bluuebunny/crossref_metadata_2025 huggingface dataset:
Imaging subsurface strain at atomic steps on Si(111)
Authors: Pohland O. , Tong X. , Gibson J. M.
Published: July 2002

Using diffraction contrast in a transmission electron microscope, we show that the subsurface strain around a monatomic step can be revealed on Si(111). The strain appears because small associated lattice plane rotations change the Bragg conditions locally. By image matching with models of the strain field, we are able to identify the magnitude of the strain at the step. While monolayer steps at surfaces have been previously observed, weak beam images reveal contrast which allows for the direct analysis of the associated strain.
Photo-enhanced chemical vapor deposition: System design considerations
Authors: Lian S. , Fowler B. , Krishnan S. , Jung L. , Li C. , Manna I. , Samara D. , Banerjee S.
Published: July 2002

ArF excimer laser-enhanced photochemical vapor deposition of Si from Si2H6 in an UHV deposition chamber has been used to achieve Si epitaxy at temperatures as low as 250 °C. The system design criteria are discussed. Modified Schimmel etching/Nomarski microscopy, transmission electron microscopy, and reflection high energy electron diffraction have been used to study the microstructure of Si films as a function of laser power, substrate temperature and disilane partial pressure. The growth rates were observed to be linearly dependent on laser intensity and Si2H6 partial pressure. The morphology of the films is excellent and defects such as dislocation loops and stacking faults are not seen.
Photoemission study of Au, Ge, and O2 deposition on NH4F etched Si(111)
Authors: Terry J. , Cao R. , Wigren C. , Pianetta P.
Published: July 2002

We have studied the interaction of a metal Au, a semiconductor Ge, and a nonmetal O2, with the NH4F etched Si(111) surface with photoemission spectroscopy. Two components were present in Si 2p core-level spectra from the H-terminated surface. We observed the flatband condition from the as-etched, n-type, Si(111) surface. We performed stepwise depositions of Au and measured the band bending with photoemission spectroscopy. The Fermi level pinned near midgap as Au was deposited onto the as-etched surface. After the deposition of 1 ML of Au, a Au-silicide layer formed. This interfacial component indicated that the passivating H layer was compromised. As the Au coverage was increased, layers of pure Au formed between the bulk silicon and the Au-silicide layer. The observed behavior was nearly identical to that of Au deposition on the Si(111) 7×7 surface [Phys. Rev. Lett. 67, 2187 (1991)]. Next, we tested the ability of the monohydride layer to sustain surfactant assisted growth of Ge. Ge islanding was observed at 400 °C indicating that good surfactant growth was not obtained. This was consistent with the recent results of Sakai and Tatsumi [Appl. Phys. Lett. 61, 52 (1994)] who reported that the surface roughness was nearly the same for surfaces grown with or without H at this temperature. Although the monohydride layer was not a good surfactant for the Si(111) surface at this temperature, further study at different temperatures is needed to determine the ability of the ideal monohydride layer to act as a surfactant. Finally, we observed no oxidation of the as-etched surface at room temperature upon exposure to molecular oxygen.
Soft x-ray photoelectron spectroscopy study of the reaction of XeF2 with GaAs
Authors: Simpson W. C. , Varekamp P. R. , Shuh D. K. , Yarmoff J. A.
Published: July 2002

The room temperature reaction of atomic F (via XeF2 vapor) with GaAs(110) wafers is studied employing synchrotron-based soft x-ray photoelectron spectroscopy. Both film growth and etching occur simultaneously in this reaction, as the GaAs substrate is consumed in forming a GaF3 film while the excess As is liberated. The intermediate reaction products GaF, AsF, and/or elemental As, as well as tricoordinate Ga and As atoms, are present at the GaF3–GaAs interface throughout the various stages of film growth.
Fabrication and characterization of extremely smooth large area gold surfaces
Authors: Woodard Nathan G. , Lafyatis Gregory P.
Published: July 2002

We describe our work on gold surfaces that are made by peeling gold films off various smooth glass substrates. We find that we are able to routinely and reliably produce extremely smooth, large area gold surfaces: typically, for areas ≤40 μm square we find the residual roughness of our samples is an order of magnitude less than that of surfaces produced using conventional techniques. While we intend to use these to measure the van der Waals force between alkali atoms and gold surfaces, other potential uses include samples for fundamental surface physics investigations, scanning tunneling microscopy substrates, and reflective optics. We provide details as to how we make these extremely smooth samples and discuss our activities to characterize them.
A critical evaluation of thermal mass flow meters
Authors: Tison S. A.
Published: July 2002

Many semiconductor processes require that stable and known flows of gas be delivered to the processing chamber. The thermal mass flow meter (TMFM) is used almost exclusively in the semiconductor industry for the admission of process gases. While TMFM’s have been used in the semiconductor industry for over twenty years, much still remains to be understood about their behavior. The abundance of TMFM manufacturers that make instruments which are supposedly interchangeable complicates the use of TMFM’s because the instruments generally have different designs and performance. While some attempt has been made via written standards to address the specifications of the instruments, these standards do not address all performance issues and cannot eliminate the systematic errors in the original manufacturers calibration of the TMFM’s. Further, the TMFM’s used to measure the process gases are generally calibrated with nitrogen and ‘‘corrected’’ for other gases, but the correction factors are not well understood and are of questionable reliability. It is also important to understand how the TMFM’s perform under conditions that differ from the laboratory conditions where they were calibrated and the measurement errors that are introduced as a result of these different operating conditions. This article presents data on the performance of five low-flow TMFM’s, from different manufacturers, with full scale ranges of 1.5×10−6–3.7×10−6 mol/s (2–5 sccm). The manufacturers’ calibration of the TMFM’s with nitrogen as compared to the National Institute of Standards and Technology (NIST) measured values differed by up to 17%. Three of the five tested TMFM’s were within the manufacturers’ stated tolerance of ±1% of full scale. While some of the instruments’ initial calibration was poor, all of the TMFM’s were stable to within ±1% of full scale over the test interval of nine months. The gas correction factors for five gases (argon, helium, hydrogen, sulfur hexafluoride, and hexafluoroethane) were measured and compared to manufacturers’ recommended values along with the temperature and flow dependence of the gas correction factors. Some of the gas correction factors agreed with the manufacturers’ recommended values to within ±1% while others differed by as much as 13%.
Kinetic study of low energy ion-enhanced polysilicon etching using Cl, Cl2, and Cl+ beam scattering
Authors: Chang Jane P. , Sawin Herbert H.
Published: July 2002

