bluuebunny/crossref_metadata_2025 huggingface dataset:
Summary of ISO/TC 201 Standard: VII ISO 15472 : 2001—surface chemical analysis—x‐ray photoelectron spectrometers—calibration of energy scales
Authors: Seah M. P.
Published: January 2005

This international standard specifies a method for calibrating the binding energy scales of x‐ray photoelectron spectrometers, for general analytical purposes, using unmonochromated Al or Mg x‐rays or monochromated Al x‐rays. It is only applicable to instruments that have an ion gun for sputter cleaning. This international standard further specifies a method to establish a calibration schedule, to test for the binding energy scale linearity at one intermediate energy, to confirm the uncertainty of the scale calibration at one low and one high binding energy value, to correct for small drifts of that scale and to define the expanded uncertainty of the calibration of the binding energy scale for a confidence level of 95%. This uncertainty includes contributions for behaviour observed in inter‐laboratory studies but does not cover all of the defects that could occur. This international standard is not applicable to instruments with binding energy scale errors that are significantly non‐linear with energy, to instruments operated in the constant retardation ratio mode at retardation ratios of <10, to instruments with a spectrometer resolution worse than 1.5 eV or to instruments requiring tolerance limits of ±0.03 eV or less. This international standard does not provide a full calibration check, which would confirm the energy measured at each addressable point on the energy scale and would have to be performed in accordance with the manufacturer's recommended procedures. © Crown Copyright 2001. Published by John Wiley & Sons, Ltd.
Solvent effects on polymer surface structure
Authors: Chen Jiaxing , Zhuang Hengzhong , Zhao Jin , Gardella Joseph A.
Published: January 2005

The surface modification of polymeric materials has been of great research interest in the last few years because of its importance in applications such as biomaterials and coatings. The bulk composition of polymeric materials often cannot provide the desired surface properties in these applications. For example, low‐surface‐energy materials can be obtained via the process of surface segregation. The properties of the solvents used in these processes are critical for surface formation in these polymers. Solvent properties such as polarity, volatility and specific interaction properties with the polymer material are important factors in the process of surface formation. The present paper reviews recent studies of solvent effects no surface segregation in multicomponent polymer systems. Copolymers, polymer blend and multicomponent polymer solution systems are discussed. Copyright © 2001 John Wiley & Sons, Ltd.
Static time‐of‐flight secondary ion mass spectrometry and x‐ray photoelectron spectroscopy characterization of adsorbed albumin and fibronectin films
Authors: Tidwell Caren D. , Castner David G. , Golledge Stephen L. , Ratner Buddy D. , Meyer Klaus , Hagenhoff Brigit , Benninghoven Alfred
Published: January 2005

Static time‐of‐flight secondary ion mass spectrometry (ToF‐SIMS), monochromatized x‐ray photoelectron spectroscopy (XPS) and 125I radiolabeling have been used to characterize albumin films adsorbed onto titanium, gold, polytetrafluoroethylene and r.f. glow discharge‐deposited tetrafluoroethylene (TFE) substrates. A comparison between albumin and fibronectin films also was made. The intensities of characteristic amino acid mass fragments (immonium ions) detected in the static ToF‐SIMS experiments depended on the protein type, the substrate type and the adsorption conditions, demonstrating the sensitivity of static ToF‐SIMS for probing the structure of adsorbed protein films. Based on the results from albumin and fibronectin, static ToF‐SIMS can provide information about the identity of adsorbed proteins and their conformation, orientation, denaturation, etc. X‐ray photoelectron spectroscopy can distinguish pure protein films, but the higher molecular specificity of static ToF‐SIMS is more useful than XPS for examining complex protein films. The 125I radiolabeling experiments and the XPS atomic percentage of nitrogen were used to quantify the amount of adsorbed protein. Copyright © 2001 John Wiley & Sons, Ltd.
Nanoscale characterization of interfacial reactions in SrRuO3 thin film on Si substrate
Authors: Oh Sang Ho , Park Chan‐Gyung
Published: January 2005

Interfacial reactions between SrRuO3 films and Si substrate were investigated by using field‐emission transmission electron microscopy (FE‐TEM). The compositional and structural variations across the interface were analysed using energy‐dispersive x‐ray spectroscopy (EDS) and diffraction methods with an electron probe of 0.5 nm diameter. According to the morphology and composition analysed, the reaction layers between Si and SrRuO3 (from the substrate side) were identified as follows: Sr–Si–O layer; amorphous SiO2 layer; Sr–Si–O layer; and nanometre‐sized Ru‐rich grains containing Si and O. The reaction layers and their characteristics could be explained by considering the chemical reactivity of the binary constituent oxides of SrRuO3 (i.e. SrO and RuO2) with Si substrate: i.e. SrO can be stable in contact with Si because the Sr–Si–O ternary system has a stable tie‐line between SrO and Si, but RuO2 cannot be stable with Si because the Ru–Si–O ternary system has a stable tie‐line not between RuO2 and Si but between Ru and SiO2. The reduction of SrRuO3 to elemental Ru by Si is believed to be the most favourable candidate for the reaction leading to the unstable contact of SrRuO3 on Si. Copyright © 2001 John Wiley & Sons, Ltd.
Quantitative surface characterization of poly(styrene)/poly(4‐vinyl phenol) random and block copolymers by ToF‐SIMS and XPS
Authors: Liu Shiyong , Weng Lu‐Tao , Chan Chi‐Ming , Li Lin , Ho Nick K. , Jiang Ming
Published: January 2005

