Surface analysis of ultraprecise polished chemical vapor deposited diamond films using spectroscopic and microscopic techniques

Abstract

Chemical vapor deposited (CVD) diamond films of varying crystallographic orientations and sizes were thermochemically polished on steel plates. The sizes of the grains constituting the films used in this work ranged between 10 and 100 μm. Images of the surface morphologies of the films were obtained by the scanning electron microscope (SEM) before and after polishing. A stylus profilometer was used to determine the surface roughness (arithmetic mean deviation) of the as-grown diamond films. The average surface roughness was found to be about 30 μm on the growth side and about 7 μm on the substrate side. Polishing for several hours at temperatures between 750 and 1000 °C thinned the surface roughness down to about 1.3 and 1.5 nm on the growth and substrate sides, respectively, of the film as measured by the atomic force microscope. Raman spectroscopy revealed low energy nondiamond carbon lines in the frequency range between 200 and 700 cm−1 on polished surfaces of optical graded diamond films in addition to the usual graphite bands situated between 1350 and 1580 cm−1. Photoluminescence and cathodoluminescence spectra of both polished and unpolished films revealed nitrogen and silicon as the only detectable defect centers in the films. The Raman spectra of polished optical grade films also contained lines that are attributed to molecular nitrogen complexes (N2) at a frequency of 2438 cm−1, carbon–hydrogen (C–Hn) stretching vibrations at frequencies ranging from 2700 to 3200 cm−1 and molecular hydrogen complexes (H2) at a frequency of 4350 cm−1.