bluuebunny/crossref_metadata_2025 huggingface dataset:
Substrate stress controlled magnetic domains in amorphous Terfenol-D films
Authors: Su Quanmin , Zheng Y. , Roytburd A. , Wuttig Manfred
Published: July 2002

Magnetic force microscopy of amorphous compressed Terfenol-D films of micron thickness on both crystalline Si and glassy silica shows that their ferromagnetic domain structure is one dimensional and periodic. On Si the structure is aligned with respect to the easy elastic direction of the substrate. The square of the domain period is proportional to the thickness of the film. All facts indicate that the domain morphology in these films is determined by a substantial elastic contribution to the domain wall and film/substrate interaction energies.
Measurement of the thermal diffusivity of liquids by the forced Rayleigh scattering method: Theory and experiment
Authors: Nagasaka Y. , Hatakeyama T. , Okuda M. , Nagashima A.
Published: July 2002

This article is devoted to the theory and experiment of the forced Rayleigh scattering method for measurement of thermal diffusivity of liquids which can be employed in the form of an instrument operated optically in a contact-free manner. The theoretical considerations included are: (1) effect of cell wall, (2) effect of dye, (3) effect of Gaussian beam intensity distribution, (4) effect of heating duration time, and (5) effect of coupled dye and wall for a heavily absorbing sample. The errors caused by inadequate setting of optical conditions are also analyzed: (1) effects of grating thickness and (2) effects of initial temperature amplitude. Experimental verifications of the theory have been carried out through the measurements on toluene and water as standard reference substances. As a result of these experiments and theory, the criteria for optimum measuring conditions became available. To demonstrate the applicability of the present theory and the apparatus, the thermal diffusivities of toluene and methanol have been measured near room temperature under atmospheric pressure. The accuracy of the present measurement is estimated to be ±3%.
Suppressed gate current in a superlattice-insulated-gate field-effect transistor on InP
Authors: Brown E. R. , Chen C. L. , Mahoney L. J. , Maki P. A. , Nichols K. B.
Published: July 2002

A new insulating layer is used in a normally-off (i.e., enhancement-mode) field-effect transistor on an InP substrate. It consists of closely spaced, strained AlAs barriers embedded in In0.52Al0.48As between the In0.53Al0.47As channel and the metal gate. This insulating layer increases the forward-bias gate turn-on voltage by approximately 50% and reduces the gate leakage current by as much as 50 times compared to a conventional In0.52Al0.48As insulating layer. In addition, the transistor characteristics are significantly improved such that the maximum current is increased approximately three times and the peak transconductance is increased by 70%. These properties are explained by superior confinement of electrons to the channel in the presence of the AlAs barriers.
Intracavity frequency doubling of a continuous wave Ti:sapphire laser with over 70% conversion efficiency
Authors: Zhou W.-L. , Mori Y. , Sasaki T. , Nakai S. , Nakano K. , Niikura S. , Craig B.
Published: July 2002

Efficient tunable ultraviolet generation by intracavity frequency doubling of a continuous wave Ti:sapphire laser was demonstrated. Maximum output is obtained of 460 mW at 398 nm corresponding to a total infrared-to-ultraviolet conversion efficiency over 70%. High conversion efficiency was resulted from a critically phase-matched, temperature-tuned lithium triborate crystal and a novel resonator design. The observed laser damage of the crystal coatings is also discussed.
Phased array of high-power, coherent, monolithic flared amplifier master oscillator power amplifiers
Authors: Osinski J. S. , Mehuys D. , Welch D. F. , Waarts R. G. , Major J. S. , Dzurko K. M. , Lang R. J.
Published: July 2002

A monolithically integrated array of InGaAs/AlGaAs flared amplifiers driven by a single DBR laser through a power splitter network and individually addressed phase modulators is described. Phase adjustment of ≳2π per element by free-carrier effects is verified by monitoring the interference pattern of all four emitters, and typically requires <15 mA of current to obtain a 2π phase shift. Phase matching is achieved among all four diffraction-limited emitters at a pulsed output power of ≳5 W, and, combined with the proper external lensing, could therefore result in an ultranarrow, single-lobed far-field pattern whose width is determined by the extended aperture of the array.
Plasma-heating induced intensity-dependent gain in semiconductor lasers
Authors: Ning C. Z. , Moloney J. V.
Published: July 2002

Starting from a set of equations derived from a microscope theory we show that the familiar nonlinear gain of the form a/(1+I/Is) introduced in semiconductor laser rate equations phenomenologically should be replaced by a more general form of a/(1+I/Is)b. The new scaling exponent b depends on the relaxation constant γT that describes the rate of heat dissipation from plasma to the lattice due to carrier-phonon scattering.
Formation of single-domain layers in multidomain LiNbO3 crystals by proton exchange and quick heat treatment
Authors: Zhu Yong-yuan , Zhu Shi-ning , Zhang Zhi-yong , Shu Hong , Hong Jing-fen , Ge Chuan-zhen , Ming Nai-ben
Published: July 2002

Experimental studies on the formation of single-domain layers in a multidomain z-cut LiNbO3 crystal plate by proton exchange followed by quick heat treatment were performed. It was found that the direction of the spontaneous polarization in the single-domain layer points to the inside of the plate. To explain this phenomenon, an internal electric field model was proposed which is related to the proton concentration gradient.
White light emitting SrS:Pr electroluminescent devices fabricated via atomic layer epitaxy
Authors: Kong W. , Fogarty J. , Solanki R. , Tuenge R. T.
Published: July 2002

