bluuebunny/crossref_metadata_2025 huggingface dataset:
Position‐specific expression of Hox genes along the gastrointestinal tract
Authors: Yahagi Naohisa , Kosaki Rika , Ito Taichi , Mitsuhashi Takayuki , Shimada Hiroyuki , Tomita Masaru , Takahashi Takao , Kosaki Kenjiro
Published: March 2004

ABSTRACT  Hox genes play a critical role in morphogenesis of the early embryo along the anteroposterior axis. In mammals, 39 Hox genes with extensive homology are organized into 13 paralogous groups, forming four clusters on four separate chromosomes. The genes within each cluster are arranged in a 3′ to 5′ direction and expressed in a temporally and spatially coordinated manner along the anteroposterior axis in the vertebrae, limbs and viscera, including the gastrointestinal tract, but little is known about their spatial expression in the adult gastrointestinal tract. We used the quantitative polymerase chain reaction (PCR) intercalater method with SYBR GreenTM to quantify human Hox gene expression in the adult gastrointestinal tract tissue: esophagus, stomach, duodenum, jejunum, ileum, ileocecum, cecum, ascending colon, transverse colon, descending colon and rectum. Hox gene expression was normalized to glyceraldehyde‐3‐phosphate‐dehydrogenase (GAPDH) gene expression. The spatial expression pattern was analyzed by the multivariate method. The expression level of all 39 Hox genes could be measured in a reproducible manner. Genes with higher expression in the foregut‐derived segments tended to have lower expression in hindgut‐derived segments, whereas those with low expression in the former tended to have higher in the latter. Principal components analysis and permax analysis revealed a position‐specific expression pattern of Hox genes along the anteroposterior axis of the adult gastrointestinal tract. The pattern recapitulates the expression pattern in the embryonic gastrointestinal tract. We suggest that Hox genes may play a pivotal role in the position‐specific regenerative process of intestinal epithelial cells.
Sonic hedgehog expression inGli3depressed mouse embryo,Pdn/Pdn
Authors: Ueta Etsuko , Maekawa Mizuho , Morimoto Ikuyo , Nanba Eiji , Naruse Ichiro
Published: March 2004

ABSTRACT The phenotype of the genetic polydactyly/arhinencephaly mouse (Pdn/Pdn) is similar to Greig cephalopolysyndactyly syndrome (GCPS), which is induced by mutation ofGLI3. Suppression ofGli3gene expression has been observed inPdn/Pdn. Thus, the gene responsible forPdn/Pdnhas been considered to beGli3. Recently, the mutation point was demarcated, that is, a transposon was inserted into intron 3 of theGli3gene in thePdnmouse. Forward and reverse primers were constructed in intron 3 near the insertion point. A forward primer in the long terminal repeat region of the transposon was also constructed. Now we can discriminate +/+,Pdn/+,Pdn/Pdnembryos from the PCR products. After genotyping of thePdnembryos,Gli3and other correlated gene expressions, such as sonic hedgehog (Shh),Bmp‐2,Bmp‐4,ptc‐1, were analyzed by real‐time PCR method.Gli3gene expression inPdn/Pdnwas suppressed to 20–30% of +/+, and that inPdn/+was about 60% of +/+ through all the embryonic and neonatal periods examined. AsShhhas been considered to be an antagonist ofGli3,Shhexpression was analyzed, and a difference among genotypes was observed only on day 9 of gestation. We could not detect any alterations among genotypes in other gene expressions examined.Gli3andShhgene expression were also analyzed on day 9 by whole‐mountin situhybridization in the +/+ andPdn/Pdnembryos. Neuroectoderm was positive byGli3probe in +/+ but not inPdn/Pdn. Notochord, floor plate and prechordal mesoderm were positive byShhprobe both in +/+ andPdn/Pdnembryos, but ectopic and/or over‐expression ofShhwere not observed inPdn/Pdnembryos.
High molecular weight microtubule‐associated protein 2 over‐expression in neuronal migration disorders caused byN‐methyl‐d‐aspartate receptor activation in hamsters
Authors: Takano Tomoyuki , Sawai Chihiro , Takeuchi Yoshihiro
Published: March 2004

ABSTRACT To evaluate the neuronal cytoarchitectural changes in neuronal migration disorders, the immunohistochemical expression of microtubule‐associated proteins (MAPs) was analyzed using the experimental model induced by ibotenate in newborn hamsters. The cortical lesions observed after intracerebral ibotenate injections strongly resembled the following neuronal migration disorders: (1) microgyria; (2) focal subcortical heterotopia; (3) focal subependymal heterotopia; and (4) leptomeningeal glioneuronal heterotopia. Microgyria and leptomeningeal glioneuronal heterotopia had MAP2 (HM‐2: high and low‐molecular‐weight forms of MAP2) immunoreactive dendritic processes or neuronal elements. The high molecular weight isoform of MAP2 (AP‐20), which is more characteristic of mature neurons, showed enhanced expression in neurons of focal subcortical or subependymal heterotopia, although MAP1B (AA6: early form of MAP) immunoreactive elements were not detected in these heterotopic areas. We conclude that high molecular weight isoform of MAP2 is closely associated with cytoarchitectural repair and remodeling of neuronal processes, resulting in neuronal heterotopia after NMDA receptor activation.
Abnormal expression of tyrosine hydroxylase not accompanied by phosphorylation at serine 40 in cerebellar Purkinje cells of ataxic mutant mice, rolling mouse Nagoya and dilute‐lethal
Authors: Sawada Kazuhiko , Ando Masahiro , Sakata‐Haga Hiromi , Sun Xue‐Zhi , Jeong Young‐Gil , Hisano Setsuji , Takeda Noriaki , Fukui Yoshihiro
Published: March 2004

