Surface reactions of the 6H-SiC(0001) 3×3 with oxygen molecules (O₂) at high temperature were investigated using reflection high-energy electron diffraction (RHEED) and Auger electron spectroscopy (AES). The Si-terminated 3x3 surface transformed into the C-rich 1×1 surface by O₂ exposure of 1.2×10⁵L at 1000°C. Mass spectra measured during the experiment using a Quadrupole Mass Spectrometer (QMS) suggest that Si atoms and C atoms on the 3×3 surface were etched by the O₂ exposure. Morphologies of the 3×3 surfaces before and after the O₂ exposure were also observed using scanning electron microscopy (SEM). Many droplets were found on the 3×3 surface, which were determined to be Si droplets generated in the preparation process of the 3×3 phase. The Si droplets were removed from the surface by the O₂ exposure at high temperature.

抄録全体を表示

Angle-resolved photoemission spectroscopy utilizing synchrotron radiation has been used to study the adsorption state of oxygen on a HfC(111) surface. Oxygen adsorbs dissociatively on the HfC(111) surface at room temperature forming a (1×1) overlayer at the saturation coverage. The two-dimensional band structure of the chemisorption bonding states formed through the hybridization of O 2p and Hf 5d orbitals (O 2p-derived states) is measured for the HfC(111)(1×1)-O surface. It is found that the 2p_z-derived band is formed in slightly higher binding energy region relative to the 2p_x- and 2p_y-derived bands, indicating that the vertical interaction involving the 2p_z orbital is slightly more important in the chemisorption bond formation relative to the lateral interaction involving the 2p_x and 2p_y orbitals. Hf 4f spectra are measured for the clean and oxygen-covered HfC(111) surfaces, and it is found that the oxidation of the surface Hf atoms to form a Hf oxide does not proceed at room temperature.

抄録全体を表示

We have investigated sequential transformations among surface reconstructions during Ca adsorption on Si(111) by in-situ high-temperature scanning tunneling microscopy (STM). A series of striped superstructures, 3×1, 5×1, 7×1, and 2×1, were formed with Ca coverage increasing, but their transformation behaviors depended on the substrate temperature. From shifts of step positions during these transformations and detailed comparison among these structures coexisting in single STM images, we have confirmed that all of these striped structures should consist of regular arrangements of two kinds of Si chains, honeycomb and Seiwatz chains. Furthermore, we found that when a higher-coverage stripe nucleated in a domain of lower-coverage-stripe phase, the lower-coverage stripes shifted entirely within the domain, sweeping out the out-of-phase boundaries. We propose an atomistic model for the transformation including a sequential re-bonding of the Si chains.

抄録全体を表示

In this paper we investigated the coherent electronic transport properties of molecular bridges where the tape-shaped oligoporphyrin molecular wires, called as the tape-porphyrins, are bridged between the two gold electrodes by thiolate (S-Au) bonds. In particular, we focused on effects of the chemical contact at molecule/electrode interfaces on the transmission spectra. Namely, we studied the dependence of the transmission spectra on the atomic sites where S-Au bonds are connected to the tape-porphyrin molecule, and their dependence on the additional spacing functional group between the tape-porphyrin molecular edge and the S-Au bonds. When the S-Au bonds are connected to the meso atomic sites of the tape-porphyrin molecule, several resonant peaks with large amplitudes are observed around the Fermi level, which indicates that the assumed molecular bridge is conducting even at lower bias voltages. As long as they are connected to the meso sites, the transmission peaks do not change their amplitudes significantly, even if the phenyl ring is inserted between the S-Au bond and the tape-porphyrin. However, if the bulky substituents are additionally introduced at the β atomic sites, the steric rotation of the phenyl ring is considered to dramatically suppress the transmission through the molecular bridge. [DOI: 10.1380/ejssnt.2003.45]

