bluuebunny/crossref_metadata_2025 huggingface dataset:
X‐ray photoelectron spectroscopic analysis of growth and thermal stability of palladium ultra thin films on alumina/NiAl(110)
Authors: Song Weijie , Yoshitake Michiko , Lay Thi Thi
Published: August 2004

We have studied the growth and thermal stability of Pd ultra‐thin films on Al2O3/NiAl(110) in situ using x‐ray photoelectron spectroscopy. The results showed that Pd grew in a nearly layer‐by‐layer manner on the Al2O3/NiAl (110) surface at a deposition rate of 0.2 Å/min. No strong interaction between the Pd over‐layer and the substrate was observed during initial growth. After high‐temperature treatments, Pd diffused into the substrate and the alumina layer thickness increased significantly. Palladium served as a catalyst for this reaction when the temperature was lower than 570 K; PdO formed when the temperature was higher than 670 K. Copyright © 2004 John Wiley & Sons, Ltd.
Characterization of AgAsS and AgSbS amorphous films prepared by pulsed laser deposition
Authors: Wagner T. , Krbal M. , Gutwirth J. , Nemec P. , Vlcek Mir. , Frumar M. , Perina V. , Mackova A. , Hnatovitz V. , Kasap S. O. , Vlcek Mil.
Published: August 2004

Thin amorphous films of AgAsS and AgSbS systems have been prepared by pulsed laser deposition (PLD) at five different conditions, i.e. at different pulse energies and pulse repetition intervals of the KrF laser. The obtained films were analysed by RBS, ERDA (elastic recoil detection analysis) spectral analysis and also EDXA elemental analysis. The results of RBS and EDXA analysis were compared to the composition of the source bulk glass materials. Film compositions varied compared to the source material according to the deposition condition with film composition close to the stoichiometric one, i.e. AgAsS2 and AgSbS2 could be prepared by the PLD technique. RBS spectroscopy is known as an important tool for establishing depth distribution of the elements within the prepared films. The thickness of the films was chosen so that depth profiling of the entire layer is possible. ERDA allowed us to find, apart from all obvious atoms (Ag, As, Sb, S), also H atoms present in the films. The structure of the films has been studied by Raman spectroscopy as well. Vibration bands characteristic of As(Sb)S2AgAs(Sb)S2 structural units present in prepared films have been observed. The films are potentially applicable for optical memories (e.g. digital video discs). Copyright © 2004 John Wiley & Sons, Ltd.
Deposition of Ti/C compositional gradient film onto superplastic Ti‐alloy by magnetron sputtering
Authors: Sonoda T. , Watazu A. , Kato K. , Yamada T. , Asahina T.
Published: August 2004

Deposition of Ti/C compositional gradient film onto superplastic titanium‐based alloy such as Ti6Al4V or Ti4.5Al3V2Fe2Mo was performed by magnetron sputtering, in order to improve not only the biocompatibility and the abrasion resistance of the alloy but also the adhesion between the deposited film and the alloy substrate while preserving the high hardness of such ceramic coatings. The Ti/C compositional gradient films were deposited by co‐sputtering of two sputter cathodes which had pure titanium and titanium carbide targets, respectively, and their compositional gradient was realized by varying continuously the electric power supplied to each sputter cathode. Under visual observation, the obtained film appeared to be uniform and adhesive. According to AES in‐depth profiles, the carbon (C) concentration in the film gradually decreased in depth direction from the surface toward the substrate, confirming that Ti/C compositional gradient film had formed on the alloy substrate. On the basis of XRD, it was found that titanium carbide (TiC) and α‐titanium phases were formed in the films. Furthermore, the Vickers hardness of the films reached over HV = 1800. Therefore not only the biocompatibility and the abrasion resistance of the alloy but also the adhesion of the deposited hard coatings were expected to be improved by this method. Copyright © 2004 John Wiley & Sons, Ltd.
Surface characterization of titanium nitride composite coatings fabricated by reactive plasma spraying
Authors: Ingo G. M. , Kaciulis S. , Mezzi A. , Valente T. , Gusmano G.
Published: August 2004

Composite Ti, TiN, TixNy coatings have been fabricated by reactive plasma spraying (RPS), starting from Ti alloy powders and using Ar/N2 plasma gas in a N2 atmosphere. Reactively sprayed coatings produced from SP700 (Ti4.5Al3V2Mo2Fe) and Ti6242 (Ti6Al2Sn4Zr2Mo) powders, deposited onto flat substrates of Ti6Al4V, have been investigated. XPS and SEM techniques have been used to determine the chemical composition and to characterize the interface between the coatings and substrate. The results obtained show a sharp interface between the coating and substrate in terms of composition profile. The presence of unmelted Ti particles as well as the formation of nitrides was observed. Copyright © 2004 John Wiley & Sons, Ltd.
Comparison of ZrxTi1−xO4 films produced by PLD and MOCVD techniques
Authors: Kaciulis S. , Cusmà A. , Padeletti G. , Pandolfi L. , Viticoli M. , Zaldo C.
Published: August 2004

