Fabrication and characterization of a single monolayer NiSi ₂ sandwiched between a Tl capping layer and a Si(1 1 1) substrate

Abstract Single monolayers of various materials (e.g. graphene, silicine, bismuthene, plumbene, etc) have recently become fascinating and promising objects in modern condensed-matter physics and nanotechnology. However, growing a monolayer of non-layered material is still challenging. In the present study, single monolayer NiSi ₂ on Si(1 1 1) was grown for the first time, using Tl monolayer as a surfactant and stabilizer. The structural and electronic properties of the Tl/NiSi ₂ /Si(1 1 1) system were characterized using a set of experimental techniques, including low-energy electron diffraction, scanning tunneling microscopy, angle-resolved photoelectron spectroscopy, in situ four-probe transport measurements, and also first-principles density-functional-theory calculations. Nickel atoms were found to reside in the interstitial sites inside the first silicon bilayer of bulk-like-terminated Tl/Si(1 1 1)1 1 surface, with the thallium initial positions remaining almost unchanged. The electronic band structure of the system is clearly metallic, and contains electron and hole pockets related to the Tl and NiSi ₂ layers, respectively. The surface-state bands are spin-split due to the presence of a Tl layer with a strong spin–orbit coupling. Our transport measurements proved that the Tl/NiSi ₂ /Si(1 1 1) system demonstrates a metallic-type conductivity down to 2.0 K, which is the lowest temperature accessed in the experiment.