Scanning tunneling microscopy on self-assembled calix[4]resorcinarene monolayer adsorbates on Au(111)

Self-assembled Monolayers of calix[4]resorcinarene receptor molecules on Au(111) were studied by UHV scanning tunneling microscopy and X-ray photoelectron spectroscopy. Highly ordered monolayers were observed with domains oriented at an angle of 60° relative to each other. Molecularly resolved images were investigated and lattice constants found which depended on the preparation solvent. The STM images of two samples, one prepared in 1 mM chloroform/ethyl alcohol adsorbate solution and one in 1 mM hexane adsorbate solution are consistent with having a ×2 and 4×2 lattice, respectively. Received: 22 September 1999 / Accepted: 28 March 2000 / Published online: 11 May 2000     

Scanning tunnelling microscopy and electronic structure of Mn clusters on Ag(111)

Small Mn clusters (Mn₁-Mn₄) are prepared by manipulation of Mn adatoms on Ag(111) with the tip of a scanning tunnelling microscope. The apparent heights of the clusters are observed to increase monotonously from 1.6 Å for a monomer to 2.2 Å for a tetramer. Self-consistent calculations of the electronic structure of these clusters are in encouraging agreement with the experimental data.     

A scanning tunneling microscopy study of the adsorption of Xe on Pt(111) up to one monolayer

The adsorption of Xe on Pt(111) has been investigated from the arrival of the very first atoms up to completion of the monolayer using a variable-temperature Scanning Tunneling Microscope (STM). Surprisingly, in the initial stages of the adsorption Xe preferentially binds to a low coordination site, theupper edge of the platinum steps. The strong binding to these sites leads to a local repulsive interaction with further Xe atoms. Therefore, the Xe atoms located at the upper edge of the steps do not serve as nuclei for 2D Xe islands, which, instead, form on the terraces and at thelower edges of the platinum steps. Only during completion of the monolayer do these islands make contact with the atoms adsorbed at the beginning in the upper-edge positions. The full monolayer exhibits the Hexagonal Incommensurate Rotated (HIR) phase already known from earlier helium-diffraction experiments.     

铜箔上生长的六角氮化硼薄膜的扫描隧道显微镜研究

利用扫描隧道显微镜研究了采用化学气相沉积法在铜箔表面生长出的高质量的六角氮化硼薄膜. 大范围的扫描隧道显微镜图像显示出该薄膜具有原子级平整的表面, 而扫描隧道谱则显示, 扫描隧道显微镜图像反映出的是该薄膜样品的隧穿势垒空间分布. 极低偏压的扫描隧道显微镜图像呈现了氮化硼薄膜表面的六角蜂窝周期性原子排列, 而高偏压的扫描隧道显微镜图像则呈现出无序和有序排列区域共存的电子调制图案. 该调制图案并非源于氮化硼薄膜和铜箔衬底的面内晶格失配, 而极有可能来源于两者界面处的氢、硼和/或氮原子在铜箔表面的吸附所导致的隧穿势垒的局域空间分布.     

Scanning tunneling microscopy study of surface reconstruction induced by N adsorption on Cu (100) surface

The reconstructed structure of Cu (100) surface induced by atomic N adsorption is studied by using scanning tunneling microscopy (STM). The 2D structure of copper boundary between neighbouring N covered islands is found to be sensitive to the growth conditions, e.g. N⁺ bombardment time and annealing temperature. The copper boundary experiences a transition from nano-scale stripe to nano-particle when the substrate is continuously annealed at 623~K for a longer time. A well-defined copper-stripe network can be achieved by precisely controlling the growth conditions, which highlights the possibility of producing new templates for nanofabrication.     

Scanning tunneling microscopy study of the growth and self-organization of Ge nanostructures on vicinal Si(111) surfaces

The initial stages of Ge growth on Si(111) vicinal surfaces tilted in the [ $\overline 1 \overline 1 2$ ] and [ $11\overline 2 $ ] directions were studied in situ in the temperature range 350–500°C using scanning tunneling microscopy. It was shown that, at low Ge deposition rates of 10^?2 to 10^?3 BL/min, ordered Ge nanowires can form on surfaces tilted in the [ $\overline 1 \overline 1 2$ ] direction under conditions of step-layered growth. The height of a nanosized Ge wire is one or three interplanar distances and is determined by the initial height of a silicon step. It was established that, during epitaxial growth, steps with a [ $11\overline 2 $ ] front are replaced by steps with a [ $\overline 1 \overline 1 2$ ] front. As a result, the step edge is serrated and the formation of smooth nanosized Ge wires uniform in width is hampered on the serrated Si(111) surfaces tilted in the [ $11\overline 2 $ ] direction.     

