bluuebunny/crossref_metadata_2025 huggingface dataset:
Luminescence polarization of ordered GaInP/InP islands
Authors: Håkanson U. , Zwiller V. , Johansson M. K.-J. , Sass T. , Samuelson L.
Published: January 2003

The luminescence polarization properties of GaInP islands have been investigated. The islands, which form during overgrowth of InP quantum dots, were studied using scanning tunneling luminescence (STL) and photoluminescence (PL). STL from these islands shows emission at an energy below the main emission peak of the bulk GaInP. The linear PL polarization anisotropy was measured at low temperature, for which the emission from the islands shows high polarization anisotropy. The intensity maximum for the emission occurs for light polarized parallel to the elongation of the islands. The observed linear PL polarization anisotropy indicates the presence of highly ordered domains of GaInP in the islands.
Determination of the in-plane anisotropy of the electron effective mass tensor in 6H–SiC
Authors: Iwata H. P.
Published: January 2003

An experimental evidence for the strong in-plane anisotropy of the electron effective mass tensor in 6H–SiC is reported. Furthermore, two components of the mass tensor in 6H–SiC, mM−Γ* and mM−K*, have been resolved by making a theoretical bridge between Hall effect measurements and cyclotron resonance experiments, based on the Boltzmann transport equation. The method to resolve the in-plane effective mass components is also applied for 4H–SiC, which have already been resolved by cyclotron resonance. The values determined by our method are fully consistent with available experiments and calculations.
Small angle x-ray scattering for measuring pore-size distributions in porous low-κ films
Authors: Omote K. , Ito Y. , Kawamura S.
Published: January 2003

A small-angle x-ray scattering technique has been applied for characterizing pore-size distribution in porous low-κ dielectric films. The data are collected in reflection geometry using offset θ/2θ scans for avoiding strong specular reflections from the film surface and its substrate. The effects of refraction and reflection at the film surface and interface are corrected by the distorted wave Born approximation. A Γ-distribution mode is used to determine the pore-size distribution in a film. The technique has been used to analyze porous methyl silsesquioxane films. The pore sizes were found to disperse in the range from subnanometer to several nanometers, and the results agree well with those obtained by the N2 gas adsorption technique.
Shallow donor state of hydrogen in indium nitride
Authors: Davis E. A. , Cox S. F. J. , Lichti R. L. , Van de Walle C. G.
Published: January 2003

The nature of the electron states associated with hydrogen in InN has been inferred by studying the behavior of positive muons, which mimic protons when implanted into semiconductors. The muons capture electrons below 60 K, forming paramagnetic centers with a binding energy of about 12 meV. Together with an exceedingly small muon-electron hyperfine constant indicative of a highly delocalized electron wave function, the results confirm the recently predicted shallow-donor properties of hydrogen in InN.
Single domain observation for synthetic antiferromagnetically coupled bits with low aspect ratios
Authors: Tezuka N. , Koike N. , Inomata K. , Sugimoto S.
Published: January 2003

Arrays of the synthetic antiferromagnetic (SyAF) patterned bits were successfully fabricated with micron to submicron sizes. Magnetic domain structure was investigated using magnetic force microscopy (MFM) for the SyAF bits as well as monolayer bits. MFM image of Co90Fe10(10 nm)/Ru(0.6 nm)/Co90Fe10(6 nm) SyAF bits demonstrates single domain structure for even a small aspect ratio of 1, while the 10 nm Co90Fe10 monolayer bits showed multi-domain structure for the aspect ratios below 2. This result indicates the predominance of the SyAF for ultrahigh bit density magnetic random access memory devices, because the bits with aspect ratio of 1 possessing single domain structure can provide size-independent switching field.
CdS and Cd(OH)2 formation during Cd treatments of Cu(In,Ga)(S,Se)2 thin-film solar cell absorbers
Authors: Weinhardt L. , Gleim Th. , Fuchs O. , Heske C. , Umbach E. , Bär M. , Muffler H.-J. , Fischer Ch.-H. , Lux-Steiner M. C. , Zubavichus Y. , Niesen T. P. , Karg F.
Published: January 2003

The surface modifications induced by treating Cu(In,Ga)(S,Se)2 films in an aqueous ammonia hydroxide-based solution of Cd2+ ions—as used in record Cu(In,Ga)(S,Se)2 solar cells without a CdS buffer layer—have been investigated for different Cd2+ concentrations. Employing a combination of x-ray photoelectron spectroscopy, Auger electron spectroscopy, and x-ray emission spectroscopy, it is possible to distinguish two different surface modifications. For Cd2+ concentrations below 4.5 mM in the solution we observe the formation of a CdS monolayer, while higher Cd2+ concentrations lead to the additional deposition of a cadmium hydroxide film on the CdS/Cu(In,Ga)(S,Se)2 surface.
Noncontacting measurement of the inductive nonlinearity of a superconducting thin film
Authors: Claassen J. H.
Published: January 2003

Superconducting films are expected to contribute nonlinear effects in microwave circuits due to a current dependence of penetration depth λ. Data from a two-coil mutual inductance measurement can be used to extract the coefficient J0 representing a dependence of the form λ2(J)=λ2(0)[1+(J/J0)2]. A method of extracting J0, using a measurement of third-harmonic generation, is compared to one previously reported. The method is significantly easier to use and probably more accurate. Measurements on a number of YBa2Cu3O7−x films at 78 K have shown no sign of a nonquadratic nonlinearity, and give values of J0 as high as ∼100 MA/cm2.
Tunable femtosecond pulses in the near-ultraviolet from ultrabroadband parametric amplification
Authors: Tzankov Pancho , Fiebig Torsten , Buchvarov Ivan
Published: January 2003

