bluuebunny/crossref_metadata_2025 huggingface dataset:
Experimental study of electromigration in bicrystal aluminum lines
Authors: Longworth Hai P. , Thompson C. V.
Published: July 2002

We report a new experimental technique for the study of electromigration in Al lines containing controlled, single, identical grain boundaries with boundary planes perpendicular to the plane of the substrates. We show that failure times of these lines are lognormally distributed; that the median time to failure depends more strongly on the boundary orientations than the types of grain boundaries; that the deviation in the time to failure has a large component not dependent on microstructure; and that both interfacial diffusion and grain boundary diffusion appear to contribute to failure in bicrystal lines, and likely in bamboo and near-bamboo lines.
Effect of oxygen pressure on Tl2Ca2Ba2Cu3O10±δ formation
Authors: Ahn B. T. , Lee W. Y. , Beyers R.
Published: July 2002

We investigated the formation of Tl2Ca2Ba2Cu3O10±δ as a function of oxygen pressure and temperature. Our results explain some previous difficulties in forming single-phase Tl2Ca2Ba2Cu3O10±δ and suggest new routes for making bulk and thin-film Tl-Ca-Ba-Cu-O superconductors. In particular, we find that the temperature needed to form Tl2Ca2Ba2Cu3O10±δ can be greatly reduced by using low oxygen pressures during synthesis.
Atomic structure of twin boundary in NiSi2 thin films on (001)Si
Authors: Chen W. J. , Chen F. R. , Chen L. J.
Published: July 2002

High-resolution transmission electron microscopy has been applied to determine the atomic structure of the twin boundary in NiSi2. From a match with the simulated images obtained by computation, Si atoms in the type A NiSi2 are found to bond with Si atoms in the type B NiSi2 at the (111) twin-boundary plane, and the Ni atoms of both crystals are sevenfold coordinated. The result represents the first report of the atomic structure of the silicide twin boundary which is free from either elastic strain or misfit dislocations.
Effect of state filling on the modulation response and the threshold current of quantum well lasers
Authors: Zhao B. , Chen T. R. , Yariv A.
Published: July 2002

The influence of state filling (carrier population of upper subbands of quantum well laser structures) on the optical gain constant is analyzed in conventional separate confinement quantum well lasers. We find that the appreciable population in the states of the optical confinement layers causes a significant lowering of the differential gain. It is pointed out that strain induced reduction of state-filling effects is a probable cause of improved performance in the tensile strained quantum well lasers. The strategy of design for very high frequency and very low threshold current quantum well lasers is addressed.
Theoretical calculation of optical gain in InxGa1−xAs/InP quantum wells under biaxially compressive and tensile strain
Authors: Sugawara Mitsuru
Published: July 2002

We calculated the well-plane valence band structures and the optical gain in InxGa1−xAs/InP quantum wells under both biaxially compressive and tensile strain using 4×4 Luttinger–Kohn Hamiltonian matrix [ Phys. Rev. 97, 869 (1955)]. We show that tensile strain can improve the 1.5-μm laser performance as well as compressive strain due to the high joint density of states and the large TM-mode optical matrix element between the ground-state conduction and light-hole subbands.
Reactions of hydrogenated defects in fused silica caused by thermal treatment and deep ultraviolet irradiation
Authors: Levy D. H. , Gleason K. K. , Rothschild M. , Sedlacek J. H. C. , Takke R.
Published: July 2002

Nuclear magnetic resonance (NMR) was used to study hydrogen in fused silica for the first time. The 1H NMR spin-lattice relaxation time constant (T1) in synthetic fused silica was found to be strongly affected by thermal treatments, correlating with the concentration of E′ centers produced during subsequent 193-nm excimer-laser irradiation. In addition, the relative proportion of the two components in the NMR spectrum were affected by thermal treatment, although no change in the total hydrogen content was observed. The broad NMR component, because of its linewidth and dependence upon thermal processing, is postulated to be a direct signature of the NMR relaxation centers. These results are interpreted within the framework of a model in which pairs of silanol groups are consumed during thermal treatment, forming a strained bond which is susceptible to E′ center formation.
Intersubband transitions for differently shaped quantum wells under an applied electric field
Authors: Chen Weiquan , Andersson T. G.
Published: July 2002

Calculations were made to compare the Stark shifts of electron intersubband transitions in Al0.4Ga0.6As/AlxGa1−xAs quantum wells. Several differently shaped quantum wells, having the same subband spacing between the ground and first excited states, E21=124 meV (=10 μm) under zero bias, were considered. The asymmetric steplike wells showed larger intersubband Stark shifts and a relatively high oscillator strength as well as a small linewidth broadening. A linear intersubband Stark shift of ±10 meV for ±100 kV/cm with a moderate change of the oscillator strength was found for an asymmetric well with its potential shape intermediate between a square and an asymmetric triangular one.
Plasma lens fine focusing of heavy-ion beams
Authors: Boggasch E. , Tauschwitz A. , Wahl H. , Dietrich K.-G. , Hoffmann D. H. H. , Laux W. , Stetter M. , Tkotz R.
Published: July 2002

