bluuebunny/crossref_metadata_2025 huggingface dataset:
Local atomic structures near the domain boundary between the Al-√3×√3 and the 7×7 phases on Si(111): Substitutional defects
Authors: Yoshimura M. , Takaoka K. , Yao T. , Sueyoshi T. , Sato T. , Iwatsuki M.
Published: July 2002

Both Al and Si substitutional defects have been observed in the 7×7 domain and the √3×√3 domain, respectively, on the specimen prepared by higher temperature annealing up to 900 °C by scanning tunneling microscopy. At positive sample bias (+1 V) the protrusions in the √3×√3 domain appear ∼1 Å higher on the average than those in the 7×7 domain, though slight modulation in brightness can be observed in each domain. The image taken at negative sample bias (−1 V) reveals clearly the substitutional defects in both domains. The Si adatoms substituting Al in the √3×√3 domain appear in almost the same contrast as Si adatoms in the 7×7 domain. The Al adatoms substituting Si in the 7×7 domain appear ∼1.5 Å higher than Al atoms in the √3×√3 domain. These results suggest a distinct difference in the electronic structure between the Al (or Si) adatoms in both domains derived from the surrounding atomic geometry. In addition, Al preferentially substitutes the center adatom site in the 7×7 unit cell.
Scanning tunneling microscopy and spectroscopy of MoS2 thin films prepared by an intercalation–exfoliation method
Authors: Manivannan Ayyakkannu , Santiago Yolanda , Cabrera Carlos R.
Published: July 2002

Exfoliated MoS2 thin films on titanium substrates have been investigated by scanning tunneling microscopy (STM) and spectroscopy (STS). Single layers of MoS2 were placed on titanium substrates by an intercalation–exfoliation method. These layers consist of several hexagonal islands of surface atoms on the basal planes as well as axial planes with dangling bonds. The STS measurements showed a surface band gap value of 0.3 eV, which is lower than the value obtained on a single crystal of MoS2 (0.8 eV). Thus the differential conductivity measurements indicate that these films have a high density of states and conductivity due to the presence of a large number of axial planes at the interface.
Theory of scanning tunneling microscopy of oxygen-adsorbed Ag(110) and Cu(110) surfaces
Authors: Schimizu T. , Tsukada M.
Published: July 2002

Though recent observation of scanning tunneling microscopy (STM) images of Ag(110) (n×1)–O(n=1,...,7) surface revealed the unique added row structure, detailed atomic arrangement for this model has been an open question. In previous work, the optimized geometries for the (2×1) and (3×1) oxygen-adsorbed surfaces by the first-principles local density functional approximation (LDA) have been determined. The STM images for various bias voltages and scanning tunneling spectroscopy (STS) spectra are calculated for this optimized structure based on the theoretical simulation method by LDA developed in this group. The results reproduced well the clear ridge structure along the added row. Though the oxygen atom is closer to the tip, Ag atoms are more highlighted for the surface positive bias. On the other hand, the local density of states map shows the maximum amplitude at the O site. This strange feature can be explained by the effect of the tip electronic states. The similar calculation has also been performed for the Cu(2×1)–O surface and different characteristics of the substrate structure are found, which might explain the absence of the repulsion between added rows in this surface. The STM images and STS spectra are calculated for the optimized structure.
Effects of TMG/AsH3 ratio on GaAs molecular layer growth
Authors: Nishizawa Jun-ichi , Kurabayashi Toru
Published: July 2002

We have studied the molecular layer growth condition on GaAs(001) as the parameters of injection duration, injection pressure, and evacuation duration of trimethylgallium (TMG) and AsH3 in ultrahigh vacuum system. As a result, the growth rate per cycle was strongly influenced by the surface stoichiometry of arsenic during growth. The dominant parameter should be an arsenic concentration on the growing surface and depends on the product of the arsine pressure and duration injected. The growth characteristics showed three different regions as a function of the product (arsine dosage). When the arsine dosage was low, the growth rate per cycle increased linearly with the AsH3 dosage. When the dosage was in an intermediate range, the growth rate showed the existence of stable state at 70% arsenic coverage on the growing surface, and the other stable state at near 100% coverage under a higher dosage of AsH3. In addition, the fully covered arsenic surface changed to the 70% covered state during the AsH3 evacuation over 30 s. As the parameter of TMG supply, the growth rate per cycle showed an anomalously large value over the monolayer at the lower pressure of TMG near 4×10−6 Torr at 513 °C, whereas monolayer growth occurred at TMG pressures over 1×10−5 Torr. The dependence of the growth rate on the growth temperature in each region of the TMG pressure shows quite different characteristics. When the TMG pressure was 4×10−6 Torr, the decomposition of TMG was enhanced in the temperature range from 500 to 530 °C. This enhanced decomposition did not occur when the TMG pressure was as high as 5×10−5 Torr. The decomposition mechanism of TMG on the growing surface will depend not only on the growth temperature but also on the TMG pressure.
Scanning tunneling microscopy study of intermediates in the dissociative adsorption of closo-1,2-dicarbadodecaborane on Si(111)
Authors: Carpinelli J. M. , Plummer E. W. , Byun Dongjin , Dowben P. A.
Published: July 2002

