bluuebunny/crossref_metadata_2025 huggingface dataset:
CRITICAL GRAIN SIZE FOR STRUCTURAL TRANSFORMATION IN VACUUM-DEPOSITED MOLYBDENUM FILMS
Authors: KIZUKA T. , SAKAMOTO T. , HAYASHI T. , TANAKA N.
Published: October 2004

Nanometer-grained polycrystalline films were prepared by vacuum deposition of molybdenum (Mo) by using electron-beam heating. The structure and composition of the grains were analyzed by high-resolution electron microscopy and Auger electron spectroscopy, respectively. The concentration of carbon in the films was measured in relation to reduction of the grain size to nanometer scale. The grains had a bcc structure when the grain size was larger than 4 nm. On the other hand, the grains smaller than 4 nm for films had a fcc structure. Large amount of carbon was included in the grains with the fcc structure in comparison with the grains of bcc structure, although amount of other impurities such as nitrogen and oxygen was similar in both grains. It was found that the structure was transformed from bcc to fcc below the critical grain size, 4 nm, and the grains with the fcc structure were cubic Mo-C.
TIME-RESOLVED ATOMIC OBSERVATION OF FRAGMENTATION PROCESS IN GOLD CLUSTERS BY HIGH-RESOLUTION TRANSMISSION ELECTRON MICROSCOPY
Authors: KIZUKA T. , TANAKA N.
Published: October 2004

Fragmentation in gold clusters was for the first time observed by the time-resolved high-resolution transmission electron microscopy at 0.2-nm spatial resolution and 1/60 s time resolution. A gold cluster of about 1.5-nm diameter made asymmetrical fragmentation on a magnesium oxide (001) surface. It was suggested that the present fragmentation process was similar to the Coulomb explosion process.
HREM CHARACTERIZATION OF GOLD-CLUSTER STRUCTURES
Authors: ZHANG H.Q. , HAN M. , WANG Q. , WANG G.H.
Published: October 2004

High-resolution electron microscope (HREM) and computer simulation are used to investigate structural features of gold clusters produced by the inert-gas condensation method. The results indicate that (i) smaller clusters have multiple-twinned-like structure while those larger than 150 Å in diameter show single-crystal structure; (ii) the former cluster consists of either decahedral or icosahedral form and the atomic planes are not strictly parallel and distances between the planes increase towards the cluster edge; and (iii) grain boundaries between the clusters have twin structures with both long- and short-range orders.
VARIATION OF SURFACE MORPHOLOGY OF TIN PARTICLES OBSERVED BY UHV HIGH-RESOLUTION TEM
Authors: OSHIMA Y. , TAKAYANAGI K.
Published: October 2004

Phase transition of fine tin particles with diameters 4–10 nm are studied by high-resolution transmission electron microscopy under an ultrahigh-vacuum condition. For the particles with diameter above 5 nm, the transformation from solid to liquid is sharp. The melting temperature, Tm, can be explained by Pawlow’s relation, Tm=T0−S/d (T0=213°C: bulk melting point, d: diameter, S=910°C nm). However, the particles below 5 nm do not have the shape transformation like the large particles and are found to have a specific phase between the solid phase and the liquid phase. The critical particle size for this transformation, dc=5 nm, is believed to be related with surface morphology or surface melting; large solid particles have Wulff’s polyhedron. For smaller solid particles (d=5.5–6 nm), the (110) facets become slightly rounded. The solid particle below dc has almost spherical surface, having irregular atomic arrangement of surface layer.
TEMPERATURE EFFECT ON GOLD NANODISPERSION IN ORGANIC LIQUIDS
Authors: TAKEUCHI Y. , IDA T. , KIMURA K.
Published: October 2004

The temperature effect on gold nanodispersion in organic liquids was examined by optical absorption spectroscopy and transmission electron microscopy. It was found that the color of the dispersion changed from purple just after preparation under a low-temperature condition to reddish purple or pink with the elevation of temperature up to room temperature. The optical properties of this system strongly coupled with the state of dispersions such as isolation, coagulation, and coalescence to sediment. Heating the dispersion above room temperature induced the instability of the colloidal system which also resulted in the color change of the dispersion.
STABILITY OF ADSORBED HYDROGEN ON Si(100) UNDER CHANGES OF THE SURFACE POTENTIAL
Authors: KRATZER P. , HAMMER B. , GREY F. , NØRSKOV J. K.
Published: October 2004

We study the effect of an electrostatic surface potential on the chemisorption energy of H 2 on a Si (100)2×1 surface on the basis of a set of ab initio calculations. We find a sizeable destabilization of the adsorbate, because the clean surface gains in stability compared to the H-terminated surface due to charge transfer between dangling bonds and the space charge region below the surface. We rationalize our results in terms of a simple model and discuss the possibility that potential-induced destabilization is an important ingredient in understanding STM-induced nanolithography.
STUDY OF POROUS SILICON SURFACE PROPERTIES
Authors: CHEAH K. W. , LEUNG T. Y. , CHAN M. H. , SO S. K.
Published: October 2004

