bluuebunny/crossref_metadata_2025 huggingface dataset:
Effect of overexpressed adenylyl cyclase VI on β1‐ and β2‐adrenoceptor responses in adult rat ventricular myocytes
Authors: Stark Joalice C C , Haydock Stephen F , Foo Roger , Brown Morris J , Harding Sian E
Published: October 2004

Adenylyl cyclase VI (ACVI) is one of the most abundantly expressed β adrenergic receptor (βAR)‐coupled cyclases responsible for cyclic AMP (cAMP) production within the mammalian myocardium. We investigated the role of ACVI in the regulation of cardiomyocyte contractility and whether it is functionally coupled with β1 adrenergic receptor (β1AR).

Recombinant adenoviruses were generated for ACVI and for antisense to ACVI (AS). Adult rat ventricular myocytes were transfected with ACVI virus, AS or both (SAS). Adenovirus for green fluorescent protein (GFP) served as control. Myocyte contraction amplitudes (% shortening) and relaxation times (R50) were analysed. ACVI function was determined using cAMP assays.

ACVI‐transfected cells demonstrated a strong 139 kDa ACVI protein band compared to controls. ACVI myocytes had higher steady‐state intracellular cAMP levels than GFP myocytes when unstimulated (GFP vs ACVI=6.60±0.98 vs 14.2±2.1 fmol cAMP/viable cell, n=4, P<0.05) and in the presence of 1 μM isoprenaline or 10 μM forskolin.

ACVI myocytes had increased basal contraction (% shortening: GFP vs ACVI: 1.90±1.36 vs 3.91±2.29, P<0.0001) and decreased basal R50 (GFP vs ACVI: 62.6±24.2 ms (n=50) vs 45.0±17.2 ms (n=248), P<0.0001). ACVI myocyte responses were increased for forskolin (Emax: GFP=6.70±1.59 (n=6); ACVI=9.06±0.69 (n=14), P<0.01) but not isoprenaline.

ACVI myocyte responses were increased (Emax: GFP vs ACVI=3.16±0.77 vs 5.10±0.60, P<0.0001) to xamoterol (a partial β1AR‐selective agonist) under β2AR blockade (+50 nM ICI 118, 551). AS decreased both control and ACVI‐stimulated xamoterol responses (Emax: AS=2.59±1.42, SAS=1.38±0.5). ACVI response was not mimicked by IBMX. Conversely, response through β2 adrenergic receptor (β2AR) was decreased in ACVI myocytes.

In conclusion, ACVI overexpression constitutively increases myocyte contraction amplitudes by raising cAMP levels. Native ACVI did not contribute to basal cAMP production or contraction amplitude and only to a minor extent to the forskolin response. β1AR but not β2AR coupling was dependent on ACVI.

British Journal of Pharmacology (2004) 143, 465–476. doi:10.1038/sj.bjp.0705976
CRF2 receptors are highly expressed in the human cardiovascular system and their cognate ligands urocortins 2 and 3 are potent vasodilators
Authors: Wiley Katherine E , Davenport Anthony P
Published: October 2004

Systemic infusions of urocortin 1 produce a decrease in mean arterial pressure. This effect may be mediated by a direct action on novel corticotropin‐releasing factor type 2 (CRF2) receptors predicted to be expressed in blood vessels and the heart. Our objectives were to determine the presence of CRF2 receptors in the human cardiovascular system using the selective radioligand [125I]antisauvagine 30. We also investigated the potential functional roles of novel CRF2 ligands in the regulation of vascular tone in human arteries in vitro.

Radioligand binding techniques were used to characterise the CRF2 receptor. [125I]antisauvagine 30 bound specifically, saturably, reversibly and with high affinity to CRF2 receptors in human left ventricle (KD 0.21±0.03 nM, BMAX 0.80±0.18 fmol mg−1 protein), and no change in receptor density or affinity was observed in the dilated cardiomyopathy group.

Autoradiographical studies revealed highly localised binding of [125I]antisauvagine 30 to intramyocardial blood vessels. Binding sites were also detected in the myocardium and in the medial layer of internal mammary arteries.

In endothelium‐denuded human internal mammary artery in vitro, all peptides tested produced a potent and sustained vasodilator response reversing endothelin‐1‐induced constrictions (10 nM) (urocortin 1: pD2 8.39±0.32, EMAX 46±7.7%; urocortin 2: pD2 8.27±0.17, EMAX 60±8.5%; urocortin 3: pD2 8.61±0.25, EMAX 61±7.2%; CRF: pD2 8.28±0.27, EMAX: 40±10%).

We have demonstrated the presence of CRF2 receptors in the human cardiovascular system and a direct, endothelium‐independent vasodilator action of urocortins 2 and 3, which may counter‐balance the centrally mediated pressor effects of CRF and urocortin 1.

British Journal of Pharmacology (2004) 143, 508–514. doi:10.1038/sj.bjp.0705985
Allosteric modulation of semicarbazide‐sensitive amine oxidase activities in vitro by imidazoline receptor ligands
Authors: Holt Andrew , Wieland Barbara , Baker Glen B
Published: October 2004

Evidence indicates that imidazoline I2 binding sites (I2BSs) are present on monoamine oxidase (MAO) and on soluble (plasma) semicarbazide‐sensitive amine oxidase enzymes. The binding site on MAO has been described as a modulatory site, although no effects on activity are thought to have been observed as a result of ligands binding to these sites.

We examined the effects in vitro of several imidazoline binding site ligands on activities of bovine plasma amine oxidase (BPAO) and porcine kidney diamine oxidase (PKDAO) in a spectrophotometric protocol.

