bluuebunny/crossref_metadata_2025 huggingface dataset:
Structural analysis of InxGa1−xN single quantum wells by coaxial-impact collision ion scattering spectroscopy
Authors: Sumiya M. , Nakamura S. , Chichibu S. F. , Mizuno K. , Furusawa M. , Yoshimoto M.
Published: July 2002

The structures of InxGa1−xN single quantum wells (SQWs) on 3-μm-thick GaN layer for the ultraviolet, blue, and green light-emitting devices were investigated by coaxial-impact collision ion scattering spectroscopy (CAICISS). The possibility that CAICISS could analyze structural fluctuation of the ternary system like InxGa1−xN was demonstrated. It was found that In incorporated into InGaN SQWs occupied the substitutional site of Ga atom having Ga-face (+c) polarity.
Design and implementation of a rapid-mixer flow cell for time-resolved infrared microspectroscopy
Authors: Marinkovic Nebojsa S. , Adzic Aleksandar R. , Sullivan Michael , Kovacs Kevin , Miller Lisa M. , Rousseau Denis L. , Yeh Syun-Ru , Chance Mark R.
Published: July 2002

A rapid mixer for the analysis of reactions in the millisecond and submillisecond time domains by Fourier-transform infrared microspectroscopy has been constructed. The cell was tested by examination of cytochrome-c folding kinetics. The device allows collection of full infrared spectral data on millisecond and faster time scales subsequent to chemical jump reaction initiation. The data quality is sufficiently good such that spectral fitting techniques could be applied to analysis of the data. Thus, this method provides an advantage over kinetic measurements at single wavelengths using infrared laser or diode sources, particularly where band overlap exists.
Ultraviolet laser spectroscopy of jet-cooled CaNC and SrNC free radicals: Observation of bent excited electronic states
Authors: Greetham Gregory M. , Ellis Andrew M.
Published: July 2002

New electronic transitions of the CaNC and SrNC free radicals have been identified in the near ultraviolet. For CaNC one new system, labeled the D̃–X̃ transition, was observed in the 31 500–33 400 cm−1 region. Two new transitions were found for SrNC, the D̃–X̃ and Ẽ–X̃ systems spanning 29 100–31 000 and 32 750–34 000 cm−1, respectively. Jet-cooled laser excitation spectra yield complex vibrational structure, much of which is attributed to excitation of the bending vibration. This has been used to infer that the molecule adopts a nonlinear equilibrium geometry in the upper electronic state in all three band systems, in contrast to the linear ground electronic state. This structural change is accounted for by the increased diffuseness of the unpaired electron in the excited states, which favors deviation from linearity. All three new excited states are assigned A′2 symmetry and correlate with Σ+2 states in the linear molecule limit. Tentative estimates for the barriers to linearity in the D̃ 2A′ states of CaNC and SrNC have been determined as ∼700 and ∼1050 cm−1, respectively.
A lightweight balloon-borne gas chromatograph for in situ measurements of atmospheric halocarbons
Authors: Robinson A. D. , McIntyre J. D. , Harris N. R. P. , Pyle J. A. , Simmonds P. G. , Danis F.
Published: July 2002

A new lightweight gas chromatograph using a Carboxen microtrap to pre-concentrate the sample has been developed for in situ measurements of stratospheric chlorofluorocarbons (CFCs) from balloon platforms. The instrument has been developed for fast analysis of a single tracer CFC-11 (CCl3F) to maximize the vertical resolution of ascent/descent profiles. In principle a wide range of halocarbons can be measured by changing operational parameters. The instrument weights <25 kg and can easily be deployed on either the balloon flight train or on gondolas. It has a time resolution of <2 min which corresponds to a vertical resolution of 500–700 m for a typical balloon ascent and better for a controlled slow descent. The precision of the CFC-11 measurement is estimated to be 1.7% and the accuracy is currently estimated to be 2.9% with much of the uncertainty arising from the links to the absolute calibration scale. An improved calibration procedure is being developed which should reduce this uncertainty. Test flights were completed in 1998 and the instrument recently participated in the Third European Stratospheric Experiment on Ozone when a number of scientific flights were made.
Co-incorporation effects of O and Na with CulnS2 thin films
Authors: Fukuzaki Koichi , Kohiki Shigemi , Yamamoto Tetsuya , Oku Masaoki , Watanabe Takayuki
Published: July 2002

By using x-ray photoelectron spectroscopy we have examined changes in the electronic structure of CuInS2 thin films with co-incorporation of O and Na that raised up the photovoltaic performance of CdS/CuInS2 solar cells. The electron binding energies of both the core levels and valence band for the film with the co-incorporation were smaller by 0.9 eV than those for the film without the co-incorporation. For the co-incorporated film an increase in the spectral intensity of the valence band was observed below 1–6 eV from the Cu 3d10 nonbonding states, and it was due to both the Na s, p-S p hybridization and the In s-Op hybridization. The surface of the co-incorporated film can be expressed as (Cu, Na)In(S, O)2. The (Cu, Na)In(S, O)2 phase is related to the enlarged open-circuit voltage (0.75 eV) of n-CdS/p-CuInS2 solar cells.
Photochemical manipulation of discotic liquid crystal alignment by a poly(vinyl cinnamate) thin film
Authors: Furumi Seiichi , Ichimura Kunihiro , Sata Hiroaki , Nishiura Yosuke
Published: July 2002

