bluuebunny/crossref_metadata_2025 huggingface dataset:
Signal generation mechanisms, intracavity-gas thermal-diffusivity temperature dependence, and absolute infrared emissivity measurements in a thermal-wave resonant cavity
Authors: Shen Jun , Mandelis Andreas , Tsai Helen
Published: July 2002

The operating thermal power transfer mechanisms in a thermal-wave resonant cavity were explored theoretically and experimentally. Both steady-state ac (thermal-wave) and dc temperature rise were considered, and conduction and radiation heat transfer modes were found to co-exist in the cavity. By introducing controlled variable offset dc resistive heating superposed on the fixed-amplitude thermal-wave oscillation, it was also found that the thermal-diffusivity values of the intracavity gas can vary sensitively as a function of the dc temperature rise within a thin boundary layer adjacent to the cavity thermal source (a metallic Cr–Ni alloy strip). This resulted in the measurement of the temperature dependence of the thermal diffusivity of air. Furthermore, the observed dominance of thermal-wave radiation power transfer in the phase channel of the thermal-wave signal at large cavity lengths allowed the measurement of the absolute infrared emissivity of the thin Cr–Ni strip source material: ε=0.091±0.004.
A new sputtering device of radio-frequency magnetron discharge using a rectangular hollow-shaped electrode
Authors: Ohtsu Yasunori , Tsurume Yoshinobu , Fujita Hiroharu
Published: July 2002

A new sputtering device using a radio-frequency magnetron discharge with a rectangular hollow-shaped electrode has been developed for a low-pressure discharge (∼ a few mTorr). The spatial structures of the electron density, the etching rate of the target material (copper), and the deposition rate were measured in uniform and convex profiles of the externally applied magnetic field. The device realized the uniform use of the target material under the arrangement of the magnetic-field configuration. The resistivity of the deposited copper thin film was also obtained, which was found to be similar to that of conventional copper (∼10−8 Ω m).
Portable hard x-ray source for nondestructive testing and medical imaging
Authors: Boyer Craig N. , Holland Glenn E. , Seely John F.
Published: July 2002

A portable hard x-ray source has been developed for nondestructive testing, medical imaging, and flash x-ray radiography. The source is powered by a Marx generator that produces a 200 kV, 1.2 kA pulse of 60 ns full width at half maximum. The x-ray tube is composed of a tungsten anode and a mesh cathode. The time dependence of the voltage, current, and x-ray emission were measured and were in good agreement with computer simulations. The simulation model accounted for the 15 capacitors and 15 spark gap switches of the Marx generator and the perveance of the electron flow across the anode–cathode gap. The simulations indicated that the 5 J energy that was stored in the Marx generator was efficiently delivered to the x-ray tube. The measured x-ray exposure, 34 mR at a distance of 30 cm, was in good agreement with the calculated exposure. X-ray images are presented that demonstrate the capabilities of the x-ray source for medical imaging, nondestructive testing, and flash x-ray radiography.
Semi-insulating GaAs layers grown by molecular-beam epitaxy
Authors: Kordoš P. , Förster A. , Betko J. , Morvic M. , Novák J.
Published: July 2002

Temperature dependent conductivity and Hall-effect measurements were carried out on molecular-beam epitaxial GaAs layers grown at 420 °C and separated from the substrate. The layers exhibit semi-insulating properties with a room temperature resistivity of (6–7)×106 Ω cm. The electron Hall mobility is proportional to temperature as ∼T−1.1 and the room temperature value is 5900 cm2 V−1 s−1. From the (nHT−3/2) vs T−1 plot, a donor activation energy of 0.68 eV, different than in bulk semi-insulating GaAs, has been evaluated. A similar activation energy is observed in as-grown and annealed GaAs layers grown at 200–350 °C. This indicates that the high resistivity of GaAs grown at low temperatures might be explained by deep donor defects rather than As precipitates.
Nondestructive superresolution imaging of defects and nonuniformities in metals, semiconductors, dielectrics, composites, and plants using evanescent microwaves
Authors: Tabib-Azar M. , Pathak P. S. , Ponchak G. , LeClair S.
Published: July 2002

We have imaged and mapped material nonuniformities and defects using microwaves generated at the end of a microstripline resonator with 0.4 μm lateral spatial resolution at 1 GHz. Here we experimentally examine the effect of microstripline substrate permittivity, the feedline-to-resonator coupling strength, and probe tip geometry on the spatial resolution of the probe. Carbon composites, dielectrics, semiconductors, metals, and botanical samples were scanned for defects, residual stresses, subsurface features, areas of different film thickness, and moisture content. The resulting evanescent microwave probe (EMP) images are discussed. The main objective of this work is to demonstrate the overall capabilities of the EMP imaging technique as well as to discuss various probe parameters that can be used to design EMPs for different applications.
A versatile source to produce high-intensity, pulsed supersonic radical beams for crossed-beam experiments: The cyanogen radical CN(X2Σ+) as a case study
Authors: Kaiser R. I. , Ting J. W. , Huang L. C. L. , Balucani N. , Asvany O. , Lee Y. T. , Chan H. , Stranges D. , Gee D.
Published: July 2002

