First-principles based study of 8-Pmmn borophene and metal interface

Borophene, the lightest member of mono-elemental 2D materials family, has attracted much attention due to its intriguing polymorphism. Among many polymorphs, digitally discovered 8-Pmmn stands out owing to its unique tilted-Dirac fermions. However, the property of interfaces between 8-Pmmn and metal substrates has so far remained unexplored, which has critical importance of its application in any electronic devices. Here, with the help of density functional theory, we show that the unique tilted-Dirac property is completely lost when 8-Pmmn borophene is interfaced with common electrode materials such as Au, Ag, and Ti. This is attributed to the high chemical reactivity of borophene as observed from crystal orbital Hamilton population and electron localization function analysis. In an effort to restore the Dirac property, we insert a graphene/hexagonal-boron-nitride (hBN) layer between 8-Pmmn and metal, a technique used in recent experiments for other 2D materials. We show that while the insertion of graphene successfully restores the Dirac nature for all three metals, hBN fails to do so while interfacing with Ti. The quantum chemical insights presented in this work may aid in to access the Dirac properties of 8-Pmmn in experiments.