Au Reconstruction Research Articles

In situ x-ray reflectivity and diffraction studies of the Au(001) reconstruction in an electrochemical cell.

In situ x-ray specular reflectivity and glancing-incidence-angle x-ray-diffraction measurements have been performed at the Au(001) surface in a 0.01M ${\mathrm{HClO}}_{4}$ solution under potential control in an electrochemical cell. At -0.4 V versus an Ag/AgCl electrode, the gold surface exhibits a hexagonal reconstructed layer with a mass density 21% greater than the underlying bulk layers. The reconstruction disappears above 0.5 V, and the excess atoms form a new atomic layer with a density corresponding to 22% of a bulk layer. The reconstruction fully recovers below -0.3 V.

High resolution low energy electron diffraction characterization of reconstructed Au(001) surfaces

The reconstruction of Au(001) surfaces was characterized by using high resolution low energy electron diffraction through an accurate measurement of the Bragg positions of the diffraction beams. The reconstruction hexagonal overlayer was determined to have in-plane contractions of ∼ 3.6% and ∼ 19% along two orthogonal directions of the square lattice of the underlayer. These contractions result in a (28 × 5) superlattice. The step density and direction were estimated from the angular profiles of integer order beams. This finite terrace width and step direction select the preferred growth of one of the orientational reconstruction domains. From the measurement of angular profiles and relative intensities of superlattice beams, the alignment of the 28-fold reconstruction direction with the step edges was deduced.

Determination of the geometric structure of alkali induced reconstructions of Au(110)

The Au(110) surface can be made to reconstruct by the adsorption of alkali metals. We report the results of structural studies of two such reconstructions, namely the cesium induced (1 × 3) surface and the potassium induced c(2 × 2) structure.

An in situ study of reconstructed gold electrode surfaces by second harmonic generation

Second harmonic generation (SHG) was employed to monitor in situ the potential-induced reconstruction of Au(111) and Au(100) electrodes. Rotating the sample by 360° about the surface normal yields for the unreconstructed Au(111)-(1×1) surface the well-known threefold symmetry pattern in the SHG intensity, while Au(100)-(1×1) shows no rotational anisotropy, as expected for C 4v symmetry. For the reconstructed Au(111)-(1×23) surface, however, an additional onefold symmetry pattern is observed, which allows in situ monitoring of the structural transition between (1×1) and (1×23). For the reconstructed Au(100)-(5×20) surface, a threefold symmetry pattern was found.

On the stability of reconstructed gold surfaces in an electrochemical cell

It is demonstrated by a combined electrochemical and LEED, RHEED and AES study that reconstructed Au(100), (111) and (110) surfaces are stable in aqueous electrolytes under certain potential conditions. For example, the Au(100)-(5 × 20) surface is maintained only in a potential region where no specific adsorption of anions occurs. This observation may account for the difficulties in finding the reconstruction when adventitious impurities like chloride are present in solution. The Au(110)-(1 × 2) surface is much more resistant to anion adsorption, and in perchloric acid oxide formation is required to remove the (1 × 2) superstructure. The potential-induced reconstruction of Au(100), which was inferred earlier from electroreflectance measurements, was confirmed directly by electron diffraction.

Structure of the Cs-induced (1 x 3) reconstruction of Au(110).

The clean Au(110) surface exhibits a (1\ifmmode\times\else\texttimes\fi{}2) reconstruction with an atomic arrangement corresponding to a missing-row (MR) structure. By depositing Cs on this surface, we have formed two new structures with (1\ifmmode\times\else\texttimes\fi{}5) and (1\ifmmode\times\else\texttimes\fi{}3) low-energy electron diffraction (LEED) patterns, corresponding to Cs coverages of (3\ifmmode\pm\else\textpm\fi{}2)% and ${(5}_{\mathrm{\ensuremath{-}}2}^{+6}$)% of a monolayer, respectively. The superstructures therefore correspond to further substrate reconstructions. We have used medium-energy ion scattering (MEIS) with channeling and blocking to study the structure of the (1\ifmmode\times\else\texttimes\fi{}3) reconstruction. Our results show a clear indication of a missing-row-type structure which displays long and narrow (111) microfacets that go deep into the crystal. The most important surface distortions are an inwards relaxation of the first layer by 22%, and a large buckling in the third layer. Other subsurface rearrangements are such that they produce a slight smoothing of this highly corrugated structure. These results are discussed in the light of recent theoretical calculations of the total energy of the fcc (110) surfaces. In these calculations the relative stability of the different surface geometries is dominated by the s-p electrons at the surface. For the Cs/Au system, a charge transfer from the alkali to the Au substrate alters the energy distribution of these electrons and shifts the equilibrium geometry from the (1\ifmmode\times\else\texttimes\fi{}2) MR to the observed (1\ifmmode\times\else\texttimes\fi{}3) structure.

