bluuebunny/crossref_metadata_2025 huggingface dataset:
Role of liver biopsy in management of chronic hepatitis C: A systematic review
Authors: Gebo Kelly A. , Herlong Franklin H. , Torbenson Michael S. , Jenckes Mollie W. , Chander Geetanjali , Ghanem Khalil G. , El-Kamary Samer S. , Sulkowski Mark , Bass Eric B.
Published: October 2002

This systematic review addresses 2 questions pertinent to the need for pretreatment liver biopsy in patients with chronic hepatitis C: how well do liver biopsy results predict treatment outcomes for chronic hepatitis C? How well do biochemical blood tests and serologic measures of fibrosis predict the biopsy findings in chronic hepatitis C? Medline and other electronic databases were searched from January 1985 to March 2002. Additional articles were sought in references of pertinent articles and recent journals and by querying experts. Articles were eligible for review if they reported original human data from a study that used virological, histological, pathologic, or clinical outcome measures. Paired reviewers assessed the quality of each eligible study and abstracted data. Studies suggested that advanced fibrosis or cirrhosis on initial liver biopsy is associated with a modestly decreased likelihood of a sustained virological response (SVR) to treatment. Also, studies relatively consistently showed that serum aminotransferases have modest value in predicting fibrosis on biopsy; that extracellular matrix tests hyaluronic acid and laminin may have value in predicting fibrosis, and that panels of tests may have the greatest value in predicting fibrosis or cirrhosis. Biochemical and serologic tests were best at predicting no or minimal fibrosis, or at predicting advanced fibrosis/cirrhosis, and were poor at predicting intermediate levels of fibrosis. Thus, evidence suggests that liver biopsy may have some usefulness in predicting efficacy of treatment in patients with chronic hepatitis C, and biochemical blood tests and serologic tests currently have only modest value in predicting fibrosis on liver biopsy.
Treatment of chronic hepatitis C: A systematic review
Authors: Chander Geetanjali , Sulkowski Mark S. , Jenckes Mollie W. , Torbenson Michael S. , Herlong Franklin H. , Bass Eric B. , Gebo Kelly A.
Published: October 2002

This systematic review addressed 3 issues regarding current treatments for chronic hepatitis C: (1) efficacy and safety in treatment-naive patients; (2) efficacy and safety in selected subgroups of patients; and (3) effects on long-term clinical outcomes. Electronic databases were searched for articles from January 1996 to March 2002. Additional articles were identified by searching references in pertinent articles and recent journals and by questioning experts. Articles were eligible for review if they reported original human data from a study that used virological, histological, or clinical outcome measures. For data collection, paired reviewers assessed the quality of each study and abstracted data. This systematic review found that the combination of high-dose peginterferon and ribavirin was more efficacious than standard interferon and ribavirin in persons infected with hepatitis C virus (HCV) genotype 1 (sustained virologic response [SVR] rate: 42% vs. 33%) and that ranges of SVR rates were higher with peginterferon than standard interferon monotherapy in naïve patients (10% to 39% vs. 3% to 19%). Reports were consistent in showing treatment with interferon and ribavirin was more efficacious than interferon monotherapy in treatment-naive persons and previous nonresponders and relapsers. Studies were moderately consistent in showing that treatment decreases the risk for hepatocellular carcinoma (HCC). The evidence on treatment in important subgroups was limited by a lack of randomized controlled trials. Thus, the combination of peginterferon and ribavirin was the most efficacious treatment in patients with HCV genotype 1. Long-term outcomes were improved in patients with hepatitis C who achieved an SVR with treatment.
Kinetic theory for dilute dipolar systems
Authors: Bembenek Scott D. , Szamel Grzegorz
Published: October 2002

We propose a new kinetic theory to study dilute dipolar systems and apply it to the calculation of the angular velocity autocorrelation function for a system of Stockmayer molecules (Lennard-Jones particles with point dipoles) in the supercritical region. The predictions made from the theory are in excellent agreement with results obtained from molecular dynamics simulations over a broad range of densities above the critical temperature. The theory can be generalized to describe dielectric relaxation in supercritical water.
High frequency-bandwidth optical technique to measure thermal elongation time responses of near-field scanning optical microscopy probes
Authors: Biehler B. , La Rosa A. H.
Published: October 2002

A near-field scanning optical microscopy (NSOM) probe elongates when light is coupled into it. The time response of this thermal process is measured here by a new optical technique that exploits the typical flat-apex morphology of the probe as a mirror in a Fabry–Perot type cavity. Pulsed laser light is coupled into the probe to heat up the tip, while another continuous wave laser serves to monitor the elongation from the interference pattern established by the reflections from the flat-apex probe and a semitransparent metal-coated flat sample. A quarter wave plate is introduced into the interferometer optical path in order to maximize the signal to noise level, thus allowing the elongation of the tip to be monitored in real time. This optical technique, unlike other methods based on electronic feedback response, avoids limited frequency bandwidth restrictions. We have measured response time constants of 500 and 40 μs. The technique presented here will help determine the power levels, operating probe-sample distance, and pulse repetition rate requirements for safe operation of NSOM instrumentation. In addition to NSOM, the instrumentation described in this article could also impact other areas that require large working range, accuracy, and high-speed response.
Cavities with axially uniform fields for use in electron paramagnetic resonance. III. Re-entrant geometries
Authors: Hyde James S. , Mett Richard R. , Anderson James R.
Published: October 2002