While both enzymes were inhibited at high concentrations of all ligands, clonidine, cirazoline and oxymetazoline were seen, at lower concentrations, to increase activity of BPAO versus benzylamine, but not of PKDAO versus putrescine. This effect was substrate dependent, with mixed or biphasic inhibition of spermidine, methylamine, p‐tyramine and β‐phenylethylamine oxidation observed at cirazoline concentrations that increased benzylamine oxidation.

With benzylamine as substrate, clonidine decreased KM (EC50 8.82 μM, Emax 75.1% of control) and increased Vmax (EC50 164.6 μM, Emax 154.1% of control). Cirazoline decreased Vmax (EC50 2.15 μM, Emax 91.4% of control), then decreased KM (EC50 5.63 μM, Emax 42.6% of control) and increased Vmax (EC50 49.0 μM, Emax 114.4% of decreased Vmax value).

Data for clonidine fitted a mathematical model for two‐site nonessential activation plus linear intersecting noncompetitive inhibition. Data for cirazoline were consistent with involvement of a fourth site.

These results reveal an ability of imidazoline ligands to modulate BPAO kinetics allosterically. The derived mechanism may have functional significance with respect to modulation of MAO by I2BS ligands.

British Journal of Pharmacology (2004) 143, 495–507. doi:10.1038/sj.bjp.0705986
Semiconductor lasers with an inversely biased active region for generation of millimeter wave modulated signals
Authors: Toda T.
Published: October 2004

A semiconductor laser structure is proposed to introduce field effects in its active region. It has five layers of p-n-i-p-n with four electrical contacts to the doped layers, where the current injection into an inversely biased active region is based on the operation of two complementary bipolar transistors with their base-collector junction common. The inverse bias is useful to incorporate carrier transfer phenomena like Gunn effect in semiconductor lasers. Our analysis on the proposed lasers shows that its lasing operation is possible while applying a high electric field more than 106 V/m in the carrier transfer domain.
Quantum cascade photodetector
Authors: Gendron L. , Carras M. , Huynh A. , Ortiz V. , Koeniguer C. , Berger V.
Published: October 2004

A photovoltaic intersubband detector based on electron transfer on a cascade of quantum levels is presented: A quantum cascade detector (QCD). The highest photoresponse of intersubband transition-based photovoltaic detectors is demonstrated: 35mA∕W at null bias. The deduced absorption is of the same order of magnitude as that of a classical quantum-well infrared photodetector, i.e., 20%. Because they work with no dark current, QCDs are very promising for small-pixel large focal plane array applications.
Evaluation of the gauge factor for membranes assembled by single-walled carbon nanotubes
Authors: Reale A. , Regoliosi P. , Tocca L. , Lugli P. , Orlanducci S. , Terranova M. L. , Bruni G.
Published: October 2004

Samples of single-walled carbon nanotubes (SWCNTs) organized in the form of thin membranes have been investigated in order to correlate the mechanical deformation and conductivity behavior of such nanosized material. The nanotubes gauge factor of piezoresistivity has been evaluated by comparing the electrical responses induced by the deformation in SWCNT membranes and in Si substrates with the same electrical characteristics. The gauge factor of the SWCNT–Si systems was found to be a factor 2.3–2.5 larger than that of the Si substrates. We have also observed that temperature slightly enhances the piezoresistive response of the SWCNT.
Long-range order in a multilayer organic film templated by a molecular-induced surface reconstruction: Pentacene on Au(110)
Authors: Guaino Ph. , Carty D. , Hughes G. , McDonald O. , Cafolla A. A.
Published: October 2004

We describe the growth of a highly ordered pentacene film on the Au(110) surface, investigated in both real and reciprocal space using scanning tunneling microscopy and low-energy electron diffraction techniques. At high coverage, a unidirectional multilayer of π-stacked molecular row is formed with long-range order. Investigations of the interface at low molecular coverage show that this molecular arrangement is a direct consequence of a pentacene-induced surface reconstruction. Pentacene molecules initially adsorb between atomic gold rows of the Au(110)–(1×2) missing row structure and induce a (1×3) surface reconstruction, acting as a template for the organic film formation.
Effect of keto defects on the electrical properties of fluorene-based oligomers
Authors: Noh Yong-Young , Kim Dong-Yu , Yoshida Yuji , Yase Kiyoshi , Jung Byung-Jun , Lim Eunhee , Shim Hong-Ku , Azumi Reiko
Published: October 2004

The effect of ketonic defects on electrical properties, i.e., the performance of organic field-effect transistors (OFETs) was examined in fluorene end capped fused bithiophene oligomers (BFTT). The long wavelength emission at 2.1–2.3eV resulting from the ketonic defects was observed in photoluminescence spectra of BFTT films after UV irradiation in air. In addition, the peak corresponding to the carbonyl stretching mode of the fluorenone moiety at 1721cm−1 was also apparent after UV irradiation for periods longer than 6h in air. These observations confirm that ketonic defects are present in the fluorene units of BFTT after photo-oxidation. The threshold voltage (Vth), i.e., switch-on voltage, of OFETs was increased and field-effect mobility (μFET) was decreased after the formation of the ketonic defects, since these defects induce the formation of numerous trap sites in the bandgap of the semiconducting conjugated oligomer.
Exact electroelastic solutions for penny-shaped cracks under prescribed temperature or thermal flow
Authors: Wang B. L.
Published: October 2004

