bluuebunny/crossref_metadata_2025 huggingface dataset:
Proposed structure for a crossed-laser beam, GeV per meter gradient, vacuum electron linear accelerator
Authors: Huang Y. C. , Zheng D. , Tulloch W. M. , Byer R. L.
Published: July 2002

We propose a dielectric-based, multistaged, laser-driven electron linear accelerator structure operating in a vacuum that is capable of accelerating electrons to 1 TeV in 1 km. Our study shows that a GeV/m gradient is achievable using two 100 fs focused crossed-laser beams, repeated every 300 μm, operated at a peak power of 0.2 GW and an energy density of less than 2 J/cm2 on the accelerator structure.
Experimental investigation of the differential gain in semiconductor lasers and its influence on Q-switching performance
Authors: Summers H. D. , Rees P.
Published: July 2002

The gain spectra of AlGaInP, single quantum well, laser diodes were obtained by measurement of their spontaneous emission spectra and subsequent conversion according to the Einstein relations. From these spectra the ratio of differential absorption to differential gain, γ was calculated. At energies greater than the lasing transition a threefold increase in the differential absorption may be achieved in compressively strained devices, giving a value of γ=14.4. These results indicate that by detuning the saturable absorber energy within a Q-switched device by 20 meV a doubling of the inversion factor may be obtained.
Etched-surface roughness measurements from an in situ laser reflectometer
Authors: Parker M. A. , Michalak R. J. , Kimmet J. S. , Pirich A. R. , Shire D. B.
Published: July 2002

An in situ laser reflectometer is used to determine the surface roughness of III–V laser heterostructure as it etches in an electron cyclotron resonance etcher. A stochastic model links the reflectometer signals with the fluctuations of the surface height and slope, and with the size of the illuminated surface area. This technique is valuable for improving the quality of optical waveguides etched in III–V heterostructure, and the electrical contacts for optoelectronic devices.
Single-step fabrication of strongly confining quasiphase-matching waveguides in LiTaO3
Authors: Zhao Cangsang , Engelmann Reinhart
Published: July 2002

Strongly confining waveguides were fabricated in LiTaO3 at high temperature (540–610 °C) by short-time (≤6 s) rapid thermal annealing. Single-step photolithography is able to accomplish the simultaneous fabrication of a waveguide and a periodically domain-inverted structure for second-order quasiphase-matching blue-light generation. A measured normalized conversion efficiency of 7%/W cm2 for a physical length of 0.55 mm in a planar quasiphase-matching waveguide showed that this single-step process can lead to high conversion efficiency in channel waveguides.
Efficient continuous wave blue light generation in optical superlattice LiNbO3 by direct frequency doubling a 978 nm InGaAs diode laser
Authors: Lu Ya-lin , Lu Yan-qing , Zheng Jian-jun , Xue Cheng-cheng , Cheng Xiang-fei , Luo Gui-peng , Ming Nai-ben
Published: July 2002

First-order quasiphase matched blue light generation in a LiNbO3 optical superlattice was performed by direct frequency doubling of a continuous wave 978-nm diode laser. 1.27 mW output power of blue light was obtained with an incidence power of 500 mW. The frequency conversion efficiency is 0.25%.
Reconstruction of diffuse photon-density wave interference in turbid media from time-resolved transmittance measurements
Authors: Lindquist Charlotta , Pifferi Antonio , Berg Roger , Andersson-Engels Stefan , Svanberg Sune
Published: July 2002

We demonstrate an improved technique to precisely localize inhomogeneities in turbid media by means of reconstructing diffuse photon-density wave interference from time-resolved transmittance measurements applying the Fourier transform. This interference can also be obtained in the reverse mode, that is using a single source and combining the signals detected at several locations. This increases the collection efficiency and the possibility for postprocessing and allows one to evaluate the data from one measurement in different ways to make the analysis more robust.
Effect of CeO2 interlayer deposition temperature on growth behavior of Bi4Ti3O12/CeO2/MgO heterostructures
Authors: Jo W. , Park G. W. , Kim D. W. , Noh T. W.
Published: July 2002

CeO2 interlayers were used to control growth behavior of Bi4Ti3O12 thin films on MgO(001) substrates. The CeO2 layer grown at 740 °C had a preferential orientation with its c-axis normal to the film surface, so it could be used to grow an epitaxial Bi4Ti3O12(001)/CeO2(001)/MgO(001) heterostructure. On the other hand, the CeO2 layer grown at 650 °C showed a mixed texture of (001) and (111), and this interlayer enabled us to get a preferentially oriented Bi4Ti3O12(117)/CeO2(111)MgO(001) multilayer structure.
Demonstration of light-hole behavior in quaternary GaInAsSb/AlGaAsSb quantum wells using infrared photoluminescence spectroscopy
Authors: Shen W. Z. , Shen S. C. , Tang W. G. , Chang Y. , Zhao Y. , Li A. Z.
Published: July 2002

We report an infrared comparative photoluminescence and absorption study of optical properties in quaternary GaInAsSb/AlGaAsSb strained single-quantum-well structures grown by molecular beam epitaxy with the indium composition of 0.25 and 0.33. The light-hole-related luminescence structure observed in the lower indium composition sample disappears in the sample with higher indium composition due to the larger band splitting of heavy and light holes induced by the strain. This observed transition from type I to type II states for light holes is in good agreement with our theoretical prediction that it may occur for the indium composition larger than 0.30.
Structural and ferroelectric properties of the c-axis oriented SrBi2Ta2O9 thin films deposited by the radio-frequency magnetron sputtering
Authors: Song T. K. , Lee J.-K. , Jung H. J.
Published: July 2002

