A Computational Venture into the Realm of Laminated Borides and their 2D Derivatives

Abstract

Daily life in modern society is highly dependent on many different materials and techniques for manipulating them, and the technological forefront is constantly pushed further by new discoveries. Hence, materials science is a very important field of research. The field of 2D materials is a rather young subfield within materials science, sprung from the realisation of the first 2D material graphene. 2D materials have, due to their 2D morphology, a very high surface-to-weight ratio, which makes them clearly attractive for applications where the material surface is an important characteristic, such as for energy storage and catalysis. The family of 2D materials called MXenes contrast to other 2D materials through the methods used to synthesise them. Traditionally, 2D materials are mechanically exfoliated from a 3D bulk structure in which the 2D sheets are only kept together by weak van der Waals forces, while MXenes are instead chemically exfoliated by selectively etching the A element from a member of the MAX phase family. A MAX phase is a hexagonal nanolaminated crystal structure on the formula Mn+1AXn, with n = 1 − 4, where the M indicates one or several transition metals, A stands for an “A element”, commonly a metalloid, and X stands for C or N. After etching away the A element from the MAX phase the Mn+1Xn-layers are left, making up the MXene. MXenes thus show an unusual structural and chemical diversity, and the composition spectra is even further expanded by atoms and small molecules, called surface terminations, attaching to the MXene surface upon etching. These terminations in turn also influence the properties of the MXene. Hence, the MXene family shows great potential for property tailoring towards many different applications. Besides MAX phases there are many other nanolaminated materials which can not be mechanically exfoliated like graphene, and the natural question arises: can other nanolaminated materials be etched into completely new 2D materials? This thesis is concerned with the so called MAB phases – a family of laminated materials similar to MAX phases, but with B instead of C or N – and their 2D derivatives from a compu-