Self-Assembly of TBrPP-Co Molecules on an Ag/Si（111） Surface Studied by Scanning Tunneling Microscopy

Self-assembly of TBrPP-Co molecules on a Si（111）-√3t×√3 Ag substrate is studied by low-temperature scanning tunneling microscopy. With the same adsorbed amount （0.07 ML）, the molecules deposited by low-temperature evaporation show three kinds of ordered structures whereas those deposited by high-temperature evaporation have size-dependent ordered structures. The distinct differences in the self-assembly structures and in the electron density of states inside the molecule near the Fermi energy demonstrate that the Br atoms of the molecule desorb at the higher evaporation temperature.     

Reversible Vertical Manipulations of Single Pt Adatom on Pt（111） Surface with a Triple-Apex Tip

With a triple-apex tip, we investigate theoretically the vertical manipulation of single Pt adatom on the Pt（111） surface. The adatom adsorbed on the f cc site of the flat Pt（111） surface can be transferred vertically to the tip by adjusting the tip height properly. Moreover, based on the strong vertical trapping ability and the relatively weak lateral trapping ability of the tip, we propose a simple method to realize a reversible vertical manipulation of the Pt adatom from the highly coordinated sites, the kink and the step sites, of the stepped Pt（111） surface. All the vertical manipulations are completed using only the atomic force between the tip and the adatom, without the electric field.     

Magic Number Behaviour and Structures of Silicon Dioxide-Based Clusters

The lowest energy structures of （SiO2）nO2 duster skeletons with size from n = 2 to 12 is investigated theoretically by genetic algorithm. The calculations based on the Tsuneyuki-Tsukada Aoki Matsui （TTAM） and Flikkema- Bromley （FB） potentials give the same result： n = 4 and n = 8 are the magic numbers in the virtual （SiO2）nO2 cluster sequence. This conclusion is in agreement with the experimental observation on the [（SiO2）nO2H3]- cluster sequence. The comparison of the present results with those from the density-functional-theory calculations on （SiO2）nO2H4 shows that addition of II atoms to the O terminals of （SiO2）nO2 clusters to form the complex （SiO2）nO2H4 clusters has only minor influence on the relative energies and the structures of different isomers. This means that the magic behaviour of the dusters [（SiO2）nO2H3]^- （n=4,8） observed in our previous experiment is originated from the stability of the cluster skeletons （SiO2）nO2 （n = 4, 8） .     

Dynamical Behaviour of Ag and Cu Double-Layer Islands on fcc （111） Surfaces

Molecular dynamics simulations are preformed to investigate the diffusion behaviour of Ag/Cu double-layer islands on Ag(111)/Cu(111) surfaces, showing that atoms of the top island usually diffuse into the lower island by exchange mechanism when they move to the verge of the lower island via a concerted motion. Compared to the Cu adatoms, the Ag adatoms can easily form a kind of stable compact cluster of hexagonal island during their diffusion processes, and this cluster make it possible that the decay rate of the top Ag island is considerably slower than that of the Cu island. In addition, we find that the exchange mechanism is predominant compared to the jumping process in the simple potential calculation. These simulation results are in agreement with previous experimental observations and theoretical calculations.     

A Density Functional Study of Atomic Carbon Adsorption on δ-Pu（111） Surface

Adsorption of atomic carbon on 6-Pu（111） surface is investigated systematically using density functional theory with RPBE functional. The adsorption energies, adsorption structures, Mulliken population, work functions, layer and projected density of states are calculated in wide ranges of coverage, which have never been studied before as far as we know. It is found that the hcp-hollow sites is the energetically favorable site for all the coverage range considered. The repulsive interaction is identified, and the adsorption energy decreases with the coverage, while work function increases linearly with the coverage. It is found that the C-Pu interaction is very strong due to the hybridization between the C 2p states and the Pu 5 f , Pu 6p,Pu 6d states of topmost layer Plutonium atoms.     

Nitrogen Adatom Diffusion on a Ga－Rich GaN （0001） Surface

The diffusion of N adatoms on a Ga-rich GaN(O001) surface has been studied using density-functional theory.The configuration of Ga adatoms on a Ga-rich GaN surface has been identified. The first adlayer Ga adatoms are on top of the terminating substrate Ga atoms, and the outmost adlayer Ga adatoms exist randomly at the T4 or H3 sites. A very different diffusivity of N adatoms on a Ga-rich GaN(0001) surface has been found. The excess Ga adatoms on a GaN(0001) surface reduce the diffusion barrier by 0.75eV and influence the migration path. It seems that bilayer Ga adatoms are helpful for N atom diffusion.     

