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156. Comparison of the Performance of CoP-Coated and Pt-Coated Radial Junction n^+p-Silicon Microwire-Array Photocathodes for the Sunlight-Driven Reduction of Water to H_2(g)

Author

Roske, Christopher W., Popczun, Eric J., Seger, Brian, Read, Carlos G., Pedersen, Thomas, Hansen, Ole, Vesborg, Peter C. K., Brunschwig, Bruce S., Schaak, Raymond E., Chorkendorff, Ib, Gray, Harry B., and Lewis, Nathan S.

Abstract

The electrocatalytic performance for hydrogen evolution has been evaluated for radial-junction n^+p-Si microwire (MW) arrays with Pt or cobalt phosphide, CoP, nanoparticulate catalysts in contact with 0.50 M H_2SO_4(aq). The CoP-coated (2.0 mg cm^(–2)) n^+p-Si MW photocathodes were stable for over 12 h of continuous operation and produced an open-circuit photovoltage (V_(oc)) of 0.48 V, a light-limited photocurrent density (J_(ph)) of 17 mA cm^(–2), a fill factor (ff) of 0.24, and an ideal regenerative cell efficiency (η_(IRC)) of 1.9% under simulated 1 Sun illumination. Pt-coated (0.5 mg cm^(–2)) n^+p-Si MW-array photocathodes produced V_(oc) = 0.44 V, J_(ph) = 14 mA cm^(–2), ff = 0.46, and η = 2.9% under identical conditions. Thus, the MW geometry allows the fabrication of photocathodes entirely comprised of earth-abundant materials that exhibit performance comparable to that of devices that contain Pt.

Published
2015

164. Low‐Temperature Solution Synthesis of Few‐Layer 1T ′‐MoTe2 Nanostructures Exhibiting Lattice Compression

Author

Sun, Yifan, primary, Wang, Yuanxi, additional, Sun, Du, additional, Carvalho, Bruno R., additional, Read, Carlos G., additional, Lee, Chia‐hui, additional, Lin, Zhong, additional, Fujisawa, Kazunori, additional, Robinson, Joshua A., additional, Crespi, Vincent H., additional, Terrones, Mauricio, additional, and Schaak, Raymond E., additional

Published
2016
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165. Low‐Temperature Solution Synthesis of Few‐Layer 1T ′‐MoTe 2 Nanostructures Exhibiting Lattice Compression

Author

Sun, Yifan, primary, Wang, Yuanxi, additional, Sun, Du, additional, Carvalho, Bruno R., additional, Read, Carlos G., additional, Lee, Chia‐hui, additional, Lin, Zhong, additional, Fujisawa, Kazunori, additional, Robinson, Joshua A., additional, Crespi, Vincent H., additional, Terrones, Mauricio, additional, and Schaak, Raymond E., additional

Published
2016
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170. Recent Advances in Two-Dimensional Materials beyond Graphene

Author

Bhimanapati, Ganesh R., primary, Lin, Zhong, additional, Meunier, Vincent, additional, Jung, Yeonwoong, additional, Cha, Judy, additional, Das, Saptarshi, additional, Xiao, Di, additional, Son, Youngwoo, additional, Strano, Michael S., additional, Cooper, Valentino R., additional, Liang, Liangbo, additional, Louie, Steven G., additional, Ringe, Emilie, additional, Zhou, Wu, additional, Kim, Steve S., additional, Naik, Rajesh R., additional, Sumpter, Bobby G., additional, Terrones, Humberto, additional, Xia, Fengnian, additional, Wang, Yeliang, additional, Zhu, Jun, additional, Akinwande, Deji, additional, Alem, Nasim, additional, Schuller, Jon A., additional, Schaak, Raymond E., additional, Terrones, Mauricio, additional, and Robinson, Joshua A., additional

Published
2015
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172. Size- and Interface-Modulated Metal-Insulator Transition in Solution-Synthesized Nanoscale VO2-TiO2-VO2 Heterostructures.

Author

Li, Xuefei and Schaak, Raymond E.