Radio-frequency magnetron sputtering was used to deposit SrBi2Ta2O9 ferroelectric thin films on Pt(111)/Ti/SiO2/Si(001) substrates. Thin films were deposited at room temperature with argon pressures of 0.5–100 mTorr and with sputtering power of 2.5 W/cm2. The crystal orientations of thin films were strongly affected by the argon pressures, the c-axis oriented SrBi2Ta2O9 thin film was obtained with argon pressure of 30 mTorr. The crystal structures of the c-axis oriented SrBi2Ta2O9 thin film were investigated by x-ray diffraction methods: θ-2θ scan, rocking curve, and φ scans. The well aligned microstructure was observed with the average grain size of about 2000 Å in an atomic force microscopic image. Ferroelectric properties were observed for the c-axis oriented thin film: Pr*−PrΛ and Ec were 9.7 μC/cm2 and 50 kV/cm, respectively, with excitation voltage of 3 V.
Second-harmonic generation using a fiber ring resonator with a LiNbO3 waveguide and a semiconductor optical amplifier
Authors: Xu C. Q. , Shinozaki K. , Okayama H. , Kamijoh T.
Published: July 2002

Optical second-harmonic generation (SHG) using a fiber ring resonator has been demonstrated. A LiNbO3 waveguide with a periodically domain inverted structure and a semiconductor optical amplifier were used as the nonlinear and gain media, respectively. The quasiphase-matched condition was satisfied simply by tuning an optical bandpass filter in the resonator. SHG was enhanced by a factor of 280.
Low noise high-temperature superconducting bolometers for infrared imaging
Authors: Berkowitz S. J. , Hirahara A. S. , Char K. , Grossman E. N.
Published: July 2002

High-temperature superconducting bolometric infrared detectors offer the promise of matching the sensitivity of HgCdTe detectors, but with an extended detection range to longer wavelengths (λ≳15μm). We fabricated high-temperature superconducting bolometers using an all-epitaxial micromachining technology based upon a YBa2Cu3Ox thin film on a yttria-stabilized zirconia free-standing 50×50μm2 membrane supported on a LaAlO3 substrate. This structure has simultaneously a low thermal conductance and a low heat capacity. Using this technology, we have made array-compatible pixels for infrared camera applications with optical noise equivalent powers as low as 6.3×10−13 W/√Hz at 32 Hz. Over more than 1 octave of frequency range, these bolometers are limited by fundamental (chiefly phonon) noise sources rather than excess film noise.
Partitioning of Si in a Fe87Zr7Si4B2 nanocrystalline soft magnetic alloy
Authors: Zhang Y. , Hono K. , Inoue A. , Sakurai T.
Published: July 2002

We have studied partitioning of Si in nanocrystalline Fe–Zr–Si–B soft magnetic alloy by atom probe field ion microscopy (APFIM). Unlike our expectation from our previous results in nanocrystalline Fe–Si–B–Nb–Cu alloy, we have found that Si atoms are rejected from α-Fe primary crystals and partitioned into the residual amorphous phase. This result suggests that Si addition does not cause reduction in inherent magnetostriction of α-Fe nanoparticles, but it brings the volume fraction of the α-Fe particles to an optimum value so that the average magnetostriction becomes zero. This conclusion has been strengthened by comparing the changes in magnetostriction constants as a function of Si content in Fe–Zr–Si–B and Fe–Si–B–Nb–Cu alloys.
Electron paramagnetic resonance characterization of nonuniform distribution of hydrogen in silica optical fibers
Authors: Li J. , Lehman R. L. , Sigel G. H.
Published: July 2002

The hydrogen distribution within low-OH silica optical fibers has been characterized by electron paramagnetic resonance in combination with a chemical etch-back technique. The 74 G doublet, the signal generated by a hydrogen hyperfine structure of the Si E′ center, was used to investigate the spatial distribution of hydrogen reaction products in silica optical fiber and, in particular, the reaction between the twofold coordinated silicon and hydrogen. A nonuniform distribution of the 74 G species was observed with the highest concentration near the fiber surface, indicative of a corresponding nonuniform distribution of hydrogen. The polymer fiber coating appears to be the primary source of the trace amounts of hydrogen observed in the silica fibers.
Vacuum ultraviolet reflectivity measurements of thin-film electroluminescent phosphors
Authors: Lite K. , Thuemler R. L. , Plant T. K. , Wager J. F. , Morton D. C. , Sun S. S. , Mauch R. H.
Published: July 2002

Vacuum ultraviolet reflectivity measurements of three thin-film electroluminescent phosphors, zinc sulfide (ZnS), strontium sulfide (SrS), and strontium-calcium thiogallate (Sr0.45Ca0.55Ga2S4), are reported using thin-film samples. Measured ZnS reflectivity peak positions are in agreement with values previously reported in the literature. SrS room temperature reflectivity measurements are found to be consistent with previously reported low temperature measurements. Reflectivity measurements of Sr0.45Ca0.55Ga2S4 are reported for the first time; the reflectivity spectrum is found to rise monotonically above the band gap and to exhibit almost no structure, except for a small shoulder at ∼6.8 eV and a single, broad peak at ∼8.5 eV. The unusual nature of the Sr0.45Ca0.55Ga2S4 reflectivity spectrum is attributed to positional disorder in the stoichiometric thiogallate film.
The influence of wafer dimensions on the contact wave velocity in silicon wafer bonding
Authors: Bengtsson Stefan , Ljungberg Karin , Vedde Jan
Published: July 2002

