bluuebunny/crossref_metadata_2025 huggingface dataset:
Study on the transition temperature and phase formation sequence in TiZr silicides on Si(100)
Authors: Cha Taeho , Yoon Sanghyun , Lee Dongkun , Ryu Hyun , Lee Hwackjoo , Kim Changsoo , Jeon Hyeongtag
Published: July 2002

We studied the (Ti1−xZrx) silicides with various Zr atomic compositions (x=0.1, 0.3, 0.6). The effects of Zr contents on the transition (C49→C54) temperature, phase sequence, and suppression of agglomeration in TiZr alloy silicide were investigated. We codeposited the Ti and Zr films of 40 nm thickness with an e-beam evaporator in high vacuum and annealed ex situ at temperatures between 600 and 900 °C in 100 °C increments. The phase identification of TiZr silicides was carried out by x-ray diffraction (XRD) and the chemical analysis by Auger electron spectroscopy. The interface morphologies and electrical properties were investigated by the cross-sectional transmission electron microscopy and four-point probe, respectively. The increase in transition temperature was observed with increasing Zr content. TiZr alloy monosilicide was detected by XRD in the Zr composition of 60% of (TiZr) silicide at temperatures below 700 °C and finally transformed to C49 (TiZr) disilicide at temperatures above 800 °C. The interface and surface roughnesses were improved with increasing Zr content and, consistently, the resistivity of TiZr alloy silicide was decreased to μΩ due to the silicide formation and the suppression of silicide agglomeration.
Displacements parallel to the surface of reconstructed GaAs(110)
Authors: Duke C. B. , Paton A.
Published: July 2002

Analysis of measured elastic low energy electron diffraction (ELEED) intensities from GaAs(110) reveals that the relaxations parallel to the surface associated with a ω1=29° bond-length-conserving rotated surface structure can be reduced by 75% without substantially affecting the quality of the model description of these intensities. Optimizing the surface geometry while constraining the atomic displacements parallel to the surface to be zero, however, leads to a significantly inferior description of these data. A model embodying greatly reduced but nonzero parallel displacements is compatible both with the ELEED intensities and with recent ion channeling data.
Characteristics of a helium field ion gun
Authors: Konishi Morikazu , Takizawa Masaaki , Tsumori Toshiro
Published: July 2002

A helium field ion gun for a focused ion beam system was designed and constructed. The main feature of the ion gun structure is the use of a gas jet nozzle with a tungsten field emitter tip near the nozzle end. Since the helium gas jet is collimated towards the emitter tip, the local pressure in the vicinity of the tip is kept 110 times higher than the value for the location of the ion gauge which is about 20 cm away from the helium jet ion gun. Using this ion gun, current density of 1 μA/sr was obtained although the helium gas flow rate ejected from the nozzle is as small as 1.6×10−3 Torr l/s. This result indicates high efficiency of the helium gas supply to the emitter tip surface.
Advanced dynamic process simulation for an excimer laser lithography
Authors: Ohfuji Takeshi , Nalamasu Omkaram , Stone Douglas R.
Published: July 2002

This article proposes a dynamic process window matrix for effective lithography development based on accurate resist profile simulation. This process window is defined on an exposure dose-defocus plane as the area that is determined by linewidth error and sidewall angle at the resist thicknesses corresponding to the maximum and minimum linewidths. This window concept can give a practical process margin, since standing wave effects are also taken into consideration. This method is applied to the analysis of chemically amplified resist system for KrF excimer laser lithography.
Scanning tunneling microscopy of proteins of the immunoglobulin super family
Authors: Rocca-Serra Jose , Thimonier Jean , Chauvin Jean-Paul , Barbet Jacques
Published: July 2002

Three different members of the immunoglobulin super-family have been studied. An antibody molecule, prototype of the family, directed against Thy-1, another member of the family, was seen as a V shaped structure, as expected. The corresponding antigen, Thy-1, was imaged at different resolutions. Then, the complex of the two molecules was analyzed and distinctive structures corresponding to each of the two partners were observed. The third member of the family, CD4, was seen as a string of four beads, linearly disposed. Further work needed to draw more detailed conclusions on this family is in progress.
Two-directional dynamic mode force microscopy: Detection of directional force gradient
Authors: Watanabe S. , Hane K. , Ito M. , Goto T.
Published: July 2002

In this article, we report the theoretical and experimental investigations on a dynamic mode force microscopy for detecting the force gradients in two directions. The motion of the probe oscillated in two directions was analyzed on the basis of the mechanical dynamics theory to provide the ability of detecting the force gradient in vertical and lateral directions separately. When the spring constants of the cantilever probe in two orthogonal directions were different, the gradients of the attractive forces acting in two orthogonal directions were detected separately from the resonant frequency shifts. The theoretical consideration was confirmed by the experiment in which the gradients of electrostatic force acting on a fine electrode sample were measured.
Study of ion bombardment induced vacancy islands on Au(100) by scanning tunneling microscopy
Authors: Gauthier S. , Samson Y. , Girard J. C. , Rousset S. , Klein J.
Published: July 2002

The influence of the anisotropy of the (5×n) reconstructed (100) face of gold on the generation of vacancy islands by sputtering with 600 eV Ar+ ions has been investigated by scanning tunneling microscopy. The shapes of these islands, bounded by monoatomic steps, are shown to be growth shapes, rather than equilibrium shapes. The growth mechanisms leading to these shapes are discussed.
Scanning tunneling microscopy of Co on Pt(111)
Authors: Grütter P. , Dürig U. T.
Published: July 2002

The initial nucleation and subsequent growth of vapor-deposited Co on Pt(111) has been studied by scanning tunneling microscopy. The characteristic differences observed for films grown at room temperature, after annealing, and when grown at elevated substrate temperatures clearly demonstrate the delicate balance between thermodynamic equilibrium and kinetic constraints.
Scanning tunneling microscopy study of model catalysts obtained by cluster beam deposition of palladium onto highly oriented pyrolitic graphite
Authors: Cadete Santos Aires F. J. , Sautet P. , Rousset J.-L. , Fuchs G. , Mélinon P.
Published: July 2002

