Supersonic beam formation and helium-scattering from GaAs(110)
The author describes (1) his contributions to the science of supersonic beam formation, (2) the results of a {sup 4}He-scattering study from ion-damaged GaAs(110) surfaces, and (3) some preliminary results of 4He-scattering from MBE-grown GaAs(100). In our study of supersonic beam formation, we measure the angular distribution of flux from electron microscope apertures used as supersonic nozzles. This allows (1) the ideal on-axis beam intensity to be calculated and a comparison to be made with effusive beams (a fourfold intensity enhancement occurs), and allows (2) accurate calculations of flow rates through the differential stages of a supersonic beam source. He also studied (3) beam attenuation due to collisions with background gases, and show how skimmer-beam interference and condensation are avoided. The contributions (1)-(3) allow specification of the operating parameters leading to maximum beam signal. {sup 4}He-beams are then used in comparing scattering intensities from clean and Ar{sup +} ion-damaged GaAs(110). He found that the average residual surface damage due to single ion impacts decreases from small groups of defects (vacancies and adatoms) at low sample temperature T during bombardment to isolated monovacancies at higher T. This decrease occurs even in the absence of thermal annealing, and is possibly due to the T-dependent accommodation of adatom energy by the crystal. He also showed {sup 4}He-scattering data from MBE-grown As-stabilized (2 {times} 4) reconstructed GaAs(100). The scattering intensity decays with a time constant of {approximately}1 hour, about 100 times faster than a (110) surface under comparable vacuum conditions, but the cause of this instability is unknown.
- Research Organization:
- Pennsylvania State Univ., Middletown, PA (United States)
- OSTI ID:
- 5504558
- Resource Relation:
- Other Information: Thesis (Ph.D.)
- Country of Publication:
- United States
- Language:
- English
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Related Subjects
SUPERCONDUCTIVITY AND SUPERFLUIDITY
GALLIUM ARSENIDES
ION COLLISIONS
HELIUM IONS
COLLISIONS
ARGON IONS
COMPARATIVE EVALUATIONS
CRYSTAL DEFECTS
DAMAGE
ELECTRON MICROSCOPES
HELIUM 4 BEAMS
PHYSICAL RADIATION EFFECTS
SCATTERING
SUPERSONIC FLOW
SURFACES
ARSENIC COMPOUNDS
ARSENIDES
BEAMS
CHARGED PARTICLES
CRYSTAL STRUCTURE
EVALUATION
FLUID FLOW
GALLIUM COMPOUNDS
ION BEAMS
IONS
MICROSCOPES
PNICTIDES
RADIATION EFFECTS
665300* - Interactions Between Beams & Condensed Matter- (1992-)