ZrxTi1−xO4 (ZT) thin films have been deposited by pulsed laser deposition (PLD) and metallo‐organic chemical vapour deposition (MOCVD) on Pt‐covered and naked Si(100) substrates. Both techniques provide single‐phased films with a columnar structure when the substrate is heated to the 500–600 °C range. Out of this temperature range the co‐existence of other titanium oxides has been shown by XRD and XPS studies. XPS results show that the composition of optimized films is constant along the film thickness and that PLD films have higher Zr concentration than MOCVD ones. Pt induces the orientation (111) of ZT films, while the higher temperature promotes either (020) ZT orientation in PLD films or (031) ZT texture in MOCVD ones. Copyright © 2004 John Wiley & Sons, Ltd.
Plasma surface modification of Ti and TiAlV alloy
Authors: Mohai M. , Tóth A. , Sajó I. , Ujvári T. , Bertóti I.
Published: August 2004

Surface modification of commercially pure Ti and of Ti6Al4V alloy samples was performed by plasma immersion ion implantation with 25 kV energy. Plasma was generated by RF discharge in air, in nitrogen, or in a mixture of nitrogen and methane. Treatment in air plasma produced an oxide layer on the surface without appreciable incorporation of nitrogen, as detected by XPS. Significant surface enrichment of aluminium was measured after air plasma treatment of Ti6Al4V, but no such segregation was observed after nitrogen plasma treatment. These effects are interpreted by involvement of thermodynamic driving forces. Development of rutile and a sub‐stoichiometric oxide were identified on Ti while no crystalline phases could be evaluated on the Ti6Al4V upon oxidation. The cubic TiN phase was found after nitrogen PIII treatment on both Ti and Ti6Al4V. Nanomechanical tests showed a significant increase in the hardness for Ti6Al4V after oxidizing PIII treatment in air. Considerable change in hardness could not be measured, however, after nitriding PIII treatments. Copyright © 2004 John Wiley & Sons, Ltd.
Deposition and characterization of ZrTiO4 thin films
Authors: Pandolfi L. , Kaciulis S. , Padeletti G. , Cusmà A. , Viticoli M.
Published: August 2004

Thin films of zirconium titanate ZrTiO4 (ZT) were prepared by the MOCVD technique. ZT layers were deposited in air on silicon substrates by using a non‐conventional MOCVD system. The chemical composition of these films was investigated by XPS. More information on the thin film structure was obtained from the study of the Zr 3d XPS signal. The temperature of the substrate was found to be a fundamental parameter determining the stoichiometry of the films. It influences also the ordered or disordered structure of the films produced. In addition, the surface roughness of the samples before and after Ar+ ion sputtering was investigated. Copyright © 2004 John Wiley & Sons, Ltd.
Influence of magnetron deposition parameters on the stoichiometry of sputtered V2O5 films
Authors: Silversmit G. , Poelman H. , De Gryse R.
Published: August 2004

Vanadium oxide films were deposited on Si(100) substrates by reactive DC magnetron sputtering in an O2 atmosphere. The substrate temperature, oxygen pressure and sputter time were varied and their influence on the stoichiometry was examined. V 2p XPS measurements were used to determine the degree of oxidation of the sputtered vanadium oxide films. Nearly fully oxidized (V5 +) vanadium oxide films were deposited over the whole temperature and pressure range. However, at higher sputter pressures, oxidation of the Si substrates occurred, accompanied by reduction of the vanadium oxide stoichiometry. A short Ar+ bombardment for removal of surface contamination induced a strong decrease of the V5 + concentration in the vanadium oxide films. Copyright © 2004 John Wiley & Sons, Ltd.
Effect of the oxygen deficiency of ceramic TiO2−x targets on the deposition of TiO2 thin films by DC magnetron sputtering
Authors: Poelman H. , Tomaszewski H. , Poelman D. , Depla D. , De Gryse R.
Published: August 2004

The sputter deposition of stoichiometric TiO2 thin films has been investigated, in view of photocatalytic application. DC magnetron sputtering from ceramic targets in an argon/oxygen atmosphere was chosen as the deposition technique. Composite TiO2Ti targets with metallic Ti fraction from 0 to 70 wt% were prepared from TiO2 and Ti powders following a standard ceramic procedure.

The influence of target composition and sputter parameters on the film composition was examined by means of optical transmission measurements, XRD and XPS. From the former, optical absorption coefficients are calculated, which are used as a measure for the films' stoichiometry. Curve fitting of the Ti 2p3/2 photoemission line yields the composition in terms of the presence of reduced species.

Upon sputtering in argon, translucent layers are obtained for targets with up to 35 wt% Ti. For higher amounts, the optical absorption coefficient α at 550 nm increases and the layers become dark. With increasing metal Ti contribution and argon flow, more reduced Ti species contribute to the Ti 2p photoemission line.

In reactive sputter mode, near‐stoichiometric TiO2−x films are obtained for low oxygen mole fractions. For higher oxygen contributions, reduced Ti species are increasingly present for all targets. This reduction is ascribed to active re‐sputtering of the deposited layer by O− ions and the sputter yield difference between oxygen and titanium. Copyright © 2004 John Wiley & Sons, Ltd.
RBS and XPS study of TiOx layers prepared by the PVD technique
Authors: Macková A. , Peřina V. , Krumeich J. , Zemek J. , Kolouch A.
Published: August 2004

The PVD coatings were prepared using Sulzer Innotec's closed magnetic field unbalanced magnetron sputtering facility. The deposition parameters of bias and oxygen flow rate were varied. The prepared samples were analysed by RBS (Rutherford backscattering spectrometry) to determine the Ti/O ratios and the thicknesses of the coatings, and by ERDA (elastic recoil detection analysis) to investigate the hydrogen content in the surface layer. XPS was used to characterize the near‐surface composition and chemical bonding. Measurements of mechanical properties (hardness and thickness) were performed. We concluded from RBS analysis that Ti content is enhanced according to the increased bias and the decreased oxygen flow rate. We observed the increasing hardness in the case of the higher Ti content layers prepared. We found that a contaminated surface layer exists in which hydrogen, oxygen and carbon are incorporated. Copyright © 2004 John Wiley & Sons, Ltd.
Experimental verification of PTC diagrams for TiC and ZrC PVD coatings and determination of free carbon state by AES, XPS and HREELS methods
Authors: Kovalev A. I. , Wainstein D. L. , Karpman M. G. , Sidakhmedov R. Kh.
Published: August 2004

