Formation of the BiAg2 surface alloy on lattice-mismatched interfaces

Abstract

We report on the growth of a monolayer-thick BiAg 2 surface alloy on thin Ag films grown on Pt(111) and Cu(111). Using low energy electron diffraction (LEED), angle resolved photoemission spectroscopy (ARPES), and scanning tunneling microscopy (STM) we show that the surface structure of the 1 3 ML Bi/x-ML Ag/Pt(111) system (x 2) is strongly affected by the annealing temperature required to form the alloy. As judged from the characteristic (• LEED pattern, the BiAg 2 alloy is partially formed at room temperature. A gentle, gradual increase in the annealing temperatures successively results in the formation of a pure BiAg 2 phase, a combination of that phase with a (2 × 2) superstructure, and finally the pure (2 × 2) phase, which persists at higher annealing temperatures. These results complement recent work reporting the (2 × 2) as a predominant phase, and attributing the absence of BiAg 2 alloy to the strained Ag/Pt interface. Likewise, we show that the growth of the BiAg 2 alloy on similarly lattice-mismatched 1 and 2 ML Ag-Cu(111) interfaces also requires a low annealing temperature, whilst higher temperatures result in BiAg 2 clustering and the formation of a BiCu 2 alloy. The demonstration that the BiAg 2 alloy can be formed on thin Ag films on different substrates presenting a strained interface has the prospect of serving as bases for technologically relevant systems, such as Rashba alloys interfaced with magnetic and semiconductor substrates.