Hydrogen in nano‐diamond films: experimental and computational studies

Abstract

AbstractWe present studies related to the incorporation of hydrogen and its bonding configuration in diamond films composed of diamond grains of varying size which were deposited by three different methods: hot filament (HF), micro wave (MW) and direct current glow discharge (dc GD) chemical vapor deposition. The size of the diamond grains which constitute the films varies in the following way: hundreds of nm in the case of HF CVD (“sub‐micron size”, ∼300 nm), tens of nm in the case of MW CVD (3–30 nm) and a few nm in the case of dc GD CVD (“ultra nano‐crystalline diamond”, ∼5 nm). Secondary ion mass spectroscopy (SIMS) and high resolution electron energy loss spectroscopy (HR‐EELS) were applied to investigate the hydrogen trapping in the films. The hydrogen retention of the diamond films increases with decreasing grain size, indicating that most likely hydrogen is bonded and trapped in grain boundaries as well as on the internal grain surfaces. HR‐EELS analysis shows that at least part of this hydrogen is bonded to sp2‐ and sp3‐hybridized carbon, thus giving rise to typical C–H vibration modes. The vibrational spectroscopies show the increase of sp2 C–H modes in transition from sub‐micron to ultra nano‐crystalline grain size. These conclusions are supported by preliminary results of computer simulations which show that hydrogen atoms at the boundary between a nano‐diamond particle and an amorphous shell have lower energy than hydrogen atoms within either the nano‐diamond or the amorphous region. These results suggest that hydrogen is expected to be localized at the nano‐diamond/amorphous carbon interface as experimentally found. (© 2008 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)