Few-monolayer Ga film on Si(111): illusive gallenene formation and localization instead of superconductivity

Due to recently reported findings, few-atomic-layer Ga films on Si(111) are a promising system to implement advanced superconducting properties and formation of the gallenene, Ga, analogue of graphene. Motivated by these prospects, we conduct a comprehensive investigation of the Ga/Si(111) system using a set of experimental techniques, including: low-energy electron diffraction (LEED), scanning tunneling microscopy (STM), angle-resolved photoelectron spectroscopy (ARPES), and four-point-probe transport measurements, combined with DFT calculations in the framework of the ab initio random structure searching (AIRSS) technique. On the basis of temperature-dependent LEED and STM data, it is concluded that the gallenene-like STM appearance of the Ga surface is an averaged pattern associated with the fast migration of Ga adatoms. In contrast to the expected superconductivity, ARPES and transport measurements reveal electron localization due to the structural disorder, which makes the system insulating. Si(111) substrates crucially affect the superconducting properties of few-atomic-layer Ga films and formation of the gallenene analogue of graphene.