The chlorine ion-enhanced etching yield of polysilicon in the low ion energy regime was characterized as a function of Cl ion energy, ion flux, neutral-to-ion flux ratio, and the ion impingement angle by utilizing Cl+, Cl, and Cl2 beam scattering. The chlorine ionic, atomic, and molecular fluxes were controlled independently over more than an order of magnitude and at flux levels within an order of magnitude of that typically used in high density plasma processes. The etching yield increased with the increase of Cl/Cl+ flux ratio but gradually saturated at higher flux ratios as the surface became saturated with chlorine. The ion energy dependence was a linear function of (Eion1/2−Eth1/2), where the threshold energy Eth was found to be approximately 10 eV. With Cl+ ion bombardment, the etching yield of Cl was two to three times higher than that of Cl2 at higher flux ratios. The angular dependence of ion-enhanced etching yield was also measured. The etching yield was reduced by approximately 30% and 50% when ion impingement angles of 60° and 70° off-normal were used, respectively.
Structural control of TiO2 film grown on MgO(001) substrate by Ar-ion beam sputtering
Authors: Aoki Toshihiko , Maki Kunisuke , Tang Qi , Kumagai Yoshinori , Matsumoto Shigeharu
Published: July 2002

The structure of a 50-nm-thick TiO2 film grown on MgO(001) substrate maintained at 630 °C was studied by x-ray diffraction. Each film was fabricated by varying both the deposition rate of Ti atoms, which are produced by Ar-ion beam sputtering onto a Ti target, and the partial pressure of O2 gas (PO2). When Ti atoms are supplied at a rate of 0.1 nm min−1(4.0×1014 cm−2 min−1) at PO2=1.1×10−2 Pa, the TiO2 film exhibited the anatase structure whose (200) plane was parallel to the MgO(001). The TiO2 film with the rutile structure whose (110) plane was parallel to the MgO(001) was grown at the same deposition rate and PO2=3.1×10−3 Pa. Evidence demonstrating that the structure of TiO2 film is controlled only when Ti atoms and O2 molecules are supplied simultaneously is presented.
Quantum well intermixing in material systems for 1.5 μm (invited)
Authors: Marsh J. H. , Kowalski O. P. , McDougall S. D. , Qiu B. C. , McKee A. , Hamilton C. J. , De La Rue R. M. , Bryce A. C.
Published: July 2002

Precise control over local optical and electrical characteristics across a semiconductor wafer is a fundamental requirement for the fabrication of photonic integrated circuits. Quantum well intermixing is one approach, where the band gap of a quantum well structure is modified by intermixing the well and barrier layers. Here we report recent progress in the development of intermixing techniques for long wavelength applications, discussing two basic techniques. The first is a class of laser disordering techniques which take place in the solid state. The second is a novel intermixing technique involving plasma induced damage. Both techniques enable large band gap shifts to be achieved in standard GaInAsP multiple quantum well laser structures. The potential of both techniques for photonic integration is further demonstrated by the fabrication and characterisation of extended cavity lasers.
Computer modeling as a tool to predict deposition rate and film composition in the reactive sputtering process
Authors: Berg S. , Nyberg T. , Blom H.-O. , Nender C.
Published: July 2002

Reactive sputtering is a widely used technique to deposit oxides, nitrides, etc. A serious drawback of this technique, however, is the drastic decrease in deposition rate that almost always occurs when depositing compound films as compared to depositing pure metal film. In many cases it is possible to overcome this problem by operating the process in the narrow critical processing region between metallic and compound mode sputtering. In this processing region, however, the composition of the deposited compound thin film is extremely sensitive to the processing conditions. It is, therefore, very interesting to investigate the sensitivity of different processing parameters on the overall processing behavior. Computer modeling can be used as a tool to increase the understanding of this complex process. We will show that such results can be used to illustrate the individual effects of the major involved processing parameters. It also serves to assist in the work of process optimization. The relationship between target poisoning, argon current density, deposition rate, reactive gas supply, partial pressure, total pressure, and film composition have been carefully examined. In particular, we will point out a serious limitation that may arise during high rate multielement reactive sputter deposition. The effect of different reactivity of the involved elements may cause that one of the elements during deposition will not be fully oxidized.
Absolute intensities of the vacuum ultraviolet spectra in a metal-etch plasma processing discharge
Authors: Woodworth J. R. , Blain M. G. , Jarecki R. L. , Hamilton T. W. , Aragon B. P.
Published: July 2002

