bluuebunny/crossref_metadata_2025 huggingface dataset:
Self-mediated growth of single-crystal and entirely (111)-oriented C60 films on alkali halide substrates
Authors: Dai Z. , Naramoto H. , Narumi K. , Yamamoto S. , Miyashita A.
Published: July 2002

We have studied C60 film growth on alkali halide substrates, KCl (200), KBr (200), and NaCl (200), by using two or three C60 monolayers, which grow at a very low deposition rate, as a self-mediating layer. Continuously and entirely (111)-oriented epitaxial C60 films have been grown in a quite wide temperature range, 40–120 °C, and at very different deposition rates, from 1.5 to 35 Å/min. More over, single-crystal and entirely (111)-oriented C60 films with a grain size of 1–3 μm could be also grown at relative high temperature and low deposition rate, approximately 120 °C and 1.5 Å/min, respectively.
First-principles study of β-AlN thin films on β-SiC(001)
Authors: Di Felice R. , Bertoni C. M. , Catellani A.
Published: July 2002

We have investigated the initial stages of formation of cubic AlN films on SiC(001) by studying the energetics of possible structures. We have considered 1×1 and p(4×1) surface reconstructions for the films, and we have allowed for different interface arrangements including atomic mixing. The results of our first-principles calculations reveal that, in N-rich conditions, no two-dimensional film structure is stable. However, in Al-rich conditions, it is possible to stabilize a thick wetting layer of cubic AlN provided the proper interface mixing is achieved. The most stable AlN film exhibits a p(4×1) surface reconstruction.
Reduced thermal conductivity in low-temperature-grown GaAs
Authors: Jackson A. W. , Ibbetson J. P. , Gossard A. C. , Mishra U. K.
Published: July 2002

Thermal conductivity of low-temperature-grown GaAs(LT GaAs) was measured at room temperature using a self-heated photolithographically patterned platinum wire on the surface of the sample. Finite element calculations were performed to extract the thermal conductivity from the nonlinear I–V characteristic of the wires. For LT GaAs grown at a substrate temperature of 240 °C, the thermal conductivity was found to be only 23% of the value for stoichiometric GaAs. Rapid thermal annealing of the sample at 650 °C for 30 s increased the thermal conductivity to 46% of the GaAs value. Strong phonon scattering by point defects could account for reduced thermal conductivity in the as-grown material. The reduced thermal conductivity in the annealed material, however, is not consistent with our current understanding of the defects in annealed LT GaAs.
The ferroelectric properties of c-axis oriented Pb5Ge3O11 thin films prepared by metalorganic chemical vapor deposition
Authors: Li Tingkai , Zhang Fengyan , Hsu Sheng Teng
Published: July 2002

C-axis oriented ferroelectric Pb5Ge3O11 thin films were prepared on Pt/Ir-coated Si wafers by metalorganic chemical vapor deposition (MOCVD) and rapid thermal process annealing techniques. The films were specular and crack free and showed complete crystallization with c-axis orientation for growth temperatures between 500 and 550 °C. Good ferroelectric properties were obtained for a 150-nm-thick film with Pt/Ir electrodes: the remanent polarization (2Pr) and coercive field (2Ec) values were about 3.8 μC/cm2 and 93 kV/cm, respectively. The films also showed excellent fatigue characteristics: no fatigue was observed up to 1×109 switching cycles. The leakage current increased with increasing applied voltage, and is about 3.6×10−7 A/cm2 at 100 kV/cm. The dielectric constant showed behavior similar to most ferroelectric materials in that the dielectric constant changed with applied voltages. The maximum dielectric constant is about 45. High-quality MOCVD Pb5Ge3O11 films can be used for single transistor ferroelectric memory devices.
Acoustic driving effect on radiative decays of excitons in ZnSe/ZnS single quantum wells
Authors: Korotchenkov O. A. , Yamamoto A. , Goto T. , Cho M.-W. , Yao T.
Published: July 2002

We report that acoustic driving of ZnSe/ZnS quantum wells can yield ⩾30% shortening of the fast component (on the order of 102 ps) of exciton radiative decays and relatively enhanced tail emissions at greater instants. The shortening is attributed to the driving-induced relocalization of excitons to lower-energy states while the enhancement is indicative of the drift diffusion of mobile populations in the driving electric field. These results suggest that the radiative recombination predominantly occurs from localized excitons.
Revival of interband crystalline reflectance from nanocrystallites in porous silicon by immersion plating
Authors: Yamani Zain , Alaql A. , Therrien Joel , Nayfeh Osama , Nayfeh Munir
Published: July 2002

We prepared porous silicon for which the UV reflectance (3.3–6 eV) is nearly eliminated, and exhibits no features at the Si interband bulk transitions 3.3, 4.3, and 5.5 eV. Plating with a thin layer of copper is found to cause recovery of the UV bulk-like crystalline reflectance and interband resonances. This provides evidence that the loss of crystalline absorption is reversible and is not due to a permanent loss in the crystalline structure. This may relate to a recent model in which the optical activity of ultra small nanocrystallites is produced by a new Si–Si crystalline configuration (or phase), distinct from but interconnected to the diamond-like configuration by a potential barrier.
Photoluminescence study of ZnS/ZnMgS single quantum wells
Authors: Ichino K. , Ueyama K. , Kariya H. , Suzuki N. , Kitagawa M. , Kobayashi H.
Published: July 2002

