bluuebunny/crossref_metadata_2025 huggingface dataset:
Use of a PVDF pyroelectric sensor for beam mapping and profiling of a mid-infrared diode laser
Authors: Toci G. , Mazzoni M. , Mazzinghi P.
Published: July 2002

A four-quadrant PVDF position sensor, originally designed for the alignment of mid-IR laser diodes beams, was also used for mapping and profiling the beam of a diode laser emitting few μW at 5.8 μm, by masking one quadrant with a 1 mm diameter pinhole or a 100 μm width slit. This diagnostic system was used to optimize the laser collimating optics, determining a significant improvement in the spatial quality of the output beam, evaluated by means of the M2 propagation factor. Since the laser diode modulation waveform required to optimize the pyroelectric detector responsivity is a fixed frequency square wave, quite different from that used in the normal spectroscopic application of the IR diodes, care was taken to have the same single-mode emission in the wavelength range of interest. The system was intended as a diagnostic and optimization tool for spectroscopic systems applied to environmental monitoring, but it may be used as a low cost device for the characterization of low power laser beams.
High precision polarimeter system for atomic polarization and tilted-foil experiments with 1.7 keV/amu N+14 beam
Authors: Shimizu S. , Doumoto E. , Tanimoto S. , Nakamura M. , Hirayama Y. , Horie K. , Shigematsu T. , Izumi H. , Shimoda T. , Takahashi N.
Published: July 2002

A high precision atomic polarimeter system for the use in beam-foil spectroscopy experiments with a few keV/amu heavy-ion beams has been developed. The polarimeter measures the circular polarization of fluorescences from the beam ion in-flight after the beam–foil interaction. The present system has two identical such polarimeters in both sides of the beam axis to reduce the systematic errors such due to the fluctuations of beam current, background and so on. A successful use of an ultrathin carbon foil (1.5 μg/cm2), which was durable for several hours against a few hundred nA beam irradiation, enabled the beam–foil experiments with such low energy heavy-ion beams. A performance test of the polarimeter system was carried out in the tilted foil experiments with a 1.7 keV/amu N+14 beam. The atomic polarization was observed for the transition 1s22s22p3p 1D→1s22s22p3p 1P, whose fluorescence wavelength is 399.5 nm, in the N+ ion (N II). The polarization was approximately −2% for the tilt angle of −40° and showed monotone increasing with increasing tilt angle up to +2% for +40°. The polarization at 0° was (0.002±0.25)%, which is highly consistent with the expected polarization of 0%. This result indicates the high reliability of the present polarimeter system. This is the first tilted-foil experiment at such low beam energy. The present experimental technique will be very useful for studies of the polarization mechanism of the beam–foil interaction.
Production of metal oxide thin films by pulsed arc molecular beam deposition
Authors: Rexer Eric F. , Wilbur Donald B. , Mills Jeffrey L. , DeLeon Robert L. , Garvey James F.
Published: July 2002

Deposition for the first time of titanium oxide, cerium oxide, and tin oxide thin films by reactive pulsed arc molecular beam deposition is reported. To produce these thin films, oxygen gas was pulsed between a pair of electrodes situated within a vacuum chamber. A 20 μf storage capacitor was discharged between the electrode pair during the gas pulse. A substrate was placed inline with the oxygen pulse, on which an oxide coating of the electrode material was then coated. The films were analyzed by both scanning electron microscopy and electron spectroscopy for chemical analysis. There was a noted strong dependence of the film surface quality on the melting temperature of the starting electrode material.
Crystal-orientation dependence on magnetic circular dichroism spectra of MnSb epitaxial film
Authors: Akinaga H. , Suzuki Y. , Tanaka K. , Ando K. , Katayama T.
Published: July 2002

We present the crystal-orientation dependence of the magnetic circular dichroism (MCD) spectra of ferromagnetic (11̄01) and (0001) MnSb epitaxial films grown by molecular beam epitaxy on (001) GaAs and (0001) sapphire substrates, respectively, where very large anisotropy is clearly observed at around 3.0 and 4.7 eV. The anisotropy of the MCD spectra is discussed in connection with the magnetocrystalline anisotropy.
On the CdS/CuInSe2 conduction band discontinuity
Authors: Niemegeers Alex , Burgelman Marc , De Vos Alexis
Published: July 2002

Recent calculations of the electron affinity difference between CdS and CuInSe2 indicate that the conduction band (CB) minimum of CuInSe2 is below the CB minimum of CdS. As a consequence, a spike occurs in the CB at the CdS/CuInSe2 interface. Such a spike is commonly considered as in conflict with good photovoltaic performance of heterojunction solar cells. It is outlined here that the simple assumption of thermionic emission across the junction can explain an unimpeded electron transport in the case of an n+p structure (n-type window, p-type absorber), even when a spike in the CB occurs.
Piezoelectric field effects in InGaAs (111)B quantum wells
Authors: Chen X. , Molloy C. H. , Woolf D. A. , Cooper C. , Somerford D. J. , Blood P. , Shore K. A. , Sarma J.
Published: July 2002