Uniform field (UF) microwave cavities consist of three sections: the center with transverse dimensions set to the cutoff condition for a selected propagation mode, and two end sections. In the first article on UF modes, [R. R. Mett, W. Froncisz, and J. S. Hyde, Rev. Sci. Instrum. 72, 4188 (2001)] end sections were filled with dielectric 1/4 wavelength thick. In a second UF article, [J. R. Anderson, R. R. Mett, and J. S. Hyde, Rev. Sci. Instrum. 73, 3027 (2002)] the cross-sectional dimensions of the end sections were increased again setting the length to 1/4 wavelength. We describe here a third approach to end-section design in UF resonators: maintaining the cross section constant and introducing re-entrant conducting rods parallel to the electric field. Electromagnetic field distributions were simulated using the Ansoft high frequency structure simulator (HFSS) (Ansoft Corporation, Pittsburgh, PA) three-dimensional finite-element modal frequency (eigenmode) solution method. Simulation procedures are described. Re-entrant end-section UF resonators are compared with other UF types. The transition zone between sections is narrow and similar to that of the dielectric UF design. The Q value is high and similar to that in the second article.
Flow cell for in situ optical microscopy in water at high temperatures and pressures up to supercritical state
Authors: Deguchi Shigeru , Tsujii Kaoru
Published: October 2002

A high temperature and pressure flow cell for optical microscopy has been developed. The cell is designed to allow observations at temperatures and pressures above the critical point of water (374 °C, 22.1 MPa) up to 400 °C and 35 MPa. Due to the small dimension and the effective cooling system, the cell can be installed on a conventional inverted optical microscope, and observations can be done with the optical resolution of 2 μm. A microscope system incorporating the present cell has been used successfully to observe micro-organisms under hydrothermal conditions including supercritical water.
Use of biaxially oriented polypropylene film for evaluating and cleaning contaminated atomic force microscopy probe tips: An application to blind tip reconstruction
Authors: Nie H.-Y. , Walzak M. J. , McIntyre N. S.
Published: October 2002

An atomic force microscopy (AFM) image of a surface is basically a convolution of the probe tip geometry and the surface features; it is important to know this tip effect to ensure that an image truly reflects the surface features. We have found that a biaxially oriented polypropylene (BOPP) film is suitable for checking tip performance and for cleaning contaminated tips, thus making it possible to collect images of the same area of a BOPP film surface before and after the tip was cleaned. Therefore, the difference between the two different images is solely due to the contamination of the tip. We took advantage of our ability to collect AFM images of the same area using the same tip, in one instance, contaminated and, in the other, after being cleaned. First we used blind reconstruction on the image collected using the contaminated tip. Blind tip reconstruction allows one to extract the geometry of the tip from a given image. Once we had estimated the geometry of the contaminated tip, we used it to simulate the tip effect using the image collected using the cleaned tip. By comparing the simulation result with the image collected using the contaminated tip we showed that the blind reconstruction routine works well. Prior to this, there was no de facto method for testing blind reconstruction algorithms.
Figuring with subnanometer-level accuracy by numerically controlled elastic emission machining
Authors: Yamauchi Kazuto , Mimura Hidekazu , Inagaki Kouji , Mori Yuzo
Published: October 2002

A numerically controlled elastic emission machining (EEM) system has been developed to fabricate ultraprecise optical components, particularly in x-ray optics. Nozzle-type EEM heads, by which a high shear-rate flow of ultrapure water can be generated on the work surface, have been newly proposed to transport the fine powder particles to the processing surface. Using this type of EEM head, the obtainable spatial resolution in figure correction can be changed by selecting the suitable aperture size of the nozzle according to the required spatial frequency. As a result of test figuring, 1 nm level peak-to-valley (p–v) accuracy is achieved throughout the entire spatial wavelength range longer than 0.3 mm. In addition, the microroughness of the processed surface is certified to also be approximately 1 nm (p–v).
An evaporation source for ion beam assisted deposition in ultrahigh vacuum
Authors: Kirschner J. , Engelhard H. , Hartung D.
Published: October 2002

We describe the design, construction, and operation of an ion beam assisted deposition source for molecular beam epitaxy in ultrahigh vacuum. At a typical deposition rate of a monolayer per minute, the source may be operated in each of five modes: using self-ions from the vapor, self-ion plus noble gas ions from an additional gas inlet, both pulsed or continuous, or with complete suppression of ions. The source is based on electron bombardment heating of a metal rod or a crucible while the ions generated from the vapor are focused electrostatically onto the sample. Additional ions may be extracted from a noble gas stream injected into the ionization region. Examples for each of the different modes are given for Co deposition onto Cu(111), a system known to resist layer-by-layer growth.
Instrumentation for the analysis of respiratory system disorders during sleep: Design and application
Authors: de Melo Pedro Lopes , de Andrade Lemes Lucas Neves
Published: October 2002

