Initial growth stages of manganese films on the Si(100)2 × 1 surface

Initial growth stages of manganese films on the Si(100)2 × 1 surface at room temperature have been investigated using high-energy-resolution photoelectron spectroscopy, and the dynamics of the variation in their phase composition and electronic structure with the coverage growth has been revealed. It has been shown that the interfacial manganese silicide and the film of the solid solution of silicon in manganese are sequentially formed under these conditions on the silicon surface. The growth of the metal manganese film starts after the deposition of ～0.9 nm Mn. Segregation of silicon on the film surface is observed in the range of coverages up to 1.6 nm Mn.     

STM study of Pd growth on TiO2(100)-(1 × 3)

STM has been used to study the initial growth of palladium on TiO₂(100)-(1 × 3). The results demonstrate that STM is capable of imaging individual atoms which form part of a supported metal cluster. The data were obtained from small (35Ådiameter by 8Åhigh) clusters at a dispersed-equivalent coverage of about 0.01 ML. At higher coverages the clusters coalesce.     

Initial stages of the growth and magnetic properties of cobalt films on the Si(100)2 × 1 surface

Physics of the Solid State - The initial stages of the growth of cobalt films on the Si(100)2 × 1 surface and the dynamics of variation in their phase composition, electronic structure, and...     

STM investigation of the reaction of AgO added rows with CO2 on a Ag(110) surface

The formation of carbonate species by a reaction of AgO added rows with CO₂ was investigated by scanning tunneling microscopy (STM). STM observation during the reaction revealed that the AgO added rows were compressed from a (4 × 1) to a (2 × 1) phase, according to the growth of carbonate domains. Though the carbonate domains give a (1 × 2) diffraction pattern, STM images of this domain do not show a (1 × 2) structure, which indicates that the Ag substrate reconstructs to a (1 × 2) structure. Though the CO₃ species thermally decompose at a lower temperature than AgO added rows, the AgO added rows can be selectively decomposed by ultraviolet irradiation.     

Dangling-bond logic gates on a Si(100)-(2 × 1)-H surface

Atomic-scale Boolean logic gates (LGs) with two inputs and one output (i.e. OR, NOR, AND, NAND) were designed on a Si(100)-(2 × 1)-H surface and connected to the macroscopic scale by metallic nano-pads physisorbed on the Si(100)-(2 × 1)-H surface. The logic inputs are provided by saturating and unsaturating two surface Si dangling bonds, which can, for example, be achieved by adding and extracting two hydrogen atoms per input. Quantum circuit design rules together with semi-empirical elastic-scattering quantum chemistry transport calculations were used to determine the output current intensity of the proposed switches and LGs when they are interconnected to the metallic nano-pads by surface atomic-scale wires. Our calculations demonstrate that the proposed devices can reach ON/OFF ratios of up to 2000 for a running current in the 10 μA range.     

High-resolution study of dipole-active vibrations at the Ag(110) (n × 1)O surface

Atomic chemisorption of oxygen on Ag(110) at room temperature has been studied by high resolution electron energy loss spectroscopy (HREELS). It is well known that upon increasing exposure the LEED pattern sequentially changes as (n × 1), with n = 7, 6, ⋯ 2. We present the first dear evidence that the oxygen vibration frequency changes from (ω⊥ = 38.5 meV (n = 7) to 40.9 meV (n = 2). Simultaneously the surface phonon observed on Ag(110) at 13.2 meV shifts to 17.0 meV (at n = 2) and a second phonon appears at lower energies (8.7 meVatn = 2). We discuss implications of our data for the formation of the (n × 1) added row structure.     

The interaction between hexahydroxytriphenylene and the rutile TiO2(110)-(1 × 1) surface at UHV conditions

The interaction between 2,3,6,7,10,11-hexahydroxytriphenylene (HHTP) and the rutile TiO₂(110)–(1 × 1) surface under ultrahigh vacuum (UHV) conditions was investigated using X-ray photoemission spectroscopy (XPS), ultraviolet photoemission spectroscopy (UPS), near-edge X-ray absorption fine structure (NEXAFS) spectroscopy, and density functional theory (DFT) calculations. The NEXAFS results showed that HHTP molecules formed a submonolayer and a monolayer that aligned along the [001]-direction with, respectively, a more or less flat downward orientation and a more upright orientation to the TiO₂ surface. The HHTP molecules that aligned along the [001]-direction were most likely grafted onto the TiO₂(110) surface by a bidentate bridge between each of the oxygen atoms of one of the catechol units within the HHTP molecule and two adjacent Ti(5f)⁴⁺ ions on the TiO₂(110) surface. The coordination is non-dissociative in the case of the submonolayer, but dissociative in the monolayer, according to the analysis of the C1s XPS, UPS, C1s NEXAFS data and complementary DFT calculations.     