We report a photoluminescence (PL) study of ZnS/ZnMgS strained-layer single quantum wells. The main PL peak from ZnS is attributed to light-hole free excitons. Quantum confinement causes it to shift from 3.76 eV to higher energy, 3.84 eV, with decreasing well width. Hydrostatic and shear deformation potentials are determined from energies of light- and heavy-hole exciton emission, to be a=−6.4 eV and b=−1.0 eV, respectively.
Strong linear polarization in scanning tunneling microscopy-induced luminescence from porous silicon
Authors: Wu Zhanghua , Nakayama Tomonobu , Qiao Shan , Aono Masakazu
Published: July 2002

Visible luminescence with strong linear polarization (up to 80%) from porous silicon induced with scanning tunneling microscopy is reported. The external quantum efficiency is found to be close to that of the semiconductors with direct band gaps such as GaAs and CdS. These observations agree with the theoretical predictions of direct band gap and strong optical anisotropy for quantum Si wires. The observation of a strong linear polarization indicates that the delocalized states, which extend throughout the entire Si clusters and undergo quantum confinement, play an important role in the luminescence.
Initial stages of III-nitride growth
Authors: Großner Ulrike , Furthmüller Jürgen , Bechstedt Friedhelm
Published: July 2002

First-principles calculations are performed to investigate the adsorption behavior of group-III atoms and nitrogen on group-III-nitride(111) surfaces. We focus on one to three layers of cations on BN, AlN, GaN, and InN and compare their surface energies with that of the nitrogen-covered and clean surface. The resulting surface phase diagrams indicate a preference for epitaxial growth under cation-rich conditions after deposition of metal overlayers. This tendency, clearly pronounced for InN and GaN, is weakened for AlN and BN where lower III/V ratios are favorable.
Real-time monitoring of the Si carbonization process by a combined method of reflection high-energy electron diffraction and Auger electron spectroscopy
Authors: Kosugi Ryoji , Takakuwa Yuji , Kim Ki-Seon , Abukawa Tadashi , Kono Shozo
Published: July 2002

The carbonization process of a preferential-domain Si(001)2×1 surface with ethylene was investigated by a combined method of reflection high-energy electron diffraction and Auger electron spectroscopy. It is found that the carbonization process during the so-called incubation time is the Si1−xCx alloy formation before the nucleation of 3C–SiC grains. A reaction model for the Si1−xCx alloy formation and for the 3C–SiC grain growth is proposed for substrate temperatures of 600–750 °C. From the model, we postulate that the external supply of Si and C should be started just at the completion of the lateral 3C–SiC grain growth at temperatures of 600–650 °C in order to obtain thick 3C–SiC layers with a flat surface morphology.
Pulsed laser deposition of epitaxial GaNxAs1−x on GaAs
Authors: Hung W. K. , Chern M. Y. , Fan J. C. , Lin T. Y. , Chen Y. F.
Published: July 2002

Epitaxial layers of GaNxAs1−x were grown on (001) GaAs substrates by pulsed laser ablation of a GaAs target in an ammonia (NH3) atmosphere. High-resolution x-ray diffraction indicates the existence of a threshold NH3 pressure, above which the incorporated N content x increases linearly with increasing NH3 pressure. The band-gap dependence of GaNxAs1−x on x for x⩽2.9% is examined by optical absorption and photoconductivity measurements at room temperature. We found that the band-gap energy reduces with higher N composition, and our results agree approximately with the prediction based on the dielectric model.
Extremely underdamped Josephson junctions for low noise applications
Authors: Ruggiero B. , Granata C. , Esposito E. , Russo M. , Silvestrini P.
Published: July 2002

We present a design of extremely underdamped Josephson junctions either for use in experiments in the quantum limit or for devices using the switching dynamics of the junction, when a low noise level is mandatory. High resistance molybdenum meander lines integrated with the junction allow one to increase the insulation of the sample from its electromagnetic environment. We report an experimental study of the effective dissipation relevant in the thermally activated supercurrent decay presenting evidence of a substantial reduction of the dissipation level at low temperature.
GaAs/AlGaAs multiple-quantum-well in-line fiber intensity modulator
Authors: Mao Erji , Coldren Christopher W. , Harris James S. , Yankelevich Diego R. , Solgaard Olav , Knoesen André
Published: July 2002

We demonstrate a GaAs/AlGaAs multiple-quantum-well in-line fiber optic intensity modulator. Based on evanescent wave coupling between a GaAs/AlGaAs multiple-quantum-well waveguide and a single-mode fiber, this device concept combines the inherent advantages of in-line fiber devices with high-speed GaAs integrated optoelectronics. The GaAs waveguide uses distributed Bragg mirror layers to phase match to the low-index fiber. Intensity modulation of the transmitted light through the fiber is achieved by tuning the effective propagation index of the GaAs waveguide via the quantum-confined Stark effect. Initial structures show a modulation contrast (ΔT/T) of more than 53%, with an applied voltage of 5 V.
Unusual electrical behavior of Nd-doped diamond films
Authors: Terranova M. L. , Sessa V. , Piccirillo S. , Rossi M. , Micocci G. , Serra A. , Tepore A.
Published: July 2002

The semiconducting behavior of Nd-containing diamond layers, obtained from the gas phase by using a synthesis methodology, has been investigated in the range 100–500 K by performing Hall-effect and conductivity measurements. The diamond-based polycrystalline layers are characterized at the same time by relatively low values of hole density and by rather high values of conductivity, whereas the hole Hall-mobility values remain those typical of diamond single crystal. The results obtained in the range 100–500 K from the analysis of a representative sample are as follows: 2.4×1017–2.8×1018 cm−3 for hole density, 2.0×102–2.8×102 Ω−1 cm−1 for conductivity, and 6.5×102–6.4×103 cm2 V−1 s−1 for Hall mobility. Structural investigations performed by reflection high-energy electron diffraction confirmed that the incorporation of Nd doping atoms did not modify the diamond lattice parameters and did not lower the crystalline quality of the diamond film.
Control of Coulomb blockade characteristics with dot size and density in planar metallic multiple tunnel junctions
Authors: Ford E. M. , Ahmed H.
Published: July 2002