This letter describes the surface-assisted orientational photocontrol of discotic liquid crystals (DLCs) using thin films of a conventional photoresist, poly(vinyl cinnamate). Oblique illumination of a thin film of the polymer with nonpolarized UV light gave rise to inclined orientation of cinnamoyl moieties toward the light propagation through their direction-selective photochemical reactions. The DLCs were aligned on the photoirradiated film in a tilted hybrid manner, whereas the orientational direction of DLC molecules corresponds to the light propagation as a result of three-dimensional orientation of the cinnamoyl residues.
Quantitative long-range-order measurement and disordering efficiency estimation in ion-irradiated bulk Ni3Al using cross-sectional conventional transmission electron microscopy
Authors: de Almeida P. , Schäublin R. , Almazouzi A. , Victoria M. , Döbeli M.
Published: July 2002

Irradiation-induced disordering of bulk Ni3Al under 6 MeV Ni2+ irradiation is studied at room temperature. A self-consistent long-range-order quantification method for ion-irradiated intermetallics is presented using cross-sectional sample preparation and conventional transmission electron microscopy in selected area diffraction depth profiling mode. This method, which does not require the full assessment of dynamic diffraction image simulation information, is unique to precisely measure long-range-order as a function of depth or dose for a single total fluence. The disordering efficiency constant ε is estimated in the range 10.0±0.7/dpa for a total fluence of 1014 cm−2.
Hydrolysis of the amorphous silica surface. I. Structure and dynamics of the dry surface
Authors: Wilson Mark , Walsh Tiffany R.
Published: July 2002

Amorphous SiO2 surfaces are generated from bulk–liquid configurations using simulations employing a polarizable-ion model. The surfaces are characterized in terms of the ion environments as a function of depth into the surface. Comparison is made to previous simulation studies and subtle differences are highlighted and attributed to differences in the potential models. The connectivity of the surface sites is established with a view to investigating the hydrolysis of this surface. Dynamical properties are calculated using a simple projected velocity time correlation function and normal mode analysis and compared to the simulated bulk and experimental bulk and surface spectra.
Luminescence of porous silicon/terbium organic complex hybrid
Authors: Meng J. X. , Li T. K. , Wong W. K. , Cheah K. W.
Published: July 2002

A simple but effective doping method to introduce organometallic complexes into porous silicon was developed. Upon hybridization with a Tb-sulfosalicylic complex, porous silicon emits bright green emission when excited with an UV light. The photoluminescence spectrum shows that only Tb3+ ions emit efficiently while the luminescence of porous silicon and organic ligands are almost thoroughly quenched. Based on the Fourier transform infrared and photoluminescence measurements, it is proposed that Tb3+ complex was physically adsorbed in the pores of porous silicon. The origin of Tb3+ PL was also elucidated from the PL excitation spectrum measurement.
Thermal annealing recovery of intersubband transitions in proton-irradiated GaAs/AlGaAs multiple quantum wells
Authors: Hegeler F. , Manasreh M. O. , Morath C. , Ballet P. , Yang H. , Salamo G. J. , Tan H. H. , Jagadish Chennupati
Published: July 2002

Intersubband transitions in 1 MeV proton-irradiated GaAs/AlGaAs multiple quantum wells were studied using an optical absorption technique and isochronal thermal annealing. The intersubband transitions were completely depleted in samples irradiated with doses as low as 4×1014 cm−2. More than 80% recovery of these depleted transitions was achieved after the samples were thermally annealed at temperatures less than 650 °C. The total integrated areas and peak position energies of the intersubband transitions in irradiated and unirradiated samples were monitored as a function of annealing temperature. It was noted that the recovery of the depleted intersubband transitions in irradiated samples depend on the irradiation dose and thermal annealing temperature.
Wide-range thermometer based on the temperature-dependent conductance of planar tunnel junctions
Authors: Gloos K. , Poikolainen R. S. , Pekola J. P.
Published: July 2002

The effect of the Fermi–Dirac distribution on the current through standard planar tunnel junctions is a suitable basis for thermometry in a wide temperature range. In particular, it extends the range spanned by Coulomb-blockade thermometers up to room temperature.
Nanometer-scale quantum channels defined by reactive ion etching in InAs/AlSb heterojunctions
Authors: Cheng K. A. , Yang C. H. , Yang M. J.
Published: July 2002

An approach to the lateral confinement of electrons in an InAs quantum well has been developed. Conducting quantum wires, rings, and dots with lateral dimension ⩾50 nm have been fabricated by using electron-beam lithography and reactive ion etching. Due to the Fermi level pinning at InAs surface, the lateral confinement is abrupt and approximately square. Magnetotransport characterization on a series of fabricated hallbars demonstrate that, despite damage by energetic ions, the electron transport in these quantum wires is in the quasiballistic regime at 4.2 K.
Real-time determination of thermal diffusivity in a disk-shaped sample: Applications to graphite and boron nitride
Authors: Pourpoint Timothée L. , Banish R. Michael , Wessling Francis C. , Sekerka Robert F.
Published: July 2002