Strained In0.21Ga0.79As/GaAs quantum well structures have been grown by molecular beam epitaxy on (111)B GaAs substrates. Well widths between 20 and 160 Å, separated by 500 Å barriers were grown sequentially on the same substrate and subsequently characterized by low-temperature (10 K) photoluminescence. The variation of the e-hh transition energy with well width is markedly different for samples grown simultaneously on (100) and (111)B substrates due to the strain induced piezoelectric field. Using the envelope function approximation, the dependence of n=1 e-hh transitions of (111)B samples on well width can be interpreted by the presence of a built-in electric field of magnitude of 1.45×107 V/m. In contrast to the (100) sample, exciton lifetimes in the (111)B sample depend strongly on well width because of spatial separation of electrons and holes in the triangular wells. In the 160 Å well, the exciton lifetime increases to 755 ns corresponding to a reduction of about three orders of magnitude in the electron-hole wave function overlap integral.
Vanishing optical isolation barrier in double ion-implanted lithium niobate waveguide
Authors: Sarkisov S. S. , Williams E. K. , Ila D. , Venkateswarlu P. , Poker D. B.
Published: July 2002

Isolation properties at different propagation directions have been studied for an optical barrier between two superposed planar waveguides produced by MeV He+ implantation in LiNbO3. The barrier exists while the modes of the double structure propagate along the optic axis. The spacing between the modes measured with a prism coupler features efficiently isolated waveguides. The barrier ‘‘vanishes’’ when the directional angle between an extraordinary wave and the optic axis exceeds 50°. In this case the mode spacing shows strong coupling between the waveguides that makes the double structure similar to a single waveguide with double thickness.
Stress dependence of coercivity in Ni films: Thin film to bulk transition
Authors: Callegaro Luca , Puppin Ezio
Published: July 2002

The effect of uniaxial mechanical stress on the magnetic properties of electroplated Ni films was measured with a magneto-optical Kerr loop tracer. We show that the effect of stress on the coercive force is completely different for thin (20 nm) and thick (10 μm) films. The latter behaves like bulk Ni, whereas results on lower thicknesses show a continuous transition from thin film to bulklike behavior. The results are discussed by assuming different micromagnetic reversal processes for the two extremes: rotational for thin film and domain wall movement for bulk.
Electroabsorption measurements and built-in potentials in amorphous silicon p–i–n solar cells
Authors: Jiang Lin , Wang Qi , Schiff E. A. , Guha S. , Yang J. , Deng Xunming
Published: July 2002

We present a technique for using modulated electroabsorption measurements to determine the built-in potential in semiconductor heterojunction devices. The technique exploits a simple relationship between the second-harmonic electroabsorption signal and the capacitance of such devices. We apply this technique to hydrogenated amorphous silicon (a-Si:H)-based solar cells incorporating microcrystalline Si p+ layers. For one set of cells with a conventional plasma-deposited intrinsic (i) layer we obtain a built-in potential of 0.98±0.04 V; for cells with an i layer deposited using strong hydrogen dilution we obtain 1.25±0.04 V. We speculate that interface dipoles between the p+ and i layers significantly influence the built-in potential.
Gain dispersion induced subpicosecond pulse breakup in a fiber and semiconductor laser amplifier combined system
Authors: Kao Y.-H. , Goltser I. V. , Jiang M. , Islam M. N. , Raybon G.
Published: July 2002

We observe pulse breakup for 650-fs pulses propagating through 9 m of optical fiber followed by an InGaAsP amplifier. The pulses are broadened by a factor of two, and a second peak appears at about 2 ps after the main peak. To identify the responsible mechanisms, we solve numerically the propagation equations including nonlinear carrier dynamics and gain dispersion. We attribute the broadening to two photon absorption and the breakup to the interplay between linear gain dispersion and frequency chirp in the amplifier. These pulse distortions could impact devices involving fibers and semiconductor amplifiers for high speed (>200 Gb/s) optical switching or transmission.
Measurement of elastic force on a scanned probe near a solid surface
Authors: Drummond Roby M. A. , Wetsel G. C.
Published: July 2002

The physical nature of the forces acting between a laterally vibrating probe in air near a solid surface has been investigated using a calibrated method for the experimental determination of dynamic force. The frequency response of the probe vibrating near its fundamental bending resonance was measured as a function of distance as the probe approached the surface. The experimental results were compared with a continuum-mechanical model of bending waves in a rod; the nature of the forces was inferred by determining the effect of various boundary conditions on the standing-wave motion of the probe. The results conclusively show that while in the initial stage of approach the force is dominated by fluid-dynamic effects, in the final stage of approach an elastic force appears. The appearance of the elastic deformation is characterized by a shift in the resonant frequency of the vibrating probe.
Preparation and properties of an organic light emitting diode with two emission colors dependent on the voltage polarity
Authors: Mori Tatsuo , Obata Kouji , Imaizumi Kaname , Mizutani Teruyoshi
Published: July 2002

We developed an organic light emitting diode (LED) that emits orange light at the forward bias (ITO anode and Al cathode) and green light at the reverse bias (ITO cathode and Al anode). The organic LED has a triple layer structure where an emission layer with different doped guest dye on each side is interposed between two hole transport layers. Its brightness, maximum 20 cd/m2 was not strong because electrons are blocked by the hole transport layer near the cathode. However, the EL efficiency (lm/W) for the reverse bias was 13 times higher than that for the forward bias.
Coherent electron–hole correlations in quantum dots
Authors: Jönsson Lars , Steiner Matthew M. , Wilkins John W.
Published: July 2002

Using numerical time propagation of the electron–hole wave function, we demonstrate how various coherent correlation effects can be observed by laser excitation of a nanoscale semiconductor quantum dot. The lowest-lying states of an electron–hole pair, when appropriately excited by a laser pulse, give rise to charge oscillations that are manifested by beatings in the optical or intraband polarizations. A GaAs 5×25×25 nm3 dot in the effective-mass approximation, including the screened Coulomb interaction between the electron and a heavy or light hole, is simulated.
Thermoluminescence of ZnS nanoparticles
Authors: Chen Wei , Wang Zhanguo , Lin Zhaojun , Lin Lanying
Published: July 2002

