bluuebunny/crossref_metadata_2025 huggingface dataset:
Oxygen-evoked changes in transcriptional activity of the 5′-flanking region of the human amiloride-sensitive sodium channel (αENaC) gene: role of nuclear factor κB
Authors: BAINES Deborah L. , JANES Mandy , NEWMAN David J. , BEST Oliver G.
Published: July 2002

Expression of the α-subunit of the amiloride-sensitive sodium channel (αENaC) is regulated by a number of factors in the lung, including oxygen partial pressure (Po2). As transcriptional activation is a mechanism for raising cellular mRNA levels, we investigated the effect of physiological changes in Po2 on the activity of the redox-sensitive transcription factor nuclear factor κB (NF-κB) and transcriptional activity of 5′-flanking regions of the human αENaC gene using luciferase reporter-gene vectors transiently transfected into human adult alveolar carcinoma A549 cells. By Western blotting we confirmed the presence of NF-κB p65 but not p50 in these cells. Transiently increasing Po2 from 23 to 42mmHg for 24h evoked a significant increase in NF-κB DNA-binding activity and transactivation of a NF-κB-driven luciferase construct (pGLNF-κBpro), which was blocked by the NF-κB activation inhibitor sulphasalazine (5mM). Transcriptional activity of αENaC-luciferase constructs containing 5′-flanking sequences (including the NF-κB consensus) were increased by raising Po2 from 23 to 142mm Hg if they contained transcriptional initiation sites (TIS) for exons 1A and 1B (pGL3E2.2) or the 3′ TIS of exon 1B alone (pGL3E0.8). Sulphasalazine had no significant effect on the activity of these constructs, suggesting that the Po2-evoked rise in activity was not a direct consequence of NF-κB activation. Conversely, the relative luciferase activity of a construct that lacked the 3′ TIS, a 3′ intron and splice site but still retained the 5′ TIS and NF-κB consensus sequence was suppressed significantly by raising Po2. This effect was reversed by sulphasalazine, suggesting that activation of NF-κB mediated Po2-evoked suppression of transcription from the exon 1A TIS of αENaC.
Conserved hydrophobic amino acid residues in the N-terminal region of DnaA protein are involved in DnaA–DnaA interaction
Authors: MIMA Shinji , MAKISE Masaki , KOTERASAWA Motohiro , TSUCHIYA Tomofusa , MIZUSHIMA Tohru
Published: July 2002

We previously reported that a leucine-zipper-like structure (I26, L33 and L40) located in the N-terminal region of DnaA is essential for the duplex opening at oriC by DnaA. In this study, we focused on three other conserved hydrophobic amino acid residues, L3, L10 and L17, and examined the function of DnaA proteins mutated in these amino acid residues. DnaA427 (L17S) and DnaA413 (L3S, L10S and L17S) were inactive for oriC DNA replication both in vitro and in vivo. Although these mutant DnaA proteins maintained their binding activities for both ATP and oriC, they were unable to induce the opening of duplex DNA at oriC. Glutathione-S-transferase (GST)-fused wild-type DnaA interacted with wild-type DnaA but not with DnaA427 and DnaA413. Based on these results, we propose that conserved hydrophobic amino acid residues in the N-terminal region of DnaA are involved in DnaA oligomerization, in which DnaA—DnaA interaction is required.
Functional evidence for in vitro microtubule severing by the plant katanin homologue
Authors: STOPPIN-MELLET Virginie , GAILLARD Jérémie , VANTARD Marylin
Published: July 2002

Temporal and spatial assembly of microtubules in plant cells depends mainly on the activity of microtubule-interacting proteins, which either stabilize, destabilize or translocate microtubules. Recent data have revealed that the thale cress (Arabidopsis thaliana) contains a protein related to the p60 catalytic subunit of animal katanin, a microtubule-severing protein. However, effects of the plant p60 on microtubule assembly are not known. We report the first functional evidence that the recombinant A. thaliana p60 katanin subunit, Atp60, binds to microtubules and severs them in an ATP-dependent manner in vitro. ATPase activity of Atp60 is stimulated by low tubulin/katanin ratios, and is inhibited at higher ratios. Considering its properties in vitro, several functions of Atp60 in vivo are discussed.
Spermosin, a trypsin‐like protease from ascidian sperm
Authors: Kodama Eri , Baba Tadashi , Kohno Nobuhisa , Satoh Sayaka , Yokosawa Hideyoshi , Sawada Hitoshi
Published: July 2002

We have previously reported that two trypsin‐like enzymes, acrosin and spermosin, play key roles in sperm penetration through the vitelline coat of the ascidian (Urochordata) Halocynthia roretzi[Sawada et al. (1984), J. Biol. Chem.259, 2900–2904; Sawada et al. (1984), Dev. Biol.105, 246–249]. Here, we show the amino‐acid sequence of the ascidian preprospermosin, which is deduced from the nucleotide sequence of the isolated cDNA clone. The isolated ascidian preprospermosin cDNA consisted of 1740 nucleotides, and an open reading frame encoding 388 amino acids, which corresponds to a molecular mass of 41 896 Da. By sequence alignment, it was suggested that His178, Asp230 and Ser324 make up a catalytic triad and that ascidian spermosin be classified as a novel trypsin family member. The mRNA of preprospermosin is specifically expressed in ascidian gonads but not in other tissues. Purified spermosin consists of 33‐ and 40‐kDa bands as determined by SDS/PAGE under nonreducing conditions. The 40‐kDa spermosin consists of a heavy chain (residues 130–388) and a long light chain designated L1 (residues 23–129), whereas the 33‐kDa spermosin includes the same heavy chain and a shorter light chain designated L2 (residues 97–129). The L1 chain contains a proline‐rich region, designated L1(ΔL2) which is lacking in L2. Investigation with the glutathione‐S‐transferase (GST)–spermosin‐light‐chain fusion proteins, including GST–L1, GST–L2, and GST–L1(ΔL2), revealed that the proline‐rich region in the L1 chain binds to the vitelline coat of ascidian eggs. Thus, we propose that sperm spermosin is a novel trypsin‐like protease that binds to the vitelline coat and also plays a part in penetration of sperm through the vitelline coat during ascidian fertilization.
Genetic immunotherapy of established tumours with adenoviral vectors transducing murine interleukin‐12 (mIL12) subunits in a rat medullary thyroid carcinoma model
Authors: Zhang Rusheng , DeGroot Leslie J.
Published: July 2002