抄録全体を表示

Time-of-flight secondary ion mass spectrometry (TOF-SIMS) is expected to contribute to the evaluation of biomaterial surfaces interacting with proteins, cells and microbes because it requires no sample pre-treatments, such as labeling with probes and coating with metallic thin films for insulated samples. TOF-SIMS measurement provides chemical distribution of biomaterials with high spatial resolution. Since it is difficult for TOF-SIMS to generate enough characteristic secondary ions for imaging from large molecules such as proteins, multivariate analysis techniques such as principal component analysis (PCA) have been employed to characterize the spectra with fragment ions considered to be related to proteins. However, some of those fragment ions are also related to substrate especially polymers. Information theory was employed for the first time to analyze TOF-SIMS spectra of hollow-fiber dialysis membranes treated with a protein solution. TOF-SIMS spectra and images of protein adsorbed membranes and native membranes were compared based on mutual entropy in order to discriminate secondary ions related to protein from membranes. TOF-SIMS images with the fragment ion groups related to proteins and membrane were obtained respectively, and they show clearly the distribution of adsorbed protein on the dialysis membranes. [DOI: 10.1380/ejssnt.2003.67]

抄録全体を表示

We investigated the initial stages of Ag growth on a Si(111)-4×1-In surface at room temperature (RT) and low temperatures (LT, 70∼120K) in situ by reflection-high-energy electron diffraction (RHEED), scanning tunnelling microscopy (STM) and electrical resistance measurements in ultrahigh vacuum, together with on a Si(111)-7 × 7 clean surface for comparison. It has been revealed that the 4×1-In surface actually acts as a highly anisotropic template for Ag growth at RT, but not at LT. The Ag islands grown on the wetting layers were elongated along the 4×1-stripe at RT, while they were isotropic and round in shape at LT. This is due to a difference in migration ability of the arriving Ag adatoms. The anisotropic growth has been found to affect the formation of percolation paths for electrical conduction among the Ag islands; the growth conditions (deposition rate and temperature) do not affect the critical coverage for percolation so much on the 4×1-In surface, compared with in the case of isotropic growth on the 7×7 surface. The initial deposition of submonolayer-thick wetting layers has been found to induce some structural changes of the substrate surface; at RT, the 4×1-In structure changes into a 4×’2’ structure, while the 8×’2’-In structure at LT changes into a 4×1 structure. The former change induces a resistance increase, while the latter induces a resistance drop. These changes may be caused by the induced changes in surface states and band bending beneath the surface. [DOI: 10.1380/ejssnt.2003.72]

抄録全体を表示

Nanometer-sized particles of molybdenum oxide were thermally deposited and then sulfided on mica, MoS₂, and highly oriented pyrolytic graphite (HOPG) to simulate MoS₂ catalysts for the hydrodesulfurization reaction of petroleum. The topography of the particles observed by AFM reflected the interaction force dominant at the particle-substrate interfaces. Oxide particles ionically interacted with mica which restricted the mobility of the deposit and led to particles smaller in lateral dimension, whereas aggregated oxide was observed on the other non-ionic substrates. Basal-bonded MoS₂ crystals were observed on the three substrates when sulfided at 673 K. [DOI: 10.1380/ejssnt.2003.80]

抄録全体を表示

Scanning tunneling microscopy (STM) and reflection-high-energy electron diffraction (RHEED) were used to observe changes in facet structures induced by depositing Au atoms on vicinal Si surfaces misoriented from (111) toward [11-2] and [-1-12] directions. The facets structures were found to be quite different from each other for the two misorientations. Several kinds of one-dimensional stripes were observed on different facets, and the Au coverage for each facet structure was determined. The surface was almost uniformly covered by (775) facets for [11-2] vicinal by 0.25 monolayer coverage of Au, while by (557) facets for [-1-12] one at 0.2 ML. High-resolution STM images are also presented and discussed in relation to the previously proposed models of atomic structures. [DOI: 10.1380/ejssnt.2003.84]

抄録全体を表示

The resistance of Na atomic chains between two metallic electrodes is studied using an ab initio method within the density functional theory and including the effects of structural relaxation. We have found that the oscillatory behavior of the resistance of Na atomic chains with respect to the number of Na atoms, predicted previously by other groups, becomes much reduced after structural relaxation: Resistances of all the 2-, 3- and 4-atom Na chains become close to the inverse of the conductance unit (12.9 kΩ). Our results suggest that the even-odd parity of conductance may be much weaker than as was expected. [DOI: 10.1380/ejssnt.2003.120]

抄録全体を表示

We demonstrate a high yield production scheme to fabricate sub-10 nm co-planar metal-insulator-metal junctions without using electron beam lithography. The fabricating procedure contains two photolithographys followed by shadow evaporation. Ultrasmall gaps were formed in the crossing region of the two metal layers during the evaporation of the second layer. The sizes of the gaps were estimated using scanning electron microscopy images. Poly (3-hexylthiophene-2,5-diyl) layers were deposited on the junctions using a special ink-jet technique. The results of the conductivity measurement of the molecular layer indicate that these junctions can be used in the study of molecular sensors.