Closo-1,2-dicarbadodecaborane (C2B10H12) is a source compound found to be suitable for the deposition of a high resistivity form of boron-carbide (B5C), and the fabrication of boron-rich semiconductor devices. A scanning tunneling microscope (STM) was used to image these molecular icosahedra on Si(111)-(7×7). Molecular decomposition (tip induced and otherwise) produced a boron-carbide/silicon interface with pronounced heterojunction electronic characteristics. In STM, this interface is characterized by a disordering of the Si(111)-(7×7) reconstruction. We suggest, based on Auger electron spectroscopy data and low-energy electron diffraction observations, that boron atoms from the dissociated source molecules substitutionally occupy selvedge sites, as in the boron-induced (√3×√3)R30° reconstruction of Si(111).
Overlay accuracy of Canon synchrotron radiation stepper XFPA for 0.15 μm process
Authors: Saitoh K. , Ohsawa H. , Sentoku K. , Matsumoto T. , Mizusawa N. , Fukuda Y. , Uda K. , Sumitani H. , Hifumi T.
Published: July 2002

Canon has been developing a synchrotron radiation stepper system for x-ray lithography feasibility studies. We have developed a novel accurate alignment system using the dual grating lens (DGLs) method. In this article, we explain the principle of the DGL, and the results of the alignment accuracy and process applicability tests. We have evaluated alignment performance for translation (X,Y) and rotation (θ) at the center of every exposure area. We obtained the alignment accuracy 3σ of 19 nm (X), 15 nm (Y) and 0.8 μrad (θ), using etched SiN patterns on Si substrates, and the overlay accuracy in an actual dynamic random access memory fabrication process 3σ of 34 nm (X), 31 nm (Y), and 2.1 μrad (θ). After eliminating the alignment offset in each shot, the values (3σ) are 18 nm, 21 nm, 1.4 μrad, respectively. These results show that the alignment method is promising for 0.15 μm level device fabrication.
Improvements in atomic force microscopy protocols for imaging fibrous proteins
Authors: Hallett P. , Tskhovrebova L. , Trinick J. , Offer G. , Miles M. J.
Published: July 2002

Myosin is one of the main structural components of biological systems and due to its unique shape is easily recognized. This makes it an ideal subject for the development of preparation techniques for atomic force microscopy (AFM) of other fibrous proteins. Myosin, prepared using a glycerol/mica deposition technique, has been imaged using contact mode as well as the newly developed tapping mode AFM in liquid. Improved resolution using the tapping mode under propanol has allowed us to resolve the ∼7 nm half-repeat of the coiled-coil α-helix of the myosin tail. Myosin has also been imaged under aqueous conditions. We have also imaged the elastic muscle protein, titin, prepared in a similar fashion. Titin is easily deformed, making contact mode imaging in aqueous conditions a destructive process. However, by using tapping mode AFM in liquid it has been possible to image titin under aqueous conditions without damage to the molecules at a resolution equivalent to contact mode in propanol. Using tapping mode AFM in liquid it may be possible to follow protein interactions.
Number of voids formed on a line: Parameter for electromigration lifetime
Authors: Hinode Kenji , Kondo Seiichi , Deguchi Osamu
Published: July 2002

Electromigration study of various layer-structured aluminum conductors with three widths revealed that lifetime (defined as a 1% resistance increase) depends on two critical parameters: the grain size/conductor width ratio and the grain orientation. These two parameters work independently and monotonically. Investigation of the number and size of voids formed by electromigration showed that lifetime is proportional to the square of the number of voids. This relationship is independent of linewidth and current density.
Selective wet etching for highly uniform GaAs/Al0.15Ga0.85As heterostructure field effect transistors
Authors: Kitano T. , Izumi S. , Minami H. , Ishikawa T. , Sato K. , Sonoda T. , Otsubo M.
Published: July 2002

We have developed a novel selective citric acid-based etchant used for GaAs over AlGaAs, which consists of citric acid, NH4OH, and H2O2. The etching rate ratio of GaAs to Al0.15Ga0.85As was as high as 80 by optimizing the pH and citric acid/H2O2 ratio. The etch stop mechanism was investigated using x-ray photoelectron spectroscopy. The etching is stopped at the AlGaAs surface due to Al2O3 formation, whose density is higher than that on a nonselectively etched surface. This selective citric acid-based etchant was applied to the fabrication of GaAs/AlGaAs heterostructure field effect transistors (HFETs). The threshold voltages of the HFETs exhibit excellent uniformity (the standard deviation of 32 mV across the 3 in. wafer), demonstrating the applicability of this selective etchant to the gate recess process.
On the link between electron shadowing and charging damage
Authors: Hwang Gyeong S. , Giapis Konstantinos P.
Published: July 2002

Charging and topography evolution simulations during plasma etching of high aspect ratio line-and-space patterns reveal that electron shadowing of the sidewalls critically affects charging damage. Decreasing the degree of electron shadowing by using thinner masks decreases the potentials of the etched features with a concomitant reduction in Fowler–Nordheim tunneling currents through underlying thin gate oxides. Simultaneously, the potential distribution in the trench changes, significantly perturbing the local ion dynamics which, in turn, cause the notching effect to worsen. Since the latter can be reduced independently by selecting an appropriate etch chemistry, the use of thinner (hard) masks is predicted to be advantageous for the prevention of gate oxide failure.
Conductive supertips for scanning probe applications
Authors: Schössler C. , Urban J. , Koops H. W. P.
Published: July 2002

Materials machining with the scanning tunneling microscope suffers from poor linewidth compared to the atomic resolution power of the microscope. The trace of the emitted beam is widened due to electron or ion field emission from many tip locations having a low work function. To improve the result emission from a single site that delivers a beam in a confined emission angle is required. Such an emitter is obtained if a supertip is used. It consists of a blunt base tip and an attached supertip of a few nanometers in diameter and height. The supertip delivers the current from one point of field instability only. The attached miniaturized tip generates the high field required for field emission. Electron-beam induced deposition from organometallic gold compounds and a heated substrate is used to build the attached nanocrystalline supertip. Confinement of the emission angle of the emitted beam is confirmed by field emission microscope investigations. An angular confinement of ±7.2° is obtained. Supertips deliver an emission of 0.2 mA/sr as measured, and have therefore at least a tenfold higher angular emission density than conventionally etched tips. Deposited supertips require no single crystalline base and can be placed on any base material. They successfully operate in a scanning tunneling microscope in air.
Direct measurement of the effect of substrate photoelectrons in x-ray nanolithography
Authors: Carter D. J. D. , Pepin A. , Schweizer M. R. , Smith H. I. , Ocola L. E.
Published: July 2002