OBJECTIVE

Interleukin‐12 (IL12) is a heterodimeric cytokine that plays an important role in the development of cellular immunity. Studies have demonstrated antitumour activity after systemic administration of recombinant IL12. As with other cytokines, with increasing dosage and longer exposure, systemic toxicity is observed. To reduce systemic toxicity and obtain local production of IL12, we developed a replication defective adenovirus transducing two subunits of the murine IL12 (AdCMVmIL12) gene.

DESIGN

Two separate cassettes, expressing the p35 or p40 subunit of mIL12, under the control of human cytomeglavirus immediate early promoter, were inserted into the early1 (E1) region of adenovirus 5. Biological activity of virally expressed mIL12 was demonstrated in vitro through its ability to induce proliferation of mouse ConA blast cells.

RESULTS

Rat medullary thyroid carcinoma (MTC) cells infected with AdCMVmIL12 lost their tumorigenicity in their syngenic WAG/Rij rat hosts. Efficient antitumour activity was found after direct injection of the AdCMVmIL12 vector into rMTC tumours. After intratumoural treatment with AdCMVmIL12, 86% of tumour bearing animals were apparently cured, and almost all remaining tumours were stabilized. Challenge studies showed that most animals cured after the first treatment remained tumour free after reinjection of wild type rMTC cells, indicating that long‐term antitumour immunity developed.

CONCLUSIONS

This study demonstrates the construction of an adenoviral vector expressing a functional heterodimeric mIL12 and its efficient antitumour activity after in vivo delivery in an animal model of medullary thyroid carcinoma.
The Mammalian Oviduct: Aspects on Auto‐and Paracrine Mechanisms
Authors: Einspanier R , Kettler A , Gabler C , Kloas W , Einspanier A , Schams D
Published: July 2002

Contents

This review will present a characterization of basic molecular processes in the mammalian oviduct. Oviducts of the cow (Bos taurus) were examined during the various cycle stages using a combination of cell biology‐ and molecular‐biology techniques [reverse transcriptase polymerase chain reaction (RT‐PCR), RNase protection assay (RPA), immunohistology, radio‐immunoassay (RIA), receptor‐assay, cell culture]. In detail the oviductal expression of the following components was analysed: fibroblast (FGF) and vascular‐endothelial (VEGF) growth factor systems; extracellular matrix (ECM) enzymes such as plasminogenactivator (PA) and matrixmetalloproteases (MMP), adrenergic receptors (α2 and β2 AdR) and an anti‐oxidative protein (glutathionperoxidase = GPx). A specific cycle‐dependant and local regulation of the expression could be demonstrated, not only for growth factors such as FGF1 and VEGF but also for ECM components. Remarkable progesterone‐dependent increases of the β2 adrenoceptor concentrations were found in the oviductal epithelium. New observations showed the presence of antioxidative enzymes (GPx) in the bovine oviduct possibly interacting with the gametes. Obviously, a network of local factors seems to influence the function of the oviduct, controlled by peripheral hormones. Cycle–dependent interactions between the growth factor, ECM and adrenergic systems will create the optimal environment for fertilization and early embryo development in the mammalian oviduct.
Leucogyrophana, a Polyphyletic Genus of the Order Boletales (Basidiomycetes)
Authors: Jarosch M. , Besl H.
Published: July 2002

Abstract: This study aimed to test the monophyly and present generic concept of the genus Leucogyrophana (Basidiomycetes, Boletales). DNA sequence data were generated from the nuclear encoded 28S gene using the primer combination LR0R‐LR5. Molecular results were compared with chemical data. Molecular phylogenetic and chemosystematic analysis emphasized the heterogeneity among Leucogyrophana species. Taxonomical interpretation of the data presented lead to the proposal of the new genus Hydnomerulius for a part of the genus Leucogyrophana in its former circumscription.
Observation of the D-center in 6H-SiC p-n diodes grown by chemical vapor deposition
Authors: Mazzola Michael S. , Saddow Stephen E. , Neudeck Philip G. , Lakdawala V. K. , We Susan
Published: July 2002

The D-center in 6H-SiC is a boron-related deep hole trap observed previously in LPE-grown 6H-SiC diodes. We report deep level transient spectroscopy (DLTS) measurements in which the D-center signature is observed in high-purity n- and p-type epitaxial layers formed by chemical vapor deposition (CVD). An activation energy of 0.58 eV and a capture cross section between 1×10−14 cm2 and 3×10−14 cm2 was determined for this level. Even though the D-center in these diodes is thought to arise from unintended trace contamination, we observed within the same diode a factor of twenty greater density of this level in the n-type layer than in the p-type layer, which is explained by a recently proposed site competition model for impurity doping during 6H-SiC CVD growth.
Electrochromism of sputtered fluorinated titanium oxide thin films
Authors: Gutarra A. , Azens A. , Stjerna B. , Granqvist C. G.
Published: July 2002

