bluuebunny/crossref_metadata_2025 huggingface dataset:
Observation of quantum interference effects in submicron CoSi2 wires in Si(100)
Authors: Lenssen D. , Mantl S.
Published: July 2002

We report on the structural and electrical characterization of submicron wide cobalt disilicide wires with widths down to 170 nm fabricated by ion beam synthesis. This versatile technique consists of implantation of cobalt through a special implant mask followed by a rapid thermal annealing step. We observed quantum interference effects in CoSi2 wires, which we attribute to weak localization with strong spin-orbit scattering and superconducting fluctuations. Cross-sectional transmission electron microscopy micrographs showed that the thinnest wires have diamondlike shapes due to energetically preferred {111} facets. Analysis of the magnetoresistance at temperatures between 2 and 4 K yielded relatively large phase coherence lengths of 0.5–2.5 μm very similar to values obtained for epitaxial CoSi2 layers indicating the high crystalline quality of the wires.
The quantum dot spectrometer
Authors: Jimenez J. L. , Fonseca L. R. C. , Brady D. J. , Leburton J. P. , Wohlert D. E. , Cheng K. Y.
Published: July 2002

We propose a novel photodetector capable of multi-spectral channel operation. The device makes use of the ability of a quantum dot plane to capture an optical spectrum, and of a resonant-tunneling structure to perform spectrally sensitive read-out. We present a design made out in the InAs–GaAs–AlxGa1−xAs system. We also present realistic simulations of the optical channel capabilities, as well as a discussion of the possible problems of the device.
Hydrogenated amorphous silicon transverse junction solar cell
Authors: Kroon M. A. , van Swaaij R. A. C. M. M. , Zeman M. , Kuznetsov V. I. , Metselaar J. W.
Published: July 2002

In this letter, we introduce a new thin film solar cell design on amorphous silicon, called the transverse junction solar cell. In this concept, the p-i-n junction is formed perpendicular to the surface. With conventional deposition and silicon device processing techniques test cells have been made with a conversion efficiency up to 5.2%±1.4% under standard AM1.5 illumination.
The piezoelectric coefficient of gallium nitride thin films
Authors: Muensit S. , Guy I. L.
Published: July 2002

A laser interferometer was used to measure the d33 piezoelectric coefficient of wurtzite GaN. The GaN was in the form of 1 μm thick films, grown by chemical vapor deposition and the measurement of the piezoelectric coefficient was made with a spatial resolution of 100 μm. Sample mounting was found to play an important part in the observed response. For rigidly mounted samples, the measured d33 was 2.0±0.1 pm V−1.
Crystalline silicon carbon nitride: A wide band gap semiconductor
Authors: Chen L. C. , Chen C. K. , Wei S. L. , Bhusari D. M. , Chen K. H. , Chen Y. F. , Jong Y. C. , Huang Y. S.
Published: July 2002

Crystalline thin films of SiCN have been grown by microwave plasma-enhanced chemical vapor deposition using H2, CH4, N2, and SiH4 gases. The ternary compound (C;Si)xNy exhibits a hexagonal structure and consists of a network wherein the Si and C are substitutional elements. While the N content of the compound is about 35–40 at. %, the extent of Si substitution varies and can be as low as 10 at. %. Optical properties of the SiCN compounds have been studied by photoluminescence (PL), piezoreflectance (PzR), and photothermal deflection (PDS) spectroscopies. From the PzR measurement, we determine the direct band gap of the new crystals to be around 3.8 eV at room temperature. PDS measurement shows two absorption features with the first peak at around 3.2 eV which is related to an indirect band gap. The second PDS peak occurred around 3.8 eV and is quite consistent with the direct band gap determined by PzR. From the PL measurement, it is also found that the SiCN compounds have a near band edge emission centered around 3.26 eV at room temperature, which is consistent with the fundamental band gap obtained from the PDS measurement. These optical results indicate the potential of SiCN for blue and uv optoelectronic applications.
Homogeneous photorefractive polymer/nematogen composite
Authors: Zhang J. , Singer K. D.
Published: July 2002

A photorefractive composite consisting of the polymer poly(N-vinylcarbazole) (PVK) doped with 4,4′-n-pentylcyanobiphenyl (5CB) and C60 is reported. The material shows no sign of phase separation, is stable, and does not require a plasticizer agent. Gain coefficients over 100 cm−1 are observed. Measurements of orientational and electro-optic responses indicate that the orientational response is large, but markedly inhibited.
Elastic energy of strained islands: Contribution of the substrate as a function of the island aspect ratio and inter-island distance
Authors: Ponchet A. , Lacombe D. , Durand L. , Alquier D. , Cardonna J.-M.
Published: July 2002

The finite element method is applied to strain-induced islands. The distribution of the elastic energy in the island and the substrate is determined as a function of the island aspect ratio and inter-island distance. When the height-over-base ratio increases, the total elastic energy density decreases and the relative contribution of the substrate increases. When the inter-island distance decreases, the elastic energy density increases and the relative contribution of the substrate decreases. The influence of the aspect ratio on the relaxation rate is amplified for short inter-island distances.
Free-electron-laser near-field nanospectroscopy
Authors: Cricenti A. , Generosi R. , Perfetti P. , Gilligan J. M. , Tolk N. H. , Coluzza C. , Margaritondo G.
Published: July 2002