Cluster beam deposition is used to obtain model catalysts (palladium on highly oriented pyrolitic graphite). The supported particles are characterized by transmission electron microscopy (TEM) and scanning tunneling microscopy. Decoration of graphite steps and formation of groups of palladium particles on the graphite surface are imaged by TEM. High spatial resolution observations show periodic (√3×√3)R30° charge density modulations of graphite around the supported particles. Such modulations are explained following the work of Mizes and Foster [Science 244, 559 (1989)] that take into account the fact that the particles act as perturbations to the graphite wave functions. On the basis of this explanation, the interactions of palladium and platinum (Xhie et al., Phys. Rev. B 43, 8917 (1991)] with the HOPG are compared. The results of this comparison are in complete agreement with the different catalytic behavior of the two metals in presence of reactions of hydrogenation of unsaturated hydrocarbons.
Growth of iron on iron whiskers
Authors: Stroscio Joseph A. , Pierce D. T.
Published: July 2002

Real space views of the homoepitaxial growth of Fe on Fe(001) whiskers is reported, observed by scanning tunneling microscopy (STM), during the initial stages of growth. Scaling of the Fe island sizes and separation distributions are observed as a function of the diffusion rate to the deposition rate. A measure of the surface diffusion of the Fe atoms is obtained over the temperature range of 20–250 °C from the temperature dependence of the island density. The effect of the diffusion kinetics is also observed in the surface morphology as a decrease in surface roughness with increasing temperature in thin Fe films. A comparison of real and reciprocal space techniques is obtained from a comparison of STM images and reflection-high-energy-electron-diffraction measurements during growth.
Adsorbates in ambient operated scanning tunneling microscopy: Their appearance, mobility during scanning, and role in surface diffusion measurements
Authors: Campbell P. A. , Davis P. R. , Walmsley D. G.
Published: July 2002

Adsorbed species are commonly observed when operating a scanning tunneling microscope in an air environment. Often the quality of images is poor, characteristically appearing streaked, as the tip instantaneously interacts with the adsorbates during scanning. On other occasions, the adsorbates are imaged readily and by changing the tunneling parameters, may be forced to relocate, or in the extreme, may be evaporated by the action of the tunnel current. Furthermore, the subtleties of scanning tunneling microscope imaging allow the possibility of adsorbed species appearing not only as mounds, but as holes as well, depending on the value of the adsorbate work function relative to that of the underlying substrate. It is found that when a combination of both ‘‘mound-like’’ and ‘‘hole-like’’ adsorbate is present, there is a bias-dependent preference for the tip to interact with a particular type. A threshold field is also apparent for the passive removal of adsorbates. It is also found that the presence of adsorbates hinders the surface diffusion process.
Observation of vacuum-deposited naphthalocyanine molecules using scanning tunneling microscopy
Authors: Manivannan A. , Nagahara L. A. , Yanagi H. , Fujishima A.
Published: July 2002

Scanning tunneling microscopy has been used to investigate the molecular orientation of iron and cobalt naphthalocyanines (Ncs). FeNc molecules deposited onto NaCl at 250 °C grew in a squarelike pattern with a lattice spacing of approximately 1.5 nm; CoNc deposited under the same conditions showed a similar spacing of 1.5 nm, however, the structure was more columnlike. The difference in the structure is due to the orientation of the molecular planes. In the case of FeNc, the molecular planes are parallel to the NaCl substrate, whereas the CoNc molecules are lying perpendicular to the substrate.
Structure of nickel silicide on Si(001): An atomic view
Authors: Khang Yoonho , Kahng S. J. , Mang K. M. , Jeon D. , Lee J. H. , Kim Y. N. , Kuk Y.
Published: July 2002

The structure of epitaxially grown Ni silicide on Si(001) has been studied by scanning tunneling microscopy. Atomically resolved STM images of this surface show unreconstructed (1×1) NiSi2 islands and a (2×1) adsorbed Ni layer. The NiSi2 islands often contain twin boundaries with inverse pyramidal structures and ‘‘facet bars’’ at increased coverage. From observed images, it is suggested that the poor reproducibility in the Schottky barrier height of this interface originates from the complex interface structure.
Si donors (SiGa) in GaAs observed by scanning tunneling microscopy
Authors: Zheng J. F. , Liu X. , Weber E. R. , Ogletree D. F. , Salmeron M.
Published: July 2002

We report the direct observation of SiGa donors in the top six layers of GaAs(110). Surface SiGa has a localized electronic feature due to its dangling bond, while subsurface SiGa produces delocalized protrusions in filled and empty state scanning tunneling microscopy images, with a full width at half-maximum of ∼25 Å and a height from ∼0.2 to 2 Å, depending on the sample bias and location under the surface. The delocalized features of subsurface SiGa can be understood in terms of the perturbation of the local band structure by the Coulomb potential of SiGa.
Wigner glass on the magnetite (001) surface observed by scanning tunneling microscopy with a ferromagnetic tip
Authors: Wiesendanger R. , Shvets I. V. , Coey J. M. D.
Published: July 2002

A clean and well-ordered (001) surface of a slightly nonstoichiometric natural single crystal of magnetite has been prepared under ultrahigh vacuum conditions by in situ thermal annealing. The surface was carefully characterized by low energy electron diffraction, Auger electron spectroscopy, and x-ray photoelectron spectroscopy prior to our scanning tunneling microscope investigations. Atomic resolution was achieved by using either tungsten or in situ prepared ferromagnetic iron tips. In contrast to the results obtained with the tungsten tips, the ferromagnetic probe tips revealed an atomic-scale contrast between the different magnetic iron ions of magnetite on the octahedrally coordinated B sites which form static arrays of pairs with short-range order. The clean magnetite (001) surface appears to be in a Wigner glass state even at room temperature with electron pairs localized on adjacent ions as the basic unit. The degree of order is likely to be limited by the slight nonstoichiometry of the magnetite sample as deduced from temperature-dependent measurements of the electrical resistivity.
Local transformation of C60 fullerite into a new amorphous phase of carbon using a scanning tunneling microscope
Authors: Lang H. P. , Wiesendanger R. , Thommen-Geiser V. , Hofer R. , Güntherodt H.-J.
Published: July 2002

