Vibrational Properties and Specific Heat of Ultrananocrystalline Diamond: Molecular Dynamics Simulations

• Published in: Journal of physical chemistry. C Vol. 115; no. 44; pp. 21691 - 21699
• Main Authors: Adiga, Shashishekar P, Adiga, Vivekananda P, Carpick, Robert W, Brenner, Donald W
• Format: Journal Article
• Language: English
• Published: American Chemical Society 10.11.2011
• Subjects: C: Nanops and Nanostructures
• ISSN: 1932-7447; 1932-7455
• DOI: 10.1021/jp207424m

Ultrananocrystalline diamond (UNCD) has become a widely studied material with many potential applications in nanotechnology due to its attractive thermal, mechanical, and chemical properties. While several experimental techniques including Raman spectroscopy have been used to characterize the structural and dynamical properties of UNCD, a detailed understanding of the vibrational dynamics at the atomic level is still lacking. Here, using molecular dynamics simulations, we investigate the structure and dynamics of UNCD to elucidate the role of the grain boundary and interior atoms in detail. Our study considers a UNCD model of 4 nm average grain size, constructed using the Voronoi method. We analyzed the local structure and vibrational properties of the grain boundary and interior atoms. Further, we computed the specific heat of UNCD as a function of temperature from the vibrational spectra. We find that the specific heat of UNCD shows enhancements of approximately 20% over that of single-crystal diamond at 300 K. The excess specific heat in UNCD in comparison to single-crystal diamond is found to be maximum at approximately 350 K. The resolution of the specific heat according to the local structure shows that the excess specific heat arises predominantly from the grain boundaries.