bluuebunny/crossref_metadata_2025 huggingface dataset:
A SYNCHROTRON RADIATION STUDY OF THE FORMATION OF CuxSey AND NaxCuySez THIN FILMS ON Cu SUBSTRATES: Cl2-INDUCED OUT-DIFFUSION OF Na
Authors: SALTAS V. , PAPAGEORGOPOULOS C. A. , PAPAGEORGOPOULOS D. C. , TONTI D. , PETTENKOFER C. , JAEGERMANN W.
Published: April 2003

In this paper we study the growth of Cu x Se y and Na x Cu y Se z thin films on polycrystalline Cu substrates. The investigation took place in situ by means of photoemission spectroscopy with synchrotron radiation, in UHV. Deposition of elemental Se with a dense flux on a polycrystalline Cu substrate at RT and subsequent heating to 100°C causes the formation of a thick Cu 2-x Se film (with x equal or very close to zero). A phase transition of this copper selenide occurs by annealing at 200°C. Deposited Na on the Cu 2-x Se film is diffused into the bulk, resulting in the formation of a Na x Cu y Se z compound. Exposure to Cl 2 at 120°C causes the out-diffusion of Na to the surface, where NaCl is formed. The Na diffusion in and out of the copper selenide film is analogous to alkali intercalation–deintercalation from TX 2 layer compounds.
IN SITU HALL MEASUREMENTS OF Fe AND Cr SUBMONOLAYERS ON Si(111) OF n- AND p-TYPE CONDUCTIVITY
Authors: GALKIN N. G. , GOROSHKO D. L. , KONCHENKO A. V. , IVANOV V. A. , ZAKHAROVA E. S. , KRIVOSHCHAPOV S. TS.
Published: April 2003

By the method of in situ Hall effect measurements at room temperature, it was shown that the formation of a clean Si (111)(7×7) surface at high temperature annealing (T=1250°, t=120–180 s) of n-type conductivity silicon results in a change of the majority carriers on a surface. But on a surface of p-type conductivity silicon it results in the formation of a hole accumulated layer. Various dynamics of changes in the Hall voltage and resistivity voltage within the limits of the first monolayer of room temperature adsorption of iron and chromium on substrates with a p–n junction and with a hole accumulated layer are not connected with conductivity along an absorbed layer. To understand the mechanism of conductivity in a system adsorbed layer Fe(Cr)/ Si (111)(7×7), it is necessary to take into account two effects: (a) destruction of the superstructure Si (111)(7×7); (b) formation of donor-type surface states of Fe(Cr) in the band gap of silicon. Destruction of the localized surface states of the superstructure Si (111)(7×7) plays the greatest role, when the density of donor-type surface states is very small. It corresponds to adsorption of Cr on Si (111) of p-type conductivity. The greatest contribution of donor-type surface states to the conductivity of the surface space-charge layer was observed with adsorption of Fe on Si (111) of n-type conductivity. Conductivity through the adsorbed iron (chromium) layer began with a thickness more than three monolayers.
APPLICATION OF THE PHOTO-INDUCED CHARGE EFFECT TO STUDY LIQUIDS AND GASES
Authors: IVANOV O. , KONSTANTINOV L.
Published: April 2003

The possibility is shown of developing a new method based on the surface photo-charge effect (SPCE) to study liquids, gases and vapors. The main idea is that, due to the strong susceptibility of this effect to the state of the irradiated interface, each change in the liquid- or gas-contacting surfaces would cause changes in the observed signals. The experiments performed so far support such a possibility.
OXYGEN-DERIVED DOS FEATURES IN THE VALENCE BAND OF METALS
Authors: SUN CHANG Q. , LI S.
Published: April 2003

From the perspective of sp orbital hybrid bonding and its consequence on the behavior of valence electrons, new insight is presented into the nature of oxygen-derived features in the valence band and above of metals. It is suggested that the crystal geometry and the surface morphology may vary from surface to surface and from material to material but the oxygen-derived features in energy space are substantially the same in nature. The derived features can be consistently specified as oxygen–metal bonding (-5 to -8 eV), a nonbond lone pair of oxygen (-1 to -2 eV), holes of metal ions (~EF) and antibonding metal dipole states (>EF), other than the addition of the 2s or 2p states of the isolated oxygen additives.
THE ATOMIC STRUCTURE OF Si(111)-$(\sqrt{3}\times\sqrt{3})$R30°-Ga DETERMINED BY AUTOMATED TENSOR LEED
Authors: CHEN WENHUA , WU HUASHENG , HO WING KIN , DENG B. C. , XU GENG , TONG S. Y.
Published: April 2003

The atomic structure of the Si (111)-[Formula: see text]R30°-Ga surface has been studied by comparing measured low-energy electron diffraction (LEED) intensity (IV) curves with calculated IV spectra using the method of automated tensor LEED. The experimental LEED IV curves used in this work contain many beams and a wide energy range. The results show that the Ga atoms occupy T4 sites, at 2.62 Å above the second-atomic-layer Si atoms. The Ga–Si vertical spacing is 1.44 Å and the bond length between the Ga atom and the first-layer Si atom is 2.52 Å. Large bucklings are found in the first and second Si bilayers below the adatom layer.
THE ADSORPTION AND REACTION OF ACETALDEHYDE ON CLEAN Ag(111)
Authors: WU G. , STACCHIOLA D. , COLLINS M. , TYSOE W. T.
Published: April 2003

The adsorption of acetaldehyde has been studied on clean Ag(111) using temperature-programmed desorption (TPD) and reflection–absorption infrared (RAIRS) spectroscopies. Acetaldehyde adsorbs at 80 K via the oxygen lone pair in an η1(O) configuration. It is found that a portion of the adsorbed acetaldehyde desorbs at low temperatures (~ 160 K) and also polymerizes. Based on this and other work, it is proposed that the surface polymer consists of an open chain with a desorption temperature that shifts with coverage.
SCREENING OF THE PHOTON FIELD IN SURFACE PHOTOEMISSION FROM SIMPLE METALS
Authors: NATSCHLÄGER S. , ALBERICH J. , BARBERÁN N. , BAUSELLS J. , RUPPIN R. , SIMÓ C.
Published: April 2003

