bluuebunny/crossref_metadata_2025 huggingface dataset:
Solar wind density and velocity control of auroral brightness under normal interplanetary magnetic field conditions
Authors: Shue J.‐H. , Newell P. T. , Liou K. , Meng C.‐I.
Published: December 2002

In this study we determine relationships between auroral brightness and each of the solar wind density and velocity under normal interplanetary magnetic field (IMF) conditions using Polar Lyman‐Birge‐Hopfield long band (∼170.0 nm) images and Interplanetary Monitoring Platform 8 solar wind data. Since IMF and season are parameters that can affect the auroral brightness, the determination of the relationships is performed on the basis of the IMF Bz polarity and season to reduce some contamination from these two parameters. It is found that for southward IMF and the winter case the solar wind density and velocity increase the auroral brightness mainly on the nightside. For southward IMF and the summer case the density and velocity also increase the auroral brightness mainly on the nightside, but the increase is not as large as that for southward IMF and the winter case.
Causes, characteristics and consequences of convective diapirism on Europa
Authors: Nimmo Francis , Manga Michael
Published: December 2002

We investigate the hypothesis that the ∼10 km diameter dome‐shaped features seen on Europa's surface are caused by strongly temperature‐dependent convection, in which upwellings form isolated diapirs or thermals. We use the observed lower limit on dome diameter of 4 km to deduce that the conductive (stagnant) lid thickness must be ≤5 km. Such a lid thickness implies a minimum surface heat flux of 90 mWm−2, compatible with recent estimates of tidal heating. We also use the mean observed dome diameter to infer a lower thermal boundary layer thickness of ∼1 km. We find that the ice is probably deforming in the diffusion creep regime with a grain size in the range 0.02–0.06 mm. The fraction of internal heating is >0.5, the ice viscosity 1012–1013 Pa s, and the crustal solidification rate<5km/Ma.
Remote sensing of cirrus cloud properties in the presence of lower clouds: An ATSR‐2 case study during the Interhemispheric Differences in Cirrus Properties From Anthropogenic Emissions (INCA) experiment
Authors: González Albano , Wendling Peter , Mayer Bernhard , Gayet Jean‐Francois , Rother Tom
Published: December 2002

The retrieval of cirrus cloud microphysical properties in a multilayer cloud system is a challenge due to the usually low optical thickness of the ice cloud under investigation. However, it is estimated that about 50% of all cirrus clouds occur in such multilayer systems. Here, we present a method that uses a combination of five observations by the dual‐view ATSR‐2 radiometer onboard the ERS‐2 satellite. Using the channels at 0.87 and 1.6 μm in both nadir and forward views and the nadir view of the 3.7 μm band, the retrieval can clearly separate a thin high cloud from a highly reflective low water cloud and thus determine the optical thickness and effective particle size of the cirrus quantitatively. This is confirmed by a comparison of the retrieved parameters with in situ aircraft observations made on 23 March 2000 near Punta Arenas, Chile, where good agreement was observed. An important finding of this study was that the pixel‐to‐pixel variability of the low cloud cannot be neglected. In other words, the optical thickness of the low cloud needs to be included as a retrieval parameter, because the assumption of constant optical properties leads to large degree of uncertainties in the derived ice cloud parameters.
Effects of turbulence on growth and metabolism of periphyton in a laboratory flume
Authors: Hondzo Miki , Wang Hong
Published: December 2002

Laboratory experiments were conducted to investigate the effect of fluid motion on the growth and metabolism of the freshwater periphyton Spirogyra and Stigeocloniom. The only growth‐limiting factor was the effect of fluid motion; all the other environmental conditions, such as light, temperature, and nutrients were not limiting growth. The growth rates of periphyton were measured in terms of the chlorophyll‐a concentration, and the metabolism was characterized by dissolved oxygen concentration measurements. The periphyton growth and corresponding photosynthetic rates were the lowest in a stagnant fluid. In a moving fluid the periphyton growth was mediated by the fluid flow conditions at the channel bottom. The results indicate critical conditions, corresponding to the detachment of periphyton in the channel bed. A functional dependence between the periphyton detachment and fluid flow conditions is proposed.
Regulation of In Situ Skeletal Muscle Arteriolar Tone: Interactions Between Two Parameters
Authors: FRISBEE JEFFERSON C.
Published: December 2002

Objective: The growing understanding of the complexity of mechanisms regulating arteriolar tone demands that a systematic determination of how these processes interact to alter diameter be undertaken. This study examined how five mediators of skeletal muscle distal arteriolar tone [adenosine concentration, oxygen content, α‐adrenergic activation (norepinephrine), intravascular pressure and wall shear rate], taken two parameters at a time, interact to regulate vessel diameter.

Methods: The reactivity of distal arterioles of in situ rat cremaster muscle after alterations in each of the above mediators was assessed. In addition, arteriolar responses to all two‐parameter combinations were evaluated to determine the effect of altered environment on vascular reactivity to stimuli.

Results: Arteriolar dilation to adenosine was unaltered by changes in other parameters. In contrast, wall shear rate‐induced arteriolar dilation was impaired by 60–88% after increases in the other parameters. Myogenic reactivity was reduced by 28% with elevated O2 and by 65% with norepinephrine (because of vessel closure) and was impaired by 89% with elevated adenosine. O2‐induced arteriolar reactivity was impaired by 56% with increased adenosine and by 44% with increased norepinephrine concentration but was largely unaffected by elevated intravascular pressure. Adrenergic reactivity was attenuated with elevated intravascular pressure (by 69%) and O2 (by 54%) because of vessel closure but was unaltered with elevated adenosine.