We describe a methodology for determining thermal diffusivities in real time by using temperature measurements at only two locations in a cylindrical sample. The technique is based on an analytical solution of heat transfer in a circular cylinder. This methodology does not require knowing the initial temperature increase or any timing between the applied and measured response. Starting with a heated cylindrical region having a unique fraction of the sample radius, and unique temperature measurement locations, the analytical solution for temperature at three specific radii can be approximated, after an initial transient, by a constant plus a single term that decreases exponentially with time. There are three special radii that fulfill the required condition. The data are analyzed by taking logarithms of the differences of the temperature versus time at these three radii, resulting in lines having slopes at large times that are proportional to the thermal diffusivity. Surprisingly, other choices of the size of the heated region and the measurement locations lead to similar results, except with longer transients. Experimental results for graphite and boron nitride agree with our numerical simulations and with the manufacturer’s data. This technique is applicable to solids and to liquids if heat transport due to convection is negligible.
Dependence of open-circuit voltage in hydrogenated protocrystalline silicon solar cells on carrier recombination in p/i interface and bulk regions
Authors: Pearce Joshua M. , Koval Randy J. , Ferlauto Andre S. , Collins Robert W. , Wronski Christopher R. , Yang Jeffrey , Guha Subbhendu
Published: July 2002

Contribution of carrier recombination from the p/i interface regions and the bulk to the dark current–voltage (JD–V) and short-circuit current–open-circuit voltage (Jsc–Voc) characteristics of hydrogenated amorphous-silicon (a-Si:H) p–i–n and n–i–p solar cells have been separated, identified, and quantified. Results are presented and discussed here which show that a maximum 1 sun Voc for a given bulk material can be validly extrapolated from bulk dominated Jsc–Voc characteristics at low illumination intensities.
Shear force surface contrast on self-assembly monolayers
Authors: Vaccaro L. , Bernal M.-P. , Marquis-Weible F. , Duschl C.
Published: July 2002

Shear force measurements on self-assembly monolayers, which show domains of opposite water affinity, are performed with conventional Al-coated and functionalized near-field probes. Approach curves are discussed, illustrating the influence of the wettability properties of the tip as well as the sample on the oscillation amplitude damping of the probe.
Laser-driven atomic-probe-beam diagnostics
Authors: Knyazev B. A. , Greenly J. B. , Hammer D. A.
Published: July 2002

A new laser-driven atomic-probe-beam diagnostic (LAD) is proposed for local, time-resolved measurements of electric field and ion dynamics in the accelerating gap of intense ion beam diodes. LAD adds new features to previous Stark-shift diagnostics which have been progressively developed in several laboratories, from passive observation of Stark effect on ion species or fast (charge-exchanged) neutrals present naturally in diodes, to active Stark atomic spectroscopy (ASAS) in which selected probe atoms were injected into the gap and excited to suitable states by resonant laser radiation. The LAD scheme is a further enhancement of ASAS in which the probe atoms are also used as a local (laser-ionized) ion source at an instant of time. Analysis of the ion energy and angular distribution after leaving the gap enables measurement, at the chosen ionization location in the gap, of both electrostatic potential and the development of ion divergence. Calculations show that all of these quantities can be measured with sub-mm and ns resolution. Using lithium or sodium probe atoms, fields from 0.1 to 10 MV/cm can be measured.
Monte Carlo simulation of the chemisorption kinetics and initial oxide formation on Al(111)
Authors: Oner D. E. , Chakarova R. , Zorić I. , Kasemo B.
Published: July 2002

Monte Carlo (MC) simulations, based on the lattice–gas approach, of the coverage-dependent chemisorption kinetics and initial oxide formation on Al(111) are presented. Three different adsorption mechanisms for the early chemisorption phase, discussed in the literature, are considered: (i) “hot” dimer dissociation; (ii) abstractive dissociation; and (iii) “normal” dissociation without “hot” fragments. The simulation results are compared with the experimental scanning tunnel microscope (STM) results by Brune et al. [J. Chem Phys. 99, 2128 (1993)]. The best agreement between the MC simulations and the STM results is obtained with the hot dimer mechanism.
Quantum codes for controlling coherent evolution
Authors: Sharf Yehuda , Havel Timothy F. , Cory David G.
Published: July 2002

Control over spin dynamics has been obtained in nuclear magnetic resonance (NMR) via coherent averaging, which modifies the effective internal Hamiltonian, and via quantum codes, which can protect against decoherent evolution. Here, we discuss the design and implementation of quantum codes that enable modification of the internal Hamiltonian. A detailed example is given of a quantum code for protecting two data spins from evolution under a weak coupling term in the Hamiltonian, using an “isolated” ancilla that does not evolve on the experimental time scale. The code is realized in a three-spin system by liquid-state NMR spectroscopy on 13C-labeled alanine, and tested for two initial states. It is also shown that with internal interactions and isolated ancillae, codes exist that do not require the ancillae to initially be in a (pseudo-) pure state. Finally, it is shown that even with nonisolated ancillae, quantum codes exist which can protect against evolution under weak coupling. An example is presented for a six-qubit code that protects two data spins to first order.
Bistable output from a coupled-resonator vertical-cavity laser diode
Authors: Fischer A. J. , Choquette K. D. , Chow W. W. , Allerman A. A. , Geib K. M.
Published: July 2002

We report a monolithic coupled-resonator vertical-cavity laser with an ion-implanted top cavity and a selectively oxidized bottom cavity which exhibits bistable behavior in the light output versus injection current. Large bistability regions over current ranges as wide as 18 mA have been observed with on/off contrast ratios of greater than 20 dB. The position and width of the bistability region can be varied by changing the bias to the top cavity. Switching between on and off states can be accomplished with changes as small as 250 μW to the electrical power applied to the top cavity. The bistable behavior is the response of the nonlinear susceptibility in the top cavity to the changes in the bottom intracavity laser intensity as the bottom cavity reaches the thermal rollover point.
Simulation of multilayered resonant tunneling diodes using coupled Wigner and Boltzmann distribution function approaches
Authors: Garcı́a-Garcı́a J. , Martı́n F.
Published: July 2002

