A MODEL FOR TRAPPING AND REEMISSION AT HYDROGEN-ION IMPLANTATION

A simple two-parameter model for re-emission at hydrogen ion implantation is proposed. The model takes into account diffusion, molecular desorption and hydrogen-defect interaction. Comparison of the model with experiments on hydrogen and deuterium re-emission from stainless steel, molybdenum, tungsten, boron nitride, carbon and pyrocarbon demonstrates a good agreement. Two fitting parameters are used in the model: (1) the recycling factor R = D/K where D is the diffusion coefficient and K the surface recombination coefficient and (2) the defect factor PHI(d) equal to the maximum areal concentration of hydrogen being able to be trapped in defects. At high temperature R(T) and PHI(d)(T) follow exponential dependences in accordance to thermal activation of the processes involved. At low temperatures R(T) and PHI(d)(T) functions deviate from the exponents, presumably due to domination of some radiation enhanced processes. Comparison of our R and PHI(d) values with those available from other experiments shows that the fitting parameters in our model have reasonable values.