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1.
《Surface science》1995,341(3):L1085-L1090
Scanning tunneling microscopy was used to study the morphological evolution of Si(111)-7 × 7 exposed to molecular bromine. Etching at 900 K results in the removal of adatoms and conversion from the 7 × 7 surface to a 1 × 1 Br-terminated structure. Removal is dominated by bilayer step retreat with edge profiles that reflect etching anisotropies. Unique structures attributed to regrowth of Si released during step etching were consistent with six-membered Si rings terminated with Br. The distribution of such rings near the steps reflects the local bonding and etching anisotropies for the steps. Theoretical analyses of these rings terminated with Cl determine bond lengths, bond angles, and charge transfer within the ring.  相似文献   

2.
《Surface science》1995,325(3):L441-L447
Scanning tunneling microscopy (STM) was used to investigate room temperature adsorption and dissociation of SiH4 on Si(111)(7 × 7) surfaces. The data show a pronounced site selectivity for this process. Initially the reaction involves exclusively the corner holes and the adjacent Si adatoms of the (7 × 7) reconstruction, with preferential adsorption of SiH3 groups in the corner holes and of H atoms on one of the adjacent corner adatoms. For higher SiH4 exposures the reactivity of the corner adatoms is significantly reduced, hydrogen adsorption occurs preferentially on the center adatoms. Deposited SiHx groups (x = 2, 3) nucleate now in small clusters on the terraces. A higher density of these SiHx clusters on domain boundaries or at steps indicates a higher reactivity of these defect sites.  相似文献   

3.
4.
《Surface science》1991,247(1):L221-L223
Using a scanning tunnelling microscope we have observed an interesting new fault on the Si(111)-7 × 7 surface, corresponding to an adatom registry shift of 1 bulk unit cell in the [1̄1̄2] direction. We propose a model to account for the structure along the fault.  相似文献   

5.
《Surface science》1996,367(2):L47-L53
Scanning tunneling microscopy (STM) is used to study surface diffusion of a special type of point defects at Si(111)-7 × 7 surfaces. These defects survive even after annealing up to 1250°C. They appear darker than Si adatoms at the tunneling biases ranging from −3 to +3 V, but they are not true vacancies. We found that these vacancy-like defects (hereafter, we refer to them as pseudo-vacancies) are not caused by adsorption of major contaminants in the vacuum chamber, nor by dopants. We also observed migration of pseudo-vacancies between nearest neighboring Si adatom sites at temperatures above 500°C. Most of the jumps are within a half of the 7 × 7 unit cell. Thousands of STM images were recorded from 520 to 610°C and the activation energies and frequency factors were determined. Varying the tunneling current produces almost no effect on the diffusion, but varying the scanning speed produces a small effect.  相似文献   

6.
Schottky contacts were prepared by evaporation of silver on H-terminated Si(111) surfaces at room temperature. The Si(111)H-(1×1) surfaces were obtained by wet-chemical etching in buffered hydrofluoric acid. The zero-bias barrier heights and the ideality factors, which were determined fromI/V characteristics measured with these contacts, were found to be linearly correlated. This plot gives a zero-bias barrier height of 0.74 eV for an ideality factor of 1.01 which is obtained for image-force lowering of the barrier only. The barrier heights observed here equal the one found with Ag/Si(111)-(1×1) contacts. They were prepared by Ag evaporation onto clean Si(111)-(7×7) surfaces at room temperature and subsequent heat treatments. The present result is explained by the desorption of the hydrogen adatoms during the deposition of Ag and the existence of a (1×1)-structure at the Ag/Si(111) interface.  相似文献   

7.
8.
《Surface science》1989,217(3):L430-L434
Si(111)7 × 7 surfaces were exposed to hydrogen atoms and changes of the surfaces during the exposure and subsequent annealing were in-situ observed by ultrahigh vacuum reflection electron microscopy. At room temperature the structure transformed to the so-called δ−7 ×7 structure which gave superlattice reflections mainly along lines which connect the neighboring fundamental reflections. The surface images did not show orientational domains, which indicated that the δ−7 × 7 structure is not composed of three domains of a 7 × 1 structure. Atomic step configurations did not change during the process. This was also the case when the δ−7 × 7 structure transformed to the 7 × 7 structure of the clean surface by annealing above 450 °C.  相似文献   