A previous two-step hydrodynamic model calculation of angle-resolved photoemission has been improved by modeling the surface with a soft analytic function. The same ground state potential is used to screen the photon field and to calculate the electronic wave functions. The implemented code can be used for arbitrary ground state densities along the perpendicular direction. Mathematical and physical aspects of the model are discussed extensively. The behavior of the main peak of the spectrum in response to the variation of some parameters leads us to the conclusion that the peak cannot be interpreted as the direct excitation of multipole modes. This conclusion was suggested in the previous two-step model calculation.
SURFACE OPTIMIZATION OF RBa2Cu3O7-δ(R=Y, Nd) EPITAXIAL HIGH Tc FILMS FOR IN SITU PHOTOEMISSION STUDIES
Authors: ABRECHT M. , SCHMAUDER T. , ARIOSA D. , TOUZELET O. , RAST S. , ONELLION M. , PAVUNA D.
Published: April 2003

One of the intrinsic difficulties for in situ photoemission studies of high Tc oxide films is the surface volatility, especially the oxygen loss. In order to solve this problem, we have constructed a dedicated system for high Tc film surface studies, in particular for ARPES measurements. Here we briefly describe our pulsed laser deposition (PLD) system that is linked to the photoemission chamber at the Synchrotron Radiation Center (SRC) in Wisconsin, and discuss crystallographic and electronic properties measured on epitaxial YBa 2 Cu 3 O 7-δ (YBCO) and NdBa 2 Cu 3 O 7-δ (NBCO) films. Resistivity and XRD studies show that the best c axis epitaxial films, with Tc (onset)=92 K (Tc0=90.5 K ), are monophase and single crystalline with crystal coherence up to almost 1 μm. Initial core level photoemission study indicates that, for YBCO on SrTiO 3 (without any buffer layer), the Ba oxide layer tends to be the dominant surface layer. Further experiments are underway to reproducibly detect sharp Fermi edge and perform ARPES study on optimally doped film surfaces.
ELECTRON ENERGY LOSS SPECTROSCOPY AND ANNULAR DARK FIELD IMAGING AT A NANOMETER RESOLUTION IN A SCANNING TRANSMISSION ELECTRON MICROSCOPE
Authors: STÉPHAN O. , GLOTER A. , IMHOFF D. , KOCIAK M. , MORY C. , SUENAGA K. , TENCÉ M. , COLLIEX C.
Published: April 2003

The basics of electron energy loss spectroscopy (EELS) performed in the context of a scanning transmission electron microscope are described. This includes instrumentation, information contained in an EELS spectrum, data acquisition and processing, and some illustrations by a few examples.
HIGH RESOLUTION ELECTRON ENERGY LOSS SPECTROSCOPY APPLIED TO A GRAPHITE SURFACE MODIFIED BY ION BOMBARDMENT
Authors: ROY DENIS , PORTAIL MARC , LAYET JEAN-MARC
Published: April 2003

This work presents the application of the technique known as high resolution electron energy loss spectroscopy (HREELS) to the study of a modern technological surface. First the physics of the interaction of low energy electrons with surfaces is briefly reviewed. The dielectric theory of inelastic electron scattering is outlined, with its application to surfaces and the excitation of phonons, polaritons and plasmons. Then a study of the modification of a graphite surface by Ar and H ion bombardment is presented, in relation with graphite surfaces modified by plasma wall interactions in fusion reactors. The observations of phonons and low energy plasmons are reported, with the C–H stretching vibrations as well following the H + bombardment. These observations are related to structural and chemical modifications induced by the ion bombardment.
X-RAY DIFFRACTION FOR SURFACES AND BURIED INTERFACES
Authors: RENAUD G.
Published: April 2003

The application of X-rays to the structural characterization of surfaces and interfaces, in situ and in UHV, is discussed on selected examples. Grazing incidence X-ray diffraction is not only a very powerful technique for quantitatively investigating the atomic structure of surfaces and interfaces, but is also very useful for providing information on the interfacial registry for coherent interfaces or on the strain deformation, island and grain sizes for incoherent epilayers.
SPECTROSCOPIC INVESTIGATION OF SURFACES AND INTERFACES BY USING INFRARED-VISIBLE SUM AND DIFFERENCE FREQUENCY GENERATION
Authors: TADJEDDINE ABDERRAHMANE
Published: April 2003

The nonlinear optical techniques of visible-infrared sum (SFG) and difference (DFG) frequency generation are addressed as a vibrational probe of surfaces and interfaces between media of inversion symmetry.
SYNCHROTRON LIGHT IN A NUTSHELL
Authors: MARGARITONDO G.
Published: April 2003

I present an extremely simple derivation of the underlying physics and basic equations of the five most important properties of synchrotron light sources.
REFLECTION ANISOTROPY SPECTROSCOPY: AN OPTICAL PROBE OF SURFACES AND INTERFACES
Authors: MARTIN D. S. , WEIGHTMAN P.
Published: April 2003

Reflection anisotropy spectroscopy (RAS) is a nondestructive surface-sensitive optical probe capable of operation within a wide range of environments. RAS has been applied to semiconductor surfaces and has found use as an in situ monitor of semiconductor growth. Surface sensitivity has been demonstrated with the detection of reconstructions, dimer orientations, and adsorption. More recently, RAS has been used to probe the surface optical properties of metals. In this article, some aspects of the RAS technique are described, including an analysis of the passage of polarized light through the RA spectrometer, which results in frequency-dependent terms related to the real and imaginary RA. A short review of recent applications of RAS is given.
NEW UNDERSTANDINGS FOR THREE-DIMENSIONAL NUCLEATION (I)
Authors: LIU X. Y.
Published: April 2003

