bluuebunny/crossref_metadata_2025 huggingface dataset:
Influence of cathode material and SiCl4 gas on inductively coupled plasma etching of AlGaN layers with Cl2∕Ar plasma
Authors: Zhirnov Evgeny , Stepanov Sergei , Wang Wang Nang , Shreter Y. G. , Takhin D. V. , Bochkareva N. I.
Published: November 2004

The influence of cathode coverplate material on inductively coupled plasma etching of GaN and AlGaN with 1% and 10% of Al was investigated. It was revealed that coverplate material has a great impact on the etching of Al-containing layers. Results obtained with a graphite coverplate and a Si wafer on top of a quartz coverplate indicate that etch products of coverplate material such as SiClx, CClx reactive species and SiClx+, CClx+ ions play a significant role in fast and smooth etching of Al-containing layers. They act as getters to remove oxygen in the process chamber and as effective etchers for oxide layers formed by background oxygen in the process chamber. Experiments where SiCl4 gas was added to Cl2∕Ar plasma confirmed the role of SiClx reactive species and SiClx+ ions for fast and smooth etching of AlGaN layers.
Amorphous silicon nitride films of different composition deposited at room temperature by pulsed glow discharge plasma immersion ion implantation and deposition
Authors: Afanasyev-Charkin I. V. , Jacobsohn L. G. , Averitt R. D. , Nastasi M.
Published: November 2004

Amorphous hydrogenated silicon nitride (a-SiNx:H) films of different compositions (0⩽x⩽1.18) were prepared by pulsed glow discharge plasma immersion ion implantation and deposition. The processing gases were silane and nitrogen at a substrate temperature ⩽50°C. The properties of the films were investigated using Rutherford backscattering, elastic recoil detection analysis, UV–visible optical absorption, Fourier transform infrared, and Raman spectroscopies, and nanoindentation. Depending on the value of x, the band gap of the films changes from 1.54to4.42eV, and hardness changes from 11.2to15.3GPa. Changes in the film properties are caused by formation of Si–N bonds and by reducing disorder in the films. It is shown that hard and transparent silicon nitride films can be obtained at room temperature.
Structure and mechanical properties of Ti–Si–N films deposited by combined DC/RF reactive unbalanced magnetron sputtering
Authors: Ding X. Z. , Zeng X. T. , Liu Y. C. , Yang Q. , Zhao L. R.
Published: November 2004

Ti–Si–N nanocomposite films with Si content between 0 and 13.5at.% were deposited by combined DC/RF reactive unbalanced magnetron sputtering. The composition, structure, and mechanical properties of the as-deposited Ti–Si–N films were measured by energy dispersive analysis of x rays, x-ray diffraction (XRD), and nanoindentation experiments, respectively. All of the Ti–Si–N films exhibited a higher hardness than pure TiN films deposited under similar conditions. The highest hardness (∼41GPa) was obtained in the film with Si content of about 8at.%. Ti–Si–N films also exhibited a higher resistance to plastic deformation (i.e., higher ratio H3∕E*2) than pure TiN. XRD patterns revealed that the as-deposited films were composed of cubic TiN crystallites with a preferential orientation of (111). With increase of RF power applied to the Si targets, the TiN (111) peak intensity or TiN crystallite size increased in the lower RF power range but decreased in the higher RF power range, showing a maximum at an RF power of 500W (power density ∼1.14W∕cm2), corresponding to a Si content of about 5at.% in the film.
Improvement of electrochemical properties in LiCoO2 cathode films grown on Pt∕TiO2∕SiO2∕Si substrates by liquid-delivery metalorganic chemical vapor deposition
Authors: Choi Woon-Gi , Yoon Soon-Gil
Published: November 2004

The structural and electrochemical properties of LiCoO2 cathode films grown on Pt∕TiO2∕SiO2∕Si substrates at 500°C by liquid-delivery metalorganic chemical vapor deposition (LDMOCVD) were investigated as a function of Li∕Co mol ratio. The electrochemical properties such as initial discharge capacity and cyclic retention were improved through the study of Raman spectra of as-grown and annealed LiCoO2 films. The deposition temperature of 500°C was chosen to characterize the films because films grown at 500°C showed a typical high temperature hexagonal phase without Co3O4 impurities in the films. The optimum annealing condition of as-grown samples with Li∕Co=2.0 and 3.0 was at 700°C for 30min in an oxygen ambient. The highest initial discharge capacity and capacity retention were obtained in Li‖LiCoO2 cells grown with Li∕Co=3.0 and 2.0, respectively, and were approximately 38μAhcm−2μm and 77%, respectively. The compositional window for an optimum electrochemical property exists in the range of Li∕Co=2.0to3.0 in an as-grown temperature of 500°C and annealing temperature of 700°C for 30min in O2.
Current-pressure characteristics of planar magnetron discharges in rare gases
Authors: Escrivão M. L. , Pereira P. J. S. , Cabral M. H. , Teixeira M. R. , Maneira M. J. P.
Published: November 2004

The variation of current intensity with pressure, at constant voltage, (I-p characteristics), was obtained for planar magnetron discharges in neon, krypton, and xenon on a copper target. The analysis of those curves confirms that an equation of the same type as the one recently obtained by the authors for an argon–copper discharge is an adequate relation to describe the dependence of current intensity on pressure and voltage for planar magnetron discharges in rare gases. That equation accounts for a bimodal behavior corresponding to the sum of a “magnetron term” and a “diode term.”
In situ x-ray diffraction observation of multiple texture turnovers in sputtered Cr films
Authors: Zhao Z. B. , Rek Z. U. , Yalisove S. M. , Bilello J. C.
Published: November 2004