We measure the dissolution rate of poly(methylmethacrylate) (PMMA) as a function of height above substrates of silicon and thin films suitable as bases for gold electroplating: a “thick-gold” film (10 nm Ti/10 nm Au), and a “thin-gold” film (10 nm Ti/1.8 nm Au). For the thick-gold film, a dramatic increase is seen in the PMMA dissolution rate starting approximately 50 nm above the substrate. This is attributed to increased x-ray absorption and photoelectron generation in the thick gold. An increased dissolution rate is not seen for the other two substrates. Our measurements are compared with simulations and with our experience in replicating sub-50-nm device structures. We point out two consequences of this increased exposure due to substrate-generated electrons. The first is an increased exposure rate near the resist/substrate interface which can lead to development at the interface in the dark areas. The second is an increase in exposure near a resist/substrate interface at the boundary between shadowed and unshadowed regions, leading to an undercut in the resist profile.
Accurate critical dimension control by using an azide/novolak resist process for electron-beam lithography
Authors: Yamamoto Jiro , Uchino Shou-ichi , Ohta Hiroya , Yoshimura Toshiyuki , Murai Fumio
Published: July 2002

Nanofabrication with accurate critical dimension control was investigated with a nonchemically amplified resist. The resist consists of 3,3′-dimethoxy-4,4′-diazidobiphenyl and cresol novolak (novolak). By using novolak with a small weight-average molecular weight (Mw), small resist surface roughness (nano edge roughness) was significantly suppressed down to 3 nm. Nanofabrications of 20-nm lines and spaces (L and S) and 20-nm dot patterns had been demonstrated with the resist. The pattern line-width linearity, the minimum size that the fabricated patterns width were equal to the designed ones, was also preserved down to 30-nm L and S. We investigated use of electron-beam/optical lithography to enhance throughput in nanofabrication. Fine gate structure of 70 nm with a large pad was demonstrated with the hybrid exposure.
Thermal stability of Pd/Zn and Pt based contacts to p-In0.53Ga0.47As/InP with various barrier layers
Authors: Leech Patrick W. , Reeves Geoffrey K. , Zhou Wei , Ressel Peter
Published: July 2002

Pd/Zn/Au contacts to p-In0.53Ga0.47As/InP with various types of barrier layers to the indiffusion of Au have been examined by Rutherford backscattering spectrometry (RBS). For the metallizations with a barrier layer of Pd, the aging of the contacts at 400 °C for 20 h produced a widespread indiffusion of Au for all thicknesses of the Pd. In comparison, the incorporation of a layer of Pt or amorphous LaB6 in the contacts prevented an indiffusion of Au and significantly reduced any outdiffusion of the semiconductor elements. The presence of the barrier layer of Pt or LaB6 produced little or no detrimental increase in ρc for this contact system. In the as-deposited Pd-based contacts, a layer of Zn in the structure was necessary in order to produce a minimum value of ρc. After annealing at 500 °C, a specific contact resistance in the range 8–10×10−6 Ω cm2 was obtained for all of the contacts based on Pd/Zn/Au. A comparison has been made with the characteristics of Pt/Ti/Pt/Au contacts to p-In0.53Ga0.47As/InP which were shown as stable against the indiffusion of Au.
Quantification of secondary-ion-mass spectroscopy depth profiles using maximum entropy deconvolution with a sample independent response function
Authors: Dowsett M. G. , Chu D. P.
Published: July 2002

We describe a new method for extracting the secondary-ion-mass spectroscopy response function from measured data for δ layers. The method was developed to reduce the danger of incorporating sample dependent behavior in the response, and is particularly appropriate for use with sub-keV profile energies where the depth resolution is so high that structure can be observed in layers with nm-scale thickness. We demonstrate this method on a system of variously spaced boron δ layers grown in silicon by molecular beam epitaxy. The deconvolved boron distributions for different primary ion beam energies, ranging from 500 eV to 6 keV, appear to be self-consistent and the corresponding depth resolutions are all increased significantly. Deltas with a 2 nm spacing are resolved without deconvolution using a normally incident 250 eV O2+ beam and the depth resolution (Rayleigh criterion) achievable under these conditions with deconvolution is <1 nm. Segregation of boron at the near surface side of the δ layers is clearly visible in these deconvolved data. These features would have been removed using an uncorrected response.
Investigation of particle formation during the plasma enhanced chemical vapor deposition of amorphous silicon, oxide, and nitride films
Authors: Rao N. P. , Wu Z. , Nijhawan S. , Ziemann P. , Campbell S. , Kittelson D. B. , McMurry P.
Published: July 2002

