What orchestrates the self-assembly of glycine molecules on Cu(100)?

The structures of two competing phases and their interrelationship in the self-organization of glycine molecules on a Cu(100) surface were clarified. Despite their similar structural energies predicted using first-principles calculation, completely different mechanisms were found to stabilize the two phases. The balance and coordination of the two mechanisms that induce a variety of self-assembled structures in this attractive system were revealed. Furthermore, the importance of the microscopic arrangement of the molecules in designing the macroscopic electronic structures was directly demonstrated.     

The first excited state in 23Al and its influence on 22Mg(p,γ)23Al

The excitation energy of the first excited state in ²³Al was determined by the ²⁴Mg(⁷Li, ⁸He) reaction. The state is observed to be at 460 ± 60 keV and belongs to the first excited A = 23 isospin quartet. The results are used to compute the coefficients of the isobaric multiplet mass equation. The influence of this state, a resonance in the ²²Mg(p,γ) channel, on the reaction flow in rp-process nucleosynthesis is discussed in detail.     

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.     

Solid-phase synthesis of manganese silicides on the Si(100)2 × 1 surface

The solid-phase synthesis of manganese silicides on the Si(100)2 × 1 surface coated at room temperature by a 2-nm-thick manganese film has been investigated using high-energy-resolution photoelectron spectroscopy with synchrotron radiation. The dynamics of variation of the phase composition and electronic structure of the near-surface region with increasing sample annealing temperature to 600°C, has been revealed. It has been shown that, under these conditions, a solid solution of silicon in manganese, metallic manganese monosilicide MnSi, and semiconductor silicide MnSi_1.7 are successively formed on the silicon surface. The films of both silicides are not continuous, with the fraction of the substrate surface occupied by them decreasing with increasing annealing temperature. The binding energies of the Si 2p and Mn 3p electrons in the compounds synthesized have been determined.     

Simulation of multilayer homoepitaxial growth on Cu （100） surface

The processes of multilayer thin Cu films grown on Cu (100) surfaces at elevated temperature (250--400\,K) are simulated by mean of kinetic Monte Carlo (KMC) method, where the realistic growth model and physical parameters are used. The effects of small island (dimer and trimer) diffusion, edge diffusion along the islands, exchange of the adatom with an atom in the existing island, as well as mass transport between interlayers are included in the simulation model. Emphasis is placed on revealing the influence of the Ehrlich--Schwoebel (ES) barrier on growth mode and morphology during multilayer thin film growth. We present numerical evidence that the ES barrier does exist for the Cu/Cu(100) system and an ES barrier $E_{\rm B} >0.125$\,eV is estimated from a comparison of the KMC simulation with the realistic experimental images. The transitions of growth modes with growth conditions and the influence of exchange barrier on growth mode are also investigated.     

A metallic surface state with uniaxial spin polarization on Tl/Ge(111)-(1 × 1)

We show that a metallic surface state is formed on Tl/Ge(111)-(1 × 1). The surface state forms electron pockets around K of the surface Brillouin zone. A first-principles calculation reveals that the electron pockets are composed of a single branch of a spin-split surface-state band. The spin quantization axis is along the surface normal and inverts according to the time-reversal symmetry. Since this spin-split branch is the unique metallic band on this surface, the surface conductivity should be governed by this spin-split branch, suggesting a possible spin-polarized electric current.     

One-dimensional diffusion of vacancies on Sr/Si(100)-c(2×4) surface

An Sr/Si(100)-c(2×4) surface is investigated by high-resolution scanning tunneling microscopy (STM) and scanning tunneling spectroscopy (STS). The semiconductor property of this surface is confirmed by STS. The STM images of this surface shows that it is bias-voltage dependent and an atomic resolution image can be obtained at an empty state under a bias voltage of 1.5 V. Furthermore, one-dimensional (1D) diffusion of vacancies can be found in the room-temperature STM images. Sr vacancies diffuse along the valley channels, which are constructed by silicon dimers in the surface. Weak interaction between Sr and silicon dimers, low metal coverage, surface vacancy, and energy of thermal fluctuation at room temperature all contribute to this 1D diffusion.     

Deposition behaviour of single Si adatom on p(2×2) Si(100) surface

The deposition of a single Si adatom on the p(2×2) reconstructed Si(100) surface has been simulated by an empirical tight-binding method. Using the perfect and defective Si surfaces as the deposition substrates, the deposition energies are mapped out around the research areas. From the calculated energy plots, the binding sites and several possible diffusion paths are achieved. The introduced defects will make the deposition behaviour different from that on the perfect surface.     

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.     

Influence of carbon fiber’s surface state on interlaminar shear properties of CFRP laminate

In order to investigate the influence of carbon fiber’s surface state on the interlaminar shear properties of carbon fiber-reinforced plastic (CFRP) laminate, the carbon fiber’s surface state was modified by thermal treatment at elevated temperatures. The interlaminar shear strength (ILSS) of CFRP laminates reinforced with treated fibers was measured by means of short-beam shear test, and the surface state of fiber was characterized by Electron Spectroscopy for Chemical Analysis (ESCA) analysis to reveal the dominate factor for controlling the ILSS. Combining the ILSS measurement with the ESCA analysis, the results indicated that: (1) the ILSS is strongly dependent on the oxygen-containing functional groups on the surface of carbon fiber; (2) the fiber treated at 600?°C has the highest oxygen-containing functional groups that lead to the highest ILSS of CFRP; and (3) at temperatures beyond 600?°C, the oxygen-containing functional groups decrease with increasing the heat treatment temperature, resulting in a low ILSS of CFRP laminates. Furthermore, from the microstructure observation, it was found that the CFRP mainly failed in the mode of multi-interlaminar shear. The multi-interlaminar shear failure in the CFRP laminates with low ILSS is more severe due to a weak fiber-matrix interface.     

