The interfacial layer between layered chalcogenides and GaAs(111)B: The case of MBE-grown <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML"> <mml:msub> <mml:mi>NiTe</mml:mi> <mml:mn>2</mml:mn> </mml:msub> </mml:math> -GaAs(111)B

Epitaxial thin films of the lamellar transition metal dichalcogenide ${\mathrm{NiTe}}_{2}$ have been grown by molecular beam epitaxy on GaAs(111)B substrates. Using in-plane grazing-incidence x-ray diffraction measurements, we show that two distinct epilayers form during growth: (1) an epitaxial interface contact layer, with a 2D hexagonal lattice structure with in-plane lattice parameter matching the GaAs(111)B surface, and (2) the epitaxial ${\mathrm{NiTe}}_{2}$ thin film. The in-plane lattice constant of the ${\mathrm{NiTe}}_{2}$ film is observed to increase while the out-of-plane parameter decreases, both approaching their bulk values, as the film thickness increases. The interfacial contact layer is ascribed to Te atoms substituting for the upper As atoms of the GaAs(111)B (2x2) surface on exposure to Te at the onset of growth, forming a (1x1) Ga--Te hexagonal contact layer with no dangling bonds, which acts as a quasi-van der Waals substrate. We show that a similar contact layer is seen also in the growth of other Te and Se compounds. The presence of this interfacial contact layer, which seems universal for chalcogenide growth on GaAs(111)B, may have significance for understanding the electronic and optical properties of epitaxial layered materials in contact with the substrate.