Conclusions: These data suggest that (1) individual mediators contributing to the regulation of arteriolar tone exist within a hierarchy of importance and (2) mechanisms regulating arteriolar tone can be impacted by unidentified alterations in other processes. Ongoing investigation into interactions between multiple processes regulating arteriolar tone will allow for a more integrated understanding of how microvessels regulate their diameter.
Integrated organic light-emitting device/fluorescence-based chemical sensors
Authors: Savvate’ev V. , Chen-Esterlit Z. , Aylott J. W. , Choudhury B. , Kim C.-H. , Zou L. , Friedl J. H. , Shinar R. , Shinar J. , Kopelman R.
Published: December 2002

A fluorescent chemical sensor platform, integrating an organic light-emitting device (OLED) light-source with a fluorescent probe, is demonstrated for a subsecond-fast oxygen sensor. The integration results in strong light coupling and negligible heating of the sensor film or analyte. The potential in vivo operation of compact, stand-alone, battery-powered, OLED-based miniaturized sensor arrays for chemical and biological applications is discussed.
Tunable ferromagnetic resonance peak in tunneling magnetoresistive sensor structures
Authors: Nazarov Alexey V. , Cho Hae Seok , Nowak Janusz , Stokes Scott , Tabat Ned
Published: December 2002

Noise properties of submicron scale tunneling magnetoresistive (TMR) sensors were investigated at frequencies up to 3 GHz. Noise spectral density was measured as a function of frequency, applied field, and bias current. Noise spectral density versus frequency dependence exhibits a pronounced peak, tunable over a wide frequency range. This peak appears to originate from current-driven precession of magnetization. The peak center frequency can be as low as 200 MHz and has a strong dependence on applied field and bias current. The damping constant α of the main precession mode in the TMR sensor free layer was found to be in the range of 0.05–0.18. It is shown that the magnetic state of a magnetoresistive sensor depends on the bias current and may be characterized by noise properties. The magnetoresistive element can operate as a source of high-frequency radiation with 1 nW emitting power from a 0.1 μm2 junction and signal to noise ratio of 10 dB.
Creation of a gradient polymer-fullerene interface in photovoltaic devices by thermally controlled interdiffusion
Authors: Drees M. , Premaratne K. , Graupner W. , Heflin J. R. , Davis R. M. , Marciu D. , Miller M.
Published: December 2002

Efficient polymer-fullerene photovoltaic devices require close proximity of the two materials to ensure photoexcited electron transfer from the semiconducting polymer to the fullerene acceptor. We describe studies in which a bilayer system consisting of spin-cast 2-methoxy-5-(2′-ethylhexyloxy)-1,4-phenylenevinylene copolymer (MEH-PPV) and sublimed C60 is heated above the MEH-PPV glass transition temperature in an inert environment, inducing an interdiffusion of the polymer and the fullerene layers. With this process, a controlled, bulk, gradient heterojunction is created bringing the fullerene molecules within the exciton diffusion radius of the MEH-PPV throughout the film to achieve highly efficient charge separation. The interdiffused devices show a dramatic decrease in photoluminescence and concomitant increase in short circuit currents, demonstrating the improved interface.
I-Line lithography of poly-(3,4-ethylenedioxythiophene) electrodes and application in all-polymer integrated circuits
Authors: Touwslager F. J. , Willard N. P. , de Leeuw D. M.
Published: December 2002

Industrialization of polymer electronics requires the use of safe solvents. To that end an I-line lithography process for conducting thin poly(3,4-ethylenedioxythiophene) films has been developed. The fully waterborne process is based on photocrosslinking using bisazide- and polyazide-type photoinitiators. The minimum feature size realized comprises 2.5 μm wide lines separated by 1 μm spacings. The sheet resistance is 1 kΩ/square. The process has been applied to fabricate all-polymer integrated circuits. The technology is demonstrated with functional 15-bit code generators.
Deep-ultraviolet emission of AlGaN/AlN quantum wells on bulk AlN
Authors: Gaska R. , Chen C. , Yang J. , Kuokstis E. , Khan A. , Tamulaitis G. , Yilmaz I. , Shur M. S. , Rojo J. C. , Schowalter L. J.
Published: December 2002

An approach for growing high-quality AlGaN/AlN multiple quantum wells (MQW) emitting in deep UV region is proposed. The structures are deposited on bulk AlN substrates. Structural analysis by using x-ray diffraction confirms high crystalline quality of these structures. Photoluminescence dependences on excitation intensity and temperature under band-to-band excitation of AlN barrier layers and under selective excitation of the quantum wells are presented. Al0.5Ga0.5N/AlN MQW grown on bulk AlN demonstrate emission at 260 nm with high emission intensity. Stimulated emission of these structures at 258 nm was observed. The results prove great potential of growing structures with high-aluminum-content layers on bulk AlN substrates.
GaN metal–semiconductor–metal ultraviolet photodetector with IrO2 Schottky contact
Authors: Kim Jong Kyu , Jang Ho Won , Jeon Chang Min , Lee Jong-Lam
Published: December 2002

Iridium oxide (IrO2) was used as the Schottky barrier materials of GaN metal–semiconductor–metal (MSM) ultraviolet photodetector. Annealing an Ir contact at 500 °C under O2 ambient, the reverse leakage current density at −5 V reduced by the four orders of magnitude, to ∼10−6 A/cm2. Simultaneously, Schottky barrier height and optical transmittance increased to 1.48 eV and 74.8% at 360 nm, respectively. The dramatic improvement originated from the formation of IrO2 by the annealing, resulting in the increase in the responsivity of the GaN MSM photodetector by one order of magnitude, in comparison with the photodetector with Pt Schottky contact.
Si-based omnidirectional reflector and transmission filter optimized at a wavelength of 1.55 μm
Authors: Lee Hyun-Yong , Makino Hisao , Yao Takafumi , Tanaka Akinori
Published: December 2002