Atomic layer epitaxy has been employed to fabricate white light emitting ZnS:Pr and SrS:Pr thin film electroluminescent devices. Electrical and optical properties of these devices have been characterized and compared. It is found that SrS:Pr devices are significantly brighter and more efficient than ZnS:Pr devices. The effect of ZnS buffer layers on the electrical characteristics of the SrS electroluminescent devices is discussed.
Excitation and relaxation of Yb3+ in InPAs and InP
Authors: Godlewski M. , Kozanecki A. , Bergman J. P. , Monemar B.
Published: July 2002

Excitation and relaxation mechanisms of Yb3+ ions in InP and InP0.93As0.07 alloy have been studied based on optically detected cyclotron resonance (ODCR), temperature dependent photoluminescence (PL), and PL decay measurements. It is shown with use of ODCR that charge carriers, most probably electrons, are captured by Yb3+ ions. PL transients show that the decay rate of the Yb3+ PL decreases with increasing As contents. Evidence is presented proving that the excited state of the Yb3+ ion decays by transfer of energy to the band states of InP, while in the case of InPAs, the energy may also be transferred to an exciton bound at the Yb3+ ion.
Optical detection of local field in vinylidene fluoride copolymer
Authors: Hasegawa Kazushige , Tomioka Akihiro , Miyano Kenjiro
Published: July 2002

Electro-absorption spectroscopy has been used to monitor the local field in a ferroelectric copolymer of vinylidene fluoride and trifluoroethylene. The local-field factor deduced is in good agreement with the previous numerical simulation.
Direct evidence for the existence of exciton bound on Yb3+ ion in In(P,As) crystals
Authors: Kozanecki A. , Szczerbakow A.
Published: July 2002

Temperature dependence of luminescence was measured in InPxAs1−x:Yb crystals (x=7% and 12%) and in reference undoped material (x=8%). A simple correlation between Yb doping and the number of thermally activated bands in the near-band-edge spectral region of In(P,As) alloys was found. A new luminescence band located at ∼25 meV below the free-carrier, band-to-band emission was observed in Yb-doped alloys only. A one-to-one correspondence between the appearance of this band and the quenching of the intra-4f-shell photoluminescence of Yb3+ ions is shown. These observations are taken as direct evidence for participation of excitons bound on Yb3+ ion in the excitation and quenching processes of the 4f shell.
On the mobility of n-channel metal–oxide–semiconductor transistors prepared by low-pressure rapid thermal chemical vapor deposition
Authors: McLarty P. K. , Misra V. , Hill W. , Wortman J. J. , Hauser J. R. , Morfouli P. , Ouisse T.
Published: July 2002

The factors affecting the channel mobility of metal–oxide–semiconductor transistors fabricated using as-deposited rapid thermal chemical vapor deposition (RTCVD) of silicon dioxide are investigated and compared to thermal silicon dioxide at various temperatures. The results indicate that the observed differences in the mobility values of thermal and rapid thermal chemical vapor deposed oxides at channel concentrations where Coulombic scattering is important is due to increased oxide trapping in the RTCVD films. It was also observed that the rapid thermal chemical vapor deposited oxides exhibited slightly larger mobility degradation rates at high fields when compared to thermal oxides.
Multiple-crystal x-ray topographic characterization of periodically domain-inverted KTiOPO4 crystal
Authors: Hu Z. W. , Thomas P. A. , Gupta Mool C. , Risk W. P.
Published: July 2002

A periodically domain-inverted KTiOPO4 crystal has been characterized for the first time by multiple-crystal multiple-reflection x-ray topography. The striation contrast within the domain- inverted regions has been revealed in high strain-sensitivity reflection topographs. The origin of formation of the striation contrast and the mechanism of domain inversion in KTiOPO4 are discussed in terms of the structural characteristics of KTiOPO4.
Energy loss near-edge structure for materials containing light elements by reflection electron energy loss spectroscopy
Authors: Hayashi Toshinori , Araki Kiyoaki , Takatoh Shuji , Enokijima Toru , Yikegaki Tetsurou , Futami Toru , Kurihara Yoshifumi , Tsukajima Jun’ichi , Takamoto Kiichi , Fujikawa Takashi , Usami Seiji
Published: July 2002

A reflection electron energy loss spectroscopy system has been developed to investigate local surface atomic structures around light elements such as C, N, and O. Electrons scattered inelastically on a surface with a small scattering angle are energy analyzed. This system was used to measure energy loss near-edge structures (ELNESs) for materials such as BN, graphite, and NiO. The comparison between ELNES and x-ray absorption near edge structure suggests that the ELNES is useful for the atomic structure analyses of surfaces.
Magnetic properties and magnetostriction in TbFe2 compound with the addition of manganese or gallium
Authors: Tang Y. J. , Luo H. L. , Gao N. F. , Liu Y. Y. , Pan S. M.
Published: July 2002

In the present study magnetic and magnetostrictive properties of Tb(Fe1−xTx)2 (T=Mn, Ga) compounds were examined by magnetic measurement, Mössbauer, and x-ray study. Mössbauer study shows that the easy magnetization direction of the compounds may deviate slightly from the major axis of symmetry and the average isomer shift of the compounds decreases with increasing the x value, which was attributed to the charge transfer from 3d electrons of Mn atoms or 4p electrons of Ga atoms into the 3d band of Fe. It was also found from x-ray measurement that the spontaneous magnetostriction λ111 decreased due to Mn or Ga substitution, which can be understood on the basis of the single-ion model. The increase of the polycrystal magnetostriction λs due to Mn substitution was also found and can be ascribed to the increase of λ100, which may be caused by the filling of d bands due to substitution.
Edge-emitting quantum well laser with Bragg reflectors
Authors: Yang F. , Blood P. , Roberts J. S.
Published: July 2002