A series of Cr films were deposited onto native oxides of (100) Si substrates via a confocal deposition geometry in a magnetron sputter chamber. The film growth chamber was incorporated with an in situ x-ray diffraction system, which allowed the collection of x-ray diffraction data on the growing film in a quasi real time fashion without interruption of film deposition. The in situ x-ray diffraction, coupled with other ex situ characterization techniques, was used to study structural evolutions of the Cr films deposited at various Ar pressures. It was observed that the evolution of the crystallographic structures of Cr films was very sensitive to both deposition conditions and film thickness. With the confocal deposition geometry, the Cr films developed various types of out-of-plane textures. In addition to the (110) and (100) types of textures commonly reported for vapor deposited Cr films, the (111) and (112) types of textures were also observed. The film deposited at low Ar pressure (2mTorr) developed strong (111) type texture. With the increase in either Ar pressure or film thickness, the Cr films tended to develop (112) and (100) types of texture. At high Ar pressures (>10mTorr), several changes in texture type with increasing film thickness were observed. The sequence can be described as (110)→(112)→(100). The strong tendency for these films to ultimately assume the (100) type of texture could be related to significant rises in substrate temperatures during the late stages of film growth with high Ar pressures. The observation of the multiple texture type changes suggests that the evolution of Cr films is controlled by complex growth kinetics. The competitive growth of grains with different orientations can be altered not only by controllable deposition parameters such as Ar pressure, but also by the variations of in situ film attributes (e.g., residual stress and substrate temperature) occurring concurrently with film growth.
Characteristics of organic film deposited by plasma-enhanced chemical-vapor deposition using a benzocyclobutene resin
Authors: Sugitani Suehiro , Matsuzaki Hideaki , Enoki Takatomo
Published: November 2004

Characteristics of organic film deposited by plasma-enhanced chemical-vapor deposition (CVD) at temperatures below 250°C using a liquid source of benzocyclobutene (BCB) resin were investigated and compared with standard spin-coated BCB film. CVD film with a thickness of 0.3μm was successfully deposited on a 3in. wafer with a thickness uniformity of 3%. The dielectric constant, breakdown voltage, stress, and moisture absorption of the CVD film are similar to those of spin-coated film. However, using Fourier transform infrared spectroscopy, Auger electron spectroscopy, and pyrolysis gas chromatography/mass spectroscopy, it was found that the CVD film has almost no methyl-siloxane, which exists in spin-coated film. Therefore, CVD film can be etched by reactive-ion etching using only O2 gas. The step-coverage of the CVD film is conformal and considered advantageous for use in ultrafine structures.
Dry etching of NiFe∕Co and NiFe∕Al–O∕Co multilayers in an inductively coupled plasma of Cl2∕Ar mixture
Authors: Ra H.-W. , Hahn Y. B. , Song K. S. , Park M. H. , Hong Y. K.
Published: November 2004

Dry etching of NiFe∕Co and NiFe∕Al–O∕Co multilayers was carried out in inductively coupled Cl2∕Ar plasmas. An ion-enhanced etch mechanism took a critical role for desorption of chlorine etch products. NiFe∕Al–O∕Co showed a faster etch rate than NiFe∕Co at various etch conditions. Anisotropic and smooth features were obtained using a photoresist mask. Sidewall contamination with etch products was observed at a higher Cl2 concentration (>50%). Postetch cleaning of the etched samples in deionized water reduced the chlorine residues substantially.
Infrared spectroscopic study of atomic layer deposition mechanism for hafnium silicate thin films using HfCl2[N(SiMe3)2]2 and H2O
Authors: Kang Sang-Woo , Rhee Shi-Woo , George Steven M.
Published: November 2004

In situ Fourier transform infrared (FT-IR) spectroscopy was used to study the atomic layer deposition mechanism of hafnium silicate films with dichlorobis[bis(trimethylsilyl)amido] hafnium (HfCl2[N(SiMe3)2]2) and water. The surface species was monitored during atomic layer deposition using vacuum chambers designed for in situ FT-IR spectroscopy studies. Vibrational spectroscopy reveals the gain and loss of surface species during the two surface half-reactions. The behavior of the functional group (such as O–Η, Si–(CH3)x, and C–H was monitored and from that, the temperature dependence of the growth rate and the film composition could be explained. It was also found that Si–O–Si peaks between 1000 and 1200cm−1 were formed when water was dosed above 300°C, which could explain the incorporation mechanism of Si into the film.
Room temperature preparation of activated and crystallized p-type Si1−xGex thin film on glass substrate by intense, pulsed, ion beam evaporation
Authors: Hirai M. , Iwashita R. , Arikado T. , Suematsu H. , Jiang W. , Yatsui K. , Takeda M. , Uchitomi N.
Published: November 2004

A boron doped Si1−xGex thin film has been successfully prepared on a quartz (SiO2) glass substrate at room temperature (RT) by irradiating an intense, pulsed, ion beam on a Si–Ge–B pellet. As a result, in situ boron doped Si1−xGex thin film was found to be crystallized. In addition, by van der Pauw measurement, the resistivity, carrier density, and mobility of the thin film were observed as ρ=2.3×10−3Ωcm, n=7.2×1020cm−3, and μ=3.8cm2∕Vs, respectively. Thus, the boron doped Si1−xGex thin film was clarified to be not only crystallized but also activated without heat treatment.
Low temperature epitaxy of reactively sputtered ZnO on sapphire
Authors: Ruthe K. C. , Cohen D. J. , Barnett S. A.
Published: November 2004

