Optical characterization and electronic doping of atomic chains on vicinal Si(111)-Au surfaces

The adsorption of gold on flat and stepped Si(111) surfaces induces regular and spatially-dense nanostructure arrays, through formation of single or multiple atomic Au chains within the terraces as well as rows of Si dangling bonds and honeycomb structures at the step edge [1]. Changes in the vicinal angle are well known to determine the surface structural motifs: the terrace width [1] and step morphology [2], the presence or absence of adatoms [3], the chain structure and metallicity [3], spin polarisation at the step edge [4]. Nonetheless, the relationship between these parameters is complicated. The need to perform precise atomistic simulations in close connection with a range of experimental techniques is clear from the ongoing controversy over the basic geometry of several such systems [5]. One technique that offers precise microscopic insight is reflectance anisotropy spectroscopy (RAS), which is particularly sensitive to the intrinsic 1D nature of these Au-stabilized systems. [6] In this presentation we will demonstrate how careful simulations of RAS experiments [6,7] using density functional theory provides direct insight into the surface reconstruction geometry (step morphology and buckling, Si/Au stoichiometry) and electronic structure (chain metallicity, adatom doping) across a range of similar systems. [8,9]. In particular we will demonstrate the ability of RAS to probe the delicate interplay between charge distribution at the step edge, adatoms, and gold chains, and when carried out in tandem with hydrogen doping, how it offers a novel route for tuning the unique properties of these systems. [7] [1] F. Himpsel et al, J. Phys.: Cond. Mat 13, 11097 (2001) [2] N. McAlinden and J. F. McGilp, Euro. Phys. Letters 92, 67008 (2010) [3] S.C. Erwin et al, Phys. Rev. B 80, 155409 (2009) [4] S.C. Erwin and F. J. Himpsel, Nature Commun. 1:58 (2010). [5] T. Abukawa and Y. Nishigaya, Phys. Rev. Lett. 110, 036102 (2013); S. Kwon and M. Kang, Phys. Rev. Lett. 113 086101 (2014); J. Kautz, M.W. Copel, M. S. Gordon, R. M. Tromp, and S. J. van der Molen, Phys. Rev. B 89, 035416 (2014). [6] N. McAlinden and J. F. McGilp, J. Phys. Condens. Matter 21, 474208 (2009) [7] C. Hogan, E. Speiser, S. Chandola, N. Esser, J. Aulbach, J. Schafer, in preparation. [8] C. Hogan, N. McAlinden, J. McGilp, Phys Stat Sol B 249, 1095-1104 (2012) [9] C. Hogan, E. Ferraro, N. McAlinden, J. F. McGilp, Phys. Rev. Lett. 111, 087401 (2013).