The fine-focusing capability of a current-carrying, "active" plasma lens has been demonstracted for the first time. A cylindrically symmetric argon discharge plasma pulsed with an oscillating current of over 20 kA in amplitude served as a current conducting medium. With this plasma lens has been demonstrated for the first time. A cylindrically symmetric argon discharge plasma pulsed with an oscillating current of over 20 kA in amplitude served as a current conducting medium. With this plasma lens the diameter of an incident 2.2-GeV gold ion beam from the linear accelerator UNILAC at GSI-Darmstadt was focused from initially 10 to about 0.25 mm, at a focal length of only 140 mm. The gradient of the azimuthal magnetic field exceeded 120 T/m. The striking features of this first-order and strong-focusing plasma lens favor its use as a precise high-gradient focusing device for high-energy charged particles.
Thermoplasticity and parallel-plate poling of electro-optic polyimide host thin films
Authors: Valley J. F. , Wu J. W. , Ermer S. , Stiller M. , Binkley E. S. , Kenney J. T. , Lipscomb G. F. , Lytel R.
Published: July 2002

We demonstrate the first polyimide guest/host system which exhibits stable electro-optic response after parallel-plate poling. Such systems are based on a class of polyimides which, once cured, possess a clear glass transition in their dielectric relaxation spectra, characteristic of thermoplasticity. After doping with compatible nonlinear optical molecules the polyimide host system can first be thermally imidized (cured) and then poled with an electric field. High glass transition temperatures are achieved leading to excellent thermal stability of the poled electro-optic response.
Intersubband transitions in quantum well heterostructures with delta-doped barriers
Authors: Pandey Lakshmi N. , George Thomas F.
Published: July 2002

A single quantum well doped by a negative delta-function potential (δ-potential) in the barrier regions is analyzed in terms of the optical transitions in between subbands. The first two states of the quantum well do not change at all as a function of the strength of the δ-potential up to a certain value, whereas the third one gets lowered almost exponentially. An important point is that the δ-potential brings a state from the continuum to the bound region. There is a range of the strength of the δ-potential during which the transition energy for the first to second state decreases rapidly, and at a certain strength the first and second states disappear, and the third and fourth, which have been brought from the continuum, take their places. The oscillator strengths of the allowed transitions have a kind of oscillatory behavior in that range.
Influence of hydrogen on the step flow growth of GaAs on vicinal surfaces by gas-source migration enhanced epitaxy
Authors: Asahi H. , Hisaka T. , Kim S. G. , Kaneko T. , Yu S. J. , Okuno Y. , Gonda S.
Published: July 2002

Step flow growth of GaAs on the vicinal surfaces by gas-source migration enhanced epitaxy (MEE), the combination of gas-source molecular beam epitaxy and MEE, is studied with the reflection high-energy electron diffraction (RHEED) intensity oscillation. It is found that the use of the thermally cracked AsH3 instead of solid As (As4) as an As source enhances step flow growth of GaAs on the (001) surface misoriented toward the [110] direction. The same tendency is also observed in the MEE growth using As4 under the hydrogen supply. It is considered that the enhancement of step flow growth in the gas-source MEE is caused by the hydrogen atoms terminated at the steps.
H2S-treated GaP(001) surface studied by low-energy electron diffraction, Auger electron spectroscopy, and x-ray photoelectron spectroscopy
Authors: Fukuda Y. , Sanada N. , Kuroda M. , Suzuki Y.
Published: July 2002

The GaP(001) surface treated by H2S has been studied using low-energy electron diffraction (LEED), Auger electron spectroscopy (AES), and x-ray photoelectron spectroscopy (XPS). We, for the first time, find the new surface structure, S/GaP(001)-(1×2), obtained by H2S treatment at 450 °C. The coverage of sulfur is estimated to be half monolayer by AES measurement. XPS results indicate that only Ga—S bonds are formed on the surface.
Spectral cathodoluminescence of impurity phases in Y1Ba2Cu3O7−δ superconductors
Authors: Barkay Z. , Deutscher G. , Grunbaum E. , Dwir B.
Published: July 2002

Spectral cathodoluminescence (CL) of the Y1Ba2Cu3O7−δ high Tc superconducting pellet and its related components (Y2O3, BaCO3, CuO) was studied in the scanning electron microscope (SEM). Characteristic CL spectra of the Y1Ba2Cu3O7−δ component phases and the Y2BaCuO5 impurity phase were obtained. These spectra were used for detecting unfamiliar luminescent impurity grains in the Y1Ba2Cu3O7−δ pellets. The dispersive CL SEM image was compared with the morphological information.
Nonlinear optical property of CdTe microcrystallites doped glasses fabricated by laser evaporation method
Authors: Ohtsuka S. , Koyama T. , Tsunetomo K. , Nagata H. , Tanaka S.
Published: July 2002

Samples of CdTe microcrystallites doped glasses were fabricated by a high energy pulsed laser evaporation method. In order to fabricate a CdTe doped glass, synthesis of CdTe microcrystallites and formation of SiO2 films were carried out alternately on a fused silica glass substrate. The absorption edge of the CdTe doped glasses shifted to a higher energy region than that of the bulk CdTe due to the quantum size effect as the particle size of CdTe microcrystallites decreased. The third-order nonlinear susceptibility of χ(3) was estimated to be 4×10−7 esu at 580 nm using the method of degenerate four wave mixing.
Atomic force microscopy on homoepitaxial SrTiO3 films grown under monitoring of intensity oscillation in reflection high energy electron diffraction
Authors: Yoshimoto M. , Ohkubo H. , Kanda N. , Koinuma H. , Horiguchi K. , Kumagai M. , Hirai K.
Published: July 2002

Homoepitaxial SrTiO3 film growth by laser molecular beam epitaxy (MBE) was tuned up to a level as to give not only fine streak in the reflection high energy electron diffraction (RHEED) pattern but also the intensity oscillation persisting more than 70 unit cell lengths. The films thus produced were verified to have atomically flat surfaces (root-mean-square roughness of 0.12 nm) and very high crystal quality (χmin of 2%) by the analyses of atomic force microscopy and the Rutherford backscattering, respectively.
Charge trapping centers in N-rich silicon nitride thin films
Authors: Warren W. L. , Kanicki J. , Rong F. C. , Poindexter E. H. , McWhorter P. J.
Published: July 2002