STM characterization of size-selected V1, V2, VO,and VO2 clusters on a TiO2(110)-(1 × 1) surface at room temperature

We use ultra-high vacuum scanning tunneling microscopy (UHV–STM) to probe, at the atomic level, the structure of mass-selected isolated V₁, V₂, VO and VO₂ clusters deposited on rutile TiO₂(110) by ion soft landing. All four species interact differently with the TiO₂ surface and the ultimate binding site and configuration strikes a balance between the gas-phase structure and the ligation of this cluster by the TiO₂ surface. Our results show that vanadium atoms prefer to bind in the upper threefold hollow sites on the surface and have a slight tendency to pair along the [1–10] direction, while vanadium dimers bind to the surface oriented along the [001] direction exclusively. VO clusters bind with the vanadium atom in the upper threefold hollow site and with the oxygen atom bound to an adjacent fivefold coordinated Ti atom (5c-Ti). The VO₂ cluster also binds with the vanadium atom in the upper threefold hollow site and with both oxygen atoms bound to adjacent 5c-Ti atoms or with only one oxygen bound to the surface and the other directed out of the plane of the surface.     

Peculiarities of the initial stage of growth of niobium-based nanostructures on a Si(111)-7 × 7 surface

The initial stage of growth of nanoislands prepared by thermal deposition of niobium on the reconstructed surface of Si(111)-7 × 7 in ultrahigh vacuum is experimentally investigated. The morphological and electrophysical properties of niobium-based nanostructures are studied by means of low-temperature scanning tunneling microscopy and spectroscopy. It is found that upon the deposition of niobium on a substrate at room temperature, clusters and nanoislands are formed on the silicon surface, having a characteristic lateral size of 10 nm with the metallic type of tunneling conductivity at low temperatures. Upon the deposition of niobium on a heated substrate, quasi-one-dimensional (1D) and quasi-two-dimensional (2D) structures with typical lateral dimensions of up to 200 nm and three-dimensional pyramidal islands with semiconducting type of tunneling conductivity at low temperatures are formed.     

The adsorption of nitric oxide on a silicon (100) 2 × 1 surface studied with Auger electron spectroscopy

We present an Auger electron spectroscopy (AES) study of the adsorption of nitric oxide (NO) on a clean Si(100)2 × 1 surface at 300 and 550 K. Accurate measurement reeveal well resolved fine structure at Auger SiL_2.3VV transitions at 62 and 83 eV. These peaks can be attributed to SiO and SiN bonds. Furthermore, it is argued that the broadening in the SiLi_2.3VV Auger transition at 83 eV at 300 K may be composed of two nearby peaks, which could be attributed to two different kinds of chemical bonding, SiN and SiO. The absence of a peak at 69 eV at room temperature strongly suggests the NO adsorption on a Si(100)2 × 1 surface to be molecular. Dissociation of NO on the Si(100)2 × 1 surface is observed at 550 K.     

Observation of a line growth fault on the Si(111)-7 × 7 surface using STM

Using a scanning tunnelling microscope we have observed an interesting new fault on the Si(111)-7 × 7 surface, corresponding to an adatom registry shift of 1 bulk unit cell in the [1̄1̄2] direction. We propose a model to account for the structure along the fault.     

Adsorption behavior of iron phthalocyanine on a Ag（110） surface

An investigation on the growth behavior of FePc on a Ag(110) surface is carried out by using scanning tunneling microscopy(STM).At an FePc coverage of 3.5 ML,an ordered superstructure(densely packed) with a lateral shift is observed.The densely packed superstructure can be attributed to the substrate commensuration and the intermolecular van der Waals attractive interaction.The in-plane lateral shift in the superphase is specifically along the direction of [10] azimuth.The results provide a new perspective to understanding the intermolecular and the molecule-substrate interactions.     