A scanning tunneling microscope (STM) has been used to locally transform C60 molecules of a C60 fullerite thin film on Au(111) into a new amorphous form of carbon by application of a pressure in the GPa range. From the vertical tip movement during the transformation process, the local collapse of two monolayers of C60 is inferred. Based on atomically resolved STM images of this ‘‘collapsed fullerite’’ (CF) structure, a pair correlation function characteristic of an amorphous structure with a nearest-neighbor peak at 2.7 Å is presented here. The two-dimensional power spectrum of the real-space data exhibits no spots but rings, which are attributed to first and second nearest-neighbor distances of the CF structure. An analysis of the number of nearest-neighbors of each atomic feature shows that about 50% of the atoms have in-plane bonds to one other atom, and 40% have bonds to two other atoms.
Lithographic evaluation of a positive-acting chemically amplified resist system under conventional and projection electron-beam exposures
Authors: Tarascon R. G. , Novembre A. E. , Bolan K. , Blakey M. , Knurek C. , Fetter L. , Huggins H. A. , Liddle J. A. , Nalamasu O.
Published: July 2002

New resist materials and processes are necessary to pattern sub-0.18 μm design rule circuits with advanced x-ray and electron-beam lithographic technologies. We have evaluated a new deep-ultraviolet multicomponent positive-acting chemically amplified resist (ARCH: advanced resist chemically amplified), that exhibits excellent resolution under deep-ultraviolet exposure, and furthermore an overcoat is not used to protect against any basic airborne contaminants. Different formulations of the resist system were studied with electron-beam lithography in an attempt to enhance sensitivity and maintain wide process latitude and high resolution. In our study we compare the lithographic characteristics of the resist under electron-beam exposure, with either a Cambridge EBMF vector scan system operating at 40 keV or a JEOL JBX-5DII system operating at 50 keV, to those obtained at 100 keV with a scattering with angular limitation projection electron lithography (SCALPEL) experimental tool. Using the direct write exposure tool at 50 keV, the basic resist formulation displayed a 0.09 μm resolution and a sensitivity of 25 μC/cm2. When an enhanced resist system was studied, a sensitivity of 9 μC/cm2 was displayed with comparable resolution. The resolution of the positive-acting resist material exposed with SCALPEL was not only affected by the writing tool, but also by the mask tone.
Effects of O2 addition to SiCl4/SiF4 and the thickness of the capping layer on gate recess etching of GaAs-pseudomorphic high electron mobility transistors
Authors: Murad S. K. , Cameron N. I. , Beaumont S. P. , Wilkinson C. D. W.
Published: July 2002

The effects of the addition of a small amount of O2 to SiCl4/SiF4 plasma and the thickness of the GaAs capping layer on gate recess etching of GaAs pseudomorphic high electron mobility transistor (p-HEMT) devices have been studied. During gate recessing of GaAs/AlGaAs p-HEMTs using a selective reactive ion etching (RIE) process in SiCl4/SiF4 plasma [see S. K. Murad, N. I. Cameron, P. D. Wang, S. P. Beaumont, and C. D. W. Wilkinson, Microelectron. Eng. 27, 439 (1995)], it was found that the profile of the gate changes dramatically from undercut to nearly vertical with no lateral etching when the thickness of the capping layer was reduced below 40 nm. This vertical profile puts the gate metal too close to the recess edges in devices with a ≤30 nm capping layer. The addition of a very small amount of O2 to SiCl4/SiF4 plasma was seen to increase GaAs etch rates remarkably, while maintaining the high selectivity over AlGaAs. This increase in the etch rate agrees well with optical emission spectroscopic observations which indicate that the Cl emission has increased by more than an order of magnitude for the addition of only 1.5% of O2 to SiCl4/SiF4 plasma. This selective RIE process of SiCl4/SiF4/O2 was applied to gate recess etching of GaAs/AlGaAs/InGaAs p-HEMTs with various capping layer thicknesses. The profile of the T gates changed from nearly vertical (with no undercut or gate offset) to undercut with a lateral etch rate depending on the thickness of the capping layer. The lateral etching rate also strongly depends on the O2 flow. The p-HEMT devices gate recessed using this process (SiCl4/SiF4/O2) exhibited an ft of 120 GHz, gm of 700 mS/mm and a gain of 9.5 dB at 94 GHz.
Evolution of surface morphology in the initial stage of nitridation of the Si(111)-7×7 surface by nitrogen ions
Authors: Sook Ha Jeong , Park Kang-Ho , Yun Wan Soo , Lee El-Hang , Park Seong-Ju
Published: July 2002

The evolution of surface morphology in the initial stage of nitridation of Si(111)-7×7 has been investigated by using a scanning tunneling microscope (STM) and low energy electron diffraction (LEED). The STM and LEED measurements were done on the Si(111) surface nitrided under different experimental conditions including the variations in the nitrogen ion energy, nitrogen ion dose, nitridation temperature, and the postannealing temperature. A growth mechanism of the silicon nitride layer in the initial stage was proposed based upon a comparison of the surface morphology obtained under different nitridation conditions. For the growth of uniform and large silicon nitride islands, it was necessary to have proper heat treatment of the surface. In particular, the surface postannealed at 980 °C after nitridation at 950 °C produced dramatically enlarged flat silicon nitride islands compared to that postannealed at the same temperature after nitridation at room temperature, and is probably due to improved mobilities of the reacting species with elevation of the nitridation temperature.
Electroluminescence from ZnSTe:Al alloy and investigation of local current distributions by conducting atomic force microscopy
Authors: Mao J. M. , Sou I. K. , Xu J. B. , Wilson I. H.
Published: July 2002