Omnidirectional (omni-) reflector and transmission filter optimized at a wavelength of 1.55 μm have been realized using Si/SiO2 one-dimensional photonic crystals (1D PCs). Photonic band structures in the PCs with and without a defect layer have been also analyzed. The 1D PCs fabricated have very large omnidirectional photonic band gaps (omni-PBGs), and their measured reflectance spectra are in very good agreement with the calculated results. The omni-PBG in a six-pair Si/SiO2 1D PC (no defect layer, a filling factor η=0.406) exists in a normalized frequency range of 0.223–0.297. Introducing a defect layer generates a defect state in the PBG, and it behaves like electronic impurity levels in the gap with a change in thickness of the defect layer (dD). A six-pair Si/SiO2 1D PC with the structure parameters of η=4.060, dH (Si thickness)=95.3 nm, dL (SiO2 thickness)=234.9 nm, and dD=2.336⋅dH could act as a 1.55 μm-transmission filter for normal incidence light.
Fabrication technique for filling-factor tunable titanium dioxide colloidal crystal replicas
Authors: Nishimura Suzushi , Shishido Atsushi , Abrams Neal , Mallouk Thomas E.
Published: December 2002

Filling-factor tunable titanium dioxide replicas of colloidal crystals were fabricated by using a liquid phase deposition (LPD) technique. Ammonium hexafluorotitanate [(NH4)2TiF6] was used as a precursor, which was converted slowly to titanium dioxide by hydrolysis with boric acid. After the oxide was formed in voids of latex colloidal crystals, the latex was removed by calcination. By applying the LPD process to the replica again, the filling factor of the replica could be increased in a controllable fashion. With 203 nm template spheres, the peak shift in the ∼490 nm stop band depended linearly on the deposition time for the first 20 min, at a rate of 4.4 nm/min. Thus the position of the Bragg reflection peak could be adjusted precisely by controlling the filling factor of the replica structure.
Resonant detection of subterahertz and terahertz radiation by plasma waves in submicron field-effect transistors
Authors: Knap W. , Deng Y. , Rumyantsev S. , Shur M. S.
Published: December 2002

We report on the experiments on resonant photoresponse of the gated two-dimensional electron gas to the terahertz radiation. The visible-light-induced, metastable increase of the carrier density in the transistor channel shifts the resonance position to the higher gate voltages, in agreement with plasma wave detection theory. In this way, an unambiguous proof of the origin of the observed resonant detection is provided. The visible light illumination also leads to an increase of the electron mobility and, as a result, to an increase of the resonant detection quality factor. Resonant detection of the harmonics of the Gunn diode-based emission system is demonstrated up to 1.2 THz.
Damp-heat induced sulfate formation in Cu(In,Ga)(S,Se)2-based thin film solar cells
Authors: Heske C. , Groh U. , Weinhardt L. , Fuchs O. , Holder B. , Umbach E. , Bostedt C. , Terminello L. J. , Zweigart S. , Niesen T. P. , Karg F.
Published: December 2002

To investigate the impact of damp heat treatments on the electronic and chemical structure of Cu(In,Ga)(S,Se)2-based thin film solar cells, we have performed a detailed soft x-ray emission study of the ZnO/CuIn(S,Se)2 and ZnO/CdS/CuIn(S,Se)2 interfaces. By comparing the sulfur L2,3 emission spectra of pristine and damp-heat treated samples, we find a sulfate formation at the ZnO/CuIn(S,Se)2 and the ZnO/CdS interface. The intensity behavior as a function of ZnO film thickness further reveals a diffusion of sulfur atoms into the ZnO film, leading to the formation of zinc sulfate in the ZnO window layer of damp-heat-treated Cu(In,Ga)(S,Se)2-based solar cells.
Single-electron tunneling to insulator surfaces detected by electrostatic force
Authors: Klein L. J. , Williams C. C.
Published: December 2002

The detection of single-electron tunneling events between a metallic scanning probe tip and an insulating surface is demonstrated by an electrostatic force method. When a voltage-biased oscillating atomic force microscopy tip is placed within tunneling range of the surface of an insulator, single-electron tunneling events are observed between the tip and electronic states at the surface. The events cause an abrupt reduction in cantilever oscillation amplitude, due to the instantaneous reduction of the force gradient at the tip. In most cases, only a single electron tunnels to or from the surface. Experimental data show that no physical contact is made during the tunneling events.
Photodetection in the visible, ultraviolet, and near-infrared with silicon microdischarge devices
Authors: Park S.-J. , Eden J. G. , Ewing J. J.
Published: December 2002

The photosensitivity of 50 and 100 μm square microdischarge devices having an inverted pyramidal Si cathode has been demonstrated and characterized in the ultraviolet, visible, and near-infrared (350–1200 nm). When operating with 500 Torr of Ne, (100 μm)2 microdischarge devices exhibit responsivities of 700±150 and 570±120 A W−1 at 850 and 660 nm, respectively, or more than an order of magnitude larger than peak values typical of commercially available Si avalanche photodiodes. Maximum sensitivity occurs in the 800–900 nm region for the larger (100 μm square) devices but is blueshifted to 600–650 nm for (50 μm)2 detectors. The peak response for the 50 μm square device is 950±250 A W−1 (at ∼625 nm), an increase of ∼35% over that for the (100 μm)2 detector. The experimental results indicate that the semiconductor photocathode determines the spectral response of the device whereas the plasma serves as an electron multiplier. The sensitivity and dynamic range of this new hybrid semiconductor/plasma photodetector suggest that arrays of microdischarge photodetectors are potentially valuable for spectroscopic and biochemical applications.
Light-induced absorption changes in In-doped congruent LiNbO3
Authors: Sunarno Steven , Tomita Yasuo , Zhang Guoquan
Published: December 2002