In our laboratory a novel and convenient technique has been developed to generate an intense pulsed cyano radical beam to be employed in crossed molecular beam experiments investigating the chemical dynamics of bimolecular reactions. CN radicals in their ground electronic state Σ+2 are produced in situ via laser ablation of a graphite rod at 266 nm and 30 mJ output power and subsequent reaction of the ablated species with molecular nitrogen, which acts also as a seeding gas. A chopper wheel located after the ablation source and before the collision center selects a 9 μs segment of the beam. By changing the delay time between the pulsed valve and the choppper wheel, we can select a section of the pulsed CN(X2Σ+) beam choosing different velocities in the range of 900–1920 ms−1 with speed ratios from 4 to 8. A high-stability analog oscillator drives the motor of the chopper wheel (deviations less than 100 ppm of the period), and a high-precision reversible motor driver is interfaced to the rotating carbon rod. Both units are essential to ensure a stable cyanogen radical beam with velocity fluctuations of less than 3%. The high intensity of the pulsed supersonic CN beam of about 2–3×1011 cm−3 is three orders of magnitude higher than supersonic cyano radical beams employed in previous crossed molecular beams experiments. This data together with the tunable velocity range clearly demonstrate the unique power of our newly developed in situ production of a supersonic CN radical beam. This versatile concept is extendible to generate other intense, pulsed supersonic beams of highly unstable diatomic radicals, among them BC, BN, BO, BS, CS, SiC, SiN, SiO, and SiS, which are expected to play a crucial role in interstellar chemistry, chemistry in the solar system, and/or combustion processes.
A novel method for determining thin film density by energy-dispersive x-ray reflectivity
Authors: Wallace W. E. , Wu W. L.
Published: July 2002

A technique utilizing the reflection of x-rays to determine material density at flat surfaces is described. The effects of sample misalignment limit the accuracy of x-ray reflectivity as typically practiced. These effects may be properly accounted for by measuring the critical angle for reflection at many different x-ray wavelengths simultaneously from which an extrapolation of the position of the critical angle at infinite wavelength may be made. This extrapolation has the effect of correcting for sample misalignment. Use of the technique is demonstrated for single-crystal silicon surfaces and for silica spin-on-glass thin films.
Development of large radio frequency driven negative ion sources for fusion
Authors: Vollmer O. , Falter H. , Frank P. , Heinemann B. , Kraus W. , Massmann P. , McNeely P. , Riedl R. , Speth E. , Trainham R. , Wilhelm R.
Published: July 2002

A new large area, high power rf source for negative ion beam systems has been developed. The source operates very reliably and has the potential for long pulse operation. Current densities up to 15 mA/cm2 could be extracted with a cold plasma grid at 0.65 Pa source pressure. By pure volume production 9 mA/cm2 current density at the same pressure level has been achieved with the addition of argon to the source operating gas.
Production of submicrometer period Bragg gratings in optical fibers using wavefront division with a biprism and an excimer laser source
Authors: Rizvi N. H. , Gower M. C.
Published: July 2002

Biprisms are used as a method of wavefront division with an excimer laser source to holographically write first-order Bragg gratings in single-mode optical fibers. Gratings with a period of 556 nm and peak reflectivity of 62% are produced using single pulses from a krypton fluoride (KrF) laser. A comparison is made between grating production with line-narrowed and nonline narrowed lasers.
Modified donor–acceptor pair luminescence in heavily nitrogen-doped zinc selenide
Authors: Kothandaraman C. , Neumark G. F. , Park R. M.
Published: July 2002

The luminescence from heavily doped ZnSe:N shows a deep broadband whose position was found to depend strongly on the excitation intensity and sample temperature. The peak was found to shift towards higher energies with increasing intensity, but in contrast to the standard donor–acceptor pair (DAP) model, shifted towards lower energies with increasing temperatures. This behavior is explained using a modified DAP model that takes into account the perturbations of the band and impurity states caused by fluctuations in the concentrations of the ionized impurities. This model led to an estimate of 2.52 eV for the PL peak, with a width of 140 meV, for the case of low temperature and low excitation intensity, in rough agreement with our observations. The effect of these fluctuations on film conductivity is also discussed.
Wavelength insensitive passive polarization converter fabricated by poled polymer waveguides
Authors: Oh Min-Cheol , Shin Sang-Yung , Hwang Wol-Yon , Kim Jang-Joo
Published: July 2002

A passive TE to TM polarization mode converter is fabricated by using poled polymer waveguides. The optic axis of the poling induced waveguide is slowly rotated 90° by using a slowly varying structure of poling electrodes. Thus the polarization conversion is achieved as the guided mode propagates through the waveguide. TE to TM mode conversion is observed with a polarization extinction ratio higher than 30 dB, and the excess loss is less than 1 dB. The polarization conversion is relatively insensitive to wavelength since the device contains no periodic structures. These devices are easier to fabricate than others containing periodic structures.
Carrier capture efficiency of AlGaAs/GaAs quantum wires affected by composition nonuniformity of an AlGaAs barrier layer
Authors: Wang Xue-Lun , Ogura Mutsuo , Matsuhata Hirofumi
Published: July 2002

Effects of composition nonuniformity of an AlGaAs barrier layer on the carrier capture efficiency of an AlGaAs/GaAs quantum wire (QWR) grown on nonplanar substrates are investigated using photoluminescence measurements. The photogenerated carriers first experience a redistribution from the high Al composition region to the low Al composition region in the AlGaAs barrier layer due to the potential difference caused by the composition nonuniformity before they are captured by quantum well or QWR regions. Such a carrier redistribution greatly affects the carrier capture efficiency of QWR structures.
Biaxial alignment of TiN films prepared by ion beam assisted deposition
Authors: Gerlach J. W. , Preckwinkel U. , Wengenmair H. , Kraus T. , Rauschenbach B.
Published: July 2002

The biaxial alignment of TiN on Si(111) films prepared by nitrogen ion beam assisted deposition at room temperature was studied. By reactive deposition within a nitrogen environment a preferred {111} orientation was obtained the growing TiN crystallites. In contrast, a nitrogen ion bombardment perpendicular to the surface of the substrate during deposition causes an {001} alignment of the crystallites. A 55° ion beam incidence produces both {111}-orientation relative to the surface and {100}-orientation relative to the ion beam. This results in a totally fixed orientation of the crystallites. Simultaneous UV-light illumination during ion bombardment promotes a uniformly oriented growth.
Selective area growth of metal nanostructures
Authors: Adams D. P. , Mayer T. M. , Swartzentruber B. S.
Published: July 2002