The contact wave velocity in silicon wafer bonding is experimentally found to decrease with wafer thickness and to be only weakly dependent on wafer diameter. Wafers of different thicknesses ranging from 270 to 5000 μm, were dipped in HF:H2O before bonding to give the surfaces hydrophobic properties. A model based on energy conservation can explain the main characteristics of the experimental results. The contact wave velocity is determined by the amount of energy available as kinetic energy for the entrapped gas in the gap between the wafers. By increasing wafer thickness, the elastic energy stored in the material is increased, and the contact wave velocity is decreased.
Ultrafast electron and hole tunneling in (Ga,In)As/(Al,In)As asymmetric double quantum wells
Authors: Ten S. , Krol M. F. , Guerreiro P. T. , Peyghambarian N.
Published: July 2002

We present unambiguous experimental evidence for the dramatic dependence of hole tunneling rates on in-plane momentum in (Ga,In)As/(Al,In)As asymmetric double quantum wells. Holes generated near the band edge tunnel on hundred picosecond time scales, whereas holes excited with large excess energy tunnel on subpicosecond time scales. The mechanism responsible for this increase of more than three orders of magnitude in the hole tunneling rate is nonresonant delocalization of hole wave functions by band mixing in the valence band.
The effects of carbon on TlBa2Ca2Cu3Ox phase formation in the TlF–Ba2Ca2Cu3Oz system
Authors: Sung Y. S. , Zhang X. F. , Kostic P. J. , Miller D. J.
Published: July 2002

The effects of carbon on TlBa2Ca2Cu3Ox phase formation in the TlF–Ba2Ca2Cu3Oz system were investigated by varying the carbon contents in Ba2Ca2Cu3Oz precursor powders that were mixed with TlF and reacted to form the superconducting phase. It was found that carbon induced Tl2Ba2Ca2Cu3Oy phase formation resulting in superlattices formed by c-axis intergrowths between TlBa2Ca2Cu3Ox and Tl2Ba2Ca2Cu3Oy. The superlattices were highly regular and uniform throughout the samples. While TlBa2Ca2Cu3Ox was the main phase at low carbon content (0.231 wt %), Tl2Ba2Ca2Cu3Oy became the dominant phase at high carbon content (0.472 wt %) even with a 1:2:2:3 (Tl:Ba:Ca:Cu) starting composition.
Surface micromachined interferometer-based optical reading technique
Authors: Christenson G. L. , Tran A. T. T. D. , Miller S. A. , Haronian D. , Lo Y. H. , MacDonald N. C.
Published: July 2002

A surface micromachined suspended interferometer and an atomic force microscope (AFM) are incorporated into a novel optical reading technique. The AFM tip mechanically deflects the suspended membrane as it scans past a data bit on the membrane surface. The data are read by monitoring the changing interference pattern generated in the optical aperture of the interferometer. When operated in parallel, there exists the potential for high speed, high density data reading.
Transport in gated undoped GaAs/AlxGa1−xAs heterostructures in the high density and high mobility range
Authors: Herfort J. , Hirayama Y.
Published: July 2002

The two-dimensional electron gas with electron densities higher than 1016 m−2 which is formed at the interface in undoped GaAs/AlxGa1−xAs heterostructure by the electric field generated by a top gate is studied. Despite the high electron density in the sample, rather high mobilities of about 100 m2/Vs can be achieved with sufficient small gate leakage currents. The population of the second subband is studied from Shubnikov-de Haas measurements in these devices.
Ion scattering for in situ characterization of composition of La2−xSrxCuO4 films
Authors: Hucknall P. K. , Sugden S. , Sofield C. J. , Harker A. H. , Mächler E. , Locquet J.-P.
Published: July 2002

Ion scattering techniques in the 5–50 keV range have the potential to yield quantitative information on the composition of high-temperature superconductor (HTc) films. To demonstrate this we have designed and built an ion scattering spectrometer, compact enough for in situ use, as an analytical tool for vacuum deposition processes. Data collected from La2−xSrxCuO4 films demonstrate the excellent mass resolution available using heavy incident ions. Modeling of the data has been carried out using both a simple empirical method and a full Monte Carlo code. In addition to stoichiometric information, the contribution of light recoiled elements to the spectrum is determined. The estimated composition, based on these models is compared with the composition obtained using high energy Rutherford backscattering spectrometry (RBS) to verify the quantitative capabilities of the technique.
Influence of strain conditions on exciton dynamics and on thermal stability of photoluminescence of ZnCdSe/ZnSe quantum wells
Authors: Godlewski M. , Bergman J. P. , Monemar B. , Kurtz E. , Hommel D.
Published: July 2002

Distinctly different exciton properties in pseudomorphic and strain relaxed ZnCdSe/ZnSe structures grown on GaAs are demonstrated. For pseudomorphic or partly strained structures temperature stability of photoluminescence depends on the distance from the ZnCdSe quantum well to GaAs/ZnSe interface and less on confinement energies. Densities of two-dimensional localized states and averaged localization energies, as seen by excitons, are determined from the photoluminescence kinetics measurements. These values are compared with the ones reported for contemporary GaAs/AlGaAs structures.
The origin of room temperature luminescence in Si–Ge quantum wells: The case for an interface localization model
Authors: Turton R. J. , Jaros M.
Published: July 2002

Photoluminescence from a Gem–Sin–Gem structure has recently been demonstrated at room temperature by Gail et al. [Appl. Phys. Lett. 66, 2978 (1995)]. Experimental measurements have shown that this luminescence is associated with the fourfold degenerate conduction minima which lie in the plane of the interface. In this letter, we report full-scale microscopic calculations on both perfect and imperfect structures of this type which demonstrate that these results cannot be explained either by a ‘‘zone-folding’’ or an alloy scattering model. We propose an alternative mechanism which links the luminescence to anomalous localization at the heterointerfaces.
Layered defective lanthanum titanate thin films prepared by pulsed laser ablation of potassium lanthanum titanate ceramics
Authors: Xiong S. B. , Ding W. P. , Liu Z. G. , Chen X. Y. , Guo X. L. , Yu T. , Zhu Y. Y. , Hu W. S.
Published: July 2002

