bluuebunny/crossref_metadata_2025 huggingface dataset:
Thromboxane receptor stimulation associated with loss of SKCa activity and reduced EDHF responses in the rat isolated mesenteric artery
Authors: Crane G J , Garland C J
Published: May 2004

The possibility that thromboxane (TXA2) receptor stimulation causes differential block of the SKCa and IKCa channels which underlie EDHF‐mediated vascular smooth muscle hyperpolarization and relaxation was investigated in the rat isolated mesenteric artery.

Acetylcholine (30 nM–3 μM ACh) or cyclopiazonic acid (10 μM CPA, SERCA inhibitor) were used to stimulate EDHF‐evoked smooth muscle hyperpolarization. In each case, this led to maximal hyperpolarization of around 20 mV, which was sensitive to block with 50 nM apamin and abolished by repeated stimulation of mesenteric arteries with the thromboxane mimetic, U46619 (30 nM–0.1 μM), but not the α1‐adrenoceptor agonist phenylephrine (PE).

The ability of U46619 to abolish EDHF‐evoked smooth muscle hyperpolarization was prevented by prior exposure of mesenteric arteries to the TXA2 receptor antagonist 1 μM SQ29548.

Similar‐sized smooth muscle hyperpolarization evoked with the SKCa activator 100 μM riluzole was also abolished by prior stimulation with U46619, while direct muscle hyperpolarization in response to either levcromakalim (1 μM, KATP activator) or NS1619 (40 μM, BKCa activator) was unaffected.

During smooth muscle contraction and depolarization to either PE or U46619, ACh evoked concentration‐dependent hyperpolarization (to −67 mV) and complete relaxation. These responses were well maintained during repeated stimulation with PE, but with U46619 there was a progressive decline, so that during a third exposure to U46619 maximum hyperpolarization only reached –52 mV and relaxation was reduced by 20%. This relaxation could now be blocked with charybdotoxin alone. The latter responses could be mimicked with 300 μM 1‐EBIO (IKCa activator), an action not modified by exposure to U46619.

An early consequence of TXA2 receptor stimulation is a reduction in the arterial hyperpolarization and relaxation attributed to EDHF. This effect appears to reflect a loss of SKCa activity.

British Journal of Pharmacology (2004) 142, 43–50. doi:10.1038/sj.bjp.0705756
Effects of Trolox on the activity and gene expression of cytochrome P450 in hepatic ischemia/reperfusion
Authors: Eum Hyun‐Ae , Lee Sun‐Mee
Published: May 2004

The aim of this study was to investigate the effect of Trolox on hepatic microsomal cytochrome P450 (CYP) activity and gene expression during ischemia and reperfusion (I/R).

Rats were subjected to 60 min of hepatic ischemia, and 5 h (acute phase) and 24 h (subacute phase) of reperfusion. Rats were treated intravenously with Trolox (2.5 mg kg−1) or vehicle, 5 min before reperfusion.

The serum alanine aminotransferase level and lipid peroxidation were increased as a result of I/R. These increases were attenuated by Trolox. Reduced glutathione concentration decreased in I/R group, and this decrease was inhibited by Trolox.

Both total hepatic CYP content and NADPH‐cytochrome P450 reductase activity decreased after I/R, which were restored by Trolox.

CYP1A1 activity and its protein level decreased 24 h after reperfusion; decreases which were prevented by Trolox. Both the activity and mRNA expression of CYP1A2 decreased 24 h after reperfusion. The decrease in CYP1A2 mRNA was prevented by Trolox. CYP2B1 activity and mRNA expression decreased 5 h after reperfusion. The decrease in CYP2B1 activity was prevented by Trolox. In contrast, the CYP2E1 activity and its protein level increased 5 h after reperfusion and this increase was prevented by Trolox.

The expression of TNF‐α and iNOS mRNAs increased after I/R. Trolox inhibited increase in iNOS mRNA expression.

Trolox ameliorates hepatic drug‐metabolizing dysfunction, as indicated by abnormalities in CYP isoforms during I/R, and this protection is likely due to the scavenging of reactive oxygen species.

British Journal of Pharmacology (2004) 142, 35–42. doi:10.1038/sj.bjp.0705758
Enhanced inhibition of the EDHF phenomenon by a phenyl methoxyalaninyl phosphoramidate derivative of dideoxyadenosine
Authors: Griffith Tudor M , Chaytor Andrew T , Edwards David H , Daverio Felice , McGuigan Christopher
Published: May 2004

In rabbit arteries endogenous production of cAMP facilitates electrotonic signalling via gap junctions, thus explaining the ability of P‐site inhibitors of adenylyl cyclase to attenuate EDHF‐type responses. In the present study, we show that a lipophilic phosphoramidate pronucleotide derivative of dideoxyadenosine, 2′,3′‐ddA‐PMAPh, exhibits enhanced activity as an inhibitor of EDHF‐type smooth muscle hyperpolarizations induced by acetylcholine (ACh) compared to the parent nucleoside 2′,3′‐ddA, and that the effects of both compounds can be reversed by the cAMP phosphodiesterase inhibitor IBMX. Neither 2′,3′‐ddA nor 2′,3′‐ddA‐PMAPh depress ACh‐evoked endothelial hyperpolarization directly. Modifications in the lipophilicity of dideoxyadenosine and its direct intracellular delivery as a mononucleotide may thus enhance the ability to inhibit adenylyl cyclase and depress electrotonic signalling via myoendothelial gap junctions.