抄録全体を表示

We have developed a ultrahigh-vacuum system for electrical conductivity measurements with high surface sensitivity by using monolithic micro-four-point probe method (probe spacing being ∼ μ m) at temperatures ranging from ∼10 K to 400 K, combined with simultaneous structure analysis by reflection-high-energy electron diffraction (RHEED). This apparatus enables direct measurements of electrical conductivity at the topmost atomic layers on crystal surfaces as a function of temperature. Then, the surface transport properties are unambiguously correlated with surface structures, especially with temperature-induced surface phase transitions. The apparatus including the electrical measurement system is described in detail, together with some typical data from Si(111)-7 × 7 clean surface. [DOI: 10.1380/ejssnt.2003.50]

抄録全体を表示

It has been discussed the notion of an organized molecular assemblies as the key problem of the low-dimension systems physics and the supramolecular chemistry. An organized molecular assembly is a group of atoms or molecules built in a solid matrix due to chemical or intermolecular interactions and possessing, in total, the ability to produce a definite response to the given perturbation. The effectiveness of this approach has been shown on examples the search for systems that evolve to the formation of two dimensional organized molecular assemblies at the boundary between a semiconductor crystal and a dielectric and also creating quantum dots and chemical sensors.

抄録全体を表示

Using scanning tunneling microscopy observations, the ability of group III metals, In, Al, Ga and Tl, to form identical-size magic nanoclusters upon high-temperature adsorption on Si(100) has been examined. Magic clustering has been detected in In/Si(100) and Al/Si(100) systems. In both cases, atomic structure of the nanocluster is plausibly described by the model of Bunk et al. [Appl.Surf.Sci. 123/124, 104 (1998)], in which six metal atoms and seven Si atoms form a stable pyramid-like cluster. In the case of In/Si(100) system, the perfectly-ordered 4×3 superlattice built of magic nanoclusters can be formed. The Al/Si(100) nanoclusters has been found to form local arrays with a 4×5 periodicity. In Ga/Si(100) and Tl/Si(100) systems, no indication of magic clustering has been detected. The criteria for magic cluster formation are discussed.

抄録全体を表示

We review recent advances in ab initio calculations of surface optical second harmonic (SH) responses of several systems: Si(001)-adsorbate surfaces, Si(111) surface, GaN(0001) surface, and Ni/Cu(001) surface. Optical second harmonic generation (SHG) has recently become a tool for studying surface electronic states. However, the interpretation of experimental SHG data has been rather difficult due to the lack of guiding theoretical predictions. For well understanding of the results of the measured SH intensity, a number of ab initio theoretical calculations have been competitively developed in these several years, and they are reviewed in this contribution. The results indicate that for simple covalent systems such as the Si surface, quantitative agreement between experiment and calculation has been obtained. [DOI: 10.1380/ejssnt.2003.57]

抄録全体を表示

During observation of reflection high-energy electron diffraction, characteristic x-rays are emitted from surfaces. The intensities of these x-rays change with change in the incident glancing angle (θ_g) of the primary electron beam, since density distribution of electrons near the surface changes with change in θ_g. By analyzing θ_g dependence of x-ray intensities, the depth distribution of elements near the surface can be determined without destruction of the surface. Resolution of depth in this method is one monolayer at the uppermost layers. By using this method, various growth motions of elements, such as substitution, alloying and floating were observed during growth of metals on metal-covered Si(111) surfaces. Morphology and growth modes of metals were significantly altered by preadsorption of other metals, and sometimes very flat metal films that would be applicable for fabrication of future electronic nano devices were obtained. In this review, the method for analysis of depth distribution of elements and growth modes of metals (Au, Ag, Ga, In and Sn) on an Si(111) surface precovered by another metal are described. [DOI: 10.1380/ejssnt.2003.91]

