c(2×2)O吸附Cu(001)表面结构、电子态与STM图像的研究

用投影子缀加波和CP分子动力学方法研究了贵金属Cu(001)面的表面结构、弛豫以及O原子的c(2×2)吸附状态. 研究结果得出在这种吸附结构中，O原子与衬底Cu原子之间的垂 直距离约为0069nm，Cu—O键长为0.194nm，功函数约为5.29 eV；吸附O原子形成金属性能带结构，由于Cu—O的杂化作用,在费米能以下约6.7 eV处出现了局域的表面态.用Tersoff-Hamann途径计算了该表面的扫描隧道显微镜图像，并讨论了与实验结果之 间的关系. 关键词： Cu(001)-c(2×2)/O 电子态 STM图像     

甘氨酸在Cu(111)表面吸附的扫描隧道显微镜研究

用超高真空扫描隧道显微镜(UHV-STM)研究了室温下甘氨酸在Cu(111)表面的吸附行为.实验发现,在低覆盖度下甘氨酸分子在表面表现为二维气体.当覆盖度足够高时,甘氨酸分子最终会形成二维固相结构,为(4×8)超结构.针对这种结构提出了两种可能的结构模型,模型能够很好地解释STM图.当覆盖度介于气相和固相之间时,根据蒸镀条件和退火条件的不同,表面可能出现两种不同的中间相,一种为条纹结构,另一种为六角结构,对于中间相有待于进一步的研究 关键词： 表面吸附 甘氨酸 铜 扫描隧道显微术     

Ge在Ru(0001)表面上生长及其性质研究

报道Ge在Ru(0001)表面上生长以及相互作用行为的扫描隧道显微镜（STM）和x射线光电子能谱（XPS）研究. STM的实验结果表明Ge在Ru(0001)表面的生长呈典型的Stranski_Krastanov生长模式，Ge的覆盖度小于单原子层时呈层状生长，而从第二层开始呈岛状生长. XPS测量显示衬底Ru(0001)与Ge的相互作用很弱. Ru(0001)表面的Ru 3d5/2和Ru 3d3/2芯态结合能分别处于2798和2840 eV. 随着Ge的生长，到Ge层的厚度为20个单原子层，衬底Ru 3d芯态结合能减小了约02 eV，而Ge 3d芯态结合能从Ge低覆盖度时的289 eV增加到了290 eV，其相对位移约为01 eV. 关键词： Ge Ru表面 生长 相互作用     

Na原子在Si(111)-(7×7)表面的吸附:从二维原子气到纳米团簇阵列

作者利用扫描隧道显微镜 (STM)详细研究了室温下Na原子在Si(111) (7× 7)表面的吸附 .对STM图像及功函数变化的分析表明 ,当Na原子覆盖度小于临界覆盖度 (0 .0 8ML)时 ,Na原子具有类气态的性质并可以在一个吸附能阱中快速移动 .从STM图像可看出这种移动导致的对比度调制 .在临界覆盖度以上 ,Na原子自组装形成团簇阵列 .第一原理模拟计算的结果与作者的实验结论很好吻合 .     

用扫描隧道显微镜操纵Cu亚表面自间隙原子

在超高真空环境下使用扫描隧道显微镜研究了吸附有双甘氨肽分子的Cu(001)表面.在一定的 偏压条件下，针尖在该表面扫描后会形成纳米尺度的Cu团簇，这些团簇可以根据意愿排列成 字母或图形.团簇的高度同偏压、隧道电流以及时间等条件有密切关系.在室温下可以稳定存 在的团簇为制造纳米器件提供了技术上的可能性.实验结果表明，形成团簇的Cu原子不是来 自Cu衬底表面或是针尖.化学吸附在Cu表面的双甘氨肽分子，受到隧道电场的作用会在Cu表 面形成张应变场，Cu亚表面自间隙原子在张应变场作用下迁移到表面是形成团簇的原因. 关键词： 扫描隧道显微镜 纳米尺度Cu团簇 自间隙原子     

