785 nm Raman Spectroscopy of CVD Diamond Films
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1039-P15-02
785 nm Raman Spectroscopy of CVD Diamond Films Paul William May, James A Smith, and Keith N Rosser School of Chemistry, University of Bristol, Cantock's Close, Bristol, BS8 1TS, United Kingdom
ABSTRACT Raman spectroscopy is a powerful technique often used to study CVD diamond films, however, very little work has been reported for the Raman study of CVD diamond films using near infrared (785 nm) excitation. Here, we report that when using 785 nm excitation, the Raman spectra from thin polycrystalline diamond films exhibit a multitude of peaks (over 30) ranging from 400-3000 cm-1. These features are too sharp to be photoluminescence, and are a function of film thickness. For films >30 µm thick, freestanding films, and for films grown in diamond substrates the Raman peaks disappear, suggesting that the laser is probing the disordered small-grained interface between the diamond and substrate. Some of the peaks change in relative intensity with time (‘blinking’), and the spectra are very sensitive to position on the substrate – this is reminiscent of the behaviour seen in SERS spectra.. INTRODUCTION Raman spectroscopy is a powerful technique often used to study CVD diamond films [1,2]. Excitation using laser wavelengths in the UV and visible regions are most commonly used, and for diamond films these typically produce spectra with a limited number of characteristic peaks, including the diamond peak (~1332 cm-1), the D and G bands from graphitic impurities, and sometimes the 1150 and 1450 cm-1 bands from sp2 carbon impurities at the grain boundaries of nanophase diamond. Very little work has been reported, however, for the study of CVD diamond films using near infrared (785 nm, 1.58 eV) excitation, which is exceptionally sensitive to sp2 carbon. A few groups have used 785 nm excitation to study carbon films, but these have usually concentrated on studies of non-diamond carbon, such as measuring the dispersion of the G band in amorphous carbon films [3,4], carbon nanotubes and onions [5], or the graphitic residues following polishing of diamond [6]. It has also been used in combination with excitation from other wavelengths to study diamondoid molecules [7], revealing a multitude of peaks in the range 400-1500 cm-1 corresponding to the numerous different vibrations of the carbon framework in each molecule. It was suggested that the Raman spectrum from a sufficiently large diamondoid molecule would eventually resemble that seen for nanocrystalline diamond particles or films [8]. For CVD diamond films, however, the only Raman spectra reported using 785 nm excitation concerns the shift of the diamond line and Fano resonance effects during heavy boron doping [9], and some simple characterisation [10]. Very recently, Veres et al. [11] reported 785 nm Raman spectra from nanocrystalline diamond films with varying grain sizes, and found that samples with larger grains (>125 nm) exhibited spectra with a number of well distinguished sharp peaks. They suggested that this was due to the increased band gap of the larger c
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