In this article we report absolute intensities of vacuum ultraviolet (VUV) and near ultraviolet emission lines (4.8–18 eV) for discharges used to etch aluminum in a commercial inductively coupled plasma reactor. We report line intensities as functions of wafer type, pressure, gas mixture, and radio frequency excitation level. In a standard aluminum etching mixture containing Cl2 and BCl3 almost all the light emitted at energies exceeding 8.8 eV was due to neutral atomic chlorine. Optical trapping of the VUV radiation in the discharge complicates calculations of VUV fluxes to the wafer. However, we measured total photon fluxes to the wafer at energies above 8.8 eV on the order of 4×1014 photons/cm2 s with a nonreactive wafer and 0.7×1014 photons/cm2 s with a reactive wafer. The majority of the radiation was between 8.9 and 9.3 eV. At these energies, the photons have enough energy to create electron-hole pairs in SiO2 and may penetrate up to a micron into the SiO2 before being absorbed. Relevance of these measurements to VUV photon-induced damage of SiO2 during etching is discussed.
Auger depth profiling studies of interdiffusion and chemical trapping at metal–InP interfaces
Authors: Shapira Y. , Brillson L. J.
Published: July 2002

We have used Auger electron spectroscopy (AES) combined with Ar+ sputtering to profile the chemical composition of UHV-cleaved InP(110) interfaces with Au, Al, Cu, Ni, Ti, and Ag films. We observe pronounced anion and cation segregation to the free metal surface which depend sensitively on the metal–InP reactivity. Reactive metal (e.g., Al, Ti, or Ni) interlayers at Au–InP interfaces decrease anion diffusion and surface segregation monotonically with increasing interlayer thickness and AES depth profiles indicate a P accumulation at or just below the intimate metal–InP interface. These and other sputter-AES studies suggest that the lower (higher) Schottky barriers of reactive (unreactive) metals are associated with cation (anion) depletion within the InP bulk and on anion accumulation at the intimate InP–metal interfaces.
The effect of infrared flash lamp annealing on the electrical properties of modulation-doped GaAs/N–AlGaAs structures
Authors: Kajikawa Y. , Mizuguchi K. , Murotani T. , Fujikawa K. , Sonoda T.
Published: July 2002

The difference between furnace annealing and infrared flash lamp annealing on the electrical properties of modulation-doped GaAs/N–AlGaAs structures grown by MBE was observed. After furnace annealing at about 700 °C, the electron mobility at 77 K decreased drastically due to diffusion of Si impurity ions from the N–AlGaAs layer into the undoped GaAs layer. In contrast to this, the mobility remained at a high value using flash lamp annealing, offering an excellent alternative annealing method for modulation-doped GaAs/N–AlGaAs structures.
Surface effects in γ-ray-induced changes of minority-carrier lifetime
Authors: Hava S.
Published: July 2002

Measurements of minority-carrier lifetimes (τ) in shallow-junction GaAs LED’s under varying gas-pressure conditions prior to and following γ irradiation indicate (1) τ is noticeably influenced by gaseous ambient and, (2) this influence is greater following irradiation than prior to irradiation. This dependence of τ upon surface phenomena indicates γ irradiation changes surface conditions considerably. Combination of both mechanisms on surface effects can be utilized to bring about noticeable improvement in diode speed of response using only modest dosages of nuclear irradiation (up to 60% improvement for only 13 Mrad). It is believed that γ irradiation affects trap density particularly, while changes in gas type and pressure change both trap density and electron capture cross sections at the surface through adsorption–desorption processes. This is believed to be the first time γ ray induced decrease of τ has been studied in different post-irradiation gaseous environments.
‘‘Pinning’’ of energy levels of transition-metal impurities
Authors: Tersoff J. , Harrison Walter A.
Published: July 2002

The dependence of cation-substitutional transition-metal impurity levels upon the host semiconductor is calculated self-consistently in a defect-molecule approach. Heterojunction band lineups and Schottky barrier heights can be calculated within the same tight-binding model. In all three systems, the characteristic behavior is determined by an approximate local charge neutrality condition imposed by electrostatic self-consistency (‘‘pinning’’), with a dangling-bond level playing the role of the ‘‘neutrality level.’’ In this way we explain the observed correlation between transition-metal impurity levels, heterojunction band lineups, and Schottky barriers.
Fermi level dependent native defect formation: Consequences for metal–semiconductor and semiconductor–semiconductor interfaces
Authors: Walukiewicz W.
Published: July 2002

The amphoteric native defect model of the Schottky barrier formation is used to analyze the Fermi level pinning at metal/semiconductor interfaces for submonolayer metal coverages. It is assumed that the energy required for defect generation is released in the process of surface back-relaxation. Model calculations for metal/GaAs interfaces show a weak dependence of the Fermi level pinning on the thickness of metal deposited at room temperature. This weak dependence indicates a strong dependence of the defect formation energy on the Fermi level, a unique feature of amphoteric native defects. This result is in very good agreement with experimental data. It is shown that a very distinct asymmetry in the Fermi level pinning on p- and n-type GaAs observed at liquid nitrogen temperatures can be understood in terms of much different recombination rates for amphoteric native defects in those two types of materials. Also, it is demonstrated that the Fermi level stabilization energy, a central concept of the amphoteric defect system, plays a fundamental role in other phenomena in semiconductors such as semiconductor/semiconductor heterointerface intermixing and saturation of free carrier concentration.
Positive resist image by dry etching: New dry developed positive working system for electron beam and deep ultraviolet lithography
Authors: Pierrat C. , Tedesco S. , Vinet F. , Lerme M. , Dal’Zotto B.
Published: July 2002