There is considerable interest in understanding particle formation in microelectronic fabrication processes since process generated particles are a major source of yield loss in the industry. In this work, particle formation in a plasma enhanced chemical vapor deposition process has been studied using a newly developed instrument—the particle beam mass spectrometer (PBMS)—capable of measuring number densities and size distributions of submicron particles in vacuum environments with pressures >50 mTorr. Experiments have been conducted during the deposition of amorphous silicon, oxide, and nitride films, and particle formation correlated with process parameters such as plasma power and substrate temperature. For the measurements reported, the PBMS has been operated in a downstream monitoring mode, i.e., the PBMS sampled gases from the reactor exhaust during the deposition. Particle formation was observed during the amorphous silicon and oxide runs, but not during the nitride experiments. For the processes in which particle formation was observed, measured particle concentrations decreased with decreasing plasma power and increasing substrate temperature. The measured particle size distributions peaked at ∼0.09 μm for the amorphous silicon, and ∼0.04 μm for the oxide runs. The measured particle diameters compared reasonably well with values obtained from scanning electron microscope (SEM) analysis of particle samples collected on SEM stubs during deposition.
Facet investigation in selective epitaxial growth of Si and SiGe on (001) Si for optoelectronic devices
Authors: Vescan L. , Grimm K. , Dieker C.
Published: July 2002

The facet evolution and growth rate of Si on {hkl} facets were investigated in the temperature range 700–850 °C using multilayer structures with thick Si and very thin SiGe markers prepared by selective epitaxial growth using low pressure chemical vapor deposition. The most stable facet, observed at all temperatures, is the high index plane {113}. It is the dominant facet up to the top of all mesas (∼1μm thick). Even at the corners of square dots steep {113} facets developed [angle of 72° with the (001) plane]. Several facets reported here are observed for the first time. In the 〈110〉 zone it is the {119} facet, while in the 〈100〉 zone two facets with Miller indices h≠k≠l≠h, the {018} and {0 1 12}, are found. The measured growth rate relationship is R111<R110<R113<R018<R119<R0112<R001. The activation energy of the growth rate Rhkl on the facet is roughly equal to the activation energy for growth on (001), which implies that the same step involved in the deposition limits the growth rate on (001) and on {hkl} surfaces (at least for the {111} and {113} facets). Only the {113} and {110} facets extend and grow from the beginning of the epitaxy up to the top. The first demonstration of photoluminescence from SiGe quantum wells grown on {113} Si is given.
Epitaxial growth of Al2O3/Si heterostructures
Authors: Zborowski J. T. , Golding T. D. , Forrest R. L. , Marton D. , Zhang Z.
Published: July 2002

We have performed an investigation into the synthesis of Al2O3/Si heterostructures grown by gas source molecular beam epitaxy. The study has been motivated by the potential of the aluminum oxide as a barrier material for silicon, enabling Si based tunneling resonant diodes, as well as the possibility for a coherent silicon on insulator material with low dislocation density. The films have been grown on Si(111) orientation, in a gas source molecular beam epitaxy chamber equipped with silane, nitrous oxide gas sources, and solid state aluminum cell. The growth temperature was varied between 700 and 900 °C. A silicon thin film has been grown above 950 °C with the source material obtained from cracking of silane gas at the growth surface. The samples were characterized by x-ray diffraction (XRD), x-ray photoelectron spectroscopy, Rutherford backscattering spectroscopy, Auger electron spectroscopy, and scanning electron microscopy. The films growth rate has been found to be very sensitive to the growth temperature and aluminum flux decreasing rapidly above 700 °C. The films grown on Si(111) substrate are γ-Al2O3, a deficient spinel structure, and are oriented in the (100) direction, which allows for lattice constant matching between the surface nets of silicon and aluminum oxide. This result differs from the one presented by Wado et al. (Ref. Reference 8). The small full width at half maximum of the peaks in the XRD spectra indicates a small mosaic spread and large coherence lengths confirming good crystalline quality.
Interaction of GaSe with GaAs(111): Formation of heterostructures with large lattice mismatch
Authors: Rumaner Lee E. , Olmstead Marjorie A. , Ohuchi Fumio S.
Published: July 2002

We have studied the epitaxial growth of GaSe, a layered van der Waals material, on GaAs, a zinc-blende-structure semiconductor. This heterostructure exhibits a 6% lattice mismatch, and is a prototypical example of van der Waals epitaxy, where the weak van der Waals interaction allows the misfit to be accommodated without the formation of electronically active defects. GaSe was supplied to the growing surface from a single GaSe Knudsen cell. Reflection high energy electron diffraction and x-ray photoemission spectroscopy studies of the nucleation of GaSe indicate Se reacts with the GaAs surface to remove the surface dangling bonds prior to GaSe formation. This is followed by the oriented growth of stoichiometric GaSe layers, that are rotationally aligned with the underlying GaAs substrate. The termination of the GaAs dangling bonds most likely occurs by Se substitution for As in the surface layer of GaAs(111) B and by direct bonding of Se to surface Ga on GaAs(111) A surfaces. In addition, photoemission measurements indicate that the subsurface Se uptake into the GaAs(111) A lattice is higher than that in the (111) B lattice.
Development of wide range energy focused ion beam lithography system
Authors: Kinokuni M. , Sawaragi H. , Mimura R. , Aihara R. , Forchel A.
Published: July 2002

A wide range energy focused ion beam system with post objective lens retarding and accelerating field optics has been developed. This system employs two objective lens elements in tandem. The first objective lens element (OL1) is a conventional einzel lens, the second one (OL2) is a retarding and accelerating mode immersion lens. The post objective lens retarding optics is very effective to obtain a low energy fine focused beam. While the post objective lens acceleration optics is not optically attractive, it has other merits. A very high energy ion beam, more than 100 keV, can be obtained by relatively small apparatus. It is also possible to change the landing energy without adjustments of ion beam alignment. The optimized deflector system has been designed for the above mentioned optics. Stitching accuracies of the system were evaluated, and the measured stitching errors are 0.115 μm (2δ) on the X axis and 0.088 μm (2δ) on the Y axis.
Operational experience with a valved antimony cracker source for use in molecular beam epitaxy
Authors: Hall E. , Naone R. , English J. E. , Blank H.-R. , Champlain J. , Kroemer H.
Published: July 2002

