bluuebunny/crossref_metadata_2025 huggingface dataset:
Accurate pattern registration for integrated circuit tomography
Authors: Levine Zachary H. , Grantham Steven , Neogi Suneeta , Frigo Sean P. , McNulty Ian , Retsch Cornelia C. , Wang Yuxin , Lucatorto Thomas B.
Published: July 2002

As part of an effort to develop high resolution microtomography for engineered structures, a two-level copper integrated circuit interconnect was imaged using 1.83 keV x rays at 14 angles employing a full-field Fresnel zone plate microscope. A major requirement for high resolution microtomography is the accurate registration of the reference axes in each of the many views needed for a reconstruction. A reconstruction with 100 nm resolution would require registration accuracy of 30 nm or better. This work demonstrates that even images that have strong interference fringes can be used to obtain accurate fiducials through the use of Radon transforms. We show that we are able to locate the coordinates of the rectilinear circuit patterns to 28 nm. The procedure is validated by agreement between an x-ray parallax measurement of 1.41±0.17 μm and a measurement of 1.58±0.08 μm from a scanning electron microscope image of a cross section.
Shear strength measurements in the TiAl-based alloy Ti–48Al–2Nb–2Cr–1B during shock loading
Authors: Millett J. C. F. , Bourne N. K. , Jones I. P.
Published: July 2002

The lateral stress in a titanium aluminide alloy has been investigated under different impact conditions during shock loading, using embedded manganin stress gauges. From this, the variation of the materials shear strength with longitudinal stress has been determined. Results show that shear strength increases rapidly with increasing impact stress, as would be expected in a material that displays a high degree of work hardening. The results from this alloy have also been compared to those of a similar material, which was tested in a different microstructural state. Significant differences were noted and explained in terms of the variation in phase distribution and grain size.
New diagnostic method for monitoring plasma reactor walls: Multiple total internal reflection Fourier transform infrared surface probe
Authors: Godfrey Anna R. , Ullal Saurabh J. , Braly Linda B. , Edelberg Erik A. , Vahedi Vahid , Aydil Eray S.
Published: July 2002

Films and adsorbates that deposit on reactor walls during plasma etching and deposition affect the discharge properties such as the charged particle and reactive radical concentrations. A systematic study of this plasma–wall interaction is made difficult by a lack of diagnostic methods that enable one to monitor the chemical nature of the reactor wall surface. A new diagnostic technique based on multiple total internal reflection Fourier transform infrared (MTIR-FTIR) spectroscopy was developed to monitor films and adsorbates on plasma etching and deposition reactor walls with monolayer sensitivity. Applications of this MTIR-FTIR probe are demonstrated. Specifically, we use this probe to (i) detect etch products and films that deposit on the reactor walls during Cl2 plasma etching of Si, (ii) determine the efficacy of a SF6 plasma to clean films deposited on reactor walls during Cl2/O2 etching of Si, and (iii) monitor wafer-to-wafer etching reproducibility.
Small-signal impedance characteristics of quantum-well laser structures
Authors: Giudice G. E. , Kuksenkov D. V. , Temkin H.
Published: July 2002

Small-signal impedance characteristics of quantum-well laser structures are analyzed. A simple analytical expression for the frequency dependence of below-threshold small-signal impedance is derived and verified experimentally. It is shown that the differential carrier lifetime and quantum-well transport and capture times can be extracted from electrical impedance measurements.
Bipolar phototransport in π-conjugated polymer /C60 composites
Authors: Balberg I. , Naidis R. , Lee M.-K. , Shinar J. , Fonseca L. F.
Published: July 2002

Conjugated polymer/fullerene composite films that exhibit steady-state phototransport properties of a unipolar or bipolar photoconductor, depending on the relative concentration of the components, are described. The observed behavior of the composites, in which each component has its own percolation path but its carrier content is not high enough to quench the carriers in the other component, is shown to be due to the coupling of the recombination processes in the two components.
Fractal dewetting of a viscous adhesive film between separating parallel plates
Authors: Thamida S. K. , Takhistov P. V. , Chang H.-C.
Published: July 2002

A dewetting cylindrical film between two separating plates is observed to produce fractal finger patterns that penetrate radially inward. In lieu of the classical tip splitting, this fractal is generated by successive shielding of alternating fingers. By analyzing this key shielding dynamics via a forced two-dimensional Hele–Shaw model with global force balance, a self-similar scaling for the shielding distance and shielding time were obtained for every generation of shielding events. The theory predicts that the plate detach time is reduced by a factor of 12 due to the fractal fingers. This is confirmed experimentally for large Bond numbers when there are sufficient fingers to justify a continuum approximation in the theory. A cumulative node number density, which is not a power law, is also predicted but not confirmed experimentally.
Scalings for fragments produced from drop breakup in shear flow with inertia
Authors: Renardy Yuriko Y. , Cristini Vittorio
Published: July 2002

When a drop is sheared in a matrix liquid, the largest daughter drops are produced by elongative end pinching. The daughter drop size is found to scale with the critical drop size that would occur under the same flow conditions and fluid properties. Daughter drop volumes saturate to just below 60% of the critical volume as the mother drop size increases. For large Reynolds number, the daughter drop radius scales with the −13 case power of the capillary number when the Reynolds number is fixed.
Subband electron properties of modulation-doped AlxGa1−xN/GaN heterostructures with different barrier thicknesses
Authors: Jiang C. P. , Guo S. L. , Huang Z. M. , Yu J. , Gui Y. S. , Zheng G. Z. , Chu J. H. , Zheng Z. W. , Shen B. , Zheng Y. D.
Published: July 2002