室温下单个甘氨酸分子在Cu(111)表面的操纵研究

先用低能电子衍射(LEED)证明了甘氨酸(NH₂-CH₂-COOH)能在室温下在Cu单晶表面产生比较稳定的吸附，然后用扫描隧道显微镜(STM)进一步研究了其吸附情况，看到单个甘氨酸分子在Cu(111)面上吸附稳定并至少有三种吸附状态.分子操纵研究结果表明，甘氨酸分子是被针尖“推着”移动的，它在Cu(111)面有固定的吸附位，并且移动时其吸附状态可以不变.研究结果表明，甘氨酸适合做室温下小分子的可控操纵研究，并且也说明室温下小分子的可控操纵是可能的. 关键词：     

tetracene分子在Ru(100)表面的吸附结构及其电子态研究

利用紫外光电子能谱(UPS)、角分辨紫外光电子能谱(ARUPS)和扫描隧道显微镜(STM)等方法研究了tetracene分子在Ru(100)表面上吸附的电子态,吸附位置和吸附取向.UPS实验显示,与tetracene分子有关的光电子谱峰在费米能级以下2.1,3.5,4.8,6.0,7.1和9.2eV处;ARUPS结果表明,tetracene分子的分子平面基本平行于衬底表面;从STM图像中可以看到tetracene分子的长轴沿[0001]和[1■10]两个晶向.基于密度泛函理论的从头算计算证实了上述结论.当分子长轴沿[0001]晶向时,分子中心位置在衬底表面的“短桥位”上,当分子长轴沿[1210]晶向时,分子中心位置在衬底表面的“四原子中心空位”上.     

氯原子在Cu(111)表面的吸附结构和电子态

密度泛函理论(DFT)总能计算研究了不同覆盖度下氯原子在Cu(111)表面的吸附结构和表面电子态。计算结果表明，清洁Cu(111)表面自由能 为15.72 ，表面功函数φ为4.753eV。在1/4ML和1/3ML覆盖度下，每个氯原子在Cu(111)表面fcc谷位的吸附能分别等于3.278eV/atom和3.284eV/atom。在1/2ML覆盖度下，两个紧邻氯原子分别吸附于fcc和hcp谷位，氯原子的平均吸附能为2.631eV/atom。在1/3ML覆盖度下，fcc和hcp两个位置每个氯原子吸附能的差值约为2meV/atom，与正入射X光驻波实验结合蒙特卡罗方法得到结果(<10meV/atom)基本一致。在1/4ML、1/3ML和1/2ML覆盖度下，吸附后Cu(111)表面的功函数依次为5.263eV、5.275eV和5.851eV。吸附原子和衬底价轨道杂化形成的局域表面电子态位于费米能级以下约1.2eV、3.6eV和4.5eV等处。吸附能和电子结构的计算结果表明，氯原子间的直接作用和表面铜原子紧邻氯原子数目是决定表面结构的两个重要因素。     

tetracene 分子在Ru(1010)表面的吸附结构及其电子态研究

利用紫外光电子能谱(UPS)、角分辨紫外光电子能谱(ARUPS)和扫描隧道显微镜(STM)等方法研究了tetracene分子在Ru(1010)表面上吸附的电子态，吸附位置和吸附取向.UPS实验显示，与tetracene分子有关的光电子谱峰在费米能级以下2.1, 3.5, 4.8, 6.0, 7.1和9.2 eV处；ARUPS 结果表明，tetracene分子的分子平面基本平行于衬底表面；从STM图像中可以看到tetracene分子的长轴沿［0001］和［1210］两个晶向.基于密度泛函理论的从头算计算证实了上述结论.当分子长轴沿［0001］晶向时，分子中心位置在衬底表面的“短桥位”上，当分子长轴沿［1210］晶向时，分子中心位置在衬底表面的“四原子中心空位”上. 关键词： tetracene分子 Ru(1010)表面 吸附结构 吸附电子态     

甘氨酸在Cu(001)表面的吸附结构

结合低能电子衍射(LEED)及其消失斑点规律和扫描隧道显微镜(STM)手段确定了室温下甘氨酸在Cu(001)表面能形成c(2×4)和两种(2×4)吸附结构((2×4)₁和(2×4)₂),并推断出在两种(2×4)结构单胞中两甘氨酸分子的羧基相对于衬底的吸附取向一致,而它们的氨基则不同.实验中还观察到c(2×4)与(2×4)₂结构能相互转变成窄条相互穿插共存,这说明几种吸附结构能量相近. 关键词：     