British Journal of Pharmacology (2004) 142, 27–30. doi:10.1038/sj.bjp.0705782
Influence of vapors of volatile organic compounds on spectral shift of bending vibrations of freely suspended ferroelectric liquid-crystal films
Authors: Yablonskii Serguei V. , Nakano Kazuyuki , Ozaki Masanori , Yoshino Katsumi
Published: May 2004

The influence of the vapors of volatile inert fluorocarbon compounds on the mechanical properties of freely suspended ferroelectric liquid-crystal films has been studied. It was shown that spectral shift of bending vibrations of freely suspended films depends on the mass variations of the associated ambient gas as well as on the adsorption of the vapors of volatile fluorocarbon compounds onto the film surface. It was also shown that adsorption layers similar to surfactants decrease the film surface tension by 11%–35% (4–12.5 dyn/cm).
Field-effect transistor based on KTaO3 perovskite
Authors: Ueno K. , Inoue I. H. , Yamada T. , Akoh H. , Tokura Y. , Takagi H.
Published: May 2004

An n-channel accumulation-type field-effect transistor (FET) has been fabricated utilizing a KTaO3 single crystal as an active element and a sputtered amorphous Al2O3 film as a gate insulator. The device demonstrated an ON/OFF ratio of 104 and a field-effect mobility of 0.4 cm2/V s at room temperature, both of which are much better than those of the SrTiO3 FETs reported previously. The field-effect mobility was almost temperature independent down to 200 K. Our results indicate that the Al2O3/KTaO3 interface is worthy of further investigations as an alternative system of future oxide electronics.
Highly resistive p-PbTe films with carrier concentration as low as 1014 cm−3
Authors: Sandomirsky V. , Butenko A. V. , Kolobov I. G. , Ronen A. , Schlesinger Y. , Sipatov A. Yu. , Volubuev V. V.
Published: May 2004

We propose here a model according to which a high density of semiconductor–insulator interface states can deplete practically the whole film volume, provided that the film thickness is of the order of Debye screening length. We demonstrated this experimentally by showing that thin p-PbTe films, thermally deposited on mica substrate, have an unusually low concentration of free holes, as low as 1014 cm−3 at 100 K, resulting in a very high value of resistance, Hall constant, and Seebeck coefficient, respectively. Such low concentration of free carriers allows an investigation of a whole series of phenomena in AIVBVI semiconductors, such as injection currents, injection electroluminescence, electronic memory phenomena, electric field effect control of thermopower, and more.
Radiative efficiency limits of solar cells with lateral band-gap fluctuations
Authors: Rau U. , Werner J. H.
Published: May 2004

The radiative recombination limit of photovoltaic power conversion under one sun terrestrial illumination is calculated for solar cells with lateral fluctuations of the band-gap energy. A simple analytical model quantifies the fluctuations by the standard deviation σEg from the mean band gap. The calculated maximum efficiency decreases by 1.7% (absolute) for σEg=50 meV and by 6.1% for σEg=100 meV with respect to a uniform band gap.
Liquid-phase fabrication of patterned carbon nanotube field emission cathodes
Authors: Oh S. J. , Zhang J. , Cheng Y. , Shimoda H. , Zhou O.
Published: May 2004

High-resolution electron field emission cathodes were fabricated at room temperature by a high throughput electrophoresis process using functionalized carbon nanotubes (CNTs). Well-defined and adherent CNT patterns with 20 μm feature size were achieved on a variety of substrates with fine control of the CNT morphology. The cathodes show uniform emission pattern across the entire surfaces and emission current with long-term stability. This room-temperature liquid-phase process is efficient and has no intrinsic limit on the deposition area. The emission characteristics of these cathodes compare favorably to those from other fabrication methods for CNT based field emission display applications.
Hybrid near-field scanning optical microscopy tips for live cell measurements
Authors: Kapkiai Luka K. , Moore-Nichols David , Carnell Jonathan , Krogmeier Jeffrey R. , Dunn Robert C.
Published: May 2004

We report a near-field scanning optical microscopy (NSOM) probe that enables high-resolution imaging of living cells under physiological buffered conditions. The hybrid design combines a conventional fiber optic near-field probe with a standard atomic force microscopy cantilever. Imaging of fluorescent latex spheres suspended in an acetate matrix demonstrates the subdiffraction limited fluorescence and topography capabilities of the tips. The reduced spring constant of the hybrid tip is also shown to be amenable to measurements on living cells. NSOM fluorescence and topography measurements on living human arterial smooth muscle cells under buffered conditions are demonstrated.
A polymer blend approach to fabricating the hole transport layer for polymer light-emitting diodes
Authors: Yan He , Huang Qinglan , Scott Brian J. , Marks Tobin J.
Published: May 2004

This contribution describes an approach to fabricating high-efficiency hole-transport layers (HTLs) for polymer light-emitting diodes (PLEDs). HTLs fabricated by this approach have two components: a siloxane-derivatized, crosslinkable, hole-transporting material and a hole-transporting polymer. These HTLs exhibit high transparency, have no corrosive effects on the indium tin oxide anode, and have minimal pixel “cross-talk” potential. PLEDs that are fabricated using these HTLs exhibit superior performance (40% greater maximum current efficiency) versus analogous devices using a conventional poly(3,4-ethylenedioxythiophene)-poly(styrenesulfonate) (PEDOT-PSS) HTL. Most importantly, this approach has considerable flexibility and can be applied as a general strategy to manipulate energy level alignments in PLEDs.
X-ray photoelectron spectroscopy study on SiO2/Si interface structures formed by three kinds of atomic oxygen at 300 °C
Authors: Shioji M. , Shiraishi T. , Takahashi K. , Nohira H. , Azuma K. , Nakata Y. , Takata Y. , Shin S. , Kobayashi K. , Hattori T.
Published: May 2004