This letter provides an exact solution for a thermal penny-shaped crack in piezoelectric media. An arbitrarily distributed temperature field applied on the crack faces is considered first. Closed-form expressions for the stress and electric displacement intensity factors at the crack border are given. Electrically impermeable cracks, electrically permeable cracks, and the permittivity of the medium inside the cracks are considered. Then, crack tip field intensity factors for a prescribed thermal flow on the crack faces are obtained. The solutions are mainly provided for transversely isotropic materials, but results for isotropic materials and dielectrics are also given.
Ultrasensitive radio-frequency pseudomorphic high-electron-mobility-transistor readout for quantum devices
Authors: Oukhanski Nikolai , Hoenig Eckhardt
Published: October 2004

Two versions of a cryogenic multistage pseudomorphic high-electron-mobility field-effect transistor amplifier (based on the AlGaAs/InGaAs/GaAs heterostructure) have been designed for quantum device readout and tested at an ambient temperature ∼380mK. The minimum noise temperature of the first amplifier version is below 110±25mK(∼80±20hf∕kB) at 28.6 MHz, estimated from the noise of input 10 kΩ resistance and coupled input tank circuit with an active resistance at the resonant frequency RS(f0)≈17.9kΩ. Its minimum voltage spectral noise density, with respect to the input, is about 200pV∕(Hz)1∕2 and the corner frequency of the 1∕f noise is close to 300 kHz. For the amplifier with the lowest designed back action, the minimum noise temperature below 130±30mK(∼100±25hf∕kB) at 26.8 MHz was estimated when coupled to an input tank circuit with RS(f0)≈61.8kΩ. The power consumption of the amplifiers is in the range of 100–600 μW.
Recovering image resolution in reconstructing digital off-axis holograms by Fresnel-transform method
Authors: Ferraro Pietro , De Nicola Sergio , Finizio Andrea , Pierattini Giovanni , Coppola Giuseppe
Published: October 2004

The resolution of amplitude and phase reconstruction of images from digital holograms by the Fresnel transformation method is limited by the pixel width in the reconstructed image plane. The reconstruction pixel depends on distance, wavelength, and number of pixels in the hologram. The spatial frequencies, in the reconstructed image, are band limited by the size of the reconstruction pixel. Undersampling can occur, in the image plane, in the reconstructed amplitude and/or wrapped phase maps. Recovery of reconstructed undersampled spatial frequencies, is possible by the fictitious enlargement of the digital hologram. Correct profile reconstruction of a silicon microelectromechanical structure is demonstrated, applying the proposed method.
Highly photoconductive amorphous carbon nitride films prepared by cyclic nitrogen radical sputtering
Authors: Katsuno T. , Nitta S. , Habuchi H. , Stolojan V. , Silva S. R. P.
Published: October 2004

We report on the growth of amorphous carbon nitride films (a-CNx) showing the highest conductivity to date. The films were prepared using a layer-by-layer method (a-CNx:LL), by the cyclical nitrogen radical sputtering of a graphite radical, alternated with a brief hydrogen etch. The photosensitivity S of these films is 105, defined as the ratio of the photoconductivity σp to the dark conductivity σd and is the highest value reported thus far. We believe that the carriers generated by the monochromatic light (photon energy 6.2eV) in the a-CNx:LL films are primarily electrons, with the photoconductivity shown to increase with substrate deposition temperature.
An approach for electrical self-stabilization of high-temperature superconducting wires for power applications
Authors: Aytug T. , Paranthaman M. , Zhai H. Y. , Gapud A. A. , Leonard K. J. , Martin P. M. , Goyal A. , Thompson J. R. , Christen D. K.
Published: October 2004

Electrical and thermal stability of high-temperature superconducting (HTS) wires∕tapes are essential in applications involving efficient production, distribution, and storage of electrical energy. We have developed a conductive buffer layer structure composed of bilayer La0.7Sr0.3MnO3∕Ir on a textured Ni–W alloy metal tape to functionally shunt the HTS layer to the underlying substrate. The key feature is the Ir layer, which serves as a barrier to both inward diffusion of oxygen and outward diffusion of metal substrate cations during fabrication. Electrical and microstructural property characterizations of YBa2Cu3O7-δ films on short prototype conductors demonstrate self-field critical current density values, Jc, exceeding 2×106A∕cm2 at 77K and excellent electrical coupling to the underlying metal substrate, with no unwanted insulating oxide interfaces. Implementing this approach in power technologies would significantly increase the engineering current density of the conductor and reduce overall process costs.
Miniaturization and embedding of soliton-based electro-optically addressable photonic arrays
Authors: D’Ercole A. , Palange E. , DelRe E. , Ciattoni A. , Crosignani B. , Agranat A. J.
Published: October 2004

We achieved the soliton-based miniaturized integration of electro-optic devices in a photorefractive paraelectric bulk crystal, by driving self-trapping through an external bias field in a top-sided electrode geometry. The ensuing spatially resolved electric field manifests a localized voltage-dependent region in which a quasi-uniform field leads to screening-like self-trapped waves at considerably low voltages without sample miniaturization, along with their electro-optic beam manipulation. By replicating the electrode structure, our achievements constitute the basic building block that paves the way to digitally addressable volume photonic manipulator arrays.
Electrical characteristics and suppressed boron penetration behavior of thermally stable HfTaO gate dielectrics with polycrystalline-silicon gate
Authors: Yu Xiongfei , Zhu Chunxiang , Li M. F. , Chin Albert , Du A. Y. , Wang W. D. , Kwong Dim-Lee
Published: October 2004