From a coupling model between the Boltzmann transport equation and the quantum Liouville equation, we have developed a simulator based on the Wigner distribution function (WDF) approach that can be applied to resonant tunneling diodes (RTDs) and other vertical transport quantum devices. In comparison to previous WDF simulators, the tool allows one to extend the simulation domains up to hundreds of nanometers, which are the typical dimensions required for the study of actual multilayer structures. With these improvements, a level of agreement between theory and experiment comparable to that obtained by using other simulators based on Green functions has been achieved. The results of this work reveal that the WDF formalism can be alternatively used to study the behavior of actual multilayered RTDs.
Time-to-space conversion of Tbits/s optical pulses using a self-organized quantum-well material
Authors: Ishi Junko , Kunugita Hideyuki , Ema Kazuhiro , Ban Takuma , Kondo Takashi
Published: July 2002

We report a time-to-space conversion technique using a material which has a large χ(3)(≃10−6 esu) and a fast response time (<7 ps) at room temperature. The material is a self-organized quantum-well system consisting of inorganic well layers and organic barrier layers. We achieve a high conversion sensitivity even for nJ-order optical pulses. We demonstrate serial-to-parallel conversion of nJ-order Tbits/s signals at room temperature with conversion rates of 140 GHz.
Enhancement of the thermal stability of magnetic tunnel junctions employing artificial ferrimagnets
Authors: Dimopoulos T. , Tiusan C. , da Costa V. , Ounadjela K. , van den Berg H. A. M.
Published: July 2002

We have fabricated magnetic tunnel junctions that use Co/Ru/Co and Co/Ru/Co50Fe50 artificial ferrimagnet (AFi) systems as hard magnetic electrodes and AlOx as tunnel barrier. The thermal behavior of the two AFis, incorporated in tunnel junctions, presents dramatic differences, the most remarkable being the much greater thermal stability of the Co/Ru/CoFe system. This stems from the improvement of the interfaces the CoFe alloy forms with its adjacent Ru and AlOx layers. After successive annealing steps up to 400 °C, junctions incorporating the Co/Ru/CoFe system still present a significant tunnel magnetoresistance signal of nearly 20%, and most importantly, an almost intact magnetic rigidity of the hard magnetic system, being very promising for spin-electronic devices.
Finite-temperature properties of disordered and ordered Pb(Sc0.5Nb0.5)O3 alloys
Authors: Hemphill R. , Bellaiche L. , Garcı́a Alberto , Vanderbilt David
Published: July 2002

A first-principles-derived approach is used to study the properties of rocksalt-ordered and disordered Pb(Sc0.5Nb0.5)O3 (PSN) alloys. The paraelectric-to-ferroelectric transition temperature Tc is strongly dependent on the atomic configuration, while the piezoelectric response versus T/Tc is nearly independent of the chemical order. Our calculations are consistent with the experimental finding of Chu et al. [J. Appl. Phys. 77, 1671 (1995)] that, at T=Tc, ordered PSN undergoes a normal ferroelectric transition, while disordered PSN transforms from a relaxor state to a ferroelectric state.
Quasipersistent change in Hall sensitivity after illumination
Authors: Schurig E. , Besse P.-A. , Manic D. , Popovic R. S.
Published: July 2002

A quasipersistent change in the magnetic sensitivity of nonplate-like Hall sensors after light exposure has been discovered. The recovery time constant is about 10 min. The observed effect is very similar to the persistent photoconductivity (PPC) which has been described some time ago in silicon bulk material. Surprisingly, the new effect is about 1 order of magnitude stronger than the PPC. The similar recovery behavior of both effects suggests a common origin in precipitated oxygen clusters in the active zone. The amplitude of the variations is highly dependent on the cluster concentration in the substrate. The presented Hall sensors give a sensitive means to characterize the oxygen-denuded zone in Czochralski wafers.
Photovoltaic properties of CuGaSe2 homodiodes
Authors: Schön J. H. , Klenk M. , Schenker O. , Bucher E.
Published: July 2002

CuGaSe 2 -homodiodes were prepared by diffusion of Sb into n-type material. Total area solar energy conversion efficiencies up to 9.4% were obtained for standard solar illumination (air mass 1.5/AM1.5). Moreover, the analysis of illuminated and dark current–voltage characteristics revealed reduced recombination losses compared to conventional ZnO/CdS/CuGaSe2 diodes, leading to filling factors exceeding 70%. Hence, the use of homodiodes is very promising for efficient solar energy conversion in wide-band-gap Cu–III–VI2 chalcopyrites.
Characterization of strain in Si1−xGex films using multiple angle of incidence ellipsometry
Authors: Mukerjee Subroto , Venkataraman V.
Published: July 2002

In this letter we characterize strain in Si1−xGex based heterojunction bipolar transistors and modulation doped field effect transistors grown by rapid thermal chemical vapor deposition exploiting the phenomenon of strain-induced birefringence. The technique used is multiple angle of incidence ellipsometry at a wavelength of 670 nm to measure the ordinary and extraordinary refractive indices of the Si1−xGex films. We report measurements on thin fully strained films (with thicknesses less than the critical thickness) with Ge concentration varying from 9% to 40% with an accuracy of the order of 1 part in 104 and propose an empirical relation between the difference in the ordinary and extraordinary refractive indices (δn) and the Ge concentration (x) given by δn(x)=0.18x−0.12x2.
Negative differential conductance in planar one-dimensional/zero-dimensional/one-dimensional GaAs/AlGaAs structures
Authors: Worschech L. , Reitzenstein S. , Forchel A.
Published: July 2002