ZnO films were grown on c-plane sapphire by dc reactive magnetron sputtering. X-ray diffraction measurements showed that an epitaxial relationship of ZnO[101¯0]∥Al2O3[112¯0] and ZnO[21¯1¯0]∥Al2O3[11¯00] was maintained down to a substrate temperature Ts≈80°C, corresponding to <17% of the ZnO melting point. The low-temperature epitaxy was explained by the energetic species produced during sputtering and a high mobility of Zn surface atoms in low-oxygen conditions. Crystalline perfection improved with increasing Ts, decreasing growth rate, and decreasing oxygen-to-zinc flux ratio. Dense microstructures with flat surfaces were achieved at Ts≈200°C, although at Ts≈80°C films tended to transition to a columnar Zone 1 microstructure from a Zone T microstructure with increasing film thickness. In general, Ts=200–300°C and an oxygen-to-zinc flux ratio of ≈300 yielded a favorable combination of good optical transparency, crystalline perfection, flat surfaces, and dense microstructure.
Low-temperature preparation of GaN-SiO2 interfaces with low defect density. I. Two-step remote plasma-assisted oxidation-deposition process
Authors: Bae Choelhwyi , Lucovsky Gerald
Published: November 2004

In previous studies, device-quality Si-SiO2 interfaces and dielectric bulk films (SiO2) were prepared using a two-step process: (i) remote plasma-assisted oxidation (RPAO) to form a superficially interfacial oxide (∼0.6nm) and (ii) remote plasma-enhanced chemical vapor deposition (RPECVD) to deposit the oxide film. The same approach has been applied to the GaN-SiO2 system. Without an RPAO step, subcutaneous oxidation of GaN takes place during RPECVD deposition of SiO2, and on-line Auger electron spectroscopy indicates a ∼0.7-nm subcutaneous oxide. The quality of the interface and dielectric layer with/without RPAO process has been investigated by fabricated GaN metal-oxide-semiconductor capacitors. Compared to single-step SiO2 deposition, significantly reduced defect state densities are obtained at the GaN-SiO2 interface by independent control of GaN-GaOx interface formation by RPAO and SiO2 deposition by RPECVD.
Low-temperature preparation of GaN-SiO2 interfaces with low defect density. II. Remote plasma-assisted oxidation of GaN and nitrogen incorporation
Authors: Bae Choelhwyi , Lucovsky Gerald
Published: November 2004

Low-temperature remote plasma-assisted oxidation and nitridation processes for interface formation and passivation have been extended from Si and SiC to GaN. The initial oxidation kinetics and chemical composition of thin interfacial oxide were determined from analysis of on-line Auger electron spectroscopy features associated with Ga, N, and O. The plasma-assisted oxidation process is self-limiting with power-law kinetics similar to those for the plasma-assisted oxidation of Si and SiC. Oxidation using O2∕He plasma forms nearly pure GaOx, and oxidation using 1% N2O in N2 forms GaOxNy with small nitrogen content, ∼4–7at.%. The interface and dielectric layer quality was investigated using fabricated GaN metal-oxide-semiconductor capacitors. The lowest density of interface states was achieved with a two-step plasma-assisted oxidation and nitridation process before SiO2 deposition.
Preparation and characterization of high-quality TiN films at low temperature by filtered cathode arc plasma
Authors: Zhang Y. J. , Yan P. X. , Wu Z. G. , Xu J. W. , Zhang W. W. , Li X. , Liu W. M. , Xue Q. J.
Published: November 2004

High-quality TiN films were successfully deposited on silicon and stainless-steel substrates at low temperature using an improved filtered cathode arc plasma technique developed in our lab. Atomic force microscope, x-ray diffractometer, x-ray photoelectron spectroscopy, and a nanoindenter were employed to characterize the TiN thin films. The microhardness of the TiN films have a high value up to 41GPa, which is far higher than that of TiN compounds deposited by conventional chemical vapor deposition and physical vapor deposition methods (20Gpa or so). The films are of a stronger preferred crystalline orientation, very smooth surface, and high reflectivity. The effects of the negative substrate bias on the preferred crystalline orientation, surface roughness, deposition rate, and microhardness of Tin thin films are discussed in detail.
Two-photon absorption laser induced fluorescence on O and O3 in a dc plasma for oxidation of aluminum
Authors: Knechten K. , Kniknie B. J. , Engeln R. , Swagten H. J. M. , Koopmans B. , van de Sanden M. C. M. , de Jonge W. J. M.
Published: November 2004

It has been conjectured that atomic oxygen and ozone can have a great influence on the plasma oxidation of ultrathin aluminum for magnetic tunnel junctions. In order to measure the density of O and ozone, two-photon absorption laser induced fluorescence measurements are performed in the dc glow plasma that is used for the oxidation process. It was found that ozone is much more abundantly present compared to atomic oxygen. Using in situ, real-time ellipsometry measurements, we prove that ozone is not directly involved in the oxidation process.
Near-infrared diode laser hydrogen fluoride monitor for dielectric etch
Authors: Xu Ning , Pirkle David R. , Jeffries Jay B. , McMillin Brian , Hanson Ronald K.
Published: November 2004

A hydrogen fluoride (HF) monitor, using a tunable diode laser, is designed and used to detect the etch endpoints for dielectric film etching in a commercial plasma reactor. The reactor plasma contains HF, a reaction product of feedstock gas CF4 and the hydrogen-containing films (photoresist, SiOCH) on the substrate. A near-infrared diode laser is used to scan the P(3) transition in the first overtone of HF near 1.31μm to monitor changes in the level of HF concentration in the plasma. Using 200ms averaging and a signal modulation technique, we estimate a minimum detectable HF absorbance of 6×10−5 in the etch plasma, corresponding to an HF partial pressure of 0.03mTorr. The sensor could indicate, in situ, the SiOCH over tetraethoxysilane oxide (TEOS) trench endpoint, which was not readily discerned by optical emission. These measurements demonstrate the feasibility of a real-time diode laser-based sensor for etch endpoint monitoring and a potential for process control.
Study of preferred orientation of zinc oxide films on the 64°LiNbO3 substrates and their applications as liquid sensors
Authors: Jian Shiou-Jen , Chu Sheng-Yuan , Huang Tung-Yi , Water Walter
Published: November 2004