Titanium-oxide-based films were prepared by reactive dc magnetron sputtering in Ar+O2+CF4. Pronounced electrochromism was found in LiClO4+propylene carbonate. The maximum coloration efficiency was 37 cm2/C at a wavelength of ∼0.7 μm. Polaron hopping is believed to cause the absorption. Coloration/bleaching was performed for up to 2×104 cycles without apparent degradation.
Surface potential fluctuations in metal–oxide–semiconductor capacitors fabricated on different silicon carbide polytypes
Authors: Bano E. , Ouisse T. , Di Cioccio L. , Karmann S.
Published: July 2002

The standard deviation σs of the surface potential fluctuations affecting metal–oxide–silicon carbide capacitors has been extracted from low frequency conductance and capacitance measurements. These fluctuations may become very large for thermal oxides and aluminum-doped epilayers. They must induce large errors in usual metal–oxide–semiconductor characterization techniques and are most probably the main reason for observing an activated transport in silicon carbide inversion layers.
Sharpened electron beam deposited tips for high resolution atomic force microscope lithography and imaging
Authors: Wendel M. , Lorenz H. , Kotthaus J. P.
Published: July 2002

We employ the vibrating tip of an atomic force microscope as a lithographic tool to mechanically pattern a thin photoresist layer covering a GaAs–AlGaAs heterostructure. High aspect ratio electron beam deposited tips, additionally sharpened in an oxygen plasma, are used to minimize the dimensions of the fabricated quantum electronic devices. The fabrication parameters of the tips and the sharpening process are investigated. With these ultrasharp tips we are able to produce lines and holes with periods down to 9 nm in photoresist. In addition, the very sharp tips yield substantial improvements in the imaging mode.
Optical and electrochemical properties of dc magnetron sputtered Ti–Ce oxide films
Authors: Azens A. , Kullman L. , Ragan D. D. , Granqvist C. G. , Hjörvarsson B. , Vaivars G.
Published: July 2002

Reactive dc magnetron sputtering was used to make mixed Ti–Ce oxide films with a Ce/Ti ratio γ between 0 and 0.6. Their optical and electrochemical properties were strongly dependent on the composition. Films with 0.3<γ<0.6 were optically passive under charge insertion, which makes them suitable as counterelectrodes in transparent electrochromic devices.
High temperature chemical vapor deposition of SiC
Authors: Kordina O. , Hallin C. , Ellison A. , Bakin A. S. , Ivanov I. G. , Henry A. , Yakimova R. , Touminen M. , Vehanen A. , Janzén E.
Published: July 2002

A growth process has been investigated for the epitaxial growth of silicon carbide. The technique can simply be described as chemical vapor deposition (CVD) at high temperatures, hence the name high temperature CVD (HTCVD). The growth process however, differs greatly from that of the CVD process due to the significant sublimation and etch rates at the extreme growth temperatures (1800–2300°C). The grown rates obtained with the HTCVD are in the order of several tens of μm/h to 0.5 mm/h. The purity and crystallinity of the growth layers are outstanding showing strong free exciton related photoluminescence.
Three-dimensional potential analysis of radiation pressure exerted on a single microparticle
Authors: Sasaki Keiji , Tsukima Mitsuru , Masuhara Hiroshi
Published: July 2002

A system that makes it possible to precisely and instantaneously observe a potential energy of laser trapping as a function of three-dimensional position was developed for analyzing radiation pressure acting on a single microparticle in solution. Position sensing with a quadrant photodiode and total internal reflection microscopy are applied for measuring thermal Brownian motion of the trapped particle with ∼10 nm resolution, and a trapping potential profile is estimated by a thermodynamical analysis based on the Boltzmann distribution. Characteristic features of the present system are discussed.
Luminescence characteristics of impurities-activated ZnS nanocrystals prepared in microemulsion with hydrothermal treatment
Authors: Xu S. J. , Chua S. J. , Liu B. , Gan L. M. , Chew C. H. , Xu G. Q.
Published: July 2002

Cu-, Eu-, or Mn-doped ZnS nanocrystalline phosphors were prepared at room temperature using a chemical synthesis method. Transmission electron microscopy observation shows that the size of the ZnS clusters is in the 3–18 nm range. New luminescence characteristics such as strong and stable visible-light emissions with different colors were observed from the doped ZnS nanocrystals at room temperature. These results strongly suggest that impurities, especially transition metals and rare-earth metals-activated ZnS nanoclusters form a new class of luminescent materials.
Silicon nanocrystallites in buried SiOx layers via direct wafer bonding
Authors: Kahler U. , Hofmeister H.
Published: July 2002

A combination of SiO vapor-deposition and direct wafer bonding is used to produce buried layers of SiOx. By thermally induced decomposition, Si nanocrystals embedded in SiO2 are obtained. Decomposition of the silicon suboxide is observed by studying the Si-O-Si stretching vibration in the infrared range. This phase separation process is found to start already at 400 °C and to be mostly complete after 1 h at 800 °C. Annealing at 1000 °C yields well established Si nanocrystallites of considerable density with diameters about 4 nm buried in the interface layer between the bonded silicon wafers.
High-efficiency interband cascade lasers with peak power exceeding 4 W/facet
Authors: Bradshaw J. L. , Yang Rui Q. , Bruno J. D. , Pham J. T. , Wortman D. E.
Published: July 2002