A new dry developed high resolution positive working system: positive resist image by dry etching PRIME for e-beam and deep UV lithography is proposed. This system is derived from photolithographic diffusion enhanced silylating resist diffusion enhanced silylating resist (DESIRE) process. In this report, we present the advantages of a top imaging scheme for e-beam lithography: forward scattering and proximity effects are considerably minimized. Due to very high contrast (about 6), resolution limits were pushed down to 75 nm lines and spaces in 0.35 μm thick resist; holes of 0.2 μm in 1.2 μm thick resist were obtained. Under deep UV exposure, 0.2 μm lines and spaces in 0.7 μm thick resist were resolved with a mask aligner.
Reactive ion etching of InP, InGaAs, InAlAs: Comparison of C2H6/H2 with CCl2F2/O2
Authors: Pearton S. J. , Hobson W. S. , Baiocchi F. A. , Emerson A. B. , Jones K. S.
Published: July 2002

The reactive ion etching of InP, InGaAs, and InAlAs in CCl2F2/O2 or C2H6/H2 discharges was investigated as a function of the plasma parameters pressure, power density, flow rate, and relative composition. The etch rates of these materials are a factor of 3–5× faster in CCl2F2/O2 (∼600–1000 Å min−1) compared to C2H6/H2 (160–320 Å min−1). Significantly smoother morphologies are obtained with C2H6/H2 etching provided the composition of the plasma is no more than 10%–20% by volume of C2H6. At higher ethane compositions, polymer formation increases leading to micromasking and rough surface morphologies. Subsurface disorder is limited to <300 Å deep for both gas chemistries for plasma power densities of 0.85 W cm−2.The C2H6/H2 mixture leaves an In-rich surface in all cases, but this surface is free of any residual contamination, whereas the CCl2F2/O2 chemistry leaves chlorofluorocarbon residues ∼20–50 Å thick on the surface of all three In-based materials.
Structural and chemical properties of InAs layers grown on InP(100) surfaces by arsenic stabilization
Authors: Hollinger G. , Gallet D. , Gendry M. , Santinelli C. , Viktorovitch P.
Published: July 2002

The structure of arsenic stabilized InP surfaces prepared by annealing InP under an arsenic pressure is examined using reflected high-energy electron diffraction, x-ray photoelectron spectroscopy, and x-ray photoelectron diffraction (XPD). It is shown that 1.3–2.6 monolayers of strained InAs are formed on the InP surface when the annealing temperature ranges from 450 to 575 °C. XPD patterns are used to distinguish between arsenic atoms located in the first, second, and third InAs layer. A surface structural degradation is shown to occur at 575 °C.
Molecular-beam epitaxy of CdTe on large area Si(100)
Authors: Sporken R. , Lange M. D. , Faurie J. P. , Petruzzello J.
Published: July 2002

We have grown CdTe directly on 2- and 5-in. diam Si(100) by molecular-beam epitaxy and characterized the layers by in situ reflection high-energy electron diffraction, double crystal x-ray diffraction, scanning electron microscopy, transmission electron microscopy, and low-temperature photoluminescence. The films are up to 10-μm thick and mirror-like over their entire surface. Even on 5-in. diam wafers, the structural and thickness uniformity is excellent. Two domains, oriented 90° apart, are observed in the CdTe films on oriented Si(100) substrates, whereas single-domain films are grown on Si(100) tilted 6° or 8° toward [011]. The layers on misoriented substrates have better morphology than those on oriented Si(100), and the substrate tilt also eliminates twinning in the CdTe layers. First attempts to grow HgCdTe on Si(100) with a CdTe buffer layer have produced up to 10-μm thick layers with cutoff wavelengths between 5 and 10-μm and with an average full width at half-maximum of the double-crystal x-ray diffraction peaks of 200 arc s.
HgTe contacts to p-HgCdTe
Authors: Turner Arthur M.
Published: July 2002

HgTe contacts were fabricated on p-HgCdTe and compared to electroless Au contacts. Both metals resulted in contacts to multiwire infrared HgCdTe which were nonohmic as deposited, but became ohmic with a specific contact resistance below 0.1 Ω cm2 after a 150 °C anneal. Electroless Au contacts became ohmic at a lower anneal temperature, usually 100 °C, while HgTe contacts required anneal temperatures in the 140–150 °C range. However, HgTe contacts are much more reproducible because they adhere well to HgCdTe. Precontact surface preparations which did not result in an oxidized HgCdTe surface produced the lowest HgTe contact resistances. Exposure of the HgTe surface to a short ion mill caused type conversion of the HgCdTe and therefore highly resistive and rectifying contacts.
Digital etching of III–V multilayered structures combined with laser ionization mass spectroscopy: Photon-assisted depth profiling
Authors: Bourne Orson L. , Hart D’Arcy , Rayner David. M. , Hackett Peter Andrew
Published: July 2002

A photochemical method for depth profiling multilayered structures of GaAs and AlGaAs is presented. The process combines surface chlorination reactions using molecular chlorine, desorption of surface chlorides, and single step laser ionization time-of-flight mass spectroscopy. Pulsed excimer lasers are used for the desorption and ionization steps. The etch rates approached a monolayer per pulse for both substrates. Prospects for improving the resolution of the process in the lateral and vertical dimensions are discussed.
Field emission properties of diamondlike carbon films made by a novel laser evaporation technique
Authors: Choi J. O. , Huh J. W. , Choi Y. H. , Kim M. J. , Kim H. , Cho Y. R. , Jeong H. S.
Published: July 2002

