Review—Electronic Properties of 2D Layered Chalcogenide Surfaces and Interfaces grown by (quasi) van der Waals Epitaxy

Abstract

The growth of two-dimensional layered chalcogenides on two- or three-dimensional substrates, named (quasi) van der Waals epitaxy, has been pioneered by the group of A. Koma at Tokyo University in 1985. The passive nature of the van der Waals surface is important in energy converting interfaces as solar cells and photoelectrochemical cells. For those reasons the two-dimensional materials have intensively been studied by us in the early 90s of the last century. The growth of different 2D/2D, 2D/3D and 3D/2D heterostructures has been studied with an emphasis on the electronic structure of the materials and their interfaces, which have been characterized using photoelectron spectroscopy and are reviewed in this contribution. Our work includes a discussion of the coupling of electronic states across the interfaces, which influences the growth behavior and determines energy band alignment. The weak electronic coupling allowed the first experimental determination of the band structure of a single layer of a 2D chalcogenide, namely WS2. We also review the electronic structure of a GaSe half-sheet terminated Si(111) surface, which provides an ideal platform for the integration of 2D materials with Si microelectronics.