Direct observation of an ordered step surface reconstruction on Au(111) by scanning tunneling microscopy

Experiments with a scanning tunneling microscope (STM) are reported which include the first surface topographic images of Au(111), cleaned and annealed in ultrahigh vacuum. The STM system used for this work includes in situ sample manipulation for sample cleaning, annealing and characterization. Topographs with very large atomically flat (111) regions are obtained and no corrugation on the scale of about 0.1 Å is observed. Some single atomic steps are observed. Surprisingly, ordered arrays of single steps are observed over a large region. These represent a type of surface reconstruction whose repeat period agrees with values derived from previous LEED, TEM and ion scattering measurements. These results represent the first critical information about the surface topography of the Au(111) surface.     

Observation of sputtering damage on Au(111)

The morphology of a Au(111) surface has been observed with the STM (scanning tunneling microscope) after ion bombardment with 2.5 keV Ne⁺ ions at about 400 K. Mostly triangular and hexagonal shaped vacancy islands are seen in the STM topographs. They are bounded by monatomic steps, oriented along the closed packed 110 directions. The general morphology confirms the conclusions inferred from TEAS (thermal energy atom scattering) measurements on ion bombarded Pt(111) surfaces. The observation of a propensity for the formation of {100} microfacetted 110 ledges is discussed.     

Au-CdSe纳米异质结在Au(111)表面上的分散与STM表征

研究单个Au-CdSe纳米异质结在经过表面修饰的Au(111)上的分散并进行STM表征. 发现衬底表面的自组装分子层的顶端功能基团对于形成良好的异质结分散状态非常重要. STM表明,巯基和羧酸基都能与异质结的Au纳米颗粒部分形成强烈的相互作用,从而将异质结有效地抓住,避免了团聚现象,便于异质结形成孤立分散的样品结构. 还可以采用条件适中的氩离子溅射技术来清除样品表面残留的有机物,从而得到较清晰的单个Au-CdSe纳米异质结的STM图像.     

(111) facets as the origin of reconstructed Au(110) surfaces

The Au(110) surface has been investigated by scanning tunneling microscopy. The reconstructed surface consists of long ribbons of narrow (111) facets along the [1$\text{1}$0] direction with maximum three free rows. Two-row facets give rise to the 1 × 2 reconstruction of the missing-row type, while three-row facets account for the 1 × 3 reconstruction. Disorder arises from locally random sequences of the two facets.     

Electric-dipole layer on Au(111) surfaces

We measured the barrier height (BH) a UHV scanning tunneling microscope on Au(111) surfaces with Au, Pt, and carbon nanotube tips. The 222?{^[¯] }3^[¯]\sqrt\Box3\Box]] reconstruction was observed with all the tips, and the current-voltage relation reflected the density of states of the tips. The BH measured on the reconstructed Au(111) surface using a modulation method showed a bias-polarity dependence as 30%, at low currents (<100 pA) irrespective of the tip material, while on unreconstructed Au surfaces, BH values were independent of the bias polarity, suggesting a dipole layer originating from the reconstructed Au(111) surface.     

Gold-adatom-mediated bonding in self-assembled short-chain alkanethiolate species on the Au(111) surface

Microscopic evidence for Au-adatom-induced self-assembly of alkanethiolate species on the Au(111) surface is presented. Based on STM measurements and density-functional theory calculations, a new model for the low-coverage self-assembled monolayer of alkanethiolate on the Au(111) surface is developed, which involves the adsorbate complexes incorporating Au adatoms. It is also concluded that the Au(111) herringbone reconstruction is lifted by the alkanethiolate self-assembly because the reconstructed surface layer provides reactive Au adatoms that drive self-assembly.     

Manipulation and control of a single molecular rotor on Au (111) surface

Three different methods are used to manipulate and control phthalocyanine based single molecular rotors on Au (111) surface: (1) changing the molecular structure to alter the rotation potential; (2) using the tunnelling current of the scanning tunnelling microscope (STM) to change the thermal equilibrium of the molecular rotor; (3) artificial manipulation of the molecular rotor to switch the rotation on or off by an STM tip. Furthermore, a molecular `gear wheel' is successfully achieved with two neighbouring molecules.     

Ordered structures of two sulfur containing donor molecules on the Au(111) surface

We report experiments by low energy electron diffraction (LEED) and scanning tunneling microscopy (STM) on ordered structures of two sulfur-containing π-conjugated molecules on the Au(111)-surface, namely tetrabenzothianthrene (TBTA) and tetrathiotetracene (TTT). These molecules are candidates for donors in charge transfer salts. On Au(111) both molecules form long-range ordered structures that are commensurate to the top-most surface layer. For TBTA, the reconstruction of the Au(111) surface is maintained, whereas it is lifted by TTT. Both molecules lie flat on the surface. For TBTA, the structure indicates that the molecule is planarized upon adsorption.     