We have examined the behavior of the Si dangling-bond center in regard to charge trapping in N-rich amorphous hydrogenated silicon nitride thin films. The effects of multiple electron and hole injections were monitored by electron paramagnetic resonance. These results continue to support a model in which the Si dangling bond is a negative U defect in N-rich nitrides, and that a change in charge state of pre-existing diamagnetic positively and negatively charged sites is responsible for the memory properties of silicon nitride thin films.
Lattice relaxed impurity and persistent photoconductivity in nitrogen doped 6H-SiC
Authors: Dissanayake A. S. , Jiang H. X.
Published: July 2002

The impurity properties in n-type N doped single crystal 6H-SiC semiconductors have been studied by conductivity measurements. A slow decay of the dark current and persistent photoconductivity (PPC) have been observed at low temperatures. Different energy barriers have been obtained at different conditions. Measured donor binding energy, the electron capture barrier, and the emission barrier are 34.6±1.0, 14.9±0.3, and 45.6±1.2 meV, respectively. Our results suggest that PPC in SiC has a similar origin as that in AlxGa1−xAs. However the amount of lattice relaxation in SiC is much smaller compared with that in AlxGa1−xAs. Experimental results reported in this letter will help to understand the properties of lattice relaxed impurities. It also explains why different energy levels have been obtained previously by different methods.
CuInSe2 homojunction diode fabricated by phosphorus doping
Authors: Kohiki Shigemi , Nishitani Mikihiko , Negami Takayuki , Wada Takahiro
Published: July 2002

Homojunction diodes were fabricated by doping of phosphorus to n-type Cu-In-Se thin films. The junction prepared by P implantation at the energy of 50 keV with the dose of 1×1015 ions/cm2 showed a rectification ratio of more than 100. Conduction in Cu-In-Se thin films, whose crystal structure is of the chalcopyrite type, changes from n- to p-type in such a way that group V elements (N, P, Sb, or Bi) substitute for Se in the film.
GaxIn1−xP multiple-quantum-wire heterostructures prepared by the strain induced lateral layer ordering process
Authors: Chen A. C. , Moy A. M. , Pearah P. J. , Hsieh K. C. , Cheng K. Y.
Published: July 2002

We report the in situ growth of GaxIn1−xP multiple-quantum-wire (MQWR) structures by gas source molecular beam epitaxy. The MQWRs were formed through a strain induced lateral layer ordering (SILO) process occurring spontaneously when (GaP)n/(InP)n short-period superlattices were grown on (100)-oriented on-axis GaAs substrates. In one sample, cross-sectional transmission electron microscopy estimated average quantum-wire cross sections of 50 Å×100 Å with lengths of over 3000 Å leading to a linear density of 100 wires/μm. The existence of the MQWRs is also supported by polarized photoluminescence spectroscopy. Anisotropy ratios for two orthogonal polarizations were measured to be an order of magnitude larger than any previously reported. These data support the existence of MQWRs and demonstrate that the SILO growth process is a consistent and reproducible method of MQWR fabrication.
Dynamic model for pseudomorphic structures grown on compliant substrates: An approach to extend the critical thickness
Authors: Teng D. , Lo Y. H.
Published: July 2002

We use a dynamic model to analyze the critical thickness for pseudomorphic structures grown on thin membranes considering the strain relaxation process. Our results show that a pseudomorphic structure of arbitrary thickness can be achieved on a semiconductor membrane which works as a compliant substrate. The analysis on GaAs/InGaAs material system shows that the membrane should be thinner than 1200 Å for 1% strain and 1 μm for 0.5% strain. Such thickness can be achieved by existing technology. Using the proposed method, semiconductor lasers of yellow and green colors, among many new devices, can be fabricated with strained InGaP/InAlGaP active and cladding layers on GaAs substrates.
Spectroscopic ellipsometry studies of HF treated Si (100) surfaces
Authors: Yao Huade , Woollam John A. , Alterovitz Samuel A.
Published: July 2002

Both ex situ and in situ spectroscopic ellipsometry (SE) measurements have been employed to investigate the effects of HF cleaning on Si surfaces. The hydrogen-terminated (H-terminated) Si surface was modeled as an equivalent dielectric layer, and monitored in real time by SE measurements. The SE analyses indicate that after a 20-s 9:1 HF dip without rinse, the Si (100) surface was passivated by the hydrogen termination and remained chemically stable. Roughness of the HF-etched bare Si (100) surface was observed, in an ultrahigh vacuum (UHV) chamber, and analyzed by the in situ SE. Evidence for desorption of the H-terminated Si surface-layer, after being heated to ∼550 °C in the UHV chamber, is presented and discussed. This is the first use of an ex situ and in situ real-time, nondestructive technique capable of showing state of passivation, the rate of reoxidation, and the surface roughness of the H-terminated Si surfaces.
Synthesis and characterization of rf-planar magnetron sputtered KTaxNb1−xO3 thin films
Authors: Sashital S. R. , Krishnakumar S. , Esener S.
Published: July 2002

Thin ferroelectric films of potassium tantalate niobate (KTN) have been grown by rf planar magnetron sputtering on sapphire, platinum coated silicon, and GaAs substrates. X-ray diffraction analysis indicate epitaxial growth with (100) orientation. The KTN films exhibit dielectric anomalies at temperatures between −4 and 9 °C and peak dielectric constant ε of nearly 2000. Films have a smooth surface morphology, and excellent optical transparency. The electro-optic effect and electrical properties of such KTN thin films are reported.
Optimization of YBa2Cu3O7−δ submicrometer structure fabrication
Authors: Barth Roland , Spangenberg Bernd , Jaekel Christian , Roskos Hartmut G. , Kurz Heinrich , Holzapfel Bernhard
Published: July 2002