Using an ultrabroadband amplification technique in a β-barium borate noncollinear optical parametric amplifier, pumped by the third harmonic of a 1 kHz Ti:sapphire laser, we generate tunable femtosecond pulses in the range of 335–480 nm with energies of a few hundred nJ. The developed setup is an amplification source with a bandwidth of more than 200 THz and provides femtosecond pulses in the near-ultraviolet spectral range using coherent amplification. Parts of the amplified white-light continuum spectrum were compressed to 24–35 fs using a prism pair. Further improvements could make it possible to generate tunable ultraviolet pulses as short as 4–5 fs.
Electronic and transport properties of reduced and oxidized nanocrystalline TiO2 films
Authors: Rothschild A. , Komem Y. , Levakov A. , Ashkenasy N. , Shapira Yoram
Published: January 2003

Electronic properties of reduced (vacuum-annealed) and oxidized (air-annealed) TiO2 films were investigated by in situ conductivity and current–voltage measurements as a function of the ambient oxygen pressure and temperature, and by ex situ surface photovoltage spectroscopy. The films were quite conductive in the reduced state but their resistance drastically increased upon exposure to air at 350 °C. In addition, the surface potential barrier was found to be much larger for the oxidized versus the reduced films. This behavior may be attributed to the formation of surface and grain boundary barriers due to electron trapping at interface states associated with chemisorbed oxygen species.
Densification-induced conductivity percolation in high-porosity pharmaceutical microcrystalline cellulose compacts
Authors: Strømme M. , Niklasson G. A. , Ek R.
Published: January 2003

The percolation theory is established as a useful tool in the field of pharmaceutical materials science. It is shown that percolation theory, developed for analyzing insulator–conductor transitions, can be applied to describe imperfect dc conduction in pharmaceutical microcrystalline cellulose during densification. The system, in fact, exactly reproduces the values of the percolation threshold and exponent estimated for a three-dimensional random continuum. Our data clearly show a crossover from a power-law percolation theory region to a linear effective medium theory region at a cellulose porosity of ∼0.7.
Correlated charge detection for readout of a solid-state quantum computer
Authors: Buehler T. M. , Reilly D. J. , Brenner R. , Hamilton A. R. , Dzurak A. S. , Clark R. G.
Published: January 2003

The single-electron transistor (SET) is a prime candidate for reading out the final state of a qubit in a solid-state quantum computer. Such a measurement requires the detection of subelectron charge motion in the presence of random charging events. We present a detection scheme where the signals from two SETs are cross-correlated to suppress unwanted artifacts due to charge noise. This technique is demonstrated by using the two SETs to detect the charge state of two coupled metal dots, thereby simulating charge transfer and readout in a two-qubit system. These measurements indicate that for comparable buried dopant semiconductor architectures, the minimum measurement time required to distinguish between the two charge states is of the order of 10 ns.
Local probing of thermal properties at submicron depths with megahertz photothermal vibrations
Authors: Tomoda M. , Shiraishi N. , Kolosov O. V. , Wright O. B.
Published: January 2003

We demonstrate the imaging of buried features in a microstructure—a tiny hole in an aluminum thin film covered by a chromium layer—with nanometer lateral resolution using a transient temperature distribution restricted to within ∼0.5 μm of the sample surface. This is achieved by mapping photothermally induced megahertz surface vibrations in an atomic force microscope. Local thermal probing with megahertz-frequency thermal waves is thus shown to be a viable method for imaging subsurface thermal features at submicron depths.
Effect of surfaces on the size-dependent elastic state of nano-inhomogeneities
Authors: Sharma P. , Ganti S. , Bhate N.
Published: January 2003

The effect of surface energies, strains, and stresses on the size-dependent elastic state of embedded inhomogeneities are investigated. At nanolength scales, due to the increasing surface-to-volume ratio, surface effects become important and induce a size dependency in the otherwise size-independent classical elasticity solutions. In this letter, closed-form expressions are derived for the elastic state of eigenstrained spherical inhomogeneities with surface effects using a variational formulation. Our results indicate that surface elasticity can significantly alter the fundamental nature of stress state at nanometer length scales. Additional applications of our work on nanostructures such as quantum dots, composites, etc. are implied.
Exact solutions for reconnective annihilation in magnetic configurations with three sources
Authors: Tassi E. , Titov V. S. , Hornig G.
Published: January 2003

Exact solutions of the steady resistive three-dimensional magnetohydrodynamics equations in cylindrical coordinates for an incompressible plasma are presented. The solutions are translationally invariant along one direction and in general they describe a process of reconnective annihilation in a curved current layer with nonvanishing magnetic field. In the derivation of the solutions the ideal case with vanishing resistivity and electric field is considered first and then generalized to include the effects of finite electric field and resistivity. Particular attention is devoted to the analysis of how the latter ones influence the presence of singularities in the solutions. In this respect comparisons with the purely two-dimensional case are made and the resulting important differences are highlighted. Finally, applications of the solutions for modeling an important class of solar flares are discussed.
Generation of magnetic field and electrostatic shock wave driven by counterstreaming pair plasmas
Authors: Haruki Takayuki , Sakai Jun-Ichi
Published: January 2003