Magnetotransport properties of modulation-doped Al0.22Ga0.78N/GaN heterostructures with different barrier thicknesses of 25–100 nm have been investigated in magnetic fields up to 9 T at 1.4 K. Fast Fourier transform has been applied to obtain the subband density and mobility of the two-dimensional electron gas in these heterostructures. High electron density of 1.18×1013 cm−2 and quantum mobility of ∼8200 cm2 V−1 s−1 are obtained when the barrier thickness is 75 nm, which indicates that there exists a critical barrier thickness between 50 and 100 nm in the modulation-doped Al0.22Ga0.78N/GaN heterostructures. We also find that the elastic strain relaxation of the barrier does not significantly enhance the quantum mobilities of the ground subbands, however, it has strong effect on the mobilities of the excited states. The experimental values obtained in this work are useful for the design and optimization AlxGa1−xN/GaN device.
Atomic scale investigations of the Co/Pt(111) interface structure and magnetic properties
Authors: Moon D. W. , Ha Y. H. , Park Y. , Lee J.-W. , Kim J. , Shin S.-C.
Published: July 2002

The interface structure of an ultrathin Co overlayer on a Pt(111) crystal was investigated with atomic-layer resolution medium-energy ion scattering spectroscopy and surface magneto-optical Kerr effect (SMOKE). For a 7 ML Co, interdiffusion begins at 673 K to form a heavily distorted Co–Pt surface alloy layer with little change in SMOKE intensity. However, annealing at 773 K formed a 30 atomic-layer-thick Co–Pt substitutional alloy with 3.7% maximum tensile strain, at which the SMOKE intensity increased more than 200%. The enhancement of the Kerr intensity is discussed with the interface alloy formation.
Influence of localized nitrogen states on material gain in InGaAsN/GaAs quantum-well lasers
Authors: Yong J. C. L. , Rorison J. M. , White I. H.
Published: July 2002

The effect of the nature of nitrogen incorporation in the InGaAsN/GaAs quantum well system on gain is investigated. The nitrogen is considered to be either fully incorporated within the lattice or to be incorporated as a localized acceptor. In the latter case this results in conduction-band anticrossing, causing nonparabolicity. The resulting gains from the two extreme limits are compared and found to be similar. This shows that the nature of the nitrogen incorporation is not a key issue in the performance of InGaAsN/GaAs quantum well lasers for 1.3 μm applications.
Studies of thin film growth and oxidation processes for conductive Ti–Al diffusion barrier layers via in situ surface sensitive analytical techniques
Authors: Dhote A. M. , Auciello O. , Gruen D. M. , Ramesh R.
Published: July 2002

Conducting diffusion barrier layers play a critical role in high-density memory integration. We recently demonstrated that Ti–Al can be used as a diffusion barrier layer for the integration of ferroelectric capacitors with complementary metal–oxide semiconductor devices for the fabrication of nonvolatile ferroelectric random access memories (NVFRAMs). Here, we discuss results from systematic studies designed to understand Ti–Al film growth and oxidation processes using in situ ion beam sputter deposition in conjunction with complementary in situ atomic layer-resolution mass spectroscopy of recoil ion (MSRI) and surface sensitive x-ray photoelectron spectroscopy (XPS). The concurrent MSRI/XPS analysis revealed that amorphous Ti–Al layers produced by tailored sputter-deposition methods are resistant to oxidation to at least 600 °C, and that oxidation occurs only when the a-Ti–Al layers are exposed to oxygen at >600 °C, via the segregation of Ti species to the surface and TiO2 formation. The a-Ti–Al layers discussed in this letter could be used in the double functionality of a bottom electrode/diffusion barrier for the integration of ferroelectric capacitors with Si substrates for the fabrication of NVFRAMs and other devices.
Annealing effects on the microstructure of Ge/Si(001) quantum dots
Authors: Liao X. Z. , Zou J. , Cockayne D. J. H. , Wan J. , Jiang Z. M. , Jin G. , Wang Kang L.
Published: July 2002

Ge/Si(001) multilayer islands produced by gas-source molecular-beam epitaxy at 575 °C were investigated using energy-filtering transmission electron microscopy. Results show, for as-grown samples, not only a continuous enlargement of island size in upper layers but also a continuous increase of Ge concentration within islands in upper layers. As a result of the increasing island size and Ge concentration within the islands, the island density in upper layers decreases. For samples annealed at 900 °C for 5 min, the aspect ratio of buried islands increases significantly, and the average Ge concentration within islands of different layers becomes uniform.
Transport spectroscopy of the ultrasmall silicon quantum dot in a single-electron transistor
Authors: Saitoh Masumi , Saito Toshiki , Inukai Takashi , Hiramoto Toshiro
Published: July 2002

We investigate electron transport through the ultrasmall silicon quantum dot in a single-electron transistor. The device is fabricated in the form of a silicon point-contact channel metal–oxide–semiconductor field-effect transistor. The size of the formed dot is estimated to be as small as 5.3 nm. Negative differential conductance is clearly observed up to 25 K. It turns out that this is caused by discreteness of quantum levels in the silicon dot and variation of the tunneling rates to each level. The fine structure of conductance persists up to 77 K. Modeling of the electron transport through the silicon dot is carried out. Good agreement between experiment and calculation is obtained, which confirms the validity of our model.
12 W continuous-wave diode lasers at 1120 nm with InGaAs quantum wells
Authors: Bugge F. , Erbert G. , Fricke J. , Gramlich S. , Staske R. , Wenzel H. , Zeimer U. , Weyers M.
Published: July 2002