The thermal stability and electrical characteristics of HfTaO gate dielectric with polycrystalline-silicon gate have been investigated. The incorporation of Ta into HfO2 enhances the crystallization temperature of film dramatically. Transmission electron microscopy micrographs confirm that HfTaO with 43% Ta film remains amorphous even after activation annealing at 950°C for 30s, and the formation of low-κ interfacial layer is observably reduced. The capacitance–voltage curve of metal–oxide–semiconductor capacitor using HfTaO gate dielectric fits well with simulated curve, indicating good interface property between HfTaO and substrate. In addition, the boron penetration behaviors of HfTaO films are sufficiently suppressed as manifested by the narrow flat-band voltage shift. The negligible flat-band voltage shift in HfTaO with 43% Ta film is observed and attributed to its amorphous structure after device fabrication.
Experimental demonstration of Bloch mode parity change in photonic crystal waveguide
Authors: Cluzel B. , Gérard D. , Picard E. , Charvolin T. , Calvo V. , Hadji E. , de Fornel F.
Published: October 2004

We experimentally show coupling between two photonic crystal waveguide Bloch modes having a different parity. A monomode ridge waveguide etched in a silicon-on-insulator substrate and connecting to the photonic crystal waveguide allows us to excite the even Bloch mode. Transmission measurements, performed on a broad spectral range, show the even mode propagation along the defect line. Then, spectrally resolved near-field patterns obtained by using a scanning near-field optical microscope in collection mode for wavelengths, inside and outside the multimode region of the photonic crystal waveguide, clearly demonstrate coupling phenomenon between even and odd modes.
Real-time formation, accurate positioning, and fluid filling of single rolled-up nanotubes
Authors: Deneke Ch. , Schmidt O. G.
Published: October 2004

We apply real-time video microscopy to monitor the formation of rolled-up InAs∕GaAs tubes in great detail. The roll-up process is highly nonlinear at the beginning, linear at an intermediate stage, and ceases for long etching times. This self-limitation effect allows precise positioning of the tubes on a substrate surface. We investigate the formation of rolled-up nanotubes (RUNTs) on lithographically patterned substrates as a function of sacrificial layer thickness and tube diameter, and our results are well-described by a simple diffusion model. We fill well-positioned RUNTs of well-defined lengths with dye liquid and we observe strong fluorescence signal of these structures in the red spectral range.
Evaluation of the internal field in lithium niobate ferroelectric domains by an interferometric method
Authors: de Angelis M. , De Nicola S. , Finizio A. , Pierattini G. , Ferraro P. , Grilli S. , Paturzo M.
Published: October 2004

We report on the evaluation of internal electric field of a ferroelectric engineered-domain in a LiNbO3 wafer crystal by detecting optical path length variation with a noninvasive interferometric inspection method. The lithium niobate wafer has been patterned and subjected to electric field poling to obtain two antiparallel ferroelectric domains separated by a single domain wall. The crystal has been mounted into one arm of a Mach–Zehnder-type interferometer to study the phase map and evaluate the effects of domain reversion by a digital holographic technique. Evaluation of the internal field and consequent variation of the electro-optical properties of the different domains is analyzed.
Magnetic fields and fluxes probed by coherent low-energy electron beams
Authors: Degiovanni Alain , Bardon Jacques , Georges Vincent , Morin Roger
Published: October 2004

The magnetization of a nanometer size Ni needle is observed using the coherent electron beam originating from an electron point source. This at one and the same time displays the local (Lorentz force) and the nonlocal (Aharonov–Bohm phase shift) magnetic effects. The experiments are performed at three orders of magnitude lower electron energy than previous nonlocal effects observations. These experiments open a way to quantitative magnetization measurements and to magnetic imaging at a nanometer scale.
Antenna effects in terahertz apertureless near-field optical microscopy
Authors: Wang Kanglin , Mittleman Daniel M. , van der Valk Nick C. J. , Planken Paul C. M.
Published: October 2004

We have performed measurements on terahertz (THz) apertureless near-field microscopy that show that the temporal shape of the observed near-field signals is approximately proportional to the time-integral of the incident field. Associated with this signal change is a bandwidth reduction by approximately a factor of 3 which is observed using both a near-field detection technique and a far-field detection technique. Using a dipole antenna model, it is shown how the observed effects can be explained by the signal filtering properties of the metal tips used in the experiments.
Interfacial characteristics of HfO2 grown on nitrided Ge (100) substrates by atomic-layer deposition
Authors: Kim Hyoungsub , McIntyre Paul C. , Chui Chi On , Saraswat Krishna C. , Cho Mann-Ho
Published: October 2004

The microstructural and electrical properties of Ge-based metal–oxide–semiconductor capacitors containing high-k gate dielectric layers were investigated with and without the presence of a GeOxNy interface layer. The effect of this nitrided layer on thermal stability of the metal oxide/Ge structures was probed by medium energy ion energy spectroscopy (MEIS). Atomic-layer deposited HfO2 on a chemical oxide-terminated Ge (100) surface exhibited poor capacitance–voltage behavior; however, direct substrate surface nitridation at 600°C in NH3 ambient before HfO2 deposition improved the carrier trapping characteristics. Diffusion of metal impurities (including Hf) into the interfacial oxide/Ge-substrate may be an important source of the measured degradation of electrical properties. MEIS results suggested that the GeOxNy interface layer may inhibit Hf diffusion into the underlying semiconductor at the temperatures investigated.
Valence photoelectron spectra of an electron-beam-irradiated C60 film
Authors: Onoe Jun , Nakao Aiko , Hida Akira
Published: October 2004

Valence photoelectron spectra of an electron-beam (EB) irradiated C60 film, which exhibited metallic electron-transport properties in air at room temperature, are presented. The electronic structure of the C60 film became closer to that of graphite as the EB-irradiation time increased, and its density of states around the Fermi level was eventually greater than for the graphite. This suggests that the electronic structure of the C60 film changed from a semiconductor to a semimetal and/or metal by EB irradiation. Interestingly, the electronic structure remained metallic even after five days of air exposure, which is the reason for the metallic electron-transport property in our previous report [Appl. Phys. Lett. 82, 595 (2003)].
Large enhancement of the piezoelectric response in perovskite crystals by electric bias field antiparallel to polarization
Authors: Budimir Marko , Damjanovic Dragan , Setter Nava
Published: October 2004