Sleep breathing disorders are estimated to be present in 2%–4% of middle-aged adults. Serious adverse consequences, such as systemic arterial hypertension, myocardial infraction, and cerebrovascular disease, can be related to these conditions. Intellectual deficits associated with attention, memory, and problem-solving have also been associated with a poor quality of sleep. The main causes of these disorders are obstructions resulting from repetitive narrowing and closure of the pharyngeal airway, which have been monitored by indirect measurements of temperature, displacement, and other highly invasive procedures. The measurement of mechanical impedance of the respiratory system by the forced oscillation technique (FOT) has recently been suggested to quantify the respiratory obstruction during sleep. It is claimed that the noninvasive and dynamic characteristics of this technique would allow a noninvasive and accurate analysis of these events. In spite of this high scientific and clinical potential, there is no detailed description of a complete instrumentation system to implement this promising technique in sleep studies. In this context, the purpose of this study was twofold: (1) describe the development of a new computer-based system for identification of the mechanical impedance of the respiratory system during sleep by the FOT and (2) evaluate the performance of this device in the description of respiratory events in conditions including no, mild, serious disease, and therapeutic procedures. These evaluations confirmed the desirable features achieved in laboratory tests and the high scientific and clinical potential of this system.
A precision method for laser focusing on laser beam induced current experiments
Authors: Poce-Fatou J. A. , Martı́n J. , Alcántara R. , Fernández-Lorenzo C.
Published: October 2002

Using the laser beam induced current (LBIC) technique for the study of solar cells and photovoltaic devices, it is possible to obtain images representing the different degrees of quantum efficiency observed on the surface of these elements. Since the resolution of these images depends on the size of the spot used, the laser beam is directed through a focusing lens, which allows us to obtain significantly small sizes. This article puts forward a method for precise focusing of the laser beam used in the LBIC study of photovoltaic devices by analyzing line scans over sharp structures. The technique is applied to characteristic heterogeneities of solar cells such as the fingers used to collect the induced current, the grain boundaries characteristic of polycrystalline solar cells, and the small surface areas with a quantum efficiency different from that of its adjacent areas. The validity of the proposed method has been evaluated by carrying out virtual experiments where the focusing technique has been applied to heterogeneities reproducing the ones we mentioned above. A criterion for calculating the Gaussian diameter of the laser spot using LBIC signal analysis is also discussed in this work from a theoretical point of view.
Three-axis superconducting gravity gradiometer for sensitive gravity experiments
Authors: Moody M. Vol , Paik Ho Jung , Canavan Edgar R.
Published: October 2002

Superconducting differential accelerometers have been used to test Newton’s inverse square law and have been proposed for other sensitive experiments. These include searches for spin-mass coupling, detecting Earth’s gravitomagnetic field, and testing the Equivalence Principle. This article discusses the principle and performance of a sensitive three-axis gravity gradiometer. This device utilizes quantized flux and the Meissner effect to provide stable test mass levitation and signal coupling, and superconducting quantum interference devices to provide very low-noise amplification of the signals. The instrument comprises a total of nine superconducting accelerometers, six linear and three angular. This configuration permits simultaneous measurement of the diagonal components of the gravity gradient tensor as well as platform acceleration in all six degrees of freedom. An analysis of this instrument is presented along with experimental results. Methods to correct for various motion-induced errors are demonstrated. Other error sources are also discussed. The resulting performance of the superconducting gravity gradiometer is 2×10−11 s−2 Hz−1/2.
Ion and electron beam assisted growth of nanometric SimOn structures for near-field microscopy
Authors: Sánchez E. J. , Krug J. T. , Xie X. S.
Published: October 2002

We report the fabrication of nanometric, conformal, smooth dielectric coatings on the ends of apertureless near-field optical probes by both ion beam and electron beam assisted deposition techniques (IBAD and EBAD). The ion beam provides a higher SimOn growth rate than the electron beam, though the undesirable implantation of Ga ions may outweigh the benefits of rapid growth. Wavelength dispersive x-ray spectroscopy reveals that the electron beam deposited dielectric has a stoichiometry of SinO2n. We present two near-field optics applications of EBAD and IBAD grown dielectric layers. EBAD deposited coatings can be used to reduce fluorescence quenching in apertureless near-field scanning optical microscopy, while IBAD fabricated structures are suited for micro/nano-optics.
Vibration isolation with magnet springs
Authors: Puppin Ezio , Fratello Vincenzo
Published: October 2002

We describe a vibration isolation apparatus where four couples of repelling magnets ensure the loading force to a suspended table. This table is mechanically confined within its otherwise unstable equilibrium position with four ball bearings connected to the table and sliding along four vertical shafts. The vibration isolation efficiency of this device is excellent and its performances can be directly compared to those attained with state of the art optical tables at a fraction of their cost and weight. Another advantage is that no external supply of energy or compressed air is needed.
Reactive sputter deposition of alumina thin films using a hollow cathode sputtering source
Authors: Pradhan Anshu A. , Shah S. Ismat , Unruh Karl M.
Published: October 2002

Reactive sputtering allows deposition of insulating compounds that cannot be easily prepared using conventional dc sputtering methods. However, this technique suffers from problems related to the poisoning of the target and associated hysteresis effects. In addition, the operating conditions that yield the highest growth rate are unstable, and feedback control is required to maintain the system at the optimal operating point. In order to address some of these issues, we have developed a new hollow cathode sputtering (HCS) source. In addition to the inherent advantages of high deposition rates and the capability for coating complex surfaces, we have found that the hollow cathode sputtering source does not exhibit the hysteresis behavior generally observed in planar reactive sputtering systems and is stable at all operating points without feedback control. We have characterized a HCS source for reactively depositing alumina thin films. The deposition rate increases on increasing the oxygen concentration. Pure alumina thin films can be deposited with high growth rates at very low-power densities.
Femtosecond electron ejection in liquid acetonitrile: Evidence for cavity electrons and solvent anions
Authors: Xia Chungeng , Peon Jorge , Kohler Bern
Published: October 2002