ABSTRACT  This study examined immunohistochemically the expression of an enzymatically active form of tyrosine hydroxylase (TH), phosphorylated TH at Ser40 (phospho‐TH), in the cerebellum of ataxic mutant mice, rolling mouse Nagoya (RMN) and dilute‐lethal (DL). TH immunostaining appeared in some Purkinje cells in RMN and DL, but in a few of the Purkinje cells of littermate controls for both mutants. In all groups of mice, there were no phospho‐TH immunoreactive Purkinje cells in the cerebellum, although the subsets of TH immunoreactive Purkinje cells were found in the adjacent sections. The results suggest that TH expression in the Purkinje cells of ataxic mutants abnormally increases without activation of this enzyme by phosphorylation. This may mean that TH in Purkinje cells is not related to catecholamine synthesis.
Population‐based case‐control teratologic study of topical miconazole
Authors: Czeizel Andrew Endre , Kazy Zoltán , Puhó Erzsébet
Published: March 2004

ABSTRACT  Miconazole cream is used in Hungary to treat fungal genital and skin infections in pregnant women, but it causes anxiety for both patients and medical doctors due to the category C classification of the drug regarding teratogenic or fetotoxic risk. The objective of this case–control study was to analyze the teratogenic potential of topical miconazole used during pregnancy in the mothers of babies with congenital abnormalities and in matched control mothers of babies without congenital abnormalities. The population‐based data set of the Hungarian Case–Control Surveillance of Congenital Abnormalities between 1980 and 1996 included 22 843 women who had newborns or fetuses with congenital abnormalities, and 38 151 pregnant women who had newborn infants without any defects (controls). In the case group, 24 (0.11%) and in the control group, 46 (0.12%) pregnant women were treated with miconazole (crude odd ratio [OR]: 0.9 with 95% confidence interval [CI]: 0.6–1.6). Different congenital abnormality groups were evaluated in case–control pairs and a higher prevalence of miconazole treatment was not found during the second or third month of pregnancy. Thus, treatment with topical miconazole during pregnancy does not increase the risk of congenital abnormalities.
Amorphous fluorocarbon polymer (a-C:F) films obtained by plasma enhanced chemical vapor deposition from perfluoro-octane (C8F18) vapor I: Deposition, morphology, structural and chemical properties
Authors: Biloiu Costel , Biloiu Ioana Arabela , Sakai Yosuke , Suda Yoshiyuki , Ohta Akitsugu
Published: March 2004

The method of obtaining amorphous fluorocarbon polymer (a-C:F) films by plasma enhanced chemical vapor deposition in a capacitively coupled, 13.56 MHz reactor, from a new monomer, namely perfluoro-octane (C8F18) vapor, is presented. For monomer pressure ranging from 0.2 to 1 Torr and input power density from 0.15 to 0.85 W/cm3, the maximum deposition rate reached 300 nm/min, while 10% monomer dilution with argon led to a deposition rate of 200 nm/min. The film surface and bulk morphologies, chemical and structural compositions were investigated using scanning electron microscopy, x-ray photoelectron spectroscopy, and Fourier transform infrared spectroscopy. It was revealed that the films have a dense and compact structure. The fluorine to carbon ratio (F/C) of the films was between 1.57 and 1.75, and the degree of cross-linking was between 55% and 58%. The relative amount of perfluoroalkyl (CF2) groups in the films was 29%. The FTIR spectra showed absorption bands corresponding to the different vibrational modes of CF, CF2, and CF3 moieties.
Remote plasma enhanced atomic layer deposition of TiN thin films using metalorganic precursor
Authors: Kim Ju Youn , Seo Sangwon , Kim Do Youl , Jeon Hyeongtag , Kim Yangdo
Published: March 2004

TiN films were deposited by remote plasma enhanced atomic layer deposition (PEALD) method using tetrakis-dimethyl-amino-titanium precursor and hydrogen, hydrogen/nitrogen mixture, and nitrogen plasmas. Remote PEALD method showed a relatively wide temperature window compared to that of conventional ALD process due to the increased reactivity of reactant gas. TiN films showed significantly lower impurity contents than those of the films deposited by other methods such as plasma enhanced chemical vapor deposition, metalorganic chemical vapor deposition, and conventional ALD using the same precursor. TiN films deposited using N2 plasma showed better characteristics than the films deposited using H2 and H2/N2 mixture plasmas. TiN films deposited by remote PEALD at 250 °C showed the resistivity value as low as about 300 μΩ cm and exhibited excellent conformal step coverage on 0.25-μm-wide and 2.5-μm-deep contact hole structure.
Poly (ethylene terephthalate) decomposition process in oxygen plasma; emission spectroscopic and surface analysis for oxygen–plasma reaction
Authors: Kumagai Hidetoshi , Hiroki Denbo , Fujii Nobuyuki , Kobayashi Takaomi
Published: March 2004