乙烯在Ni（110）表面吸附的几何结构

用理论计算的方法研究了不同覆盖度的乙烯在Ni（110）表面吸附的位置.乙烯的吸附几何结构在团簇计算中进行了局部优化.在低覆盖度下，单个乙烯分子占据了短桥位和顶位之间的中间位置.乙烯分子的C—C轴大致沿衬底的Ni原子链排列（即沿<110>晶向），C—C轴与衬底Ni（110）表面有10°的倾斜角.乙烯分子的C—C键的键长为0151nm.在高覆盖度下(05ML)，乙烯在Ni (110)上形成了有序的c（2×4）相，在一个表面元胞内的两个乙烯分子的吸附位置类似于低覆盖度时的结果，但乙烯分子的C—C 键键长分别为0142和0143nm.     

Dependence of work function on coverage for aluminum/tungsten in the field electron microscope

Aluminum adsorption on tungsten has been investigated by field electron microscope techniques. Changes in average work function and work functions of the (001) plane and (111) region were determined as a function of aluminum deposition. The average work function exhibits a minimum of about (4.11 × 0.04)eV (relative to an assumed value of 4.50 eV for the tungsten substrate) and reaches a value of (4.21 ± 0.04) eV for thick deposits. The (001) plane and (111) region exhibit complicated work function dependences on aluminum coverage. Some qualitative observations of aluminum on tungsten surface diffusion are also reported.     

基于多层膜偏振元件的软X射线磁光Faraday偏转测量

在北京同步辐射装置(BSRF)的3W1B软X射线光束线上利用自行研制的同步辐射软X射线综合偏振测量装置对Ni的M_2,3边附近(60—70 eV)进行了软X射线磁光(magneto-optical)法拉第效应(Faraday effect)的偏转测量，实验装置主要由起偏器，检偏器，样品架,圆形钕铁硼永磁铁和MCP探测器组成，偏振元件(起偏元件和检偏元件)均采用反射式非周期性Mo/Si宽带多层膜.实验采用反射起偏和反射检偏的模式，得到一系列能量范围在60—70 eV间的法拉第偏转角结果， 关键词： 软X射线 磁光Faraday效应 综合偏振测量装置 宽带多层膜     

The adsorption of CO on Cu surfaces studied by electron energy loss spectroscopy

Electron energy loss spectroscopy (ELS) in the energy range of electronic transitions (primary energy 30 < E₀ < 50 eV, resolution ΔE ≈ 0.3 eV) has been used to study the adsorption of CO on polycrystalline surfaces and on the low index faces (100), (110), (111) of Cu at 80 K. Also LEED patterns were investigated and thermal desorption was analyzed by means of the temperature dependence of three losses near 9, 12 and 14 eV characteristic for adsorbed CO. The 12 and 14 eV losses occur on all Cu surfaces in the whole coverage range; they are interpreted in terms of intramolecular transitions of the CO. The 9 eV loss is sensitive to the crystallographic type of Cu surface and to the coverage with CO. The interpretation in terms of d(Cu) → 2π¹(CO) charge transfer transitions allows conclusions concerning the adsorption site geometry. The ELS results are consistent with information obtained from LEED. On the (100) surface CO adsorption enhances the intensity of a bulk electronic transition near 4 eV at E₀ < 50 eV. This effect is interpreted within the framework of dielectric theory for surface scattering on the basis of the Cu electron energy band scheme.     

