021/acsnano.6b02246
The vision of nanoscale self-assembly research is the programmable synthesis of macroscale structures with controlled long and short-range order that exhibit a desired set of properties and functionality. However, strategies to reliably isolate and manipulate the nanoscale building blocks based on their size, shape, or chemistry are still in their infancy. Among the promising candidates, DNA-mediated self-assembly has enabled the programmable assembly of nanoparticles into complex architectures. In particular, two-dimensional assembly on substrates has potential for the development of integrated functional devices and analytical systems. Here, we combine the high-resolution patterning capabilities afforded by electron-beam lithography with the DNA-mediated assembly process to enable direct-write grayscale DNA density patterning. This method allows modulation of the functionally active DNA surface density to control the thermodynamics of interactions between nanoparticles and the substrate. We demonstrate that size-selective directed assembly of nanoparticle films from solutions containing a bimodal distribution of particles can be realized by exploiting the cooperativity of DNA binding in this system. To support this result, we study the temperature-dependence of nanoparticle assembly, analyze the DNA damage by X-ray photoelectron spectroscopy and fluorescence microscopy, and employ molecular dynamics simulations to explore the size-selection behavior.Keywords: directed assembly; DNA nanotechnology; electron-beam lithography; nanoparticle assembly; nanopatterning; self-assembly
Co-reporter:Qianqian Li, Heguang Liu, Zhenpeng Yao, Jipeng Cheng, Tiehu Li, Yuan Li, Chris Wolverton, Jinsong Wu, and Vinayak P. Dravid
ACS Nano 2016 Volume 10(Issue 9) pp:8788
Publication Date(Web):August 26, 2016
DOI:10.1021/acsnano.6b04519
There are economic and environmental advantages by replacing Li with Na in energy storage. However, sluggishness in the charge/discharge reaction and low capacity are among the major obstacles to development of high-power sodium-ion batteries. Among the electrode materials recently developed for sodium-ion batteries, selenium shows considerable promise because of its high capacity and good cycling ability. Herein, we have investigated the mechanism and kinetics of both sodiation and lithiation reactions with selenium nanotubes, using in situ transmission electron microscopy. Sodiation of a selenium nanotube exhibits a three-step reaction mechanism: (1) the selenium single crystal transforms into an amorphous phase Na0.5Se; (2) the Na0.5Se amorphous phase crystallizes to form a polycrystalline Na2Se2 phase; and (3) Na2Se2 transforms into the Na2Se phase. Under similar conditions, the lithiation of Se exhibits a one-step reaction mechanism, with phase transformation from single-crystalline Se to a Li2Se. Intriguingly, sodiation kinetics is generally about 4–5 times faster than that of lithiation, and the kinetics during the different stages of sodiation is different. Na-based intermediate phases are found to have improved electronic and ionic conductivity compared to those of Li compounds by first-principles density functional theory calculations.Keywords: alloying reaction; DFT calculation; in situ electron diffraction; in situ transmission electron microscopy; lithium-ion battery; selenium cathodes; sodium-ion battery
Co-reporter:Jeffrey D. Cain, Fengyuan Shi, Jinsong Wu, and Vinayak P. Dravid
ACS Nano 2016 Volume 10(Issue 5) pp:5440
Publication Date(Web):May 3, 2016
DOI:10.1021/acsnano.6b01705
Due to their unique optoelectronic properties and potential for next generation devices, monolayer transition metal dichalcogenides (TMDs) have attracted a great deal of interest since the first observation of monolayer MoS2 a few years ago. While initially isolated in monolayer form by mechanical exfoliation, the field has evolved to more sophisticated methods capable of direct growth of large-area monolayer TMDs. Chemical vapor deposition (CVD) is the technique used most prominently throughout the literature and is based on the sulfurization of transition metal oxide precursors. CVD-grown monolayers exhibit excellent quality, and this process is widely used in studies ranging from the fundamental to the applied. However, little is known about the specifics of the nucleation and growth mechanisms occurring during the CVD process. In this study, we have investigated the nucleation centers or “seeds” from which monolayer TMDs typically grow. This was accomplished using aberration-corrected scanning transmission electron microscopy to analyze the structure and composition of the nuclei present in CVD-grown MoS2–MoSe2 alloys. We find that monolayer growth proceeds from nominally oxi-chalcogenide nanoparticles which act as heterogeneous nucleation sites for monolayer growth. The oxi-chalcogenide nanoparticles are typically encased in a fullerene-like shell made of the TMD. Using this information, we propose a step-by-step nucleation and growth mechanism for monolayer TMDs. Understanding this mechanism may pave the way for precise control over the synthesis of 2D materials, heterostructures, and related complexes.Keywords: chalcogenides; chemical vapor deposition; growth; inorganic fullerene; transition metal dichalcogenides; two-dimensional materials
Co-reporter:Stanley S. Chou; Yi-Kai Huang; Jaemyung Kim; Bryan Kaehr; Brian M. Foley; Ping Lu; Conner Dykstra; Patrick E. Hopkins; C. Jeffrey Brinker; Jiaxing Huang
Journal of the American Chemical Society 2015 Volume 137(Issue 5) pp:1742-1745
Publication Date(Web):January 22, 2015
DOI:10.1021/ja5107145
Lithiation-exfoliation produces single to few-layered MoS2 and WS2 sheets dispersible in water. However, the process transforms them from the pristine semiconducting 2H phase to a distorted metallic phase. Recovery of the semiconducting properties typically involves heating of the chemically exfoliated sheets at elevated temperatures. Therefore, it has been largely limited to sheets deposited on solid substrates. Here, we report the dispersion of chemically exfoliated MoS2 sheets in high boiling point organic solvents enabled by surface functionalization and the controllable recovery of their semiconducting properties directly in solution. This process connects the scalability of chemical exfoliation with the simplicity of solution processing, ultimately enabling a facile method for tuning the metal to semiconductor transitions of MoS2 and WS2 within a liquid medium.
Co-reporter:Manish K. Jaiswal, Lina Pradhan, Shaleen Vasavada, Mrinmoy De, H.D. Sarma, Anand Prakash, D. Bahadur, Vinayak P. Dravid
Colloids and Surfaces B: Biointerfaces 2015 Volume 136() pp:625-633
Publication Date(Web):1 December 2015
DOI:10.1016/j.colsurfb.2015.09.058
•Synthesis of Fe3O4 magnetic nanostructures (MNS) using high temperature decomposition of iron salt in organic media to get monodisperse size distribution.•Surface modification of nanostructures with nitro-dopamine anchored polyethylene glycol to achieve ultrastable aqueous suspension.•Drug release kinetics study and bladder cancer cell treatment efficacy evaluation of thermoresponsive hydrogel (HG) embedded with Fe3O4 nanostructures.•In vivo biodistribution studies of the HG-MNS system using magnetic resonance imaging (MRI).Bladder cancer is one of the deadliest forms of cancer in modern medicine which despite recent progress has remained incurable and challenging for researchers. There is unmet need to address this endemic as the number of patients are growing by about 10,000 every year world-wide. Here, we report a minimally invasive magnetic chemotherapy method to address this problem where polyethylene glycol (PEG) functionalized Fe3O4 magnetic nanostructures (MNS) are homogeneously embedded in thermally responsive poly(N-isopropylacrylamide, NIPAAm) hydrogels (HG). The system (HG-MNS) loaded with anti-cancer drug doxorubicin (DOX) incubated with cancer cell lines subjected to external radiofrequency (RF) field can remotely stimulate the release of drug smartly at the site. The in vitro efficacy investigated on bladder cancer (T-24) cell lines showed the potential of the system in dealing with the disease successfully. Further, the materials preferential accumulation via systemic delivery was studied using swiss mice model. Vital tissue organs like liver, lung and heart were analysed by magnetic resonance imaging (MRI). A detail accounts of the materials optimization, cytotoxicity and anti-proliferation activity tests with apoptosis analysis by flow cytometry after RF exposure (250 kHz) to the cells and in vivo biodistribution data are discussed in the paper.