Emission spectroscopy was applied to observe the reaction process of poly (ethylene terephthalate) (PET) in an oxygen (O2) plasma generated by a microwave discharge. As the PET was exposed in the O2 plasma flow, light emitted from the PET surface was monitored. In the diagnosis measurement, several emission peaks assigned to the Hα atomic line at 652 nm, Hβ at 486 nm, OH (2Σ→2Π) transition near 244–343 nm and CO (b3 Σ→a3 Σ) near 283–370 nm were observed and measured at various discharge times. These results indicated that after the plasma etching, the PET sample was decomposed by the oxygen plasma reaction, and then, hydrogen abstraction and carbon oxidation processes. We also observed the time profile of oxygen atom, as the atom-emission intensity at 777 nm was monitored. As Hβ atomic and OH molecule lines appeared in the presence of PET, the O atom intensity was significantly reduced. In the surface analysis on Fourier transform infrared and x-ray photoelectron spectroscopy measurements, it was found that for the PET surface treated by O2 plasma containing excited atomic oxygen species, ester bands were broken and carbonization formed on the PET surface.
Influence of negative ion resputtering on ZnO:Al thin films
Authors: Rieth Loren W. , Holloway Paul H.
Published: March 2004

The influence of negative ion resputtering (NIR) by oxygen ions during sputter deposition of aluminum doped zinc oxide (ZnO:Al) thin films is investigated. A planar rf diode sputter deposition source with a ceramic ZnO:Al2O3 (98 wt %:2 wt %) target is used for deposition at 250, 500 and 1000 W. The resulting thin films are characterized by four point probe, Hall measurements, secondary ion mass spectrometry (SIMS), x-ray diffraction (XRD), and atomic force microscopy (AFM). The resistivity and carrier concentration show an order of magnitude variation between 2×10−2 and 1.5×10−3 Ω cm and 7.2×1019 and 5.4×1020 cm−3, respectively, with the position on the substrate and deposition power. The Hall mobility changes are small, from 4.7 to 11.5 cm2/V s. Data from SIMS show that the variations in electrical properties do not result from contamination by alkali metals or changes in the Al dopant concentration. Spectra from XRD have one predominant peak near 34.4° indicating that the film is wurtzite and strongly textured in the (002) basal direction. All peaks are lower in 2θ than literature values, which indicates an expanded lattice in the c direction. Grain size estimates based on AFM data suggest that changes in grain size are not large enough to cause the changes in electrical properties. Compensation of free carriers by interstitial oxygen ions due to implantation and Frenkel pair generation resulting from an energetic oxygen ion flux are consistent with the data, and are postulated to be the mechanisms by which NIR influences the electrical properties of ZnO. The flux of negative ions is estimated to be 1% of the total ion flux. The correlation between NIR and the influence of deposition parameters is discussed.
Role of fluorocarbon film formation in the etching of silicon, silicon dioxide, silicon nitride, and amorphous hydrogenated silicon carbide
Authors: Standaert T. E. F. M. , Hedlund C. , Joseph E. A. , Oehrlein G. S. , Dalton T. J.
Published: March 2004

The etching of Si, SiO2, Si3N4, and SiCH in fluorocarbon plasmas is accompanied by the formation of a thin steady-state fluorocarbon film at the substrate surface. The thickness of this film and the substrate etch rate have often been related. In the present work, this film has been characterized for a wide range of processing conditions in a high-density plasma reactor. It was found that the thickness of this fluorocarbon film is not necessarily the main parameter controlling the substrate etch rate. When varying the self-bias voltage, for example, we found a weak correlation between the etch rate of the substrate and the fluorocarbon film thickness. Instead, for a wide range of processing conditions, it was found that ion-induced defluorination of the fluorocarbon film plays a major role in the etching process. We therefore suggest that the fluorocarbon film can be an important source of fluorine and is not necessarily an etch-inhibiting film.
Effect of the substrate bias voltage on the physical characteristics of copper films deposited by microwave plasma-assisted sputtering technique
Authors: Thièry F. , Pauleau Y. , Ortega L.
Published: March 2004

Pure copper films have been deposited by microwave plasma-assisted sputtering on (100)-oriented single crystal silicon substrates mounted on a water-cooled substrate holder either maintained at the floating potential or biased to various dc voltages ranging from 0 to −125 V. The argon pressure was fixed at 0.13 Pa and argon ions from the discharge produced in a distributed electron cyclotron resonance microwave plasma chamber were used for sputtering of a copper target biased to −600 V. The crystallographic structure and surface morphology of copper films were determined by x-ray diffraction techniques and atomic force microscopy, respectively. The magnitude of residual stresses developed in these films was calculated from the radius of curvature of Si substrates. The electrical resistivity of films was deduced from the thickness and sheet resistance of films determined by profilometry and four point probe measurements. The evolution of the deposition rate, surface roughness, microstructure, magnitude of residual stresses, and electrical resistivity of films was investigated as a function of the substrate bias voltage. The major characteristics of copper films were found to vary significantly as the negative substrate bias voltage increased from −40 to −125 V or with increasing argon ion energy. The resputtering process of a fraction of copper atoms by energetic incident argon ions was responsible for the modification of characteristics of films deposited on biased substrates. The quality of copper films in terms of surface morphology and electrical resistivity in particular was found to be excellent for incident argon ion energy values lower than 70 eV.
Orientation selective epitaxial growth of CeO2(100) and CeO2(110) layers on Si(100) substrates
Authors: Inoue Tomoyasu , Sakamoto Naomichi , Ohashi Masayuki , Shida Shigenari , Horikawa Akihiro , Sampei Yoshiyuki
Published: March 2004

