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in creator/contributor: "Ghosh, V.J."

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Positron implantation profiles in elemental and multilayer systems

Different Monte Carlo schemes for modeling positron and electron implantation in solids have been briefly reviewed. Results (mean depth, backscattered fraction, profile shapes) of the Monte Carlo schemes are compared with experimental data and each other. Qualitatively, results of the different Monte Carlo schemes are the same; the most significant difference is in the value of the mean implantation depth. The scaled profiles (for positron implantation in any material) generated by the differen… more

Date: July 1, 1994

Creator: Ghosh, V. J.

Item Type: Article

Partner: UNT Libraries Government Documents Department

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Thermal desorption spectroscopy (TDS) of hydrogen from niobium

Thermal desorption spectroscopy is often used to determine the activation energy of desorption of an adsorbate on a substrate as well as the order of the kinetics. In the case of flash desorption of an adsorbate from a surface obeying second order kinetics, a plot of Log(theta/sub o/T/sub p//sup 2/) vs 1/T/sub p/ (where theta/sub o/ is the initial surface coverage and T/sub P/ is the temperature of the maximum desorption rate, i.e., the desorption temperature) will yield a straight line, the sl… more

Date: January 1, 1982

Creator: Ghosh, V.J.; Pick, M.A.; Welch, D.O. & Dienes, G.J.

Item Type: Article

Partner: UNT Libraries Government Documents Department

open access

Positron implantation in solids

The Monte Carlo technique for modeling positron prior to annihilation and electron implantation in semi-infinite metals is described. Particle implantation is modelled as a multistep process, a series of collisions with the atoms of the host material. In elastic collisions with neutral atoms there is no transfer of energy. The particle loses energy by several different channels, excitation of the electron gas, ionization of the ion cores, or, at low energies, by phonon excitation. These competi… more

Date: December 31, 1993

Creator: Ghosh, V. J.; Lynn, K. G. & Welch, D. O.

Item Type: Article

Partner: UNT Libraries Government Documents Department

open access

Monte Carlo studies of positron implantation in elemental metallic and multilayer systems

We have used a Monte Carlo computer code developed at Brookhaven {sup 1,2} to study the implantation profiles of 1-10 keV positrons incident on a wide range of semi-infinite metals and multilayer systems. Our Monte Carlo program accounts for elastic scattering as well as inelastic scattering from core and valence electrons, and includes the excitation of plasmons. The implantation profiles of positrons in many metals as well as Pd/Al, and Al/Co/Si multilayers are presented. Scaling relations an… more

Date: December 1, 1992

Creator: Ghosh, V. J.; Welch, D. O. & Lynn, K. G.

Item Type: Article

Partner: UNT Libraries Government Documents Department

open access

Monte Carlo studies of positron implantation in elemental metallic and multilayer systems

We have used a Monte Carlo computer code developed at Brookhaven [sup 1,2] to study the implantation profiles of 1-10 keV positrons incident on a wide range of semi-infinite metals and multilayer systems. Our Monte Carlo program accounts for elastic scattering as well as inelastic scattering from core and valence electrons, and includes the excitation of plasmons. The implantation profiles of positrons in many metals as well as Pd/Al, and Al/Co/Si multilayers are presented. Scaling relations an… more

Date: January 1, 1992

Creator: Ghosh, V. J.; Welch, D. O. & Lynn, K. G.

Item Type: Article

Partner: UNT Libraries Government Documents Department

open access

Defect profiling in elemental and multilayer systems: Correlations of fitted defect concentrations with positron implantation profiles

The results of several positron annihilation (Doppler broadening) experiments have been analyzed using the BNL Monte Carlo implantation profiles and the program VEPFIT. The program VEPFIT has been modified so that scaled, parameterized multilayer profiles can also be used as the initial condition for the diffusion equation solution. The authors have looked at both elemental (e.g. amorphous silicon) and multilayer (e.g. Pd/Si) system. Strong correlations between the input implantation profile pa… more

Date: August 1, 1994

Creator: Ghosh, V. J.; Nielsen, B.; Lynn, K. G. & Welch, D. O.

Item Type: Article

Partner: UNT Libraries Government Documents Department

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The SPRITE and POS-SPRITE user report: An extensible calculation of particle, positron and electron implantation in solids

SPRITE (Simulation of Particle Reemission, Implantation and Transmission--Extensible) is a Fortran computer program designed to model the transport of a stream of energetic particles as they scatter through a solid or multilayer. SPRITE is intended to be a user-friendly and easily-extensible engine for performing basic transport calculations, and SPRITE incorporates such physics as is required to simulate the transport process, but specifically omits the details of the scattering mechanisms. PS… more

Date: October 20, 1997

Creator: Ritley, K.A.; Ghosh, V.J.; Lynn, K.G.; McKewown, M. & Welch, D.O.

Item Type: Report

Partner: UNT Libraries Government Documents Department

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Optimization of the Hyspec Design Using Monte Carlo Simulations.

HYSPEC is a direct geometry spectrometer to be installed at the SNS [1] on beamline 14B where it will view a cryogenic coupled hydrogen moderator, The ''hybrid'' design combines time-of-flight spectroscopy with focusing Bragg optics to provide a high monochromatic flux on small single crystal samples, with a very low background at an extended detector bank. The instrument is optimized for an incident energy range of 3-90meV. It will have a medium energy resolution (2-10%) and will provide a flu… more

Date: April 25, 2005

Creator: Ghosh, V. J.; Hagen, M. E.; Leonhardt, W. J.; Zaliznyak, I.; Shapiro, S. M. & Passell, L.

Item Type: Article

Partner: UNT Libraries Government Documents Department

open access

The Methods of Producing and Analyzing Polarized Neutron Beams for Hyspec at the SNS.

The Hybrid Spectrometer (HYSPEC), under construction at the SNS on beam line 14B, is the only inelastic scattering instrument designed to enable polarization of the incident and the scattered neutron beams. A Heusler monochromator will replace the graphite crystal for producing polarized neutrons. In the scattered beam it is planned to use a collimator--multi-channel supermirror bender array to analyze the polarization of the scattered beam over the final energy range from 5-20 meV. Other metho… more

Date: April 25, 2005

Creator: Shapiro, S. M.; Passell, L.; Zaliznyak, A.; Ghosh, V. J.; Leonhardt, W. L. & Hagen, M. E.

Item Type: Article

Partner: UNT Libraries Government Documents Department

open access

Nitrogen vacancy complexes in nitrogen irradiated metals

Gas desorption and positron annihilation techniques have been employed to study the evolution of nitrogen associated defects in nitrogen irradiated metals: Fe, Ni, Mo and W. Nitrogen in these metals has a rather high affinity to vacancy type defects. The results obtained for low irradiation dose show that substitutional nitrogen (NV; with V = vacancy) is formed. The nitrogen vacancy complex dissociates at temperatures ranging from 350 K for Ni to 900 K for Mo and 1,100 K for W. At high doses de… more

Date: December 31, 1996

Creator: Veen, A. van; Westerduin, K.T.; Schut, H.; Melker, E.J.E.; Thijsse, B.J.; Nielsen, B. et al.

Item Type: Report

Partner: UNT Libraries Government Documents Department

open access

Two-detector Doppler broadening profiles in Al

Low-background Doppler broadening profiles have been measured in Al. The KKR methodology has been used to calculate the profile and study the effect of positron-electron correlation.

Date: September 1997

Creator: Mijnarends, P. E.; Kruseman, A. C.; van Veen, A.; Ghosh, V. J.; Asoka-Kumar, P.; Bansil, A. et al.

Item Type: Article

Partner: UNT Libraries Government Documents Department