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.

Heterojunction microwire array semiconductor devices

Abstract: A heterojunction semiconductor device including an array of microstructures, each microstructure including a microwire of a first semiconductor material and a coating of a second semiconductor material forming a heterojunction with the microwire; a first electrical contact and a second electrical contact, one of which is connected to the microwire and the other of which is connected to the coating, is described. Also described are considerations for configuring the array of microstructures, and methods of forming the array of microstructures.

Semiconducting ZnSnxGe1−xN2 alloys prepared by reactive radio-frequency sputtering

Abstract: We report on the fabrication and structural and optoelectronic characterization of II-IV-nitride ZnSn_x Ge(1−x)N_2 thin-films. Three-target reactive radio-frequency sputtering was used to synthesize non-degenerately doped semiconducting alloys having <10% atomic composition (x = 0.025) of tin. These low-Sn alloys followed the structural and optoelectronic trends of the alloy series. Samples exhibited semiconducting properties, including optical band gaps and increasing in resistivities with temperature. Resistivity vs. temperature measurements indicated that low-Sn alloys were non-degenerately doped, whereas alloys with higher Sn content were degenerately doped. These films show potential for ZnSn_x Ge_(1−x)N_2 as tunable semiconductor absorbers for possible use in photovoltaics, light-emitting diodes, or optical sensors.

Photoelectrochemical Behavior of n-GaAs and n-AlxGa1-xAs in CH3CN

Abstract: Current density vs potential, open-circuit voltage vs temperature, and differential capacitance vs potential measurements have been used to show that n-GaAs and n-AlxGa1-xAs electrodes exhibit partial Fermi level pinning in contact with CH3CN over a wide range of redox potentials. Despite a change of over 1.2 V in redox potential of the solution, the open-circuit voltage only changed by ∼300 mV. The slope of the open-circuit voltage vs redox potential of the solution was typically 0.33−0.44. Differential capacitance vs potential data also yielded a barrier height change of less than 300 mV for over 1.2 V change in the redox potential of the solution. The dependence of the current density vs potential behavior of n-GaAs/CH3CN−ferricenium−ferrocene+/0 on variables such as the illumination intensity, dopant density of the semiconductor, concentration of redox acceptor in the solution, crystal face, electrolyte, and cell temperature was evaluated. The resultant kinetic data indicate that surface-state recombi...

High-resolution X-ray photoelectron spectroscopy of chlorine-terminated GaAs(111)A surfaces.

Abstract: Oxide-terminated and Cl-terminated GaAs(111)A surfaces have been characterized in the As and Ga 3d regions by high-resolution, soft X-ray photoelectron spectroscopy. The Cl-terminated surface, formed by treatment with 6 M HCl(aq), showed no detectable As oxides or As^0 in the As 3d region. The Ga 3d spectrum of the Cl-terminated surface showed a broad, intense signal at 19.4 eV and a smaller signal at 21.7 eV. The Ga 3d peaks were fitted using three species, one representing bulk GaAs and the others representing two chemical species on the surface. The large peak was well-fitted by the bulk GaAs emission and by a second doublet, assigned to surface Ga atoms bonded to Cl, that was shifted by 0.34 eV from the bulk GaAs 3d emission. The smaller peak, shifted by 2.3 eV in binding energy relative to the bulk GaAs Ga 3d signal, is assigned to Ga(OH)_3. The data confirm that wet chemical etching allows for the formation of well-defined, Cl-terminated GaAs(111)A surfaces free of detectable elemental As, that can provide a starting point for further functionalization of GaAs.

Characterization of the Electrical Properties of Individual p-Si Microwire/Polymer/n-Si Microwire Assemblies

Abstract: The electrical properties of individual p- and n-type silicon microwires have been investigated using a direct contact formation technique, in which an Ohmic contact between the tungsten probe and microwire was produced by applying mechanical force to the probe/microwire junction. This method alleviated the need for lithography or a high-temperature process to form a metal/Si ohmic contact. The technique was also used to characterize the Si microwire/conducting polymer junctions in a single cell of a membrane-supported bilayer Si microwire structure that is of interest for the direct production of fuels from sunlight. The data indicate that the combination of PEDOT–PSS–Nafion and highly doped Si microwires is suitable, from an electrical resistance perspective, to be used in a solar fuels generation device.

I and i

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 …

A low-cost, high-efficiency solar cell based on dye-sensitized colloidal TiO2 films

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.

疟原虫var基因转换速率变化导致抗原变异[英]／Paul H, Robert P, Christodoulou Z, et al//Proc Natl Acad Sci U S A

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。

Heterogeneous photocatalyst materials for water splitting

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)