It is found that epitaxial CeO2 layers with (100) or (110) orientation can be selectively grown on Si(100) substrates by controlling substrate bias in reactive dc magnetron sputtering. Adopting a two step growth method; ultrathin metallic Ce layer deposition at room temperature followed by a silicidation process at 800 °C, and subsequent reactive sputtering in an Ar/O2 mixture environment, the CeO2(100) layer is grown on practical Si(100) surfaces prepared by the usual wet cleaning method.
Simple method of gas flow ratio optimization in high rate deposition of SiO2 by electron cyclotron resonance plasma enhanced chemical vapor deposition
Authors: Daineka D. , Bulkin P. , Girard G. , Drévillon B.
Published: March 2004

We propose a simple method to optimize silane-to-oxygen flow ratio in low pressure, high-density plasma enhanced chemical vapor deposition of SiO2 from silane/oxygen mixtures. It is well known that the increase of SiH4/O2 flow ratio R results in degradation of oxide quality. We have found that the critical flow ratio can be estimated from the analysis of the difference between gas pressures with and without plasma. The evolution of optical properties of the films shows that the critical value obtained from pressure measurements gives a good indication of the limits for the deposition of optical quality SiO2.
Temperature-resolved Fourier transform infrared study of condensation reactions and porogen decomposition in hybrid organosilicon-porogen films
Authors: Burkey Daniel D. , Gleason Karen K.
Published: March 2004

Composite organosilicon/porogen thin films were deposited via pulsed-plasma chemical vapor deposition. The organosilicon monomer was polymerized using water as the oxidant, allowing incorporation of silanol (Si–OH) moieties for subsequent condensation reactions and crosslinking for enhanced mechanical properties. The porogen monomer [methylmethacrylate (MMA)] was codeposited in the same step, and the degree of MMA incorporation was shown to scale with both the peak plasma power and porogen flow rate. Fourier transform infrared (FTIR) spectroscopy spectra of the composite material show features from both the organosilicon precursor and the porogen species, indicating that both materials are successfully incorporated into the thin film. The kinetics of both the condensation reaction and porogen removal were determined by a temperature/time-resolved FTIR method. The condensation reaction and crosslinking events occur between 100 and 425 °C. Porogen decomposition occurs simultaneously between approximately 325 and 400 °C, which is consistent with the decomposition of poly(methylmethacrylate). Using these data, the activation energy for the primary decomposition mode was found to be approximately 53.6 kJ/mol (12.8 kcal/mol). Both the index of refraction and the dielectric constant scale with the degree of porogen removal, suggesting the formation of free volume in the films. The lowest index of refraction and dielectric constant obtained was 1.404 and 2.3, respectively, for a 1 h anneal at 425 °C. Worst-case thickness loss for the films was approximately 36% of the as-deposit thickness.
Measurement of absolute radical densities in a plasma using modulated-beam line-of-sight threshold ionization mass spectrometry
Authors: Agarwal Sumit , Quax Guido W. W. , van de Sanden M. C. M. , Maroudas Dimitrios , Aydil Eray S.
Published: March 2004

Using modulated beam line-of-sight threshold ionization mass spectrometry (LOS-TIMS) we measured absolute O, O2, and Ar densities, and the average neutral-gas temperature in an O2/Ar electrical discharge as a function of pressure in the plasma chamber and the mole fraction of Ar in O2; the pressure and mole fraction range was 25–200 mTorr and 0–0.90, respectively. Although LOS-TIMS is a versatile tool for measuring absolute radical densities, it requires careful vacuum design and calibration to account for various sources of error such as the contribution to the quadrupole mass spectrometer (QMS) ion current from the background gases, the ion mass-to-charge ratio dependent sensitivity of the various QMS components, and space-charge limitations in the QMS ionizer. In addition, collisions within the molecular beam extracted from the discharge must be taken into account particularly for higher plasma chamber pressures (>75 mTorr). In our measurements, these effects are carefully considered and the consequences of ignoring them are discussed. The O atom density increases with pressure and O2 mole fraction in the feed gas and is in the range of 2.1×1018–2.6×1019 m−3. At low pressures, our measurements show that the O2 translational temperature is higher than that for Ar.
Correlation between density and oxidation temperature for pyrolytic-gas passivated ultrathin silicon oxide films
Authors: Yamada Hiroshi
Published: March 2004

Pyrolytic-gas passivation (PGP) with a small amount nitrogen gas enhances the breakdown reliability of silicon oxide gate films. To clarify the reliability retention of the PGP-grown films oxidized at low temperature, densities (ρox’s) of the 3.5–6.5-nm-thick PGP-grown films on Si(100) oxidized at 700–900 °C were investigated. Since ρox’s correlate well with the reliability and are useful as an index of the intrinsic structural characteristics of the films. Moreover, changes in ρox and nitrogen content corresponding to oxidation temperature are similar to those in breakdown reliability and interface state density (Dit), respectively. In addition, ρox’s of the 700 °C-grown PGP films do not deteriorate as much when compared with those of the films grown by normal ultradry oxidation at 800 °C and their Dit’s are less than about 6×1010/eV cm2. This suggests that PGP probably improves the reliability by generating the higher-ρox microscopic structure with few Si dangling bonds and effective passivation.
Magnetic domain structures in ultrathin FexNi(1−x) films on Cu(111): Dependence on film thickness and stoichiometry
Authors: Sato Y. , Johnson T. F. , Chiang S. , Giacomo J. A. , Zhu X. D. , Land D. P. , Nolting F. , Scholl A.
Published: March 2004