Using the high-brilliant synchrotron radiation at SPring-8 we have studied the SiO2/Si interface structures, the interface state densities, and the uniformities of ∼1-nm-thick oxide films formed by three kinds of atomic oxygen at 300 °C by measuring Si 2p photoelectron spectra at the photon energy of 1050 eV and the energy loss spectra of O 1s photoelectrons at the photon energy of 714 eV. Among silicon oxide films studied here the abrupt compositional transition at SiO2/Si interface, the smallest deviation in interface state density, the interface state density comparable to that for thermal oxide formed in dry oxygen at 950 °C, and the highest uniformity was obtained with oxide film formed in krypton-mixed oxygen (Kr:O2=97:3) plasma.
Electrodeless wet etching of GaN assisted with chopped ultraviolet light
Authors: Hwang Z. H. , Hwang J. M. , Hwang H. L. , Hung W. H.
Published: May 2004

Electrodeless photoelectrochemical (PEC) etching of GaN was studied in a K2S2O8/KOH solution irradiated with ultraviolet (UV) light either continuously or periodically. The rate of recombination of electrons and holes at dislocation defects is greater than for crystalline GaN, resulting in a rough etched surface with hexagonal pyramids. The shorter the interval of UV irradiation, the smoother is the etched GaN surface; a chopped UV source thus serves to improve the morphology of the etched surface. A uniform and smooth GaN surface was obtained with a root-mean-square roughness 0.37 nm through electrodeless PEC etching in a solution (KOH 0.01 M, K2S2O8 0.05 M) with a chopper frequency 2500 Hz (i.e., duration of irradiation 0.2 ms).
Quantum key distribution over 122 km of standard telecom fiber
Authors: Gobby C. , Yuan Z. L. , Shields A. J.
Published: May 2004

We report a demonstration of quantum key distribution over a standard telecom fiber exceeding 100 km in length. Through careful optimization of the interferometer and single photon detector, we achieve a quantum bit error ratio of 8.9% for a 122 km link, allowing a secure shared key to be formed after error correction and privacy amplification. Key formation rates of up to 1.9 kbit/s are achieved depending upon fiber length. We discuss the factors limiting the maximum fiber length in quantum cryptography.
Observation of a Be-correlated donor state in GaN
Authors: Albrecht F. , Reislöhner U. , Pasold G. , Hülsen C. , Witthuhn W. , Grillenberger J. , Dietrich M. ,   The ISOLDE collaboration
Published: May 2004

A Be-related donor level was identified in the band gap of GaN. Thermal admittance spectroscopy (TAS) was combined with the radiotracer principle by applying the radioactive isotope Be7 which was implanted into n-type and p-type GaN. TAS spectra of n-type GaN recorded, repeatedly, during the elemental transmutation of 7Be to 7Li reveal one shallow donor level undergoing concentration changes correlated to the radioactive decay 7Be→7Li;T1/2=53.3d). From this, a relation is deduced between Be and this level at 390 meV below the conduction band edge of GaN. Furthermore, the implantation of 7Be was observed to enhance the hole concentration significantly in Mg-doped p-type GaN. A Be-correlated acceptor state was not detected.
Heteroepitaxial growth of wurtzite InN films on Si(111) exhibiting strong near-infrared photoluminescence at room temperature
Authors: Gwo S. , Wu C.-L. , Shen C.-H. , Chang W.-H. , Hsu T. M. , Wang J.-S. , Hsu J.-T.
Published: May 2004

High-quality InN epitaxial films have been grown by nitrogen-plasma-assisted molecular-beam epitaxy on Si(111) substrates using a double-buffer technique. Growth of a (0001)-oriented single crystalline wurtzite–InN layer was confirmed by reflection high-energy electron diffraction, x-ray diffraction, and Raman scattering. At room temperature, these films exhibited strong near-infrared (0.6–0.9 eV) photoluminescence (PL). In addition to the optical absorption measurement of absorption edge and direct band nature, the PL signal was found to depend linearly on the excitation laser intensity over a wide intensity range. These results indicate that the observed PL is due to the emission of direct band-to-band recombination rather than the band-to-defect (or impurity) deep emission.
Improved quantum efficiency in nonpolar (112̄0) AlGaN/GaN quantum wells grown on GaN prepared by lateral epitaxial overgrowth
Authors: Koida T. , Chichibu S. F. , Sota T. , Craven M. D. , Haskell B. A. , Speck J. S. , DenBaars S. P. , Nakamura S.
Published: May 2004

Radiative and nonradiative excitonic transitions in nonpolar (112̄0) AlxGa1−xN/GaN multiple quantum wells (MQWs) grown on the GaN template prepared by lateral epitaxial overgrowth (LEO-GaN) were investigated. The structural advantages of using nonpolar orientations were confirmed by a moderate shift of the photoluminescence (PL) peak energy and negligible change in low-temperature PL lifetime with decreasing GaN well width, both of which are the results of eliminating quantum-confined Stark effects due to the polarization fields that exist in polar (0001) MQWs. Appearance of the correct in-plane light polarization and improved internal quantum efficiency for the PL peak in the MQWs on LEO-GaN were attributed to the reduction in densities of nonradiative defects and bound states.
Ferro- and piezoelectric properties of polar-axis-oriented CaBi4Ti4O15 films
Authors: Kato Kazumi , Fu Desheng , Suzuki Kazuyuki , Tanaka Kiyotaka , Nishizawa Kaori , Miki Takeshi
Published: May 2004

Polar-axis-oriented CaBi4Ti4O15 (CBTi144) films were fabricated on Pt foils using a complex metal alkoxide solution. The 500-nm-thick film showed the columnar structure and consisted of well-developed grains. The a/b-axis orientation of the ferroelectric films is considered to be associated with the preferred orientation of Pt foil. The film showed good ferro- and piezoelectric properties. The Pr and Ec were 25 μC/cm2 and 306 kV/cm, respectively, at an applied voltage of 115 V. The d33 was characterized as 30 pm/V by piezoresponse force microscopy. The values were twice as large as those of the CBTi144 thin film with random orientation. The polar-axis-oriented CBTi144 films would open up possibilities for devices as Pb-free piezoelectric materials.
Diffusion and segregation effects in doped manganite/titanate heterostructures
Authors: Simon J. , Walther T. , Mader W. , Klein J. , Reisinger D. , Alff L. , Gross R.
Published: May 2004