We have fabricated edge-emitting GaAs/AlGaAs quantum well lasers in which the outer cladding layers have been replaced by multilayer Bragg reflectors. The reflectance peak spans the intrinsic spontaneous emission spectrum of the wells and there are no allowed vertical cavity modes within this spectrum. Compared with an equivalent alloy structure the threshold current of these lasers is reduced by 25%. This is due to a reduction in the spontaneous recombination current rather than an increase in internal efficiency. Studies of spontaneous emission normal to the sample surface show that the emission intensity is significantly reduced. We suggest that the threshold current is reduced by reduction in the spontaneous recombination rate due to a combination of inhibition of the emission and photon recycling.
Determination of oxide fixed charge at the top and bottom Si/SiO2 interfaces of silicon-on-insulator devices
Authors: Arnold Emil
Published: July 2002

A method for characterizing thin-silicon-on-insulator (SOI) devices is described that allows separate determination of the oxide fixed charges at the top and bottom Si/SiO2 interfaces, as well as the average dopant concentration in the SOI layer. These are obtained from the characteristics of a depletion-type SOI MOS transistor, without the need to rely on the knowledge of the flatband voltage. The technique is based on the determination of the bias voltage at which the SOI film and its interfaces become completely depleted (under conditions where minority carriers are not available), and the voltages at which either interface becomes inverted (inversion charge being provided by illumination). The application of this technique is demonstrated experimentally and verified by numerical simulations.
Phosphorus doping of silicon by proton induced nuclear reactions
Authors: Abril Isabel , Garcia-Molina Rafael , Erokhin Konstantin M. , Kalashnikov Nicolay P.
Published: July 2002

We propose a method to dope silicon with phosphorus by means of the nuclear resonant reaction 30Si(p,γ)31P, which takes place when a natural silicon target is bombarded with a few MeV proton beam. This alternative method considerably reduces the usual target damage produced by the more commonly used direct phosphorus implantation.
Growth of high-quality YBa2Cu3O7−x films on CeO2 buffer of mixed (001)/(111) orientation on sapphire
Authors: Zaitsev A. G. , Kutzner R. , Wördenweber R.
Published: July 2002

High-quality epitaxial YBa2Cu3O7−x (YBCO) thin films are grown on large area (1ub;-21ubx02) sapphire (r-cut) substrates buffered by CeO2 of mixed (001) and (111) orientation. It is shown that (001) and (111) CeO2 epitaxy on (1ub;-21ubx02) sapphire is possible with further growth of well-oriented (001) YBCO on both orientations of CeO2. In the case of (111) CeO2 one of the equivalent in-plane trigonal directions, i.e., [10ub;-21ubx], [ub;-21ubx10], or [01ub;-21ubx], is aligned along either [02ub;-22ubx1], or [2ub;-22ubx01] crystallographic axis of sapphire, which is indicated by the φ-scan x-ray diffraction pattern of the (115) CeO2 reflex. The resulting (001) YBCO film grown on the (001)/(111) CeO2 buffer reveals no disorientations in the a-b plane other than conventional 90° twinning. The YBCO films exhibited very smooth surface and were free of screw dislocations. The high quality of the YBCO films is confirmed by the microwave surface resistance of Rs≤0.44 mΩ at 10 GHz and 77 K.
Molecular beam epitaxy of pseudomorphic silicon/carbon superlattices on silicon substrates
Authors: Faschinger W. , Zerlauth S. , Stangl J. , Bauer G.
Published: July 2002

We describe the molecular beam epitaxy growth of superlattices where silicon layers with a thickness between 3 and 10 nm alternate with very thin carbon layers. High resolution x-ray diffraction reveals that the superlattices are of excellent crystalline quality and are pseudomorphic with respect to the silicon substrate. From a dynamical simulation of the diffraction spectra we conclude that the nominal carbon layers are in fact silicon–carbon alloys with a carbon content up to 50%. Given the large lattice mismatch of more than 10% of such an alloy to the silicon substrate, astonishingly thick superlattices with up to 100 periods can be grown without lattice relaxation.
Fabrication of large area silicon solar cells by rapid thermal processing
Authors: Sivoththaman S. , Laureys W. , Nijs J. , Mertens R.
Published: July 2002

Large area n+pp+ solar cells have been fabricated on 10 cm×10 cm pseudo-quasi-square CZ silicon wafers (1 Ω cm, p-type) predominantly used by the photovoltaic (PV) industry. All the high-temperature steps have been performed by rapid thermal processing (RTP). Emitter formation, back surface field (BSF) formation, and surface oxidation have been performed in just two RTP steps each lasting 50 s. Solar cells of 15% efficiency have been fabricated this way, demonstrating the applicability of this low thermal budget technology to large area, modulable size, industrial quality Si wafers. Furthermore, the rapid thermal oxidation (RTO) is shown to result in good quality thin oxides with Si/SiO2 interface trap densities (Dit)<1011 cm−3 eV−1 near-midgap.
Measurement of the minority carrier mobility in the base of heterojunction bipolar transistors using a magnetotransport method
Authors: Betser Y. , Ritter D. , Bahir G. , Cohen S. , Sperling J.
Published: July 2002

The minority carrier mobility in the base of an InP/GaInAs heterojunction bipolar transistor (HBT) is obtained by measuring the change in base current induced by a magnetic field applied perpendicular to the direction of the current flow. The obtained mobility is consistent with results of the zero-field time of flight technique.
Fundamental investigation of reflectometry as a density fluctuation diagnostic (invited)
Authors: Rhodes T. L. , Baang S. , Chou A. E. , Domier C. W. , Luhmann N. C. , Peebles W. A.
Published: July 2002

