Indium phosphide solar cells: status and prospects for use in space

The current status of indium phosphide cell research is reviewed and state of the art efficiencies compared to those of GaAs and Si. It is shown that the radiation resistance of InP cells is superior to that of either GaAs or Si under 1 MeV electron and 10 MeV proton irradiation. Using lightweight blanket technology, a SEP array structure and projected cell efficiencies, array specific powers are obtained for all three cell types. Array performance is calculated as a function of time in orbit. The results indicate that arrays using InP cells can outperform those using GaAs or Si in orbits where radiation is a significant cell degradation factor. It is concluded that InP solar cells are excellent prospects for future use in the space radiation environment

Formation and characterization of inorganic membranes from zeolite-silica microcomposites

Small crystals of zeolites (500-1000 nm) with two- and three-dimensional channel systems (faujasite and ZSM-5 structures) were embedded in amorphous thin films derived from TEOS hydrolyzed in alcoholic solution. Scanning electron microscopy studies show that the zeolites can be quite evenly dispersed in the membrane, resulting in single layers of zeolite crystals protruding out of the amorphous matrix. In situ FT-IR studies with a series of probe molecules revealed that in most membranes the zeolites were 100% accessible from the gas phase. The membranes excluded molecules which are larger than the pore openings of the zeolite embedded in the composite

Uniformity of the pseudomagnetic field in strained graphene

We present a study on the uniformity of the pseudomagnetic field in graphene as a function of the relative orientation between the graphene lattice and straining directions. For this, we strained a regular micron-sized graphene hexagon by deforming it symmetrically by displacing three of its edges. By simulations, we found that the pseudomagnetic field is strongest if the strain is applied perpendicular to the armchair direction of graphene. For a hexagon with a side length of 1 ${\rm \mu}$m, the pseudomagnetic field has a maximum of 1.2 T for an applied strain of 3.5% and it is uniform (variance $< 1$%) within a circle with a diameter of $\sim 520$ nm. This diameter is on the order of the typical diameter of the laser spot in a state-of-the-art confocal Raman spectroscopy setup, which suggests that observing the pseudomagnetic field in measurements of shifted magneto-phonon resonance is feasible.Comment: 7 pages, 5 figure

Oxometalate-glass composites and thin films

New glass-composites with ion exchange properties have been developed. Ammonium 12-molybdophosphate (AMP) (ΝΗ4)3ΡΜοΐ2θ4ο, and ammonium 12-tungstophosphate (AWP) (Nh4)3PW12O40, known for their ion exchange capabilities, are included either in preformed aerogels with defined pore size, or are added to sol-gel mixtures during the process of gel formation. Characterization is carried out by FTIR, Raman and EXAFS spectroscopy. Ion exchange capacities for the oxometalate precursors are determined for silver and rubidium and are compared to those of the glass composites. Glass composites show high ion exchange capacity, but some portion of the metalate complexes leaches from the glass during the procedure. This is in contrast to thin composite films, which have almost no porosity and do not show loss of metalate. EXAFS spectroscopy demostrates that the oxometalate microstructure is maintained in glass composites and that rubidium ions after ion exchange in glasses occupy similar cation positions as in the precursor compounds

Advanced photovoltaic power system technology for lunar base applications

The development of an advanced photovoltaic power system that would have application for a manned lunar base is currently planned under the Surface Power element of Pathfinder. Significant mass savings over state-of-the-art photovoltaic/battery systems are possible with the use of advanced lightweight solar arrays coupled with regenerative fuel cell storage. The solar blanket, using either ultrathin GaAs or amorphous silicon solar cells, would be integrated with a reduced-g structure. Regenerative fuel cells with high-pressure gas storage in filament-wound tanks are planned for energy storage. An advanced PV/RFC power system is a leading candidate for a manned lunar base as it offers a tremendous weight advantage over state-of-the-art photovoltaic/battery systems and is comparable in mass to other advanced power generation technologies

A possible radiation-resistant solar cell geometry using superlattices

A solar cell structure is proposed which uses a GaAs nipi doping superlattice. An important feature of this structure is that photogenerated minority carriers are very quickly collected in a time shorter than bulk lifetime in the fairly heavily doped n and p layers and these carriers are then transported parallel to the superlattice layers to selective ohmic contacts. Assuming that these already-separated carriers have very long recombination lifetimes, due to their across an indirect bandgap in real space, it is argued that the proposed structure may exhibit superior radiation tolerance along with reasonably high beginning-of-life efficiency

Thermal annealing of GaAs concentrator solar cells

Isochronal and isothermal annealing tests were performed on GaAs concentrator cells which were irradiated with electrons of various energies to fluences up to 1 x 10(exp 16) e/sq cm. The results include: (1) For cells irradiated with electrons from 0.7 to 2.3 MeV, recovery decreases with increasing electron energy. (2) As determined by the un-annealed fractions, isothermal and isochronal annealing produce the same recovery. Also, cells irradiated to 3 x 10(exp 15) or 1 x 10(exp 16) e/sq cm recover to similar un-annealed fractions. (3) Some significant annealing is being seen at 150 C although very long times are required

GaAs and 3-5 compound solar cells status and prospects for use in space

Gallium arsenide solar cells equal or supass the best silicon solar cells in efficiency, radiation resistance, annealability, and in the capability to produce usable power output at elevated temperatures. NASA has been involved in a long range research and development program to capitalize on these manifold advantages, and to explore alternative III-V compounds for additional potential improvements. The current status and future prospects for research and development in this area are reviewed and the progress being made toward development of GaAs cells suitable for variety of space missions is discussed. Cell types under various stages of development include n(+)/p shallow homojunction thin film GaAs cells, x100 concentration ratio p/n and n/p GaAs small area concentrator cells, mechanically-stacked, two-junction tandem cells, and three-junction monolithic cascade cells, among various other cell types

Nonlocal orbital magnetism of 3d adatoms deposited on the Pt(111) surface

The orbital magnetic moment is still surprisingly not well understood, in contrast to the spin part. Its description in finite systems, such as isolated atoms and molecules, is not problematic, but it was only recently that a rigorous picture was provided for extended systems. Here we focus on an intermediate class of systems: magnetic adatoms placed on a non-magnetic surface. We show that the essential quantity is the ground-state charge current density, in the presence of spin-orbit coupling, and set out its first-principles description. This is illustrated by studying the magnetism of the surface Pt electrons, induced by the presence of Cr, Mn, Fe, Co and Ni adatoms. A physically appealing partition of the charge current is introduced. This reveals that there is an important nonlocal contribution to the orbital moments of the Pt atoms, extending three times as far from each magnetic adatom as the induced spin and local orbital moments. We find that it is as sizable as the latter, and attribute its origin to a spin-orbital susceptibility of the Pt surface, different from the one responsible for the formation of the local orbital moments.Comment: 6 pages, 3 figures, submitte

Advanced photovoltaic power system technology for lunar base applications

Advanced photovoltaic/electrochemical (batteries or regenerative fuel cells for storage) power system options for a lunar base are discussed and compared. Estimated system masses are compared with those projected for the SP-100 nuclear system. The results of the comparison are quantified in terms of the mass saved in a scenario which assembles the initial base elements in Low Earth Orbit (LEO) and launches from there to the lunar surface. A brief summary is given of advances in photovoltaic/electrochemical power system technologies currently under development in the NASA/OAST program. A description of the planned focussed technology program for surface power in the new Pathfinder initiative is also provided