Scanning-tunneling-microscope imaging of clean and alkali-metal-covered Cu(110) and Au(110) surfaces

Abstract

A combined experimental and theoretical study of the scanning-tunneling-miscroscope (STM) imaging properties of clean and alkali-metal covered Cu(110) and Au(110) surfaces is presented. The clean surfaces are imaged in the STM experiments as parallel strings of Cu or Au atoms, respectively, vVhich represent the close-packed rows in the topmost layer. For the (1 X 2) missing-row reconstructed Au(110) surface the corrugation amplitude of the reconstruction shows a maximum as a function of tip-sample distance. On the Cu(110) surface, which does not reconstruct spontaneously in its clean state, adsorbed alkali-metal atoms (K, Cs) induce a missing-row reconstruction with the missing substrate metal rows running along the densely packed [110]direction. On both surfaces, adatoms are located in the missingrow furrows. The alkali atoms are usually not visible in the STM picture but, rather, images are obtained typical for the reconstructed metal substrate. For certain tunneling conditions, image inversion is observed. K-covered Au(110)-(1X2) and Cu(110)-(1X2) surfaces exhibit distinct corrugation maxima similar to the clean Au(110)-(1X2) surface, if the tip-sample distance is varied. A theory of scanningtunneling microscopy is applied that accounts for a realistic treatment of the electronic structure of the sample surface. The tunnel current is evaluated using a Green-function technique. In the theory, adsorbed potassium atoms appear transparent on Cu(110) because they substitute for sample metal atoms and are embedded in the first layer of Cu atoms. Therefore, the 4s resonance is centered energetically well below the Fermi level and has only a small spectral weight at the Fermi level. The corrugation maximum and the image inversion are found to be a consequence of the tip-sample interaction.

Theory of long-range forces in AFM and current versus distance curves in STM on Au(111)

“…At these intermediate tip-sample distances the tunnelling electrons are nearly perfectly reflected by the sample and therefore the tunnelling current is significantly reduced compared to its exponential behaviour displayed at larger and smaller distances. The experimentally measured values, reported by Doyen et al [1] on the Au(1 1 0)(1 · 2) missing row reconstructed surface, are in agreement with theory in this distance range.…”

“…Au (1 1 1) In contrast to the expected exponential decay on Au(1 1 1), the variation of the tunnelling con- (*) data on Au(1 1 0)(1 · 2) missing row reconstruction, (+) on K/Au(1 1 0)(1 · 2) at bias voltages U ¼ À550 meV and U ¼ À590 meV, respectively [1]; ()) data for a tungsten tip on Ag(1 1 1) at U ¼ 490 meV [2]. ductance shows a local minimum at intermediate tip-sample distances superimposed on the exponential decrease (cf.…”

“…In the example of the (1 · 2) missing row reconstructed Au(1 1 0) surface in Fig. 1, however, for relative distances beyond 3 A the tunnelling current J ðzÞ varies much faster with the tip-sample separation z compared to the rate of change on the K/Au(1 1 0)(1 · 2) surface at potassium coverage of 0.25 ML [1] and on the Ag(1 1 1) surface [2]. Au(1 1 0)(1 · 2) is a very open surface with each second densely packed row in the [1 1 0] direction missing, exposing thus the (1 1 1) facets.…”

“…Blue stars: data on Au(1 1 0)(1 · 2) missing row reconstruction[1]; black symbols: data on Au(1 1 0)[9]; blue curve: data on Cu(1 1 1)[2]; green curve: data on Ag(1 1 1)[2]. (For the colour coding used in this figure, see the web version of this paper.)Fig.…”

Lithium incorporation into a silica thin film: Scanning tunneling microscopy and density functional theory

“…1,2,4 At intermediate coverage, the alkali atoms often self-assemble into regular arrays on the metal surface in order to maximize their mutual distance. [5][6][7] By this means, the repulsive dipole-dipole interaction and the subsequent layer depolarization are restrained. Already this simple picture, first suggested by Langmuir and Gurney, 8 provides a good description for the general adsorption behavior of alkali atoms on metal surfaces.…”