Excess electrons were studied in liquid acetonitrile at room temperature by femtosecond pump–probe spectroscopy. Using ≈200 fs, 265 nm laser pulses, electrons were ejected into the liquid by photodetachment from iodide ions and, in separate experiments, by photoionization of indole. A strong and broad absorption band with a maximum near 1400 nm was observed in both systems. A second absorption band was observed at wavelengths below 620 nm for iodide solutions, but was not seen in photoexcited indole due to overlapping excited state absorption. The bands are in good agreement with ones seen previously in nanosecond pulse radiolysis experiments [I. P. Bell, M. A. J. Rodgers, and H. D. Burrows, J. Chem. Soc., Faraday Trans. 1 73, 315 (1977)]. Bell, Rodgers, and Burrows assigned the visible and IR bands to absorption by acetonitrile dimer and monomer anions, respectively. Our results strongly question this interpretation. Instead, we assign the short-wavelength absorption band to a solvent-bound valence anion consisting of one or two acetonitrile molecules and the IR band to a solvated or cavity electron. Low-level quantum chemical calculations indicate that valence anion formation is strongly correlated with CCN bending, but do not provide a clear indication of whether a monomer or dimer valence anion is favored. The highly mobile cavity electron is scavenged by added chloroform at a bimolecular reaction rate of (1.02±0.03)×1011 M−1 s−1. The appearance of both absorption bands within our time resolution suggests that the two forms of the excess electron are produced by prompt reaction with the iodide charge-transfer-to-solvent (CTTS) excited state. In support of this mechanism, strong static scavenging by chloroform was observed at both visible and IR wavelengths. For iodide in acetonitrile, the signal in the IR decays biexponentially due to competition between geminate recombination of the cavity electron with the parent iodine atom and its reaction with the solvent. Geminate recombination between the solvated electron and the parent iodine atom occurs with a characteristic time constant of ≈30 ps, while additional solvent anions are formed in a slow reaction with a time constant of ≈260 ps. Approximately 30% of the solvated electrons photodetached from iodide undergo geminate recombination. There is no evidence for geminate reaction between the promptly formed solvent anion and iodine, suggesting that these species are formed at larger initial separation than the IR-absorbing cavity electron/iodine atom pair. In indole, geminate recombination occurs on a slower time scale of ≈135 ps.
An ab initio parametrized interatomic force field for silica
Authors: Tangney P. , Scandolo S.
Published: October 2002

We present a classical interatomic force field for liquid SiO2 which has been parametrized using the forces, stresses and energies extracted from ab initio calculations. We show how inclusion of more electronic effects in a phenomenological way and parametrization at the relevant conditions of pressure and temperature allow the creation of more accurate force fields. We compare the results of simulations with this force field both to experiment and to the results of ab initio molecular dynamics simulations and show how our procedure leads to comparisons which are greatly improved with respect to the most widely used force fields for silica.
The d 1Πg(v=1) Rydberg state of O2: Optical-optical double-resonance and Huggins-band ozone-photolysis, resonance-enhanced multiphoton-ionization studies with a b 1Σg+(v=0)-state platform
Authors: O’Keeffe P. , Ridley T. , Sheard H. A. , Lawley K. P. , Donovan R. J. , Lewis B. R.
Published: October 2002

Resonance-enhanced multiphoton-ionization spectra are presented of the d 1Πg←←b 1Σg+(1,0) transition of O2, the b(v=0) state generated both by photolysis of O3 in the Huggins bands and also by direct excitation of single J levels in an optical-optical double-resonance (OODR) experiment. The ozone-photolysis-derived spectra reveal a preferential formation of b(v=0) fragments with high J, the rotational distributions exhibiting significant dependence on the photolysis wavelength. Rotational analyses of the OODR and ozone-photolysis-derived spectra indicate that the d(v=1) Rydberg state is multiply perturbed by successive vibrational levels of the II 1Πg valence state. The OODR technique allows the first full resolution of the low-J levels of d(v=1) and the high-J levels favored by the ozone-photolysis technique are reported here for the first time.
An examination of the five-site potential (TIP5P) for water
Authors: Lı́sal Martin , Kolafa Jiřı́ , Nezbeda Ivo
Published: October 2002

Parameterization of the five-site model (TIP5P) for water [M. W. Mahoney and W. L. Jorgensen, J. Chem. Phys. 112, 8910 (2000)] has been examined by several computer simulation methods accounting properly for long-range forces. The structural and thermodynamic properties at a pressure of 1 atm over the temperature range (−25 °C,+75 °C) and the vapor–liquid coexistence have been determined. It is shown that the simple spherical cutoff method used in the original simulations to find optimized parameters of this five-site model yields results that differ from those obtained by both the Ewald summation and reaction field methods. Consequently, the pivot property to which the parameters were adjusted, the location of the density maximum at 1 atm, does not agree with experimental values. The equilibrium properties then show only a fair agreement with experimental data and are uniformly inferior to those of the four-site TIP4P water over the entire coexistence range.
Ab initio molecular dynamics: Propagating the density matrix with Gaussian orbitals. III. Comparison with Born–Oppenheimer dynamics
Authors: Schlegel H. Bernhard , Iyengar Srinivasan S. , Li Xiaosong , Millam John M. , Voth Gregory A. , Scuseria Gustavo E. , Frisch Michael J.
Published: October 2002

