bluuebunny/crossref_metadata_2025 huggingface dataset:
High-temperature compressive plastic deformation of Nd2Fe14B single crystals
Authors: Kuhrt Ch. , Schultz L. , Schnitzke K. , Hock S. , Behrensmeier R.
Published: July 2002

The compressive deformation behavior of Nd2Fe14B single crystals at temperatures between 900 and 1100 °C has been investigated. Considerable ductility occurs only at temperatures above 1000 °C, suggesting that the plasticity of the Nd2Fe14B phase has very little effect on the formation of texture during die-upsetting of microcrystalline Nd-Fe-B hard magnetic alloys.
Normal incidence hole intersubband absorption long wavelength GaAs/AlxGa1−xAs quantum well infrared photodetectors
Authors: Levine B. F. , Gunapala S. D. , Kuo J. M. , Pei S. S. , Hui S.
Published: July 2002

The first long wavelength quantum well infrared photodetector based on valence band intersubband absorption holes is demonstrated. A normal incidence quantum efficiency of η=28% and detectivity of D*λ=3.1×1010 cm √Hz/W at T=77 K, for a cutoff wavelength λc=7.9 μm, have been achieved.
Novel CH4/H2 metalorganic reactive ion etching of Hg1−xCdxTe
Authors: Semu Allen , Montelius Lars , Leech Patrick , Jamieson David , Silverberg Per
Published: July 2002

We have for the first time shown that CH4/H2 metalorganic reactive ion etching (MORIE) of Hg1−xCdxTe is feasible for mesa-etching to dimensions less than 2 μm. Process parametric effects on etch rate, surface anisotropy, and surface stoichiometry were studied with particular emphasis on the methane to hydrogen MORIE process ratio as well as Hg1−xCdxTe alloy composition. A laser interferometric detection scheme was employed for in situ measurement of etch rates as well as for end-point detection. A self-induced etch-stop mechanism for certain etch-gas compositions is also demonstrated.
Stereo laser micromachining of silicon
Authors: Bloomstein T. M. , Ehrlich D. J.
Published: July 2002

A technique has been developed for 1-μm resolution, high speed micromachining of three-dimensional (3D) silicon parts. The method, based on acousto-optic deflection of laser microchemical chlorine etching reactions, creates parts directly from a file generated with computer-aided design/computer-aided manufacturing (CAD/CAM) software. In this demonstration, 1-μm3 pixels are removed at a rate of 2×104 pixels/s. The laser-driven process relies on one of the fastest-known sustained gas/solid interface reactions, and the size- and pressure-scaling laws permit micromachining at ≳2×105 μm3/s at 10-μm resolution. This is ∼3000 times the rate of current electrodischarge matching methods. Exchange of the etchant gas for organometallic vapor precursors has permitted laser deposition of 3D platinum and cobalt metallization on the laser-etched structures. It is proposed that this approach can satisfy the need for primary patterning of 3D parts and molds for micromechanics, in analogy with two-dimensional (2D) electron-beam patterning of masks for microelectronics.
Epitaxial growth and properties of YBa2Cu3Ox-Pb(Zr0.6Ti0.4)O3-YBa2Cu3Ox trilayer structure by laser ablation
Authors: Boikov Yu. A. , Esayan S. K. , Ivanov Z. G. , Brorsson G. , Claeson T. , Lee J. , Safari A.
Published: July 2002

We have grown YBa2Cu3Ox-Pb(Zr0.6Ti0.4)O3-YBa2Cu3Ox multilayer structure on SrTiO3 and Al2O3 substrates using laser ablation. The deposition conditions for the growth of trilayers and their properties are studied in this investigation. Scanning electron microscope images and x-ray diffraction analyses indicate that all the constituent films in the trilayer grow epitaxially on SrTiO3 and were highly oriented on Al2O3. Transport measurements on these multilayers show that top YBa2Cu3Ox films have good superconducting properties.
Determination of the residual stress tensor in Cu/W multilayers by x-ray diffraction
Authors: Goudeau Ph. , Badawi K. F. , Naudon A. , Gladyszewski G.
Published: July 2002

A direct determination of the residual stress tensor in Cu/W multilayers has been performed by x-ray diffraction using the ‘‘sin2 ψ’’ method. In tungsten sublayers, we found a compressive and isotropic stress in the plane parallel to the multilayer surface of a very high value equal to −6.4 GPa. Furthermore, using stress-strain relations, the tungsten lattice structure resulting from strains is calculated: the strained W bcc structure is found to be similar to a monoclinic-like structure leading to important modifications of the diffraction pattern.
Synthesis of diamond from methane and nitrogen mixture
Authors: Badzian Andrzej , Badzian Teresa , Lee S.-Tong
Published: July 2002

We have found that diamond can be synthesized from a mixture of CH4 and N2 without adding any H2. This new synthesis is sharply different from the common practice of diamond growth by chemical vapor deposition, which uses a hydrogen-rich mixture of CH4 and H2. In this new approach, nitrogen becomes an active component of microwave plasma leading to diamond growth. Nitrogen participates in abstraction of hydrogen from the diamond surface. We hypothesize that formation of HCN is an indication of hydrogen abstraction that allows diamond to grow from CH4+N2 mixtures. As a consequence of surface processes, the crystal structure of the grown diamond is distorted. The sequence of tetrahedral layers is mixed (cubic and hexagonal) and it suffers from turbostatic disorder. Diamond films were characterized by x-ray diffraction, Auger electron spectroscopy, x-ray photoelectron spectroscopy, and Raman spectroscopy.
Influence of electric and magnetic fields on THz radiation
Authors: Zhang X.-C. , Jin Y. , Kingsley L. E. , Weiner M.
Published: July 2002

