Showing papers by "Bei Peng published in 2003"

Fracture strength of ultrananocrystalline diamond thin films—identification of Weibull parameters

Abstract: The fracture strength of ultrananocrystalline diamond (UNCD) has been investigated using tensile testing of freestanding submicron films. Specifically, the fracture strength of UNCD membranes, grown by microwave plasma chemical vapor deposition (MPCVD), was measured using the membrane deflection experiment developed by Espinosa and co-workers. The data show that fracture strength follows a Weibull distribution. Furthermore, we show that the Weibull parameters are highly dependent on the seeding process used in the growth of the films. When seeding was performed with microsized diamond particles, using mechanical polishing, the stress resulting in a probability of failure of 63% was found to be 1.74 GPa, and the Weibull modulus was 5.74. By contrast, when seeding was performed with nanosized diamond particles, using ultrasonic agitation, the stress resulting in a probability of failure of 63%, increased to 4.13 GPa, and the Weibull modulus was 10.76. The tests also provided the elastic modulus of UNCD, whi...

Mechanical Properties of Ultrananocrystalline Diamond Thin Films Relevant to MEMS/NEMS Devices

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.

Strength of Ultrananocrystalline Diamond Thin films – Identification of Weibull Parameters

Abstract: The fracture strength of ultrananocrystalline diamond (UNCD) thin films, grown by microwaveplasma- enhanced chemical-vapor deposition (PECVD), was measured using the membrane deflection experiment (MDE) developed by Espinosa and coworkers. The data show that UNCD fracture strength appears to follow a Weibull distribution. Furthermore, we show that the Weibull parameters are highly dependent on the seeding process used in the growth of the films. When seeding was performed with micron-size diamond particles, using mechanical polishing of the substrate, the stress, resulting in a probability of failure of 67%, was found to be 1.74 GPa, and the Weibull modulus was 5.74. By contrast, when seeding was performed with nano-size diamond particles, using ultrasonic agitation, the stress, resulting in a probability of failure of 67%, increased to 4.13 GPa and the Weibull modulus was 10.76. The investigation highlights the role of microfabrication defects on material properties and reliability, as a function of seeding technique, when identical PECVD chemistry is employed. The parameters identified in this study are expected to aid the designer of MEMS/NEMS devices employing UNCD films.