We present a study of the sputter etching step in the fabrication sequence of YBa2Cu3O7−δ submicrometer structures down to 200 nm linewidth. We identify oxygen effusion as the main reason for process-induced degradation of superconductivity. Oxygen reloading by plasma oxidation after pattern transfer efficiently recovers both the transition temperature Tc and the critical current density jc of the YBa2Cu3O7−δ submicrometer structures. Liquid-nitrogen cooling of the substrate is shown to efficiently suppress oxygen effusion during sputter etching. Critical current densities above 106 A/cm2 at 77 K are obtained for 0.75 μm wide and 10 μm long bridges.
Strain relaxation in high-speed p-i-n photodetectors with In0.2Ga0.8As/GaAs multiple quantum wells
Authors: Bender G. , Larkins E. C. , Schneider H. , Ralston J. D. , Koidl P.
Published: July 2002

We have used high-resolution x-ray diffraction and photocurrent spectroscopy to investigate strain relaxation in In0.2Ga0.8As/GaAs multiple quantum wells and its influence on the optoelectronic and electronic properties of high-speed p-i-n photodetectors. In combination with numerical simulations and subband calculations, both methods allowed us to determine the degree of lattice relaxation. The results consistently show that lattice relaxation does not occur abruptly, but that the degree of relaxation increases gradually with increasing number of wells. In spite of the onset of lattice relaxation, these photodetectors exhibit a quantum efficiency of unity and recombination lifetimes in excess of 500 ps.
Growth and ferroelectric properties of Bi2VO5.5 thin films with metallic LaNiO3 electrodes
Authors: Prasad K. V. R. , Varma K. B. R. , Raju A. R. , Satyalakshmi K. M. , Mallya R. M. , Hegde M. S.
Published: July 2002

Novel ferroelectric bismuth vanadate, Bi2VO5.5 (BVO), thin films have been grown between lattice matched metallic LaNiO3 (LNO) layers deposited on SrTiO3 (STO) by the pulsed laser deposition technique. LNO/BVO/LNO/STO and Au/BVO/LNO/STO trilayer structures exhibited c-oriented (001) growth of BVO. LNO has been found to be a good metallic electrode with sheet resistance ∼20 Ω in addition to aiding c-axis oriented BVO growth. The dielectric constant, εr of LNO/BVO/LNO/STO, at 300 K was about 12. However, when an Au electrode was used on top of BVO/LNO/STO film, it showed a significant improvement in the dielectric constant (εr=123). The ferroelectric properties of BVO thin films have been confirmed by hysteresis behavior with a remnant polarization, Pr=4.6×10−8 C/cm2 and coercive field, Ec=23 kV/cm at 300 K.
Transport study of ZnSe:N employing Zn(Se,Te) graded contacts
Authors: Fan Y. , Han J. , He L. , Saraie J. , Gunshor R. L. , Hagerott M. M. , Nurmikko A. V.
Published: July 2002

Hall effect measurements for temperatures ranging from 77 to 320 K on a series of p-ZnSe films grown on GaAs substrates are reported. The ZnSe epilayers were doped using a nitrogen plasma source during growth by molecular beam epitaxy. A Zn(Se,Te) graded band-gap layer was used to provide ohmic contacts over the temperature range of the measurements. The activation energy of nitrogen in ZnSe at the infinite dilution limit was found to be 114 meV, and compensation ratios ranged from 6% to 11%.
Heterostructure bipolar transistor with enhanced forward diffusion of minority carriers
Authors: Luryi Serge , Grinberg Anatoly A. , Gorfinkel Vera B.
Published: July 2002

We consider the minority transport in a heterostructure bipolar transistor whose base band gap narrows down toward the collector in N discontinuous steps. Assuming that the potential energy drop at each step is sufficiently large to prevent the reverse flow of minority carriers, we show that the total base propagation delay τ is shorter by a factor of N compared to the diffusive delay in a flat base of the same width. Moreover, if the length of each step is sufficiently narrow, then for large N the magnitude ‖α‖ of the base transport factor α=‖α‖exp(−iωτ) decreases so slowly with increasing frequency ω that it becomes feasible to obtain an active behavior of the transistor above its own conventional cutoff frequencies.
Two-dimensional study on the effects of nonamorphizing silicon implantation damage on phosphorus diffusion
Authors: Frank Carlos X. , Law Mark E.
Published: July 2002

A new experimental study is performed to determine the lateral extent of silicon implantation damage on diffusion in silicon. The experimental technique is designed to allow easy comparison between damaged and nondamaged areas to facilitate specific measurements. Junction depth is measured under stripes of varying widths that protect from implantation damage as well as at points that receive the full amount of implantation damage. A roughly exponentially decaying profile of junction depth as a function of increasing stripe width is observed. Good correlation between measured and suprem−iv predicted values is observed.
Intrinsic current bistability in InAs/AlxGa1−xSb resonant tunneling devices
Authors: Chow D. H. , Schulman J. N.
Published: July 2002