Using Landau–Ginzburg–Devonshire theory and tetragonal BaTiO3 as an example, this letter demonstrates that strong electric bias fields applied antiparallel to spontaneous polarization may lead to a large enhancement of piezoelectric properties in monodomain perovskite crystals with multiple phase transitions. At temperatures close to tetragonal–orthorhombic phase transition, the largest enhancement is approximately along the [111] axis. The enhancement is due to the field induced dielectric softening of the crystal.
Performance enhancement of high-speed SiGe-based heterojunction phototransistor with substrate terminal
Authors: Shi Jin-Wei , Pei Z. , Yuan F. , Hsu Y.-M. , Liu C.-W. , Lu S. C. , Tsai M.-J.
Published: October 2004

Heterojunction phototransistors (HPTs) are requested to have high electrical bandwidth (∼1GHz) performance for their application of high-speed digital fiber communication. In this letter, a method is disclosed to enhance the speed performance of Si∕SiGe-based HPTs, which can overcome the low quantum efficiency drawback (∼0.1A∕W) of Si-based high-speed photodetectors at the wavelength of 850nm due to its large internal gain. By use of the substrate terminal of HPT, the speed performance can be enhanced greatly with much less reduction in optical gain as compared to the traditional technique with base-terminal-bias. Under proper optical power excitation and the common ground of substrate and emitter terminals, we can achieve 1.8GHz fast-Fourier-transformed electrical bandwidth with 0.7A∕W responsivity simultaneously. The demonstrated device structure can serve as a key component in the short-reach fiber communication system.
Piezoresponse in the light of surface adsorbates: Relevance of defined surface conditions for perovskite materials
Authors: Peter F. , Szot K. , Waser R. , Reichenberg B. , Tiedke S. , Szade J.
Published: October 2004

We report on the influence of a surface layer prevailing on perovskites on the piezoelectricity measured by piezoresponse force microscopy. Surface sensitive measurements show that this layer consists of chemisorbates and physisorbates. The surface layer can be removed to a large extent by heating the sample under ultrahigh vacuum conditions. It is shown that the effect of this treatment on the piezoresponse of the material is significant as the potential difference applied to the sample is no longer reduced by a voltage drop across the adsorbate layer. As a consequence the internal electric field is higher in comparison to the presence of a layer and so the piezoresponse is higher as well.
Site-selective 900nm quasi-three-level laser emission in Nd-doped strontium lanthanum aluminate
Authors: Aka G. , Vivien D. , Lupei V.
Published: October 2004

Neodymium-doped strontium lanthanum aluminate crystals Sr1−xLax−yNdyMgxAl12-xO19 contain two structural Nd centers with slightly different spectroscopic properties, whose proportion is determined by the composition parameter x. By choosing a composition with x=0.4, which grants the dominance of one of these centers (the center C1), whose properties are suitable for quasi-three-level Nd laser scheme, efficient 901nm continuous-wave laser emission (slope efficiency ∼0.74) was obtained under 792nm Ti:sapphire laser pumping. Preliminary experiments evidence the possibility of obtaining 450.5nm radiation by frequency doubling. Owing to the large absorption linewidth (∼4nm) this crystal shows good prospect for diode laser pumping.
Spin dynamics of the antiferromagnetic-to-ferromagnetic phase transition in FeRh on a sub-picosecond time scale
Authors: Thiele Jan-Ulrich , Buess Matthias , Back Christian H.
Published: October 2004

The antiferromagnetic-to-ferromagnetic phase transition in FeRh films induced by heating with a femtosecond laser pulse was investigated using the time-resolved magneto-optical Kerr effect. An initial rise time of the magneto-optical signal of about 500fs is found as the FeRh is heated through the transition. The data offer a complementary view to previous pump–probe experiments on “simple” ferromagnetic materials and allow a glimpse at the complex interplay between lattice, electron and spin dynamics governing the first-order antiferromagnetic-to-ferromagnetic phase transition of FeRh.
Trends in ferromagnetism, hole localization, and acceptor level depth for Mn substitution in GaN, GaP, GaAs, and GaSb
Authors: Mahadevan Priya , Zunger Alex
Published: October 2004

We examine the intrinsic mechanism of ferromagnetism in dilute magnetic semiconductors by analyzing the trends in the electronic structure as the host is changed from GaN to GaSb, keeping the transition metal impurity fixed. In contrast with earlier interpretations which depended on the host semiconductor, it is found that a single mechanism is sufficient to explain the ferromagnetic stabilization energy for the entire series.
Maxwell–Wagner effect in hexagonal BaTiO3 single crystals grown by containerless processing
Authors: Yu Jianding , Paradis Paul-François , Ishikawa Takehiko , Yoda Shinichi
Published: October 2004

Oxygen-deficient hexagonal BaTiO3 single crystals, with dielectric constant ε′∼105 and loss component tan δ∼0.13 at room temperature and a linear temperature dependence of ε′ in the range 70–100K, was analyzed by impedance spectroscopy analysis. Two capacitors, bulk and interfacial boundary layer, were observed, and the colossal dielectric constant was mainly dominated by the interfacial boundary layers due to Maxwell–Wagner effect. After annealing the oxygen-deficient hexagonal BaTiO3 at 663K, the ε′ and tanδ became, respectively, 2×104 and 0.07 at room temperature. This work showed an important technological implication as annealing at lower temperatures would help to obtain materials with tailored dielectric properties.
Temperature-dependent magnetic interface location in interdiffused exchange biased bilayers
Authors: Lund M. S. , Fitzsimmons M. R. , Park S. , Leighton C.
Published: October 2004

