Lower thermal conductivity of body centered cubic carbon (C14): a comparative study with diamond.

In recent years, the material preparation technology has ushered into a stage of rapid development, increasingly more carbon materials are found to display superior properties, making them suitable for designing nano-scale devices. Within the applications of electronic devices, a considerable amount of consumed energy has to be converted into heat; thus the efficiency of heat transport inside these devices can largely determine their overall performance. Decent elucidations of the heat transport mechanisms within low-dimensional materials will be helpful to achieve thermal management control of the related devices and furthermore, to improve their conversion efficiency. It is well understood that the heat transport within these kinds of materials is largely associated with their structural features. In this study, we focused on a novel material, body centered cubic carbon (C14), which is composed of sp3 hybridized carbon atoms. Such a novel material displays superior electronic properties; however, its thermal properties remain to be investigated. In order to systematically evaluate the practical applicability of this novel material, first-principles calculations were employed to systematically solve its structure; furthermore, its thermal conductivity, phonon dispersion spectrum, phonon properties, Grüneisen parameters, scattering phase space and mechanical properties were all described in detail. We found that C14 performs well in heat transport; and via systematical comparison with another allotrope, diamond, its transport mechanism was further summarized. We hope the physical insights provided by this study could serve as theoretical support for nano-scale device design.

Computational Evaluation of Al-Decorated g-CN Nanostructures as High-Performance Hydrogen-Storage Media.

Density functional theory (DFT) calculations were employed to solve the electronic structure of aluminum (Al)-doped g-CN and further to evaluate its performance in hydrogen storage. Within our configurations, each 2 × 2 supercell of this two-dimensional material can accommodate four Al atoms, and there exist chemical bonding and partial charge transfer between pyridinic nitrogen (N) and Al atoms. The doped Al atom loses electrons and tends to be electronically positive; moreover, a local electronic field can be formed around itself, inducing the adsorbed H2 molecules to be polarized. The polarized H2 molecules were found to be adsorbed by both the N and Al atoms, giving rise to the electrostatic attractions between the H2 molecules and the Al-doped g-CN surface. We found that each 2 × 2 supercell can adsorb at most, 24 H2 molecules, and the corresponding adsorption energies ranged from -0.11 to -0.31 eV. The highest hydrogen-storage capacity of the Al-doped g-CN can reach up to 6.15 wt%, surpassing the goal of 5.50 wt% proposed by the U.S. Department of Energy. Additionally, effective adsorption sites can be easily differentiated by the electronic potential distribution map of the optimized configurations. Such a composite material has been proven to possess a high potential for hydrogen storage, and we have good reasons to expect that in the future, more advanced materials can be developed based on this unit.