Highly strained InGaAs quantum wells were grown by metalorganic vapor-phase epitaxy. By lowering the growth temperature to 530 °C, a maximum photoluminescence wavelength of 1192 nm was achieved. High-power diode lasers with a maximum lasing wavelength of 1175 nm were fabricated. A continuous-wave output power of 12 W at a heat-sink temperature of 25 °C was obtained at a lasing wavelength of 1120 nm.
Binding energy of vacancies to clusters formed in Si by high-energy ion implantation
Authors: Kalyanaraman R. , Haynes T. E. , Holland O. W. , Gossmann H.-J. L. , Rafferty C. S. , Gilmer G. H.
Published: July 2002

Measurements of the binding energy (Eb) of vacancies to vacancy clusters formed in silicon following high-energy ion implantation are reported. Vacancy clusters were created by 2 MeV, 2×1015 cm−2 dose Si implant and annealing. To prevent recombination of the excess vacancies (Vex) with interstitials from the implant damage near the projected range (Rp), a Si-on-insulator substrate was used such that the Rp damage was separated from the Vex by the buried oxide (BOX). Two Vex regions were observed: one in the middle of the top Si layer (V1ex) and the other at the front Si/BOX interface (V2ex). The rates of vacancy evaporation were directly measured by Au labeling following thermal treatments at temperatures between 800 and 900 °C for times ranging from 600 to 1800 s. The rate of vacancy evaporation from V2ex was observed to be greater than from V1ex. The binding energy of vacancies to clusters in the middle of the silicon top layer was 3.2±0.2 eV as determined from the kinetics for vacancy evaporation.
Magnetic imaging of ion-irradiation patterned Co/Pt multilayers using complementary electron and photon probes
Authors: Kusinski G. J. , Krishnan K. M. , Denbeaux G. , Thomas G. , Terris B. D. , Weller D.
Published: July 2002

The three-dimensional magnetic structure and reversal mechanism of patterned Co/Pt multilayers, were imaged using complementary Lorentz transmission electron microscopy (in-plane component) and magnetic transmission x-ray microscopy (perpendicular magnetization). The Co/Pt films with perpendicular anisotropy were patterned by ion irradiation through a stencil mask to produce in-plane magnetization in the irradiated regions. The boundaries of the patterns, defined by the transition from out-of-plane to in-plane magnetization, were found to be determined by the stencil mask. The nucleation fields were substantially reduced to 50 Oe for the in-plane regions and 1 kOe for the perpendicular regions, comparing to 4.5 kOe for the as-grown film. The perpendicular reversals were found to always originate at the pattern boundaries.
Evanescent wave absorption by Xe(1s5) lying on a discharge tube wall
Authors: Bratescu M.-A. , Sakai Y. , Kamada T.
Published: July 2002

A simple and sensitive detection method of Xe(1s5) excited atoms in the vicinity of a discharge wall with laser-collision induced fluorescence (LCIF) produced by evanescent wave absorption is proposed. The signal to noise (S/N) ratio was 102. The hyperfine structure (hfs) in the Xe LCIF spectra induced by resonant absorption of Xe(1s5→2p6) was confirmed to be identical with the hfs in laser absorption spectra, although the detection point (xPD) on the discharge wall was chosen independently of the position of the EW absorption (xEW). The insignificantly large fluorescence, which appeared for incident light angles to a prism larger than 4.8°, is explained by the fact that the refracted light emerged in a plasma. The Xe(1s5) number density in a dc Xe discharge, although roughly estimated, on the tube wall between the electrodes is presented.
Approach interactions of scanned probes in dynamic pecking mode
Authors: Wetsel G. C. , Farahi R. H. , Richardson C. J. K. , Spicer J. B.
Published: July 2002

Sharp, conical, metallic tips oriented perpendicular to the axis of a rod vibrating in bending (pecking mode) are used as force sensors in scanned force probes and as optical scatterers in apertureless near-field optical microscopes. We have measured the displacement of such probes as a function of frequency and tip-sample separation during approach of the probe tip to a solid-sample surface. We have also developed a nonlinear model describing the attenuation of the probe motion during approach that takes into account the variation of the force on the probe during each cycle of vibrational motion. The experimental data and the theory are in good agreement. The results enable proper design of tip-sample-distance control systems, inference of material parameters, and an improved understanding of apertureless-near-field-optical-microscope measurements.
Patterning of epitaxial MnAs on GaAs by direct optical writing
Authors: Ramsteiner M. , Zhu H. J. , Däweritz L.
Published: July 2002

We demonstrate patterning of ferromagnetic MnAs layers on GaAs substrates by optical writing with a focused laser beam. Depending on the writing conditions, stripes with ridge- and groove-shaped cross sections can be produced without damage of the GaAs substrate. Using in situ control by resistance measurements, conditions for the preparation of completely insulating stripes can be established. The formation of insulating and paramagnetic Mn3O4 during optical writing is verified by Raman scattering.
Near-field microscopy and spectroscopy of third-harmonic generation and two-photon excitation in nonlinear organic crystals
Authors: Shen Yuzhen , Swiatkiewicz Jacek , Markowicz Przemyslaw , Prasad Paras N.
Published: July 2002