Neutralization process of Xe^q＋ ion grazing on Al（111） surface

A code has been developed to simulate the neutralization and grazing process of slow highly charged ion Xe^q＋ on Al（111） surface under the classical-over-the-barrier model. The image energy gain of Xeq＋ ions are calculated and compared with experiment data. The simulation results of image energy gain are in good agreement with the experiment data. Meanwhile, in the present work, the reflection coefficient of incident Xe^q＋ on Al（111） surface as a function of the incidence angle, energy and charge state is also studied.     

One-dimensional diffusion of vacancies on an Sr/Si(100)-c(2×4) surface

An Sr/Si(100)-c(2×4) surface is investigated by high-resolution scanning tunneling microscopy(STM) and scanning tunneling spectroscopy(STS).The semiconductor property of this surface is confirmed by STS.The STM images of this surface shows that it is bias-voltage dependent and an atomic resolution image can be obtained at an empty state under a bias voltage of 1.5 V.Furthermore,one-dimensional(1D) diffusion of vacancies can be found in the room-temperature STM images.Sr vacancies diffuse along the valley channels,which are constructed by silicon dimers in the surface.Weak interaction between Sr and silicon dimers,low metal coverage,surface vacancy,and energy of thermal fluctuation at room temperature all contribute to this 1D diffusion.     

Nitric oxide adsorption on the Si(100)(2×1) surface — a vibrational study

High-resolution vibrational electron energy loss spectroscopy has been used to study the adsorbed state of NO on the Si(100)(2×1) surface. At 300 K, NO is adsorbed dissociatively on the Si(100) surface in the disordered structure, and the Si₃N and SiOSi species are formed. By heating at 1200–1300 K, the O adatoms are removed from the surface and the silicon nitride is formed; the (2×1) structure is recovered, which is interpreted to indicate that the nitride is formed mainly in the subsurface region.     

Theoretical simulation of STM image of C60 molecules on Si(100)-(2 × 1) surface

Theoretical simulation of STM image of C₆₀ molecules on Si(100)-(2 × 1) surface was performed by the DV-Xα-LCAO method. The results excellently reproduced the internal stripe pattern of the STM image of C₆₀ observed by experiment. We confirm that it is the interaction between C₆₀ and the Si substrate which causes this internal structure.     

STM study of structural changes on Si(100)2×1-Sb surface induced by atomic hydrogen

Using scanning tunneling microscopy (STM) and low energy electron diffraction (LEED), we have studied the structural changes of the Si(100)2×1-Sb surface caused by hydrogen adsorption at both room temperature (RT) and 300°C. We have found that the ordering of a 2×1-Sb surface is more stable against atomic hydrogen exposure at 300°C than at RT, and that some Sb atoms desorb during atomic hydrogen exposure at 300°C. However, upon hydrogen exposure at both temperatures, we have observed neither three-dimensional islands nor the hydrogen terminated Si substrate which were reported for hydrogen interaction with the other metal/Si systems. On the 2×1-Sb surface exposed to atomic hydrogen of 1000 L at RT followed by 550°C annealing, long bright lines similar to those reported for the Bi/Si(100) system have also been found.     

Bonding geometry of Mn-wires on the Si(100)(2 × 1) surface

The bonding geometry of monoatomic Mn-wires, which form on the reconstructed Si(100)(2 × 1) surface at room temperature, was investigated with scanning tunneling microscopy (STM). The Mn-wire structures are always perpendicular to the Si-dimer rows and the images exhibit a strong modulation of their apparent height as a function of bias voltage. The Mn-wire structures appear as depressions in the empty state images for bias voltages around 0.7 V, and as protrusions for all other bias voltages. It is suggested that the wire-images are defined by mixed Mn-Si states, either through a hybridization between the Mn d-states and the Si-p states, or backbonding from Mn-d electrons into the broken Si-dimer bond. The dominant bonding geometry shows that the Mn-wire maxima are positioned in between the Si-dimer rows, and a small percentage of about 20% is in registry with the Si-dimer rows, and might be described as defective wires. The experimental STM images cannot currently be described in a satisfactory manner with theoretical bonding models from the literature.     

The role of substrate surface termination in the deposition of?(111)?CdTe on?(0001) sapphire

The small lattice mismatch and sixfold symmetry offered by the (0001) planes of sapphire make it an ideal substrate candidate for the deposition of (111) CdTe films. There, however, exists a wide disparity in film quality among various researchers with both single crystal and highly twinned, multidomain films being reported. We have developed a pulsed laser deposition process that enables us to deposit nearly single-domain (111) CdTe films exhibiting excellent surface morphology. Such films are deposited on as-received sapphire substrates in vacuum conditions where oxygen is readily available. If, however, film deposition is preceded by the deposition of a submonolayer of aluminum prior to film growth then a secondary CdTe domain emerges with an in-plane orientation having a 180°-in-plane offset from the first domain. These multidomain films show poor crystallographic and morphological properties, similar to what has been reported elsewhere. It is concluded that the singly terminated (0001) sapphire substrates are a prerequisite for the deposition of high-quality (111) CdTe films.