Co-reporter:Manish K. Jaiswal, Mrinmoy De, Stanley S. Chou, Shaleen Vasavada, Reiner Bleher, Pottumarthi V. Prasad, Dhirendra Bahadur, and Vinayak P. Dravid
ACS Applied Materials & Interfaces 2014 Volume 6(Issue 9) pp:6237
Publication Date(Web):April 9, 2014
DOI:10.1021/am501067j
We report the development of thermoresponsive magnetic hydrogels based on poly(N-isopropylacrylamide) encapsulation of Fe3O4 magnetic nanostructures (MNS). In particular, we examined the effects of hydrogels encapsulated with poly-ethylene glycol (PEG) and polyhedral oligomeric silsesquioxane (POSS) surface modified Fe3O4 MNS on magnetic resonance (MR) T2 (transverse spin relaxation) contrast enhancement and associated delivery efficacy of absorbed therapeutic cargo. The microstructural characterization reveal the regular spherical shape and size (∼200 nm) of the hydrogels with elevated hydrophilic to hydrophobic transition temperature (∼40 °C) characterized by LCST (lower critical solution temperature) due to the presence of encapsulated MNS. The hydrogel-MNS (HGMNS) system encapsulated with PEG functionalized Fe3O4 of 12 nm size (HGMNS-PEG-12) exhibited relaxivity rate (r2) of 173 mM–1s–1 compared to 129 mM–1s–1 obtained for hydrogel-MNS system encapsulated with POSS functionalized Fe3O4 (HGMNS-POSS-12) of the same size. Further studies with HGMNS-PEG-12 with absorbed drug doxorubicin (DOX) reveals approximately two-fold enhance in release during 1 h RF (radio-frequency) field exposure followed by 24 h incubation at 37 °C. Quantitatively, it is 2.1 μg mg–1 (DOX/HGMNS) DOX release with RF exposure while only 0.9 μg mg–1 release without RF exposure for the same period of incubation. Such enhanced release of therapeutic cargo is attributed to micro-environmental heating in the surroundings of MNS as well as magneto-mechanical vibrations under high frequency RF inside hydrogels. Similarly, RF-induced in vitro localized drug delivery studies with HeLa cell lines for HGMNS-PEG-12 resulted in more than 80% cell death with RF field exposures for 1 h. We therefore believe that magnetic hydrogel system has in vivo theranostic potential given high MR contrast enhancement from encapsulated MNS and RF-induced localized therapeutic delivery in one nanoconstruct.Keywords: cellular uptake of hydrogels; magneto-thermo responsive polymers; MR active hydrogels; PEG-functionalized Fe3O4; poly(N-isopylacrylamide); POSS-functionalized Fe3O4;
Co-reporter:Yi-Kai Huang, Jeffrey D. Cain, Lintao Peng, Shiqiang Hao, Thomas Chasapis, Mercouri G. Kanatzidis, Christopher Wolverton, Matthew Grayson, and Vinayak P. Dravid
ACS Nano 2014 Volume 8(Issue 10) pp:10851
Publication Date(Web):September 18, 2014
DOI:10.1021/nn504664p
The palette of two-dimensional materials has expanded beyond graphene in recent years to include the chalcogenides among other systems. However, there is a considerable paucity of methods for controlled synthesis of mono- and/or few-layer two-dimensional materials with desirable quality, reproducibility, and generality. Here we show a facile top-down synthesis approach for ultrathin layers of 2D materials down to monolayer. Our method is based on controlled evaporative thinning of initially large sheets, as deposited by vapor mass-transport. Rather than optimizing conditions for monolayer deposition, our approach makes use of selective evaporation of thick sheets to control the eventual thickness, down to a monolayer, a process which appears to be self-stopping. As a result, 2D sheets with high yield, high reproducibility, and excellent quality can be generated with large (>10 μm) and thin (∼1–2 nm) dimensions. Evaporative thinning promises to greatly reduce the difficulty involved in isolating large, mono- and few-layers of 2D materials for subsequent studies.Keywords: 2D synthesis; bismuth selenide; transmission electron microscopy; two-dimensional (2D) materials;
Co-reporter:Langli Luo, Jinsong Wu, Junming Xu, and Vinayak P. Dravid
ACS Nano 2014 Volume 8(Issue 11) pp:11560
Publication Date(Web):October 22, 2014
DOI:10.1021/nn504806h
Electrode materials based on conversion reactions with lithium ions have shown much higher energy density than those based on intercalation reactions. Here, nanocubes of a typical metal oxide (Co3O4) were grown on few-layer graphene, and their electrochemical lithiation and delithiation were investigated at atomic resolution by in situ transmission electron microscopy to reveal the mechanism of the reversible conversion reaction. During lithiation, a lithium-inserted Co3O4 phase and a phase consisting of nanosized Co–Li–O clusters are identified as the intermediate products prior to the subsequent formation of Li2O crystals. In delithiation, the reduced metal nanoparticles form a network and breakdown into even smaller clusters that act as catalysts to prompt reduction of Li2O, and CoO nanoparticles are identified as the product of the deconversion reaction. Such direct real-space, real-time atomic-scale observations shed light on the phenomena and mechanisms in reaction-based electrochemical energy conversion and provide impetus for further development in electrochemical charge storage devices.Keywords: conversion/deconversion reaction; electron diffraction; in situ high-resolution electron microscopy; lithium-ion battery; metal oxide electrode;
Co-reporter:Jiaqing He, Mercouri G. Kanatzidis, Vinayak P. Dravid
Materials Today 2013 Volume 16(Issue 5) pp:166-176
Publication Date(Web):May 2013
DOI:10.1016/j.mattod.2013.05.004
One of the intellectual challenges for next generation thermoelectric materials revolves around the synthesis and fabrication of hierarchically organized microstructures that do not appreciably compromise the innate high power factor of the chosen thermoelectric system, but significantly reduce lattice thermal conductivity to enhance the overall figure of merit, ZT. An effective emerging strategy is to introduce nanostructures into bulk thermoelectric materials, which allow for diverse phonon scattering mechanisms to reduce thermal conductivity. In this review, we present key examples to show the intricate but tractable relationship across all relevant length-scales between various microstructural attributes (point, line, interfacial and mesoscale defects; as well as associated elastic and plastic strain) and lattice thermal conductivity in systems based on PbTe matrices. We emphasize the need for an overarching panoscopic approach that enables specific design strategies for the next generation of thermoelectric materials.
