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.

STRUCTURES OF AND METHODS FOR FORMING VERTICALLY ALIGNED Si WIRE ARRAYS

Abstract: A structure consisting of vertically aligned wire arrays on a Si substrate and a method for producing such wire arrays. The wire arrays are fabricated and positioned on a substrate with an orientation and density particularly adapted for conversion of received light to energy. A patterned oxide layer is used to provide for wire arrays that exhibit narrow diameter and length distribution and provide for controlled wire position.

Infrared Vibrational Spectroscopy of Isotopically Labeled Ethyl-Terminated Si(111) Surfaces Prepared Using a Two-Step Chlorination/Alkylation Procedure

Abstract: Fourier transform infrared (FTIR) spectroscopy was used to investigate C2H5−Si(111) surfaces prepared using a chlorination/alkylation method. After alkylation, in addition to ethyl groups, such surfaces showed the presence of hydrogen bonded to atop silicon surface atoms. Systematic isotopic substitution of protic solvents and reagents with their fully or partially deuterated counterparts revealed the origin of the surface-bound hydrogen on the C2H5−Si(111) surfaces. The presence or absence of the Si−H stretch at 2080 cm−1 and the Si−D stretch at ∼1510 cm−1, respectively, indicated that the hydrogen originated from the methyl group of the ethyl Grignard reagent.

Synthesis and Characterization of Silicon Nanorod Arrays for Solar Cell Applications

Abstract: Silicon nanorods have been grown by chemical vapor deposition of silane, using both gold and indium as catalysts for the vapor liquid solid (VLS) process. Conditions for optimal rod morphology for each catalyst were identified by varying silane partial pressure and temperature in the range P = 0.05-1 Torr and T = 300-600 C, respectively. In most cases, catalyst particles were formed by partial de-wetting of evaporated films of the catalytic material to form droplets with diameters of tens to hundreds of nanometers. Also, periodic arrays of catalyst particles with controlled size and spacing were achieved both by the use of porous alumina membranes and also by electron-beam lithography. Using these techniques, silicon nanorods were grown with diameters of 100 nm to microns and lengths of microns to tens of microns. Four-point and gate-bias-dependent resistance measurements were made on single wires, and these indicate that rods we have grown with gold catalysts and phosphine doping have metal-like conductivity.

Evaluation of flow schemes for near-neutral pH electrolytes in solar-fuel generators

Abstract: The electrochemical performance of three different types of membrane-containing electrolyte-flow schemes for solar-driven water splitting has been studied quantitatively using 1-dimensional and 2-dimensional multi-physics models. The three schemes include a recirculation scheme with a well-mixed bulk electrolyte, a recirculation scheme with laminar flow fields, and a fresh-feed scheme with laminar flow fields. The Nernstian potential loss associated with pH gradients at the electrode surfaces, the resistive loss between the cathode and anode, the product-gas crossovers, and the required pumping energy in all three schemes have been evaluated as a function of the operational current density, the flow rates for the electrolyte, and the physical dimensions of the devices. The trade-offs in the voltage loss, safety considerations, and energy inputs from the balance-of-systems required to produce a practical device have been evaluated and compared to membrane-free devices as well as to devices that operate at extreme pH values.

Energy-band alignment of II-VI/Zn3P2 heterojunctions from x-ray photoemission spectroscopy

Abstract: The energy-band alignments for zb-ZnSe(001)/α-Zn_(3)P_2(001), w-CdS(0001)/α-Zn_(3)P_2(001), and w-ZnO(0001)/α-Zn_(3)P_2(001) heterojunctions have been determined using high-resolution x-ray photoelectron spectroscopy via the Kraut method. Ab initio hybrid density functional theory calculations of the valence-band density of states were used to determine the energy differences between the core level and valence-band maximum for each of the bulk materials. The ZnSe/Zn_(3)P_2 heterojunction had a small conduction-band offset, ΔEC, of −0.03 ± 0.11 eV, demonstrating a nearly ideal energy-band alignment for use in thin-film photovoltaic devices. The CdS/Zn_(3)P_2 heterojunction was also type-II but had a larger conduction-band offset of ΔEC = −0.76 ± 0.10 eV. A type-III alignment was observed for the ZnO/Zn_(3)P_2 heterojunction, with ΔEC = −1.61 ± 0.16 eV indicating the formation of a tunnel junction at the oxide–phosphide interface. The data also provide insight into the role of the II-VI/Zn_(3)P_2 band alignment in the reported performance of Zn_(3)P_2 heterojunction solar cells.

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)