Thin films of Lanthanum titanate have been prepared on SiO2 coated Si and fused silica substrates by excimer ultraviolet laser ablation of potassium lanthanum titanate ceramics (K2La2Ti3O10). X-ray θ–2θ scans revealed that the films as-grown at a substrate temperature of 750–850 °C were single phase defective perovskite, and exhibited superstructure line in addition to the lines expected for the foundamenal perovskite structure. The films can be produced by escaping of potassium from K2La2Ti3O10 and the superstructure line observed was considered to arise from the ordered arrangement of the A-site vacancies. The chemical compositions of the films were determined by x-ray photoelectron spectroscopy (XPS). Optical waveguiding properties were demonstrated by m-line measurement using a rutile prism coupling method. The as grown films are colorless and transparent, and have the effective refractive index of 1.917 for TE modes at 632.8 nm.
Surface morphology effect on the photoresponse of high temperature superconducting microbridges
Authors: Chou Hsiung , Chen H. Z. , Chen Y. C. , Lin T. L. , Chow T. C. , Wang T. P.
Published: July 2002

Three Y1Ba2Cu3O7−δ superconducting thin films with 20%, 60%, and 100% coverage of precipitates were fabricated into microbridges of 25×650 μm2 by a conventional photolithography method. These microbridges exhibit a Tco(R=0) from 83.6 to 87.2 K and a transition width of about 1.8 K. These also have (dR/dt)max values of about 71–78 Ω/K. We find that the fewer the precipitates on the film, the better the thermal conduction, and a larger responsivity (S) can be achieved. The best responsivity of 783 V/W measured at Ib=8 mA, Top=86.8 K, and f=2 Hz for various wavelengths of light sources is obtained from the film with 20% precipitation. The photoresponse signals decay exponentially with the precipitation coverages, which indicates that these precipitates behave as thermal resistance layers that smooth out the ac incident signal, suppress the rise in microbridge temperature, and result in a smaller photoresponse signal for the bolometer.
Measurement of electro-optic effects in single crystal films of N-(4-nitrophenyl)-L-prolinol
Authors: Xu Jianjun , Zhou Ligui , Thakur M.
Published: July 2002

The electro-optic properties of single crystal films of N-(4-nitrophenyl)- L-prolinol (NPP) were evaluated. The direct coating technique was used to form the electrodes on the surface of the single-crystal film samples. The ac voltage and lock-in technique were used to measure the electro-optic coefficients. The electro-optic effects for different orientation of electrodes on a single-crystal film sample were measured. The dependence of the field induced birefringence on the orientation of electric field with respect to the charge transfer axis was evaluated. The results show that for NPP |n3xr12− n3yr22|=340 pm/V and r12=65 pm/V. The results are promising for various application in electro-optics involving appropriate device geometries.
A widely tunable (0.54–1.01 μm) double-pass fiber Raman laser
Authors: Ilev Ilko K. , Kumagai Hiroshi , Toyoda Koichi
Published: July 2002

We present a novel and simple double-pass fiber Raman laser in the visible and near-IR regions, based on the use of a fiberoptic autocollimation technique with Littrow-prism-tuned emission. When the Raman medium is a 40-m-long 68-μm-core-diam graded-index multimode fiber with powerful (above 100 kW pulse power coupled into the fiber) nanosecond pumping using the second harmonic of a Nd:YAG laser (λp=532 nm), we obtain widely tunable generation in both the visible and near- IR. By using the double-pass fiber Raman laser with various lengths of the multimode fiber, continuously tunable generation over a wide spectral range (0.54–1.01 μm) is obtained.
Design and operation of a two-cavity third harmonic Ka-band gyroklystron
Authors: Lawson W. , Hogan B. , Flaherty M. K. E. , Metz H.
Published: July 2002

We present the operating characteristics of a two-cavity third harmonic gyroklystron experiment. The input cavity utilizes a 9.854 GHz TE011 mode which is driven by a 100 kW magnetron. The TE031 output cavity has a resonant frequency of 29.57 GHz. The nominal beam voltage and current are 435 kV and 210 A, respectively. The pulse length is about 1 μs and the average ratio of parallel to perpendicular velocity is near one. Peak powers above 1.8 MW are achieved with an efficiency of about 2% and a gain of 14 dB. The theoretical simulations are in good agreement with the experimental results.
Microstructure fabrication using oxidation on partially Ga-terminated Si(111) surfaces
Authors: Maruno S. , Fujita S. , Watanabe H. , Ichikawa M.
Published: July 2002

Oxidation of partially Ga-terminated Si(111) surfaces with clean 7×7 striped areas along atomic step edges was investigated using scanning reflection electron microscopy. Molecular oxygen exposure of 100 L at the substrate temperatures of 410 °C oxidized Ga atoms on the Ga-terminated areas as well as Si atoms on the clean 7×7 areas. The Ga oxides were selectively desorbed over the Si oxides during annealing. This results in the formation of stripe-patterned Si oxides on the surface. After growth of an 8-monolayer Si film and subsequent annealing, Si grooves with a depth of about 1 nm and a width around 200 nm were formed along the step edges by excess Si-assisted thermal desorption of the Si oxides.
Optimization of pyroelectricity in the smectic-C* phase of a liquid-crystalline terpolymer
Authors: Geer R. E. , Naciri J. , Ratna B. R. , Shashidhar R.
Published: July 2002