Field emission properties of nonhydrogenated diamondlike carbon (DLC) films prepared by a novel laser evaporation technique have been investigated. A key feature of the novel technique is using a scanning pulsed laser beam that irradiates a graphite target with a focused beam and constant laser power density. The technique has the main advantage of easy scale-up for uniform and large area coating. The results show that the DLC films exhibit an electron emission threshold field as low as 10 V/μm and a current density of 100 mA/cm2 at 40 V/μm. Additionally, a bright image of cathodoluminescence has been obtained successfully from a fully frit-sealed diode-structured field emission display using the DLC film emitters.
Microscopic description of electronic structure and scattering in disordered antimonide-based heterostructures
Authors: Shaw M. J. , Hagon J. P. , Corbin E. A. , Jaros M.
Published: July 2002

Quantitative theoretical predictions of the carrier lifetimes in a number of imperfect GaxIn1−xSb–InAs superlattices are presented. Strain-dependent empirical pseudopotentials are used to provide a microscopic description of the stationary states in the structures and scattering theory is employed to extract lifetime information. The effect of interface islands is examined, and lifetimes are found to depend upon the detailed size, shape, and composition of the islands. The effect of higher order multiple scattering events is seen to be significant. For isolated isovalent Sb substitutional defects in the InAs layers, a lifetime of ≈0.4 μs is found to be typical. This is shown to be an order of magnitude shorter than in the case of As defects in the alloy layers.
Reproducibility and Variability in Neural Spike Trains
Authors: de Ruyter van Steveninck Rob R. , Lewen Geoffrey D. , Strong Steven P. , Koberle Roland , Bialek William
Published: July 2002

To provide information about dynamic sensory stimuli, the pattern of action potentials in spiking neurons must be variable. To ensure reliability these variations must be related, reproducibly, to the stimulus. For H1, a motion-sensitive neuron in the fly's visual system, constant-velocity motion produces irregular spike firing patterns, and spike counts typically have a variance comparable to the mean, for cells in the mammalian cortex. But more natural, time-dependent input signals yield patterns of spikes that are much more reproducible, both in terms of timing and of counting precision. Variability and reproducibility are quantified with ideas from information theory, and measured spike sequences in H1 carry more than twice the amount of information they would if they followed the variance-mean relation seen with constant inputs. Thus, models that may accurately account for the neural response to static stimuli can significantly underestimate the reliability of signal transfer under more natural conditions.
Single-Molecule Transistors
Authors: Kouwenhoven Leo
Published: July 2002

Chemists and physicists have recently joined forces to create transistor devices on a nanometer scale. In his Perspective, Kouwenhoven discusses results reported by Bockrath
et al
. in the same issue (p.
1922
) in which carbon nanotubes were used to create switching elements that behave like transistors. Such devices are completely governed by the laws of quantum mechanics and open the possibilities for fundamentally different kinds of circuits at enormously higher density.
Triton's Distorted Atmosphere
Authors: Elliot J. L. , Stansberry J. A. , Olkin C. B. , Agner M. A. , Davies M. E.
Published: July 2002

A stellar-occultation light curve for Triton shows asymmetry that can be understood if Triton's middle atmosphere is distorted from spherical symmetry. Although a globally oblate model can explain the data, the inferred atmospheric flattening is so large that it could be caused only by an unrealistic internal mass distribution or highly supersonic zonal winds. Cyclostrophic winds confined to a jet near Triton's northern or southern limbs (or both) could also be responsible for the details of the light curve, but such winds are required to be slightly supersonic. Hazes and clouds in the atmosphere are unlikely to have caused the asymmetry in the light curve.
Genetic Testing for Cancer Risk
Authors: Ponder Bruce
Published: July 2002

Genetic testing for cancer susceptibility is already part of the clinical management of families with some of the well-defined (but uncommon) inherited cancer syndromes. In cases where the risks associated with a predisposing mutation are less certain, or where there is no clearly effective intervention to offer those with a positive result, its use is more controversial. Careful evaluation of costs and benefits, and of the efficacy of interventions in those found to be at risk, is essential and is only just beginning. An immediate challenge is to ensure that both health professionals and the public understand clearly the issues involved.
Role of Inositol 1,4,5-Trisphosphate Receptor in Ventral Signaling in
Xenopus
Embryos
Authors: Kume Shoen , Muto Akira , Inoue Takafumi , Suga Kei , Okano Hideyuki , Mikoshiba Katsuhiko
Published: July 2002

The inositol 1,4,5-trisphosphate (IP
3
) receptor is a calcium ion channel involved in the release of free Ca
2+
from intracellular stores. For analysis of the role of IP
3
-induced Ca
2+
release (IICR) on patterning of the embryonic body, monoclonal antibodies that inhibit IICR were produced. Injection of these blocking antibodies into the ventral part of early
Xenopus
embryos induced modest dorsal differentiation. A close correlation between IICR blocking potencies and ectopic dorsal axis induction frequency suggests that an active IP
3
-Ca
2+
signal may participate in the modulation of ventral differentiation.
Decoupled Temporal Patterns of Evolution and Ecology in Two Post-Paleozoic Clades
Authors: McKinney Frank K. , Lidgard Scott , Sepkoski J. John , Taylor Paul D.
Published: July 2002