Mid-IR (3.8–3.9 μm) interband cascade lasers based on InAs/GaInSb type-II heterostructures have been demonstrated at temperatures up to 210 K. From several lasers at temperatures above 100 K, we observed a slope greater than 750 mW/A per facet corresponding to a differential external quantum efficiency exceeding 460%. Also, a peak optical output power exceeding 4 W/facet and peak power efficiency of 7% were observed from one laser at 80 K.
Fundamental limits to magnetic-field sensitivity of flux-gate magnetic-field sensors
Authors: Koch R. H. , Deak J. G. , Grinstein G.
Published: July 2002

In this letter we determine the theoretical limit of the magnetic-field sensitivity of the flux-gate magnetometer. In order to do so, we have developed a model for the white noise of a flux gate based on the fundamental dynamics of the magnetic material forming the flux-gate core. Solving this model, we predict that the white noise of a physically realizable flux gate with a volume of 2×10−8 m3 is less than 100 fT/Hz. The white noise varies with the lossy susceptibility of the core and inversely with the volume. We also compare the measured white noise of a thin-film flux gate with the predictions of our model and find that the measured and predicted noise agree reasonably well.
Organic light-emitting diodes using an in situ thermally polymerized hole transporting layer
Authors: Jiang Xuezhong , Liu Sen , Liu Michelle S. , Ma Hong , Jen Alex K.-Y.
Published: July 2002

We have fabricated highly efficient organic light-emitting diodes (LEDS) using in situ thermally polymerized hole transporting materials containing triphenylamine/tetraphenyldiaminobiphenyl as side chains. Double-layer LEDs made with these thermally polymerized polymers as the hole transporting layer and tris(8-hydroxyquinoline) aluminum as the emitting layer showed comparable brightness but lower turn-on voltages and better quantum efficiencies than the device made with the conventional hole transporting molecule, N-N′-diphenyl-N,N′-bis(3-methylphenyl)(1,1′-biphenyl)-4,4′-diamine.
Pulsed field ionization–photoelectron bands for CO2+(A 2Πu and B 2Σu+) in the energy range of 17.2–19.0 eV: An experimental and theoretical study
Authors: Liu Jianbo , Hochlaf M. , Ng C. Y.
Published: July 2002

The vacuum ultraviolet (VUV) pulsed field ionization–photoelectron (PFI–PE) spectra for CO2 have been measured in the energy range of 17.2–19.0 eV, showing complex vibronic structures for the CO2+(A 2Πu and B 2Σu+) states. The PFI–PE spectra for CO2+(A 2Πu and B 2Σu+) are dominated by the v1+ (symmetric stretching) vibrational progressions, and weak bands due to excitation of both even and odd quanta of the v2+ (bending) and v3+ (antisymmetric stretching) modes are observed in the VUV–PFI–PE spectra. The simulation of rotational contours resolved in the PFI–PE vibronic bands associated with excitation to CO2+(A 2Π3/2,1/2u;v1+=0–5,v2+=0,v3+=0) and CO2+(B 2Σu+;0,0,0) has yielded accurate ionization energies for the formation of these states from CO2(X 1Σg+). Three-dimensional potential energy functions (PEFs) for CO2+(B 2Σu+) have also been generated theoretically using the complete active space self-consistent field and internally contracted multireference configuration interaction methods. Based on these PEFs, vibrational energy levels for CO2+(B 2Σu+), together with the Franck–Condon factors for their formation from CO2(X 1Σg+), have been calculated. With the guide of these theoretical predictions, the vibrational bands resolved in the PFI–PE spectrum for CO2+(B 2Σu+) have been satisfactorily assigned. This assignment reveals the nature of many vibrational PFI–PE bands as originated from anharmonic resonance interactions and members of Fermi polyads.
Two-stream instability and oscillatory regimes induced in ballistic diodes and field-effect transistors
Authors: Gribnikov Z. S. , Vagidov N. Z. , Mitin V. V.
Published: July 2002

Two groups of current carriers naturally coexist in ballistic and quasiballistic diodes and field-effect transistors (FETs): (1) traversing ballistic current carriers emitted by a source and absorbed by a drain, and (2) nontraversing (nonparticipating in a current flow) carriers that are in equilibrium with the drain carrier reservoir. Therefore, the convective two-stream instability develops in such diodes and FETs with appropriate physical and geometrical parameters. It can result in oscillatory regimes. In this article, we consider development of the two-stream instability in n+nn+ diodes with a doped bulk n-base, n+nn+ diodes with a modulation doped n-channel base, and also in diodes with a gated n-channel base (that is in ballistic FETs) where a gate potential controls electron concentration in the channel. Since oscillatory regimes in such devices are restricted by pair electron–electron interaction between electrons belonging to the two different streams and participating in the instability process, we suggest a new type FET with two parallel n channels. Current-carrying electrons from the primary channel interact with slow electrons from the parallel additional channel that simultaneously serves as a controlling gate for the primary channel. In this design, electron streams participating in the two-stream instability are spatially separated, and their pair interaction is suppressed. Along with analytic estimates, we present results of numerical simulations for the ballistic FETs that prove the existence of oscillatory regimes in terahertz frequency ranges.
Reduction of threading dislocation density in GaN using an intermediate temperature interlayer
Authors: Bourret-Courchesne E. D. , Kellermann S. , Yu K. M. , Benamara M. , Liliental-Weber Z. , Washburn J. , Irvine S. J. C. , Stafford A.
Published: July 2002

