A first-principles study of Group IV dimer chains on Si(100)

Abstract

First-principles calculations of Pb and Sn dimer chains on Si(100) are performed up to 0.5 ML coverage, including the possibility of mixed PbSi and SnSi dimer chains. Simulated STM images for pure Pb and Sn dimer chains are found to have a better agreement with experimental observations. In order to understand whether the STM images are influenced by the dynamics of the dimer chains, we have studied the rocking barriers of dimer chains on Si(100). The rocking frequencies of Pb dimer chains are found to be small, therefore the dynamics of the Pb dimer chain will have little effects on the STM images. However, a dynamical effect may have to be taken into account for Sn dimer chains due to their higher rocking frequency. We have also studied the tendency of intermixing of Ge, Pb, and Sn with Si on a Si(100) surface. Our analysis shows that the formation of mixed dimers depends on the source of Si atoms available for Pb and Sn to carry out the intermixing. Mixed dimer chains are energetically more favorable than the pure dimer chains only when Si atoms are codeposited with Pb or Sn, or the dimer chains are formed near step edges of the Si(100) substrate. A mechanism similar to Ge intermixing with Si on Si(100) is not favored by Pb and Sn, and there is a lack of a favorable channel for Pb and Sn to intermix with Si to form mixed dimers when Si is not deposited epitaxially in experiments, which can hinder the formation of PbSi and SnSi dimer chains.