We report the transport properties of monolayer and bilayer graphene from first principles calculations and Boltzmann transport theory (BTE). Our resistivity studies on monolayer graphene show Bloch-Grüneisen behavior in a certain range of chemical potentials. By substituting boron nitride in place of a carbon dimer of graphene, we predict a twofold increase in the Seebeck coefficient. A similar increase in the Seebeck coefficient for bilayer graphene under the influence of a small electric field ∼ 0.3 eV has been observed in our calculations. Graphene with impurities shows a systematic decrease of electrical conductivity and mobility. We have also calculated the lattice thermal conductivities of monolayer graphene and bilayer graphene using phonon BTE which show excellent agreement with experimental data available in the temperature range 300-700 K.
The phonon dispersion, density of states, Grüneisen parameters, and the lattice thermal conductivity of single-and multi-layered boron nitride were calculated using first-principles methods. For the bulk h-BN we also report the two-phonon density of states. We also present simple analytical solutions to the acoustic vibrational mode-dependent lattice thermal conductivity. Moreover, computations based on the elaborate Callaway-Klemens and the real space super cell methods are presented to calculate the sample length and temperature dependent lattice thermal conductivity of single-and multi-layered hexagonal boron nitride which shows good agreement with experimental data.
Using combination of Density Functional Theory and Monte Carlo simulation, we study the phase stability and electronic properties of two dimensional hexagonal composites of boron nitride and graphene, with a goal to uncover the role of the interface geometry formed between the two. Our study highlights that preferential creation of extended armchair interfaces may facilitate formation of solid solution of boron nitride and graphene within a certain temperature range. We further find that for band-gap engineering, armchair interfaces or patchy interfaces with mixed geometry are most suitable. Extending the study to nanoribbon geometry shows that reduction of dimensionality makes the tendency to phase segregation of the two phases even stronger. Our thorough study should form an useful database in designing boron nitride-graphene composites with desired properties.
Two-dimensional group IV transition-metal dichalcogenides have encouraging thermoelectric applications since their electronic and lattice properties can be manipulated with strain. In this paper, we report the thermoelectric parameters such as electrical conductivity, Seebeck coefficients, electrical relaxation times, and the mode dependent contributions to the lattice thermal conductivity of ZrX 2 (X = S, Se, Te) from first principles methods. Our calculations indicate that due to tensile strain, the powerfactor increases while simultaneously decreasing the lattice thermal conductivity thus enhancing the thermoelectric figure of merit. Tensile strain widens the bandgap which corresponds to higher powerfactor. The lattice thermal conductivity decreases due to the stiffening of the out-of-plane phonon modes thus reducing the anharmonic scattering lifetimes and increasing the thermoelectric figure-of-merit.
We present first principles study of thermoelectric transport properties of sandwiched heterostructure of Graphene (G)/hexagonal Boron Nitride (BN)/G, based on Boltzmann transport theory for band electrons using the bandstructure calculated from the Density Functional Theory (DFT) based plane-wave method.Calculations were carried out for three, four and five BN layers sandwiched between Graphene layers with three different arrangements to obtain the Seebeck coefficient and Power factor in T ∼ 25 − 400K range. Moreover, using Molecular Dynamics (MD) simulations with very large simulation cell we obtained the thermal conductance (K) of these heterostructures and obtained finally the Figure-of-Merit (ZT ). These results are in agreement with recently reported experimental measurements.
We use density functional theory based first-principles method to investigate the bandstructure and phase stability in the laterally grown hexagonal C x (BN) 1−x , two-dimensional Graphene and h-BN hybrid nanomaterials, which were synthesized by experimental groups recently (Liu et al, Nature Nanotech, 8, 119 (2013)).Our detail electronic structure calculations on such materials, with both armchair and zigzag interfaces between the Graphene and h-BN domains, indicate that the band-gap decreases non-monotonically with the concentration of Carbon. The calculated bandstructure shows the onset of Dirac cone like features near the band-gap at high Carbon concentration (x ∼ 0.8). From the calculated energy of formation, the phase stability of C x (BN) 1−x was studied using a regular solution model and the system was found to be in the ordered phase below a few thousand Kelvin. Furthermore, using the Boltzmann transport theory we calculate the electrical resistivity from the bandstrcture of C x (BN) 1−x at different temperature (T ), which shows a linear behaviour when plotted in the logarithmic scale against T −1 , as observed experimentally..
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