Reflectometry is currently used to monitor density fluctuations and turbulent correlation lengths in fusion plasmas. Various models have been used to interpret the experimental data and to determine the regimes of validity of the reflectometer fluctuation measurements. Heretofore, these models have not been validated by direct comparison with experiment. In this paper the first comparison between a controlled laboratory experiment and a one-dimensional numerical model is presented. It is found that the model is unable to predict the observed high degree of spatial localization and dependence on perturbation wave number. The implications of these disagreements are discussed, together with suggestions for their resolution.
Quantitative high resolution electron microscopy of III-V compounds: A fuzzy logic approach
Authors: Hillebrand R. , Hofmeister H. , Werner P. , Gösele U.
Published: July 2002

In the study of interdiffusion phenomena in layered structures of III-V compounds by high resolution electron microscopy, contrast features in the micrographs can be correlated with the variation of the chemical composition of the crystals. For quantitative interpretation of the micrographs a fuzzy logic approach is adapted to extract chemical information. The linguistic variable ‘‘similarity of images’’ is derived from the standard deviation (SD) of their difference patterns, which proved to be an appropriate measure. The approach developed is used to analyze simulated contrast tableaus of GaAs/P (As/P variation) and experimental micrographs of Al/GaAs (Al/Ga variation).
Photoluminescence properties of 13×13 nm GaAs quantum wires buried in trench structures reduced by growing GaAs/AlAs superlattice layers
Authors: Sogawa T. , Ando S. , Kanbe H.
Published: July 2002

We report lateral-size control of GaAs/AlAs trench-buried quantum wires (QWRs) on a scale of 10 nm by metalorganic chemical vapor deposition using nonplanar substrates. The lateral width is reduced to 12–13 nm by growing GaAs/AlAs superlattice layers (SLs) on the (110) sidewall facets of the trenches, where the roughness of the SL sidewalls is approximately several monolayers. Low-temperature photoluminescence (PL) properties of nearly square 13×13 nm QWRs buried in the trenches exhibit a strong PL blue shift of 85 meV with respect to the band-gap energy of GaAs bulk and PL polarization anisotropy of 25% due to two-dimensional quantum confinement effects. The emission from Ga-rich AlGaAs regions in the trenches constituting AlGaAs vertical quantum wells was also observed. We demonstrate that substituting GaAs/AlAs SLs for the AlGaAs layer effectively eliminates the undesired emission levels caused by the inevitable Al content fluctuation in the AlGaAs layer grown on nonplanar structures.
Photoluminescence investigation of Hg acceptor in GaAs
Authors: Ka O. , Fons P. J.
Published: July 2002

Photoluminescence spectroscopy has been used to investigate the behavior of Hg, implanted into MBE-grown GaAs. A new recombination path in the near-band-edge region at 1.51291 eV is identified with the neutral Hg-bound exciton recombination (Hg°X), with a localization energy following an anti-Haynes’ rule. The electron-acceptor and donor-acceptor transitions are displayed at 1.466 and 1.463 eV, respectively. From the temperature dependence of the photoluminescence, the value of 52.5 meV is extracted for the binding energy of the Hg acceptor in GaAs. With the resonant excitation of the Hg°X line, the electronic signature of the Hg acceptor in GaAs is further evidenced, with the observation of two-hole transitions. Transitions to 2s as well as 3s states are resolved, with Raman shifts of 37.2 and 44.8 meV, respectively. The corresponding binding energies are thus 15.3 and 7.7 meV, respectively.
Surface mode coupling in GaAs/AlGaAs laser diodes—A novel concept for a single laser mode emission
Authors: Köck A. , Freisleben S. , Gmachl C. , Gornik E. , Rosenberger M. , Korte L. , de Souza P. L.
Published: July 2002

We demonstrate a novel concept for a mode selection mechanism in surface emitting laser diodes. This concept is based on a strong coupling process between the laser mode and a surface mode on top of the laser diode. The mode selection mechanism is the result of a strong feedback from the surface mode into the laser diode. Nearly single-modelike emission spectra are achieved from surface emitting GaAs/AlGaAs laser diodes and qualitatively explained by a model based on ray optics. The main advantage of this type of laser diode is its simple fabrication and the possibility of adjusting the desired wavelength independent of the growth process by external technological parameters.
Thermal oxidation kinetics of (100) and (111) silicon in nitrous oxide
Authors: De Meo Renzo C. , Chow T. P.
Published: July 2002

Thermal oxidation of (100) and (111) silicon (Si) in a nitrous oxide (N2O) ambient has been studied. The oxidation rate follows a parabolic to linear behavior. The activation energies in the parabolic regime were found to be 2.02 and 1.54 eV/molecule for (100) and (111) Si, respectively. The activation energy for the linear rate constant is estimated to be 1.61 and 1.37 eV/molecule for (100) and (111) Si, respectively. The limiting mechanism for the parabolic regime is attributed to the diffusion of oxidant through a surface oxynitride layer. The gradual shift to linear behavior is unusual and is in direct contrast with the Grove–Deal model [J. Appl. Phys. 36, 3770 (1965)]. Finally, secondary ion mass spectrometry shows a temperature dependent distribution and concentration of nitrogen at the interface.
Helical peniotron backward wave oscillators
Authors: Lin A. T. , Lin Chih-Chien
Published: July 2002

The performance of peniotron backward wave oscillators which utilize the axis-encircling beam generated by a combined solenoidal and wiggler magnetic field was investigated through computer simulations. The potential advantages of this new configuration are that it is capable of converting both beam longitudinal and transverse energy into radiation and reducing the severity of mode competition.
Electron drift time in silicon drift detectors: A technique for high precision measurement of electron drift mobility
Authors: Castoldi A. , Rehak P.
Published: July 2002