Several PVD coatings based on Ti and Zr carbides and on HSS steel were investigated. The partial pressure of the active gas (N2, C2H2) and substrate temperature were varied over a wide range. The PTC diagrams for prediction of coating compositions, dependent on substrate temperature and gas pressure, were calculated using the thermodynamic technique for phase equilibria based on the principle of maximum entropy in an isolated thermodynamic system. The chemical composition, and electronic and atomic structure of coatings were investigated using the AES, XPS and HREELS methods. Comparison of the calculated chemical composition of coatings with one measured by AES shows good agreement. XPS analysis of the C 1s line in carbides of Ti and Zr shows the presence of carbon in non‐stoichiometric carbides and in the free state. The fraction of bound and free carbon was measured by relation of the shifted and normal C 1s peaks. HREELS spectra near the line of elastically scattered electrons show a peak at 165 meV (1332 cm−1 in Raman spectroscopy) corresponding to sp3 hybridization of carbon. Copyright © 2004 John Wiley & Sons, Ltd.
The cathodoluminescence generated in ZnS phosphor powder with non‐luminescent ZnS coatings: a comparison of experimental data with Monte Carlo calculations
Authors: Swart H. C. , Greeff A. P.
Published: August 2004

Field emission displays (FEDs) are a possible alternative to other display technologies. They work similarly to CRTs, but instead of an electron gun they have an array of tiny metallic tips acting as electron emitters. This array is situated in close proximity to the phosphor screen and produces light by a process of cathodoluminescence (CL). During prolonged electron beam irradiation a non‐luminescent ZnO layer forms on the irradiated surface of the ZnS phosphor powder according to the electron‐stimulated surface chemical reactions (ESSCR) mechanism. The low‐energy electrons used in FEDs have a shallow penetration depth and since the CL is dependent upon the energy loss in the ZnS bulk itself, growth of the ZnO layer significantly degrades the CL intensity. Monte Carlo techniques may be used to simulate the electron trajectories and energy loss in many different types of materials. Energy loss profiles in the ZnS for different non‐luminescent ZnS coatings of known thickness were determined using the Monte Carlo electron trajectory simulations. Since only energy loss in the ZnS powder results in CL an increase in the thickness of the ZnS coating decreases the CL intensity accordingly. Simulations were performed for electron energies varying from 2 to 10 keV and at incident angles accommodating for the morphology of the phosphor powder. These results compared very well with the experimental results measured by other authors. Copyright © 2004 John Wiley & Sons, Ltd.
Annealing of CVD un‐doped diamond: a photoemission investigation
Authors: Filippi M. , Calliari L. , Pucella G. , Verona‐Rinati G.
Published: August 2004

The temperature evolution of the surface region of an undoped chemical vapour deposited (CVD) diamond film is characterized via UV and x‐ray induced photoemission. Methods are proposed to diagnose and to overcome possible electrostatic charging problems connected with the poor conductivity of the film. The position of the relevant energy levels is measured and the transition from a negative to a positive electron affinity surface is observed. For the bare diamond surface, an electron affinity χ = 0.4 eV is derived while the film conductivity is shown to decrease on going from the surface towards the bulk. Copyright © 2004 John Wiley & Sons, Ltd.
Characterization of the interface of PZT sol–gel layers on metallic substrates
Authors: Dutschke Anke , Meinhardt Jürgen
Published: August 2004

Ferroelectric lead zirconate titanate layers can be used for several industrial applications. Usually they are prepared as thin films on silicon substrates with different ground electrodes to be integrated into microelectronic devices. Thin steel substrates are of special interest because of their flexibility which enables several new applications in sensors and actuators. These applications require a film thickness of several micrometres, which can be achieved by several coating and annealing steps.

We have studied the interfaces of sol–gel derived PZT (53/47) layers on a commercially available CrNi alloy in view of formation of secondary phases and diffusion processes, using transmission electron microscopy (TEM) combined with energy dispersive x‐ray spectroscopy (EDX) and XPS. The effect of different thermal annealing treatments on the thickness of a non‐ferroelectric interface containing NiO and NiCr2O4 between the steel substrate and PZT film was studied. The diffusion of Cr from the metallic substrate into the PZT layer during the annealing process leads to formation of Pb2(CrO4)O at the interface. The results are related to the electrical properties of the films. Copyright © 2004 John Wiley & Sons, Ltd.
Investigation of the nickel/emissive oxide interface in thermionic emitters
Authors: Barber D. K. , Jenkins S. N. , Whiting M. J. , Baker M. A.
Published: August 2004

