bluuebunny/crossref_metadata_2025 huggingface dataset:
Morphology of Silver Thin Films Deposited on TiO2(110) Surfaces
Authors: Abriou D. , Gagnot D. , Jupille J. , Creuzet F.
Published: August 2003

The growth mode of silver films deposited at room temperature on TiO 2(110) surfaces has been examined by means of atomic force microscopy (AFM) and X-ray photoelectron spectroscopy (XPS) in ultrahigh vacuum (UHV) conditions, On clean vacancy-free TiO 2(110) surfaces, 0.1-nm-thick (on average) Ag deposits form a two-dimensional (2D) layer. When the thickness of the silver overlayer is increased, 3D clusters are shown to appear while the 2D film is preserved, furthermore, the influence of surface oxygen vacancies on the growth of Ag/TiO 2(110) is evidenced by well-characterized differences in the morphology of 9-nm-thick silver deposits.
Influence of Alumina Surface Structure on Growth and Adsorption Properties of Pd Particles
Authors: Stará I. , Gonzalez V. , Jungwirthová I. , Mašek K. , Matolín V.
Published: August 2003

The partial CO dissociation observed on small Pd particles deposited on γ-alumina and only molecular adsorption of CO on Pd/(0001) α-alumina model catalysts show that the surface structure of alumina can influence the reactivity of supported clusters. To understand the effect of metal–support interaction, Pd particles were deposited on alumina substrates of different surface structure [(0001), (1-102)]. The surface of alumina substrates was investigated by means of reflection high energy electron diffraction (BREED). The growth of Pd particles, their structure and orientation were observed by RHEED. In order to compare the catalytic properties of supported Pd particles, the study of CO and O adsorption was performed by temperature-programmed desorption (TPD) using molecular beam techniques.
RHEED Study of Pd Particle Growth on α-Alumina and NaCl Substrates
Authors: Bruna J. C. , Gillet M. , Gonzales V. , Masek K. , Matolín V.
Published: August 2003

Three-dimensional Pd particles were prepared by heteroepitaxial growth on NaCl (001) and α- Al 2 O 3 (0001) substrates. During the deposition the particle structure and orientation were characterized by reflection high energy electron diffraction. It was shown that the particle epitaxial planes conserved the substrate surface symmetry — hexagonal or cubic. A CCD camera and a computer data treatment system were used for precise investigation of lattice parameter variation given by the particle interaction with the substrates. It was found that generally the lattice parameter parallel to the substrate remained constant due to the particle accommodation to the substrate while the perpendicular lattice parameter varied with particle size. Particle size was investigated by transmission electron microscopy.
X-ray Investigations of the Surface Layers of the Perovskite-Type Ferroelectric Crystals
Authors: Surowiak Z. , Wawrzała P. , Dudkevich V. P.
Published: August 2003

The physical nature of surface layers of the BaTiO 3 and PbTiO 3 ferroelectric perovskite-type crystals has been investigated by X-ray diffraction. It has been found that the surface layers with an extremely high piezoelectric deformation are formed at the positive electrode at room temperature under the influence of the dc electric field, This effect is caused by a nonlinear potential distribution, The thickness and the piezoelectric deformation of the surface layer increase with the external electric field, The time of formation of the negative space charge layer in the anodic region is close to the Maxwell relaxation time. The Schottky-type surface potential barrier, existing in the absence of the external electric field, is formed as a result of capture of the electric charge carriers by the surface states.
Growth and Analysis of Red, Green and Blue Luminescent Oxide Thin Films
Authors: Hirata G. A. , Mckittrick J. , Devlin D.
Published: August 2003

The growth and characterization of europium ( Eu 3+) and terbium ( Tb 3+) doped yttrium aluminum garnet ( Y 3 Al 5 O 12 or YAG) and undoped ZnGa 2O4 photoluminescent thin films deposited on sapphire substrates at 400°C by excimer pulsed laser ablation is reported. Smooth, continuous 500-nm-thick amorphous films were produced with compositions depleted in oxygen. Luminescence measurements on the as-deposited and on annealed samples revealed that heat treatments at temperatures > 800°C were necessary to induce crystallization and reoxygenate, which coincided with the onset of luminescence. Annealing produced randomly oriented grains on the order of 15-200 nm.
Cleavage Planes in CuInSe2
Authors: Shukri Z. A. , Champness C. H.
Published: August 2003

All angles between facets in CuInSe 2 Bridgman-grown crystals were measured and confirmed, by X-ray Laue patterns and diffractometry, to be accounted for by three planes: {101}, {112} and {110}. The {110} facets were less frequent and were found to consist of {112} microcleavages. The {101} cleavages occurred most frequently and it is speculated that this is due to the smaller energy required to break a smaller number of the stronger Se–Cu bonds (compared with the weaker Se–In bonds) than for {112} cleavages.
Surface Phonon Dispersion in Graphite and its Modification Under Interaction with Lanthanum
Authors: Siebentritt Susanne , Pues Roland , Rieder Karl-Heinz , Shikin Alexander M.
Published: August 2003

