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Search indexed NASA NTRS and DOE OSTI research on propulsion, heat transfer, battery materials and energy systems. Follow report and document links to the original sources.

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At least 19 records
All sourcesNASA NTRSDOE OSTI
NASA NTRS1985

Recombination phenomena in high efficiency silicon solar cells

The dominant recombination phenomena which limit the highest efficiency attainable in silicon solar cells under terrestrial sunlight are reviewed. The ultimate achievable efficiency is limited by the two intrinsic recombination mechanisms, the interband Auger recombination and interband Radiative recombination, both of which occur in the entire cell body but principally in the base layer. It is suggested that an optimum (26%) cell design is one with lowly doped 50 to 100 micron thick base, a perfect BSF, and zero extrinsic recombination such as the thermal mechanism at recombination centers the Shockley-Read-Hall process (SRH) in the bulk, on the surface and at the interfaces. The importance of recombination at the interfaces of a high-efficiency cell is demonstrated by the ohmic contact on the back surface whose interface recombination velocity is infinite. The importance of surface and interface recombination is demonstrated by representing the auger and radiative recombination losses by effective recombination velocities. It is demonstrated that the three highest efficiency cells may all be limited by the SRH recombination losses at recombination centers in the base layer.

Sah, C. T.↗
NASA NTRS2000

Photoionization and Recombination

Theoretically self-consistent calculations for photoionization and (e + ion) recombination are described. The same eigenfunction expansion for the ion is employed in coupled channel calculations for both processes, thus ensuring consistency between cross sections and rates. The theoretical treatment of (e + ion) recombination subsumes both the non-resonant recombination ("radiative recombination"), and the resonant recombination ("di-electronic recombination") processes in a unified scheme. In addition to the total, unified recombination rates, level-specific recombination rates and photoionization cross sections are obtained for a large number of atomic levels. Both relativistic Breit-Pauli, and non-relativistic LS coupling, calculations are carried out in the close coupling approximation using the R-matrix method. Although the calculations are computationally intensive, they yield nearly all photoionization and recombination parameters needed for astrophysical photoionization models with higher precision than hitherto possible, estimated at about 10-20% from comparison with experimentally available data (including experimentally derived DR rates). Results are electronically available for over 40 atoms and ions. Photoionization and recombination of He-, and Li-like C and Fe are described for X-ray modeling. The unified method yields total and complete (e+ion) recombination rate coefficients, that can not otherwise be obtained theoretically or experimentally.

Nahar, Sultana N.↗
NASA NTRS1994

Expression and purification of recombinant polyomavirus VP2 protein and its interactions with polyomavirus proteins

Recombinant polyomavirus VP2 protein was expressed in Escherichia coli (RK1448), using the recombinant expression system pFPYV2. Recombinant VP2 was purified to near homogeneity by sodium dodecyl sulfate-polyacrylamide gel electrophoresis, electroelution, and Extracti-Gel chromatography. Polyclonal serum to this protein which reacted specifically with recombinant VP2 as well as polyomavirus virion VP2 and VP3 on Western blots (immunoblots) was produced. Purified VP2 was used to establish an in vitro protein-protein interaction assay with polyomavirus structural proteins and purified recombinant VP1. Recombinant VP2 interacted with recombinant VP1, virion VP1, and the four virion histones. Recombinant VP1 coimmunoprecipitated with recombinant VP2 or truncated VP2 (delta C12VP2), which lacked the carboxy-terminal 12 amino acids. These experiments confirmed the interaction between VP1 and VP2 and revealed that the carboxyterminal 12 amino acids of VP2 and VP3 were not necessary for formation of this interaction. In vivo VP1-VP2 interaction study accomplished by cotransfection of COS-7 cells with VP2 and truncated VP1 (delta N11VP1) lacking the nuclear localization signal demonstrated that VP2 was capable of translocating delta N11VP1 into the nucleus. These studies suggest that complexes of VP1 and VP2 may be formed in the cytoplasm and cotransported to the nucleus for virion assembly to occur.