Counts of taxonomic diversity are the prevailing standards for documenting large-scale patterns of evolution in the fossil record. However, the secular pattern of relative ecological importance between the bryozoan clades Cyclostomata and Cheilostomata is not reflected fully in compilations of generic diversity or within-fauna species richness, and the delayed ecological recovery of the Cheilostomata after the mass extinction at the Cretaceous-Tertiary boundary is missed entirely. These observations demonstrate that evolutionary success and ecological dominance can be decoupled and profoundly different, even over tens of millions of years.
Interpreting Differential Temperature Trends at the Surface and in the Lower Troposphere
Authors: Santer B. D. , Wigley T. M. L. , Gaffen D. J. , Bengtsson L. , Doutriaux C. , Boyle J. S. , Esch M. , Hnilo J. J. , Jones P. D. , Meehl G. A. , Roeckner E. , Taylor K. E. , Wehner M. F.
Published: July 2002

Estimated global-scale temperature trends at Earth's surface (as recorded by thermometers) and in the lower troposphere (as monitored by satellites) diverge by up to 0.14°C per decade over the period 1979 to 1998. Accounting for differences in the spatial coverage of satellite and surface measurements reduces this differential, but still leaves a statistically significant residual of roughly 0.1°C per decade. Natural internal climate variability alone, as simulated in three state-of-the-art coupled atmosphere-ocean models, cannot completely explain this residual trend difference. A model forced by a combination of anthropogenic factors and volcanic aerosols yields surface-troposphere temperature trend differences closest to those observed.
Regulation of
C. elegans
Life-Span by Insulinlike Signaling in the Nervous System
Authors: Wolkow Catherine A. , Kimura Koutarou D. , Lee Ming-Sum , Ruvkun Gary
Published: July 2002

An insulinlike signaling pathway controls
Caenorhabditis elegans
aging, metabolism, and development. Mutations in the
daf-2
insulin receptor–like gene or the downstream
age-1
phosphoinositide 3-kinase gene extend adult life-span by two- to threefold. To identify tissues where this pathway regulates aging and metabolism, we restored
daf-2
pathway signaling to only neurons, muscle, or intestine. Insulinlike signaling in neurons alone was sufficient to specify wild-type life-span, but muscle or intestinal signaling was not. However, restoring
daf-2
pathway signaling to muscle rescued metabolic defects, thus decoupling regulation of life-span and metabolism. These findings point to the nervous system as a central regulator of animal longevity.
Spatially Resolved Spin-Injection Probability for Gallium Arsenide
Authors: LaBella V. P. , Bullock D. W. , Ding Z. , Emery C. , Venkatesan A. , Oliver W. F. , Salamo G. J. , Thibado P. M. , Mortazavi M.
Published: July 2002

We report a large spin-polarized current injection from a ferromagnetic metal into a nonferromagnetic semiconductor, at a temperature of 100 Kelvin. The modification of the spin-injection process by a nanoscale step edge was observed. On flat gallium arsenide [GaAs(110)] terraces, the injection efficiency was 92%, whereas in a 10-nanometer-wide region around a [1̄11]-oriented step the injection efficiency is reduced by a factor of 6. Alternatively, the spin-relaxation lifetime was reduced by a factor of 12. This reduction is associated with the metallic nature of the step edge. This study advances the realization of using both the charge and spin of the electron in future semiconductor devices.
Cloning, Nucleotide Sequencing, and Analysis of the Gene Encoding an AmpC β-Lactamase in
Acinetobacter baumannii
Authors: Bou Germán , Martínez-Beltrán Jesús
Published: July 2002

A clinical strain of
Acinetobacter baumannii
(strain Ab RYC 52763/97) that was isolated during an outbreak in our hospital and that was resistant to all β-lactam antibiotics tested produced three β-lactamases: a TEM-1-type (pI, 5.4) plasmid-mediated β-lactamase, a chromosomally mediated OXA-derived (pI, 9.0) β-lactamase, and a presumptive chromosomal cephalosporinase (pI, 9.4). The nucleotide sequence of the chromosomal cephalosporinase gene shows for the first time the gene encoding an AmpC β-lactamase in
A. baumannii
. In addition, we report here the biochemical properties of this
A. baumannii
AmpC β-lactamase.
Antipneumococcal Activities of GAR-936 (a New Glycylcycline) Compared to Those of Nine Other Agents against Penicillin-Susceptible and -Resistant Pneumococci
Authors: Hoellman Dianne B. , Pankuch Glenn A. , Jacobs Michael R. , Appelbaum Peter C.
Published: July 2002

GAR-936, a new glycylcycline, had lower MICs (≤0.016 to 0.125 μg/ml) for 201 penicillin- and tetracycline-susceptible and -resistant pneumococcal strains than tetracycline (≤0.06 to 128 μg/ml), minocycline (≤0.06 to 16.0 μg/ml), or doxycycline (≤0.06 to 32.0 μg/ml). GAR-936 was also bactericidal against 11 of 12 strains tested at the MIC after 24 h, with significant kill rates at earlier time points.
Activities of Antimicrobial Agents against Intracellular Pneumococci
Authors: Mandell Gerald L. , Coleman Elizabeth J.
Published: July 2002

Pneumococci can enter and survive inside human lung alveolar carcinoma cells. We examined the activity of azithromycin, gentamicin, levofloxacin, moxifloxacin, penicillin G, rifampin, telithromycin, and trovafloxacin against pneumococci inside and outside cells. We found that moxifloxacin, trovafloxacin, and telithromycin were the most active, but only telithromycin killed all intracellular organisms.
Randomized Prospective Controlled Trial of Recombinant Granulocyte Colony-Stimulating Factor as Adjunctive Therapy for Limb-Threatening Diabetic Foot Infection
Authors: de Lalla Fausto , Pellizzer Giampietro , Strazzabosco Marco , Martini Zeno , Du Jardin Giovanni , Lora Luciano , Fabris Paolo , Benedetti Paolo , Erle Giuseppe
Published: July 2002