This paper presents a precise absolute measurement of the drift velocity and mobility of electrons in high resistivity silicon at room temperature. The electron velocity is obtained from the differential measurement of the drift time of an electron cloud in a silicon drift detector. The main features of the transport scheme of this class of detectors are: the high uniformity of the electron motion, the transport of the signal electrons entirely contained in the high-purity bulk, the low noise timing due to the very small anode capacitance (typical value 100 fF), and the possibility to measure different drift distances, up to the wafer diameter, in the same semiconductor sample. These features make the silicon drift detector an optimal device for high precision measurements of carrier drift properties. The electron drift velocity and mobility in a 10 kΩ cm NTD n-type silicon wafer have been measured as a function of the electric field in the range of possible operation of a typical drift detector (167–633 V/cm). The electron ohmic mobility is found to be 1394 cm2/V s. The measurement precision is better than 1%.
Purely optical measurement of the resistivity distribution of semi-insulating InP:Fe by means of the photorefractive effect
Authors: Wittmann G. , Winnacker A.
Published: July 2002

Electrical homogeneity is an essential requirement for semi-insulating (SI)InP:Fe wafers. A method is presented to measure the spatial distribution of resistivity at room temperature via the photorefractive effect. The experimental conditions are presented and discussed. The potential of the method is demonstrated by applying it to SI liquid encapsulated Czochralski grown material.
A general purpose multiquantum electron paramagnetic resonance spectrometer
Authors: Strangeway Robert A. , Mchaourab Hassane S. , Luglio Juan R. , Froncisz W. , Hyde James S.
Published: July 2002

We describe the design, construction, and characterization of an X-band multiquantum electron paramagnetic resonance (MQEPR) microwave bridge, with MQ electron–electron double resonance and MQ electron–nuclear double resonance capabilities. The main feature of the bridge is the use of double-balanced mixers as double sideband modulators to generate multiple irradiation fields with variable frequency separation. The microwave source is a low phase noise Gunn diode oscillator, the frequency of which is translated by a nominal 300±Δf MHz. This approach, called double sideband/fixed filter (DSB/FF), allows the use of fixed bandpass microwave filters to reduce incident spurious products to at least −70 dBc. Each frequency is amplified separately to avoid system-generated intermodulation (IM) sidebands in the incident irradiation. As a result, the dominant source of system intermodulation is the nonlinearity in the receiver system, consisting of a low noise amplifier (LNA) and a double-balanced signal mixer. A detailed analysis of receiver-generated IM products is presented. The use of the loop-gap resonator with a high resonator efficiency parameter, Λ, and low Q is essential to achieve a balance between microwave power and system IM sidebands. It is shown that even at maximum incident power, the levels of these sidebands can be reduced to 51 dB below the MQEPR response by switching out the LNA. This permits the extension of MQEPR applications into systems where high power is required. The operation modes of the bridge are briefly described. Alternative bridge designs are considered and compared with the DSB/FF design. It is found that the DSB/FF approach gives the best overall performance with greater flexibility and compatibility with multiple operation modes.
Measurement of complex dielectric permittivity of partially inserted samples in a cavity perturbation technique
Authors: Subramanian V. , Sivasubramanian V. , Murthy V. R. K. , Sobhanadri J.
Published: July 2002

Suitable correction factors are incorporated in the measurement of shift in resonance frequency and full width at half-maximum in the cavity perturbation technique when the sample is inserted partially into the cavity. The present approach is observed to be more accurate compared to the available theories and it does not have limitations concerning the shape of the sample. Several standard samples are taken for the present measurement and compared with the full insertion method. Some of the samples are partially inserted into the cavity step by step and the experimental results are compared with the present approach and that of Lehndroff.
Passive Q switching of the alexandrite laser with a Cr4+:Y2SiO5 solid-state saturable absorber
Authors: Kuo Yen-Kuang , Birnbaum Milton
Published: July 2002

Passive Q switching of a flashlamp-pumped alexandrite laser with a Cr4+:Y2SiO5 (Cr4+:YSO) solid-state saturable absorber has been demonstrated at room temperature. An output of a single Q-switched laser pulse of 20 mJ in energy and 70 ns in duration was obtained. The output wavelength of the Q-switched laser pulse and the free-running laser was 753 nm.
Growth of single diamond crystallites around nanometer-scale silicon wires
Authors: Dennig Paul A. , Liu Harvey I. , Stevenson David A. , Pease R. Fabian W.
Published: July 2002

Diamond crystallites were nucleated and grown from the vapor phase on silicon substrates previously processed into arrays of nanometer-scale silicon wires. We found that the nanowires did not aid nucleation, and that the nucleation density on the nanowire base was very low (<104 cm−2). Most importantly, we discovered that single diamond crystallites grew around the nanowires, infiltrating the nanowire arrays, forming new composite structures. This discovery clearly shows how inclusions can be trapped in vapor grown diamond crystallites, and challenges the common assumption that growth precursors on the diamond surface are relatively immobile.
Reducing domain boundaries of surface reconstruction during molecular beam epitaxy on Si(111)
Authors: Hibino H. , Ogino T.
Published: July 2002

