Epitaxy of silicon doped gallium arsenide by molecular beam method

The molecular beam method is a versatile experimental technique which may be used to grow high quality single crystal thin films in the range from 100Å to several microns with precise control of uniformity and thickness. Films may be doped by an additional molecular beam containing the doping material simultaneously impinging on the substrate surface with the film molecular beams. Epitaxial GaAs thin films doped with silicon were grown by the molecular beam method in an ultrahigh vacuum system in which high energy electron diffraction and mass spectrometric measurements could be made during growth or by stopping growth momentarily. The crystallinity and beam intensity parameters of these films were thus studied during growth. The doping profiles and the amount of compensation were evaluated by the Schottky barrier diode method and the photo luminescence spectra.     

Direct exposure to gallium arsenide upregulates costimulatory activity of murine macrophages

Gallium arsenide (GaAs) is an intermetallic semiconductor compound used in the electronics industry. Acute exposure of animals to GaAs systemically suppresses several immune functions while paradoxically causing inflammation at the exposure site. We investigated the effect of GaAs on costimulatory activity of murine peritoneal macrophages, 5 days after ip exposure. Costimulation by macrophages was determined by activation of CD4(+) helper T cell hybridomas to secrete interleukin-2 in the presence of immobilized monoclonal anti-CD3 antibody. Both peritoneal exudate cells (PEC) and resident peritoneal cells exposed to GaAs provided greater costimulation to the T cells than vehicle control cells. Resident peritoneal cells exposed to GaAs were also more efficient than latex bead-exposed cells, indicating that phagocytosis alone did not cause the GaAs effect. Double immunofluorescence staining and flow cytometric analysis revealed that GaAs-exposed PEC had increased cell surface expression of costimulatory B7-1 and B7-2 molecules and intracellular adhesion molecule-1 (ICAM-1) compared to controls. In addition to these molecules, resident peritoneal macrophages exposed to GaAs also expressed significantly higher levels of heat-stable antigen (HSA). Monoclonal antibodies specific for these costimulatory molecules significantly inhibited T cell activation, demonstrating that the molecules on GaAs-exposed cells were functional. In contrast, GaAs did not upregulate costimulatory molecules on splenic macrophages. These findings suggest that direct GaAs exposure improves macrophage costimulatory activity, possibly by activating the cells, which may contribute to respiratory inflammation caused by inhalation of GaAs particles.     

Hepatic and renal metallothionein induction following single oral administration of gallium arsenide in rats

Metallothionein genes (MT) are inducible by a variety of agents, including heavy metals. We report the induction of MT expression by gallium arsenide (GaAs), a superior intermetallic semiconductor material at two time intervals following single oral exposure in rats. The data is also supplemented with two additional groups exposed to gallium (III) as gallium oxide and arsenic (III) as sodium arsenite to determine which of the two moieties in GaAs is responsible for any such possible effects. The results indicate that GaAs administration does significantly induces MT in hepatic tissues accompanied by an increase in cytosolic glutathione, arsenic, zinc and copper concentration. It thus proves that arsenic moiety is chiefly responsible for such an effect.