Confining barriers for surface state electrons tailored by monatomic Fe rows on vicinal Au111 surfaces

We fabricated monatomic Fe wires on vicinal Au(111) surfaces and found that decoration of step edges with Fe adatoms has a significant influence on the behavior of surface state electrons confined between regularly arranged steps. On a surface with Fe monatomic rows, angle-resolved photoemission spectra measured in the direction perpendicular to the steps shows parabolic dispersion, in contrast to one-dimensional quantum-well levels observed on a clean surface. Simple analysis using a one-dimensional Kronig-Penney model reveals potential barrier reduction from 20 to 4.6 eV A, suggesting an attractive nature of the Fe adatoms as scatterers.     

Understanding formation of molecular rotor array on Au(111) surface

The motion of single molecules on surfaces plays an important role in nanoscale engineering and bottom-up construction of complex devices at single molecular scale. In this article, we review the recent progress on single molecular rotors self-assembled on Au(111) surfaces. We focus on the motion of single phthalocyanine molecules on the reconstructed Au(111) surface based on the most recent results obtained by scanning tunneling microscopy (STM). An ordered array of single molecular rotors with large scale is self-assembled on Au(111) surface. Combined with first principle calculations, the mechanism of the surface-supported molecular rotor is investigated. Based on these results, phthalocyanine molecules on Au (111) are a promising candidate system for the development of adaptive molecular device structures.     

The influence of sulfur adsorption on the step structure of vicinal Mo(100): a LEED and STM study

The effect of sulfur adsorption on the step structure of vicinal Mo(100) surfaces has been studied with scanning tunneling microscopy (STM) and low energy electron diffraction (LEED). STM was used for low densities of steps on a nominally flat (100) surface. LEED was used to study the more highly and regularly stepped (910), (911), and (28,4,1) oriented surfaces. Steps and the sulfur adsorbate were found to have a strong interaction. The presence and orientation of steps on the surface governed the formation of ordered domains of sulfur, and sulfur modified the structure of the steps on the surface. Both techniques show that monatomic steps predominate on the clean surfaces. When sulfur was adsorbed on the surfaces, however, steps coalesced to form groups of steps, double atomic height steps, and multiple height steps, depending on sulfur coverage and initial step density. The results are discussed in the framework of the theory of equilibrium crystal shape and provide information on how the Mo step-step interactions are affected by sulfur adsorption.     

Local Au coverage as driving force for Au induced faceting of vicinal Si(0 0 1): a LEEM and XPEEM study

Adsorption of Au at 850°C on a regular stepped 4° vicinal Si(0 0 1) surface results in a dramatic change of the step morphology: the surface decomposes into areas which are perfectly flat with a (0 0 1) orientation and (1 1 9) facets. Low energy electron microscopy shows the dynamics of the faceting process in real space while X-ray photoemission electron microscopy (XPEEM) allows a spatially resolved determination of the Au coverage at different stages of the faceting process. At a critical Au coverage of ≈1/3 ML (0 0 1) terraces are formed which extend anisotropically along the step edges of the surface. The steps in between the terraces bunch and form step bands in order to conserve the macroscopic miscut of the sample. Driving force for this morphological transformation is a complex (5×3.2) reconstruction formed on the (0 0 1) terraces. XPEEM shows this phase separation also for the Au coverage: on the (0 0 1) terraces the Au coverage is up to 40% higher compared to the step bands. With further increasing Au coverage the width of the Au rich terraces increases while the step bands become steeper. In a second step Au adsorbs on the step bands transforming them into well defined and smooth (1 1 9) facets.     

Influence of the surface morphology of single-crystal Si(111) substrates on the magnetic properties of epitaxial cobalt films

The epitaxial films Co(111)/Cu(111)-R30°/Si(111) have been grown on the atomically smooth and vicinal Si(111) surfaces. The roughnesses of the substrate and the cobalt film have been determined using scanning tunneling microscopy. The dependence of the coercive force has been investigated as a function of the azimuthal angle. The dependence of the magnetic anisotropy and the coercive force on the surface roughness has been determined. It has been shown that, in the epitaxial cobalt films deposited on the atomically smooth silicon surfaces, crystalline anisotropy of the 〈110〉 type leads to the isotropy of the magnetization reversal processes. The step-induced uniaxial anisotropy has been observed upon deposition on the vicinal surfaces. The films deposited on the atomically smooth surfaces have a complex domain structure.     

