bluuebunny/crossref_metadata_2025 huggingface dataset:
On the role of pre-existing, unhealed cracks on the bending strain response of Ag-clad (Bi,Pb)2Sr2Ca2Cu3Ox tapes
Authors: Polak M. , Parrell J. A. , Polyanskii A. A. , Pashitski A. E. , Larbalestier D. C.
Published: July 2002

Studies of the transport critical current (Ic), magnetization, magnetic flux penetration, and microstructure of pressed and rolled Ag-clad (Bi,Pb)2Sr2Ca2Cu3Ox tapes (2223) have been made as a function of bending strain. Pressed tapes exhibited markedly less degradation of Ic from strain than did rolled tapes, while the magnetization of pressed tapes declined much more rapidly with bending strain than did either of the transport currents. Magneto-optical imaging of nonbent pressed samples revealed a network of flux-penetrated defect channels that were primarily oriented parallel to the tape axis. Bending such samples to a small strain increased the visibility of these defects, believed to be cracks. This network correlates well to the cracks produced in intermediate thermomechanical processing deformation steps. The greater sensitivity of the transport current of rolled samples to bending is further direct proof of the fact that the tape “remembers” the cracks induced in the core during intermediate deformation and that heat treatment after the deformation does not heal all damage.
Modified substrate spontaneous emission in broad area semiconductor lasers
Authors: Wright Malcolm W. , Dente Gregory C. , Bossert David J. , Tilton Michael L.
Published: July 2002

We observe modification of the spontaneous emission spectrum emitted through the substrate of a quantum well semiconductor laser. The effect is driven by the proximity of the quantum well active region to the p-side electrical contact of the device, representing an excellent example of cavity quantum electrodynamics. Modification of the spontaneous emission rate and spectrum can be substantial; it must be accounted for in order to infer modal gain or carrier heating phenomena in the device correctly.
Controllable drain cut-in voltage with strong negative differential resistance in GaAs/InGaAs real-space transfer heterostructure
Authors: Su Jan-Shing , Hsu Wei-Chou , Lin Yu-Shyan , Lin Wei
Published: July 2002

Three-terminal GaAs/InGaAs/GaAs pseudomorphic real-space transfer heterostructure employing graded channel as the emitter layer grown by low-pressure metal-organic chemical-vapor deposition has been fabricated. We observe controllable drain cut-in voltage characteristics with strong negative differential resistance. The largest peak-to-valley current ratio of the proposed device is about 33 000 at room temperature. Moreover, we observe an energy exchange effect between electrons.
Fermi energy pinning at the surface during growth of n- and p-type GaAs
Authors: Chen C. Y. , Cohen R. M. , Simons D. S. , Chi P. H.
Published: July 2002

The Te donor concentration has been used as a probe to infer the surface carrier concentration during growth by organometallic vapor phase epitaxy. With the partial pressure of Te held constant during the growth of an npn structure, the Te concentration is found to remain nearly unchanged across the p-n junctions. This result is used to show that the carrier concentration at the growing surface shifts by a negligible amount as the growth is switched between n- and p-type GaAs. When combined with previous results for p-type GaAs, we conclude that the Fermi energy at the (100)-oriented surface remains pinned between 100 and 200 meV below the intrinsic Fermi energy, independent of the type or the concentration of dopant used.
Dynamic alignment of magnetic materials
Authors: Zhang Y. D. , Budnick J. I.
Published: July 2002

The inherent relation between the crystal and magnetic structures for magnetically ordered materials makes it possible to align magnetic particles using magnetic means. The traditionally used static alignment method can only align the particles in one dimension. This report describes dynamic alignment methods which cause the magnetic particles to orient in various patterns according to one’s needs. In particular, particles can be aligned in all three spatial directions thus forming a single-crystallike aggregate of polycrystalline materials.
Domain boundaries in epitaxial wurtzite GaN
Authors: Xin Y. , Brown P. D. , Humphreys C. J. , Cheng T. S. , Foxon C. T.
Published: July 2002