抄録全体を表示

An important function of microscopy is the chemical analysis of the sample. Chemical analysis with an atomic resolution microscope can mean two different things. First, for a sample of known composition or adsorbed species, it means distinguishing the chemical species from the atomic image. Second, for a sample of unknown composition, it means the identification of the chemical components from the atomic resolution image. Here I compare available methods of chemical identification in field ion microscopy (FIM) and scanning tunneling microscopy (STM), and report our progress in achieving true atomic resolution for a non-destructive chemical analysis of a sample surface using STM.[DOI: 10.1380/ejssnt.2003.102]

抄録全体を表示

The development is briefly reviewed of the cathodes that have brought about epoch-making progresses in surface science and electron beam technology: the carbon filament by Edison(1884), the tungsten filament by Langmuir(1913), the LaB₆-cathode by Lafferty(1951) and the Zr-O/W(100) cathode by Swanson(1979). These developments stimulated the surface scientists in those days to devise atomic level characterization tools for elucidating such characteristics of the cathodes as high brightness, high stability and long service life. These approaches have led to many discoveries of practical importance; the water-vapor cycle on the tungsten surface (Langmuir), the double layer formation on the Cs/W(100)-surface (MacRae, et al.), the critical temperature for the stoichiometric evaporation in LaB₆-cathode (Aono, et al.) and the self-recovery function on the Zr-O/W(100) surface (Shimizu, et al.). [DOI: 10.1380/ejssnt.2003.106]

抄録全体を表示

Electron probe microanalysis (EPMA) under grazing-exit conditions allows us to perform microscopic surface analysis, thin-film analysis and particle analysis. To evaluate the thickness and density of thin-films, it is necessary to calculate X-ray intensities as a function of the exit angle. In this paper, we propose a procedure to calculate X-ray intensities as a function of grazing-exit angle. Monte Carlo simulation is used to determine the depth distribution of the electron-induced X-ray production and a multilayer model is applied to include the grazing emission process. The exit angle resolved curves, calculated for Ni thin films, were compared with experimental curves. A good agreement between the experimental plots and the calculated curves indicates that the proposed computational approach can be applied successfully to the calculation of EPMA intensities. Appling this calculation, the lateral resolution of EPMA was also evaluated at different take-off angles. It was suggested that the lateral resolution would be improved under grazing-exit conditions. [DOI: 10.1380/ejssnt.2003.111]

抄録全体を表示

Insulators with high dielectric constants (so-called high-k) have been intensively investigated for the replacement of SiO₂ gate dielectric of MOS transistors for high-speed ULSIs in near future. The characterization results of the Hf-silicate gate dielectric, especially in terms of its structural transformation during high temperature annealing, are presented. Phase separation and micro-crystallization in Hf-silicates were evaluated using XPS, TEM, and XRD. Impurity diffusion through the dielectric was also examined using the backside SIMS of the p⁺-poly-Si/Hf-silicate/Si-substrate system. It has also been revealed that such thermal stability problems for Hf-silicates can be solved with nitrogen incorporation in the film using the physical analyses outlined above. [DOI: 10.1380/ejssnt.2003.116]

抄録全体を表示

Well lattice-matched monolayer films of hexagonal boron nitride (h-BN) can be grown on Ni(111) surfaces, representing a nominally ideal interface for preparing ultimately thin metal-insulator-metal (MIM) structures. In a detailed study, combining local and non-local probes, the presence of characteristic defect lines is uncovered, and a model for their atomic structure is proposed. They have a strong influence on the growth morphologies of metal deposits. For room temperature deposition, they act as anchors for cluster nucleation, thus effectively short circuiting the MIM structure. For high-temperature deposition, the defects collect Co adatoms very efficiently and lead to Co intercalation underneath the h-BN film. [DOI: 10.1380/ejssnt.2003.124]

抄録全体を表示

The microcalorimeter energy dispersive x-ray spectrometer, the silicon drift detector (SDD), and polycapillary x-ray optics are recent developments that have significantly advanced analytical x-ray spectrometry for electron beam instruments. The microcalorimeter EDS is capable of high resolution operation (∼ 5 eV wide peaks) over a wide range of photon energies (250 eV ∼ 10 keV). The microcalorimeter EDS can be successfully applied to peak interference problems that are not accessible with the conventional semiconductor EDS such as TiN and BaTiO₃. Polycapillary x-ray optics can augment the collection angle of the microcalorimeter EDS to increase its sensitivity. The SDD is capable of extremely high count rates, up to 1 MHz, and is especially useful for high speed x-ray mapping. [DOI: 10.1380/ejssnt.2003.130]