We report measurement of the influence of electric and magnetic fields on optically induced THz electromagnetic radiation from semiconductors at normal incidence. The measurements show that electric and magnetic fields strongly influence the amplitude and phase of transient carrier-generated THz radiation, but do not affect THz optical rectification generated by the bulk second order nonlinear susceptibility, for static electric fields up to 104 V/cm.
Misfit dislocation microstructure and kinetics for InxGa1−xAs/InP(100) and (110) interfaces under tensile and compressive stress
Authors: Hull R. , Logan R. A. , Weir B. E. , Vandenberg J. M.
Published: July 2002

Misfit dislocation microstructures and strain relaxation kinetics are studied for 1% lattice mismatched (100) and (110) interfaces under tensile and compressive stress in the InxGa1−xAs/InP system. Misfit dislocations are observed to be either 60° a/2〈101〉 total [for (100) compressive and (110) tensile configurations] or 90° a/6〈112〉 partial [dominant for (100) tensile and (110) compressive configurations] types. Relaxation kinetics are observed to be substantially faster for 90° a/6〈112〉 than 60° a/2〈101〉 dislocations. This produces significantly different relaxation rates for (100) versus (110) interfaces and compressive versus tensile stress. The relaxation is also found to be an extremely strong function of excess stress, with an increase of about two orders of magnitude of dislocation density per 100 MPa increase in excess stress for interfacial dislocation densities in the range 102–106 cm−1.
Thermal stability of the unstable fcc-Fe50Cu50 phase prepared by mechanical alloying
Authors: Jiang J. Z. , Gonser U. , Gente C. , Bormann R.
Published: July 2002

An unstable fcc-Fe50Cu50 alloy has been prepared by milling of elemental powder blends. The structure and the decomposition behavior of the alloy were studied by x-ray diffraction and Mössbauer spectroscopy. A broad distribution of different local environments of the iron atoms was observed in the fcc-FeCu phase. This indicates that Fe and Cu are mixed on an atomic level. In the initial state of decomposition, iron atoms precipitated coherently in the fcc-FeCu matrix as fcc-Fe particles. At higher annealing temperatures the particle size increased during the thermal treatment, and the fcc-Fe precipitates transformed into the bcc-Fe structure.
In surface segregation and growth-mode transition during InGaAs growth by molecular-beam epitaxy
Authors: Toyoshima H. , Niwa T. , Yamazaki J. , Okamoto A.
Published: July 2002

An In surface segregation effect during the growth of InGaAs on GaAs by molecular-beam epitaxy has been studied by reflection high-energy electron diffraction measurements supported by a segregation model. Indium atoms segregate at a ratio of more than 0.8 under the conventional growth conditions for InGaAs, which causes the formation of accumulated In atoms on the surface. The transition from two-dimensional to three-dimensional growth occurs when the amount of In reaches around 1.7 monolayer with a nominal alloy composition greater than 0.25. This transition determines the upper limit on the In composition of the InGaAs layer for application as an electron channel in modulation-doped field-effect transistors.
Dislocation generation mechanisms for GaP on Si grown by metalorganic chemical vapor deposition
Authors: Soga Tetsuo , Jimbo Takashi , Umeno Masayoshi
Published: July 2002

Dislocation generation mechanisms for GaP on Si substrates by metalorganic chemical vapor deposition are described. Dislocations are not observed at the GaP/Si interface when the layer thickness is less than 90 nm. The presented high resolution transmission electron microscopy shows two kinds of dislocations with the extra-half plane in the GaP layer and Si substrate. These observations predict that the misfit dislocations are formed at the growth temperature while the dislocations with the extra-half plane in the GaP layer are formed during the cooling process, owing to the difference of the thermal expansion.
Vanishing Freedericksz transition threshold voltage in a chiral nematic liquid crystal
Authors: Crandall Karl A. , Fisch Michael R. , Petschek Rolfe G. , Rosenblatt Charles
Published: July 2002

A negative dielectric anisotropy cholesteric liquid crystal, oriented homeotropically in a wedged capacitance cell, was subjected to an applied electric field. The Freedericksz transition threshold voltage was found to depend on the local thickness of the sample, and was found to vanish at a thickness of order 3/2 P, where P is the pitch of the cholesteric in the bulk. The results are consistent with a continuum elastic theory. A discussion of the technological ramifications is presented.
Correlation between x-ray diffraction patterns and strain distribution inside GaInP/GaAs superlattices
Authors: He X. G. , Erdtmann M. , Williams R. , Kim S. , Razeghi M.
Published: July 2002

Strong correlation between x-ray diffraction characteristics and strain distribution inside GaInP/GaAs superlattices has been reported. It is found that the symmetry of (002) diffraction patterns can be used to evaluate the interface strain status. A sample with no interfacial strains has a symmetric (002) diffraction pattern and weak (004) diffraction pattern. It is also demonstrated that strain distribution in superlattices can be readily estimated qualitatively by analyzing x-ray diffraction patterns.
High-efficiency, all-solid-state exciters for high-repetition-rated, high-power TEA CO2 lasers
Authors: Tanaka Hiroshi , Hatanaka Hidekazu , Obara Minoru , Midorikawa Katsumi , Tashiro Hideo
Published: July 2002