Using high resolution electron energy loss spectroscopy (HREELS) the surface phonon dispersion of graphite has been determined in the Γ K direction over the whole energy range and the whole Brillouin zone. By depositing lanthanum and annealing we prepared a GIC-like phase which grows on top of an intermediate carbide. The phonon dispersion of this phase shows the same modes as graphite, but the optical ones are softened and the acoustical ones are stiffened. This is described within a Born-von Karman model. The evolution of the phonon dispersion gives a first hint that the GIC-like phase may develop in two stages: first a monolayer graphite on top of the carbide and then the very thin GIC layer.
Scanning Force Microscopy Study of Ultrathin Films of Nickel-Phthalocyanine on Graphite
Authors: Santucci S. , Di Nardo S. , Lozzi L. , Ottaviano L. , Passacantando M. , Picozzi P.
Published: August 2003

Small amounts of purified nickel-phthalocyanine (Ni-PC) have been deposited at room temperature in ultrahigh vacuum onto highly oriented pyrolytic graphite, and studied "in situ" and "ex situ" (in air) with two different atomic force microscopes. The measurements have been taken on samples as prepared either subsequently annealed at 300°C. The growth mode is not uniform; the PC molecules coalesce into small submicrometric crystallites in the critical size range where the transition from the α to the β crystalline phase of phthalocyanines takes place. We show images of both α-like and β-like crystallites. A contact mode AFM image of an α-like crystallite showing intramolecular resolution is also presented.
Structural and Phase Transitions on Water Ice Surface Under HCl Exposure: Implication for Stratosphere Conditions
Authors: Persiantseva N. M. , Popovicheva O. B. , Rakhimova T. V.
Published: August 2003

The HCl-ice interaction has been investigated over a wide HCl pressure range of 10-7–10-4 Torr and ice temperatures 150–240 K. The Three characteristic values for HCl uptake efficiency were obtained which indicate the change of phase state and structure of the ice surface at increasing HCl pressure. The low value γ ≈ 0.1 ± 0.02 corresponds to HCl vapor interaction with pure ice and is realized at the atmosphere conditions. The value γ ≈ 0.5 ± 0.1 indicates the formation of hexahydrate HCl • 6H 2 O with increase of HCl pressure. And the largest value of γ ≈ 0.8 ± 0.1 is observed at appearance of liquid or amorphous solid 4:1 H 2O:HCl.

The HCl uptake kinetics is analyzed. The flow of HCl molecules from the ice surface into the bulk is shown to play an important role in the redistribution of HCl molecules. It defines a low surface concentration of the adsorbed HCl molecules under stratospher condition at early times of interaction.
Au 6 × 6 on Si(111): Evidence for a 2D Pseudoglass
Authors: Marks L. D. , Grozea D. , Feidenhans'l R. , Nielsen M. , Johnson R. L.
Published: August 2003

The atomic structure of the Au 6 × 6 on Si(111) phase has been determined using direct methods and surface X-ray diffraction data. This surface structure is very complicated, with 14 independent gold atoms, relaxations in 24 independent silicon sites and three partially occupied gold sites. In one sense the structure can be described as microdomains of the parent [Formula: see text] on Si(111) structure. A better description is in terms of a tiling of incomplete pentagonal and trimer units, essentially a pseudopentagonal glass. In terms of these structural units it appears possible to explain all the gold structures in the coverage range of 0.8–1.5 monolayers as pseudoglasses with strong short range order but varying degrees of long range order.
HREELS Studies of Hydrogen Adsorption on Pd(311)
Authors: Schilbe P. , Farías D. , Rieder K. H.
Published: August 2003

The adsorption of hydrogen on Pd(311) at 100 K has been investigated by high resolution electron energy loss spectroscopy (HREELS). The observed vibration energies are similar to former values reported on low index Pd surfaces, which allowed relating the vibration modes with the different adsorption sites on the (311) surface. In contrast to Ni(311) and Rh(311), hydrogen adsorption is found to begin at the fourfold-coordinated instead of the threefold-coordinated sites. The latter sites are occupied only at coverages greater than 0.5 ML. The hydrogen adsorption behavior on Pd(311) seems to be ruled by the possibility of occupying threefold and fourfold sites and by the H–H repulsion.
Pressure Renormalization for Premelting Phenomena
Authors: Wiatrowski Grzegorz , Wojtczak Leszek
Published: August 2003

We develop the pressure renormalization of a phonon potential for atoms interacting anharmonically, starting from a fully dynamical Hamiltonian description in pseudoharmonic approximation. We derive a generalized equation for the correlation function of atom–atom displacement across a thin film, which under certain conditions reduces to the one previously discussed in the literature. Our theory yields expressions for a series of melting temperatures in terms of the microscopic parameters of a layered system using Lindemann's argument. The global instability temperature is obtained due to the distribution of displacement correlations in the surface region while the local melting transition is recognized as a process of surface premelting which expands into the stable bulk with increasing temperature. The pressure dependencies of instability and premelting temperatures are mainly discussed.
Simulation of Local Surface Modification in STM by ab initio Quantum Chemistry
Authors: Gurin V. S.
Published: August 2003

Surface modification by means of STM has became a well-known method for the artificial formation of nanometer and atomic scale structures. The physical nature of surface modification can consist in a wide range of phenomena (from mechanical indentation up to specific tip-induced chemistry). The high electrical field at the STM tip is considered to be the main feature of STM modification experiments. The field strength is comparable with intramolecular ones and can influence the chemical bonding in surface structures. The model of STM-stimulated modification is considered using the quantum-chemical ab initio approach for a surface cluster in the high electrical field. The destabilization effect, energy level shift, and bond polarization under the STM tip field occur and can show the atomistic nature of surface transformations in STM.
Photoelectron Diffraction Imaging of Microcrystallites on the Surface of a Ni Polycrystal
Authors: Zharnikov M. , Neuber M. , Grunze M.
Published: August 2003

