共查询到20条相似文献,搜索用时 125 毫秒
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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079±001eV,088±005eV. 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 相似文献
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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 相似文献
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采用第一性原理方法研究了NH3分子在LiH(100)晶面的表面吸附情况.通过研究LiH(100)/NH3体系的吸附位置、吸附能和电子结构,发现NH3分子在LiH(100)晶面主要是化学吸附,初始位置为NH3分子中N-H键在Li顶住时失去一个H原子,并在LiH(100)面形成NH2基,其吸附能为0.511 eV,属于强化学吸附,吸附作用最强.此时NH2基与附近H原子和Li原子之间为离子键作用,NH2基中N—H键为共价键;NH3分子中另一个H原子与LiH表面的一个H原子形成一个H2分子逸出表面.H2分子中H-H键为明显的共价键. 相似文献
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用扫描隧道显微镜(STM)研究了亚单层In原子引起的Ge(112)-(4×1)-In表面重构.结合随偏压极性不同而显著不同的STM图象和相应的“原子图象”,为这个重构提出了一个原子结构模型,供进一步研究参考.其中,In原子的吸附位置与它在Si(112)表面的吸附位置一致,但与Al原子和Ga原子在Si(112)表面的吸附位置不同.这个吸附位置的不同主要是由In原子较长的共价键键长引起的
关键词:
表面结构
In
Ge
扫描隧道显微镜(STM) 相似文献
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Miao Zhao Peng Jiang Ke DengAi-Fang Yu Yan-Zhong HaoSi-Shen Xie Jie-Lin Sun 《Applied Surface Science》2011,257(8):3243-3247
Two-dimensional ordered patterns of n-tetradecane (n-C14H30) and n-hexadecane (n-C16H34) molecules at liquid/graphite interface have been directly imaged using scanning tunneling microscope (STM) under ambient conditions. STM images reveal that the two different kinds of molecules self-organize into ordered lamellar structures in which alkane chains of the molecules extend along one of three equivalent lattice axes of highly oriented pyrolytic graphite (HOPG) basal plane. For n-C14H30 molecules, the molecular axes are observed to tilt by 60° with respect to inter-lamellar trough lines and the carbon backbones of the alkane chains are perpendicular to the HOPG basal plane in an all-trans conformation. However, for n-C16H34 molecules, the molecular axes are perpendicular to lamellar borders (90°) and the planes of the all-trans carbon skeletons are parallel to the graphite basal plane. The results clearly indicate that outmost hydrogen atoms of the alkane chains dominate atom-scaled features of the STM images. That is, in the case of long-chain alkane molecules, topographic effects dominantly determine STM image contrast of the methylene regions of the alkane chains that are adsorbed on HOPG. 相似文献
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Partial electron density plots were calculated for various arrangements of perylene-3,4,9,10-tetracarboxylic-dianhydride (PTCDA) molecules on graphite to understand why scanning tunneling microscopy (STM) images of PTCDA on graphite exhibit superstructure contrast variations. In agreement with experiment, the contrast of the partial electron density plot depends strongly on the orientation and position of PTCDA on graphite. This observation originates from the fact that the overlap between the orbitals of the adsorbate and substrate is strongly affected by their relative arrangement. The HOMO or LUMO density of an adsorbate molecule can be inadequate in interpreting STM images of adsorbate molecules. 相似文献
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Theory predicts that the currents in scanning tunneling microscopy (STM) and the attractive forces measured in atomic force microscopy (AFM) are directly related. Atomic images obtained in an attractive AFM mode should therefore be redundant because they should be similar to STM. Here, we show that while the distance dependence of current and force is similar for graphite, constant-height AFM and STM images differ substantially depending on the distance and bias voltage. We perform spectroscopy of the tunneling current, the frequency shift, and the damping signal at high-symmetry lattice sites of the graphite (0001) surface. The dissipation signal is about twice as sensitive to distance as the frequency shift, explained by the Prandtl-Tomlinson model of atomic friction. 相似文献
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Scanning tunneling microscopy (STM) at liquid helium temperature is used to image potassium adsorbed on graphite at low coverage (≈0.02 monolayer). Single atoms appear as protrusions on STM topographs. A statistical analysis of the position of the atoms demonstrates repulsion between adsorbates, which is quantified by comparison with molecular dynamics simulations. This gives access to the dipole moment of a single adsorbate, found to be 10.5±1 D. Time-lapse imaging shows that long-range order is broken by thermally activated diffusion, with a 30 meV barrier to hopping between graphite lattice sites. 相似文献