By using a two-dimensional (2D) relativistic fully electromagnetic particle-in-cell code, the interaction process of counterstreaming pair (electron–positron) plasmas is investigated. The counterstreaming plasmas become unstable against the collisionless electromagnetic counterstreaming instability, similar to the Weibel instability. In the linear phase, magnetic and electric fields with the scale of skin depth size are generated through the electromagnetic counterstreaming instability. The behavior of plasma in the nonlinear phase is also made clear. The small-scale magnetic fields coalesce with each other, merging through the inverse cascade process which occurs characteristically in 2D dynamics, and change into larger unit. The large-scale magnetic fields propagate more slowly than the initial plasma flow as a low-frequency wave. Behind the magnetic fields, plasmas are isotropically heated by the mixing of counterstreaming plasmas. On the other hand, the electric fields propagate the same as the initial plasma flow. Ahead of the generated magnetic fields, the electric field component along the stream is amplified through the electrostatic counterstreaming instability and the electrostatic shock waves are formed. High-energy particles are also produced from the electrostatic shocks. These simulation results may be applied to the synchrotron gamma-ray burst model.
Self-consistent dusty sheaths in plasmas with two-temperature electrons
Authors: Chutov Yu. I. , Kravchenko O. Yu. , Pshenychnyj A. F. , Smirnov R. D. , Asano K. , Ohno N. , Takamura S. , Tomita Y.
Published: January 2003

The parameters of self-consistent dusty sheaths are investigated using computer simulations of the temporal evolution of one-dimensional slab plasma with two-temperature electrons and dust particles. The evolution is caused by collection of electrons and ions by an electrode (wall) and also by dust particles, which are initially injected into the plasma around the electrode (wall). A peculiarity of the sheaths is a nonmonotonic spatial distribution of the electric potential that causes protection of the electrode (wall) from fast ions. The degree of protection depends on the temperature and density ratios of both electron components.
Cylindroid rigid-wall simulation of the influence of gas pressure in pulsed laser deposition of LiNbO3 films
Authors: Yang X. , Wu X. L. , Zhang Z. Y. , Siu G. G. , Dong Z. G. , Fang L. , Shen M. R.
Published: January 2003

We have demonstrated that gas pressure (pG) is a key parameter for fabricating stoichiometric LiNbO3 thin films during laser ablation. To theoretically describe the influence of pG, a cylindroid rigid-wall model was presented. It was shown that there exist two critical pressures related to Li and Nb: pLi and pNb(pLi<pNb). They separate pG into three intervals. When pG<pLi, pG has little influence on film stoichiometry and the obtained films contain fixed Li deficiency. When pLi⩽pG⩽pNb, pG plays an important role in forming stoichiometric films. When pG⩾pNb, the change of pG does not affect film stoichiometry, but the film growth because of greatly reduced energies of the species that reach the substrate. The presented theory was in good agreement with experiments. This model provides a useful way for growing multicomponent films by pulsed laser deposition.
Spin injection through different g-factor heterointerfaces using negative trions for spin detection
Authors: Ghali M. , Kossut J. , Heiss W.
Published: January 2003

We demonstrate using the formation and the optical signatures of negatively charged excitonic complexes, trions, as a sensitive detector for spin injection. In our study, spin-polarized electrons are optically injected from a Cd0.97Mn0.03Te spin aligning layer to CdTe quantum well (QW) via a nonmagnetic Cd0.98Mg0.02Te spacer. In photoluminescence measurements, for the excitation above the Cd0.97Mn0.03Te band gap, we find a gradual change in the circular polarization of the trion emission from a negative value at low magnetic fields to a positive one at high fields with a transition at B∼3 T. This polarization behavior is in contrast to that for selective excitation below the spin aligner band gap and evidences unambiguously a redistribution of the electron spin population between the electron Zeeman sublevels in the QW due the spin injection of effectively polarized electrons from the magnetic spin injector.
Correlation between the photoluminescence lifetime and defect density in bulk and epitaxial ZnO
Authors: Koida T. , Chichibu S. F. , Uedono A. , Tsukazaki A. , Kawasaki M. , Sota T. , Segawa Y. , Koinuma H.
Published: January 2003

Influences of point defects on the nonradiative processes in ZnO were studied using steady-state and time-resolved photoluminescence (PL) spectroscopy making a connection with the results of positron annihilation measurement. Free excitonic PL intensity naturally increased with the increase in the nonradiative PL lifetime (τnr). Density or size of Zn vacancies (VZn) decreased and τnr increased with increasing growth temperature in heteroepitaxial films grown on a ScAlMgO4 substrate. Use of homoepitaxial substrate further decreased the VZn density. However, τnr was the shortest for the homoepitaxial film; i.e., no clear dependence was found between τnr and density / size of VZn or positron scattering centers. The results indicated that nonradiative recombination processes are not solely governed by single point defects, but by certain defect species introduced by the presence of VZn such as vacancy complexes.
Large magnetoresistance in magnetically frustrated ruthenates
Authors: Mamchik A. , Chen I.-W.
Published: January 2003

A large negative magnetoresistance effect is found in Fe-doped ruthenates of perovskite and layered perovskite structures. These new materials are magnetically glassy, and can be derived from a parent compound that is either magnetic or nonmagnetic. The magnetoresistance is nearly linear with the magnetic field up to 9 T and is stronger at lower temperature. Atomic-level spin valves associated with Fe cations on B sites that regulate electron transport in response to an external magnetic field are suggested to be the mechanism responsible.
Crystallographic dependence of the lateral undercut wet etching rate of InGaP in HCl
Authors: Cich M. J. , Johnson J. A. , Peake G. M. , Spahn O. B.
Published: January 2003