By using high-resolution electron beam lithography and wet etching, we have fabricated semiconducting islands between quantum wires from GaAs/AlGaAs modulation-doped heterostructures. The zero-dimensional islands were realized by displacing a 180 nm section at the center of a 1 μm long and 180 nm wide straight wire in well-controlled steps perpendicular to the wire direction. The narrow connections between the island and the wires introduce potential barriers. Finite bias voltages applied between the source and the drain of the electron waveguide structures permit to observe negative differential conductance, which is interpreted in terms of resonant tunneling of electrons through the barriers. Furthermore, we observe Coulomb blockade oscillations in the differential conductance of the structures.
Modal competition in implant-apertured index-guided vertical-cavity surface-emitting lasers
Authors: Seurin Jean-François P. , Liu Guobin , Chuang Shun Lien , Chirovsky Leo M. F. , Hobson W. S. , Lopata J.
Published: July 2002

We present a detailed theoretical study on the optical and L–I characteristics of implant-apertured index-guided vertical-cavity surface-emitting lasers. Our theory is based on a beam propagation method combined with thermal, gain, and rate-equation models. Spatial hole burning and modal competition are taken into account. Our results are in excellent agreement with the experimental data and show the effect of the current aperture size (determined by the ion implant) on the modal performance of these devices. In particular, the current-aperture size can be fixed independently from the index-guide size to obtain minimum threshold, single-mode operation.
Frequency-induced structure variation in electrorheological fluids
Authors: Wen Weijia , Ma Hongru , Tam Wing Yim , Sheng Ping
Published: July 2002

We show that by changing the frequency of the externally applied electric field there can be significant variation in the column structure of the electrorheological (ER) fluids, with attendant yield stress implications. This phenomenon is quantitatively explained by the Debye-type relaxation associated with ER fluids’ solid particles. First-principle predictions based on the Debye-type dielectric constant are in excellent agreement with the experiments.
Dynamic time expansion and compression using nonlinear waveguides
Authors: Findikoglu A. T. , Jia Q. X. , Hahn S. F.
Published: July 2002

We have used coplanar waveguides made from nonlinear dielectric strontium titanate and superconducting YBa2Cu3O7 electrodes to perform dynamic time expansion (DTE) and dynamic time compression (DTC) on fast signals with nanosecond duration. Experiments on 7.8-cm-long waveguides using bipulses with peak-to-peak amplitude on the order of 10 V and peak-to-peak separation of about 1 ns yielded DTC of about −50%, and DTE of about +50%. The implementation of DTE in fast detectors and data acquisition systems at the analog-to-digital conversion stage could enable these systems to operate with improved time resolution. The DTC could be used at the output of high-speed analog-to-digital converters or in radar applications.
Oxidation study of plasma-enhanced chemical vapor deposited and rf sputtered hydrogenated amorphous silicon carbide films
Authors: Choi W. K. , Lee L. P. , Foo S. L. , Gangadharan S. , Chong N. B. , Tan L. S.
Published: July 2002

An oxidation study of plasma-enhanced chemical vapor deposited (PECVD) and rf sputtered hydrogenated amorphous silicon carbide (a-Si1−xCx:H) films was carried out using the infrared (IR) and electron spin resonance (ESR) techniques. a-Si1−xCx:H films with x=0.3, 0.5, and 0.8 were prepared with the PECVD method and significant oxide growth can only be obtained in a-Si0.2C0.8:H film. IR results showed that Si–CH3 bonds provide the necessary porous structure for oxide growth. The oxide quality was found to be poor when compared to oxide obtained from pure silicon. Annealing in nitrogen enhances the porosity of the PECVD films and results in faster oxide growth. For sputtered films, oxide growth can only be observed in film containing Si–CH3 bonds. We are not able to separate the contributions of the Si–H, Si–C, Si–CH3, and the Si dangling bonds to the oxide growth for the PECVD and rf sputtered films.
Reduction in leakage current density of Si-based metal–oxide–semiconductor structure by use of catalytic activity of a platinum overlayer
Authors: Yuasa Toshiro , Asuha  , Yoneda Kenji , Todokoro Yoshihiro , Kobayashi Hikaru
Published: July 2002

We have developed a method to reduce leakage current density through a SiO2 layer of Si-based metal–oxide–semiconductor structure. In this method, a ∼3-nm-thick platinum (Pt) layer is deposited on the SiO2 layer, followed by the heat treatment at 300 °C in oxygen. After the removal of the Pt layer, the density of leakage current for this structure is decreased to less than 1/1000 with no increase in the thickness of the SiO2 layer. The reduction in leakage current density is attributed to (i) a decrease in the density of defect states such as Si dangling bonds and suboxide species, and (ii) improvement of the uniformity of the oxide thickness, both of which are caused by dissociated oxygen ions injected from Pt to SiO2.
Computation of Lie transfer maps for perturbed Hamiltonian systems
Authors: Healy Liam M.
Published: July 2002

Time evolution of a Hamiltonian system can be viewed as a canonical transformation; therefore perturbations, giving rise to near-identity deviations from an unperturbed solution, can be represented by products of Lie transformations, or, together with the unperturbed solution, Lie transfer maps. In this paper I broaden the applicability to all perturbed Hamiltonian systems the method of Dragt and Finn and subsequent co-workers, who developed a representation using a product of Lie transformations factored by phase space variable order. In the present paper, perturbation parameters are no longer necessarily associated with the phase space variables; this method treats both “internal” and “external” perturbations on an equal footing, and a rank is assigned to each variable to reflect the degree of perturbation it represents. With the companion program PGLT, analytic development of the Lie transfer maps is relatively easy for many systems.
Gettering of Co in Si by high-energy B ion-implantation and by p/p+ epitaxial Si
Authors: Benton J. L. , Boone T. , Jacobson D. C. , Rafferty C. S.
Published: July 2002