Subjects
*METAL-insulator transitions, *SOLUTION (Chemistry), *NANOSTRUCTURED materials synthesis, *VANADIUM oxide, *TITANIUM dioxide, *HETEROSTRUCTURES
Abstract

The M1 form of vanadium dioxide, which exhibits a reversible insulator-metal transition above room temperature, has been incorporated into nanoscale heterostructures through solution-phase epitaxial growth on the tips of rutile TiO2 nanorods. Four distinct classes of VO2-TiO2-VO2 nanorod heterostructures are accessible by modulating the growth conditions. Each type of VO2-TiO2-VO2 nanostructure has a different insulator-metal transition temperature that depends on the VO2 domain sizes and the TiO2-VO2 interfacial strain characteristics. [ABSTRACT FROM AUTHOR]

Published
2017
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173. Solution synthesis of few-layer WTe2 and MoxW1−xTe2 nanostructures.

Author

Sun, Yifan, Fujisawa, Kazunori, Terrones, Mauricio, and Schaak, Raymond E.

Abstract

Transition metal ditellurides are gaining widespread attention due to their rich polymorphism and distinct electronic properties when compared to transition metal disulfides and diselenides. Here, we report the direct synthesis of Td-WTe2 nanostructures via a low-temperature solution-based method. A comprehensive structural characterization reveals the anisotropic pathway by which the few-layer WTe2 nanostructures grow, as well as the co-existence of multiple stacking motifs. The versatility of this synthetic approach is further expanded to access nanostructured MoxW1−xTe2 alloys across the entire solid solution that spans the 1T′-MoTe2 and Td-WTe2 end members, where the elemental composition and crystal structure can be systematically tuned by modulating the metal reagent ratios. The ability to access transition metal ditellurides using solution synthesis methods complements traditional gas-phase fabrication techniques and provides an alternative strategy for manufacturing an expanded library of composition-tunable TMD nanostructures. [ABSTRACT FROM AUTHOR]

Published
2017
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174. Multi-Step Topochemical Pathway to Metastable Mo2AlB2and Related Two-Dimensional Nanosheet Heterostructures

Author

Alameda, Lucas T., Lord, Robert W., Barr, Jordan A., Moradifar, Parivash, Metzger, Zachary P., Steimle, Benjamin C., Holder, Cameron F., Alem, Nasim, Sinnott, Susan B., and Schaak, Raymond E.

Abstract

The rational synthesis of metastable inorganic solids, which is a grand challenge in solid-state chemistry, requires the development of kinetically controlled reaction pathways. Topotactic strategies can achieve this goal by chemically modifying reactive components of a parent structure under mild conditions to produce a closely related analogue that has otherwise inaccessible structures and/or compositions. Refractory materials, such as transition metal borides, are difficult to structurally manipulate at low temperatures because they generally are chemically inert and held together by strong covalent bonds. Here, we report a multistep low-temperature topotactic pathway to bulk-scale Mo2AlB2, which is a metastable phase that has been predicted to be the precursor needed to access a synthetically elusive family of 2-D metal boride (MBene) nanosheets. Room-temperature chemical deintercalation of Al from the stable compound MoAlB (synthesized as a bulk powder at 1400 °C) formed highly strained and destabilized MoAl1–xB, which was size-selectively precipitated to isolate the most reactive submicron grains and then annealed at 600 °C to deintercalate additional Al and crystallize Mo2AlB2. Further heating resulted in topotactic decomposition into bulk-scale Mo2AlB2–AlOxnanolaminates that contain Mo2AlB2nanosheets with thickness of 1–3 nm interleaved by 1–3 nm of amorphous aluminum oxide. The combination of chemical destabilization, size-selective precipitation, and low-temperature annealing provides a potentially generalizable kinetic pathway to metastable variants of refractory compounds, including bulk Mo2AlB2and Mo2AlB2–AlOxnanosheet heterostructures, and opens the door to other previously elusive 2-D materials such as 2-D MoB (MBene).

Published
2019
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180. Comparison of the Performance of CoP-Coated and Pt-Coated Radial Junction n+p-Silicon Microwire-Array Photocathodes for the Sunlight-Driven Reduction of Water to H2(g)

Author

Roske, Christopher W., primary, Popczun, Eric J., additional, Seger, Brian, additional, Read, Carlos G., additional, Pedersen, Thomas, additional, Hansen, Ole, additional, Vesborg, Peter C. K., additional, Brunschwig, Bruce S., additional, Schaak, Raymond E., additional, Chorkendorff, Ib, additional, Gray, Harry B., additional, and Lewis, Nathan S., additional

Published
2015
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188. A Year for Nanoscience