For the properties of devices based on oxide multilayers, interfaces play a crucial role. For ferromagnetic tunnel junctions the sign of the spin polarization depends on the barrier material and the interface termination. Here, we present a transmission electron microscopy study of heteroepitaxial trilayer systems consisting of a SrTiO3 insulating barrier sandwiched between La2/3D1/3MnO3 (D=Ca or Ba) electrodes grown on SrTiO3 substrates. Intermixing during growth depends on the earth alkaline ion: Ca segregates to the surface of the growing epitaxial thin film, leading to a Ca rich interface layer between the bottom electrode and the barrier. In contrast, no Ba segregation could be detected in the well lattice-matched Ba-doped film. In addition, a significant diffusion of both Ca and Ba into the SrTiO3 tunneling barrier is found, whereas the diffusion of Mn is negligibly small. Our results explain the different tunneling magnetoresistance in various manganite based tunnel junctions.
InGaN/GaN quantum-well heterostructure light-emitting diodes employing photonic crystal structures
Authors: Wierer J. J. , Krames M. R. , Epler J. E. , Gardner N. F. , Craford M. G. , Wendt J. R. , Simmons J. A. , Sigalas M. M.
Published: May 2004

Electrical operation of InGaN/GaN quantum-well heterostructure photonic crystal light-emitting diodes (PXLEDs) is demonstrated. A triangular lattice photonic crystal is formed by dry etching into the top GaN layer. Light absorption from the metal contact is minimized because the top GaN layers are engineered to provide lateral current spreading, allowing carrier recombination proximal to the photonic crystal yet displaced from the metal contact. The chosen lattice spacing for the photonic crystal causes Bragg scattering of guided modes out of the LED, increasing the extraction efficiency. The far-field radiation patterns of the PXLEDs are heavily modified and display increased radiance, up to ∼1.5 times brighter compared to similar LEDs without the photonic crystal.
Two-dimensional computational model for electrochemical micromachining with ultrashort voltage pulses
Authors: Kenney Jason A. , Hwang Gyeong S. , Shin Woonsup
Published: May 2004

We have developed a computational model to simulate electrochemical micromachining of conducting substrates with ultrashort voltage pulses. This theoretical approach integrates (i) a circuit model to describe charging and discharging of electrochemical double layers and electric field variation in electrolytes and (ii) the level set method to simulate feature profile evolution during electrochemical etching. Our simulation results of transient current responses and etch profile evolution are qualitatively in agreement with experimental observations. From our simulations, we find that the resolution of etched features is a strong function of the substrate double layer capacity which may be controlled by electrolyte concentration and pulse duration.
Thermionic and tunneling cooling thermodynamics
Authors: Chua Hui Tong , Wang Xiaolin , Gordon Jeffrey M.
Published: May 2004

We unambiguously identify and derive the irreversibilities and entropy fluxes of the quantum and classical processes that intrinsically limit the performance of thermionic and tunneling chillers. The fundamental tradeoff between cooling flux and efficiency can then be evaluated, including the ramifications for feasible cooling regimes. Quantitative illustrations are provided for real solid-state devices. We cast these results as trajectories in the temperature-entropy plane and unify the thermodynamic perspective of these quantum chillers with that of conventional cooling cycles.
Postdeposition organic coating and self-assembly of gas phase prepared FePt nanoparticles on lipid reservoir films
Authors: Terheiden Annegret , Mayer Christian , Moh Karsten , Stahlmecke Burkhard , Stappert Sonja , Acet Mehmet , Rellinghaus Bernd
Published: May 2004

A method for the postdeposition organic coating of metallic nanoparticles is introduced. FePt nanoparticles from the gas phase are deposited onto Si substrates which are pre-coated with multilayers of phospholipid molecules by spin coating. If the substrate temperature is just below or above the temperature, at which the phospholipids undergo a phase transition from the liquid crystalline into an intermediate phase, the particles are enwrapped by the lipids. The particles exhibit a clear tendency to self-assemble in regular two-dimensional particle arrangements.
Dynamics of polarization modes in photonic crystals based on arrays of vertical-cavity surface-emitting lasers
Authors: Guerrero Gilles , Boiko Dmitri L. , Kapon Eli
Published: May 2004

Polarization dynamics in coherent arrays of vertical-cavity surface-emitting lasers are studied experimentally. The two degenerate polarization lasing modes expected in infinitely large arrays are observed at different frequencies in finite-size structures. The frequency splitting increases with decreasing array size and reaches 60 GHz in 2×2 arrays. This splitting is attributed to the coupling of the two polarization states through depolarization and scattering effects at the boundary of the array. Small arrays lase in the two-frequency regime, whereas large ones oscillate in the single-frequency domain.
Spin-transfer-induced precessional magnetization reversal
Authors: Kent A. D. , Özyilmaz B. , del Barco E.
Published: May 2004

A magnetoelectronic device is proposed in which a spin-current pulse produces a rapid reversal of the magnetization of a thin film nanomagnet. A spin-transfer torque induces the reversal and the switching speed is determined by the precession frequency of the magnetization in a thin film element’s demagnetization field. Micromagnetic simulations show that this switching occurs above a threshold pulse current and can be faster than 50 ps. In contrast to present spin-transfer devices, the switching does not require an initial fluctuation or deviation of magnetic layers from collinear alignment and is far more energy efficient. This device operates at room temperature and can be realized with present-day magnetic nanostructure technology.
Fabrication and magnetic properties of fcc CoXPt1−X nanowires
Authors: Mallet Jeremy , Yu-Zhang K. , Chien Chia-Ling , Eagleton Tom S. , Searson Peter C.
Published: May 2004