We report the behavior of steps and out-of-phase boundaries (OPBs) of 7×7 reconstruction on Si(111) during Si molecular beam epitaxy. During step-flow growth, Si atoms are preferentially incorporated into the crystal at positions where steps are connected with OPBs on the lower terraces, resulting in sawtooth shaped steps. This heterogeneous advancement of steps causes OPBs to rearrange and thereby reduce in number.
Asymmetric high temperature superconducting Josephson vortex-flow transistors with high current gain
Authors: Gerdemann R. , Bauch T. , Fröhlich O. M. , Alff L. , Beck A. , Koelle D. , Gross R.
Published: July 2002

We have fabricated Josephson vortex-flow transistors (JVFTs) based on asymmetric parallel arrays of YBa2Cu3O7−δ bicrystal grain boundary junctions. The critical current Ic and the voltage V at fixed bias current Ib were measured as a function of the control current Ictrl through a control line inductively coupled to the array. For JVFTs with an asymmetric in-line geometry a high current gain g=∂Ic/∂Ictrll ranging between about 20 at 40 K and 14 at 70 K was achieved. This current gain is much higher than that obtained for symmetric devices and results from the self-field effect of the electrode currents. In contrast to the current gain the transresistance rm=∂V/∂Ictrl of the JVFTs could not be enhanced by an asymmetric device structure. The current-voltage characteristics of the asymmetric JVFTs show pronounced step-like structures caused by the self-field of the electrode currents.
Nonlinear polarization switching in a semiconductor single quantum well optical amplifier
Authors: Lin Ming-Shan , Huang Ding-Wei , Yang C. C. , Hong Minghwei , Chen Young-Kai
Published: July 2002

Efficient nonlinear or power-dependent polarization switching in a semiconductor quantum-well amplifier is reported. In the experiment, an amplifier with an InGaAs/GaAs single quantum well structure which lases at 974 nm is used. Efficient self-switching is observed at 940 nm with signals 3 psec wide when gain and absorption saturation occur in the TM and TE polarization modes, respectively. The switching peak intensity is estimated to be lower than 13.2 MW/cm2. A theoretical model is adopted to show the consistent trends of switching behaviors with the experimental data.
Infrared radiation from bending magnet edges in an electron storage ring
Authors: Bosch R. A. , May T. E. , Reininger R. , Green M. A.
Published: July 2002

The infrared radiation emitted by electrons entering or exiting a storage ring bending magnet, which is termed ‘‘edge’’ radiation, is computed. The numerical results are in agreement with experimental observations at a wavelength of 1 μm. A comparison is made with the infrared synchrotron radiation emitted from the central region of a bending magnet for wavelengths of 1 μm–1000 μm. The flux of the edge radiation is lower than that of the synchrotron radiation for the shorter wavelengths studied, and greater for the longer wavelengths. However, the brightness of the edge radiation is higher for all of the wavelengths studied. This suggests that edge radiation may be a promising infrared radiation source.
Performance of tantalum-silicon-nitride diffusion barriers between copper and silicon dioxide
Authors: Angyal M. S. , Shacham-Diamand Y. , Reid J. S. , Nicolet M.-A.
Published: July 2002

Amorphous, 10-nm-thick tantalum-silicon-nitride (TaSiN) layers were found to be effective diffusion barriers between copper and thermal silicon dioxide. The films were electrically evaluated using TaSiN/Cu/TaSiN-oxide-silicon capacitors and bias thermal stress (BTS) treatments; the capacitors were stressed at 300 °C with electric fields in excess of 1 MV/cm for up to 80 h. High frequency capacitance versus voltage characteristics were recorded at room temperature before and after BTS treatment. Based upon comparisons between these (C–V) curves, barrier failure was concluded to have not occurred.
Observation of optically pumped midinfrared intersubband luminescence in a coupled quantum wells structure
Authors: Lavon Y. , Sa’ar A. , Moussa Z. , Julien F. H. , Planel R.
Published: July 2002

We have observed midinfrared emission due to intersubband transitions in a coupled quantum wells structure. The excitation process involves optical pumping of the carriers from the ground subband into the third subband and a generation of a population in the third subband. The luminescence is produced by a radiative transition of the photoexcited carriers from the third to the second subband, followed by a fast relaxation into the ground subband due to a resonance LO-phonon assisted relaxation process. The emission signal persists from low temperatures up to room temperature with a maximum efficiency at 190 K.
Distinguishing the As- or Ga-rich initial reconstruction in short-pulse supersonic nozzle beam epitaxy of GaAs in real time by millisecond time-resolved reflectance difference
Authors: Cui Jie , Zhang Suian , Tanaka Akihiko , Aoyagi Yoshinobu
Published: July 2002

For short-pulse supersonic nozzle beam epitaxy growth of GaAs on an As-rich initial surface, we measured the fast evolutions of As dimer density and Ga dimer density in real time by using a millisecond time-resolved reflectance difference (RD) system. Under the impingement of a trimethylgallium short pulse, the (2×4)β, (2×4)γ, and c(4×4) initial reconstructed surfaces show very different transient RD signals which can be used to distinguish the initial reconstruction of the GaAs surface in real time during the epitaxy.
Growth of ZnSe/MgS strained-layer superlattices by molecular beam epitaxy
Authors: Teraguchi N. , Mouri H. , Tomomura Y. , Suzuki A. , Taniguchi H. , Rorison J. , Duggan G.
Published: July 2002

Growth of ZnSe/MgS strained-layer superlattices (SLSs) has been carried out by molecular beam epitaxy. The crystal quality of SLSs degraded with MgS thickness of more than about 3 monolayers. Photoluminescence due to the transition between quantized levels was observed. Photoluminescence peak energies higher than 3.0 eV at 77 K were observed, which are comparable to that of ZnMgSSe quaternary material.
Structural properties of low temperature plasma enhanced chemical vapor deposited silicon oxide films using disilane and nitrous oxide
Authors: Song Juho , Lee G. S.
Published: July 2002

