To obtain polycrystals with large and uniform grain size, diamond particles have been selectively formed on a SiO 2 dot-patterned Si substrate using plasma-assisted CVD. After pretreatment by abrasive powders to increase diamond nucleation densities on both Si and SiO2, an Ar beam is used to irradiate obliquely the pretreated surface. As a result, diamond can no longer nucleate on Si, it nucleates only on one edge of the SiO2 dots and grows over the Si substrate to about 10 #m. Well defined polycrystals having equal grain sizes have been obtained. The role of the Ar beam irradiation on Si and on SiO2 is also discussed.
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