Electroluminescent devices have been fabricated by depositing Al-doped ZnSTe onto GaAs substrates by molecular beam epitaxy. A moderately bright blue-light emission was observed at room temperature. Electroluminescence spectra reveal that light emission is mostly from impact excitation of Te isoelectronic centers in these structures. Surface morphologies and concurrent current images by using conducting atomic force microscopy indicate electrical inhomogeneity in such structures. Nonuniform light emission may be inferred from nonuniform current distributions on the submicrometer scale.
Surface roughness development during photoresist dissolution
Authors: Flanagin Lewis W. , Singh Vivek K. , Willson C. Grant
Published: July 2002

The minimization of nanoscale roughness in patterned images has become a priority for the process of photolithography in the production of microprocessors. In order to probe the molecular basis for surface roughness, the development of photoresist has been simulated through application of the critical-ionization model to a three-dimensional molecular lattice representation of the polymer matrix. The model was adapted to describe chemically amplified photoresists of the sort now commonly used in microlithography. Simulations of the dependence of the dissolution rate and surface roughness on the degree of polymerization, polydispersity, and fractional deprotection agree with experimental results. Changes in surface roughness are shown to correlate with the length of the experimentally observed induction period. Model predictions for the effect of void fraction and developer concentration on roughness are also presented. Observations of differences in the effect of developer concentration on top-surface and sidewall roughness are explained by a critical development time predicted by the simulation.
Surface diagnostics of dry etched III–V semiconductor samples using focused ion beam and secondary ion mass spectrometry
Authors: Yu Siyuan , Heard Peter , Cakmak Bulent , Penty R. V. , White I. H.
Published: July 2002

In order to optimize the H2/CH4 reactive ion etching process for InP, the surface composition of etched samples has been analyzed by means of a focused ion beam and secondary ion mass spectrometry. Harmful species of chlorine and oxygen have been identified as causing surface roughness and etch-rate fluctuations. Polymer distribution on the masked surface and etched surface phosphor abundance have been studied for various gas mixtures and rf power, establishing optimized CH4-rich etching conditions under which surface P content is closest to unetched material and polymer deposition is acceptable.
Comment on: “Epitaxial silicon grown on CeO2/Si(111) structure by molecular beam epitaxy”
Authors: Paparazzo E.
Published: July 2002

An article by Jones et al. [J. Vac. Sci. Technol. B 16, 2686 (1998)] on the epitaxial growth of Si/CeO2/Si(111) structures is commented upon. The area of major disagreement regards the interpretation that the authors propose to explain their x-ray photoemission spectroscopy (XPS) results, specifically the statement that Ce metal segregates to the surface of the overgrown silicon layer as a result of CeO2 decomposition. It is shown that the XPS results can be accounted for only by assuming that Ce2O3-like species, and not Ce metal, segregate to the surface. The surface chemistry of Ce–O–Si systems and some methodological aspects associated with their XPS analysis are discussed.
Wavelength-independent optical lithography
Authors: Pau S. , Nalamasu O. , Cirelli R. , Frackoviak J. , Timko A. , Watson P. , Klemens F. , Timp G.
Published: July 2002

We propose and demonstrate a multiple exposure lithographic technique with resolution limited by processing and not by exposure wavelength. We implement this technique using binary masks and conventional illumination at λe=248 nm and show that various types of patterns of dimension up to λe/10 can be printed.
Aerosol Effect on Cloud Droplet Size Monitored from Satellite
Authors: Bréon Francois-Marie , Tanré Didier , Generoso Sylvia
Published: July 2002

Aerosol concentration and cloud droplet radii derived from space-borne measurements are used to explore the effect of aerosols on cloud microphysics. Cloud droplet size is found to be largest (14 micrometers) over remote tropical oceans and smallest (6 micrometers) over highly polluted continental areas. Small droplets are also present in clouds downwind of continents. By using estimates of droplet radii coupled with aerosol load, a statistical mean relationship is derived. The cloud droplet size appears to be better correlated with an aerosol index that is representative of the aerosol column number under some assumptions than with the aerosol optical thickness. This study reveals that the effect of aerosols on cloud microphysics is significant and occurs on a global scale.
The Effect of Smoke Particles on Clouds and Climate Forcing
Authors: Kaufman Yoram J. , Fraser Robert S.
Published: July 2002

Smoke particles from biomass burning can generate forcing of climate by modifying cloud microphysics and reflectance of sunlight. Cloud modification, critical to an understanding of climate change, is uncertain and variable. Satellite data over the Amazon Basin and Cerrado were analyzed for cloud reflectance and droplet size and for smoke concentration. Smoke increased cloud reflectance from 0.35 to 0.45, while reducing droplet size from 14 to 9 micrometers. The regional variability of the smoke effect was correlated to the availability of water vapor. During the 3 months of biomass burning in the dry season, the smoke-cloud forcing of climate was only −2 watts per square meter in this region, much smaller than what can be inferred from model predictions.
Overview and Initial Results of the Very Long Baseline Interferometry Space Observatory Programme
Authors: Hirabayashi H. , Hirosawa H. , Kobayashi H. , Murata Y. , Edwards P. G. , Fomalont E. B. , Fujisawa K. , Ichikawa T. , Kii T. , Lovell J. E. J. , Moellenbrock G. A. , Okayasu R. , Inoue M. , Kawaguchi N. , Kameno S. , Shibata K. M. , Asaki Y. , Bushimata T. , Enome S. , Horiuchi S. , Miyaji T. , Umemoto T. , Migenes V. , Wajima K. , Nakajima J. , Morimoto M. , Ellis J. , Meier D. L. , Murphy D. W. , Preston R. A. , Smith J. G. , Tingay S. J. , Traub D. L. , Wietfeldt R. D. , Benson J. M. , Claussen M. J. , Flatters C. , Romney J. D. , Ulvestad J. S. , D'Addario L. R. , Langston G. I. , Minter A. H. , Carlson B. R. , Dewdney P. E. , Jauncey D. L. , Reynolds J. E. , Taylor A. R. , McCulloch P. M. , Cannon W. H. , Gurvits L. I. , Mioduszewski A. J. , Schilizzi R. T. , Booth R. S.
Published: July 2002