In a recently developed approach to ab initio molecular dynamics (ADMP), we used an extended Lagrangian to propagate the density matrix in a basis of atom centered Gaussian functions. Results of trajectory calculations obtained by this method are compared with the Born–Oppenheimer approach (BO), in which the density is converged at each step rather than propagated. For NaCl, the vibrational frequency with ADMP is found to be independent of the fictitious electronic mass and to be equal to the BO trajectory result. For the photodissociation of formaldehyde, H2CO→H2+CO, and the three body dissociation of glyoxal, C2H2O2→H2+2CO, very good agreement is found between the Born–Oppenheimer trajectories and the extended Lagrangian approach in terms of the rotational and vibrational energy distributions of the products. A 1.2 ps simulation of the dynamics of chloride ion in a cluster of 25 water molecules was used as a third test case. The Fourier transform of the velocity–velocity autocorrelation function showed the expected features in the vibrational spectrum corresponding to strong hydrogen bonding in the cluster. A redshift of approximately 200 cm−1 was observed in the hydroxyl stretch due to the presence of the chloride ion. Energy conservation and adiabaticity were maintained very well in all of the test cases.
Vibrational spectroscopy of HOD in liquid D2O. II. Infrared line shapes and vibrational Stokes shift
Authors: Lawrence C. P. , Skinner J. L.
Published: October 2002

We present semiclassical calculations of the infrared line shapes for the three intramolecular vibrations of dilute HOD in liquid D2O. In these calculations the vibrations of HOD are treated quantum mechanically, and the rotations and translations of all the molecules are treated classically. The approach and model, which is based on earlier work of Oxtoby and of Rey and Hynes, was discussed in detail in Paper I, on vibrational energy relaxation in the same system, of this series. A novel feature of our approach is a self-consistent renormalization scheme for determining the system and bath Hamiltonians for a given vibrational state of the HOD molecule. Our results for the line shapes are in reasonable agreement with experiment. We also explore the extent to which the frequency fluctuations leading to the line shape are Gaussian. Finally, we calculate the vibrational Stokes shift for the OH stretch fundamental. Our result, which is nonzero only because the specification of the bath Hamiltonian depends on the vibrational state of the HOD molecule (as a result of the self-consistent renormalization scheme), is 57 cm−1, in good agreement with the experimental number of 70 cm−1.
Finite-size and surface effects on the glass transition of liquid toluene confined in cylindrical mesopores
Authors: Morineau Denis , Xia Yongde , Alba-Simionesco Christiane
Published: October 2002

Some of the most regular porous silicates (MCM-41 and SBA-15), with several different pore diameters from 2.4 to 8.7 nm, are used to study the van der Waals fragile liquid toluene in confined geometry. We measure two major macroscopic signatures of a glass transition, i.e., a discontinuous change in the heat capacity and in the thermal expansion, by adiabatic calorimetry and neutron scattering experiments. A nontrivial size dependence of the glass transition features, most notably a nonmonotonic variation of the mean glass transition temperature, is observed. The range of the glass transition is found extremely broad. This supports the notion of competition between surface boundary conditions and cutoff or finite-size effects.
Fourier moment analysis of velocity-map ion images
Authors: Bass Mark J. , Brouard Mark , Clark Andrew P. , Vallance Claire
Published: October 2002

An alternative to inverse Abel transform and forward convolution methods is presented for extracting dynamical information from velocity-map ion images. Unlike most competing methods, that presented here does not require the probed three-dimensional distribution to possess cylindrical symmetry. The new method involves analysis of the Fourier moments of images measured in different experimental geometries, and allows speed distributions, angular differential cross sections, and angular momentum alignment and orientation to be determined from raw images of the products of photodissociation and photon-initiated bimolecular reactions. The methodology is developed within the semiclassical framework of Dixon’s bipolar moment formalism [R. N. Dixon, J. Chem. Phys. 85, 1866 (1986)], although it is equally applicable to other common formulations of the product scattering distribution. To allow a comparison of the method with the Abel inversion, which requires that the velocity distribution of the probed product has an axis of cylindrical symmetry, the method is applied to newly acquired experimental images of atomic chlorine produced in the photolysis of NOCl. Extraction of product rotational alignment information is illustrated using newly acquired images of rotationally aligned NO formed by NO2 photolysis. Application of the Fourier moment methodology to studies of bimolecular reactions is also demonstrated, using simulated images for the reaction H+D2→HD(v=0,j=0,9)+D.
Scanning μ-superconduction quantum interference device force microscope
Authors: Veauvy C. , Hasselbach K. , Mailly D.
Published: October 2002

