Thickness induced metal–nonmetal transition in ultrathin electrodeposited Ge films

Elemental Ge has been electrodeposited from 35 mM GeCl4 solution in 1-butyl-3-methyl imidazolium hexafluoro phosphate ([BMIm]PF6) on Si(1 1 1):H substrate at room temperature and studied by in situ electrochemical scanning tunneling microscopy (EC-STM) and scanning tunneling spectroscopy (STS). The initial stage of electrodeposition showed roughening of the surface with amorphous deposits all over the substrate. An ordered (2 × n) reconstruction was found to form in the 1–2 ML coverage regime. The remarkable observation, which is reported here for the first time is a metal-to-nonmetal transition as the thickness of the deposited Ge layer on Si(1 1 1):H increased from 2 ML to about 3 nm.