First experiments at the Vanderbilt free electron lasers measured the local reflectivity of a PtSi/Si system. The reflectivity in the scanning near-field optical microscope images revealed features that were not present in the corresponding shear-force (topology) images and which were due to localized changes in the bulk properties of the sample. The size of the smallest detected features clearly demonstrated that near-field conditions were reached. The use of different photon wavelengths (0.653, 1.2, and 2.4 μm) enabled us to probe regions of different depth.
Annealing cycle dependence of preferential arsenic precipitation in AlGaAs/GaAs layers
Authors: Hung C.-Y. , Harris J. S. , Marshall A. F. , Kiehl R. A.
Published: July 2002

The spatial distribution of arsenic precipitates formed in a nonstoichiometric AlGaAs/GaAs quantum well is examined for different annealing temperatures and times. Preferential precipitation in the GaAs layer of samples annealed at 600 °C is found to be much weaker than in samples annealed at 850 °C because of the reduced diffusion of arsenic at lower temperatures. Nevertheless, it is demonstrated that strong preferential precipitation is possible at low annealing temperatures, provided that the annealing time is sufficiently long. Limitations to the preferential precipitation process imposed by interface mixing and the decrease in gallium vacancy concentration during annealing are also examined.
Selective-area and lateral epitaxial overgrowth of III–N materials by metal organic chemical vapor deposition
Authors: Park J. , Grudowski P. A. , Eiting C. J. , Dupuis R. D.
Published: July 2002

We describe the characteristics of single-crystal GaN regions obtained by selective-area and subsequent lateral epitaxial overgrowth using metal organic chemical vapor deposition. Under certain deposition conditions, the surface kinetics of the metal organic chemical vapor deposition process results in lateral growth of single-crystal GaN over the masked region. The lateral-to-vertical relative growth rate depends upon the orientation of stripe openings, the ratio of the “open” stripe width to the “masked” stripe width, and the growth conditions (e.g., temperature and V/III ratio). The specific orientations of the growth facets on the sidewalls of the laterally growing stripes are also dependent upon the growth conditions. The cathodoluminescence intensity of the GaN films indicate that improved materials are grown over the oxide mask.
Compensation ratio-dependent concentration of a VInH4 complex in n-type liquid encapsulated Czochralski InP
Authors: Fung S. , Zhao Y. W. , Beling C. D. , Xu X. L. , Gong M. , Sun N. F. , Sun T. N. , Chen X. D. , Zhang R. G. , Liu S. L. , Yang G. Y. , Qian J. J. , Sun M. F. , Liu X. L.
Published: July 2002

The concentration of hydrogen–indium vacancy complex VInH4 in liquid encapsulated Czochralski undoped and Fe-doped n-type InP has been studied by low-temperature infrared absorption spectroscopy. The VInH4 complex is found to be a dominant intrinsic shallow donor defect with concentrations up to ∼1016 cm−3 in as-grown liquid encapsulated Czochralski InP. The concentration of the VInH4 complex is found to increase with the compensation ratio in good agreement with the proposed defect formation model of Walukiewicz [W. Walukiewicz, Phys. Rev. B 37, 4760 (1998); Appl. Phys. Lett. 54, 2094 (1989)], which predicts a Fermi-level-dependent concentration of amphoteric defects.
Efficient gettering of low concentrations of copper contamination to hydrogen induced nanocavities in silicon
Authors: Kinomura A. , Williams J. S. , Wong-Leung J. , Petravic M. , Nakano Y. , Hayashi Y.
Published: July 2002

The efficient gettering to hydrogen-induced cavities in Si has been successfully demonstrated for low concentrations of Cu, unintentionally introduced during wafer processing. Secondary ion mass spectrometry showed up to 5×1012 cm−2Cu could be introduced into a silicon wafer and trapped at cavities. Neutron activation analysis indicated that, in samples with cavities, the Cu within the bulk was below the detection limit (around 4×1011 cm−2), while Cu was detected throughout the bulk of samples without cavities.
Annealing conditions for intrinsic CdTe
Authors: Berding M. A.
Published: July 2002

Equilibrium native defect densities in CdTe are calculated from ab initio methods, and compared with experimental results. We find that CdTe is highly compensated p type under tellurium-saturated conditions, with the cadmium vacancy as the dominant acceptor and the tellurium antisite as the compensating donor. This finding is in agreement with recent experiments that find a much larger deviation from stoichiometry than would be predicted by the electrically active defects. Under cadmium-saturated conditions, cadmium interstitials are predicted to dominate and the material is found to be n type. Native defect concentrations and the corresponding carrier concentrations are predicted as a function of processing conditions, and can serve as a guide to postgrowth anneals to manipulate the conductivity of undoped material for applications in x- and γ-ray spectrometers. Furthermore, we show that by choosing appropriate annealing conditions and extrinsic dopants, one can increase the operating efficiency of nuclear spectrometers by reducing the density of specific native defects that produce midgap trapping states.
Improved thermal stability of nonpolymeric organic glasses by doping with fullerene C60
Authors: Krieg T. , Petr A. , Barkleit G. , Dunsch L.
Published: July 2002

The doping of nonpolymeric organic glasses with C60 is found to improve their thermal stability. Films of triphenylamine dimer (TPD) N,N′-diphenyl-N,N′-(3-methyl-phenyl)-1,1′-biphenyl-4,4′-diamine, doped with fullerene C60 and 7,7,8,8-tetracyano-quinodimethane (TCNQ) on a level between 10 and 20 mol %, were prepared using vacuum codeposition techniques. While undoped and TCNQ-doped TPD films tend to crystallize under ambient conditions, no crystallization occurs on C60-doped TPD films on minimum doping level of 15 mol %. The crystallization can be suppressed even at temperatures about 333 K, the glass transition temperature of pure TPD, if the doping level of the C60-doped TPD films reaches 20 mol %.
Optical properties of doped InGaN/GaN multiquantum-well structures
Authors: Dalfors J. , Bergman J. P. , Holtz P. O. , Sernelius B. E. , Monemar B. , Amano H. , Akasaki I.
Published: July 2002