9.
The interaction of O2 and CO2 with the Si(111)-7 × 7 surface has been studied with X-ray photoelectron spectroscopy (XPS). It was found that both O2 and CO2 molecules can readily oxidize the Si(111)-7 × 7 surface to form thin oxide films. Two oxygen species were identified in the oxide film: oxygen atoms binding to on-top sites of adatom/rest atoms with an O 1s binding energy of ~ 533 eV as well as to bridge sites of adatom/rest atom backbonds at ~ 532 eV. These two oxygen species can be interconverted thermally during the annealing process. Due to the low oxidation capability, the silicon oxide film formed by CO2 has a lower O/Si ratio than that of O2.  相似文献   

10.
Fullerene (C60) molecules on an Si(111)-(7 × 7) surface have been investigated using non-contact scanning non-linear dielectric microscopy (NC-SNDM) under an ultra-high vacuum. The topography, the interface between the C60 molecule and Si adatoms, and the internal structure of the C60 molecules were successfully investigated. For ~ 0 ML and ~ 0.4 ML coverage, both phase reversal sites and sites without phase reversal could be observed in the first order phase (θ1) image. On the other hand, for 1 ML coverage, phase reversal could not be identified. These results indicate that charge transfer only occurred from Si adatoms to C60 molecules at three-fold symmetric sites on the Si(111)-(7 × 7) surface, and the electric dipole moment is reflected in the electronic state of the C60 molecules. The internal structure of C60 molecules was clearly observed in topography by the second order amplitude (A2) feedback signal for 1 ML coverage, reflecting the LDOS originating from the t1u orbital.  相似文献   

11.
We investigate the adsorption of organic molecular semiconductor perylene on(7 × 7) reconstructed Si(111)surface by ultraviolet photoemission spectroscopy.It is observed that seven features that derive from the organic material are located at 0.71,2.24,4.0,5.9,7.46,8.65 and 9.95 eV in binding energy.The theoretical calculation results reveal the most stable adsorption geometry of organic molecule perylene on Si(111)(7 × 7) substrates is at the beginning of deposition.  相似文献   

12.
The diffusion of strontium atoms on the Si(111) surface at room temperature has been investigated using scanning tunnel microscopy and simulation carried out in terms of the density functional theory and the Monte Carlo method. It has been found that the reconstruction of a clean silicon surface with a 7 × 7 structure has a profound effect on the diffusion process. The average velocity of motion of a strontium atom in a unit cell of the 7 × 7 structure has been calculated. The main diffusion paths of a strontium atom and the corresponding activation energies have been determined. It has been demonstrated that the formation of scanning tunnel microscope images of the Si(111)-7 × 7 surface with adsorbed strontium atoms is significantly affected by the shift of the electron density from the strontium atom to the nearest neighbor silicon adatoms in the 7 × 7 structure.  相似文献   

13.
Ge atoms have been deposited on domain-patterned clean Si(111)-(7 × 7) and oxidized Si(111)-(7 × 7) surfaces. Clustering of Ge from the deposited Ge adatoms on these two kinds of surfaces shows contrasting patterns. On the clean Si surface, clustering predominantly occurs on domain boundaries, which include step edges on two sides. This leaves small domains denuded. Ge diffusion length has been estimated from the size of these denuded domains. For large domains, additional clustering is observed within the domains. For the oxidized Si surface, the pattern formation is in sharp contrast with that for the clean Si surface. In this case the domain boundaries remain relatively empty and there is strong clustering within the domains leading to the formation of dense Ge nanoislands within the domains. This contrasting pattern formation has been explained via a reaction diffusion model.  相似文献   