Adult diabetic patients admitted to our Diabetes Center from September 1996 to January 1998 for severe, limb-threatening foot infection were consecutively enrolled in a prospective, randomized, controlled clinical study aimed at assessing the safety and efficacy of recombinant human granulocyte colony-stimulating factor (G-CSF) (lenograstim) as an adjunctive therapy for the standard treatment of diabetic foot infection. Forty patients, all of whom displayed evidence of osteomyelitis and long-standing ulcer infection, were randomized 1:1 to receive either conventional treatment (i.e., antimicrobial therapy plus local treatment) or conventional therapy plus 263 μg of G-CSF subcutaneously daily for 21 days. The empiric antibiotic treatment (a combination of ciprofloxacin plus clindamycin) was further adjusted, when necessary, according to the results of cultures and sensitivity testing. Microbiologic assessment of foot ulcers was performed by both deep-tissue biopsy and swab cultures, performed at enrollment and on days 7 and 21 thereafter. Patients were monitored for 6 months; the major endpoints (i.e., cure, improvement, failure, and amputation) were blindly assessed at weeks 3 and 9. At enrollment, both patient groups were comparable in terms of both demographic and clinical data. None of the G-CSF-treated patients experienced either local or systemic adverse effects. At the 3- and 9-week assessments, no significant differences between the two groups could be observed concerning the number of patients either cured or improved, the number of patients displaying therapeutic failure, or the species and number of microorganisms previously yielded from cultures at day 7 and day 21. Conversely, among this small series of patients the cumulative number of amputations observed after 9 weeks of treatment appeared to be lower in the G-CSF arm; in fact, only three patients (15%) in this group had required amputation, whereas nine patients (45%) in the other group had required amputation (
P
= 0.038). In conclusion, the administration of G-CSF for 3 weeks as an adjunctive therapy for limb-threatening diabetic foot infection was associated with a lower rate of amputation within 9 weeks after the commencement of standard treatment. Further clinical studies aimed at precisely defining the role of this approach to this serious complication of diabetes mellitus appear to be justified.
Nonenzymatic Chloramphenicol Resistance Mediated by IncC Plasmid R55 Is Encoded by a
floR
Gene Variant
Authors: Cloeckaert Axel , Baucheron Sylvie , Chaslus-Dancla Elisabeth
Published: July 2002

The IncC plasmid R55, initially described in the 1970s and isolated from
Klebsiella pneumoniae,
confers nonenzymatic chloramphenicol resistance. The gene coding for this resistance was cloned and sequenced and shows 95 to 97% nucleotide identity with the recently reported
floR
gene from
Salmonella enterica
serovar Typhimurium DT104 and from
Escherichia coli
animal isolates, respectively, conferring cross-resistance to florfenicol.
Chloromethane Utilization Gene Cluster from
Hyphomicrobium chloromethanicum
Strain CM2
T
and Development of Functional Gene Probes To Detect Halomethane-Degrading Bacteria
Authors: McAnulla Craig , Woodall Claire A. , McDonald Ian R. , Studer Alex , Vuilleumier Stephane , Leisinger Thomas , Murrell J. Colin
Published: July 2002

Hyphomicrobium chloromethanicum
CM2
T
, an aerobic methylotrophic member of the α subclass of the class
proteobacteria
, can grow with chloromethane as the sole carbon and energy source.
H. chloromethanicum
possesses an inducible enzyme system for utilization of chloromethane, in which two polypeptides (67-kDa CmuA and 35-kDa CmuB) are expressed. Previously, four genes,
cmuA
,
cmuB
,
cmuC
, and
purU
, were shown to be essential for growth of
Methylobacterium chloromethanicum
on chloromethane. The
cmuA
and
cmuB
genes were used as probes to identify homologs in
H. chloromethanicum
. A
cmu
gene cluster (9.5 kb) in
H. chloromethanicum
contained 10 open reading frames:
folD
(partial),
pduX
,
orf153
,
orf207
,
orf225
,
cmuB
,
cmuC
,
cmuA
,
fmdB
, and
paaE
(partial). CmuA from
H. chloromethanicum
(67 kDa) showed high identity to CmuA from
M. chloromethanicum
and contains an N-terminal methyltransferase domain and a C-terminal corrinoid-binding domain. CmuB from
H. chloromethanicum
is related to a family of methyl transfer proteins and to the CmuB methyltransferase from
M. chloromethanicum
. CmuC from
H. chloromethanicum
shows identity to CmuC from
M. chloromethanicum
and is a putative methyltransferase.
folD
codes for a methylene-tetrahydrofolate cyclohydrolase, which may be involved in the C
1
transfer pathway for carbon assimilation and CO
2
production, and
paaE
codes for a putative redox active protein. Molecular analyses and some preliminary biochemical data indicated that the chloromethane utilization pathway in
H. chloromethanicum
is similar to the corrinoid-dependent methyl transfer system in
M. chloromethanicum
. PCR primers were developed for successful amplification of
cmuA
genes from newly isolated chloromethane utilizers and enrichment cultures.
Gene Cloning and Functional Characterization by Heterologous Expression of the Fructosyltransferase of
Aspergillus sydowi
IAM 2544
Authors: Heyer Arnd G. , Wendenburg Regina
Published: July 2002