A systematic investigation of the photoluminescence spectra from InGaN/GaN multiquantum-well structures with different levels of Si doping in the quantum well has been carried out, in order to study the screening of the strain induced piezoelectric field and potential fluctuations. It is found that the emission energy strongly depends on the carrier concentration, originating from the doping or photogeneration. The observed strong shift with Si doping can only partly be explained by the screening of the piezoelectric field. The main shift is suggested to be related to the screening of the localization potentials.
High-Tc directly coupled direct current SQUID gradiometer with flip-chip flux transformer
Authors: Tian Y. J. , Linzen S. , Schmidl F. , Dörrer L. , Weidl R. , Seidel P.
Published: July 2002

We have designed and fabricated a flip-chip-type gradiometer as a sensor for measurement of weak magnetic signals. The gradiometer consists of a directly coupled direct current superconducting quantum interference device (SQUID) gradiometer coupled to a flux transformer made from a YBa2Cu3O7*/YBa2Cu3O7/CeO2/YSZ multilayer on 2 in. Si wafer, where YBa2Cu3O7*(YBCO*) is a nonsuperconducting crystalline film. The coupling coefficient of 0.18 is obtained for the flip-chip gradiometer. The transformer increases effectively the resolutions of the gradiometer. We obtain a magnetic field gradient resolution of 73 fT cm−1 Hz−1/2 in the white region, and 596 fT cm−1 Hz−1/2 at 1 Hz. The magnetocardiograms were successfully measured at a distance of nearly 100 mm from the gradiometer center to the human heart in a shielded room.
Anomalous critical current in double-barrier Nb/Al–AlOx–Al–AlOx–Nb devices
Authors: Nevirkovets I. P. , Ketterson J. B. , Lomatch S.
Published: July 2002

Double-barrier Nb/Al–AlOx–Al–AlOx–Nb devices with a “dirty” middle Al layer were fabricated and investigated. An anomalously large Josephson critical current at low temperatures and a nonmonotonic dependence of the device resistance on the thickness of the middle Al layer were found.
Dielectric exchange: The key repulsive or attractive transient forces between atomic force microscope tips and charged surfaces
Authors: Teschke O. , de Souza E. F.
Published: July 2002

Attractive as well as repulsive forces between electrically neutral tips and charged surfaces are measured directly with an atomic force microscope. The exchange of the volume of a region of the electric double layer of a mica surface immersed in water with a dielectric constant εDL by the tip with a dielectric constant εTip is responsible for the repulsion at large distances from the surface (starting at ∼100 nm, diffuse layer) and followed by an attraction when the tip is immersed in the Stern layer (∼2 nm). The force versus distance measured curves for high approaching velocities (⩾30 μm/s) were fitted to the expression of the dielectric exchange force derived by using a continuum theory for a sharpened pyramidal tip immersed in a spatially variable dielectric constant double-layer electric field. The dielectric exchange effect gives a consistent description of the force acting on the tip by assuming a double-layer region of disorganized water with εDL∼80 at distances far away from the surface followed by a region of lower dielectric constant resulting from the alignment of the water molecules due to the mica surface charge.
Role of peripheral vacuum regions in the control of the electron cyclotron resonance plasma uniformity
Authors: Ueda Yoko , Muta Hiroshi , Kawai Yoshinobu
Published: July 2002

Spatial measurements of the ion saturation current density indicate stable vacuum regions in a periphery of electron cyclotron resonance (ECR) plasma. The vacuum regions have a possibility to contribute to plasma uniformity by behaving as a waveguide for the incident electromagnetic waves. Mode conversion of electromagnetic waves with long wavelength to the right circular polarized wave was observed experimentally at a certain radial position. Furthermore, microwave propagation in a partially filled plasma chamber was examined numerically. The simulation indicated that the electromagnetic waves with long wavelengths propagated in a periphery of the plasma were converted into the extraordinary wave or electrostatic waves outside the ECR region and that the power absorption took place at the local regions. Physical considerations toward these results imply the reason why the plasma uniformity is influenced by magnetic field gradient.
Temperature and polarization dependence of LiNbO3 quasiphase-matched wavelength converters
Authors: Xu C. Q. , Fujita K. , Ogawa Y. , Kamijoh T.
Published: July 2002

Temperature and polarization characteristics of 1.55-μm-band LiNbO3 quasiphase-matched (QPM) wavelength converters have been studied by second-harmonic generation (SHG). It is found that the shift of the QPM wavelength is linearly proportional to temperature over the measured temperature range between 10 and 40 °C, with a temperature tolerance (corresponding to a 3 dB reduction in the QPM conversion efficiency) of greater than 10 °C for a 10-mm-long device. With respect to the angle θ of the injected fundamental light polarization direction, the SHG power changes as a function of sin4 θ, with a tolerance of over 60°. Theoretical explanations for the observed results are also presented.
Rapid surface topography using a tapping mode atomic force microscope
Authors: Ookubo Norio , Yumoto Seiji
Published: July 2002