A series of spin‐cast films of poly(styrene‐co‐4‐vinyl phenol) (STVPh) random copolymers and polystyrene‐b‐poly(4‐vinyl phenol) (PS‐b‐PVPh), which have the same building units but different chain architecture, were analysed by x‐ray photoelectron spectroscopy (XPS) and time‐of‐flight secondary ion mass spectrometry (ToF‐SIMS). The XPS results show that there was no surface segregation of any component for the STVPh random copolymers. The calibration curves for ToF‐SIMS intensity as a function of the VPh content were obtained for the STVPh random copolymers. These calibration curves were used to determine the surface chemical composition of the block copolymers. The ToF‐SIMS results agreed well with the angle‐dependent XPS results. Time‐of‐flight SIMS also was shown to be able to distinguish PS‐b‐PVPh from the STVPh random copolymers by the absence of the peaks corresponding to the St–VPh or St–St–VPh sequence structures. Copyright © 2001 John Wiley & Sons, Ltd.
Grazing‐incidence x‐ray photoemission spectroscopy and the accuracy of thickness measurements of CMOS gate dielectrics
Authors: Jach Terrence , Landree Eric
Published: January 2005

Grazing‐incidence x‐ray photoelectron spectroscopy (GIXPS) is a method that offers promise as a non‐destructive technique to measure the thickness and chemical state of ultrathin gate dielectric films. This method utilizes the non‐linear dependence of the photoelectron yield on the radiation incidence angle to characterize a given layer structure. The accuracy of the results also depends on the input parameters, such as photoemission cross‐sections, indices of refraction and electron attenuation lengths within the incident x‐ray energy range of application (1–2 keV). Uncertainties in these parameters have consequences not only for GIXPS but also for other techniques that rely on them for materials analysis. We present a study of the impact of uncertainty in the photoionization cross‐sections and atomic scattering factors on the GIXPS measurement of film thickness and density. A test of the accuracy of the index of refraction is demonstrated by measurements of a native oxide layer on Si at incident energies below and above the Si K edge. We also discuss the effects of surface and interface roughness. Published in 2001 by John Wiley & Sons, Ltd.
Study of semiconductor surfaces and interfaces using electromodulation
Authors: Pollak Fred H.
Published: January 2005

The modulation spectroscopy technique of electromodulation (EM) is a major tool for the study and characterization of a number of semiconductor surfaces/interfaces and also for the evaluation of process‐induced damage at surfaces. The most useful forms of EM are photoreflectance (PR) and contactless electroreflectance (CER) because they are sensitive to surface/interface electric fields and often yield the sharpest structure (third‐derivative lineshape of the unmodulated spectrum in the case of bulk/thin‐film material). For sufficiently high electric fields the PR/CER spectra may exhibit Franz–Keldysh oscillations, which are a direct measure of the relevant electric field. Furthermore, PR and CER require no special mounting of the sample and hence can be employed in situ (PR) or non‐destructively on wafer‐sized material. This article will discuss some recent applications of PR/CER for the investigation of a number of surfaces/interfaces, such as: process‐induced effects on the surface of Si; Fermi‐level pinning on a number of III–V materials, including low‐temperature‐grown GaAs (with excess As) and wurtzite GaN; Schottky barrier formation; process‐induced damage (sputtering, reactive ion etching, chemically assisted ion beam etching) on III–V materials; homojunctions (GaAs/GaAs); heterojunctions (GaAlAs/GaAs, ZnSe/GaAs, CdTe/GaAs, AlInAs/InP, InGaAs/InP, InGaAs/InAlAs and wurtzite InGaN/GaN); and device structures such as heterojunction bipolar transistors and pseudomorphic high‐electron‐mobility transistors. A number of these studies have been performed in situ with an ultrahigh vacuum environment. Copyright © 2001 John Wiley & Sons, Ltd.
Optical second harmonic spectroscopy of semiconductor surfaces: advances in microscopic understanding
Authors: Downer M. C. , Mendoza B. S. , Gavrilenko V. I.
Published: January 2005

Even‐order non‐linear optical spectroscopy has emerged as an unusually sensitive technique for non‐invasive analysis of surfaces and buried interfaces of centrosymmetric materials. The forefront challenges are: to develop reliable microscopic computational methods for calculating and interpreting measured surface non‐linear spectra; to relate non‐linear surface spectra quantitatively to linear optical surface probes such as reflectance‐difference spectroscopy (RDS); and to develop convenient methods for acquiring non‐linear optical spectra over bandwidths (several electron‐volts) that encompass multiple electronic surface resonances. We review recent advances in both calculation and measurement of non‐linear spectra, with emphasis on reconstructed and adsorbate‐covered silicon surfaces in epitaxial growth environments. Copyright © 2001 John Wiley & Sons, Ltd.
Self‐recovery function of p(1×1)‐Sc‐O/W(100) system used as Schottky emitter
Authors: Iida S. , Nagatomi T. , Takai Y.
Published: January 2005

