Nitrogen and hydrogen related infrared absorption in CVD diamond films E. Titus a, * , N. Ali a , G. Cabral a , J.C. Madaleno a , V.F. Neto a , J. Gracio a , P Ramesh Babu b , A.K. Sikder c , T.I. Okpalugo d , D.S. Misra c a Department of Mechanical Engineering, University of Aveiro, 3810-193, Portugal b Materials Ireland, Polymer research Centre, School of Physics, Dublin, Ireland c Department of Physics, Indian Institute of Technology (IIT), Bombay, India d Northern Ireland Bio-Engineering Centre, NIBEC, University of Ulster, UK Abstract In this paper, we investigate on the presence of hydrogen and nitrogen related infrared absorptions in chemical vapour deposited (CVD) diamond films. Investigations were carried out in cross sections of diamond windows, deposited using hot filament CVD (HFCVD). The results of Scanning Electron Microscopy (SEM), Fourier Transform Infrared (FTIR) and Raman spectroscopy carried out in a cross section of self-standing diamond sheets are presented. The FTIR spectra showed several features that have not been reported before. In order to confirm the frequency of nitrogen related vibrations, ab-initio calculations were carried out using GAMESS program. The investigations showed the presence of several C – N related peaks in one-phonon (1000 – 1333 cm  1 ). The deconvolution of the spectra in the three-phonon region (2700 – 3150 cm  1 ) also showed a number of vibration modes corresponding to sp m CH n phase of carbon. Elastic recoil detection analysis (ERDA) was employed to compare the H content measured using FTIR technique. Using these measurements we point out that the oscillator strength of the different IR modes varies depending upon the structure and H content of CVD diamond sheets. 1. Introduction The extraordinary behaviour of nitrogen in CVD diamond is continuing to attract considerable interest from many research- ers working on the CVD of diamond films and coatings. Indeed, the failure to n -doped diamond and a number of experimental results [1–3] showing that the single substitu- tional nitrogen in CVD diamond behaves rather differently than in natural diamond, have intensified this interest. It is widely accepted that nitrogen acts as an impurity in CVD diamond, which strongly affects its optical, electrical and mechanical properties. Nitrogen is one of the major impurities in natural diamond as well and it has been used as a characteristic for the classification of the same. A number of nitrogen related centers in natural as well as CVD diamond have been identified using FTIR technique [4]. In CVD diamond, hydrogen is another impurity that plays a major role in controlling various characteristics of the material. The source of hydrogen in CVD diamond lattice is mainly the high concentration ( 99% by vol.) of H 2 gas present in the gas mixture. 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 [5]. The study of IR absorption in C–H stretch region is important not only for identifying various possible modes of vibration, but also for the quantitative estimation of hydrogen bonded to the diamond lattice. As the absorption is due to the superposition of vibrations from different modes where carbon is in different configuration, the quantitative calculation of H content using a unique value of the oscillator strength often proves erroneous. Jacob and Unger [6] pointed out that the constant (A n ) proportional to the oscillator strength does not have a unique value and depends upon the structure of the C:H films. A n for polymer-like films with H / C ratio around 1 increases by a factor of 4 with decreasing of H / C ratio. Hence