In an atomic force microscope (AFM), it is possible to scan at high speeds without sacrificing resolution if the imaging is accomplished by combining the rapidly varying signal from the vibrating cantilever, which indicates the detailed surface features, with the more slowly varying feedback control signal to the piezotube. Scanning speed in this case is limited by the fundamental resonance of the cantilever—not, as in conventional AFM, by the feedback bandwidth—and about 10 s is required to image a surface area of 21 μm2 for 512×512 scanning points.
Deformation field in single-crystal fields semiconductor substrates caused by metallization features
Authors: Noyan I. C. , Wang P.-C. , Kaldor S. K. , Jordan-Sweet J. L.
Published: July 2002

The results of an x-ray microdiffraction study of the deformation field surrounding Ni thin film pads on a 111-type Si wafer are reported. The strain fields were mapped by measuring the Si 333 reflection intensities over an area containing several pads. The positions of the pads were simultaneously determined by recording the Ni Kα fluorescence as a function of position. The results indicate that, contrary to the results from analytical solutions and finite-element models, the position of maximum strain contrast is slightly outside the pad edge.
Tip–sample distance feedback control in a scanning evanescent microwave microscope
Authors: Duewer Fred , Gao C. , Takeuchi I. , Xiang X.-D.
Published: July 2002

We have developed a means of tip–sample distance regulation for a scanning evanescent microwave microscope over conductive samples. Changes in resonant frequency and quality factor are measured, where changes in resonant frequency are related to the tip–sample capacitance and changes in quality factor are related to microwave absorption. With the analytical expression of the tip–sample capacitance as a function of tip–sample distance, we can quantitatively regulate the tip–sample separation. We demonstrated simultaneous noncontact imaging of topography and surface resistance with high spatial resolution.
High-power on-chip microrefrigerator based on a normal- metal/insulator/superconductor tunnel junction
Authors: Fisher P. A. , Ullom J. N. , Nahum M.
Published: July 2002

We present measurements and theoretical modeling of two normal/insulator/superconductor tunnel junction microrefrigerators. The first device, fabricated on a thick silicon substrate, had a cooling power of 36 pW, an active volume of 350 μm3, and a temperature drop for electrons of 2 mK from a 300 mK bath. The second device, fabricated on a thin silicon nitride membrane, had a cooling power of 4 pW and cooled both electrons and phonons in a similar volume by almost 2 mK from a bath of 300 mK. These are the largest cooling powers and active volumes for electron and phonon refrigeration reported to date.
Site-selective x-ray absorption fine structure: Selective observation of Ga local structure in DX center of Al0.33Ga0.67As:Se
Authors: Ishii Masashi , Yoshino Yoko , Takarabe Ken-ichi , Shimomura Osamu
Published: July 2002

In order to discuss the local structure of deep level carrier traps, the site-selective x-ray absorption fine structure (XAFS) by measuring the x-ray photon-energy dependence of the capacitance of a Schottky barrier diode is proposed. Dropping of the localized electron into a core hole arising from x-ray absorption of the atom in the carrier trap, not in bulk, increases the capacitance. The site-selective XAFS is adopted for the local structure analysis of DX center in Al0.33Ga0.67As:Se. The Ga K-edge site-selective XAFS is different from the conventional XAFS, suggesting that Ga in the DX center with a large lattice relaxation is selectively observed.
Grazing-incidence-based hollow taper for infrared laser-to-fiber coupling
Authors: Ilev Ilko K. , Waynant Ronald W.
Published: July 2002

Based on grazing incidence, a simple uncoated hollow glass taper as an alternative technique for efficient infrared laser-to-fiber coupling is presented. Because of the mutual action of the direct parallel laser excitation, the mode-coupling process, and mode filtering, the hollow taper serves as a mode converter that transforms the highly multimode intensity distribution of the input laser emission into a high-quality smooth profile at the taper output. When an uncoated Pyrex-glass hollow taper is used for direct launching, without any intermediate focusing elements, of a powerful infrared Er:YAG laser emission (λ=2.94 μm), we obtain high laser-to-taper (81%), taper-to-fiber (96%), and total laser-to-fiber (78%) coupling efficiencies.
Optical and structural evidence of the grain-boundary influence on the disorder of polycrystalline CdTe films
Authors: Iribarren A. , Castro-Rodrı́guez R. , Caballero-Briones F. , Peña J. L.
Published: July 2002

We report the linear behavior of the band-tail parameter as a function of the reciprocal of the grain size in polycrystalline CdTe. On the other hand, the study of the full width at half maximum of the x-ray diffraction peak shows a similar behavior, which indicates that the disorder increases as grain size diminishes. A theoretical analysis justifies that the behavior is ruled by the contribution of the grain-boundary traps, and the trap concentration is calculated. Both results constitute experimental evidences of the grain-boundary disorder, which was quantified, and demonstrate that it is caused by the extension of the grain-boundary effect into the grain.
Cathodoluminescence spectroscopy and imaging of individual GaN dots
Authors: Petersson Anders , Gustafsson Anders , Samuelson Lars , Tanaka Satoru , Aoyagi Yoshinobu
Published: July 2002

Uncapped GaN dots on AlGaN barrier material, grown by metal organic chemical vapor deposition on 6H–SiC substrates, were studied. Cathodoluminescence (CL) microscopy and scanning electron microscopy (SEM) were used to investigate both luminescence and structure of individual GaN dots. The correlation between the luminescence and the actual position of self-assembled dots was demonstrated. The position of a dot was established with high resolution SEM and a CL image was used to display the corresponding luminescence. The spectrum from a single dot was obtained by positioning the electron beam on one particular dot. The luminescence from dots with a lateral size of 100 nm and a height of 40 nm was determined to be 3.47 eV.
Evaluation of strain and In content in (InGaN/GaN) multiquantum wells by x-ray analysis
Authors: Krost A. , Bläsing J. , Lünenbürger M. , Protzmann H. , Heuken M.
Published: July 2002