The preferred (002) orientation of zinc oxide (ZnO) films has been grown and demonstrated on 64°LiNbO3 substrates using a rf magnetron sputtering system. The film orientations and crystallinity are strongly dependent on the rf power, total chamber pressure, ratio of argon to oxygen, and substrate temperature. We investigated the crystalline structure of the films by x-ray diffraction and scanning electron microscopy. Highly oriented (002) films were obtained under a total chamber pressure of 1.33Pa, containing 40% oxygen and 60% argon, and a substrate temperature around 120°C. Love-wave devices based on this structure (ZnO∕IDTs∕64°LiNbO3) are presented.
In situ composition monitoring using reflection high-energy electron diffraction for SrTiO3 thin films grown by reactive coevaporation
Authors: Peng Luke S.-J. , Moeckly Brian H.
Published: November 2004

We have used in situ reflection high-energy electron diffraction (RHEED) to monitor the composition of SrTiO3 (STO) thin films during growth by reactive coevaporation. This is accomplished through careful calibration of the relation between the Ti content and the STO lattice constant determined by RHEED. X-ray diffraction analysis of the films indicates that the rocking-curve and 2θ-scan peak widths of the STO (002) reflection are significantly improved after adopting this RHEED monitoring technique. This method thus results in improved epitaxial growth of STO thin films with reduced compositional fluctuations.
InN epitaxial growths on Yttria stabilized zirconia (111) step substrates
Authors: Honke T. , Fujioka H. , Ohta J. , Oshima M.
Published: November 2004

We have performed epitaxial growths of InN on Yttria stabilized zirconia (YSZ) (111) substrates which have steps and atomically flat terraces using pulsed laser deposition (PLD). The epitaxial relationship between InN and YSZ turns out to be InN[11¯00]∕∕YSZ[11¯0] and InN[0001¯]∕∕YSZ[111], which gives a small lattice mismatch of 2.3%. We have found that the full width at half maximum (FWHM) for the InN2¯024¯ x-ray rocking curve is 980arcseconds. Transmission electron microscopy (TEM) observations have revealed that the threading dislocation density in the InN films is less than 1×109cm−2 and the InN∕YSZ hetero-interface is atomically abrupt. We have also found that the lattice relaxation starts from the beginning of the growth and ends at a film thickness of approximately 5nm. After the lattice relaxation, the surface flatness is restored and the growth proceeds in the layer-by-layer mode.
Electron-cyclotron-resonance sputtering apparatus for multilayered optical bandpass filters applicable to wavelength division multiplexing
Authors: Jin Yoshito , Shimada Masaru , Ono Toshiro
Published: November 2004

A new apparatus for fabricating narrow-bandpass multilayer filters applicable to wavelength-division multiplexing and the development of this apparatus are described. Electron-cyclotron-resonance (ECR) sputtering with two plasma sources is used in the apparatus. The plasma is produced from a mixture of Ar and O2 gas and, with a metallic target, generates stable “metal-mode” deposition. That is, the target is sputtered in a metallic state, and this is followed by oxide-film formation, which is enhanced by exposure of the substrate to the ECR plasma. SiO2 and Ta2O5 films formed by ECR sputter-deposition in metal-mode are suitable for optical multilayer filters because this form of deposition provides surface smoothness, low loss, and stability of refractive index. Uniformity of deposition is good, with variations in thickness over a 200mm diameter within ±0.43% for SiO2 and ±0.27% for Ta2O5. The refractive indices of the SiO2 and Ta2O5 films are 1.46 and 2.10 at a wavelength of 1550nm. Surfaces are very smooth, with typical root-mean-square roughness values of only 0.13nm for the Ta2O5 film and 0.19nm for the SiO2 film. We describe how we deposited multilayered structures consisting of 43 layers on an optical glass substrate, alternately SiO2 and Ta2O5, and thus fabricated a narrow-band bandpass filter. We demonstrate a thin full width at half maximum of only 0.224nm and bandpass filtering uniformity within ±0.1% over the whole 100mm diameter substrate.
Interface formation during the yttrium oxide deposition on Si by pulsed liquid-injection plasma enhanced metal-organic chemical vapor deposition
Authors: Durand C. , Vallée C. , Dubourdieu C. , Gautier E. , Bonvalot M. , Joubert O.
Published: November 2004

