Dramatic reduction of surface recombination by in-situ surface passivation of silicon nanowires

Nanowires have unique optical properties [1-4] and are considered as important building blocks for energy harvesting applications such as solar cells. [2, 5-8] However, due to their large surface-to-volume ratios, the recombination of charge carriers through surface states reduces the carrier diffusion lengths in nanowires a few orders of magnitude,[9] often resulting in the low efficiency (a few percent or less) of nanowire-based solar cells. [7, 8, 10, 11] Reducing the recombination by surface passivation is crucial for the realization of high performance nanosized optoelectronic devices, but remains largely unexplored. [7, 12-14] Here we show that a thin layer of amorphous silicon (a-Si) coated on a single-crystalline silicon nanowire (sc-SiNW), forming a core-shell structure in-situ in the vapor-liquid-solid (VLS) process, reduces the surface recombination nearly two orders of magnitude. Under illumination of modulated light, we measure a greater than 90-fold improvement in the photosensitivity of individual core-shell nanowires, compared to regular nanowires without shell. Simulations of the optical absorption of the nanowires indicate that the strong absorption of the a-Si shell contributes to this effect, but we conclude that the effect is mainly due to the enhanced carrier lifetime by surface passivation

Evidence of hyperinsulinaemia and hypoxaemia in the cord blood of neonates born to mothers with gestational diabetes

ArticleThe original publication is available at http://www.samj.org.zaIncreased cord blood C-peptide levels in neonates born to mothers with gestational diabetes (GD) were directly correlated with the increased relative birth weight ratio (BWR) of these neonates. In addition, the percentage oxygen saturation of the cord blood was inversely correlated with cord blood C-peptide levels and with the relative BWR. These correlations were absent in neonates delivered to normal mothers. The results indicate the presence of both hyperinsulinaemia and mild hypoxaemia in neonates of mothes with GD. In poorly controlled diabetic pregnancy this hypoxaemia may constitute an important fetal risk factor.Publishers' versio

The role of photonics in energy

A.F.N. acknowledges support from the Fundação de Amparo a Pesquisa no Estado de São Paulo (FAPESP) and the Conselho Nacional de Desenvolvimento Científico e Tecnológico (CNPq) of Brazil. D.O’C. acknowledges support from the U.S. National Science Foundation (Grant DMR-1309459). J.J.P. acknowledges support from the U.S. Office of Naval Research. I.D.W.S. acknowledges support from the Engineering and Physical Sciences Research Council of the UK (Grants EP/K00042X and EP/L012294) and the European Research Council of the European Union (Grant 321305). N.T. acknowledges support from the U.S. National Science Foundation (Grants ECCS 1408051 and DMR 1505122).In celebration of the 2015 International Year of Light, we highlight major breakthroughs in photonics for energy conversion and conservation. The section on energy conversion discusses the role of light in solar light harvesting for electrical and thermal power generation; chemical energy conversion and fuel generation; as well as photonic sensors for energy applications. The section on energy conservation focuses on solid-state lighting, flat-panel displays, and optical communications and interconnects.Publisher PDFPeer reviewe

The extended Pedersen hypothesis

[No abstract available]Articl