共查询到19条相似文献,搜索用时 609 毫秒
1.
2.
3.
用AES和LEFD在700—800℃温度范围内研究了硫在钼(111)表面上的偏析动力学和表面结构。样品加热到800℃硫迅速地偏析到表面上并逐步地取代了表面上的碳。加热到700℃硫没有明显的表面偏析。硫的偏析主要受它的体扩散速率的控制,表面碳的存在也抑制了硫的表面偏析。不同温度下的偏析动力学实验后,分别进行了低能电子衍射实验,观察到钼(111)(31/2×31/2)R30°-硫和1/3(44-99)-硫两种表面结构的低能
关键词: 相似文献
4.
5.
本工作运用运动学低能电子衍射和数据平均方法(KLEED和CMTA),对Si(111)31/2×31/2-Al表面的原子结构进行研究。在大的参数范围内对T4和H模型进行优化后,发现T4模型与实验符合得更好(RVHT=0.158),并且定出Al原子和最上面六层Si原子的位置。该模型中所有键长相对于体内值的变化都在5%以内。它与由全动力学低能电子衍射(DL-EED)分析得到的模型完全相符。这一成功的应用再次表明改进后的KLEED和CMTA方法是一种简单、实用、可靠的表面结构分析手段,用它对一些很复杂的表面进行结构分析已成为可能。
关键词: 相似文献
6.
7.
8.
采用广义梯度近似的密度泛函理论方法计算了3C-SiC(001)-(2×1)表面的原子及电子结构.计算结果表明,3C-SiC(001)-(2×1)表面为非对称性的Si二聚体模型,其二聚体的Si原子间键长为0.232 nm.电子结构的计算结果表明,在费米能级处有明显的态密度,因此3C-SiC(001)-(2×1)表面呈金属性.在带隙附近存在四个表面态带,一个位于费米能级附近,一个位于费米能级以上5 eV处,另外两个位于费米能级以下的价带中.
关键词:
碳化硅
密度泛函理论计算
原子结构
电子结构 相似文献
9.
采用一种简易的化学置换反应方法在泡沫镍基底上生长花针状的金纳米结构,并将其作为表面增强拉曼散射(SERS)基底,主要研究置换时间对SERS基底性能的影响。采用COMSOL Multiphysics仿真软件对金纳米粒子高度分别为100,150,175,200 nm的基底进行电磁增强仿真,得到最大电场强度分别为20.112,29.060,24.766,21.382 V/m,计算得到增强因子分别为1.64×105、7.13×105、3.76×105和2.09×105。使用罗丹明6G(R6G)溶液作为探针分子,对不同置换时间下的泡沫镍镀金基底进行拉曼表征、检测极限测试以及拉曼mapping测试。测试结果表明,置换时间为10 min的基底增强效果是最佳的,对R6G分子的检测浓度可以达到10-8 mol·L-1,在613,774,1364 cm-1这三个R6G分子的拉曼位移特征峰处的相对标准偏差值分别为11.3%、10.9%和11.9%,说明基底... 相似文献
10.
基于第一性原理密度泛函理论的赝势平面波方法,对Si(111)基外延稳定正交相OsSi2的能带结构、态密度以及光电特性进行了研究.研究结果表明,Si(111)基外延稳定正交相的OsSi2是一种间接带隙半导体,禁带宽度为0.625 eV;其价带主要是由硅的3s,3p态电子和锇的5d态电子构成,导带主要由锇的5d态电子与硅的3s,3p态电子构成;其静态介电函数为15.065,折射率为3.85,吸收系数最大峰值为3.9665×105cm-1.利用理论计算的能带结构和态密度研究了Si(111)基外延稳定正交相OsSi2的介电函数、折射率、吸收系数、光电导率和能量损失函数的变化规律,为Si(111)基外延OsSi2的应用提供了理论基础. 相似文献
11.
In order to determine the structure of complex and/or stepped surfaces that are very difficult to or even beyond the capability of the full dynamic low-energy electron diffraction calculation, recently we have proposed the quasi-kinematic low-energy electron diffraction (QKLEED) approach and employed it to solve the structure of some important surfaces such as Si(111)-(31/2×31/2) R30°-Al and Si(111)-(31/2×31/2) R30°-Ag. In the present paper, following the highlights of QKLEED we give the latest application of it, i.e., the structural determination of the Si(111)-(31/2×31/2) R30°-Au, Si(111)-(31/2×31/2) R30°-Sn, and Pd(001)-c(2×2)-Mn surfaces. 相似文献
12.