Near-field microscopy and spectroscopy of third-harmonic generation and two-photon excitation are demonstrated on a subdiffraction-limited scale. Near-field measurements of both the intensity dependence and the spectral dependence are performed on nonlinear organic nanocrystals of 4-(N, N-diethylamino)-β-nitrostyrene. The in-plane local anisotropies of third-order susceptibilities are observed, which is revealed to be associated to two-photon allowed π–electron transition. The local spectra exhibit the crystal symmetry on a nanometric scale.
Polarization charges and polarization-induced barriers in AlxGa1−xN/GaN and InyGa1−yN/GaN heterostructures
Authors: Jia L. , Yu E. T. , Keogh D. , Asbeck P. M. , Miraglia P. , Roskowski A. , Davis R. F.
Published: July 2002

Polarization charges are measured and the formation of large electrostatic barriers arising primarily as a consequence of the presence of polarization-induced charge densities is deduced from capacitance–voltage analysis of n-type AlxGa1−xN/GaN and InyGa1−yN/GaN heterostructures. In structures consisting of 5–10 nm AlxGa1−xN or InyGa1−yN surrounded by n-GaN, capacitance–voltage profiling studies combined with elementary electrostatic analysis yield experimental estimates of polarization charge densities, which are compared with values expected based on the combined effects of spontaneous and piezoelectric polarization. These results imply the existence of electrostatic barriers that are due primarily to the large polarization charge densities at each heterojunction interface and the resulting potential difference maintained across the thin AlxGa1−xN or InyGa1−yN layers. The electrostatic barriers formed in these structures are large in comparison to the heterojunction conduction-band offsets, demonstrating the utility of polarization-based engineering of electrostatic barriers in nitride semiconductor heterostructures.
Optical emission from ultrathin strained type-II InP/GaP quantum wells
Authors: Hatami F. , Mussler G. , Schmidbauer M. , Masselink W. T. , Schrottke L. , Hao H.-Y. , Grahn H. T.
Published: July 2002

We describe the growth and optical emission from ultrathin strained InP quantum wells grown on GaP substrates using gas-source molecular-beam epitaxy. The InP thickness was varied between 0.5 and 1.6 monolayers. Intense photoluminescence was emitted from the structures; time-resolved measurements indicate rather long carrier lifetimes of about 19 ns. With decreasing InP coverage, the emission lines are shifted from 2.18 to 2.28 eV due to quantum size effects. We explain the emission as spatially indirect recombination of electrons from the GaP X valleys with holes in InP and its phonon replicas.
Resonant scattering in delta-doped heterostructures
Authors: Robinson I. K. , Nilsson P. O. , Debowska-Nilsson D. , Ni W. X. , Hansson G. V.
Published: July 2002

We demonstrate the utility of resonant x-ray scattering in probing the structure of doping layers at a heterostructure interface. The positions of germanium layers inserted at the interface of a silicon epitaxial film assert a strong influence of the phase of the scattered intensity along the crystal truncation rods. The phase of the scattering, and hence the internal structure of the layers, can be determined conveniently by analyzing its energy dependence in the vicinity of the Germanium absorption edge at 11.103 keV.
Superhard, conductive coatings for atomic force microscopy cantilevers
Authors: Ronning C. , Wondratschek O. , Büttner M. , Hofsäss H. , Zimmermann J. , Leiderer P. , Boneberg J.
Published: July 2002

Boron carbide thin films were grown by mass selected ion beam deposition using low energy B11+ and C12+ ions at room temperature. The amorphous films exhibit any desired stoichiometry controlled by the ion charge ratio B+/C+. Films with a stoichiometry of B4C showed the optimal combination of a high mechanical strength and a low electrical resistivity for the coating of atomic force microscopy (AFM) silicon cantilevers. The properties of such AFM tips were evaluated and simultaneous topography and Kelvin mode AFM measurements with high lateral resolution were performed on the systems (i) Au nanoparticles on a p-WS2 surface and (ii) conducting/superconducting YBa2Cu3O7−x.
Dry thermal oxidation of a graded SiGe layer
Authors: Lim Y. S. , Jeong J. S. , Lee J. Y. , Kim H. S. , Shon H. K. , Kim H. K. , Moon D. W.
Published: July 2002

A method for the dry thermal oxidation of a strained SiGe layer is proposed. By oxidation of a graded Si1−xGex layer, the effect of Ge pileup was significantly reduced and the undesirable strain relaxation by defect formation is prohibited. After oxidation, the oxidized SiGe layer was homogenized by postannealing process, and thereby a SiO2/SiGe interface with good structural properties was obtained. During postannealing, the homogenization was significantly enhanced by strain-induced diffusion, and it was clearly proved by the uphill diffusion. This result can propose an alternative oxidation method of strained SiGe/Si heterostructures.
Formation of nonradiative defects in molecular beam epitaxial GaNxAs1−x studied by optically detected magnetic resonance
Authors: Thinh N. Q. , Buyanova I. A. , Chen W. M. , Xin H. P. , Tu C. W.
Published: July 2002

The formation of two nonradiative defects (i.e., an AsGa-related complex and an unknown deep-level defect with g=2.03) in GaNxAs1−x epilayers and GaAs/GaNxAs1−x multiple-quantum-well structures, grown by molecular beam epitaxy, is studied by the optically detected magnetic resonance technique. It is shown that contributions by these defects in competing carrier recombination strongly vary with the nitrogen composition. An increase in the growth temperature or postgrowth rapid thermal annealing significantly reduces the influence of the nonradiative defects studied, and is accompanied by a remarkable improvement in the optical properties of the structures.
Spectral narrowing of photoluminescence and improvement of electroluminescent properties in conducting polymers with Si atoms in main chains
Authors: Yoshida Y. , Nishihara Y. , Ootake R. , Fujii A. , Ozaki M. , Yoshino K. , Kim H. K. , Baek N. S. , Choi S. K.
Published: July 2002