In this article, we investigate the main mechanisms of interfacial SiO2 and silicate formation during yttrium oxide deposition on Si substrates by plasma-enhanced metal-organic chemical vapor deposition using a pulsed-liquid injection delivery source. The precursor supplier system is based on a sequential injection of Y-precursor diluted in an organic solvent. A detailed study of interface thickness and chemical nature is carried out combining angle-resolved x-ray photoelectron spectroscopy, transmission electron microscopy, and electron energy loss spectroscopy. We found that the flow rate of injected reactive species, controlled by the injection frequency, has a strong effect on the plasma gas phase and plays a key role in the SiO2 and silicate formation. For a 1Hz injection frequency deposition, a silicate layer is formed on a thick SiO2 interface [Si∕SiO2(∼3.6nm)∕SixOyYz], whereas deposition at 5Hz induces an oxidized yttrium layer with an interfacial layer composed of a SiO2 and Y-silicate mixture [Si∕SiO2+SixOyYz(∼2nm)∕YxOyCz]. To understand the actual SiO2 origin, the effect of the oxygen plasma on the silicon oxidation was investigated. According to our results, the silicon oxidation by the oxygen O* species from the plasma is strongly enhanced by the presence of organic compounds in the plasma gas phase from reactions between the solvent molecule and the oxygen. This reaction is mostly favored at a low solvent flow rate, which can explain the thicker SiO2 layer observed for the 1Hz sample compared to the 5Hz. When introducing yttrium precursor in addition to the solvent, a Y-based silicate is formed via consumption of the SiO2 by yttrium. The silicate formation is enhanced when a large quantity of SiO2 is available, which is the case for the 1Hz sample. According to this study, a high flow of reactive species is preferred to reduce the interface layer thickness.
Investigation of fluorocarbon plasma deposition from c-C4F8 for use as passivation during deep silicon etching
Authors: Labelle Catherine B. , Donnelly Vincent M. , Bogart Gregory R. , Opila Robert L. , Kornblit Avi
Published: November 2004

The passivation step used in the “Bosch” process (alternating etching and deposition steps) to perform deep anisotropic silicon etching has been examined in detail. The effect of pressure, inductively coupled plasma power, temperature, flow rate, and bias power on both deposition rate and film composition has been explored over a relatively wide range. Deposition rate was found to vary significantly as a function of temperature, power, and pressure. In contrast, only two film composition regimes were observed: high fluorine-to-carbon ratio (F:C) films (∼1.6) at low pressure∕high power versus low F:C films (∼1.2) at high pressure∕low power. Optical emission spectroscopy of the deposition plasmas also show only two regimes: C2, C3, and F emission dominated (high F:C films) and CF2 emission dominated (low F:C films). A two-step deposition mechanism is assumed: carbon deposition followed by fluorination. Low F concentration and deposition from large fluorine-deficient CxFy species in the CF2-rich plasmas result in the low F:C ratio films. Films deposited during an actual Bosch cycle generally mirror these bulk films, with slight differences. Analysis of etch:deposition rate ratios as a function of film F:C ratio indicates that, for the conditions studied here, a F:C ratio of 1.45 is optimal for Bosch processing (i.e., has the lowest etch:deposition rate ratio). Further analysis is needed to determine the effect of passivant F:C ratio on feature profiles.
Two-dimensional spatial survey of the plasma potential and electric field in a pulsed bipolar magnetron discharge
Authors: Vetushka A. , Karkari S. K. , Bradley J. W.
Published: November 2004

Emissive and Langmuir probe techniques have been used to obtain two-dimensional (2D) spatial maps of the plasma potential Vp, electric field E, and ion trajectories in a pulsed bipolar magnetron discharge. The magnetron was pulsed at a frequency of 100kHz, with a 50% duty cycle and operated at an argon pressure of 0.74Pa. The pulse wave form was characterized by three distinct phases: the “overshoot,” “reverse,” and “on” phases. In the “on” phase of the pulse, when the cathode voltage is driven to −670V, the 2D spatial distribution of Vp has a similar form to that in dc magnetron, with significant axial and radial electric fields in the bulk plasma, accelerating ions to the sheath edge above the cathode racetrack region. During the “overshoot” phase (duration 200ns), Vp is raised to values greater than +330V, more than 100V above the cathode potential, with E pointing away from the target. In the “reverse” phase Vp has a value of +45V at all measured positions, 2V more positive than the target potential. In this phase there is no electric field present in the plasma. In the bulk of the plasma, the results from Langmuir probe and the emissive probe are in good agreement, however, in one particular region of the plasma outside the radius of the cathode, the emissive probe measurements are consistently more positive (up to 45V in the “on” time). This discrepancy is discussed in terms of the different frequency response of the probes and their perturbation of the plasma. A simple circuit model of the plasma-probe system has been proposed to explain our results. A brief discussion of the effect of the changing plasma potential distribution on the operation of the magnetron is given.
Prediction of SiC etching in a NF3∕CH4 plasma using neural network
Authors: Kim Byungwhan , Lee Byung Teak
Published: November 2004

Silicon carbide (SiC) was etched in a NF3∕CH4 inductively coupled plasma. The etch process was modeled by using a neural network called generalized regression neural network (GRNN). For modeling, the process was characterized by a 24 full factorial experiment with one center point. To test model appropriateness, additional test data of 16 experiments were conducted. The GRNN prediction performance was optimized by means of a genetic algorithm (GA). Compared to a conventional GRNN model, the GA-GRNN model demonstrated a significant improvement of more than 85%. Predicted model behaviors were highly consistent with actual measurements. From the GA-optimized model, several plots were predicted to examine etch mechanisms. The model predicted that parameter effects are a complex function of plasma conditions. The etch rate was strongly correlated to the variations in the pressure-induced dc bias. This was also illustrated for the variations in the gas ratio.
Measurements of scattering by suspensions of irregularly shaped sand particles and comparison with a single parameter modified sphere model
Authors: Thorne Peter D. , Buckingham Michael J.
Published: November 2004

Measurements are presented of multi-frequency underwater acoustic backscattering from suspensions of glass spheres and sands. The data were collected in a sediment tower, specifically designed for such measurements and capable of generating a homogeneous suspension over a distance of approximately 1 m. The glass sphere data were collected to assess the capability of the system and for calibration. The measurements on suspensions of sands were obtained as part of on-going studies into the measurement of nearbed sediment transport processes using acoustics. Utilizing the backscattered sound from sand suspensions, both the form function and total scattering cross section of the sediments have been measured for a range of sediments and particle sizes. Interpretation of the observations has been carried out within a framework of sphere scattering. The results show enhanced scattering for suspensions of sand grains, relative to that of similar size spherical scatterers and the enhancement can be described by a function dependent on the particle size and the wave number of the insonifying sound, with one free parameter.
By Carrot or by Stick: Cognitive Reinforcement Learning in Parkinsonism
Authors: Frank Michael J. , Seeberger Lauren C. , O'Reilly Randall C.
Published: November 2004