GaN thin films with a reduced threading dislocation density have been produced by organometallic vapor phase epitaxy using an intermediate temperature interlayer. A description of the growth process is presented with characterization results. Reduction of the dislocation density was obtained by insertion of a single thin interlayer grown at an intermediate temperature after the initial growth at high temperature. A large percentage of the threading dislocations present in the first GaN epilayer are found to bend in the interlayer and do not propagate in the top layer grown at higher temperature in a lateral growth mode.
Electrochromic devices embodying W oxide/Ni oxide tandem films
Authors: Azens A. , Vaivars G. , Veszelei M. , Kullman L. , Granqvist C. G.
Published: July 2002

Six-layer electrochromic devices of indium tin oxide (ITO)/NiOxHy/WO3/ZrP-electrolyte/WO3/ITO were made by reactive dc magnetron sputtering and lamination. The WO3 layer between the acidic ZrP-based electrolyte and the NiOxHy layer served as optically passive protective layer. The optical inactivity of the protective layer could be understood from arguments based on electron density of states.
Eu
3+
-doped microcavities fabricated by sol–gel process
Authors: Bellessa J. , Rabaste S. , Plenet J. C. , Dumas J. , Mugnier J. , Marty O.
Published: July 2002

The fabrication of microcavities by a sol–gel process and their optical properties are described. The cavities are constituted of an Eu3+-doped SiO2 active layer inserted between two Bragg mirrors, fabricated by stacking alternatiely undoped TiO2 and SiO2 sol–gel thin films. Eu3+ luminescence modification due to the cavity effect, intensity enhancement and modification of the line shape has been observed, and shows a cavity quality factor of 1200. The reflectivity factor of the associated Bragg mirrors reaches 99.8% for seven alternate SiO2/TiO2 layers.
Molecular dynamics simulations of solvent reorganization in electron-transfer reactions
Authors: Hartnig Christoph , Koper Marc T. M.
Published: July 2002

We present molecular dynamics simulations of solvent reorganization in electron-transfer reactions in water. Studying a series of solutes with the same core radius (typical for chlorine) but with varying charge from −3 to +3, the simulations show that the single-solute solvent reorganization energy depends quite strongly on the solute’s charge, in contrast with the continuum Marcus theory. Due to the ion-dipole interactions, electrostriction plays an important role for charged species. The effective radius of a neutral species is comparatively larger, making the solvent reorganization energy small. Strong increases in the solvent reorganization energy occur when the solute is charged to either −1 to +1, due to the significantly smaller effective radius caused by the ion-dipole interactions. However, the effect is nonsymmetric because the center of the water dipole can approach closer to the negative species than to the positive species. Hence, the nonlinearity occurs mainly in the transition from 0 to –1. For higher charges (+3, +2, −2, −3), dielectric saturation causes a decrease in the reorganization energy with increasing charge. We also calculate the equilibrium activation energy for an outer-sphere electrochemical electron-transfer reaction of the X+e−⇌X− type, with varying of the core radius of the X species. The deviations from Marcus theory are relatively small for large reactants, but get more significant for small reactants. This is mainly due to the fact that the changes in electrostriction have a comparatively large effect for small solutes.
A new implementation of four-component relativistic density functional method for heavy-atom polyatomic systems
Authors: Yanai Takeshi , Iikura Hisayoshi , Nakajima Takahito , Ishikawa Yasuyuki , Hirao Kimihiko
Published: July 2002

A new four-component Dirac–Kohn–Sham (DKS) method is presented. The method provides a computationally efficient way to perform fully relativistic and correlated ground state calculations on heavy-atom molecular systems with reliable accuracy. The DKS routine has been implemented in the four-component Dirac–Hartree–Fock program system REL4D. Two-component generally contracted, kinetically balanced Gaussian-type spinors (GTSs) are used as basis spinors. The one-electron and Coulomb integrals are computed analytically, and exchange-correlation potentials are calculated with a numerical grid-quadrature routine. An approximation scheme is presented to reduce the evaluation time of the two-electron repulsion integrals over full sets of small-component GTSs, (SS|SS). Benchmark calculations for the ground states of the group IB hydrides, MH, and dimers, M2 (M=Cu, Ag, and Au), by the DKS method are presented.
Effects of nitridation in gate oxides grown on 4H-SiC
Authors: Jamet Philippe , Dimitrijev Sima , Tanner Philip
Published: July 2002

Experiments have demonstrated that nitridation provides critically important improvements in the quality of SiO2–SiC interface. This article provides results and analysis aimed at developing the much needed understanding of the mechanisms and effects associated with both annealing of pregrown oxides and direct growth in NO and N2O environments. According to the model proposed in the article, nitridation plays a double role: (1) creation of strong Si≡N bonds that passivate interface traps due to dangling and strained bonds, and (2) removal of carbon and associated complex silicon–oxycarbon bonds from the interface. This understanding of the effects of nitridation is experimentally verified and used to design a superior process for gate oxide growth in the industry-preferred N2O environment.
A unique polarized x-ray facility at the Advanced Photon Source
Authors: Freeland J. W. , Lang J. C. , Srajer G. , Winarski R. , Shu D. , Mills D. M.
Published: July 2002

To use the unique element-specific nature of polarized x-ray techniques to study a wide variety of problems related to magnetic materials, we have developed a dual-branch sector that simultaneously provides both hard and soft x-ray capabilities. This facility, which is located in sector 4, is equipped with two different insertion devices providing photons in both the intermediate (0.5–3 keV) and hard x-ray regions (3–100 keV). This facility is designed to allow the simultaneous branching of two undulator beams generated in the same straight section of the ring.
Growth of single-crystal CrN on MgO(001): Effects of low-energy ion-irradiation on surface morphological evolution and physical properties
Authors: Gall D. , Shin C.-S. , Spila T. , Odén M. , Senna M. J. H. , Greene J. E. , Petrov I.
Published: July 2002