Co-reporter:Jonathan W. Hennek ; Jeremy Smith ; Aiming Yan ; Myung-Gil Kim ; Wei Zhao ; Vinayak P. Dravid ; Antonio Facchetti ;Tobin J. Marks
Journal of the American Chemical Society 2013 Volume 135(Issue 29) pp:10729-10741
Publication Date(Web):July 2, 2013
DOI:10.1021/ja403586x
In oxide semiconductors, such as those based on indium zinc oxide (IXZO), a strong oxygen binding metal ion (“oxygen getter”), X, functions to control O vacancies and enhance lattice formation, hence tune carrier concentration and transport properties. Here we systematically study, in the IXZO series, the role of X = Ga3+ versus the progression X = Sc3+ → Y3+ → La3+, having similar chemical characteristics but increasing ionic radii. IXZO films are prepared from solution over broad composition ranges for the first time via low-temperature combustion synthesis. The films are characterized via thermal analysis of the precursor solutions, grazing incidence angle X-ray diffraction (GIAXRD), atomic force microscopy (AFM), X-ray photoelectron spectroscopy (XPS), and scanning transmission electron microscopy (STEM) with high angle annular dark field (HAADF) imaging. Excellent thin-film transistor (TFT) performance is achieved for all X, with optimal compositions after 300 °C processing exhibiting electron mobilities of 5.4, 2.6, 2.4, and 1.8 cm2 V–1 s–1 for Ga3+, Sc3+, Y3+, and La3+, respectively, and with Ion/Ioff = 107–108. Analysis of the IXZO TFT positive bias stress response shows X = Ga3+ to be superior with mobilities (μ) retaining >95% of the prestress values and threshold voltage shifts (ΔVT) of <1.6 V, versus <85% μ retention and ΔVT ≈ 20 V for the other trivalent ions. Detailed microstructural analysis indicates that Ga3+ most effectively promotes oxide lattice formation. We conclude that the metal oxide lattice formation enthalpy (ΔHL) and metal ionic radius are the best predictors of IXZO oxygen getter efficacy.
Co-reporter:Stanley S. Chou +; Mrinmoy De +; Jaemyung Kim +; Segi Byun +; Conner Dykstra +; Jin Yu ; Jiaxing Huang + +
Journal of the American Chemical Society 2013 Volume 135(Issue 12) pp:4584-4587
Publication Date(Web):March 11, 2013
DOI:10.1021/ja310929s
MoS2 is a two-dimensional material that is gaining prominence due to its unique electronic and chemical properties. Here, we demonstrate ligand conjugation of chemically exfoliated MoS2 using thiol chemistry. With this method, we modulate the ζ-potential and colloidal stability of MoS2 sheets through ligand designs, thus enabling its usage as a selective artificial protein receptor for β-galactosidase. The facile thiol functionalization route opens the door for surface modifications of solution processable MoS2 sheets.
Co-reporter:Dattatray J. Late, Yi-Kai Huang, Bin Liu, Jagaran Acharya, Sharmila N. Shirodkar, Jiajun Luo, Aiming Yan, Daniel Charles, Umesh V. Waghmare, Vinayak P. Dravid, and C. N. R. Rao
ACS Nano 2013 Volume 7(Issue 6) pp:4879
Publication Date(Web):May 28, 2013
DOI:10.1021/nn400026u
Most of recent research on layered chalcogenides is understandably focused on single atomic layers. However, it is unclear if single-layer units are the most ideal structures for enhanced gas–solid interactions. To probe this issue further, we have prepared large-area MoS2 sheets ranging from single to multiple layers on 300 nm SiO2/Si substrates using the micromechanical exfoliation method. The thickness and layering of the sheets were identified by optical microscope, invoking recently reported specific optical color contrast, and further confirmed by AFM and Raman spectroscopy. The MoS2 transistors with different thicknesses were assessed for gas-sensing performances with exposure to NO2, NH3, and humidity in different conditions such as gate bias and light irradiation. The results show that, compared to the single-layer counterpart, transistors of few MoS2 layers exhibit excellent sensitivity, recovery, and ability to be manipulated by gate bias and green light. Further, our ab initio DFT calculations on single-layer and bilayer MoS2 show that the charge transfer is the reason for the decrease in resistance in the presence of applied field.Keywords: density functional theory; gas sensor; gate bias; light irradiation; MoS2
Co-reporter:Dattatray J. Late;Bin Liu;Jiajun Luo;Aiming Yan;H. S. S. Ramakrishna Matte;Matthew Grayson;C. N. R. Rao
Advanced Materials 2012 Volume 24( Issue 26) pp:3549-3554
Publication Date(Web):
DOI:10.1002/adma.201201361
Co-reporter:Jiaqing He, John Androulakis, Mercouri G. Kanatzidis, and Vinayak P. Dravid
Nano Letters 2012 Volume 12(Issue 1) pp:343-347
Publication Date(Web):December 12, 2011
DOI:10.1021/nl203626n
Alkali metal doped p-type PbTe is a canonical thermoelectric material studied extensively for heat-to-power generation at high temperature. Most reports have indirectly indicated alkali metals to be conventional with PbTe forming homogeneous solid solutions. Using transmission electron microscopy (TEM), we show the presence of platelet-like nanostructures in these systems containing Na and/or K. By combining further TEM and semiclassical theoretical calculations based on a modified Debye model of the lattice thermal conductivity, we explain the lack of efficacy of these nanostructures for strong phonon scattering. These findings are important in the understanding of alkali metals as carriers in p-type lead chalcogenides. These results also underscore that not all nanostructures favorably scatter phonons in a matrix; an insight that may help in further improvements of the power factor and the overall figure of merit.