Porous silicon is a material with a coral-like structure which has a fractal surface. To study these aspects of porous silicon and its relationship with the luminescence property, we have used atomic force microscopy (AFM). Samples were prepared using either pure HF or HF diluted with ethanol. From the results of AFM, distinct structural difference was observed from samples prepared by these two etchants. If we relate the structures to their respective photoluminescence spectra, it appears that finer structure produced shorter wavelength peak photoluminescence. However, the columns of the samples were too large for one to attribute the luminescence to quantum confinement only. Hence, an alternative model may be required to explain the luminescence mechanism. We have also observed that the composition of the etchant can also affect the evolution of the fractal dimension with respect to etching time. Probing of the surfcace electron states was performed using photothermal deflection spectroscopy (PDS). In order to ensure that only porous silicon layer was probed, free-standing films of various porosity were produced for the PDS measurement. The probe energy range was from 0.56 eV to 2.5 eV so that both the bulk states and the surface states were probed. The results showed that there is a clear blueshift of the energy band gap with respect to porosity, and the absorption coefficient decreases with porosity increase at a fixed photon energy. Overtones of hydrides and fluorides of silicon were also observed.
AN INVESTIGATION OF OXYGEN ADSORPTION ON α-Cu0.82Al0.18(100) USING LOW ENERGY ION SCATTERING
Authors: ZHU L. , MUHLEN E. ZUR , O’CONNOR D. J. , KING B. V.
Published: October 2004

The adsorption of oxygen on α- Cu 0.82 Al 0.18(100) has been investigated using low energy ion scattering. It was found that initially oxygen adsorbed on Al sites and then it adsorbed on Cu sites before all Al sites were occupied at room temperature. Al segregation induced by oxygen adsorption was found at oxygen exposure >10 L. Upon heating the sample to 300°C, oxygen that adsorbed previously on the Cu sites bonded to thermally segregated Al atoms and kept them on the surface. Experimental results suggest that Al oxide islands were formed upon heating. At the sample temperature of 300° C, an Al oxide layer was formed at oxygen exposure 3500 L.
AN INVESTIGATION OF STRUCTURAL DETAILS FOR THE ${\rm Cu}\left({110} \right) - \left( {\begin{array}{*{20}c} {\,\,\,2} 2 \\ { - 1} 1 \\\end{array}} \right)-{\rm P}$ RECONSTRUCTED SURFACE
Authors: LIU W. , MITCHELL K. A. R.
Published: October 2004

An exhaustive tensor LEED study for the half monolayer (ML) structure formed by P at the (110) surface of copper confirms the reconstruction reported earlier [Chem. Phys. 198, 235 (1995)]. All P atoms occupy identical six-coordinate sites; the reconstruction involves 0.25 ML of “added Cu” atoms at hollow sites, each bonded to two neighboring P atoms, which line up along the [Formula: see text] direction. Appreciable relaxations, both vertical and lateral, are identified for atoms in the first four layers. The new feature found here is that the displacements indicated by tensor LEED for individual atoms appear to follow trends that are broadly consistent with reasonable structural chemical principles.
A MODEL FOR THE MUTUAL INFLUENCE OF CHEMISORPTION AND MULTILAYER SEGREGATION
Authors: ZHANG HUI , CONG SHULIN
Published: October 2004

The Green function method and the chemisorption theory of Einstein and Schrieffer are used to calculate the chemisorption energies of O and CO on the multilayer segregated Ni-Cu disordered binary alloy within the many-coupled self-consistent coherent potential approximation. In general cases, the chemisorption-induced surface segregation can change the surface component and the chemisorption property to varying degrees. When the mutual influence of chemisorption and multilayer segregation is considered, the changes appear slightly mild. The chemisorption energy for O/Ni-Cu (CO/Ni-Cu) depends sensitively on O(CO) coverage θ, and decreases with increasing θ.
ATOM DYNAMICS ON Pt, Ir AND Cu SURFACES: AN EXPERIMENTAL STUDY USING VARIOUS TECHNIQUES
Authors: TSONG TIEN T. , CHEN CHONGLIN , FU TSU-YI , TZENG YI-REN
Published: October 2004

Some metallic adsorbed atoms on fcc metal surfaces can exchange with substrate atoms well below the room temperature. For homogeneous systems, the atomic exchange is a mechanism for self-diffusion. For heterogeneous systems, it is a mechanism for point alloy formation of only the top surface layer but it will also induce self-diffusion. We present experimental evidence found from FIM, HREELS and LEIS studies. These experiments and their relations to available theories and molecular dynamic simulations of this phenomenon are also mentioned. In addition, we present evidence for the ascending motion of step edge atoms to the upper terrace for the Ir (111) surface, and the result of a measurement of the potential barrier height of the ascending motion and the dissociation energy of step edge atoms to the lower terrace.
COMPLEX SURFACE STRUCTURES FROM LEED
Authors: VAN HOVE M. A.
Published: October 2004

The complexity of surface structures solved routinely with low-energy electron diffraction (LEED) has increased dramatically in recent years. This paper describes the evolution of the complexity that has become achievable, provides illustrations of complicated structures solved recently, and discusses the outlook for the future.
ULTRATHIN PSEUDOMORPHIC FILMS: STRUCTURE DETERMINATION AND STRAIN ANALYSIS
Authors: JONA F. , MARCUS P. M.
Published: October 2004

This paper is a review of the procedure followed in studies of ultrathin pseudomorphic films by means of quantitative analysis of low-energy electron diffraction intensities and subsequent strain analysis of the bulk. Two examples are discussed in detail: ( Fe on Rh {001}), for the case in which the unit mesh of the substrate surface and the unit mesh of the growth plane of the film material are similar and differ only in size (so-called Case-1 epitaxy); and [ Co on TiAl(010) ], for the case in which the two unit meshes are not similar, but differ from one another in both shape and size (so-called Case-2 epitaxy). Both examples show that these procedures can use the measured bulk strain to discriminate between body-centered-cubic and face-centered-cubic structures for the equilibrium phase of the epitaxial film.
AB-INITIO STUDIES OF DIFFUSION AND GROWTH PHENOMENA ON SEMICONDUCTOR SURFACES
Authors: KAXIRAS EFTHIMIOS
Published: October 2004