A scanning probe technique is presented: Scanning μ-superconducting quantum interference device (SQUID) force microscopy (SSFM). The instrument features independent topographic and magnetic imaging. The force microscope uses a piezoelectric quartz tuning fork as the detector and magnetic imaging is obtained by scanning μ-SQUID microscopy. The μ-SQUID is placed at the edge of a silicon chip attached to the tuning fork. A topographic vertical resolution of 0.02 μm is demonstrated and magnetic flux as weak as 10−3 Φ0 is resolved with a 1 μm diameter μ-SQUID loop. The SSFM operates in a dilution refrigerator in a cryogenic vacuum. Sample and probe can be cooled to 0.45 K.
Measurements of anisotropic thermoelectric properties in superlattices
Authors: Yang B. , Liu W. L. , Liu J. L. , Wang K. L. , Chen G.
Published: October 2002

Thermoelectric properties, i.e., thermal conductivity, electrical conductivity, and the Seebeck coefficient, have been measured in the directions parallel (in-plane) and perpendicular to the interface of an n-type Si(80 Å)/Ge(20 Å) superlattice. A two-wire 3ω method is employed to measure the in-plane and cross-plane thermal conductivities. The cross-plane Seebeck coefficient is deduced by using a differential measurement between the superlattice and reference samples and the cross-plane electrical conductivity is determined through a modified transmission-line method. The in-plane thermal conductivity of the Si/Ge superlattice is 5–6 times higher than the cross-plane one, and the electrical conductivity shows a similar anisotropy. The anisotropy of the Seebeck coefficients is smaller in comparison to electrical and thermal conductivities in the temperature range from 150 to 300 K. However, the cross-plane Seebeck coefficient rises faster with increasing temperature than that of the in-plane direction.
Anisotropic lattice models of electrolytes
Authors: Kobelev Vladimir , Kolomeisky Anatoly B.
Published: October 2002

Systems of charged particles on anisotropic three-dimensional lattices are investigated theoretically using Debye–Hückel theory. It is found that the thermodynamics of these systems strongly depends on the degree of anisotropy. For weakly anisotropic simple cubic lattices, the results indicate the existence of order–disorder phase transitions and a tricritical point, while the possibility of low-density gas–liquid coexistence is suppressed. For strongly anisotropic lattices this picture changes dramatically: The low-density gas–liquid phase separation reappears and the phase diagram exhibits critical, tricritical, and triple points. For body-centered lattices, the low-density gas–liquid phase coexistence is suppressed for all degrees of anisotropy. These results show that the effect of anisotropy in lattice models of electrolytes amounts to reduction of spatial dimensionality.
Coiling-chirality changes in carbon microcoils obtained by catalyzed pyrolysis of acetylene and its mechanism
Authors: Yang Shaoming , Chen Xiuqin , Motojima Seiji
Published: October 2002

As can be seen in the double helix of DNA, the single helix of proteins, etc., the three-dimensional (3D) helical/spiral structure is a fundamental structure of living things, and affords them critical functionalities. Helically coiled carbon fibers, which usually take the peculiar form of either a microcoil or a helix or twisted form, referred to as “carbon microcoils hereafter,” are of great interest due to their novel functionality and various potential applications. They can potentially be used in electromagnetic absorbers and/or filters, 3D composites, smart tunable electrical devices, microsensors, chiral catalysts, etc.
Self-aligned gated field emission devices using single carbon nanofiber cathodes
Authors: Guillorn M. A. , Melechko A. V. , Merkulov V. I. , Hensley D. K. , Simpson M. L. , Lowndes D. H.
Published: October 2002

We report on the fabrication and operation of integrated gated field emission devices using single vertically aligned carbon nanofiber (VACNF) cathodes where the gate aperture has been formed using a self-aligned technique based on chemical mechanical polishing. We find that this method for producing gated cathode devices easily achieves structures with gate apertures on the order of 2 μm that show good concentric alignment to the VACNF emitter. The operation of these devices was explored and field emission characteristics that fit well to the Fowler–Nordheim model of emission was demonstrated.
Exciton formation dynamics in crescent-shaped Quantum Wires
Authors: Yasuhira T. , Komori K. , Akimoto R. , Wang X. L. , Watanabe M. , Ogura M.
Published: October 2002

We have investigated the ultrafast carrier dynamics in optically high-quality V-grooved GaAs/AlGaAs quantum wires using a highly sensitive nonlinear spectroscopy technique. It is found that, with resonant excitation, there is a blueshift due to exciton–exciton interaction within 0.3 ps followed by a redshift due to exciton relaxation. With nonresonant excitation, the redshift occurs due to the phonon emission during exciton formation. As a result, the exciton formation time and the exciton lifetime in the quantum wires are found to be 5 and 110 ps, respectively.
Control of magnetization reversal process with pinning layer in FePt thin films
Authors: Zhao Z. L. , Wang J. P. , Chen J. S. , Ding J.
Published: October 2002

The magnetization reversal processes of in situ ordered FePt thin films prepared by magnetron sputtering have been studied. A kind of nonmagnetic Ru pinning layer inserted in the FePt magnetic layer was described to introduce controllable pinning sites. The magnetization reversal mechanism of FePt thin films was observed to shift from the typical domain-wall motion behavior to the nucleation mode with Ru pinning layer inserted. Coercivity enhancement was also observed with relative thinner Ru pinning layer inserted in the FePt film.
Effect of high-density plasma etching on the optical properties and surface stoichiometry of ZnO
Authors: Ip K. , Baik K. H. , Overberg M. E. , Lambers E. S. , Heo Y. W. , Norton D. P. , Pearton S. J. , Ren F. , Zavada J. M.
Published: October 2002