The effects of heating temperature for the preparation of an Sc‐O/W(100) surface were investigated. Surface properties of the Sc‐O/W(100) surface prepared by heating at ∼1600 and ∼1700 K were significantly different from those prepared at ∼1500 K, which is the operating temperature of the Sc‐O/W(100) emitter. By heating at ∼1700 K the p(1×1) structure formed by Sc–O complexes was confirmed, whereas the p(2×1)‐p(1×2) double‐domain structure was obtained by heating at ∼1500 K. The surface properties prepared by heating at ∼1700 K were found to be very stable, and the surface has a self‐recovery function against residual gas ion sputtering at the operating temperature of the emitter. The present results strongly suggested that pretreatment of the Sc‐O/W(100) emitter by heating at ∼1700 K and device operation at ∼1500 K result in high reproducibility of the superior electron emission property of the Sc‐O/W(100) emitter. Copyright © 2005 John Wiley & Sons, Ltd.
Surface reconstructions in two and three dimensions: In on Si(111)
Authors: Pavlovska A. , Bauer E.
Published: January 2005

The surface reconstructions of indium (In) grown on Si(111) at coverages above one monolayer (ML) were studied by low‐energy electron microscopy. Two‐dimensional well‐ordered In layers were prepared by deposition at room temperature on the Si(111)‐(√3 × √3)‐R30° ‐In surface because room temperature growth of indium on clean Si(111)‐(7 × 7) substrate is disordered. Three new surface reconstructions were observed when the thickness of the In layer increases from 1 to 2 ML: (2 × 1); (1.5√3 × 1.5√3)‐R30° and a mixture of (√7 × √3) and ‘(1 × 1)‐R30°’. On the double layer In grows at room temperature epitaxially in the form of three‐dimensional crystals with predominant (100) orientation. The In(100) surface on top of these three‐dimensional crystals is reconstructed in the same manner as found in an earlier low‐energy electron diffraction study of the (100) surface of bulk In crystal. The preferred (100) orientation can be explained very well by the fact that the (√7 × √3) phase of the double layer has a centered square unit mesh that has a very small misfit with the centered unit mesh of the reconstructed In(100) surface. With increasing temperature the In(100) surface of the three‐dimensional microcrystals deconstructs at ∼120 °C. At the same temperature the (√7 × √3) structure of the two‐dimensional In layer undergoes a reversible transition to a (1 × 1) pattern that is attributed to disordering of the In double layer. At low temperatures a third monolayer of In with a packing density of a slightly compressed In(111) plane grows on the double layer. Copyright © 2005 John Wiley & Sons, Ltd.
Local structure change of Rh on alumina after treatments in high‐temperature oxidizing and reducing environments
Authors: Dohmae K. , Nonaka T. , Seno Y.
Published: January 2005

The effects of high‐temperature oxidization and reduction on the local structures of Rh in Rh/Al2O3 catalysts were investigated. After oxidization at 1200 °C, XPS measurements indicated that the Rh was in a highly oxidized state. Extended x‐ray absorption fine structure (EXAFS) analysis for the highly oxidized Rh showed a shorter distance between the Rh atom and the next cation than that in Rh2O3. The shortened distance agrees with the Rh substitution model, in which Rh substituted for the inner Al site of the α‐Al2O3 lattice. Stepwise reductions with XPS measurements after oxidization at 1200 °C revealed that the Rh that diffused into γ‐Al2O3 was more resistant to reduction than that diffused into α‐Al2O3. The Rh aged at 600 °C was oxidized but had no specific local structure. Copyright © 2005 John Wiley & Sons, Ltd.
Analysis of phonons in graphene sheets by means of HREELS measurement and ab initio calculation
Authors: Yanagisawa H. , Tanaka T. , Ishida Y. , Matsue M. , Rokuta E. , Otani S. , Oshima C.
Published: January 2005

We have grown epitaxial thin sheets of graphene on BC3/NbB2(0001) and measured phonon dispersion curves of the graphene sheets by means of high‐resolution electron energy‐loss spectroscopy (HREELS). The phonon dispersion curves have been calculated on the basis of ab initio calculations. The observed curves were in good agreement with theoretical curves. The quality of crystallinity of the graphene layers was high compared with the bulk graphite crystals. In this paper, we demonstrate that the combination of HREELS measurement and ab initio calculations is extremely effective for investigation of honeycomb‐structured materials. Copyright © 2005 John Wiley & Sons, Ltd.
Thin Co films on Cu(111) studied by electron capture spectroscopy
Authors: Schleberger Marika , Manske Jörg , Dirska Michael
Published: January 2005

We have studied thin films of Co on Cu(111) single crystals with electron capture spectroscopy (ECS). The magnetism from the cobalt layer can be detected clearly in remanence and as a function of the outer magnetic field. The measured circular polarization of the emitted light is related directly to the structural and magnetic changes of the system, depending on the cobalt layer thickness. We find the set‐in of in‐plane magnetization at ∼2 monolayers of cobalt and the saturation of our signal at a film thickness of 7–8 monolayers. At coverages above 3–4 monolayers the increasing growth of hcp cobalt domains at the expense of fcc cobalt domains gives rise to a linearly increasing ECS signal up to 7.5 monolayers. We attribute this to the fact that the fcc cobalt domains are covered with copper, whereas the hcp cobalt domains expose cobalt in the upper layer. Monte‐Carlo simulations of our ion scattering experiments show that great experimental care has to be taken in order to avoid excessive sputtering damage to the sample. By using moderate primary ion energies and small angles of incidence, thin films can be investigated with ECS in the grazing incidence geometry without changing the film structure. Copyright © 2005 John Wiley & Sons, Ltd.
Application of metal cluster complex ion beam for low damage sputtering
Authors: Fujimoto Toshiyuki , Mizota Takeshi , Nonaka Hidehiko , Kurokawa Akira , Ichimura Shingo
Published: January 2005