The magnetic domain structures in thin FexNi(1−x) alloy films grown on Cu(111) have been investigated by the photoemission electron microscope (PEEM). By tuning the photon energy to respective x-ray absorption edges, element-specific information can be obtained with PEEM. We have observed clear ferromagnetic domains on samples with an iron concentration of x⩽0.6 and x=1.0. The PEEM images indicate that Fe and Ni form a good alloy on Cu(111), with the same domain structures and the magnetization in each domain aligned for both elements. The domain sizes and shapes exhibit dependence on thickness, stoichiometry x, and substrate quality.
Effects of substrates and heat treatment on growing behavior and luminescent characteristics of ZnGa2O4:Mn thin film
Authors: Chung Sung Mook , Kim Young Jin
Published: March 2004

ZnGa 2 O 4 : Mn phosphor thin films were deposited on ZnO:Ga/glass, ZnO:Al/glass, ZnO/ITO/glass, and ITO/glass by rf magnetron sputtering. Effects of substrates and heat treatment on the structural and luminescent properties were investigated. The surface morphology, growing behavior, and luminescent properties of thin films depend on the crystallinity of the substrates. Thin film phosphors were heat-treated in a N2+vacuum, vacuum (∼10−3 Torr), and air atmosphere, respectively. The annealing conditions did not affect the surface morphology and crystallinity of the films. However, the Ga/Zn atomic ratios and luminescent characteristics were dependent on these conditions.
Crystallographic structure and composition of vanadium nitride films deposited by direct sputtering of a compound target
Authors: Liao M. Y. , Gotoh Y. , Tsuji H. , Ishikawa J.
Published: March 2004

Vanadium nitride thin films (VN) were sputter-deposited on silicon substrates in an argon gas atmosphere with a VN compound target. Nearly stiochiometric cubic VN films with different crystallographic orientations were achieved at ambient substrate temperature. The crystallographic structure of the film could be controlled through adjusting working argon pressure. Films with preferred (100) and (111) orientations were obtained at pressures of 0.5 and 2.0 Pa, respectively, regardless of the sputtering power; while amorphous film may form at a middle pressure of 1.0 Pa. Composition of the resultant films was analyzed by Rutherford backscattering spectroscopy. It was revealed that nitrogen deficiency was responsible for the amorphous state. The electronic states related to nitrogen vacancy were disclosed by valence band spectrum. The film compositional variation was discussed in the text.
Growth of chemical vapor deposition aluminum titanate films at different CO2/H2 and aluminum butoxide inputs
Authors: Kuo Dong-Hau , Shueh Cheng-Nan
Published: March 2004

Amorphous aluminum titanate films are prepared on silicon substrates by low-pressure chemical vapor deposition (CVD) using a mixture of aluminum tri-sec-butoxide (ATSB), titanium tetrachloride (TiCl4), CO2, and H2 as the reactants (the ATSB/TiCl4/CO2/H2 system). The effects of the CO2/H2 and ATSB inputs and substrate temperature on the growth, microstructure, and composition of the CVD Al2O3–TiO2 films are discussed. The films have an increased growth rate and an increased Ti content at lower temperatures. The adsorption-controlled reaction is identified, which is attributed to the gas/solid reaction to weaken the film/substrate interface. The growth rates are also higher at higher H2 and ATSB flows. The film thickness is 0.47–1.13 μm for the CO2/H2-varying system and of 0.34–1.37 μm for the ATSB-varying system at deposition temperatures of 350–500 °C. The proposed reactions are presented to explain the film growth. The determined adsorption energy can explain the effect of temperature on composition.
Ion doses for low-energy ion-assist applications
Authors: Kaufman H. R. , Harper J. M. E.
Published: March 2004

We present simple, convenient procedures for calculating ion doses for ion-assist applications such as cleaning and property modification. For many of these applications, gridless ion sources of the end-Hall type are particularly well-suited to the generation of high ion-beam currents at ion energies low enough to minimize damage.
Influence of substrate misorientation on vibrational properties of In1−x−yGaxAlyAs grown on InP
Authors: Tripathy S. , Thwin-Htoo  , Chua S. J.
Published: March 2004

Using micro-Raman scattering, we have investigated the vibrational properties of nominal In1−x−yGaxAlyAs (x=0.13, y=0.34) layers that were grown lattice matched to InP (100) substrates by molecular-beam epitaxy. In order to control and optimize crystalline quality of these layers, the quaternary alloy films were also grown on (100) substrates oriented 1°, 2°, 3°, and 5° toward the [1̄10] direction. Atomic force microscopy has been employed to investigate the surface topography. The micro-Raman technique has been applied to evaluate the quality of these epitaxial films. Optical phonons show three-mode behavior in these quaternary alloys and the dominant bands observed in the spectra are of three binaries, namely, the GaAs-, InAs-, and AlAs-like optical phonons. The narrowest Raman linewidth and much weaker forbidden modes observed in the layer grown on InP(100) oriented 2° toward the [1̄10] direction, suggest the best crystalline quality among the quaternary alloys grown on misoriented substrates.
Atomic transport and stability during annealing of HfO2 and HfAlO with an ultrathin layer of SiO2 on Si(001)
Authors: Chang Hyo Sik , Hwang Hyunsang , Cho Mann-ho , Kim Hyun Kyung , Moon Dae Won
Published: March 2004