Optical properties of conducting polymers with Si atoms in main chains, such as optical absorption, photoluminescence (PL), and electroluminescence (EL), have been studied. The electronic energy structures have been determined by optical and electrochemical measurements. The strong PL with high quantum efficiency has been clarified, and spectral narrowing has been observed by pulse excitation of a nitrogen laser. Intense blue or red EL has also been demonstrated and the emission efficiency has been improved by anode surface modification and annealing.
Three-dimensional calculation of field electron energy distributions from open hydrogen-saturated and capped metallic (5,5) carbon nanotubes
Authors: Mayer A. , Miskovsky N. M. , Cutler P. H.
Published: July 2002

We present three-dimensional simulations of field emission from open and capped (5,5) carbon nanotubes, with consideration of hydrogen saturation of the open structure. The transfer-matrix methodology used for the calculations reproduces appropriate band-structure effects due to the periodic repetition of a basic unit of the nanotubes and the use of Bachelet pseudopotentials. The total-energy distributions of field-emitted electrons contain peaks, which are related to standing waves in the shell of the nanotubes and to resonant states at the apex of the closed structure. These peaks move to lower energies with increasing electric field. The results indicate that field emission is more efficient with the open structure and that hydrogen saturation of the dangling bonds results in a further enhancement of the current.
Experimental verification of the electronic structure of MgB2 using electron energy-loss spectroscopy
Authors: Keast V. J.
Published: July 2002

Recently, it was found that MgB2 is a superconductor with a transition temperature of 39 K. Electronic structure calculations suggest that an incompletely filled σ band in the covalently bonded B layers is critical to the superconductivity. In this work, electron energy-loss spectroscopy was used to verify the electronic structure of MgB2 and qualitative agreement with calculations in the literature was observed.
Evidence of electron-emission-enhanced nucleation of diamonds in microwave plasma-enhanced chemical vapor deposition
Authors: Perng Kuoguang , Liu Kuo-Shung , Lin I-Nan
Published: July 2002

The bias-enhanced nucleation (BEN) of diamonds on a Si substrate, using a SiO2 mask and microwave plasma-enhanced chemical vapor deposition (MPE-CVD), was examined. Experimental results indicate that the electron-emission-enhanced nucleation mechanism proposed herein governs the nucleation of diamonds on the partially patterned SiO2/Si substrate. The variation of nucleation density on the partially patterned SiO2/Si substrate also reveals that the BEN of diamonds in the MPE-CVD process follows the proposed mechanism.
Mechanism of photoluminescence in GaN/Al0.2Ga0.8N superlattices
Authors: Chen C. H. , Chang H. J. , Chen Y. F. , Fann W. S. , Jiang H. X. , Lin J. Y.
Published: July 2002

We present photoluminescence (PL) and time-resolved photoluminescence measurements in GaN/Al0.2Ga0.8N superlattices grown by metalorganic chemical vapor deposition under the optimal GaN-like growth conditions. We found that the carrier confinement of our samples is better than most of the previous reports. The dependence of the PL emission energy and intensity on temperature, in the low temperature regime, is consistent with recombination mechanisms involving localized states attributed to a small degree of interface fluctuations. Picosecond time-resolved photoluminescence spectroscopy has been employed to probe the well-width dependence of the lifetime of these superlattices. We see that the recombination lifetime increases with the decrease of well width. This behavior can be interpreted by the fact that the effect of localization keeping carriers away from nonradiative pathways can be enhanced by a decrease in the well width. This explanation is consistent with the temperature-dependent PL data.
Evidence of spin-polarized tunneling in phase-separated manganites La1/3Sr2/3−xBaxMnO3 (0⩽x⩽0.67)
Authors: Jiang Y. , Yuan S. L. , Hu J. F. , Liu L.
Published: July 2002

Polycrystalline La1/3(Sr,Ba)2/3MnO3 (0⩽x⩽0.67) bulk samples were fabricated by solid-state reaction. Structural analysis by Rietveld refinement shows the phase separation while x exceeds 0.1. This phase separation leads to dramatic changes in transport properties for the samples. For the sample La1/3Ba2/3MnO3, the current–voltage and dynamic conductance characteristics demonstrate a spin-polarized tunneling behavior below ∼150 K. The spin-polarized tunneling induces a large magnetoresistance under low magnetic field.
Enhancement of oxidation rate of a-Si nanoparticles during dehydrogenation
Authors: Das D. , Farjas J. , Roura P. , Viera G. , Bertran E.
Published: July 2002

Oxidation of amorphous silicon (a-Si) nanoparticles grown by plasma-enhanced chemical vapor deposition were investigated. Their hydrogen content has a great influence on the oxidation rate at low temperature. When the mass gain is recorded during a heating ramp in dry air, an oxidation process at low temperature is identified with an onset around 250 °C. This temperature onset is similar to that of hydrogen desorption. It is shown that the oxygen uptake during this process almost equals the number of hydrogen atoms present in the nanoparticles. To explain this correlation, we propose that oxidation at low temperature is triggered by the process of hydrogen desorption.
Thermoelectric figure of merit for parallel transport in superlattices
Authors: Antonyuk V. B. , Mal’shukov A. G. , Ma Zhongshui , Chao K. A.
Published: July 2002