To what extent do we learn from the positive versus negative outcomes of our decisions? The neuromodulator dopamine plays a key role in these reinforcement learning processes. Patients with Parkinson's disease, who have depleted dopamine in the basal ganglia, are impaired in tasks that require learning from trial and error. Here, we show, using two cognitive procedural learning tasks, that Parkinson's patients off medication are better at learning to avoid choices that lead to negative outcomes than they are at learning from positive outcomes. Dopamine medication reverses this bias, making patients more sensitive to positive than negative outcomes. This pattern was predicted by our biologically based computational model of basal ganglia–dopamine interactions in cognition, which has separate pathways for “Go” and “NoGo” responses that are differentially modulated by positive and negative reinforcement.
Acetylation by Tip60 Is Required for Selective Histone Variant Exchange at DNA Lesions
Authors: Kusch Thomas , Florens Laurence , MacDonald W. Hayes , Swanson Selene K. , Glaser Robert L. , Yates John R. , Abmayr Susan M. , Washburn Michael P , Workman Jerry L.
Published: November 2004

Phosphorylation of the human histone variant H2A.X and H2Av, its homolog in
Drosophila melanogaster
, occurs rapidly at sites of DNA double-strand breaks. Little is known about the function of this phosphorylation or its removal during DNA repair. Here, we demonstrate that the
Drosophila
Tip60 (dTip60) chromatin-remodeling complex acetylates nucleosomal phospho-H2Av and exchanges it with an unmodified H2Av. Both the histone acetyltransferase dTip60 as well as the adenosine triphosphatase Domino/p400 catalyze the exchange of phospho-H2Av. Thus, these data reveal a previously unknown mechanism for selective histone exchange that uses the concerted action of two distinct chromatin-remodeling enzymes within the same multiprotein complex.
Rescue of Dystrophic Muscle Through U7 snRNA-Mediated Exon Skipping
Authors: Goyenvalle Aurélie , Vulin Adeline , Fougerousse Françoise , Leturcq France , Kaplan Jean-Claude , Garcia Luis , Danos Olivier
Published: November 2004

Most mutations in the dystrophin gene create a frameshift or a stop in the mRNA and are associated with severe Duchenne muscular dystrophy. Exon skipping that naturally occurs at low frequency sometimes eliminates the mutation and leads to the production of a rescued protein. We have achieved persistent exon skipping that removes the mutated exon on the dystrophin messenger mRNA of the
mdx
mouse, by a single administration of an AAV vector expressing antisense sequences linked to a modified U7 small nuclear RNA. We report the sustained production of functional dystrophin at physiological levels in entire groups of muscles and the correction of the muscular dystrophy.
Molecular Detection of
Coxiella burnetii
in the Sera of Patients with Q Fever Endocarditis or Vascular Infection
Authors: Fenollar F. , Fournier P. E. , Raoult D.
Published: November 2004

In the absence of a specific diagnosis based on serology, chronic Q fever is inevitably fatal. However, diagnosis is often delayed because the test is not widely available. To shorten the diagnostic delay, we adapted a nested-PCR assay with serum as a template and the LightCycler as a thermal cycler, termed LCN-PCR. We retrospectively and prospectively applied this method to samples from 48 patients diagnosed with Q fever endocarditis or vascular infection and to samples from 100 controls with endocarditis caused by other microorganisms. We also prospectively applied this technique to samples from 30 patients treated for a Q fever endocarditis and to samples from 13 patients with a convalescent acute Q fever with ambiguous immunoglobulin G (IgG) phase I titer. LCN-PCR had a specificity of 100%. It was positive only in samples from patients with evolutive Q fever, as none of the samples from patients with a treated chronic Q fever or with a convalescent acute Q fever presented positive results. When performed prospectively on recently stored sera, the sensitivity of LCN-PCR is 64% (7 of 11 samples;
P
= 0.004), but the efficiency of LCN-PCR was dramatically altered by the storage of specimens at −20°C. High IgG phase I titers decreased the sensitivity of LCN-PCR. A significant difference was observed among LCN-PCR results for sera with IgG phase I titers of ≥1:25,600 compared to sera with IgG phase I titers of <1:25,600 (0 of 15 samples versus 13 of 33 samples;
P
= 0.004). In patient samples with titers below 1:25,600 tested prospectively, sensitivity was 100% (7 of 7). The LCN-PCR assay may be helpful in establishing an early diagnosis of chronic Q fever.
Development of a PCR Method for Rapid Identification of New
Streptococcus mutans
Serotype
k
Strains
Authors: Nakano Kazuhiko , Nomura Ryota , Shimizu Noriko , Nakagawa Ichiro , Hamada Shigeyuki , Ooshima Takashi
Published: November 2004