Co-reporter:Jiaqing He, I. D. Blum, Hui-Qiong Wang, S. N. Girard, J. Doak, Li-Dong Zhao, Jin-Cheng Zheng, G. Casillas, C. Wolverton, M. Jose-Yacaman, D. N. Seidman, M. G. Kanatzidis, and V. P. Dravid
Nano Letters 2012 Volume 12(Issue 11) pp:5979-5984
Publication Date(Web):October 16, 2012
DOI:10.1021/nl303449x
The morphology of crystalline precipitates in a solid-state matrix is governed by complex but tractable energetic considerations driven largely by volume strain energy minimization and anisotropy of interfacial energies. Spherical precipitate morphologies are favored by isotropic systems, while anisotropic interfacial energies give energetic preference to certain crystallographically oriented interfaces, resulting in a faceted precipitate morphology. In conventional solid–solution precipitation, a precipitate’s morphological evolution is mediated by surface anchoring of capping molecules, which dramatically alter the surface energy in an anisotropic manner, thereby providing exquisite morphology control during crystal growth. Herein, we present experimental evidence and theoretical validation for the role of a ternary element (Na) in controlling the morphology of nanoscale PbS crystals nucleating in a PbTe matrix, an important bulk thermoelectric system. The PbS nanostructures formed by phase separation from a PbI2-doped or undoped PbTe matrix have irregular morphologies. However, replacing the iodine dopant with Na (1–2 mol %) alters dramatically the morphology of the PbS precipitates. Segregation of Na at PbTe/PbS interfaces result in cuboidal and truncated cuboidal morphologies for PbS. Using analytical scanning/transmission electron microscopy and atom-probe tomography, we demonstrate unambiguously that Na partitions to the precipitates and segregates at the matrix/precipitate interfaces, inducing morphological anisotropy of PbS precipitates. First-principles and semiclassical calculations reveal that Na as a solute in PbTe has a higher energy than in PbS and that Na segregation at a (100) PbTe/PbS interface decreases the total energy of matrix/precipitate system, resulting in faceting of PbS precipitates. These results provide an impetus for a new strategy for controlling morphological evolution in matrix/precipitate systems, mediated by solute partitioning of ternary additions.
Co-reporter:Stanley S. Chou ; Mrinmoy De ; Jiayan Luo ; Vincent M. Rotello ; Jiaxing Huang ;Vinayak. P. Dravid
Journal of the American Chemical Society 2012 Volume 134(Issue 40) pp:16725-16733
Publication Date(Web):September 10, 2012
DOI:10.1021/ja306767y
The role of conventional graphene-oxide in biosensing has been limited to that of a quenching substrate or signal transducer due to size inconsistencies and poor supramolecular response. We overcame these issues by using nanoscale GOs (nGO) as artificial receptors. Unlike conventional GO, nGOs are sheets with near uniform lateral dimension of 20 nm. Due to its nanoscale architecture, its supramolecular response was enhanced, with demonstrated improvements in biomacromolecular affinities. This rendered their surface capable of detecting unknown proteins with cognizance not seen with conventional GOs. Different proteins at 100 and 10 nM concentrations revealed consistent patterns that are quantitatively differentiable by linear discriminant analysis. Identification of 48 unknowns in both concentrations demonstrated a >95% success rate. The 10 nM detection represents a 10-fold improvement over analogous arrays. This demonstrates for the first time that the supramolecular chemistry of GO is highly size dependent and opens the possibility of improvement upon existing GO hybrid materials.
Co-reporter:Dattatray J. Late;Bin Liu;H. S. S. Ramakrishna Matte;C. N. R. Rao
Advanced Functional Materials 2012 Volume 22( Issue 9) pp:1894-1905
Publication Date(Web):
DOI:10.1002/adfm.201102913
Abstract
There has been emerging interest in exploring single-sheet 2D layered structures other than graphene to explore potentially interesting properties and phenomena. The preparation, isolation and rapid unambiguous characterization of large size ultrathin layers of MoS2, GaS, and GaSe deposited onto SiO2/Si substrates is reported. Optical color contrast is identified using reflection optical microscopy for layers with various thicknesses. The optical contrast of these thin layers is correlated with atomic force microscopy (AFM) and Raman spectroscopy to determine the exact thickness and to calculate number of the atomic layers present in the thin flakes and sheets. Collectively, optical microscopy, AFM, and Raman spectroscopy combined with Raman imaging data are analyzed to determine the thickness (and thus, the number of unit layers) of the MoS2, GaS, and GaSe ultrathin flakes in a fast, non-destructive, and unambiguous manner. These findings may enable experimental access to and unambiguous determination of layered chalcogenides for scientific exploration and potential technological applications.
Co-reporter:Shih-Han Lo;Jiaqing He;Kanishka Biswas;Mercouri G. Kanatzidis
Advanced Functional Materials 2012 Volume 22( Issue 24) pp:5175-5184
Publication Date(Web):
DOI:10.1002/adfm.201201221
Abstract
Transmission electron microscopy studies show that a PbTe-BaTe bulk thermoelectric system represents the coexistence of solid solution and nanoscale BaTe precipitates. The observed significant reduction in the thermal conductivity is attributed to the enhanced phonon scattering by the combination of substitutional point defects in the solid solution and the presence of high spatial density of nanoscale precipitates. In order to differentiate the role of nanoscale precipitates and point defects in reducing lattice thermal conductivity, a modified Callaway model is proposed, which highlights the contribution of point defect scattering due to solid solution in addition to that of other relevant microstructural constituents. Calculations indicate that in addition to a 60% reduction in lattice thermal conductivity by nanostructures, point defects are responsible for about 20% more reduction and the remaining reduction is contributed by the collective of dislocation and strain scattering. These results underscore the need for tailoring integrated length-scales for enhanced heat-carrying phonon scattering in high performance thermoelectrics.
Co-reporter:Dattatray J. Late, Bin Liu, H. S. S. Ramakrishna Matte, Vinayak P. Dravid, and C. N. R. Rao
ACS Nano 2012 Volume 6(Issue 6) pp:5635
Publication Date(Web):May 12, 2012
DOI:10.1021/nn301572c
Field effect transistors using ultrathin molybdenum disulfide (MoS2) have recently been experimentally demonstrated, which show promising potential for advanced electronics. However, large variations like hysteresis, presumably due to extrinsic/environmental effects, are often observed in MoS2 devices measured under ambient environment. Here, we report the origin of their hysteretic and transient behaviors and suggest that hysteresis of MoS2 field effect transistors is largely due to absorption of moisture on the surface and intensified by high photosensitivity of MoS2. Uniform encapsulation of MoS2 transistor structures with silicon nitride grown by plasma-enhanced chemical vapor deposition is effective in minimizing the hysteresis, while the device mobility is improved by over 1 order of magnitude.Keywords: field effect transistor; hysteresis; moisture; molybdenum disulfide; PECVD; photosensitivity; silicon nitride
Co-reporter:Jun Liu;Jonathan W. Hennek;D. Bruce Buchholz;Young-geun Ha;Sujing Xie;Robert P. H. Chang;Antonio Facchetti;Tobin J. Marks
Advanced Materials 2011 Volume 23( Issue 8) pp:992-997
Publication Date(Web):
DOI:10.1002/adma.201004198
Co-reporter:Mrinmoy De ; Stanley S. Chou
Journal of the American Chemical Society 2011 Volume 133(Issue 44) pp:17524-17527
Publication Date(Web):September 28, 2011
DOI:10.1021/ja208427j
We have investigated the efficacy of graphene oxide (GO) in modulating enzymatic activity. Specifically, we have shown that GO can act as an artificial receptor and inhibit the activity of α-chymotrypsin (ChT), a serine protease. Most significantly, our data demonstrate that GO exhibits the highest inhibition dose response (by weight) for ChT inhibition compared with all other reported artificial inhibitors. Through fluorescence spectroscopy and circular dichroism studies, we have shown that this protein–receptor interaction is highly biocompatible and conserves the protein’s secondary structure over extended periods (>24 h). We have also explored GO–enzyme interactions by controlling the ionic strength of the medium, which attenuates the host–guest electrostatic interactions. These findings suggest a new generation of enzymatic inhibitors that can be applied to other complex proteins by systematic modification of the GO functionality.