A comprehensive x-ray analysis including Θ–2Θ scans, reciprocal space mapping, and x-ray reflectivity of 10×(InGaN/GaN) multiple quantum wells (MQWs) is presented. The layers were grown by low-pressure metal–organic chemical-vapor deposition. The strain state and the In concentration in (InGaN/GaN) MQW systems are evaluated with the help of reciprocal space maps around the symmetric (0002) and asymmetric (101̄5) Bragg reflections. Depending on the In incorporation, the MQW system is fully strained, partially relaxed, or exhibits phase decomposition effects. The room-temperature photoluminescence emission energy of a fully strained 10×(In0.125Ga0.875N/GaN) MQW sample is 2.792 eV, which is 133 meV less than the calculated energy gap of 2.925 eV.
Enhanced coercivity of exchange-bias Fe/MnPd bilayers
Authors: Tang Y. J. , Roos B. , Mewes T. , Demokritov S. O. , Hillebrands B. , Wang Y. J.
Published: July 2002

We present detailed studies of the enhanced coercivity of exchange-bias bilayer Fe/MnPd, both experimentally and theoretically. We have demonstrated that the existence of large higher-order anisotropies due to exchange coupling between different Fe and MnPd layers can account for the large increase of coercivity in the Fe/MnPd system. The linear dependence of coercivity on inverse Fe thickness is well explained by a phenomenological model by introducing higher-order anisotropy terms into the total free energy of the system.
Room temperature manipulation of the heterofullerene C59N on Si(100)-2×1
Authors: Butcher M. J. , Jones F. H. , Moriarty P. , Beton P. H. , Prassides K. , Kordatos K. , Tagmatarchis N.
Published: July 2002

The absorption of the heterofullerene C59N on the Si(100)-2×1 surface has been investigated using scanning tunneling microscopy (STM) under ultrahigh vacuum conditions. The molecules are adsorbed in monomer form in the troughs between silicon dimer rows. It is possible to use the tip of the STM to manipulate the molecules parallel and perpendicular to the dimer rows in a controlled fashion at room temperature. To determine the stability of the C59N monomer we have examined the response of pairs of molecules to STM manipulation and found that the Si(100)-2×1 surface inhibits conversion to (C59N)2 dimers.
Photonic band engineering through tailored microstructural order
Authors: Ballato John , Dimaio Jeffrey , James Andrew , Gulliver Eric
Published: July 2002

Colloidal solids of monosized, solution-derived SiO2 were prepared under forced and unforced sedimentation conditions to tailor the level of particulate order. Photonic band gaps were observed in the blue part of the visible spectrum and their spectral shape is shown experimentally to correlate directly to the degree of long- and short-range particulate order. These results are discussed by analogy to the x-ray diffraction of crystals and glasses as is the practical applicability of “photonic glasses” with respect to the more widely studied “photonic crystals.”
Electrically tunable, room-temperature quantum-cascade lasers
Authors: Müller Antoine , Beck Mattias , Faist Jérôme , Oesterle Ursula , Ilegems Marc
Published: July 2002

Electrical tuning of two-section quantum-cascade lasers is systematically investigated as a function of temperature and optical power. In pulsed operation, the active region design exhibits a low threshold current density (5.2 kA/cm2), a high peak (100 mW), and average (3 mW) powers at 300 K. The strong linear Stark tuning of the laser transition allows large tuning ranges of 40 cm−1, corresponding to a wavelength tune from 9.75 to 10.15 μm at 260 K for a peak optical output power of 10 mW. The tuning range is still 20 cm−1 at the same optical output power at T=300 K.
Evidence from scanning tunneling microscopy in support of a structural model for the InSb(001)-c(8×2) surface
Authors: Davis A. A. , Jones R. G. , Falkenberg G. , Seehofer L. , Johnson R. L. , McConville C. F.
Published: July 2002

In this letter we present evidence from scanning tunneling microscopy studies in support of a recently proposed structural model for the indium-terminated c(8×2) surface of InSb(001). This structural model, by Norris and co-workers, is based on a surface x-ray diffraction study [Surf. Sci. 409, 27 (1998)], and represents a significant departure from previously suggested models for the c(8×2) reconstruction on any (001) surface of the common III–V semiconductor materials. Although filled state images of the InSb(001)-c(8×2) surface have previously been published, empty states image of sufficient quality to extract any meaningful information have not previously been reported. The observations are in excellent agreement with the recently proposed model for this surface reconstruction.
Spin-polarized scanning tunneling microscopy on ferromagnets
Authors: Wulfhekel Wulf , Kirschner Jürgen
Published: July 2002

A straightforward approach to spin-polarized scanning tunneling microscopy based on the magnetotunnel effect between a ferromagnetic tip and a ferromagnetic sample is demonstrated. By periodically changing the magnetization of the tip in combination with a lock-in technique, topographic and spin-dependent parts of the tunnel current are separated and the topography and the magnetic structure of the sample are recorded simultaneously. Results are given for polycrystalline Ni and single crystalline Co(0001) surfaces, revealing a high spin contrast, low data acquisition times, and a resolution down to 10 nm. Potentials and limitations of this technique are discussed.
Structure determination of a planar defect in SrBi2Ta2O9
Authors: Yan Y. , Al-Jassim M. M. , Xu Z. , Lu X. , Viehland D. , Payne M. , Pennycook S. J.
Published: July 2002