Coulomb gap width has been controlled in a planar metallic structure made by focused ion-beam deposition with landing energies in the range 10 eV–1 keV. Gold islands form by surface diffusion, with size and density determined by dose and landing energy. Increasing the dose reduces the Coulomb gap systematically as larger islands form and density is reduced. Lower ion landing energy increases the operating temperature despite an apparent increase in island size. Multiple tunnel junctions of lengths 10–200 nm have been fabricated and Coulomb blockade observed up to 200 K, with strong nonlinearities evident at room temperature. Single-electron transport through a single island has also been observed, exhibiting a periodic Coulomb staircase.
The dual wavelength Bi-vertical cavity surface-emitting laser
Authors: Carlin J. F. , Stanley R. P. , Pellandini P. , Oesterle U. , Ilegems M.
Published: July 2002

We present a monolithically integrated vertical coupled cavity surface-emitting laser diode which exhibits stable laser emission at two design wavelengths simultaneously. The device consists of two slightly asymmetric coupled vertical cavities containing strained InGaAs quantum wells as the gain media. The shorter cavity is pumped electrically. Lasing starts on the short wavelength mode at 927 nm. The laser emission then acts as an optical pump for the quantum wells in the longer cavity and provides additional gain for the long wavelength mode, resulting in a subsequent laser emission at 955 nm. With increasing injection current, the device maintains stable emission at the two wavelengths. The threshold for dual lasing is 4 kA/cm2 and dual lasing is stable over six times the threshold.
Activation volume for antimony diffusion in silicon and implications for strained films
Authors: Zhao Yuechao , Aziz Michael J. , Gossmann Hans-J. , Mitha Salman , Schiferl David
Published: July 2002

The diffusivity of Sb in Si is retarded by pressure, characterized at 860 °C by an activation volume of V*=+0.07±0.02 times the Si atomic volume. V* is close to values inferred from atomistic calculations for a vacancy mechanism. Our results for hydrostatic pressure are used to predict the effect of biaxial strain on Sb diffusion. The prediction matches measured behavior for Sb diffusion in biaxially strained Si and Si–Ge films. This work lends additional support to the predominance of the vacancy mechanism for Sb diffusion and demonstrates the first steps in the development of a capability for predicting the effect of nonhydrostatic stress on diffusion.
From visible to white light emission by GaN quantum dots on Si(111) substrate
Authors: Damilano B. , Grandjean N. , Semond F. , Massies J. , Leroux M.
Published: July 2002

GaN quantum dots (QDs) in an AlN matrix have been grown on Si(111) by molecular-beam epitaxy. The growth of GaN deposited at 800 °C on AlN has been investigated in situ by reflection high-energy electron diffraction. It is found that a growth interruption performed at GaN thicknesses larger than three molecular monolayers (8 Å) instantaneously leads to the formation of three-dimensional islands. This is used to grow GaN/AlN QDs on Si(111). Depending on their sizes, intense room-temperature photoluminescence is observed from blue to orange. Finally, we demonstrate that stacking of QD planes with properly chosen dot sizes gives rise to white light emission.
Polarity sensitive bistable color effect in cholesteric liquid crystals with an asymmetric polymer network
Authors: Sikharulidze D. , Tchanishvili A. , Petriashvili G. , Scaramuzza N. , Barberi R. , Bartolino R.
Published: July 2002

A polarity sensitive bistable color effect has been observed in cholesteric liquid crystal—polymer mixtures where a gradient of the polymer network density is created by strongly absorbed UV light. The switching between two stable states is driven by electric pulses of the same amplitude and duration but with opposite electric polarity. The effect could be of great interest for practical applications in color display technology.
Thin gate oxide behavior during plasma patterning of silicon gates
Authors: Vallier L. , Desvoivres L. , Bonvalot M. , Joubert O.
Published: July 2002

We have evidenced an unexpected behavior of thin gate oxide layers (thickness in the range 2–4 nm) exposed to plasma processes developed for the patterning of 0.1 μm silicon gates. During the low-energy overetch step of the process, an oxidation of the bulk underlying silicon takes place, leading to the growth of the gate oxide layer. Experimental results obtained from in situ kinetic and spectroscopic ellipsometry measurements and supported by x-ray photoelectron spectroscopy analyses are presented to highlight this phenomenon.
Ordering-induced band structure effects in GaInP2 studied by ballistic electron emission microscopy
Authors: Kozhevnikov M. , Narayanamurti V. , Mascarenhas A. , Zhang Y. , Olson J. M. , Smith D. L.
Published: July 2002

We have analyzed the second voltage derivative (SD) of the ballistic electron emission microscopy (BEEM) spectra of GaInP2. We associate two peaks observed in the SD-BEEM spectra of disordered GaInP2 on n+ GaAs substrate with the Γ and L conduction minima, Δ(Γ−L)∼0.35 eV. An additional third peak appearing in the SD-BEEM spectrum of ordered GaInP2 (η∼0.5) is associated with the L-band splitting due to the ordering-induced “folding” of one of the four L valleys onto the Γ̄ point. According to our results, this splitting is ∼ 0.13 eV.
Displacement measurement and surface profiling using semi-insulating photoconductive semiconductors and linearly frequency-ramped lasers
Authors: Jin Feng , Khurgin Jacob B. , Trivedi Suhdir , Wang Chen-Chia , Gad Esam
Published: July 2002