The thermoluminescence (TL) of ZnS nanoparticles is reported. The TL intensity increases as the particle size is decreased. The consistency of the size dependence of the TL with that of the surface fluorescence indicates that the TL may be related to the surface states. TL may be caused by the recombination of carriers released from the surface states or defect sites by heating. Smaller particles have higher surface/volume ratio and more surface states, therefore contain more accessible carriers for TL. Besides, the carrier recombination rate increases upon decreasing size due to the increase of the overlap between the electron and hole wave functions. These two effects may make the TL increase upon decreasing size of the particles. The appearance of TL prior to any radiation reveals that trapped carriers have pre-existed. The investigation of TL may provide some useful information about the surface states that may explain the size dependence of the surface fluorescence.
Gas-condensation synthesis of nanocrystalline BaTiO3
Authors: Li Shaoping , Eastman Jeffrey A. , Thompson Loren J.
Published: July 2002

Nanocrystalline BaTiO3 has been prepared by a gas-condensation process. BaTiO3 and Ti sources are vaporized simultaneously in either a helium or an oxygen environment using an electron beam evaporation system. The stoichiometry of nanocrystalline BaTiO3 powders can be controlled precisely and reproducibly. Nanocrystalline BaTiO3 powders, with an average particle size of less than 20 nm, can be obtained by postannealing the as-evaporated powders at a temperature of 700 °C. These powders show good sintering behavior with a high density at a sintering temperature as low as 1250 °C. Differential thermal analysis indicated that nanocrystalline BaTiO3was formed through the reaction of Ba/Ti oxidized clusters. Dielectric properties of ceramics from nanocrystalline BaTiO3 are also reported.
On the single domain nature of stoichiometric LiNbO3 grown from melts containing K2O
Authors: Bermúdez V. , Dutta P. S. , Serrano M. D. , Diéguez E.
Published: July 2002

Stoichiometric crystals of LiNbO3 were grown by the Czochralski technique from a congruent melt with 6 wt% of K2O flux dopant. The crystals were always single domain irrespective of the seed history. Analysis of the domain structure at the seed-crystal boundary reveals a domain inversion in certain cases. During crystal growth, self-poling of initially unpoled congruent LiNbO3 seeds was observed. It is thought that the monodomain nature of the crystals is attributed to the reduction of native defects due to their stoichiometric Li-Nb composition.
Photoluminescence of CuInS2 thin films and solar cells modified by postdeposition treatments
Authors: Töpper K. , Bruns J. , Scheer R. , Weber M. , Weidinger A. , Bräunig D.
Published: July 2002

The photoluminescence of CuInS2 thin films and solar cells is investigated as a function of postdeposition treatments for different temperatures and excitation intensities. Annealing in hydrogen atmosphere causes an increase of PL intensity at 1.445 eV by more than a factor of 100, while subsequent annealing in oxygen or air ambient passivates this transition, which is ascribed to a donor-acceptor pair recombination between a sulphur vacancy and a copper vacancy. A defect mechanism is suggested that assumes the passivation of sulphur vacancies by oxygen in grain surfaces which can be activated by hydrogen annealing.
Study of surface-emitted stimulated emission in GaN
Authors: Bidnyk S. , Schmidt T. J. , Park G. H. , Song J. J.
Published: July 2002

We report the results of a study of spatially resolved surface-emitted stimulated emission in GaN epilayer samples under conditions of strong optical pumping. We observe that even at excitation powers near the damage threshold, no surface-emitted stimulated emission occurs from samples with a high quality GaN epilayer. In parts of the samples with inferior surface quality, we show that stimulated emission comes from cracks, burned spots, and other imperfections, and is due to the scattering of a photon flux propagating parallel to the surface. Our results suggest that these defects are effective scattering centers and can severely affect the accuracy of optical gain measurements.
The composition and structure of InGaAs/InAlAs interfaces at the monatomic scale
Authors: Mountjoy G. , Crozier P. A. , Fejes P. L. , Tsui R. K. , Kramer G. D.
Published: July 2002

We have applied high-resolution chemical imaging in a transmission electron microscope to study compositional variations across an InGaAs/InAlAs double quantum well structure in the (100) orientation. The structures of interest are grown on an InP support and consist of two 40 Å layers of InGaAs separated by 20 Å of InAlAs. For this (InGa)x(InAl)1−xAs system, we have obtained compositional information with an accuracy of about 20% and a maximum spatial resolution of 1/4 unit cell. The results clearly show compositional irregularities on a monatomic scale.
Correlation between the signs of the magnetoresistance and of the interlayer coupling in MnGa/(Mn,Ga,As)/MnGa trilayers
Authors: Van Roy W. , Akinaga H. , Miyanishi S. , Asamitsu A.
Published: July 2002

A correlation is found between the sign of the magnetoresistance ΔR=(RP−RAP) and the sign of the interlayer coupling in MnGa/(Mn,Ga,As)/MnGa trilayers (subscript P, AP=parallel, antiparallel magnetic alignment of both MnGa layers). Ferromagnetic coupling results in ΔR<0, antiferromagnetic coupling results in ΔR>0. This correlation has not been observed before and can not be explained by the usual model for giant magnetoresistance in magnetic multilayers.
Growth and structural characterization of highly oriented sputter-deposited (111), (110), and (100) Co/Cu superlattices
Authors: Smith David J. , Modak A. R. , Rabedeau T. A. , Parkin S. S. P.
Published: July 2002