We present data for a valved antimony cracker for use in solid-source molecular beam epitaxy. Both aspects of this source, the cracker and the valve, are characterized. In particular, the valve is shown to exhibit excellent performance in terms of control and reproducibility. As a demonstration of the capabilities of this source, continuously graded layers from GaAs to GaSb were grown by using the source in conjunction with a valved arsenic cracker. We discuss the influence of this source and other growth parameters on composition, structure, and morphology of these graded layers.
p-n junction-based wafer flow process for stencil mask fabrication
Authors: Rangelow I. W. , Shi F. , Volland B. , Sossna E. , Petrashenko A. , Hudek P. , Sunyk R. , Kostic I. , Butschke J. , Letzkus F. , Springer R. , Ehrmann A. , Gross G. , Kaesmaier R. , Oelmann A. , Struck T. , Unger G. , Chalupka A. , Haugeneder E. , Lammer G. , Löschner H. , Tejeda R. , Lovell E. , Engelstad R.
Published: July 2002

The development of stencil masks is considered to be critical to the success of the new ion projection lithography technology. We present here a p-n junction wafer flow process where all fabrication steps are realized on a bulk Si wafer except the final trench etching through the 2–4-μm-thick Si membrane. Stencil masks were produced in a conventional complementary metal-oxide-semiconductor 150 mm wafer line, using an e-beam direct writing tool for patterning. The resist patterns were transferred by standard reactive ion etching (RIE) into a stress-controlled SiON hard mask layer. Subsequent to depositing an Al metal layer for contact to the n-doped wafer surface, the membrane was realized by a wet chemical etch which implemented well established reverse biased p-n junction etch stop techniques. Then, openings through the Si membrane were etched by RIE or inductively coupled plasma etching. Finally, the remaining hard mask layer was removed in BHF. The realized Si membrane diameter was 120 mm with a stencil pattern field of 60 mm×60 mm. Results from LMS-IPRO placement measurements are in agreement with the simulation of the stencil mask fabrication process using finite element methods.
Study on improved electron emission characteristics of micropatterned diamond-like carbon films
Authors: Shin I. H. , Lee T. D.
Published: July 2002

Diamond-like carbon (DLC) films have been grown on silicon substrates by pulsed Nd–YAG laser ablation using an oscillating graphite target. Excellent field-emission characteristics of the DLC films micropatterned in 0.5 μm spacing were obtained. When the columnar DLC structure was tested in a vertical direction, high area density of emission sites and good field-emission uniformity were observed. These findings indicate that the patterned and particle-filtered DLC film has a high potential as a cold cathode electron source for field-emission display. Also, the field-emission characteristics and electrical resistivity of the DLC film after annealing at high temperature is discussed together with the analysis of Raman spectroscopy.
Effect of an In1−xAlxSb buffer layer on InSb thin film mobility
Authors: Partin D. L. , Heremans J. , Thrush C. M.
Published: July 2002

Indium antimonide magnetoresistors are used for magnetic position sensors in very demanding automotive environments such as crankshaft and camshaft angular position sensors for engine control. Growth of very thin InSb layers is desirable to increase the sheet resistance, which makes it possible to reduce the size of a magnetoresistor. However, the minimum thickness of indium antimonide used in production devices is typically limited to at least 1.5 μm by crystallographic defects arising from growth on lattice mismatched substrates and by the device requirement of very large electron mobilities. The use of a highly resistive In1−x AlxSb buffer layer was studied to determine its effects on the electron mobility of the InSb active layer. With optimized buffer layers, InSb active layers with 0.55 μm thickness could be grown with electron mobilities of approximately 40 000 cm2 V−1 s−1 at room temperature and 30 000 cm2 V−1 s−1 at 200 °C.
MARS: Femtosecond laser mask advanced repair system in manufacturing
Authors: Haight Richard , Hayden Dennis , Longo Peter , Neary Timothy , Wagner Alfred
Published: July 2002

Presently available nanosecond laser based tools for removing Cr defects from photomasks have proven inadequate to the task due to the thermal nature of the ablation process which produces metal splatter, haze, reduced transmission, and pitting of the quartz substrate. These problems are virtually nonexistent when employing femtosecond pulses of light to ablate Cr defects in a nonthermal process. Photomasks repaired with ultrashort light pulses exhibit transmission approaching 100%, no observable glass damage, and exceptional spatial resolution. We have built a femtosecond pulsed laser mask repair system which is presently operating successfully in a manufacturing environment.
Surface quantification by ion implantation through a removable layer
Authors: Stevie F. A. , Roberts R. F. , McKinley J. M. , Decker M. A. , Granger C. N. , Santiesteban R. , Hitzman C. J.
Published: July 2002

Quantification at the surface or in the near-surface region has been difficult to achieve for analytical techniques such as secondary ion mass spectrometry (SIMS) and total reflection x-ray fluorescence (TXRF). Ion implantation through a removable layer with energy selected to place the peak of the implant at the interface between the layer and the substrate can provide a known concentration of any element at the interface. When the layer is removed, the surface and near-surface regions of the substrate have known concentrations of the element of interest. Changes in the dose of the ion implant can be used to vary the concentration at the surface. Surface roughness after the oxide has been removed has been considered and does not appear to be significant. Earlier studies of implants into oxide provided the data required to determine the implant energy. Standards have been created for boron, phosphorus, arsenic, and nitrogen. Initial studies have also been made for magnesium, aluminum, calcium, iron, nickel, and copper. Applications have been made for SIMS ultrashallow analyses, surface SIMS, time-of-flight (TOF)-SIMS, and TXRF. Usage of this method for Auger electron spectroscopy and x-ray photoelectron spectroscopy quantification should also be viable.
Evidence for an Ancient Osmium Isotopic Reservoir in Earth
Authors: Meibom Anders , Frei Robert
Published: July 2002