Target displacement measurement and surface profiling are demonstrated experimentally using coherence frequency domain reflectometry and the photo-emf optical difference frequency sensor that was recently shown to generate steady state dc photocurrents linearly proportional to the optical frequency differences between two laser beams interfering inside semi-insulating photoconductive semiconductors. The simplicity and spatial adaptivity of photo-emf optical frequency sensors eliminate the stringent requirements of optical alignment and calculation-intensive signal processing found in conventional coherence frequency domain reflectometry systems.
1.55 μm single mode lasers with complex coupled distributed feedback gratings fabricated by focused ion beam implantation
Authors: König H. , Rennon S. , Reithmaier J. P. , Forchel A. , Gentner J. L. , Goldstein L.
Published: July 2002

Complex coupled GaInAsP/InP distributed feedback lasers were developed based on maskless focused ion beam lithography. By combining implantation enhanced wet chemical etching and implantation induced thermal quantum well intermixing a refractive index grating was defined self-aligned to a gain grating forming a complex coupled grating lateral to a ridge waveguide. The devices show single mode emission at wavelengths around 1.55 μm with linewidths <2 MHz and side mode suppression ratios of more than 40 dB for continuous wave operation at room temperature. A high single mode yield (>90%) over a large tuning range (88 nm) was achieved.
Subwavelength resolution in a transmission acoustic microscope configuration using fiber-tip sensors
Authors: Koch Christian
Published: July 2002

Subwavelength resolution in a transmission acoustic microscope configuration is demonstrated using optical fiber-tip sensors as small-sized acoustic probes. A slit with a width of 1/20 of the acoustic wavelength Λ representing the object was detected with a lateral resolution of the outer fiber diameter which was ≈1/10 Λ, and with a proper signal-to-noise ratio. Fiber preparation techniques may raise the resolution to the fiber core dimensions, and simultaneous detection of an acoustic and an optical image is proposed.
Electrical isolation of a silicon δ-doped layer in GaAs by ion irradiation
Authors: Danilov I. , de Souza J. P. , Boudinov H. , Murel A. V. , Daniltsev V. M. , Shashkin V. I.
Published: July 2002

The electrical isolation of a n-type δ-doped layer embedded into undoped GaAs was studied using proton or helium ion bombardment. The threshold dose for isolation Dth of the δ-doped layer was found to be ≈2 times higher than that predicted for thick doped layers of similar carrier concentration. The thermal stability of the isolation, i.e., the persistence of sheet resistance Rs at values >109Ω/□ after subsequent thermal annealing, is limited to temperatures below 400 °C. This temperature limit for the thermal stability Tsm is markedly lower than those observed in wider doped layers in which Tsm is ≅650 °C. A previously isolated δ-doped layer presents p-type conductivity after annealing at temperatures >600 °C .
Integration of amorphous and polycrystalline silicon thin-film transistors through selective crystallization of amorphous silicon
Authors: Pangal K. , Sturm J. C. , Wagner S.
Published: July 2002

Selective exposure of a hydrogenated amorphous silicon (a-Si:H) film to a room-temperature hydrogen plasma using a patterned masking layer and a subsequent anneal at 600 °C, results in patterned polycrystalline and amorphous silicon regions. However, most of the hydrogen in the amorphous silicon is lost, leading to severe degradation in its properties. In this letter, we report the rehydrogenation of amorphous silicon films following this anneal to give a-Si:H thin-film transistors with a mobility as high as 1.2 cm2/V s and ON/OFF current ratios of ∼106. This process was used to integrate amorphous and polycrystalline silicon transistors on a single substrate with only one more lithography and processing step than that required for a single type of transistor.
Hole trapping due to anode hole injection in thin tunnel gate oxides in memory devices under Fowler–Nordheim stress
Authors: Samanta Piyas
Published: July 2002

Hole trapping characteristics in thin (10 nm) thermally grown silicon dioxide (SiO2) in flash memory device with n-type floating polycrystalline silicon (poly-Si) gate have been theoretically investigated under Fowler–Nordheim (FN) constant current and voltage stress. Theoretical results of gate voltage shift ΔVG or ΔVFN due to trapped holes show good agreement with experimental data of Park and Schroder [IEEE Trans. Electron Devices ED-45, 1361 (1998)] during constant current injection. Our theoretical analysis based on hole injection from the poly-Si gate (anode) at injected electron fluence Qinj as low as 0.01 C/cm2 address that constant voltage stress degrades the gate oxide quality faster than constant current stress due to enhanced charge trapping and trap creation rate under constant voltage stress.
Quantum well heterostructures grown by molecular beam epitaxy on silicon-on-gallium arsenide substrates
Authors: London Joanna M. , Postigo Pablo A. , Fonstad Clifton G.
Published: July 2002

Silicon-on-gallium arsenide (SonG) wafers have recently been proposed as optimal substrates for monolithic integration of GaAs-based optoelectronic devices with silicon electronics. In this letter it is demonstrated that high quality quantum well heterostructures can be grown on SonG substrates under conditions consistent with the survival of pre-existing electronics. Photoluminescence and cathodoluminescence measurements confirm that these layers are sufficiently high quality to allow integration of light emitting and laser diodes on SonG substrates.
Near-field scanning optical microscopy as a simultaneous probe of fields and band structure of photonic crystals: A computational study
Authors: Fan Shanhui , Appelbaum Ian , Joannopoulos J. D.
Published: July 2002