In a previous study, we isolated and characterized a new serotype
k
of
Streptococcus mutans
from human blood and oral cavities. Analysis of the genes involved in biosynthesis of the serotype-specific polysaccharide of serotype
k
strains revealed that the serotype
k
-specific nucleotide alignment was commonly present in the 5′ region of the
rgpF
gene (350 bp from the initial sequence) compared to the reference strains, and then a method for rapid identification of serotype
k
strains was developed by use of PCR with primers designed on the basis of the sequence of the variable region. PCR assays with primers specific for amplification of serotype
k
strains showed a negative reaction with serotype
c
,
e
, and
f
strains and a positive reaction with serotype
k
strains, with the sensitivity for identification of the serotype
k
strains shown to range from 5 to 50 cells. Next, the frequency of positive reactions for serotype
k
-specific primers was surveyed with DNA taken from saliva samples from 200 subjects (2 to 18 years of age), and 10 of those showed a positive reaction, which was higher than the frequency in our previous survey with a serological method. In addition, all saliva samples from subjects with serotype
k
strains in our previous study were shown to be positive with the serotype
k
-specific primers. These results indicate that this new PCR method is effective for identification of subjects with
S. mutans
serotype
k
.
Distribution of Putative Adhesins in Different Seropathotypes of Shiga Toxin-Producing
Escherichia coli
Authors: Toma Claudia , Martínez Espinosa Estela , Song Tianyan , Miliwebsky Elizabeth , Chinen Isabel , Iyoda Sunao , Iwanaga Masaaki , Rivas Marta
Published: November 2004

The distribution of eight putative adhesins that are not encoded in the locus for enterocyte effacement (LEE) in 139 Shiga toxin-producing
Escherichia coli
(STEC) of different serotypes was investigated by PCR. Five of the adhesins (Iha, Efa1, LPF
O157/OI-141
, LPF
O157/OI-154
, and LPF
O113
) are encoded in regions corresponding to genomic O islands of
E. coli
EDL933, while the other three adhesins have been reported to be encoded in the STEC megaplasmid of various serotypes (ToxB [O157:H7], Saa [O113:H21], and Sfp [O157:NM]). STEC strains were isolated from humans (
n
= 54), animals (
n
= 52), and food (
n
= 33). They were classified into five seropathotypes (A through E) based on the reported occurrence of STEC serotypes in human disease, in outbreaks, and in the hemolytic-uremic syndrome (M. A. Karmali, M. Mascarenhas, S. Shen, K. Ziebell, S. Johnson, R. Reid-Smith, J. Isaac-Renton, C. Clark, K. Rahn, and J. B. Kaper, J. Clin. Microbiol.
41:
4930-4940, 2003). The most prevalent adhesin was that encoded by the
iha
gene (91%; 127 of 139 strains), which was distributed in all seropathotypes.
toxB
and
efa1
were present mainly in strains of seropathotypes A and B, which were LEE positive.
saa
was present only in strains of seropathotypes C, D, and E, which were LEE negative. Two fimbrial genes,
lpfA
O157
/
OI-141
and
lpfA
O157
/
OI-154
, were strongly associated with seropathotype A. The fimbrial gene
lpfA
O113
was present in all seropathotypes except for seropathotype A, while
sfpA
was not present in any of the strains studied. The distribution of STEC adhesins depends mainly on serotypes and not on the source of isolation. Seropathotype A, which is associated with severe disease and frequently is involved in outbreaks, possesses a unique adhesin profile which is not present in the other seropathotypes. The wide distribution of
iha
in STEC strains suggested that it could be a candidate for vaccine development.
Evaluation of a Rapid Immunochromatographic Assay for Identification of
Candida albicans
and
Candida dubliniensis
Authors: Marot-Leblond Agnes , Grimaud Linda , David Sandrine , Sullivan Derek J. , Coleman David C. , Ponton Jose , Robert Raymond
Published: November 2004

Candida dubliniensis
was first established as a novel yeast species in 1995. It is particularly associated with recurrent episodes of oral candidosis in human immunodeficiency virus (HIV)-infected patients, but it has also been detected at other anatomical sites and at a low incidence level in non-HIV-infected patients. It shares so many phenotypic characteristics with
C. albicans
that it is easily misidentified as such. No rapid, simple, and commercial test that allows differentiation between
C. dubliniensis
and
C. albicans
has been developed, until now. Accurate species identification requires the use of genotype-based techniques that are not routinely available in most clinical microbiology diagnostic laboratories. The present study was designed to evaluate the efficiency of a new test (the immunochromatographic membrane [ICM] albi-dubli test; SR2B, Avrillé, France) to differentiate between
C. albicans
and
C. dubliniensis
. The organisms evaluated were strains whose identities had previously been confirmed by PCR tests and freshly isolated clinical strains and included 58
C. albicans
isolates, 60
C. dubliniensis
isolates, and 82 isolates belonging to other species of yeast. The ICM albi-dubli test is based on the principle of immunochromatographic analysis and involves the use of two distinct monoclonal antibodies that recognize two unrelated epitopes expressed by both species or specific to only one species. The assay requires no complex instrumentation for analysis and can be recommended for routine use in clinical microbiology laboratories. Results are obtained within 2 h and 30 min and are easy to interpret. This evaluation demonstrated the good performance of this immunochromatographic test for
C. albicans
and
C. dubliniensis
isolated on Sabouraud dextrose agar, CHOROMagar Candida, and CandidaSelect, with sensitivities and specificities ranging from 93.1 to 100%. These parameters decreased, however, to 91.4% when the test was performed with yeast isolated with Candida ID.
Genotypic Diversity of
Francisella tularensis
Infecting
Dermacentor variabilis
Ticks on Martha's Vineyard, Massachusetts
Authors: Goethert Heidi K. , Shani Inbar , Telford Sam R.
Published: November 2004

