Search

High purity n-type silicon single crystal with resistivity in the order of 4000 Ω cm has been irradiated with high-energy oxygen ions at room temperature up to a fluence of 5E15 ions/cm2. The energy of the beam was varied from 3 to 140 MeV using a rotating degrader to achieve a depthwise near-uniform implantation profile. Radiation induced defects and their dynamics have been studied using positron annihilation spectroscopy along with isochronal annealing up to 700 °C in steps of 50 °C for 30 min. After annealing the sample at 200 °C for 30 min, formation of silicon tetravacancies has been noticed. The formation of the tetravacancies was found to be due to agglomeration of divacancies present in the irradiated sample. An experimentally obtained positron lifetime value of 338±10 ps has been reported for silicon tetravacancies, which has a very close agreement with the value obtained from recent theoretical calculations. The tetravacancies were found to dissociate into trivacancy clusters upon further annealing. The trivacancies thus obtained were observed to agglomerate beyond 400 °C to form larger defect clusters. Finally, all the defects were found to anneal out after annealing the sample at 650 °C.

Inter University Consortium for DAE Facilities Silicon surface barrier (SSB) detectors have been fabricated with oxygen enriched, high-resistivity, detector grade, n-type FZ silicon. Oxygen enrichment of the wafer was done by high-energy (140 MeV) oxygen ion implantation. Annealing of the irradiated silicon wafer was done to minimize the irradiation-induced defect concentration. Positron annihilation lifetime studies were used to select the annealing temperature. A comparative study was carried out among various SSB detectors made from as-grown, as-irradiated and annealed silicon wafers. Detector made from the annealed wafer worked satisfactorily and its performance was comparable with that of a detector made from as-grown crystal.

Detector grade n-type float-zone silicon irradiated with 140 MeV O 6+ ions to a dose of 5×1015 particles/cm2 was studied by positron annihilation spectroscopy. Vacancy clusters containing five vacancies were detected in the irradiated sample. Isochronal annealing studies of the irradiated sample reveal the dissociation of five-vacancy clusters and formation of vacancy agglomerates V3, V6 and vacancy-oxygen complexes in the temperature range 250-500 °C. The vacancy-oxygen complexes dissociate at 550 °C and released vacancies agglomerate around 600 °C to form voids comprising 10 vacancies. In the temperature range 600-700 °C, the voids dissociate and around 750 °C advanced vacancy-oxygen complexes VmOn (n>m) form. © 2005 Elsevier B.V. All rights reserved.

Particle-induced X-ray emission (PIXE) analysis was employed in the present study to investigate the chemopreventive potential of vanadium in influencing trace elemental profile and antioxidant status in chemical carcinogenesis. The elements with Za 15‐40 were studied. Data reveal remarkable alterations in elemental composition in the hepatic tissue of diethylnitrosamine (DENA)-induced Sprague‐Dawley male rats (intraperitoneal (ip) dose: 200 mg/kg body weight) after four weeks of induction. Several elements like Mn, Cu, Zn, Rb showed large depletion while other elements like Fe, Ca, K, Br showed large enhancement in comparison to that of the normal control animals. These elements compete for binding sites in the cell, change its enzymatic activity and exert direct or indirect action on the carcinogenic process. Supplementary vanadium (0.5 ppm ad libitum in drinking water) has shown eAective modulation by alteration in the concentration of trace elements in the tumorigenic tissue (P < 0:001‐0:005). Data reflect a definite correlation between elemental composition, antioxidant status in the initiation phase of carcinogenesis and the period of exposure to vanadium. The possibility of selecting vanadium as a therapeutic agent for chemoprevention is discussed in the light of its influence in maintaining trace elemental homeostasis, a parameter of importance in cancer prevention research. ” 2000 Elsevier Science B.V. All rights reserved.

High-resistivity detector-grade p-type silicon wafers have been implanted with swift oxygen (O6+) ions under two different conditions. One of the wafers was implanted effectively with a pulsed beam of varied energy (3-140MeV) to a total fluence of 5 × 1015ionscm-2, resulting in a depth-wise near-uniform implantation profile. The other wafer was directly irradiated with a 140MeV steady oxygen beam to the same fluence. Radiation-induced defects produced in the samples and their isochronal annealing behaviours were studied by positron annihilation lifetime spectroscopy and Doppler broadening of positron annihilation radiation measurements. The lifetime spectra of the irradiated samples were fitted with three lifetimes. Trapping model analysis was carried out with the de-convoluted lifetimes to characterize the defect states. The defect-related lifetime τ2 in both the irradiated samples was found to be due to an admixture of divacancy (V 2) and divacancy-oxygen (V2O) complexes. A marked difference in the defect reordering process has been observed between the two samples, which is explained by taking into account the effect of injection annealing by minority carriers which are produced by the energetic beam prior to forming displacement damage. © IOP Publishing Ltd.