Highly oriented, sputter-deposited (111), (110), and (100) Co/Cu superlattices have been grown simultaneously on substrates of Al2O3 (sapphire), MgO (110), and (100), respectively, using thin seed layers of Pt or Pd deposited at ∼500 °C. High-resolution electron microscopy and x-ray scattering demonstrate that the films are epitaxial and of excellent crystallinity.
Surface second-harmonic generation from two interfaces of polyimide film coated on a substrate
Authors: Sakai Takahiro , Yoo Jeong-Geun , Kinoshita Yoshitaka , Ishikawa Ken , Takezoe Hideo , Fukuda Atsuo , Nihira Takayasu , Endo Hideyuki
Published: July 2002

Side chain orientation of polyimide (PI) films for liquid crystal alignment has been studied by surface second-harmonic generation (SHG). SHG from two interfaces of the film was separately observed using thick films, in which SH light from the rear interface was almost absorbed in the film. For as-coated films, the average tilt angle of the side chain at the air-PI interface is smaller than that of the other interface. Rubbing action caused in-plane anisotropy only for the air-PI interface. The distribution function of the side chain of the rubbed PI film was also discussed.
Removal of thin layer for trace element analysis of solid surface in subnanometer scale using laser-ablation atomic fluorescence spectroscopy
Authors: Oki Yuji , Matsunaga Kenji , Nomura Takumi , Maeda Mitsuo
Published: July 2002

Laser-ablation atomic fluorescence (LAAF) spectroscopy has extremely high sensitivity in the analysis of trace elements. Using the ArF laser-ablation technique at a wavelength of 193 nm, removal of thin surface layer of the order of 1.1 nm/shot for the first 50 shots and 0.4 nm/shot after that is demonstrated for a solid glass sample. A constant fluorescence signal from Na atoms is obtained for each shot. There is a possibility of determining the depth distribution of an element with subnanometer resolution by applying LAAF spectroscopy.
High performance ZnSTe photovoltaic visible-blind ultraviolet detectors
Authors: Sou I. K. , Man C. L. , Ma Z. H. , Yang Z. , Wong G. K. L.
Published: July 2002

ZnS 1−x Te x -based Schottky photodiodes have been fabricated on various substrates using the molecular beam epitaxy technique. The photovoltage output of these photovoltaic devices is determined using Fourier transform interferometric spectroscopy. The results show that these devices (with Te<10%) are highly sensitive in the ultraviolet but are visible blind. An external quantum efficiency of over 50% has been achieved on a device grown on a GaP substrate and over 40% on a Si substrate.
Linewidth and underlayer influence on texture in submicrometer-wide Al and AlCu lines
Authors: Hurd J. L. , Rodbell K. P. , Gignac L. M. , Clevenger L. A. , Iggulden R. C. , Schnabel R. F. , Weber S. J. , Schmidt N. H.
Published: July 2002

The local texture in three types of patterned, thin-film, Al and AlCu interconnections on Si semiconductor devices is investigated by electron backscatter diffraction. Two types of standard planar metal structures were investigated: (1) blanket Al and (2) blanket Al–0.5 wt % Cu on TiN/Ti underlayers. Both were deposited on amorphous SiO2 substrates followed by reactive ion etching to define 0.45–10 μm wide lines and >10×10 μm2 pads. Damascene structures were also investigated in which Al–0.5 wt % Cu films were deposited into preformed Ti-lined amorphous SiO2 trenches, 0.3–5.0 μm wide by 0.4 μm deep, followed by chemical–mechanical polishing to remove the metal overburden. For these three types of structures, distinctly different behaviors were observed: the two planar metal samples exhibited either little change or a large increase in their (111) fiber texture strength with decreasing linewidth, while the damascene samples showed a marked decrease in the (111) fiber texture with decreasing linewidth and feature size. In addition, a novel trimodal (111) texture distribution was found in 0.3 μm wide damascene lines in which appreciable TiAl3 formed.
In situ infrared ellipsometry study of hydrogenated amorphous carbon/Si interface formation
Authors: Heitz T. , Drévillon B. , Bourée J. E. , Godet C.
Published: July 2002

The early stages of the growth of plasma-deposited hydrogenated amorphous carbon films on c-Si have been studied by in situ infrared ellipsometry. Different types of polymeric films have been obtained under soft plasma conditions. From the evolution of optical properties, a uniform growth is observed for films having the highest sp2 carbon atom content. In contrast, when the film bulk is a highly saturated polymer, where carbon configurations are mostly sp3, an interlayer of about 20 Å is evidenced, correlated with the formation of sp2 CHn bonds. Moreover, infrared data tend to prove that this interlayer formation is incompatible with the presence of SiC at the interface.
Temporal solitary subpicosecond pulse propagation in a dye-doped polymer slab waveguide with a negative nonlinear refractive index
Authors: Yamakawa Shiro , Hamashima Keigo , Kinoshita Takeshi , Sasaki Keisuke
Published: July 2002

Subpicosecond (150 fs) temporal solitary pulse propagation is observed in an azo-dye-Disperse Red 1 doped (DR1) polymer waveguide. The negative nonlinear refractive index enables the generation of bright soliton in the medium with positive group velocity dispersion. Moreover, the pulse narrowing up to 97 fs based on the high-order soliton is observed. The magnitude of the nonlinear refractive index of the DR1-doped PMMA (poly[methyl methacrylate] film is estimated by cross-correlation measurement and the assumption-free pulse-form retrieval technique.
Light-coupling masks for lensless, sub-wavelength optical lithography
Authors: Schmid Heinz , Biebuyck Hans , Michel Bruno , Martin Olivier J. F.
Published: July 2002