The dynamic pyroelectric response in the smectic-C* (SmC*) phase of a novel class of polysiloxane terpolymers is reported. In these terpolymers methyl groups and two distinct types of mesogenic side chains are attached to the siloxane backbone. Our investigations reveal that the magnitude and temperature dependence of the pyroelectric signal, as well as the temperature range of the SmC* phase, can be controlled by varying the relative side-chain composition. This permits optimization of the pyroelectric properties over a temperature range extending to subambient. Specifically, the pyroelectric coefficient p can be made very nearly temperature independent, and the ratio p/ε′ extremely high, making these materials suitable for uncooled infrared detectors.
Biomagnetic measurements with an integrated YBa2Cu3O7 magnetometer in a hand-held cryostat
Authors: Schilling M. , Krey S. , Scharnweber R.
Published: July 2002

With low-noise magnetometers made from high-temperature superconductors, mobile applications of superconducting quantum interference device (SQUID) magnetometry become possible. Due to the high volume heat of evaporation of liquid nitrogen, a SQUID magnetometer can be operated in a small size cryostat for some hours. For the first time biomagnetic measurements are presented using an integrated YBa2Cu3O7 magnetometer mounted in a hand-held cryostat with a content of 100 cm3 of liquid nitrogen. These measurements and the noise properties are compared to those made in a conventional cryostat. The low-noise magnetometer consists of a multiloop pick-up coil coupled inductively to a dc SQUID based on ramp-type Josephson junctions with PrBa2Cu3O7 barriers.
Evaluation of molecular beam epitaxially grown AlGaAs/GaAs heterojunctions for bipolar transistor with InGaAs emitter contact layer
Authors: Izumi Shigekazu , Sakai Masayuki , Shimura Teruyuki , Hayafuji Norio , Sato Kazuhiko , Otsubo Mutsuyuki
Published: July 2002

Molecular beam epitaxially grown AlGaAs/GaAs heterojunctions were characterized by isothermal capacitance transient spectroscopy to study the performance of bipolar transistors with lattice-mismatched InGaAs emitter contact layer. A deep level around 0.48 eV is found to be a recombination center in the N-AlGaAs/p+-GaAs junction which might be induced by oxygen. Anomalous signals are also observed under an isothermal condition where the edge of the depletion layer reaches the graded InGaAs/AlGaAs heterointerface. Two electron traps with activation energies of 0.26 and 0.62 eV are identified as dominant factors.
Effect of plasticization of dye doped polymer on second-order optical nonlinearity induced by electric field
Authors: Sugihara Takashi , Fujii Kouji , Haga Hiroshi , Yamamoto Sadahiko
Published: July 2002

The nonlinear molecules dispersed in the polymer with low glass transition temperature (Tg) can be easily reoriented. The plasticizer is utilized in order to lower the Tg of the polymer matrix. We measured the frequency responses of second-harmonic generation in a dye doped plasticized polymer to clarify the electric field dependence of the second-order optical nonlinearity. We utilize poly(methyl methacrylate) doped with 2-methyl-4-nitroaniline as the dye doped polymer. di(ethyl-2 hexyl) phthalate is used as the plasticizer. The experimental results show that the rotational mobility was enhanced up to ten times by a DOP dose of 13.5 wt% in comparison with a dose of 0 wt% at 20°C. Therefore, this method is useful to increase the controllability of the optical nonlinearity by the electric field at room temperature.
High resolution imaging of electronic devices via x-ray diffraction topography
Authors: Beard W. T. , Green K. A. , Zhang X.-J. , Armstrong R. W.
Published: July 2002

Measurements are reported for x-ray diffraction topography (XRDT) images of implantation and superstructure details in an integrated circuit device investigated with the reflection method of line modified-asymmetric crystal topography (LM-ACT). The x-ray penetration depth and the micron grain size of thin-film nuclear emulsions used to record the diffraction images are shown to limit spatial resolution in the x-ray topographs.
The driving force of Si adsorbate transfer on a Si(001) surface
Authors: Doi Takahisa , Ichikawa Masakazu , Hosoki Shigeyuki
Published: July 2002

The driving force of Si adsorbates deposited on a Si(001) surface is investigated by reflection electron microscopy. When the sample is heated by direct current, the transferred length of the adsorbates x is proportional to the square root of the heating time t at t<tc and x is proportional to t at t≳tc, where tc is the critical time. This indicates that the dominant force of the Si adsorbates changes from thermal diffusion to electromigration at tc.
Improvement of AlGaAs/AlGaAs interface by in situ low-temperature H2 annealing in metalorganic vapor phase epitaxial regrowth
Authors: Gotoh S. , Horikawa H.
Published: July 2002

A new type of thermal treatment for air-exposed AlGaAs surfaces, in situ low-temperature H2 annealing, has been developed regrowing AlGaAs in metalorganic vapor phase epitaxy. The quality of regrown interface was evaluated by photoluminescence (PL) spectrum from Al0.3Ga0.7As/GaAs/Al 0.3Ga0.7As quantum wells near the interface of the initial AlGaAs layer. Remarkable recovery of PL intensity was observed by this newly developed process, indicating that initial air-exposed AlGaAs surface states are reduced.
Acoustoelectric current saturation in c-axis fiber-textured polycrystalline zinc oxide films
Authors: Pompe T. , Srikant V. , Clarke D. R.
Published: July 2002

Acoustoelectric current saturation, which until now has only been observed in piezoelectric single crystals, is observed in thin polycrystalline zinc oxide films. Epitaxial ZnO films on c-plane sapphire and textured ZnO polycrystalline films on fused silica both exhibit current saturation phenomenon. The values of the saturation current densities are in the range 105–106 A/cm2, depending on the carrier concentration in the film, with corresponding saturation electric fields of 3–5×103 V/cm. In addition to the current saturation, the electrical properties of the films degraded with the onset of the acoustoelectric effect but could be restored by annealing at 250 °C in a vacuum for 30 min.
Large conductance anisotropy in a novel two-dimensional electron system grown on vicinal (111)B GaAs with multiatomic steps
Authors: Nakamura Y. , Koshiba S. , Sakaki H.
Published: July 2002