We demonstrate the feasibility of employing near-field scanning optical microscopy (NSOM) imaging to simultaneously obtain both the eigenfield distribution and the band-structure information of a photonic crystal. We introduce the NSOM measurement configuration required and simulate the imaging process, with both the tip and the sample included, using three-dimensional finite-difference time-domain calculations. Both the field-pattern and the frequency–wave-vector relations of photonic crystal eigenmodes are revealed by analyzing simulated images.
Low-field magnetic resonance imaging with a high-Tc dc superconducting quantum interference device
Authors: Schlenga K. , McDermott R. , Clarke John , de Souza R. E. , Wong-Foy A. , Pines A.
Published: July 2002

A spectrometer incorporating a high transition temperature dc superconducting quantum interference device (SQUID) is used to obtain nuclear magnetic resonance signals from protons in mineral oil at room temperature in fields up to 3 mT. The spatial separation between the SQUID magnetometer at 77 K and the sample at room temperature is less than 1 mm. At 2 mT, the signal is easily resolved in a single scan. Two-dimensional images of samples consisting of pieces of lucite or glass immersed in mineral oil are obtained at 2 mT.
Quantized conductance of multiwalled carbon nanotubes
Authors: Delaney P. , Di Ventra M. , Pantelides S. T.
Published: July 2002

We report calculations of the transport properties of multiwalled carbon nanotubes based on a scattering-theoretic approach that takes into account scattering within each tube, between tubes, and at the metal contacts. We find that only the outer tube contributes to the conductance, as has been implied by experiments. Referring to experiments performed with liquid-metal contacts, we also explain why the measured conductance is close to an integer number of conductance quanta, when the tubes are immersed in the liquid metal for several hundreds of nanometers and is not an integer when they are immersed for only a few nanometers. Finally, we propose that the observed conductance of only one quantum (instead of the expected two quanta) is due to intertube interactions.
Effects of interfacial oxides on Schottky barrier contacts to n- and p-type GaN
Authors: Cao X. A. , Pearton S. J. , Dang G. , Zhang A. P. , Ren F. , Van Hove J. M.
Published: July 2002

Schottky contacts were formed on n- and p-type GaN after either a conventional surface cleaning step in solvents, HCl and HF or with an additional treatment in (NH4)2S to prevent reformation of the native oxide. Reductions in barrier height were observed with the latter treatment, but there was little change in diode ideality factor. A simple model suggests that an interfacial insulating oxide of thickness 1–2 nm was present after conventional cleaning. This oxide has a strong influence on the contact characteristics on both n- and p-type GaN and appears to be responsible for some of the wide spread in contact properties reported in the literature.
Electron effective mass in hexagonal GaN
Authors: Witowski A. M. , Pakuła K. , Baranowski J. M. , Sadowski M. L. , Wyder P.
Published: July 2002

Far-infrared magneto-optical investigations of shallow donors in epitaxial GaN layers on sapphire were carried out by means of Fourier transform spectrometry up to 23 T. From the splitting of the donor p states in a magnetic field, the cyclotron effective mass for conduction electrons was found to be m*=0.222 m0. A precise determination of the mass was made possible by the high quality of the spectra and by taking into account high magnetic field data above 12 T.
Ab initio investigation of C incorporation mechanisms on Si(001)
Authors: Liu C.-L. , Borucki L. J. , Merchant T. , Stoker M. , Korkin A.
Published: July 2002

Ab initio calculations were performed to investigate adsorption and diffusion of C on the Si(001) surface at different surface and subsurface sites. Incorporation mechanisms of both substitutional and interstitial C during film deposition and growth were proposed. A surface diffusion process resulting in interstitial C incorporation was identified and the calculated energy barrier of ∼1.0 eV is consistent with the experimental value of 0.94±0.04 eV. The results support experimental observations of several groups: higher growth rates and lower temperatures favor the substitutional C incorporation.
Photocontrol of spin-glass state in Mg1.5FeTi0.5O4 spinel ferrite films
Authors: Muraoka Y. , Tabata H. , Kawai T.
Published: July 2002

A spin-glass state up to 210 K has been found in (Mg, Fe){Mg,Fe,Ti}2O4 spinel ferrite thin films formed on α-Al2O3(0001) substrates. The films exhibit long-time relaxation of the magnetization in zero-field-cooled operation below 210 K; also, the ac susceptibility measurements show the presence of frequency-dependent cusp temperature. Both of the above observations are characteristic features of a spin glass. The change of magnetic state in the films from a spin glass to ferrimagnet has been achieved over a wide temperature range below 160 K by means of light irradiation.
Influence of gas flow stoichiometry on the luminescence of organometallic-vapor-phase-grown ZnxCd1−xSe epilayers
Authors: Zhang X. B. , Hark S. K.
Published: July 2002

Zn x Cd 1−x Se epilayers were grown by organometallic vapor phase epitaxy using various VI/II flow ratios at a temperature of 420 °C. Cathodoluminescence (CL) spectroscopy and imaging were used to study their luminescent properties. Both near-band gap emissions (NBE) and deep-level emissions (DLE) were found in the CL spectra. We found that the width of the NBE peak and the intensity of the DLE relative peak to that of NBE increase with an increase in the VI/II flow ratio. Both effects are traced to the presence of pyramidal growth hillocks on the surface of the epilayer and to their increased density at high VI/II ratios. Monochromatic CL images show that there are two kinds of luminescent centers contributing to the NBE. The one that emits at slightly lower energies is only found, together with the DLE centers, within the growth hillocks. The one that emits at a slightly higher energy is found from surrounding areas. The concomitant appearance of DLE centers and low energy NBE centers shows that they share a common origin. Excitation intensity dependence of the photoluminescence of the NBE centers identifies as donor–acceptor-pair recombinations.
Q-switched operation of a coupled-resonator vertical-cavity laser diode
Authors: Fischer A. J. , Chow W. W. , Choquette K. D. , Allerman A. A. , Geib K. M.
Published: July 2002