We discuss the application of ab-initio quantum-mechanical calculations, based on pseudopotential local-density-functional theory, to diffusion and growth phenomena on semiconductor surfaces. We examine in detail two specific examples: adatom diffusion on the Ge (111) c (2×8) reconstructed surface and surfactant-mediated homoepitaxial growth on Si substrates. In these examples, the combination of results from first-principles calculations and simple simulations helps elucidate complex dynamical phenomena. We also make predictions on the feasibility of using hydrogen as a surfactant on Si substrates, by drawing analogies between the chemical behavior of group-V or group-VI adsorbates and Si-H complexes.
LEEM/STM STUDIES OF NONREACTIVE AND REACTIVE GROWTH ON SILICON SURFACES
Authors: TSONG I. S. T.
Published: October 2004

The nucleation and growth behavior of two very different systems are studied by low-energy electron microscopy (LEEM) and scanning tunneling microscopy (STM). The first is a nonreactive system of Pb growth on the Si(100) surface at room temperature and the second is a reactive system in which nitride layers are formed on Si(111) during reaction with NH 3 at high temperatures. In both cases, the mobilities of the diffusing species have a strong influence on the resulting growth morphologies.
FACETING INDUCED BY ULTRATHIN METAL FILMS ON W(111) AND Mo(111): STRUCTURE, REACTIVITY, AND ELECTRONIC PROPERTIES
Authors: MADEY THEODORE E. , GUAN J. , NIEN C.-H. , DONG C.-Z. , TAO H.-S. , CAMPBELL R. A.
Published: October 2004

We have studied ultrathin films of transition and noble metals on Mo(111) and W(111) using Auger spectroscopy, LEED, thermal desorption spectroscopy (TDS) and scanning tunneling microscopy (STM). The atomically rough, open bcc(111) surfaces are morphologically unstable when covered by films ≥ 1 monolayer thick of certain metals, i.e. they form faceted structures. For example, using a UHV STM to study Pd/W(111) , we find that the Pd-covered W(111) surface becomes completely faceted to three-sided {211} pyramids upon annealing, for Pd coverages greater than a critical coverage θc. Formation of pyramidal facets also occurs when W(111) or Mo(111) surfaces are dosed with Pt, Au, Ir, Rh, oxygen or sulfur. In contrast, monolayer films of Ti, Co, Ni, Cu, Ag and Gd do not induce massive reconstruction or faceting on W(111) and Mo(111) surfaces. The faceting appears to be thermodynamically driven but kinetically limited: faceting is caused by an increased anisotropy in surface free energy that occurs for the film-covered surfaces. An interesting correlation has been observed for both substrates: faceting occurs for overlayer elements having Pauling electronegativities greater than 2.0, suggesting that surface electronic effects are controlling the structural instability of both Mo(111) and W(111) . Structure sensitivity in a model catalytic reaction, n-butane hydrogenolysis, is observed over planar and faceted Pt/W(111) . We have also used soft x-ray photoemission spectrosocopy (SXPS) based on synchrotron radiation methods to characterize the bimetallic interface; for Pt, Pd and Au on W(111) , we find that substrate core level shift effects associated with interface formation are substantial, while those associated with faceting are rather subtle.
THE SURFACE STRUCTURES OF Pd(100)-(1×1) AND c(2×2)-K
Authors: BURCHHARDT J. , LUNDGREN E. , NIELSEN M.M. , ANDERSEN J.N. , ADAMS D.L.
Published: October 2004

The surface structure of the Pd (100)- c (2×2)-K phase formed by adsorption of K at room temperature has been determined by quantitative analysis of low-energy electron-diffraction (LEED) intensity-energy measurements. K atoms occupy four-fold hollow sites on a slightly perturbed substrate. The vertical distance between the K layer and the first Pd layer is determined to be 2.13±0.06 Å, which corresponds to an effective hard-sphere radius of 1.83 Å for the adsorbed K atoms. The second Pd layer is rumpled with a splitting of 0.04 Å between two bilayers. An analysis of LEED intensities measured for the clean Pd(100) surface confirms previous reports of an expansion of the first interlayer spacing. Adsorption of K in the c (2×2) structure results in a reduction of this expansion from 5% to 1%.
RELATIONSHIPS BETWEEN SURFACE PLASMON ENERGY AND THE SURFACE ELECTRONIC ENVIRONMENT OF A RANGE OF SEMICONDUCTORS
Authors: MATTHEW J.A.D. , PARKER S.
Published: October 2004

It is shown that the ratios of observed surface plasmon energies to the corresponding bulk plasmon energies are consistently less than [Formula: see text] for a wide range of semiconductor surfaces. A simple dielectric model shows how this robust property relates to the surface electronic environment.
AN STM STUDY OF THE INITIAL STAGES OF OXIDATION OF Ni3Al(110)
Authors: COTTERILL G.F. , NIEHUS H. , O’CONNOR D.J.
Published: October 2004

The initial stages of oxygen adsorption on Ni 3 Al (110) at 9700 K have been studied by scanning tunneling microscopy (STM) and low energy electron diffraction (LEED). We report the observation of two different reconstructed surface phases. First, on the well-ordered surface, after exposure to O 2 at 970 K for doses <5L, a saturation coverage (1/4 ML) of Ni 3 Al {110} c(2×2)- O is observed. Secondly, we report an oxygen-induced reconstruction which is incommensurate with the substrate, resulting after an incomplete annealing of the suface following Ar + bombardment. A structure model for this phase is proposed.
ATOMIC STRUCTURE STUDY OF THE Ag/MgO(100) SURFACE BY AN AB INITIO, TOTAL ENERGY MOLECULAR CLUSTER METHOD USING DENSITY FUNCTIONAL THEORY
Authors: SPIESS LAURENT
Published: October 2004