The generic heterogeneous effect of foreign particles on 3D nucleation was examined both theoretically and experimentally. It shows that the nucleation observed under normal conditions includes a sequence of progressive heterogeneous processes, characterized by different interfacial correlation function f(m, x) s . At low supersaturations, nucleation will be controlled by the process with a small interfacial correlation function f(m, x), which results from a strong interaction and good structural match between the foreign bodies and the crystallizing phase. At high supersaturations, nucleation on foreign particles having a weak interaction and poor structural match with the crystallizing phase (f(m, x)→1) will govern the kinetics. This frequently leads to the false identification of homogeneous nucleation. Genuine homogeneous nucleation, which is the up-limit of heterogeneous nucleation, may not be easily achievable under gravity. In order to check these results, the prediction is confronted with nucleation experiments of some crystals. The results are in excellent agreement with the theory. Apart from this, the implications for epitaxial growth have also been discussed. In order to grow crystals epitaxially, the supersaturation should be kept at a low level, despite a good structural match between the crystal and substrate.
NEW UNDERSTANDINGS FOR TWO-DIMENSIONAL NUCLEATION (II)
Authors: LIU X. Y.
Published: April 2003

Foreign particles adsorbed on flat crystal surfaces can serve as two-dimensional nucleation centers for the growth. In this paper, a kinetic model for heterogeneous two-dimensional nucleation is presented. The free energy barrier of two-dimensional nucleation in the presence of foreign particles and the kinetics for the nucleation and growth are examined theoretically. It follows that the contact angle, size and density of adsorbed foreign particles play a crucial role in controlling the 2D nucleation barrier and growth kinetics. The theory can be successfully applied to interpret experiments of dislocation-free growth.
POROUS SILICON: INFLUENCE OF ETCHING TEMPERATURE ON MICROSTRUCTURE AND LUMINESCENCE
Authors: BLACKWOOD D. J. , ZHANG Y.
Published: April 2003

Electrochemical etching in solutions based on hydrofluoric acid has been widely used to form light-emitting porous silicon. However, the effects of a number of the experimental parameters on the quality of the porous silicon produced have yet to be fully investigated. In the present paper the influence of temperature and viscosity of the etching solution is evaluated in terms of the morphology and porosity of the porous silicon produced as well as the wavelength of the photoluminescence or electroluminescence subsequently emitted. It was found that under stimulation from a UV light source the wavelength of the photoluminescence emitted from the porous silicon films blueshifted with decreasing etching temperature. SEM and AFM investigations revealed that this blueshifting of the photoluminescence resulted from the production of smaller nanocrystals at the lower etching temperatures.
APPLICATION OF AUGER ELECTRON SPECTROSCOPY AND X-RAY PHOTOELECTRON SPECTROSCOPY ANALYSIS IN FAILURE ANALYSIS OF WAFER FABRICATION
Authors: CHEN H. Y. , MO Z. Q. , AN L. H. , HUA Y. N.
Published: April 2003

In this study, field emission AES and small-area XPS techniques were used to analyze surface composition and depth profiles on discolored bondpads to identify possible root causes for nonstick failure. In wafer fabrication, the discolored bondpad problem was found in the fab process with hot Al alloy metallization, which had resulted in nonstick failure during the assembly bonding process. Analytical results indicated that discolored bondpads with nonstick failure might be due to TiN residue introduced during the bondpad opening etching process. The possible root cause of TiN residue on bondpads was then confirmed to be arisen from ARC (TiN) layer underetched during the bondpad opening etching process. The solution to eliminate TiN residue on bondpads was taken to increase the etch time at the bondpad opening fab process.
STUDY OF THE MORPHOLOGICAL MODIFICATIONS INDUCED BY LASER ANNEALING OF PREAMORPHIZED SILICON
Authors: CHONG Y. F. , PEY K. L. , LU Y. F. , WEE A. T. S. , SEE A.
Published: April 2003

Atomic force microscopy was employed to characterize the morphological modifications induced by laser annealing of preamorphized silicon. Laser irradiation was performed at different fluence with fixed pulse durations of 23 ns. In all cases, the laser fluence used is above the threshold fluence that is needed to melt the preamorphized layer. Roughness measurements show that the surface roughness of the silicon samples increases when the laser fluence increases. Since the laser anneal was performed in air, the changes in morphology may be associated with the surface oxide formed. When a high fluence was employed, the extension of melting was sufficient to remove all surface features of the as-implanted sample but apparently there was not enough time to completely redistribute the material upon solidification. As a result, ripple-like periodic structures are formed on the surface. Therefore, a low laser fluence should be used whenever possible in the annealing of silicon samples.
NUMERICAL SIMULATIONS OF ATOMIC-SCALE FRICTION BETWEEN SOLID SURFACES
Authors: KAWAGUCHI TAKAAKI , MATSUKAWA HIROSHI
Published: April 2003

Atomic-scale frictional phenomena at solid surfaces, such as pinning and dissipative sliding of solids, are studied theoretically and numerically. The pinning behavior at realistic solid surfaces shows the universality determined by the spatial dimension of the interface between solids, regardless of the spatial dimension of solids. We find complicated sliding velocity dependence with peak structures in the kinetic frictional force. Using a perturbation technique, it is understood that such velocity dependence is caused by resonance effects between two solids.
THE INVESTIGATION OF SURFACE TOPOGRAPHY DEVELOPMENT IN Si(001) AND Si(111) DURING SIMS DEPTH PROFILING
Authors: LAU G. S. , TOK E. S. , WEE A. T. S. , LIU R. , LIM S. L.
Published: April 2003

