Pure hydrogen references synthesized by low energy ion implantation into amorphous silicon

Abstract

We developed a hydrogen standard by ion implantation in amorphous silicon, produced by implantation of 170 keV 28Si with 2·1015 at./cm2 in a silicon wafer (1 0 0) to obtain an amorphous depth of a few hundred of nanometers. The tilt and twist angles of the target were fixed to avoid channeling and the sample was cooled during the implantation. The amorphous silicon was then irradiated successively with hydrogen at 3.0 and 1.5 keV with doses 1.0 and 0.7·1017 at./cm2 respectively. The characteristics of the standards (retained dose, depth profile and stability under irradiation) were investigated by elastic recoil detection analysis (ERDA) and resonant nuclear reaction analysis (RNRA) with a 1H(15N,αγ)12C reaction at 6.385 MeV. These properties were compared with another previously developed standard (hydrogen implantation in monocrystalline silicon (1 0 0)). Results showed that, for the same implanted dose, the retained dose is about 55% larger in amorphous silicon. Furthermore, we showed these new standards are stable under beam irradiation for low current (10 nA/mm2) and could be used as IBA reference. Stability for higher currents (100 nA/mm2) showed a 10% release after an integrated charge about 2 mC. We showed that this release which occurs at the beginning of irradiation is due to desorption of the H-contamination layer on the surface. Implanted hydrogen remains stable under irradiation. We conclude that those standards are suitable target to study nuclear reactions of astrophysical interest, namely the 1H(13C,γ)14N reaction.