We have calculated the thermoelectric figure of merit of a superlattice with the temperature gradient and the electric field applied parallel to the interfaces. Including the heat flow between the barriers and the wells, we have derived the temperature distribution in the sample, from which the expressions of the resultant thermal conductivity and hence the figure of merit are obtained. Our numerical result provides relevant information for achieving a high figure of merit.
Enhanced transmission through photonic-crystal-based bent waveguides by bend engineering
Authors: Moosburger Jürgen , Kamp Martin , Forchel Alfred , Olivier Ségolène , Benisty Henri , Weisbuch Claude , Oesterle Ursula
Published: July 2002

We have studied the transmission of light through two-dimensional photonic-crystal-based waveguides with two 60° bends. The waveguides consist of three or five missing rows of holes inside a triangular photonic crystal block fabricated on an AlGaAs/GaAs waveguide structure. Fine tuning of the bend design results in a severe impact on the transmission behavior, leading to losses as low as 1.1 dB/bend. Measurements of losses in the bends were performed by a comparison with a straight guide of identical length.
Analysis of gain saturation in In0.02Ga0.98N/In0.16Ga0.84N multiple quantum wells
Authors: Kyhm K. , Taylor R. A. , Ryan J. F. , Someya T. , Arakawa Y.
Published: July 2002

A way of analyzing the data in a variable stripe length method gain experiment is presented. We confirm that the stripe length dependence of the gain in In0.02Ga0.98N/In0.16Ga0.84N multiple quantum wells is caused by the change of the chemical potential along the excited stripe due to the interaction of the carrier and photon densities, and the gain threshold density is estimated. A trial function assuming a Lorentzian line shape for the stripe length dependence of the gain is compared with the edge emission intensity as a function of the stripe length. This is found to fit very well with our data, even beyond the saturation region.
Evolution of end-of-range damage and transient enhanced diffusion of indium in silicon
Authors: Noda T.
Published: July 2002

Correlation of evolution of end-of-range (EOR) damage and transient enhanced diffusion (TED) of indium has been studied by secondary ion mass spectrometry and transmission electron microscopy. A physically based model of diffusion and defect growth is applied to the indium diffusion system. Indium implantation with 200 keV, 1×1014/cm2 through a 10 nm screen oxide into 〈100〉 p-type Czochralski silicon wafer was performed. During postimplantation anneal at 750 °C for times ranging from 2 to 120 min, formation of dislocation loops and indium segregation into loops were observed. Simulation results of evolution of EOR defects show that there is a period that {311} defects dissolve and release free interstitials before the Ostwald ripening step of EOR dislocation loops. Our diffusion model that contains the interaction between indium and loops shows the indium pileup to the loops. Indium segregation to loops occurs at a pure growth step of loops and continues during the Ostwald ripening step. Although dislocation loops and indium segregation in the near-surface region are easily dissolved by high temperature annealing, EOR dislocation loops in the bulk region are rigid and well grown. It is considered that indium trapped by loops with a large radius is energetically stable. It is shown that modeling of the evolution of EOR defects is important for understanding indium TED.
Detection wavelength of InGaAs/AlGaAs quantum wells and superlattices
Authors: Choi K. K. , Bandara S. V. , Gunapala S. D. , Liu W. K. , Fastenau J. M.
Published: July 2002

InGaAs/AlGaAs quantum well structures have been shown to be versatile for infrared detection. By changing the material composition, one can tune the detection wavelength from 2 to 35 μm and beyond. However, there have been few systematic calculations on the absorption wavelength of these structures with respect to their structural parameters. In this work we have adopted the transfer-matrix method to calculate both their energy levels and the wave functions. From this calculation, the absorption and the responsivity spectra of the structures can be predicted. The theory agrees with the experimental result of the test structures. Supported by the experimental evidence, we applied the calculation to a general class of midwavelength detectors and thus established a useful guideline for the detector design in this wavelength range.
Enhancement of parametric pumping due to Andreev reflection
Authors: Wang Jian , Wei Yadong , Wang Baigeng , Guo Hong
Published: July 2002

We report properties of parametric electron pumping in the presence of a superconducting lead. Due to a constructive interference between the direct reflection and the multiple Andreev reflection, the pumped current is greatly enhanced. For both quantum point contacts and double barrier structures at resonance, we obtain exact solutions in the weak pumping regime showing that IpNS=4IpN, which should be compared with the result of conductance GNS=2GN. Numerical results are also provided for the strong pumping regime showing interesting Andreev assisted pumping behavior.
Effects of visible light illumination during plasma enhanced chemical vapor deposition growth on the film properties of hydrogenated amorphous silicon
Authors: Sakata I. , Yamanaka M.
Published: July 2002

Experimental studies have revealed that defect related properties in hydrogenated amorphous silicon (a-Si:H) can be modified by visible-light illumination during plasma enhanced chemical vapor deposition growth; light-induced degradation after growth and initial defect density has been reduced in the samples prepared under illumination with and without a shield mesh separating the plasma region and a substrate in the deposition chamber, respectively. These properties are metastable below the deposition temperature and are a result of the counterbalance between illumination and the thermal effects during growth. The reduction of the light-induced changes in the present samples does not relate to changes in hydrogen bonding. The defect annihilation reaction during growth has been enhanced and the reaction barrier has been lowered from 0.57 to 0.34 eV under illumination. It has also been found that the defect density depends exponentially on the intensity of incident visible light.
1.5 kW high-peak-power vacuum ultraviolet flash lamp using a pulsed silent discharge of krypton gas
Authors: Kawanaka J. , Shirai T. , Kubodera S. , Sasaki W.
Published: July 2002