Antiferromagnetic (AF) binary alloys are attractive choices for exchange pinning of ferromagnets (F) in applications. Unfortunately, inducing AF ordering in these alloys often requires annealing which leads to interdiffusion at the AF∕F interface and a subsequent, and poorly understood, reduction in exchange bias. We report a study of the effects of interdiffusion in epitaxial NiMn∕Ni bilayers. Using polarized neutron reflectometry, we deduce that the competition between AF and F interactions in the interdiffused region leads to a temperature-dependent magnetic interface location, “glassy” behavior, memory effects, and low-temperature training. The results have important implications for the understanding of the temperature dependence of the exchange bias in these materials.
Rashba effect on the plasma oscillations in a coupled bilayer of electrons and holes
Authors: Gumbs Godfrey
Published: October 2004

We consider the effect of spin-orbit (SO) coupling on the plasma oscillations for a coupled system of two-dimensional electron or heavy hole (HH) gases. The Rashba effect lifts the degeneracy of the energy spectrum and produces a linear term for electrons but a cubic term for HH states in wave vector space. The SO coupling gives rise to two plasmon branches for a single layer due to transitions within a subband and between subbands. The interlayer coupling splits each of these branches. We present numerical results for the frequency of the collective excitations as a function of wave vector and the Rashba parameter. The application to optical characterization studies is discussed.
Crystalline quality of bonded silicon-on-insulator characterized by spectroscopic ellipsometry and Raman spectroscopy
Authors: Nguyen N. V. , Maslar J. E. , Kim Jin-Yong , Han Jin-Ping , Park Jin-Won , Chandler-Horowitz D. , Vogel E. M.
Published: October 2004

The crystalline quality of silicon-on-insulator fabricated by a wafer bonding technique was examined by spectroscopic ellipsometry and Raman spectroscopy. The detailed modeling of the experimental ellipsometric data yields information about structural defects in the silicon-on-insulator layer. The dielectric function of the silicon on insulator that best models the experimental ellipsometric data includes a physical mixture of crystalline silicon and about 4%–7% of amorphous silicon, suggesting a slight lack of long-range order of the silicon atoms in the silicon-on-insulator layer. The use of a dielectric function other than that of pure crystalline silicon is supported by Raman spectroscopic results that indicate the presence of structural defects in the silicon-on-insulator layer. These structural defects may be due to the effects of hydrogen implantation used in the fabrication process of silicon-on-insulator, and∕or the strain imposed by the lattice mismatch between the buried layer and the silicon substrate, and subsequently relaxed under high-temperature annealing.
Splitting of surface plasmon frequencies of metal particles in a nematic liquid crystal
Authors: Park Sung Yong , Stroud D.
Published: October 2004

We calculate the effective dielectric function for a suspension of small metallic particles immersed in a nematic liquid crystal (NLC) host. For a random suspension of such particles in the dilute limit, we calculate the effective dielectric tensor exactly and show that the surface plasmon resonance of such particles splits into two resonances, polarized parallel and perpendicular to the NLC director. At higher concentrations, we calculate this splitting using a generalized Maxwell–Garnett approximation (MGA), which can also be applied to a small metal particle coated with NLC. To confirm the accuracy of the MGA for NLC-coated spheres, we also use the discrete dipole approximation. The calculated splitting is comparable to that observed in recent experiments on NLC-coated small metal particles.
Extremely surface-sensitive hysteresis loop measurement with a spin-polarized metastable helium atom beam
Authors: Kurahashi M. , Suzuki T. , Yamauchi Y.
Published: October 2004

The sample current induced by the deexcitation of He* atoms on a ferromagnetic surface was found to depend on the He* spin direction. This spin dependence was used for measuring the hysteresis loop of an Fe film on Cu(100). The hysteresis loop is extremely surface specific because the spin dependence is due to the electron emission via the He* deexcitation that occurs on the vacuum side of the topmost surface layer. The hysteresis loop for a 2.2ML Fe film on Cu(100) has been found to agree well with that measured with the surface magneto-optic Kerr effect.
Anisotropy and magnetotransport in ordered magnetic antidot arrays
Authors: Castaño F. J. , Nielsch K. , Ross C. A. , Robinson J. W. A. , Krishnan R.
Published: October 2004

Magnetic films containing ordered arrays of holes (“antidots”) with period ∼200nm have been prepared using porous anodic alumina substrates with square and hexagonal symmetries. Large area (∼cm2) single-layer CoFe ordered antidot arrays show well-defined in-plane magnetic anisotropy related to the symmetry of the arrays, and the anisotropic magnetoresistance is smaller than that of a continuous film. For NiFe∕Cu∕CoFe antidot arrays, the giant magnetoresistance ratio of the patterned films is of similar magnitude to that of the unpatterned film, and shares the symmetry of the substrate. This behavior is attributed to the geometry of the antidots, which confine the magnetization of each layer parallel to the current flow.
Antiferromagnetic coupling in ferromagnetic oxide trilayer films composed of Sr0.7Ca0.3RuO3 and La0.6Sr0.4MnO3
Authors: Uozu Y. , Nakajima T. , Nakamura M. , Ogimoto Y. , Izumi M. , Miyano K.
Published: October 2004