The clean and Ag-covered MgO(100) surface is investigated by an all-electron, total energy, ab initio DMol molecular method (Density functional theory for Molecular systems). A large cluster of 100 atoms (including 50 oxygen and 50 magnesium) is built to represent the surface. A point charge embedding is used to investigate the electronic properties. The small relaxation of the surface, referred to as rumpling, is exhibited and shown to have barely no effect on the adsorption of Ag on the surface. The oxygen site is found to be the most stable for Ag atom adsorption, in good agreement with previous ab initio theoretical studies. The adsorption of a five-Ag-atom layer on the MgO(100) surface provides new and interesting results concerning the surface coverage dependence. We have used the unique ability of cluster methods to study the structural effects of the 3% mismatch at the Ag/MgO(100) interface, and we show that Ag atoms are likely to grow on the surface without epitaxy at low coverages.
SURFACE PLASMONS ON UNIAXIAL CRYSTALS WITH GRATING SURFACES
Authors: COSTA FILHO R.N. , FREIRE V.N. , FARIAS G.A.
Published: October 2004

In this paper we calculate the dispersion relation of surface plasmons propagating on uniaxial crystals, upon which a periodic grating has been built. The Rayleigh–Fano method is used, resulting in an infinite number of branches. We consider different orientations of the optical axis of the crystal, with respect to the direction of propagation. It is observed that the splitting of the surface plasmons depends not only on the ratio between the amplitude of the grating and its period (ζo/a), but also on the factor of anisotropy [Formula: see text], which changes for each optical orientation. Numerical results for the dispersion relation are obtained for α- SiO 2, and show the influence of the factor γ on the convergence of matrices.
ISLAND-SIZE DISTRIBUTIONS OF Ag ON Pd(111)
Authors: FISCHER R. , FAUSTER TH. , VON DER LINDEN W. , DOSE V.
Published: October 2004

Island-size distributions of submonolayer Ag films on Pd(111) adsorbed at 90 K and after annealing of the film are recovered from two-photon photoemission spectra of the first image state. The inversion of the ill-conditioned problem with the maximum-entropy method reveals magic numbers in the island-size distributions. Hypothesis testing within the framework of Bayesian probability theory indicates a critical nucleus size i=1. After annealing of the film large islands coexist with small clusters in a two-phase state.
ELECTRONIC STRUCTURE OF THE CRYSTALLINE SILICON/n-FOLD SiO2 RING INTERFACE
Authors: ZAVODINSKY V.G. , KUYANOV I.A.
Published: October 2004

Using the ab initio local density approach we have studied the electronic structure of the systems consisting of the six-, four- and three-fold planar SiO 2 rings placed upon the surface of the silicon cluster. The interaction of the six- and four-fold rings with the silicon surface changes the electronic structure of the silica particle very weakly and the surface insulator band gap of 7–8 eV remains in their densities of states. The electronic structure of the three-fold planar ring undergoes a significant reconstruction. Its surface band gap is 3.7 eV instead of 7.6 eV for the free particle case. Two groups of the interfacial states were found inside the silicon semiconductor band gap.
ORDERED AND DISORDERED RIPPLING IN THE CoAl(110)-(1×1) SURFACE
Authors: BLUM V. , RATH C. , CASTRO G.R. , KOTTCKE M. , HAMMER L. , HEINZ K.
Published: October 2004

A quantitative structural analysis of CoAl(110)-(1×1) by low energy electron diffraction shows that the topmost layer of the surface is rippled by an amplitude of 0.18 Å, with aluminum atoms pulled out of the surface and the average distance to the second layer only slightly expanded. In contrast to the perfect stoichiometry found for the top layer and the chemical order in the bulk, about 20% of the second layer Al atoms are substituted by Co. This is probably due to preferential sputtering during the course of sample preparation and incomplete subsequent reordering. A new version of Tensor LEED allows the detection of some disordered rippling induced by the substitutional disorder in this layer, with substitutional cobalt being 0.05 Å above the ideal aluminum position. The quality of the theory–experiment fit is mirrored by a Pendry R factor value of R=0.10.
SURFACE DIFFUSION AND ANISOTROPIC LATERAL INTERACTIONS
Authors: MYSHLYAVTSEV A.V. , ZHDANOV V.P. , NORTON P.R.
Published: October 2004

Anisotropic lateral interactions between particles on a rectangular lattice result in anisotropy in the coverage dependence of the chemical diffusion coefficient. This effect is studied in the framework of the lattice-gas model taking into account repulsive lateral interactions in the ground state and also lateral interactions in the activated state. To calculate the diffusion coefficient, the transfer-matrix technique is employed.
MOLYBDENUM AND NITROGEN COSEGREGATION ON Fe–3.5%Mo–N(110)
Authors: VILJOEN E.C. , ELTESTER B. , UEBING C.
Published: October 2004