We have developed two high-efficiency, all-solid-state exciters for pumping TEA CO2 lasers, and experimentally proved their energy scalability, high-efficiency operation, and high repetition rate operation. The small-scale all-solid-state exciter of the two-stage magnetic pulse compressor was operated with an output transfer energy of 8.8 J/pulse and energy transfer efficiency of 78%, and the average CO2 laser power of 117 W was obtained at 250 pps using this exciter. The larger all-solid-state exciter of three-stage magnetic pulse compressor is ten times as large as the small one, and operated with an output transfer energy of 95 J/pulse and an energy transfer efficiency of 84%. With the larger exciter, a CO2 laser output of 9.1 J/pulse was obtained with a total laser efficiency of 8.1%. As a result, the scalability of the exciter for the CO2 laser has been demonstrated.
In situ sensitive measurement of stress in thin films
Authors: Leusink G. J. , Oosterlaken T. G. M. , Janssen G. C. A. M. , Radelaar S.
Published: July 2002

A method for the in situ measurement of mechanical stress in thin films deposited in a vacuum system is presented. The bending of the substrate, a measure for mechanical stress in the deposited layer, is detected by reflecting two parallel laser beams off the surface of the substrate and measuring the angle between the two reflected beams. A hollow mirror in the path of the reflected beams acts as an ‘‘optical cantilever’’ and increases the sensitivity of this method. In the present setup it is possible to detect the difference between a flat substrate and a substrate with a radius of curvature of 6.5 km.
Experiment with a biased disk at the K.V.I. ECRIS
Authors: Gammino S. , Sijbring J. , Drentje A. G.
Published: July 2002

Some measurements have been done on the source ECRIS 1 at K.V.I., showing the beneficial effect to the output currents when a biased disk is positioned in the first stage, as reported by the Grenoble ECRIS group. The increase is in the order of 40% and it can be explained by the enrichment of the electron density in the plasma. Different saturation voltages for different charge states tend to confirm this explanation, suggesting new experiments, as, for example, the substitution of the first stage by an electron gun.
A high-energy spherical grating monochromator for soft x rays at the Daresbury SRS
Authors: Surman M. , Cragg-Hine I. , Singh J. , Bowler B. J. , Padmore H. A. , Norman D. , Johnson A. L. , Walter W. K. , King D. A. , Davis R. , Purcell K. G. , Thornton G.
Published: July 2002

A vertically dispersing high-energy spherical grating monochromator (HESGM) has been installed on the synchrotron radiation source (SRS) at the Daresbury Laboratory. The instrument has no entrance slit and provides a high intensity source of x rays of energy 250–1400 eV focused into a small spot suitable for surface spectroscopy. Photoabsorption features of 240 meV have been resolved, but the resolution of the instrument is dependent on the SRS stored beam current. The degree of linear polarization has been measured at the carbon K edge to be 0.80.
Results from the low-power 60 GHz gyrotron collective Thomson scattering diagnostic on TFTR
Authors: Machuzak John S. , Woskov Paul P. , Gilmore James , Bretz Norton L. , Park Hyeon K. , Bindslev Henrik
Published: July 2002

A low-power 60 GHz gyrotron collective Thomson scattering diagnostic has been operating on TFTR to test the feasibility of detecting alpha particles when scattering perpendicular to the magnetic field. An enhanced scattered signal is predicted to result from the interaction of the energetic ions with plasma resonances in the lower hybrid frequency range. Millimeter-wave power levels at the plasma were approximately 200 W for typical pulse lengths of 50 ms. Deuterium and possible fusion product ion cyclotron frequencies and their harmonics were observed during neutral beam heating. These spectra are similar to ion cyclotron emission spectra which are detected with radio-frequency probes on TFTR at the plasma edge. Also, ion cyclotron resonance heating fundamental and harmonic fluctuations were observed. However, a signal has not been definitively detected in the lower hybrid frequency range which correlates to alpha particles. Broadband noise was observed during neutral beam heating which is greater than the predicted alpha particle signal.
Analysis of x-ray spectra obtained in foam Z-pinch experiments
Authors: MacFarlane J. J. , Wang P. , Nash T. J. , Derzon M. S. , Allshouse G. A. , Deeney C.
Published: July 2002

Foam Z-pinch experiments have recently been performed on SATURN to study issues associated with the initiation, acceleration, and stagnation phases of the pinch. Time-integrated x-ray crystal spectra have been recorded from experiments with 5 mg/cc Si aerogel loads and 10 mg/cc agar loads. In this article, we describe results from collisional-radiative equilibrium calculations performed to analyze the Si, Na, and S K-shell emission observed in the spectra. Particular attention is paid to density and opacity effects on intensity ratios involving Heα, He intercombination, and Li-like satellite lines.
Theoretical aspects of the use of pulsed reflectometry in a spheromak plasma
Authors: Cohen Bruce I. , Hooper E. Bickford , Spang M. C. , Domier C. W.
Published: July 2002

Pulsed reflectometry using both ordinary (O) and extraordinary (X) modes has the potential of providing time- and space-resolved measurements of the electron density, the magnitude of the magnetic field, and the magnetic shear as a function of radius. Such a diagnostic also yields the current profile from the curl of the magnetic field. This research addresses theoretical issues associated with the use of reflectometry in the Sustained Spheromak Physics Experiment spheromak experiment at the Lawrence Livermore National Laboratory. We have extended a reflectometry simulation model to accommodate O- and X-mode mixed polarization and linear mode conversion between the two polarizations. A Wentzel–Kramers–Brillouin–Jeffreys (WKBJ) formula for linear mode conversion agrees reasonably well with direct numerical solutions of the wave equation, and we have reconstructed the magnetic pitch–angle profile by matching the results of the WKBJ formula with the mode conversion data observed in simulations using a least-squares determination of coefficients in trial functions for the profile. The reflectometry data also yield information on fluctuations. Instrumental issues, e.g., the effects of microwave mixers and filters on model reflectometry pulses, have been examined to optimize the performance of the reflectometry diagnostics.
A versatile electron detector for studies on ion-surface scattering
Authors: Lemell C. , Stöckl J. , Winter HP. , Aumayr F.
Published: July 2002