Metal cluster complexes, including the colloidal metal cluster, were applied to establish the low damage sputtering method. Electro‐spray‐like ionization using an ink‐jet nozzle has the potential to produce a cluster ion beam. A colloidal Au cluster of size 5 nm made a large crater‐like hole at the carbon sheet. Copyright © 2005 John Wiley & Sons, Ltd.
Development of ultrahigh vacuum floating‐type low‐energy ion gun with differential pumping facilities for high‐resolution depth profiling
Authors: Mizuhara Y. , Bungo T. , Nagatomi T. , Takai Y. , Suzuki S. , Kikuchi K. , Sato T. , Uta K.
Published: January 2005

An ultrahigh vacuum floating‐type low‐energy ion gun (UHV‐FLIG) with a differential pumping system was developed. The developed UHV‐FLIG ensured high ion current densities of ∼45 and ∼20 µA cm−2 for Ar+ ions of 300 and 100 eV, respectively, under the UHV condition of the analysis chamber below ∼4 × 10−6 Pa. The application of the developed UHV‐FLIG to Auger electron spectroscopy (AES) sputter depth profiling of a GaAs/AlAs superlattice material revealed that the ultimate high depth resolution of ∼1.0 nm was achieved by sputter etching using 100 eV Ar+ ions. The present results confirmed that lowering the primary energy of Ar+ ions to 100 eV is still significantly effective for achieving higher depth resolution in sputter depth profiling. Copyright © 2005 John Wiley & Sons, Ltd.
Deconvolution of SIMS depth profiles of As multiple delta layers in silicon
Authors: Lee J. W. , Kim K. J. , Kim H. K. , Moon D. W.
Published: January 2005

We investigated the deconvolution of SIMS depth profiles of arsenic multiple delta layers in silicon. Two samples with spacings of 50 and 5/10 nm between the arsenic‐doped silicon delta layers of thickness 1.0 and 0.5 nm, respectively, were used for the study. Time‐of‐flight SIMS analysis with sputtering of 0.5 keV Cs+ at 45° incident angle has been performed to obtain the SIMS depth profile. We observed five clearly separated peaks in the 50 nm spacing sample but eight poorly separated peaks in the 5/10 nm spacing sample. After deconvolution, however, we could obtain very thin and sharp clearly separated peaks in both samples. The separability of the overlapping peaks was much improved, especially in the region of 5 nm spacing. An improvement in depth resolution by a factor of ∼3 and a gain in maximum peak intensity by a factor of ∼4 were achieved. We could not find any significant loss or gain of peak intensity during the deconvolution procedure. The physical validity of the deconvolution method is supported by non‐destructive medium‐energy ion scattering spectroscopy analysis, which can measure the thickness of the arsenic‐doped silicon delta layer in a silicon matrix quantitatively. Copyright © 2005 John Wiley & Sons, Ltd.
Study of solid/solid interface by transmitted x‐ray reflectivity
Authors: Inoue Koji , Kitahara Amane , Matsushita Kiyohiko , Kikkawa Hiroyuki , Nakabayashi Fumitomo , Ageishi Naoya , Terauchi Hikaru , Sakata Osami , Takahashi Isao
Published: January 2005

In this paper, we demonstrate investigations of metal thick layer/semiconductor interfaces (Au/Si and Ga/GaAs) by x‐ray reflectivity under transmission geometry (TXR), which could not be performed by conventional x‐ray reflectivity due to the macroscopic thickness and surface roughness of the overlayers. We obtain precise electron density by using the two maxima in diffuse scattering of TXR caused by the Fresnel transmission function (the so‐called Yoneda wings). From in situ TXR measurements of Ga/GaAs with elevating temperature, the onset of structural variation at the interface is found to be 520 K. Such an interfacial variation at an extraordinarily low temperature agrees with an ex situ SEM study of an etched GaAs surface. Copyright © 2005 John Wiley & Sons, Ltd.
Fluorine Kα x‐ray fluorescence spectra of LuF3 and NaF using synchrotron radiation
Authors: Kaibuchi Kazuki , Nagasono Mitsuru , Liu Zhenlin , Koja Yusuke , Fukushima Akiko , Shin Shik , Takahashi Hideyuki , Kawai Jun
Published: January 2005

The F Kα x‐ray fluorescence spectrum of LuF3 is excited by monochromated synchrotron radiation and a satellite peak is observed at the higher energy side of the F Kα1, 2 lines. The intensity of this peak depends on the incident x‐ray energy; the presence of the threshold energy to excite the satellite proves that the satellite is assigned to Kα3, 4 due to the transition 1s−12p−1→ 2p−2. The Kα3, 4/Kα1, 2 intensity ratio for LuF3 is 0.20, which is significantly weaker than that for NaF (0.46). It is observed that the Kα1, 2 line width of LuF3 is significantly broader than that for NaF. Copyright © 2005 John Wiley & Sons, Ltd.
Development of photoelectron spectro‐holography apparatus
Authors: Ishii Hideshi , Mamaishin Shuichi , Tamura Keiji , Chu Wei‐Guo , Owari Masanori , Doi Makoto , Tsukamoto Katsumi , Takahashi Sadayuki , Iwai Hideo , Watanabe Katsumi , Kobayashi Hideo , Kita Yoshiteru , Yamazui Hiromichi , Taguchi Masami , Shimizu Ryuichi , Nihei Yoshimasa
Published: January 2005