The crystallographic dependence of the lateral etch rate in 12 M HCl of InGaP lattice matched to GaAs has been measured. The etch rate at 20 °C is found to have twofold rotational symmetry about [100] and varies between <0.01 μm/min for mesas oriented along 〈011〉 directions and ∼0.9 μm/min for mesas 55° and 125° from [011] towards [01̄1]. Etch fronts consist of {111}A planes. The etch rate also depends on the direction of etch step flow, suggesting that reconstruction plays an important role during InGaP wet etching.
High power light emission of IV–VI lead salt multiple-quantum-well structure grown by molecular-beam epitaxy on 〈111〉 BaF2 substrate
Authors: Majumdar A. , Xu H. Z. , Khosravani S. , Zhao F. , Jayasinghe L. , Shi Z.
Published: January 2003

Up to 4.9 W peak output power at room temperature and 61.5 W at 180 K were observed from photoluminescence of a PbSe/PbSrSe multiple-quantum-well (MQW) structure grown by molecular-beam epitaxy. Our theoretical calculation indicates that the lifted degeneracy of quantum-well structures on 〈111〉 orientation provides higher modal gain. This plus the improved epitaxial material quality of MQWs contribute to the high output power. The observed output powers are much higher than those of reported light emission of IV–VI lead salt materials.
Investigation of buffer traps in an AlGaN/GaN/Si high electron mobility transistor by backgating current deep level transient spectroscopy
Authors: Marso M. , Wolter M. , Javorka P. , Kordoš P. , Lüth H.
Published: January 2003

The influence of a substrate voltage on the dc characteristics of an AlGaN/GaN high electron mobility transistor (HEMT) on silicon (111) substrate is profited to investigate traps that are located between the substrate and the two-dimensional electron gas channel. The transient of the drain current after applying a negative substrate voltage is evaluated in the temperature range from 30 to 100 °C. With this method, known as backgating current deep level transient spectroscopy, majority carrier traps with activation energy of 200 meV as well as minority carrier traps at 370 meV are identified. The experiments are performed on completed HEMTs, allowing the investigation of the influence of device fabrication technology.
Highly efficient prism coupling to whispering gallery modes of a square μ cavity
Authors: Pan Yong-Le , Chang Richard K.
Published: January 2003

By using prism coupling to a square μ cavity, over 75% energy transfer to the whispering gallery modes (Q>106) by frustrated total internal reflection was observed. A good comparison was found between measured data and theoretical model (based on a Fabry–Perot resonator), for the dependence of the coupling and linewidth of the whispering gallery modes (WGMs) as a function of relative separation between the prism and the μ cavity. By selecting the incident angle at the prism interface, the coupling to all four different sets of WGMs can be changed to coupling to only one set of WGMs.
Fabrication of p-pentacene/n-Si organic photodiodes and characterization of their photoelectric properties
Authors: Kim S. S. , Choi Y. S. , Kim Kibum , Kim J. H. , Im Seongil
Published: January 2003

We have fabricated p-pentacene/n-Si organic photodiodes by thermal evaporation of pentacene films at 25 (RT), 60, and 80 °C. Our pentacene films exhibit the main absorption peak (highest occupied molecular orbital-lowest unoccupied molecular orbital gap transition) at 1.82 eV and photoelectric effects were clearly observed from our p-pentacene/n-Si diodes when illuminated by a monochromatic red light of 1.85 eV (670 nm). Excellent photoresponsivity of 2.6 A/W and the photoresponse time of less than 40 ns have been demonstrated. The photodiodes exhibited typical rectifying behavior in the dark and the leakage current increases with the deposition temperature.
High-performance planar light-emitting diodes
Authors: Cecchini Marco , Piazza Vincenzo , Beltram Fabio , Lazzarino Marco , Ward M. B. , Shields A. J. , Beere H. E. , Ritchie D. A.
Published: January 2003

High-speed planar light-emitting diodes fabricated within a single high-mobility quantum well are demonstrated. Devices were fabricated by photolithography and wet chemical etching starting from p-type modulation-doped Al0.5Ga0.5As/GaAs heterostructures grown by molecular beam epitaxy. Electrical and optical measurements from room temperature down to 1.8 K show high spectral purity, high external efficiency, and extremely short recombination times of the order of 50 ps. Time-resolved electroluminescence measurements demonstrate subnanosecond modulation time scale.
Structure of direct-current microdischarge plasmas in helium
Authors: Kothnur Prashanth S. , Yuan Xiaohui , Raja Laxminarayan L.
Published: January 2003

A one-dimensional, self-consistent, continuum model is used to elucidate plasma phenomena in a parallel-plate dc microdischarge with a 250 μm gap at a pressure of 250 Torr. The microdischarge is found to have a bulk plasma region and a cathode sheath region with sizes that are comparable. Depending on the discharge current densities, peak electron densities of order up to 1014 cm−3 are predicted. Electron temperature of several eV are predicted within the cathode sheath while temperatures between 2 and 3 eV are observed in the bulk plasma. Gas temperatures of the order of 1000 K are predicted, emphasizing the importance of gas heating phenomena in dc microdischarges.
White light emission from single component polymers fabricated by spin coating
Authors: Tsai Mu-Lin , Liu Ching-Yang , Hsu Ming-Ann , Chow Tahsin J.
Published: January 2003