Magnetic and transport properties of trilayer films composed of ferromagnetic metals Sr0.7Ca0.3RuO3 (SCRO) and La0.6Sr0.4MnO3 (LSMO) on SrTiO3 (001) substrate were studied. Decrease in magnetization below Curie temperature of SCRO indicates antiferromagnetic coupling between SCRO and LSMO layers resulting from superexchange interaction. Resistivity is found to be lower in antiparallel magnetic configuration, which is due to negative spin polarization of SCRO.
Near-band edge light emission from silicon semiconductor on insulator diodes
Authors: Zhao J. , Zhang G. , Trupke T. , Wang A. , Hudert F. , Green M. A.
Published: October 2004

Light-emitting diodes have been designed and fabricated on commercial crystalline silicon semiconductor on insulator wafers. Strong infrared light emission has been observed from these diodes under forward bias conditions with an external quantum efficiency of 2×10−6. The band edge phonon-assisted photoluminescence from the top single-crystalline silicon layer is responsible for such emission with a spectrum peaked at 1.135μm wavelength. Due to negligible reabsorption of spontaneously emitted photons within the extremely thin silicon layer, the short wavelength emission is significantly stronger in relative terms compared to emission from bulk-silicon light-emitting devices.
Formation of order molecular nanostructures on the Si(111)-(7×7) surface by patterned assembly
Authors: Zhang Y. P. , Yong K. S. , Lai Y. H. , Xu G. Q. , Wang X. S.
Published: October 2004

The well-defined and patterned copper clusters formed on the Si(111)-(7×7) surface have been employed as a template for selective binding of molecules, forming ordered molecular nanostructures. Scanning tunneling microscopic studies show that thiophene molecules preferentially bind to the copper clusters through the S–Cu interaction involving S lone-pair electrons. Large-scale two-dimensional thiophene molecular nanostructures can be obtained using this patterned assembly technique. Our experiments demonstrate the feasibility for controllable growth of ordered molecular nanostructures on Si(111) surface.
Type of dissociated misfit dislocation in perovskite films on LaAlO3
Authors: Lu C. J.
Published: October 2004

A type of dissociated misfit dislocation in epitaxial Ba0.3Sr0.7TiO3 thin films on (001) LaAlO3 substrates has been studied by high-resolution transmission electron microscopy. The dislocation has a Burgers vector [210] and is dissociated into four partial dislocations with Burgers vectors of type 12⟨110⟩. All partials can relieve the localized misfit strain and they are interacted with three 12⟨110⟩ stacking faults lying on (001). The partials were generated during island nucleation and mosaic growth of the BSTO film, while a small amount of excess TiO2 during film deposition favored the formation of the 12⟨110⟩ stacking faults.
High-power-density spot cooling using bulk thermoelectrics
Authors: Zhang Yan , Shakouri Ali , Zeng Gehong
Published: October 2004

We demonstrate a three-dimensional (3D) bulk silicon microcooler, which has the advantages of high cooling power densities and is less dependent on thermoelectric element’s thickness as compared with the same device with one-dimensional (1D) geometry. We measured a maximum cooling of 1.2°C for a 40×40μm2 area bulk silicon microcooler device, which is equivalent to an estimated cooling power density of 580W∕cm2. In this unique geometry, both current and heat spreading in 3D allows the maximum cooling temperature to exceed the conventional 1D thermoelectric model’s theoretical limit 0.5ZTc2.
Domain structure of sintered SmCo5 magnets studied by magneticforce microscopy
Authors: Szmaja Witold , Grobelny Jarosław , Cichomski Michał
Published: October 2004

The domain structure of sintered SmCo5 permanent magnets at the surface perpendicular to the alignment axis was investigated by magnetic force microscopy (MFM). The main domains forming a maze pattern of typically 3–5μm in width and surface reverse spikes of typically 1–2μm in size are observed. This coarse domain structure is similar to those present in sufficiently thick uniaxial crystals with strong magnetocrystalline anisotropy, reported in earlier investigations performed by Bitter pattern method or magneto-optic Kerr microscopy. In addition to the coarse domain structure, a complicated system of the fine surface domains of 10–200nm in width is observed. The thickness of the zone below the surface filled with these fine scale domains is estimated to be 100 nm and their presence is related to the reduction of the magnetostatic energy close to the specimen surface. Practically no correlation between the magnetic domain structure and the surface topography, the latter revealed by atomic force microscopy, was observed. The high spatial resolution and high surface sensitivity of the MFM technique are demonstrated.
Fabrication of ZnS∕SiC nanocables, SiC-shelled ZnS nanoribbons (and sheets), and SiC nanotubes (and tubes)
Authors: Hu J. Q. , Bando Y. , Zhan J. H. , Golberg D.
Published: October 2004

Here we report on the synthesis of ZnS∕SiC nanocables and SiC nanotubes and other relevant structures via a controllable two-stage thermal process using ZnS nanowires, nanoribbons, and sheets as templates. Within the cables, the ZnS cores are polytypes of fcc- and hcp-ZnS with ∼50–130nm diameter, and the SiC shells are polycrystalline β-SiC with ∼15–50nm thickness. SiC nanotubes were formed through simple removal of ZnS cores from the cables. Room-temperature photoluminescence of the SiC nanotubes displays a strong green emission band centered at ∼517nm. The nanostructures described herewith may be valuable in the blocks of advanced semiconducting devices.
Dense Fe cluster-assembled films by energetic cluster deposition
Authors: Peng D. L. , Yamada H. , Hihara T. , Uchida T. , Sumiyama K.
Published: October 2004