Co X Pt 1−X alloy nanowires were fabricated by electrochemical template synthesis from a solution containing both Co(II) and Pt(II) ions. Over a wide range of deposition conditions, single-phase, fcc CoXPt1−X alloy nanowires were obtained. The nanowires exhibit both shape and magnetocrystalline anisotropy leading to large coercivity and high remanence along the wire axis. The magnetocrystalline anisotropy constant Ku was determined for 〈111〉 textured nanowires.
Design of fully spatially coherent extreme-ultraviolet light sources
Authors: Libertun Ariel R. , Zhang Xiaoshi , Paul Ariel , Gagnon Etienne , Popmintchev Tenio , Backus Sterling , Murnane Margaret M. , Kapteyn Henry C. , Christov Ivan P.
Published: May 2004

We demonstrate experimentally that, in order to generate fully spatially coherent extreme-ultraviolet (EUV) beams using high-harmonic generation, it is necessary to guide the driving laser beam over long interaction lengths in gas-filled hollow waveguides. Numerical simulations show that, in propagating the laser through a long plasma-filled guide, the laser beam forms a stable eigenmode with uniform spatial phase, even at very high levels of ionization. This results in a compact, highly spatially coherent, EUV source useful for applications in EUV metrology, microscopy, interferometry, and holography.
Characterization of phototransistor internal gain in metamorphic high-electron-mobility transistors
Authors: Kang Hyo-Soon , Choi Chang-Soon , Choi Woo-Young , Kim Dae-Hyun , Seo Kwang-Seok
Published: May 2004

We characterize the phototransistor internal gain of metamorphic high-electron-mobility transistors (mHEMTs). When the mHEMT operates as a phototransistor, it has internal gain provided by the photovoltaic effect. To determine this internal gain, photoresponse characteristics dominated by the photoconductive effect as well as the photovoltaic effect are investigated. When the device is turned off, it acts as a photoconductor, and by calculating photoconductor gain, the primary photodetected power can be determined, which indicates the absorbed optical power. The ratio between this and the photodetected power due to the photovoltaic effect represents phototransistor internal gain. It is demonstrated that the phototransistor internal gain is function of optical modulation frequency.
Synthesis and characterization of two-layer-structured ZnO p-n homojunctions by ultrasonic spray pyrolysis
Authors: Bian J. M. , Li X. M. , Zhang C. Y. , Chen L. D. , Yao Q.
Published: May 2004

The two-layer-structured ZnO p-n homojunctions were prepared on single-crystal Si (100) substrate by depositing undoped n-type ZnO film on N–In codoped p-type ZnO film using ultrasonic spray pyrolysis. The crystal structure and morphology of the obtained ZnO homojunctions were examined by x-ray diffraction, scanning electron microscopy, and atomic force microscopy. The two-layer structure was confirmed by secondary ion mass spectroscopy depth profile analysis. The current–voltage (I–V) characteristics derived from the undoped ZnO/N–In codoped ZnO two-layer structure clearly show the rectifying characteristics of typical p-n junctions.
Molecular weight dependence of birefringence of thin films of the conjugated polymer poly[2-methoxy-5-(2′-ethyl-hexyloxy)-1, 4-phenylenevinylene]
Authors: Koynov Kaloian , Bahtiar Ayi , Ahn Taek , Bubeck Christoph , Hörhold Hans-Heinrich
Published: May 2004

We prepared thin films of the conjugated model polymer poly[2-methoxy-5-(2′-ethyl-hexyloxy)-1, 4-phenylenevinylene] (MEH-PPV) by the spin coating of polymer samples whose weight-average molecular weight was varied from 104–106 g/mol. Waveguide prism coupling and polarized optical transmission and reflection spectroscopy were used to determine the refractive index, birefringence, and intrinsic absorption coefficient of each film. We show that these optical constants significantly depend on the molecular weight of the polymers. With decreasing molecular weight, the birefringence is strongly reduced and a nearly isotropic refractive index is approached. We conclude that the molecular weight primarily determines the extent of polymer chain alignment in the film plane.
Determination of density profile of ultrathin SiO2/Si3N4/SiO2/Si(001) multilayer structures using x-ray reflectivity technique
Authors: Banerjee S. , Ferrari S. , Piagge R. , Spandoni S.
Published: May 2004

In this report, we present an analysis of a SiO2/Si3N4/SiO2/Si(001) ultrathin multilayer structure using the x-ray reflectivity technique. The trilayer was grown using low-pressure chemical vapor deposition with each layer having a nominal thickness of ∼50 Å. Here, we propose an approach to analyze ultrathin multilayer films using two analysis schemes in tandem, i.e., distorted wave Born approximation and exact recursive formalism for x-ray reflectivity. We observe that, when SiO2 is deposited on a Si substrate, the electron density is lower than when it is deposited on Si3N4. We also observe that the two interfaces of the nitride (Si3N4) film are different, i.e., the interfacial width with the lower SiO2 is larger than the width with the top SiO2 layer.
Propagation loss in GaN-based ridge waveguides
Authors: Skorka O. , Meyler B. , Salzman J.
Published: May 2004