An innovative electron detector geometry for measuring electron multiplicities and absolute total electron yields from particle-induced electron emission is described. This setup has been successfully applied in coincidence measurements of slow singly and multiply charged ion-induced electron emission from a clean monocrystalline gold surface at grazing incidence of projectile ions. We describe characteristic features and operation of the electron detector which may also prove useful in various other experimental situations.
Practical aspects of Kelvin probe force microscopy
Authors: Jacobs H. O. , Knapp H. F. , Stemmer A.
Published: July 2002

We discuss practical aspects of Kelvin probe force microscopy (KFM) which are important to obtain stable images of the electric surface potential distribution at high spatial resolution (<100 nm) and high potential sensitivity (<1 mV) on conducting and nonconducting samples. We compare metal-coated and semiconducting tips with respect to their suitability for KFM. Components of the metal coating can become detached during scanning, introducing sudden offset jumps in the potential maps (typically up to 350 mV between adjacent scan lines). However, n-doped silicon tips show no substantial tip alterations and, therefore, provide a stable reference during the experiment (offset jumps typically up to 40 mV between adjacent scan lines). These semiconducting tips must be electrically connected via contact pads. We use InGa and colloidal silver pads which are easily applied to the substrate supporting the cantilever and have a low enough differential contact resistance (350 Ω and 2.2 kΩ, respectively). Furthermore, we introduce a simple procedure to fine tune the feedback which detects the electric surface potential and show how the basic KFM setup has to be modified to gain access to the necessary control signals.
Investigation of different oven types for sample evaporation in the CAPRICE electron cyclotron resonance ion source
Authors: Lang R. , Bossler J. , Schulte H. , Tinschert K.
Published: July 2002

The operation of the CAPRICE-type electron cyclotron resonance ion source (ECRIS) at the high charge state injector of GSI requires a great variety of different ion species (between Z=3 and Z=92) to be delivered to the accelerator. As most of the elements have to be produced from nongaseous materials, oven evaporation has become an elaborate and routinely used technique at GSI. Besides an evaporator for high vapor pressure materials (T⩽300 °C) a standard oven system is used for temperatures between 600 °C and 1500 °C. Several modifications of this standard oven have been developed to adapt it to the operating conditions for different materials. The respective characteristics are described and operational experiences are reported. In order to extend the available temperature regime up to 2000 °C, a new type of oven is being developed which completely avoids any ceramics in its high temperature zone. Thus the number of materials accessible for evaporation is considerably extended. First experiences obtained with this high temperature oven are presented.
Structural characterization of aluminum films deposited on sputtered-titanium nitride/silicon substrate by metalorganic chemical vapor deposition from dimethylethylamine alane
Authors: Li Xiaodong , Kim Byoung-Youp , Rhee Shi-Woo
Published: July 2002

Al films deposited on sputtered-TiN/Si substrate by metalorganic chemical vapor deposition (MOCVD) from dimethylethylamine alane (DMEAA) were characterized using x-ray diffraction (XRD), Auger electron spectroscopy (AES), atomic force microscopy (AFM), and transmission electron microscopy (TEM). The TiN film sputtered on the Si has a preferred orientation along the growth direction with the 〈111〉 of the film parallel to the Si〈111〉. Sputtering of the TiN film on the Si induced strains at the interface. The TiN/Si interface is flat while the Al/TiN interface is rough. There exist many dislocations at the Al/TiN interface. The Al2O3 phase was formed at the Al/TiN interface during the early stages of Al deposition. In the Al grains, there exist many tangled dislocations and a few Al2O3 particles. With increasing deposition time, the Al film surface roughness increases.
Slowing the oxidation of Cu in Cu–Co nanocrystals by Co surface passivation
Authors: Kaatz F. H. , Harris V. G. , Kurihara L. , Rolison D. R. , Edelstein A. S.
Published: July 2002

Heating chemically prepared nanocrystals of Cu80Co20 causes Co to precipitate preferentially on the surface of the Cu nanocrystals. X-ray diffraction and x-ray photoelectron spectroscopies show that the Co significantly retards the oxidation of the Cu nanocrystals.
Properties of Schottky contact of Al on SiGe alloys
Authors: Jiang R. L. , Liu J. L. , Li J. , Shi Y. , Zheng Y. D.
Published: July 2002

Electrical properties of Schottky contacts of Al on p-Si1−xGex alloys were investigated. The Si1−xGex strained layers were grown on p-Si substrates by using rapid thermal process/very low pressure-chemical vapor deposition. Low reverse currents were obtained. It was found that the Schottky barrier height of Al/p-Si1−xGex contacts decreased with increasing Ge fraction. The decrement is in accordance with the decrement of the band gap of the strained Si1−xGex. The Fermi level at the interface is pinned at about 0.43 eV below the conduction band. The influence of strain relaxation for SiGe alloy layers and the Si sacrificial cap layers on the properties of Schottky contacts were also investigated.
Large-area double-side pulsed laser deposition of YBa2Cu3O7−x thin films on 3-in. sapphire wafers
Authors: Lorenz M. , Hochmuth H. , Natusch D. , Börner H. , Lippold G. , Kreher K. , Schmitz W.
Published: July 2002