Non-NASA Center↗
NASA NTRS1977

The influence of autoionization accompanied by excitation on dielectronic recombination and ionization equilibrium

In the process of dielectronic recombination, the doubly excited state formed by radiationless capture may autoionize preferentially into an excited state of the recombining ion. This additional autoionization process has not been discussed in previous treatments of dielectronic recombination. The dielectronic recombination rates for certain nonhydrogenic Fe ions, although still larger than the direct radiative recombination rates, are found to be substantially reduced by the inclusion of the additional autoionization rate in the branching ratio for the stabilizing radiative transition. Consequently, the temperatures of maximum equilibrium abundance are significantly lower than those predicted by recent calculations. Finally, the radiative energy loss rate coefficients are calculated for radiation processes involving electron Fe-ion collisions in high-temperature plasmas. Electron impact excitation of resonance line radiation is the dominant radiative cooling mechanism in steady-state plasmas at temperatures where ions with bound electrons are abundant. However, it is found that the radiation emitted during dielectronic recombination can be more important than direct recombination radiation and bremsstrahlung.

Jacobs, V. L.↗
NASA NTRS1980

'Bottleneck' calculation of ion-electron recombination coefficients for lithium-like ions

The ion-electron recombination coefficients for the lithium-like ions C IV, O VI, Ne VIII, Si XII and Ar XVI are computed by the bottleneck method of Byron et al. (1962). In this method, the minimum rate of transitions down the ladder of energy level is taken as the limiting recombination rate, and the particular energy level corresponding to the minimum transition rate is found. The partial collisional radiative recombination coefficient is obtained in terms of the equilibrium population, the rate of collisional de-excitation, the mean radiative transition probability from the bottleneck level and the total transition probability from a level above the bottleneck level to all levels below it. The full collisional-radiative recombination is then obtained by the addition of the values of the radiative recombination coefficient and the three-body recombination coefficient to the ground level. Results of the calculation are shown to be in good agreement with those of Drawin and Emard (1975) for the case of hydrogen. It is also noted that the process of dielectronic recombination, which is not accounted for here, may be significant at lower densities.

Kastner, S. O.↗
NASA NTRS1973

Excitation of the CO fourth positive system by the dissociative recombination of CO2/+/ ions.

The fourth positive system of CO has been excited in a static afterglow experiment by the dissociative recombination of CO2(+) ions. From combined absolute optical and microwave measurements the specific recombination coefficient for exciting the CO system was found to be (2 plus 1 or minus 0.5) x 10 to the minus 8th cu cm/sec. This value represents approximately 5% of the total recombination coefficient (4.0 plus or minus 0.5) x 10 to the minus 7th cu cm/sec measured in this experiment, implying that CO2(+) dissociative recombination will contribute significantly to the excitation of the CO fourth positive system in the Martian airglow. Corroborative electron heating experiments showed that the magnitude of the specific recombination coefficient decreased as the electron temperature was increased. Evidence was also found for the presence of vibrationally excited ions in the CO2(+) plasma, a result which indicates that analogous laboratory studies on the dissociative recombination of O2(+), N2(+), and NO(+) ions may have also involved vibrationally hot plasmas.

Gutcheck, R. A.↗
NASA NTRS1977

The influence of autoionization accompanied by excitation on the dielectronic recombination and the ionization equilibrium of silicon ions

The dielectronic recombination rate coefficients have been calculated for the various ionization stages of silicon. Account has been taken of all stabilizing radiative transitions and all autoionization processes which involve a single-electron electric-dipole transition of the recombining ion core. For certain ions the dielectronic recombination rates, although still larger than the direct radiative recombination rates, are found to be substantially reduced when account is taken of the effects of a previously neglected autoionization process in which the excited recombining ion core undergoes a delta n = 0 transition to a lower excited state. The temperatures at which these ions have their maximum abundance in corona equilibrium are significantly reduced when use is made of the new dielectronic recombination rates. Calculations are also presented for the total rates of radiative energy loss from isothermal steady-state plasmas due to the line and continuum emission of silicon ions.