GaN ridge waveguides were fabricated by selective area growth in an organometallic vapor phase epitaxial system. The growth enhancement on a 3.5 μm wide exposed channel versus the masked area width was measured. The propagation losses of a series of GaN multimode waveguides, with different widths, were measured by the outscattering technique at λ=488 nm. The internal optical loss of the GaN ridge waveguide was found to be αint∼4.45 cm−1. Sidewall scattering loss (αscat) and the additional optical loss due to metal electrodes were also measured. The fabricated waveguides may be a basic component for integrated optic circuits.
Indium-assisted synthesis on GaN nanotubes
Authors: Yin Long-Wei , Bando Yoshio , Zhu Ying-Chun , Golberg Dmitri , Yin Long-Wei , Li Mu-Sen
Published: May 2004

Gallium nitride (GaN) nanotubes in a high yield were synthesized by a simple indium-assisted thermal evaporation method in the presence of NH3 gas flowing. A vapor–liquid–solid process was proposed for formation of the GaN nanotubes. The synthesized GaN nanotubes were amorphous and partially filled with indium, several micrometers in length, 40–50 nm in outer diameter, and 7 nm for the tube wall thickness. The representative photoluminescence spectrum at room temperature exhibits a great shift from the band gap of 3.40 eV (365 nm) of bulk GaN to high energy of 3.63 eV (342 nm). The synthetic route for the GaN nanotubes is simple and effective, and could provide great opportunities for both fundamental and technological applications.
Broadband 1400 nm emission from Ni2+ in zinc—alumino—silicate glass
Authors: Suzuki Takenobu , Ohishi Yasutake
Published: May 2004

Broadband near-infrared emission from Ni2+ in zinc–alumino–silicate glass was observed at room temperature. The emission band had a peak at ∼1400 nm with a bandwidth more than 300 nm, and covered the O, E, S, C, and L bands (1260–1625 nm). The emission lifetime was more than 200 μs even at room temperature. The observed near-infrared emission could be attributed to the A2g3(3F)→3T1g(3F) transition of Ni2+ in octahedral sites. This nickel-doped glass can be expected as an amplification medium for tunable lasers and broadband optical amplifiers for the wavelength division multiplexing transmission system applications.
Interface mixing and phase transformations in Xe-ion-irradiated Co/Fe bilayers
Authors: Zhang K. , Gupta R. , Müller G. A. , Schaaf P. , Lieb K. P.
Published: May 2004

Bilayers of polycrystalline Co(37 nm)/Fe(37 nm) were deposited onto Si wafers via electron-gun evaporation and irradiated at room temperature with 200 keV Xe+ ions to fluences of 5×1014–1×1016/cm2. The magneto-optical Kerr effect, Rutherford backscattering spectroscopy and x-ray diffraction were used to characterize the magnetization and microstructure of the films. Xe fluences of up to 5×1015 ions/cm2 were found to induce a four-fold magnetic anisotropy in the originally isotropic films, as a consequence of the phase transformation of hexagonal Co to face-centered-cubic Co caused by ion irradiation. Xe fluences exceeding 7×1015 ions/cm2 produced a uniaxial magnetic texture, which is explained by strong Co/Fe interface mixing and possibly ion-induced formation of CoFe grains at the interface.
Fabrication of ZnO quantum dots embedded in an amorphous oxide layer
Authors: Kim Kyoung-Kook , Koguchi Nobuyuki , Ok Young-Woo , Seong Tae-Yeon , Park Seong-Ju
Published: May 2004

ZnO quantum dots (QDs) have been fabricated by the growth of SiO2/ZnO films/Si substrate and subsequent rapid-thermal annealing in a N2 ambient. Transmission electron microscopy (TEM) results show that the ZnO QDs 3–7 nm in size are formed and embedded in the amorphous silicon oxide interfacial layer when annealed at 850 °C. Photoluminescence (PL) at room temperature from the 850 °C-annealed samples reveals only high-energy emission at about 3.37 eV, while PL at 10 K shows a broad spectra with a tail up to about 3.5 eV. The TEM and PL results indicate that the broad spectra are caused by the presence of the ZnO QDs and hence by the quantum confinement effect.
Modification of the refractive index of lithium niobate crystals by transmission of high-energy He2+4 and D+ particles
Authors: Andreas B. , Peithmann K. , Buse K. , Maier K.
Published: May 2004

We report reductions of the refractive index of congruently melting lithium niobate crystals of up to 6×10−3 by exposure of z-cut samples with high-energy 4He2+ and D+ particles which are transmitted through the crystals.
Neutron reflectivity study of ultrathin SiO2 on Si
Authors: Bertagna Valérie , Erre René , Saboungi Marie-Louise , Petitdidier Sébastien , Lévy Didier , Menelle Alain
Published: May 2004

Neutron reflectivity was applied to the study of ultrathin silicon oxide films, of interest due to the requirement for reduced dimensions of the elemental components in microelectronic devices [I. Eisele and W. Hansch, Thin Solid Films 369, 60 (2000); C. Battaglin et al., Thin Solid Films 351, 176 (1999)]. Silicon oxides were prepared using three different ways: Chemical, electrochemical, and thermal oxidation. From neutron reflectivity, it was possible to derive the oxide thickness, the Si/SiO2 interface roughness, and the density of the layer. In complementary measurements, the chemistry of the chemical and thermal surface layers was obtained by infrared spectroscopy. The anodic oxides were found to be as dense as thermal oxides, but the chemical one was less dense. This result was checked by Fourier transform infrared spectroscopy.
Virgin magnetization of a magnetically shielded superconductor wire: Theory and experiment
Authors: Genenko Yu. A. , Yampolskii S. V. , Pan A. V.
Published: May 2004

On the basis of exact solutions to the London equation, the magnetic moment of a type II superconductor filament surrounded by a soft-magnet environment is calculated and the procedure of extracting the superconductor contribution from magnetic measurements is suggested. A comparison of theoretical results with experiments on MgB2/Fe wires allows the estimation of the value of critical current for the first magnetic flux penetration.
Semiconductor–superlattice frequency multiplier for generation of submillimeter waves
Authors: Klappenberger F. , Renk K. F. , Renk P. , Rieder B. , Koshurinov Yu. I. , Pavelev D. G. , Ustinov V. , Zhukov A. , Maleev N. , Vasilyev A.
Published: May 2004