Surface cosegregation phenomena were studied at elevated temperatures on the (110) surface of a Fe–3.5%Mo–N single crystal by means of Auger electron spectroscopy (AES) and low energy electron diffraction (LEED). Cosegregation of molybdenum and nitrogen, being due to the strong chemical interactions between the two solutes, was found to cause the formation of a two-dimensional MoN surface compound. The stability of this compound was investigated in the temperature range of 500–700°C. Above 600°C desorption of molecular nitrogen occurs. The maximum surface coverages of the segregants, which were established at temperatures of around 500°C, corresponded to less than a full monolayer of the MoN surface compound. LEED investigations revealed a complex diffraction pattern of the MoN–covered Fe–3.5%Mo–N(110) alloy surface which is not fully understood yet. However, no facetting of the bcc(110) surface occurred. This finding is in sharp contrast to previous results obtained on (110)-oriented surfaces of ferritic alloys with various 3d metals, such as Fe–15%Cr–N and Fe–3%V–C, N. It is concluded that the maximum MoN surface coverage is too small to induce the facetting of the bcc(110) alloy surface.
MAGNETIC X-RAY CIRCULAR DICHROISM IN PHOTOELECTRON SPECTROSCOPY AND DIFFRACTION
Authors: TOBIN J.G. , WADDILL G.D. , TAMURA E. , STERNE P. , BEDROSSIAN P.J. , PAPPAS D.P. , GUO X. , TONG S.Y.
Published: October 2004

In this paper, we discuss a series of photoelectron-spectroscopy (PS) and photoelectron-diffraction (PD) studies utilizing magnetic x-ray circular dichroism and fully spin-specific, multiple-scattering calculations for analysis of the experimental results. The test system used was perpendicularly magnetized, ferromagnetic monolayer Fe/Cu(001), prepared and probed at low temperature. Two sets of states were used: the Fe2p at binding energies of over 700 eV (large spin–orbit and small exchange splittings) and the Fe3p at a binding energy of near 53 eV (spin–orbit and exchange splittings approximately equal). The PS and PD measurements made were angularly resolving and compared to calculational results which were similarly angularly dependent. Both “exchange shifts” and intensity variations of spectral structure were observed. The impact of “j-state mixing” was seen in both the Fe2p and 3p spectra. Our results indicate a ferromagnetically ordered FCC Fe with a lattice parameter near that of bulk Cu. Nevertheless, the sensitivity of the multiple-scattering calculations of both the Fe2p and Fe3p simulations to local order has been used to show that the overlayer structure posseses some level of imperfection or disorder as well.
KINETICS, DYNAMICS AND MUTUAL INTERACTIONS OF DEFECTS ON Si(001)
Authors: ZHANG ZHENYU , WU FANG , LAGALLY MAX G.
Published: October 2004

This article gives a critical review of the recent progress in the understanding of the physical properties of defects on Si(001). Mainly two classes of defects will be considered: point defects, including adatoms, ad-dimers, atom vacancies and dimer vacancies; and line defects, including steps, dimer strings, antiphase boundaries and vacancy lines. The focus will be on the kinetic and dynamic properties of the defects. Also discussed are their mutual interactions. A combination of extensive theoretical and experimental studies has provided clear answers to several fundamental questions about defect energetics and dynamics, and in some other cases has resulted in plausible solutions. In surveying some open or controversial issues, likely future directions will be discussed as well.
MANIPULATING ATOMS ONE BY ONE WITH A SCANNING TUNNELING MICROSCOPE
Authors: HUANG DEHUAN , YAMAMOTO YOSHIHISA
Published: October 2004

By using an STM operated in ultrahigh vacuum, we can extract single Si atoms from any predetermined positions of the Si(111)-(7×7) surface through field evaporation. This technique enables us to create novel atomic-scale structures, and even to fabricate a single atom groove and chain on the surface. The extracted Si atoms can be redeposited onto the surface, although the crystallographic position of these deposited Si atoms changes as their density increases. We have demonstrated that natural Si vacancy defects existing on the surface can be repaired by this technique. The deposited Si atoms can be reremoved by picking them up again with the tip, the substrate atomic arrangement remaining unperturbed. We can also remove individual hydrogen atoms from hydrogen-passivated Si(100)-(2×1) surfaces. A chain with equal separation of Si dimers produced by hydrogen desorption has been created. These results demonstrate the potential of STM for the construction of electronic devices with atomic dimensions.
ULTRATHIN METAL FILMS BY DESIGN: EXPLOITING THE CLOSE CORRELATION BETWEEN STRUCTURE AND MAGNETISM
Authors: WUTTIG M. , FELDMANN B.
Published: October 2004

To design ultrathin metal films with desired properties, it is necessary to understand the close correlation between film structure and film properties. In this paper several examples of the relationship between the magnetism and the structure of thin metallic films are presented. It is demonstrated that for iron films on Cu(100) and Cu 3 Au (100) and for MnCu surface alloys, unusual film structures are often accompanied by unusual magnetic properties. While two fcc phases, which differ in their crystallographic and magnetic states, have been stabilized on Cu(100) depending upon film thickness, no fcc modification is observed on Cu 3 Au (100). This can be understood qualitatively if the different contributions to the total energy of the film are considered. For the weak magnets Mn and Fe studied here, this points towards a pronounced contribution of the surface to stabilizing unusual magnetic phases. This is demonstrated even quantitatively for the Cu (100) c(2×2) Mn phase, where an unusual surface-layer corrugation is accompanied by a large magnetic moment. An improved understanding of the energies that govern the correlation between structural and magnetic properties should widen the opportunities for designing ultrathin films with desired magnetic characteristics.
STRUCTURAL AND ELECTRONIC PROPERTIES OF THE Li/Si(001) SURFACE
Authors: CHUNG J.W.
Published: October 2004