Oxide cathodes act as electron sources in cathode‐ray tubes (CRTs). In an attempt to understand the processes leading to degradation in their performance over their lifetimes, SEM, EDX and AES have been used to examine the Ni base/emissive oxide interface. Oxide cathodes from dummy electron gun tubes were investigated after 0 h and 1000 h lifetime testing. The interface was studied (a) from above, by stripping away the emissive oxide using adhesive tape, and (b) in cross‐section. After fabrication and processing (0 h exposure), cracks exist at grain boundaries on the surface of the Ni base, probably due to thermal grooving. The activator elements, Al and Mg, are enriched on the metal surface: Al on the Ni surface and Mg at the crack mouths. After 1000 h of lifetime testing the cracks had widened and deepened, and the activator concentrations in the interface region had increased. Cross‐sections reveal that chemical processes involving Mg occur primarily within the cracks, whilst those involving Al predominate at the Ni/oxide interface and on the oxide layer itself. An interfacial layer develops during cathode operation containing the elements Al, Mg, Ba and Sr. Further work is required to fully understand the degradation and activator reaction processes and to clarify the principal mechanism leading to reduced cathode performance as a function of lifetime. Copyright © 2004 John Wiley & Sons, Ltd.
A study of the formation of yttrium silicides epitaxially grown on Si(111)
Authors: Rogero C. , Polop C. , Sacedón J. L. , Martín Gago J. A.
Published: August 2004

We present an investigation of the growth of ultrathin yttrium silicide films (YSi2) epitaxially grown on n‐type Si(111) as a function of the thermal treatment. Combining STM images with a quantitative spot profile LEED analysis we have studied the crystalline quality of the YSi2−x (0 ≤ x ≤ 0.3) and we have related it to the silicide formation temperature. We have distinguished a short temperature range for the formation of the two‐dimensional p(1 × 1) YSi2, and three growth regimes for the three‐dimensional (√3 × √3)R30° YSi1.7. For annealing temperatures lower than 375°C the silicide is not completely formed; at around 420°C the surface exhibits long atomically flat terraces, and for temperatures higher than 525°C a significant increase in the number of defects takes place. Copyright © 2004 John Wiley & Sons, Ltd.
XPS study of Cu/substrate systems obtained by pulsed laser deposition
Authors: Lai X. Ch. , Pushkin M. A. , Troyan V. I.
Published: August 2004

In this paper XPS was used to study the evolution of Cu 2p3/2 peaks with the increase of the metal coverage on different types of substrate: Ni, HOPG (highly orientated pyrolytic graphite) and KBr. The results showed that: (i) the binding energy of the Cu 2p3/2 peak in the system Cu/HOPG decreases with surface coverage, while in the system Cu/Ni it increases; (ii) with the increase of the Cu coverage in all the systems studied a general trend of the Cu 2p3/2 peak is the reduction of FWHM (full width at half maximum), but the degree of the FWHM change depends greatly on the type of the substrate. The results obtained for binding energy change are discussed in relation to the initial and final state contributions. The results indicate that the final state contributes more to the change of the binding energy in the more 3‐dimensional structure Cu/HOPG system, while in the more 2‐dimensional Cu/Ni system the initial state contribution dominates. The FWHM change is analysed in terms of the size distribution of clusters and change of the lifetime of the holes left by the photoelectrons, which is affected by the size of the clusters and the degree of the hybridization between the s and d electrons. Copyright © 2004 John Wiley & Sons, Ltd.
Characterization of thin oxide films on GaAs substrates by optical methods and atomic force microscopy
Authors: Franta D. , Ohlídal I. , Klapetek P. , Ohlídal M.
Published: August 2004

In this paper the results of optical and atomic force microscopy characterization of oxide thin films prepared by thermal oxidation of GaAs single crystal wafers at a temperature of 500°C in air are presented. The optical characterization is performed using multi‐sample modification of the method based on combining variable angle spectroscopic ellipsometry and near‐normal spectroscopic reflectometry. It is shown that the films exhibit the rough lower boundaries and refractive index profile inhomogeneities. The spectral dependences of the refractive index and extinction coefficient of these films are presented within the wide spectral region, i.e., 210–900 nm. The values of the thicknesses and roughness parameters characterizing the oxide films are introduced as well. Copyright © 2004 John Wiley & Sons, Ltd.
Characterization of sol–gel derived glass composite thin films
Authors: Shimamura A. , Hübert Th. , Thust H.
Published: August 2004

A comprehensive analysis of composition and structure is essential for the development of new materials with tailored properties. We will demonstrate the application of SEM, XPS and XRD for the development of thin films containing nano‐scaled electrical conductive particles for application in hybrid resistors.

The films were prepared using the sol–gel process and precursor solutions were synthesized from an acid hydrolysis of a mixture of TEOS, water and ethanol. Alcoholic solutions of ruthenium chloride were then allocated to obtain up to 30 vol% filler in the films. The films were precipitated by dip‐coating on silicon, silica or glass sheets and heat treated at up to 600°C in air or nitrogen atmospheres.

A nano‐structured morphology could be identified consisting of homogeneously dispersed crystalline RuO2 particles of 10 to 180 nm in size, in an amorphous SiO2 matrix. Film morphology can be varied using the synthesis process. The resistivity of the films was measured by an I–V measurement system. It changes drastically from 109Ω·cm to 10−2Ω·cm according to the amount of dispersed conductive particles.