We report the design and demonstration of a novel resonant tunneling device displaying bistability in operating current over a range of applied voltage. The device is based on a type II InAs/AlxGa1−xSb (0.4<x<0.6) double barrier heterostructure. This structure permits the simultaneous accumulation of electrons and holes in the quantum well/barrier region, resulting in a dependence of the steady-state charge distribution on the bias history of the device. This dependence is experimentally manifested as an ‘‘S’’-shaped negative differential resistance region under current-controlled measurement conditions or as hysteretic I-V behavior under voltage-controlled conditions. Room temperature operating currents in excess of 2.5×105 A/cm2 are observed, along with peak-to-valley voltage ratios up to 1.5.
Force sensing microcantilever using sputtered zinc oxide thin film
Authors: Itoh T. , Suga T.
Published: July 2002

A force sensing microcantilever has been developed with sputtered ZnO thin film sandwiched electrodes. Typical cantilever dimensions are 150 μm long×50 μm wide×3.5 μm thick. The ZnO film with thickness of 1.0 μm has high resistivity (≳2.0×107 Ω m) and good piezoelectricity. By detecting the change of the resistance between the electrodes, the static deflection of the cantilever end can be sensed. The ac deflection of the cantilever can be measured with high sensitivity by using the piezoelectric effect. The cantilever in question is useful for scanning force microscopy both in static contact mode and in dynamic mode.
Ge growth on Si using atomic hydrogen as a surfactant
Authors: Sakai Akira , Tatsumi Toru
Published: July 2002

We have examined the effect of adsorbed atomic hydrogen (H) on the evolution of Ge films on Si(001) and (111) substrates in solid-source molecular-beam epitaxy. The H flux was supplied separately from the Ge flux. By cross-sectional high-resolution transmission electron microscopy it was observed that H acted as a surfactant during growth, suppressing island formation of Ge on both substrates. The effect of the H surfactant on variation of the growth mode is also discussed.
Peniotron forward wave self-oscillations
Authors: Lin A. T. , Lin Chih-Chien
Published: July 2002

The forward propagating absolute instability in peniotron interaction can be utilized to build forward wave oscillators. This is demonstrated by performing computer simulations which also reveal that the peniotron interaction is able to suppress the gyrotron interaction and attains the efficiency without the influence of the gyrotron mode.
Sulfurization of SiO2 surface for polycrystalline silicon growth on SiO2/Si structure at 250 °C
Authors: Wang K. C. , Hwang H. L. , Yew T. R.
Published: July 2002

A study of sulfurizing SiO2 surfaces for the growth of Si/SiO2/Si structures was done in the present work. The silicon film was deposited at 250 °C by plasma enhanced chemical vapor deposition. All of the deposited Si films with or without sulfur treatment were of amorphous phases with a H2/(SiH4+H2) flow ratio less than 92%. For those films deposited at the H2/(SiH4+H2) flow ratio of 92%, a transition amorphous Si layer appeared between the SiO2 and polycrystalline silicon films in those samples without sulfur treatment. No transition amorphous Si layer was present in the sample deposited with sulfur treatment, and the largest grain size of polycrystalline silicon was estimated to be around 500 Å. The polycrystalline phase was obtained in all the silicon films deposited on SiO2/Si substrate with a H2/(SiH4+H2) flow ratio larger than 92%. This technique would be applicable towards thin film transistor fabrication.
High efficiency and low threshold current strained V-groove quantum-wire lasers
Authors: Tiwari Sandip , Pettit G. David , Milkove Keith R. , Legoues Francoise , Davis Robert J. , Woodall Jerry M.
Published: July 2002

Multi-quantum-wire strained lasers are reported in the Ga1−xInxAs/Ga1−xAlxAs semiconductor material system with a minimum threshold current of 188 μA and maximum powers of ≊50 μW in continuous multimode operation at wavelengths of ≊980 nm and differential output of ≊0.5 μW/μA. The structures, fabricated by molecular-beam epitaxy, are self-aligned, self-isolated, and minimize electrical and optical losses. Internal quantum efficiencies are ≊83% and internal losses are ≊4.2 cm−1. Characteristic temperatures of ≊260 K, and an increase in threshold current and lasing wavelength under externally applied stress changing from compressive to tensile conditions, show that the major determinants of lasing threshold are density of states and optical losses.
Interface effects on YBa2Cu3O7−δ ultrathin film growth monitored by in situ resistance measurement
Authors: Shen W. P. , Lehane C. , Zheng J. P. , Kwok H. S.
Published: July 2002

The growth dynamics of pulsed laser deposited ultrathin YBa2Cu3O7−δ films on various substrates was explored using an in situ resistance measurement technique. The results indicate that an interface region exists before the onset of uniform growth. On MgO and YSZ substrates, the first 30–50 Å has a small contribution to the conductivity of the film. This interface layer is less than one unit cell thick on better lattice-matched substrates, such as SrTiO3, LaAlO3, and CeO2. The thinnest interface layer was found on PrBa2Cu3O7−δ . Misfit strain relaxation and island growth mechanism can be used to explain experimental observations. The superconductivity degradation for ultrathin YBa2Cu3O7−δ films is also discussed. In situ resistance measurement can be an excellent method to study the ultrathin film growth mechanism.
Application of Pd/Co multilayers for perpendicular magnetic recording
Authors: Lairson Bruce M. , Perez Jessie , Baldwin Chandler
Published: July 2002

We demonstrate that Pd/Co multilayers can have superior properties for perpendicular magnetic recording media using a contact probe head. The multilayers are capable of generating relatively large signal amplitudes compared to conventional perpendicular CoCrTa alloy media, with a more than twofold increase in signal amplitude at 145 kilo flux changes per inch. We have also investigated the effect of Cr alloying of the Co layer to reduce the demagnetization energy of the magnetic layer. Cr reduced both the demagnetizing energy of the magnetic layer and the surface anisotropy of the Pd/CoCr interface.
In situ time-resolved monitoring of PH3 induced exchange reactions on GaAs under metalorganic vapor phase epitaxy conditions
Authors: Jönsson J. , Reinhardt F. , Zorn M. , Ploska K. , Richter W. , Rumberg J.
Published: July 2002

