用扫描隧道显微镜测量局域功函数

用扫描隧道显微镜在Cu（111）-Au和Pt（111）-Ag表面上对局域功函数进行了测量．在扫描的同时通过测量隧道电流对针尖样品间距离变化的响应，可以在得到扫描隧道显微镜（STM）图的同时得到功函数图．用这种方法，成功地观察到Au，Ag覆盖层与Cu，Pt衬底间的功函数的差别．结果表明：Au覆盖层的功函数介于Cu（111）和Au（111）的功函数之间，这与其它方法的结果一致．在Pt（111）-Ag表面观察到了局域功函数随覆盖层厚度的变化．本工作表明：扫描隧道显微镜在研究功函数与表面结构的关系方面是十分有用的；用测量局域功函数的方法还可以区分表面不同种的物质 关键词：     

天冬氨酸在Cu(001)表面吸附的扫描隧道显微镜研究

用扫描隧道显微镜(STM)研究了室温下天冬氨酸在Cu(001)表面的吸附行为.实验发现,在较 低的覆盖度下,天冬氨酸分子在Cu(001)表面存在两种吸附状态.从STM数据估算出两种吸附 状态下天冬氨酸分子在Cu(001)表面的扩散激活能分别为079±001eV,088±005eV. 随着覆盖度的提高,天冬氨酸分子最终在Cu(001)表面形成一均匀衬度的吸附层,但并不形 成有序吸附结构,也不能使台阶发生小面化.天冬氨酸分子的这些吸附特点是迄今研究过的 所有氨基酸在Cu(001)表面吸附时不具有的. 关键词： 表面吸附 扫描隧道显微镜 氨基酸     

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     

Ag(111)和Au(111)上铋的初始生长行为

半金属铋(Bi)的表面合金具有的Rashba效应,和其具体结构性质有重要关联.本文结合扫描隧道显微镜(STM)和密度泛函理论(DFT),系统地研究了Bi原子在Ag(111)和Au(111)上的不同初始生长行为.在室温Ag(111)上,连续的Ag2Bi合金薄膜会优先在Ag台阶边缘形成;在570 K Ag(111)上,随着...     

C60分子在Si（111）-7×7表面分子束外延生长的STM研究

在超高真空中采用分子束外延(molecular beam epitaxial)技术进行C₆₀分子在硅（111）-7×7表面的生长,并利用扫描隧道显微镜进行原位研究.室温下,相对于无层错半胞（unfaulted half unit cell）,C₆₀更易于吸附在有层错半胞（faulted half unit cell）.表面台阶处的电子悬挂键密度最高,通过控制温度和时间进行退火处理后,C₆₀分子会向着台阶的方向扩散并聚集.测量分子在不同吸附位 关键词： 60分子')" href="#">C₆₀分子 分子束外延 Si(111)-7×7 超高真空扫描隧道显微镜     

Si(111)7×7表面孤立C_(60)分子的吸附取向及局域电子态研究

利用低温扫描隧道显微镜对Si(111) 7× 7表面的孤立C60 分子成像 ,结合局域密度泛函方法计算 ,确定了C60 在不同吸附位置的分子取向 .同时进行的扫描隧道谱揭示了C60 吸附后的局域电子态 .     