Study of metal surfaces by scanning tunneling microscopy with field ion microscopy

The reconstruction of Au and Ni surfaces has been studied by scanning tunneling microscopy (STM). The correlation between the tunneling tip geometry, observed by field ion microscopy, and the resultant STM image leads to an operational definition of STM resolution. New structural models for Ni(110)–H and Ni(110)–Au surfaces are proposed.

Potential-induced surface reconstruction of Au(100)

We have found that at the metal-electrolyte interface an Au(100)−(1×1) surface can reconstruct already at room temperature into its hexagonal (5×20) form, when a negative potential is applied. The activation barrier for reconstruction is obviously lowered significantly by charging the electrode negatively, which can be rationalized within the model of Heine and Marks by the accumulation of excess electrons at the surface. The transition (1×1)→(5×20) depends strongly on the electrode potential and, to some extent, on the electrolyte composition. In 5 mM H 2SO 4 at −0.4 V versus SCE, the Au(100)−(1×1) surface can reconstruct almost completely into (5×20) within a few minutes. The kinetics of this potential-induced surface reconstruction has been investigated and its mechanism will be briefly discussed.

Profile and plan-view imaging of reconstructed surface structures of gold

Profile and plan-view high resolution images of reconstructed surface structures of gold are described. Profile images are sensitive to displacements of surface atoms normal to the surfaces. They also show displacements parallel to the surface but only along one direction perpendicular to the electron beam direction. The plan-view images, on the other hand, show displacements parallel to the surfaces. Thus, the effectiveness of the two methods depends on the characteristics of the reconstruction. Profile imaging is effective for studies of the reconstructions of Au(001)5 × 28 and Au(110)2 × 1) , but plan-view images are effective for studies of the reconstruction of Au(111)22 × 1 . In this sense the methods are complementary.

Switching of the Au(110) reconstruction by Ag deposition and alloying

Switching of the Au(110) reconstruction by Ag deposition and alloying

Switching of the Au(110) reconstruction by Ag deposition and alloying

Two- and three-dimensional alloy surfaces of the Ag-Au(110) system have been studied by evaporation of Ag onto a Au(110) substrate. Annealing up to 200°C caused surface diffusion and ordering, while annealing to 250°C or higher induced bulk diffusion with the formation of a three-dimensional alloy. At 20°C, Ag caused streaking of the LEED pattern, followed by a (1×1) structure with high background. Heating to 150–200°C allowed the observation of the sequence 1×2→streaks→1×3→streaks→1×1. The results are interpreted within the framework of the “glue” model, in which classical many-body forces play a dominant role.

The structure of H 2SO 4 monolayers on Au (111)

Au (111) electrodes have been emersed from sulphuric acid solutions and their surfaces studied in UHV by LEED, RHEED and AES. It is shown that, after evacuation, sulphuric acid forms an ordered two-dimensional overlayer on Au (111), the structure of which bears some relation to that of crystalline H 2SO 4. This H 2SO 4 overlayer, which is independent of the emersion potential, does not remove the (1 × 23) surface reconstruction of Au (111).

