Hydrogen concentration and bonding in nano-diamond films of varying grain sizes grown by different chemical vapor deposition methods

Abstract

Hydrogen in a variety of forms (molecular hydrogen, atomic hydrogen, hydrocarbon radicals) is involved in diamond formation. The present work studies 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 (CVD). The size of diamond grains which constitute the films varies in the following way: hundreds of nm in the case of HF CVD (similar to 300 nm), tens nm in the case of MW CVD (3-30 nm) and a few nm in the case of dc GD CVD (similar to 5 nm). Raman spectroscopy, 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 retention of hydrogen in the films increases with decreasing grain size, indicating that most likely hydrogen is bonded and trapped in grain boundaries as well as on the films surfaces. Raman and HR-EELS analysis show that hydrogen is bonded to sp(2)- and sp(3)-hybridized carbon, giving rise to typical C-H vibration modes. (C) 2007 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.