14.
The phase composition, electronic structure, and magnetic properties of ultrathin cobalt films (no thicker than 20 ?) applied on a Si(111)7 × 7 surface at room temperature are studied by high-resolution photoelectron spectroscopy using synchrotron radiation and magnetic linear dichroism. It is shown that, as the cobalt thickness increases, first interface cobalt silicide and then an island (discontinuous) film of silicon-in-cobalt solid solution form on the silicon surface. A metal cobalt film starts growing after the deposition of a ∼7-?-thick Co layer. It is found that the ferromagnetic ordering of the system, which is characterized by surface magnetization, sets in after the deposition of a ∼6-?-Co layer at the stage of Co-Si solid solution formation.  相似文献   

15.
《Surface science》1988,197(3):L269-L272
A two-dimensional Hubbard Hamiltonian is introduced in order to analyse the many-body effects associated with a dangling bond Si(111) 7×7 surface state located at the Fermi energy. Our results indicate that many-body effects can offer an explanation of recently reported experimental data.  相似文献   

16.
We report the formation and local electronic structure of Ge clusters on the Si(111)-7$\times $7 surface studied by using variable temperature scanning tunnelling microscopy (VT-STM) and low-temperature scanning tunnelling spectroscopy (STS). Atom-resolved STM images reveal that the Ge atoms are prone to forming clusters with 1.0~nm in diameter for coverage up to 0.12~ML. Such Ge clusters preferentially nucleate at the centre of the faulted-half unit cells, leading to the `dark sites' of Si centre adatoms from the surrounding three unfaulted-half unit cells in filled-state images. Bias-dependent STM images show the charge transfer from the neighbouring Si adatoms to Ge clusters. Low-temperature STS of the Ge clusters reveals that there is a band gap on the Ge cluster and the large voltage threshold is about 0.9~V.  相似文献   

17.
18.
《Surface science》1993,296(2):L21-L26
The room temperature (RT) adsorption of ammonia (NH3) on Si(111)√3 × √3-Al and Si(111)√3 × √3-Ag surfaces has been studied using LEED and AES. The transformation from Si(111)√3 × √3-Al surface structure to Si(111)1 × 1-(Al, H) upon NH3 exposure has been found to be similar to the previously observed structural transformation induced by exposure in the atomic hydrogen. It has been demonstrated that the transformation is caused by hydrogen atoms which are generated by NH3 dissociation on the Si(111)√3 × √3-Al surface. It has been estimated that about 0.1 ML of ammonia molecules is needed to complete the structural transformation. No interaction of NH3 with the Si(111)√3 × √3-Ag surface has been found. The dissociation of NH3 molecules is believed to be impossible on this surface  相似文献   

19.
In this article we investigate the complex 1D mesoscopic model of adatom diffusion and the evolution of an ordered phase on the substrate surface. The analysis of the theoretical model is compared with the experimental results of the spreading of Au adatoms on Si(111)-(7×7) surface. The steady state solutions and their stability conditions are determined within the concept of the traveling-wave solution. It is shown that the formation of the ordered phase (5×2) and the difference in the diffusion of Au on (7×7) and on (5×2) structure results in a sharp edge of diffusion front which corresponds to the coverage of a saturated (5×2) phase. This edge moves linearly in time and α can be determined by experiment. The system of model equations enables the damped waves solution or temporary evolution of two steps.  相似文献   

20.
We have used scanning tunneling microscopy to probe the effect of oxygen exposure on an ensemble of Ag islands separated by a Ag wetting layer on Si(111)-7 × 7. Starting from a distribution dominated by islands that are 1 layer high (measured with respect to the wetting layer), coarsening in ultrahigh vacuum at room temperature leads to growth of 2-layer islands at the expense of 1-layer islands, which is expected. If the sample is exposed to oxygen, 3-layer islands are favored, which is unexpected. There is no evidence for oxygen adsorption on top of Ag islands, but there is clear evidence for adsorption in the wetting layer. Several possible explanations are considered.  相似文献   

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