The oxygen ion-beam induced surface roughening observed during SIMS (secondary ion mass spectrometry) depth profiling of both the Si (001) and Si (111) surfaces has been studied by atomic force microscopy (AFM) as a function of both sputtered-depth and by varying the incident angles of the primary [Formula: see text] ion beam in the range of 44°–56°. Our result shows a surface orientation dependence of surface roughening whereby the transition roughening depth as well as the sputtering rate were observed to be greater in Si (111) than in Si (001). The orientation dependence was particularly obvious when increasing the incident angle of the [Formula: see text] ion beam from 44° to 56°. In addition, prominent elongated triangular and rectangular features are observed from sputtered Si (001) and Si (111) surfaces respectively at 56° incidence. These features may be associated with the formation of {111} and {001} facets on the sputtered Si (001) and Si (111) surfaces respectively.
SURFACE AND STRUCTURAL PROPERTIES OF COPPER FILMS DEPOSITED BY METAL ORGANIC CHEMICAL VAPOR DEPOSITION FOR Si TECHNOLOGY
Authors: ZHANG D. H. , LOH S. W. , LI C. Y. , FOO P. D. , XIE JOSEPH
Published: April 2003

The effects of a Cu flash layer deposited by the ionized metal plasma (IMP) technique on the properties of copper films deposited by metal organic chemical vapor deposition (MOCVD) are investigated. It is found that by incorporating a Cu flash layer prior to the MOCVD deposition, the surface morphology, interface, electrical conduction and structural properties of the MOCVD Cu films can be significantly improved and they also vary with the thickness of the flash copper. This observation will be very useful for copper metallization in deep submicron integrated circuits.
STUDY OF Cu DIFFUSION IN Cu/TaN/SiO2/Si MULTILAYER STRUCTURES
Authors: ZHANG D. H. , LOH S. W. , LI C. Y. , FOO P. D. , XIE JOSEPH , LIU R. , WEE A. T. S. , ZHANG L. , LEE Y. K.
Published: April 2003

This paper reports the effect of a flash copper layer, sandwiched between a copper film deposited by metal-organic chemical vapor deposition (MOCVD) and a TaN barrier metal, on copper diffusion through TaN barrier to Si substrate after rapid thermal annealing at different temperatures. It is found that for the structure of CVD Cu/TaN/SiO 2/ Si , which has no flash Cu layer, Cu could diffuse through the 25-nm-thick TaN barrier layer at an annealing temperature of 600°Cfor 180 s. However, by incorporating a flash Cu layer between the CVD Cu film and the TaN barrier, Cu diffusion can be significantly reduced. In addition to Cu , the out-diffusion of Si and oxygen, and the interaction between them can also be reduced by the incorporated flash Cu layer, due likely to the change of the crystallographic orientation of the CVD Cu films.
RHEED AND XPS STUDIES OF THE DECOMPOSITION OF SILICON DIOXIDE BY THE BOMBARDMENT OF METAL IONS
Authors: WANG S. J. , ONG C. K. , XU S. Y. , CHEN P. , CHAI J. W. , TJIU W. C. , PAN J. S. , HUAN A. C. H. , FENG W. , LIM J. S. , YOO W. J. , CHOI W. K.
Published: April 2003

In this paper, we report the RHEED and XPS studies of the decomposition of silicon dioxide by the bombardment of metal ions and the growth of ultrathin crystalline zirconia oxide film on silicon. Through XPS analysis, it was found that silicon dioxide could be decomposed by the bombardment of Zr ions in high temperature and lower partial pressure. Silicon dioxide was decomposed into evaporated silicon oxide, while part of the oxygen in silicon dioxide reacted with metal Zr ions to form stable zirconia oxide film. The metal ions reacted with silicon dioxide homogenously. Because of the smoothness of native silicon dioxide surface and atomically abrupt silicon dioxide interface with silicon, native oxide layer on silicon wafer was evenly removed and a sharp stable crystalline zirconia oxide interface with silicon was formed. The crystalline yittria-stabilized zirconia oxide (YSZ) film with equivalent electrical oxide thickness 1.46 nm show excellent electrical properties, the interface state density less than 2 × 1011 eV -1 cm -2 and leakage current 1.1 × 10-3 A/cm 2 at 1.0 V bias. It demonstrates that this method can be used to the deposition of high-κ metal oxide as alternative dielectrics for future generation device.
AFM AND XPS CHARACTERIZATION OF ZINC–ALUMINUM ALLOY COATINGS WITH ATTENTION TO SURFACE DROSS AND FLOW LINES
Authors: HARDING FELIPE A. , ALARCON NELSON A. , TOLEDO PEDRO G.
Published: April 2003

Surfaces of various zinc–aluminum alloy (Zn–Al) coated steel samples are studied with attention to foreign surface dross by atomic force microscopy (AFM) and X-ray photoelectron spectroscopy (XPS/ESCA). AFM topographic maps of zinc–aluminum alloy surfaces free of dross reveal the perfect nanoscale details of two kinds of dendrites: branched and globular. In all magnifications the dendrites appear smooth and, in general, very clean. XPS analysis of the extreme surface of a Zn–Al sample reveals Al, Zn, Si and O as the main components. The XPS results show no segregation or separation of phases other than those indicated by the ternary Al–Zn–Si diagram. For surfaces of Zn–Al plagued with impurities, high resolution AFM topographic maps reveal three situations: (1) areas with well-defined dendrites, relatively free of dross; (2) areas with small, millimeter-sized black spots known as dross; and (3) areas with large black stains, known as flow lines. Dendrite deformation and dross accumulation increase notably in the neighborhood, apparently clean to the naked eye, of dross or flow lines. XPS results of areas with dross and flow lines indicate unacceptable high concentration of Si and important Si phase separation. These results, in the light of AFM work, reveal that dross and flow lines are a consequence of a high local concentration of Si from high melting point silica and silicate impurities in the Zn–Al alloy source.
MISSING "SHEETS" IN THE RECIPROCAL SPACE REPRESENTATION OF THE DISORDERED SURFACE WITH ONE-DIMENSIONAL DOMAIN BOUNDARIES
Authors: TOK E. S. , ZHANG J. , KAMIYA I. , XIE M. H. , NEAVE J. H. , JOYCE B. A.
Published: April 2003