The results show that composition–structure–property relations can be described by use of sophisticated analytical methods. Copyright © 2004 John Wiley & Sons, Ltd.
Surface investigations of bonded perfluoro polyether monolayers on gold surfaces
Authors: Alamarguy D. , Noël S. , Schneegans O. , Meyer R. , Tristani L. , Di Meo A.
Published: August 2004

Thin films of functionalized perfluorinated polyether have been deposited on gold surfaces. XPS of freshly deposited layers rinsed in the proper solvent has shown that a thiolate bond is formed. Spectra performed on layers aged 15 days before the rinsing process display drastically different features. Fewer molecules are rinsed off and the main component of the sulfur peak corresponds to free sulfur. Conducting‐probe AFM is then used to characterize the mechanical and electrical properties of these layers. Confirmation of the higher thickness of the aged rinsed films is obtained from the delay between the mechanical and the electrical contacts. Copyright © 2004 John Wiley & Sons, Ltd.
XPS analysis of electronic density of iron tetraazamacrocycle through Fe 2p binding energies on the 3‐imidazolilpropyl‐modified surface of oxidized n‐Si(100)
Authors: Andresa Juliana Salvador , Moreira Leonardo Marmo , Magalhães Janildo Lopes , Gonzalez Eduardo Perez , Landers Richard , Rodrigues‐Filho Ubirajara Pereira
Published: August 2004

This paper describes the preparation of metallo‐organic thin films of [FeTIM(CH3CN)2]2 + complex, where TIM stands for 2,3,9,10‐tetramethyl‐1,4,8,11‐tetraazacyclotetradeca‐1,3,8,10‐tetraene on oxidized silicon wafer, SiO2/Si, previously treated with 3‐imidazolilpropyltrimethoxysilane, 3‐IPTS. X‐ray photoemission lines of Fe 2p were used to probe the iron chemical environment in the physically and chemically adsorbed macrocycle complexes. As FeTIM can bind CO, NO or N‐heterocycle, a built‐on Si wafer sensor device could be envisaged for these molecules. Copyright © 2004 John Wiley & Sons, Ltd.
In situ analysis of PMPSi by spectroscopic ellipsometry and XPS
Authors: Čechal J. , Tichopádek P. , Nebojsa A. , Bonaventurová Zrzavecká O. , Urbánek M. , Spousta J. , Navrátil K. , Šikola T.
Published: August 2004

In the paper in situ monitoring of the UV‐light‐ and thermal‐treatment of PMPSi thin films by real‐time spectroscopic ellipsometry and XPS is reported. The films were treated both under ultrahigh vacuum and oxygen atmosphere. The results of this study indicate that the SiSi bonds in the polymer main chain (Si‐backbone) were primarily broken at the UV‐light treatment. However, the Si radicals recombined into the polymer‐like chains causing no remarkable chemical shifts. The UV‐light treatment under enhanced sample temperature (≈80 °C) in oxygen atmosphere resulted in the more intense degradation of the PMPSi film. This can be related to cutting off the volatile methyl groups from the polymer main chains. Copyright © 2004 John Wiley & Sons, Ltd.
ToF‐SIMS investigations of the degeneration processes of self‐assembled monolayers of alkanethiols on gold
Authors: Sohn S. , Schröder M. , Lipinsky D. , Arlinghaus H. F.
Published: August 2004

Time‐of‐flight secondary ion mass spectrometry (ToF‐SIMS) has been used to study the degeneration process of self‐assembled monolayers (SAMs) of alkanethiols on gold upon ambient air exposure. Alkanethiol SAMs with varying alkyl chain length n ranging from n = 1 to n = 17 were prepared simultaneously and analysed after being stored at ambient air for specific time periods. Static SIMS spectra show a range of mass signals characteristic for non‐degenerated SAMs, like gold‐alkanethiolate clusters, on the one hand, and for degenerated SAMs, like alkanesulfonates, on the other. These characteristic mass signals enable the observation of degeneration processes. We found that the rate of degeneration increases rapidly with decreasing alkyl chain length. Furthermore, for short‐chain alkanethiol SAMs with n ≤ 3, a randomly initialized degeneration plays a major role, whereas for long‐chain alkanethiol SAMs, the degeneration starts at domain boundaries and defects, propagating into intact domains. Copyright © 2004 John Wiley & Sons, Ltd.
Difference in the annealing behaviour of thin films of PS/PMMA blends and copolymers as revealed by ToF‐SIMS and AFM
Authors: Kailas L. , Nysten B. , Bertrand P.
Published: August 2004

Surface characterization of thin films of polystyrene (PS)/poly(methyl methacrylate) (PMMA) blends and diblock copolymers was done using time‐of‐flight secondary ion mass spectrometry (ToF‐SIMS) and atomic force microscopy (AFM) in order to compare their annealing behaviour. The spin‐cast films, of 12 nm thickness, were annealed at 160°C for different time periods ranging from 2 hours to 1 week. ToF‐SIMS spectra of annealed blends showed a decrease in the concentration of PS and an increase in the concentration of PMMA on the surface as compared to the as‐cast sample. The spectra of copolymers showed an increase in concentration of PS on the surface on annealing, with PMMA concentration decreasing. AFM images with the help of SIMS information allowed us to conclude that in the case of blends, PS formed droplet‐like domains on a PMMA matrix and, in copolymers, PS with its lower surface free energy segregated to the surface without complete phase separation, which is not possible for copolymers. Copyright © 2004 John Wiley & Sons, Ltd.
Tribosurface and lubricant characterization by ToF‐SIMS
Authors: Gunst U. , Zabel W.‐R. , Poll G. , Arlinghaus H. F.
Published: August 2004