抄録全体を表示

The growth of Mn and Gd on a vicinal Au(111) surface is observed by scanning tunneling microscopy at room temperature. One-dimensional nanostructures have been fabricated with Mn adatoms. Dosed Mn atoms are adsorbed at lower corners of {111} steps, and Mn adlayers grow in a step-flow growth mode on (111) terraces. On the other hand, there is no tendency for Gd to form one-dimensional structures. Dosed Gd atoms nucleate not only at lower corners of the steps but also on the terraces. As the coverage is increased, Gd adislands isotropically grow in size around the nucleation sites on the terraces. The mechanism of these different growth manners is qualitatively discussed. [DOI: 10.1380/ejssnt.2003.142]

抄録全体を表示

Space charge in a point cathode thermionic emission gun has been studied with numerical method. The method is an iterative one, consisting of the field determination using the integral form of Poisson's equation, the direct ray tracing in 3D, and the estimation of space charge from the traced rays. The rays are traced for limited emitting conditions. The estimated space charge is treated as a number of the coaxial charged rings with different radii and positions. Using the method, the potential distribution around the cathode tip was examined at different cathode temperatures. The numerical results at the cathode temperatures of 2800 K and 2950 K are given, and the influence of space charge is discussed. [DOI: 10.1380/ejssnt.2003.147]

抄録全体を表示

In this article, we detail the development and application of reflection high-energy positron diffraction (RHEPD). A fine positron beam with a coherence length of approximately 170 Å was obtained by the electrostatic lens system. The beam quality is good enough to observe the RHEPD patterns from a clean Si(111)7×7 and SiC(0001) surfaces. The rocking curve associated with the Si(111)7×7 surface revealed the fact that the vertical position of the adatom layer relative to the first layer is sufficiently relaxed towards the vacuum region than that expected from the electron diffraction experiments. After the high temperature hydrogen etching, the SiC surface became atomically smooth. It was found that Si face is somewhat unstable to the oxygen adsorption as compared to C face. The rocking curves were reproduced assuming the attachment of oxygen atoms at T₁ site with a bond length of 1.88Å. Heating the SiC surface in the ultra-high vacuum after the sacrificial oxidation and hydrofluoric etching, an atomically flat carbon rich surface appeared.[DOI: 10.1380/ejssnt.2003.152]

抄録全体を表示

We investigated performances and functions of the noncontact atomic force microscope (NC-AFM) method. As a result, we found that the NC-AFM functions not only as the atomic resolution microscope but also novel atomic tools based on a mechanical method as follows; a three-dimensional mapping tool of atomic force between the tip and sample atoms, a discrimination tool of atomic force mechanisms and atom species of the sample surface, a control tool of atomic force and atom position on the sample surface, and an atom manipulation tool. [DOI: 10.1380/ejssnt.2003.158]

抄録全体を表示

The large potential energy stored in highly charged ions is liberated when these ions recombine during impact on a solid surface. For certain target species this can cause enhanced sputtering and nanodefect formation. We summarize the properties of slow highly charged ions which are relevant for surface interaction and propose their use as a new and very selective tool for nanostructuring of surfaces. [DOI: 10.1380/ejssnt.2003.171]

抄録全体を表示

Quantum mechanics of one-dimensional time-independent system whose energy level statistics obeys the Gaussian ensemble is numerically studied. Recently the nano-size quantum dots and anti-dots made by the highly sophisticated fabrication process on the heterojunction structure of semiconductors often exhibit the anomalous physical behaviors. In order to understand them the study of the lower dimensional quantum electron transport from the viewpoint of quantum chaos is inevitably important. One-dimensional conserved systems are known to be integrable. However, at least numerically, it is also shown that we can construct the potential for the Schrödinger equation that reproduces a finite number of given energy levels of chaotic regime, e.g., the random matrix theory. In this work a potential is constructed numerically by the standard gradient method or by the inverse scattering method. The more energy levels of chaotic regime we take, the more complicated and finer the ripples of the potential become The potential has fractal structure at high energy limit. [DOI: 10.1380/ejssnt.2003.175]

抄録全体を表示