We investigate visible and near-infrared light-induced absorption changes caused by intrinsic defect centers in congruently melting and reduced LiNbO3:In with a single-shot picosecond pulse at 532 nm. It is found that the dark decay dynamics of optically induced shallow centers strongly depend on In concentrations. Two types of optically induced shallow centers having dark decay time constants on the orders of milliseconds and tens of microseconds are observed in LiNbO3 doped with In below the damage-resistant threshold concentrations. Only one of the two types is observed in LiNbO3 doped with In above it. The origin of these shallow centers is also discussed.
Fe/ZnSe(001) Schottky-barrier height evaluated by photoemission
Authors: Eddrief M. , Marangolo M. , Corlevi S. , Guichar G.-M. , Etgens V. H. , Mattana R. , Mosca D. H. , Sirotti F.
Published: December 2002

We present the Schottky-barrier height determination for the Fe/ZnSe(001) system performed by core and valence level photoelectron emission spectroscopy. Above the thickness of 2 ML, the Fe–Fermi level position is stabilized at 1.6 eV above the valence-band maximum of the n-type undoped ZnSe. This corresponds to a Schottky-barrier height value of 1.1 eV. A bulk-like d-band electronic structure could be observed for thickness as thin as 2 ML of Fe.
Visible spectrum (654 nm) room temperature continuous wave InP quantum dot coupled to InGaP quantum well InP–InGaP–In(AlGa)P–InAlP heterostructure laser
Authors: Walter G. , Holonyak N. , Heller R. D. , Dupuis R. D.
Published: December 2002

Data are presented demonstrating the cw 300 K visible spectrum (654 nm) laser operation of a single 7.5 monolayer InP quantum dot (QD) layer coupled by a 20 Å In0.5Al0.3Ga0.2P barrier to an auxiliary 70 Å In0.5Ga0.5P quantum well (QW) that, via resonant tunneling, assists carrier collection, thermalization, and lateral rearrangement in the QDs. The simple stripe-geometry (530 μm×10 μm) InP QD+InGaP QW heterostructure laser, enhanced by the QW and operating on an upper QD state (42% quantum efficiency), is capable of over 10 mW/facet cw 300 K operation in spite of the weak heat sinking of probe operation.
Synthesis and magnetic behavior of an array of nickel-filled carbon nanotubes
Authors: Bao Jianchun , Zhou Quanfa , Hong Jianming , Xu Zheng
Published: December 2002

Highly-ordered arrays of Ni-filled carbon nanotubes have been fabricated by a second-order template method. First, an array of aligned carbon nanotubes was generated in a porous alumina membrane by catalytic pyrolysis of acetylene. The desired material, such as nickel, was then filled into the aligned carbon nanotubes by electrodeposition. The remarkable features of this method are: (i) high yield of metal-filled carbon nanotubes, and (ii) the wall thickness of the carbon nanotubes, and the length, diameter, and structure of the metal nanowires in the carbon nanotubes are controllable via changing experimental conditions. This method should be applicable for preparation of other metal- and alloy-filled carbon nanotubes, and allow the reliable technological application in nanoelectronic devices, high-density magnetic memories, electrochemical energy storages and sensors, etc.
Superconductivity depression in ultrathin YBa2Cu3O7−δ layers in La0.7Ca0.3MnO3/YBa2Cu3O7−δ superlattices
Authors: Sefrioui Z. , Varela M. , Peña V. , Arias D. , León C. , Santamarı́a J. , Villegas J. E. , Martı́nez J. L. , Saldarriaga W. , Prieto P.
Published: December 2002

We report on the depression of the superconducting critical temperature of ultrathin YBa2Cu3O7 (YBCO) layers, when their thickness is reduced in the presence of La0.7Ca0.3MnO3 (LCMO) magnetic layers in [LCMO (15 unit cells)/YBCO (N unit cells)] superlattices. The thickness of the manganite layer is kept at 15 unit cells and the YBCO thickness is varied between N=12 and N=1 unit cells. The structural analysis, using x-ray diffraction and electron microscopy, shows sharp interfaces with little structural disorder. While a critical temperature, TC=85 K, is found for 12 YBCO unit cells, superconductivity is completely suppressed for YBCO layer thickness below 3 unit cells. The possible interaction between superconductivity and magnetism is investigated.
Thermal activation and reversal time in antiferromagnetically coupled media
Authors: Margulies D. T. , Moser A. , Schabes M. E. , Fullerton Eric. E.
Published: December 2002

The thermally-activated magnetization reversal process of the lower layer in antiferromagnetically coupled media is investigated. The temperature dependence of the hysteresis loops is used to determine the magnetic parameters of the lower layer and to predict its reversal time. We discuss this reversal time both with and without transitions recorded in the media, and present an experimental technique that demonstrates thermally activated writing of the lower layer.
Formation of oriented nanocrystals in an amorphous alloy by focused-ion-beam irradiation
Authors: Tarumi R. , Takashima K. , Higo Y.
Published: December 2002

Structural changes of a Ni–P amorphous alloy under focused-ion-beam (FIB) irradiation have been examined using transmission electron microscopy. On the irradiated plane, the formation of crystallographically orientated nanosized crystals (NCs), with the particle size of approximately 10 nm, was observed. A series of electron diffraction analyses have revealed that NCs have a face-centered-cubic (fcc) structure and the following orientation relationships between the NCs and the FIB direction were found. These are, irradiated plane//(111)fcc and FIB direction//〈110〉fcc.
Humidity sensors based on pentacene thin-film transistors
Authors: Zhu Zheng-Tao , Mason Jeffrey T. , Dieckmann Rüdiger , Malliaras George G.
Published: December 2002