One-dimensional disorder in a reconstructed surface can give rise to sheetlike structures in reciprocal space. For disorder caused by one-dimensional domain boundaries such as those that occur on the GaAs {100}(2 × 4) surface, sheetlike structures are only present at fractional order diffraction features. The absence of these sheets at integral diffraction features is explained using kinematic theory of diffraction and "selection rules" for these sheetlike structures are established. Applications of these rules are demonstrated using optical transmission diffraction.
FABRICATION OF CARBON NANOTUBE FILM ARRAYS FOR FIELD EMISSION FLAT PANEL DISPLAY APPLICATION
Authors: SUN Z. , LI Y. J. , CHEN G. Y. , LAU S. P. , TAY B. K. , CHEN J. S. , CHEAH L. K.
Published: April 2003

The unique electron field emission properties of carbon nanotube films are promising for flat panel display application as the cold cathode. In this work, the multiwall carbon nanotube (10–102 nm in diameter, and 103–104 nm in length) film arrays (the pixel size: 50 μ m ×50 μ m ) were deposited on the patterned Ni–Si substrate from hydrocarbon precursor ( C 2 H 2/ H 2) by chemical vapor deposition at low temperature (550°C). The patterned films were characterized by scanning electron microscopy and Raman spectroscopy. The carbon nanotube film arrays exhibit good electron emission properties, e.g. low threshold emission field (below 2 V/μm), high emission current density (above 1 mA/cm2 at 10 V/μm), and high emission luminance spot density on the phosphor coated-ITO(indium tin oxide)-glass anode. These properties are good enough for high-resolution flat panel display application using carbon nanotube film arrays as the cathode.
PHOTOEMISSION BEAMLINE AT THE SIAM PHOTON LABORATORY
Authors: SONGSIRIRITTHIGUL PRAYOON , PAIRSUWAN W. , ISHII T. , KAKIZAKI A.
Published: April 2003

This report describes the first beamline for the Siam Photon Laboratory. The beamline has been designed to utilize synchrotron radiation in the VUV and soft X-ray regions generated by the Siam Photon Source. The beamline will be used for angle-resolved and high-resolution photoemission experiments to investigate electronic structures of surfaces and interfaces of solids.
MOLECULAR SELF-ASSEMBLY OF SULFONATED POLYANILINE THIN FILMS
Authors: SIM W. S. , GOH F. Y.
Published: April 2003

Multilayer polymer thin films with well-defined molecular architectures have been fabricated by an electrostatic self-assembly process involving sequential exposure of glass substrates to polyelectrolyte solutions of sulfonated polyaniline and hexadimethrine bromide. Ultraviolet-Visible (UV-Vis) Spectroscopy indicates layer-by-layer growth of alternating monolayers of oppositely charged polymer chains whose structural integrity is verified by X-ray Photoelectron Spectroscopy (XPS). The surface roughness is measured to be ~3 nm by Atomic Force Microscopy (AFM). The potential applications of these films in optoelectronic devices are discussed.
NANOSCALE SINGLE POLYMER CHAINS ON A CHIP: POLY(GLYCIDYLMETHACRYLATE) GRAFTED ON SILICON (100) SURFACES
Authors: WANG Y. , SHELDEN R. A. , KANG E.-T.
Published: April 2003

In previous studies reported in the literature it was shown that polymer chains could be sparsely grown on a mica surface and then imaged, after appropriate solvent treatment, as nanoscale "molecular droplets," each droplet consisting of a single polymer chain. With a view to eventual molecule-size devices on a chip, we wished to obtain such structures on silicon wafers. The method employed was UV-initiated graft polymerization. Previous studies had shown that silicon wafers that were plasma-treated and then exposed to air formed peroxide-like compounds on the surface. These could then be UV-irradiated in the presence of monomers to obtain surface-grafted polymer. It was expected that under sparse conditions of grafting, molecular droplets could be obtained in this way on silicon wafers. The monomer selected in the present work was glycidylmethacrylate (GMA), of special interest because poly(GMA) is a potential biomolecule surface linker. Single chain molecular droplets were indeed obtained when the polymerization time was sufficiently short, and an appropriate postpolymerization solvent treatment was used.
A STUDY ON ELECTROLUMINESCENCE FROM Au/Ge-CONTAINING SILICON OXIDE/p-Si AND Au/Si-RICH SILICON OXIDE/p-Si STRUCTURES
Authors: MA S. Y. , GUO Y. P. , WANG Y. Y. , LIU X. Q.
Published: April 2003

Ge-containing silicon oxide (GSO) films (5–15 nm) and Si-rich silicon oxide (SSO) films (5–15 nm) were deposited using the RF magnetron sputtering technique with a Ge–SiO 2 and a Si–SiO 2 composite target, respectively. The Au/GSO/p-Si and Au/SSO/p-Si structures were fabricated and their electroluminescence (EL) characteristics were comparatively studied. Both of the Au/GSO/p-Si and Au/SSO/p-Si structures have rectifying behavior. All the EL spectra from the two types of the structure have almost unchanged peak positions around 650 nm (~1.9 eV) and are independent of applied forward biases. The EL mechanisms for the Au/GSO/p-Si and Au/SSO/p-Si structures have been discussed.
SURFACE CHARACTERISTICS OF THICK, FREE-STANDING DIAMOND FILM PREPARED BY CHEMICAL ETCHING AND RAPID THERMAL PROCESSING
Authors: HUANG BOHR-RAN , LOH KIAN PING , HSU JUNG-FU , CHANG MING-CHIN
Published: April 2003