Co-reporter:Tae Hee Han ; Yi-Kai Huang ; Alvin T. L. Tan ; Vinayak P. Dravid ;Jiaxing Huang
Journal of the American Chemical Society 2011 Volume 133(Issue 39) pp:15264-15267
Publication Date(Web):September 6, 2011
DOI:10.1021/ja205693t
Oxidative etching of graphene flakes was observed to initiate from edges and the occasional defect sites in the basal plane, leading to reduced lateral size and a small number of etch pits. In contrast, etching of highly defective graphene oxide and its reduced form resulted in rapid homogeneous fracturing of the sheets into smaller pieces. On the basis of these observations, a slow and more controllable etching route was designed to produce nanoporous reduced graphene oxide sheets by hydrothermal steaming at 200 °C. The degree of etching and the concomitant porosity can be conveniently tuned by etching time. In contrast to nonporous reduced graphene oxide annealed at the same temperature, the steamed nanoporous graphene oxide exhibited nearly 2 orders of magnitude increase in the sensitivity and improved recovery time when used as chemiresistor sensor platform for NO2 detection. The results underscore the efficacy of the highly distributed nanoporous network in the low temperature steam etched GO.
Co-reporter:J. Q. He ; J. R. Sootsman ; L. Q. Xu ∣∣; S. N. Girard ; J. C. Zheng ∣∣; M. G. Kanatzidis ;V. P. Dravid
Journal of the American Chemical Society 2011 Volume 133(Issue 23) pp:8786-8789
Publication Date(Web):May 10, 2011
DOI:10.1021/ja2006498
The Pb- and Sb- dual nanostructured PbTe system exhibits anomalous electronic transport behavior wherein the carrier mobility first increases and then decreases with increase in temperature. By combining in situ transmission electron microscopy observations and theoretical calculations based on energy filtering of charge carriers, we propose a plausible mechanism of charge transport based on interphase potential that is mediated by interdiffusion between coexisting Pb and Sb precipitates. These findings promise new strategies to enhance thermoelectric figure of merit via dual and multinanostructuring of miscible precipitates.
Co-reporter:Jiaqing He ; Joseph R. Sootsman ; Steven N. Girard ; Jin-Cheng Zheng ; Jianguo Wen ; Yimei Zhu ; Mercouri G. Kanatzidis
Journal of the American Chemical Society 2010 Volume 132(Issue 25) pp:8669-8675
Publication Date(Web):June 4, 2010
DOI:10.1021/ja1010948
We have investigated the possible mechanisms of phonon scattering by nanostructures and defects in PbTe-X (X = 2% Sb, Bi, or Pb) thermoelectric materials systems. We find that among these three compositions, PbTe-2% Sb has the lowest lattice thermal conductivity and exhibits a larger strain and notably more misfit dislocations at the precipitate/PbTe interfaces than the other two compositions. In the PbTe-Bi 2% sample, we infer some weaker phonon scattering BiTe precipitates, in addition to the abundant Bi nanostructures. In the PbTe-Pb 2% sample, we also find that pure Pb nanoparticles exhibit stronger phonon scattering than nanostructures with Te vacancies. Within the accepted error range, the theoretical calculations of the lattice thermal conductivity in the three systems are in close agreement with the experimental measurements, highlighting the important role of misfit dislocations, nanoscale particles, and associated interfacial elastic strain play in phonon scattering. We further propose that such particle-induced local elastic perturbations interfere with the phonon propagation pathway, thereby contributing to further reduction in lattice thermal conductivity, and consequently can enhance the overall thermoelectric figure of merit.
Co-reporter:Jiaqing He;Steven N. Girard;Mercouri G. Kanatzidis
Advanced Functional Materials 2010 Volume 20( Issue 5) pp:764-772
Publication Date(Web):
DOI:10.1002/adfm.200901905
Abstract
The reduction of thermal conductivity, and a comprehensive understanding of the microstructural constituents that cause this reduction, represent some of the important challenges for the further development of thermoelectric materials with improved figure of merit. Model PbTe-based thermoelectric materials that exhibit very low lattice thermal conductivity have been chosen for this microstructure–thermal conductivity correlation study. The nominal PbTe0.7S0.3 composition spinodally decomposes into two phases: PbTe and PbS. Orderly misfit dislocations, incomplete relaxed strain, and structure-modulated contrast rather than composition-modulated contrast are observed at the boundaries between the two phases. Furthermore, the samples also contain regularly shaped nanometer-scale precipitates. The theoretical calculations of the lattice thermal conductivity of the PbTe0.7S0.3 material, based on transmission electron microscopy observations, closely aligns with experimental measurements of the thermal conductivity of a very low value, ∼0.8 W m−1 K−1 at room temperature, approximately 35% and 30% of the value of the lattice thermal conductivity of either PbTe and PbS, respectively. It is shown that phase boundaries, interfacial dislocations, and nanometer-scale precipitates play an important role in enhancing phonon scattering and, therefore, in reducing the lattice thermal conductivity.
Co-reporter:K.C. Barick, M. Aslam, Vinayak P. Dravid, D. Bahadur
Journal of Colloid and Interface Science 2010 Volume 349(Issue 1) pp:19-26
Publication Date(Web):1 September 2010
DOI:10.1016/j.jcis.2010.05.036
Clustered nanoassemblies of Mn doped ZnO and co-doped ZnO (Mn, Sn co-doped ZnO; Mn, Sb co-doped ZnO; and Mn, Bi co-doped ZnO) were prepared by refluxing their respective precursors in diethylene glycol medium. The co-doping elements, Sn, Sb and Bi exist in multi oxidation states by forming Zn–O–M (M = Sb, Bi and Sn) bonds in hexagonal wurtzite nanostructure. The analyses of detailed structural characterization performed by XRD, X-ray photoelectron spectroscopy (XPS) and high resolution transmission electron microscopy (HRTEM), show that co-doping ions are successfully incorporated into the ZnO nanostructure and do not appear as precipitates or secondary phases. HRTEM analysis also confirmed the oriented attachment of nanocrystals as well as their defect structures. The formation/activation of higher amount of intrinsic host defects, for instance, oxygen vacancies in co-doped ZnO as compared to Mn doped ZnO sample is evident from Raman spectra. The doped and co-doped samples exhibit ferromagnetic like behavior at room temperature presumably due to the presence of defects. Specifically, it has been observed that the incorporation of dopant and co-dopants into ZnO structure can modulate the local electronic structure due to the formation/activation of defects and hence, cause significant changes in their structural, vibrational, optical and magnetic properties.The incorporation of dopants/co-dopants into ZnO clustered nanoassemblies could modulate local electronic structure due to formation/activation of defects which significantly alters their structural, vibrational, optical and magnetic properties.