When a pentacene thin-film transistor is exposed to humidity, its saturation current decreases. This decrease was found to be reversible and can therefore be used to measure the amount of relative humidity in atmosphere. The sensitivity was found to depend on the thickness of the pentacene layer. The microscopic origin of the sensing mechanism is discussed.
Single-electron transistors and memory cells with Au colloidal islands
Authors: Wu C. S. , Chen C. D. , Shih S. M. , Su W. F.
Published: December 2002

In this study, single-electron transistors and memory cells with Au colloidal islands linked by C60 derivatives have been fabricated by hybridization of top–down advanced electron-beam lithography and bottom–up nanophased-material synthesis techniques. Low-temperature transport measurements exhibit clear Coulomb-blockade-type current–voltage characteristics and hysteretic-type gate-modulated current. The hysteresis is attributed to the presence of electrically isolated charge–storage islands. With the guidance provided by Monte Carlo simulation, we propose a circuit model and give an estimate of the sample parameters.
Pseudo-digital quantum bits
Authors: Friesen Mark , Joynt Robert , Eriksson M. A.
Published: December 2002

Quantum computers are analog devices; thus they are highly susceptible to accumulative errors arising from classical control electronics. Fast operation—as necessitated by decoherence—makes gating errors very likely. In most current designs for scalable quantum computers, it is not possible to satisfy both the requirements of low decoherence errors and low gating errors. Here, we introduce a hardware-based technique for pseudo-digital gate operation. We perform self-consistent simulations of semiconductor quantum dots, finding that pseudo-digital techniques reduce operational error rates by more than two orders of magnitude, thus facilitating fast operation.
Atomic structure of steps and defects on the clean diamond (100)-2×1 surface studied using ultrahigh vacuum scanning tunneling microscopy
Authors: Stallcup R. E. , Perez J. M.
Published: December 2002

We report ultrahigh vacuum scanning tunneling microscopy studies of the clean nonhydrogen-terminated diamond (100)-2×1 surface showing single- and double-layer steps that are rebonded. The main defects observed are single, multiple, and row dimer vacancies, and antiphase boundaries. Buckling of dimers is not observed, consistent with symmetric dimers.
Role of SrRuO3 buffer layers on the superconducting properties of YBa2Cu3O7 films grown on polycrystalline metal alloy using a biaxially oriented MgO template
Authors: Jia Q. X. , Foltyn S. R. , Arendt P. N. , Groves J. R. , Holesinger T. G. , Hawley M. E. , Lu P.
Published: December 2002

A SrRuO3 (SRO) buffer layer has been developed for growth of superconducting YBa2Cu3O7 (YBCO) thick films on polycrystalline metal substrates where a biaxially oriented MgO layer—produced by ion-beam-assisted deposition (IBAD)—was used as a template. By using such an architecture, we have routinely deposited YBCO films with an in-plane mosaic spread in the range of 3°–6° in full width at half maximum. A critical current density of 3.0×106 A/cm2 in self-field at 75 K for a film thickness of over 1.3 μm has been achieved. We believe that the SRO buffer layer plays a significant role in the much improved performance of YBCO conductors built on IBAD MgO. The features of SRO, such as good lattice match with both MgO and YBCO, excellent thermal stability in an oxidizing environment, and planarization of growing surface, make it the ideal choice as the buffer layer for high-performance superconductor coatings.
Electrical properties of SrBi2Ta2O9 ferroelectric thin films at low temperature
Authors: Yang Pingxiong , Carroll David L. , Ballato John , Schwartz Robert W.
Published: December 2002

The temperature dependence of electrical properties for SrBi2Ta2O9 thin film capacitors with platinum electrodes (Pt/SBT/Pt) on silicon wafers was studied from 10 to 300 K. With a decrease in temperature from 300 to 200 K, the remanent polarization of the thin films shows about an 11% reduction from its 300 K value; however, it is reduced by about 87% reduction from its 200 K value when the temperature drops from 200 to 100 K. With a decrease to 200 K, the polarization fatigue was significant, and the capacitor shows an approximate 29% reduction in polarization from its initial value following 1010 cycles. The dielectric response and leakage current of the thin films were also studied over the same lower temperature region. These results are helpful in the understanding of the fatigue-free behavior observed in SrBi2Ta2O9 thin films at room temperature and provide additional insight into their use for ferroelectric memory applications.
Cooling-rate-dependent dielectric properties of (Pb(Mg1/3Nb2/3)O3)0.67(PbTiO3)0.33 single crystals in ferroelectric phase
Authors: Yan Feng , Bao Peng , Wang Yening , Chan Helen L. W. , Choy Chung Loong
Published: December 2002

The dielectric properties of (Pb(Mg1/3Nb2/3)O3)0.67(PbTiO3)0.33 single crystals in the temperature range from room temperature to 250 °C have been studied. A very sharp change of dielectric permittivity due to the spontaneous relaxor–ferroelectric phase transition was observed. The most interesting result is that the dielectric permittivity in ferroelectric phase is strongly dependent on the cooling rate across the relaxor–ferroelectric phase transition. We assume that the cooling rate can influence the grain size of ferroelectric subdomains in ferroelectric phase and can therefore influence the dielectric properties.
Gratingless enhanced microwave transmission through a subwavelength aperture in a thick metal plate
Authors: Hibbins Alastair P. , Sambles J. Roy , Lawrence Chris. R.
Published: December 2002

