共查询到20条相似文献,搜索用时 31 毫秒
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.
A mechanism behind the saturation of the photocurrent and occurrence of negative differential photoconductivity in Mn4Si7-Si〈Mn〉-Mn4Si7 and Mn4Si7-Si〈Mn〉-M heterojunctions is found. Mn4Si7-Si〈Mn〉-Mn4Si7 and Mn4Si7-Si〈Mn〉-M structures are studied with a model of back-to-back diodes. Photocurrent-voltage characteristics are taken at high constant and pulsed applied biases. It is found that the nonlinearity of the photocurrent-voltage characteristics and photoconductivity kinetics are due to the quenching of photoconductivity by Joule self-heating. 相似文献
4.
《中国物理快报》2020,(2)
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
5.
本文基于有相互作用的结构件的概念,对Si(111)7×7结构模型的稳定性进行研究。利用紧束缚法,计算了各种结构件的形成能及其相互作用能。由这些结构件可灵活地构成各种大单胞的表面结构并对其进行总能计算,而避免了大工作量的计算。对Si(111)5×5和7×7DAS模型,我们得到其表面能分别为-0.467eV和-0.477eV,与Qian和Chadi的结果很接近。并指出,Harrison提出的7×7吸附原子模型和Binnig等人提出的7×7吸附原子-空位模型都是不稳定的。 相似文献
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7.
《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
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11.
《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
12.
《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
13.
《Physics letters. A》1988,130(3):166-170
A complete determination of individual atomic coordinates for the Si(111) 7×7 surface has been carried out by dynamical low-energy electron diffraction. The dimer-adatom-stacking fault (DAS) model, after large vertical and lateral relaxations, was found to produce calculated spectra in remarkably good agreement with the data. Atoms in the faulted half of the unit cell are raised from those of the unfaulted half. Adatoms at corner sites are higher than those at center sites. 相似文献
14.
《Surface science》1989,209(3):L144-L150
A gold-deposited area of 0.1 mm diameter and several monolayers thick on the Si(111)7 × 7 surface is annealed at 700° C. In the diffusion process, the concentric oscillatory rings of the √3 × √3 and 5 × 1 structures are formed in an area of 0.4 mm diameter and observed by the dark field image in scanning LEED microscopy in an ultra-high vacuum. The diffusion is apparently independent of surface steps and crystallographic orientation from a macroscopic viewpoint. The formation of the periodic rings with the different surface structures and coverages is interpreted by using the surface diffusion equation and regarded as an intermediate phase prior to achieving the equilibrium state. 相似文献
15.
《Surface science》1990,227(3):L125-L129
16.
采用包络函数方法对生长在Ge03Si07(001)衬底上势垒区δ掺杂量子阱Ge03Si07/Si/Ge03Si07的电子能带结构及子带间光吸收特性进行了自洽的计算.对光吸收系数与量子阱的阱宽、δ掺杂位置及δ掺杂密度间的变化关系进行了讨论.最后对由高浓度的二维电子气的退极化效应所引起的频率位移进行了研究 相似文献
17.
The initial stages of the formation of iron silicides in the Fe/Si(111)7 × 7 system in the course of solid-phase epitaxy are investigated using high-resolution photoelectron spectroscopy (~100 meV) with synchrotron radiation. The spectra of the Si 2p core and valence-band electrons obtained after deposition of iron coverages of up to 28 monolayers on the surface of the sample and subsequent isochronous annealings at 650°C are measured and analyzed. It is shown that the first to form under Fe deposition is an ultrathin film of the metastable silicide FeSi with a CsCl-type structure, on which a layer of the Fe-Si solid solution with segregated silicon grows. At coverages in excess of 10 monolayers, an iron film grows on the surface of the sample. Annealing of a silicon crystal coated with a Fe layer leads to the sequential formation of two stable silicide phases, namely, the ?-FeSi and β-FeSi2 phases, in the near-surface region of the sample. It is found that the process of solid-phase synthesis of the ?-FeSi phase passes through the stage of transformation of the iron film into the Fe-Si solid solution. 相似文献
18.
I. Ošťádal P. Sobotík J. Mysliveček T. Jarolímek 《Czechoslovak Journal of Physics》1999,49(11):1613-1619
Initial stages of Ag on Si(111)−(7 × 7) surface nucleation were studied at submonolayer coverage. Samples were prepared by
thermal evaporation of Ag from tungsten wire under UHV conditions (p<2.5 × 10−8 Pa). Various deposition rates (0.002–0.1 ML s−1) were used to prepare Ag island films with coverages (0.002–2) ML (1 ML ≈ 7.58 × 1014 atoms cm−2) at room temperature. We observed preferential growth on faulted half unit cells (F cells). At constant coverage both the
island density and ratio of occupied F and U (unfaulted) cells are independent of the deposition rate, which is an evidence
for dominant influence of substrate structure. The preference of nucleation in the F cells against U cells decreases with
the coverage until the ratio is 1:1 for 1 ML Ag film. We have observed that presence of an Ag island in any type of the half
unit cell (F or U) considerably reduces nucleation probability in neighbouring cells. This results in forming of structural
patterns observed among randomly grown Ag-islands which is a new feature found for Ag/Si(111)−(7 × 7) system.
Presented at the VIII-th Symposium on Surface Physics, Třešt’ Castle, Czech Republic, June 28 – July 2, 1999.
This work was supported by the Grant Agency of Charles University — projects GAUK 34/97 and 147/99, by the Grant Agency of
Czech Republic — project GAČR 202/97/1109 and by the Ministry of Education grant VS 97116. 相似文献
19.
《Surface science》2002,496(1-2):43-48
Fluorine etching on the Si(1 1 1)-7×7 surfaces using fluorinated fullerene molecules as a fluorine source has been investigated. At room temperature, adsorbed fluorinated fullerene molecules reacted with the Si(1 1 1)-7×7 surface to create a localized distribution of fluorine on the surface. Nanoscale etch pits were created by annealing at 300 °C, due to the adsorption of the fluorine localized around the C60Fx molecules. Annealing at 400 °C resulted in the delocalized fluorine distribution on the surface and healing of the etch pits, due to the enhancement of the diffusion of both the fluorine and silicon atoms. Subsequent annealing at 500 °C led to desorption of SiF2 reactants formed on the surface. The fluorine diffusion process was found to be an elemental process in the etching because the diffusion of adsorbed fluorines is a key for the formation of the SiF2 species and their subsequent desorption. 相似文献