A novel selectively doped AlGaAs/GaAs heterojunction was successfully formed on a vicinal (111)B substrate, in which both quasiperiodic and aperiodic multiatomic steps with the average spacings of ∼20 nm are introduced. It is found that the electrical conductance G⊥ of two-dimensional electrons across the steps is far lower than that of G∥ along the steps and the ratio G∥/G⊥ exceeds 100 at 18 K. While G∥ is almost independent of temperature T below ∼70 K, G⊥ increases exponentially with 1/T with the activation energy of ∼5 meV, indicating the presence of potential barriers for the electron motion across the aperiodic steps.
Mechanism of self-pumped phase conjugation in photorefractive crystals
Authors: Xie Ping , Dai Jian-Hua , Wang Peng-Ye , Zhang Hong-Jun
Published: July 2002

A two-dimensional model for the self-pumped phase conjugation in a photorefractive crystal is presented. In the model, no internal reflections at a corner of the crystal are explicitly considered, aside from some low intensity scattered radiation at the crystal surfaces. The numerical simulations of the curved beam path inside the crystal show agreement with experimental observations. The numerical results of high-reflectivity and high-fidelity phase conjugation are consistent with experimental results.
Fabrication of GaInAs quantum disks using self-organized InP islands as a mask in wet chemical etching
Authors: Sopanen M. , Lipsanen H. , Ahopelto J.
Published: July 2002

GaInAs quantum disks are fabricated by wet chemical etching from a GaInAs/GaAs near-surface quantum well using self-organized InP islands as an etch mask. InP islands are formed in coherent Stranski–Krastanow growth mode by metalorganic vapor phase epitaxy. The free-standing GaInAs/GaAs columns, produced by a three-step etching process, are overgrown at 550 °C. The luminescence efficiency per emitting area from the regrown quantum disks is one order of magnitude larger than that from a regrown reference quantum well.
Electron spectroscopy study of the silver-diamond(100)-H interface
Authors: Pitter M. , Hugenschmidt M. B. , Behm R. J.
Published: July 2002

The interaction between silver and a boron doped diamond single crystal has been characterized by Auger electron spectroscopy, ionization loss spectroscopy, and low energy electron diffraction. Silver deposition (equivalent film thickness 3–15 Å) at room temperature results in the formation of silver islands. During subsequent thermal annealing, silver islands cluster and finally desorb. In contrast to other metals, neither intermixing nor graphitization or carbide formation at the silver-diamond interface are observed.
p-i-n-i-p photodetector proposal and integration with waveguides
Authors: Bruno A. , Huet F. , Carre M. , Foucher M. , Billard M. , Devaux F. , Brandon J. , Menigaux L. , Carenco A. , Scavennec A.
Published: July 2002

We propose a photodiode configuration suited for waveguide integration, and top and side illumination. This configuration based on a pair of p-i-n photodiodes, laid out alongside of one another, requires only one metallization type, and therefore, reduces the number of technological steps. A waveguide–photodiode integration illustrates this photodetector concept. The single heterostructure waveguide integrated evanescently with this p-i-n-i-p photodetector exhibits a 19 GHz bandwidth, as a result of the very low (30 fF) capacitance of a 20 μm long detector. Related to its symmetrical features, this p-i-n-i-p photodetector is a means to improve fabrication yield of integrated optoelectronic devices.
Phase time for coherent transport in two-dimensional structures
Authors: Abramo Antonio , Casarini Paolo , Jacoboni Carlo
Published: July 2002

In this letter the expression of the phase time is derived for a two-dimensional coherent wave packet traveling through a generic mesoscopic system. The obtained analytical expression generalizes the definition of phase time for a single one-dimensional scattering state to the case of coherent transport through two-dimensional multichannel mesoscopic structures, and results in a suitable average of the single-mode phase times. As an application, numerical results for a quantum wire and a double-barrier resonant-tunneling diode with and without an ionized impurity are also presented.
Heterodyne detection of THz radiation with a superconducting hot-electron bolometer mixer
Authors: Semenov A. D. , Gousev Yu. P. , Nebosis R. S. , Renk K. F. , Yagoubov P. , Voronov B. M. , Gol’tsman G. N. , Syomash V. D. , Gershenzon E. M.
Published: July 2002

We report on the use of a superconducting hot-electron bolometer mixer for heterodyne detection of terahertz radiation. Radiation with a wavelength of 119 μm was coupled to the mixer, a NbN microbridge, by a hybrid quasioptical antenna consisting of an extended hyperhemispherical lens and a planar logarithmic spiral antenna. We found, at an intermediate frequency of 1.5 GHz, a system double side band noise temperature of ≊40 000 K and conversion losses of 25 dB. We also discuss the possibilities of further improvement of the mixer performance.
Magnetostatic surface wave propagation in a yttrium iron garnet double layer
Authors: Voronko A. I. , Vetoshko P. M. , Volkovoy V. B. , Boardman A. D. , Boyle J. W. , Wallis R. F.
Published: July 2002

Energy switching is investigated, both theoretically and experimentally, between two identical ferromagnetic films. The frequency region, and the applied magnetic field direction selected, permits a magnetostatic surface wave to be generated in each film. After the exact theory for this magnetostatic directional coupler is given, an experimental study of the evolution of the magnetic field distribution is presented. Good agreement between theory and experiment is obtained.
Optical excitation of paramagnetic nitrogen in chemical vapor deposited diamond
Authors: Graeff C. F. O. , Rohrer E. , Nebel C. E. , Stutzmann M. , Güttler H. , Zachai R.
Published: July 2002