Light-coupling masks (LCMs) based on structured organic polymers that make conformal contact with a substrate can constitute an amplitude mask for light-based lithographies. The LCM is exposed through its backside, from where the light is differentially guided by the structures towards the substrate. Images of arbitrarily shaped features having dimensions much smaller than that of the vacuum wavelength of the exposing light are formed in the resist in a 1:1 correspondence to their size in light-guiding portions of the mask. LCMs allow pattern replication at high resolution and densities over large areas in photoresist without the need for elaborate projection optics.
Quantum confined Stark effect of II-VI heterostructures suitable as modulators in the blue–green spectral region
Authors: Michler P. , Lilienkamp T. , Ebeling W. , Gutowski J. , Behringer M. , Fehrer M. , Hommel D.
Published: July 2002

We present a systematic and quantitative investigation of the quantum confined Stark effect in (Zn, Cd)Se/Zn(S,Se) quantum well structures at room temperature. For this purpose, differential transmission spectroscopy is performed on two samples with different thicknesses of the active layers (4×5 nm and 10 nm) and compared to model calculations. We observe a Stark shift of 18 meV in the heavy-hole exciton peak for an electric-field change from 82 to 175 kV/cm for the 4×5 nm sample. In contrast, the 10 nm sample shows a rather weak and more Franz–Keldysh-like signal. Furthermore, we have analyzed the spectral behavior of the linewidth enhancement factor αH. Values between 5.1 and 0.2 are found at the energy of absolute maximum of the absorption change for the 4×5 nm sample.
Heterodyning scheme employing quantum interference
Authors: Khurgin Jacob B. , Saif Babak , Seery Bernard
Published: July 2002

We propose a method of heterodyne detection of far-infrared signals using quantum interference between one- and two-photon absorption. We suggest different implementations of the scheme using multiple quantum well detectors and evaluate its sensitivity.
Strain and defect microstructure in ion-irradiated GeSi/Si strained layers as a function of annealing temperature
Authors: Glasko J. M. , Elliman R. G. , Zou J. , Cockayne D. J. H. , Fitz Gerald J. D.
Published: July 2002

High-energy (1 MeV), ion irradiation of GeSi/Si strained layers at elevated temperatures can cause strain relaxation. This study examines the defects responsible for relaxation and for the evolution of the strain during subsequent annealing. Three distinct annealing stages are identified and correlated with the defect microstructure. In the temperature range from 350 to 600 °C, a gradual recovery of strain is observed. This is shown to correlate with annealing of small defect clusters and the growth of voids. The voids are visible at annealing temperatures in excess of 600 °C, consistent with an excess vacancy concentration in the irradiated alloy layer. In the temperature range 600–750 °C, the strain recovers to a maximum value which is correlated with the ripening of voids, dissolution of alloy layer {113} rodlike defects, and {113} planar interstitial defects in the substrate. At temperatures in the range 750–1000 °C, strain relaxation is observed and is correlated with the growth of intrinsic dislocations within the alloy layer. These intrinsic, looplike dislocations nucleate at the alloy–substrate interface and grow within the alloy layer, toward the surface.
Theory of linear electro-optic effect near the E1 and the E1+Δ1 energies
Authors: Chen Y. H. , Yang Z.
Published: July 2002

A theoretical k*p model for the linear electro-optic (LEO) spectrum near the E1/E1+Δ1 energies is presented. The calculated spectrum reproduces the important features of the experimental ones. In particular, it explains the observed energy shifts of the resonance near the E1/E1+Δ1 energies, and the predicted LEO coefficient agrees well with the experimental one. The predicted linewidth, on the other hand, is about twice that of the observed one. The LEO strength is found to be dominated by the excitons. This is qualitatively consistent with the observed large change of LEO strength with temperature.
On the correlation between the carbon content and the electrical quality of thermally grown oxides on p-type 6H–Silicon carbide
Authors: Vathulya Vickram R. , Ning Wang Dong , White Marvin H.
Published: July 2002

Thermal oxides on p-type silicon carbide exhibit high densities of interface states and fixed charge. Understanding the effect of the oxide composition on the electrical properties is imperative to improve the quality of oxides on p-type silicon carbide. In this work, we use angle resolved x-ray photoelectron spectroscopy to profile the oxide composition. The result is a direct correlation between the carbon content in the oxide and the density of interface states and fixed charge as determined by electrical capacitance–voltage measurements.
Depth-resolved cathodoluminescence study of ZnxCd1−xSe epilayer grown on (001) InP by metal organic chemical vapor phase deposition
Authors: Zhang X. B. , Won H. K. , Hark S. K.
Published: July 2002

Optical properties of zincblende structured ZnxCd1−xSe epilayer grown on InP by metal organic chemical vapor phase deposition at temperatures of 360, 400, and 440 °C are investigated with low temperature cathodoluminescence spectroscopy (CL). Both near band gap and deep level emissions are found for the samples grown at 400 °C and above, but deep level emissions are absent for the sample grown at 360 °C. We conclude that the growth temperature should be kept below the temperature at which InP begins to decompose and diffusion of III–V constituents into the epilayer occurs. Evidence of this diffusion comes from an analysis of depth resolved CL studies, which shows that the deep level emissions occur mainly at the epilayer/substrate interface. By monitoring the ratio of the intensity of the deep level emissions to that of the near band emissions, we find that this ratio is larger for samples grown at high temperatures than those at low temperatures. Indium diffusion from the substrate into the epilayer is most likely the source of these deep levels.
Unusual power dependence of two-tone intermodulation in high-Tc superconducting microwave resonators
Authors: Willemsen Balam A. , Kihlstrom K. E. , Dahm T.
Published: July 2002