Nanometer-scale metal lines are fabricated onto Si(100) substrates by scanning tunneling microscope (STM) based lithography and subsequent chemical vapor deposition. An STM tip is first used to define areas for metal layer growth by electron stimulated desorption of adsorbed hydrogen. Exposure to Fe(CO)5 at 275 °C results in preferential deposition of Fe onto Si dangling bond sites (i.e., depassivated areas defined by the STM tip), while the monohydride resist remains intact in surrounding areas. Fe metal lines with widths ∼10 nm are constructed using this selective-area, autocatalytic growth technique.
Polymer and polymer/metal interface characterization via Fowler–Nordheim tunneling measurements
Authors: Hümmelgen I. A. , Roman L. S. , Nart F. C. , Péres L. O. , de Sá E. L.
Published: July 2002

In this letter we present a procedure used to characterize metal/polymer interfaces via Fowler-Nordheim tunneling current measurements and use it to obtain the electron affinity of the PPV (poly p-phenylene vinylene) and to calculate the metal/PPV barrier heights using different Al/PPV/metal (metal: Ga,In,Sn) structures.
Refractive indices of zincblende structure β-GaN(001) in the subband-gap region (0.7–3.3 eV)
Authors: Vidal M. A. , Ramírez-Flores G. , Navarro-Contreras H. , Lastras-Martínez A. , Powell R. C. , Greene J. E.
Published: July 2002

Refractive indices n and absorption coefficients α of epitaxial metastable zincblende structure β-GaN(001) were determined over the subband-gap energy range between 0.8–3.1 eV from an analysis of optical transmission spectra. n was found to vary from 2.25 to 0.8 eV (1.55 μm) to 2.50 at 3.1 eV (0.4 μm) with an energy E (eV) dependence that is well described by a Sellmeir-type dispersion relationship, n2(E)=1+148/(38.3−E2). The refractive indices of β-GaN are 3%–4% smaller than previously reported values for hexagonal α-GaN.
Photonic band gap quantum well and quantum box structures: A high-Q resonant cavity
Authors: Lin Shawn-Yu , Hietala V. M. , Lyo S. K. , Zaslavsky A.
Published: July 2002

We have tested a series of high-Q photonic band gap (PBG) resonant cavities in the mm-wave regime and achieved a cavity-Q of 2.3×104, the highest value reported among all two- and three-dimensional PBG cavities. We have also systematically varied the size and reflectivity of such cavities to study their effect on cavity properties such as cavity modal frequency, linewidth, and cavity Q value. We show that the resonant frequencies can be tuned throughout the PBG regime and that linewidths (or equivalently Q value) can be varied over two orders of magnitude (i.e., a Q value from ∼2.7×102 to 2.3×104).
Qualitative model for the fatigue-free behavior of SrBi2Ta2O9
Authors: Al-Shareef H. N. , Dimos D. , Boyle T. J. , Warren W. L. , Tuttle B. A.
Published: July 2002

SrBi2Ta2O9 (SBT) thin films are known to exhibit no polarization fatigue with electric field cycling. However, we have discovered that optical illumination combined with a bias voltage near the switching threshold can result in significant (≳90%) suppression of the switchable polarization of SBT thin film capacitors. A similar effect has also been reported for Pb(ZrxTi1−x)O3 (PZT) capacitors. However, it is found that electric field cycling of the optically fatigued SBT capacitors results in near-complete recovery of the suppressed polarization. In contrast, electric field cycling of optically fatigued PZT capacitors does not result in any polarization recovery. These results suggest that optical fatigue in both SBT and PZT capacitors results from pinning of domain walls due to trapping of the photogenerated carriers at domain boundaries, whereas the recovery exhibited by SBT thin films indicates that the domain walls are more weakly pinned in SBT than in PZT thin films. Consequently, the fatigue-free behavior of SBT thin films during electric field cycling can be viewed as a competition between domain wall pinning due to charge trapping and domain wall unpinning by the cycling field; the latter process occurring at least as rapidly as the former.
Growth of Si and C δ-doped nipi doping superlattices in GaAs by metal organic vapor phase epitaxy
Authors: Li G. , Jagadish C. , Johnston M. B. , Gal M.
Published: July 2002

We have optimized growth conditions of metal organic vapor phase epitaxy (MOVPE) in order to grow Si and C δ-doped nipi doping superlattices in GaAs. Trimethylaluminium (TMAl) and silane (SiH4) were used as p-type and n-type doping precursors, respectively. We report that at 630 °C, full compensation of free electrons and holes can be obtained in the MOVPE-grown Si and C δ-doped nipi doping superlattices over a very wide range of the sheet carrier densities (1012–1013 cm−2) by choosing proper TMAl flow rate and Si δ-doping time or SiH4 flow rate. The experimental results on electrical and optical characterization of Si and C δ-doped nipi doping superlattices in GaAs with 150 Å thick undoped spacer layers are presented.
Formation of coherent superdots using metal-organic chemical vapor deposition
Authors: Ledentsov N. N. , Böhrer J. , Bimberg D. , Kochnev I. V. , Maximov M. V. , Kop’ev P. S. , Alferov Zh. I. , Kosogov A. O. , Ruvimov S. S. , Werner P. , Gösele U.
Published: July 2002