Iridosmine grains from placer deposits associated with peridotite-bearing ophiolites in the Klamath mountains have extremely radiogenic
186
Os/
188
Os ratios and old Re-Os minimum ages, from 256 to 2644 million years. This indicates the existence of an ancient platinum group element reservoir with a supra-chondritic Pt/Os ratio. Such a ratio may be produced in the outer core as a result of inner core crystallization that fractionates Os from Pt. However, if the iridosmine Os isotopic compositions are a signature of the outer core, then the inner core must have formed very early, within several hundred million years after the accretion of Earth.
A 3000-Year Climatic Record from Biogenic Silica Oxygen Isotopes in an Equatorial High-Altitude Lake
Authors: Rietti-Shati M. , Shemesh A. , Karlen W.
Published: July 2002

A record of oxygen isotopes in biogenic opal, 4200 to 1200 calibrated years before the present, from a high-altitude proglacial lake on Mount Kenya, East Africa, exhibits short-term fluctuations on a time scale of centuries as well as long-term variations. The short-term fluctuations are attributed to changes in the glacier meltwater input, and the long-term variations are related to changes in lake temperature. The record indicates that the climate was warm in Equatorial East Africa from 2300 to 1500 years before the present.
Anomalous Polarization Profiles in Sunspots: Possible Origin of Umbral Flashes
Authors: Socas-Navarro H. , Bueno J. Trujillo , Ruiz Cobo B.
Published: July 2002

We present time-series spectropolarimetric observations of sunspots in the Ca II infrared triplet lines, which show a periodic occurrence of anomalous, asymmetric, circular polarization profiles in the umbral chromosphere. The profiles may be caused by the periodic development of an unresolved atmospheric component in a downward flowing magnetized environment. This active component with upward directed velocities as high as 10 kilometers per second is connected to the umbral flash (UF) phenomenon. We can explain the observations with a semiempirical model of the chromospheric oscillation and of the sunspot magnetized atmospheric plasma during a UF event.
Zidovudine Phosphorylation Determined Sequentially over 12 Months in Human Immunodeficiency Virus-Infected Patients with or without Previous Exposure to Antiretroviral Agents
Authors: Hoggard Patrick G. , Lloyd Judy , Khoo Save H. , Barry Michael G. , Dann Louise , Gibbons Sara E. , Wilkins Edmund G. , Loveday Clive , Back David J.
Published: July 2002

We sought to determine whether the intracellular activation of zidovudine (ZDV) varied over time and with previous antiretroviral exposure in human immunodeficiency virus-infected individuals and to examine whether there is an association between virological responses and intracellular phosphorylation. A total of 23 patients (12 treatment naı̈ve, 11 previously treated with ZDV) who commenced ZDV as part of dual nucleoside therapy were prospectively monitored for 12 months or until withdrawal from the study. No association was observed between virological responses at 2 weeks and 3 months and ZDV phosphorylation. The mean intracellular concentrations of ZDV mono-, di-, and triphosphates did not change significantly over time or with previous ZDV exposure. The rate of formation of total ZDV phosphates was increased in patients with CD4 counts <100 cells/mm
3
. Previous reports from in vitro cell culture experiments or cross-sectional cohort studies suggesting alterations of ZDV phosphorylation over time are not confirmed by this longitudinal study.
Mupirocin Prophylaxis against Methicillin-Susceptible, Methicillin-Resistant, or Vancomycin-Intermediate
Staphylococcus epidermidis
Vascular-Graft Infection
Authors: Giacometti A. , Cirioni O. , Ghiselli R. , Goffi L. , Viticchi C. , Mocchegiani F. , Riva A. , Orlando F. , Saba V. , Scalise G.
Published: July 2002

A rat model was used to investigate the efficacy of mupirocin in the prevention of vascular prosthetic graft infection due to
Staphylococcus epidermidis
strains with different susceptibility patterns (methicillin susceptible, methicillin resistant, and with intermediate resistance to vancomycin). The effect of mupirocin-soaked Dacron was compared to that of perioperative intraperitoneal prophylaxis with vancomycin. Graft infections were established in the back subcutaneous tissue of adult male Wistar rats by implantation of Dacron prostheses (1 cm
2
) followed by topical inoculation with 5 × 10
7
CFU of one staphylococcal strain. The study included a control group (no graft contamination), three contaminated groups that did not receive any antibiotic prophylaxis, three contaminated groups that received mupirocin-soaked grafts, three contaminated groups in which perioperative intraperitoneal vancomycin prophylaxis (10 mg/kg of body weight) was administered, and three contaminated groups that received mupirocin-soaked grafts and perioperative intraperitoneal vancomycin prophylaxis (10 mg/kg). The grafts were sterilely removed 7 days after implantation, and the infection was evaluated by using sonication and quantitative agar culture. Data analysis showed the efficacy of mupirocin against all three strains, with growth of the strains in treated rats significantly different than that in the untreated control. In addition, mupirocin was more effective than vancomycin against the strain with intermediate susceptibility to the glycopeptide. Finally, the combination of mupirocin and vancomycin produced complete suppression of the growth of all of the strains.
Gemifloxacin Is Effective in Experimental Pneumococcal Meningitis
Authors: Smirnov A. , Wellmer A. , Gerber J. , Maier K. , Henne S. , Nau R.
Published: July 2002

