Phonon mean free path in few layer, two-dimensional hexagonal structures

Gholivand, Hamed
Two-dimensional materials such as graphene and few layer hexagonal Boron Nitride (h-BN) have been the center of attention in the last decade. These materials provide anisotropic and exclusive properties making them ideal candidates for the modern electronic and optoelectronic applications. With the enhancements in fabrication techniques and the ability to separate thin layers their popularity is continuously increasing. Understanding the thermal properties of these materials is necessary to make better devices. Phonon mean free path (MFP) is one of the most thermal properties that determines the limits of ballistic-diffusive thermal transport in micro and nanoscale domains. In this study thermal properties, specifically the phonon MFP behavior, of few layer graphene, h-BN, and composite graphene/h-BN structures were studied after obtaining the phonon dispersion of each material. After, finding the thermal properties of discrete phonon modes, a plot of accumulated thermal conductivity with respect to phonon MFP of phonons is obtained to understand the ballistic-diffusive limits of in such structures. Bulk structures of graphene and h-BN were also analyzed for comparison purposes and it was observed that single layer structures will experience ballistic effects more since they have considerably higher MFP than their bulk counterparts. 


Phonon Mean Free Path in Few Layer Graphene, Hexagonal Boron Nitride, and Composite Bilayer h-BN/Graphene
Gholivand, Hamed; Donmezer, Nazli (Institute of Electrical and Electronics Engineers (IEEE), 2017-09-01)
In this study, ab-initio calculations were performed to obtain the phonon dispersions of seven different structures: single layer graphene, bilayer graphene, graphite, single layer h-BN, bilayer h-BN, bulk h-BN, and finally composite bilayer h-BN/graphene. Using these dispersions specific heat, group velocity, and single mode relaxation times of phonons were obtained to calculate their thermal conductivities, and mean free paths at room temperature. Calculated variables were used to understand the effects o...
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Citation Formats
H. Gholivand, “Phonon mean free path in few layer, two-dimensional hexagonal structures,” M.S. - Master of Science, Middle East Technical University, 2017.