Remarkably enhanced transmission of microwave radiation through a single subwavelength slit in a thick metallic substrate surrounded by just a pair of parallel deep and narrow grooves is recorded. By also patterning the output face of the metal slab with two grooves there is strong exit beam confinement. There are no gratings in this structure and, hence, the transmission mechanism is not related to the conventional grating coupling of surface plasmons on the upper and lower surfaces of the substrate. Instead, the slit and the four grooves are all resonant, which is the essence of the functioning of the arrangement. The enhancement is due to the collective excitation of the Fabry–Pérot mode in the slit and the cavity modes in the grooves. A finite-element modeling code is used to optimize the response of the structure, and to investigate the electromagnetic fields in the vicinity of the substrate.
Red, green, and blue upconversion luminescence of trivalent-rare-earth ion-doped Y2O3 nanocrystals
Authors: Matsuura Daisuke
Published: December 2002

Trivalent-rare-earth ion-doped Y2O3 nanocrystals have been synthesized, and their photoluminescence properties have been studied under 980 nm laser diode excitation. The crystallite size estimated by x-ray diffractometry and scanning electron microscopy was about 30–40 nm. In Yb3+ and Tm3+ codoped Y2O3 nanocrystals, the bright blue emissions near 450 and 480 nm have been noticeable due to the 1D2–3F4 and 1G4–3H6 transitions of Tm3+, respectively. The bright green emissions of Er3+ doped Y2O3 nanocrystals appeared near 530 and 550 nm were assigned to the 2H11/2–4I15/2 and 4S3/2–4I15/2 transitions of Er3+, respectively. The ratio of the intensity of green luminescence to that of red luminescence has decreased with an increase of concentration of Yb3+ in Er3+ doped Y2O3 nanocrystals. In sufficient quantities of Yb3+ to Er3+, the bright red emission near 660 nm has been predominant due to the 4F9/2–4I15/2 transition of Er3+. The primary color components are in these red, green, and blue emissions, from which a wide spectrum of colors, including white, would be produced by appropriate mixing them.
Single-crystalline Si on insulator in confined structures fabricated by two-step metal-induced crystallization of amorphous Si
Authors: Liu Yaocheng , Deal Michael D. , Saraswat Krishna C. , Plummer James D.
Published: December 2002

We present a technology and its mechanism to obtain single-crystalline Si pillars on SiO2 using a two-step Ni-induced crystallization process on amorphous Si pillars with confined sizes. The amorphous Si pillars with a Ni cap were first annealed at 400 °C for 15 h so that a single-crystalline NiSi2 template was formed on top of each pillar. In the second step, they were annealed at 550 °C for 2 h, during which single-crystalline Si pillars were formed by NiSi2-mediated solid-phase epitaxy. These single-crystalline Si pillars can be used for advanced vertical metal–oxide–semiconductor transistors and surround-gate structures, especially where low-temperature processing is required.
Observation of coreless edge and mixed dislocations in Mg-doped Al0.03Ga0.97N
Authors: Cherns D. , Wang Y. Q. , Liu R. , Ponce F. A.
Published: December 2002

Transmission electron microscopy has been used to examine the core structure of threading dislocations in heavily Mg-doped Al0.03Ga0.97N thin films. It is shown that edge and mixed, but not screw, dislocations have hollow cores with diameters typically 1–5 nm. A model is presented where hollow core formation is initiated by the segregation and subsequent precipitation of Mg at these dislocation cores. The implications for understanding the formation of hollow core dislocations in other GaN films are discussed.
Retardation of oxidation in Co nanocolumns: Scanning tunneling microscopy study
Authors: Singh J. P. , Yang G.-R. , Lu T.-M. , Wang G.-C.
Published: December 2002

The oxidation of Co nanocolumns grown by the glancing angle deposition technique was studied ex situ using scanning tunneling microscopy and spectroscopy. The normalized conductance (dI/dV)/(I/V) of a single nanocolumn shows a nonoxidized Co peak at about −0.7 eV corresponding to the 3d valence electrons which was absent in the conventional film. It is argued that a retardation of the oxidation occurred in the Co nanocolumn due to the lack of grain boundaries in the isolated nanocolumns.
Influence of carrier mobility and contact barrier height on the electrical characteristics of organic transistors
Authors: Bolognesi A. , Di Carlo A. , Lugli P.
Published: December 2002

We have investigated the electrical properties of organic thin-film transistors by way of two-dimensional drift-diffusion simulations. The dependence of the electrical characteristics on the mobility model and on the Schottky barrier height of the contacts is analyzed. We found that both the field dependence of the carrier mobility and the barrier height of the contacts are responsible for the nonlinearity of the output characteristics in the low bias region. We have then extracted the mobility from the simulated characteristics using standard metal–oxide–semiconductor analytic relations and compared to the mobility used in the simulation. The discrepancy found between the two mobilities is mainly induced by the presence of the contact barrier.
Delta-doped AlGaN/GaN metal–oxide–semiconductor heterostructure field-effect transistors with high breakdown voltages
Authors: Fan Z. Y. , Li J. , Lin J. Y. , Jiang H. X.
Published: December 2002

The fabrication and dc characteristics of AlGaN/GaN-based heterostructure field-effect transistors (HFETs) by employing the δ-doped barrier and the SiO2 insulated gate are reported. The device grown on sapphire substrate has a high drain-current-driving and gate-control capabilities as well as a very high gate-drain breakdown voltage of 200 V for a gate length of 1 μm and a source-drain distance of 3 μm. The incorporation of the SiO2 insulated gate and the δ-doped barrier into HFET structures reduces the gate leakage and improves the two-dimensional channel carrier mobility, and thereby allows one to take the inherent advantage of AlGaN/GaN HFETs with relatively high Al contents—the device structure is capable to deliver higher electron density (or drain current density) yet ensures an excellent pinch-off property as well as small gate leakage current. These characteristics indicate a great potential of this structure for high-power-microwave applications.
Laterally doped heterostructures for III–N lasing devices
Authors: Komirenko S. M. , Kim K. W. , Kochelap V. A. , Zavada J. M.
Published: December 2002

