ナノ結晶CVDダイヤモンド薄膜の弾性定数と内部組織の関係(<小特集>高精度な新非破壊検査技術)

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This paper studies the relationship between elastic constants and microstructure of chemical vapor deposition (CVD) diamond thin films deposited by the hot-filament CVD method with a small amount of N_2 impurities for decreasing the grain size. The size is of the order of 10nm, which we call nanocrystalline diamond (NCD). The N_2 flow rate was 0.0-1.0 sccm and the film thickness was about 12μm. Three elastic constants C_<11>, C_<12>, and C_<66> were measured by resonant ultrasound spectroscopy coupled with laser-Doppler interferometry (RUS/LDI). The diagonal elastic constants, C_<11>, C_<66>, and E_1 of CVD diamond thin films decrease with the increase of the N_2 flow rate. However, the off-diagonal elastic constant C_<12> increases with the increase of the N_2 flow rate. The micromechanics model we propose consistently explains the enhancement of C_<12> when thin pancake-shaped graphite inclusions on the grain boundaries are introduced, whose c axes are oriented along the minor direction randomly distributed in isotropic diamond matrix. Thus, this result indicates that oriented graphitic phase exists at the grain boundaries in NCD films.
2006-12-25