A polymeric material prepared from single monomers is described, which emits white electroluminescence. The broad emission band is composed of a blue emission from anthracene and a red emission from aggregates. Single and double layer devices of light emitting diode were fabricated and examined.
Single-crystal barium titanate thin films by ion slicing
Authors: Izuhara T. , Gheorma I.-L. , Osgood R. M. , Roy A. N. , Bakhru H. , Tesfu Yiheli M. , Reeves M. E.
Published: January 2003

Thin barium titanate films, 0.5–8 μm thick, are obtained from a single-crystal bulk sample using ion slicing. The process, based on ion implantation and anodic bonding, separates thin films having areas of ∼1×1 cm2, from bulk crystals. The quality of the film is characterized by measurement of surface roughness and dielectric properties. The film permittivity retains its single-crystal value.
Response spectra from mid- to far-infrared, polarization behaviors, and effects of electron numbers in quantum-dot photodetectors
Authors: Aslan B. , Liu H. C. , Korkusinski M. , Cheng S.-J. , Hawrylak P.
Published: January 2003

Photoresponse characteristics of InAs/GaAs self-assembled quantum-dot infrared photodetectors in a wide spectral region from the mid- to far-infrared are reported. Clear polarization behaviors with a dominant P-polarized response in the mid-infrared and a strong S-response in the far infrared are shown. These behaviors can be qualitatively understood in view of the quantum-dot shape of a large in-plane diameter and a small height in the growth direction. With a set of three samples, effects of the number of electrons per dot on the spectra are investigated.
Scattering polarizer with anisotropic crystals in a polyolefin polymer
Authors: Okumura Takamitsu , Ishikawa Takeshi , Koike Yasuhiro , Tagaya Akihiro
Published: January 2003

A scattering polarizer containing calcium carbonate whiskers (aragonite) in a polyolefin polymer has been developed. A selective multiple scattering technique, generating transmitted linearly polarized light and backward scattered light, has been demonstrated. A refractive index match and mismatch arises from the uniaxial orientation of the host polymer and the alignment of aragonite in the drawing direction. The dependence of the transmittance on the polarization direction of the incident light has been observed. The polarizing efficiency has been measured to be 60% with a 150-μm thickness.
High sensitivity of positron annihilation to thermal oxidation of polyethylene
Authors: Ito Kenji , Kobayashi Yoshinori , Nanasawa Atsushi
Published: January 2003

We demonstrate the high sensitivity of positron annihilation to compositional changes related to the thermal degradation of polyethylene (PE). Positron annihilation γ-ray and lifetime measurements were conducted for PE films with and without antioxidant (1000-ppm Ciba® IRGANOX® 1076), subjected to heat treatment at 100 °C for different periods, to a maximum of 30 days. For the film without antioxidant, the positron Doppler parameter (S) and ortho-positronium formation probability (Io−Ps) appreciably decreased with increased heat treatment times, whereas they barely changed for the film with antioxidant. This, together with the Fourier transform infrared measurements, demonstrated that the variations of S and Io−Ps are caused by the thermal oxidation of PE. The S parameter was found to be sensitive to the early stage of degradation, where the carbonyl concentration is inferred to be lower than 100 ppm. The high sensitivity results from the large positron mobility in PE and from the high positron affinity of oxygen-containing polar groups. This work provides the basis for an application of positron annihilation to sensitive detection of the initial degradation of PE and other nonpolar polymers.
Photoluminescence of metalorganic-chemical-vapor-deposition-grown GaInNAs/GaAs single quantum wells
Authors: Manasreh M. O. , Friedman D. J. , Ma W. Q. , Workman C. L. , George C. E. , Salamo G. J.
Published: January 2003

Photoluminescence (PL) spectra of interband transitions in GaInNAs/GaAs single quantum wells grown by metalorganic chemical vapor deposition on semi-insulating GaAs substrates were measured at 77 K for several samples grown with different In compositions and dimethylhydrazine (DMH)/III ratios. The results show that the PL intensity increases as the In mole fraction is increased from 0% to 25%, but the PL intensity is degraded for samples with an In mole fraction of 30% or higher. The peak position energies of the PL spectra were investigated as a function of the DMH/III ratio. Thermal annealing effect induced a blueshift in the PL spectra peak position energy in samples grown with high DMH/III ratios.
Photoconductivity and spin-dependent photoconductivity of hydrosilylated (111) silicon surfaces
Authors: Lehner A. , Kohl F. , Franzke S. A. , Graf T. , Brandt M. S. , Stutzmann M.
Published: January 2003

Organic monolayers were prepared on hydrogen-terminated (111) silicon surfaces by thermally induced hydrosilylation with alkenes. The electronic properties of the modified surfaces were studied by photoconductivity and spin-dependent photoconductivity measurements (electrically detected magnetic resonance) and compared to the oxidized and hydrogen-terminated silicon surfaces. The photoconductivity at low intensity of illumination (monomolecular recombination regime) indicates that the hydrosilylated surface has nearly as few defects as the surfaces treated in HF vapor. The paramagnetic defects detected in the spin-dependent photoconductivity are identified as the silicon dangling bond Pb-center. The density of defects at the hydrosilylated (111) silicon surface is determined by electron spin resonance measurements to be about 1013 cm−2.
Formation and optical properties of InAs/GaAs quantum dots for applications as infrared photodetectors operating at room temperature
Authors: Kim M. D. , Noh S. K. , Hong S. C. , Kim T. W.
Published: January 2003