The interaction of moving counterparts with lubricants generates tribosurfaces and tribointerfaces. These tribological boundary layers and their characteristics are important for the lifetime of sliding and rolling bearings. The properties of these structurally and chemically untailored surfaces are of interest for the design of long‐life lubricants and high‐hardness, wear‐resistant surfaces. ToF‐SIMS is a means for characterizing lubricants and the elemental and molecular surface compositions of tribological boundary layers. Especially the capability for the retrospective analysis of depth and lateral chemical distributions on the basis of parallel mass detection and high mass resolution enables tribological research of formerly unknown chemical surface and interface distributions. We have used ToF‐SIMS to investigate lubricants for high‐speed applications, as well as for the tribosurface characterization of high‐speed rolling element bearings. The results show that ToF‐SIMS is a very useful surface‐diagnostic tool for obtaining information about surface compositions of tribological systems. The measured surface spectra as well as lateral and depth distributions correlate with tribological models and give insights into tribological interaction mechanisms at micro‐ and nanoscopic levels. Copyright © 2004 John Wiley & Sons, Ltd.
The very beginning of plastic deformation during sliding contact on amorphous carbon coatings
Authors: Wienss A. , Jacoby B.
Published: August 2004

Various thin amorphous carbon coatings (5–12 nm) as well as silicon oxide surfaces were scratched by means of a diamond tipped cantilever, simulating a hard scratching particle with a radius of 80–100 nm. Using advanced image processing, ultra‐shallow scratches with depths of only 1–2 Å can be visualized and analysed, even on surfaces with RMS roughness values up to 10 Å. This enables us to evaluate the conditions in terms of local pressure and speed under which plastic deformation initially takes place. Different deformation mechanisms could be deduced for different types of surfaces. Repeated measurements suggest a local compression of the amorphous low‐density structures underneath the tip. Using a simple force balance model, it can be estimated that in the initial phase of plastic deformation, the lateral force acting on the tip is dominated by the friction force and not yet by a ploughing term.

This sub‐nanometre scratching technique has been developed for the mechanical characterization and optimization of ultra‐thin amorphous carbon coatings used as protective layers in hard disk drives. Copyright © 2004 John Wiley & Sons, Ltd.
Surface analysis of metals using tribostimulated electron emission
Authors: Momose Yoshihiro , Iwashita Masahisa
Published: August 2004

A new surface analysis method using tribostimulated electron emission (called TriboEE) has been developed to estimate the ability for metals in practical use to emit electrons. This method uses an exoelectron emission phenomenon observed only while metal surfaces are mechanically rubbed with a polytetrafluoroethylene (PTFE) rotator. The number of electrons emitted from copper and iron metals during rubbing was measured using a newly hand‐made electron counting device, and its relationship to the XPS results of the metal surfaces was investigated. The metal surfaces were prepared as follows: ultrasonic cleaning in acetone (sample I), abrasion with an emery paper (II), and oxidation by heating in air (III). The number of emitted electrons depended strongly on the preparations, resulting in the order I ≈ II < III for copper and II ≪ I ≈ III for iron. The number of emitted electrons for each surface preparation tended to increase with an increase in the surface composition of fluorine of PTFE debris attached to the surface. The adsorption amount of the fluorine for sample III was much greater than that for samples I and II. Copyright © 2004 John Wiley & Sons, Ltd.
A lateral force microscopy study of friction between glassy carbon and different surfaces
Authors: Stiess S. , Richter A. , King B. V. , Reitsma M. , Smith R.
Published: August 2004

A Nanoscope III atomic force microscope (AFM) was used to measure the friction between glassy carbon microspheres, glued to the AFM cantilever, and flat surfaces of silicon, carbon, steel and silver. The measured friction data was fitted using the Derjaguin–Müller–Toporov (DMT) model. The work of adhesion between the spheres and the surfaces ranged from 0.45 mNm−1 for the carbon surface to 19 mNm−1 for the silicon surface. The work of adhesion was found to be proportional to the interfacial shear strength for silver, steel and carbon. Copyright © 2004 John Wiley & Sons, Ltd.
Tribological interactions at the wheel–workpiece interface in surface grinding of construction stone
Authors: Xu Xipeng
Published: August 2004

This study was conducted to elucidate the interactions at the tool–workpiece interface during surface grinding of three typical granites—black, gray and red—by using a diamond wheel. The consumed power, the forces and temperatures generated at the grinding zone were in‐process monitored and the morphological features of ground granite surfaces were examined. The average load per diamond grit, energy partitions at the wheel–granite interface, and diamond tip temperatures were subsequently estimated based on the measurements of force, power and temperature. The normal force was found to be comparable for the three workpieces, but the tangential force was greater in either wet grinding red granite or dry grinding black granite due to their different removal mechanisms and friction conditions. Approximately linear relationships between the power and ploughed surface area generated per unit time per unit width were established for the three granites and the surface energy for the red granite was found to be higher than for the other two granites. The energy partitions into the granite were found to be about one‐third. Copyright © 2004 John Wiley & Sons, Ltd.
A study of the surface chemistry, morphology and wear of silicon based MEMS
Authors: Li J. , Cui Z. , Baker M. A.
Published: August 2004