A pulsed laser deposition (PLD) technique for YBa2Cu3O7−x (YBCO) thin films with CeO2 buffer layers and gold contact films on both sides of 3-in. diameter sapphire wafers, which are applied for microwave strip-line filters, is described and some results of structural and compositional characterization are given. This large-area multilayer PLD technique allows for a homogeneous and reproducible YBCO deposition on both wafer sides with inductively measured critical current densities of 3×106–5×106 A/cm2 at 77 K with a YBCO thickness of 350–500 nm. The results indicate that PLD seems to have unique capabilities for fast deposition of high-quality large area oxide multilayers.
Imprint of (Pb,La)(Zr,Ti)O3 thin films with various crystalline qualities
Authors: Lee J. , Ramesh R.
Published: July 2002

(Pb,La)(Zr,Ti)O3 (PLZT) thin films with various crystalline qualities, i.e., epitaxial, oriented, and polycrystalline, have been grow. These PLZT thin films cooled at various oxygen cooling pressures were found to have different asymmetric switching and imprint behaviors, depending on the crystalline quality of the PLZT thin films. It was found that the initial polarization state of as-grown PLZT thin films is an important indicator to determine further imprint behavior. Epitaxial PLZT thin-film capacitors were prepolarized in an as-grown state and further exhibited the large dependence of asymmetric switching and imprint behavior on the oxygen cooling pressure. On the other hand, oriented or polycrystalline PLZT capacitors exhibited very weak polarization and little dependence of the initial prepolarization state on the oxygen cooling pressure. Consequently, the PLZT capacitors containing polycrystalline nature had a strong resistance to the imprint failure.
Leakage current and electrical breakdown in metal-organic chemical vapor deposited TiO2 dielectrics on silicon substrates
Authors: Kim Hyeon-Seag , Gilmer D. C. , Campbell S. A. , Polla D. L.
Published: July 2002

The leakage current through 190 Å TiO2 deposited through metal-organic chemical vapor deposition on p-type silicon substrates has been measured as a function of temperature for both accumulation and inversion biases. When biased into inversion, the current initially is temperature independent, suggesting that the current in this regime is dominated by tunneling. Above 100 °C however it shows standard thermionic emission behavior up to 160 °C where it again becomes temperature independent. The leakage under accumulation bias was independent of temperature up to 70 °C while it shows standard thermionic emission behavior. The barrier for emission was between 0.94 and 1.0 eV for all samples measured. Both ramped voltage and time dependent dielectric breakdown measurements were carried out on these films. The lack of a breakdown event in constant current stress suggests that these films may be extremely robust as gate dielectrics in future metal-oxide-semiconductor field-effect transistors.
Surface lifetimes of Ga and growth behavior on GaN (0001) surfaces during molecular beam epitaxy
Authors: Guha S. , Bojarczuk N. A. , Kisker D. W.
Published: July 2002

We report a study of the desorption behavior of Ga on the GaN(0001) surface and the growth behavior of GaN during molecular beam epitaxy. A desorption activation energy of 2.2±0.2 eV is measured for Ga adatoms. Porous columnar features in the GaN microstructure are observed that are enhanced by higher growth temperatures and eliminated by growing Mg or Si doped GaN. We propose a model for this observation.
Derivation of simplified analytic formulae for magneto-optical Kerr effects
Authors: You Chun-Yeol , Shin Sung-Chul
Published: July 2002

We have derived simplified analytic expressions for various magneto-optical Kerr effects of an optically thick medium having an arbitrary magnetization direction. We have found that the simplified formulae for the Kerr effects of p and s waves consisted of a product of two factors: the prefactor dependent pure optical parameters of the system and the main factor of the polar Kerr effect for a normal incidence case. The measured magneto-optic polar Kerr rotation angles of Co/Pd multilayers and the longitudinal Kerr rotation angles of Cu/Co multilayers with varying incident angles could be well fitted using the simplified analytical formulae.
Room temperature electroluminescence from dislocation-rich silicon
Authors: Sveinbjörnsson Einar Ö. , Weber Jörg
Published: July 2002

We report on electroluminescence at room temperature from forward biased n+–p silicon diodes containing high densities (108–109 cm−2) of dislocations at the junction interface. In addition to electroluminescence from band-to-band transitions, we observe a signal with a comparable intensity peaked at ∼1.6 μm (0.78 eV). From luminescence studies below room temperature we deduce that the 1.6 μm emission originates from the well known dislocation-related center D1. The D1 electroluminescence intensity at room temperature increases linearly with current density with no observable saturation. The external efficiency of the D1 electroluminescence at room temperature was estimated to be of the order 10−6.
Diamond-like carbon films grown by very high frequency (100 MHz) plasma enhanced chemical vapor deposition technique
Authors: Kumar Sushil , Dixit P. N. , Sarangi D. , Bhattacharyya R.
Published: July 2002

Diamond-like carbon films were grown by VHF-PECVD technique. Since the self-bias potential developed in a VHF plasma is very low, sufficiently high negative dc voltage was applied to the substrates in order to make DLC film being grown reasonably hard. Also a comparative study of VHF grown films was made with rf (13.56 MHz) discharge grown films (grown in the same PECVD reactor). This made it possible to investigate the specific effects of excitation fre- quency while keeping other parameters constant. Deposition rate (rd) was found to be about 5 times higher for VHF grown films. Marginal variation in optical band gap (Eg) and refractive index (n) were observed in VHF grown films with variation in deposition parameters. Maximum value of hardness recorded was 1500 kg/mm2 in the case of rf and 902 kg/mm2 in the case of VHF grown films, within the range of deposition parameters. Stress values were in the range 1.7×109−2.9×109 Nm−2 for VHF and 3.6×109−4.6×109 Nm−2 for rf grown films.
Theory of composite BxCyNz nanotube heterojunctions
Authors: Blase X. , Charlier J.-C. , De Vita A. , Car R.
Published: July 2002