The formation and optical properties of lateral quantum-dot infrared photodetector (QDIP) structures utilizing uniform-sized InAs QDs obtained by controlling the intensity of the reflection high-energy diffraction pattern and the As/In flux ratio were investigated. The thickness of the pseudomorphic, strained InAs wetting layer increased slightly with decreasing As/In flux ratio. The characteristic peaks corresponding to the interband and the intersubband transitions were observed, respectively, in the photoluminescence and Fourier transform infrared spectra. The absorption spectrum showed an absorption peak corresponding to the intersubband transition at around 10 μm. These results indicate that InAs/GaAs QDs obtained by controlling growth conditions hold promise for potential applications in QDIP devices operating at room temperature.
Spin-wave wells with multiple states created in small magnetic elements
Authors: Bayer C. , Demokritov S. O. , Hillebrands B. , Slavin A. N.
Published: January 2003

We have observed several localized modes in the spin-wave spectrum of a permalloy microstripe (length 90 μm, width 1 μm, thickness 0.033 μm) magnetized along its width. The mode frequencies increase from 4.5 to 8 GHz with increasing applied field (0–1.1 kOe). These modes are interpreted as multiple spin–wave eigenstates in effective potential wells created by a strongly inhomogeneous internal magnetic field in the stripe near its edges.
Circular magnetic bistability induced by tensile stress in glass-covered amorphous microwires
Authors: Chizhik A. , Gonzalez J. , Zhukov A. , Blanco J. M.
Published: January 2003

Investigations of magnetic reversal in Co-rich glass covered amorphous microwires were performed using the magneto-optical Kerr-effect technique. The appearance of circular magnetic bistability was found in the presence of external tensile stress. A tensile-induced large Barkhausen jump of circular magnetization is associated with a change of the value of the magnetostriction constant induced by stress and by rearrangement of domain structure in the outer shell of the microwire.
Pyramidal-plane ordering in AlGaN alloys
Authors: Benamara M. , Kirste L. , Albrecht M. , Benz K. W. , Strunk H. P.
Published: January 2003

This letter reports the identification of long-range ordering in AlGaN compounds along the pyramidal planes by transmission electron microscopy. This ordering consists of the alternate stacking of GaN and AlN layers on {11̄01} planes and is evidenced by the comparison of experimental diffraction patterns along [011̄0] and [112̄0] with calculated patterns. A formation model of this ordering is presented. It is based upon Ga incorporation on reduced-N coordination sites that are located at step edges on {11̄01} pit facets.
Linewidth enhancement factor of lattice-matched InGaNAs/GaAs quantum wells
Authors: Seo Woon-Ho , Donegan John F.
Published: January 2003

The linewidth enhancement factors of lattice-matched 1.5 μm wavelength InGaNAs/GaAs and InGaAs/InP single-quantum-well structures are calculated using microscopic theory and 10×10 effective-mass Hamiltonian. InGaNAs/GaAs quantum wells have a lower threshold carrier density and higher differential gain resulting in a lower linewidth enhancement factor compared with InGaAs/InP quantum wells. For applications which require high gain and carrier densities, InGaNAs/GaAs quantum wells have a much lower linewidth enhancement factor over a temperature range 300–400 K. This lower value originates from the large electron effective mass caused by the nitrogen incorporation. The linewidth enhancement factor of InGaNAs is almost clamped as a function of carrier density and temperature compared with InGaAs. This effect is due to the enhanced match between conduction-valence band density of states and the improved electron confinement caused by the large conduction band offset and deep quantum wells.
Effect of microstructural change on magnetic property of Mn-implanted p-type GaN
Authors: Baik Jeong Min , Jang Ho Won , Kim Jong Kyu , Lee Jong-Lam
Published: January 2003

A dilute magnetic semiconductor was achieved by implanting Mn ions into p-type GaN and subsequent annealing. The ferromagnetic property was obtained after annealing at 800 °C. This was attributed to the formation of Ga–Mn magnetic phases. Higher temperature annealing at 900 °C reduced the ferromagnetic signal and produced antiferromagnetic Mn–N compounds such as Mn6N2.58 and Mn3N2, leaving N vacancies. This provides evidence that N vacancies play a critical role in weakening the ferromagnetic property in the Mn-implanted GaN.
Wavelength selectivities of organic photoconductive films: Dye-doped polysilanes and zinc phthalocyanine/tris-8-hydroxyquinoline aluminum double layer
Authors: Aihara S. , Hirano Y. , Tajima T. , Tanioka K. , Abe M. , Saito N. , Kamata N. , Terunuma D.
Published: January 2003

Organic photoconductors sensitive to blue, green, and red light were fabricated using coumarin 6 (C6)-doped poly(m-hexoxyphenyl)phenylsilane (PHPPS), rhodamine 6G (R6G)-doped polymethylphenylsilane (PMPS), and zinc phthalocyanine (ZnPc)/tris-8-hydroxyquinoline aluminum (Alq3) double layer, respectively. Selectivities of the spectral responses of these films were good enough to divide the incident light into three color components, indicating the possibility of color separation without prism for video cameras. The quantum efficiency of a ZnPc/Alq3 double-layer film is over an order of magnitude better than those of C6/PHPPS and R6G/PMPS blend films due to the dissociation of electron–hole pair generated at the interface between ZnPc and Alq3.
Classical and quantum transport in focused-ion-beam-deposited Pt nanointerconnects
Authors: Lin J.-F. , Bird J. P. , Rotkina L. , Bennett P. A.
Published: January 2003