Double positioning boundaries on {12̄10} and {11̄00} planes in wurtzite GaN epilayer grown by molecular beam epitaxy on {1̄1̄1̄}B GaP are described. Transmission electron microscopy observations demonstrate that the {12̄10} boundary extending a short distance along the c axis is characterized by a displacement of 1/2〈101̄1〉 and is associated with single growth faults in the basal plane. This boundary forms as a consequence of island coalescence. Conversely, the {11̄00} boundary originates at the epilayer/substrate interface and runs through the whole epilayer, while g.R analysis combined with high resolution electron microscopy suggests a displacement of 1/3n〈112̄0〉 (n>3) in the basal plane with an additional shift along 〈0001〉 of 1/n〈0001〉(n>3).
Interactions at interface between Cu99Ti1 thin films and polyimide
Authors: Kondoh E. , Nguyen T. P. , Plachke D.-W. , Carstanjen H. , Arzt E.
Published: July 2002

Material characteristics and chemistry of the interface formed between Cu99Ti∼1 films and polyimide were investigated. Plasma pretreatment of the polyimide surface and post-metallization annealing were used to modify the interface. Composition analysis data taken from the interface indicated no significant Cu diffusion into the polyimide layer and accretion of nitrogen at the interface. The formation of Cu and Ti compounds by carbonyl bond breaking, suggested by x-ray photoelectron spectroscopy, could explain suppression of Cu diffusion and drastic increase of adhesion strength.
Thickness variation compensation in a Fabry–Perot modulator array using a self-tuned Fabry–Perot structure
Authors: Harvey Phil , Esener Sadik
Published: July 2002

A method is presented for compensating cavity thickness variations in conventional Fabry–Perot devices through the replacement of the input mirror with a holographic mirror, resulting in a self-tuned Fabry–Perot (STFP) device. The technique is suitable for integrating large arrays of electro-optic Fabry–Perot modulators with silicon circuitry. Experimental results of a STFP modulator are presented showing cavity thickness compensation of an electrooptic 9/65/35 bulk lead lanthanum zirconate titanate crystal having thickness variations corresponding to ~6 Fabry–Perot fringes in a 2.5×2.5mm2 area. The compensated modulator used an in situ recorded Fe-doped LiNbO3 holographic mirror, and had a uniform backreflection over a 2.5×2.5mm2 area.
Optical antenna: Towards a unity efficiency near-field optical probe
Authors: Grober Robert D. , Schoelkopf Robert J. , Prober Daniel E.
Published: July 2002

We demonstrate that an antenna can be used to realize a near-field optical probe that combines spatial resolution well below the diffraction limit with transmission efficiency approaching unity. The probe consists of a planar bow-tie antenna with an open-circuited gap at its apex. We present proof-of-principle measurements using microwave radiation and discuss scaling the antenna to the visible optical spectrum.
Effect of applied electric field on the molecular orientation of epitaxially grown organic films
Authors: Hayashi Kouichi , Kawato Shin’ichi , Fujii Yasuhiro , Horiuchi Toshihisa , Matsushige Kazumi
Published: July 2002

In order to control and obtain desired molecular orientations, we investigated the effects of applying an electric field during the epitaxial growth of organic crystals in this study. We deposited interdigitated gold electrodes on polished KCl (001) substrates, and then grew copper phthalocyanine (CuPc) thin films, applying the voltages during evaporation process. Using an energy dispersive grazing incidence x-ray diffraction system, we evaluated the orientations of α-CuPc crystals relative to the KCl substrates. The CuPc crystals with applied electric fields were found to orient in different directions from those of the usual epitaxially grown films without applied electric fields. These facts suggest that the combination of applying an electric field and epitaxial growth provide us a new method to control the molecular orientation in the organic thin films.
Single-level interface states in semiconductor structures investigated by admittance spectroscopy
Authors: Krispin Peter
Published: July 2002

Single-level interface states in n-type GaAs, which were incorporated by planar doping of deep-level defects, are investigated. Discrete electronic traps are directly identified as interface states by admittance-bias spectra. It is experimentally demonstrated that the characteristic response time is determined by both the emission and the capture rate when interface states are investigated by admittance spectroscopy. The transition between capture- and emission-controlled admittance spectra is observed.
Physical characteristics of N2 annealing on room-temperature-deposited ion plating oxide
Authors: Yeh Ching-Fa , Chen Tai-Ju , Kao Jiann-Shiun
Published: July 2002