The applicability of the forward scattering of photoelectrons in electron microscopy is demonstrated for the characterization and investigation of the polycrystalline substrates. The well-resolved images of individual microcrystallites on the surface of Ni polycrystal have been obtained by using the Ni 2p3/2 photoelectrons (E kin = 635 eV ) collected at a widely variable direction of emission. By using the forward scattering approach, not only crystallites resolved by an optical microscope but also the microcrystallites, which were not distinguished by the optical method, have been easily identified through the photoelectron diffraction contrast. This contrast amounted to almost 50% of the whole intensity scale and could be observed directly during the acquisition of the images. Crystallographic information on the orientation of the microcrystallites constituting the polycrystal was obtained: some crystallites with the low index surfaces were identified, some microcrystallites with the same orientation were recognized, and the symmetry of the surfaces of the individual crystallites was partly controlled. An approximate identification of the crystallographic orientation of several individual microcrystallites in the investigated Ni polycrystal has been achieved.
Adsorption-Oxidation of CH3OH on V2O5; Reactivity of the Structural Defects
Authors: Sambeth Jorge , Gambaro Luis , Thomas Horacio
Published: August 2003

In previous work the CH 3 OH adsorption–oxidation process on the (010) plane of V 2 O 5 was studied both theoretically and experimentally. In the present work, we have studied this process on idealized structural defects (kinks, steps, corners) of the (010) plane of V 2 O 5. The study was based on calculations of the variation of the total system energy by the extended Hückel method (ASED — atom superposition and electron delocalization). The results demonstrated that the oxidation of CH 3 OH to H 2 CO on the (010) plane is more favorable than on the structural defects and that the kink can be suitable for the oxidation of CH 3 OH to CO 2.
Energy Eigenvalues and Periodic Orbits for the Circular Disk or Annular Infinite Well
Authors: Robinett R. W.
Published: August 2003

We compute the Fourier transform [ρ(L)] of the quantum-mechanical energy level density for the problem of a particle in an annular infinite well (or circular disk) of outer (inner) radius R max =RR min =fR. For various values of f=R min /R we then explicitly compare ρ(L) to the lengths of the classical periodic orbits. We also comment on the diffraction peak seen by Reimann et al. in this system, noting that at least one recurrence of that feature is present in the spectrum, and discussing the corresponding effective path lengths for these features.
The Chemisorption of C on Al(111)
Authors: Mola E. E. , Appignanesi G. A. , Vicente J. L.
Published: August 2003

The chemisorption of C atoms on Al(111) was studied by means of the semiempirical MNDO method. The incorporation of the C adatom into the clusters was considered and the most favorable chemisorption site was evaluated. The hcp in-surface site was identified as the most stable adsorption site, in agreement with recent scanning tunneling microscopy (STM) experiments. This fact allowed us to use the MNDO method to evaluate the interaction energy of two chemisorbed C atoms in order to understand the observed formation of an ordered carbon underlayer. The low mobility of single isolated C adatoms revealed in STM experiments is also discussed.
Analytical Treatment of a Heterogeneous Reaction
Authors: Vicente J. L. , Maltz A. , Mola E. E.
Published: August 2003

An analytical method has been used to study the kinetics of a generic heterogeneous catalytic reaction, A + B → AB. This reaction includes the elementary steps of adsorption and desorption of reactants A and B, surface reaction through the Langmuir-Hinshelwood mechanism, and desorption of the product AB. Despite its simplicity, this analytical approach shows some of the general features observed by simulating the present mechanism on a large N × N lattice.5–7 The rate of reaction depends on the rate of desorption of reactants with a maximum at a value similar to those found by performing heavy simulations. Coverage fluctuations of reactants, as a function of their rate of desorption on a 2 × 2 lattice, have a behavior similar to that found on large N × N lattices.
Simulation of Thermal Desorption from Nanometer Catalyst Particles
Authors: Zhdanov V. P. , Kasemo B.
Published: August 2003

General equations are derived to describe monomolecular desorption from small supported catalyst particles in the cases where (i) the desorption process occurs simultaneously from different facets and (ii) adsorbed molecules are allowed to jump from the catalyst onto the support, diffuse on the support, and then desorb (a so-called spillover effect). Numerical calculations carried out on the basis of obtained equations indicate that the TPD spectra for interconnected facets might be qualitatively different from those for extended single crystals. The support-mediated channel has been shown to be important if the binding energy on the support is not too low.
Co as Adsorbate and Reaction Product in the Systems Fe(110)/Cs+Co and Fe(110)/Cs+Co2
Authors: Seyller Th. , Rührnschopf K. , Borgmann D. , Wedler G.
Published: August 2003

The effect of preadsorbed Cs on the electronic structure and thermal stability of CO adsorbed at 80 K on Fe(110) has been studied using ultraviolet photoelectron spectroscopy (UPS) and X-ray photoelectron spectroscopy (XPS). With increasing Cs coverage the O1s and C1s core levels of CO are shifted to lower binding energies (-0.8 eV). In the presence of one-monolayer Cs the thermal stability of CO is enhanced, leading to a decomposition temperature of about 510 K, a value roughly 100 K higher than on the clean Fe(110) surface (~ 420 K). This is explained in terms of an increased back-donation leading to an electrostatic interaction between CO and Cs.