The stability and electronic properties of composite BxCyNznanotube heterojunctions were studied using both ab initio and semi-empirical approaches. C/BN and BC2N/BN superlattices or isolated junctions were investigated as specific examples of the wide variety of electronic devices that can be realized using such nanotubes. The characteristics of these junctions are predicted to be largely independent of the radius, helicity, multiplicity, or degree of perfection of the constituting nanotubes.
Perpendicular giant magnetoresistance of NiFe/Cu multilayered nanowires
Authors: Dubois S. , Marchal C. , Beuken J. M. , Piraux L. , Duvail J. L. , Fert A. , George J. M. , Maurice J. L.
Published: July 2002

We have prepared by electrodeposition Ni80Fe20/Cu multilayered nanowires into the pores of polymer membranes and performed giant magnetoresistance (GMR) measurements in the current perpendicular to the layer planes geometry. GMR ratios as high as 80% have been obtained at 4.2 K. Two types of structure have been studied: conventional Ni80Fe20/Cu multilayers and multilayers composed of Ni80Fe20/Cu/Ni80Fe20 trilayers magnetically isolated by long Cu rods.
Refrigeration of a dielectric membrane by superconductor/insulator/normal-metal/insulator/superconductor tunneling
Authors: Manninen A. J. , Leivo M. M. , Pekola J. P.
Published: July 2002

We have applied tunneling of electrons between a normal metal and a superconductor to refrigerate a thin dielectric membrane attached to the normal electrode of a superconductor/ insulator/normal-metal/insulator/superconductor (SINIS) structure. Starting from T≈200 mK, a decrease in temperature of several mK was observed, measured by a separate thermometer on the membrane. It should be straightforward to improve the refrigerator performance to the level of the recently demonstrated SINIS electron cooling method, such that the drop in the lattice temperature would be more than an order of magnitude larger.
Ordering temperatures in Cu–Al–Ni shape memory alloys
Authors: Recarte V. , Lambri O. A. , Pérez-Sáez R. B. , Nó M. L. , San Juan J.
Published: July 2002

The ordering temperatures Tc1 (disordered β to B2 order) and Tc2 (B2 to L21 order) have been obtained in Cu–Al–Ni shape memory alloys with different concentrations by electrical resistivity. The dependence of the ordering temperatures on the concentration has been established. Also, a modification of the theoretical calculations has been proposed to predict the ordering temperatures in Cu–Al–Ni ternary alloys. A good agreement between the theoretical ordering temperatures and the experimental results has been found.
Photostimulated luminescence of Ce3+-doped alkali borate glasses
Authors: Qiu Jianrong , Shimizugawa Y. , Iwabuchi Y. , Hirao K.
Published: July 2002

Photostimulated luminescence phenomena have been observed in Ce3+-doped alkali borate glasses prepared under a reducing atmosphere. When the x-ray irradiated glasses were excited by a He–Ne laser (633 nm), photostimulated luminescence at about 360 nm due to the 5d–4f transition of Ce3+ ions was observed. The intensity of photostimulated luminescence of the Ce3+-doped alkali borate glasses increased in the order of lithium borate<sodium borate<potassium borate. The luminescence appears to result from the photostimulated recombination of hole and electron traps which leave electrons in a long-lived excited state.
Plastic behavior of nanophase Ni: A molecular dynamics computer simulation
Authors: Van Swygenhoven H. , Caro A.
Published: July 2002

We report molecular dynamics computer simulations of low temperature-high load plastic deformation of Ni nanophase samples with several mean grain sizes in the range of 3–5 nm. The samples are polycrystals nucleated from different seeds, with random location and orientation. Among the mechanisms responsible for the deformation, grain boundary sliding and motion, as well as grain rotation are identified. No dislocation activity is detected, in contrast to the behavior of coarse grain metals. Interpreting the results in terms of grain boundary viscosity, a linear dependence of strain rate with the inverse of the grain size is obtained.
In-situ observations of classical grain growth mechanisms during sintering of copper nanoparticles on (001) copper
Authors: Yeadon M. , Yang J. C. , Averback R. S. , Bullard J. W. , Olynick D. L. , Gibson J. M.
Published: July 2002

The sintering of randomly oriented copper nanoparticles in the size range 4–20 nm with a single crystal (001) copper substrate has been studied in real time using a novel in situ ultrahigh vacuum (UHV) transmission electron microscope. The particles were generated in situ using an UHV DC sputtering attachment and deposited directly onto an electron transparent copper foil inside the microscope. We demonstrate that these particles reorient upon heating to assume the same orientation as the substrate by a classical mechanism involving neck growth and grain boundary motion.
Low noise p-π-n GaN ultraviolet photodetectors
Authors: Osinsky A. , Gangopadhyay S. , Gaska R. , Williams B. , Khan M. A. , Kuksenkov D. , Temkin H.
Published: July 2002

We report on the fabrication and characterization of p-π-n GaN ultraviolet detectors. The peak responsivity at ∼363  nm is measured to be 0.1 A/W in the photovoltaic mode, and 0.14 A/W with a bias of −15 V. Speed measurements have shown the photoresponse to be RC-limited with the response time decreasing from 17.4 ns at zero bias to 10.3 ns at −6 V bias. For a 200×200 μ m2 device, we measure the dark current to be 2.7 pA at −3 V bias, and a noise density of less than 10−25 A2/Hz, the noise floor of the measurement. Extrapolating the noise data taken at higher reverse biases, we estimate the noise equivalent power to be 6.6×10−15 W/Hz1/2.
Multimodal impurity redistribution and nanocluster formation in Ge implanted silicon dioxide films
Authors: von Borany J. , Grötzschel R. , Heinig K. H. , Markwitz A. , Matz W. , Schmidt B. , Skorupa W.
Published: July 2002

