INTERACTIONS OF LOW-ENERGY (10-600 EV) NOBLE-GAS IONS WITH A GRAPHITE SURFACE - SURFACE PENETRATION, TRAPPING AND SELF-SPUTTERING BEHAVIORS

Abstract

Penetration, trapping and self-sputtering behaviors of the He+, Ne+ and Ar+ ions impinging onto a graphite surface are investigated in the energy range of 10-600 eV. The low energy ion beams are directed onto the surface and their trapped portion is measured by Auger electron spectroscopy and thermal desorption mass spectrometry. Classical trajectory simulation is performed for systematic interpretation of the experimental findings. The penetration probability rapidly increases with energy in the threshold region of 10-100 eV, above which the rate of increase slows down. The penetration probability for Ne and Ar is close to unity at higher energies. Trapping exhibits a qualitatively similar energy dependency to penetration. However, the probability of trapping is lower in magnitude than the penetration and decreases in the order of He > Ne > Ar. At high doses self-sputtering efficiently occurs for these low energy trapped atoms, especially for Ne and Ar atoms as they are trapped near the surface. He ions penetrate into significantly deeper layers than the other ions. The deeper penetration of He results in inefficient sputtering of the trapped atoms, and an increase in the trapped portion of the He beam at high doses. Thermal desorption behavior of the trapped Ar atoms suggests that they are held strongly between the graphite basal planes. A considerable fraction of the He gases desorbs at room temperature, implying that they are relatively mobile inside the lattice.