Bulk, single-crystal ZnO was etched in Cl2/Ar and CH4/H2/Ar inductively coupled plasmas as a function of ion impact energy. For CH4/H2/Ar, the etch rate (R) increases with ion energy (E) as predicted from a model of ion enhanced sputtering by a collision–cascade process, R∝(E0.5−ETH0.5), where the threshold energy, ETH, is ∼96 eV. Band edge photoluminescence intensity decreases with incident ion energy in both chemistries, with a 70% decrease even for low energies (∼116 eV). Surface roughness is also a function of ion energy with a minimum at ∼250 eV, where Auger electron spectroscopy shows there is no measurable change in near-surface stoichiometry from that of unetched control samples.
How to affect stacking fault energy and structure by atom relaxation
Authors: Cai J. , Lu C. , Yap P. H. , Wang Y. Y.
Published: October 2002

By a simulated annealing method with a parameterized tight-binding potential, the properties of structure and energy of a generalized stacking fault are investigated. It is shown that for metal Pd, the second-layer spacing from the stacking fault plane expands initially and then contracts with the variation of the stacking fault variable from 0 to 1. The effect of atom relaxation on stacking fault energy is shown to be small. For another metal Pt, the second-layer spacing contracts and the effect of atom relaxation on the stacking fault energy is found to be obvious. In addition, the calculated stacking fault energy is in agreement with experimental results for the two metals.
High epitaxial quality Y2O3 high-κ dielectric on vicinal Si(001) surfaces
Authors: Apostolopoulos G. , Vellianitis G. , Dimoulas A. , Alexe M. , Scholz R. , Fanciulli M. , Dekadjevi D. T. , Wiemer C.
Published: October 2002

Thin films of Y2O3 were grown by molecular-beam epitaxy on silicon aiming at material with adequate crystal quality for use as high-κ gate replacements in future transistors. It was found that Y2O3 grows in single-crystalline form on 4° misoriented Si(001), due to an in-plane alignment of 〈110〉Y2O2 to the silicon dimer direction. The Y2O3 layers exhibit a low degree of mosaicity, a small proportion of twinning and sharp interfaces. This represents a significant improvement compared to material grown on exact silicon surfaces.
Scanning Kelvin force microscopy imaging of surface potential variations near threading dislocations in GaN
Authors: Hsu J. W. P. , Ng H. M. , Sergent A. M. , Chu S. N. G.
Published: October 2002

Scanning Kelvin force microscopy is applied to study the charge nature of threading dislocations on GaN surfaces. On the oxidized surface, the surface potential maps show little change near dislocations, indicating that if the dislocations are charged in the bulk, the charges are either screened or depleted due to band bending. After cleaning in hot H3PO4, the potential near dislocations located at domain boundaries and inside domains is found to be lower, consistent with excess local negative fixed charges. Curiously, no contrast was seen for the screw dislocations at the centers of growth spirals even after H3PO4 treatment. Thus, either these screw dislocations have no gap states, or if they do have gap states, the positions are higher in energy (closer to conduction band edge) than the gap states of other dislocations.
Reduction of effective dielectric constant of gate insulator by low-resistivity electrodes
Authors: Saito Kunio , Jin Yoshito , Shimada Masaru
Published: October 2002

On metal–oxide–semiconductor capacitors, the effective dielectric constant (keff) values extracted from high-frequency capacitance–voltage measurements were found to decrease when gate electrodes of very low resistivity were used. The equivalent-oxide thickness increase reaches about 1 nm with the low-resistivity electrodes. We examined gate insulators of SiO2, Al2O3, and HfO2 and gate electrodes of Al, TiN, Au, Cr, and TaN. The equivalent-oxide thickness increase can be prevented by inserting a high-resistivity metal film only 0.3 nm thick between the very low-resistivity metal and the insulator. The present results suggest that keff is reduced by the screening of ionic insulators with free electrons of the metal due to a quantum effect.
Lateral diffusion of titanium disilicide as a route to contacting hybrid Si/organic nanostructures
Authors: Palermo V. , Buchanan M. , Bezinger A. , Wolkow R. A.
Published: October 2002

We characterized microscopic patterns of TiSi2 using atomic force microscopy and scanning tunneling microscopy, to test the possibility of using silicide contacts for experiments on the nanoscopic scale. We observed the effect on the morphology of incomplete formation of the disilicide, and studied the growth of lateral extension due to atomic diffusion. Upon diffusion, the silicide forms a neat and clean interface some hundreds of nanometers from the bulk electrode. That spreading phenomenon is our central focus, as we believe it may be useful in future efforts to make narrowly spaced contacts.
Atomic and electronic structures of doped grain boundaries in SrTiO3
Authors: Chang Hyunju , Choi Youngmin , Lee Jae Do , Yi Hongsuk
Published: October 2002

