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TDS Investigation of Hydrogen Retention in Graphites and Carbon Based Materials

Retention of 200 eV H2+ ions (Ei = 100 eV/nucl) in fine grain graphite of MPG-8 type, graphite of RGT type (C + 3.5% TiC), CFC of N11 type, crystalline boron carbide and hydrocarbon films was investigated by means of thermal desorption spectrometry. The implantation dose varied between 5 × 1021 and 6 × 1024 H/m2. Temperature of the samples during implantation was 470 ± 10 K. The measurements showed that hydrogen retention at high fluences increased in the following order: B4C, MPG-8 and CFC, RGT, CH-films. The main part of trapped hydrogen and CH4 molecules are collected in deep layers beyond the kinetic ion range. Slowing down of the retention rate in graphites at fluences around 5 × 1023 H/m2 may account for the approach of the hydrogen trapping rate and the rate of the hydrogen release from the sputtered surface. Hydrogen retention in B4C saturates near the fluence 1024 H/m2. Saturation of the CH4 release was observed in all graphites and in boron carbide at fluences around 1024 H/m2. The features of the hydrogen retention in deep layers of materials under low energy ion implantation are discussed.