Co-reporter:Bin Liu, Tao Sun, Jiaqing He, and Vinayak P. Dravid
ACS Nano 2010 Volume 4(Issue 11) pp:6836
Publication Date(Web):October 28, 2010
DOI:10.1021/nn101952q
Nanostructures of multiferroic materials have drawn increasing interest due to the enhanced magnetoelectric coupling and potential for next-generation multifunctional devices. Most of these structures are typically prepared by thin film evaporation approaches. Herein, however, we report a novel sol−gel-based process to synthesize epitaxial BaTiO3−CoFe2O4 nanocomposite thin films via phase separation and enhanced heterogeneous nucleation. The magnetoelectric coupling effect is investigated by examining the temperature-dependent magnetization of the composite film, which manifests as a sharp and significant drop (>50%) of the magnetization at the vicinity of a BaTiO3 ferroelectric phase transition. We propose that the phase transition in BaTiO3 is mediated by the tensile strain due to intimate coupling to CoFe2O4 phase, which has rarely been reported before. The significant coupling effect is attributed to the small substrate clamping, and the large areal distribution of intimate heteroepitaxial interfaces between the three-dimensionally distributed ferroelectric and magnetic nanostructured phases.Keywords: epitaxy; magnetoelectric; multiferroic; nanocomposite; sol−gel
Co-reporter:Shan-Wei Fan, Arvind K. Srivastava, Vinayak P. Dravid
Sensors and Actuators B: Chemical 2010 Volume 144(Issue 1) pp:159-163
Publication Date(Web):29 January 2010
DOI:10.1016/j.snb.2009.10.054
We demonstrate that the soft e-beam lithography (soft-eBL) fabricated polycrystalline ZnO nanolines show reproducible response to ppm-level H2 and NO2 even at room temperature, due to the intrinsic Joule heating effect in such nanodevices. The Joule heating effect is confirmed by studying the resistance–temperature relationship of the sensor as well as the persistent photoconductivity phenomena in ZnO. We note that Joule heating increases the nanoline temperature to around 72 °C, which enhances the oxidation–reduction reaction at the ZnO surface. Therefore, the nanolines show faster photoresponse than the thin film. These results may help tailor and optimize gas sensor devices for improved performance.
Co-reporter:Vinayak P. Dravid
Journal of Materials Chemistry A 2009 vol. 19(Issue 25) pp:4295-4299
Publication Date(Web):11 May 2009
DOI:10.1039/B903201K
A nanoscale patterning approach for ceramic oxides, based on the combination of electron beam lithography and liquid precursor (so-called soft-electron beam lithography, soft-eBL), is elaborated in the context of control over “internal microstructure”. Soft-eBL synergistically combines the traditional top-down approach with the emerging bottom-up method. Depending on the thermal treatment, a wide variety of “tailored” microstructures can be obtained, ranging from nanoscale porosity to single-crystal epitaxy. Such exquisite control over the size, shape, materials diversity and the internal microstructure of nanopatterns provides an excellent platform for further detailed and quantitative understanding of the role of spatial and dimensional constraints on fundamentals of nucleation, growth and external shape evolution of oxides.
Co-reporter:K. C. Barick, M. Aslam, Yen-Po Lin, D. Bahadur, Pottumarthi V. Prasad and Vinayak P. Dravid
Journal of Materials Chemistry A 2009 vol. 19(Issue 38) pp:7023-7029
Publication Date(Web):11 Aug 2009
DOI:10.1039/B911626E
This work demonstrates a new class of magnetic resonance (MR) active aqueous Fe3O4 magnetic nanoparticle nanoassemblies (Fe3O4 MNNA) of ∼40 nm size comprising ∼6 nm particles. They exhibit enhancement in T2 MR contrast as compared to 6 nm isolated counterparts (Fe3O4MNP) and commercial contrast agent, ferumoxytol. This significant improvement in the T2 MR signal arises from the synergistic magnetism of multiple Fe3O4nanoparticles assembled in Fe3O4 MNNA. These nanoassemblies also show better colloidal stability, higher magnetization, good specific absorption rate (under external AC magnetic field) and cytocompatibility with cells. Further, the functional groups (–NH2) present on the surface of Fe3O4 particles can be accessible for routine conjugation of biomolecules through well-developed bioconjugation chemistry. Specifically, a new MR active colloidal amine-functionalized Fe3O4 nanoassembly with enhanced T2 contrast properties has been fabricated, which can also be used as an effective heating source for hyperthermia treatment of cancer.
Co-reporter:Tao Sun, Suresh Donthu, Michael Sprung, Kenneth D’Aquila, Zhang Jiang, Arvind Srivastava, Jin Wang, Vinayak P. Dravid
Acta Materialia 2009 Volume 57(Issue 4) pp:1095-1104
Publication Date(Web):February 2009
DOI:10.1016/j.actamat.2008.10.049
Abstract
Pristine and Pd-doped nanoporous SnOx thin films were fabricated via a sol–gel route. The Pd-doped film exhibited enhanced H2 gas-sensing performance, in terms of higher sensitivity and shorter response time. Structural characterization was performed to investigate the effect of Pd doping on the microstructure evolution of the films. The grain and pore size of Pd-doped film, as measured using transmission electron microscopy and grazing-incidence small-angle X-ray scattering (GISAXS), are both smaller than those of undoped film. In particular, the pore size evolution of the films during annealing was quantitatively monitored in situ using synchrotron-based GISAXS. Knudsen gas diffusion and depletion layer models were employed to evaluate the microstructure influence on the gas sensitivity semi-quantitatively. The results suggest that the microstructure of the Pd-doped film is critical for improving the gas sensitivity but cannot account for the total sensitivity enhancement, implying other mechanisms could play a more important role.
Co-reporter:Hrushikesh M. Joshi, Yen Po Lin, Mohammed Aslam, P. V. Prasad, Elise A. Schultz-Sikma, Robert Edelman, Thomas Meade and Vinayak P. Dravid
The Journal of Physical Chemistry C 2009 Volume 113(Issue 41) pp:17761-17767
Publication Date(Web):September 18, 2009
DOI:10.1021/jp905776g
Cobalt ferrite magnetic nanostructures were synthesized via a high temperature solution phase method. Spherical nanostructures of various sizes were synthesized with the help of seed mediated growth of the nanostructures in the organic phase, while faceted irregular (FI) cobalt ferrite nanostructures were synthesized via the same method but in the presence of a magnetic field. Magnetic properties were characterized by superconducting quantum interference device (SQUID) magnetometry, relaxivity measurements, and thermal activation under RF field, as a function of size and shape. The results show that the saturation magnetization of the nanostructures increases with an increase in size, and the FI nanostructures exhibit lower saturation magnetization than their spherical counterparts. The relaxivity coefficient of cobalt ferrite nanostructures increases with an increase in size, while FI nanostructures show a higher relaxivity coefficient than spherical nanostructures with respect to their saturation magnetization. In the case of RF thermal activation, the specific absorption rate (SAR) of nanostructures increases with an increase in the size. The contribution sheds light on the role of size and shape on important magnetic properties of the nanostructures in relation to their biomedical applications.