A medium-energy ion scattering spectroscopy study has been carried out on HfO2/SiO2/Si and HfAlO/SiO2/Si stacks with 5-nm-thick dielectric layers prepared by atomic layer chemical vapor deposition at 300 °C. We observed that there are negligible interface strain and surface silicon for the as-deposited sample. After annealing in nitrogen, the crystallization of HfO2 started to occur between 500 °C and 600 °C. As the annealing temperature increased, a silicate layer is formed at the top of the HfO2 film. However, the HfAlO film with about 25% Al did not exhibit surface silicon and crystallization. Adding Al2O3 to HfO2 can suppress the existence of surface Si but can build up compressive strain at the oxide/Si interface layer. After annealing, excess Si that is prone to move may displace Al in order to relax the interface strain. On the other hand, HfAlO film exhibits much stronger resistance to oxygen diffusion than HfO2 and tends toward densification during N2 annealing.
Extremely low-outgassing material: 0.2% beryllium copper alloy
Authors: Watanabe Fumio
Published: March 2004

Exploration for low-outgassing materials for use in ultrahigh vacuum and extreme high-vacuum systems is one of the most important topics of a vacuum researcher. We have found that a copper alloy containing 0.2% beryllium (0.2% BeCu) can attain an extremely low hydrogen outgassing rate of 10−14 Pa (H2) m/s order. Almost the entire surface of 0.2% BeCu is dominated by a BeO layer, after a 400 °C×72 h prebakeout treatment in an ultrahigh vacuum. This layer functions as a barrier to the processes of oxidization and permeation of hydrogen. In addition, this layer resists carbon contamination. Temperature-programmed desorption spectra show only a single peak for water at 150 °C and small quantities of any other desorption gases. Therefore, an in situ bakeout process in which the temperature simply ramps up to 150 °C and immediately ramps back down is enough for degassing; it does not require an ordinary sustained-temperature bakeout. Using an outgassing sample consisting of 0.2% BeCu disks housed in a 0.2% BeCu nipple chamber, a lowest outgassing rate of the 5.6×10−14 Pa (H2) m/s was measured by the pressure-rise method after pump cutoff. The pressure-rise versus time curve was completely nonlinear. It rises over time to a constant slope of 1/2 in a log–log plot, due to hydrogen diffusion from the bulk, but this requires over a week at room temperature. The hydrogen outgassing from the 0.2% BeCu bulk is completely dominated by a diffusion-limited mechanism. This article will describe why we obtain such low-outgassing rates with 0.2% BeCu. It is based on the observed surface changes with prebakeout treatment seen by x-ray photoelectron spectroscopy, and the improvement of hydrogen outgassing measurements by the pressure-rise method. A comparison is made to ordinary stainless steel. In addition, the concept of an outgassing reduction method will be discussed from a review of the published ultralow-outgassing data and reduction methods.
Determination of titanium temperature and density in a magnetron vapor sputtering device assisted by two microwave coaxial excitation systems
Authors: Leroy O. , de Poucques L. , Boisse-Laporte C. , Ganciu M. , Teulé-Gay L. , Touzeau M.
Published: March 2004

We present an optical absorption diagnostic technique devoted to the simultaneous determination of titanium density and temperature during sputtering of Ti. These measurements were performed in a type of ionized physical vapor deposition reactor, consisting of a magnetron sputtering device assisted by two microwave systems for the ionization of the sputtered vapor of the magnetron. Our goal is to optimize the ionization in this reactor in order to improve the deposition process (film quality, recovery of the layers, etc.) compared to standard magnetron sputtering systems. In order to determine both titanium neutral and ion densities, we have used a titanium hollow cathode vapor lamp powered with pulsed power supply. Measurements were carried out at different positions in the reactor at different pressures (1–15 Pa). We have studied the effect of magnetron current from 100 mA to 2 A and of microwave power from 100 W to 1 kW. At lower pressures, we have shown that the titanium is not thermalized close to the magnetron, whereas it is thermalized at 10 Pa at all positions. The neutral titanium density is typically between 1010 and 3×1011 cm−3, and the ion density is ∼109 cm−3. The effect of microwave power is the decrease of neutral titanium density and the increase of its temperature. At a position located 1 cm after the crossing of the microwave plasma area, we showed that the illumination of the microwave plasma increases the degree of ionization of Ti from 2% to 10%.
Mechanisms of SiO2 film deposition from tetramethylcyclotetrasiloxane, dimethyldimethoxysilane, and trimethylsilane plasmas
Authors: Zhang Jianming , Wavhal Dattatray S. , Fisher Ellen R.
Published: March 2004

The deposition of SiO2 films from alkoxysilane/O2 and alkoxysilane/N2O plasmas has been investigated using 1, 3, 5, 7-tetramethylcyclotetrasiloxane, dimethyldimethoxysilane, and trimethylsilane as Si precursors. Films were analyzed using Fourier transform infrared spectroscopy, x-ray photoelectron spectroscopy, spectroscopic ellipsometry, and scanning electron microscopy. Film deposition rates and hydrocarbon incorporation in the SiO2 films decrease with addition of O2 or N2O. High-quality SiO2 films are deposited at high oxidant concentrations with all three precursors. The effects of applied rf plasma power, substrate temperature, and substrate position in the reactor on film quality and deposition rate were also examined. Negative apparent activation energies for film deposition have been observed, suggesting a deposition process dominated by surface adsorption/desorption reactions. Gas phase species in these plasmas were studied with optical emission spectroscopy and mass spectrometry and are correlated with film deposition. For films deposited from low oxidant-containing plasmas, post deposition treatment with an O2 plasma serves to remove hydrocarbon contamination.
Microstructure of α-alumina thin films deposited at low temperatures on chromia template layers
Authors: Andersson Jon M. , Czigány Zs. , Jin P. , Helmersson U.
Published: March 2004