High angular resolution images of extragalactic radio sources are being made with the Highly Advanced Laboratory for Communications and Astronomy (HALCA) satellite and ground-based radio telescopes as part of the Very Long Baseline Interferometry (VLBI) Space Observatory Programme (VSOP). VSOP observations at 1.6 and 5 gigahertz of the milli–arc-second–scale structure of radio quasars enable the quasar core size and the corresponding brightness temperature to be determined, and they enable the motions of jet components that are close to the core to be studied. Here, VSOP images of the gamma-ray source 1156+295, the quasar 1548+056, the ultraluminous quasar 0014+813, and the superluminal quasar 0212+735 are presented and discussed.
Self-Assembly of Ordered Microporous Materials from Rod-Coil Block Copolymers
Authors: Jenekhe Samson A. , Chen X. Linda
Published: July 2002

Rod-coil diblock copolymers in a selective solvent for the coil-like polymer self-organize into hollow spherical micelles having diameters of a few micrometers. Long-range, close-packed self-ordering of the micelles produced highly iridescent periodic microporous materials. Solution-cast micellar films consisted of multilayers of hexagonally ordered arrays of spherical holes whose diameter, periodicity, and wall thickness depended on copolymer molecular weight and composition. Addition of fullerenes into the copolymer solutions also regulated the microstructure and optical properties of the microporous films. These results demonstrate the potential of hierarchical self-assembly of macromolecular components for engineering complex two- and three-dimensional periodic and functional mesostructures.
Control of SIV Rebound Through Structured Treatment Interruptions During Early Infection
Authors: Lori Franco , Lewis Mark G. , Xu Jianqing , Varga Georg , Zinn Donald E. , Crabbs Carrol , Wagner Wendeline , Greenhouse Jack , Silvera Peter , Yalley-Ogunro Jake , Tinelli Carmine , Lisziewicz Julianna
Published: July 2002

In a randomized controlled trial with acute simian immunodeficiency virus (SIV)–infected macaques, both highly active antiretroviral therapy (HAART) and HAART with fixed-schedule structured treatment interruption (STI-HAART; alternating 3 weeks on and 3 weeks off therapy) suppressed viral load. In the STI-HAART group, T cell virus-specific immune response (VIR) and control of viral rebound increased concurrently during subsequent interruptions. In contrast, VIR did not increase and SIV rebounded after permanent treatment withdrawal in all animals on continuous HAART. Fixed-schedule STI-HAART appears to be an effective alternative to continuous HAART for the early treatment of retroviral infection.
Suppression of Posttreatment Recurrence of Experimental Visceral Leishmaniasis in T-Cell-Deficient Mice by Oral Miltefosine
Authors: Murray Henry W.
Published: July 2002

T-cell-deficient nude mice infected with
Leishmania donovani
were treated with miltefosine and then given either no treatment or intermittent miltefosine. Intracellular visceral infection recurred in untreated mice but was suppressed by once- or twice-weekly oral administration of miltefosine. Miltefosine may be useful as oral maintenance therapy for T-cell-deficient patients with visceral leishmaniasis.
Identification and Characterization of the Point Mutation Which Affects the Transcription Level of the Chromosomal 3-
N
-Acetyltransferase Gene of
Streptomyces griseus
SS-1198
Authors: Ishikawa Jun , Sunada Atsuko , Oyama Ritsuko , Hotta Kunimoto
Published: July 2002

We determined the molecular basis for the enhanced expression of the
aac(3)-Xa
gene encoding an aminoglycoside 3-
N
-acetyltransferase in
Streptomyces griseus
. A C→T substitution was identified at the putative promoter of the mutant gene. RNA analyses demonstrated that the substitution caused a marked increase in the production of the gene-specific transcripts. Therefore, it seemed very likely that the
aac(3)-Xa
gene was activated by the substitution resulting in the emergence of a stronger promoter.
Molecular Characterization of the β-Lactamases from Clinical Isolates of
Moraxella
(
Branhamella
)
catarrhalis
Obtained from 24 U.S. Medical Centers during 1994–1995 and 1997–1998
Authors: Richter Sandra S. , Winokur Patricia L. , Brueggemann Angela B. , Huynh Holly K. , Rhomberg Paul R. , Wingert Elizabeth M. , Doern Gary V.
Published: July 2002

The β-lactamases from 403
Moraxella
(
Branhamella
)
catarrhalis
clinical isolates obtained during 1994–1995 and 1997–1998 U.S. multicenter surveillance studies were characterized by isoelectric focusing. The overall prevalences of the BRO-1 and BRO-2 enzymes among β-lactamase-positive isolates were estimated to be 97.5 and 2.5%, respectively. The minimum inhibitory concentrations (MICs) of ampicillin for all BRO-2-producing isolates were ≤1 μg/ml; however, numerous β-lactamase-positive isolates for which the ampicillin MICs were ≤1 μg/ml produced the BRO-1 enzyme (88.1%).
Pronounced Postantibiotic Effect of Quinupristin-Dalfopristin in Static Cultures of
Staphylococcus aureus
: an Effect Not Seen with Other Antibiotics
Authors: Pfeil Esther , Wiedemann Bernd
Published: July 2002