We have purified a fructosyltransferase from conidia of the inulin-producing fungus
Aspergillus sydowi
IAM 2544 and obtained peptide sequences from proteolytic fragments of the protein. With degenerated primers, we amplified a PCR fragment that was used to screen a cDNA library. The fructosyltransferase gene from
Aspergillus sydowi
(EMBL accession no.
AJ289046
) is expressed in conidia, while no expression could be detected in mycelia by Northern blot analysis of mycelial RNA. The gene encodes a protein with a calculated molecular mass of 75 kDa that is different from all fructosyltransferases in the databases. The only homology that could be detected was to the invertase of
Aspergillus niger
(EMBL accession no.
L06844
). The gene was functionally expressed in
Escherichia coli
, yeast, and potato plants. With protein extracts from transgenic bacteria and yeast, fructooligosaccharides could be produced in vitro. In transgenic potato plants, inulin molecules of up to 40 hexose units were synthesized in vivo. While in vitro experiments with protein extracts from conidia of
Aspergillus sydowi
yielded the same pattern of oligosaccharides as extracts from transformed bacteria and yeast, in vivo inulin synthesis with fungal conidia leads to the production of a high-molecular-weight polymer.
Fate and Dissemination of
Bacillus subtilis
Spores in a Murine Model
Authors: Hoa Tran Thu , Duc Le Hong , Isticato Rachele , Baccigalupi Loredana , Ricca Ezio , Van Pham Hung , Cutting Simon M.
Published: July 2002

Bacterial spores are being consumed as probiotics, although little is known about their efficacy or mode of action. As a first step in characterizing spore probiotics, we have studied the persistence and dissemination of
Bacillus subtilis
spores given orally to mice. Our results have shown that spores do not appear to disseminate across the mucosal surfaces. However, we found that the number of spores excreted in the feces of mice was, in some experiments, larger than the original inoculum. This was an intriguing result and might be explained by germination of a proportion of the spore inoculum in the intestinal tract, followed by limited rounds of cell growth and then sporulation again. This result raises the interesting question of whether it is the spore or the germinated spore that contributes to the probiotic effect of bacterial spores.
Genetic Differentiation between Sympatric Populations of
Bacillus cereus
and
Bacillus thuringiensis
Authors: Vilas-Boas Gislayne , Sanchis Vincent , Lereclus Didier , Lemos Manoel Victor F. , Bourguet Denis
Published: July 2002

Little is known about genetic exchanges in natural populations of bacteria of the spore-forming
Bacillus cereus
group, because no population genetics studies have been performed with local sympatric populations. We isolated strains of
Bacillus thuringiensis
and
B. cereus
from small samples of soil collected at the same time from two separate geographical sites, one within the forest and the other at the edge of the forest. A total of 100
B. cereus
and 98
B. thuringiensis
strains were isolated and characterized by electrophoresis to determine allelic composition at nine enzymatic loci. We observed genetic differentiation between populations of
B. cereus
and
B. thuringiensis
. Populations of a given
Bacillus
species—
B. thuringiensis
or
B. cereus
—were genetically more similar to each other than to populations of the other
Bacillus
species. Hemolytic activity provided further evidence of this genetic divergence, which remained evident even if putative clones were removed from the data set. Our results suggest that the rate of gene flow was higher between strains of the same species, but that exchanges between
B. cereus
and
B. thuringiensis
were nonetheless possible. Linkage disequilibrium analysis revealed sufficient recombination for
B. cereus
populations to be considered panmictic units. In
B. thuringiensis,
the balance between clonal proliferation and recombination seemed to depend on location. Overall, our data indicate that it is not important for risk assessment purposes to determine whether
B. cereus
and
B. thuringiensis
belong to a single or two species. Assessment of the biosafety of pest control based on
B. thuringiensis
requires evaluation of the extent of genetic exchange between strains in realistic natural conditions.
trans
-Sialidase Inhibition Assay, a Highly Sensitive and Specific Diagnostic Test for Chagas' Disease
Authors: Buchovsky A. S. , Campetella O. , Russomando G. , Franco L. , Oddone R. , Candia N. , Luquetti A. , Gonzalez Cappa S. M. , Leguizamon M. S.
Published: July 2002

For the diagnosis of Chagas' disease, the
trans
-sialidase inhibition assay was able to resolve the results for samples with borderline results, to detect as positive 60% of samples that were negative by conventional serology, and to discriminate idiopathic from chagasic megaviscera or cardiopathy. No cross-reaction with sera from patients with other diseases was observed.
Generation and Serological Characterization of Murine Monoclonal Antibodies against O Antigens from
Acinetobacter
Reference Strains
Authors: Pantophlet Ralph , Brade Lore , Brade Helmut
Published: July 2002

O-antigen-specific monoclonal antibodies were generated against
Acinetobacter
strains from international type culture collections and characterized by enzyme immunoassay and Western and colony blotting. The antibodies aid in the further completion of an O-serotyping scheme for
Acinetobacter
and, due to their high specificity, are especially useful to all working with these strains.
PrP
Sc
Is Not Detected in Peripheral Blood Leukocytes of Scrapie-Infected Sheep: Determining the Limit of Sensitivity by Immunohistochemistry
Authors: Herrmann Lynn M. , Baszler Timothy V. , Knowles Donald P. , Cheevers William P.
Published: July 2002

Peripheral blood leukocytes (PBLs) from scrapie-infected sheep were evaluated for the presence of PrP
Sc
by using dissociated retropharyngeal lymph node (DRLN) cells and immunohistochemistry (IHC). PrP
Sc
-positive cells were detected in 2.05% ± 0.28% of 3 × 10
6
DRLN cells, but were not detected in 3 × 10
6
PBLs from scrapie-infected sheep. Titration of DRLN cells mixed with PBLs showed that IHC detects a minimum of 0.00205% or 60 PrP
Sc
-positive cells in 3 × 10
6
PBLs.