Polarity governs atomic interaction through two-dimensional materials

Abstract

Transparency of two-dimensional (2D) materials to inter-molecular interactions has been an unresolved problem. Previous researchers found that water droplets interact with underlying substrates through graphene, as if the graphene is "transparent". However, graphene's transparency determined by droplet wetting angles has been controversial. Recently, precise atomic alignment between epitaxial films and substrates through monolayer graphene has been discovered in a GaAs/graphene/GaAs structure. This finding experimentally confirms the existence of remote atomic interaction through graphene. However, the mechanism of remote interaction through 2D materials at atomic-scale and its relationship with the bonding chemistry of 2D materials have not been fully understood.

This thesis reports a systematic understanding of remote atomic interaction through two-dimensional (2D) materials, unveiling the general rules for atomic potential "transparency" that can be universally applied to any 2D material. Our findings indicate that: (1) the degree of ionicity of 3D materials determines the potential field penetration depth, and (2) the iconicity of 2D material interlayer governs the degree of screening of the field from the 3D materials. Thus, pure ionically-bonded materials can substantially transmit their potential through 2D materials. We demonstrate that such ionic bonding potential can penetrate through three layers of graphene as it has no polarity. However, the potential can be screened even by one layer of hexagonal Boron Nitride (hBN) with strong ionic bonding character.

This discovery will enable the growth of all types of materials across the periodic table including group I-VII, II-VI, and 111-V as single-crystalline forms on 2D materials followed by exfoliation to form freestanding single-crystalline thin films. These thin films can then be fabricated to produce electronic and photonic devices. At the same time, the cost of the substrates during manufacturing can be dramatically reduced since the substrates can be reused without any post-release treatment after exfoliation.