We study the electrical properties of Pt nanointerconnects, formed on SiO2 substrates by focused-ion-beam deposition. Studies of their temperature-dependent resistivity reveal a small residual-resistivity ratio, and a Debye temperature that differs significantly from that of pure Pt, indicative of the disordered nature of the nanowires. Their magnetoresistance shows evidence for weak antilocalization at temperatures below 10 K, with a phase-breaking length of ∼100 nm, and a temperature dependence suggestive of quasi-one-dimensional interference.
Fabrication approach for molecular memory arrays
Authors: Li Chao , Zhang Daihua , Liu Xiaolei , Han Song , Tang Tao , Zhou Chongwu , Fan Wendy , Koehne Jessica , Han Jie , Meyyappan Meyya , Rawlett A. M. , Price D. W. , Tour J. M.
Published: January 2003

We present an approach to tackle long-standing problems in contacts, thermal damage, pinhole induced short circuits and interconnects in molecular electronic device fabrication and integration. Our approach uses metallic nanowires as top electrodes to connect and interconnect molecular wires assembled on electrode arrays in crossbar architectures. Using this simple and reliable approach, we have revealed intriguing memory effects for several different molecular wires, and demonstrated their applications in molecular memory arrays. Our approach has great potential to be used for fast screening of molecular wire candidates and construction of molecular devices.
Silver-coated silicon pillar photonic crystals: Enhancement of a photonic band gap
Authors: Poborchii Vladimir , Tada Tetsuya , Kanayama Toshihiko , Moroz Alexander
Published: January 2003

For a two-dimensional lattice of Si pillars it is shown both experimentally and theoretically that a photonic band gap for the light polarized perpendicular to pillars can be strongly enhanced by means of a silver coating of the pillars. A sizable omnidirectional photonic band gap is demonstrated for both square and triangular lattice of silver-coated Si pillars in the near-infrared and visible spectral range.
Effect of Ag photodoping on deep-level emission spectra of ZnO epitaxial films
Authors: Lee Hyun-Yong , Ko Hang-Ju , Yao Takafumi
Published: January 2003

Effect of Ag photodoping into ZnO films grown by molecular beam epitaxy has been examined via the real-time measurement of photoluminescence (PL) spectra using a HeCd laser at room temperature. While an asymmetric deep-level (green-yellow) broadband (D) is observed in PL of as-grown ZnO, it appears to change to two distinct bands (at 2.29 and 2.50 eV) in the illuminated Ag/ZnO. From the result of a Gaussian fitting, the yellow band at 2.29 eV is evaluated to relate with photodoped Ag atoms. With increasing the laser illumination time (photodoping), the PL intensity of broadband (ID) decreases and contrarily, the intensity of the near band edge emission observed at 3.297 eV (INB) shows a tendency to increase. We believe that the Ag can be photodoped into ZnO at 300 K and it contributes to the suppression of deep-level band, which results in an increase of INB.
Strain-induced growth of SiO2 dots by liquid phase deposition
Authors: Liu C. W. , Hsu B.-C. , Chen K.-F. , Lee M. H. , Shie C.-R. , Chen Pang-Shiu
Published: January 2003

Silicon dioxide dots are deposited on the Si cap layers of self-assembled Ge dots using a liquid phase deposition method. The Si capping layer directly above the Ge dots has a tensile strain, while the Si cap on the wetting layer is not strained. The tensile strain can enhance the silicon dioxide nucleation and deposition on Si surface, and SiO2 dots are directly formed on the top of Ge dots with the SiO2 wetting layers between the dots. The step height and base width of the dots increase with the deposition time. A metal-oxide-semiconductor photodetector is fabricated using the liquid-phase-deposited oxide, and has a responsivity of 0.08 mA/W at 1550 nm.
Photoluminescence from surfactant-assembled Y2O3:Eu nanotubes
Authors: Wu Changfeng , Qin Weiping , Qin Guanshi , Zhao Dan , Zhang Jisen , Huang Shihua , Lü Shaozhe , Liu Huangqing , Lin Haiyan
Published: January 2003

Y 2 O 3 : Eu nanotubes were fabricated by a surfactant assembly mechanism. The tubular structure was characterized by transmission electron microscopy. Under an ultraviolet-light excitation, the nanotubes show a relatively intense emission peak at 618 nm besides the 610 nm peak, different from that of single Y2O3:Eu nanocrystallites. The results of laser-selective excitation indicate that the emission centers near the surface of nanotube walls exhibit inhomogenously broadened spectra without spectral structures while the two sites (sites B and C) inside the nanotube walls present legible spectral structures. It is concluded by the number and peak positions of Stark levels that the sites B and C possess different site symmetries.
Direct evidence for grain-boundary depletion in polycrystalline CdTe from nanoscale-resolved measurements
Authors: Visoly-Fisher Iris , Cohen Sidney R. , Cahen David
Published: January 2003

We use scanning probe microscopy-based methods for direct characterization of a single grain boundary and a single grain surface in solar cell-quality CdTe, deposited by closed-space vapor transport. We find that scanning capacitance microscopy can serve to study polycrystalline electronic materials, notwithstanding the strong topographical variations. In this way, we find a barrier for hole transport across grain boundaries, a conclusion supported by the much more topography-sensitive scanning kelvin probe microscopy, with some variation in barrier height between different boundaries.
Structural and electrical properties of an electron-beam-irradiated C60 film
Authors: Onoe Jun , Nakayama Tomonobu , Aono Masakazu , Hara Toshiki
Published: January 2003

