Direct observation of an ordered step surface reconstruction on Au(111) by scanning tunneling microscopy

Experiments with a scanning tunneling microscope (STM) are reported which include the first surface topographic images of Au(111), cleaned and annealed in ultrahigh vacuum. The STM system used for this work includes in situ sample manipulation for sample cleaning, annealing and characterization. Topographs with very large atomically flat (111) regions are obtained and no corrugation on the scale of about 0.1 Å is observed. Some single atomic steps are observed. Surprisingly, ordered arrays of single steps are observed over a large region. These represent a type of surface reconstruction whose repeat period agrees with values derived from previous LEED, TEM and ion scattering measurements. These results represent the first critical information about the surface topography of the Au(111) surface.     

Nonstochastic behavior of atomic surface diffusion on Cu(111) down to low temperatures

Atomic diffusion is usually understood as a succession of random, independent displacements of an adatom over the surface's potential energy landscape. Nevertheless, an analysis of molecular dynamics simulations of self-diffusion on Cu(111) demonstrates the existence of different types of correlations in the atomic jumps at all temperatures. Thus, the atomic displacements cannot be correctly described in terms of a random walk model. This fact has a profound impact on the determination and interpretation of diffusion coefficients and activation barriers.     

Self-assembly and growth of manganese phthalocyanine on an Au（111） surface

Self-assembly and growth of manganese phthalocyanine (MnPc) molecules on an Au(111) surface is investigated by means of low-temperature scanning tunneling microscopy. At the initial stage, MnPc molecules preferentially occupy the step edges and elbow sites on the Au(111) surface, then they are separately adsorbed on the face-centered cubic and hexagonal closely packed regions due to a long-range repulsive molecule—molecule interaction. After the formation of a closely packed monolayer, molecular islands with second and third layers are observed.     

Spin-polarized surface states on Fe-deposited Au(111) surface: A theoretical study

We have studied electronic structure of Fe-deposited Au(111) by performing ab initio density functional theory calculations. We find that the magnetic moment on the deposited Fe layer is enhanced as compared to that in bulk iron. We observe a large number of new states on the Fe-deposited surface — one of which is in the majority spin channel having similar dispersion to that on the clean surface, and others in the minority spin channel. The effective mass of electrons in surface states near the Fermi level increases on Fe deposition. The electronic properties are found to be insensitive to the stacking of near-surface layers. We need to use very thick slabs in our calculations to avoid splitting of surface states due to spurious interactions between the two surfaces of the slab. Using the local density of states profiles for different surface states, we conclude that in scanning tunneling microscope experiments one can detect two of the surface states — one in the majority channel below the Fermi level, and another in the minority channel appearing just above the Fermi energy. We compare our results to those from scanning tunneling spectroscopy experiments.     

Electrocompression of the Au(111) surface layer during Au electrodeposition

In situ grazing-incidence x-ray diffraction studies of reconstructed Au(111) electrodes in aqueous electrolyte solutions are presented, which reveal a significantly increased compression of the Au surface layer during Au electrodeposition as compared to Au(111) surfaces under ultrahigh vacuum conditions or in the Au-free electrolyte. The compression increases towards more negative potentials, reaching 5.3% at the most negative potentials studied. It may be explained within a simple thermodynamic model by a release of potential-induced surface stress.     

STM study of selenium adsorption on Au(111) surface

Adsorption of chalcogen atoms on metal surfaces has attracted increasing interest for both the fundamental research and industrial applications. Here, we report a systematic study of selenium(Se) adsorption on Au(111) at varies substrate temperatures by scanning tunneling microscopy. At room temperature, small Se clusters are randomly dispersed on the surface. Increasing the temperature up to 200℃, a well-ordered lattice of Se molecules consisting of 8 Se atoms in ringlike structure is formed. Further increasing the temperature to 250℃ gives rise to the formation of Se monolayer with Au(111)-3~(1/2) ×3~(1/2) lattices superimposed with a quasi-hexagonal lattice. Desorption of Se atoms rather than the reaction between the Se atoms and the Au substrate occurs if further increasing the temperature. The ordered structures of selenium monolayers could serve as templates for self-assemblies and our findings in this work might provide insightful guild for the epitaxial growth of the two-dimensional transition metal dichalcogenides.     