We report Q-switched operation from an electrically injected monolithic coupled-resonator structure which consists of an active cavity with InGaAs quantum wells optically coupled to a passive cavity. The passive cavity contains a bulk GaAs region which is reverse biased to provide variable absorption at the lasing wavelength of 990 nm. Cavity coupling is utilized to effect large changes in output intensity with only very small changes in passive cavity absorption. The device is shown to produce pulses as short as 150 ps at repetition rates as high as 4 GHz. A rate equation approach is used to model the Q-switched operation yielding good agreement between the experimental and theoretical pulse shape. Small-signal frequency response measurements also show a transition from a slower (∼300 MHz) forward-biased modulation regime to a faster (∼2 GHz) modulation regime under reverse-bias operation.
Change in electrical resistivity associated with the glass transition in a continuously cooled Pd40Cu30Ni10P20 melt
Authors: Haruyama O. , Kimura H. , Inoue A. , Nishiyama N.
Published: July 2002

We report a reversible change in electrical resistivity accompanied with the glass transition (glass transition temperature Tg=570 K) in a Pd40Cu30Ni10P20 bulk glass. The bulk glass with a diameter of about 5 mm and length of 30 mm was produced at a maximum cooling rate of 1.2 K/s. This bulk glass showed a negative temperature coefficient of resistivity −0.81×10−4 K−1, at room temperature, −4.17×10−4 K−1 in the supercooled liquid region, and −2.75×10−4 K−1 in the liquid state. The undercooled liquid alloy beyond eutectic temperature Tm=804 K did not show the onset of crystallization until room temperature. The behavior of resistivity around Tg was in accordance with the heating to and cooling from the melt. This suggests that the amorphous structure might vary reversibly according to the glass transition in the present glass.
Very high-current-density Nb/AlN/Nb tunnel junctions for low-noise submillimeter mixers
Authors: Kawamura Jonathan , Miller David , Chen Jian , Zmuidzinas Jonas , Bumble Bruce , LeDuc Henry G. , Stern Jeff A.
Published: July 2002

We have fabricated and tested submillimeter-wave superconductor–insulator–superconductor (SIS) mixers using very high-current-density Nb/AlN/Nb tunnel junctions (Jc≈30 kA cm−2). The junctions have low-resistance-area products (RNA≈5.6 Ω μm2), good subgap-to-normal resistance ratios Rsg/RN≈10, and good run-to-run reproducibility. From Fourier transform spectrometer measurements, we infer that ωRNC=1 at 270 GHz. This is a factor of 2.5 improvement over what is generally available with Nb/AlOx/Nb junctions suitable for low-noise mixers. The AlN-barrier junctions are indeed capable of low-noise operation: we measure an uncorrected double-sideband receiver noise temperature of TRX=110 K at 533 GHz for an unoptimized device. In addition to providing wider bandwidth operation at lower frequencies, the AlN-barrier junctions will considerably improve the performance of THz SIS mixers by reducing rf loss in the tuning circuits.
Optical fiber for dispersion addressing
Authors: Donlagić Denis , Culshaw Brian
Published: July 2002

This letter presents a fully distributed forward propagating system, suitable for use with microbend sensors. The principle relies on selected mode launch in specially designed multimode fiber where a short pulse is launched into the fundamental mode. In the presence of microbend disturbance located down the sensing fiber, light couples from the fundamental to higher-order modes that propagate at different group velocity than the fundamental mode. The position of the disturbance is determined by the time delay between the pulse carried by the fundamental mode and by the pulse carried by higher-order modes. The group velocity difference is maximized by proper construction of the refractive index profile of the proposed fiber. Experimentally produced fibers exhibited difference of group velocities in ranges over 1%. This allows for easy reconstruction of position and amplitude of microbend deformations located down the sensing fiber.
Power dependence of the injection lock band of angled-grating distributed feedback lasers
Authors: Gallant D. J.
Published: July 2002

Experimental measurements of the injection lock band of an angled-grating distributed feedback laser have been performed systematically as a function of the unlocked slave laser power. Fringe visibility measurements were used to ascertain the quality of the lock between the master and slave laser as a function of master coupling level and frequency detuning. Experimental data show increasing spectral instabilities under optical injection as the slave laser power is increased, resulting in the stable portion of the lock band decreasing in width.
Substitutional carbon incorporation during Si1−x−yGexCy growth on Si(100) by molecular-beam epitaxy: Dependence on germanium and carbon
Authors: Liu J. P. , Osten H. J.
Published: July 2002

We present results on the kinetics of substitutional carbon incorporation during growth of Si1−x−yGexCy alloys on silicon (100) using solid-source molecular-beam epitaxy. Substitutional carbon concentration decreases with increasing germanium content for samples grown at 400 °C with the same carbon flux and growth rate. The reduction in substitutional carbon concentration is small at low carbon flux, increasing significantly at higher carbon fluxes. The results indicate that the effect of either Ge or C concentration can dominate the substitutional C incorporation, depending on the total C concentration range.
Channeling as a mechanism for dry etch damage in GaN
Authors: Haberer Elaine D. , Chen Ching-Hui , Abare Amber , Hansen Monica , Denbaars Steve , Coldren Larry , Mishra Umesh , Hu Evelyn L.
Published: July 2002

