Characterization of acoustic Lamb wave propagation in polycrystalline diamond films by laser ultrasonics

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Abstract
The propagation of acoustic Lamb waves in free standing chemical vapor depositedpolycrystallinediamond has been studied using a laser ultrasonic technique. The influence of film morphology, quality, and thickness on the waves has been assessed. Acoustic waves with high velocities in the range 8700–12 200 ms −1 were observed; the lowest values were recorded for films with the lowest crystal quality and highest nondiamond content. High quality films with differing crystal textures or thickness show little variation. The influence of temperature on the dispersion characteristics of Lamb wave propagating in a 50 mm diam polycrystallinediamond wafer were also investigated. Little variation was apparent across the range studied (30–250 °C). Material parameters extracted from the dispersion chracteristics of the acoustic signal together with scanning electron microscopy studies suggested that void, microcrack, and grain boundary density most influences the propagation of low frequency Lamb waves in free standing CVD diamondfilms.

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