Detection and gettering of Co contamination in processed Si is an important issue in integrated circuit fabrication. In this work, Co was intentionally introduced into Si by ion implantation, and its diffusion monitored by secondary ion mass spectroscopy. The surface layer recombination lifetime in p/p+ epitaxial Si is unaffected by the Co at doses of 1×1011 cm−2 or 1×1012 cm−2. In the case of 2.5 MeV, 4×1014 B/cm2 ion implanted bulk Si, two mechanisms for Co redistribution during high temperature furnace, 900 °C, 30 min, processing are evident. First, regions of high boron concentration provide gettering sites for Co contamination. Second, the final distribution of Co in Si reflects ion-implantation induced defect evolution during annealing. Both mechanisms will operate during device processing and will control the effect of the metal on the electrical properties of the Si.
Correlation between the gate bias dependence of the probability of anode hole injection and breakdown in thin silicon dioxide films
Authors: Samanta Piyas , Sarkar C. K.
Published: July 2002

Hole injection from the anode in thin silicon dioxide (SiO2) films in n+-polycrystalline silicon gate–oxide–silicon structures has been theoretically investigated during high-field Fowler–Nordheim electron injection from both substrate (positive gate bias) and gate (negative gate bias). Theoretical results of the gate bias dependence of the probability of anode hole injection per injected electron αh as a function of electric field or injection current density are shown to be directly correlated to experimentally observed polarity dependence of destructive breakdown in thin SiO2 films.
High-resolution observation of the growth motion of elements on surfaces and at interfaces
Authors: Yamanaka Toshiro , Shimomura Naoharu , Ino Shozo
Published: July 2002

The results of high-resolution, real-space observations of the behaviors of elements on surfaces and at interfaces during growth of Ga on Si(111)-∛×∛-Ag are presented. Site exchange and surrounding other elements were directly observed using a high-resolution ultrahigh vacuum scanning electron microscope (SEM) newly combined with characteristic x-ray spectroscopy under a grazing detection-angle condition. Compared with the resolution of conventional SEM-energy dispersive x-ray spectrometry (several μm), resolution in elementary analysis has been significantly improved due to a small beam size and cut off of x-rays from deep regions, and local elementary analysis of surface structures of only about 10–20 nm in size is possible by the present method.
Superluminescence in InAsSb circular-ring-mode light-emitting diodes for CO gas detection
Authors: Sherstnev V. V. , Monahov A. M. , Krier A. , Hill G.
Published: July 2002

We report on the superluminescence of an InAsSb light-emitting diode, operating at 4.6 μm, suitable for carbon monoxide gas detection. The source is based on an optical whispering (or circulating) mode which is generated near the edges of the mesa and which is responsible for the superluminescence. A pulsed optical output power in excess of 2.2 mW at room temperature has been measured, making these emitters suitable for use in cost-effective instruments for the environmental monitoring of carbon monoxide at 4.6 μm.
Contribution of the ultrafast, short-distance intermolecular electron transfer to the fluorescence quenching rate in solution
Authors: Iwai Shinichiro , Murata Shigeo , Tachiya M.
Published: July 2002

In a previous paper [S. Iwai et al., J. Chem. Phys. 112, 7111 (2000)] we have found ultrafast electron transfer (ET) which occurs between donor and acceptor molecules at short distances. We incorporate this ultrafast ET in the calculation of the second-order ET rate in order to explain the discrepancies between experimental [D. Rehm and A. Weller, Isr. J. Chem. 8, 259 (1970)] and theoretical [M. Tachiya and S. Murata, J. Phys. Chem. 96, 8441 (1992)] ET rates. The effect of the short-distance ET is significant in the Marcus normal region where the Marcus-type ET is not very fast. Compared to the case where the original Marcus equation is used as the first-order ET rate, the calculated second-order rate is found to increase by several orders of magnitude in the normal region. Thus the discrepancy between theory and experiment is potentially resolved and the importance of the short-distance ET in fluorescence quenching demonstrated.
Preparation and single molecule structure of electroactive polysilane end-grafted on a crystalline silicon surface
Authors: Furukawa Kazuaki , Ebata Keisuke
Published: July 2002

Electrically active polysilanes of poly(methylphenylsilane) (PMPS) and poly[bis(p-n-butylphenyl)silane] (PBPS), which are, respectively, known as a good hole transporting material and a near-ultraviolet electroluminescent material, are end-grafted directly on a crystalline silicon surface. The single polysilane molecules are clearly distinguished one from the other on the surface by means of atomic force microscopy observations. End-grafted single molecules of PMPS are observed as dots while end-grafted PBPS appear as worms extending for more than 100 nm on the crystalline silicon surface.
Avalanche multiplication and ionization coefficient in AlGaAs/InGaAs p-n-p heterojunction bipolar transistors
Authors: Yan Bei Ping , Wang Hong , Ng Geok Ing
Published: July 2002

