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Nathan S. Lewis

Bio: Nathan S. Lewis is an academic researcher from California Institute of Technology. The author has contributed to research in topics: Semiconductor & Silicon. The author has an hindex of 112, co-authored 720 publications receiving 64808 citations. Previous affiliations of Nathan S. Lewis include Lawrence Berkeley National Laboratory & Massachusetts Institute of Technology.


Papers
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Journal ArticleDOI
TL;DR: The SXPS data indicate that functionalization by the two-step chlorination/alkylation process proceeds cleanly to produce oxide-free Si surfaces terminated with the chosen alkyl group.
Abstract: Hydrogen-terminated, chlorine-terminated, and alkyl-terminated crystalline Si(111) surfaces have been characterized using high-resolution, soft X-ray photoelectron spectroscopy from a synchrotron radiation source. The H-terminated Si(111) surface displayed a Si 2p_(3/2) peak at a binding energy 0.15 eV higher than the bulk Si 2p_(3/2) peak. The integrated area of this shifted peak corresponded to one equivalent monolayer, consistent with the assignment of this peak to surficial Si−H moieties. Chlorinated Si surfaces prepared by exposure of H-terminated Si to PCl_5 in chlorobenzene exhibited a Si 2p_(3/2) peak at a binding energy of 0.83 eV above the bulk Si peak. This higher-binding-energy peak was assigned to Si−Cl species and had an integrated area corresponding to 0.99 of an equivalent monolayer on the Si(111) surface. Little dichloride and no trichloride Si 2p signals were detected on these surfaces. Silicon(111) surfaces alkylated with C_nH_(2n+1)^− (n = 1 or 2) or C_6H_5CH_2^− groups were prepared by exposing the Cl-terminated Si surface to an alkylmagnesium halide reagent. Methyl-terminated Si(111) surfaces prepared in this fashion exhibited a Si 2p_(3/2) signal at a binding energy of 0.34 eV above the bulk Si 2p_(3/2) peak, with an area corresponding to 0.85 of a Si(111) monolayer. Ethyl- and C_6H_5CH_2-terminated Si(111) surfaces showed no evidence of either residual Cl or oxidized Si and exhibited a Si 2p_(3/2) peak ∼0.20 eV higher in energy than the bulk Si 2p_(3/2) peak. This feature had an integrated area of ∼1 monolayer. This positively shifted Si 2p_(3/2) peak is consistent with the presence of Si−C and Si−H surface functionalities on such surfaces. The SXPS data indicate that functionalization by the two-step chlorination/alkylation process proceeds cleanly to produce oxide-free Si surfaces terminated with the chosen alkyl group.

85 citations

Journal ArticleDOI
TL;DR: In this article, high-structured silicon microwire (Si MW) arrays have been synthesized and characterized as absorbers for solar energy-conversion systems, allowing for efficient collection of photogenerated carriers from impure materials.
Abstract: Highly structured silicon microwire (Si MW) arrays have been synthesized and characterized as absorbers for solar energy-conversion systems. These materials are of great interest for applications in solar energy conversion, including solar electricity and solar fuels production, due to their unique materials properties, form factors, ease of fabrication, and device-processing attributes. The Si MW array geometry allows for efficient collection of photogenerated carriers from impure materials that have short minority-carrier diffusion lengths while simultaneously allowing for high optical absorption and high external quantum yields for charge-carrier collection. In addition, Si MW arrays exhibit unique mesoscale optical behavior and can be removed from the growth substrate to provide flexible, processable arrays of Si microwires ordered in a variety of organic polymers and ionomers. The unique photon-management properties of Si MW arrays, combined with their high internal surface area and controlled morpho...

83 citations

Patent
25 Sep 2001
TL;DR: In this paper, a chemical analyte can be detected based on a change in electrical or optical properties of the sensors, which can be identified by measuring the electrical and optical properties.
Abstract: Sensors, sensor arrays and sensing methods provide for detection of a chemical analyte in a fluid. Sensors include a plurality of conductive and nonconductive regions in contact with a measuring apparatus. One or more sensors include a plurality of particles that include a metallic core. Preferably, the particles also include one or more capping ligands coupled to the metallic core. Exposure of the sensors to a fluid containing a chemical analyte causes the analyte to react with the metal core, preferably by displacing one or more of the capping ligands. The chemical analyte can be detected based on a change in electrical or optical properties of the sensors.

82 citations

Journal ArticleDOI
TL;DR: This thematic issue contains reviews of various aspects of Solar Energy Conversion, where solar panels provide a known, scalable technology to capture and convert sunlight into electricity.
Abstract: This thematic issue contains reviews of various aspects of Solar Energy Conversion. The sun provides the largest energy source known to man, with more energy from sunlight striking the earth in 1 h than all of the energy consumed on the planet in an entire year. Solar panels provide a known, scalable technology to capture and convert sunlight into electricity. Moreover, the costs of Si-based photovoltaic panels have declined continuously in the past decade, to the point where solar electricity is now cost-competitive in certain regions and niche markets. Nevertheless, solar energy conversion continues to attract fervent efforts devoted to the discovery and development of new materials, concepts, devices, and systems that can provide new and/or dramatically improved functionality and scalability.