High-density Fe cluster-assembled films were produced at room temperature by an energetic cluster deposition. Though cluster-assemblies are usually sooty and porous, the present Fe cluster-assembled films are lustrous and dense, revealing a soft magnetic behavior. Size-monodispersed Fe clusters with the mean cluster size d=9nm were synthesized using a plasma-gas-condensation technique. Ionized clusters are accelerated electrically and deposited onto the substrate together with neutral clusters from the same cluster source. Packing fraction and saturation magnetic flux density increase rapidly and magnetic coercivity decreases remarkably with increasing acceleration voltage. The Fe cluster-assembled film obtained at the acceleration voltage of −20kV has a packing fraction of 0.86±0.03, saturation magnetic flux density of 1.78±0.05Wb∕m2, and coercivity value smaller than 80A∕m. The resistivity at room temperature is ten times larger than that of bulk Fe metal.
Formation of columnar (In,Ga)As quantum dots on GaAs(100)
Authors: He J. , Nötzel R. , Offermans P. , Koenraad P. M. , Gong Q. , Hamhuis G. J. , Eijkemans T. J. , Wolter J. H.
Published: October 2004

Columnar (In,Ga)As quantum dots (QDs) with homogeneous composition and shape in the growth direction are realized by molecular-beam epitaxy on GaAs(100) substrates. The columnar (In,Ga)As QDs are formed on InAs seed QDs by alternating deposition of thin GaAs intermediate layers and monolayers of InAs with extended growth interruptions after each layer. The height of the columnar (In,Ga)As QDs is controlled by varying the number of stacked GaAs∕InAs layers. The structural and optical properties are studied by cross-sectional scanning tunneling microscopy, atomic force microscopy, and photoluminescence spectroscopy. With increase of the aspect ratio of the columnar QDs, the emission wavelength is redshifted and the linewidth is reduced.
Temporal and noise characteristics of continuous-wave-pumped continuum generation in holey fibers around 1300nm
Authors: de Matos C. J. S. , Popov S. V. , Taylor J. R.
Published: October 2004

The noise of continuous-wave-pumped broadband continua generated in a holey fiber is characterized in two different all-fiber configurations. An amplified spontaneous emission seeded ytterbium-doped fiber source and fiber Bragg grating based Yb laser were employed to initiate Raman-soliton continuum generation in 100m of anomalously dispersive holey fiber with spectral width of 300nm and spectral power density over 10mW/nm. Low noise operation makes these sources suitable for optical coherence tomography applications.
Formal description of diffraction in optical systems: Calculations and experimental evidence
Authors: Ferré-Borrull Josep , Bosch Salvador
Published: October 2004

We present a rigorous mathematical formulation of the diffraction process in optical systems, provided the aperture stop is much smaller than the remaining components. This mathematical scheme allows us to develop methods for the exact numerical calculation of the complex amplitude for any optical system consisting of lenses and an aperture stop placed at any space (either input, output, or intermediate). The procedure eliminates the need of using the exit pupil for calculations and evidences the practical inaccuracies that may arise due to the use of the exit pupil. We present several results for a meniscus lens working with an aperture stop placed before the lens, so that the comparison between the standard calculation procedures, our methods, and the experiment is clearly illustrated.
Structure adjustment during high-deposition-rate growth of microcrystalline silicon solar cells
Authors: Mai Y. , Klein S. , Geng X. , Finger F.
Published: October 2004

Preparation of microcrystalline silicon for solar cell applications is investigated under high-pressure, high-power conditions with plasma-enhanced chemical vapor deposition at 95MHz. It is found that the deposition rate depends mainly on the amount of silane in the reaction zone. Changes in the discharge power affect the deposition rate very little. This points to silane depletion under these process conditions. The amount of H radicals, on the other hand, increases with increasing discharge power and leads to structure changes of the material. Making use of this effect, optimum phase mixture material at the transition from highly crystalline to amorphous growth can be deposited at considerably higher deposition rates without loss in solar cell performance.
Quantum-confined Stark effect and built-in dipole moment in self-assembled InAs∕GaAs quantum dots
Authors: Jin Peng , Li C. M. , Zhang Z. Y. , Liu F. Q. , Chen Y. H. , Ye X. L. , Xu B. , Wang Z. G.
Published: October 2004

Quantum-confined Stark effect and built-in dipole moment in self-assembled InAs∕GaAs quantum dots (QDs), which are grown at relative low temperature (460°C) and embedded in GaAs p–i–n structure, have been studied by dc-biased electroreflectance. Franz–Keldysh oscillations from the undoped GaAs layer are used to determine the electric field under various bias voltages. Stark shift of −34meV for the ground-state interband transition of the QDs is observed when the electric field increases from 105 to 308kV∕cm. The separation of the electron and hole states in the growth direction of 0.4nm, corresponding to the built-in dipole moment of 6.4×10−29Cm, is determined. It is found that the electron state lies above that of the hole, which is the same as that predicted by theoretical calculations for ideal pyramidal InAs QDs.
Highly-efficient broadband waveguide outcoupling in light-emitting diodes with self-organized polymer blends
Authors: Corcoran N. , Ho P. K. H. , Arias A. C. , Mackenzie J. D. , Friend R. H. , Fichet G. , Huck W. T. S.
Published: October 2004

Self-organized, two-dimensional micron-scale photonic structures have been fabricated within the emissive layer of polymer blend light-emitting diodes (LEDs). The relief-and-phase grating is achieved by phase separation of two semiconducting polymers directed by a surface chemical pattern. Short-wavelength oscillations are found pinned (and are thus phase-locked) to the domain boundaries. These high-frequency harmonics mimic short-period gratings in providing efficient waveguide outcoupling but without spectral dispersion. This provides a general way to harness the waveguide modes trapped in polymer LEDs, doubling their external quantum and power efficiencies while maintaining spectral integrity with viewing angle.