Author

Chan, Warren C. W., primary, Gogotsi, Yury, additional, Hafner, Jason H., additional, Hammond, Paula T., additional, Hersam, Mark C., additional, Javey, Ali, additional, Kagan, Cherie R., additional, Khademhosseini, Ali, additional, Kotov, Nicholas A., additional, Lee, Shuit-Tong, additional, Möhwald, Helmuth, additional, Mulvaney, Paul A., additional, Nel, Andre E., additional, Nordlander, Peter J., additional, Parak, Wolfgang J., additional, Penner, Reginald M., additional, Rogach, Andrey L., additional, Schaak, Raymond E., additional, Stevens, Molly M., additional, Wee, Andrew T. S., additional, Willson, C. Grant, additional, and Weiss, Paul S., additional

Published
2014
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193. Low-temperature polyol synthesis of AuCuSn2 and AuNiSn2: Using solution chemistry to access ternary intermetallic compounds as nanocrystals

Author

Leonard, Brian M., Bhuvanesh, Nattamai S. P., and Schaak, Raymond E.

Subjects
Polyols -- Electric properties, Tin compounds -- Electric properties, Copper compounds -- Electric properties, Gold compounds -- Electric properties, Chemistry
Abstract

Low-temperature solution routes originally developed for the synthesis of nanocrystals and nanocrystalline powders can be exploited to access new ordered intermetallics with ternary compositions. The Au-Cu-Sn system was studied since ternary phase diagrams are difficult to map.

Published
2005

194. Reactive AgAuS and Ag3AuS2 Synthons Enable the Sequential Transformation of Spherical Nanocrystals into Asymmetric Multicomponent Hybrid Nanoparticles.

Author

Xuefei Li and Schaak, Raymond E.

Subjects
*HETEROSTRUCTURES, *NANOCRYSTALS, *HETERODIMERS, *NANOPARTICLES, *NANOSTRUCTURED materials
Abstract

Nanoscale heterostructures that interface with multiple distinct materials provide opportunities to engineer functional complexity into single-particle constructs. However, existing synthetic pathways to such hybrid nanoparticles emphasize surface-seeded growth, which limits the scope of accessible systems. Here, we introduce an alternative approach that transforms isotropic nanocrystals into asymmetric, multicomponent Janus particles through sequential deposition, reactive phase segregation, and cation exchange processes that are mediated by an unusual class of reactive synthons. After Ag-Au seed particles had formed and had reacted with sulfur, a series of segregated Au1-xAgx-AgAuS and Au1-xAgx-Ag3AuS2 hybrid nanoparticles form. The AgAuS and Ag3AuS2 domains provide a synthetic entryway into solution-mediated cation exchange reactions, with the compositions of the Ag-Au-S synthons defining the components, morphologies, and interfaces of the hybrid nanoparticle products. Upon cation exchange with Pb2+, Au1-xAgx-AgAuS forms Ag1-xAux-PbS heterodimers while Au1-xAgx-Ag3AuS2 forms Ag1-xAux-Ag2S-PbS heterotrimers. The process by which isotropic metal nanoparticles transform into asymmetric hybrid nanoparticles through reactive Ag-Au-S synthons provides important insights that will be applicable to the retrosynthetic design of complex nanoscale heterostructures having expanded multifunctionality and synergistic properties. [ABSTRACT FROM AUTHOR]

Published
2017
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196. Solution-Mediated Growth of Two-Dimensional SnSe@GeSe Nanosheet Heterostructures.

Author

Du Sun and Schaak, Raymond E.

Subjects
*HETEROSTRUCTURES, *TRANSITION metal chalcogenides, *VAPOR-plating
Abstract

Nanosheet heterostructures that directly interface multiple distinct metal chalcogenides are important two-dimensional materials with unique synergistic properties. Solution routes to these materials offer potential advantages over existing vapor deposition and exfoliation/restacking methods, but they remain difficult to implement and control. Here, we show that SnSe can be grown in solution on micrometer-sized GeSe nanosheets and establish guidelines for achieving controllable deposition. Heating GeSe nanosheets in oleylamine with various amounts of SnCl2 and TOP-Se reveals distinct regimes that favor growth of SnSe on the edge sites vs basal planes of GeSe. Using continuous injection to better control concentrations and reagent delivery, SnSe can be grown on GeSe to produce two distinct types of crystallographically aligned SnSe@GeSe nanosheet heterostructures. [ABSTRACT FROM AUTHOR]

Published
2017
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