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Results for “X-ray beam induced current”

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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NASA NTRS1985

High-purity silicon crystal growth investigations

The study of silicon sheet material requirements for high efficiency solar cells is reported. Research continued on obtaining long lifetime single crystal float zone silicon and on understanding and reducing the mechanisms that limit the achievement of long lifetimes. The mechanisms studied are impurities, thermal history, point defects, and surface effect. The lifetime related crystallographic defects are characterized by X-ray topography and electron beam induced current.

Ciszek, T. F.↗

NASA NTRS1992

The growth and characterization of Al(x)Ga(1-x)As/Ge heterostructures

The effects of the growth temperature and the Al(x)Ga(1-x)As layer thickness on the structural, optical, and electrical properties of Al(x)Ga(1-x)As/Ge heterostructures grown for photovoltaic applications were investigated using different-thickness (between 1 micron and 5 microns) Al(x)Ga(1-x)As layers grown by MOCVD in the temperature range between 660 and 780 C. Results obtained from double-crystal X-ray rocking curve measurements, electron beam induced current, cross-sectional TEM, Raman spectroscopy, SIMS, and steady-state and time-resolved photoluminescence measurements are presented. It was found that the highest minority carrier lifetime, 2.41 ns, was obtained for T(G) = 780 C, but the lowest interfacial recombination velocity, 1.6 x 10 exp 4, was obtained at 660 C.

Choi, S. W.↗

NASA NTRS2000

Correlation of EBIC and SWBXT Imaged Defects and Epilayer Growth Pits in 6H-SiC Schottky Diodes

We show the first direct experimental correlation between the presence of closed core screw dislocations in 6H-SiC epilayers with recombination centers, as well as with some of the small growth pits on the epilayer surface in lightly-doped 6H-SiC Schottky diodes. At every Synchrotron White-Beam X-ray Topography (SWBXT)-identified closed core screw dislocation, an Electron Beam Induced Current (EBIC) image showed a dark spot indicating a recombination center, and Nomarski optical microscope and Atomic Force Microscope (AFM) images showed a corresponding small growth pit with a sharp apex on the surface of the epilayer.

Schnable, C. M.↗

NASA NTRS1989

X-ray beam method for displacement measurement in hostile environments

A new method of extensometry using an X-ray beam was devised, and the results of current testing reveal it to be highly feasible. This technique has been shown to provide a non-contacting system that is immune to problems associated with density variations in gaseous environments, that plague currently available optical methods. This advantage is a result of the non-refracting penetrating nature of X-rays. The method is based on X-ray-induced X-ray fluorescence of targets, which subsequently serve as fudicial markers. Some target materials have melting points over 1600 degrees C which will facilitate measurement at extremely high temperatures. A highly focused intense X-ray beam, which is produced using a Johansen 'bent crystal', is then scanned across the target, which responds by fluorescing X-rays when stimulated by the incident beam. This secondary radiation is monitored using a detector. By carefully measuring beam orientation, change in target edge position can be determined. Many variations on this basic theme are now possible such as two targets demarcating a gage length, or a beam shadowing method using opaque targets.

Jordan, Eric H.↗

NASA NTRS1975

Plasma phenomena at magnetic neutral points

A model of the plasma focus is considered, in which large axial electric fields are induced by the imploding current sheet during the final few nanoseconds of the collapse phase. This field provides a mechanism for creation of a beam of electrons of highly suprathermal energies. For this beam, the bremsstrahlung radiation is calculated, which is expected either from electron-deuteron collisions in the focused plasma itself or from the beam as it reaches the walls of the device. Comparison with experimental results indicates that the walls are the more likely source of these hard X-rays and also find qualitative agreement of the expected angular distribution of X-rays with experiment.

Sturrock, P. A.↗

NASA NTRS2005

Surface charging and x-ray emission from insulator surfaces induced by collisions with highly charged ions : relevance to cometary and planetary sp

Characteristic X-ray emission lines are detected from simulants of comet surfaces as they undergo collisions with highly charged ions (HCIs). The HCI projectiles are O+2-O+7. Ion energies are varied in the range (2-7)q keV, where q is the ion charge state. The targets are the insulator minerals olivine, augite, and quartz. It is found that the emission of characteristic K-L, K-M X-rays appears to proceed during positive charging of the surface by the HCI beam. When one uses low-energy, flood-gun electrons to neutralize the surface charge, the X-ray emission is eliminated or greatly reduced, depending on the flood-gun current. Acceleration of background electrons onto the charged surface results in excitation of elemental transitions, including the K-L2 and K-L3 target X-ray emission lines of Mg and Si located spectroscopically at 1253.6 and 1739.4 eV, respectively. Also observed are emission lines from O, Na, Ca, Al, and Fe atoms in the target and charge-exchange lines via surface extraction of electrons by the O+q electric field. Good agreement is found in the ratio of the measured X-ray yields for Mg and Si relative to the ratio of their electron-impact K-shell ionization cross sections. The present study may serve as a guide to astronomers as to specific observing X-ray energies indicative of solar/stellar wind or magnetospheric ion interactions with a comet, planetary surface, or circumstellar dust.

comets↗