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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 73 records · Page 4
All sourcesNASA NTRSDOE OSTI
NASA NTRS1992

Probing hot-carrier transport and elastic scattering using ballistic-electron-emission microscopy

Ballistic-electron-emission microscopy (BEEM) has been used to characterize electron transport and scattering in metal/semiconductor structures. A SiO2 layer at the Au/Si interface was patterned to form transmitting and nontransmitting regions. By analyzing the BEEM current profiles at the boundaries of these regions, information on the spatial distribution of electrons after transport through the Au layer can be derived. A detailed comparison is made between the results presented here and models which involve modification of the electron distribution by scattering.

Milliken, A. M.↗
NASA NTRS1974

Boltzmann equation for the electron gas of a nondegenerate plasma

The collision terms in the Boltzmann equation associated with various processes are derived. For processes having a Fokker-Planck (F-P) limit, the associated F-P operator is derived by means of physical arguments to determine the form of the operator; its multiplying constant is fixed by calculating the total energy exchange rate and comparing with the rate computed by other means. In this manner, the F-P operator is derived for electron-ion scattering, electron-electron scattering in the high-velocity limit, electron-atom elastic scattering, Compton scattering, and the high-velocity limit for inelastic scattering. Other processes considered are bremsstrahlung, radiative-recombination, photoionization, collisional ionization of atoms, and suprathermal-particle ionization of atoms.

Gould, R. J.↗
NASA NTRS2012

Application of P-wave Hybrid Theory to the Scattering of Electrons from He+ and Resonances in He and H ion

The P-wave hybrid theory of electron-hydrogen elastic scattering [Phys. Rev. A 85, 052708 (2012)] is applied to the P-wave scattering from He ion. In this method, both short-range and long-range correlations are included in the Schroedinger equation at the same time, by using a combination of a modified method of polarized orbitals and the optical potential formalism. The short-correlation functions are of Hylleraas type. It is found that the phase shifts are not significantly affected by the modification of the target function by a method similar to the method of polarized orbitals and they are close to the phase shifts calculated earlier by Bhatia [Phys. Rev. A 69, 032714 (2004)]. This indicates that the correlation function is general enough to include the target distortion (polarization) in the presence of the incident electron. The important fact is that in the present calculation, to obtain similar results only a 20-term correlation function is needed in the wave function compared to the 220- term wave function required in the above-mentioned calculation. Results for the phase shifts, obtained in the present hybrid formalism, are rigorous lower bounds to the exact phase shifts. The lowest P-wave resonances in He atom and hydrogen ion have been calculated and compared with the results obtained using the Feshbach projection operator formalism [Phys. Rev. A, 11, 2018 (1975)]. It is concluded that accurate resonance parameters can be obtained by the present method, which has the advantage of including corrections due to neighboring resonances, bound states and the continuum in which these resonance are embedded.

Bhatia, A. K.↗
NASA NTRS1980

Quantum mechanical study of elastic scattering and rotational excitation of CO by electrons

Coupling calculations of differential, integral, and momentum transfer cross sections for pure elastic scattering and rotational excitation of CO by electron impact are reported. The calculations are based on a static charge distribution that has correct dipole and quadrupole moments, has cusps at the nuclei, and is augmented by an SCF treatment of charge polarization and a local approximation for exchange. The rotationally summed cross sections, with no adjustable parameters in the scattering calculation, are in reasonably good agreement with the experimental cross sections but are somewhat larger at small scattering angles.

Onda, K.↗
NASA NTRS1986

Studies of electron-molecule collisions - Applications to e-H2O

Elastic differential and momentum transfer cross sections for the elastic scattering of electrons by H2O are reported for collision energies from 2 to 20 eV. These fixed-nuclei static-exchange cross sections were obtained using the Schwinger variational approach. In these studies the exchange potential is directly evaluated and not approximated by local models. The calculated differential cross sections, obtained with a basis set expansion of the scattering wave function, agree well with available experimental data at intermediate and larger angles. As used here, the results cannot adequately describe the divergent cross sections at small angles. An interesting feature of the calculated cross sections, particularly at 15 and 20 eV, is their significant backward peaking. This peaking occurs in the experimentally inaccessible region beyond a scattering angle of 120 deg. The implication of this feature for the determination of momentum transfer cross sections is described.

Brescansin, L. M.↗
NASA NTRS1991

Theoretical studies of molecular collisions

The following subject areas are covered: (1) total integral reactive cross sections and vibrationally resolved reaction probabilities for F + H2 = HF + H; (2) a theoretical study of inelastic O + N2 collisions; (3) body frame close coupling wave packet approach to gas phase atom-rigit rotor inelastic collisions; (4) wave packet study of gas phase atom-rigit motor scattering; (5) the application of optical potentials for reactive scattering; (6) time dependent, three dimensional body frame quantal wave packet treatment of the H + H2 exchange reaction; (7) a time dependent wave packet approach to atom-diatom reactive collision probabilities; (8) time dependent wave packet for the complete determination of s-matrix elements for reactive molecular collisions in three dimensions; (9) a comparison of three time dependent wave packet methods for calculating electron-atom elastic scattering cross sections; and (10) a numerically exact full wave packet approach to molecule-surface scattering.