Chlorine chemisorption and surface chloride formation on Au(111)

The adsorption-desorption properties of the gold(111)-chlorine system have been investigated. Thermal desorption experiments following chlorine adsorption at 298 K indicated two desorption processes: the high temperature peak (ΔH = 217 kJmol^?1) showed desorption of equal numbers of molecukr and atomic chlorine species, while the lower temperature peak (ΔH = 140 kJmol^?1) was due to the desorption of Cl₂ only. Chlorine adsorption led to a maximum work function change of +0.5 V and electron-stimulated desorption proceeded with constant cross-section (1.4 × 10¹⁸ cm²), until all chlorine had been removed from the surface These observations are consistent with the immediate formation of a surface chloride (AuCl₃) during chlorine adsorption on Au(111) at 298 K without the intervention of an initial adsorbed overlayer.     

Surface diffusion of Cr adatoms on Au(111) by quantum tunneling

The low-temperature surface diffusion of isolated Cr adatoms on Au(111) has been determined using nonperturbing x rays. Changes in the x-ray magnetic circular dichroism spectral line shape together with Monte Carlo calculations demonstrate that adatom nucleation proceeds via quantum tunneling diffusion rather than over-barrier hopping for temperatures <40K. The jump rates are shown to be as much as 35 orders of magnitude higher than that expected for thermal over-barrier hopping at 10 K.     

Kinetics of the diffusion of an impurity atom on a fcc(111) surface

An analytical study of the migration of an embedded impurity atom over a solid surface under the influence of the diffusion of vacancies is performed. The case of small surface coverages of both vacancies and impurity atoms is considered. It is shown that the realization of multiple collisions of a single impurity atom with vacancies imparts a Brownian character to its motion. At long times, the dependence of the mean square displacement on the time differs little from the linear, whereas the spatial density distribution is close to the Gaussian, features that makes it possible to introduce a diffusion coefficient. For the latter, an analytical expression is derived, which differs from the product of the diffusion coefficient of vacancies and their relative concentration only by a numerical factor. The dependence of the diffusion coefficient of an impurity atom on the ratio of the frequency of its jumps to the frequency of jumps of vacancies is analyzed. In the kinetic mode, when the frequency of jump ω of the imurity atom is small, the diffusion coefficient of the impurity depends linearly on ω, whereas in the opposite case, a saturation occur and its dependence on the frequency of jumps of the impurity atom disappears.     

Understanding formation of molecular rotor array on Au(111) surface

The motion of single molecules on surfaces plays an important role in nanoscale engineering and bottom-up construction of complex devices at single molecular scale. In this article, we review the recent progress on single molecular rotors self-assembled on Au(111) surfaces. We focus on the motion of single phthalocyanine molecules on the reconstructed Au(111) surface based on the most recent results obtained by scanning tunneling microscopy (STM). An ordered array of single molecular rotors with large scale is self-assembled on Au(111) surface. Combined with first principle calculations, the mechanism of the surface-supported molecular rotor is investigated. Based on these results, phthalocyanine molecules on Au (111) are a promising candidate system for the development of adaptive molecular device structures.     

Direct observation of surface diffusion and atomic interactions on metal surfaces

The unique attributes of the field ion microscope permit the direct observation of surface diffusion of single atoms and simple atomic clusters on perfect crystal planes. A brief review of the principles and techniques of such studies is presented along with a collection of much of the existing experimental data. Emphasis is placed on more recent work such as the diffusion of adatoms under the influence of a driving force, the kinetics of cluster formation and dissociation, and how the interatomic force between two atoms on a surface is related to the diffusion parameters and the pair distribution function.     

Organizing C60 molecules on a nanostructured Au(111) surface

We have studied, using scanning tunneling microscopy, the adsorption of C₆₀ molecules on a nanostructured Au(111) surface consisting of artificially created two-dimensional cavities. These cavities, one atomic layer deep, are found to be effective as molecular traps at room temperature. Gold atoms at step edges are found to respond to the adsorption of C₆₀ molecules and gross faceting is observed for steps connected with R30° oriented C₆₀ molecular islands. Structural models are proposed to establish the step structures related to all three types of molecular islands.