Investigations of polycrystalline chemical vapor deposited diamond films by electron-spin-resonance (ESR), light-induced (L)ESR, and the constant photoconductivity method have identified dispersed substitutional nitrogen (P1 center) as the main paramagnetic form of N incorporated in the CVD diamond. The density of N-related paramagnetic states is strongly affected by illumination and heat treatment. It is found that the P1 center in CVD diamond gives rise to a deep donor state about 1.5 eV below the conduction band.
Relaxation oscillation behavior in polarization additive pulse mode-locked fiber ring lasers
Authors: Namiki S. , Ippen E. P. , Haus H. A. , Tamura K.
Published: July 2002

The noise characteristics of a polarization additive pulse mode-locked erbium-doped fiber soliton ring laser are examined. Relaxation oscillations are found only when the cw background copropagates with the soliton and not when the soliton operates alone. This observation proves that the mode-locked pulse stream has a strong self-stabilization that exempts the soliton from the relaxation oscillations, leading to extremely quiet operation.
Propagation of sheet electron beam through a planar, five-period electromagnetic wiggler
Authors: Ravi Kumar A. V. , Jain K. K.
Published: July 2002

An experimental study on the propagation of a sheet electron beam of energy ∼200 keV, current ∼80–250 A, and pulse duration of ∼100–150 ns through a planar five-period electromagnetic wiggler has been carried out as a part of the development of a pulsed, high-power mm wave free-electron laser. Beam focusing is observed for peak wiggler magnetic fields up to 2.5 kG, and enhancements in propagated beam current efficiencies by 40%–65% are found for different values of the initial beam current.
Self-aligned sidewall gated resonant tunneling transistors
Authors: Kolagunta V. R. , Janes D. B. , Chen G. L. , Webb K. J. , Melloch M. R. , Youtsey C.
Published: July 2002

Three-terminal vertical quantum structures using a self-aligned sidewall gating technique have been developed. Resonant tunneling transistors with physical widths of about 0.7 μm demonstrate pinch-off of the resonant peak at room temperature. Comparable gating characteristics for forward and reverse drain-source biases indicate that the gating action is vertically uniform, making this topology suitable for the fabrication of low-dimensional structures and study of multiple quantum well devices.
Low-temperature processing of superconducting Tl2Ba2Ca1Cu2Ox films on CeO2 buffered sapphire
Authors: O’Connor J. D. , Dew-Hughes D. , Bramley A. P. , Grovenor C. R. M. , Goringe M. J. , Morley S. M.
Published: July 2002

Tl2Ba2Ca1Cu2Ox thin films with excellent alignment have been grown on CeO2 buffered R-plane sapphire using an ex situ anneal step in argon atmospheres at temperatures of 720–740 °C. With this low-temperature process we have overcome the serious problem of reaction layers being formed at the CeO2/Tl2Ba2Ca1Cu2Ox interface, which can degrade film properties. The presence of a sharp CeO2/Tl2Ba2Ca1Cu2Ox interface has been confirmed by x-ray diffraction, transmission electron microscopy, and high resolution electron microscopy observations. Films have well connected morphologies, with critical temperature (Tc) values of up to 101.6 K and critical current density (Jc) values of up to 1.25×105 A cm−2.
Three dimensional polarization dependence of OH bands absorption in potassium niobate crystals
Authors: Tong Xiaolin , Yariv Amnon , Zhang Min , Agranat Aharon
Published: July 2002

Absorption band countered on wave numbers 3504 and 6843 cm−1 have been observed in potassium niobate crystals. These absorption bands correspond to the transition energies of O–H stretching vibration, from the ground state to the first excited state and to the second excited state, respectively. Absorption bands around 3992 and 4476 cm−1 are attributed to the combination of O–H vibration plus libration. The integrated absorption intensities around 3504, 3992, and 4476 cm−1 are three dimensional polarization dependent which indicates the motion properties of hydrogen ions in the lattice.
Evidence for hole traps at the amorphous silicon/amorphous silicon–germanium heterostructure interface
Authors: Palsule C. , Paschen U. , Cohen J. D. , Yang J. , Guha S.
Published: July 2002

Voltage-pulse stimulated capacitance transient measurements on a series a-Si:H/a-Si, Ge:H devices disclose a large density of hole traps at or very close to the heterojunction interface. The transient signal magnitude is independent of temperature or applied bias, ruling out charge polarization effects or a defect creation process caused by the filling pulse. While the areal density of such hole traps is considerable (within a factor of 2 of 1011 cm−2 for all samples) these traps do not appear to behave as recombination centers. Also, the treatment of the a-Si:H/a-Si,Ge:H interface during growth can significantly alter the concentration of these traps.
Monolithic p-i-n GaAlAs multiple quantum well photorefractive device
Authors: Tayebati Parviz , Hantzis Christos , Sacks R. N.
Published: July 2002

In this letter, we report a monolithic p-i-n multiple quantum-well (MQW) GaAlAs photorefractive device operating in reflection mode. The device structure consists of a photorefractive structure grown with low temperature grown GaAlAs charge blocking layers on top of a 20 period n-type GaAlAs/AlAs quarter wave stack mirror. The device operates by double passing mutually coherent beams through the photorefractive structure exhibiting nearly 0.23% input diffraction efficiency. Because of fast sweep time in ultranarrow-barrier MQWs used here, the writing energy density of approximately 20 nJ/cm2 is a nearly seven (7) improvement over previously reported devices using 100 Å GaAlAs barriers.
Acceptor assessment and the role of carbon in semi-insulating GaAs
Authors: Moore W. J. , Henry R. L.
Published: July 2002

