Diamond films produced in the low-pressure hat flame have been examined using Raman spectroscopy. The effect of the oxy-acetylene gas mixture (R = O-2/C2H2 gas ratio of 0.95 to 1.06) and substrate temperature (650-850 degrees 'C) on the form of the non-diamond carbon as well as the diamond phase purity and crystallinity. are reported. An assessment of the diamond crystallinity was achieved by inspection of the full-width-at-half-maximum (FWHM) of the Raman line observed at 1332 +/- 0.5 cm(-1) representing sp(3)-bonded carbon. This analysis revealed a FWHM as low as similar to4.3 cm(-1) for the optimum growth conditions of an R = 1.05 and substrate temperatures of 650-750 degreesC. The broad non-diamond carbon component in the 1350cm(-1) to 1650cm(-1) range was deconvoluted into three distinct Gaussian peaks at 1355 +/-1.5cm(-1) 1470 +/- 7.5cm(-1), and 1550 +/- 4.0cm. These peaks remained in the same relative proportion regardless of the processing conditions, and the total area of the non-diamond peaks was found to correspond linearly with the background luminescence. A relative comparison of the diamond and non-diamond carbon was used to qualitatively estimate the diamond film phase purity.