Exposure of GaAs and InGaAs to PH3 is a standard step in gas switching sequences for metalorganic vapor phase epitaxy (MOVPE) growth of heterostructures in the technologically important GaAsP, InGaP, and InGaAsP material systems. The exchange of group-V atoms was monitored in situ by reflectance anisotropy spectroscopy when GaAs is exposed to PH3. The c(4×4) reconstructed, As-terminated GaAs surface is then replaced by a P-terminated structure. At standard MOVPE growth temperatures and pressures the time constant for this reaction is of the order of 100 ms. The temperature and pressure dependence of the As by P exchange is reported, and the activation energy was determined to be 1.64 eV. It is concluded that PH3 enhances the desorption of As.
Photoluminescence of InAs/AlSb single quantum wells
Authors: Fuchs F. , Schmitz J. , Obloh H. , Ralston J. D. , Koidl P.
Published: July 2002

A photoluminescence study of InAs/AlSb single quantum well structures with a width varying between 20 and 5 nm is presented. Using Fourier-transform spectroscopy, the spatially indirect radiative recombination is observed. Excitation of the photoluminescence at 1.32 μm instead of excitation in the visible leads to broadening and blueshifting of the spectra. This behavior is explained by a photoinduced increase of the electron concentration. The optically induced blueshift of the low energy onset of the spectra is attributed to screening of an acceptor level in the AlSb barrier near the InAs/AlSb interface, located about 80 meV above the AlSb valence band maximum. The blueshift of the high energy of the luminescence spectra is limited to a transition energy of 420 meV, providing evidence for the existence of a deep level in the AlSb barriers.
Low-threshold 1.3-μm wavelength, InGaAsP strained-layer multiple quantum well lasers grown by gas source molecular beam epitaxy
Authors: Shiau Guang-Jye , Chao Chih-Ping , Burrows Paul E. , Forrest Stephen R.
Published: July 2002

We report the growth, by gas source molecular beam epitaxy (GSMBE) of low-threshold 1.3-μm wavelength strained-layer In0.86Ga0.14As0.52P0.48/In0.86Ga0.14 As0.3P0.7 separate confinement heterostructure multiple quantum well lasers. Threshold currents as low as 16 mA were measured for a 390×5-μm ridge laser, and a threshold current density of Jth=490 A/cm2 was achieved for a 1200×5-μm device. Apparently, this is the lowest value of Jth reported to date for 1.3-μm lasers grown by GSMBE, and is comparable to the best devices grown by other techniques such as chemical beam epitaxy and metalorganic vapor phase epitaxy.
Fabrication and measurement of a Nb based superconducting single electron transistor
Authors: Harada Y. , Haviland D. B. , Delsing P. , Chen C. D. , Claeson T.
Published: July 2002

A new four-layer resist system was developed to fabricate small capacitance niobium tunnel junctions. Nb/AlOx/Al junctions were used to make a superconducting single electron transistor composed of two dc SQUIDs in series. The current-voltage characteristics were measured and two types of resonant tunneling of Cooper pairs were observed at different magnetic fields.
Photosensitivity in phosphorus-doped silica glass and optical waveguides
Authors: Malo B. , Albert J. , Bilodeau F. , Kitagawa T. , Johnson D. C. , Hill K. O. , Hattori K. , Hibino Y. , Gujrathi S.
Published: July 2002

Irradiation of hydrogen loaded or flame brushed phosphorus doped, germanium free silica glass with a 193-nm ArF excimer laser changes the optical absorption at ultraviolet wavelengths by 40–140 dB/mm and the refractive index by more than 2×10−4. Bragg gratings with 90%–95% reflectivity are photoinduced in channel optical waveguides made from this glass. The thermal stability of the photosensitivity is measured by annealing up to 700 °C.
Near-field optical data storage using a solid immersion lens
Authors: Terris B. D. , Mamin H. J. , Rugar D. , Studenmund W. R. , Kino G. S.
Published: July 2002

A near-field optical technique, using a new type of solid immersion lens (SIL), has been developed and applied to the writing and reading of domains in magneto-optic material. The SIL is a truncated glass sphere which serves to increase the numerical aperture of the optical system by n2, where n is the index of refraction of the lens material. Using a SIL made from n=1.83 glass and illuminating with 780 nm light, we have achieved a 317 nm spot size. We have resolved a 500 nm period grating, and written and read 350 nm diameter magnetic domains. The technique should be capable of a 125 nm focused spot size using blue light.
High-resolution Rutherford backscattering study of ultrathin YBaCuO film growth on SrTiO3 and MgO
Authors: Hüttner D. , Günther U. , Meyer O. , Reiner J. , Linker G.
Published: July 2002

Medium energy ion scattering in combination with an electrostatic high-resolution detector system was applied to study the initial growth of YBaCuO thin films on (100) SrTiO3 and MgO substrates. Ultrathin films with thicknesses in the range of 0.4 to 3.6 nm were deposited by inverted cylindrical magnetron sputtering. From the absolute determination of coverage as a function of depth the following growth features were deduced: on both substrates the films grow in blocks of one unit cell and full coverage with a homogeneous film is achieved at 3.6-nm thickness. In the initial stage of nucleation, on SrTiO3 the growth of an additional block layer is initiated only after completion of the preceding layer, while island growth is observed on MgO with different coverage values on three layer levels appearing simultaneously.
Novel plastic strain-relaxation mode in highly mismatched III-V layers induced by two-dimensional epitaxial growth
Authors: Trampert A. , Tournié E. , Ploog K. H.
Published: July 2002