The effects of N2 annealing on the physical properties of room-temperature-deposited ion plating (IP) oxide have been characterized. As-deposited IP oxide exhibits higher refractive index and dielectric constant values than high-temperature-annealed IP oxide. Strained bonds existing in as-deposited oxide can be relaxed by N2 annealing depending on the annealing temperature. After annealing at 800 °C, the physical characteristics of IP oxide are comparable to those of thermal oxide.
Copper, hydrogen, and titanium incorporation in potassium lithium tantalate niobate single crystals
Authors: Tong Xiaolin , Zhang Min , Yariv Amnon , Agranat Aharon J.
Published: July 2002

In this study we propose a model that describes the diffusion of copper, hydrogen, and titanium through the liquid/solid interface in potassium lithium tantalate niobate crystals. Copper and hydrogen ions may occupy potassium/lithium vacant sites. Hydrogen ions are also able to stay at tantalate/niobate vacant sites in the presence of titanium. This model shows that the hydrogen concentration can be dramatically reduced in KLTN:Cu,X,Ycrystals (where X, Yare any first row transition metals but not Ti or Cu), and is in agreement with experimental results.
n
-type delta doped strained quantum well lasers for improved modulation bandwidth
Authors: Buchinsky O. , Blumin M. , Sarfaty R. , Fekete D. , Orenstein M. , Eisenstein G.
Published: July 2002

Improved dynamic properties of strained single quantum well (QW) lasers were obtained by the incorporation of an n-type δ doping at close proximity to the strained QW active layer. The resultant modulation bandwidth was almost doubled, from 3.5 GHz to more than 6.2 GHz. The increased modulation bandwidth is attributed to an improved carrier injection resulting from the enhancement of the carrier transit time into the QW, as well as a decrease in the significance of the adverse contribution of carrier transport effects.
Compact lumped-element microwave resonators using epitaxial YBa2Cu3O7−x/NdAlO3/YBa2Cu3O7−x trilayers
Authors: Rao Muralidhar R.
Published: July 2002

Thick, high-quality epitaxial trilayers of YBa2Cu3O7−x/NdAlO3/YBa2Cu3O7 were grown on (100) MgO substrates by pulsed laser deposition. Compact resonators based on such trilayers were designed, fabricated, and tested. The resonant frequencies of the resonators were varied from 1.6 to 9.4 GHz by varying the device geometry within a die size of 2×2 mm. The values of the capacitive and inductive elements of the resonator and series resistance were estimated, and the frequency response of the circuit model was simulated. The measured and simulated resonant frequencies, insertion losses, and quality factors were in agreement. The contact resistivity of the Ag-YBa2Cu3O7−x contacts at the capacitor pads was found to dominate the loss in the resonator.
Synthetic wide bandpass x-ray polarizers
Authors: Cross J. O. , Bennett B. R. , Bell M. I. , Kuhn K. J.
Published: July 2002

A wide bandpass x-ray polarizer for photon energies near 8358 eV (LIII absorption edge of erbium) has been grown using molecular beam epitaxy. The results illustrate a general approach to preparing graded-lattice diffracting optical components. The active optical element is an 8-μm-thick single crystal film of In0.51Ga0.49Sb grown on a GaAs (001) substrate. The alloy was chosen to ensure maximum linear polarization for the (006) Bragg reflection at the target energy. The polarizer reflectivity has a full width at half-maximum of 27 eV in a fixed geometry with an angle of 90° between the incident and diffracted beams.
The pseudo-ordered structure in light emitting porous and nanocrystalline silicon films
Authors: Wang L. C. , Liu X. N. , Yan F. , Bao X. M. , Feng D. , Rainforth W. M.
Published: July 2002