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D. V. Abramov S. M. Arakelyan A. F. Galkin L. D. Kvacheva I. I. Klimovskiĭ M. A. Kononov L. A. Mikhalitsyn A. O. Kucherik V. G. Prokoshev V. V. Savranskiĭ 《JETP Letters》2006,84(5):258-261
The melting of carbon at a pressure of about 1 atm is observed. The escape of liquid carbon from the heating region and its spread over the sample surface are observed in the experiments. The structural changes in graphite occurring in the melting region are determined from scanning tunneling microscope (STM) images obtained by means of an atomic force microscope and from Raman spectra. The STM images exhibit significant rearrangement of the structure of the graphite surface in the region of the escape of liquid carbon. The Raman spectra show that the graphite ordering degree increases significantly. 相似文献
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F. Atamny T.F. Fässler A. Baiker R. Schlögl 《Applied Physics A: Materials Science & Processing》2000,71(4):441-447
The shape and the atomic arrangement of monolayer steps of graphite have been characterized by STM. The origin of the appearance
of the imaged features along the steps is discussed, addressing for the first time both morphological and electronic considerations.
Extended Hückel theoretical calculations of nanotubes are used to identify the contribution of the electronic structure to
the STM image of monolayer steps. We show that mechanical tip–sample interactions dominate the imaging process of graphite,
leading to step deformation during scanning and negative STM contrast of the atom positions in the hexagonal unit cell.
Received: 11 April 2000 / Accepted: 18 April 2000 / Published online: 23 August 2000 相似文献
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To modulate the tunneling gap with the lock-in amplifier in the scanning tunneling microscopy(STM), information of the tunneling current variation can be obtained. The local potential barrier distribution of graphite surface atoms is got by means of such technology. Compared with STM image under topography observation mode, the local potential barrier image has higher resolu tion and less influence on the tip and better anti-interference capability. Obs erved results of the graphite are given and discussed in this paper. 相似文献
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STM studies of the characteristics of the surface fabrication process using chemical and electrical methods 总被引:1,自引:0,他引:1
C. Wang G. Shang X. Qiu C. Bai 《Applied Physics A: Materials Science & Processing》1999,68(2):181-185
2 surface using STM yielded appreciably different results. It is observed that the threshold pulse voltage is lower than that
for graphite at comparable tunneling conditions. The minimum dimension of the as-produced features is appreciably larger than
those on graphite. Both observations indicate higher surface instability for 1TTaS2 as compared with graphite.
Received: 27 March 1998 相似文献
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Ayyakkannu Manivannan Andr Morneau Diego J. Díaz Carlos R. Cabrera 《Surface science》1996,350(1-3):239-246
The study of metallic carbonyl clusters as precursors in tailoring the heterogeneous metal catalysts has been of great importance. The catalytic nature of the adsorbed clusters in thin film form depends on the chemical properties of the substrate used. The metal-support interaction will determine various properties such as the surface morphology, adsorption features and the structural orientations. We report a scanning tunneling microscopy (STM) study of an osmium carbonyl cluster (Os3(CO)11(NCCH3)) adsorbed on highly oriented pyrolytic graphite (HOPG). STM measurements showed that the osmium carbonyl cluster interacts with HOPG in such a way that it adsorbs on the basal plane showing regular lattice structure, whereas the axial planes of the HOPG surface shows no ordered structure. The regular cluster lattice structure of the carbonyl cluster on the basal plane of the graphite has lattice parameters of a=1.4 nm and b=1.5 nm. We believe that the regular orientation of the cluster indicates a monolayer adsorption of the cluster on the graphite basal planes. Scanning tunneling spectroscopy (STS) measurements also indicated an insulating behavior for the cluster molecules on HOPG, with a significant energy gap value of ca. 300 mV. The cluster interaction at the active sites, i.e. axial planes of the graphite, was also observed by in situ STM measurements. 相似文献