To achieve a high-density electron-hole plasma in group-III nitrides for efficient light emission, we propose a planar two-dimensional (2D) p-i-n structure that can be formed in the quantum well layers due to efficient activation of donors and acceptors in the laterally, selectively doped barriers. We show that strongly nonequilibrium 2D electron-hole plasma with density above 1012 cm−2 can be realized in the i region of the laterally biased p-i-n structure, enabling the formation of interband population inversion and stimulated emission from such a lateral current pumped emitter (LACE). We suggest that implementation of the lateral p-i-n structures provides an efficient way of utilizing potential-profile-enhanced doping of superlattices and quantum wells for electric pumping of nitride-based lasers.
Highly crystalline 5H-polytype of sp3-bonded boron nitride prepared by plasma-packets-assisted pulsed-laser deposition: An ultraviolet light emitter at 225 nm
Authors: Komatsu Shojiro , Kurashima Keiji , Kanda Hisao , Okada Katsuyuki , Mitomo Mamoru , Moriyoshi Yusuke , Shimuzu Yoshiki , Shiratani Masaharu , Nakano Toshiki , Samukawa Seiji
Published: December 2002

Highly crystalline 5H-polytypic form of sp3-bonded boron nitride (BN) was grown by pulsed-laser-vaporization of BN, where synchronous reactive-plasma packets assisted the crystal growth in the vapor phase. The structure of the product crystallites (∼5 μm) was confirmed by using transmission electron diffraction and electron energy loss spectroscopy. This material proved to have a sharp and dominant band at 225 nm by cathodoluminescence at room temperatures and corresponding monochromatic images revealed that they uniformly emitted the ultraviolet light. Considering that cubic BN has already been doped as p- and n-type semiconductors, this material may be applied to the light-emitting devices working at almost the deepest limit of the UV region that is functional without vacuum.
Hole transport in amorphous-crystalline-mixed and amorphous pentacene thin-film transistors
Authors: Choo M. H. , Kim Jae Hoon , Im Seongil
Published: December 2002

We report on the hole transport behavior in amorphous-crystalline-mixed and amorphous pentacene thin-film transistors. Five organic thin-film transistors (OTFTs) were fabricated by evaporating the pentacene films at rates of 1, 3, 5, and 7 Å/s at 25 °C (RT), and 7 Å/s at 60 °C. The field-effect mobility increased with the deposition rate even though the crystalline quality of the pentacene film degraded from an amorphous-crystalline-mixed phase to an amorphous phase. With our optimum deposition rate of 5 Å/s at RT, we obtained a saturation current (ID-SAT) of about 4 μA at a gate bias of −40 V, the field-effect mobility of 0.1 cm2/V s, and the on/off current ratio of 105. For the OTFT prepared with a deposition rate of 7 Å/s at 60 °C, an amorphous pentacene channel layer with a high mobility of ∼0.3 cm2/V s and the on/off current ratio of 104 were observed.
Backilluminated ultraviolet photodetector based on GaN/AlGaN multiple quantum wells
Authors: Zhang S. K. , Wang W. B. , Yun F. , He L. , Morkoç H. , Zhou X. , Tamargo M. , Alfano R. R.
Published: December 2002

The operation of backilluminated ultraviolet (UV) photodetector based on GaN/Al0.27Ga0.73N multiple quantum wells (MQWs) is reported. The MQW structure was deposited on a 1-μm-thick Al0.35Ga0.65N buffer layer which was epitaxied on a sapphire substrate. Coplanar Ohmic contacts were made on the top side of the MQW structure. By illuminating the Ohmic contact positions from the backside of the detector, a flat and narrow band spectral response is achieved in the UV wavelength range from 297 nm to 352 nm. The electron-heavy hole absorption in the MQW region produces the sharp long-wavelength cutoff at 352 nm and the band-to-band absorption of the Al0.35Ga0.65N buffer layer introduces the sharp short-wavelength cutoff at 297 nm. The polarization-induced electric fields result in a redshift of the long-wavelength cutoff. The response time is measured to be RC limited and determined to be 5 μs at a 50 Ω load.
Thickness dependence of exchange bias and structure in MnPt and MnNi spin valves
Authors: Toney Michael F. , Samant Mahesh G. , Lin Tsann , Mauri Daniele
Published: December 2002

We describe x-ray diffraction and magnetic measurements of annealed MnPt and NiMn spin valves as a function of MnPt (NiMn) film thickness. Thin films (≲5–10 nm) are not chemically ordered and hence not antiferromagnetic, which explains the lack of exchange coupling in these films. With increasing thickness, the L10 chemical order develops (through coexistence between fcc and L10 phases) and there is a strong correlation between chemical order and exchange coupling. The lack of chemical order in the thin films is likely due to a lack of nucleation sites for the L10 phase.
Electrical resistivity of polypyrrole nanotube measured by conductive scanning probe microscope: The role of contact force
Authors: Park J. G. , Lee S. H. , Kim B. , Park Y. W.
Published: December 2002

Polypyrrole (PPy) nanotubes were synthesized using the pores of track-etched polycarbonate membrane as a template. Its size depends on the pore diameter of template, range from 50 to 200 nm. Direct I–V measurements of PPy nanotube (diameter of 120 nm) deposited on Au were done using a metal-coated tapping-mode atomic-force-microscope tip. Linear I–V characteristics are observed, and the resistance is decreased as the contact force is increased. Using the Hertz model, the elastic modulus E and electrical resistivity ρ are estimated to be E∼1 GPa and ρ∼1 Ωcm. These values are consistent with those obtained in bulk PPy film.
Crossover of magnetotransport process toward spin-polarized tunneling in manganite thin films
Authors: Taniyama T. , Yamasaki M. , Yamazaki Y.
Published: December 2002