Jacobs, V. L.↗
NASA NTRS1961

Effect of Surface Preparation and Gas Flow on Nitrogen Atom Surface Recombination

The effects of surface preparation and gas flow on the recombination of nitrogen atoms at copper and platinum surfaces were determined. Atoms were generated by an electrodeless 2450-megacycle-per-second discharge, and their concentration was measured by gas-phase titration with nitric oxide. Test surfaces were either vacuum-evaporated films or spheres machined from bulk metal and cemented around small glass-bead thermistors. Heat released by recombination was measured as the difference in electrical energy required to maintain a given thermistor temperature with and without a catalytic surface exposed. Recombination coefficients measured at flow velocities of 1120, 1790, 2250, and 3460 centimeters per second and at pressures of 0.42 and 0.59 millimeter of mercury showed that flow conditions had no effect. The results were also independent of atom concentration. A rough indication of the temperature dependence was obtained; it was greater for copper than for platinum. Platinum films deposited on platinum or on glass had the same activity - about 3 percent of the atoms impinging recombined. With copper, however, the glass substrate greatly reduced the percent of atoms recombining over that of a bulk copper substrate where 4 percent of the impinging atoms recombined. This effect could be overcome by depositing a second film on top of the first. Bulk metal samples were subjected to various surface treatments including polishing, degreasing with a chlorinated hydrocarbon, washing with nitric acid, and rinsing with water. Polished, degreased platinum had low activity compared to an evaporated film, but nitric acid treatment made it equivalent. Polished, degreased copper was only slightly less active than a copper film; nitric acid etching decreased the activity still further, probably by preferentially exposing facets of low catalytic efficiency.

Prok, George M.↗
NASA NTRS1976

Interfacial recombination at /AlGa/As/GaAs heterojunction structures

Experiments were conducted to determine the interfacial recombination velocity at Al0.25Ga0.75As/GaAs and Al0.5Ga0.5As/GaAs heterojunctions. The recombination velocity was derived from a study of the injected minority-carrier lifetime as a function of the junction spacing. It is found that for heterojunction spacings in excess of about 1 micron, the interfacial recombination can be characterized by a surface recombination velocity of 4,000 and 8,000 cm/sec for the two types of heterojunctions, respectively. For double-heterojunction spacings below 1 micron, the constancy of the minority-carrier lifetime suggests that the interfacial recombination velocity decreases effectively. This effect is technologically very important since it makes it possible to construct very low-threshold injection lasers. No such effect is observed in single-heterojunction diodes.

Ettenberg, M.↗
NASA NTRS1976

Recombination of O2/+/ in the ionosphere

In spite of the excellent agreement between various laboratory measurements of the recombination rate of O2(+) with electrons, it is still questionable whether the laboratory results apply in the ionosphere, because although the radiative lifetime of vibrating O2(+) is not well known, indications are that it may be very long. Whether the laboratory results apply in the atmosphere depends on whether the recombination rate is dependent on the vibrational state of the O2(+) ion and on whether the ions are deactivated (or not) in both the laboratory experiments and the atmosphere prior to recombination. To obtain reliable answers to these questions, the present study was carried out to determine the recombination of O2(+) in the ionosphere from in situ measurements of the relevant temperatures and densities made by the open source mass spectrometer carried by the AE-C satellite. The photochemistry involved is discussed. The results show that the ionospheric determination of the recombination rate of O2(+) with electrons agrees with the laboratory measurements of Walls and Dunn (1974) for electron temperatures between 1200 and 2000 K.

Torr, D. G.↗
NASA NTRS1977

The structure of W49 A as deduced from molecular and recombination line observations

The molecular cloud complex W49 A has been observed in the 2.6-mm CO line, the 2-cm H2CO line, and the H76-alpha recombination line. These observations are most consistent with a picture of the complex in which a large H II region lies between two massive molecular clouds. Using a simple hydrodynamic model coupled with calculations of radiative transfer in the recombination lines, it is found that many of the spectral-line and continuum observations obtained on this region can be naturally explained, including: (1) the multiple structure observed in the molecular lines and the single structure in the recombination lines; (2) the local standard of rest (LSR) velocities of both the molecular and recombination lines; (3) the velocity gradients observed in the lines; (4) the continuum emission from the H II region; and (5) the line widths and line-to-continuum ratios of the recombination lines.

Mufson, S. L.↗