Polysilicon microelectromechanical systems (MEMS) are the subject of intense research activity. This paper reports on the surface chemistry, topography and nanowear properties of a MEMS test structure fabricated at Sandia National Laboratories, studied using XPS and atomic force microscopy (AFM). XPS C 1s and Si 2p spectra from the polysilicon components, silicon nitride substrate and a reference Si wafer are compared. The results confirm the presence of a self‐assembled monolayer (SAM) on the MEMS surface. An island‐like morphology is found on both polysilicon and silicon nitride surfaces of the MEMS. The islands take the form of caps, being up to 0.5 µm in diameter and 20 nm in height. It is concluded that a dual columnar and equiaxed microstructure develops during growth of these low pressure chemical vapour deposition (LPCVD) layers and the islands are caps to the columnar structures. A 35 µN load applied to the AFM diamond tip leads to a wear depth of 1.4 ± 0.13 nm and 2.1 ± 0.06 nm on the polysilicon and silicon nitride MEMS equiaxed surfaces, respectively. Under the same load, greater wear of the columnar caps on both surfaces is observed. The results suggest that the morphology present on the polysilicon surface will be worn flat during operation and will not adversely affect the wear properties of the polysilicon components. Copyright © 2004 John Wiley & Sons, Ltd.
Low frictional copper oxide film prepared with sodium hydroxide solution
Authors: Oishi T. , Goto M. , Kasahara A. , Tosa M.
Published: August 2004

In order to prepare a copper oxide film with low friction, we studied the chemical treatment of copper in aqueous sodium hydroxide solution. Copper plate with roughness about 100 nm as substrate was immersed in 0.1–10 M NaOH (M ≡ mol/dm3) for a fixed reaction time. The XRD result showed that copper oxide film of CuO or Cu2O grew on the surface of the substrate. SEM observation showed that the substrate surface became rough with the reaction time. A friction coefficient (µ) as low as 0.08 was achieved in the air when the substrate was immersed in 10 M of NaOH for 1000 sec. The coefficient changed from 0.08 to 0.4 according to the reaction time and the NaOH concentration. The change in friction coefficient as a function of surface roughness of the oxide film indicated that the surface morphology on the sub‐micrometre scale could strongly affect the friction of the oxide film. The coefficient of the oxide film measured in a vacuum was nearly as low as the coefficient in the air. The prepared copper oxide film can be therefore a good candidate for solid lubricant both in the air and in a vacuum. Copyright © 2004 John Wiley & Sons, Ltd.
Interface study for liquid–solid state surface by means of the S K‐edge NEXAFS method
Authors: Yagi S. , Matsumura Y. , Soda K. , Hashimoto E. , Taniguchi M.
Published: August 2004

The adsorption behavior of a sulfur‐containing amino acid molecule on a transition metal surface has been investigated in the bio‐catalytic and surface reaction fields. For a liquid sample there are many difficulties in x‐ray absorption fine structure (XAFS) measurement in the soft x‐ray energy region. In this study we have constructed a new XAFS measurement system with He‐path and Be window at soft x‐ray beamline (BL‐3) at the Hiroshima Synchrotron Radiation Center (HSRC). Copyright © 2004 John Wiley & Sons, Ltd.
Sensitivity of score tests for zero‐inflation in count data
Authors: Lee Andy H. , Xiang Liming , Fung Wing K.
Published: August 2004

In many biomedical applications, count data have a large proportion of zeros and the zero‐inflated Poisson regression (ZIP) model may be appropriate. A popular score test for zero‐inflation, comparing the ZIP model to a standard Poisson regression model, was given by van den Broek. Similarly, for count data that exhibit extra zeros and are simultaneously overdispersed, a score test for testing the ZIP model against a zero‐inflated negative binomial alternative was proposed by Ridout, Hinde and Demétrio. However, these test statistics are sensitive to anomalous cases in the data, and incorrect inferences concerning the choice of model may be drawn. In this paper, diagnostic measures are derived to assess the influence of observations on the score statistics. Two examples that motivated the application of zero‐inflated regression models are considered to illustrate the importance of sensitivity analysis of the zero‐inflation tests. Copyright © 2004 John Wiley & Sons, Ltd.
Modelling the distribution of ischaemic stroke‐specific survival time using an EM‐based mixture approach with random effects adjustment
Authors: Ng S. K. , McLachlan G. J. , Yau Kelvin K. W. , Lee Andy H.
Published: August 2004

A two‐component survival mixture model is proposed to analyse a set of ischaemic stroke‐specific mortality data. The survival experience of stroke patients after index stroke may be described by a subpopulation of patients in the acute condition and another subpopulation of patients in the chronic phase. To adjust for the inherent correlation of observations due to random hospital effects, a mixture model of two survival functions with random effects is formulated. Assuming a Weibull hazard in both components, an EM algorithm is developed for the estimation of fixed effect parameters and variance components. A simulation study is conducted to assess the performance of the two‐component survival mixture model estimators. Simulation results confirm the applicability of the proposed model in a small sample setting. Copyright © 2004 John Wiley & Sons, Ltd.
Statistical assessment of mediational effects for logistic mediational models
Authors: Huang Bin , Sivaganesan Siva , Succop Paul , Goodman Elizabeth
Published: August 2004

The concept of mediation has broad applications in medical health studies. Although the statistical assessment of a mediational effect under the normal assumption has been well established in linear structural equation models (SEM), it has not been extended to the general case where normality is not a usual assumption. In this paper, we propose to extend the definition of mediational effects through causal inference. The new definition is consistent with that in linear SEM and does not rely on the assumption of normality. Here, we focus our attention on the logistic mediation model, where all variables involved are binary. Three approaches to the estimation of mediational effects—Delta method, bootstrap, and Bayesian modelling via Monte Carlo simulation are investigated. Simulation studies are used to examine the behaviour of the three approaches. Measured by 95 per cent confidence interval (CI) coverage rate and root mean square error (RMSE) criteria, it was found that the Bayesian method using a non‐informative prior outperformed both bootstrap and the Delta methods, particularly for small sample sizes. Case studies are presented to demonstrate the application of the proposed method to public health research using a nationally representative database. Extending the proposed method to other types of mediational model and to multiple mediators are also discussed. Copyright © 2004 John Wiley & Sons, Ltd.
Estimating vaccine efficacy using auxiliary outcome data and a small validation sample
Authors: Chu Haitao , Halloran M. Elizabeth
Published: August 2004