In a rabbit model of
Streptococcus pneumoniae
meningitis, 5 mg of gemifloxacin mesylate (SB-265805) per kg/h reduced the bacterial titers in cerebrospinal fluid (CSF) almost as rapidly as 10 mg of ceftriaxone per kg/h (Δlog CFU/ml/h ± standard deviation [SD], −0.25 ± 0.09 versus −0.38 ± 0.11; serum and CSF concentrations of gemifloxacin were 2.1 ± 1.4 mg/liter and 0.59 ± 0.38 mg/liter, respectively, at 24 h). Coadministration of 1 mg of dexamethasone per kg did not affect gemifloxacin serum and CSF levels (2.7 ± 1.4 mg/liter and 0.75 ± 0.34 mg/liter, respectively, at 24 h) or activity (Δlog CFU/ml/h ± SD, −0.26 ± 0.11).
Streptococcus gordonii
Strains Resistant to Fluorodeoxyuridine Contain Mutations in the Thymidine Kinase Gene and Are Deficient in Thymidine Kinase Activity
Authors: Franke C. A. , Bolman T. M. , Ottum S. A. , Jones K. F. , Hruby D. E.
Published: July 2002

Mutants of
Streptococcus gordonii
resistant to 5-fluorodeoxyuridine (FUdR
r
) were isolated. Each strain contained a point mutation resulting in the premature termination of the thymidine kinase (TK) open reading frame (
tdk
). In vitro translation of the mutant
tdk
coding regions resulted in synthesis of truncated TK polypeptides deficient in TK activity.
Consequences of VanE-Type Resistance on Efficacy of Glycopeptides In Vitro and in Experimental Endocarditis Due to
Enterococcus faecalis
Authors: Lafaurie Matthieu , Perichon Bruno , Lefort Agnes , Carbon Claude , Courvalin Patrice , Fantin Bruno
Published: July 2002

The consequences on glycopeptide activity of low-level resistance to vancomycin due to VanE-type resistance were evaluated in vitro and in experimental endocarditis caused by
Enterococcus faecalis
BM4405 (MICs of vancomycin and teicoplanin: 16 and 0.5 μg/ml, respectively), its susceptible derivative BM4405-1, and susceptible
E. faecalis
JH2-2. After 24 h of incubation, vancomycin at 8 μg/ml was not active against
E. faecalis
BM4405 whereas it was bacteriostatic against strains BM4405-1 and JH2-2. Against all three strains, vancomycin at 30 μg/ml and teicoplanin at 8 or 30 μg/ml were bacteriostatic but bactericidal when combined with gentamicin. In rabbits with aortic endocarditis due to VanE-type resistant strain BM4405, treatment with a standard dose of vancomycin generated subinhibitory plasma concentrations (i.e., peak of 36.3 ± 2.1 μg/ml and trough of 6.0 ± 2.2 μg/ml) and led to no significant reduction in mean aortic valve vegetation counts compared to no treatment of control animals. In contrast, a higher dosing regimen of vancomycin (i.e., resulting in a peak of 38.3 ± 5.2 μg/ml and a trough of 15.0 ± 8.3 μg/ml), providing plasma concentrations above the MIC for the entire dosing interval, led to significant and similar activities against all three strains, which were enhanced by combination with gentamicin. Treatment with teicoplanin led to results similar to those obtained with vancomycin at a high dose. No subpopulations with increased resistance to glycopeptides were selected in vitro or in vivo. In conclusion, the use of a high dose of vancomycin was necessary for the treatment of experimental enterococcal endocarditis due to VanE-type strains.
In Vivo Efficacy of Telithromycin (HMR3647) against
Streptococcus pneumoniae
and
Haemophilus influenzae
Authors: Okamoto Hiroki , Miyazaki Shuichi , Tateda Kazuhiro , Ishii Yoshikazu , Yamaguchi Keizo
Published: July 2002

The in vivo activity of telithromycin against erythromycin A- and penicillin G-resistant
Streptococcus pneumoniae
was superior to that of azithromycin, clarithromycin, cefdinir, and levofloxacin. In respiratory tract infections caused by erythromycin A-susceptible
S. pneumoniae
or
Haemophilus influenzae
in mice, telithromycin was more effective than clarithromycin and comparable to azithromycin.
In Vitro Activities and Postantifungal Effects of the Potent Dolastatin 10 Derivative Auristatin PHE
Authors: Woyke Tanja , Pettit George R. , Winkelmann Günther , Pettit Robin K.
Published: July 2002

The pentapeptide dolavaline-valine-dolaisoleuine-dolaproine-phenylalanine-methyl ester (auristatin PHE) is a derivative of the anticancer drug dolastatin 10 (dolavaline-valine-dolaisoleuine-dolaproine-dolaphenine). Broth microdilution assays with a wide variety of yeast and filamentous fungal species demonstrated the specificity of auristatin PHE for
Cryptococcus neoformans
and several species of
Trichosporon
. The duration of the postantifungal effect (PAFE) for
C. neoformans
was determined for exposure times ranging from 30 min to 2 h. For the derivative, a PAFE was detectable after 45 min of exposure. The effect plateaued after 1 h of exposure, with a PAFE of approximately 6.5 h at four or eight times the auristatin PHE MIC. In contrast, there was no measurable PAFE after 1 h of exposure to dolastatin 10. Human serum greatly prolonged the PAFE of auristatin PHE at eight times the MIC. Auristatin PHE arrested
C. neoformans
in the budding stage, possibly due to a tubulin-inhibitory action. Auristatin PHE has potential as a narrow-spectrum fungicidal agent and as a probe that can be used to study cryptococcal cell division.
Emergence of Multiple Human Cytomegalovirus Ganciclovir-Resistant Mutants with Deletions and Substitutions within the UL97 Gene in a Patient with Severe Combined Immunodeficiency
Authors: Wolf Dana G. , Yaniv Isaac , Ashkenazi Shai , Honigman Alik
Published: July 2002