Characterization of Ag adsorption on TiC（001） substrate： an ab initio study

Ag adsorptions at 0.25-3 monolayer （ML） coverage on a perfect TIC（001） surface and at 0.25 ML coverage on C vacancy are separately investigated by using the pseudopotential-based density functional theory. The preferential adsorption sites and the adsorption-induced modifications of electronic structures of both the substrate and adsorbate are analysed. Through the analyses of adsorption energy, ideal work of separation, interface distance, projected local density of states, and the difference electron density, the characteristic evolution of the adatom-surface bonding as a function of the amount of deposited silver is studied. The nature of the Ag/TiC bonding changes as the coverage increases from 0.25 to 3 MLs. Unlike physisorption in an Ag/MgO system, polar covalent component contributes to the Ag/TiC interfacial adhesion in most cases, however, for the case of 1-3 ML coverage, an additional electrostatic interaction between the absorption layer and the substrate should be taken into account. The value of ideal work of separation, 1.55 J/m^2, for a 3-ML-thick adlayer accords well with other calculations. The calculations predict that Ag does not wet TIC（001） surface and prefers a three-dimensional growth mode in the absence of kinetic factor. This work reports on a clear site and coverage dependence of the measurable physical parameters, which would benefit the understanding of Ag/TiC（001） interface and the analysis of experimental data.     

Al（111）与Ag（001）表面电子结构与稳定性的研究

采用ＬＭＴＯ－ＡＳＡ方法，对几种不同方法获得的不尽相同的Ａｇ（１１１）“稳定表面”的表面电子结构进行了系列对比研究，给出了这些不同表面弛豫结构的电子结构特性，根据表面能的大小，指出了最稳定表面结构应为单层向内弛豫表面，并对该类表面结构的电子结构特性作了分析和讨论。     

A Study of Surfactant-Induced Growth of Ag on Ag （111）

A new growth model is introduced to describe surfactant-induced growth of Ag on Ag （111） with realistic physical parameters. In this model, the A-S exchange mechanism is considered for the first time. Using the Monte Carlo simulations, the influence of exchange mechanism, surface temperature T, the exchange barrier Eεx, and the coverage of surfactant θM on the growth mode and morphology during multilayer film growth of Ag/Ag （111） are studied in detail Both the referenced value of surfactant coverage and the method to obtain perfect layer-by-layer film in surfactantinduced Ag/Ag （111） system are provided. Our simulation results are consistent with many experimental observations for surfactant-induced growth of Ag on Ag （111）.     

Large-Area Self-Assembly of Rubrene on Au（111） Surface

Large-area self-assembly of rubrene has been fabricated on Au（111） surface and studied by scanning tunnelling microscopy. The rubrene monolayer on A u（111） surface is characterized by well-ordered row-like structures similar to the a-b plane of rubrene single crystal. However, the directions of the neighboured molecular rows are opposite to each other. In a two-layer film of rubrene on Au（111） surface, the arrangements of the top molecular rows are determined by the underneath rows, suggesting an orthorhombic crystal structure with a = 1.26 nm, b = 4.36 nm, c = 0.17nm for multilayer ofrubrene on Au（111）.     

Structural Stabilities of Ordered Arrays of Nb4 Clusters on NaCI（IO0） Surface

Adsorption of ordered （2 × 2） arrays of Nb4 clusters on the insulating surface of NaCI（100） is studied by the first-principles calculations within the density functional theory. The calculations on the relaxed geometries and cohesive energies show that both the tetrahedron and quadrangle-Nb4 can be stably adsorbed on this substrate, which may have important applications. The adsorption of quadrangle-Nb4 on the NaCl（100） surface is more stable than that of tetrahedron-Nb4. Both the Nb4 clusters studied and a single Nb atom prefer the top site of the Cl atom in the NaCl（100） surface. Electronic structure analysis suggests that the interactions between the Nb4 clusters and the substrate are weak.     

Pits and adatoms at the interface of 1-ML C84/Ag （111）

We prepare a well-defined C84 monolayer on the surface of Ag （111） and study the geometric structure by scanning tunneling microscopy （STM）. The C84 molecules form a nearly close-packed incommensurate R30° lattice. The lattice is long-distance ordered with numerous local disorders. The monolayer exhibits complex bright/dim contrast; the largest height difference between the molecules can be greater than 0.4 nm. Annealing the monolayer at 380 ℃ can desorb part of the molecules, but more than sixty percent molecules stay on the Ag （111） surface even after the sample has been annealed at 650 ℃. Our analyses reveal that the 7-atom pits form beneath many molecules. Some other molecules sit at the 1-atom pits. Ag adatoms （those removed substrate atoms, accompanying the pit formation） play a very important role in this system. The adatoms can either stabilize or destabilize the monolayer, depending on the distribution manner of the adatoms at the interface. The distribution manner is determined by the co-play of the following factors： the dimension of the interstitial regions of the C84 overlayer, the number of the adatoms, and the long-distance migration of part adatoms.     