CrN layers, 0.5 μm thick, were grown on MgO(001) at Ts=570–775 °C by ultrahigh vacuum magnetically unbalanced magnetron sputter deposition in pure N2 discharges at 20 mTorr. Layers grown at Ts⩽700 °C are stoichiometric single crystals exhibiting cube-on-cube epitaxy: (001)CrN||(001)MgO with [100]CrN||[100]MgO. At higher temperatures, N2 desorption during deposition results in understoichiometric polycrystalline films with N fractions decreasing to 0.35, 0.28, and 0.07 with Ts=730, 760, and 775 °C, respectively. The surface morphologies of epitaxial CrN(001) layers were found to depend strongly on the incident ion-to-metal flux ratio JN2+/JCr which was varied between 1.7 and 14 with the ion energy maintained constant at 12 eV. The surfaces of layers grown with JN2+/JCr=1.7 consist of self-organized square-shaped mounds, due to kinetic roughening, with edges aligned along orthogonal 〈100〉 directions. The mounds have an average peak-to-valley height 〈h〉=5.1 nm and an in-plane correlation length of 〈d〉=0.21 μm. The combination of atomic shadowing by the mounds with low adatom mobility results in the formation of nanopipes extending along the growth direction. Increasing JN2+/JCr to 14 leads, due to increased adatom mobilities, to much smoother surfaces with 〈h〉=2.5 nm and 〈d〉=0.52 μm. Correspondingly, the nanopipe density decreases from 870 to 270 μm−2 to <20 μm−2 as JN2+/JCr is increased from 1.7 to 6 to 10. The hardness of dense CrN(001) is 28.5±1 GPa, but decreases to 22.5±1 GPa for layers containing significant nanopipe densities. The CrN(001) elastic modulus, 405±15 GPa, room-temperature resistivity, 7.7×10−2 Ω cm, and relaxed lattice constant, 0.4162±0.0008 nm, are independent of JN2+/JCr.
The relative reactivity of the stretch–bend combination vibrations of CH4 in the Cl (2P3/2)+CH4 reaction
Authors: Yoon Sangwoon , Henton Sarah , Zivkovic Aleksandar N. , Crim F. Fleming
Published: July 2002

Direct infrared absorption prepares CH4 in two nearly isoenergetic vibrationally excited states, the symmetric stretch–bend combination (ν1+ν4) and the antisymmetric stretch–bend combination (ν3+ν4), for a study of the effect of stretching vibrations of CH4 on the reaction, CH4+Cl(2P3/2)→CH3+HCl. Comparison of intensities in the action spectra with those in the simulated absorption spectra shows that vibrational excitation of methane to the ν1+ν4 state promotes the reaction more efficiently than excitation to the ν3+ν4 state by a factor of 1.9±0.5. The reaction of methane in both vibrational states produces a substantial fraction (35%) of the CH3 products with the umbrella mode (ν2) excited, which we attribute to the presence of the bending vibration (ν4) in the combination states. The similarity of the vibrational population distributions of the products for the two excitations implies that the differences in the action spectra arise from the relative reactivity of the states rather than from population of different product states. This result is consistent with theoretical calculations that predict a stronger coupling of the symmetric stretching vibration to the reaction coordinate than the antisymmetric stretch. Analyzing the infrared laser power dependence of the signal with a simple two state model shows that the reaction cross section of the ν1+ν4 state of methane is 19±5 times larger than that of methane molecules in their ground or thermally populated vibrational states.
Striations in CZ silicon crystals grown under various axial magnetic field strengths
Authors: Kim K. M. , Smetana P.
Published: July 2002

Inhibition of fluid flow instabilities in the melt by the axial magnetic field in Czochralski silicon crystal growth (AMCZ) is investigated precisely by a high-sensitivity striation etch in conjunction with temperature measurements. The magnetic field strength (B) was varied up to 4.0 kG, incremented mostly in 0.5-kG/2.5-cm crystal length. The convection flow was substantially suppressed at B≥1.0 kG. A low oxygen level of 2–3 ppm and a high resistivity of 400 Ω cm is achieved in the AMCZ silicon crystals at B≥1.0 kG. Random striations at B=0, characteristic of turbulent convection, assumed progressively a periodicity, indicative of oscillatory convection at 0.35<B≤4.0 kG. The striation contrast or ‘‘intensity’’ decreased steadily with the increase in B. At B=4 kG, most of the crystal was free of striations, although some weak, localized periodic striations persisted near the crystal periphery. Spreading-resistance measurement shows, however, a uniform dopant distribution in all crystal sections grown at 0.35<B≤4.0 kG within a few percent.
Point-defect generation during oxidation of silicon in dry oxygen. II. Comparison to experiment
Authors: Dunham Scott T. , Plummer James D.
Published: July 2002

In the companion paper [J. Appl. Phys. 59, 2541 (1986)], we developed a model based on a continuity equation approach for the supersaturation of interstitials during oxidation in dry O2. The analysis resulted in an expression having the experimentally observed sublinear dependence of oxidation rate without requiring any assumptions of nonlinearity. Through observations of the dependence of the linear rate constant at the linear-parabolic model of oxidation on ambient oxygen pressure, predictions were made of how the interstitial supersaturation will vary with oxidation rate at a given temperature. In this paper, those predictions are compared to data for the enhanced diffusion of phosphorus in 〈100〉 silicon during oxidation at 900 and 1000 °C in both 100% O2 and O2-Ar mixtures as well as existing data for oxidation enchanced diffusion and stacking fault growth.
Raman scattering studies of chemical-vapor-deposited cubic SiC films of (100) Si
Authors: Feng Z. C. , Mascarenhas A. J. , Choyke W. J. , Powell J. A.
Published: July 2002