We report on the magnetoresistive features of well-characterized polycrystalline manganite thin films as a function of film thickness. A crossover of the magnetization process from domain wall displacement to magnetic rotation of each grain is observed around a thickness of 25 nm, accompanied with the maximum of the coercivity. The thickness dependence of the electrical resistivity clearly distinguishes the transport mechanism at 25 nm, below which the magnetoresistance can be well scaled by ∼(M/MS)2, using the magnetization M and the saturation magnetization MS. Spin-polarized tunneling transport between adjacent grains provides a comprehensive picture for the magnetotransport data.
Two-color hologram multiplexing from the colored state in stoichiometric LiNbO3:Tb,Fe
Authors: Lee Myeongkyu , Hatano Hideki , Tanaka Satoru , Yamaji Takashi , Kitamura Kenji , Takekawa Shunji
Published: December 2002

We have performed two-color hologram multiplexing in stoichiometric LiNbO3:Tb,Fe, which exhibits a photochromic effect. One hundred angle-multiplexed holograms of nearly equivalent strength have been recorded from the colored state by use of 850 nm recording beams and a 436 nm gating light. The stored holograms were highly resistant against erasure during continuous readout. It was estimated that 80 million readouts with a bit rate of 1 Gbit/s is possible before the diffracted signal intensity decays to half of its initial value.
Fabrication of nanometer-spaced electrodes using gold nanoparticles
Authors: Khondaker Saiful I. , Yao Zhen
Published: December 2002

A simple and highly reproducible technique is demonstrated for the fabrication of metallic electrodes with nanometer separation. Commercially available bare gold colloidal nanoparticles are first trapped between prefabricated large-separation electrodes to form a low-resistance bridge by an ac electric field. A large dc voltage is then applied to break the bridge via electromigration at room temperature, which consistently produces gaps in the sub-10 nm range. The technique is readily applied to prefabricated electrodes with separation up to 1 μm, which can be defined using optical lithography. The simple fabrication scheme will facilitate electronic transport studies of individual nanostructures made by chemical synthesis. As an example, measurement of a thiol-coated gold nanoparticle showing a clear Coulomb staircase is presented.
Transverse mode-locking in microcavity lasers
Authors: Gordon R. , Heberle A. P. , Cleaver J. R. A.
Published: December 2002

We experimentally demonstrate mode-locking between the transverse modes of a laser. A vertical-cavity surface-emitting laser with evenly-spaced transverse modes is shown to emit a train of 2.1±0.1 ps pulses with an 11 ps repetition rate and a timing jitter of 235±30 fs. Transverse mode-locking in microcavity lasers has potential to improve the compactness, stability, integrability, repetition rate tunability, and efficiency of ultrafast optical communication sources.
Significant enhancement of irreversibility field in clean-limit bulk MgB2
Authors: Braccini V. , Cooley L. D. , Patnaik S. , Larbalestier D. C. , Manfrinetti P. , Palenzona A. , Siri A. S.
Published: December 2002

Low resistivity MgB2 bulk samples annealed in Mg vapor show an increase in irreversibility field μ0H*(T) by a factor of ∼2 in both transport and magnetic measurements. The best sample displayed a magnetic irreversibility field μ0HM*>14 T at 4.2 K and ∼6 T at 20 K. These changes were accompanied by an increase of the 40 K resistivity from 1 to 18 μΩ cm and a lowering of the resistivity ratio from 15 to 3, while the critical temperature Tc decreased by only 1–2 K. These results show that systematic processing changes can make MgB2 attractive for magnet applications.
Magnetic properties of self-assembled interacting nanoparticles
Authors: Kechrakos D. , Trohidou K. N.
Published: December 2002

The temperature-dependent magnetization and the hysteresis properties (remanence and coercivity) of magnetic nanoparticle arrays are studied by Monte Carlo simulations. An oscillatory variation of the remanence with layer coverage and accompanying peaks in the coercive field are predicted at low temperatures, due to dipolar interparticle interactions. The blocking temperature of the arrays decreases with the inverse cube of the interparticle spacing (Tb∼d−3) and it remains almost unchanged with film thickness above one monolayer. Our results are compared with recent experiments on self-assembled Co nanoparticle arrays.
Measurements of α-factor in 2–2.5 μm type-I In(Al)GaAsSb/GaSb high power diode lasers
Authors: Shterengas L. , Belenky G. L. , Gourevitch A. , Kim J. G. , Martinelli R. U.
Published: December 2002

Spectra of the linewidth enhancement factor (α) of room-temperature-operated high-power 2–2.5 μm In(Al)GaAsSb/GaSb type-I quantum-well (QW) lasers were measured using Hakki–Paoli technique. Values of α at threshold were in the range 2.5 to 4 for all devices under study. Devices emitting 1 W cw power at λ=2.5 μm have 1.5%–1.6% compressively strained QW active region and the lowest α equal to 2.5. Measured average filament spacings in near field are in rough agreement with predictions given by experimental α-factor values.
Thermal spike analysis of interface mixing induced by swift heavy ions
Authors: Szenes G.
Published: December 2002

Interface mixing induced by energetic ions is discussed, applying the author’s thermal spike model. Diffusion in the ion-induced melt is assumed. An expression is derived for the variation of the mixing rate k with the electronic stopping power Se. The experimental results recently reported by the Stuttgart group on NiO, ZnO, CuO, and Cu2O layers on SiO2 substrate are analyzed and good agreement is found with the predictions of the model for k and for the threshold of Se for melt formation. Average diffusion coefficients in the spike are estimated, and Dd≈0.053, 0.03, and 0.004 cm2/s are obtained for Zn, Ni, and Cu ions, respectively.