pH-Independent, 520 mV Open-Circuit Voltages of Si/Methyl Viologen^(2+/+) Contacts Through Use of Radial n^+p-Si Junction Microwire Array Photoelectrodes

The effects of introducing an n^+-doped emitter layer have been evaluated for both planar Si photoelectrodes and for radial junction Si microwire-array photoelectrodes. In contact with the pH-independent, one-electron, outer-sphere, methyl viologen redox system (denoted MV^(2+/+)), both planar and wire array p-Si photoelectrodes yielded open-circuit voltages, V_(oc), that varied with the pH of the solution. The highest V_(oc) values were obtained at pH = 2.9, with V_(oc) = 0.53 V for planar p-Si electrodes and V_(oc) = 0.42 V for vapor−liquid−solid catalyzed p-Si microwire array samples, under 60 mW cm^(−2) of 808 nm illumination. Increases in the pH of the electrolyte produced a decrease in V_(oc) by approximately −44 mV/pH unit for planar electrodes, with similar trends observed for the Si microwire array electrodes. In contrast, introduction of a highly doped, n^+ emitter layer produced V_(oc) = 0.56 V for planar Si electrodes and V_(oc) = 0.52 V for Si microwire array electrodes, with the photoelectrode properties in each system being essentially independent of pH over six pH units (3 < pH < 9). Hence, formation of an n^+ emitter layer not only produced nearly identical photovoltages for planar and Si microwire array photoelectrodes, but decoupled the band energetics of the semiconductor (and hence the obtainable photovoltage) from the value of the redox potential of the solution. The formation of radial junctions on Si microwire arrays thus provides an approach to obtaining Si-based photoelectrodes with high-photovoltages that can be used for a variety of photoelectrochemical processes, including potentially the hydrogen evolution reaction, under various pH conditions, regardless of the intrinsic barrier height and flat-band properties of the Si/liquid contact

Evaluation of Pt, Ni, and Ni–Mo electrocatalysts for hydrogen evolution on crystalline Si electrodes

The dark electrocatalytic and light photocathodic hydrogen evolution properties of Ni, Ni–Mo alloys, and Pt on Si electrodes have been measured, to assess the viability of earth-abundant electrocatalysts for integrated, semiconductor coupled fuel formation. In the dark, the activities of these catalysts deposited on degenerately doped p^+-Si electrodes increased in the order Ni < Ni–Mo ≤ Pt. Ni–Mo deposited on degenerately doped Si microwires exhibited activity that was very similar to that of Pt deposited by metal evaporation on planar Si electrodes. Under 100 mW cm^(−2) of Air Mass 1.5 solar simulation, the energy conversion efficiencies of p-type Si/catalyst photoelectrodes ranged from 0.2–1%, and increased in the order Ni ≈ Ni–Mo < Pt, due to somewhat lower photovoltages and photocurrents for p-Si/Ni–Mo relative to p-Si/Ni and p-Si/Pt photoelectrodes. Deposition of the catalysts onto microwire arrays resulted in higher apparent catalytic activities and similar photoelectrode efficiencies than were observed on planar p-Si photocathodes, despite lower light absorption by p-Si in the microwire structures

10 µm minority-carrier diffusion lengths in Si wires synthesized by Cu-catalyzed vapor-liquid-solid growth

The effective electron minority-carrier diffusion length, L_(n,eff), for 2.0 µm diameter Si wires that were synthesized by Cu-catalyzed vapor-liquid-solid growth was measured by scanning photocurrent microscopy. In dark, ambient conditions, L_(n,eff) was limited by surface recombination to a value of ≤ 0.7 µm. However, a value of L_(n,eff) = 10.5±1 µm was measured under broad-area illumination in low-level injection. The relatively long minority-carrier diffusion length observed under illumination is consistent with an increased surface passivation resulting from filling of the surface states of the Si wires by photogenerated carriers. These relatively large L_(n,eff) values have important implications for the design of high-efficiency, radial-junction photovoltaic cells from arrays of Si wires synthesized by metal-catalyzed growth processes