We report on a semiconductor–superlattice frequency multiplier for the generation of submillimeter waves. A monochromatic microwave-pump field (frequency near 100 GHz) periodically excited a superlattice into states of negative differential conductivity giving rise to space-charge domain creation and annihilation joint with a nonsinusoidal high-frequency current and radiation at harmonics of the pump field. A highly doped GaAs/AlAs superlattice allowed the conversion of pump to third-harmonic radiation at 300 GHz with an efficiency of about 1% (power∼30 μW).
Antiferromagnetism at the YBa2Cu3O7/La2/3Ca1/3MnO3 interface
Authors: Haberkorn N. , Guimpel J. , Sirena M. , Steren L. B. , Saldarriaga W. , Baca E. , Gómez M. E.
Published: May 2004

The magnetic properties of a series of YBa2Cu3O7−x/La2/3Ca1/3MnO3 (YBCO/LC1/3MO) superlattices grown by dc sputtering at high oxygen pressures (3.5 mbar) show the expected ferromagnetic behavior. However, field-cooled hysteresis loops at a low temperatures show the unexpected existence of exchange bias effect associated with the existence of ferromagnetic/antiferromagnetic (AF) interfaces. The blocking temperature (TB) is found to be thickness dependent and the exchange bias field (HEB) is found to be inversely proportional to the ferromagnetic layer thickness, as expected. The presence of an AF material is probably associated with interface disorder and Mn valence shift toward Mn4+.
Phonon–boundary scattering in ultrathin single-crystal silicon layers
Authors: Liu W. , Asheghi M.
Published: May 2004

Thermal engineering of many nanoscale sensors, actuators, and high-density thermomechanical data storage devices, as well as the self-heating in deep submicron transistors, are largely influenced by thermal conduction in ultrathin silicon layers. The present study measures the lateral thermal conductivity of single-crystal silicon layers of thicknesses 20 and 100 nm at temperatures between 20 and 300 K, using Joule heating and electrical–resistance thermometry in suspended microfabricated structures. The thermal conductivity of the 20 nm thick silicon layer is ∼22 W m−1 K−1, which is nearly an order of magnitude smaller than the bulk value at room temperature. In general, a large reduction in thermal conductivity resulting from phonon–boundary scattering, particularly at low temperatures, is observed. It appears that the classical thermal conductivity theory that accounts for the reduced phonon mean-free paths based on a solution of the Boltzmann transport equation along a layer is able to capture the ballistic, or nonlocal, phonon transport in ultrathin silicon films.
High-performance polycrystalline silicon thin-film transistor with multiple nanowire channels and lightly doped drain structure
Authors: Wu Yung-Chun , Chang Ting-Chang , Chang Chun-Yen , Chen Chi-Shen , Tu Chun-Hao , Liu Po-Tsun , Zan Hsiao-Wen , Tai Ya-Hsiang
Published: May 2004

This investigation examines polycrystalline silicon thin-film transistors (TFTs) with multiple nanowire channels and a lightly doped drain (LDD). A device with an LDD structure exhibits low leakage current because the lateral electrical field is reduced in the drain offset region. Additionally, multiple nanowire channels can generate fewer defects in the polysilicon grain boundary and have more efficient NH3 plasma passivation than single-channel TFTs, further reducing leakage current. They exhibit superior electrical characteristics to those of single-channel TFTs, such as a higher ON/OFF current ratio (>108), a better subthreshold slope of 110 mV/decade, an absence of drain-induced barrier lowering, and suppressed kink-effect. Devices with the proposed TFTs are highly promising for use in active-matrix liquid-crystal display technologies.
Hydrogen-induced degradation in epitaxial and polycrystalline (Ba,Sr)TiO3 thin films
Authors: Lee Jang-Sik , Li Y. , Lin Y. , Lee Sang Yeol , Jia Q. X.
Published: May 2004

A comparative study of hydrogen-induced degradation in epitaxial and polycrystalline (Ba,Sr)TiO3 (BST) thin films has been carried out. Epitaxial BST was prepared on SrRuO3 (SRO)/SrTiO3 (STO), whereas polycrystalline BST was deposited on SRO/SiOx/Si. After the Pt top electrode deposition, we have measured the dielectric response and leakage current characteristics before and after annealing in forming gas (6% hydrogen/94% argon) at 450 °C for 1 h. Even though both samples have the same capacitor architecture, Pt/BST/SRO, the degree of degradation after annealing in forming gas was found to be quite different. Epitaxial BST films were highly immune to hydrogen degradation; however, polycrystalline BST films degraded severely in terms of both dielectric and electrical properties. We show that the grain boundary is one of the main sources of hydrogen-induced degradation.
Methodology for optimizing viewing characteristics of top-emitting organic light-emitting devices
Authors: Wu Chung-Chih , Lin Chun-Liang , Hsieh Ping-Yuan , Chiang Huo-Hsien
Published: May 2004

Top-emitting organic light-emitting devices (OLEDs) have a few technical merits for active-matrix OLED displays. Generally stronger microcavity effects inherent in top-emitting OLEDs, however, complicate optimization of device efficiency and other viewing characteristics. In this letter, using the rigorous classical electromagnetic model, we analyze emission characteristics of top-emitting OLEDs as a function of device structures. From the comprehensive analysis, trends in the dependence of emission characteristics on device structures are extracted, and accordingly, a general methodology for optimizing viewing characteristics of top-emitting OLEDs for display applications is suggested. The effectiveness of the analysis and the methodology is confirmed by experimental results.
Large effects due to electron–phonon-impurity interference in the resistivity of Pt/C-Ga composite nanowires
Authors: Lin J.-F. , Bird J. P. , Rotkina L. , Sergeev A. , Mitin V.
Published: May 2004