A method for identifying and quantifying acceptor contamination in semi-insulating (SI) GaAs is described. The method has been applied to commercial SI GaAs and to NRL zone-refined ingots. Results indicate that carbon is not the only acceptor present in significant concentrations in typical SI GaAs. Zinc is present in essentially all samples and is the dominant shallow acceptor in a significant fraction of the commercial material studied. The method consists of moving the Fermi level to the ground state of the shallowest acceptor present, usually carbon, by diffusing copper into the material. An infrared transmission measurement identifies the neutral acceptors from their electronic 1s-2p intrasite excitation. The strength of the absorption is proportional to the neutral acceptor concentration. Sensitivities are greatest for shallow acceptors where neutral acceptor concentrations as low as 5×1012 cm−3 can be identified and quantified.
Very small oxide-confined vertical-cavity surface-emitting lasers with a bulk active region
Authors: Deng H. , Deng Q. , Deppe D. G.
Published: July 2002

Data are presented characterizing very small oxide aperture vertical-cavity surface-emitting lasers with a 0.5-μm-thick bulk GaAs active region. The transverse far field is independent of the aperture size for diameters ⩽3 μm, although threshold reduction occurs with reducing aperture size down to ∼0.5 μm diam. Threshold reduction is attributed to improved overlap between the optical mode and gain profile. The large signal temporal response is characterized using optical gain switching.
Ultrahigh vacuum atomic force microscope study of 10–30 nm scale GaAs ridge structure formation by molecular beam epitaxy
Authors: Koshiba S. , Tanaka Ichiro , Nakamura Y. , Noge H. , Sakaki H.
Published: July 2002

The evolution of GaAs ridge structure formation by molecular beam epitaxy on a patterned substrate has been investigated using an ultrahigh vacuum atomic force microscope. It is found that the morphology of ridges can be quite irregular with random formation of various facets in the intermediate phase of growth, but self-smoothing processes of the lateral facets take place later on, leading to very sharp and smooth ridge structures in the end. The ridge top is quite sharp and straight with the height fluctuation of within 1–2 nm over the length of 1.4 μm. The role of the Ga atom flows from the side (111)B surfaces to the top (001) surface and their local modulations are considered to account for these observations.
Scanning tunneling microscopy of the atomic structure of the GaAs (110) surface at reduced tip sample separation
Authors: Heinrich A. J. , Wenderoth M. , Rosentreter M. A. , Schneider M. A. , Ulbrich R. G.
Published: July 2002

A scanning tunneling microscope was used to study the GaAs (110) surface at small tip-sample distances of about 2–3 Å. Atomically resolved images in this new mode referred to as near contact imaging mode revealed corrugation maxima both on the As and on the Ga surface sites at one sample voltage. These dual atom images differ significantly from the simultaneously measured conventional filled-state images at larger tunneling gap widths of 4–9 Å which show the As sublattice only. We interpret the dual atom images in terms of local tip induced modifications of the electronic surface states. These modifications are dragged along the surface with the scanning movement of the tip.
Calculation of temperature dependent threshold current density of ZnCdSe/ZnSe quantum well laser including many body effects
Authors: Bandyopadhyay A. , Basu P. K.
Published: July 2002

We have calculated the threshold current density of the ZnCdSe/ZnSe quantum well laser as a function of temperature by incorporating many body Coulomb interactions, both the heavy- and light hole subbands, as well as the temperature and energy dependencies of linewidth for laser transition. The effect of finite well width and well depth in the Coulomb interaction is also considered instead of taking strictly two-dimensional Coulomb potential. The calculated values of nominal threshold current density are 1.5 times larger than the values calculated without considering Coulomb interaction, whereas calculations using strictly two-dimensional Coulomb potential show 7% overestimation. Good agreement is obtained between the reported experimental results and the theoretical threshold current densities for a Zn0.83Cd0.17Se/ZnSe multiple quantum well laser assuming a value of 0.8 for the internal quantum efficiency.
Magnetism of epitaxial Mn1−xNixAs films on GaAs(001)
Authors: Shin T. , Park M. C. , Park Y. , Rothberg G. M. , Harbison J. P. , Tanaka M.
Published: July 2002

We have studied the magnetic, magneto-optic, and structural properties of Mn1−xNixAs films grown by molecular beam epitaxy on GaAs(001). The compositions are x=0.1, 0.2, 0.3 with a thickness about 100 nm. In the magneto-optical Kerr effect, Mn0.9Ni0.1As displays distinct longitudinal and polar Kerr rotations. At x=0.2, the effects are smaller, and are undetectable at x=0.3. Magnetometry yields a linear dependence of magnetization on Ni concentration. X-ray diffraction shows a gradual transition from hexagonal to orthorhombic structure. In contrast, bulk Mn1−xNixAs alloys at 300 K are paramagnetic and orthorhombic for x>0.02 and transform to an hexagonal phase at x=0.22.
Blue light second harmonic generation in the organic crystal ortho-Dicyanovinyl-anisole
Authors: Grossman Carl H. , Schulhofer-Wohl Samuel , Thoen Erik R.
Published: July 2002

Type I phase matched second harmonic generation (SHG) in the organic crystal ortho-Dicyanovinyl-anisole (DIVA) has been measured for a range of near infrared fundamental wavelengths (855–960 nm). Turning curves for type I phase matched SHG were derived from measured refractive index values and show noncritical phase matching at 860. Measured type I phase matched SHG is in close agreement with the calculated results and gives effective SHG coefficients ranging from 1.9 to 5.9 times as large as d32 of potassium niobate.