Using cross-section and plan-view transmission electron microscopy we demonstrate that the initial plastic relaxation of highly mismatched layers grown along [100] is governed by the growth mode. During MBE growth of InAs on GaAs in the Stranski-Krastanov (SK) mode, 60o -type dislocations are generated at the island edges and then glide to the interface to relieve the strain. The resulting interfacial microstructure consists of an inefficient arrangement of misfit dislocations. On the other hand, when InAs is forced to grow in a two-dimensional (2D) mode, only pure edge-type dislocations are generated and they are located exactly at the epilayer/substrate interfacial plane. These results are explained by a different dislocation nucleation mechanism imposed by the planar morphology of the highly strained film.
Growth of clean amorphous silicon–carbon alloy films by hot-filament assisted chemical vapor deposition technique
Authors: Kumbhar A. S. , Bhusari D. M. , Kshirsagar S. T.
Published: July 2002

Amorphous silicon–carbon (a-SiC) alloy films were deposited by using the hot-filament chemical vapor deposition technique. The gas mixture containing different concentrations of silane in methane with additional dilution in hydrogen formed the source gas. Films were characterized for infrared and optical absorption and Raman scattering. The films deposited under ‘‘starving’’ hot-filament conditions exhibited properties characteristic of stoichiometric carbon-free a-SiC material.
Monolayer nitridation of silicon surfaces by a dry chemical process using dimethylhydrazine or ammonia
Authors: Takami Seiichi , Egashira Yasuyuki , Honma Itaru , Komiyama Hiroshi
Published: July 2002

A hydrogen-terminated silicon surface was successfully converted to a surface covered with a monolayer of nitrogen. Nitridation was carried out in a vacuum chamber using either dimethylhydrazine [H2N–N(CH3)2] or ammonia at a pressure of 1 mTorr and at temperatures ranging from 400 to 600 °C. In situ x-ray photoelectron spectroscopy measurements revealed that the binding energy and the full width at half-maximum in the nitrogen spectra are the same as those in bulk Si3N4. Nitrogen content at the surface increased as the nitridation time increased and, below 500 °C, saturated at a value that approximately corresponds to a monolayer thickness. These results show the effectiveness of dry chemical processes for preparing uniform Si surfaces terminated with specific atoms or molecules other than hydrogen.
Improved instrument for medium energy electron diffraction and microscopy of surfaces
Authors: Elibol C. , Ou H.-J. , Hembree G. G. , Cowley J. M.
Published: July 2002

The REMEDIE system for reflection electron microscopy and electron diffraction at intermediate energies (0.5–20 keV) has been rebuilt with an improved imaging resolution of better than 10 nm, a convenient and versatile system for observation diffraction patterns and provision for specimen preparation and treatment suitable for surface structural studies. The current capabilities of the instrument are illustrated by results obtained from cleaved and annealed silicon (111) surfaces with or without thin deposited silver and gold layers.
Small sensitive pressure transducer for use at low temperatures
Authors: Griffioen W. , Frossati G.
Published: July 2002

A sensitive diaphragm-type pressure transducer suitable for use at very low temperatures is described. This device was optimized for pressures up to 3.5 MPa, but sensors for other pressure ranges can be readily manufactured. The external pressure deflects two sapphire disks which causes a change in capacitance between the platinum electrodes sputtered on the disks. The transducer can easily resolve changes of 1 Pa at 3.5 MPa, while reproducibility and hysteresis, though not fully tested yet, are better than 10 Pa. The transducer is 610 μm thick and 8 mm diameter.
Antenna for unidirectional propagation of fast Alfvén waves in a tokamak
Authors: Akiyama H. , Gahl J. , Rathbun K. , Kristiansen M. , Hagler M.
Published: July 2002

A slow wave antenna has been designed to propagate Alfvén waves unidirectionally in the Texas Tech Tokamak. The antenna receives 30-kW rf pulses at 4–20 MHz, directly from a 50-Ω transmission line, without matching circuitry. Unidirectional Alfvén waves are successfully excited in the tokamak over a wide range of frequencies. Power coupling is approximately 36% with a little higher coupling during excitation of a pronounced toroidal eigenmode.
Rapid scanning fluorometer based on constant energy synchronous scanning
Authors: Jonell Kerkhoff M. , Hart L. P. , Winefordner J. D.
Published: July 2002

A rapid scanning fluorometer based on constant energy synchronous fluorescence scanning at 200 nm/s has been developed. Constant energy synchronous fluorescence spectrometry involves measurement of fluorescence as both excitation and emission monochromators are scanned with a constant energy difference being maintained. Spectral information is collected in the forward to reverse directions and is processed in real time. A discussion of the instrumentation and software is given. A theoretical comparison between the photomultiplier tube (PMT) detection system used with this system and a silicon intensified target vidicon (SIT) detection system has been given. Calculations indicate that the signal-to-noise ratio S/N for the PMT system should be about 5–40× greater than for the SIT system. A comparison of the experimental figures of merit (detection limits, scan speed, analysis time) of the rapid scan constant energy synchronous fluorescence spectrometer with video fluorometers has also been made, again showing the superiority of the rapid scan synchronous system.
Lanthanum hexaboride tapered filament in a plasma source
Authors: Pincosy P. A. , Leung K. N.
Published: July 2002