Structural Stabilities of Ordered Nb4 Clusters on the Cu（111） and Cu（100） Surfaces

Based on first-principles calculations, we show that very high-density periodic arrays of Nb4 clusters with both the tetrahedron and quadrangle configurations can be stably absorbed on the Cu（111） and Cu（100） surfaces, with the quadrangle configurations more stable than the tetrahedron ones. The strong covalent bonding between atoms within the Nb4 clusters contributes to the stability of Nb4 adsorptions on the Cu surfaces. The energy barriers for the tetrahedron to the quadrangle-Nb4 on Cu（111） and （100） are around 1.21 eV and 0.94 eV/cluster, respectively. The stable adsorption of high-density Nb4 on these surfaces should have important applications.     

Energy loss on of low energy ion N^＋q grazing the A1（111） surface

The total energy loss of N^＋q ions （for v 〈 Bohr velocity） grazing on the Al（111） has been simulated without any ＇fit＇ parameter and compared with the experimental data. The energy loss due to the charge exchange, happening before the N^＋q hits the Al（111） surface, is studied. The present simulation shows that the energy loss strongly depends on the charge state of the projectile and the lattice orientation of Al（111） surface. The calculated total energy loss agrees with experimental data very well.     

Strain-Driven Formation of Nanostripes on In/Si（113） Surface

Periodic nanostripe arrays are observed on In/Si（113） surface using scanning tunneling microscopy. The stripe superstructures are identified as N × 1 reconstructions elongating in [211] or [121] direction and consisting of one vacancy line, one Si adatom row, and N - 2 In rows, in which N = 5 is predominant. The vacancy line formation relieves the strain induced by the Si adatom row and In rows, and plays an important role in stabilizing the stripe structures. The stability of nanostripe structures is demonstrated by analyzing the strain-mediated interaction of vacancy lines in the framework of the Frenkel-Kontorova model, which indicates that the predominant vacancy line period of N = 5 corresponds to the minimum Frenkel Kontorova energy.     

Initial Processes of Sulfur Adsorption on Si（100） Surface

The adsorption of one monolayer S atoms on ideal Si（100） surface is studied by using the self-consistent tight binding linear muffon-tin orbital method. Energies of adsorption systems ors atoms on different sites are calculated. It is found that the adsorbed S atoms are more favorable on B1 site （bridge site） with a distance 0.131 nm above the Si surface. The .S, Si mixed layer might exist at S/Si（100） interface. The layer projected density of states are calculated and compared with that of the clean surface. The charge transfers are also investigated.     

Microstructural Properties of Single Crystalline PbTe Thin Films Grown on BaF2（111） by Molecular Beam Epitaxy

Single crystal PbTe thin films have been grown on BaF2 （111） by using solid source molecular beam epitaxy. The studies of evolution of the surface morphology with the increasing growth temperature from 375 to 525℃ by AFM show that PbTe epilayers exhibit smooth surface morphologies with atomic layer scale roughness and are crack free. It is found that for PbTe grown at 475℃, the morphology is dominated by triangles and the rms roughness is 3.987nm. Compared to the rms roughnesses of 0.432nm and 0.759nm for the samples grown at 375 and 525℃ respectively, the surface of the PbTe layer grown at 475℃ is much rougher. This roughening transition is due to the interaction between the elastic relaxation and the plastic relaxation during the strain relaxation process. In contrast to the result of the morphology that the PbTe epitaxial layer grown at 375℃ has most smooth surface, as observed from the line width of x-ray diffraction curves at higher growth temperature improves the crystal quality of the single-crystalline Pb Te layer.     

Structures and Electronic Properties of CuN （N≤13） Clusters

A systematic study on the structures and electronic properties of copper clusters has been performed using the density functional theory. In the calculation, there are many isomers near the ground state for small copper clusters. Our results show that the three-dimensional isomers of copper clusters start from Cu7 cluster and then show a tendency to form more compact structures. The results of the formation energy and the second derivative of binding energy with duster size show that besides N = 8, N =11 is also a magic number. Furthermore, it is the first time to find that the ground state of 11-atom clusters is a biplanar structure as same as the 13-atom cluster. The clear odd-even alternation as cluster size for the formation energy indicates the stability of electronic close shell existed in the range studied.