The atomic structure of a planar defect with a (001) habit plane in single crystal layered perovskite SrBi2Ta2O9 is determined by high-resolution Z-contrast imaging. We found that the defect forms a structure, with two Sr–Ta–O perovskite blocks connected by a metallic Sr2 plane, rather than a Bi2O2 layer as in the perfect crystal. This defect is expected to be an efficient hole trap and may have important implications for the electronic properties and the ferroelectric response of the SrBi2Ta2O9 material.
Enhanced harmonic generation in aperiodic optical superlattices
Authors: Gu Ben-Yuan , Dong Bi-Zhen , Zhang Yan , Yang Guo-Zhen
Published: July 2002

We find that harmonic generation can be enhanced with aperiodic optical superlattice (AOS) structures realized by inverting poled ferroelectric domains in sample. The optimal design of the AOS can be achieved with use of the simulated annealing method. The constructed AOSs can implement multiple wavelength second-harmonic generation and the coupled third-harmonic generation with an identical effective nonlinear coefficient. The simulations show that the constructed AOSs can enhance harmonic generation compared with the Fibonacci optical superlattice. The physical origin of this enhancement is ascribed to the constructive interference effect.
Optical and structural properties of InAs quantum dots in a GaAs matrix for a spectral range up to 1.7 μm
Authors: Maximov M. V. , Tsatsul’nikov A. F. , Volovik B. V. , Bedarev D. A. , Egorov A. Yu. , Zhukov A. E. , Kovsh A. R. , Bert N. A. , Ustinov V. M. , Kop’ev P. S. , Alferov Zh. I. , Ledentsov N. N. , Bimberg D. , Soshnikov I. P. , Werner P.
Published: July 2002

We demonstrate the possibility of extending the spectral range of luminescence due to InAs quantum dots (QDs) in a GaAs matrix up to 1.7 μm. Realization of such a long wavelength emission is related to formation of lateral associations of QDs during InAs deposition at low substrate temperatures (∼320–400 °C).
Observation of large-scale surface undulations due to inhomogeneous dislocation strain fields in lattice-mismatched epitaxial layers
Authors: Springholz G.
Published: July 2002

The surface structure of highly relaxed IV–VI heteroepitaxial layers is studied using scanning tunneling and scanning force microscopy. For bilayer structures consisting of highly relaxed EuTe layers covered by thick PbTe buffer layers, huge surface undulations with amplitudes as large as 50 Å are observed. These undulations are completely decoupled from the epitaxial surface step structure and can be observed even for rather large cap layer thicknesses. The deconvolution of the surface profiles shows that the surface undulations are purely caused by the nonuniform misfit dislocation network at the EuTe/PbTe interface. On the contrary, no indication is found that these dislocation strain fields give rise to surface structures formed by preferential growth.
Electron transport in the AlGaAs/InGaAs double-heterostructure pseudomorphic high-electron-mobility transistor
Authors: Gui Yongsheng , Guo Shaoling , Zheng Guozhen , Chu Junhao , Fang Xiaohua , Qiu Kai , Wang Xingwu
Published: July 2002

Variable magnetic-field Hall measurement has been used to investigate the transport properties in the double-heterostructure pseudomorphic high-electron-mobility transistor in the temperature range from 1.6 to 240 K. The experimental data have been analyzed by using a hybrid approach consisting of the mobility spectrum (MS) technique followed by a multicarrier fitting (MCF) procedure. Both the Shubnikov–de Haas measurements and the hybrid MS+MCF approach agree well with the theoretical calculations. The resulting temperature dependence of mobility and concentration for ground subbands and excited subbands shows that the excited subbands play an important role in the observed transport behavior.
The use of a surfactant (Sb) to induce triple period ordering in GaInP
Authors: Fetzer C. M. , Lee R. T. , Shurtleff J. K. , Stringfellow G. B. , Lee S. M. , Seong T. Y.
Published: July 2002

A surfactant is used to induce an ordered structure in an epitaxial layer. The addition of small amounts of triethylantimony during the organometallic vapor phase epitaxy growth of GaInP on (001) GaAs substrates is shown to remove CuPt ordering with a resultant increase in band gap energy. Increasing the concentration of Sb in the vapor beyond a critical Sb to P ratio [Sb/P(v)] of 4×10−4 gives a reversal of this behavior. The band gap energy is observed to decrease by 50 meV at a concentration of Sb/P(v)=1.6×10−3, coincident with the formation of an ordered phase with a period triple the normal lattice spacing along the [111] and [1̄1̄1] directions. The formation of this new ordered structure is believed to be related to high concentrations of Sb on the surface, which leads to a change in the surface reconstruction from (2×4)-like to (2×3)-like, as indicated by surface photoabsorption performed in situ.
Electron emission from thin-film ferroelectric cathodes
Authors: Liu F. , Fleddermann C. B.
Published: July 2002

Electron emission from thin-film (<1 μm thick) ferroelectric cathodes has been investigated. The cathodes were made using sol-gel deposition and standard microelectronic patterning techniques and were excited using either dc or pulsed bias. Repeatable emission current densities up to 10 μA/cm2 were measured from 0.8-μm-thick lead-niobium-zirconium-titanate cathodes driven in the pulsed mode with switch voltages up to 22 V. Intermittent emission up to 20 mA/cm2 was measured for higher switch voltages. The dependence of emission current on switch voltage, grid dimensions, and extraction voltage will be presented.
Origin of the nonradiative 〈112̄0〉 line defect in lateral epitaxy-grown GaN on SiC substrates
Authors: Hacke P. , Domen K. , Kuramata A. , Tanahashi T. , Ueda O.
Published: July 2002