Quinupristin-dalfopristin produced postantibiotic effects (PAEs) on exponentially growing (log phase) and nongrowing (lag phase) cultures of 0.4 to 6.9 h. PAEs of the other antibiotics tested were 0.5 to 1.9 h, determined with exponentially growing cultures. None of these antibiotics show a PAE on lag-phase bacteria.
Bioavailability of Once- and Twice-Daily Regimens of Didanosine in Human Immunodeficiency Virus-Infected Children
Authors: Abreu Thalita , Plaisance Karen , Rexroad Vivian , Nogueira Susie , Oliveira Ricardo Hugo , Evangelista Lucia A. , Rangel Rosana , Silva Irene S. , Knupp Cathy , Lambert John S.
Published: July 2002

The bioavailability of didanosine at 180 mg/m
2
once daily was compared to that at 90 mg/m
2
twice daily in 24 children with advanced human immunodeficiency virus infection. Children were studied at steady state using optimal sampling and prior pharmacokinetic parameter estimates. Relative bioavailability was 0.95 ± 0.49, supporting the potential clinical adequacy of once-daily dosing.
Modulation of Erm Methyltransferase Activity by Peptides Derived from Phage Display
Authors: Giannattasio Robert B. , Weisblum Bernard
Published: July 2002

Combinatorial peptide display on phage M13 protein pIII was used to discover peptide sequences that selectively bind to ErmC′ methyltransferase from
Bacillus subtilis
. One peptide, Ac-LSGVIAT-NH
2
, inhibited methylation in vitro with a 50% inhibitory concentration of 20 μM. Interestingly, the set of six peptides which inhibited ErmC′ stimulated ErmSF, a homologous methyltransferase from
Streptomyces fradiae
. Thus, Ac-LSGVIAT-NH
2
may not act directly at the catalytic center of ErmC′, but may modulate its activity by binding at a structurally unrelated, but functionally linked, site.
Dendrimers, a New Class of Candidate Topical Microbicides with Activity against Herpes Simplex Virus Infection
Authors: Bourne N. , Stanberry L. R. , Kern E. R. , Holan G. , Matthews B. , Bernstein D. I.
Published: July 2002

Dendrimers are large highly branched macromolecules synthesized from a polyfunctional core. They have shown a variety of biological properties, including, in some instances, antiviral activity. In this study, five dendrimers were evaluated for in vitro activity against herpes simplex virus (HSV) types 1 and 2 by cytopathic effect (CPE) inhibition and plaque reduction (PR) assay in human foreskin fibroblast cells. All of the compounds were active against both virus types in the CPE inhibition assay, in which drug was added to the cells prior to the addition of virus. Antiviral activity was reduced or lost in the PR assays, in which the cells were incubated with the virus before the drug was added. The prophylactic efficacy suggested that the dendrimers might have potential as topical microbicides, products intended to be applied to the vaginal or rectal mucosa to protect against sexually transmitted infections. Three dendrimers were evaluated for this application against genital HSV infection in mice. Two of the compounds, BRI-2999 and BRI-6741, significantly reduced infection rates when 15 μl of a 100-mg/ml solution was administered immediately prior to intravaginal challenge, and the most effective compound, BRI-2999, provided significant protection even when applied 30 min before challenge. This is the first report of microbicidal activity by dendrimers in vivo.
In Vitro Susceptibilities of 400 Spanish Isolates of
Neisseria gonorrhoeae
to Gemifloxacin and 11 Other Antimicrobial Agents
Authors: Berrón S. , Vázquez J. A. , Giménez M. J. , de la Fuente L. , Aguilar L.
Published: July 2002

The in vitro activity of gemifloxacin versus those of 11 other antimicrobial agents against 400 strains of
Neisseria gonorrhoeae
was determined by microdilution with supplemented GC agar. A total of 37.5% of the strains were β-lactamase positive. A total of 70 and 6.4% of the β-lactamase-negative strains exhibited intermediate and high-level penicillin resistance, respectively. Ceftriaxone and gemifloxacin were the most active drugs (MICs at which 90% of isolates are inhibited, 0.01 versus 0.007 μg/ml, respectively), with 100% of strains inhibited by 0.12 μg/ml.
Comparison of Once-Daily versus Twice-Daily Administration of Cefdinir against Typical Bacterial Respiratory Tract Pathogens
Authors: Ross Gigi H. , Hovde Laurie Baeker , Ibrahim Khalid H. , Ibrahim Yasir H. , Rotschafer John C.
Published: July 2002

In an in vitro pharmacodynamic model, a twice-daily cefdinir dosing regimen was more effective than a once-daily regimen against common bacterial respiratory pathogens in producing 3-log
10
killing and preventing the occurrence of regrowth at 24 h. Twice-daily administration is likely the more appropriate cefdinir dosing strategy for the treatment of community-acquired pneumonia.
Pharmacokinetic-Pharmacodynamic Modeling of Electroencephalogram Effect of Imipenem in Rats with Acute Renal Failure
Authors: Dupuis Antoine , Limosin Anne , Paquereau Joël , Mimoz Olivier , Couet William , Bouquet Serge
Published: July 2002

The epileptogenic activity of imipenem was investigated in rats with experimental renal failure induced by uranyl nitrate injection by using electroencephalogram (EEG) recording and a pharmacokinetic-pharmacodynamic model including an effect compartment. Results previously obtained with healthy rats were used to estimate the dose of imipenem required to induce an observable but nonlethal EEG effect on the assumption that only the pharmacokinetic parameters of the model would be affected by renal failure. Good agreement was observed between the predicted and observed effects.
Influence of Prior Exposure to Zidovudine on Stavudine Phosphorylation In Vivo and Ex Vivo
Authors: Hoggard P. G. , Sales S. D. , Phiboonbanakit D. , Lloyd J. , Maher B. A. , Khoo S. H. , Wilkins E. , Carey P. , Hart C. A. , Back D. J.
Published: July 2002