We demonstrate direct growth of electronically coupled zero-dimensional structures forming a super-quantum dot using metal-organic chemical vapor deposition. After the first sheet with InGaAs pyramids is formed on GaAs surface, alternate short-period GaAs-InGaAs deposition leads to spontaneous formation of layered structures driven by the energetics of Stranski–Krastanow growth. As a result columnlike InGaAs structures each having a characteristic lateral size of ∼23 nm at the top and composed of many closely packed InGaAs parts are formed. The full width at half maximum of superdot luminescence of 28 meV at 8 K indicates good average uniformity of the superdot ensemble. Absorption is found to be resonant with luminescence.
Photonic band-structure effects in the visible and near ultraviolet observed in solid-state dielectric arrays
Authors: Rosenberg A. , Tonucci R. J. , Bolden E. A.
Published: July 2002

Two-dimensional photonic band-structure effects have been observed in the visible and near-uv regions, between 350 and 800 nm. These effects appear in all-solid-state arrays of glass cylinders in a glass matrix. The arrays have center-to-center nearest-neighbor separations between 0.188 and 0.278 μm, perfect long-range order, and low refractive index contrast. For light propagating perpendicular to the cylinder axes, very narrow attenuations appear in the transmission spectra as a result of the photonic band structure. The positions of these attenuations are determined by the periodicity, composition, and symmetry of the arrays.
Degradation of Si1−xGex epitaxial devices by proton irradiation
Authors: Ohyama H. , Hayama K. , Vanhellemont J. , Poortmans J. , Caymax M. , Takami Y. , Sunaga H. , Nashiyama I. , Uwatoko Y.
Published: July 2002

Irradiation damage in n+-Si/p+-Si1−xGex/n-Si epitaxial diodes and heterojunction bipolar transistors by protons is studied. The degradation of the performance increases with increasing proton fluence, whereas it decreases with increasing germanium content and proton energy. The damage coefficient for proton irradiation is nearly the same as for neutron irradiation and is about three orders of magnitude larger than that for electron irradiation. This difference is due to the different number of knock-on atoms and the nonionizing energy loss, which is correlated to the difference of mass and the possibility of nuclear collisions.
Controlled electroluminescence spectra of porous silicon diodes with a vertical optical cavity
Authors: Araki Minoru , Koyama Hideki , Koshida Nobuyoshi
Published: July 2002

It is demonstrated that a porous silicon (PS) optical cavity is available for the electroluminescence (EL) PS diode configuration. The PS diode is composed of a thin Au film, a light-emitting PS layer, a multilayered PS mirror, a p-type Si substrate, and an ohmic contact. When a sufficient bias voltage is applied to the diode, a uniform visible light emission is observed through the top contact. The EL intensity is fairly proportional to the driving current over a wide range of operation. The bandwidth of the EL spectrum is significantly reduced in comparison to that of the conventional PS diodes, owing to a resonance effect induced between the Au film and the multilayered PS mirror. These results suggest that the PS technology is a promising process for applications in monolithic integrated optoelectronics.
Indium doping of CdTe polycrystalline films prepared by co-sputtering of CdTe–In–Cd targets
Authors: Becerril M. , Zelaya-Angel O. , Ramı́rez-Bon R. , Espinoza-Beltrán F. J. , González-Hernández J.
Published: July 2002

Indium doped CdTe polycrystalline films were grown on Corning glass substrates at room temperature by co-sputtering from a CdTe–Cd–In target. The elemental Cd and In were glued onto the CdTe target covering small areas. The electrical, structural, and optical properties were analyzed as a function of the concentration of both elements. It was found that when Cd and In are simultaneously incorporated, the electrical resistivity drops and the carrier concentration increases. In both cases the changes are of several orders of magnitude. From the results, we conclude that, using this deposition technique, n-type In doped CdTe polycrystalline films can be produced.
X-ray absorption fine structure determination of the local environment of Er3+ in glass
Authors: Peters P. M. , Houde-Walter S. N.
Published: July 2002

Erbium LIII-edge x-ray absorption fine structure (XAFS) and I13/24 excited state lifetime measurements were performed on aluminosilicate, fluorosilicate, and phosphate glasses with varying erbium concentration. The local erbium environment is shown to be unique in each host. In the aluminosilicate, erbium is found to have 6.4 nearest oxygen neighbors at a distance of 2.22 Å and with a Debye–Waller factor of 0.031 Å2. Erbium in the fluorosilicate glass was found to be more highly coordinated with 7.5 nearest neighbor anions. Erbium in the phosphate glass is found to have a smaller disorder factor of 0.021 Å2 when compared with the silicate glasses. No variation of the environment (3 shells) is observed with changes in rare earth concentration, while the excited state lifetime varies from 1.0 to 9.8 ms in the aluminosilicates, suggesting the absence of erbium clustering at XAFS detectable distances.
Fast commutation of high current in double wire array Z-pinch loads
Authors: Davis J. , Gondarenko N. A. , Velikovich A. L.
Published: July 2002

A dynamic model of multi-MA current commutation in a double wire array Z-pinch load is proposed and studied theoretically. Initially, the load is configured as nested concentric wire arrays, with the current driven through the outer array and imploding it. Once the outer array or the annular plasma shell formed from it approaches the inner array, the imploded plasma might penetrate through the gaps between the wires, but the azimuthal magnetic field is trapped due to both the high conductivity of the inner wires and the inductive coupling between the two parts of the array, causing a rapid switching of the total current to the inner part of the array.
Photopumped laser operation of an oxide post GaAs–AlAs superlattice photonic lattice
Authors: Evans P. W. , Wierer J. J. , Holonyak N.
Published: July 2002