Atomic arrangements and electronic properties of the Li-adsorbed Si(001) surface are briefly reviewed. Characteristic features of a series of ordered structures with increasing Li coverage at room temperature are described. Structural models invoking a dimer flipping mechanism are discussed for the first two ordered structures, (2×2)-Li and (2×1)-Li, which are proposed as reconstructions of the silicon substrate. It is shown that the metallic phase found at an initial stage of adsorption is a result of substrate metallization, which explains the presence of an intraband surface plasmon. The features of the surface band structures for the first two ordered structures are discussed in terms of variation of the binding sites with coverage. All the unique features of the Li/Si(001) surface essentially exhibit the size effects of Li.
ELECTRONIC STRUCTURE OF STRAINED VANADIUM OVERLAYERS ON W(100) AND Ta(100)
Authors: DE COSS R.
Published: October 2004

We study the role of hybridization and overlayer–substrate lattice mismatch in determining the surface electronic structure of strained V monolayers and bilayers on W(100) and Ta(100). The local density of states is calculated in the tight-binding approximation within the surface-Green-function-matching formalism. For one monolayer of V on W(100) and Ta(100), the strong monolayer–substrate 3d–5d hybridization determines the features of the surface local density of states, with essentially no differences between 1V/W(100) and 1V/Ta(100). For the bilayer we find that the electronic structure of the topmost layer depends strongly on the lattice mismatch between overlayer and substrate. In particular, we find that the surface local density of states at the Fermi level in 2V/Ta(100) is 69% higher than in 1V/Ta(100); the lattice mismatch between bulk constants of V and Ta is 9.0%. These results indicate that strain induces strong band narrowing in vanadium overlayers on transition metals, despite the large overlayer–substrate hybridization, but depends critically on the film thickness.
SOFT MODE OF MAGNONS ON A (001) SURFACE FOR A SEMI-INFINITE CUBIC FRUSTRATED ANTIFERROMAGNET
Authors: TAMINE M.
Published: October 2004

We make a theoretical study of the (001) surface magnons dispersion curves. Their localized energy states are calculated by Green function and matching procedure methods which are used simultaneously in the case of semi-infinite cubic frustrated Heisenberg antiferromagnets. Magnetic frustration phenomena originate from competing effects between the first neighbor [Formula: see text] and second neighbor [Formula: see text] interactions. This magnetic frustration is quantized by the [Formula: see text] ratio. It is the first time that such a detailed application of the matching procedure is presented in order to calculate the surface magnon dispersion. It is found that, when [Formula: see text], a magnetic phase transition also exists at the surface, as previously observed in the bulk, in accordance with the results predicted by computer simulation.
ATOMIC STRUCTURE OF (100) SURFACES OF ZINCBLENDE COMPOUND SEMICONDUCTORS
Authors: KAHN A.
Published: October 2004

This paper provides an overview of our current understanding of atomic geometries of (100) surfaces of III–V, II–VI and I–VII zincblende structure semiconductors. The origins of atomic reconstructions of polar surfaces are reviewed. Fundamental principles are described from which the main aspects of reconstructions at (100) surfaces can be derived. These principles are used to explain and predict stoichiometries and atomic arrangements on these complex surfaces. The most recent structural models of (100) surfaces are reviewed in light of these principles.
SYNTHESIS AND MECHANICAL PROPERTIES OF CRYSTALLINE CARBON NITRIDE SUPERHARD COATINGS
Authors: CHUNG YIP-WAH
Published: October 2004

Crystalline β- C 3 N 4 was predicted to have mechanical properties similar to those of diamond. Until recently, only amorphous carbon nitride coatings were made in spite of numerous attempts. This lack of success in making crystalline coatings suggests that β- C 3 N 4 is metastable. Using TiN as seeding layers and under proper processing conditions, we were able to synthesize fully crystalline carbon nitride composite coatings with hardness in the 45–55 GPa range, which is at the low end of diamond. Suggestions for further improvements and implementation with other deposition techniques will be made.
EMISSION ELECTRON DIFFRACTION AND HOLOGRAPHY: A THEORETICAL SURVEY
Authors: FONDA L.
Published: October 2004

The first part of this article reviews emission electron diffraction, a very powerful tool for investigating short order surface structures. Within the standard single particle approach, the correct multiple scattering formalism and its single scattering cluster, plane and spherical wave approximations are treated in detail. The simple direct methods exploiting low energy backscattering and high energy forward focusing, which can provide information on topmost crystal layers, are discussed. In general, one needs to compare experiment and theory via trial-and-error extensive multiple scattering calculations for a series of guessed test structures. Only structures explicitly taken into account in the analysis can be determined with certainty by these methods. Emission electron holographic approaches, of less resolving power than emission electron diffraction, are discussed in the second part of the paper. They are direct methods which can provide an approximate initial structure which is then to be refined by the multiple scattering approach. Ways to eliminate twins, self-hologram peaks and angular anisotropies, appearing in these approaches, are also discussed.
ATOMIC STRUCTURE AND COMPOSITION OF CLEAN AND ADSORBATE MODIFIED SURFACES OF ORDERED AND RANDOM ALLOYS
Authors: ZEHNER D. M.
Published: October 2004

As a consequence of bulk truncation, the atomic structure and composition within the surface region of an ordered or random alloy may differ significantly from that of the bulk. Specifically, the response to the rearrangement resulting from the reduction of surface energy may cause elemental redistribution within the outermost layers and two- or three-dimensional atomic reordering. Furthermore, the presence of adsorbates may have a pronounced effect on these properties and cause significant changes. These properties for some surfaces of transition-metal aluminides, transition-metal carbides, and random alloys will be presented.
PT-METAL ALLOY SURFACES: SYSTEMATIC TRENDS
Authors: GAUTHIER Y.
Published: October 2004