Intracellular phosphorylation of stavudine (d4T) and zidovudine (ZDV) was investigated in peripheral blood mononuclear cells (PBMCs) isolated from ZDV-naive and ZDV-experienced human immunodeficiency virus (HIV)-positive patients. An in vivo study measured the amount of d4T triphosphate (d4TTP), while an ex vivo study assessed the capacity of cells to phosphorylate added d4T. Endogenous dTTP was also measured. d4TTP and dTTP were determined in vivo using a reverse transcriptase chain termination assay. In ex vivo studies, d4T (1 μM) was incubated in resting and phytohemagglutinin-stimulated (10 μg ml
−1
; 72 h) PBMCs for 24 h. After washing and methanol extraction, radiolabeled anabolites were detected by high-performance liquid chromatography. d4TTP reached its highest level 2 to 4 h after dosing (0.21 ± 0.14 pmol/10
6
cells;
n
= 27 [mean ± standard deviation]). Comparison of ZDV-naive and ZDV-experienced individuals showed no significant difference in levels of d4TTP (ZDV naive, 0.23 ± 0.17 pmol/10
6
cells [
n
= 7] versus ZDV experienced, 0.20 ± 0.14 pmol/10
6
cells [
n
= 20];
P
= 0.473) or the d4TTP/dTTP ratio (0.14 ± 0.12 [
n
= 7] and 0.10 ± 0.08 [
n
= 20], respectively;
p
= 0.391). Ex vivo data demonstrated no significant difference in the formation of d4TTP or total d4T phosphates in naive and experienced patients (0.086 ± 0.055 pmol/10
6
cells in ZDV-naive patients [
n
= 17] versus 0.081 ± 0.038 pmol/10
6
cells in ZDV-experienced patients [
n
= 22];
P
= 0.767). The ability of HIV-infected patients to phosphorylate d4T in vivo and ex vivo was unchanged with increasing exposure to ZDV.
Efficacy of an Evernimicin (SCH27899) In Vitro and in an Animal Model of Lyme Disease
Authors: Pavia Charles S. , Wormser Gary P. , Nowakowski John , Cacciapuoti Anthony
Published: July 2002

The MICs of evernimicin at which 90% of
Borrelia burgdorferi
patient isolates were inhibited ranged from 0.1 to 0.5 μg/ml. Evernimicin was as effective as ceftriaxone against
B. burgdorferi
in a murine model of experimental Lyme disease. As assessed by culturing the urinary bladders of infected C3H mice, no live
Borrelia
isolates were recoverable following antibiotic treatment.
New Mutation in ParE in a Pneumococcal In Vitro Mutant Resistant to Fluoroquinolones
Authors: Janoir Claire , Varon Emmanuelle , Kitzis Marie-Dominique , Gutmann Laurent
Published: July 2002

For an in vitro mutant of
Streptococcus pneumoniae
selected on moxifloxacin four- to eightfold-increased MICs of new fluoroquinolones, only a twofold-increased MIC of ciprofloxacin, and a twofold-decreased MIC of novobiocin were observed. This phenotype was conferred by two mutations: Ser81Phe in GyrA and a novel undescribed His103Tyr mutation in ParE, outside the quinolone resistance-determining region, in the putative ATP-binding site of topoisomerase IV.
In Vitro Uptake of SCH 27899 (Evernimicin) by Rat Alveolar Macrophages
Authors: Zbaida Shmuel , Brieland Joan , Krieter Philip , Loebenberg David , Krishna Gopal , Horne Debra , Lu Xiaowen , Yuan Yuan , Hare Roberta , Cayen Mitchell N. , Patrick James E.
Published: July 2002

The in vitro uptake of [
14
C]evernimicin ([
14
C]SCH 27899) by primary cultures of rat alveolar macrophages and hepatocytes was determined. Both cell populations exhibited linear rates of uptake. However, the initial rate of drug uptake by alveolar macrophages was about threefold higher than that by hepatocytes. These findings demonstrate that [
14
C]evernimicin is taken up by rat alveolar macrophages, supporting the likelihood that the drug is able to reach sites of infection.
Molecular Analysis of Tn
1546
-Like Elements in Vancomycin-Resistant Enterococci Isolated from Patients in Europe Shows Geographic Transposon Type Clustering
Authors: Schouten Marinus A. , Willems Rob J. L. , Kraak Wilma A. G. , Top Janetta , Hoogkamp-Korstanje Jacomina A. A. , Voss Andreas
Published: July 2002

Resistance mechanism relatedness was studied in 18 clinical, European
vanA
vancomycin-resistant enterococci. Molecular analysis revealed 10 Tn
1546
-like elements, suggesting two evolutionary lineages. Lineage I dominated the European mainland, and lineage II dominated the United Kingdom and Israel. Geographic clustering reflected different types of meat consumption between countries, since each lineage is associated with colonization of different animals.
Bactericidal Activities of BMS-284756, a Novel Des-F(6)-Quinolone, against
Staphylococcus aureus
Strains with Topoisomerase Mutations
Authors: Lawrence Laura E. , Frosco MaryBeth , Ryan Brenda , Chaniewski Susan , Yang Hyekyung , Hooper David C. , Barrett John F.
Published: July 2002