Summary Abstract: The elastic properties and the reconstruction of Au and Pt (011) surfaces

Summary Abstract: The elastic properties and the reconstruction of Au and Pt (011) surfaces

The reconstruction and relaxation of Ir(110) and Au(110) surfaces

We have applied medium-energy ion scattering using channeling and blocking to study the Au(110) and Ir(110) surfaces. Both surfaces are composed of rows of close-packed atoms which, when atomically clean, exhibit (1×2) reconstructions, i.e., a doubling of the unit cell in the direction perpendicular to the rows. We find that the Au(110) reconstruction corresponds to a missing row structure with a large contraction of the first interplanar spacing. We directly show that the contraction is accompanied by deep, multilayer distortions of the surface. The clean Ir(110) surface is similar to Au(110), characterized by a missing row reconstruction but with a smaller contraction of the first interplanar spacing. We have also examined the phase transition on Ir(110) from a (1×2) structure to an oxygen stabilized (1×1) structure. For the two phases, the yield of backscattered ions shows drastic differences only observable in the blocking directions, differences that could not have been observed in a conventional ion channeling experiment.

Structure and dynamics of periodic and randomly distributed surface features by high resolution helium atom scattering

The scattering of helium atoms from surfaces has recently been methodically improved so as to make feasible new, high resolution studies of surface structures and vibrations. Examples are presented on structural studies of Au(111) reconstruction which reveal structures with a lattice spacing of 64 Å and provide evidence for soliton domain walls. Other experiments on rare gas physisorbed layers show new buckling structures of the overlayers. Inelastic scattering from clean surfaces yields information on surface phonon dispersion curves, and this is illustrated by two recent studies of the Pt(111) and Si(111) 2×1 clean surfaces and of physisorbed rare gases on a Pt(111) surface. Other new experiments measure the size and structure of single defects (adsorbed molecules and steps) on an atomic scale from the observed interference patterns. Finally the use of helium atom scattering to detect low frequency adsorbate vibrations in the meV range is illustrated for chemisorbed CO molecules on Pt(111).

Simulation of Au(100) reconstruction by use of the embedded-atom method.

The embedded-atom method of Daw and Baskes is used to calculate the reconstruction of the Au(100) surface. The state of minimum surface energy for a 5 x 5 unit cell is attained by adding five atoms to the surface layer, resulting in a 1 x 5 reconstruction giving a slightly buckled quasitriangular surface with 20% higher areal atomic density than the truncated surface. These results are compared with experiment and with the recent calculation of Ercolessi, Tosatti, and Parrinello. The experimental results and both calculations agree semiquantitatively.

Au(100) reconstruction in the glue model

Using a classical many-body force model (the “glue” hamiltonian) carefully optimized to reproduce a large variety of properties of gold, we have undertaken a study of the reconstructed Au(100) surface. Molecular dynamics (MD) is used as a tool for searching the lowest surface energy configuration of 12-layer slabs with variable cell sizes. The denser, nearly triangular topmost layer previously discussed with smaller MD cells is found to relax into a subtle (34 × 5) pattern involving a two-dimensional lattice of “point” solitons. We give a thorough description of the resulting in surface structure—including multilayer relaxations—and of its energetics at T = 0. Our results compare favourably with existing data for Au(100) and particularly with STM micrographs.

Au(100) reconstruction in the glue model

Au(100) reconstruction in the glue model

Structure of Au(110) determined with medium-energy-ion scattering.

Results of a study of the Au (110) reconstruction using medium-energy-ion scattering with channeling and blocking are reported. The data show clear and direct evidence for a missing-row model, unequivocally demonstrate that the first-layer spacing undergoes a large contraction, and show the presence of distortions in deeper layers. This model is similar to one derived from analysis of low-energy electron-diffraction data, but differs qualitatively with conclusions from x-ray scattering and transmission electron diffraction.

A neon scattering study of the structure of the reconstructed Au(110) surface

Neon and He scattering from the (1 × 2) reconstruction of Au(110) shows that the surface is strongly corrugated in the [001] azimuth and weakly corrugated in the [1 1 0] azimuth. A classical analysis of the double maxima of lobular scattering observed with neon beam in the [001] azimuth and their angular shift with incident angle and energy was carried out. The results are in good agreement with the missing row model but do not agree with any of the other models for the surface structure which have been suggested to date. Coupled-states calculations are reported for the He-scattering data. Again the results support the missing row model. In order to obtain even qualitative agreement with the data it was necessary to use a soft-wall potential in both the classical and quantum calculation.