Raman backscattering studies for a series of cubic SiC (3C-SiC) single-crystal films grown on (100)Si by way of chemical vapor deposition (CVD) with SiC film thicknesses dSiC from 600 Å to 17 μm are performed. Raman spectra of samples with dSiC>4 μm show a sharp and strong feature which obeys the selection rule for the 3C-SiC LO(Γ) phonon line. The Raman signals from the SiC film and the Si substrate show the same polarization behavior which confirms that the crystalline orientations of the Si substrate and 3C-SiC film are the same. Although there is a big lattice mismatch of 20% between 3C-SiC and Si the observed Raman shifts between 3C-SiC/Si and free 3C-SiC films are ≤2 cm−1 and reflect strains of 0.1%–0.2% in films thicker than 4 μm. Some interesting enhancements of Si and 3C-SiC Raman signals are reported. The Si 522 cm−1 phonon from a Si wafer is enhanced in intensity by a factor of 2–3 due to a CVD overlayer of cubic SiC. Furthermore, the 3C-SiC longitudinal optical phonon at the Γ point, LO(Γ), from SiC/Si samples is enhanced by a factor of 2 or 3 following the removal of the Si substrate. The strict selection rules are no longer obeyed in this case. The former is possibly due to the electric-field-induced inelastic scattering from the SiC/Si heterojunction. The latter is explained by the multiple reflection in free 3C-SiC films. Our theoretical analysis shows that if the cross section for forward scattering is about one order of magnitude larger than that for backscattering, this enhancement will appear. The forward scattering has different selection rules from the back scattering and thus could lead to the appearance of the forbidden transverse optical phonon and the depolarization of the 3C-SiC Raman phonons from the SiC free films. The variation of the Raman spectrum with incident power has also been studied. The Raman cross section for 3C-SiC is estimated by a new method. The wavelength shifts of 3C-SiC LO(Γ) phonons taken from SiC/Si or free films are measured and explained.
Characterization of planar Ti:LiNbO3 optical waveguides in the visible and near-infrared spectral range
Authors: Irrera Fernanda , Valli Marco
Published: July 2002

Several Ti:LiNbO3 waveguides have been fabricated in dry and wet atmosphere, varying the diffusion time. The effect of water vapor on the diffusion process has been investigated. Effective indices and attenuation at λ=0.6328, 1.15, and 1.52 μm have been measured. In the dry case, the Ti in-diffusion proceeds more rapidly than in the wet case, and the two diffusion coefficients have been calculated. Also, it has been observed that the presence of water vapor in the atmosphere does not completely prevent the phenomenon of Li2O out-diffusion, while the importance of the boat and the furnace materials in this process has been verified. Attenuation measurements showed that particular care must be taken, when working with waveguides diffused for short times, for two reasons. (1) The ratio diffusion length/wavelength, i.e., the normalized frequency v, decreases, and modes approach the cutoff, becoming more lossy. Of course, this is more evident working at long wavelength. (2) The surface roughness can strongly affect the attenuation value.
Studies of thermal drift as a source of output instabilities in Ti:LiNbO3 optical modulators
Authors: Nagata Hirotoshi , Kiuchi Kazumasa , Saito Tsutomu
Published: July 2002

The thermal drifts of z-cut Ti:LiNbO3 optical modulators are investigated. The behaviors of the drifts are influenced by the optical phase retardations of the modulators which are introduced during the modulator fabrication rather than the packaging process. It is also found that the time-dependent drift occurs which becomes the dominant process at high temperatures.
Electrical and optical properties of undoped InP grown at low temperature by atomic layer molecular beam epitaxy
Authors: Postigo P. A. , Dotor M. L. , Huertas P. , Golmayo D. , Briones F.
Published: July 2002

The electrical and optical properties of undoped InP layers grown at low temperatures by solid source atomic layer molecular beam epitaxy are investigated. Phosphorus surface coverage during epitaxy is controlled by monitoring the evolution of reflection high-energy electron diffraction pattern during growth. An accurate phosphorus supply by means of a valved cracking phosphorus cell is employed. The relation between phosphorus incorporation and the electronic properties of the epilayers is examined, and it is found that, at a substrate temperature of 340 °C, residual electron concentration increases linearly with phosphorus flux. Residual doping of InP layers grown at 340 °C has been reduced down to 1×1016 cm−3, and Hall mobilities of 3260 cm2/V s at 300 K and 14 830 cm2/V s at 65 K are reported. Low-temperature photoluminescence of low background doping layers is dominated by near band transitions.
Pulsed electrothermal technique for measuring the thermal diffusivity of dielectric films on conducting substrates
Authors: Bauer Siegfried , De Reggi Aimé S.
Published: July 2002

A simple technique for measuring the thermal diffusivity of dielectric films on thermally sinking substrates is proposed and demonstrated. It is an outgrowth of the thermal pulse technique for measuring charge and polarization profiles. The thermal diffusivity is derived from the transient electrical response induced by a thermal pulse applied to a dc voltage-biased sample. Because the response is proportional to the bias voltage, the signal-to-noise ratio is adjustable independently of the thermal pulse energy and may be made as large as required for determining the diffusivity with high precision. Measuring times of around 1 ms or shorter are sufficient for polymers with thicknesses up to 10 μm. Experimental results for two different polyimide films spin coated on crystalline silicon substrates are presented and discussed.
Phase-matched optical second-harmonic generation in GaN and AlN slab waveguides
Authors: Hahn D. N. , Kiehne G. T. , Ketterson J. B. , Wong G. K. L. , Kung P. , Saxler A. , Razeghi M.
Published: July 2002