The antistaphylococcal activities of BMS-284756 (T-3811ME), levofloxacin, moxifloxacin, and ciprofloxacin were compared against wild-type and
grlA
and
grlA/gyrA
mutant strains of
Staphylococcus aureus
. BMS-284756 was the most active quinolone tested, with MICs and minimal bactericidal concentrations against
S. aureus
wild-type strain MT5,
grlA
mutant MT5224c4, and
grlA/gyrA
mutant EN8 of 0.03 and 0.06, 0.125 and 0.125, and 4 and 4 μg/ml, respectively. In the time-kill studies, BMS-284756 and levofloxacin exhibited rapid killing against all strains. Ciprofloxacin, however, was not bactericidal for the double mutant, EN8. BMS-284756 and levofloxacin were bactericidal (3 log
10
decrease in CFU/ml) against the MT5 and MT5224c4 strains at two and four times the MIC within 2 to 4 h. Against EN8, BMS-284756 was bactericidal within 4 h at two and four times the MIC, and levofloxacin achieved similar results within 4 to 6 h. Both the wild-type strain MT5 and
grlA
mutant MT5224c4 should be considered susceptible to both BMS-284756 and levofloxacin, and both quinolones are predicted to have clinical efficacy. The in vivo efficacy of BMS-284756, levofloxacin, and moxifloxacin against
S. aureus
strain ISP794 and its single mutant 2C6(1)-1 directly reflected the in vitro activity: increased MICs correlated with decreased in vivo efficacy. The 50% protective doses of BMS-284756 against wild-type and mutant strains were 2.2 and 1.6 mg/kg of body weight/day, respectively, compared to the levofloxacin values of 16 and 71 mg/kg/day and moxifloxacin values of 4.7 and 61.6 mg/kg/day. BMS-284756 was more potent than levofloxacin and equipotent with moxifloxacin against ISP794 both in vitro and in vivo, while BMS-284756 was more potent than levofloxacin and moxifloxacin against 2C6(1)-1.
In Vitro Antianaerobic Activity of Ertapenem (MK-0826) Compared to Seven Other Compounds
Authors: Hoellman Dianne B. , Kelly Linda M. , Credito Kim , Anthony Lauren , Ednie Lois M. , Jacobs Michael R. , Appelbaum Peter C.
Published: July 2002

Ertapenem, imipenem, meropenem, ceftriaxone, piperacillin, piperacillin-tazobactam, clindamycin, and metronidazole were agar dilution MIC tested against 431 anaerobes. Imipenem, meropenem, and ertapenem were the most active β-lactams (MICs at which 50% of the strains are inhibited [MIC
50
s], 0.125 to 0.25 μg/ml; MIC
90
s, 1.0 to 2.0 μg/ml). Time-kill studies revealed that ertapenem at two times the MIC was bactericidal for 9 of 10 strains after 48 h. The kinetics for other β-lactams were similar to those of ertapenem.
Pharmacodynamic Interaction of Doxycycline and Artemisinin in
Plasmodium falciparum
Authors: Sponer Ulrike , Prajakwong Somsak , Wiedermann Gerhard , Kollaritsch Herwig , Wernsdorfer Gunther , Wernsdorfer Walther H.
Published: July 2002

Parallel in vitro tests, assessing the inhibition of schizont maturation, were conducted with 31 fresh isolates of
Plasmodium falciparum
from Thailand, using artemisinin, doxycycline, and combinations of both. The activities of artemisinin and doxycycline are obviously not correlated. Both compounds showed consistent synergism at 50% effective concentration (EC
50
), EC
90
, and EC
99
levels.
Multicenter Study on Spreading of the
tet
(M) Gene in Tetracycline-Resistant
Streptococcus
Group G and C Isolates in Argentina
Authors: Jeric P. E. , Lopardo H. , Vidal P. , Arduino S. , Fernandez A. , Orman B. E. , Sordelli D. O. , Centrón D.
Published: July 2002

A prospective multicenter study on invasive infections caused by beta-hemolytic streptococci was performed over 6 months and involved 42 centers from 16 cities in Argentina. Among 33 isolates recovered, 9 group G
Streptococcus
isolates (39.1%) and 2 group C
Streptococcus
isolates (20%) exhibited resistance to tetracycline and harbored the
tet
(M) gene. Genealogical analysis revealed that tetracycline resistance has a polyclonal origin in Argentina.
Stability of New Carbapenem DA-1131 to Renal Dipeptidase (Dehydropeptidase I)
Authors: Park Sung Wook , We Jeoung Soon , Kim Gye Won , Choi Seong Hak , Park Haeng Soon
Published: July 2002

The stability of DA-1131 to renal dipeptidase (RDPase) (EC 3.4.13.19) was compared with that of imipenem and meropenem by
V
max
/

K
m

ratios as an index of the enzyme's preference for substrates. Our results showed a decreasing order of imipenem (6.24), meropenem (2.41), and DA-1131 (1.39). The biochemical evaluation of DA-1131 as the least preferred substrate of RDPase suggests its potential use as a novel β-lactam antibiotic which may be usable without coadministration of RDPase inhibitors once its clinical suitability is proven.
Optimal Dose of Amoxicillin in Treatment of Otitis Media Caused by a Penicillin-Resistant Pneumococcus Strain in the Gerbil Model
Authors: Parra Araceli , Ponte Carmen , Cenjor Carlos , García-Calvo Gloria , Giménez María José , Aguilar Lorenzo , Soriano Francisco
Published: July 2002

Amoxicillin at doses of 0.2 to 5 mg/kg of body weight was administered for the treatment of pneumococcal otitis media in a gerbil model. Doses greater than or equal to 2.5 mg/kg, which resulted in concentrations in middle ear fluid of ≥1.4 μg/ml and concentrations in serum higher than the MIC (1 μg/ml) for ≥14% of the dosing interval, were both clinically and bacteriologically effective.
In Vitro Activities of the Des-Fluoro(6) Quinolone BMS-284756 against Aerobic and Anaerobic Pathogens Isolated from Skin and Soft Tissue Animal and Human Bite Wound Infections
Authors: Goldstein Ellie J. C. , Citron Diane M. , Merriam C. Vreni , Warren Yumi A. , Tyrrell Kerin L. , Fernandez Helen
Published: July 2002

BMS-284756, a new des-fluoro(6) quinolone, was very active against 240 aerobic and 180 anaerobic isolates from bite victims. It inhibited 403 of 420 (96%) isolates, including those of
Moraxella
spp., CDC group EF-4, and
Eikenella corrodens
at ≤2 μg/ml and those of all
Pasteurella
spp. and
Bergeyella zoohelcum
at ≤0.015 μg/ml.
Fusobacterium russii
and 6 of 11
Fusobacterium nucleatum
isolates of animal bite origin were resistant, but isolates of human bite origin were susceptible, which suggests that they were of a different subspecies.