Dip-coating process: Silicon sheet growth development for the large-area silicon sheet task of the low-cost silicon solar array project

The objective of this research program is to investigate the technical and economic feasibility of producing solar-cell-quality sheet silicon by coating one surface of carbonized ceramic substrates with a thin layer of large-grain polycrystalline silicon from the melt. The past quarter demonstrated significant progress in several areas. Seeded growth of silicon-on-ceramic (SOC) with an EFG ribbon seed was demonstrated. Different types of mullite were successfully coated with silicon. A new method of deriving minority carrier diffusion length, L sub n from spectral response measurements was evaluated. ECOMOD cost projections were found to be in good agreement with the interim SAMIS method proposed by JPL. On the less positive side, there was a decrease in cell performance which we believe to be due to an unidentified source of impurities

Silicon on ceramic process. Silicon sheet growth development for the large-area silicon sheet task of the low-cost silicon solar array project

The technical and economic feasibility of producing solar-cell-quality sheet silicon was investigated. The sheets were made by coating one surface of carbonized ceramic substrates with a thin layer of large-grain polycrystalline silicon from the melt. Significant progress was made in all areas of the program

Silicon on Ceramic Process: Silicon Sheet Growth and Device Development for the Large-area Silicon Sheet and Cell Development Tasks of the Low-cost Solar Array Project

The technical and economic feasibility of producing solar cell quality sheet silicon was investigated. It was hoped this could be done by coating one surface of carbonized ceramic substrates with a thin layer of large-grain polycrystalline silicon from the melt. Work was directed towards the solution of unique cell processing/design problems encountered with the silicon-ceramic (SOC) material due to its intimate contact with the ceramic substrate. Significant progress was demonstrated in the following areas; (1) the continuous coater succeeded in producing small-area coatings exhibiting unidirectional solidification and substatial grain size; (2) dip coater succeeded in producing thick (more than 500 micron) dendritic layers at coating speeds of 0.2-0.3 cm/sec; and (3) a standard for producing total area SOC solar cells using slotted ceramic substrates was developed

Lithium-6: A Probe of the Early Universe

I consider the synthesis of 6Li due to the decay of relic particles, such as gravitinos or moduli, after the epoch of Big Bang Nucleosynthesis. The synthesized 6Li/H ratio may be compared to 6Li/H in metal-poor stars which, in the absence of stellar depletion of 6Li, yields significantly stronger constraints on relic particle densities than the usual consideration of overproduction of 3He. Production of 6Li during such an era of non-thermal nucleosynthesis may also be regarded as a possible explanation for the relatively high 6Li/H ratios observed in metal-poor halo stars.Comment: final version, Physical Review Letters, additional figure giving limits on relic decaying particle

Modelling the direct effect of aerosols in the solar near-infrared on a planetary scale

International audienceWe used a spectral radiative transfer model to compute the direct radiative effect (DRE) of natural plus anthropogenic aerosols in the solar near-infrared (IR), between 0.85?10 µm, namely, their effect on the outgoing near-IR radiation at the top of atmosphere (TOA, ?FTOA), on the atmospheric absorption of near-IR radiation (?Fatmab) and on the surface downward and absorbed near-IR radiation (?Fsurf, and ?Fsurfnet, respectively). The computations were performed on a global scale (over land and ocean) under all-sky conditions, using spectral aerosol optical properties taken from the Global Aerosol Data Set (GADS) supplemented by realistic data for the rest of surface and atmospheric parameters. The computed aerosol DRE, averaged over the 12-year period 1984?1995 for January and July, shows that aerosols produce a planetary cooling by increasing the scattered near-IR radiation back to space (by up to 6 Wm?2), they warm the atmosphere (by up to 7 Wm?2) and cool the surface (by up to 12 Wm?2). However, they can also slightly warm the Earth-atmosphere system or cool the atmosphere (by less than 1 Wm?2) over limited areas. The magnitude of the near-IR aerosol DRE is smaller than that of the combined ultraviolet (UV) and visible DRE, but it is still energetically important, since it contributes to the total shortwave (SW) DRE by 22?31%. On a global mean basis, the DREs ?FTOA, ?Fatmab, ?Fsurf, and ?Fsurfnet are equal to about 0.48, 0.37, ?1.03 and ?0.85 Wm?2, i.e. their magnitude is similar to that of climate forcing associated with increasing concentrations of greenhouse gases. The aerosol induced near-IR surface cooling combined with the atmospheric warming, affects the thermal dynamics of the Earth-atmosphere system, by increasing the atmospheric stability, decreasing thus cloud formation, and precipitation, especially over desertification threatened regions such as the Mediterranean basin. This, together with the fact that the sign of near-IR aerosol DRE is sometimes opposite to that of UV-visible DRE, demonstrates the importance of performing detailed spectral computations to provide estimates of the climatic role of aerosols for the Earth-atmosphere system

Radiative decay of a massive particle and the non-thermal process in primordial nucleosynthesis

We consider the effects on big bang nucleosynthesis (BBN) of the radiative decay of a long-lived massive particle. If high-energy photons are emitted after the BBN epoch ($t \sim 1 - 10^3$ sec), they may change the abundances of the light elements through photodissociation processes, which may result in a significant discrepancy between standard BBN and observation. Taking into account recent observational and theoretical developments in this field, we revise our previous study constraining the abundance of the radiatively-decaying particles. In particular, on the theoretical side, it was recently claimed that the non-thermal production of $^6$Li, which is caused by the photodissociation of \hefour, most severely constrains the abundance of the radiatively-decaying particle. We will see, however, it is premature to emphasize the importance of the non-thermal production of $^6$Li because (i) the theoretical computation of the $^6$Li abundance has large uncertainty due to the lack of the precise understanding of the $^6$Li production cross section, and (ii) the observational data of $^6$Li abundance has large errors.Comment: 15 pages, using REVTeX and 3 postscript figure