Mechanical properties of ultrananocrystalline diamond thin films relevant to MEMS/NEMS devices |
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Authors: | H D Espinosa B C Prorok B Peng K H Kim N Moldovan O Auciello J A Carlisle D M Gruen D C Mancini |
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Institution: | (1) Department of Mechanical Engineering, Northwestern University, 60208-3111 Evanston, IL;(2) Materials Science and Experimental Facilities Divisions, Argonne National Laboratory, 60439 Argonne, IL |
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Abstract: | The mechanical properties of ultrananocrystalline diamond (UNCD) thin films were measured using microcantilever deflection
and membrane deflection techniques. Bending tests on several free-standing UNCD cantilevers, 0.5 μm thick, 20 μm wide and
80 μm long, yielded elastic modulus values of 916–959 GPa. The tests showed good reproducibility by repeated testing on the
same cantilever and by testing several cantilevers of different lengths. The largest source of error in the method was accurate
measurement of film thickness. Elastic modulus measurements performed with the novel membrane deflection experiment (MDE),
developed by Espinosa and co-workers, gave results similar to those from the microcantilever-based tests. Tests were performed
on UNCD specimens grown by both micro and nano wafer-seeding techniques. The elastic modulus was measured to be between 930–970
GPa for the microseeding and between 945–963 GPa for the nanoseeding technique. The MDE test also provided the fracture strength,
which for UNCD was found to vary from 0.89 to 2.42 GPa for the microseeded samples and from 3.95 to 5.03 for the nanoseeded
samples. The narrowing of the elastic modulus variation and major increase in fracture strength is believed to result from
a reduction in surface roughness, less stress concentration, when employing the nanoseeding technique. Although both methods
yielded reliable values of elastic modulus, the MDE was found to be more versatile since it yielded additional information
about the structure and material properties, such as strength and initial stress state. |
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Keywords: | Thin films nanomaterials experimental techniques fracture size effects |
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