High-performance Si microwire photovoltaics

Crystalline Si wires, grown by the vapor–liquid–solid (VLS) process, have emerged as promising candidate materials for lowcost, 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 (L_n » 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

Si microwire-array solar cells

Si microwire-array solar cells with Air Mass 1.5 Global conversion efficiencies of up to 7.9% have been fabricated using an active volume of Si equivalent to a 4 μm thick Si wafer. These solar cells exhibited open-circuit voltages of 500 mV, short-circuit current densities (J_(sc)) of up to 24 mA cm^(-2), and fill factors >65% and employed Al_2O_3 dielectric particles that scattered light incident in the space between the wires, a Ag back reflector that prevented the escape of incident illumination from the back surface of the solar cell, and an a-SiN_x:H passivation/anti-reflection layer. Wire-array solar cells without some or all of these design features were also fabricated to demonstrate the importance of the light-trapping elements in achieving a high J_(sc). Scanning photocurrent microscopy images of the microwire-array solar cells revealed that the higher J_(sc) of the most advanced cell design resulted from an increased absorption of light incident in the space between the wires. Spectral response measurements further revealed that solar cells with light-trapping elements exhibited improved red and infrared response, as compared to solar cells without light-trapping elements

Photoelectrochemical Hydrogen Evolution Using Si Microwire Arrays

Arrays of B-doped p-Si microwires, diffusion-doped with P to form a radial n+ emitter and subsequently coated with a 1.5-nm-thick discontinuous film of evaporated Pt, were used as photocathodes for H_2 evolution from water. These electrodes yielded thermodynamically based energy-conversion efficiencies >5% under 1 sun solar simulation, despite absorbing less than 50% of the above-band-gap incident photons. Analogous p-Si wire-array electrodes yielded efficiencies <0.2%, largely limited by the low photovoltage generated at the p-Si/H_2O junction

The relationships between resilience, care environment, and social-psychological factors in orphaned and separated adolescents in Western Kenya

The relationships between care environment, resilience, and social factors in orphaned and separated adolescents and youths (OSAY) in western Kenya are complex and under-studied.Survey responses from OSAY living in Charitable Children’s Institutes (CCI) and family-based care settings (FBS) in Uasin Gishu County, Kenya were used to examine the associations between 1) care environment and resilience; 2) care environment and factors thought to promote resilience (e.g. social, family, and peer support); and 3) resilience and these same resilience-promoting factors, using multivariable linear and logistic regressions. This cross-sectional study included 1202 OSAY (50.4% female) aged 10–26 (mean = 16; SD = 3.5). The mean resilience score in CCIs was 71 (95%CI = 69–73) vs. 64 (95%CI = 62–66) in FBS. OSAY in CCIs had higher resilience (β = 7.67; 95%CI = 5.26–10.09), social support (β = 0.26; 95%CI = 0.14–0.37), and peer support (β = 0.90; 95%CI = 0.64–1.17) than those in FBS. OSAY in CCIs were more likely to volunteer than those in FBS (OR = 3.72; 95%CI = 1.80–7.68), except in the male subgroup. Family (β = 0.42; 95%CI = 0.24–0.60), social (β = 4.19; 95%CI = 2.53–5.85), and peer (β = 2.13; 95%CI = 1.44–2.83) relationships were positively associated with resilience in all analyses. Volunteering was positively associated with resilience (β = 5.85; 95%CI = 1.51–10.19). The factor most strongly related to resilience in both fully adjusted models was peer support. This study found a strong relationship between care environment and resilience. Care environment and resilience each independently demonstrated strong relationships with peer support, social support, and participating in volunteer activities. Resilience also had a strong relationship with familial support. These data suggest that resilience can be developed through strategic supports to this vulnerable population

Reliability and validity of the RS14 in orphaned and separated adolescents and youths in western Kenya