The structural and electrical properties of an electron-beam (EB)-irradiated C60 film have been examined at room temperature, using in situ infrared (IR) spectroscopy and ex situ four-probe measurements. IR results show that the irradiated film is neither graphite nor carbon nanotube-like but a peanut-shaped C60 polymer. Current–voltage curve shows that the polymer exhibits a metallic property with a drastically reduced resistivity of 7 Ω cm in comparison with 108–1014 Ω cm for solid C60. This indicates the possibility of applying C60 molecules in EB nanofabrication processes and large potential for developing carbon-based nanodevices.
Fabrication and characterization of heteroepitaxial p-n junction diode composed of wide-gap oxide semiconductors p-ZnRh2O4/n-ZnO
Authors: Ohta Hiromichi , Mizoguchi Hiroshi , Hirano Masahiro , Narushima Satoru , Kamiya Toshio , Hosono Hideo
Published: January 2003

A reactive solid-phase epitaxy technique was applied to fabricate all-oxide transparent p-n heterojunctions composed of p-ZnRh2O4 and n-ZnO thin layers. Polycrystalline ZnRh2O4 was deposited on a ZnO epitaxial layer at room temperature. Thermal annealing of the bilayer sample at 950 °C in air converts the polycrystalline ZnRh2O4 layer to an epitaxial single-crystalline layer. The resultant p-n heterojunctions have an abrupt interface and exhibit a distinct rectifying I–V characteristic. The threshold voltage is ∼2 V, agreeing well with the band-gap energy of ZnRh2O4. It also exhibits photovoltage with UV-light illumination, which originates mainly from the n-ZnO layer.
The Devil is in the Detail: Visualising Analogical Thought in Retail Location Decisionmaking
Authors: Clarke Ian , Mackaness William , Ball Barbara , Horita Masahide
Published: January 2003

Retailers use analogues (similar stores) routinely in the process of site assessment, either as a basic method of sales forecasting in its own right, or as a check on more complex quantitative models. In earlier stages of our research, we identified intuitive or qualitative causal knowledge structures derived from cognitive mapping interviews with UK retail directors to classify new sites according to their degree of likeness on these same attributes. Here, we focus on how the analogues identified by our qualitative system can be visualised effectively for use in location analysis. We discuss the role of analogy in retail location decisionmaking and the advantages and disadvantages of different methods of visualisation. We evaluate the visual aspects of the system developed in the course of our research with reference to users' qualitative responses. The central issue appears to be the value users place on the system being able to summarise analogues simply on key dimensions at a general level, as well as its ability to ‘drill down’ into the detail so that analogue representativeness can be established.
Spatial Openness as a Practical Metric for Evaluating Built-up Environments
Authors: Fisher-Gewirtzman Dafna , Wagner Israel A
Published: January 2003

This paper reports on a primary metric tool developed in a collaboration between an architecture researcher and a computer science researcher. The development of this tool emerged from the concept that the spatial openness (SO)—the volume of free space measured from all possible observation points—is an important quality indicator of alternative spatial configurations within given constraints; this concept is based on the idea that the geometry and morphology of the built-up environment influence perception. Previous work showed that comparative SO measurements in alternative spatial configurations are correlated with the comparative perceived density, and in particular that a higher value of SO indicates a lower perceived density. We present a feasible 3D computational method for measuring SO and demonstrate its potential use in the design process. The SO metric is a step towards the development of quantitative comparative evaluation of building shapes and spatial configurations related to the 3D observation of open space.
Computing with Emergence
Authors: Knight Terry
Published: January 2003

The concept of emergence has its roots in 19th-century philosophy. Today it is central to many computational systems which retain the hallmarks of emergence laid out much earlier. The role of emergence in creative design and its unique embodiment in shape grammars have been emphasized by March, Stiny, and others. Shape grammars generate emergent shapes—shapes not predefined in a grammar. Emergent shapes are not only the output of a shape grammar computation; they can be the input for further computation. The history of emergence and its characterization in shape grammars are discussed here. Different sorts of shape emergence in grammars are then distinguished: anticipated, possible, and unanticipated. Unanticipated emergent shapes are shapes not premeditated by the author or user of a grammar. Generally, unanticipated shapes require on-the-spot definitions of rules to compute with them. However, for some interesting design problems, it is possible to know in advance what to do with unanticipated shapes, and to predefine rules accordingly. Special rules for computing with unanticipated shapes are proposed here. These rules allow for processes that have previously been handled extragrammatically—outside of grammars—to be handled within grammars. Examples of applications of these rules within a single grammar and across parallel grammars are given.
Using GIS to Estimate the Replacement Potential of Solar Energy for Urban Dwellings
Authors: Rylatt Mark , Gadsden Stuart , Lomas Kevin
Published: January 2003

This paper focuses the novel GIS-related aspects of a prototype planning support system for urban planners and energy advisers. The system design combines commercial database and GIS packages to provide a flexible means of predicting the solar energy potential and energy consumption of dwellings. By incorporating customised tools designed to derive useful data directly from digital maps and aerial photographs, it addresses the significant problem of data collection for urban-scale energy modelling. In conjunction with data generated by a new dynamic default data system, the map-derived data provide the necessary input for an embedded domestic energy model and a solar energy calculation engine. In this way, robust estimates can be obtained, at almost arbitrary scales of resolution, of the potential for solar energy to replace delivered domestic energy and to mitigate emissions of carbon dioxide.