Martha's Vineyard, Mass., has been the site of two outbreaks of tularemia (1978 and 2000). Although most patients from both outbreaks presented with pneumonic disease and although aerosol transmission has been suggested, the bite of a dog tick and exposure to rabbits remain the only proven modes of transmission. The factors that precipitated the tularemia outbreaks or the proximal determinants of human risk remain undescribed. We sought to test the hypothesis that the ongoing outbreak is due to a recent introduction event as opposed to amplification of a cryptic enzootic cycle. From 2001-2003, we collected 4,246 dog ticks and tested them in pools for evidence of tularemia by PCR. We then measured the genetic diversity of
Francisella tularensis
by using multiple-locus variable-number tandem repeat analysis. The prevalence of
F. tularensis
in dog ticks averaged 0.7%. From 29 positive pools, we identified 10 unique genotypes, which was an unexpectedly large degree of diversity (Simpson's index = 0.86). This degree of genetic diversity is inconsistent with a recent introduction event. We conclude that there has been long-standing enzootic transmission of tularemia on the island.
Nasopharyngeal versus Oropharyngeal Sampling for Detection of Pneumococcal Carriage in Adults
Authors: Watt James P. , O'Brien Katherine L. , Katz Scott , Bronsdon Melinda A. , Elliott John , Dallas Jean , Perilla Mindy J. , Reid Raymond , Murrow Laurel , Facklam Richard , Santosham Mathuram , Whitney Cynthia G.
Published: November 2004

Several studies have shown that nasopharyngeal sampling is more sensitive than oropharyngeal sampling for the detection of pneumococcal carriage in children. The data for adults are limited and conflicting. This study was part of a larger study of pneumococcal carriage on the Navajo and White Mountain Apache Reservation following a clinical trial of a seven-valent pneumococcal conjugate vaccine. Persons aged 18 years and older living in households with children enrolled in the vaccine trial were eligible. We collected both nasopharyngeal and oropharyngeal specimens by passing a flexible calcium alginate wire swab either nasally to the posterior nasopharynx or orally to the posterior oropharynx. Swabs were placed in skim milk-tryptone-glucose-glycerin medium and frozen at −70°C. Pneumococcal isolation was performed by standard techniques. Analyses were based on specimens collected from 1,994 adults living in 1,054 households. Nasopharyngeal specimens (11.1%; 95% confidence interval [CI], 9.8 and 12.6%) were significantly more likely to grow pneumococci than were oropharyngeal specimens (5.8%; 95% CI, 4.8 to 6.9%) (
P
< 0.0001). Few persons had pneumococcal growth from both specimens (1.7%). Therefore, both tests together were more likely to identify pneumococcal carriage (15.2%; 95% CI, 13.7 to 16.9%) than either test alone. Although we found that nasopharyngeal sampling was more sensitive than oropharyngeal sampling, nasopharyngeal sampling alone would have underestimated the prevalence of pneumococcal carriage in this adult population. Sampling both sites may give more accurate results than sampling either site alone in studies of pneumococcal carriage in adults.
Prevalence and Molecular Analysis of Macrolide and Fluoroquinolone Resistance among Isolates of
Streptococcus pneumoniae
Collected during the 2000-2001 PROTEKT US Study
Authors: Brown Steven D. , Farrell David J. , Morrissey Ian
Published: November 2004

The PROTEKT US (Prospective Resistant Organism Tracking and Epidemiology for the Ketolide Telithromycin in the United States) surveillance program was established to determine the prevalence and mechanisms of antibacterial resistance among bacterial pathogens from patients with community-acquired respiratory tract infections. In year 1 of the PROTEKT US study, 10,103 isolates of
Streptococcus pneumoniae
, including 3,133 erythromycin-resistant strains and 81 levofloxacin-resistant strains, were collected from 206 centers. We report on the molecular analyses of these resistant strains. The resistance genotypes among the 3,044 typed macrolide-resistant isolates overall were
mef
(A) (
n
= 2,157; 70.9%),
erm
(B) (
n
= 530; 17.4%),
mef
(A)
erm
(B) (
n
= 304; 10.0%), and
erm
(A) subclass
erm
(TR) (
n
= 5; 0.2%). Fifty (1.6%) macrolide-resistant isolates were negative for the
mef
and the
erm
resistance genes. Seventy-eight (96.3%) of the 81 levofloxacin-resistant isolates analyzed possessed multiple mutations in the
gyrA
,
gyrB
,
parC
, and/or
parE
quinolone resistance-determining regions. A total of 43 known multilocus sequence typing (MLST) profiles (or single- or double-locus variants) accounted for 75 of 81 isolates. There was no evidence of dissemination of fluoroquinolone-resistant clones within the United States; however, 12 isolates with the same MLST profile were located in one center in Massachusetts. Almost 90% of the erythromycin-resistant isolates and approximately one-third of the levofloxacin-resistant isolates were multidrug resistant.
Detection and Selection of Microsatellites in the Genome of
Paracoccidioides brasiliensis
as Molecular Markers for Clinical and Epidemiological Studies
Authors: Nascimento Érika , Martinez Roberto , Rodrigues Lopes André , de Souza Bernardes Luciano Angelo , Pomponio Barco Carolina , Goldman Maria Helena S. , Taylor John W. , McEwen Juan G. , Pasetto Nobrega Marina , Nobrega Francisco G. , Goldman Gustavo H.
Published: November 2004

Paracoccidioides brasiliensis
, a thermodimorphic fungus, is the causative agent of the prevalent systemic mycosis in Latin America, paracoccidioidomycosis (PCM). Here, we describe the microsatellite patterns observed in a collection of
P. brasiliensis
random sequence tags. We identified 1,117 microsatellite patterns in about 3.8 Mb of unique sequences (0.47% of the total DNA used in the analysis). The majority of these microsatellites (87.5%) are found in noncoding sequences. We used two polymorphic microsatellites located on noncoding and coding sequences, as well as two microsatellites located on introns, as molecular markers to discriminate
P. brasiliensis
isolates, to look for relationships between the genetic background of the strains and the types of human disease they cause. We did not observe any correlation between the clinical form of human PCM and four simple sequence repeat patterns analyzed.