Etch damage of GaN was investigated using a quantum-well probe structure. A clear decrease in photoluminescence (PL) intensity was observed and was aggravated with increasing ion-beam voltage. The magnitude of decrease in PL intensity was much larger than expected, even greater than for GaAs subjected to similar etch conditions. Angle-dependent bombardment studies were carried out to investigate channeling as a damage mechanism in GaN. The large decrease in PL intensity observed near normal incidence or along the [0001] direction suggests that channeling is a damage mechanism for low-energy bombardment in GaN.
Exploring the effects of tensile and compressive strain on two-dimensional electron gas properties within InGaN quantum wells
Authors: LeBoeuf S. F. , Aumer M. E. , Bedair S. M.
Published: July 2002

With the advent of high-quality AllnGaN quaternary cladding, InGaN quantum wells (QWs) have now been studied under both compressive and tensile strain, as well as no strain at all! This has allowed the experimental investigation of the two-dimensional electron gas (2DEG) properties within InGaN QWs that have been subjected to a full range of strain, opening the doors to a new realm of strain engineering. We present the capacitance–voltage-derived 2DEG properties of several In0.08Ga0.92N QWs subject to various degrees of strain. Strained In0.08Ga0.92N QWs clad with GaN exhibit better 2DEG confinement than their unstrained Al0.24In0.09Ga0.67N-clad counterparts. For the case of compressive-strained QWs, it was found that the peak 2DEG concentration increases linearly with well width. In contrast, such dependence was not observed for the case of unstrained QWs with lattice-matched cladding. Of further interest, the 2DEGs for compressive and tensile In0.08Ga0.92N QWs are localized at opposite interfaces, which is attributed to strain-induced piezoelectric fields pointing in opposite directions.
Thermoelectric power factor in superlattice systems
Authors: Broido D. A. , Reinecke T. L.
Published: July 2002

A formalism is given for the power factor for thermoelectric transport in quantum well and wire superlattices using full electronic band structure and the complete inelastic Boltzmann equations for carrier-phonon scattering. Detailed calculations are given for realistic PbTe quantum well and quantum wire superlattices. In the quantum well case the dependence of the power factor on potential is much weaker than in previous work, and its behavior is traced to the underlying physics. Results are also given for the dependence of the power factors on growth direction.
Identifying the adaptive mechanism in globular proteins: Fluctuations in densely packed regions manipulate flexible parts
Authors: Yilmaz Lutfu Safak , Atilgan Ali Rana
Published: July 2002

A low-resolution structural model based on the packing geometry of α-carbons is utilized to establish a connection between the flexible and rigid parts of a folded protein. The former commonly recognizes a complementing molecule for making a complex, while the latter manipulates the necessary conformational change for binding. We attempt analytically to distinguish this control architecture that intrinsically exists in globular proteins. First with two-dimensional simple models, then for a native protein, bovine pancreatic trypsin inhibitor, we explicitly demonstrate that inserting fluctuations in tertiary contacts supported by the stable core, one can regulate the displacement of residues on loop regions. The positional fluctuations of the flexible regions are annihilated by the rest of the protein in conformity with the Le Chatelier–Braun principle. The results indicate that the distortion of the principal nonbonded contacts between highly packed residues is accompanied by that of the slavery fluctuations that are widely distributed over the native structure. These positional arrangements do not appear in a reciprocal relation between a perturbation and the associated response; the effect of a movement of residue i on residue j is not equal to that of the same movement of residue j on residue i.
Dynamic nuclear polarization by spin injection
Authors: Johnson Mark
Published: July 2002

A theory is presented to describe quantitatively how nuclear spin polarization can be induced in a metal by a dc electric bias current driven through the sample. The bias current is spin polarized by passing through a thin ferromagnetic film in interfacial contact with the sample, with the polarization axis determined by the magnetization orientation of the ferromagnetic layer. The nuclear spins are polarized due to spin angular momentum transfer from the electrons to the nuclei mediated by the contact hyperfine interaction. Upon reversing the polarity of the bias current, the sign of the nuclear polarization is reversed. Unlike other methods of dynamic nuclear polarization, spin-injected dynamic nuclear polarization is a zero frequency technique that in principle does not require an applied magnetic field.
Latency effects and periodic structures in light-induced frustrated etching of Fe:doped LiNbO3
Authors: Boyland Alexander J. , Mailis Sakellaris , Barry Ian E. , Eason Robert W. , Kaczmarek Malgosia
Published: July 2002

Single crystals of z-cut 0.05% Fe:doped lithium niobate (Fe:LiNbO3), have been etched in a mixture of HF and HNO3 acids, under simultaneous illumination from a ∼100 mW 488 nm wavelength Ar ion laser light source, focused to power densities of ∼50 W cm−2 at the crystal surface exposed to the etchant. Etching is partially inhibited in illuminated regions, and the degree of inhibition shows a systematic latency: sites illuminated early in the etch run resist further etching even after the light is removed. Etched structures additionally exhibit regular periodic features of ∼0.5 μm scale length. Details of these structures are shown, and the latent etching effect is discussed.
Improvement of interface formation between metal electrode and polymer film by polymer surface modification using ion sputtering
Authors: Liao L. S. , Fung M. K. , Cheng L. F. , Lee C. S. , Lee S. T. , Inbasekaran M. , Woo E. P. , Wu W. W.
Published: July 2002