Data are presented on the laser operation of photoexcited active hexagonal photonic lattices consisting of a GaAs–AlAs superlattice slab waveguide patterned with Zn-disordered AlGaAs posts that are converted to oxide. The semiconductor-oxide-post photonic lattice structure lases without the benefit of cleaved edges or other reflecting interfaces owing to strong local optical feedback provided by the high refractive index contrast between oxide posts and the active GaAs–AlAs superlattice. As the pump area is increased at constant pump power, the threshold intensity decreases as higher Q modes in an effectively larger cavity are excited. Similar hexagonal photonic lattices with nonoxidized posts (disordered AlGaAs posts) operate as lasers, but only with the assistance of cleaved edges and by shifting to longer wavelength. The oxide post photonic lattice is compatible with current-driven photonic lattice lasers or active filters.
Lattice engineered compliant substrate for defect-free heteroepitaxial growth
Authors: Ejeckam F. E. , Lo Y. H. , Subramanian S. , Hou H. Q. , Hammons B. E.
Published: July 2002

Presented here is proof-of-principle that a thin single crystal semiconductor film—when twist-wafer bonded to a bulk single crystal substrate (of the same material)—will comply to the lattice constant of a different single crystal semiconductor thick film grown on its surface. In our experiment, a 100 Å film of GaAs was wafer bonded to a GaAs bulk substrate, with a large twist angle between their 〈110〉 directions. The resultant twist boundary ensures high flexibility in the thin film. Dislocation-free films of In0.35Ga0.65P(∼1% strain) were grown with thicknesses of 3000 Å, thirty times the Matthews–Blakeslee critical thickness, on twist-wafer-bonded films of GaAs.
Selective Cu-atom transportation from a tip of scanning tunneling microscope onto an Ag(110) surface by chemical reaction
Authors: Okawa Y. , Tanaka K.
Published: July 2002

Cu-atom transportation from a tip of scanning tunneling microscope onto an Ag(110) surface was performed using chemical reactions. A copper coated tungsten tip was obtained by scanning a Cu surface. By scanning an Ag(110) surface with the copper coated tip in the presence of O2, the growth of Cu–O rows was observed on the surface, that is, a chemical transportation of Cu atoms occurs by reacting with oxygen. When an Ag(110) surface was covered with an Ag–O domain and a carbonate domain, a selective chemical transportation of Cu atoms from the tip onto the carbonate domain was attained. Contrary to this, when the Cu atoms were vaporized over the surface, the Cu atoms preferentially reacted with the Ag–O domain.
Structure and uniaxial magnetocrystalline anisotropy of intermetallic compounds La2Co17−xTix
Authors: Liu Quanlin , Liang Jingkui , Rao Guanghui , Tang Weihua , Sun Jirong , Chen Xiaolong , Shen Baogen
Published: July 2002

The crystal structure and magnetic properties of intermetallic compounds La2Co17−xTix (0.8⩽x⩽1.2) have been investigated by x-ray powder diffraction and magnetic measurement. The lattice parameters of La2Co17−xTix with the rhombohedral Th2Zn17-type structure are a=8.518–8.531 Å, c=12.344–12.379 Å. Ti atoms show a strong preference for occupying 6c crystallographic positions. The La2Co17−xTix compounds are ferromagnetic. The Curie temperature decreases from 972 to 872 K, and the saturation magnetic moment decreases from 23.2 to 21.3 μB/f.u. with x=0.8–1.2. The La2Co16Ti compound exhibits favorable uniaxial anisotropy, and the easy magnetization direction is parallel to the c axis. The anisotropy field is 23 kOe at 1.5 K for this compound.
Performance of corrugated quantum well infrared photodetectors
Authors: Chen C. J. , Choi K. K. , Chang W. H. , Tsui D. C.
Published: July 2002

Corrugated quantum well infrared photodetectors (C-QWIPs) utilize total internal reflection to couple normal incident light into the detectors. In this work, we performed a systematic study on C-QWIPs with cutoff wavelength λc ranging from 5 to 17.3 μm and device areas ranging from 50×50 μm2 to 500×500 μm2. We found that the coupling efficiency of the C-QWIPs is, indeed, independent of both the detection wavelength and the pixel size, as expected. Compared to devices with a standard 45° edge coupling, the C-QWIP increases the background photocurrent to a dark current ratio by a factor between 2.4 and 4.4, thereby increasing the background limited temperature by 3–5 K. At the same time, the detectivity D* is also increased by a factor around 2.4. For λc=9.4 μm, the peak detectivity Dp* and the blackbody detectivity Dbb* at 78 K are measured to be 4.5×1010 cm Hz/W and 4.5×109 cmHz/W, respectively.
Enhanced thermal stability and microhardness in Zr–Ti–Cu–Ni–Be bulk amorphous alloy by carbon addition
Authors: Wang Wei-Hua , Wei Q. , Bai H. Y.
Published: July 2002

The effects of carbon addition on thermal stability and hardness of Zr41Ti14Cu12.5Ni10Be22.5 bulk amorphous alloy were investigated. It is found that a small amount of carbon addition further extends the supercooled liquid range and enhances the thermal stability and strength of the alloy. More carbon addition results in the formation of a crystalline and amorphous mixture accompanied by a pronounced increase in microhardness. The effects of the carbon addition on the amorphous alloy are discussed from the structural point of view.
Effect of Te as a surfactant on the optical properties of InAs self-assembled quantum dots
Authors: Sáfar G. A. M. , Rodrigues W. N. , Cury L. A. , Chacham H. , Moreira M. V. B. , Freire S. L. S. , de Oliveira A. G.
Published: July 2002

We report on optical experiments in self-assembled InAs quantum dots grown on (100) and (311)A GaAs surfaces which were precovered with Te. We observe a strong reduction of the luminescence intensity with increasing Te coverage in the (100)-oriented samples. The Te-induced luminescence reduction is, however, much smaller in the (311)A oriented samples.
Compositional inhomogeneity and immiscibility of a GaInN ternary alloy
Authors: Wakahara Akihiro , Tokuda Takashi , Dang Xiao-Zhong , Noda Susumu , Sasaki Akio
Published: July 2002