Observations of clean Si(111) and gold-deposited Si(111) surfaces have been performed using micro-probe reflection high-energy electron diffraction. It was found that many atomic steps on a Si(111) surface run in nearly the same direction, about 9° off the [1̄1̄2] direction. When gold was deposited on this surface at a substrate temperature of about 800°C, 5 × 1, diffuse √3 × √3R30°, sharp √3 × √3 R30° structures and Au clusters appeared on the surface with continuation of the deposition. During the deposition process, it was found that one kind of Si(111) 5 × 1 Au domain grew selectively along these atomic steps and nearly covered the entire surface. A phenomenon of gold clusters moving during the deposition was also observed. These clusters all moved in nearly the same direction so as to climb the atomic steps. 相似文献
13.
Epitaxially grown GaAs(001), (111) and (1?1?1?) surfaces and their behaviour on Cs adsorption are studied by LEED, AES and photoemission. Upon heat treatment the clean GaAs(001) surface shows all the structures of the As-stabilized to the Ga-stabilized surface. By careful annealing it is also possible to obtain the As-stabilized surface from the Ga-stabilized surface, which must be due to the diffusion of As from the bulk to the surface. The As-stabilized surface can be recovered from the Ga-stabilized surface by treating the surface at 400°C in an AsH3 atmosphere. The Cs coverage of all these surfaces is linear with the dosage and shows a sharp breakpoint at 5.3 × 1014 atoms cm?2. The photoemission reaches a maximum precisely at the dosage of this break point for the GaAs(001) and GaAs(1?1?1?) surface, whereas for the GaAs(111) surface the maximum in the photoemission is reached at a higher dosage of 6.5 × 1014 atoms cm?2. The maximum photoemission from all surfaces is in the order of 50μA Im?1 for white light (T = 2850 K). LEED measurements show that Cs adsorbs as an amorphous layer on these surfaces at room temperature. Heat treatment of the Cs-activated GaAs (001) surface shows a stability region of 4.7 × 1014 atoms cm?2 at 260dgC and one of 2.7 × 1014 atoms cm?2 at 340°C without any ordering of the Cs atoms. Heat treatment of the Cs-activated GaAs(111) crystal shows a gradual desorption of Cs up to a coverage of 1 × 1014 atoms cm?2, which is stable at 360°C and where LEED shows the formation of the GaAs(111) (√7 × √7)Cs structure. Heat treatment of the Cs-activated GaAs(1?1?1?) crystal shows a stability region at 260°C with a coverage of 3.8 × 1014 atoms cm?2 with ordering of the Cs atoms in a GaAs(1?1?1?) (4 × 4)Cs structure and at 340°C a further stability region with a coverage of 1 × 1014 at cm?2 with the formation of a GaAs(1?1?1?) (√21 × √21)Cs structure. Possible models of the GaAs(1?1?1?) (4 × 4)Cs, GaAs(1?1?1?)(√21 × √21)Cs and GaAs(111) (√7 × √7)Cs structures are given. 相似文献
14.
D.C. Sheppard G.S. Parkinson A. Hentz A.J. Window P.D. Quinn D.P. Woodruff P. Bailey T.C.Q. Noakes 《Surface science》2011,605(1-2):138-145
100 keV H+ scattering has been used to investigate the structure of the methylthiolate/Au(111) interface in the Au(111)(√3 × √3)R30° phase. Adsorption of the thiolate onto the clean Au(111) surface leads to a large drop in the scattered ion yield due to the lifting of the clean surface ‘herring-bone’ reconstruction, but the thiolate-covered surface shows an ion yield higher than that of an unreconstructed Au(111) surface, providing direct evidence of a significant number of Au atoms that are displaced from their bulk-terminated positions at the buried interface. Simulations for two different Au adatoms models at the interface, namely, the Au-adatom-monothiolate (AAM) and Au-adatom-dithiolate (AAD) models, show significant sensitivity to the exact values of interlayer spacings and atomic vibrational amplitudes, but the comparison with experimental results appears to favour the AAD model with 0.17 ML Au adatoms in bridging sites at the interface. 相似文献
15.
