Evolution of geometric and electronic structure in ultrathin In films on Cu(001)

Abstract

We have studied the initial growth and the evolution of the atomic and electronic structure of ultrathin In films on Cu(001) at 110--300 K by scanning-tunneling microscopy, low-energy electron diffraction, Auger-electron spectroscopy, work-function measurement, and angle-resolved ultraviolet photoelectron spectroscopy. While the deposition at 110--200 K results in the In adsorption on Cu(001) terraces, In atoms deposited at 300 K are initially incorporated into the topmost layer of the substrate. At coverages between 0.26 and 0.35 ML $(1 \mathrm{ML}=1.53\ifmmode\times\else\texttimes\fi{}{10}^{15} {\mathrm{cm}}^{\ensuremath{-}2}),$ surface dealloying occurs and In atoms form an overlayer on top of the Cu(001) terrace. A variety of phases, including seven long-range-ordered ones, are formed depending on the deposition temperature (110--300 K) and the In coverage (0--1 ML). When In is deposited at 110--200 K, the surface shows two superstructures, which are metastable and transform irreversibly to other phases upon annealing. When In is deposited onto Cu(001) at 300 K, the surface exhibits three distinct superstructures different from those obtained at 110--200 K, and two of them undergo reversible phase transitions upon the temperature increase. For In deposition at 300 K, a surface resonance band is observed, whose intensity is highest around the completion of a monolayer, indicating that the resonance has a large amplitude at the In-Cu interface. Coverage-dependent photoemission data show that the resonance splits off from the Cu $4sp$ band at $\ensuremath{\sim}0.3 \mathrm{ML}$ and shows a nearly free electron like dispersion similar to that of the Cu $4sp$ band. A similar interface resonance state is observed for the surface grown at 110 K, while the dispersion is modulated due to the unmatched interface structure. The mechanism of formation of the surface resonance and its relevance to the evolution of the geometric structure is discussed.