Compositional inhomogeneity in a GaInN ternary alloy layer is investigated. A theoretical estimation of the interaction parameter based on the delta lattice parameter suggests that the immiscibility of InN in a nitride alloy is very strong. We investigate the compositional splitting and the existence of InN inclusion in the GaInN epilayer grown on sapphire (0001) substrates. The mechanism of compositional inhomogeneity is discussed.
High carrier lifetime InSb grown on GaAs substrates
Authors: Michel E. , Mohseni H. , Kim J. D. , Wojkowski J. , Sandven J. , Xu J. , Razeghi M. , Bredthauer R. , Vu P. , Mitchel W. , Ahoujja M.
Published: July 2002

We report on the growth of near bulklike InSb on GaAs substrates by molecular beam epitaxy despite the 14% lattice mismatch between the epilayer and the substrate. Structural, electrical, and optical properties were measured to assess material quality. X-ray full widths at half-maximum were as low as 55 arcsec for a 10 μm epilayer, peak mobilities as high as ∼125 000 cm2/V s, and carrier lifetimes up to 240 ns at 80 K.
Infrared near-field imaging of implanted semiconductors: Evidence of a pure dielectric contrast
Authors: Lahrech A. , Bachelot R. , Gleyzes P. , Boccara A. C.
Published: July 2002

In this letter, we demonstrate the ability of our reflection mode scanning near-field optical microscope functioning in the mid-infrared to reveal infrared dielectric contrast in absence of any topographical contrast. This contrast is induced by local structures prepared by low energy boron implantation in silicon.
Long-wavelength infrared photodetectors based on InSbBi grown on GaAs substrates
Authors: Lee J. J. , Kim J. D. , Razeghi M.
Published: July 2002

We demonstrate the operation of InSbBi infrared photoconductive detectors grown by low-pressure metalorganic chemical vapor deposition on semi-insulating GaAs substrates. The fabricated photodetector showed a cutoff wavelength of 7.7 μm at 77 K. The responsivity of the InSbBi photodetector at 7 μm was about 3.2 V/W at 77 K. The corresponding Johnson-noise limited detectivity was 4.7×108 cm Hz1/2/W. The carrier lifetime was estimated to be about 86 ns from the voltage-dependent responsivity measurements.
Organic solid-state lasers with imprinted gratings on plastic substrates
Authors: Berggren M. , Dodabalapur A. , Slusher R. E. , Timko A. , Nalamasu O.
Published: July 2002

Optically pumped laser emission has been observed from thin films of 8-hydroxyquinolinato aluminum (Alq) doped with a DCM dye deposited on a diffraction grating formed by imprinting a film of BCB with a mold. The BCB film, which is 4 μm thick, is deposited on a silicon or a flexible plastic substrate. Laser emission occurs at a wavelength near 655 nm which corresponds to the third order of the grating, which has a periodicity of ∼0.6 μm.
Changes in structure and nature of defects by annealing of fluorinated amorphous carbon thin films with low dielectric constant
Authors: Yokomichi Haruo , Hayashi Tohru , Masuda Atsushi
Published: July 2002

Thermal stability of fluorinated amorphous carbon (a-C:F) thin films with a low dielectric constant was investigated by electron spin resonance (ESR), infrared (IR) absorption, optical absorption, and x-ray photoelectron spectroscopy (XPS) as well as measurements of film thickness and dielectric constant. IR and XPS measurements suggested that the strength of the CF3 and CF2 bonding configurations against annealing are weaker than that of the CF bonding configuration. ESR measurements revealed that the dangling bond density decreased by one order of magnitude after annealing at 300 °C and increased after annealing at 400 °C. Furthermore, the g value and the linewidth of the ESR spectrum decreased with increasing annealing temperature. Based on these results, the changes in structure and defect configuration are discussed.
Significant reduction of cathodoluminescent degradation in sulfide-based phosphors
Authors: Fitz-Gerald J. M. , Trottier T. A. , Singh R. K. , Holloway P. H.
Published: July 2002

The degradation of cathodoluminescent (CL) brightness under prolonged electron-beam excitation of phosphors has been identified as one of the outstanding critical issues for flat-panel field-emission displays. In this letter, we have demonstrated that a TaSi2 coating on Y2O2S:Eu3+ phosphors substantially inhibits the cathodoluminescent degradation characteristics without reducing its efficiency. The coating was deposited by pulsed laser deposition of TaSi2 targets onto a fluidized bed containing phosphor particles. Cathodoluminescent degradation experiments conducted at 2 keV and at 150 μA/cm2, showed that the CL brightness decreased by more than 50% after a Coulomb load of 15 C/cm2 on the uncoated material. In contrast, the TaSi2-coated phosphor powders showed much less degradation, with CL brightness only decreasing by approximately 12% after electron irradiation with the same dose.
Metal–oxide–semiconductor capacitance–voltage characteristics and band offsets for Si1−yCy/Si heterostructures
Authors: Rim K. , Mitchell T. O. , Singh D. V. , Hoyt J. L. , Gibbons J. F. , Fountain G.
Published: July 2002

Metal–oxide–semiconductor (MOS) capacitors were fabricated on in situ doped n- and p-type Si1−yCy/Si heterostructures grown on Si substrates by chemical vapor deposition. Strained Si1−yCy epitaxial layers with substitutional carbon contents up to 1.6% were studied. High frequency and quasistatic capacitance–voltage (C–V) measurements exhibit well-behaved MOS characteristics, indicating high electronic material quality. Band alignments were extracted from MOS C–V measurements and one-dimensional device simulations performed over a range of temperatures. The conduction band energy of strained Si1−yCy is lower than that of Si by approximately 65 meV for 1 at. % carbon, while the valence band shows negligible offset to Si valence band.
Improvement of Ge self-organized quantum dots by use of Sb surfactant
Authors: Peng C. S. , Huang Q. , Cheng W. Q. , Zhou J. M. , Zhang Y. H. , Sheng T. T. , Tung C. H.
Published: July 2002