X-ray photoemission study of physically absorbed SF6

The physical adsorption of octahedral SF₆ on Ru(001) has been studied with X-ray photoelectron spectroscopy (XPS) in an attempt to see effects on the energy levels resulting from the conformation of the molecule on the surface. Near 80 K surface coverages up to a monolayer have been studied at various steady state pressures of SF₆. Kinetic studies, core level binding energies, and peak areas indicate that the surface species studied was a physically adsorbed monolayer of sf₆. The sticking coefficient of SF₆, at ? 80 K is approximately unity. Also, a multilayer structure was observed at the highest pressures of SF₆. The binding energy of the F(ls) peak for monolayer coverage is centered at 688.2 ± 0.2 eV relative to the Ru Fermi level. while the multilayer F(ls) peak is shifted more than 3.5 eV to higher binding energy. The F(ls) linewidth for one monolayer has a full width at half maximum of 1.75 ± 0.1 eV. The F(ls) linewidth of the multilayer peak narrows with increasing coverage. Its narrowest observed linewidth was 1.35 eV ± 0.1 eV or approximately the same as that found in the gas phase. One of the mechanisms which may account for the F(ls) linewidth with monolayer coverage is a difference in F(ls) binding energy between those F atoms in contact with the substrate and those further away. This may be due to the variation in chemical environment and relaxation effects as a function of distance from tlie substrate. A classical image force calculation including finite screening effects of the substrate indicates that there is a differential binding energy, ΔW. between the F ligands; ΔW = 0.85 ± 0.25 eV, for realistic ranges of adsorption distances from the substrate and screening lengths in the substrate. The observed broadening of the monolayer F(ls) level is consistent with a ΔW of 0.7 ± 0.1 eV, indicating the possible existence of such a mechanism. Adsorption of a monolayer of SF₆ onto the Ru covered with a monolayer of oxygen shifts the F(ls) peak to lower binding energy by 0.8 eV. Similar effects due to oxygen have been observed previously in the physical adsorption of Xe on W(111).     

The adsorption of Xe and CO on a Cu (311) single crystal surface

LEED, electron energy loss spectroscopy and surface potential measurements have been used to study the adsorption of Xe and CO on Cu (311). Xe is adsorbed with a heat of 19 ± 2 kJ mol^/t-1. The complete monolayer has a surface potential of 0.58 V and a hexagonal close-packed structure with an interatomic distance of 4.45 ± 0.05 Å. CO gives a positive surface potential increasing with coverage to a maximum of 0.34 V and then falling to 0.22 V at saturation. The heat of adsorption is initially 61 ± 2 kJ mol^?1, falling as the surface potential maximum is approached to about 45 kJ mol^?1. At this coverage streaks appear in the LEED pattern corresponding to an overlayer which is one-dimensionally ordered in the [011&#x0304;] direction. Additional CO adsorption causes the heat of adsorption to decrease further and the overlayer structure to be compressed in the [011&#x0304;] direction. At saturation the LEED pattern shows extra spots which are tentatively attributed to domains of a new overlayer structure coexisting with the first. Electron energy loss spectra (EELS) of adsorbed CO show two characteristic peaks at 4.5 and 13.5 eV probably arising from transitions between the electronic levels of chemisorbed CO.     

Chlorine adsorption on copper: III. Angle-resolved electron energy loss spectroscopy

Electronic excitations on Cu(001) and Cu(001)c(2 × 2)-Cl have been investigated by angle-resolved electron energy loss spectroscopy at an angular resolution of Δθ = ±1° and an energy resolution of ΔE = 60 meV. Primary energies in the 50–100 eV range were chosen and the specular reflection was studied for angles 35° ? θ ? 71° with respect to the surface normal. The results are summarized as follows: The specular Cu(001) spectra are compared to optical data and good agreement is found for the energetic position of direct transitions. The electronic losses observed for the ordered overlayer system may be interpreted by one-electron excitations from occupied surface bands (known from angle-resolved photoemission results) into an empty band with a minimum energy at 0.4 eV above the Fermi level.     

Adsorption and desorption of hydrogen on bare and Xe-covered Cu(111)

Using polarization-modulated ellipsometry to monitor adsorbate coverage in-situ, we studied the activated adsorption of filament-heated molecular hydrogen on Cu(111) and subsequent isothermal desorption of hydrogen adatoms. The adsorption is characterized by a zeroth-order kinetic with a constant sticking probability of S₀=0.0062 up to θ=0.25, followed by a Langmuir kinetic until the saturation coverage θ_s=0.5 is reached. The desorption follows a second-order kinetic with an activation energy of 0.63 eV and a pre-exponential factor of 1×10⁹ /s. A pre-adsorbed monolayer of Xe atoms on Cu(111), with a desorption activation energy of 0.25 eV and a pre-exponential factor of 8×10¹⁴ /s, efficiently blocks the subsequent adsorption of hot molecular hydrogen, making physisorbedXe useful as templates for spatial patterning of hydrogen adatom density on Cu(111). PACS 68.43.Jk; 78.68.+m; 81.15.-z; 82.40.Np