Some effects of heteroatom size and reactivity on low-energy ion implantation in diamond, revealed by X-ray induced electron spectroscopy and oxidative depth profiling

Abstract

The bombardment of (110) diamond surfaces by 600 eV rare gas and nitrogen ions, and the subsequent erosion of the partially disordered surfaces by microwave-excited nitric oxide at 380 °C, have been studied by means of X-ray induced electron spectroscopy. Both implant and substrate peaks were monitored as a function of erosion time to give semiquantitative depth profiles for both the ion-induced disorder in the substrate and the concentrations of the implanted species. Uptake of the rare gases at the surface amounted to 2-5 at. %, whereas that of nitrogen reached about 50 at. %. Great heteroatom penetration (200-1000 Å) occurred in all cases, especially during implantation at 380 °C, although the majority of the implanted species always lay within 25 Å of the surface. The surface concentration of neon (only), however, was greatly reduced by heating, so that its concentration profile peaked 10 Å below the surface. Nitrogen, xenon and neon penetrated to greater depths than did argon or krypton, and also induced greater disorder; but the most extensive disruption, near-total throughout ca. 50 Å, resulted from He⁺ bombardment. Comparisons of Auger and photoelectron energies between gas and solid indicated the extra-atomic relaxation energy for inert monatomic implants to be ca. 3 eV. During erosion of Kr⁺ and Xe⁺ bombarded surfaces, however, the emergence of additional peaks with reduced relaxation energies showed that krypton and xenon (only) could aggregate in subsurface microcavities. Implanted nitrogen exhibited chemical shifts (after correction for relaxation) of up to 4.7 eV, comparable with those in nitriles, and split interstitial sites are proposed as possible locations for these bonded heteroatoms. Some implications of these results are discussed.