Phase-matched optical second-harmonic (SH) generation was observed in GaN and AlN slab waveguides. Phase matching was achieved by waveguide modal dispersion. By tuning the output wavelength of an optical parametric amplifier, several phased-matched SH peaks were observed in the visible spectrum covering blue to red wavelengths. The peak positions are in agreement with the values calculated using the dispersive refractive indices of the film and substrate materials.
The multilayer-modified Stoney’s formula for laminated polymer composites on a silicon substrate
Authors: Kim Jin S. , Paik Kyung W. , Oh Seung H.
Published: July 2002

The thermomechanical behavior of multilayer structures is a subject of perennial interest. Stoney’s formula has long been one of the most important tools for understanding thermomechanical stress for single-layered structures like spin-coated polyimides or deposited metal thin film on substrates. In today’s microelectronics, however, as multilayer substrates have become widely available, the “modified version” of Stoney’s formula for multilayer applications is not only useful but necessary. While the majority of reports in the literature have focused on single-layer analysis, in this study, we examined an extended usage of Stoney’s formula for multilayer analysis. A simple model, the multilayer-modified Stoney’s formula, which predicts the stress contribution of each individual layer is proposed and verified through experiments and numerical analysis. Using various kinds of materials employed in a typical lamination-based multichip module technology, the thermomechanical behavior of the lamination-based multilayer substrates was measured by a laser profilometry during thermal cycling. The measured values were compared with calculated values using the multilayer-modified Stoney’s formula.
General contraction of Gaussian basis sets. I. Atomic natural orbitals for first- and second-row atoms
Authors: Almlöf Jan , Taylor Peter R.
Published: July 2002

A general contraction scheme for Gaussian basis sets is presented. The contraction coefficients are defined by the natural orbitals obtained from an atomic configuration-interaction calculation. Such atomic natural orbitals provide an excellent basis for molecular electronic structure calculations. Large primitive sets can be contracted to only a few functions without significant loss in either the SCF or correlation energy. Polarization functions can be included using the same approach.
On the dissociation energy of BH
Authors: Bauschlicher Charles W. , Langhoff Stephen R. , Taylor Peter R.
Published: July 2002

The dissociation energy (D0) of the X 1Σ+ state has been determined to be 81.5±0.5 kcal/mol. This value includes an estimate for basis set incompleteness and for core–core and core–valence correlation. The barrier in the A 1Π state potential is estimated to be 1.9±0.2 kcal/mol. By analyzing the tunneling through the barrier we demonstrate that D0 and the predissociation limit differ by about 0.8–0.9 kcal/mol. Thus the experimental predissociation limit of 82.5±0.4 kcal/mol is consistent with the values computed for D0 and the barrier in this work.
Electron attachment to the chlorosilanes and chloromethanes
Authors: Wan Hai-Xing , Moore John H. , Tossell John A.
Published: July 2002

The cross sections for dissociative attachment in the chlorosilanes and chloromethanes for electrons in the energy range 0.2–5.0 eV have been measured. In addition, measurements of the total electron scattering cross sections of the chloromethanes in the 0.2–12.0 eV range are reported. It is observed that dissociative attachment is much more probable in the chloromethanes than the chlorosilanes. This is explained by quantum mechanical calculations which reveal qualitative differences in the nature of the electron–molecule complex for the silanes as compared to the methanes.
Cavitation of a Lennard-Jones fluid between hard walls, and the possible relevance to the attraction measured between hydrophobic surfaces
Authors: Bérard D. R. , Attard Phil , Patey G. N.
Published: July 2002

A Lennard-Jones fluid confined between two planar hard walls is simulated using grand canonical Monte Carlo, and capillary evaporation is found for liquid subcritical bulk states. General methods are given for simulating a metastable fluid beyond coexistence. For the systems studied, the liquid and the gas phases coexist in equilibrium at a separation of ∼5 diam, the spinodal cavitation separation is at ∼4 diam, and the spinodal condensation separation is at ≳15 diam. The interaction pressure between the walls is found to be attractive and increases rapidly as the spinodal separation is approached. On the equilibrium liquid branch, the net pressure still appears significantly larger than the van der Waals attraction at separations of ∼10 diam. A simple analytic theory is given, which relates the force to the approach of the separation-induced phase transition. It is suggested that this is the microscopic origin of the measured attractions between hydrophobic surfaces in water.
Molecular beam study of dissociative sticking of methane on Ni(100)
Authors: Holmblad P. M. , Wambach J. , Chorkendorff I.
Published: July 2002

This paper reports a detailed molecular beam study of the dissociative sticking of methane incident on clean Ni(100). It is demonstrated that the sticking coefficient depends strongly on the translational energy of the molecule. It is also observed that an increase in the vibrational energy of the methane leads to a dramatic enhancement of the sticking, emphasizing that the initial vibrational state is of crucial importance. These results are consistent with a mechanism of direct activated dissociative chemisorption where the dynamics is dominated by a barrier in the potential energy surface mainly located in the vibrational coordinates. Normal-energy scaling is only approximately observed. The effect of surface temperature is also investigated but is found to be smaller than activation by translational or vibrational energy. A simplified analysis in terms of state resolved sticking curves, Sν(Ei), considering only the vibrational C–H stretch modes of methane as relevant for the sticking, gives a good description of the data. These sticking curves enables a calculation of the thermal sticking coefficient which is found to be in excellent agreement with bulb experiments directly probing this.