The structural properties of low temperature plasma enhanced chemical vapor deposited SiO2 films using Si2H6 and N 2O have been studied. It is observed that the degree of compaction of as-deposited SiO2 films, upon subsequent annealing, increases up to 4%. The shift of Si-O-Si stretching peak wave number of the as-deposited SiO 2 films (Δω=−20 cm−1) compared to the undensified SiO 2 films is attributed to 9.4% increase in the film density, resulting in smaller Si-O-Si bridging bond angle of 138°. It is also believed that the high temperature annealing results in the reduction of hydroxyl containing species in the film and in turn drives the dielectric constant towards that of thermal SiO2 films.
Fabrication of low-loss and high-Δn single-mode fluoride fiber for 1.3 μm praseodymium-doped fiber amplifiers
Authors: Fujiura Kazuo , Kanamori Terutoshi , Ohishi Yasutake , Terunuma Yukio , Nakagawa Koichi , Sudo Shoichi , Sugii Kiyomasa
Published: July 2002

The crystallization properties of ZrF4-based fluoride glasses containing PbF2 are clarified and single-mode fibers for an optical amplifier operating at 1.3 μm are fabricated. The crystallization tendency increases as the PbF2 content of the glasses increases and the optimum PbF2 content ranges from 11 to 12.5 mol % in terms of glass stability and refractive indices. The 4%-Δn single-mode fiber with a transmission loss of 44 dB/km at 1.2 μm was prepared as the amplifier host fiber. ZrF4-based glass with a PbF2 content of 11 mol % was used as a core glass and HfF4-based glass was used as a cladding glass.
Nonlinear self-channeling of a laser beam at the surface of a photorefractive fiber
Authors: Kamshilin A. A. , Raita E. , Prokofiev V. V. , Jaaskelainen T.
Published: July 2002

We experimentally observed the self-channeling of the light beam in photorefractive Bi12TiO20 fiberlike sample owing to the strong fanning effect. It results in significant speed up of the photorefractive response time in waveguides and in anomalous dependence of the response time on the applied ac electric field amplitude: the higher electric field, the faster response.
Electromechanical model for vibrating-wire instruments
Authors: Pádua A. A. H. , Fareleira J. M. N. A. , Calado J. C. G. , Wakeham W. A.
Published: July 2002

A methodology to formulate equivalent electric circuits to vibrating-wire sensors is presented, as well as examples of its application. Vibrating-wire sensors have been used in a number of instruments built for measurement of the density and viscosity of fluids up to high pressure and in wide temperature ranges. These instruments are based on a rigorous theoretic model describing both the mechanics of oscillation and the hydrodynamic effects arising from the presence of the sample fluid surrounding the vibrating wire. The equivalent circuits proposed in this work are essential in order to interpret the output signals of the sensor in terms of its mechanical parameters. Design choices dictate the type of pertinent electromechanical analogy. The use of equivalent circuits made possible the simultaneous measurement of the density and viscosity of fluids using one single sensor, which is a demonstration of a complete understanding of its behavior.
Photoluminescence of ordered Ga0.5In0.5P grown by metalorganic vapor phase epitaxy
Authors: Dong Jian-Rong , Wang Zhan-Guo , Liu Xiang-Lin , Lu Da-Cheng , Wang Du , Wang Xiao-Hui
Published: July 2002

Optical properties of ordered Ga0.5In0.5P epitaxial layers grown by metalorganic vapor phase epitaxy are investigated by photoluminescence (PL) in a temperature range of 10–200 K using excitation power densities between 0.35 W/cm2 and 20 W/cm2. It is found that the intensity of the highest-energy PL peak of the ordered Ga0.5In0.5P epilayer decreases first, then increases and finally goes down again with increasing temperature. A model of ordered Ga0.5In0.5P epitaxial layers is proposed, in which the ordered Ga0.5In0.5P epilayer is regarded as a type-II quantum well structure with band-tail states, and the dependence of PL spectra on the temperature and excitation intensity is reasonably explained.
A transient polarization grating method to study tumbling and bending dynamics of DNA
Authors: Naimushin Alexei N. , Fujimoto Bryant S. , Delrow Jeffrey J. , Schurr J. Michael
Published: July 2002

A transient polarization grating (TPG) instrument was developed to investigate the tumbling and bending dynamics of various DNAs over the time range from 20 ns to 10 μs. This TPG experiment employs pulsed writing beams with orthogonal polarizations and a continuous-wave probe beam. Detection of the diffracted probe light is performed via a photon counting method. Methylene blue intercalated in DNA is used as the chromophore to create the gratings. TPG experiments performed on DNA molecules containing 200 base-pairs yield a relaxation time for tumbling that is in reasonable accord with prior work. This TPG experiment achieves a significant gain in signal-to-random-noise ratio over a direct photoinduced dicroism experiment, and eliminates an important source of systematic error that could significantly alter the tail of the decay curve, where bending and end-over-end tumbling dominate the relaxation. However, the proportionality constant between the diffracted signal and photo-induced dichroism in the sample is an additional unknown in the data analysis.
Techniques for neutron diffraction on solidified gases to 10 GPa and above: Applications to ND3 phase IV
Authors: Klotz S. , Gauthier M. , Besson J. M. , Hamel G. , Nelmes R. J. , Loveday J. S. , Wilson R. M. , Marshall W. G.
Published: July 2002