We improved the photoelectron spectro‐holography apparatus for high‐speed and high‐energy photoelectron detection. The combination of an aperture for ±1.4° acceptance angle at the diffraction plane and a 64‐channel detector realized the high‐speed XPS and rapid x‐ray photoelectron diffraction (XPED) measurements Furthermore, high‐energy XPS and XPED measurements excited by Cu Kα have been performed. Copyright © 2005 John Wiley & Sons, Ltd.
Surface structure analysis of Zr‐O/W(100) at high temperature by x‐ray photoelectron diffraction
Authors: Tamura Keiji , Amano Mikiya , Chu Wei‐guo , Ishii Hideshi , Owari Masanori , Kawano Takashi , Nagatomi Takakiyo , Takai Yoshizo , Oshima Chuhei , Shimizu Ryuichi , Nihei Yoshimasa
Published: January 2005

Temperature dependence of the surface structure of Zr‐O/W(100) was obtained by low‐energy electron diffraction observation to check the phase transition of the surface. After flashing the Zr‐O/W(100) to 1500 K, the c(2 × 4) + c(4 × 2) double‐domain structure was clearly observed at room temperature. This surface changed to the p(1 × 1) phase over 1300 K, accompanied by a decrease in the work function. The temperature dependence of the work function was obtained from the shift of the energy distributions of secondary electrons. The reversible phase transition of the Zr‐O/W(100) surface and the decrease in the work function of 2 eV at high temperature were checked. X‐ray photoelectron diffraction (XPD) measurements at 1500 K have been performed to investigate the surface structure at the working temperature of the Zr‐O/W(100) electron emitter. The O1s XPED pattern included some patterns that can be regarded as the influence of Zr–O complexes on the W(100) surface. Copyright © 2005 John Wiley & Sons, Ltd.
Wedge‐shaped and flat cross‐sections for quantitative characterization of the electrostatic potential distributions across p‐n junctions by electron holography
Authors: Wang Zhouguang , Kato Takeharu , Hirayama Tsukasa , Kato Naoko , Sasaki Katsuhiro , Saka Hiroyasu
Published: January 2005

Both flat and wedge‐shaped cross‐sectional specimens were fabricated by focused ion beam (FIB) milling of the same implanted Si/Si p‐n junction sample. The junction potential distributions in both kinds of specimens were examined by using electron holography, and their differences were compared. Some parameters needed for characterizing junction potential distributions quantitatively, such as the thickness of the electrically dead layer on the surface, can be obtained only from wedge‐shaped cross‐sections, and it is shown that the two‐dimensional potential distributions in practical semiconductor devices can be measured accurately only by combining the results obtained using both of these specimen geometries. Copyright © 2005 John Wiley & Sons, Ltd.
Ultimate sized nano‐dots formed by electron beam‐induced deposition using an ultrahigh vacuum transmission electron microscope
Authors: Tanaka M. , Shimojo M. , Han M. , Mitsuishi K. , Furuya K.
Published: January 2005

We have successfully fabricated nano‐dots containing tungsten or gold from metal‐organic gas sources by electron beam‐induced deposition in an ultrahigh vacuum transmission electron microscope. The size of the dots can be controlled by changing the time for irradiation and the partial pressure of the precursor. The smallest particle size fabricated from W(CO)6 is ∼1.5 nm in diameter, which is close to the theoretical resolution limit. Copyright © 2005 John Wiley & Sons, Ltd.
Transmission electron microscopy observation of the structure of TiO2 nanotube and Au/TiO2 nanotube catalyst
Authors: Akita Tomoki , Okumura Mitsutaka , Tanaka Koji , Ohkuma Kayoko , Kohyama Masanori , Koyanagi Tsuguo , Date Masakazu , Tsubota Susumu , Haruta Masatake
Published: January 2005

A TiO2 nanotube catalyst was synthesized and observed by analytical transmission electron microscopy (TEM) combined with scanning transmission electron microscopy (STEM) and electron energy‐loss spectroscopy (EELS). It was revealed that the crystalline structure of the TiO2 nanotube is different from that of anatase and rutile TiO2. It was found that gold nanoparticles could be supported successfully on the TiO2 nanotube when applied using the deposition precipitation method. The catalytic activity of an Au/TiO2 nanotube for CO oxidation and H2 oxidation was examined and found to be different from Au on anatase or and rutile TiO2 catalyst. Copyright © 2005 John Wiley & Sons, Ltd.
Cost‐effectiveness analysis when the WTA is greater than the WTP
Authors: Willan Andrew R. , O'Brien Bernie J. , Leyva Rina A.
Published: January 2005

The incremental cost effectiveness ratio has long been the standard parameter of interest in the assessment of the cost‐effectiveness of a new treatment. However, due to concerns with interpretability and statistical inference, authors have suggested using the willingness‐to‐pay for a unit of health benefit to define the incremental net benefit as an alternative. The incremental net benefit has a more consistent interpretation and is amenable to routine statistical procedures. These procedures rely on the fact that the willingness‐to‐accept compensation for a loss of a unit of health benefit (at some cost saving) is the same as the willingness‐to‐pay for it. Theoretical and empirical evidence suggest, however, that in health care the willingness‐to‐accept is about twice as much as the willingness‐to‐pay. We use Bayesian methods to provide a statistical procedure for the cost‐effectiveness comparison of two arms of a randomized clinical trial that allows the willingness‐to‐pay and the willingness‐to‐accept to have different values. An example is provided. Copyright © 2001 John Wiley & Sons, Ltd.
Group sequential test strategies for superiority and non‐inferiority hypotheses in active controlled clinical trials
Authors: Wang Sue‐Jane , James Hung H. M. , Tsong Yi , Cui Lu
Published: January 2005