Nonradiative line defects are observed by cathodoluminescence in 〈2̄110〉 directions in [11̄00]-oriented GaN stripes grown by lateral epitaxy on SiC substrates. Using transmission electron microscopy, the origin is determined to be principally screw dislocations. We observe the screw dislocations in vertically [0001] stacked configurations and forming dislocation loops and half loops contained in two of the three planes of the form {11̄00}. The dislocations are believed to serve to relax the anisotropic stresses experienced in the lateral epitaxy-overgrown stripes.
Resistless pattern definition and Si selective-area deposition using an ultrathin SiO2 mask layer treated by SiHCl3
Authors: Yasuda T. , Nishizawa M. , Yamasaki S.
Published: July 2002

We report a selective-area deposition process using an ultrathin SiO2 mask on which SiHCl3 is chemisorbed. The key step of this process is resistless pattern definition utilizing electron-stimulated desorption (ESD) of Cl and Cl-containing groups from the mask surface. Compared to the previous report utilizing ESD of O from SiO2, sensitivity to the incident electron beam has been improved by a factor exceeding 104. Selective-area deposition of Si on the Cl-desorbed regions is demonstrated using an Si2H6 source gas.
Laser-assisted scanning tunnelling microscope detection of a molecular adsorbate
Authors: Smith D. A. , Owens R. W.
Published: July 2002

Optical excitation has been combined with the scanning tunneling microscope and a laser-induced change in the tunneling gap width of about 0.25 Å, shows a resonance effect with the electronic absorption of the sample, a monolayer of the J-aggregating dye 1,1′-diethyl-2,2′-cyanine bromide on a silver substrate. The strength of the effect is reduced by spacing the J aggregate away from the silver substrate using a carboxylic acid functionalized alkylthiol self-assembled monolayer. We propose that the origin of the resonant response is the nonradiative decay of the molecular excited state into the underlying metal substrate that causes local heating and thermal expansion.
Two-dimensional theory of chirality. II. Relative chirality and the chirality of complex fields
Authors: Le Guennec Patrick
Published: July 2002

Chirality can equally be correctly viewed as a dichotomous symmetry property, as in Kelvin’s historical conception, and as a continuous phenomenon. This highly paradoxical result is proved, in this and the previous article (I) [Le Guennec, J. Math. Phys. 41, 5954 (2000)], in the case of the basic ingredient of quantum mechanics, square-integrable (L2) wave functions. In the continuous conception, chirality appears as the combination of two complementary forms—absolute and relative chirality. Accordingly, while (I) focused on the conceptual issue and on the 2D theory of absolute chirality, this article focuses on 2D relative chirality. We show that relative chirality is a continuous phenomenon described by relative radial functions and relative chiral loops whose features are surprisingly close to those of their absolute counterparts. This is illustrated on a 2D model of cis-trans isomerism. We then show that chirality as such is the “addition” of absolute and relative chirality just as a vector is the addition of its projection on a basis. As a test of versatility, the continuous conception of chirality is extended to 2D complex fields and Fourier transforms. Why this conception of chirality is possible in L2 spaces is tentatively discussed.
Conversion of red light into green light in LiTaO3:Ho
Authors: Ryba-Romanowski W. , Dereń P. J. , Gołąb S. , Dominiak-Dzik G.
Published: July 2002

Intense green luminescence associated with the S25–5I8 transition of Ho3+ in holmium doped LiTaO3 crystals has been excited at room temperature and at 15 K by a 647.1 nm line of a krypton ion laser. Based upon the analysis of excited states relaxation dynamics and of the rise of upconverted luminescence it is concluded that the mechanism involved is an excited state absorption from the long lived I75 level. Efficient single wavelength excitation of upconverted luminescence in LiTaO3:Ho is due to the advantageous coincidence of transition energies of the ground and excited state absorptions.
Experimental analysis of mode coupling and plasma turbulence induced by magnetic fields
Authors: Ferreira A. A. , Heller M. V. A. P. , Caldas I. L.
Published: July 2002

Wavelet spectrum and bispectrum techniques are applied to study the development of temporal turbulence induced by a confinement toroidal magnetic field in a toroidal magnetoplasma created by radio frequency waves. For low magnetic fields the plasma is roughly uniform and the analyzed electrostatic linear frequency spectra are essentially determined by the driven radio frequencies. However, by increasing the toroidal magnetic field, gradients in the plasma radial profiles and broader frequency spectra are observed. Thus, spectral components with frequencies higher than those injected in the plasma are excited. Moreover, this variation of magnetic field also induces nonlinear phase coupling between low frequency coherent peaks and continuous high frequency spectral components.
Study of space charge layer in silver bromide microcrystals by means of ultraviolet photoelectron spectroscopy
Authors: Tani Tadaaki , Inami Yoshiyasu
Published: July 2002