The temperature-dependent resistivity of highly disordered Pt/C-Ga composite nanowires is shown to be well described by the interference of electron–phonon scattering and elastic electron scattering from boundaries and defects. The strongly disordered nature of these wires, combined with a high value of their Debye temperature, are responsible for the pronounced nature of the interference effects in their resistivity.
Room-temperature growth of a carbon nanofiber on the tip of conical carbon protrusions
Authors: Tanemura Masaki , Okita T. , Yamauchi H. , Tanemura S. , Morishima R.
Published: May 2004

Glassy carbon was Ar+-ion bombarded with a simultaneous Mo supply under ultrahigh vacuum conditions using a microprotrusion fabrication system that consists of a differentially pumped ion gun and a seed-material supply source. Conical protrusions were formed by sputtering with a seed supply, and carbon nanofibers (CNFs) grew on the tips even at room temperature. The length of CNFs reached up to ∼10 μm, and their diameter was almost uniform (50 nm) in the growth direction. The short CNFs aligned in the ion beam direction, whereas the long ones were non-aligned. The CNF growth on a glassy carbon surface was ascribed to the enhanced surface texturing and to the massive redeposition of C atoms onto cones, both of which are specific to the oblique ion bombardment: The former would lead to an increase in the number of possible nucleation sites for the CNF growth, and the C atoms arising from the latter process would migrate toward the conical tips, thus forming CNFs.
Size dependence of the work function in InAs quantum dots on GaAs(001) as studied by Kelvin force probe microscopy
Authors: Yamauchi T. , Tabuchi M. , Nakamura A.
Published: May 2004

We have investigated a work function of single InAs quantum dots (QDs) on GaAs(001) correlating with the dot size by means of Kelvin force probe microscopy. The observed contact potential difference (CPD) of the single QD is lower than that of an InAs wetting layer, and increases with decreasing QD height. The height dependence of the CPD is well interpreted in terms of the quantum size effect by which the amount of accumulated charges in the QD is determined through the confinement energy levels in the QD.
A hybrid Al0.10Ga0.90As/AlAs bilayer electron system with tunable g-factor
Authors: De Poortere E. P. , Shayegan M.
Published: May 2004

We have fabricated a device composed of two closely coupled two-dimensional electron systems, one of which resides within an AlAs quantum well at the X point of the Brillouin zone, while the other is contained at the Γ point in the alloy Al0.10Ga0.90As, grown directly below the AlAs. The electronic properties of these two systems are strongly asymmetric: the respective cyclotron masses in the AlAs and the Al0.10Ga0.90As layers, measured in units of the free electron mass, are ∼0.5 and 0.07, while the effective electron g-factors are approximately 7 and 0. With the help of front and back gates, we can confine mobile carriers to either or both of the two quantum wells, as confirmed by magnetotransport measurements.
Exchange bias of antiferromagnets with random anisotropies and perfectly compensated interfaces
Authors: Mewes T. , Stamps R. L.
Published: May 2004

An alternative mechanism for exchange bias for ferromagnet/antiferromagnet bilayers with completely compensated interfaces is proposed and analyzed within the biquadratic coupling model. We show that a distribution of anisotropies in the antiferromagnet can lead to the appearance of exchange bias in a bilayer with a perfectly compensated interface without defects. The energy associated with the unidirectional anisotropy that gives rise to the shifted hysteresis curve is stored in antiferromagnetic domain walls between regions in the antiferromagnet with different anisotropy. This mechanism also leads naturally to an enhanced coercivity of the ferromagnet which is caused by the anisotropy in the antiferromagnet.
Blue-light emission from sputtered Ti:SiO2 films without annealing
Authors: Hanaizumi Osamu , Ono Kazutaka , Ogawa Yuichi , Matsumoto Toshiaki , Yoda Hidehiko , Shiraishi Kazuo
Published: May 2004

Blue-light emission from Ti:SiO2 sputtered films was observed at room temperature without annealing and it could be seen by the naked eye. The peaks of photoluminescence spectra were located at 3.03–3.05 eV and full width at half maximum ranged from 0.38–0.40 eV, which were almost the same in samples having different energies of absorption edge. SiOx layers may contribute to emission, which are interfacial regions between Ti particles and surrounding SiO2 medium, and the size of Ti particles may affect the efficiency of emission.
Domain-engineered Pb(Mg1/3Nb2/3)O3–PbTiO3 crystals: Enhanced piezoelectricity and optimal domain configurations
Authors: Liu Dan , Li JiangYu
Published: May 2004

In this letter, we report a mesoscopic theory of ferroelectrics to explain the dramatically enhanced piezoelectricity in relaxor ferroelectric single crystals poled along a nonpolar axis, where the coexistence of several variants leads to complicated domain configurations. The engineered domain configuration is constructed first using energy minimization approach, and the effective moduli of single crystals with engineered domain configuration are then determined using the lamination theory. Using this approach, we calculate the effective electromechanical moduli of Pb(Mg1/3Nb2/3)O3–PbTiO3 (PMN-PT) crystals poled along [001] and [011] directions, which agree well with experimental observations. In addition, we demonstrate that PMN-PT crystals electromechanically poled by an electric field along [001] direction and an additional positive shear stress σ12 possess superior electromechanical coupling factors k31 and k33 simultaneously, while crystals with other domain configurations demonstrate much lower k31. The analysis reveals that greatly enhanced electromechanical coupling can be obtained in domain-engineered ferroelectric crystals, and offers insight on the design and optimization of ferroelectrics for enhanced functional properties.