Physical and Thermoelectric Properties of 2D B$_4$C Nanosheets

TL;DR

This study uses DFT simulations to explore the properties of 2D B$_4$C nanosheets, revealing their metallic nature and potential for thermoelectric applications, which differs from the bulk semiconductor form.

Contribution

It is the first detailed theoretical investigation of the structural, electronic, and thermoelectric properties of 2D B$_4$C nanosheets, guiding future experimental synthesis.

Findings

B$_4$C nanosheets can be cleaved with low formation energies.

Nanosheets exhibit metallic behavior unlike bulk B$_4$C.

Seebeck coefficients remain comparable to bulk across temperatures.

Abstract

Boron carbide (B$_4$C) has been well studied both theoretically and experimentally in its bulk form due to its exceptional hardness and use as a high temperature thermoelectric. However, the properties of its two-dimensional nanosheets are not well established. In this paper, using van der Waals corrected density-functional theory (DFT) simulations, we show that the bulk B$_4$C can be cleaved along different directions to form B$_4$C nanosheets with low formation energies. We find that there is minimal dependence of the formation energies on the cleavage planes and surface terminations. Whilst the density of states of the bulk B$_4$C indicate that it is a semiconductor, the B$_4$C nanosheets are found to be predominantly metallic. We attribute this metallic behaviour to a redistribution of charges on the surface B-C bonds of the films. The Seebeck coefficients of the the B$_4$C films remain comparable to those of the bulk, and are nearly constant as a function of temperature. Our results provide guidance for experimental synthesis efforts and future application of B$_4$C nanosheets in nanoelectronic and thermoelectric applications.