Ultraviolet photoelectron spectroscopy has been successfully used to measure the heights of the tops of the valence bands of the surfaces of AgBr layers on Ag substrates for the verification of the space charge layer model. According to this model, the positive space charge layer (composed of negative charges with excess negative kink sites on the surface and corresponding positive charges with interstitial silver ions in the interior) is formed in silver halides, causing the difference in the electronic energy levels between their surface and interior. The depression of the positive space charge layer of AgBr caused by such adsorbates as photographic stabilizers and antifoggants was estimated from the decrease in the ionic conductivity of cubic AgBr microcrystals by the adsorbates. It was confirmed by the decrease in the heights of the tops of the valence bands of the surfaces of AgBr layers caused by the adsorbates in the presence of thin gelatin membranes on their surfaces. This result provided the explanation for the fact that the adsorbates increased the number of the microcrystals which formed latent image centers on the surface and decreased the number of the microcrystals, which formed latent image centers in the interior.
On the decomposition of the modified Kadomtsev–Petviashvili equation and explicit solutions
Authors: Dai H. H. , Geng Xianguo
Published: July 2002

The (2+1)-dimensional modified Kadomtsev–Petviashvili equation is decomposed into two known (1+1)-dimensional soliton equations. A Darboux transformation of the two known (1+1)-dimensional soliton equations is derived with the help of a gauge transformation of the spectral problem. As an application, explicit solutions of the two (1+1)-dimensional soliton equations and two new explicit solutions of the (2+1)-dimensional modified Kadomtsev–Petviashvili equation are obtained.
Argon scattering from liquid indium: Simulations with embedded atom potentials and experiment
Authors: Chase D. , Manning M. , Morgan J. A. , Nathanson G. M. , Gerber R. Benny
Published: July 2002

An embedded-atom type potential for liquid indium is developed by fitting bulk liquid thermodynamic and structural data. An empirical pairwise Ar–In interaction is also proposed. Molecular-dynamics simulations of argon scattering from liquid indium are carried out and compared with molecular beam scattering data. Very good agreement is found between the experimental and theoretical angular and energy scattering distributions. This supports the potential functions used. Implications for the atomic-scale structure of liquid In and for gas–surface energy transfer are briefly discussed.
Dual WDVV equations in N=2 supersymmetric Yang–Mills theory
Authors: Ohta Yűji
Published: July 2002

This paper studies the dual form of Witten–Dijkgraaf–Verlinde–Verlinde (WDVV) equations in N=2 supersymmetric Yang–Mills theory by applying a duality transformation to WDVV equations. The dual WDVV equations called in this paper are nonlinear differential equations satisfied by dual prepotential and are found to have the same form with the original WDVV equations. However, in contrast with the case of weak coupling calculus, the perturbative part of dual prepotential itself does not satisfy the dual WDVV equations. Nevertheless, it is possible to show that the nonperturbative part of dual prepotential can be determined from dual WDVV equations, provided the perturbative part is given. As an example, the SU(4) case is presented. The nonperturbative dual prepotential derived in this way is consistent to the dual prepotential obtained by D’Hoker and Phong.
Surface roughness measurement on microchannels by atomic force microscopy using a bent tapered fiber probe
Authors: Chen Sy-Hann , Lin Heh-Nan , Yang Chii-Ron
Published: July 2002

We demonstrate a high-resolution and nondestructive surface roughness measurement on microchannels by atomic force microscopy with the use of a bent tapered optical fiber probe. The probe was fabricated by a combination of laser heating-pulling and electric arc bending. Microchannels with a width of 41.5 μm and a height of 31.9 μm were fabricated on polycarbonate by excimer laser ablation and the resultant roughness was measured to be 4.8 nm.
Two-dimensional, highly directive currents on large circular loops
Authors: Margetis Dionisios , Fikioris George
Published: July 2002

Properties of idealized, two-dimensional current distributions on circular loops are investigated analytically via the solution of a constrained optimization problem. The directivity in the far field is maximized under a fixed C=N/T, where N is the integral of the square of the current magnitude and T is the total radiated power. C enters the ensuing Fourier series for the current implicitly through a Lagrange multiplier α. For non-negative α and large electrical radius ka, the directivity and the current are evaluated approximately via combined use of the Poisson summation formula and the Mellin transform technique. As a result, a geometrical-ray representation for the current is derived for the case of directivities that are slightly larger than that of the uniform distribution. The analysis indicates certain advantages of large radiating structures for moderate values of the constraint C. In the limit C→∞ of Oseen’s “Einstein needle radiation,” an asymptotic formula for the directivity is obtained. Possible extensions of these results to classes of smooth convex loops are briefly discussed.
Photonic band gap structure and transmissivity of frequency-dependent metallic–dielectric systems
Authors: Keskinen M. J. , Loschialpo P. , Forester D. , Schelleng J.
Published: July 2002

The complex photonic band gap (PBG) structure of frequency-dependent metallic–dielectric systems, using actual measured values for index of refraction, has been computed using nonlinear numerical techniques. Transmissivity and reflectivity were also computed and compared with the PBG structure. For application to PBG systems consisting of alternate layers of Ag and MgF2 over a range of frequencies from the near ultraviolet to the near infrared, we find that features of the PBG structure, transmissivity, and reflectivity are distinctly different from those computed using the Drude model. These features include plasma resonant structure not included in the Drude model.
Elastic deformation of wafer surfaces in bonding
Authors: Han Weihua , Yu Jinzhong , Wang Qiming
Published: July 2002

A model has been proposed for describing elastic deformation of wafer surfaces in bonding. The change of the surface shape is studied on the basis of the distribution of the periodic strain field. With the condition of diminishing periodic strain away from the interface, Airy stress function has been found that satisfies the elastic mechanical equilibrium. The result reveals that the wavy interface elastically deforms a spatial wavelength from the interface.