SCANNING TUNNELING MICROSCOPY STUDY OF ALKALI METAL ADSORPTION ON THE Si (001) 2x1 SURFACE (original) (raw)
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Physical Review B, 1998
Using scanning tunneling microscopy ͑STM͒, the process of the Si(111)3ϫ1-Na phase formation induced by Na adsorption on the Si(111)7ϫ7 samples with a terrace width of 3000-6000 Å has been studied. The STM monitoring of the successive stages of the 7ϫ7 to 3ϫ1 transformation enables us to elucidate its main regularities. The redistribution of Si atoms in a top Si͑111͒ layer has been found to play a critical role in the Si(111)3ϫ1-Na growth mode. As a result of the Si redistribution, initially flat Si(111)7ϫ7 terrace converts into the two-level system of the 3ϫ1-Na islands on the 3ϫ1-Na terrace. From the quantitative consideration of the Si mass transport balance, the top Si atom density of the Si(111)3ϫ1-Na phase has been determined to be 4/3 monolayer. ͓S0163-1829͑98͒02535-1͔
Physical Review B, 2003
The adsorption and diffusion of single Pb atoms on Si(111)-(7ϫ7) surfaces have been studied by scanning tunneling microscopy ͑STM͒ and first-principles density functional calculations. STM experiments at temperatures from 100 to 130 K have revealed three regions of preferential adsorption, inside each half-unit cell, as well as real time diffusion events between them. The stable adsorption sites have been determined by firstprinciples calculations and by comparing simulated and measured STM images. The activation barriers for the motion inside the half-unit cells have been calculated and measured experimentally. A very good agreement between calculations and experiments has been found.
Surface Science, 1996
Indium adsorption and desorption processes on Si(111) surfaces were observed in situ by UHV high-temperature STM. By the deposition of In on the Si(lll)7 X 7 surfaces at 380°C, the surface structure changed successively to f3-x 73-, 3~ × 3~ and 4 × 1. The number densities of silicon atoms in the restructuring layers for the v~ X 7~-, ~ × 3~-, and 4 x 1 structures were evaluated to be about 0, 1 and 2 ML, respectively. High-resolution STM images were also taken after the deposition.
Study of adsorption of Al atom on Si(111)7×7 surface
Surface Science, 2004
We investigated adsorption of an Al atom on the Si(1 1 1)7 • 7 surface by using a scanning tunneling microscope. The evaporated Al atom displaced a Si center adatom of the surface; the expelled Si atom diffused inside a half unit cell of the Si(1 1 1)7 • 7 surface. The adsorbed single Al atom, which shows bias voltage dependency, hopped among three center adatom sites inside the half unit cell. Ab initio molecular orbital method was used to investigate the adsorption of Al atom on the surface.
2006
Initial hydrogen adsorption on the Si(1 1 1) 7 · 7 surface was studied by scanning tunneling microscopy (STM) in an ultrahigh vacuum. Room temperature adsorbed hydrogen on the adatom in the 7 · 7 reconstruction led to depression of adatoms in the STM images. The hydrogen uptake curve at the adatom site as a function of hydrogen exposure time was well represented by Langmuir adsorption. No preferential adsorption was seen among four inequivalent adatoms in the 7 · 7 reconstruction. Adsorption of the adjacent center and corner adatoms respectively showed $10% higher adsorption. Even though the number of reacted adatoms in the half unit of the 7 · 7 reconstruction was statistically random, the number of reacted adatoms in the nearest neighbor half unit was enhanced as the number of reacted sites increased in the half unit.
Surface Science, 2000
The initial stages of barium adsorption on Si(100)-(2×1) at room temperature has been studied by ultrahigh vacuum scanning tunneling microscopy (STM ) under both positive and negative sample-bias imaging conditions. Two distinct adsorption sites have been identified by the high-resolution STM images. It was found that, with the substrate held at room temperature, barium atoms can occupy both valley-bridge sites in the trough between silicon dimers and silicon-vacancy sites. It is possible to image the barium atoms at valley-bridge sites with both negative and positive sample bias, revealing filled and empty surface states, respectively. For barium atoms adsorbed at vacancy sites, however, it is only possible to obtain filled-state images, and imaging with positive sample bias will induce the removal of the atom, possibly transferred to the tip, revealing a missing silicon dimer below.
Adsorption geometry of (2×1) Na on Si(001)
Physical Review B, 1990
We have carried out a fully dynamical low-energy electron-diffraction intensity spectra analysis of the Si(001) (2X1)-Na system. We found that at coverage e, =0.5 (i.e. , defined as one Na atom per Si dimer), the Na atoms adsorbed as ordered one-dimensional overlayer chains at quasihexagonal 0 sites proposed by Levine. The vertical distance of the Na atoms above the substrate was 1.85 A, 0 which gave a nearest-neighbor Na-Si bond length of 2.975 A. The "effective" Na radius at this 0
Atomic and electronic structure of the Si(001)2×1–K surface
Surface Science, 2004
The plane-wave pseudopotential density functional theory method has been used to study the Si(0 0 1)2 · 1-K adsorption system for 0.5 and 1.0 monolayer coverage. The minimum energy atomic configuration for 0.5 monolayer coverage was found to correspond to the potassium atom in each 2 · 1 surface unit cell occupying the valley bridge site. A double-layer model was determined to be the optimised geometry of the Si(0 0 1)2 · 1-K chemisorption system for 1.0 monolayer coverage. The geometry of this double-layer model was found to be in good agreement with the current experimental data. A detailed analysis of the electronic structure of this double-layer model has also been performed. The overall dispersion of the occupied and unoccupied surface state bands has been shown to be in excellent agreement with the angle-resolved and inverse photoemission data. The nature and dispersion of the surface states of the doublelayer model in the vicinity of the energy gap provide evidence of strong interactions, both between the two inequivalent potassium atoms in each 2 · 1 surface unit cell, and between these adatoms and the underlying substrate.
Analytical and Bioanalytical Chemistry, 2002
An overview is given on the use of scanning tunneling microscopy (STM) for investigation of the adsorption of hydrogen on Si(111)7×7 both at room temperature and at elevated temperature to finally obtain a hydrogen-saturated surface of Si(111). The initial stages are characterized by high reactivity of Si adatoms of the 7×7 structure. After adsorption of hydrogen on the more reactive sites in the beginning of the adsorption experiments a regular pattern, which is different for room and elevated temperature, is observed for the less reactive sites. In agreement with previous work, local 1×1 periodicity of the rest atom layer and the presence of di-and trihydride clusters is observed for hydrogen-saturated surface. STM has also been used to characterize surfaces from which the hydrogen atoms have been removed by thermal desorption. Finally, tip-induced desorption by large positive sample-bias voltages and by increasing the tunneling current will be described.
STM observations of Ag adsorption on the Si(111)-E3◊E3Ag surface at low temperatures
2000
We have systematically studied the structural evolutions during adsorption of additional Ag atoms on the Si(111)-E3◊E3-Ag surface at 70 K by scanning tunneling microscopy. In the coverages less than 0.02 ML (monolayer), the Ag adatoms distribute randomly as monomers on the E3◊E3-Ag surface. With coverage increase up to 0.1 ML, two-dimensional (2D) nuclei consisting of four Ag adatoms appear, the