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.

Spectral tuning of plasmon-enhanced silicon quantum dot luminescence

Abstract: In the presence of nanoscale silver island arrays, silicon quantum dots exhibit up to sevenfold luminescence enhancements at emission frequencies that correspond to the collective dipole plasmon resonance frequency of the Ag island array. Using electron-beam lithography to alter the pitch and particle diameter, this wavelength-selective enhancement can be varied as the metal array resonance wavelength is tuned from 600 to 900 nm. The luminescence intensity enhancement upon coupling is attributed to an increase in the radiative decay rate of the silicon quantum dots.

CoP as an Acid-Stable Active Electrocatalyst for the Hydrogen-Evolution Reaction: Electrochemical Synthesis, Interfacial Characterization and Performance Evaluation

Abstract: Films of CoP have been electrochemically synthesized, characterized, and evaluated for performance as a catalyst for the hydrogen-evolution reaction (HER) The film was synthesized by cathodic deposition from a boric acid solution of Co2+ and H2PO2– on copper substrates followed by operando remediation of exogenous contaminants The films were characterized structurally and compositionally by scanning-electron microscopy, energy-dispersive X-ray spectroscopy, X-ray photoelectron spectroscopy, and Raman spectrophotometry The catalytic activity was evaluated by cyclic voltammetry and chronopotentiometry Surface characterization prior to electrocatalysis indicated that the film consisted of micrometer-sized spherical clusters located randomly and loosely on a slightly roughened surface The composition of both the clusters and surface consisted of cobalt in the metallic, phosphide, and amorphous-oxide forms (CoO·Co2O3) and of phosphorus as phosphide and orthophosphate The orthophosphate species, produced

High-performance Si microwire photovoltaics

Abstract: Crystalline Si wires, grown by the vapor–liquid–solid (VLS) process, have emerged as promising candidate materials for low-cost, thin-film photovoltaics. Here, we demonstrate VLS-grown Si microwires that have suitable electrical properties for high-performance photovoltaic applications, including long minority-carrier diffusion lengths (Ln ≫ 30 µm) and low surface recombination velocities (S ≪ 70 cm·s−1). Single-wire radial p–n junction solar cells were fabricated with amorphous silicon and silicon nitride surface coatings, achieving up to 9.0% apparent photovoltaic efficiency, and exhibiting up to ∼600 mV open-circuit voltage with over 80% fill factor. Projective single-wire measurements and optoelectronic simulations suggest that large-area Si wire-array solar cells have the potential to exceed 17% energy-conversion efficiency, offering a promising route toward cost-effective crystalline Si photovoltaics.

Comparison of the Electrical Properties and Chemical Stability of Crystalline Silicon(111) Surfaces Alkylated Using Grignard Reagents or Olefins with Lewis Acid Catalysts

Abstract: Four methods were used to functionalize crystalline Si(111) surfaces with alkyl groups (C_nH_(2n+1), n = 1, 2, 6, 8): chlorination with PCl_5 followed by alkylation with C_nH_(2n+1)MgX (X = Cl, Br), chlorination with Cl_2(g) followed by alkylation with C_nH_(2n+1)MgX, Lewis acid-mediated reduction of a terminal alkene, and anodization in diethyl ether containing 3.0 M CH_3MgI. The chemical properties of each surface were characterized as a function of time exposed to air using X-ray photoelectron spectroscopy, and the electrical properties of the various surfaces were probed using time-resolved radio frequency (rf) photoconductivity decay methods. Both chlorination/alkylation routes produced alkylated Si surfaces that displayed low ( 600 h of exposure to air. Surfaces functionalized through this route also displayed a significantly lower rate of oxidation than did unalkylated, H-terminated or Cl-terminated Si(111) surfaces. In contrast, surfaces modified by the Lewis acid-catalyzed reduction of 1-hexene and 1-octene exhibited high S values (S > 400 cm s^(-1)) when initially exposed to air and oxidized as rapidly as H-terminated Si(111) surfaces. Methyl-terminated Si(111) surfaces functionalized by anodization in a solution of CH_3MgI in ether exhibited stable, albeit high, S values (460 cm s^(-1)), indicating that the surface had been partially modified by the anodization process. The fractional monolayer coverage of oxide on the alkylated surface after exposure to air was determined for each functionalization technique. Although all four of the functionalization routes studied in this work introduced alkyl groups onto the Si surface, subtle changes in the extent and quality of the alkyl termination are significant factors in determining the magnitude and degree of chemical and electrical passivation of the resulting functionalized Si surfaces.

Methods for comparing the performance of energy-conversion systems for use in solar fuels and solar electricity generation

Abstract: The energy-conversion efficiency is a key metric that facilitates comparison of the performance of various approaches to solar energy conversion. However, a suite of disparate methodologies has been proposed and used historically to evaluate the efficiency of systems that produce fuels, either directly or indirectly, with sunlight and/or electrical power as the system inputs. A general expression for the system efficiency is given as the ratio of the total output power (electrical plus chemical) divided by the total input power (electrical plus solar). The solar-to-hydrogen (STH) efficiency follows from this globally applicable system efficiency but only is applicable in the special case for systems in which the only input power is sunlight and the only output power is in the form of hydrogen fuel derived from solar-driven water splitting. Herein, system-level efficiencies, beyond the STH efficiency, as well as component-level figures of merit are defined and discussed to describe the relative energy-conversion performance of key photoactive components of complete systems. These figures of merit facilitate the comparison of electrode materials and interfaces without conflating their fundamental properties with the engineering of the cell setup. The resulting information about the components can then be used in conjunction with a graphical circuit analysis formalism to obtain “optimal” system efficiencies that can be compared between various approaches. The approach provides a consistent method for comparison of the performance at the system and component levels of various technologies that produce fuels and/or electricity from sunlight.

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)