These results are compared to the properties of CO which is formed when CO 2 is adsorbed on the Cs-precovered Fe(110) surface, CO formed from adsorbing CO 2 shows neither core level binding energy shift nor enhanced thermal stability. It is concluded that CO formed from adsorbing CO 2 is not affected by the preadsorbed Cs, i.e. there is no or at least significantly less increased backbonding and therefore no electrostatic interaction between Cs and CO in that system. It seems to be in a state comparable to the state of CO in the Fe(110)/CO adsorption system.
Numerical Simulation of Pt Overlayers on Ni(111) and Co(0001)
Authors: Légaré P. , Cabeza G. F. , Castellani N. J.
Published: August 2003

The growth of pseudomorphic Pt layers (from one to four) on Ni(111) and Co(0001) has been investigated by the ECT–BFS method. The behaviors on the two substrates are very similar. The growth of the first layer appears to be highly favorable as the energy of the system is negative. Higher coverages could be stabilized with huge relaxations perpendicularly to the surface. The evolution of the plane-by-plane energies (separated in stress and chemical contributions) and relaxations during the growth is presented and discussed. The always-stabilizing chemical interaction at the interface makes it likely that interdiffusion of metals could be a competing mechanism.
Synchrotron Radiation FTIR Spectroscopic Studies of Water on Ni(110)
Authors: Kovar M. , Kasza R. V. , Griffiths K. , Norton P. R. , Williams G. P. , Van Campen D.
Published: August 2003

The adsorption of water on Ni(110) at 92-230 K has been studied by Fourier transform infrared reflection-absorption spectroscopy (FTIR-RAS) in the 200-2000 cm-l frequency range using a synchrotron radiation source. For water adsorbed at 90-180 K and coverage θ(0≤θ≤0.5 monolayers), two IR bands at frequencies of ~ 667 and 806 cm-1 can always be observed despite the absence of an O–H stretch band. For water adsorbed at 180 K followed by annealing to 230 K, two IR bands are again observed, at 767 and 947 cm-1. In both cases we attribute the bands to water wagging and rocking modes. At 180 K, they are rather broad and indicative of interactions in the ordered c (2 × 2) water layer; long range dipole–dipole interactions could be important in stabilizing this 0.5 ML structure at 180 K. At 230 K the bands are believed to originate from the water molecules in water-hydroxyl complexes which occur in well-ordered 2 × 1 islands.
Negative Direct Recoil Spectroscopy Study of the Initial Oxidation of the Mg(0001) Surface
Authors: Mitrovic B. C. , O'Connor D. J. , Shen Y. G.
Published: August 2003

The sub monolayer oxygen-covered Mg(0001) surface has been studied by negative direct recoil spectroscopy (DRS) with the aim of detecting or dismissing the presence of subsurface oxygen atoms. Recorded incidence scans show that at room temperature and with the coverage of 70% of saturation, as measured by DRS, one of two subsurface sites (oC and tA) may be populated. This supports a recent investigation of this surface using forward focusing of Auger electrons, where the most likely occupied subsurface site was found to be the oC site. Furthermore, it was found that about 90% of the oxygen still remains above the surface, while only about 10% penetrates below the surface.
Effect of a Composition Discontinuity on the Evolution of a Bimetal Interface Studied by Photoemission Microscopy: Au Patch Deposited on a Ag/Si(111) Surface
Authors: Kovač J. , Günther S. , Kolmakov A. , Marsi M. , Kiskinova M.
Published: August 2003

The evolution of a 2 ML Au rectangular patch deposited on a [Formula: see text] surface containing three-dimensional Ag islands was studied by scanning photoemission microscopy. The surface composition and electronic structure of the Au patch and of the transition region between the patch and the Au-free Ag/Si area were characterized on a submicron scale at room temperature and after annealing at various temperatures up to 993 K. The spatial expansion of the Au patch due to Au surface diffusion and the chemical state of Ag and Au in the different interface zones were examined by chemical mapping and by analysis of the Ag 3d and Au 4f core level and valence band spectra, taken at selected spots of the surface, From the analysis of the Au 4f core level line shape, we identified a chemical state for Au at the forefront of the Au migration on the [Formula: see text] surface and assigned it to an adsorption site on top of Si trimers. This was the dominating Au species for low (< 0.2 ML) Au coverages, Following the evolution of the Au patch upon annealing we discovered substantial differences in its composition and structural changes compared to a continuous 2 ML Au film deposited on a [Formula: see text] surface. The important role of the Ag and Au surface diffusion in the evolution of an interface containing compositional discontinuities was discussed.
Monte Carlo Simulations of the Kinetics of Protein Adsorption
Authors: Zhdanov V. P. , Kasemo B.
Published: August 2003