Co-reporter:K. C. Barick ; M. Aslam ; Vinayak P. Dravid ;D. Bahadur
The Journal of Physical Chemistry C 2008 Volume 112(Issue 39) pp:15163-15170
Publication Date(Web):September 4, 2008
DOI:10.1021/jp802361r
Size tunable transition metal (Mn, Ni) doped ZnO nanocrystals have been synthesized through a soft chemical route. These nanocrystals self-aggregated themselves in a highly mesoporous spherical superstructure of broad size distribution. The formation of nanocrystals and porous spherical superstructures can be understood as a result of a combination of factors such as the presence of negatively charged carboxylate ions, van der Waals force, the polar nature of ZnO crystal surfaces, and oriented attachment. Monodispersed porous spheres were obtained by size selective separation and then assembled into a face-centered cubic (FCC) close packed superstructure with its (111) plane oriented parallel to the sample surface. The assembled structures exhibit the presence of the photonic stop band in the (111) direction, and the nanocrystals display ferromagnetic like behavior presumably due to defects.
Co-reporter:S. Donthu;V. Dravid;T. Sun
Advanced Materials 2007 Volume 19(Issue 1) pp:125-128
Publication Date(Web):12 DEC 2006
DOI:10.1002/adma.200601223
Soft electron-beam lithography, a simple high-resolution patterning technique, is used to fabricate single-grain-wide nanostructures, as seen in the figure, of functional ceramic materials, such as zinc oxide and bismuth ferrite. Structural characterization of these nanostructures reveal that average grain size decreases with line width (see the plot in the figure).
Co-reporter:Gajendra Shekhawat;Soo-Hyun Tark
Science 2006 Vol 311(5767) pp:1592-1595
Publication Date(Web):17 Mar 2006
DOI:10.1126/science.1122588
Abstract
A promising approach for detecting biomolecules follows their binding to immobilized probe molecules on microfabricated cantilevers; binding causes surface stresses that bend the cantilever. We measured this deflection, which is on the order of tens of nanometers, by embedding a metal-oxide semiconductor field-effect transistor (MOSFET) into the base of the cantilever and recording decreases in drain current with deflections as small as 5 nanometers. The gate region of the MOSFET responds to surface stresses and thus is embedded in silicon nitride so as to avoid direct contact with the sample solution. This approach, which offers low noise, high sensitivity, and direct readout, was used to detect specific binding events with biotin and antibodies.
Co-reporter:A.K. Srivastava, Vinayak P. Dravid
Sensors and Actuators B: Chemical 2006 Volume 117(Issue 1) pp:244-252
Publication Date(Web):12 September 2006
DOI:10.1016/j.snb.2005.11.034
Detection of volatile organic compounds (VOCs) using non-selective sensor requires an array of multiplexed sensors followed by pattern recognition approach. Based on this concept, we compare three different approaches for selective detection of ethanol, ammonia, toluene, acetone and chloroform at different concentrations using non-selective sensors which are: (a) an array of sensors operated at a fixed temperature (hybrid class sensors), (b) operating one sensor at different temperatures (mono-class sensors), and (c) operating all sensors in an array at different temperatures (hybrid and mono-class sensors). Contrary to common practice of using sensors with partially overlapping response patterns (hybrid class sensors) in an array, we demonstrate that even one type of sensors (mono-class sensors) operated at different temperatures can be used for the selective detection of VOCs. It is further shown that an array consisting of hybrid and mono-class sensors each operated at different temperatures not only results in approaching 100% classification but also the quantified samples fall within 10% of error, which is an encouraging result.
Co-reporter:Gajendra S. Shekhawat
Science 2005 Vol 310(5745) pp:89-92
Publication Date(Web):07 Oct 2005
DOI:10.1126/science.1117694
Abstract
A nondestructive imaging method, scanning near-field ultrasound holography (SNFUH), has been developed that provides depth information as well as spatial resolution at the 10- to 100-nanometer scale. In SNFUH, the phase and amplitude of the scattered specimen ultrasound wave, reflected in perturbation to the surface acoustic standing wave, are mapped with a scanning probe microscopy platform to provide nanoscale-resolution images of the internal substructure of diverse materials. We have used SNFUH to image buried nanostructures, to perform subsurface metrology in microelectronic structures, and to image malaria parasites in red blood cells.
Co-reporter:M. Aslam, Lei Fu, Ming Su, K. Vijayamohanan and Vinayak P. Dravid
Journal of Materials Chemistry A 2004 vol. 14(Issue 12) pp:1795-1797
Publication Date(Web):19 May 2004
DOI:10.1039/B402823F
We demonstrate a simple one-step process for the synthesis of water-dispersed spherical gold nanoparticles using the multifunctional molecule oleyl amine (OLA) that electrostatically complexes with aqueous chloroaurate ions, reduces them, and subsequently caps the nanoparticles thus formed. The gold particles thus formed were of the fcc phase and were fairly monodisperse with particular concentrations of capping molecules.
Co-reporter:X. Liu;L. Fu;S. Hong;V.P. Dravid;C.A. Mirkin
Advanced Materials 2002 Volume 14(Issue 3) pp:
Publication Date(Web):29 JAN 2002
DOI:10.1002/1521-4095(20020205)14:3<231::AID-ADMA231>3.0.CO;2-R
Co-reporter:Mrinmoy De, Stanley S. Chou, Hrushikesh M. Joshi, Vinayak P. Dravid
Advanced Drug Delivery Reviews (November 2011) Volume 63(Issues 14–15) pp:1282-1299
Publication Date(Web):1 November 2011
DOI:10.1016/j.addr.2011.07.001
The development of MRI contrast agents has experienced its version of the gilded age over the past decade, thanks largely to the rapid advances in nanotechnology. In addition to progress in single mode contrast agents, which ushered in unprecedented R1 or R2 sensitivities, there has also been a boon in the development of agents covering more than one mode of detection. These include T1–PET, T2–PET T1–optical, T2–optical, T1–T2 agents and many others. In this review, we describe four areas which we feel have experienced particular growth due to nanotechnology, specifically T2 magnetic nanostructure development, T1/T2–optical dual mode agents, and most recently the T1–T2 hybrid imaging systems. In each of these systems, we describe applications including in vitro, in vivo usage and assay development. In all, while the benefits and drawbacks of most MRI contrast agents depend on the application at hand, the recent development in multimodal nanohybrids may curtail the shortcomings of single mode agents in diagnostic and clinical settings by synergistically incorporating functionality. It is hoped that as nanotechnology advances over the next decade, it will produce agents with increased diagnostics and assay relevant capabilities in streamlined packages that can meaningfully improve patient care and prognostics. In this review article, we focus on T2 materials, its surface functionalization and coupling with optical and/or T1 agents.Download high-res image (250KB)Download full-size image
Co-reporter:Eve D. Hanson, Fengyuan Shi, Thomas C. Chasapis, Mercouri G. Kanatzidis, Vinayak P. Dravid
Journal of Crystal Growth (15 February 2016) Volume 436() pp:138-144
Publication Date(Web):15 February 2016
DOI:10.1016/j.jcrysgro.2015.11.033
•A Bi-rich tetradymite material is confined to two dimensions for the first time.•A facile evaporative thinning method is successfully extended to a ternary system.•We report a large composition shift from Se-doped Bi2Te3 to final Bi-rich nanosheet.•An in-depth preferential vapor pressure mechanism explains these composition shifts.High bulk conductance obscures the behavior of surface states in the prototypical topological insulators Bi2Te3 and Bi2Se3. However, ternary phases of Bi2Te3−ySey with balanced donor and acceptor levels may lead to large bulk resistivity, allowing for the observation of the surface states. Additionally, the contribution of the bulk conductance may be further suppressed by nanostructuring, increasing the surface-to-volume ratio. Herein we report the synthesis of a ternary tetradymite newly confined to two dimensions. Ultra-thin large-area stable nanosheets were fabricated via evaporative thinning of a Bi2Te2.9Se0.1 original phase. Owing to vapor pressure differences, a compositional shift to a final Bi-rich phase is observed. The Se/Te ratio of the nanosheet increases tenfold, due to the higher stability of the Bi–Se bonds. Hexagonal crystal symmetry is maintained despite dramatic changes in thickness and stoichiometry. Given that small variations in stoichiometry of this ternary system can incur large changes in carrier concentration and switch majority carrier type, the large compositional shifts found in this case imply that compositional analysis of similar CVD and PVD grown materials is critical to correctly interpret topological insulator performance. Further, the characterization techniques deployed, including STEM-EDS and ToF-SIMS, serve as a case study in determining such compositional shifts in two-dimensional form.