We present here the data available for selected Pt-based bimetallic alloys. Attention is paid to ordered or chemically disordered single crystal samples obtained by alloying Pt with six different metals and for which detailed information is known regarding the structural arrangement and the composition profile over the first few layers from vacuum. This series of compounds shows systematic trends, and emphasis is put on the effect of the bulk concentration, crystal orientation and chemical element associated with Pt on the segregation profile. From a structural point of view, alloys generally behave like their pure constituents, although segregation-induced strains may play an important role, particularly for reconstructed surfaces. Finally, it is stated that short range reconstruction, i.e. chemical ordering and atom displacements, takes place in most (all?) disordered alloy surfaces with likely strong implications for their actual catalytic properties.
STRUCTURAL STUDY OF ALLOY FORMATION AT THE Co-Pt(111) INTERFACE
Authors: GALEOTTI MONICA , ATREI ANDREA , BARDI UGO , CORTIGIANI BRUNETTO , ROVIDA GIANFRANCO , TORRINI MARCO
Published: October 2004

This study examines the structure of the surface alloys that form at the surface of the system formed by depositing cobalt on the clean Pt(111) surface. Using mainly XPD as a structure-sensitive technique, surface alloys were observed to form in this system after annealing at temperatures of about 600 K or higher. When starting with a single atomic layer of cobalt, diffusion leads to a surface phase where Pt atoms occupy mainly the topmost layer while cobalt atoms are mainly located in the second layer from the surface. Multi-atomic-layer alloying, with the formation of an epitaxial, random substitutional Co-Pt(111) alloy, is observed at higher temperatures.
COMBINED STM AND RBS INVESTIGATION OF THE NUCLEATION AND GROWTH OF Au ON Ni(110): ALLOYING AND DEALLOYING
Authors: NIELSEN L. PLETH , STENSGAARD I. , BESENBACHER F. , LÆGSGAARD E.
Published: October 2004

We have performed in-situ Scanning Tunneling Microscopy (STM) and Rutherford Backscattering Spectroscopy (RBS) investigations of the room-temperature (RT) growth of Au on Ni(110) . At low coverages, we observe the formation of a Au/Ni surface alloy, even though Au is immiscible with bulk Ni at RT. At a critical Au coverage of θ Au = 0.4 ML (monolayer), we observe a “dealloying” phase transition where 0.16 ML of Au is “popping” out of the alloyed surface layer and nucleates into [001]-directed dimer/trimer Au chains. Increasing the Au coverage further causes the nucleation and growth of more [001]-directed chains, i.e. their mutual distance in the [Formula: see text] direction decreases until the chain structure finally saturates in a p(5 × 3) structure at θ Au = 0.93 ML . The formation of a surface alloy at low coverage is supported by theoretical calculations within the Effective-Medium Theory (EMT), and an atomic model for the [001]-directed Au chains is developed from a detailed interplay between experiments and theoretical calculations.
SEGREGATION IN MULTICOMPONENT ALLOYS: ORDERED CrN AND CrC SURFACE PHASES ON A Fe-15%Cr-C, N(100) SINGLE CRYSTAL
Authors: UEBING C. , SCHEUCH V. , KISKINOVA M. , BONZEL H. P.
Published: October 2004

In general the chemical composition of multicomponent alloy surfaces exhibits significant deviations from the bulk composition due to thermally activated segregation processes. Upon cosegregation epitaxially stabilized two-dimensional surface compounds are formed on substrate surfaces of suitable orientation, e.g. CrN on Fe-15%Cr-N(100) and CrC on Fe-15%Cr-C(100) . The important role of the epitaxial stabilization manifests itself by the fact that on Fe-15%Cr-C(100) crystals the formation of cubic CrC surface precipitates is possible upon nonequilibrium cosegregation of the constituent components. Such a chromium carbide with rocksalt structure is not stable in the bulk of bcc Fe-Cr-C alloys .

Angle-resolved photoemission of Cr 2 p 3/2, N 1s and C 1s core level photoelectrons is used to determine the structure of the CrN surface compound and of the CrC surface precipitate on a Fe-15%Cr-C,N(100) single crystal. Both surface phases exhibit a sharp 1×1 LEED pattern. Polar angle intensity distributions of photoelectrons (x-ray photoelectron diffraction) are recorded in the [001] and [011] azimuths, respectively. For CrN the angular intensity distributions exhibit forward scattering peaks for Cr 2 p 3/2 but not for N 1s. Most likely, the CrN phase consists of a CrN compound layer with significant N outward relaxation of about 0.6 Å and a second completed Cr layer. Single scattering cluster (SSC) calculations indicate that the Cr-Cr interlayer distance is expanded by about 26% with respect to the bcc lattice. For CrC , on the other hand, Cr 2 p 3/2 and C 1s show both strong forward scattering features in all distributions. The CrC phase consists of at least three complete compound layers with NaCl structure.
ANGLE-RESOLVED PHOTOEMISSION SPECTRA CALCULATIONS IN NONMAGNETIC ALLOYS
Authors: GINATEMPO B.
Published: October 2004