Ab initio study of surface electronic structure of phosphorus donor impurity on Ge(111)-(2×1) surface

We present the results of numerical modeling of the electronic properties of the Ge(111)-(2 × 1) surface in the vicinity of a P donor impurity atom near the surface. We have shown that, in spite of well-established bulk donor impurity energy level position at the very bottom of the conduction band, the surface donor impurity might produce an energy level below the Fermi energy, depending on impurity atom local environment. It has been demonstrated that the impurity located in subsurface atomic layers is visible in scanning tunneling microscopy experiment. The quasi-one-dimensional character of the impurity image observed in scanning tunneling microscopy experiments is confirmed by our computer simulations.     

How atoms move in the (1 × 1) to (1 × 2) surface reconstruction of fcc (110) planes

The result of a recent study of atomic steps in the (1 × 1) to (1 × 2) surface reconstruction of Pt and Ir (110) planes using ns pulsed-laser heating can only be understood by highly correlated jumps of atoms within a small [110] atom-row. We argue in favor of a simultaneous jump of the entire small [110] row of atoms, possibly stimulated by surface phonon waves propagating in the direction normal to, and also parallel to, the atom-row direction. Surface reconstruction of fcc (110) planes evolves with long-range atomic diffusion, thus the transition occurs relatively slowly. Reconstruction of fcc (001) planes evolves with short-range atomic movements, and the transition occurs very rapidly.     

Self-assembled line growth of allyl alcohol on the H-terminated Si(100)-(2 × 1) surface

Using first-principles density-functional calculations, we investigate the growth mechanism of allyl alcohol (ALA) line on the H-terminated Si(100)-(2 × 1) surface. Unlike the allyl mercaptan (CH₂ = CH ? CH₂ ? SH) line, which was observed to grow across the Si dimer rows, we find that ALA (CH₂ = CH ? CH₂ ? OH) has the line growth along the Si dimer row. The self-assembled growth of ALA line occurs via the radical chain reaction mechanism, similar to the case of a typical alkene molecule, styrene. Our calculated energy profile along the reaction pathway shows that the different growth direction of ALA line compared with that of allyl mercaptan line is ascribed to the great instability of the oxygen radical intermediate, which prevents the line growth across the dimer rows.     

A first-principles study on initial processes of a Ni adatom on the H-terminated Si(0 0 1)-(2×1) surface

We studied the adsorption, surface diffusion, and penetration, i.e. the initial processes of a Ni adatom on the H-terminated Si(001)-(2×1) surface by the first-principles theoretical calculations. As concerns the adsorption, two different types were found. When Ni is deposited onto the Si dimer row, it once captures H from the dimer Si, though it eventually returns H, with no activation energy barrier. Then, Ni moves to the most stable site, which is the off-centered bridge (B) site between the dimer rows, with the activation energy of 0.65 eV. On the other hand, Ni deposited between the dimer rows captures no H and moves to the B site without the energy barrier. Thus an adsorbed Ni atom invariably arrives at the most stable B site at the room temperature. As for the surface diffusion, it needs the activation energies of 0.66 and 1.19 eV for Ni to migrate from the B site in the directions parallel and perpendicular to the dimer row, respectively. Therefore, we concluded that the surface diffusion of Ni is restricted in the valley between the dimer rows at the room temperature. Furthermore, since the penetration of Ni is blocked on this surface, it was also concluded that the surface hydrogenation suppresses silicidation.     

HREELS study of C70 molecules adsorbed on a Si(1 1 1)-(7×7) surface

We have measured the coverage dependence of vibrational excitation spectra of C₇₀ molecules adsorbed on a Si(1 1 1)-(7×7) surface using high-resolution electron-energy-loss spectroscopy. At the monolayer coverage, the intensity of the 57 meV peak increases, and those of the 83 and 178 meV peaks decrease. Taking into account the dipole selection rule, the change in intensity of the 57 meV peak indicates that the average angle between the long axes of C₇₀ molecules and surface normal is about 40°. The decreases in intensities of the 83 and 178 meV peaks suggest that the rotational motion of molecules is quenched upon adsorption. We will discuss the Coriolis interaction between the accidentally degenerate A₂″ and E₁′ modes.