Iodine adlayer structures on Au(111) as discerned by atomic-resolution scanning tunnelling microscopy: relation to iodide electrochemical adsorption

Coverage-dependent adlayer structures of iodine on Au(111) in air or organic solvents obtained by using a high-precision “beetle” — type scanning tunnelling microscope are reported in comparison with those obtained under potential control in aqueous electrochemical environments. The well-known (√3 × √3)R30° structure (Θ_I = 0.33) was only observed at the electrochemical interface at low potentials. Instead, two higher coverage adlattices are evident from the present STM images. The first comprises a (5 × √3) structure (Θ_I = 0.40), with a pair of iodine rows compressed by 20% in the R30° substrate direction. The second high-coverage phase (Θ_I ≈ 0.44) consists of a hexagonal iodine overlayer compressed and rotated a few degrees from the R30° direction, giving rise to a long-range (~ 20 Å) corrugation in the STM image. The virtues of quantitative atomic-resolution STM for deducing such complex adiayer structures are pointed out.     

The Si(111)−(5 × 1) Au structure

By combining recent results from STM, LEEM, LEED and X-ray diffraction a structure model is developed for the (5 × 1) structure observed in the Au/Si(111) system at low coverages.     

STM manipulation of a subphthalocyanine double-wheel molecule on Au(111)

A new class of double-wheel molecules is manipulated on a Au(111) surface by the tip of a scanning tunneling microscope (STM) at low temperature. The double-wheel molecule consists of two subphthalocyanine wheels connected by a central rotation carbon axis. Each of the subphthalocyanine wheels has a nitrogen tag to monitor its intramolecular rolling during an STM manipulation sequence. The position of the tag can be followed by STM, allowing us to distinguish between the different lateral movements of the molecule on the surface when manipulated by the STM tip.     

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...     

Surface morphology of a Si(310) substrate used for molecular beam epitaxy of CdHgTe: II. Si(310) surface annealed in As4 vapors

The morphology of a hydrogenated Si(310) surface annealed in As₄ vapors is studied by fast electron diffraction and scanning tunneling microscopy. It is established that, at annealing temperatures above 700°C, the surface morphology is changed; namely, (311) facets and steps with heights equal to several interplanar distances are formed. At temperatures below 600°C, there is no surface faceting and the height of steps is equal to two interplanar distances. This makes this surface suitable for growing A²B⁶-based heterostructures.     

Ex situ STM imaging with atomic resolution of Ni(111) electrodes passivated in sulfuric acid

Scanning tunneling microscopy has been used to study in air Ni(111) electrodes passivated in 0.05M H₂SO₄ at + 650 mV/SHE. Before passivation, the Ni(111) single crystal surface has steps along the 〈1&#x0304;10〉 directions with terraces having a width of a few hundred nanometers. After passivation, a mosaic structure is formed with crystallites of 2 to 3 nm in size and strip-like features extended mainly along the [12&#x0304;1] direction whose width ranges from 2 to 3 nm and which appear to be locally tilted from 5 to 13°. Atomic resolution imaging has been achieved on both of these features. It reveals a corrugated lattice whose parameters are 0.30 ± 0.02 nm and 117 ± 3° in agreement with those of NiO(111). The crystallites have smooth step edges along [1&#x0304;01] and [011&#x0304;]. The STM imaging of the passive film as well as its mosaic structure are discussed.     

Interaction of HNCO with Au(111) surfaces

The surface chemistry of isocyanic acid, HNCO, and its dissociation product, NCO, was studied on clean, O-dosed and Ar ion bombarded Au(111) surfaces. The techniques used are high resolution energy loss spectroscopy (HREELS) and temperature-programmed desorption (TPD). The structure of Ar ion etched surface is explored by scanning tunneling microscopy (STM). HNCO adsorbs molecularly on Au(111) surface at 100 K yielding strong losses at 1390, 2270 and 3230 cm^? 1. The weakly adsorbed HNCO desorbs in two peaks characterized by T_p = 130 and 145 K. The dissociation of the chemisorbed HNCO occurs at 150 K to give NCO species characterized by a vibration at 2185 cm^? 1. The dissociation process is facilitated by the presence of preadsorbed O and by defect sites on Au(111) produced by Ar ion bombardment. In the latter case the loss feature of NCO appeared at 2130 cm^? 1. Isocyanate on Au(111) surface was found to be more stable than on the single crystal surfaces of Pt-group metals. Results are compared with those obtained on supported Au catalysts.