A 1.5 kW high-peak-power discharge lamp with short emission duration of 140 ns has been developed in the vacuum ultraviolet spectral region. Our numerical calculation ensured that the peak emission at 147 nm was due to singlet excimers (1Σ), which were mainly produced via electron-collisional mixing of triplet excimers (3Σ).
Reconstruction defects on partial dislocations in semiconductors
Authors: Justo João F. , Assali Lucy V. C.
Published: July 2002

Using ab initio total energy calculations, we investigated the structural and electronic properties of reconstruction defects, or antiphase defects, in the core of a 30° partial dislocation in silicon and gallium arsenide. In GaAs, we identified two different reconstruction defects in the dislocation cores, corresponding to a Ga undercoordinated atom, and an As undercoordinated atom. Formation energies of these reconstruction defects were compared to experimental results on the concentration of electrically active centers in deformed semiconducting materials.
Effective boundary conditions for magnetohydrodynamic flows with thin Hartmann layers
Authors: Pothérat A. , Sommeria J. , Moreau R.
Published: July 2002

Here we build some effective boundary conditions to be used in numerical calculations in order to avoid the thin meshing usually required in problems involving Hartmann layers near a locally plane wall. Wall models are provided for both tangential and normal electric current density and velocity. In particular, a condition on the normal derivative of the tangential velocity is derived. A wide variety of problems is covered as the only restriction is that the magnetic Reynolds number has to be small at the scale of the Hartmann layer. The cases of perfectly conducting or insulating wall are examined, as well as the case of a thin conducting wall. The newest result is a condition on the normal velocity accounting for inertial effects in the Hartmann layer.
Insulator thickness dependence of tunnel magnetoresistance effect in a model of Co/Al-oxide/Co junctions
Authors: Kokado Satoshi , Ichimura Masahiko , Onogi Toshiyuki , Sakuma Akimasa , Arai Reiko , Hayakawa Jun , Ito Kenchi , Suzuki Yoshio
Published: July 2002

The tunnel magnetoresistance (TMR) effect in Co/Al-oxide/Co junctions was studied on a model exhibiting positive spin polarization, in which an Al monolayer is regarded as the terminating layer of the ferromagnetic electrode, and the s electron of Al behaves as the tunnel electron. In this model, the TMR ratio decreases when an insulator becomes ultrathin. It was shown that the decrease originates from an increase in the self-energy corrections due to the electrodes with parallel magnetization configuration.
Lateral composition modulation in short period superlattices: The role of growth mode
Authors: Dorin C. , Mirecki Millunchick J. , Chen Y. , Orr B. G. , Pearson C. A.
Published: July 2002

The role of the growth mode on lateral composition modulation is studied in short period superlattices of AlAs/InAs and GaAs/InAs. Reflection high energy electron diffraction and scanning tunneling microscopy are used to monitor the growth mode and the quality of the interfaces. Cross-sectional transmission electron microscopy indicates that samples that grow via the layer-by-layer growth mode do not exhibit lateral composition modulation and the superlattice structure is well defined. Lateral composition modulation forms when roughening occurs during growth. However, too much roughening, i.e., three-dimensional island nucleation destroys the regularity of the composition modulation in both the lateral and vertical directions. These results are in general agreement with theoretical predictions.
Simultaneous determination of Poisson ratio, bulk lattice constant, and composition of ternary compounds: In0.3Ga0.7As, In0.3Al0.7As, In0.7Ga0.3P, and In0.7Al0.3P
Authors: Hoke W. E. , Kennedy T. D. , Torabi A.
Published: July 2002

A technique using the common (004) x-ray diffraction spectrum is demonstrated for the simultaneous determination of Poisson ratio, bulk lattice constant, and alloy composition for ternary compounds with lattice constants near the midpoint between GaAs and InP. Thin, strained layers of InGaAs, InAlAs, InGaP, and InAlP were grown. By careful choice of ternary composition and thickness, the same composition was grown on both GaAs and InP substrates without measurable relaxation in the (004) x-ray spectrum. The diffraction equation was simultaneously solved for the Poisson ratio and bulk lattice constant of the ternary compound. Subsequently the ternary composition was determined by applying Vegard’s law. The resulting Poisson ratios agreed well with the compositional averages of the binary endpoints. By extrapolating the results for InAlAs, a Poisson ratio of 0.33 was determined for AlAs.
Epitaxial SnO2 thin films grown on (1̄012) sapphire by femtosecond pulsed laser deposition
Authors: Dominguez J. E. , Pan X. Q. , Fu L. , Van Rompay P. A. , Zhang Z. , Nees J. A. , Pronko P. P.
Published: July 2002

An ultrafast (100 fs) Ti sapphire laser (780 nm) was used for the deposition of SnO2 thin films. The laser-induced plasma generated from the SnO2 target was characterized by optical emission spectroscopy and electrostatic energy analysis. It was found that the ionic versus excited-neutral component ratio in the plasma plume depends strongly on the amount of background oxygen introduced to the deposition chamber. Epitaxial SnO2 films with high quality and a very smooth surface were deposited on the (1̄012) sapphire substrate fabricated at 700 °C with an oxygen background pressure of ∼0.1 mTorr. The films are single crystalline with the rutile structure, resulting from the high similarity in oxygen octahedral configurations between the sapphire (1̄012) surface and the SnO2 (101) surface. Hall effect measurements showed that the electron mobility of the SnO2 film is lower than that of bulk single crystal SnO2, which is caused by the scattering of conduction electrons at the film surface, substrate/film interface, and crystal defects.
Comparison between ZnO films grown by femtosecond and nanosecond laser ablation
Authors: Perrière J. , Millon E. , Seiler W. , Boulmer-Leborgne C. , Craciun V. , Albert O. , Loulergue J. C. , Etchepare J.
Published: July 2002