Kouri, Donald J.↗
NASA NTRS1969

Cosmic neutrinos

Cosmic neutrinos detection, using inverse beta decay and elastic scattering by electrons to overcome solar neutrino problem

Reines, F.↗
NASA NTRS1972

Use of the Glauber approximation in atomic collisions - A progress report.

Recent progress in the use of the Glauber (1970) theory for estimating atomic collision cross sections is reviewed. It appears that the Glauber approximation is reliable for electron-hydrogen elastic scattering and excitation at incident energies exceeding 30 eV. For more complicated atomic collisions, the usefulness of the Glauber approximation has not yet been significantly tested.

Gerjuoy, E.↗
NASA NTRS1975

Glauber exchange amplitudes

The extrapolation method of Ochkur, valid for intermediate energies (about 50 eV), is applied to the exchange form of the Glauber amplitudes. In the case of elastic scattering of electrons from hydrogen atoms at 54.4 Ev the 'post' and 'prior' forms of the exchange amplitude are equivalent, whereas for the case of inelastic scattering there is a minute discrepancy between the two forms of the amplitude. The results are compared with the close-coupling calculation. The investigation is expected to be useful for optically forbidden exchange-allowed transitions due to electron impact at intermediate energies.

Madan, R. N.↗
NASA NTRS1989

Studies of elastic e-NH3 collisions

Differential and momentum-transfer cross sections for the elastic scattering of electrons by NH3 have been obtained for collision energies of between 2.5 and 20 eV using the fixed-nuclei static-exchange approximation of the Schwinger variational principle. At intermediate and large scattering angles, good agreement is found between calculated and relative experimental cross sections. The differential cross sections reveal evidence of a weak d-wave enhancement around 8 eV.

Pritchard, H. P.↗
NASA NTRS1989

Polarization effects in low-energy e-CH4 collisions

Polarization effects on the cross sections for elastic scattering of electrons by the CH4 molecule, for collision energies from 7.5 down to 0.02 eV, are presently studied on the basis of Takatsuka and McKoy's (1981) Schwinger multichannel formulation. While the closed-channel expansion through which polarization effects are encompassed is not fully converged, the cross sections obtained nevertheless exhibit a Ramsauer-Townsend minimum in the 0.1-0.2 eV range; this is about 0.3 lower than the experimentally obtained value. At 7.5 eV, however, the calculated differential cross-sections are in excellent agreement with measured values.

Lima, M. A. P.↗
NASA NTRS1990

Elastic scattering of e- and e+ from Rb and Cd

Differential cross section results are calculated for the elastic scattering of electrons and positrons from the ground state of Rb and Cd atoms. An optical model potential approach is used for the calculation. Results are compared with the available electron impact experimental results.

Pangantiwar, A. W.↗
NASA NTRS1978

Model potentials for electron scattering - Converged close coupling calculations for the differential cross section for e/-/N2 at 30-50 eV

A calculation has been made of the elastic scattering and rotational excitation cross sections for e(-)-N2 scattering at 30 and 50 eV using quantum chemical techniques specially designed to be applicable to elastic and inelastic electron scattering by general polyatomic molecules. The angle dependence of the sum of the elastic and rotational excitation differential cross sections is in good agreement with experiment at all scattering angles at both energies, but at 50 eV the difference from experiment exceeds the experimental uncertainty at small scattering angles and near the minimum of the differential cross section. At large scattering angles the rotational excitation cross sections are predicted to exceed the elastic scattering cross sections. The absolute cross sections agree with experiment at some angles but at other angles are as much as 51% (30 eV) or 90% (50 eV) higher; this may be due at least in part to the difficulty of putting the experimental results on an absolute scale.

Onda, K.↗
NASA NTRS1980

Elastic scattering and vibrational excitation of CO2 by 4, 10, 20 and 50 eV electrons

Elastic and vibrationally inelastic differential, integral and momentum-transfer cross sections for electrons scattered by CO2 molecules are reported at 4, 10, 20 and 50 eV impact energies. The elastic cross sections are placed on an absolute scale by means of a relative flow technique. The inelastic cross sections are normalised to the elastic ones by using the inelastic to elastic intensity ratios. Data are reported for up to ten features in the 0.0 to 0.4 eV energy-loss region.

Register, D. F.↗
NASA NTRS1982

Calculation of a mirror asymmetric effect in electron scattering from chiral targets

A dynamical calculation is presented of the helicity induced in an initially unpolarized electron beam after elastic scattering from an optically active medium, a process analogous to the circular polarization induced in unpolarized light following Rayleigh scattering from chiral targets. The calculation is based on the bound helical electron model of a chiral molecule, according to which the major contribution to the helicity is provided by the perturbation of the electron bound state by the spin-orbit interaction of the bound electrons moving in the electric field of the molecular core. The net helicity acquired is found to depend directly on a molecular asymmetry factor and the square of the atomic number of the heaviest atom in an asymmetric environment. For the case of carbon, the induced helicity is on the order of 0.00001, which would account for its lack of observation in a recent experiment. Results may have implications for the origin of optical activity in biological molecules by the differential ionization of D and L isomers by beta-decay electrons.

Rich, A.↗