The past decade has been characterized by rapid progress in Monte Carlo simulations of protein folding in a solution. This review summarizes the main results obtained in the field, as a background to the major topic, namely corresponding advances in simulations of protein adsorption kinetics at solid–liquid interfaces. The latter occur via diffusion in the liquid towards the interface followed by actual adsorption, and subsequent irreversible conformational changes, resulting in more or less pronounced denaturation of the native protein structure. The conventional kinetic models describing these steps are based on the assumption that the denaturation transitions obey the first-order law with a single value of the denaturation rate constant kr. The validity of this assumption has been studied in recent lattice Monte Carlo simulations of denaturation of model protein-like molecules with different types of the monomer–monomer interactions. The results obtained indicate that, due to trapping in metastable states, (i) the transition of a molecule to the denatured state is usually nonexponential in time, i.e. it does not obey the first-order law, and (ii) the denaturation transitions of an ensemble of different molecules are characterized by different time scales, i.e. the denaturation process cannot be described by a single rate constant kr. One should, rather, introduce a distribution of values of this rate constant (physically, different values of kr reflect the fact that the transitions to the altered state occurs via different metastable states). The phenomenological kinetics of irreversible adsorption of proteins with and without a distribution of the denaturation rate constant values have been calculated in the limits where protein diffusion in the solution is, respectively, rapid or slow. In both cases, the adsorption kinetics with a distribution of kr are found to be close to those with a single–valued rate constant kr, provided that the average value of kr in the former case is equal to kr in the latter case. This conclusion holds even for wide distributions of kr. The consequences of this finding for the fitting of global experimental kinetics on the basis of phenomenological equations are briefly discussed.
Sublimation and Phase Transitions on Si(111) Surface Observed by Ultra High Vacuum Scanning Electron Microscopy
Authors: Homma Yoshikazu
Published: August 2003

We studied the atomic step behavior on Si(111) during sublimation using ultrahigh vacuum scanning electron microscopy. A (111) plane with step spacings as large as several tens of micrometers could be obtained at the bottom of a crater by heating a vicinal Si(111) substrate with craters at around 1200°C in an ultrahigh vacuum. The step spacing on the plane was determined by nucleation of macrovacancies at the center of the plane while steps moved in a step flow manner, and was related to the adatom diffusion length. Above 1200°C, we found a transition-like increase in the step spacing. The electric current direction that induced step bunching changed at around the transition temperature. We attributed these phenomena to incomplete surface melting on the Si(111) surface. We also investigated the influence of heating current on the 7 × 7 phase transition using the wide Si(111) plane and found that the size of the 7 × 7 phase just below the transition temperature depended on the current direction.
ZnSe Growth on Lattice-Matched InxGa1-xAs Substrates
Authors: Heun S. , Lantier R. , Paggel J. J. , Sorba L. , Rubini S. , Bonanni B. , Franciosi A. , Lomascolo M. , Cingolani R. , Bonard J.-M. , Ganière J.-D.
Published: August 2003

The properties of ZnSe epilayers fabricated by molecular beam epitaxy on lattice-matched In x Ga 1-x As buffers grown on GaAs(001) substrates have been investigated by means of photoluminescence spectroscopy and transmission electron microscopy. For suitable values of x and ternary-layer thickness, the partial character of the strain relaxation within the III–V layer can be compensated for, minimizing the residual strain in the ZnSe overlayer. Large reductions in the dislocation density and Y-line emission as compared to conventional ZnSe/GaAs heterostructures can be reproducibly obtained.
Surface-Morphological Information in RHEED
Authors: Kawamura Takaaki
Published: August 2003

Surface-morphological information obtainable from RHEED intensity and its oscillation is studied based on multiple scattering calculations. The surface atomic density and the surface step density are used as the measure of surface morphology. RHEED intensity variations from growing surfaces produced by a Monte Carlo simulation are calculated by using large unit mesh surfaces. The homoepitaxial growth on Si(100) is taken as an example. The results show that RHEED intensity varies primarily as a function of surface atomic density at a low glancing angle as long as the surface island is not so large (less than 20 atomic units). RHEED intensity variations as a function of the surface step density are calculated from surfaces with different surface step density but the same atomic density. It turns out that the dominance of the information between the surface atomic density and the surface step density can be changed by choosing the diffraction condition of the incident beam.
Ultimate TEM Observation of Tungsten Clusters on MgO(001) Surfaces
Authors: Tanaka N. , Kimata H. , Takashima T. , Kizuka T.
Published: August 2003

The surface diffusion process of tungsten (W) atoms and clusters on MgO(001) surfaces was successfully studied by time-resolved high resolution electron microscopy (TRHREM) in the time resolution of 1/60 s. The observation was realized by optimizing the thickness of MgO films and by using a special imaging technique, such as the off-Bragg HREM method. During the observation, W clusters composed of four and five atoms adsorbed on MgO(001) surfaces were detected in images reproduced from the videotape images. The multislice image simulation for the interpretation of the image contrast showed a possibility of discrimination of the atomic configuration of clusters such as "bcc," "on-top" or "fcc" type clusters, from the image contrast at the center of the clusters. The reason for the discrimination was clarified through the multislice image simulation, suggesting that the lattice mismatch between the clusters and the MgO lattice was a key factor in determining the image contrast.
Selective Area Growth by Periodic Supply Molecular Beam Epitaxy
Authors: Bacchin G. , Tsunoda K. , Nishinaga T.
Published: August 2003