In a group sequential active controlled clinical trial, the study hypothesis may be a superiority hypothesis that an experimental treatment is more effective than the active control therapy or a non‐inferiority hypothesis that the treatment is no worse than the active control within some non‐inferiority range. When it is necessary to plan for testing the superiority and the non‐inferiority hypotheses, we propose an adaptive group sequential closed test strategy by which the sample size is planned for testing superiority and is to be increased for showing non‐inferiority given that it is deemed more plausible than superiority based on the observed sample path during the course of the trial. The proposed adaptive test strategy is valid in terms of having the type I error probability maintained at the targeted α level for both superiority and non‐inferiority. It has power advantage or sample size saving over the traditional group sequential test designed for testing either superiority only or non‐inferiority only. Copyright © 2001 John Wiley & Sons, Ltd.
Meta‐analysis of binary data: which within study variance estimate to use?
Authors: Chang Bei‐Hung , Waternaux Christine , Lipsitz Stuart
Published: January 2005

We applied a mixed effects model to investigate between‐ and within‐study variation in improvement rates of 180 schizophrenia outcome studies. The between‐study variation was explained by the fixed study characteristics and an additional random study effect. Both rate difference and logit models were used. For a binary proportion outcome pi with sample size ni in the ith study, (p̂i(1−p̂i)ni)−1 is the usual estimate of the within‐study variance σ2i in the logit model, where p̂i is the sample mean of the binary outcome for subjects in study i. This estimate can be highly correlated with logit(p̂i). We used (p̄i(1−p̄)ni)−1 as an alternative estimate of σ2i, where p̄ is the weighted mean of p̂i's. We estimated regression coefficients (β) of the fixed effects and the variance (τ2) of the random study effect using a quasi‐likelihood estimating equations approach. Using the schizophrenia meta‐analysis data, we demonstrated how the choice of the estimate of σ2i affects the resulting estimates of β and τ2. We also conducted a simulation study to evaluate the performance of the two estimates of σ2i in different conditions, where the conditions vary by number of studies and study size. Using the schizophrenia meta‐analysis data, the estimates of β and τ2 were quite different when different estimates of σ2i were used in the logit model. The simulation study showed that the estimates of β and τ2 were less biased, and the 95 per cent CI coverage was closer to 95 per cent when the estimate of σ2i was (p̄(1−p̄)ni)−1 rather than (p̂i(1−p̂)ni)−1. Finally, we showed that a simple regression analysis is not appropriate unless τ2 is much larger than σ2i, or a robust variance is used. Copyright © 2001 John Wiley & Sons, Ltd.
A note on the distribution of the number of vaccinated infected under non‐random mixing conditions
Authors: Hernández‐Suárez Carlos M.
Published: January 2005

A common situation in vaccine efficacy (VE) estimation is dealing with non‐randomly mixing populations, which may subject vaccinated and unvaccinated individuals to a different infection pressure. These conditions may lead to a bias in VE estimates. The derivation of the statistical distribution of the number of vaccinated and infected out of a sample of n infections in a VE trial is essential to develop estimates and their properties. For randomly mixing populations, it has been shown recently that this follows a hypergeometric distribution for ‘all/nothing’ vaccines, whereas it is a non‐central hypergeometric distribution for ‘leaky’ ones. Here it is shown that these distributions still hold under non‐random mixing conditions, provided that mixing preferences and contact rates are independent of vaccination status. These conditions are met when vaccine and placebo are randomized. Copyright © 2001 John Wiley & Sons, Ltd.
Use of odds ratio or relative risk to measure a treatment effect in clinical trials with multiple correlated binary outcomes: data from the NINDS t‐PA stroke trial
Authors: Lu Mei , Tilley Barbara C.
Published: January 2005

In clinical trials, when a single outcome is not sufficient to describe the underlying concept of interest, it may be necessary to compare treatment groups on multiple correlated outcomes. A global test based on a logit link function provides an estimate of the odds ratio for assessing a common treatment effect among correlated binary outcomes. In this paper we extend the use of generalized estimating equations (GEE) to calculate a common relative risk from correlated binary outcomes based on a log link function. In the context of global tests, we discuss the equivalence and difference between logit and log links and their estimates. We also derive a formula for calculating a common risk difference between two treatment groups based on multiple correlated binary outcomes with categorical covariates, assuming the asymptotic equivalency between the logit and log‐linear links. We discuss the statistical tools to be used in choosing between the logit and log links when models on different links yield contrasting results. Examples using data from the NINDS t‐PA Stroke Trials are provided. We conclude, in a study of correlated binary outcomes, that the choice of the logit or log link could be based on a comparison of goodness‐of‐link. Copyright © 2001 John Wiley & Sons, Ltd.
Group comparisons involving missing data in clinical trials: a comparison of estimates and power (size) for some simple approaches
Authors: Miller Michael E. , Morgan Timothy M. , Espeland Mark A. , Emerson Scott S.
Published: January 2005