In vaccine studies, a specific diagnosis of a suspected case by culture or serology of the infectious agent is expensive and difficult. Implementing validation sets in the study is less expensive and is easier to carry out. In studies using validation sets, the non‐specific or auxiliary outcome is measured on each participant while the specific outcome is measured only for a small proportion of the participants. Vaccine efficacy, defined as one minus some measure of relative risk, could be severely attenuated if based only on the auxiliary outcome. Applying missing data analysis techniques could thus correct the bias while maintaining statistical efficiency. However, when the sample size in the validation sets is small and the vaccine is highly efficacious, all specific outcomes are likely to be negative in the validation set in the vaccinated group. Two commonly used missing data analysis methods, the mean score method and multiple imputation, depend on the ad hoc continuity correction when none of the specific outcomes are positive and the normality or log‐normality assumption of relative risk, which may not hold when the relative risk is highly skewed, to estimate the confidence interval. In this paper, we propose a Bayesian method to estimate vaccine efficacy and its highest probability density (HPD) credible set using Monte Carlo (MC) methods when using auxiliary outcome data and a small validation sample. Comparing the performance of these approaches using data from a field study of influenza vaccine and simulations, we recommend to use the Bayesian method in this situation. Copyright © 2004 John Wiley & Sons, Ltd.
Marginalized transition models for longitudinal binary data with ignorable and non‐ignorable drop‐out
Authors: Kurland Brenda F. , Heagerty Patrick J.
Published: August 2004

We extend the marginalized transition model of Heagerty to accommodate non‐ignorable monotone drop‐out. Using a selection model, weakly identified drop‐out parameters are held constant and their effects evaluated through sensitivity analysis. For data missing at random (MAR), efficiency of inverse probability of censoring weighted generalized estimating equations (IPCW‐GEE) is as low as 40 per cent compared to a likelihood‐based marginalized transition model (MTM) with comparable modelling burden. MTM and IPCW‐GEE regression parameters both display misspecification bias for MAR and non‐ignorable missing data, and both reduce bias noticeably by improving model fit. Copyright © 2004 John Wiley & Sons, Ltd.
Separating within and between effects in family studies: an application to the study of blood pressure in children
Authors: Mann Vera , De Stavola Bianca L. , Leon David A.
Published: August 2004

In epidemiology the analyses of family or twin studies do not always fully exploit the data, as information on differences between siblings is often used while between‐families effect are not considered. We show how cross‐sectional time‐series linear regression analysis can be easily implemented to estimate within‐ and between‐families effects simultaneously and how these effects can then be compared using the Hausman test. We illustrate this approach with data from the Uppsala family study on blood pressure in children with age ranging from 5.5 to 12.3 years for the younger and from 7.5 to 13.8 years for the older siblings. Comparing the effect of differences in birth weight on blood pressure within‐family (in full siblings) and between‐families (in unrelated children) allows us to study the contributions of fixed and pregnancy‐specific maternal effects on birth weight and consequently on blood pressure. Our data showed a 0.88 mmHg decrease (95 per cent confidence interval: −1.7 to −0.03 mmHg) in systolic blood pressure for one standard deviation increase in birth weight between siblings within a family and 0.88 mmHg (95 per cent confidence interval: −1.6 to −0.2 mmHg) decrease in systolic blood pressure for one standard deviation increase in birth weight between unrelated children. These estimates were controlled for sex, age, pubertal stage, body size and pulse rate of the children at examination and for maternal body size and systolic blood pressure. The within‐ and between‐families effects were not significantly different, p=0.19, suggesting that fixed and pregnancy‐specific factors have similar effects on childhood systolic blood pressure. Copyright © 2004 John Wiley & Sons, Ltd.
Strength of accumulating evidence and data monitoring committee decision making
Authors: George Stephen L. , Freidlin Boris , Korn Edward L.
Published: August 2004

The data monitoring committee (DMC) is a vital component of a randomized clinical trial. Its responsibilities include stopping the trial early for extreme results. The decision to stop the trial must be based on a careful synthesis of statistical methodology and clinical judgment. It is critical to ensure the validity of this complex process. In this paper we present results of a survey of 21 DMC members conducted to investigate how they evaluate accumulating evidence. The results indicate that some DMC members may be over‐interpreting developing trends in the data. Copyright © 2004 John Wiley & Sons, Ltd.
CrossOver: an algorithm for the construction of efficient cross‐over designs
Authors: John J. A. , Russell K. G. , Whitaker D.
Published: August 2004

A cross‐over experiment involves the application of sequences of treatments to several subjects over a number of time periods. It is thought that the observation made on each subject at the end of a time period may depend on the direct effect of the treatment applied in the current period, and the carry‐over effects of the treatments applied in one or more previous periods. Various models have been proposed to explain the nature of the carry‐over effects. An experimental design that is optimal under one model may not be optimal if a different model is the appropriate one. In this paper an algorithm is described to construct efficient cross‐over designs for a range of models that involve the direct effects of the treatments and various functions of their carry‐over effects. The effectiveness and flexibility of the algorithm are demonstrated by assessing its performance against numerous designs and models given in the literature. Copyright © 2004 John Wiley & Sons, Ltd.