[en] In the manufacture of SIMOX a Si wafer is implanted with 1.7x10¹⁸, 180 keV oxygen ions. After implantation the wafer is annealed at 1350 deg. C. This process creates a top layer of silicon, which almost has the quality of bulk silicon, and an insulating layer of buried oxide (BOX), that separates the top layer from the Si wafer. Positron annihilation techniques are very sensitive for the open-volume defects produced during the implantation. The Doppler broadening of the annihilation radiation technique was applied to investigate the effect of dose variations and anneal temperature. The positron annihilation results show that the top silicon layer in SIMOX still contains small vacancy-oxygen clusters which cannot be observed with TEM

[en] Positron beam and 2D-ACAR investigation of cubic and coated diamonds are reported. In type IIA diamonds, positrons are mostly trapped in vacancies in the carbon lattice; in type Ia diamonds, two main defect-related annihilation sites are nitrogen-vacancy complexes (H2, H3) and the vicinity of split interstitial atoms. No correlation between principal nitrogen defects and annihilation rate was found. PAS data indicate the presence of a significant amount of vacancies in all studied diamonds, which increases the rate of nitrogen aggregation. It is shown that pressurised fluid inclusions may serve as a positron trap, giving rise to the long component in the lifetime spectra.

No abstract available

[en] A ''two-site'' immunoradiometric assay (IRMA) which allows the direct estimation of human CRH (hCRH) in plasma is described. Using this IRMA, basal levels of CRH in normal subjects ranged from 2-28 pg/mL [mean, 15 +/- 7 (+/- SD) pg/mL; n = 58]. Values in men and women were similar. Plasma CRH values within this range were also found in patients with Cushing's syndrome, Addison's disease, and Nelson's syndrome, with no correlation between plasma CRH and ACTH levels in these patients. Elevated plasma CRH levels were found in pregnant women near term [1462 +/- 752 (+/- SD) pg/mL; n = 55], and the dilution curve of this CRH-like immunoreactivity paralleled the IRMA standard curve. After its immunoadsorption from maternal plasma, this CRH-like material eluted on reverse phase high performance liquid chromatography with a retention time identical to that of synthetic CRH and had equipotent bioactivity with the synthetic peptide in the perfused anterior pituitary cell bioassay. Circulating CRH was not detected in Wistar rats, even after adrenalectomy and subsequent ether stress. Synthetic hCRH was degraded by fresh human plasma relatively slowly; 65% of added CRH remained after 1 h of incubation at 37 C. Degradation was inhibited by heat treatment (54 C; 1 h), cold treatment (4 C; 4 h), or freezing and thawing. Loss of synthetic rat CRH occurred more rapidly when fresh rat plasma was used; only 20% of added CRH remained under the same conditions. The inability to measure CRH in peripheral rat plasma may be due to the presence of active CRH-degrading enzymes which fragment the CRH molecule into forms not recognized by the CRH IRMA

[en] Low-energy (0.1-10 keV) ion scattering (LEIS) can be used to analyze the atomic composition of the outermost layer of a surface. Possibilities for quantification and in-depth information are discussed. Using a new type of energy analyzer (EARISS) which enables the simultaneous detection of a large part of the energy spectrum, a greatly improved sensitivity is obtained. Even for a catalyst consisting of a highly dispersed carbon support (1000 m²/g) and a low loading of Pd/Pt clusters, the surface composition can be determined using a 2 keV Ne⁺ ion beam current of only 30 pA. (orig.)

[en] Positron annihilation spectroscopy (PAS) is a sensitive probe for studying the electronic structure of defects in solids. We show that the high-momentum part of the Doppler-broadened annihilation spectra can be used to distinguish different elements. This is achieved by using a new two-detector coincidence system to examine the line shape variations originating from high-momentum core electrons. Because the core electrons retain their atomic character even when atoms form a solid, these results can be directly compared to simple theoretical predictions. The new approach adds increased elemental specificity to the PAS technique, and is useful in studying the elemental variations around a defect site. copyright 1996 The American Physical Society