Selective area growth (SAG) was studied by applying periodic supply epitaxy (PSE) to molecular beam epitaxy (MBE). Different growth conditions and PSE parameters were employed, and their influence on the degree of selectivity will be described in detail, The experimental results of the SAG of GaAs and AlGaAs on GaAs (001) and (111)B substrates patterned with a SiO 2 mask will be showed and discussed, The SAG of AlGaAs was found to be very difficult because AlGaAs polycrystalline islands that are formed on the mask require more energy to be decomposed due to the stronger Al–As bonds, Despite the difficulties in SAG by MBE, the PSE technique made it possible to grow selectively smooth epitaxial layers of GaAs and AlGaAs on both kinds of substrates.
Surface Structures and Growth Mode of Cu/Si(100) Surfaces Observed by Scanning Tunneling Microscopy
Authors: Itoh H. , Ann T. , Kawasaki T. , Ichinokawa T.
Published: August 2003

The surface structures and growth mode of the Cu/Si(100) quenched surfaces have been studied by low energy electron diffraction (LEED) and scanning tunneling microscopy (STM), and the superstructures of 6 × 2, 2 × 2 and c(12 × 10) were observed by LEED mixed with 2 × 1. The combination of these structures depends on segregated Cu coverage which is a function of quenching temperature and deposited Cu coverage. These structures have been analyzed by STM and it has been found that 6 × 2 is an ordered structure of Si missing dimmer defects and 2 × 2 and c(12 × 10) are structures formed by Cu–Si layers with incorporation of Cu atoms into the Si(100) surface. The c(12 × 10) structure was analyzed in detail by STM with changing bias voltage, and a result of the structure model of c(12 × 10) has been proposed, The superstructures on the Cu/Si(100) surfaces do not grow homogeneously, and form the combined domains of these structures, Such a growth mode depending on Cu coverage and quenching temperature is discussed referring to the other metal surfaces on Si.
Inelastic Scattering Components in the Si(111)-(7×7) RHEED Pattern by the Energy Filtering Method
Authors: Horio Y. , Urakami Y. , Hashimoto Y.
Published: August 2003

Energy loss spectra for several parts of the Si(111)-(7 × 7) RHEED pattern, the (0 0) specular spot, the (3/7 3/7) superspot in the zeroth Laue zone, the (0 1) fundamental spot in the first Laue zone, and the Kikuchi line and background have been measured by the recently developed retarding type energy filter in the condition of the [Formula: see text] azimuth with a 10 kV incident electron beam. It was found that there are some differences in their spectra. Energy loss spectra of the (0 0) and (3/7 3/7) spots show surface plasmon loss peaks of silicon dominantly, and the spectrum of the (0 1) spot shows the same but includes weak bulk plasmon peaks. The spectrum of the Kikuchi line mainly shows bulk plasmon peaks and that of the background has no distinct structure in the profile. Glancing angle dependences of their profiles were also measured and discussed. The experimental data show that there is a relation between the quasielastic component of the diffraction beam and the pass length of the electron beam in a vacuum region near the surface where the electron interacts with the surface plasmon. The quasielastic component of the diffraction beam decreases as the incident glancing angle and/or takeoff angle become grazing.
Direct Observations of the Strain-Limited Island Growth of Sn-Doped GaAs(100)
Authors: Dabiran A. M. , Seutter S. M. , Cohen P. I.
Published: August 2003

We have used scanning tunneling microscopy (STM) in ultrahigh vacuum and atomic force microscopy (AFM) in air to investigate the microscopic mechanisms of Sn surface segregation during the molecular beam epitaxial growth of GaAs and AlAs(100). Submonolayer amounts of Sn segregate to the surface during growth and strongly modify the growth kinetics. This is indicated by both extra-ordinary reflection high energy electron diffraction (RHEED) measurements, and the STM and AFM images of rapidly quenched growth fronts. At the high surface coverages of 0.1–0.6 monolayers of Sn, studied in this work, neither step bunching nor three-dimensional (3D) growth of GaAs(100), was observed. Instead, STM and RHEED measurements indicated a significantly enhanced layer-by-layer growth of GaAs with increasing surface coverage of Sn. STM snapshots of the initial stages of GaAs growth revealed 2D islands which contained a higher-than-equilibrium bulk concentration of Sn, in Ga-substitutional sites, of up to 50%. Other directly observed Sn effects which are presented in this work include the removal of GaAs(100) island growth anisotropy and the formation of 2D islands with a relatively narrow distribution of size and separation. The completion of the top layers is shown to proceed by the coalescence of these islands before any significant nucleation of the next layer islands. This effect is used to explain the Sn enhancement of the layer-by-layer growth which was indicated in our RHEED and scanning probe observations. A model is presented for Sn segregation which explains these results based on an island-size-dependent, strain-driven, oscillatory Sn occupation of Ga-substitutional sites and surface interstitial sites on top GaAs(100) layers during growth. This model, which introduces a strain-limiting mechanism for the size and shape of the 2D islands, can also explain the observed enhancement of postgrowth surface recovery, as well as a delayed onset in increasing adatom surface diffusion length with increasing Sn coverage. The main conclusion is that, if impurity incorporation results in significant strain, then in addition to step climbing by surface impurities, the exchange of incorporated impurities with native species in top layers can be an important path for impurity segregation during expitaxial growth.
Recent Development and Application of the XSTM
Authors: Hirayama H. , Einaga Y. , Koike M. , Takayanagi K.
Published: August 2003