Radio frequency sputtering has been used to deposit α-alumina (α-Al2O3) thin films at substrate temperatures of 280–560 °C. The films are shown to be single phased and hard. Nanoindentation gives values of 306±31 and 27±3 GPa for elastic modulus and hardness, respectively, for a substrate temperature of 280 °C. Growth of the α phase was achieved by in situ predeposition of a chromia template layer. Chromia crystallizes in the same hexagonal structure as α-alumina, with a lattice mismatch of 4.1% in the a- and 4.6% in the c-parameter, and is shown to nucleate readily on the amorphous substrates (silicon with a natural oxide layer). This results in local epitaxy of α-alumina on the chromia layer, as is shown by transmission electron microscopy. The alumina grains are columnar with grain widths increasing from 22±7 to 41±9 nm, as the temperature increases from 280 to 560 °C. This is consistent with a surface diffusion dominated growth mode and suggests that α-alumina deposition at low temperatures is possible once initial grain nucleation has occurred. Results are also presented demonstrating chromia/α-alumina growth on a technological substrate (Haynes230 Ni-based super alloy, Haynes International, Inc.).
Growth and stress evolution of hafnium nitride films sputtered from a compound target
Authors: Liao M. Y. , Gotoh Y. , Tsuji H. , Ishikawa J.
Published: March 2004

Hafnium nitride films were deposited on silicon substrates by direct sputtering a compound target in an Ar atmosphere using a radio-frequency magnetron sputtering system. X-ray diffraction, x-ray photoemission spectrum, and Rutherford backscattering spectrometry revealed the successful formation of cubic stoichiometric HfN films in a wide deposition condition range. The residual stress in stoichiometric HfN films is compressive, and depends strongly on Ar pressure and sputtering power. Unlike element metal deposition, a transition point of Ar pressure at which residual stress experiences from compressive to tensile state has not been found in stoichiometic HfN films. Although an increase in Ar pressure could lower the stress value, nitrogen enrichment was found at 2.0 Pa and much oxygen was incorporated in the film deposited at 3.0 Pa and above, which can lead to a dramatic increase in film resistivity. Shallow recoil implantation of HfN species receiving energy from fast Ar species reflected at the target surface is suggested responsible for the evolution of the stress. A possible explanation was also given for the stoichiometric composition.
Atmospheric absorption in the atmosphere up to 160 km
Authors: Sutherland Louis C. , Bass Henry E.
Published: March 2004

This paper describes new algorithms, not previously available, for predicting atmospheric absorption of sound at high altitudes. A basis for estimating atmospheric absorption up to 160 km is described. The estimated values at altitudes above 90 km must be considered as only approximate due to uncertainties about the composition of the atmosphere above 90 km and simplifying assumptions. At high altitudes, classical and rotational relaxation absorption are dominant, as opposed to absorption by molecular vibrational relaxation that is the principle atmospheric absorption loss mechanism for primary sonic booms propagating downward from a cruising supersonic aircraft. Classical and rotational relaxation absorption varies inversely with atmospheric pressure, thus increasing in magnitude at high altitudes as atmospheric pressure falls. However, classical and rotational losses also relax at the high values of frequency/pressure reached at high altitudes and thus, for audio and infrasonic frequencies, begin to decrease at altitudes in the range of 80–160 km. This paper includes: (1) modifications to the existing algorithms in the ISO/ANSI standards for atmospheric absorption at high altitudes, and (2) algorithms for definition of mean atmospheric conditions, including humidity content at high altitude conditions. Also included are suitable values for the temperature-dependent physical parameters of the atmosphere, viscosity, and the specific heat ratio, involved in defining atmospheric absorption at temperatures found at high altitudes. It has been found that carbon dioxide plays a major role in the relaxation of O2 and N2 at high altitudes due to the absence of H2O. Molecular relaxation by CO2, not covered by the current ANSI or ISO standards, is the dominant source of molecular relaxation absorption at altitudes above 60 km at frequencies of 1 Hz and above 10 km at a frequency of 10 kHz. However, at such high altitudes, classical plus rotational losses dominate reaching maximum values at 80–160 km, depending on frequency. In this regime, vibrational relaxation is less important. More accurate predictions of absorption at altitudes above 90 km would require more sophisticated models for the variation in atmospheric viscosity and specific heat ratio above such altitudes.
Deconvolution of evoked responses obtained at high stimulus rates
Authors: Delgado Rafael E. , Ozdamar Ozcan
Published: March 2004

Continuous loop averaging deconvolution (CLAD) is a new general mathematical theory and method developed to deconvolve overlapping auditory evoked responses obtained at high stimulation rates. Using CLAD, arbitrary stimulus sequences are generated and averaged responses deconvolved. Until now, only a few special stimulus series such as maximum length sequences (MLS) and Legendre sequences (LGS) were capable of performing this task. A CLAD computer algorithm is developed and implemented in an evoked potential averaging system. Computer simulations are used to verify the theory and methodology. Auditory brainstem responses (ABR) and middle latency responses (MLR) are acquired from subjects with normal hearing at high stimulation rates to validate and show the feasibility of the CLAD technique.
Mode-exciting method for Lamb wave-scattering analysis
Authors: Gunawan Arief , Hirose Sohichi
Published: March 2004