The surface characteristics and depth profile of free-standing polycrystalline diamond films chemically etched from silicon substrates have been studied using monochromatic X-ray photoelectron spectroscopy and Auger electron spectroscopy. Two different processes for isolating the diamond films from the silicon substrates have been performed. The isolated/annealed-diamond film was prepared by rapid thermal processing (RTP) of the diamond-on-silicon film at a temperature of 800°C before chemically etching the diamond film from the silicon substrate. The annealed/isolated film was prepared by first chemically etching the diamond film from the silicon substrate, and then subjecting the stand-alone film to RTP. The qualities of the film on the top faces were improved for both the isolated/annealed-diamond and annealed/isolated-diamond films as verified by Raman spectroscopy. XPS analysis revealed different oxidation characteristics on the top and bottom faces of the isolated/annealed-diamond and annealed/isolated-diamond films. Silicon was detected on the bottom surfaces. A higher silicon and oxygen intensity was observed on the isolated/annealed diamond films compared to the annealed/isolated films. This can be due to the facilitated thermal diffusion of silicon into the grain boundaries during the initial RTP step in the preparation of the isolated/annealed-diamond film.
FORMATION MECHANISM AND CRYSTALLOGRAPHIC RELATIONSHIP OF EPITAXY Ti and Al THIN FILMS IN IONIZED METAL PLASMA DEPOSITION
Authors: LI S. , LEE Y. K. , SUN C. Q. , LIANG M. H.
Published: April 2003

Ti thin film is widely used as a diffusion barrier to impede the Al/Cu migrating to the Si substrate in the applications requiring high temperature processes such as high temperature sputtering and reflow developed for via-filling. To improve the bottom coverage without losing the excellent diffusion blockage and other electronic properties, the ionized metal plasma (IMP) deposition technique has been developed. This method has better control of the angular distribution on the substrate, and thus has been used to deposit Ti as diffusion barriers for the subquarter micron device applications. However, the formation mechanism of the epitaxy Ti thin film deposited by ionic metal plasma deposition is not clear. In this work, the epitaxy Ti thin film has been characterized by the transmission electron microscope. The mechanism of the epitaxy Ti thin film formation and also the crystallographic relationship between the Ti and Al thin films in the IMP deposition have been analyzed in detail. The results show that the lattice image of the Ti layer in the sample as deposited has a square-block-like structure with the c axis perpendicular to the interfaces. This structure has anisotropic diffusion properties that can retard the diffusion of Al across the Ti layer in the initial stage of the high temperature Al sputtering or reflow processes.
A COMPARATIVE SIMULATION STUDY OF SILICON (001) SURFACE RECONSTRUCTION USING DIFFERENT INTERATOMIC POTENTIALS
Authors: XIE X. P. , LIANG M. H. , CHOO Z. M. , LI S.
Published: April 2003

We have performed a comparative study of Si (001) surface reconstruction employing molecular dynamics simulation using the interatomic potentials of Stillinger–Weber, Tersoff and Bazant–Kaxiras. Simulations were carried out for temperatures at 300 K and 1000 K using each of these three potentials. At 300 K, the three potentials were found to generate surface features comprising mainly the simple (2 × 1) reconstruction. At 1000 K, more complex reconstruction similar to the p (2 × 2) and c (2 × 2) patterns was observed on the surfaces of Stillinger–Weber and Tersoff crystals while the surface generated on Bazant–Kaxiras crystal is characterized by disorderliness with no identifiable pattern of reconstruction.
INTERFACIAL PROPERTY OF THE PSEUDOMORPHIC InGaAs/AlGaAs MULTIPLE QUANTUM WELLS
Authors: ZHANG D. H.
Published: April 2003

The effects of Be doping in the wells of the p-type pseudomorphic InGaAs/AlGaAs multiple quantum wells were characterized using photoluminescence and X-ray diffraction techniques. It is found that high doping in the wells causes shift of energy levels and deteriorates the well–barrier interfaces of the quantum well structures. The shift of the energy levels is mainly due to the band gap shrinkage while the interface roughness can be explained by interstitial doping.
RELAXATION OF Cu(100), (110) AND (111) SURFACES USING AB INITIO PSEUDOPOTENTIALS
Authors: ZHENG JIN-CHENG , WANG HUI-QIONG , WEE A. T. S. , HUAN C. H. A.
Published: April 2003

The geometries of the Cu(100), Cu(110) and Cu (111) surfaces are determined using ab initio pseudopotential calculations. Use of the Hellmann–Feynman theorem to calculate forces allows the determination of the equilibrium atomic positions with a small number of trial geometries. Our calculated results show that the surface relaxation of Cu (100) and Cu (110) surfaces are inward relaxations, while that of Cu (111) surface is slightly outward relaxation. Our results show that the forces, charge transfer and the detailed electronic structure of the Cu surface will affect the relaxation of the outermost layer. The calculated results are in good agreement with the results obtained by various experiments.
SIMULATIONS OF X-RAY PHOTOELECTRON DIFFRACTION EXPERIMENT FROM THEORETICAL CALCULATIONS
Authors: ZHENG JIN-CHENG , WANG HUI-QIONG , HUAN C. H. A. , WEE A. T. S.
Published: April 2003

In this paper, we demonstrate the simulation of XPD experiments through theoretical calculations. We present examples, e.g. oxygen-induced Cu(210) surface and oxygenated diamond surface, to illustrate how to obtain the optimized XPD experimental parameters by MSCD simulations for distinguishing two different models. Our results suggest that for the adsorbate-induced reconstructions on metal or semiconductor surfaces, XPD from adsorbate is more sensitive to the detailed surface structure than XPD from bulk elements. Whether to choose energy-scanned or angle-scanned mode will depend on the systems under investigation. One should check any limitations in the instruments used, and then perform the theoretical simulations for typical available parameters in order to select the best mode, emitters, and optimized parameters.
THIN FILMS OF SILICON NANOPARTICLES EMBEDDED IN Al2O3 MATRICES
Authors: ZHU Y. , ONG P. P.
Published: April 2003