When using ‘intent‐to‐treat’ approaches to compare outcomes between groups in clinical trials, analysts face a decision regarding how to account for missing observations. Most model‐based approaches can be summarized as a process whereby the analyst makes assumptions about the distribution of the missing data in an attempt to obtain unbiased estimates that are based on functions of the observed data. Although pointed out by Rubin as often leading to biased estimates of variances, an alternative approach that continues to appear in the applied literature is to use fixed‐value imputation of means for missing observations. The purpose of this paper is to provide illustrations of how several fixed‐value mean imputation schemes can be formulated in terms of general linear models that characterize the means of distributions of missing observations in terms of the means of the distributions of observed data. We show that several fixed‐value imputation strategies will result in estimated intervention effects that correspond to maximum likelihood estimates obtained under analogous assumptions. If the missing data process has been correctly characterized, hypothesis tests based on variances estimated using maximum likelihood techniques asymptotically have the correct size. In contrast, hypothesis tests performed using the uncorrected variance, obtained by applying standard complete data formula to singly imputed data, can provide either conservative or anticonservative results. Surprisingly, under several non‐ignorable non‐response scenarios, maximum likelihood based analyses can yield equivalent hypothesis tests to those obtained when analysing only the observed data. Copyright © 2001 John Wiley & Sons, Ltd.
Optimal estimation of transposition rates of insertion sequences for molecular epidemiology
Authors: Tanaka Mark M. , Rosenberg Noah A.
Published: January 2005

Outbreaks of infectious disease can be confirmed by identifying clusters of DNA fingerprints among bacterial isolates from infected individuals. This procedure makes assumptions about the underlying properties of the genetic marker used for fingerprinting. In particular, it requires that each fingerprint changes sufficiently slowly within an individual that isolates from separate individuals infected by the same strain will exhibit similar or identical fingerprints. We propose a model for the probability that an individual's fingerprint will change over a given period of time. We use this model together with published data in order to estimate the fingerprint change rate for IS6110 in human tuberculosis, obtaining a value of 0.0139 changes per copy per year. Although we focus on insertion sequences (IS), our method applies to other fingerprinting techniques such as pulsed‐field gel electrophoresis (PFGE). We suggest sampling intervals that produce the least error in estimates of the fingerprint change rate, as well as sample sizes that achieve specified levels of error in the estimate. Copyright © 2001 John Wiley & Sons, Ltd.
Residual mass histology in testicular cancer: development and validation of a clinical prediction rule
Authors: Steyerberg Ewout W. , Vergouwe Yvonne , Jan Keizer H. , Habbema J. Dik F. ,   for the ReHiT study group
Published: January 2005

After chemotherapy for metastatic non‐seminomatous testicular cancer, surgical resection is a generally accepted treatment to remove remnants of the initial metastases, since residual tumour may still be present (mature teratoma or viable cancer cells). In this paper, we review the development and external validation of a logistic regression model to predict the absence of residual tumour. Three sources of information were used. A quantitative review identified six relevant predictors from 19 published studies (996 resections). Second, a development data set included individual data of 544 patients from six centres. This data set was used to assess the predictive relationships of five continuous predictors, which resulted in dichotomization for two, and a log, square root, and linear transformation for three other predictors. The multiple logistic regression coefficients were reduced with a shrinkage factor (0.95) to improve calibration, based on a bootstrapping procedure. Third, a validation data set included 172 more recently treated patients. The model showed adequate calibration and good discrimination in the development and in the validation sample (areas under the ROC curve 0.83 and 0.82). This study illustrates that a careful modelling strategy may result in an adequate predictive model. Further study of model validity may stimulate application in clinical practice. Copyright © 2001 John Wiley Sons, Ltd.
Cumulative logit models for ordinal data: a case study involving allergic rhinitis severity scores
Authors: Lunn David J. , Wakefield Jon , Racine‐Poon Amy
Published: January 2005

Ordered categorical data arise in numerous settings, a common example being pain scores in analgesic trials. The modelling of such data is intrinsically more difficult than the modelling of continuous data due to the constraints on the underlying probabilities and the reduced amount of information that discrete outcomes contain. In this paper we discuss the class of cumulative logit models, which provide a natural framework for ordinal data analysis. We show how viewing the categorical outcome as the discretization of an underlying continuous response allows a natural interpretation of model parameters. We also show how covariates are incorporated into the model and how various types of correlation among repeated measures on the same individual may be accounted for. The models are illustrated using longitudinal allergy data consisting of sneezing scores measured on a four‐point scale. Our approach throughout is Bayesian and we present a range of simple diagnostics to aid model building. Copyright © 2001 John Wiley & Sons, Ltd.
Randomized clinical trials with added rescue medication: some approaches to their analysis and interpretation
Authors: White Ian R. , Bamias Christina , Hardy Pollyanna , Pocock Stuart , Warner Jacquie
Published: January 2005

Patients in some randomized clinical trials may start additional non‐randomized medication because of an exacerbation of symptoms or insufficient therapeutic effect. Typically this rescue medication reduces the observed treatment effect in intention‐to‐treat analysis. We discuss methods of analysis which take account of rescue medication in order to achieve a more meaningful comparison of the randomized treatments, focusing on trials with a repeated quantitative outcome. Ignoring all data after rescue is likely to be biased because rescued patients are a highly selected group. Instead we propose using methods based on ranks or multilevel models. The rank‐based methods assume that rescued patients have especially bad underlying outcomes. The multilevel regression model relates a patient's outcome to allocated treatment and rescue status at each time, and requires correct modelling of all prognostic factors which predict starting rescue medication and of the covariance between outcomes measured at different times. We also describe sensitivity analyses over a range of possible models for the effect of rescue medication. We illustrate these methods in a trial in Parkinson's disease. It appears that adjustment for rescue medication will not radically alter the randomized treatment comparison unless rescue medication is substantially imbalanced between randomized groups and has a substantial effect on the outcome. Copyright © 2001 John Wiley & Sons, Ltd.
Using observational data to estimate prognosis: an example using a coronary artery disease registry
Authors: DeLong Elizabeth R. , Nelson Charlotte L. , Wong John B. , Pryor David B. , Peterson Eric D. , Lee Kerry L. , Mark Daniel B. , Califf Robert M. , Pauker Stephen G.
Published: January 2005

