Correlation of the Raman spectra with the thermal conductivity of a set of diamond wafers prepared by chemical vapor dep
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Albert Feldman Materials Science and Engineering Laboratory, National Institute of Standards and Technology, Gaithersburg, Maryland 20899 (Received 11 January 2000; accepted 23 March 2001)
Raman spectroscopy, at laser excitation wavelengths of 514.5, 785, and 1064 nm, is used to study a set of chemical-vapor-deposited (CVD) diamond wafers of known thermal conductivity . The in-plane thermal conductivity (at 25 °C) of the diamond wafers ranges from 4 to 22 W cm−1 K−1 and represents a wide range of diamond quality. The spectra were obtained from both macro/micro- sampling measurements, examining the top and bottom wafer surface, as well as wafer cross-sections. Discussed are the peak positions and linewidths of the Raman bands and their relation to sp3-bonded diamond and sp2-bonded carbon in the context of diamond quality and perfection, and the effects of wafer heterogeneities. The detailed analysis of the Raman spectra provides a robust correlation with the room-temperature bulk (or macroscopic) thermal conductivity of these samples. The correlation is made through the determination of the band area ratios of the diamond Raman line at 1333 cm−1 to that of the 1550 cm−1 band characteristic of nondiamond carbon impurities. This dependence is most pronounced for the Fourier-transform Raman data obtained with infrared excitation at 1064 nm, due to resonance enhancement, and therefore allows the detection of carbon impurities, especially for high-quality CVD diamond.
I. INTRODUCTION
Diamond deposited by chemical vapor deposition (CVD) has become a material of great interest to a number of emerging technologies.1,2 CVD diamond is now available commercially, in various forms, as a material of high quality. With respect to a number of performance properties it is virtually indistinguishable from highgrade single-crystal natural diamond (type IIa). For thermal and optical applications, this material is produced as wafers typically 10 cm to 30 cm in diameter and up to 1 mm thick. The research efforts of many groups focus on the comprehensive characterization of this polycrystalline diamond in all its physical forms, as thin films, coatings, and window material.3–5 Among the many attractive materials properties of CVD diamond are its optical and thermal properties as they have, in part, been responsible for the remarkable growth in various sectors of CVD diamond technology. Presently, the a)
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applications of polycrystalline thin diamond films and wafers are mainly limited only by their cost as the quality of production material steadily improves. For CVD diamond to reach its full potential as an unmatched heatsink and optical material, production processes and quality control methods require relatively inexpensive and unambiguous approaches to assess the quality of CVD diamond. Raman spectroscopy is one of the most commonly used investigative techniques for all types of carbon materials, including CVD diamond, diamo
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