We study the power dependence of two-tone intermodulation arising in high-Tc superconducting microwave resonators as a function of each tone separately. In the regime where the intermodulation power varies as the square of the input power for equally strong tones, we observe unexpected behavior of the power dependence on the individual tones. We show that this behavior can be understood in terms of a nonlinear inductance which varies linearly with the magnitude of the input current. These findings provide a consistent phenomenological picture of the unusual power dependence and should place constraints on a microscopic description of nonlinear behavior in high-Tc films where the intermodulation products vary like the square of the input power.
Relaxation studies of thin films oriented by corona poling for a poly(p-phenyleneterephthalate) with nonlinear optical side groups
Authors: Lee Suck-Hyun , Lee Jung-Woo , Kwon O-Pil , Lee Chong-Ha , Won Young-Hee
Published: July 2002

We report relaxation studies of corona-poled aromatic polyester bearing a nonlinear optical (NLO) chromophore as a side group. The effects of film thickness on the temporal stability of the NLO coefficient and atomic force microscope observation of corona-poling-induced film surface roughening are presented. The results indicated that this material exhibits exceptionally good temporal stability of the second-harmonic generation coefficient at room temperature even though its glass transition temperature, Tg is quite low. The temporal stability of the chromophore orientation seems to result from the coupling between the chromophore and its anisotropic surface domain environment. Thus, the design strategies to lock the domain itself would be valuable for improving geometrically long-term stability of second-order NLO properties.
Nanowire networks on perfectly flat surfaces
Authors: Adelung R. , Kipp L. , Brandt J. , Tarcak L. , Traving M. , Kreis C. , Skibowski M.
Published: July 2002

A rapid process for the formation of nanowire network structures is presented. The technique uses adsorption on extremely flat layered material surfaces (vertical variation of only 6 Å over 10 μm). Adsorbed atoms or molecules assemble along lines due to subtle strain effects which are produced after chemical growth by substrate cooling. Within 1–3 min complete macroscopic networks (cm scale) of thin (5–250 nm) semiconducting or metallic wires with a typical mesh size of the order of microns can be formed. First examples ranging from macroscopic to quantum mechanical properties of these networks will be given.
Interlayer coupling and enhanced coercivity in ferromagnetic/antiferromagnetic structures
Authors: Edelstein A. S. , Kodama R. H. , Miller M. , Browning V. , Lubitz P. , Cheng S. F. , Sieber H.
Published: July 2002

Magnetization and ferromagnetic resonance measurements provide evidence of ferromagnetic coupling between ferromagnetic (F) layers separated by an intervening layer of antiferromagnetic (AF) NiO of thickness, tAF, where 7 nm<tAF<13 nm. Near 300 K, due to this coupling, the coercivity Hc and M–H loop squareness in F/AF multilayers increases as one increases the number of layers. The increased Hc and squareness have potential application in thin film magnets.
Effective lifetime of electrons trapped in the oxide of a metal–oxide–semiconductor structure
Authors: Khosru Quazi Deen Mohd , Uddin Md. Nasir , Khan M. Rezwan
Published: July 2002

A simple and effective analytical model is developed to calculate the lifetime of an electron trapped in the oxide layer of a metal–oxide–semiconductor (MOS) device using quantum mechanical analysis. A new approach of applying transmission line techniques is introduced to study the time evolution of the electron wave function localized in a trap quantum well in the oxide of MOS devices. Treating it as a one-dimensional problem, with tunneling probabilities through both the interfaces, and exploiting the effective similarity with the time evolution of electron wave packet localized in a double-barrier quantum well, a model is developed to calculate the lifetime of the trapped electron under flat band condition. It is further extended to calculate the effective lifetime of electrons trapped at various trap centers in the oxide layer under externally applied electric fields. Results thus obtained are in reasonable agreement and consistent with the physical concepts and the experimental observations.
Homoepitaxial growth of GaN by metalorganic vapor phase epitaxy: A benchmark for GaN technology
Authors: Kirchner C. , Schwegler V. , Eberhard F. , Kamp M. , Ebeling K. J. , Kornitzer K. , Ebner T. , Thonke K. , Sauer R. , Prystawko P. , Leszczynski M. , Grzegory I. , Porowski S.
Published: July 2002

Carefully optimized low-pressure metalorganic vapor phase epitaxy is used for homoepitaxial growth on distinctively pretreated GaN bulk single crystal substrates. Thereby, outstanding structural and optical qualities of the material have been achieved, exhibiting photoluminescence linewidths for bound excitons as narrow as 95 μeV. These extremely sharp lines reveal fine structures, not reported for GaN. Additionally, all three free excitons as well as their excited states are visible in low-temperature photoluminescence at 2 K. These transitions are clearly identified by reflectance measurements. X-ray diffraction analysis of these layers reveal about 20 arcsec linewidth for the (0004) reflex using CuKα radiation.
Charge storage in CeO2/Si/CeO2/Si(111) structures by electrostatic force microscopy
Authors: Jones J. T. , Bridger P. M. , Marsh O. J. , McGill T. C.
Published: July 2002