With the proliferation of clinical data registries and the rising expense of clinical trials, observational data sources are increasingly providing evidence for clinical decision making. These data are viewed as complementary to randomized clinical trials (RCT). While not as rigorous a methodological design, observational studies yield important information about effectiveness of treatment, as compared with the efficacy results of RCTs. In addition, these studies often have the advantage of providing longer‐term follow‐up, beyond that of clinical trials. Hence, they are useful for assessing and comparing patients' long‐term prognosis under different treatment strategies. For patients with coronary artery disease, many observational comparisons have focused on medical therapy versus interventional procedures. In addition to the well‐studied problem of treatment selection bias (which is not the focus of the present study), three significant methodological problems must be addressed in the analysis of these data: (i) designation of the therapeutic arms in the presence of early deaths, withdrawals, and treatment cross‐overs; (ii) identification of an equitable starting point for attributing survival time; (iii) site to site variability in short‐term mortality. This paper discusses these issues and suggests strategies to deal with them. A proposed methodology is developed, applied and evaluated on a large observational database that has long‐term follow‐up on nearly 10 000 patients. Copyright © 2001 John Wiley & Sons, Ltd.
Planning a reproducibility study: how many subjects and how many replicates per subject for an expected width of the 95 per cent confidence interval of the intraclass correlation coefficient
Authors: Giraudeau B. , Mary J. Y.
Published: January 2005

Reproducibility of a quantitative outcome is usually assessed by means of the intraclass correlation coefficient (ICC). When we are interested in assessing reproducibility from only one sample, we suggest that the study be planned with regards to the expected width of the 95 per cent confidence interval of the ICC. An approximation of this latter width is derived, which allows appraisal of the influence of n the number of subjects and p the number of replicates. Through simulation studies, the approximation is shown to be of good accuracy and can therefore be used reliably. Optimal designs are also discussed such as the optimal distribution between the number of subjects and the number of replicates per subject for a fixed total number of measures. Copyright © 2001 John Wiley & Sons, Ltd.
Variable selection and Bayesian model averaging in case‐control studies
Authors: Viallefont Valerie , Raftery Adrian E. , Richardson Sylvia
Published: January 2005

Covariate and confounder selection in case‐control studies is often carried out using a statistical variable selection method, such as a two‐step method or a stepwise method in logistic regression. Inference is then carried out conditionally on the selected model, but this ignores the model uncertainty implicit in the variable selection process, and so may underestimate uncertainty about relative risks. We report on a simulation study designed to be similar to actual case‐control studies. This shows that p‐values computed after variable selection can greatly overstate the strength of conclusions. For example, for our simulated case‐control studies with 1000 subjects, of variables declared to be ‘significant’ with p‐values between 0.01 and 0.05, only 49 per cent actually were risk factors when stepwise variable selection was used. We propose Bayesian model averaging as a formal way of taking account of model uncertainty in case‐control studies. This yields an easily interpreted summary, the posterior probability that a variable is a risk factor, and our simulation study indicates this to be reasonably well calibrated in the situations simulated. The methods are applied and compared in the context of a case‐control study of cervical cancer. Copyright © 2001 John Wiley & Sons, Ltd.
A method to assess the proportion of treatment effect explained by a surrogate endpoint
Authors: Li Zhengqing , Meredith Michael P. , Hoseyni Mohammad S.
Published: January 2005

Randomized clinical trials are the standard for evaluating new drugs, devices and procedures. Traditional clinical trials entail not only considerable expense, but require considerable time to complete. The use of surrogate endpoints constitutes an effort to control cost and completion time for clinical trials. We propose a method to quantify the proportion of treatment effect explained by a surrogate endpoint based on a general model setting which includes the commonly used linear, logistic and Cox regression models. The interpretation of this quantitative measure is facilitated by graphical displays. To reduce the variability associated with the estimate, a meta‐analytic approach is proposed based on random effects models. An example using real clinical trial data is given to illustrate the proposed procedures. Copyright © 2001 John Wiley & Sons, Ltd.
Determinants of transnational new product development capability: testing the influence of transferring and deploying tacit overseas knowledge
Authors: Subramaniam Mohan , Venkatraman N.
Published: January 2005

Based on a survey of 90 transnational product introductions, we find that the transnational product development capabilities of organizations significantly depend upon their ability to transfer and deploy tacit knowledge concerning overseas markets. Specifically, we find that organizations which use cross‐national teams, teams with members who have prior overseas experience, or teams whose members communicate frequently with overseas managers in order to acquire information about tacit differences among countries have greater transnational product development capabilities. This study contributes to our understanding of how organizations transfer and deploy knowledge across borders for competitive advantage and makes an important contribution to the literature on global strategy. Copyright © 2001 John Wiley & Sons, Ltd.