The development of the cross-section scanning tunneling microscope (XSTM) and its application to the study of the cross-section of boron(B)-implanted Si wafers are reported. To obtain a cross-section of wafer samples, we examined the cleavage on the {111} plane in two ways. As a result the cleavage, by pushing the side of the sample wafer, was found to be preferable in obtaining a flat {111} cross-section from both (111) and (001) wafers. Our devices in the mounting angle and the guiding line for the cleavage are also described in detail, Using this XSTM, we observed the {111} cleaved cross-sectional surface of the B-implanted Si(111) wafer, The local surface structure was found to change on the cleaved cross-section from the 7 × 7 to the [Formula: see text] reconstruction through the disordered phase, The change was found to be consistent with the depth profile of the implanted B in the Si water. The arrangement of B and Si atoms in the disordered phase was determined by the site and the sample bias dependence of protrusions in STM images.
Surface Electrical Conduction Correlated with Surface Structures and Atom Dynamics
Authors: Hasegawa Shuji , Jiang Chun-Sheng , Nakajima Yuji , Nagao Tadaaki , Tong Xiao
Published: August 2003

By utilizing a variety of surface super structures formed on silicon surfaces, we have clarified close correlations between the atomic-scale structures and surface-electrical-conduction phenomena. In paricular, we have succeeded for the first time in experimentally confirming the electrical conduction via surface-state bands that are inherent in the surface supertructures. Also, an important phenomenon has been found: atoms adsorbed on the surface donate carriers to the surface-state band, resulting in a remarkable enhancement of conductivity. The ultimate two-dimensional electron systems composed of surface-state bands, which are made close up in our study, are expected to provide a new stage insurface physics.
Relaxation of Nanostructures on the Si(111)(7×7) Surface by High Temperature Scanning Tunneling Microscopy
Authors: Ichimiya Ayahiko , Tanaka Yoriko , Hayashi Kazuhiko
Published: August 2003

Single silicon islands have been produced on the Si(111)(7 × 7) surface by a scanning tunneling microscope (STM) tip. Thermal relaxation of the isolated islands is observed by temperature variable scanning tunneling microscopy with strong tip effects. The sizes of islands depend on time t with a functional form of (t0-t)α. It is found that α≃2/3 for single bilayer islands, and α≃1 for three-dimensional ones. During the decomposition of three-dimensional islands, step bunching of over-layers takes place, while the islands have certain facets, like a pyramid just after the creation. At the final stages of the three-dimensional island decompositions, two-dimensional ones with 5 × 5 structure always appear. We have found that characteristic 5 × 5 islands with a long lifetime are formed during relaxation, but the 7 × 7 islands have mostlt a short lifetime. Rotation of small islands is also observed during relaxation. We discuss the results in terms of two-dimensional vapor phase processes.
Mound Formation, Coarsening and Instabilities in Epitaxial Growth
Authors: Amar Jacques G. , Family Fereydoon
Published: August 2003

An introductory review of the central ideas in the kinetics of multilayer epitaxial growth is presented. A realistic model for multilayer homoepitaxial growth on fcc(100) and bcc(100) surfaces which takes into account the correct crystal structure is discussed. The effects of instabilities which lead to mound formation and coarsening are discussed, and a unified picture of the effects of attractive and repulsive interactions at ascending and descending steps on surface morphology and island nucleation is presented. An accurate prediction of the observed mound angle for Fe/Fe(100) deposition is obtained analytically and by kinetic Monte Carlo simulations. The general dependence of the mound angle and mound coarsening behavior on the temperature, deposition rate and strength of the step barrier in bcc(100) and fcc(100) growth is also presented, and compared with recent experiments.
Influence of Surface Structure on Epitaxial Growth of Si on Si(111)-(7 × 7) Substrate
Authors: Shigeta Yukichi
Published: August 2003

To make clear the influence of surface structure on epitaxial growth, we have studied the growth of Si on a Si(111)-(7 × 7) superlattice surface by using scanning tunneling microscopy and reflection high energy electron diffraction. In the initial growth stage on the 7 × 7 superlattice, multilayer islands are formed because lateral growth of the first layer is prevented by the stable 7 × 7 structure and some migrating atoms climb up the first layer and nucleate on it. However, lateral growth of the second layer on the first one is not prevented and the layer-by-layer growth starts, because the structure of the first layer is composed of small domains with some metastable surface structures, which is rather easier to rearrange than the 7 × 7 structure. The starting point of the layer-by-layer growth depends on the substrate temperature, because the surface structure formed on a growing layer is influenced by the temperature. We obtained the result that the nucleation of a two-dimensional island on the 7 × 7 superlattice is also influenced by the surface structure. The island, whose size is less than the half-unit of the 7 × 7 structure, is unstable. The result suggests that, for the nucleation on the stable surface structure, the activation energy of rearrangement of the surfue structure should be taken into the consideration of the formation energy of the nucleus.
Calculation of RHEED Intensities for Imperfect Surfaces
Authors: Maksym P. A. , Korte U. , McCoy J. M. , Gotsis H. J.
Published: August 2003

