Imaging the Surface and the Interface Atoms of an Oxide Film on Ag{111} by Scanning Tunneling Microscopy: Experiment and Theory (original) (raw)
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Applied Physics Letters, 1995
In this letter the observation by scanning tunneling microscopy of a Au(111) surface reconstruction induced by prolonged annealing of gold films in oxygen (pO2=1 bar) at high temperature (T=800 °C) is reported. At the atomic scale, the surface is characterized by a (√3×√3)R30° surface structure. In addition, the surface exhibits a long-range ordered hexagonal superstructure with a periodicity of 80 Å and a corrugation of about 0.5 Å. Convincing evidence is presented that this surface morphology is induced by chemisorption of atomic oxgyen at the Au(111) surface.
2010
We present here a scanning tunnelling microscopy (STM) study on O 2 adsorption at Ag(110) at T = 175 K, i.e. in the temperature range between the onset of O 2 dissociation and the formation of the added row reconstruction. In agreement with previous studies at lower surface coverage, we observe several structures forming upon O 2 dissociation, including Ag-O complexes randomly distributed on the surface. We suggest that the presence of the latter structures, characterized by a large cross section for low energy electrons, can account for the marked decrease of the surface electron reflectivity and for the corresponding increase of the diffuse elastic intensity previously reported in a HREELS investigation of the same system.
Theory of scanning tunneling microscopy of oxygen adsorption on Ag(110) surface
Solid State Communications
Oxygen adsorption on Ag(110) surface has been investigated by means of firstprinciples total-energy and force calculations for repeated-slab geometries within the local density approximation (LDA). The added row model composed of oxygen atom and silver atom has been believed to be one of the most realistic models. We have already obtained the optimized geometry of the added row model. Using the optimized positions, the simulation of STM images and STS spectra has been performed based on the Bardeen's perturbation theory. Compared with the experimental data, the theoretical results seem to show a fairly good correspondence. Recently, Besenbacher et.al, have published their STM
Structure of Au on Ag(110) studied by scanning tunneling microscopy
Journal of vacuum science & technology. B, Microelectronics and nanometer structures: processing, measurement, and phenomena: an official journal of the American Vacuum Society
The epitaxial growth of Au on Ag(110) has been studied by scanning tunneling microscopy up to 8 ML. In the submonolayer range the results show that gold atoms are intermixed with the silver atoms in the top two layers. Above 1 ML a two‐dimensional fingerlike growth gives rise to anisotropic three‐dimensional islands of gold, which appear to be thermal equilibrium structures. Above 5 ML, the gold overlayer forms a (1×3) reconstruction which is manifested as double rows of atoms growing along [11¯0]. The development of this reconstruction is followed as a function of coverage.
Structural transformations on an oxidized Ag(111) surface
JETP Letters, 2017
The structure of the Ag(111) surface after the adsorption of molecular oxygen at a temperature of 300 K is studied by low-temperature scanning tunneling microscopy. It is established that local surface oxide is formed at the first stage of adsorption. The subsequent adsorption of O results in the appearance of new objects with a size of 3-8 Å and a height of 1.0-1.5 Å on the Ag(111) surface, which form quasi-ordered structures with increasing degree of coating. The heating of the system obtained up to 500 K leads to a structural transition resulting in the formation of single islands of the (4 4) phase on the surface. Surface structures are identified by a simulation based on the density functional theory.
Scanning tunnelling microscopy of MgO ultrathin films on Ag(001)
Physical Review B, 2002
The morphology of ultrathin epitaxial MgO layers reactively grown on Ag͑001͒ was investigated by using scanning tunnelling microscopy. In the initial deposition stage Ag atoms are partially removed from the substrate and form extended monoatomic islands leaving vacancy islands in the substrate itself. On individual substrate terraces Ag is thereafter found at three atomic levels. For submonolayer deposition MgO condensates in form of small islands of monoatomic height, located on the original substrate, on the protruding Ag islands and on the vacancy islands as well. The largest Ag͑001͒ fractional coverage by monoatomic MgO islands is 70%. A limited amount of MgO bilayers or trilayers has also been detected ͑about 1% fractional coverage͒. At the nominal deposition of 1 ML flat, squared and connected MgO domains of about 10 nm in width form, with edges along the ͓110͔ directions. The actual substrate fractional coverage is about 85% and the occurrence of bilayers and multilayers becomes significant ͑about 30 and 5% fractional coverage, respectively͒, resulting in the formation of three-dimensional pyramidal MgO islands.
Photoelectron diffraction study of the Ag(110)-(2×1)-O reconstruction
Surface Science, 2000
The structure of the (2×1)-O adsorption phase on Ag(110) has been determined using scanned-energy mode photoelectron diffraction. The oxygen atoms have been found to occupy the long-bridge site and are almost coplanar with the top layer of silver atoms. The best agreement between multiple-scattering theory and experiment has been obtained for a missing-row (or equivalently an 'added-row') reconstruction in which the first-to-second and secondto-third interlayer spacings are 1.55±0.06 Å and 1.33±0.06 Å , respectively. Alternative buckled-row and unreconstructed surface models can be excluded.
Adsorption ofO2on Ag(111): Evidence of Local Oxide Formation
Physical Review Letters, 2016
The atomic structure of the disordered phase formed by oxygen on Ag(111) at low coverage is determined by a combination of low-temperature scanning tunneling microscopy and density functional theory. We demonstrate that the previous assignment of the dark objects in STM to chemisorbed oxygen atoms is incorrect and incompatible with trefoil-like structures observed in atomic-resolution images in current work. In our model, each object is an oxidelike ring formed by six oxygen atoms around the vacancy in Ag(111).
Characterization by scanning tunneling microscopy of the oxygen induced restructuring of Au(111
Surface Science, 1996
The morphology of the Au( 111 ) surface exposed to oxygen under high pressure ( Po2 = 1 bar) and high temperature (500 < T < 800°C) during a prolonged period of time (between 1/2 and 24 h) was investigated by scanning tunneling microscopy (STM). At the atomic scale the surface exhibits a (v/3 x x/~)R30 ° structure which is ascribed to atomic oxygen being strongly chemisorbed at the gold surface. In addition, on a larger scale, a long-range superstructure with hexagonal symmetry and a periodicity varying between 60 and 80 A is observed. This superstructure is interpreted as a moir6 type pattern arising from the periodic height modulation induced at the surface by a small lattice mismatch and a slight rotation between the topmost two gold layers. The long-range superstructure exhibits local distortions which can be explained by the high sensitivity of moir6 patterns to the exact lattice mismatch and to the rotation angle between the two layers. The observation of small reconstructed areas forming on the Au(lll) surface upon chemisorption of oxygen indicates that the restructuring proceeds via a nucleation and growth process.