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.

Further mechanistic studies of n-type silicon photoelectrodes: behavior in contact with methanol-dimethylferrocene+/0 and in contact with aqueous electrolytes

Abstract: Mechanistic studies of n-Si photoelectrodes have been conducted using aqueous and nonaqueous electrolytes. For (Me{sub 2}Fc{sup +}) between 0.3 mM and 0.050 M, the temperature dependence of V{sub oc} indicated that bulk-diffusion/recombination was the rate-limiting recombination process. In all of these experiments, conventional Shockley diode theory provided an excellent description of the solid/liquid junction properties. In a related set of experiments, HF-etched n-Si photoelectrodes ((100)- and (111)-oriented samples) and n-Si samples that had been metalized by several different methods all showed passivation in contact with Fe(CN){sub 6}{sup 3-/4-}{sub aq} or Br{sub 2}/Br{sup {minus}}{sub aq} or electrolytes. For several metalized Si samples, etches that had been reported to produce metal islands on the Si surface instead yielded Si surfaces free of metal. All Si samples that had been metalized by filament evaporation yielded I-V behavior in contact with the Ch{sub 3}OH-Me{sub 2}Fc{sup +/0} redox system that was characteristic of a pinned surface Fermi level, even for coverages of metal as low as 9 {Angstrom}. This indicates that proposed metal-insulator-semiconductor junctions with anomalously high barrier heights are difficult to obtain by such metalization and etching methods.

Near-Ideal Photodiodes from Sintered Gold Nanoparticle Films on Methyl-Terminated Si(111) Surfaces

Abstract: We report photocurrent-voltage data for improved n-Si/metal devices using CH_3-terminated n-Si(111) and Au nanoparticles (NPs). CH_3-terminated Si(111) surfaces maintain good electronic properties throughout device assembly, while the use of Au NPs as precursors to metal films circumvents the standard issues associated with interfacial reactivity of metals in Schottky barrier formation. Such devices demonstrate excellent photovoltaic properties, with photovoltages that approach the maximum values predicted for photodiodes that are limited by Si bulk diffusion/recombination processes rather than interfacial processes. These devices are compared to standard n-Si/Au devices made via thermally evaporated Au films which are well-known to be limited by junction-based recombination.

Passivation and Secondary Functionalization of Allyl-Terminated Si(111) Surfaces

Abstract: Synthesis of passivated silicon surfaces with tunable properties requires formation of a monolayer that includes a synthetically useful functional group, such as an alkene. Thus, Si(111) surfaces have been chemically and electrically passivated by attachment of an allyl monolayer. The structure of the monolayer was confirmed using infrared spectroscopy. The allyl-functionalized surface exhibited resistance to oxidation and had a low density of surface trap states. Metal-catalyzed reactions, in particular, Heck coupling and ruthenium-catalyzed olefin cross-metathesis, allowed attachment of small molecules despite the steric constraints of the dense surface-bound layer. Allyl-terminated silicon surfaces thus offer a means of attaching a variety of chemical moieties to a silicon surface through a short linking group, enabling applications in energy conversion, catalysis, and sensing.

Unprecedented, bridged dihydrogen complex of a cofacial metallodiporphyrin and its relevance to the bimolecular reductive elimination of hydrogen

Abstract: Recently, the authors characterized the first metalloporphyrin dihydrogen complex, Os(OEP)(H{sub 2}), and proposed that a similar ruthenium porphyrin dihydrogen complex, Ru(OEP)(H{sub 2}), is involved as an intermediate in the catalytic H/D isotopic exchange between water and hydrogen. They now report that treatment of a metal-metal-bonded cofacial ruthenium porphyrin dimer with a sterically bulky ligand in the presence of hydrogen gas has yielded the first known complex containing a dihydrogen ligand bound between two metals. Such a bridged dihydrogen complex is proposed as an intermediate in the bimolecular elimination of dihydrogen from two metalloporphyrin hydrides.

n-Type silicon photoelectrochemistry in methanol: Design of a 10.1% efficient semiconductor/liquid junction solar cell

Abstract: n-Type Si electrodes in MeOH solvent with 0.2 M (1-hydroxyethyl)ferrocene, 0.5 mM (1-hydroxyethyl)ferricenium, and 1.0 M LiClO4 exhibit air mass 2 conversion efficiencies of 10.1% for optical energy into electricity. We observe open-circuit voltages of 0.53 V and short-circuit quantum efficiencies for electron flow of nearly unity. The fill factor of the cell does not decline significantly with increases in light intensity, indicating substantial reduction in efficiency losses in MeOH solvent compared to previous nonaqueous n-Si systems. Matte etch texturing of the Si surface decreases surface reflectivity and increases photocurrent by 50% compared to shiny, polished Si samples. The high values of the open-circuit voltage observed are consistent with the presence of a thin oxide layer, as in a Schottky metal-insulator-semiconductor device, which yields decreased surface recombination and increased values of open-circuit voltage and short-circuit current. The n-Si system was shown to provide sustained photocurrent at air mass 2 levels (20 mA/cm2) for charge through the interface of >2,000 C/cm2. The n-Si/MeOH system represents a liquid junction cell that has exceeded the 10% barrier for conversion of optical energy into electricity.

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)