A Sb-mediated growth technique is developed to deposit Ge quantum dots (QDs) of small size, high density, and free of dislocations. These QDs were grown at low growth temperature by molecular beam epitaxy. The photoluminescence and absorption properties of these Ge QDs suggest an indirect-to-direct conversion, which is in good agreement with a theoretical calculation.
Investigation of optically active E1 transversal optic phonon modes in AlxGa1−xN layers deposited on 6H–SiC substrates using infrared reflectance
Authors: Wisniewski P. , Knap W. , Malzac J. P. , Camassel J. , Bremser M. D. , Davis R. F. , Suski T.
Published: July 2002

We report an investigation, performed in the full composition range x=0–1, of the change in infrared reflectivity spectra of AlxGa1−xN layers deposited on 6H–SiC substrates. We have found two different transverse E1(TO) phonon frequencies that can be assigned to AlN-like and GaN-like modes. The composition dependences of these frequencies can be well approximated by linear functions and the oscillator strengths scale like the corresponding Al and Ga mole fractions, respectively. On a purely experimental basis, this establishes evidence of a two-mode behavior for this controversial alloy system. The frequencies of the impurity mode of Ga in AlN (622 cm−1) and of the impurity mode of Al in GaN (643 cm−1) were determined.
Reversible bending of carbon nanotubes using a transmission electron microscope
Authors: Knechtel Walter H. , Düsberg Georg S. , Blau Werner J. , Hernández Eduardo , Rubio Angel
Published: July 2002

Multiwall carbon nanotubes can be bent by changing the current density of the electron beam in a transmission electron microscope. The effect could be observed in a small fraction of nanotubes in the investigated samples. The bending can be varied continuously, is reversible, and highly reproducible. On removing the force which makes them bend, they relax to their originally straight shape without any damage, thus exhibiting spring-like behavior. Possible mechanisms for this effect are discussed.
Improved carrier collection in intermixed InGaAs/GaAs quantum wells
Authors: Dao L. V. , Johnston M. B. , Gal M. , Fu L. , Tan H. H. , Jagadish C.
Published: July 2002

We have used photoluminescence up conversion to study the carrier capture times into intermixed InGaAs/GaAs quantum wells. We have found that the capture into the intermixed wells is markedly faster than capture into the reference (unintermixed) quantum wells. The reasons for the significant reduction in the capture time is related to the shape of the intermixed quantum well. Such a reduction in the capture time is beneficial both in terms of the quantum efficiency and the frequency response of intermixed optoelectronic devices.
Near-field optical fiber probe optimized for illumination–collection hybrid mode operation
Authors: Saiki T. , Matsuda K.
Published: July 2002

The structure of a near-field probe was optimized for illumination-collection hybrid mode (I–C mode) operation. We developed a highly sensitive probe with a sharp-edged aperture and a double-tapered structure fabricated by a chemical etching technique. Through measurement of the photoluminescence (PL, λ=1 μm) image of single quantum dots, the performance of many versions of the probe with different aperture diameters, ranging from 80 to 500 nm, was systematically evaluated. In addition to the throughput and spatial resolution, the absolute value of the PL collection efficiency of the probe in (I–C mode) was also estimated for the first time. A collection efficiency several times greater than that of an objective lens with a numerical aperture of 0.8 was achieved with high spatial resolution in the 130–200 nm (λ/8–λ/5) range.
Dry etching of GaN substrates for high-quality homoepitaxy
Authors: Schauler M. , Eberhard F. , Kirchner C. , Schwegler V. , Pelzmann A. , Kamp M. , Ebeling K. J. , Bertram F. , Riemann T. , Christen J. , Prystawko P. , Leszczynski M. , Grzegory I. , Porowski S.
Published: July 2002

Chemically assisted ion-beam etching (CAIBE) was used to remove subsurface damage from polished GaN bulk substrates prior to growth. Subsequently, GaN layers were deposited by metalorganic vapor phase epitaxy. Only the CAIBE-treated areas reveal a mirror-like surface without trenches, scratches, or holes. A dramatic increase of crystal quality is determined by low-temperature cathodoluminescence (CL). Compared to not CAIBE-treated material, the CL intensity is improved by a factor of 1000 and the linewidth is ten times narrower.
Magnetic tunnel junctions thermally stable to above 300 °C
Authors: Parkin S. S. P. , Moon K.-S. , Pettit K. E. , Smith David J. , Dunin-Borkowski R. E. , McCartney M. R.
Published: July 2002

Magnetic tunnel junctions formed from sandwiches of magnetically hard Co75Pt12Cr13 and magnetically soft Co88Pt12 ferromagnetic layers separated by thin alumina tunnel barriers are shown to be thermally stable to temperatures in excess of 300 °C. A comparison of cross-section transmission electron micrographs of an untreated sample and a similar one annealed at 350 °C indicates that the thickness of the amorphous tunnel barrier is slightly decreased after annealing. The resistance and magnetoresistance are only slightly affected by annealing at temperatures of up to ∼300 °C but then decrease monotonically at higher annealing temperatures. Interaction of the alumina layer with the adjacent ferromagnetic layers is the likely cause of this decrease.
Growth of epitaxial silicon at low temperatures using hot-wire chemical vapor deposition
Authors: Thiesen J. , Iwaniczko E. , Jones K. M. , Mahan A. , Crandall R.
Published: July 2002

