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.

Medical applications of artificial olfactometry

Abstract: The present invention provides methods for detecting the presence of an analyte indicative of various medical conditions, including halitosis, periodontal disease and other diseases are also disclosed.

X-ray photoelectron spectroscopic studies of interfacial chemistry at n-type silicon/liquid junctions

Abstract: The surface chemistry of n-type Si electrodes that had been etched, exposed to electrolyte, and electrochemically cycled has been probed using high-resolution X-ray photoelectron spectroscopy (XPS). n-Si surfaces etched in hydrofluoric acid-ethanol solutions (in air or N 2 ambients) displayed spectra in the Si 2p region that were free of detectable substrate oxide signals (≤5×10 -11 mol cm -2 SiO 2 ; equivalent to ≤4% of a monolayer)

Electrical Junction Behavior of Poly(3,4-ethylenedioxythiophene) (PEDOT) Contacts to H-Terminated and CH3-Terminated p-, n-, and n+-Si(111) Surfaces

Abstract: The electronic and photovoltaic properties of junctions between the conducting polymer poly(3,4-ethylenedioxythiophene) (PEDOT) and Si(111) surfaces have been investigated for a range of doping types, doping levels, and surface functionalization of the Si. PEDOT–poly(styrenesulfonate) (PSS) formed ohmic, low resistance contacts to H-terminated and CH_3-terminated p-type Si(111) surfaces. In contrast, PEDOT formed high barrier height (0.8–1.0 V) contacts to n-Si(111) surfaces, with CH_3-terminated n-Si(111)/PEDOT contacts showing slightly higher barrier heights (1.01 eV) than H-terminated n-Si(111)/PEDOT contacts (0.89 V). PEDOT contacts to CH_3-terminated and H-terminated n-Si(111) surfaces both produced photovoltages under illumination in accord with the Shockley diode limit based on bulk/recombination diffusion in the semiconductor. Such devices produced solar energy-conversion efficiencies of 5.7% under 100 mW cm^(–2) of simulated air mass 1.5 illumination. The electrical properties of PEDOT contacts to CH_3-terminated Si surfaces were significantly more stable in an air ambient than the electrical properties of PEDOT contacts to H-terminated Si surfaces. PEDOT films produced a low resistance, tunnel-barrier type of ohmic contact to n^+-Si(111) surfaces. Hence, through various combinations of doping type, doping level, and surface functionalization, the PEDOT/Si contact system offers a wide range of opportunities for integration into monolithic photovoltaic and/or artificial photosynthetic systems.

The Role of Band Bending in Affecting the Surface Recombination Velocities for Si(111) in Contact with Aqueous Acidic Electrolytes

Abstract: The role of band bending in affecting surface recombination velocity measurements has been evaluated by combining barrier height data with charge-carrier lifetime measurements for Si(111) surfaces in contact with a variety of acidic aqueous electrolytes. Charge-carrier lifetimes and thus surface recombination velocities have been measured by contactless radio frequency photoconductivity decay techniques for long bulk lifetime n-Si(111) samples in contact with 11 M (40% by weight) NH_4F(aq), buffered (pH = 5) HF(aq), 27 M (48% by weight) HF(aq), or concentrated 18 M H_2SO_4. Regardless of the sample history or surface condition, long charge-carrier lifetimes were observed for n-Si(111) surfaces in contact with 11 M NH_4F(aq) or buffered HF(aq). On the basis of previous barrier height measurements, this behavior is consistent with the formation of an electrolyte-induced surface accumulation layer that reduces the rate of steady-state surface recombination even in the presence of a significant density of surface trap sites. A straightforward evaluation of the surface trap state density from the measured surface recombination velocities, S, is thus precluded for such Si/liquid contacts. In contrast, a wide range of S values, depending on the history of the sample and the state of the surface, were observed for n-Si(111) surfaces in contact with 27 M HF(aq). These results in conjunction with previously measured barrier height data indicate that the charge-carrier lifetimes measured for n-Si(111) in contact with 27 M HF(aq) can be directly correlated with the surface condition and the effective surface-state trap density. These conclusions were confirmed by measurements of the apparent S values of n-Si(111) surfaces in contact with various solutions in the presence of the known deep trap, Cu. For Si(111)/HF(aq) contacts, very high (≥920 ± 270 cm s^(-1)) surface recombination velocities were observed when 0.16 mM (10 ppm) Cu^(2+) was in the solution and/or adsorbed onto the Si(111) surface as Cu^0 deposits, whereas low (100 ± 75 or 225 ± 20 cm s^(-1)) apparent surface recombination velocities were measured for Cu-contaminated Si(111) samples in contact with 0.16 mM (10 ppm) Cu^(2+)-containing 11 M NH_4F(aq) or BHF(aq) solutions, respectively.

Phototropic growth control of nanoscale pattern formation in photoelectrodeposited Se–Te films

Abstract: Photoresponsive materials that adapt their morphologies, growth directions, and growth rates dynamically in response to the local incident electromagnetic field would provide a remarkable route to the synthesis of complex 3D mesostructures via feedback between illumination and the structure that develops under optical excitation. We report the spontaneous development of ordered, nanoscale lamellar patterns in electrodeposited selenium–tellurium (Se–Te) alloy films grown under noncoherent, uniform illumination on unpatterned substrates in an isotropic electrolyte solution. These inorganic nanostructures exhibited phototropic growth in which lamellar stripes grew toward the incident light source, adopted an orientation parallel to the light polarization direction with a period controlled by the illumination wavelength, and showed an increased growth rate with increasing light intensity. Furthermore, the patterns responded dynamically to changes during growth in the polarization, wavelength, and angle of the incident light, enabling the template-free and pattern-free synthesis, on a variety of substrates, of woodpile, spiral, branched, or zigzag structures, along with dynamically directed growth toward a noncoherent, uniform intensity light source. Full-wave electromagnetic simulations in combination with Monte Carlo growth simulations were used to model light–matter interactions in the Se–Te films and produced a model for the morphological evolution of the lamellar structures under phototropic growth conditions. The experiments and simulations are consistent with a phototropic growth mechanism in which the optical near-field intensity profile selects and reinforces the dominant morphological mode in the emergent nanoscale patterns.

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)