Dissociative adsorption of molecular deuterium and thermal stability onto hydrogenated, bare and ion beam damaged poly- and single crystalline diamond surfaces

Abstract

In this work we report on dissociative adsorption of deuterium (D2) on bare, hydrogenated and ion beam bombarded polycrystalline and single crystalline diamond surfaces. Polycrystalline diamond films with an average grain size of ~300nm were deposited on silicon substrates by hot filament chemical vapor deposition technique from methane/hydrogen gas mixture. Deposited films were characterized using Raman spectroscopy, atomic force microscopy and scanning electron microscopy to estimate the phase composition and microstructure. High resolution electron energy loss spectroscopy and direct recoil spectrometry were used to study hydrogen (deuterium) bonding configuration of the upper surface region. Near surface amorphization was achieved by 1keV Ar+ implantation at ~1×1015ions/cm2 at room temperature (RT). As deposited and Ar+ bombarded films are annealed to 500–1000°C in ultra-high vacuum conditions and also under D2 partial pressure of 5×10−6Torr. For comparison, key experiments were repeated on the single crystal (100) diamond. Our results clearly show the preferential dissociative adsorption of D2 on low hybridized carbon (sp/sp2) states with activation temperature as low as RT, but with a lower thermal stability compared to pure diamond CD bonds.