We demonstrate epitaxial silicon growth of 8 Å/s at temperatures as low as 195 °C, using hot-wire chemical vapor deposition. Characterization by transmission electron microscopy shows epitaxial layers of Si. We briefly discuss various aspects of the process parameter space. Finally, we consider differences in the chemical kinetics of this process when compared to other epitaxial deposition techniques.
High dielectric constant Hf–Sn–Ti–O thin films
Authors: Schneemeyer L. F. , van Dover R. B. , Fleming R. M.
Published: July 2002

High dielectric constant Hf–Sn–Ti–O thin-film materials were identified using a compositional-spread approach. Thin films of composition Hf0.2Sn0.05Ti0.75O2 prepared at 250 °C have excellent dielectric properties: 40–70-nm-thick films with a dielectric constant of 40–60 were obtained, depending on the processing conditions, yielding a specific capacitance of 9–17 fF/μm2. Breakdown fields were measured to be about 3–4 MV/cm, yielding a figure of merit εε0Ebr∼19 μC/cm2. Leakage currents, measured at 1 MV/cm, were in the range 10−7−10−6 A/cm2.
Polarization measurements in anodized Al–Al2O3–Au diodes
Authors: Hickmott T. W.
Published: July 2002

A method of measuring polarization in metal–insulator–metal diodes is presented that utilizes quasi-dc current–voltage characteristics. For rectifying Al–Al2O3–Au diodes, negative bias establishes a reproducible polarization state. The difference between subsequent current–voltage curves with positive bias measures the amount of polarization.
The use of ionic salt dyes as amorphous, thermally stable emitting layers in organic light-emitting diodes
Authors: Chondroudis Konstantinos , Mitzi David B.
Published: July 2002

The conversion of two neutral dye molecules (D) to ionic salts (H2N–D–NH2⋅2HX) and their utilization as emitting layers in organic light-emitting diodes (OLEDs) is described. The dye salts, AEQT⋅2HCl and APT⋅2HCl, can be deposited as amorphous films using conventional evaporation techniques. X-ray diffraction and scanning electron microscopy analysis, coupled with thermal annealing studies, demonstrate the resistance of the films to crystallization. This stability is attributed to strong ionic forces between the relatively rigid molecules. OLEDs incorporating such salts for emitting layers exhibit better thermal stability compared with devices made from the corresponding neutral dyes (H2N–D–NH2). These results suggest that ionic salts may more generally enable the formation of thermally stable, amorphous emitting, and charge transporting layers.
Controllable capacitance–voltage hysteresis width in the aluminum–cerium-dioxide–silicon metal–insulator–semiconductor structure: Application to nonvolatile memory devices without ferroelectrics
Authors: Kim L. , Kim J. , Jung D. , Roh Y.
Published: July 2002

The Al/CeO2/Si metal–insulator–semiconductor (MIS) structure showed a capacitance–voltage (C–V) hysteresis, which could be controlled by variation of the CeO2 thickness. For a sample with 3000 Å CeO2, hysteresis width as high as ∼1.8 V was obtained. For nonvolatile field-effect transistors, the Al/CeO2/Si MIS structure with a reliable and controllable C–V hysteresis could be an alternative to metal–ferroelectric–semiconductor structures containing unstable, multicomponent ferroelectric materials.
Thermal breakdown, bistability, and complex high-frequency current oscillations due to carrier heating in superlattices
Authors: Steuer Haiko , Wacker Andreas , Schöll Eckehard , Ellmauer Michael , Schomburg Ekkehard , Renk Karl Friedrich
Published: July 2002

The impact of electron heating on vertical electrical transport in superlattices is shown to cause an S-shaped current–voltage characteristic in addition to the conventional N type occurring at lower fields. Our calculations are supported by experimental data. The combination of S- and N-type instabilities leads to a modified structure of the high-field domains associated with self-generated GHz oscillations.
Evidence of band bending observed by electroabsorption studies in polymer light emitting device with ionomer/Al or LiF/Al cathode
Authors: Yoon Jihyun , Kim Jang-Joo , Lee Tae-Woo , Park O-Ok
Published: July 2002

We report electroabsorption studies of indium–tin–oxide (ITO)/poly[2-methoxy-5-(2′-ethylhexyloxy)-1,4-phenylenevinylene] insulating layer/Al light-emitting devices. An ionomer and LiF were used as the insulating layer. The internal electric field was nullified at the same bias voltage of 0.6 V for different cathodes of Al, ionomer/Al, and LiF/Al. The bias voltage is close to the work-function difference between ITO and Al. Average electric field in the emitting layer was reduced by inserting the insulating layers. On the contrary, current density was increased significantly. These observations suggest band bending in the devices with ionomer/Al or LiF/Al cathode.
Room-temperature photoinduced magnetoresistance effect in GaAs including MnSb nanomagnets
Authors: Akinaga H. , Mizuguchi M. , Ono K. , Oshima M.
Published: July 2002

We show a photoinduced positive magnetoresistance (MR) effect (about 20%) under a low magnetic field (less than 0.1 T) at room temperature. The photoinduced MR effect has been observed in GaAs including nanoscale MnSb islands, when photons with the energy above the band gap of GaAs irradiated the sample. The photoinduced phenomena are due to an enhancement of tunneling probability between MnSb islands by photogenerated carriers in the GaAs matrix.
Noise imaging in stroboscopic ultrafast microscopy
Authors: Freeman M. R. , Hunt R. W. , Steeves G. M.
Published: July 2002

We describe a method for studying the presence of stochastic sample behavior within stroboscopically averaged time-resolved imaging experiments. The technique is based upon continuous noise analysis concurrent with signal acquisition. An example is presented in which details of random magnetic switching are exposed in a time-resolved scanning Kerr microscopy measurement.