Fabrication and characterization of a single monolayer NiSi2 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 NiSi2 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/NiSi2/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 NiSi2 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/NiSi2/Si(1 1 1) system demonstrates a metallic-type conductivity down to 2.0 K, which is the lowest temperature accessed in the experiment.