The relativistic theory of angle-resolved photoemission from nonmagnetic metal surfaces is reviewed. The problems arising from the application of existing theories to multicomponent systems are analyzed, in order to find out which information about the electronic structure can be univocally extracted from a detailed comparison between experiments and theory. In order to illustrate the theoretical points, angle-resolved photoemission spectra calculations, for the spin-polarized case, are presented for the ordered and disordered Cu 3 Au (1,0,0) surface. The conclusion is that, notwithstanding their drawbacks, photoemission calculations are an essential tool for understanding the experiments, and that very small details of the photoemission spectra can be related to the order-disorder transition.
ALLOYING OF THIN Ag AND Au FILMS ON Pd(111) STUDIED BY HIGH-RESOLUTION PHOTOELECTRON SPECTROSCOPY OF SURFACE STATES
Authors: FISCHER R. , FAUSTER TH.
Published: October 2004

Alloy formation by annealing of thin Ag and Au films on Pd(111) is studied by high-resolution ultraviolet and two-photon photoelectron spectroscopy of surface states. Changes in the composition of the top layer of the surface alloys are reflected in the energy of the surface states. Above an annealing temperature of 500 K on both systems, the crystal-induced surface state shifts continuously from the occupied state of the adsorbate to the unoccupied state of the substrate. The continuous shift reflects the variable composition of the alloys in the surface region which depends on the initial coverage and the annealing temperature. The spectroscopy of the unoccupied image states permits the investigation of growth and morphology of deposited metal layers. Three-dimensional island growth, layer-by-layer growth, and surface alloy formation with metastable surface configurations and diffusion of the overlayer material into the bulk are identified.
PHASE TRANSITIONS ON ALLOY SURFACES
Authors: TERAOKA Y.
Published: October 2004

Various kinds of quasi-two-dimensional order-disorder phase transitions on binary alloy surfaces are discussed on the basis of the lattice gas model with appropriate approximations. The importance of surface segregation is pointed out in understanding phase transitions on alloy surfaces. Ordered structures localized on the surfaces are found above the bulk transition temperature, and a possibility of finding surface ordered structures with a different symmetry from the bulk ordered one is discussed, too. As for both ordering and segregating alloys, semi-infinite systems with surfaces are discussed above and below the bulk transition temperatures; in particular, the relation of the surface phase transitions to the bulk ones is focused on.
DYNAMIC PROCESSES OF ALTERED LAYER FORMATION IN Cu-Pt ALLOYS UNDER ION BOMBARDMENT
Authors: LI CHUNFEI , ASAHATA TATSUYA , SHIMIZU RYUICHI
Published: October 2004

Three different experimental approaches have been developed to study the dynamic process of subsurface altered layer formation in a Cu-Pt alloy under Ar + ion bombardment: (1) sputter neutral mass spectrometry by multiphoton ionization (MPI-SNMS) for the study of preferential sputtering caused by the collision cascade process in the very initial stage of sputtering; (2) ion scattering spectroscopy (ISS)-Auger electron spectroscopy (AES) sequential measurements for investigating radiation-enhanced Gibbsian segregation in the transient stage of sputtering; (3) an approach based on ISS monitoring by prompt switching of the ion bombardment with ( He ++ Ar +) ions to that with He + ions, for revealing the cooling effect in radiation-enhanced diffusion in the final steady state of sputtering. For this we have developed a specific coevaporating device for depositing Cu and Pt simultaneously on a substrate at constant deposition rate. The coevaporating device was attached to both of the specimen chambers of the Auger microprobe, JAMP-3, and of the MPI-SNMS apparatus.

The results have clearly revealed: (i) ion bombardment causes a preferential sputtering of Cu atoms in the very initial stage of sputtering, (ii) followed by gradual formation of an altered layer as ion sputtering proceeds in the transient stage, and (iii) finally the alloy system approaches a steady state where the composition profile is controlled by cascade mixing, radiation-enhanced Gibbsian segregation and radiation-enhanced diffusion to satisfy the mass balance law. In the steady state the approach (3) has, first, revealed that the cooling effect does exist in radiation-enhanced diffusion.
SURFACE SEGREGATION ON Au3Cu(001)
Authors: SCHÖMANN S. , TAGLAUER E.
Published: October 2004

In relation to investigations of the surface composition of ordered alloys in the region of their critical temperature, the elemental concentrations of the top two atomic layers of a Au 3 Cu (001) alloy surface were determined with low energy ion scattering in the temperature range of 300–925 K. Up to 550 K the first layer consists only of Au atoms and the second layer of Cu atoms. Above this temperature desegregration occurs; from the temperature dependence a segregation enthalpy of 47 kJ/mole could be deduced. The segregation results in a contraction of the top layer distances compared to the bulk values. The segregation kinetics can be described as an exchange process between the top atomic layers with an activation energy of 0.2–0.3 eV. The temperature dependence of the surface concentration of this alloy is determined by the segregation process rather than by the bulk ordering phase transition.
APPLICATION OF ION SCATTERING TO ALLOY SURFACE ANALYSIS
Authors: O’CONNOR D. J. , SHEN Y. G. , MUHLEN E. ZUR , ZHU L. , MACDONALD R. J.
Published: October 2004

The physical and chemical interaction of an alloy with its environment is dictated not by its bulk composition but by the surface concentration of different elements and their physical arrangement. Of the tools developed to measure these properties, ion scattering (with energies of 0.1–100 keV) has the capacity to measure composition with atomic layer sensitivity and short range order in real space. These advantages have been used to investigate the surface structure, composition and oxidation of bulk alloys and surface alloys. The composition and structure have also been used as probes of order-disorder transitions. In this presentation a review will be undertaken of the information so far delivered by ion scattering, and some of the potential directions will be outlined. Examples of work recently published or currently under investigation will be used to demonstrate the special applications of LEIS to alloy surface studies.