Purpose: The 14-item Resilience Scale (RS14) is a tool designed to measure psychological resilience. It has been used effectively in diverse populations. However, its applicability is largely unknown for Sub-Saharan adolescent populations and completely unknown for orphaned and separated adolescents and youths (OSAY), a highly vulnerable population for whom resilience may be critical. This study assesses the RS14\u27s psychometric properties for OSAY in Uasin Gishu County, Kenya. Methods: Survey responses from a representative sample of 1016 OSAY (51.3% female) aged 10-25 (mean = 16; SD = 3.5) living in institutional and home-based environments in Uasin Gishu County were analyzed. The RS14\u27s psychometric properties were assessed by examining internal consistency reliability, confirmatory factor analyses, and convergent validity using correlations between resilience and each of social support and depression. Sub-analyses were conducted by age and sex. Results: Resilience scores ranged from 14-98 (mean = 66; SD = 19) with no sex-based significant difference. Resilience was higher for those aged ≥18 (mean = 69; range = 14-98) versus age \u3c18 (mean = 65; range = 14-98). Internal consistency was good (Cronbach\u27s α = .90). Confirmatory factor analysis indicated a 1-factor solution, though the model fit was only moderate. Resilience was positively correlated with social support in all ages (.22; p \u3c .001) and negatively correlated with depression in individuals age \u3c18 (-.22; p \u3c .001). The relationship between resilience and depression in individuals age ≥18 was statistically significant only in females (-.17; p = .026). Conclusion: This study demonstrates reasonable evidence that the RS14 is both valid and reliable for measuring psychological resilience in the population of OSAY in western Keny

Cancer Morbidity in Lamp Manufacturing Workers

A historical prospective study of cancer in lamp manufacturing workers in one plant was conducted. All men and women who worked for a total of at least 6 months and were employed at some time between 1960 and 1975 were included. Work histories were abstracted and subjects were divided according to whether they had worked in the coiling and wire drawing area (CWD). Cancer morbidity from 1964 to 1982 was ascertained via the provincial registry, and was compared with the site-specific incidence in Ontario, adjusting for age, sex and calendar period. Of particular interest were primary breast and gynecological cancers in women. The cancers of a priori concern were significantly increased in women in CWD, but not elsewhere in the plant. The excess was greatest in those with more than 5 yr exposure (in CWD) and more than 15 yr since first working in CWD, with eight cases of breast and gynecological cancers observed in this category compared with 2.67 expected. Only three cancers occurred in men in CWD. Environmental measurements had not been made in the past and little information was available on substances used in the 1940s and 1950s, the period when the women with the highest excess began employment. It is known that methylene chloride and trichlorethylene have been used, but not enough is known about the dates and patterns of use to draw any conclusions about their relationship with the increase in disease

Induction of Group IVC Phospholipase A2 in Allergic Asthma: Transcriptional Regulation by TNF-α in Bronchoepithelial Cells

Airway inflammation in allergen-induced asthma is associated with eicosanoid release. These bioactive lipids exhibit anti- and pro-inflammatory activities with relevance to pulmonary pathophysiology. We hypothesized that sensitization/challenge using an extract from the ubiquitous fungus, Aspergillus fumigatus (Af), in a mouse model of allergic asthma would result in altered phospholipase gene expression, thus modulating the downstream eicosanoid pathway. We observed the most significant induction in the group IVC phospholipase A2 (cPLA2γ or PLA2G4C). Our results infer that Af extract can induce cPLA2γ levels directly in eosinophils while induction in lung epithelial cells is most likely a consequence of TNF-α secretion by Af-activated macrophages. The mechanism of TNF-α-dependent induction of cPLA2γ gene expression was elucidated through a combination of promoter deletions, ChIP and overexpression studies in human bronchoepithelial cells, leading to the identification of functionally relevant CRE, NF-κB and E-box promoter elements. ChIP analysis demonstrated that RNA polymerase II, c-Jun/ATF-2, p65/p65 and USF1/USF2 complexes are recruited to the cPLA2γ enhancer/promoter in response to TNF-α with overexpression and dominant negative studies implying a strong level of cooperation and interplay between these factors. Overall, our data link cytokine-mediated alterations in cPLA2γ gene expression with allergic asthma and outline a complex regulatory mechanism