This paper presents an innovative method, called the mode-exciting method, to solve Lamb wave-scattering problems in an infinite plate. In this method, a set of Lamb wave modes is excited by appropriate boundary conditions given on the virtual edges of a finite plate. After solving numerically the elastodynamic problem defined in the finite domain, the numerical solution is decomposed into Lamb wave modes. The Lamb wave modes constitute a system of equations, which can be used to determine the scattering coefficients of Lamb waves for the original problem in an infinite plate. The advantage of the mode-exciting method is that a well-developed numerical method such as finite-element (FEM) or boundary element (BEM) can be used in the elastodynamic analysis for the finite region without any modification like coupling with other numerical techniques. In numerical examples, first the error estimation of the mode-exciting method is discussed by considering three types of error indicators. It is shown that among them, the power ratio of nonpropagating modes to propagating modes is the most suitable for the error estimation. Numerical results are then shown for scattering coefficients as a function of nondimensional frequency for edge reflection and crack scattering problems.
Finite element predictions for the dynamic response of thermo-viscoelastic material structures
Authors: Castaings M. , Bacon C. , Hosten B. , Predoi M. V.
Published: March 2004

In this paper, constitutive relations are solved in the Fourier domain using a finite-element-based commercial software. The dynamic responses of viscoelastic bars or plates to either thermal or mechanical loads are predicted by considering complex moduli (Young, Poisson, stiffness moduli) as input data. These moduli are measured in the same frequency domain as that which is chosen for modeling the wave propagation. This approach is simpler since it suppresses the necessity of establishing a rheological model. Specific output processing then allows the numerical predictions to be compared to analytical solutions, in the absence of scatterers. The performances of this technique and its potential for simulating more complicated problems like diffraction of waves or for solving inverse problems are finally discussed.
Statistical errors in the estimation of time-averaged acoustic energy density using the two-microphone method
Authors: Ghan Justin , Cazzolato Ben , Snyder Scott
Published: March 2004

Time-averaged acoustic energy density can be estimated using the auto- and cross-spectral densities between two closely spaced microphones. In this paper, an analysis of the random errors that arise using two microphone measurements is undertaken. An expression for the normalized random error of the time-averaged acoustic energy density spectral density estimate is derived. This expression is verified numerically. The lower and upper bounds of the normalized random error are derived. It is shown that the normalized random error of the estimate is not a strong function of the sound field properties, and is chiefly dependent on the number of records averaged.
Effect of handset proximity on hearing aid feedback
Authors: Stinson Michael R. , Daigle Gilles A.
Published: March 2004

The increased sensitivity of hearing aids to feedback as a telephone handset is brought near has been studied experimentally and numerically. For the measurements, three different hearing aids were modified so that the open-loop transfer function could be measured. They were mounted in the pinna of a mannikin and the change in open-loop transfer function determined as a function of handset proximity. Increases of over 20 dB were observed, most of this change occurring within the first 10 mm of separation between pinna and handset. Numerical calculations performed using a boundary element technique were in good agreement with the measurements.
The representation of periodic sounds in simulated sustained chopper units of the ventral cochlear nucleus
Authors: Wiegrebe Lutz , Meddis Ray
Published: March 2004

The nature of the neural processing underlying the extraction of pitch information from harmonic complex sounds is still unclear. Electrophysiological studies in the auditory nerve and many psychophysical and modeling studies suggest that pitch might be extracted successfully by applying a mechanism like autocorrelation to the temporal discharge patterns of auditory-nerve fibers. The current modeling study investigates the possible role of populations of sustained chopper (Chop-S) units located in the mammalian ventral cochlear nucleus (VCN) in this process. First, it is shown that computer simulations can predict responses to periodic and quasiperiodic sounds of individual Chop-S units recorded in the guinea-pig VCN. Second, it is shown that the fundamental period of a periodic or quasiperiodic sound is represented in the first-order, interspike interval statistics of a population of simulated Chop-S units. This is true across a wide range of characteristic frequencies when the chopping rate is equal to the f0 of the sound. The model was able to simulate the results of psychophysical studies involving the pitch height and pitch strength of iterated ripple noise, the dominance region of pitch, the effect of phase on pitch height and pitch strength, pitch of inharmonic stimuli, and of sinusoidally amplitude modulated noise. Simulation results indicate that changes in the interspike interval statistics of populations of Chop-S units compare well with changes in the pitch perceived by humans. It is proposed that Chop-S units in the ventral cochlear nucleus may play an important role in pitch extraction: They can convert a purely temporal pitch code as observed in the auditory nerve into a temporal place code of pitch in populations of cochlear-nucleus, Chop-S with different characteristic frequencies, and chopping rates. Thus, populations of cochlear-nucleus Chop-S units, together with their target units presumably located in the inferior colliculus, may serve to establish a stable rate-place code of pitch at the level of the auditory cortex.
Multiple scattering in single scatterers
Authors: Cai Liang-Wu
Published: March 2004

Scattering by a multilayered scatterer is analyzed via a novel multiple-scattering approach. Based on the recognition that multiple scattering occurs within single scatterers having internal interfaces, the solution procedure follows the physical process, and yields analytically exact solutions. A simple two-layered scatterer subjected to SH incident waves is used to illustrate the detailed solution procedure. The solution is then verified by a two-layered circular cylindrical scatterer, whose exact analytical solution has previously been obtained by the author [J. Acoust. Soc. Am. (2004)]. The proposed approach opens new ways for analyzing scatterers of more complicated geometrical and physical compositions.