RHEED calculation techniques for imperfect surfaces are reviewed and some applications of the calculational methods are described. Systems of interest typically consist of a perfectly ordered substrate which is periodic in three dimensions together with a surface which has imperfections in the form of disorder or steps. Calculational techniques for this type of system include: supercell methods in which the disorder is modeled by considering a large periodic system; perturbation theory in the distorted wave Born approximation where the scattering by the imperfections is taken to be a perturbation but the scattering by the periodic part of the system is treated exactly; the multislice method as used in transmission electron diffraction theory; and a promising new approach based on Green's functions. The validity of perturbation theory is investigated in detail and it is shown to give good agreement with supercell calculations in the case where the potential of the imperfections is weak or where their correlation length is small. This makes perturbation theory very suitable for treating disordered over-layers, but stepped surfaces with a large correlation length require the other methods. These methods are more expensive computationally and some possible ways of reducing the CPU time are considered. Finally, illustrative results are presented to show how the various calculational techniques can be applied to real systems. Particular cases include RHEED intensity oscillations and reflection electron microscope images.
Elementary Processes in Molecular Beam Epitaxy Studied by in situ Scanning Electron Microscopy
Authors: Inoue N.
Published: August 2003

The recent advancement in the in situ scanning electron microscopy of molecular beam epitaxy of GaAs is reviewed. The topics include two-dimensional (2D) nucleation and growth, three-dimensional (3D) roughening processes, 2D-to-step-propagation growth mode change and annealing processes after growth.

In the nucleation-and-growth mode, delayed island nucleation and nonlinear change of surface coverage are found. The mechanism of delayed nucleation is discussed in terms of site-dependent successive atomic layer growth processes. It is shown that under a critical growth condition between the 2D mode and the step propagation mode, the local growth mode changes from the 2D mode to the step propagation mode. It is found that there are three types of surface roughening, or onset of 3D growth. A 3D/2D/1D growth mode phase diagram is obtained. Some of the results are compared with the growth of Si on (111) surface.

The behavior of monolayer-deep holes during postgrowth annealing is observed. It is found that some holes are left for a long time and form big holes with each other. They extend in the [110] direction but, at the same time, shrink in the [1-10] direction. Finally, they shrink in both directions and disappear .It takes about 10 min for all the holes to disappear.

Related work by other authors is briefly described.
Beyond Intensity Oscillations
Authors: Lu T.-M. , Wang G.-C. , Zhao Y.-P.
Published: August 2003

The decay in the oscillatory amplitude of diffraction intensity from an epitaxial growth front is due to the buildup of a multilevel step structure. This can occur as a result of kinetic limitations when the substrate temperature is sufficiently low or the deposition rate is very high so that thermal equilibrium cannot be ochieved during growth. Another mechanism that can lead to a multilevel growth front is the existence of a step edge barrier at the steps so that deposited atoms cannot diffuse "downward" at the step edge which leads to a mound like structure. In this paper we describe the characteristics of the diffraction intensity angular profile from the initial layer-by-layer structure to the final multilevel structure. A particular emphasis will be placed on the characteristics of the reciprocal space structure when the amplitude of the intensity oscillation decays to zero.
N-Limited Versus Ga-Limited Growth on ${\rm GaN}(000\bar{1})$ by MBE Using NH3
Authors: Held R. , Crawford D. E. , Johnston A. M. , Dabiran A. M. , Cohen P. I.
Published: August 2003

GaN was grown on [Formula: see text] by MBE using NH 3 and a Ga Knudsen cell. The growth kinetics on samples of this polarity were investigated with desorption mass spectroscopy (DMS) and reflection high energy electron diffraction (RHEED). Both techniques were used to observe and control surface termination, Ga condensation and surface temperature. GaN growth and decomposition rates were measured by DMS. Two stable surface terminations were found to exist — N-terminated and Ga-terminated [Formula: see text]. The N-terminated surface also contained hydrogen which desorbed during growth at a rate proportional to the growth rate. Low temperature reconstructions were only observed by adding weakly adsorbed Ga on top of the Ga-terminated surface. During growth two distinct growth regimes were identified: growth under excess NH 3 and growth under excess Ga. Growth is limited in both regimes by GaN decomposition at high temperatures with an activation energy of 3.4 eV. Growth in the excess Ga regime ceased below the Ga condensation temperature. Under conditions of excess NH 3, strong but damped oscillations in the specular RHEED intensity were observed on smooth surfaces. Contrary to previous suggestions, the period of these oscillations did not correspond exactly to integral layer deposition and was not characteristic of a narrow growth front. Further, the growth mode changed from island nucleation to step flow with an activation energy of 1.2 eV. Under conditions of excess Ga, the diffraction was 2-D but RHEED intensity oscillations were not observed, indicating a step flow growth mode. In this latter regime RHEED measurements were very sensitive to termination changes on the [Formula: see text] surface, and the growth rate was found to decrease linearly with increasing Ga flux. This reduction is explained by a model in which weakly adsorbed Ga blocks reaction at strongly bound Ga. A map is presented to provide a framework for categorizing the overall growth.
The Overlayer Structure on the Si(001)-(2×3)-Ag Surface Determined by X-ray Photoelectron Diffraction
Authors: Shimomura M. , Abukawa T. , Higa M. , Nakamura M. , Shivaprasad S. M. , Yeom H. W. , Suzuki S. , Sato S. , Tani J. , Kono S.
Published: August 2003

X-ray photoelectron diffraction (XPD) patterns of Ag 3d electrons from a single domain Si(001)-(2×3)-Ag surface were examined. Single scattering cluster and multiple scattering cluster simulations of the Ag 3d XPD patterns indicate an overlayer that contains four Ag atoms aligned almost linearly along the threefold direction in the unit cell on the Si(001) surface. The four-Ag-atom arrangement is discussed in the light of other information obtained by STM, LEEM and photoemission studies, finding it very feasible.