Infection with multiple ganciclovir-resistant human cytomegalovirus mutants, containing different substitutions and deletions in the UL97 gene, was found in a patient with severe combined immunodeficiency (SCID) within 3 weeks of ganciclovir therapy. A novel 11-codon deletion at positions 590 to 600 was identified. These unique findings may be related to the nature of the immunodeficiency in the SCID patient.
In Vitro Activities of RWJ-54428 (MC-02,479) against Multiresistant Gram-Positive Bacteria
Authors: Chamberland Suzanne , Blais Johanne , Hoang Monica , Dinh Cynthia , Cotter Dylan , Bond Emmett , Gannon Carla , Park Craig , Malouin Francois , Dudley Michael N.
Published: July 2002

RWJ-54428 (MC-02,479) is a new cephalosporin with a high level of activity against gram-positive bacteria. In a broth microdilution susceptibility test against methicillin-resistant
Staphylococcus aureus
(MRSA), RWJ-54428 was as active as vancomycin, with an MIC at which 90% of isolates are inhibited (MIC
90
) of 2 μg/ml. For coagulase-negative staphylococci, RWJ-54428 was 32 times more active than imipenem, with an MIC
90
of 2 μg/ml. RWJ-54428 was active against
S. aureus, Staphylococcus epidermidis
, and
Staphylococcus haemolyticus
isolates with reduced susceptibility to glycopeptides (RWJ-54428 MIC range, ≤0.0625 to 1 μg/ml). RWJ-54428 was eight times more potent than methicillin and cefotaxime against methicillin-susceptible
S. aureus
(MIC
90
, 0.5 μg/ml). For ampicillin-susceptible
Enterococcus faecalis
(including vancomycin-resistant and high-level aminoglycoside-resistant strains), RWJ-54428 had an MIC
90
of 0.125 μg/ml. RWJ-54428 was also active against
Enterococcus faecium
, including vancomycin-, gentamicin-, and ciprofloxacin-resistant strains. The potency against enterococci correlated with ampicillin susceptibility; RWJ-54428 MICs ranged between ≤0.0625 and 1 μg/ml for ampicillin-susceptible strains and 0.125 and 8 μg/ml for ampicillin-resistant strains. RWJ-54428 was more active than penicillin G and cefotaxime against penicillin-resistant, -intermediate, and -susceptible strains of
Streptococcus pneumoniae
(MIC
90
s, 0.25, 0.125, and ≤0.0625 μg/ml, respectively). RWJ-54428 was only marginally active against most gram-negative bacteria; however, significant activity was observed against
Haemophilus influenzae
and
Moraxella catarrhalis
(MIC
90
s, 0.25 and 0.5 μg/ml, respectively). This survey of the susceptibilities of more than 1,000 multidrug-resistant gram-positive isolates to RWJ-54428 indicates that this new cephalosporin has the potential to be useful in the treatment of infections due to gram-positive bacteria, including strains resistant to currently available antimicrobials.
In Vivo Efficacy of the New Ketolide Telithromycin (HMR 3647) in Murine Infection Models
Authors: Bonnefoy Alain , Guitton Michele , Delachaume Carole , Le Priol Pascal , Girard Anne-Marie
Published: July 2002

We compared the oral antibacterial activities of telithromycin (HMR 3647), a new ketolide drug, in different infections induced in mice by
Staphylococcus aureus, Streptococcus pneumoniae
, streptococci, enterococci, and
Haemophilus influenzae
with those of various macrolides and pristinamycin. Unlike all other comparators, telithromycin displayed a high therapeutic activity, particularly in septicemia induced by erythromycin A-resistant pathogens, where the ketolide was the only active compound, displaying effective doses between 3 and 26 mg/kg of body weight. Against
H. influenzae,
telithromycin was the most effective compound. Telithromycin displayed bacteriostatic behavior against
S. pneumoniae
and
H. influenzae
. The ketolide was also active against thigh muscle infection induced by
S. aureus
. The pharmacokinetic properties of telithromycin accounted for its outstanding well-balanced oral in vivo efficacy against both gram-positive cocci, whatever their phenotype of resistance, and
H. influenzae
.
Effects of Synthetic Cecropin Analogs on in Vitro Growth of
Acholeplasma laidlawii
Authors: Borth Wayne B. , Jones V. P. , Ullman D. E. , Hu J. S.
Published: July 2002

Four synthetic peptides (Peptidyl MIMs; Demeter Biotechnologies, Inc.) were evaluated for their in vitro activity against
Acholeplasma laidlawii
. Fifty percent effective concentration values ranged from 1 to 15 μM. Three of these compounds are more lethal than cecropin B against
A. laidlawii
.
Comparative In Vitro Activities of Gemifloxacin, Other Quinolones, and Nonquinolone Antimicrobials against Obligately Anaerobic Bacteria
Authors: Kleinkauf Niels , Ackermann Grit , Schaumann Reiner , Rodloff Arne C.
Published: July 2002

The in vitro activity of gemifloxacin was compared to that of other quinolone and nonquinolone antimicrobials against 204 anaerobes by the agar dilution technique. The data indicate that gemifloxacin has a rather selective anaerobic activity. Most
Peptostreptococcus, Porphyromonas
, and
Fusobacterium
species are susceptible, while gemifloxacin's activity against other gram-negative anaerobes appears to be variable.