Silicon nanoparticles embedded in a host matrix of Al 2 O 3 thin film about 260 nm thick were prepared by using the pulsed laser deposition method. The laser target consisted of a small silicon wafer glued onto the surface of a circular Al 2 O 3 plate, which was set to rotate uniformly when laser-ablating. TEM and EDS results showed that the films consisted of silicon nanoparticles in the form of nanocrystals with diameters of less than 6 nm dispersed in the amorphous Al 2 O 3 matrices. Strong PL from the as-prepared and the annealed samples was observed. The SIMS depth profile of the silicon content of the film indicated that the silicon nanoparticles in the Al 2 O 3 matrices were arranged in fairly well demarcated thin layers sandwiched between layers of the host material. FTIR results evidently suggested that the encapsulating amorphous Al 2 O 3 material forms a good host for the prevention of atmospheric oxidation of the silicon nanoparticles. However, prolonged annealing can cause the silicon nanoparticle surface interfacing the host material to be oxidized by the oxygen mostly from the Al 2 O 3 molecules and be bonded to the Al or O–Al bonds.
SIMS STUDY OF SILICON OXYNITRIDE RAPID THERMALLY GROWN IN NITRIC OXIDE
Authors: LIU R. , KOA K. H. , WEE A. T. S. , LAI W. H. , LI M. F. , SEE A. , CHAN L.
Published: April 2003

As the gate dielectric for ULSI MOS devices scales in the ultrathin regime, it is fabricated increasingly with silicon oxynitride instead of silicon dioxide films. One way to obtain silicon oxynitride films is the rapid thermal oxidation of silicon in NO (RTNO). Earlier RTNO growth studies were not sufficiently comprehensive as well as limited by temperature uncertainty and nonuniformity across the wafer. Using a state-of-the-art rapid thermal processing (RTP) system, RTNO growth characteristics at oxidation pressures of 100 and 760 Torr, oxidation temperatures from 900 to 1200°C and oxidation times from 0 to 480 s were obtained and investigated. Anomalies in the growth characteristics were observed. It was also demonstrated that secondary ion mass spectrometry (SIMS) using the MCs + method could be used to accurately determine the depth distribution of N in ultrathin silicon oxynitride films.
EFFECT OF Y ADDITION ON THE CORROSION BEHAVIOR OF MELT-SPUN AMORPHOUS Mg–Cu RIBBONS
Authors: YAO H. B. , LI Y. , WEE A. T. S. , PAN J. S. , CHAI J. W.
Published: April 2003

Hydrogen evolution testing and anodic potentiodynamic polarization revealed that Y addition has a beneficial effect on the corrosion resistance of melt-spun amorphous Mg–Cu ribbon, which is related to the properties of the surface film of Mg–Cu and the manner in which its properties are modified as a result of Y alloying. X-ray photoelectron spectroscopy (XPS) depth profiling revealed that the breakdown of Mg–Cu was caused by the hydration of surface oxide components and the incorporation of detrimental CO 32– anions into the surface film. Y addition in Mg–Cu improves the corrosion resistance by Y 2 O 3 incorporation into the passive film, thus stabilizing the surface oxide components from hydration and preventing the incorporation of CO 32– into the passive film.
MOLECULAR DYNAMICS STUDY OF THE FRICTION PROPERTIES FOR A Ge TIP–SURFACE SYSTEM
Authors: CAI JUN , WANG JIAN-SHENG
Published: April 2003

The friction between a Ge tip and its (001)-(2 × 1) reconstructed surface is investigated by molecular dynamics (MD) simulation. It is found that when the tip and the substrate approach each other closely enough, a wear occurs under slip-stick way. At the same time, it is also found that a permanent damage occurs when the tip advances perpendicularly to the dimer rows of the surface, while such damage is not observed when the tip moves parallelly to the dimer rows. This is different from the friction phenomena on a macroscopic scale. At the microscopic level, the resulting atomic configuration and the properties of friction force vs. sliding distance depend strongly on a sliding direction.
DEPENDENCE OF THERMAL OXIDATION BEHAVIOR OF SILICON NANOCRYSTALLITES
Authors: ZHU Y. , ONG P. P.
Published: April 2003

Three kinds of nanosilicon crystallites were prepared by different methods in high vacuum. All of them were composed of tiny silicon crystallites which were initially only mildly oxidized before annealing, but their behavior upon annealing in vacuum differed substantially depending on the environment in which they resided. XPS analyses revealed that the unencapsulated nanoparticles tended to oxidize quite quickly, whereas the nanoparticles sandwiched between layers of Al 2 O 3 matrices were oxidized rather slowly even under intense annealing. In the zinc/silicon nanocrystalline mixture, the oxidation of the Si 0 state was even faster than that of the intermediate Si +1,+2,+3 states. Both the stability and formation processes of the Si - O bonds in the partially oxidized states differed considerably with different environmental surroundings. However, in all cases, the Si - O bonds of the fully oxidized Si +4 state remained the most stable, to which the less oxidized states tend to gravitate eventually.
XPS AND FTIR STUDIES OF Mo/ZSM-5 CATALYSTS FOR NONOXIDATIVE CONVERSION OF METHANE TO AROMATICS
Authors: CHEN H. Y. , TANG S. , ZHONG Z. Y. , LIN J. , TAN K. L.
Published: April 2003

