Effect of germanium auto-diffusion on the bond lengths of Ga and P atoms in GaP/Ge(111) investigated by using X-ray absorption spectroscopy.

The germanium auto-diffusion effects on the inter-atomic distance between the nearest neighbors of the Ga atom in GaP epilayers are investigated using high-resolution X-ray diffraction (HRXRD) and X-ray absorption spectroscopy. The GaP layers grown on Ge (111) are structurally coherent and relaxed but they show the presence of residual strain which is attributed to the auto-diffusion of Ge from the results of secondary ion mass spectrometry and electrochemical capacitance voltage measurements. Subsequently, the inter-atomic distances between the nearest neighbors of Ga atom in GaP are determined from X-ray absorption fine-structure spectra performed at the Ga K-edge. The estimated local bond lengths of Ga with its first and second nearest neighbors show asymmetric variation for the in-plane and out-of-plane direction of GaP/Ge(111). The magnitude and direction of in-plane and out-of-plane microscopic residual strain present in the GaP/Ge are calculated from the difference in bond lengths which explains the presence of macroscopic residual tensile strain estimated from HRXRD. Modified nearest neighbor configurations of Ga in the auto-diffused GaP epilayer are proposed for new possibilities within the GaP/Ge hetero-structure, such as the conversion from indirect to direct band structures and engineering the tensile strain quantum dot structures on (111) surfaces.

Reproduction and development in Drosophila are dependent upon catecholamines.

Drosophila melanogaster, maintained on culture media containing alpha-methyl-p-tyrosine (alpha-MT) at millimolar levels for 7 days, fail to produce viable progeny. Lesser concentrations delay development. This effect of alpha-MT, an inhibitor of tyrosine hydroxylase (TH), is partially reversible by co-administration of L-dihydroxyphenylalanine, the product of TH. Potent inhibitors of other steps in the pathway for catecholamine biosynthesis are inactive except for a partial effect with dopamine B-hydroxylase inhibition. the effect of alpha-MT is due to a combination of ovulation suppression coupled with decreases in embryonic and larval viability. Effects similar to those of alpha-MT are found with millimolar levels of reserpine, prazosin and to a lesser extent, rauwolscine. No significant effects are found with propranolol, chlorpromazine, sulpiride and SK&F 83566. Mutant alleles of the gene coding for TH are known to be lethal at the embryonic stage when homozygous in both Drosophila and mice. Taken together, these results indicate that in addition to their established roles in the nervous system catecholamines function in animal development via an action mediated through alpha-adrenoceptors.