The hole-initiated impact ionization multiplication factor Mp−1 and the ionization coefficient αp in AlGaAs/InGaAs p-n-p heterojunction bipolar transistors (HBTs) are presented. A large discrepancy is observed at low electric field when the measured data from the p-n-p HBTs are compared with those given from avalanche photodiode. The results show that the conventional impact ionization models, based on local electric field, substantially overestimate the hole impact ionization multiplication factor Mp−1. We believe that the hole ionization coefficient in p-n-p HBTs where significant dead space effects occur in the collector space charge region.
Quantization of solitons in coset space
Authors: Manjavidze J. , Sissakian A.
Published: July 2002

The perturbation theory around the soliton fields of the sin-Gordon model is developed in the coset space. It is shown by explicit calculations that all corrections to the topological soliton contribution are canceled exactly.
Formation of silicon on insulator using separation by implantation of oxygen with water plasma
Authors: Chen Jing , Wang Xi , Chen Meng , Zheng Zhihong , Yu Yuehui
Published: July 2002

Separation by plasma implantation of oxygen (SPIMOX) was developed to fabricate silicon-on-insulator (SOI) wafers based on separation by implantation of oxygen technology, however, it suffers from the coexistence of O+ and O2+ ions in the oxygen plasma, which gives rise to nonuniformity of the formed buried oxide layer. In the present work, water plasma was used as a source of oxygen (H2O+, HO+, and O+) for achieving small spread in the oxygen implant depth profile. The feasibility of SPIMOX with water plasma to form SOI wafers was explored at an ion implanter without mass separator. Cross-sectional transmission electron microscopy revealed that a uniform buried oxide layer was formed under a single crystal silicon overlayer with the present process. The interfaces between the silicon overlayer, buried oxide layer, and bulk silicon were smooth and sharp. An implant dose window has been identified for producing a desirable SOI structure.
Magnetotransport and magnetic properties of La0.7MnO3−δ and Pr0.65Ba0.05Ca0.3MnO3−δ superlattices
Authors: Pietambaram Srinivas V. , Kumar D. , Singh Rajiv K. , Lee Clinton B.
Published: July 2002

Superlattice structures consisting of La0.7MnO3−δ (LMO) and Pr0.65Ba0.05Ca0.3MnO3−δ (PBCMO) systems, in which the thickness of La0.7MnO3−δ is fixed and that of Pr0.65Ba0.05Ca0.3MnO3−δ varied from 1 to 8 unit cells, have been grown in situ on (100) LaAlO3 substrates using a pulsed-laser deposition technique. Microstructural characterization carried out on these films shows the presence of characteristic intense satellite peaks, indicating the chemical modulation of the superlattice structure. The insulator-to-metal transition and the magnetoresistance (MR) ratio are found to vary with the number of unit cells. The samples with 1, 2, 5, and 8 unit cells of Pr0.65Ba0.05Ca0.3MnO3−δ show transition temperatures of 240, 230, 150, and 160 K and MR ratios of 540%, 592%, 3150%, and 2875%, respectively. We have observed an enhancement of magnetoresistance ratios in the case of superlattices with a thickness of PBCMO greater than 5 unit cells, which may be attributed to a ferromagnetic biasing provided by the LMO layers acting as a ferromagnetic film below its transition temperature.
Optical properties of GaN grown by hydride vapor-phase epitaxy
Authors: Oh Eunsoon , Lee S. K. , Park S. S. , Lee K. Y. , Song I. J. , Han J. Y.
Published: July 2002

High-quality free-standing GaN was obtained by hydride vapor-phase epitaxy (HVPE) growth and the subsequent removal of the sapphire substrates. In the photoluminescence (PL) spectra of the as-grown HVPE-GaN, we observed a strong phonon replica peak for temperatures higher than 80 K. Both the near-band-edge emission and the yellow emission in the cathodoluminescence spectra were inhomogeneous, and correlated with the crystalline structure. With the homoepitaxial regrowth by metal–organic chemical-vapor deposition (MOCVD) in the GaN substrates, these unusual optical properties were no longer observed and the PL peak became sharper than GaN grown by MOCVD on sapphire substrates, indicating that the free-standing GaN is suitable as substrates for the growth of device structures.
Correlation of defect profiles with carrier profiles of InAs epilayers on GaP
Authors: Tsukamoto H. , Chen E.-H. , Woodall J. M. , Gopal V.
Published: July 2002

The carrier profile for InAs films grown on GaP is modeled as a first-order approximation which assumes that 90° edge dislocation intersections and the threading dislocation intersections act as shallow donors. Due to dislocation annihilation during growth, the threading dislocation intersection density decreases as the inverse of the distance x from the InAs/GaP interface, D(x)=D0x0/(x0+x), where D0 and x0 are dislocation density at the InAs/GaP interface and the first annihilation position from the interface, respectively. The carrier profile in InAs films can be described by a similar equation that is deduced from the threading dislocation intersection profile. The calculated carrier profiles agree well with measured carrier profiles. This correlation supports our hypothesis that both the edge dislocation intersections and the threading dislocation intersections act as shallow donor sources.
Reduced temperature dependence of luminescence from silicon due to field-induced carrier confinement
Authors: Lin Ching-Fuh , Chen Miin-Jang , Liang Eih-Zhe , Liu W. T. , Liu C. W.
Published: July 2002

Electroluminescence from metal–oxide–semiconductor structures on Si was experimentally found to be much less temperature dependent than photoluminescence of Si. The physical reason is attributed to the field-induced carrier confinement in a small region, which contains much less impurity states, compared to the unconfined region. Thus, electron–hole recombination by radiation emission instead of through highly temperature-dependent impurity states is increased. A proposed model well explains the reduced temperature dependence with the field-induced carrier confinement.
On “radiation-free” states in transient motion of dislocations
Authors: Markenscoff Xanthippi
Published: July 2002