An electrostatic force microscope was used to write and image localized dots of charge in a double barrier CeO2/Si/CeO2/Si(111) structure. By applying a relatively large tip voltage and reducing the tip to sample separation to 3–5 nm, charge dots 60–200 nm full width at half maximum of both positive and negative charge have been written. The total stored charge is found to be Q=±(20–200)e per charge dot. These dots of charge are shown to be stable over periods of time greater than 24 h, with an initial charge decay time constant of τ∼9.5 h followed by a period of much slower decay with τ>24 h. The dependence of dot size and total stored charge on various writing parameters such as tip writing bias, tip to sample separation, and write time is examined.
InGaAs heteroepitaxy on GaAs compliant substrates: X-ray diffraction evidence of enhanced relaxation and improved structural quality
Authors: Moran P. D. , Hansen D. M. , Matyi R. J. , Cederberg J. G. , Mawst L. J. , Kuech T. F.
Published: July 2002

In 0.44 Ga 0.56 As (3% mismatch) films 3 μm thick were grown simultaneously on a conventional GaAs substrate, glass-bonded GaAs compliant substrates employing glasses of different viscosity, and a twist-bonded GaAs compliant substrate. High-resolution triple-crystal x-ray diffraction measurements of the breadth of the strain distribution in the films and atomic force microscopy measurements of the film’s surface morphology were performed. The films grown on the glass-bonded compliant substrates exhibited a strain distribution whose breadth was narrowed by almost a factor of 2 and a surface roughness that decreased by a factor of 4 compared to the film simultaneously grown on the conventional substrate. These improvements in the film’s structural quality were observed to be independent of the viscosity of the glass-bonding media over the range of viscosity investigated and were not observed to occur for the film grown on the twist-bonded substrate.
Application of the combinatorial approach to the fabrication of a quantum well multiwavelength emitting chip
Authors: Liu Xing Quan , Li Zhi Feng , Lu Wei , Shen S. C. , Chen ChangMing , Zhu D. Z. , Hu Jun , Li MinQian
Published: July 2002

In this letter, the combinatorial approach is applied to the fabrication of a quantum well multiwavelength emitting chip. The multispecies implantation is accomplished with arsenic followed by proton to shift the emitting wavelength. More than 20 different emitting wavelengths can be observed from a single chip. This combinatorial method shows promise for wavelength-division multiplex applications and can be used to set up a library of wavelength shifts via implantation doses and implantation species.
Defect structure and electron field-emission properties of boron-doped diamond films
Authors: Chen Yung-Hsin , Hu Chen-Ti , Lin I-Nan
Published: July 2002

The correlation between electron field-emission properties of diamond films prepared by the chemical vapor deposition (CVD) process and the defect structure induced by boron doping was examined. Secondary ion mass spectroscopic analysis indicates that the solubility limit of boron in diamond is (B3+)2=5×1021 cm−3, whereas the infrared absorption (IR) spectroscopic analysis reveals that the largest boron concentration that can be incorporated as substitutional dopants is only one tenth of the solubility limit, (B3+)d=5×1020 cm−3. Including boron species higher than this concentration induces large strain and atomic defects, which are inferred by the distorted Raman resonance peak, noisy IR spectra, and twinned microstructure for diamond. Presumably, the presence of atomic defects, which behave as electron traps, is the mechanism deteriorating the electron field-emission properties of CVD diamonds.
Carrier dynamics of self-assembled InAs quantum dots on InP (311)B substrates
Authors: Hinooda S. , Fréchengues S. , Lambert B. , Loualiche S. , Paillard M. , Marie X. , Amand T.
Published: July 2002

A study of the carrier dynamics of self-assembled InAs quantum dot structures on InP (311)B substrates is presented. By time-resolved photoluminescence spectroscopy, an efficient carrier capture from the wetting layer into the quantum dots is observed under high incident excitation condition. This behavior can be attributed to carrier relaxation assisted by the Auger effect. Moreover, first excited states which have a fast decay time of ∼60 ps are observed under the same condition. These results demonstrate the possibility of the realization of performance-improved injection lasers at 1.55 μm for optical telecommunication.
Biexciton photoluminescence in cubic ZnS single crystals
Authors: Liem Nguyen Quang , Quang Vu Xuan , Thanh Do Xuan , Lee Joo In , Viswanath Annamraju Kasi , Kim Dongho
Published: July 2002

The near-band-edge emission of cubic zinc sulfide single crystals has been studied in detail by steady-state photoluminescence (PL) and time-resolved photoluminescence. Based on the peak energy positions, excitation power density and temperature dependencies of the PL spectra, we interpret the emission as recombination of the free and bound excitons and of the biexcitons. We observed the biexciton emission at 3.791 eV in cubic ZnS single crystals with very low excitation power density. Its binding energy and radiative lifetime were determined to be about 9 meV and 52 ps at 12 K, respectively.
Noise characteristics of quantum-well infrared photodetectors at low temperatures
Authors: Yao J. , Tsui D. C. , Choi K. K.
Published: July 2002

In this work, we have performed high-sensitivity measurements on the dark current and the noise current of infrared hot-electron transistors (IHETs) and their constituent quantum-well infrared photodetectors (QWIPs) at 4.2 K. We found that the dominant noise of the QWIPs in this regime is not from the expected shot noise but from the 1/f noise and possibly a bias-independent noise. Part of the 1/f noise is unrelated to impurities in the barrier and is intrinsic to the sequential tunneling mechanism in QWIPs. By filtering out the impurity-assisted tunneling current, the IHETs reduce the dark current and the 1/f noise, and improve the detector sensitivity and uniformity.
Transplanted Si films on arbitrary substrates using GaN underlayers
Authors: Guha Supratik , Gupta Arunava , Bojarczuk Nestor A. , Karasinski Joseph
Published: July 2002