The depth distribution of Ge implanted into thermally grown SiO2 films has been studied after annealing using transmission electron microscopy, Rutherford backscattering spectrometry, and x-ray diffraction. At annealing temperatures above 900 °C a significant redistribution of the as-implanted Ge profile was found. Crystalline Ge nanoclusters embedded in the SiO2 matrix are formed within a cluster band with well defined boundaries. The evolution of nanoclusters can be explained qualitatively by a model based on nucleation, growth and Ostwald ripening of Ge precipitates. Besides, chemical and interface reactions lead to the formation of additional Ge peaks near the surface and at the Si/SiO2 interface.
Piezoresistive effect in GaN–AlN–GaN structures
Authors: Gaska R. , Yang J. W. , Bykhovski A. D. , Shur M. S. , Kaminskii V. V. , Soloviov S.
Published: July 2002

We report on a high sensitivity of GaN–AlN–GaN semiconductor–insulator–semiconductor structures grown on sapphire to an applied strain. The measured static gauge factor (GF) is almost twice as large as the GF for n-type SiC films. We link the observed magnitude and sign of the gauge factor to the crystalline structure of the GaN and AlN films and to their piezoelectric constants. We show that even higher sensitivity can be achieved if the material and interface quality is improved.
Stabilization of cubic CrN0.6 in CrN0.6/TiN superlattices
Authors: Yashar P. , Chu X. , Barnett S. A. , Rechner J. , Wang Y. Y. , Wong M. S. , Sproul W. D.
Published: July 2002

A transmission electron microscopy study of CrN0.6/TiN superlattices deposited by reactive magnetron sputtering is described. The stable structure of CrN0.60 is hexagonal, but high resolution transmission electron microscopy images of the superlattices showed that CrN0.6 layers ⩽10 nm thick were cubic, while 50 nm thick layers were hexagonal. That is, the cubic CrN structure was “epitaxially stabilized” by the cubic TiN, with which there is a 2.4% lattice mismatch. The superlattices with hexagonal CrN0.6 showed high strains and defect densities within ≈5 nm of each interface, presumably due to the 5.4% volume decrease associated with the cubic-to-hexagonal transformation. The effect of this strain on the transformation is discussed.
Perpendicular coupling at Fe–FeF2 interfaces
Authors: Moran T. J. , Nogués J. , Lederman D. , Schuller Ivan K.
Published: July 2002

We have studied the exchange anisotropy of ferromagnetic Fe films grown on antiferromagnetic FeF2 single crystals. The behavior of the hysteresis loops of the Fe above and below the Néel temperature TN of FeF2 indicates a 90° rotation of the ferromagnetic easy axis due to the antiferromagnetic ordering. By examining the Fe hysteresis loops together with the FeF2 susceptibility behavior we infer that below TN the ferromagnetic and antiferromagnetic spins are coupled perpendicular to each other. This behavior can be explained by recent micromagnetic calculations on exchange bias systems, or by magnetoelastic effects.
1.3 μm InGaAsP/InP lasers on GaAs substrate fabricated by the surface activated wafer bonding method at room temperature
Authors: Chung TaekRyong , Hosoda Naoe , Suga Tadatomo , Takagi Hideki
Published: July 2002

InGaAsP/InP strained-layer quantum well ridge waveguide lasers of 1.3 μm have been successfully bonded to a GaAs substrate by surface activated wafer direct bonding at room temperature. In this method, the surfaces of two wafers are activated by Ar fast atom beam irradiation and joined under high vacuum conditions. In most cases a high bonding strength was attained. No microcracks and voids were observed by transmission electron microscopy at the bonded interface. A low threshold current density of about 500 A/cm2 has been achieved. This technique is very promising to realize monolithic integration of optoelectronic integrated circuits for optical communication and interconnections.
Controlling threading dislocation densities in Ge on Si using graded SiGe layers and chemical-mechanical polishing
Authors: Currie M. T. , Samavedam S. B. , Langdo T. A. , Leitz C. W. , Fitzgerald E. A.
Published: July 2002

A method of controlling threading dislocation densities in Ge on Si involving graded SiGe layers and chemical-mechanical polishing (CMP) is presented. This method has allowed us to grow a relaxed graded buffer to 100% Ge without the increase in threading dislocation density normally observed in thick graded structures. This sample has been characterized by transmission electron microscopy, etch-pit density, atomic force microscopy, Nomarski optical microscopy, and triple-axis x-ray diffraction. Compared to other relaxed graded buffers in which CMP was not implemented, this sample exhibits improvements in threading dislocation density and surface roughness. We have also made process modifications in order to eliminate particles due to gas-phase nucleation and cracks due to thermal mismatch strain. We have achieved relaxed Ge on Si with a threading dislocation density of 2.1×106 cm−2, and we expect that further process refinements will lead to lower threading dislocation densities on the order of bulk Ge substrates.
Oxygen vacancy mobility determined from current measurements in thin Ba0.5Sr0.5TiO3 films
Authors: Zafar Sufi , Jones Robert E. , Jiang Bo , White Bruce , Chu Peir , Taylor D. , Gillespie Sherry
Published: July 2002