In this investigation, several Mo/ZSM-5 catalysts with various Mo loadings and various reaction times were prepared, and methane conversion to aromatics without the presence of oxygen was studied by microreactor evaluation, FTIR and XPS. It was found, for the first time, that oxygen treatment before the reaction could shorten the induction period of this reaction. In situ FTIR study indicated the formation of [Formula: see text] species ( 888 cm -1) and O–Al ( 670 cm -1) on the surface of the catalyst as a result of the oxygen treatment. The two IR bands shifted to 854 and 659 cm -1 respectively when 18 O 2 was used. These oxygen species may take part in the initial reaction and shorten the induction time. The XPS study revealed the coexistence of Mo 2 C and MoO 3 species on working catalyst surfaces, and a proper Mo 2 C/MoO 3 ratio (~0.38) was identified for the best aromatization Mo/ZSM-5 catalyst. The active sites for methane conversion to aromatics should include Mo oxide as well as Mo carbide.
ROUGHNESS INFLUENCE ON SURFACE MELTING
Authors: CASTILLO ALVARADO FRAY DE LANDA , PINEDA MARGARITO CRUZ , RUTKOWSKI JERZY H. , WOJTCZAK LESZEK
Published: April 2003

The influence of surface roughness on surface melting phase transition is discussed within the molecular field theory. The roughness is characterized by the surface order parameter averaged over all the density fluctuations whose description corresponds to the discrete Gaussian solid-on-solid model. The potential governing the transition between the rough surface and the surface melting is considered in terms of the modified van der Waals equation of state. Its effective shape represents two intersecting parabolas with nonequal curvatures for the solid and liquid phases. The phase diagram shows the coexistence of two phases with rough and wet surfaces.
NO ADSORPTION ON Pd(111): THE FORMATION OF THE ISOCYANATE GROUP
Authors: GARDA GRACIELA R. , FERULLO RICARDO M. , CASTELLANI NORBERTO J.
Published: April 2003

The reactive behavior of NO on Pd(111) has been studied using a semiempirical theoretical method. The adsorption sites and the related electronic structure have been considered. In particular, the dissociation process has been studied and compared with CO. Different dissociation mechanisms have been proposed and the formation of NCO species has been considered. The results follow the trends reported in the experimental literature.
PHOTON-ENHANCED SURFACE DISSOCIATION EFFECTS IN LASER PHOTOLYSIS OF AMORPHOUS CARBON FROM CH2I2
Authors: PIGLMAYER KLAUS , LINDSTAM MIKAEL , BOMAN MATS
Published: April 2003

With near-UV Ar +-laser-induced photolysis of gaseous CH 2 I 2, efficient, large-area or localized deposition of iodine-free amorphous carbon is possible at room temperature. The method allows a separate substrate heating and thereby a tuning of the deposits properties from soft and polymer-like to diamond-like. This article reports on an observed photon–surface interaction resulting in an enhanced carbon film formation. The shape of the deposit indicates that the deposition process is supported by an increased absorption cross section of surface-adsorbed intermediate molecular fragments, with respect to flat-angle surface-impinging photons.
THE ADSORPTION AND DESORPTION PROCESSES ACCOMPANYING THE CHEMICAL VAPOUR DEPOSITION OF SILANE ON Cu(111) AND Ni(111)
Authors: SHUTTLEWORTH I. G. , ALLISON W.
Published: April 2003

The adsorption and desorption processes accompanying the deposition of silane on Cu(111) and Ni(111) have been investigated using work function change (Δϕ), Auger electron spectroscopy (AES) and thermal desorption spectroscopy (TDS). In the early stages of deposition (0–2 L), at 130 K, on the Cu(111) surface, a predominantly hydrogenic phase forms. Heating the saturated surface to Ts>400 K produces a two-phase system: Cu 2 Si alloy and clean Cu(111). The regenerated Cu(111) phase extends across (16 ± 1)% of the total surface area and this process of clean surface generation can be repeated by redosing onto the mixed phase surface. The temperature coefficient of the work function of the Cu 2 Si alloy surface is -(7 ± 2) × 10-5 eV/K. Dosing silane onto the 110 K Ni(111) surface to saturation deposits a relatively small amount (0.05 ML) of Si. However, the Δϕ and TDS spectra are significantly distorted from their pure H/Ni(111) counterparts.
EFFECT OF TEMPERATURE ON NH3 REACTIVITY WITH Si(100)2×1
Authors: ZAÏBI M. A. , SÉBENNE C. A. , LACHARME J. P.
Published: April 2003

Initially clean, (2 × 1)-reconstructed Si(100) surfaces were exposed to NH 3, until saturation, at sequentially increased temperatures of up to 600°C. The resulting surfaces have been studied by low energy electron diffraction (LEED) and by photoemission yield and Auger electron spectrometries (PYS and AES). The room temperature saturation — for which NH 3 is adsorbed in a dissociated form as NH 2 and H, either of them bonded to a single Si dimer — remains essentially unchanged up to 250°C. Beyond 250°C, NH radicals form and replace the Si dimers by flat Si–NH–Si bridges along the surface, which ends up being stabilized by a full monolayer of such bridges at 400–450°C. Beyond that starts the actual nitridation process which concerns deeper Si layers.
AN ORDERED MIXED STRUCTURE FORMED BY RESTRUCTURING TYPE COADSORPTION OF Na AND K ON Ag(001)
Authors: MIZUNO SEIGI , IMAKI MASAO , TOCHIHARA HIROSHI
Published: April 2003

Coadsorption of Na and K on Ag(001) at room temperature has been studied by low energy electron diffraction (LEED). A 3 × 3 LEED pattern was observed irrespective of the order of adsorption. For this formation, it is necessary to deposit Na and K atoms with appropriate coverage. We have determined the 3 × 3 structure by a tensor LEED analysis. It is a restructured surface and is very similar to the previously determined 3 × 3 structure formed on Ag(001) by pure Na adsorption. In the coadsorption, Na and K atoms occupy preferable sites selectively, and construct an ordered mixed structure on Ag(001). That is, small Na atoms are located in the missing row sites, while large K atoms sit on the hollow sites of four-Ag-atom islands. The reason for the site selectivity of Na and K atoms in the mixed 3 × 3 structures is discussed.