钴原子及其团簇在Rh(111)和Pd(111)表面的扫描隧道显微学研究

利用扫描隧道显微镜和扫描隧道谱(STM/STS)及单原子操纵,系统研究了单个钴原子(Co) 及其团簇在Rh (111)和Pd (111)两种表面的吸附和自旋电子输运性质. 发现单个Co原子在Rh (111)上有两种不同的稳定吸附位,分别对应于hcp和fcc空位, 他们的高度明显不同,在针尖的操纵下单个Co原子可以在两种吸附位之间相互转化. 在这两种吸附位的单个Co原子的STS谱的费米面附近都存在很显著的峰形结构, 经分析认为Rh (111)表面单个Co原子处于混价区,因此这一峰结构是d轨道共振 和近藤共振共同作用的结果.对于Rh (111)表面上的Co原子二聚体和三聚体, 其费米面附近没有观测到显著的峰,这可能是由于原子间磁交换相互作用 和原子间轨道杂化引起的体系态密度改变所共同导致.与Rh (111)表面不同, 在Pd (111)表面吸附的单个Co原子则表现出均一的高度.并且对于Pd (111)表面所有 单个Co原子及其二聚体和三聚体,在其STS谱的费米面附近均未探测到显著的电子结构, 表明Co原子吸附于Pd (111)表面具有与Rh (111)表面上不同的原子-衬底相互作用与自旋电子输运性质.     

研究单原子分子表面扩散运动的时域隧穿电流谱方法

以单个Cu原子在Si(111)(7×7)层错半单元(FHUC)内的随机扩散运动研究为例,演示了一种新的可以测量快速扩散运动的扫描隧道显微镜方法──时域隧穿电流谱方法.运用这种方法可定量地检测纳米局域区间内单原子分子的表面扩散运动,跳跃频率的测量范围达到1—104Hz,比过去已有的用扫描隧道显微镜研究表面扩散的方法提高三个量级.这种方法将会使人们在原子尺度下对快速扩散运动比如氢原子的量子扩散运动获得更进一步的理解.     

Ge在Si(111)7×7表面的选择性吸附

利用超高真空扫描隧道显微镜研究了室温条件下Ge在Si(111)7×7表面上初期吸附过程.在Ge所形成团簇中存在一个临界核.这些Ge团簇的吸附中心总是在三个增原子所围成的区域中.它们的电子结构具有类似半导体的性质,即其局域态密度在远离费米面的能级处很大,而在费米面附近的能级处非常小. 关键词： 扫描隧道显微镜 Si(111)7×7表面 Ge团簇     

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：     

Initial stage of adsorption of octithiophene molecules on Cu(111)

The initial stage of the adsorption of octithiophene (8T) molecules on a Cu(111) surface is investigated using a scanning tunneling microscope at room temperature. We find a characteristic molecular chain structure of 8T molecules on a terrace of the Cu(111) surface, which has not been reported so far for adsorption of oligothiophene molecules on metal surfaces. Up to the adsorption of 0.26 monolayer (ML), 8T molecules in the molecular chain align with their long axis parallel to the Cu<11-2> direction. With increasing coverage, there appear 8T molecules that align with their long axis parallel to the Cu<110> direction. The appearance of different molecular orientations is understood by the decrease of the number of the adsorption sites for extending the molecular chains. Fragments of 8T molecules, such as single thiophene molecules, are also observed in this work. They are trapped only at the step edges of the Cu(111) surface at the beginning and later trapped in a small Cu(111) region surrounded by 8T molecules.     

Acetylene on Cu(111): imaging a molecular surface arrangement with a constantly rearranging tip

Acetylene on Cu(111) is investigated by scanning tunnelling microscopy (STM); a surface pattern previously derived from diffraction measurements can be validated, if the variation of the STM image transfer function through absorption of an acetylene molecule onto the tip apex is taken into account. Density functional theory simulations point to a balance between short-range repulsive interactions of acetylene/Cu(111) associated with surface stress and longer range attractive interactions as the origin of the ordering.     

Triphenylene adsorption on Cu(111) and relevant graphene self-assembly

Investigations on adsorption behavior of triphenylene(TP) and subsequent graphene self-assembly on Cu(111) were carried out mainly by using scanning tunneling microscopy(STM).At monolayer coverage,TP molecules formed a longrange ordered adsorption structure on Cu(111) with an uniform orientation.Graphene self-assembly on the Cu(111) substrate with TP molecules as precursor was achieved by annealing the sample,and a large-scale graphene overlayer was successfully captured after the sample annealing up to 1000 K.Three different Moire patterns generated from relative rotational disorders between the graphene overlayer and the Cu(111) substrate were observed,one with 40 rotation between the graphene overlayer and the Cu(111) substrate with a periodicity of 2.93 nm,another with 70 rotation and 2.15 nm of the size of the Moire supercell,and the third with 100 rotation with a periodicity of 1.35 nm.     