On heating a clean Ge(111) surface above 240°C, Ge(111) 2 × 8 surface structure changes to 1 × 1 one. We have first observed twofold splitting diffuse scattering in RHEED patterns from the Ge(111) 1 × 1 surface at high temperatures. A modulated 2 × 2 structure is proposed as a structural model for the diffuse scattering. The Fermi-surface instability of dangling-bond electrons at the surface is studied as an origin of the formation of the modulated structure. 相似文献
16.
Angle-resolved ultraviolet photoelectron spectra have been measured for well defined Ag/Si(111) submonolayer interfaces of (1) , (2) “Si(111)(6 × 1)-Ag”, and (3) Ag/Si(111) as deposited at room temperature. Non-dispersive and very narrow (FWHM ~ 0.4–0.5 eV) Ag 4d derived peaks are found at 5.6 and 6.5 eV below the Fermi level for surface (1) and at 5.3 and 6.0 eV for surface (2). Dispersions of sp “binding” states in the energy range between EF and Ag 4d states have been precisely determined for surface (1). Electronic structures similar to those of the Ag(111) surface, including the surface state near EF, have been observed for surface (3). 相似文献
17.
John L. Stickney Stephen D. Rosasco Dian Song Manuel P. Soriaga Arthur T. Hubbard 《Surface science》1983,130(2):326-347
Reported are studies by LEED and Auger spectroscopy of silver layers electrodeposited on well-characterized Pt(111) surfaces from aqueous solution. Prior to electrodeposition. the Pt(111) surface was treated with I2 vapor to form the Pt(111) ()R19.1°-I superlattice which protected the Pt and Ag surfaces from attack by the electrolyte and residual gases. Electrodeposition of silver occurred in four distinct ranges of electrode potential. Ordered layers having (3 × 3) and (18 × 18) (coincidence lattice) LEED patterns were formed at all coverages from the onset of deposition to the highest coverages studied, about twenty equivalent atomic layers. Formation of ordered Ag layers has therefore been demonstrated, at least for deposits of limited thickness. Auger spectra revealed that for deposits of a few atomic layers. The iodine layer remained attached to the surface during multiple cycles of electrodeposition and dissolution of silver from iodine-free solution. Each peak of the voltammetric current-potential scan produced a change in the LEED pattern. 相似文献
18.
We report a comparison of electric-field gradients (EFGs) measured at the group-III sites on epitaxially-grown surfaces of
2×2-reconstructed GaAs and InAs crystals. For this purpose, we used 111In→111Cd perturbed-angular-correlation (PAC) spectroscopy. Sharp spectral lines characterize the perturbation functions corresponding
to both surfaces. On GaAs surface, we observe only one well-defined nuclear electric-quadrupole interaction (NQI); and on
the InAs surface, we observe a primary and a secondary NQI. Very similar but experimentally-distinguishable values of the
EFG-parameters characterize the primary interactions corresponding to the GaAs and InAs surfaces. Specifically, for the GaAs
and InAs surfaces, ω
Q
=28.0±0.2 Mrad s−1 and η=0.43±0.02 and ω
Q
=28.8±0.2 Mrad s−1 and η=0.39±0.02, and the angles between EFG z-axis and the (111) direction are 65°±3° and β=53°±3°, respectively. These unexpected results indicate that the so-called
lattice contribution to the EFG is not significant. Moreover, for the primary NQIs on both surfaces, the similar parameter
values demonstrate that chemical differences between the 111In probe and the indigenous Ga surface atoms cause no large quantitative effects. This information indicates that impurity
probes and PAC spectroscopy can be used effectively to investigate III–V surfaces.
This revised version was published online in September 2006 with corrections to the Cover Date. 相似文献
19.
用扫描隧道显微镜研究石墨被Au离子轰击后的表面损伤。实验结果表明:用低剂量(1×1012ion/cm2)530keV的Au+和4.5MeV的Au++均匀轰击石墨。在石墨表面所产生的最显著的损伤是单个入射Au离子造成的小丘,小丘的横向平均线度约为1.8nm。从高分辨的扫描隧道显微镜图象可以看出,这种损伤往往伴有多种形式的31/2×31/2R 30°的超结构(R为石墨的晶格常数) 相似文献