81 citations

Journal ArticleDOI
TL;DR: The louvered design provides a robust platform for implementation of various types of photoelectrochemical assemblies, and can provide an approach to significantly higher solar conversion efficiencies as new and improved materials become available.
Abstract: A fully integrated solar-driven water-splitting system comprised of WO3/FTO/p^(+)n Si as the photoanode, Pt/TiO_2/Ti/n^(+)p Si as the photocathode, and Nafion as the membrane separator, was simulated, assembled, operated in 1.0 M HClO_4, and evaluated for performance and safety characteristics under dual side illumination. A multi-physics model that accounted for the performance of the photoabsorbers and electrocatalysts, ion transport in the solution electrolyte, and gaseous product crossover was first used to define the optimal geometric design space for the system. The photoelectrodes and the membrane separators were then interconnected in a louvered design system configuration, for which the light-absorbing area and the solution-transport pathways were simultaneously optimized. The performance of the photocathode and the photoanode were separately evaluated in a traditional three-electrode photoelectrochemical cell configuration. The photocathode and photoanode were then assembled back-to-back in a tandem configuration to provide sufficient photovoltage to sustain solar-driven unassisted water-splitting. The current–voltage characteristics of the photoelectrodes showed that the low photocurrent density of the photoanode limited the overall solar-to-hydrogen (STH) conversion efficiency due to the large band gap of WO_3. A hydrogen-production rate of 0.17 mL hr^−1 and a STH conversion efficiency of 0.24 % was observed in a full cell configuration for >20 h with minimal product crossover in the fully operational, intrinsically safe, solar-driven water-splitting system. The solar-to-hydrogen conversion efficiency, ηS_TH, calculated using the multiphysics numerical simulation was in excellent agreement with the experimental behavior of the system. The value of ηSTH was entirely limited by the performance of the photoelectrochemical assemblies employed in this study. The louvered design provides a robust platform for implementation of various types of photoelectrochemical assemblies, and can provide an approach to significantly higher solar conversion efficiencies as new and improved materials become available.

81 citations


Cited by
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[...]

08 Dec 2001-BMJ
TL;DR: There is, I think, something ethereal about i —the square root of minus one, which seems an odd beast at that time—an intruder hovering on the edge of reality.
Abstract: There is, I think, something ethereal about i —the square root of minus one. I remember first hearing about it at school. It seemed an odd beast at that time—an intruder hovering on the edge of reality. Usually familiarity dulls this sense of the bizarre, but in the case of i it was the reverse: over the years the sense of its surreal nature intensified. It seemed that it was impossible to write mathematics that described the real world in …

33,785 citations

Journal ArticleDOI
24 Oct 1991-Nature
TL;DR: In this article, the authors describe a photovoltaic cell, created from low-to medium-purity materials through low-cost processes, which exhibits a commercially realistic energy-conversion efficiency.
Abstract: THE large-scale use of photovoltaic devices for electricity generation is prohibitively expensive at present: generation from existing commercial devices costs about ten times more than conventional methods1. Here we describe a photovoltaic cell, created from low-to medium-purity materials through low-cost processes, which exhibits a commercially realistic energy-conversion efficiency. The device is based on a 10-µm-thick, optically transparent film of titanium dioxide particles a few nanometres in size, coated with a monolayer of a charge-transfer dye to sensitize the film for light harvesting. Because of the high surface area of the semiconductor film and the ideal spectral characteristics of the dye, the device harvests a high proportion of the incident solar energy flux (46%) and shows exceptionally high efficiencies for the conversion of incident photons to electrical current (more than 80%). The overall light-to-electric energy conversion yield is 7.1-7.9% in simulated solar light and 12% in diffuse daylight. The large current densities (greater than 12 mA cm-2) and exceptional stability (sustaining at least five million turnovers without decomposition), as well as the low cost, make practical applications feasible.

26,457 citations

28 Jul 2005
TL;DR: PfPMP1)与感染红细胞、树突状组胞以及胎盘的单个或多个受体作用,在黏附及免疫逃避中起关键的作�ly.
Abstract: 抗原变异可使得多种致病微生物易于逃避宿主免疫应答。表达在感染红细胞表面的恶性疟原虫红细胞表面蛋白1(PfPMP1)与感染红细胞、内皮细胞、树突状细胞以及胎盘的单个或多个受体作用,在黏附及免疫逃避中起关键的作用。每个单倍体基因组var基因家族编码约60种成员,通过启动转录不同的var基因变异体为抗原变异提供了分子基础。

18,940 citations

Journal ArticleDOI
TL;DR: This critical review shows the basis of photocatalytic water splitting and experimental points, and surveys heterogeneous photocatalyst materials for water splitting into H2 and O2, and H2 or O2 evolution from an aqueous solution containing a sacrificial reagent.
Abstract: This critical review shows the basis of photocatalytic water splitting and experimental points, and surveys heterogeneous photocatalyst materials for water splitting into H2 and O2, and H2 or O2 evolution from an aqueous solution containing a sacrificial reagent Many oxides consisting of metal cations with d0 and d10 configurations, metal (oxy)sulfide and metal (oxy)nitride photocatalysts have been reported, especially during the latest decade The fruitful photocatalyst library gives important information on factors affecting photocatalytic performances and design of new materials Photocatalytic water splitting and H2 evolution using abundant compounds as electron donors are expected to contribute to construction of a clean and simple system for solar hydrogen production, and a solution of global energy and environmental issues in the future (361 references)

8,850 citations