Angle-resolved photoemission study of Pd(111) and Co/Pd(111)

Electronic structure of epitaxial Co films on Pd(111) has been investigated as a function of the Co overlayer thickness, by using angle-resolved photoemission spectroscopy (ARPES). It is found that experimental band structures for Pd(111) and work functions for Co/Pd(111) agree reasonably well with the results of band structure calculations. Compared to Pd(111), valence band ARPES spectra of Co/Pd(111) support the existence of the induced magnetic polarization of Pd atoms near the interface, suggesting large hybridization between Co 3d and Pd 4d states near the interface.     

Atom deposition on surface clusters: thin film growth on Pd(111)

We have studied the vapor phase deposition of single metal atoms on two-dimensional clusters at the Pd(111) surface. The system considered here are heptamers and dodecamers for the substrate temperature of 100 K. Using molecular dynamics simulations with the corrected effective medium potentials for Pd, Cu and Rh, we have found that an adatom either diffuses on the cluster or incorporates itself into the cluster depending on the size of clusters and the kind of metals in the gas/cluster system. We also discovered that incorporation of a deposited gas atom into a surface cluster at 100 K was not a consequence of the reduction of the barrier heights at the step edges and that the type of post-impact dynamics for hexagonal heptamers depends on the impact point.     

Formate-induced destabilization of the Cu(1 1 0) surface

Scanning tunneling microscopy (STM) images show that adsorbed formate has a profound affect on the step edges of Cu(1 1 0) surfaces at room temperature. For low exposures, the presence of formate enhances step fluctuations as confirmed by a correlation function analysis. For formate coverages approaching 0.5 monolayers, drastic restructuring of step edges is observed. Quantum chemical calculations help to explain this behavior.     

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     

Auger line shape changes in epitaxial (111)Pd/(111)Cu films

Epitaxial Pd films ranging in thickness from a few tenths of a monolayer up to many monolayers were formed on (111)Cu substrate films at room temperature under UHV conditions. The growth of these Pd films was monitored in situ by Auger electron spectroscopy. The line profiles of the Cu MMM (61 eV) and Pd MVV (329 eV) AES doublets varied significantly with the amount of Pd deposited. A new measure of the AES doublet line profile, called the R-factor, was defined. A graph R_pd versus Pd film thickness shows a sharp decline with increasing thickness. Superimposed on the major trend is a cyclical variation. A corresponding periodicity in R_cu was observed for the Cu MMM (61 eV) AES doublet. The results suggest that the R-factor provides a direct measure of changes in the electronic structures of the overgrowth and substrate films as the former thickens by a layer-growth mechanism.     

Local spectroscopy of image-potential-derived states: from single molecules to monolayers of benzene on Cu(111)

Stark-shifted image-potential states were measured with an STM tip for benzene adsorbed on a Cu(111) surface. A single benzene molecule locally shifts the position of the first image state toward the Fermi level by 0.2 eV relative to its position on the clean surface. The energetic position of this molecule-modified state shifts to lower energy with increasing coverage of benzene on the surface. This is attributed to local surface potential changes that are correlated with the lowering of the crystal work function due to adsorption of benzene.     

Scanning tunneling microscopy study of a Ag monolayer on Cu(111)

The structure of submonolayer Ag deposited on Cu(111) has been examined with scanning tunneling microscopy. The long diffusion length of Ag leads to the formation of large (111)-like islands nucleating from the “downhill” side of Cu step edges. The growth fronts of the Ag islands are mostly straight and lie along the 〈1&#x0304;10〉 directions. The Ag overlayer is apparently slightly compressed relative to bulk Ag, and forms a mixture of superstructures rotated slightly relative to the substrate.