Hydrogen incorporation in diamond films

Hydrogen in a variety of forms (molecular hydrogen, atomic hydrogen, hydrocarbon radicals) is involved in diamond evolution and its incorporation may give insight into the growth processes of diamond films and their related properties. The present work studies the incorporation of hydrogen in hot filament chemical vapor deposited (HF CVD) diamond films with different grain sizes and compares it to that occurring in nano-diamond films deposited from energetic species. Raman spectroscopy, secondary ion mass spectroscopy (SIMS) and high resolution electron energy loss spectroscopy (HREELS) 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. Raman and HREELS analysis show that at least part of this hydrogen is bonded to carbon forming typical C-H vibrations. Partial or full isotopic exchange of H by D in the CH4/H-2 feeding gas mixture used for growth substantiated the assignment of both the Raman and HREELS C-H related modes. This isotopic exchange also indicated that most of the hydrogen incorporated in the diamond films originates from the molecular hydrogen component of the feeding gas. (C) 2006 Elsevier B.V All rights reserved.