A directly heated lanthanum hexaboride tapered filament has been tested in a plasma generator. A uniform temperature distribution at 1820 K has been achieved. The heating and cooling power calculated from measured quantities are balanced. A maximum arc current of 80 A was obtained, limited only by the power supply and plasma generator. The corresponding hydrogen ion current density was 0.6 A/cm2 when the arc voltage was 80 V and the filament heater current was about 5 A. The filament was capable of emitting 100 A of current at an operating temperature of 1900 K. The estimated lifetime for this filament is 900 h.
Notes on UHV beryllium windows
Authors: Hartman Paul L.
Published: July 2002

Techniques are described for making large ultrahigh vacuum beryllium windows for use in synchrotron radiation installations. Procedures are given for affecting both hard brazed seals and demountable seals involving either lead or copper gaskets. Brazed seals can be made to either stainless steel or copper. Possible alternative methods are suggested.
Diode-bridge temperature sensor
Authors: Abu-Zeid M. M. , Sasburg A. G.
Published: July 2002

A simple diode bridge used as a temperature sensor with an accuracy of ±0.5 °C in the temperature range of 25–100 °C has been fabricated and tested. It was first realized using commercially available breadboard transistor arrays and then in two monolithic integrated circuits which differ in the forms of the contact holes. The performance and limitations of these sensors are presented.
Faraday cup to measure ion current in a strong magnetic field
Authors: Ivers J. D. , Roth I. S. , Nation J. A.
Published: July 2002

A Faraday cup has been designed and tested to measure the ion current density in an intense ion beam immersed in a strong magnetic field. The ion flux is charge neutralized by a low-energy codrifting electron beam. The codrifting electrons are deflected from the cup by use of an apertured magnetic plate at the entrance to the cup. Comparison of the integrated Faraday cup traces with the proton flux found from carbon activation measurements show that the ion Faraday cup consistently measured 59%±8% of the protons.
Synchronously operated streak camera driven by a GaAs photoconductive device
Authors: Gomes A. S. L. , Gouveia-Neto A. S. , Margulis W. , Taylor J. R.
Published: July 2002

Excited by the frequency doubled optically compressed 10-ps pulses from a cw mode-locked Nd:YAG laser, the amplified output from a GaAs photoconductive device was used to drive a synchronously operated Photochron IIA streak camera at 300-MHz sweep rates. A temporal jitter of ±6 ps was measured which was limited by the driving laser pulse width and amplitude stability.
Shear deformation measurement of suspended particles: Application to erythrocytes
Authors: Rasia R. J. , Porta P. E. , García Rosasco M.
Published: July 2002

Laser diffraction produced by a single layer of erythrocytes in suspension is applied to assess the cell deformation in the erythrodeformeter. It is well known that erythrocytes become elliptically deformed when a fluid shear stress is applied to them. In the erythrodeformeter the red cell suspension fills the narrow gap between two parallel disks of glass, horizontally positioned, the lower of which rotates at a controlled speed while the upper is fixedly supported. A laser beam traversing the sample layer at r distance from the center of disks, displays a diffraction pattern ‘‘at infinity.’’ At no shear stress the cells have discoidal shapes and the diffraction pattern is circular. Shear-induced elongation of cells leads to an elliptical diffraction pattern, its geometric characteristics being directly related to those of deformed cells. This deformation can be evaluated in terms of a deformation index calculated from the width and the length of the diffraction pattern ellipse. In the erythrodeformeter a similar index is evaluated from the light intensity traversing two slots of uniform width each one coincident with each of the two principal diameters of the pattern ellipse, the light intensity being measured by a photoelectric detection head.
Dual-ported memory
Authors: Scaysbrook F. F.
Published: July 2002

A method is described which enables two computers to access a common memory area. One computer will be able to read and write to memory and will arbitrate over bus access. The other computer will be able to read memory only. Both computers will be able to select various RAM chips in the common memory area as required.
University of Missouri–Rolla cloud simulation facility: Proto II chamber
Authors: White Daniel R. , Kassner James L. , Carstens John C. , Hagen Donald E. , Schmitt John L. , Alofs Darryl J. , Hopkins Alfred R. , Trueblood Max B. , Alcorn Max W. , Walker William L.
Published: July 2002

The Graduate Center for Cloud Physics Research at UMR has developed a cloud simulation facility to study phenomena occurring in terrestrial clouds and fogs. The facility consists of a pair of precision cooled-wall expansion chambers along with extensive supporting equipment. The smaller of these chambers, described in this article, is fully operational, and is capable of simulating a broad range of in-cloud thermodynamic conditions. It is currently being used to study water drop growth and evaporation for drops nucleated (activated) on well-characterized aerosol particles. Measurements have been made not only for continuous expansions (simulated updraft) but also for cyclic conditions, i.e., sequences of expansion-compression cycles resulting in alternating drop growth and evaporation. The larger of the two cloud chambers is nearing completion and will provide a broader range of conditions than the smaller chamber. The facility is supported by a fully implemented aerosol laboratory which routinely produces well-characterized condensation nuclei. The aerosol laboratory contains extensive instrumentation designed to both shape and measure the size distribution and nucleating characteristics of the generated aerosol. The cloud simulation facility also includes a humidifier to bring an air sample to a known humidity before it is put into the cloud chamber. A systematic program to infer effective condensation coefficients (of water vapor on cloud drop) under a variety of well-controlled simulated in-cloud conditions is now under way. Analysis of current experiments with standard drop growth theory indicates a variation of condensation coefficient with observation time, with values sufficiently low to explain one of the current mysteries in cloud physics: viz., the broad spread of drop sizes observed in natural clouds. This article includes a description and performance specifications of the smaller cloud simulation chamber.