The existence of "radiation-free" states in transient motion of dislocations is investigated. By analyzing an edge dislocation jumping from rest to a supersonic speed, we see that the Mach fronts disappear at vd=2c2 because at this dislocation velocity, the pole singularity in the complex plane is replaced by a removable one. However, there exist radiated stress waves propagating with velocity c2, as well as c1. Also, due to radiated longitudinal waves, there is a “force” required to be supplied to sustain such a motion.
Josephson plasma observed in underdoped (110) YBa2Cu3O7−δ films
Authors: Qiu X. G. , Koinuma H. , Iwasaki M. , Itoh T. , Sarin Kumar A. K. , Kawasaki M. , Saitoh E. , Tokura Y. , Takehana K. , Kido G. , Segawa Y.
Published: July 2002

(110) oriented YBa2Cu3O7−δ thin films have been epitaxially grown on vicinal (110)SrTiO3 substrates by pulsed-laser deposition. Films with different oxygen deficiencies were obtained by annealing under various oxygen ambient. These films have very smooth surface and with their c axis aligned in one direction in the substrate plane. Electronic transport and polarized far-infrared reflectivity measurements reveal the unique features of the c-axis charge dynamics. A c-axis far-infrared reflectivity edge associated with the Josephson plasma in the superconducting state is observed. Our results demonstrate the potential usage of (110) thin films for the investigation of intrinsic interlayer charge dynamics as well as device application of high Tc superconductors.
Enhancing type-II optical second-harmonic generation by the use of a laser beam with a rotating azimuth of polarization
Authors: Kir’yanov A. V. , Aboites V. , Mel’nikov I. V.
Published: July 2002

We propose a frequency converter which exploits laser pulses with changing state of polarization. The use of such pulses as a pump source for an extracavity doubling crystal is shown to result in the large conversion efficiency. These pulses can also provide a fairly good tool of monitoring the shape of the harmonic pulse. It is shown that temporal variations of the polarization direction experienced by the pump pulse in this system may cause considerable shortening of the harmonic pulse.
Snapback behavior of the postbreakdown I–V characteristics in ultrathin SiO2 films
Authors: Chen T. P. , Tse M. S. , Zeng X.
Published: July 2002

With the I–V measurement technique that forced a current to an ultrathin gate oxide and measured the voltage drop, a snapback phenomenon, i.e., the gate oxide was switched from a higher-impedance state to a lower-impedance state suddenly, was observed during the postbreakdown I–V measurement. The snapback could be triggered at a very low measurement current. Single or multiple snapbacks have been observed, and it was found that the occurrence of snapback was a random event. The snapback is explained in terms of the formation of an additional percolation path due to the neutralization of negatively charged traps or the generation of neutral electron traps at certain strategic positions during the measurement.
Band-edge luminescence in quaternary AlInGaN light-emitting diodes
Authors: Shatalov M. , Chitnis A. , Adivarahan V. , Lunev A. , Zhang J. , Yang J. W. , Fareed Q. , Simin G. , Zakheim A. , Khan M. Asif , Gaska R. , Shur M. S.
Published: July 2002

Operation of InGaN multiple-quantum-well (MQW) light-emitting diodes (LEDs) with quaternary AlInGaN barriers at room and elevated temperatures is reported. The devices outperform conventional GaN/InGaN MQW LEDs, especially at high pump currents. From the measurements of quantum efficiency and total emitted power under dc and pulsed pumping, we show the emission mechanism for quaternary barrier MQWs to be predominantly linked to band-to-band transitions. This is in contrast to localized state emission observed for conventional InGaN/InGaN and GaN/InGaN LEDs. The band-to-band recombination with an increased quantum-well depth improves the high-current performance of the quaternary barrier MQW LEDs, making them attractive for high-power solid-state lighting applications.
Influence of disorder and a parallel magnetic field on a quantum cascade laser
Authors: Apalkov V. M. , Chakraborty Tapash
Published: July 2002

The luminescence spectra of a quantum cascade laser (QCL) in a strong magnetic field is influenced significantly by the presence of disorder (charged or neutral) in the system. An externally applied magnetic field parallel to the electron plane causes a redshift of the luminescence peak in the absence of any disorder potential. Our results indicate that the disorder potential tends to cancel that redshift and causes a rapid decrease of the luminescence peak. A similar behavior was observed in a recent experiment on a QCL in a parallel magnetic field by S. Blaser, L. Diehl, M. Beck, and J. Faist [Physica E 7, 33 (2000)].
Graded doping profiles for reduction of carrier trapping in organic light-emitting devices incorporating doped polymers
Authors: Chang Hsin-Hua , Wu Chung-Chih , Yang Cheng-Chung , Chen Chieh-Wei , Lee Cheng-Chung
Published: July 2002

Dispersing emissive dopants into luminescent polymers is an effective approach to enhance luminescence and to tune emission color in organic light-emitting devices incorporating polymer films. However, the carrier trapping effect due to emissive dopants often causes deterioration of electrical characteristics. In this letter, we show that, by introducing a graded doping profile to match the carrier recombination zone in the doped polymer, the carrier trapping, and the deterioration of electrical characteristics can be minimized while the enhancement in efficiency maintains. The finite-source dye-diffusion thermal transfer is used to produce graded doping profiles into a luminescent polymer. The effectiveness of this approach has been demonstrated in both single-layer and heterostructure devices incorporating doped polymers.