Growth of Mn on Cu(100) studied by STM: the c(2 × 2) and pgg(4 × 2) ordered surface alloys

Abstract

The structure and growth of managanese on Cu(100) has been studied using scanning tunneling microscopy (STM), Auger electron spectroscopy (AES) and low energy electron diffraction (LEED). Depending on substrate temperature and coverage, either a c(2 × 2) or a pgg(4 × 2) ordered surface alloy is formed. Islands are observed after deposition by STM, contrary to other reports. A c(2 × 2) surface alloy is formed at a coverage of 0.5 monolayer (ML) Mn at room temperature and is present on the terrace as well as on the newly formed islands. This implies that the arriving managanese atoms are directly incorporated into the surface at room temperature by replacement of copper substrate atoms. The so-formed Cu adatoms grow into the monolayer high islands observed by STM. A pgg(4 × 2) structure is found after deposition of ≈ 1 ML Mn at 370 K. We present two models for this pgg(4 × 2) structure based on atomically resolved STM images and LEED observations. In both CuMn alloys, only half the number of atoms present for a completely filled top layer are observed. We assign this to a difference in tunneling probability between Cu and Mn and not just to structural effects such as the buckling of the Mn. The corrugation of the c(2 × 2) structure is very high for metals, between 0.02 and 0.04 nm larger than the calculated buckling of the Mn atoms. Moreover, the step edges of the c(2 × 2) alloy display an even larger corrugation.