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Nanocrystalline
Diamond: Baokang Bi, Jes Asmussen, and Brage Golding |
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The mechanical properties of nanocrystalline diamond (NCD) are poorly known, whereas single crystal diamond possesses the largest elastic modulus of any known material and consequently the highest sound speed. We have grown thick films of nanocrystalline diamond, with average grain size 30 nm. In contrast to standard CVD polycrystalline diamond growth, nanocrystalline diamond is grown under low hydrogen conditions (typically 2% of the gas mixture). The resulting films are the largest area, highest uniformity NCD films yet grown. We have investigated the propagation of surface acoustic waves (SAWs) from 0.5-1.0 GHz on ZnO/nanocrystalline diamond/Si multilayers. Surface waves are generated by piezoelectric ZnO sputtered onto the diamond subsequent to patterning the interdigital electrodes by photolithography. We have studied several dispersive SAW modes that result from different ZnO thicknesses, propagating waves over 1-5mm path lengths on NCD and polycrystalline diamond. We have discovered NCD modes with velocities greater than 10,000 m/s, the same as for single crystal diamond. Thus NCD surface waves are particularly attractive for microwave filters since their large wavelength allows the use of photolithography in fabricating GHz devices, no polishing is required because of the smooth NCD surfaces, and the material is elastically isotropic.
References: "Surface Acoustic Wave Devices Based on Nanocrystalline Diamond",
B. Bi, B. Golding, W.S. Huang, and J. Asmussen, 2001 U.S. Patent application
by Michigan State University. "Surface Acoustic Waves on Nanocrystalline Diamond," B. Bi , W.-S. Huang, J. Asmussen, and B. Golding, Diamond and Related Materials, in press, 2002.
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