Vicinal surfaces for functional nanostructures

Abstract

Vicinal surfaces are currently the focus of research. The regular arrangements of atomic steps on a mesoscopic scale reveal the possibility to functionalize these surfaces for technical applications, e.g. nanowires, catalysts, etc. The steps of the vicinal surface are well-defined defect structures of atomic size for nucleation of low-dimensional nanostructures. The concentration and therefore the coupling between the nanostructures can be tuned over a wide range by simply changing the inclination angle of the substrate. However, the coupling of these nano-objects to the substrate is just as important in controlling their electronic or chemical properties and making a functionality useable. On the basis of stepped insulating films, these aspects are fulfilled and will be considered in the first part of this review. Recent results for the epitaxial growth of wide bandgap insulating films (CaF(2), MgO, NaCl, BaSrO) on metallic and semiconducting vicinal substrates (Si(100), Ge(100), Ag(100)) will be presented. The change of the electronic structure, the adsorption behavior as well as the kinetics and energetics of color centers in the presence of steps is discussed. The successful bridging of the gap between the atomic and mesoscopic world, i.e. the functionalization of vicinal surfaces by nanostructures, is demonstrated in the second part by metal adsorption on semiconducting surfaces. For (sub)monolayer coverage these systems have in common that the surface states do not hybridize with the support, i.e. the semiconducting surfaces are insulating. Here I will focus on the latest results of macroscopic transport measurements on Pb quantum wires grown on vicinal Si(111) showing indeed a one-dimensional transport behavior.

Tailoring band gaps of insulators by adsorption at surface defects: Benzoic acids on NaCl surfaces

“…14, 17, and 50͒ and CO 2 . 51,52 The electronic structures of ionic materials are also dependent on the properties of the steps on the surfaces. 53 Hence in this section we will present the adsorption energetics and electronic properties of benzoic acids adsorbed on stepped NaCl͑100͒ surface, specifically at the ͓001͔-and the ͓011͔-oriented steps.…”

“…The computed band gap of the ͓001͔ stepped NaCl͑100͒ surface is 7.46 eV, which is just marginally larger than that of the flat NaCl͑100͒ surface, in agreement with experiments. 52 …”

Magnetic surface nanostructures

“…Stepped and kinked surfaces are commonly employed as templates for the synthesis of quasi-one-dimensional systems [84,85], such as atomically thin metal stripes and chains of atoms [43,86,87,74,88,89], structured sesquilayers [90], cluster chains [9,91] and dot arrays [92,80]. The template effect is based on the higher binding energy at the steps, in comparison to terrace sites.…”

“…Depending on the system, atoms can attach at the bottom or at the top of the step edge. If the atoms have sufficiently high diffusivity along the step edges then row-by-row step flow growth is observed during MBE growth [84]. By controlling the adlayer coverage, stripes of controllable width down to monatomic chains can be easily prepared [74].…”

Influence of small miscuts on self-ordered growth of Ge nanoislands

“…Until recently, the influence of misorientation of the substrate vicinal surface on epitaxial growth was not specially attended [12]. The step edges of atomic layers specify the modulation of non-uniform deformation fields in the deposited buffer layer [13], which, in turn, becomes the pattern for the ordered formation of nanoisland arrays.…”