We demonstrate that Si layers overgrown on GaN/sapphire substrate structures can be transferred onto host substrates by using the technique of laser-induced metallization of GaN at the GaN/sapphire interface via the reaction GaN=Ga+1/2N2. This may allow the grafting of films of Si onto substrates such as glass or plastic for microelectronic applications. We examine the debonding mechanism and propose that it occurs due to pressures of the order of a few thousand atmospheres generated with the release of nitrogen from the GaN metallization reaction.
Peltier microcalorimeter
Authors: Moon I. K. , Jung D. H. , Lee K.-B. , Jeong Y. H.
Published: July 2002

We developed an ac microcalorimeter utilizing the Peltier effect of a thermocouple junction as an ac power source. This Peltier microcalorimeter allows us to measure the absolute value of the heat capacity of small samples with submilligrams of mass. The performance of the microcalorimeter was checked in the temperature range of 15–420 K with α-Al2O3 samples of 0.54 and 2.25 mg. The absolute accuracy was ±3% for the range of 30–150 K and ±1% for 150–420 K. The precision was better than 0.5% in the whole temperature range.
Ion beam synthesis of graphite and diamond in silicon carbide
Authors: Heera V. , Skorupa W. , Pécz B. , Dobos L.
Published: July 2002

A high dose of 1×1018 cm−2, 60 keV carbon ions was implanted into single crystalline 6H silicon carbide (SiC) at elevated temperatures. The formation of carbon phases in the crystalline SiC lattice was investigated by cross sectional transmission electron microscopy. An amorphous, carbon rich phase was produced at 300 °C. Precipitates of graphite were obtained at 600 °C, whereas at 900 °C small diamond grains were produced. These grains are in perfect epitaxial relation with the surrounding SiC lattice.
Transition dipole moment of InAs/InGaAs quantum dots from experiments on ultralow-threshold laser diodes
Authors: Eliseev P. G. , Li H. , Stintz A. , Liu G. T. , Newell T. C. , Malloy K. J. , Lester L. F.
Published: July 2002

Semiconductor ultralow-threshold InAs quantum-dot lasers are investigated operating at 1230–1250 nm at room temperature (laser threshold range is of 16–83 A/cm2 for ground-state emission). The dependence of gain on current is derived from measurements of the threshold current as a function of the cavity length. The ground-state gain appears at very low current: the inversion threshold of ∼13 A/cm2 is a record low value. Analysis of these data for diodes of different molecular beam epitaxial-grown wafers leads to a squared dipole moment of the transition of ∼9.2×10−57 C2 m2 that corresponds to the length of elementary dipole of ∼0.6 nm.
Diagnostics of inductively coupled chlorine plasmas: Measurement of Cl2+ and Cl+ densities
Authors: Malyshev M. V. , Fuller N. C. M. , Bogart K. H. A. , Donnelly V. M. , Herman Irving P.
Published: July 2002

The absolute densities of positive ions (Cl2+ and Cl+) are obtained over a 2–20 mTorr pressure range and 5–1000 W input radio-frequency rf power range in a transformer-coupled Cl2 plasma. The relative number density of Cl2+ is measured by laser-induced fluorescence. These laser-induced fluorescence data are calibrated by Langmuir-probe measurements of total positive-ion density at low powers to yield absolute values for nCl2+ and are corrected for changes in rotational temperature with rf power. In turn, the nCl2+ data are used to determine the effective-mass correction for refined Langmuir-probe measurements of the total positive-ion density. The density of Cl+ is then the difference between the total positive-ion and Cl2+ densities. For all the pressures, Cl2+ is found to be the dominant ion in the capacitively coupled regime (input powers below 100 W), while Cl+ is the dominant ion at higher powers (>300 W) of the inductively coupled regime. Experimental results are compared to those from a simple global model. This work is a continuation of a study that provides a complete set of experimentally measured plasma parameters over a broad range of conditions in a chlorine plasma, produced with a commercial, inductively coupled rf source.
Magnetic behavior of nanostructured Fe films measured by magnetic dichroism
Authors: Edmonds K. W. , Binns C. , Baker S. H. , Thornton S. C. , Finetti P.
Published: July 2002

The magnetic properties of Fe nanostructured films have been studied using magnetic linear and circular dichroism in x-ray photoemission spectroscopy. The samples were prepared by the deposition of nanoscale Fe clusters, size 1–4 nm, onto thin Cu films. The linear dichroism, which is used to measure the in-plane magnetization, increases with increasing film thickness, with a sharp increase between 1 and 1.5 ML coverage. The circular dichroism, which measures the out-of-plane magnetization, is zero within the experimental error at all thicknesses studied. Capping an Fe film with an ultrathin Pd layer results in a factor of 3 decrease of the linear dichroism response.
Vibrational energy relaxation of azulene in the S2 state. II. Solvent density dependence
Authors: Yamaguchi T. , Kimura Y. , Hirota N.
Published: July 2002

We have measured the vibrational energy relaxation of azulene in the S2 state in ethane, carbon dioxide, and xenon over a wide density region by the time-resolved fluorescence spectroscopy. The reduced density of the solvent (the density divided by the critical density) has been changed from the gaslike one (lower than 0.05) to the liquidlike one (2.8 for ethane, 2.7 for carbon dioxide, and 2.0 for xenon). The density dependence of the relaxation rate is compared with that of azulene in the S0 state [D. Schwarzer, J. Troe, M. Votsmeier, and M. Zerezke, J. Chem. Phys. 105, 3121 (1996)]. Although the absolute rate largely depends on the electronic state, the density dependence of the relaxation rates is roughly the same for both electronic states, which can be considered as a side-proof of the isolated binary collision model. Possible origins for the validity of the isolated binary collision model are discussed.