We have studied the structural properties of ZnO thin films grown on Al2O3 (00.1) single-crystal substrates by pulsed-laser deposition using either a femtosecond or a nanosecond laser. Although hexagonal ZnO films deposited on sapphire substrate were epitaxially grown in both cases, the crystalline quality was found to be very different: ZnO films grown with the femtosecond laser are characterized by a higher mosaicity, a smaller crystallite size, a larger content of defects but also smaller residual stresses than ZnO films obtained by nanosecond laser ablation. These differences can be explained according to the kinetic energy of the species evolved during laser ablation as deduced from plasma characterization with a charged-coupled device camera: close to 1 KeV in the femtosecond regime for the population species emitted from the target with the highest velocity, versus a few hundreds of eV in the case of nanosecond pulses. The high energy species irradiation associated with a femtosecond laser is likely to induce a large structural disorder together with stress relaxation during ZnO films growth.
Energy level alignment driven by electron affinity difference at 3,4,9,10-perylenetetracarboxylic dianhydride/n-GaAs(100) interfaces
Authors: Park Sunggook , Kampen Thorsten U. , Zahn Dietrich R. T. , Braun Walter
Published: July 2002

Ultraviolet photoemission spectroscopy (UPS) was employed to investigate the electronic structure upon deposition of 3,4,9,10-perylenetetracarboxylic dianhydride (PTCDA) on differently treated n-GaAs(100) surfaces. Interface dipoles are found to form according to the electron affinities (EA) of the substrates and PTCDA films at the interfaces and, consequently, the vacuum level alignment rule does not hold. The results demonstrate that the energy offset between the conduction band minimum of n-doped inorganic semiconductors and the lowest unoccupied molecular orbital of organic molecular films at the interfaces can be obtained using UPS by systematically varying the EA of substrates with a known band gap.
In situ sensor for interstitial trapping during Si thermal oxidation using He implantation-induced voids
Authors: Raineri Vito , Giuffrida Stella , Rimini Emanuele
Published: July 2002

The shrinkage of voids created by He implants in silicon has been measured during thermal oxidation. The empty volume is filled by self-interstitials injected during oxidation. The increase in volume is proportional to the oxide thickness and follows the same time dependence. The captured interstitial surface density ranges between 1015 and 1016 cm−2. The amount of captured interstitials for a given oxide thickness is temperature independent above 1050 °C, but below that it decreases, indicating the presence of competing defect centers for the capture of interstitials. The method demonstrates the possibility to use void layers as in situ sensors for interstitials.
Preparation of antiferroelectric PbZrxTi1−xO3 thin films on LaSrMnO3-coated steel substrates
Authors: Seveno R. , Gundel H. W. , Seifert S.
Published: July 2002

Antiferroelectric lead zirconate titanate (PZT) thin films have been prepared by chemical solution deposition using oxide powders. The films were processed onto steel substrates coated with a conducting oxide layer of LaSrMnO3. Homogeneous and uniform films up to 3.4 μm thick and with polarization saturation values up to 35 μC/cm2 have been obtained. The compositional transition from the ferroelectric to the antiferroelectric phase at the high zirconium side of the PZT phase diagram was studied by x-ray diffraction and hysteresis loop measurements as a function of the Zr/Ti ratio. Film thickness and annealing temperature dependencies are reported.
Thermoelectric power of nitrogen-incorporated tetrahedral amorphous-carbon films
Authors: Bhattacharyya Somnath , Richter F. , Starke U. , Griessmann H. , Heinrich A.
Published: July 2002

Tetrahedral amorphous-carbon (ta-C) films were deposited using a filtered cathodic vacuum arc in which nitrogen was incorporated up to an atomic fraction (fN) of 30%. Electrical conductivity and specially thermoelectric power (S) have been performed over a wide range of temperature. The room-temperature conductivity of these samples initially increases with fN up to several orders of magnitude compared to that of ta-C, followed by no dramatic change at higher nitrogen concentration. The sign of the S is negative in the samples with fN below ∼17%, then changes to a positive value with a higher fN. From thermal annealing of the nitrogenated samples a change of the sign of S and its dependence on fN has been analyzed. The small values of both room-temperature S and small variation of conductivity at high fN in all the samples suggest that electrical properties of these films are controlled by compensation of defects.
Ductility of ultrafine grained copper
Authors: Kim Hyoung Seop , Estrin Yuri
Published: July 2002

In this letter, we address the effect of grain refinement on room-temperature ductility of copper. Recent experimental results have shown that this material, as well as a number of other single-phase metals that are ductile when coarse grained, lose their ductility with decreasing grain size in the submicrometer range. A recently developed model in which such materials are considered as effectively two-phase ones (with the grain boundaries treated as a linearly viscous second phase) was applied to analyze the stability of Cu against ductile necking. As a basis, Hart’s stability analysis that accounts for strain-rate-sensitivity effects was used [E. W. Hart, Acta Metall. 15, 351 (1967)]. The results confirm the observed trend for reduction of room-temperature ductility with decreasing grain size. The model can be applied to predicting the grain-size dependence of ductility of other metallic materials as well.