Scanning tunneling microscopy observation of copper-phthalocyanine molecules on Si(100) and Si(111) surfaces

Molecules of Cu-phthalocyanine (CuPc) deposited on Si(100) and Si(111) surfaces have been observed by an ultra high vacuum field ion scanning tunneling microscope (FI-STM). On a Si(100) surface, STM images with four-fold symmetry are observed, which reflect the shape of the CuPc molecule. The STM pictures show that CuPc molecules are deposited with the molecular plane parallel to the substrate surface and have three kinds of adsorption configurations on the dimer-row of Si(100). The images of the CuPc are modified by the electronic state of the Si(100) surface. This behavior suggests strong interaction between the molecule and the substrate. The molecular images on the Si(111) surface have a unique bias-voltage dependence. At a sample bias of 1.6 V, the molecule looks transparent by STM, and becomes dark like a vacancy at 1.2 V. From the bias dependence, the electronic interaction between the CuPc molecule and the Si surface is discussed.     

Ag growth on Si(111) with an Sb surfactant investigated by scanning tunneling microscopy

We have investigated a room-temperature growth mode of ultrathin Ag films on a Si(111) surface with an Sb surfactant using STM in a UHV system. On the Sb-passivated Si surface, small sized islands were formed up to 1.1 ML. Flat Ag islands were dominant at 2.1 ML, coalescing into larger islands at 3.2 ML. Although the initial growth mode of Ag films on the Sb-terminated Si(111) surface was Volmer-Weber (island growth), the films were much more uniform than Ag growth on clean (Si(111) at the higher coverages. From the analysis of STM images of Ag films grown with and without an Sb surfactant, the uniform growth of Ag films using an Sb surfactant appears to be caused by the kinetic effects of Ag on the preadsorbed Sb layer. Our STM results indicated that Sb suppresses the surface diffusion of Ag atoms and increases the Ag-island density. The increased island density is believed to cause coalescence of Ag islands at higher coverages of Ag, resulting in the growth of atomically flat and uniform Ag islands on the Sb surfactant layer.     

The Tamm surface state on Cu(111) and Ag(111)

It is shown, that the well-known d-electron Tamm surface-state emission observed in photoelectron spectra from Cu(111) at the M̄ point in the surface Brillouin zone, is indeed due to such a surface state and not a bulk band transition as recently suggested L. Wallden, Solid State Commun. 59, 205 (1986). A similar surface state on Ag(111) is reported.     

First-principles calculation of ZnS monolayer on Cu(111) surface

First-principles calculation is carried out on the interface of the ZnS(001) monolayerand Cu(111) surface. It is found that the ZnS monolayer significantly reconstructs aftergeometry optimization. The out-of-plane S atom has a positive displacement in thez directionwhile other atoms (Zn and S) have small displacements on the ZnS monolayer. The interfacestacking sequence has an influence on the flatness of the ZnS monolayer and the bindingenergy of the interface. There are two approaches for the ZnS monolayer to reach thelowest energy state which take place on the two kinds of S atoms in the ZnS monolayer andresult in the bulging feature. The van der Waals (vdW) interaction exists between ZnSmonolayer and Cu surface.     

Comparison of electronic structure between monolayer silicenes on Ag(111)

√√The electronic structures of monolayer silicenes(4 × 4 and■×■R13.9o) grown on Ag(111) surface are studied by scanning tunneling spectroscopy(STS) and density functional theory(DFT) calculations. While both phases have similar electronic structures around the Fermi level, significant differences are observed in the higher energy unoccupied states.The DFT calculations show that the contributions of Si 3pz orbitals to the unoccupied states are different because of their different buckled configurations.     

Two commensurate hydrogen-bonded monolayer structures of melamine on Ag(111)

Melamine (1,3,5-triazine-2,4,6-triamine) was deposited on the Ag(111) surface under ultrahigh vacuum conditions. It forms two different monolayer structures, which were investigated by low energy electron diffraction and scanning tunneling microscopy. The α-phase is a honeycomb structure containing two molecules per unit-cell. The molecular orientation within the unit-cell is determined by six hydrogen bonds. The α-phase is kinetically preferred upon deposition at room-temperature and can be transferred to the thermodynamically more stable β-phase by annealing at 333 K. The β-phase has an oblique unit-cell containing four molecules and shows a higher surface density with additional hydrogen bonds between adjacent amino groups. Both structures are commensurate. While the structural motif of the α-phase has been observed before on Au(111) and Ag–Si(111) surfaces, the structure of the β-phase has been so far only theoretically predicted.