The surface of poly (9,9-dioctylfluorene) (PFO) film was modified by 1.0 keV Ar+ irradiation with a dose of 6.5×1014 ions/cm2 prior to Ca deposition. Ultraviolet and x-ray photoelectron spectroscopic studies indicated that the modified surface could effectively block Ca diffusion into the PFO film and prevent the formation of doping-induced bipolaron states in the former forbidden energy gap. As a result, a sharper metal contact on the surface of the PFO film could be formed, compared to that on the surface without Ar+ irradiation. The results suggest that the judicial surface modification of polymer surfaces may be useful for the improvement of metal/polymer contacts and thus device performance.
IrSiN films with superior oxygen-diffusion barrier effect for stacked ferroelectric capacitors
Authors: Matsushita Shigeharu , Harada Mitsuaki , Gueshi Tatsuro , Matsushita Yoshifumi
Published: July 2002

IrSiN films (including IrSi film) formed by the reactive co-sputtering of Ir and Si targets have been investigated with regard to their oxygen-diffusion barriers in an application to stacked ferroelectric capacitors. The film properties and barrier effect were examined with relation to the N2/(Ar+N2) deposition flow ratio. In IrSiN films formed with a N2/(Ar+N2) flow ratio of 0.06 or 0.12, a shallow oxygen penetration depth of less than 20 nm was attained even under annealing in O2 at 800 °C for 40 min, and no reaction was observed with polycrystalline silicon (poly-Si) films. These films also adhered well to both poly-Si and SiO2 films. Therefore, the barriers are likely to prove extremely useful for integrated ferroelectric capacitors.
Efficient infrared imaging upconversion via quantum coherence
Authors: Boyd Robert W. , Scully Marlan O.
Published: July 2002

We show that quantum coherence can be used to achieve marked improvement in the efficiency of the process of infrared upconversion. In one particular example which we analyze in detail, we show that it is possible to convert infrared radiation at a wavelength of 100 μm to the visible with essentially 100% efficiency while maintaining diffraction-limited imaging of the infrared field.
Laser with guided pump and free-propagating resonator mode using diffusion-bonded rectangular channel waveguides
Authors: Griebner U. , Grunwald R. , Schönnagel H. , Huschke J. , Erbert G.
Published: July 2002

We report the laser performance of a short diffusion-bonded diode-pumped Yb:YAG rectangular channel waveguide of 100 μm cross section. Using an end-pumped configuration guiding only the slow axis, a high overlap of the pump mode and the nonguided resonator mode is achieved. With 4 W of pump power from two 60 μm high-power broad-stripe diodes, 0.7 W of output power with nearly diffraction-limited performance is obtained.
High-resolution lenses for sub-100 nm x-ray fluorescence microscopy
Authors: David C. , Kaulich B. , Barrett R. , Salomé M. , Susini J.
Published: July 2002

We report on the design, fabrication, and testing of Fresnel zone plates for high-resolution x-ray fluorescence microscopy using the scanning x-ray microscope at the European Synchrotron Radiation Source. The germanium lenses were optimized for operation near the sulphur absorption edge at 2472 eV photon energy. The high measured diffraction efficiencies of up to 9.6% and the good match to the spatial coherence of the undulator beam resulted in a photon flux of about 4×108 photons per second within the bandwidth of a silicon 〈111〉 monochromator. Using a test object consisting of zinc sulphide nanostructures, we were able to image features in sulphur x-ray fluorescence mode with lateral dimensions down to below 100 nm.
High-speed light modulation using complex refractive-index changes of electro-optic polymers
Authors: Harada Kenji , Munakata Katsuhiro , Itoh Masahide , Yatagai Toyohiko , Honda Yutaka , Umegaki Shinsuke
Published: July 2002

We propose a promising type of light modulator using complex refractive-index changes of electro-optic polymers in the wavelength region of absorption. The material used in this study is a high-glass-transition-temperature active-polyimide thin film. The wavelength dependence of electrically induced complex refractive-index changes and the modulation efficiency are evaluated. A modulation efficiency of 33.8% has been realized with 141 V rms applied potential at a wavelength of 633 nm. Very fast modulation at over 25 MHz has been demonstrated.
Proposed interpretation for possible solid-state amorphization in some Cu-based binary metal systems
Authors: Li Z. F. , Lai W. S. , Liu B. X.
Published: July 2002

According to a recently proposed criterion for solid-state amorphization to take place in a binary metal system, it is necessary to have a negative thermodynamic factor ΔF defined as a Gibbs free energy difference between an amorphous phase and the initial energetic state of the multilayers/or bilayer together with a relevantly large kinetic factor κ correlated to a diffusivity difference between the constituent metals of the system. The criterion is employed to discuss the possibility of solid-state amorphization in five representative Cu-based binary metal systems featuring either positive or negative heat of mixing. It turns out that the prediction based on the above argument for these Cu-based systems is in good agreement with the experimental results observed so far.
Short lifetime photoluminescence of amorphous-SiN
x
films
Authors: Yamaguchi Kenji , Mizushima Kazuki , Sassa Koichi
Published: July 2002

We observed photoluminescence (PL) of amorphous-SiNx films which showed a short radiative lifetime of about 1 ns. The spectrum form is Gaussian centered at around 2.2 eV. The samples were prepared by low-pressure chemical vapor deposition with SiH2Cl2 and NH3 gases. We propose an electron-phonon coupling model for the PL, assuming that the coupling phonon is Si–H or N–H vibrational mode and the bond length changes over 0.1 Å at an excited state due to the strong interaction.