Neutron powder diffraction can provide important structural information on hydrogenous compounds which are gases at ambient temperature. For high pressure studies, however, this technique has been seriously limited by the fact that it was impossible (a) to load such gases in large volume devices and (b) to compress them to elevated pressures above some 1 GPa. In this letter we show that, using a previously described pressure cell, a wide range of gaseous samples may be loaded and compressed to ∼10 GPa with standard tungsten carbide anvils. We illustrate the effectiveness of the technique with neutron powder diffraction data recently collected on deuterated ammonia ND3 phase IV, where accurate structural data were obtained after a few hours collection time.
Estimation of the depth resolution of secondary ion mass spectrometry at the interface SiO2/Si
Authors: Kocanda J. , Fesič V. , Veselý M. , Breza J. , Kadlečíková M.
Published: July 2002

Similarities between the processes that occur during sputtering of monocrystalline Si by reactive O2+ primary ions and the interface SiO2/monocrystalline Si by noble gas ions (e.g., by Ar+) have motivated us to utilize the semiempirical model of P. C. Zalm and C. J. Vriezema [Nucl. Instrum. Methods B 67, 495 (1992)], modified later by M. Petravić, B. G. Svensson, and J. S. Williams [Appl. Phys. Lett. 62, 278 (1993)] to calculate the decay length λb, as defined by J. B. Clegg [Surf. Interface Anal. 10, 322 (1987)], at the SiO2/Si interface. The measured and calculated results agree remarkably well. Inconsistency observed to be larger than 100% for glancing incidence angles confirms limitations of this model that were admitted already by its authors.
High-performance InP/Ga0.47In0.53As/InP metal-semiconductor-metal photodetectors with a strained Al0.1In0.9P barrier enhancement layer
Authors: Chan P. T. , Choy H. S. , Shu C. , Hsu C. C.
Published: July 2002

A reduction in the dark current and an enhancement of the breakdown voltage have been observed in interdigitated InP/Ga0.47In0.53As/InP metal-semiconductor-metal photodetectors when a cap layer of Al0.1In0.9P was grown on the epitaxial structure to increase the Schottky barrier. The devices had a dc responsivity of 0.32 A/W and an intrinsic response faster than 74 ps.
Degradation studies of proton-implanted vertical cavity surface emitting lasers
Authors: Cheng Y. Michael , Herrick Robert W. , Petroff Pierre M. , Hibbs-Brenner Mary K. , Morgan Robert A.
Published: July 2002

We analyze the degradation process of proton-implanted, top-emitting vertical cavity surface emitting lasers using cross-sectional cathodoluminescence. The spatially resolved luminescence characteristics of the active regions, and p- and n-distributed Bragg reflector (DBR) mirrors before and after degradation of the devices are presented. Degradation has been observed not only in the active regions, but also remarkably in the p-DBR mirror stacks. We show that a significant minority carrier population is present in the p mirror under normal operating conditions to drive the degradation observed in the p mirror.
Rare earth optical temperature sensor
Authors: Chubb Donald L. , Wolford David S.
Published: July 2002

A new optical temperature sensor suitable for high temperatures (⩾1700 K) and harsh environments is introduced. The key component of the sensor is the rare earth material contained at the end of a sensor that is in contact with the sample being measured. The measured narrow wavelength band emission from the rare earth is used to deduce the sample temperature. A simplified relation between the temperature and measured radiation was verified experimentally. The upper temperature limit of the sensor is determined by material limits to be approximately 2000 °C. The lower limit, determined by the minimum detectable radiation, is found to be approximately 700 K. At high temperatures 1 K resolution is predicted. Also, millisecond response times are calculated.
Suppression of lateral diffusion of excitons in GaAs quantum wells under perpendicular magnetic fields
Authors: Akiyama Hidefumi , Sakaki Hiroyuki , Matsusue Toshio
Published: July 2002

We have performed lateral diffusion measurements of photo-excited electron-hole pairs in a GaAs/AlAs multiple quantum well structure under magnetic fields applied perpendicular to the wells, by using an all-optical time-of-flight technique with a single-mode optical fiber probe. Remarkable suppression of exciton diffusion is observed, and is ascribed to the magnetic perturbation by which moving excitons are affected proportionally to the square of wave vectors.
Growth and properties of submillimeter single grain Tl2Ba2Ca2Cu3O10+x superconducting thin films
Authors: Lin H. C. , Uen T. M. , Liu C. K. , Juang J. Y. , Wu K. H. , Gou Y. S.
Published: July 2002

Distinct crystalline superconducting grains of Tl2Ba2Ca2Cu3O10+x(Tl−2223) with sizes up to 150 μm×150 μm×1 μm were prepared by a single target dc-sputtering process followed by proper postannealing at temperatures around 910 °C. A reactive ion etching process was developed to pattern an ∼10 μm wide bridge with four contact leads directly on a single grain to study its superconducting transport properties. The etching process was found to have only minimal effect on the superconducting transition temperature Tc, which was typically around 110 K. Grains grown on MgO(100) and LaAlO3(100) substrates, although displaying somewhat different in-plane orientations, all had critical current densities Jc, well above 106 A/cm2 at 77 K. The existence of only one grain boundary, however, can reduce the Jc by orders of magnitude.
Temperature-dependent critical layer thickness for strained-layer heterostructures
Authors: Kim Keunjoo , Lee Young Hee
Published: July 2002

We systematically analyze the stress-strain-temperature relationships and include thermal strain contributions to the misfit-strain only formalism of strained-layer heterostructures. Application of this theory to the GexSi1−x/Si (100) and InxGa1−xAs/GaAs (100) system demonstrates that the thermal effect lowers the critical layer thickness significantly on both systems, in excellent agreement with experimentally measured values. Empirical formulae of the critical layer thickness in terms of a mole fraction and temperature for these systems are provided.