Incorporation of hydrogen in diamond thin films Sobia Allah Rakha, Cao Jianqing, Xia Huihao, Yu Guojun ⁎, Dezhang Zhu, Jinlong Gong Shanghai Institute of Applied Physics, Chinese Academy of Sciences, Shanghai 201800, PR China abstract article info Article history: Received 28 November 2008 Received in revised form 5 March 2009 Accepted 28 April 2009 Available online 3 May 2009 PACS: 68.55.Ln 82.80.Yc 81.07.Bc Keywords: CVD diamond films Hydrogen Grain size dependence ERDA XPS RS In this investigation, diamond thin films with grain size ranging from 50 nm to 1 μm deposited using hot filament chemical vapor deposition (HFCVD) have been analyzed by elastic recoil detection analysis (ERDA) for determining hydrogen concentration. Hydrogen concentration in diamond thin films increases with decreasing grain size. Raman spectroscopy and X-ray photoelectron spectroscopy (XPS) results showed that part of this hydrogen is bonded to carbon forming C–H bonding. Raman spectra also indicated the increase of non diamond phase with the decrease in crystallite size. Incorporation of hydrogen in the samples and increase of hydrogen content in nanocrystalline sample are discussed. Large separation between filament and substrate used for the synthesis of nanocrystalline film helped to understand the large incorporation of hydrogen in nanocrystalline diamond films during growth. The study addresses the hydrogen trapping in different samples and higher hydrogen concentration in nanocrystallites by considering the synthesis conditions, growth mechanisms for different grain sized diamond films and from the quality of CVD diamond films. © 2009 Elsevier B.V. All rights reserved. 1. Introduction Understanding the interaction of hydrogen with diamond surfaces is important from a fundamental point of view and also to elucidate the role of hydrogen in the nucleation and growth of diamond films by chemical vapor deposition. The source of hydrogen in CVD diamond lattice comes mainly from the high concentration (≥ 99% by vol.) of H 2 gas present in the gas mixture for the synthesis. Such large concentration of H 2 is required to generate high concentration of atomic hydrogen (H) during growth that is essential for the synthesis of diamond via CVD routes [1–5]. Hydrogen involvement in the diamond nucleation and growth processes includes stabilization of diamond clusters and surfaces allowing nucleation and growth and removing the thermodynamic barrier which causes graphitic rather than diamond growth, preferential etching of sp 2 carbon during deposition allowing the evolution of high quality diamond films, formation of the clusters necessary for growth (e.g. CH x or C 2 H x ). Work has been done on hydrogen distribution, concentration and locations in diamond films [6–10]. Hydrogen was claimed to be found both in grain boundaries [8,9] and also be trapped at in-grain defects [10]. By infrared reflection spectroscopy [11] it was shown that C–H stretching bands did not arise from hydrogen incorporated at the grain boundaries, but rather from hydrogen bonded to bulk diamond carbon atoms. This conclusion is in contrast with the presence of a broad Gaussian NMR component [12] which is attributed to high local hydrogen densities, very likely at grain boundaries. Hydrogen is said to be distributed inhomogeneously in diamond films and it is likely to be found on the surface, at grain boundaries and dislocations or simply as lattice defects. Several studies of hydrogen determination using Elastic Recoil Detection (ERD) on polycrystalline diamond films are found in literature [13–16] and also few reports on hydrogen incorporation using methods other than ERDA in nanodiamond films [17–19] are present. The present work studies the effects of synthesis conditions on hydrogen incorporation in diamond thin films with different grain sizes ranging from 50 nm, 300 nm, and 1 μm by using the same input gas ratios for all the samples. ERD was used to measure the concentration of hydrogen on as-deposited diamond films. Raman spectroscopy and X-ray photoelectron spectroscopy (XPS) helped to explore whether some of hydrogen is bonded to carbon as well as to investigate carbon–carbon bonding. The non diamond phases, increased with decreasing grain size, are related with the increase of hydrogen concentration. We have discussed hydrogen trapping in different samples and higher concentration in nanocrystallites by considering the synthesis conditions and growth mechanisms for different grain sized diamond films. Diamond & Related Materials 18 (2009) 1247–1252 ⁎ Corresponding author. Laboratory of Nuclear Analysis Techniques (LNAT), Chinese Academy of Sciences, Shanghai, 201800, PR China. Tel./fax: +86 21 59552539. E-mail address: yuguojun@sinap.ac.cn (G.J. Yu). 0925-9635/$ – see front matter © 2009 Elsevier B.V. All rights reserved. doi:10.1016/j.diamond.2009.04.009 Contents lists available at ScienceDirect Diamond & Related Materials journal homepage: www.elsevier.com/locate/diamond