The atomic and electronic structures of pristine, Mn- and Nb-doped grain boundaries in SrTiO3 are investigated by atomistic simulations and cluster calculations. The atomic structures of (310) symmetric tilt grain boundaries in SrTiO3 are determined by atomistic simulation using empirical potentials. The defect energies of Mn(Nb)-doped models are calculated and discussed in relation to the concentration profiles of Mn(Nb) in SrTiO3 grain boundaries. The local electronic structures near Mn(Nb)-doped grain boundaries in SrTiO3 are determined using embedded cluster calculations based on the density functional theory. The charge density of each system is calculated to elucidate the electronic structure of the grain boundary. The calculation results agree well with previous experimental observations of the atomic structures and grain boundary charges near the Mn(Nb)-doped grain boundary in SrTiO3.
Nanoscale wire formation on sputter-eroded surfaces
Authors: Kim J. , Kahng B. , Barabási A.-L.
Published: October 2002

Rotated ripple structures (RRS) on sputter-eroded surfaces are potential candidates for nanoscale wire fabrication. We show that the RRS can form when the width of the collision cascade in the longitudinal direction is larger than that in the transverse direction and the incident angle of ion beam is chosen in a specific window. By calculating the structure factor for the RRS, we find that they are more regular and their amplitude is more enhanced compared to the much studied ripple structure forming in the linear regime of sputter erosion.
Ferroelectric BaPbO3/PbZr0.53Ti0.47/BaPbO3 heterostructures
Authors: Liang Chun-Sheng , Wu Jenn-Ming , Chang Ming-Chu
Published: October 2002

BaPbO 3  (BPO)/PbZr0.53Ti0.47 (PZT)/BPO heterostructures were fabricated by combining the sol-gel and rf-magnetron sputtering techniques. Experimental results indicate that the BPO bottom electrodes effectively prevent the formation of the rosette structure of PZT, producing smooth surfaces. Additionally, ferroelectric, fatigue, and leakage current properties were markedly improved when both the top and the bottom electrodes were changed from Pt to BPO. These improvements are due to a superior electrode/ferroelectric interface. BPO is better than Pt and other oxide electrodes for use in PZT ferroelectric capacitors due to its remarkably improved properties and quite low growth temperature.
Potential sputtering of proton from hydrogen-terminated Si(100) surfaces induced with slow highly charged ions
Authors: Kuroki K. , Okabayashi N. , Torii H. , Komaki K. , Yamazaki Y.
Published: October 2002

A potential sputtering mechanism of hydrogen has been studied for impact of slow highly charged Xeq+ ions (<5 keV, q=4–12) on well-defined H-terminated Si(100) surfaces. It was found that the sputtering yields of protons are proportional to qγ (γ∼5), independent of the surface condition, that is, for both Si(100)2×1-H surface and Si(100)1×1-H surface. The yield for Si(100)1×1-H surface was ten times larger than that for Si(100)2×1-H surface, although the H coverage of the former is only twice the latter. Surface roughness is found to be the key parameter to vary the yield, and also to influence the energy distribution of sputtered protons. These findings are consistently explained with a pair-wise bond-breaking model induced by a double electron capture, where the classical over barrier process plays an essential role.
Prevention of electric breakdown during ion bombardment of organic insulators using a cluster ion beam
Authors: Hirata K. , Saitoh Y. , Narumi K. , Kobayashi Y.
Published: October 2002

The charge accumulation processes of an organic insulator during monoatomic ion C1+ and cluster ion C8+ bombardments were studied by simultaneously measuring the target and secondary emission currents as functions of atomic dose. A series of abrupt changes in the currents was observed during C1+ bombardment, indicating repeated charge accumulation and electric breakdown. For C8+ bombardment, the emitting current was equilibrated with the injecting current at a dose of about 1013 atoms/cm2. The charge equilibrium prevented subsequent charge accumulation on the target and electric breakdown. By combining the cluster bombardment with the application of a suitable external electric field upon the target, the charge accumulation problem was completely eliminated.
Fabrication of nanometric single zinc and zinc oxide dots by the selective photodissociation of adsorption-phase diethylzinc using a nonresonant optical near field
Authors: Yatsui T. , Kawazoe T. , Ueda M. , Yamamoto Y. , Kourogi M. , Ohtsu M.
Published: October 2002

We demonstrated a deposition of nanometer-scale Zn dots using the selective photodissociation of adsorption-phase diethylzinc with a nonresonant optical near field, where the photon energy is lower than that of the absorption edge of gas-phase diethylzinc. We achieved nanometric prenucleation by dissociating diethylzinc molecules adsorbed on a substrate. Subsequent deposition was performed by dissociating the adsorbed molecules on the prenucleated Zn. The topographic image of the deposited Zn dot had a full width at half maximum (FWHM) of 25 nm. Furthermore, the photoluminescence intensity distribution from a single ZnO dot fabricated using laser annealing had a FWHM of 85 nm.
Contactless measurement of electrical conductivity of semiconductor wafers using the reflection of millimeter waves
Authors: Ju Yang , Inoue Kojiro , Saka Masumi , Abé Hiroyuki
Published: October 2002

We present a method for quantitative measurement of electrical conductivity of semiconductor wafers in a contactless fashion by using millimeter waves. A focusing sensor was developed to focus a 110 GHz millimeter wave beam on the surface of a silicon wafer. The amplitude and the phase of the reflection coefficient of the millimeter wave signal were measured by which electrical conductivity of the wafer was determined quantitatively, independent of the permittivity and thickness of the wafers. The conductivity obtained by this method agrees well with that measured by the conventional four-point-probe method.