Co-reporter:Tuhin Subhra Sahu, Qianqian Li, Jinsong Wu, Vinayak P. Dravid and Sagar Mitra
Journal of Materials Chemistry A 2017 - vol. 5(Issue 1) pp:NaN363-363
Publication Date(Web):2016/11/09
DOI:10.1039/C6TA07390E
Sodium-ion batteries (SIBs) have undergone extensive research efforts as compatible successors of Li-ion batteries (LIBs) for grid-scale energy storage owing to the abundance of sodium resources. However, the poor cycling stability and low rate capability of existing anodes has prevented the practical application of SIBs. To mitigate the situation we have created a 3D heterostructure electrode based on alternative layers of 2D (MoS2–graphene) and 1D (CNTs) materials via a hydrothermal route that is fundamentally different from the usual composites. For comparison, composites were prepared using the same experimental conditions with either rGO or MWCNTs. While discharging at 100 mA g−1 and 500 mA g−1, the MoS2–MWCNT@rGO could deliver a high discharge capacity of 664 mA h g−1 and 551 mA h g−1, and retained 100% and 98.4% capacity after 80 and 250 discharge–charge cycles, respectively. At 2 A g−1, it can yield an initial discharge capacity of 375 mA h g−1, maintaining 81.3% and 67% capacity after 250 and 500 cycles, respectively. The excellent performance of the MoS2–MWCNT@rGO hybrid is mainly attributed to the robust MWCNT@rGO framework with improved 3D electrical conductivity, additional porosity and excellent buffering capability. Furthermore, an in situ TEM technique was employed to explore the sodiation mechanism of the MoS2 nanosheets.
Co-reporter:K. C. Barick, M. Aslam, Yen-Po Lin, D. Bahadur, Pottumarthi V. Prasad and Vinayak P. Dravid
Journal of Materials Chemistry A 2009 - vol. 19(Issue 38) pp:NaN7029-7029
Publication Date(Web):2009/08/11
DOI:10.1039/B911626E
This work demonstrates a new class of magnetic resonance (MR) active aqueous Fe3O4 magnetic nanoparticle nanoassemblies (Fe3O4 MNNA) of ∼40 nm size comprising ∼6 nm particles. They exhibit enhancement in T2 MR contrast as compared to 6 nm isolated counterparts (Fe3O4MNP) and commercial contrast agent, ferumoxytol. This significant improvement in the T2 MR signal arises from the synergistic magnetism of multiple Fe3O4nanoparticles assembled in Fe3O4 MNNA. These nanoassemblies also show better colloidal stability, higher magnetization, good specific absorption rate (under external AC magnetic field) and cytocompatibility with cells. Further, the functional groups (–NH2) present on the surface of Fe3O4 particles can be accessible for routine conjugation of biomolecules through well-developed bioconjugation chemistry. Specifically, a new MR active colloidal amine-functionalized Fe3O4 nanoassembly with enhanced T2 contrast properties has been fabricated, which can also be used as an effective heating source for hyperthermia treatment of cancer.
Co-reporter:Vinayak P. Dravid
Journal of Materials Chemistry A 2009 - vol. 19(Issue 25) pp:NaN4299-4299
Publication Date(Web):2009/05/11
DOI:10.1039/B903201K
A nanoscale patterning approach for ceramic oxides, based on the combination of electron beam lithography and liquid precursor (so-called soft-electron beam lithography, soft-eBL), is elaborated in the context of control over “internal microstructure”. Soft-eBL synergistically combines the traditional top-down approach with the emerging bottom-up method. Depending on the thermal treatment, a wide variety of “tailored” microstructures can be obtained, ranging from nanoscale porosity to single-crystal epitaxy. Such exquisite control over the size, shape, materials diversity and the internal microstructure of nanopatterns provides an excellent platform for further detailed and quantitative understanding of the role of spatial and dimensional constraints on fundamentals of nucleation, growth and external shape evolution of oxides.
Co-reporter:Qianqian Li, Jinsong Wu, Junming Xu and Vinayak P. Dravid
Journal of Materials Chemistry A 2016 - vol. 4(Issue 22) pp:NaN8675-8675
Publication Date(Web):2016/05/09
DOI:10.1039/C6TA02051H
Replacing lithium with sodium-ion batteries for energy storage is of enormous interest, especially from practical and economic considerations. However, it has proved difficult to achieve competitive figures of merit for sodium-ion batteries due to the lack of a detailed understanding of the reaction mechanism(s). Herein, we report a sodium electrochemical conversion reaction with Co3O4 nanoparticles decorated on carbon nanotubes (Co3O4/CNTs) utilizing in situ TEM, down to the atomic-scale. We observe synergetic effects of the two nanoscale components, which provide insights into a new sodiation mechanism, facilitated by Na-diffusion along a CNT backbone and CNT–Co3O4 interfaces. A thin layer of amorphous low conductivity Na2O forms on the CNT surfaces at the beginning of sodiation. The conversion reaction results in the formation of ultrafine metallic Co nanoparticles and polycrystalline Na2O, and fast diffusion of the reaction products which might be due to the quick migration of Na2O under an electron beam. In the desodiation process, the dissociation of Na2O and formation of Co3O4 due to the de-conversion reaction are observed.
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