The current density is measured as a function of time for thin (⩽1000 Å) barium strontium titanate (BST) capacitors with platinum electrodes. The current density curve shows a peak prior to the onset of resistance degradation. The peak position on the time axis varies with applied voltage and temperature. The data are explained by the theory for space-charge-limited (SCL) current transients, and the measured current is identified as ionic current associated with oxygen vacancies. Using the SCL analysis, the mobility of the oxygen vacancies is measured as a function of temperature. The mobility obtained from current measurements is shown to be compatible with the Einstein relation for mobility and diffusivity. In summary, the ionic current associated with oxygen vacancies is shown to be an important component of the measured current in thin BST films.
Adaptive correlation filter for stabilization of interference-fiber-optic sensors
Authors: Kamshilin Alexei A. , Jaaskelainen Timo , Kulchin Yuri N.
Published: July 2002

A type of adaptive correlation filter for processing the speckle pattern emerging from an interference fiber-optic sensor is proposed. This filter is simple and self-adjustable, operating on the base of the photorefractive fanning effect. Experiments carried out with a Bi12TiO20 crystal and multimode optical fiber demonstrate high sensitivity and long-term stability of the sensor.
Poisson’s ratio measurement in tungsten thin films combining an x-ray diffractometer with in situ tensile tester
Authors: Renault P.-O. , Badawi K. F. , Bimbault L. , Goudeau Ph. , Elkaı̈m E. , Lauriat J. P.
Published: July 2002

A direct determination of the Poisson’s ratio in 150 nm polycrystalline tungsten thin films deposited by ion-beam sputtering on Duralumin substrates has been performed by combining x-ray diffraction measurements with in situ traction on the sample. X-ray diffraction experiments using the sin2 ψ method have been done at LURE, the French synchrotron facility (Orsay, France) on a four-circle diffractometer. The method described in this letter allows us to extract in a simple way and with a good precision the Poisson’s ratio of thin films on substrates from the evolution of the sin2 ψ curves as a function of applied strains. In the case of tungsten thin film, the value obtained is close to the bulk material one.
Electronic properties in p-type GaN studied by Raman scattering
Authors: Harima H. , Inoue T. , Nakashima S. , Furukawa K. , Taneya M.
Published: July 2002

Raman spectra from p-type GaN have been systematically studied in the hole density range of 5×1016–1×1018 cm−3. Contrary to the case of n-type samples, spectral profiles of the LO-phonon-plasmon coupled mode in p-type show no remarkable change with the hole density. Thus, precise evaluation of electrical transport parameters such as carrier density and mobility from the coupled mode profile is difficult. However, a continuum band has been observed in the low-frequency range of the spectra, becoming intense with the increase of the hole density. This band has been attributed to the inter-valence-band transition of holes, and the intensity can be used as a good measure of the hole density.
Superconductor digital frequency divider operating up to 750 GHz
Authors: Chen W. , Rylyakov A. V. , Patel Vijay , Lukens J. E. , Likharev K. K.
Published: July 2002

A superconductor frequency divider based on rapid single flux quantum (RSFQ) logic has been demonstrated to operate from dc to 750 GHz with an error rate less than the measurement limit (25 MHz). This high operating frequency is made possible by the use of small (0.25 μm2), high critical current density Josephson junctions along with an optimized design having parameter margins of ±30%. Simulations based on the Werthamer model are in reasonable agreement with the data and give a SFQ pulse width of 1 ps and a maximum power dissipation of 1.5 μW.
Atomic surface roughness
Authors: Yu Jin , Namba Yoshiharu
Published: July 2002

We present a well-validated model to predict the roughness on an atomic surface. Surface roughness equation is developed for atomic topography. The root-mean-square roughness σ is found to be proportional to the radii of the surface atoms or ions. Tables are provided for theoretical atomic surface roughness in pure metal crystals and ionic crystals. Finally, we report atomic-scale roughness measurements on muscovite mica cleavage with an atomic force microscope.
Mechanism of enhanced formation of C54–TiSi2 in high-temperature deposited Ti thin films on preamorphized (001)Si
Authors: Chang S. M. , Huang H. Y. , Yang H. Y. , Chen L. J.
Published: July 2002

Enhanced formation of C54-TiSi2 in high-temperature deposited Ti thin films on preamorphized (001)Si has been investigated by high-resolution transmission electron microscopy in conjunction with autocorrelation function analysis. The increase in the thickness of the amorphous TiSix layer is due to the preamorphization implantation for the most part. The dominant effect of high-temperature sputtering is to increase the density of crystallites in the amorphous TiSix layer. The enhanced formation of C54–TiSi2 in high-temperature deposited samples is attributed to the more extensive presence of silicide crystallites, which serve as nucleation sites, in the amorphous TiSix layer than that in samples deposited at room temperature.
Development of a high-quantum-efficiency single-photon counting system
Authors: Takeuchi Shigeki , Kim Jungsang , Yamamoto Yoshihisa , Hogue Henry H.
Published: July 2002

A high-quantum-efficiency single-photon counting system has been developed. In this system, single photons were detected by a visible light photon counter operated at 6.9 K. The visible light photon counter is a solid state device that makes use of avalanches across a shallow impurity conduction band in silicon. Threefold tight shielding and viewports that worked as infrared blocking filters were used to eliminate the dark count caused by room-temperature radiation. Corrected quantum efficiencies as high as 88.2%±5% (at 694 nm) were observed, which we believe is the highest reported value for a single-photon detector. The dark count increased as the exponential of the quantum efficiency with changing temperature or bias voltage, and was 2.0×104 cps at the highest quantum efficiency.