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.

Enhanced stability of silicon for photoelectrochemical water oxidation through self-healing enabled by an alkaline protective electrolyte

Abstract: Alkaline electrolytes impede the corrosion of Si photoanodes under positive potentials and/or illumination, due to the formation of a SiOx layer that etches 2–3 orders of magnitude more slowly than Si. Hence during water oxidation under illumination, pinholes in protection layers on Si photoanodes result in the local formation of a protective, stabilizing passive oxide on the Si surface. However, operation under natural diurnal insolation cycles additionally requires protection strategies that minimize the dark corrosive etching rate of Si at pinholes. We show herein that addition of [Fe(CN)6]3− to 1.0 M KOH(aq) results in a self-healing process that extends the lifetime to >280 h of an np+-Si(100) photoanode patterned with an array of Ni catalyst islands operated under simulated day/night cycles. The self-healing [Fe(CN)6]3− additive caused the exposed Si(100) surface to etch >180 times slower than the Si etch rate in 1.0 M KOH(aq) alone. No appreciable difference in etch rate or facet preference was observed between Si(100) and Si(111) surfaces in 1.0 M KOH(aq) with [Fe(CN)6]3−, indicating that the surface conformally oxidized before Si dissolved. The presence of [Fe(CN)6]3− minimally impacted the faradaic efficiency or overpotential of p+-Si/Ni electrodes for the oxygen-evolution reaction.

Irreversible electrocatalytic reduction of V(V) to V(IV) using phosphomolybdic acid

Abstract: Although VO_22^+(aq) reduction is kinetically slow at glassy carbon and Pt electrodes, phosphomolybdic acid is shown to catalyze the electrochemical reduction of VO_2^+(aq) to VO_2^+(aq) in 1.0 M H_2SO_4(aq). A second-order rate constant of 33 M^(-1) s^(-1) was observed for this process. ^(31)P NMR spectra demonstrated that PMo_(11)VO_(40)^(4-) and PMo_(18)V_2O_(40)^(50-) were the dominant P-containing species under electrocatalytic conditions. The incorporation of V^V into the polyoxoanion led to a shift in potential from E^o(VO^(2+)(aq)/VO^(2+)(aq)) = +0.80 V vs Ag/AgCl for free V^V/V^(IV) to Eo' = +0.55 V vs Ag/AgCl for V^(V)/V^(Iv) bound in the heteropolyoxometalate (PMo_(11)VO_(40_^(4-)). This shift in formal potential corresponded to an equilibrium constant of 1.7 X 10^4 M^(-1) for preferential binding of V^V over V^(IV) by the heteropolyoxoanion. This negative shift in redox potential, combined with the slow electrochemical kinetics of free VO_2^+(aq) reduction and with the facile reaction of bound V^(IV) with free V^V in 1.0 M H_2SO_4(aq), resulted in the irreversible electrocatalytic reduction of VO_2^+(aq) to VO^(2+)(aq).

Vapor sensing with arrays of carbon black-polymer composites

Abstract: Thin films of carbon black-organic polymer composites have been deposited across two metallic leads, with swelling- induced resistance changes of the films signaling the presence of vapors. To identify and classify vapors, arrays of such vapor-sensing elements have been constructed, with each element containing a different organic polymer as the insulating phase. The differing gas-solid partition coefficients for the various polymers of the sensor array produce a pattern of resistance changes that can be used to classify vapors and vapor mixtures. This type of sensor array has been shown to resolve all organic vapors that have been analyzed, and can even resolve H2O from D2O. Blends of poly(vinyl acetate) and poly(methyl methacrylate) have been used to produce a series of sensor that response to vapors with a change in resistance of a magnitude that is not simply a linear combination of the responses of the pure polymers. These compatible blend composite detectors provided additional analyte discrimination information relative to a reference detector array that only contained composites formed using the pure polymer phases. Vapor signatures from chemicals used in land mine explosives, including TNT, DNT, and DNB, have been detected in air in short sampling time and discriminated from each other using these sensor arrays.

Nanoelectrical and Nanoelectrochemical Imaging of Pt/p-Si and Pt/p+-Si Electrodes

Abstract: The interfacial properties of electrolessly deposited Pt nanoparticles (Pt-NP) on p-Si and p+-Si electrodes have been resolved on the nanometer scale using a combination of scanning probe methods. Atomic-force microscopy (AFM) showed highly dispersed Pt nanoparticles. Conductive AFM measurements showed that only about half of the particles exhibited measurable contact currents, with a factor of 10^3 difference in current. Local current-voltage measurements revealed a rectifying junction with a resistance of ≥ 10 MΩ at the Pt-NP/p-Si interface, while Pt-NP/p+-Si samples formed an Ohmic junction with a local resistance of ≥ 1 MΩ. The particles were strongly attached to the sample surface in air. However in contact with an electrolyte, the adhesion of the particles to the surface was substantially lower. Scanning electrochemical microscopy (SECM) showed smaller, but more uniform electrochemical currents for the particles relative to the currents observed in conductive AFM measurements. In accord with the conductive AFM measurements, SECM measurements showed conductance through the substrate for only a minority of the particles. These results suggest that the electrochemical performance of the electrolessly deposited Pt nanoparticles on Si is ascribable to: 1) the high resistance of the contact between the particles and the substrate; 2) the low (<50%) fraction of particles that support high currents; and 3) the low adhesion of the particles to the surface in the electrolyte.

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)