The structures of light emitting porous and nanocrystalline silicon films have been investigated using high resolution electron microscopy. A pseudo-ordered structure has been found from the Fourier transformation of the high resolution images after digital processing of the images. The structure description was distinguished from common amorphous and nanocrystalline silicon films. The formation mechanism of the pseudo-ordered structure is described in the letter.
Quantum confinement in the Si-III (BC-8) phase of porous silicon
Authors: Allan G. , Delerue C. , Lannoo M.
Published: July 2002

Porous silicon was recently shown to give rise to the same semimetallic Si-III (BC-8) phase as silicon upon application and release of high pressure. This phase is known to have a direct gap and we examine the effect of quantum confinement on its electronic structure. This is performed by combining empirical tight binding and ab initio local density calculations. The blue shift is found to be similar to what is obtained for nanocrystallites with the diamond structure and the radiative recombination rate is much larger. Comparison with experiment shows that the observed luminescence is not consistent with the quantum confinement hypothesis.
Self-trapping of two-dimensional optical beams and light-induced waveguiding in photorefractive InP at telecommunication wavelengths
Authors: Chauvet M. , Hawkins S. A. , Salamo G. J. , Segev M. , Bliss D. F. , Bryant G.
Published: July 2002

We demonstrated an experimental observation of self-trapping and self-deflection of a two-dimensional optical beam by the photorefractive effect at telecommunication wavelengths under an applied dc field. Self-trapping is effective for an intensity range related to the intensity-temperature resonance known for two-wave mixing in InP:Fe. The photorefractive index change giving rise to the trapping is measured at 10−4, while the photorefractive space-charge field is measured at about 50 kV/cm, ten times higher than the applied field. We show experimentally that this index change creates a waveguide that can be used to guide a second beam at 1.55 μm.
L
-electron effect in AlAs–GaAs–AlAs double-barrier structures
Authors: Chiang Jih-Chen , Shyu Jiann-Shing
Published: July 2002

This letter reports the theoretical study of the current–voltage characteristics of the AlAs–GaAs–AlAs double-barrier structure with a thin GaAs well and thin AlAs barriers at room temperature, within a third-neighbor sp3 bond-orbital model. We demonstrate that the tunneling current caused by the L-valley electrons gives a significant contribution to the valley current at room temperature. Moreover, if the AlAs barriers become thick enough (e.g., >3 nm), the tunneling current at room temperature may be dominated by the L electrons instead of Γ electrons.
Nonuniform conduction in B-doped chemical vapor deposited diamond studied by intra- and intergrain measurements
Authors: Sahli S. , Aslam D. M.
Published: July 2002

Current–voltage (I–V) measurements are performed on a B-doped polycrystalline diamond film chemically vapor deposited on commercially available 170-μm-thick undoped and polished polycrystalline diamond. Four-probe resistivity measurements in the temperature range of 7–200 °C, potential profile measurements across a few grains in the current range of 10−6–10−4 A, and two-probe I–V measurements within a single grain and across an individual grain boundary show that: (i) current flow is nonuniform and is affected by current level, (ii) potential barriers exist at the grain boundaries, and (iii) the probe contacts are Ohmic when the probes are placed on rough microstructures. Based on the grain size distribution, a simple model that distinguishes between conduction paths made of large grains and small grains is used to interpret these results.
Stress release at Y2BaCuO5 inclusions in fast melt processed YBa2Cu3O7−x observed by micro-Raman spectroscopy
Authors: Provoost R. , Rosseel K. , Moshchalkov V. V. , Silverans R. E. , Bruynseraede Y. , Dierickx D. , Van der Biest O.
Published: July 2002

We have studied the interface region between the superconducting YBa2Cu3O7−x (123) matrix and the embedded nonsuperconducting Y2BaCuO5 (211) inclusions in fast melt processed samples, by recording micro-Raman spectra along lines crossing these inclusions. The observed relative shifts of the 123 Raman modes indicate the accumulation of compressive stress in the bulk of the 123 material and a release of this stress around the 211 inclusions. These results show that for practical applications of the fast melt processed materials, beside strong pinning, proper mechanical properties around the pinning centers are important.
The formation of nanostructures on silicon surfaces in the presence of hydrogen
Authors: Teschke O. , Soares D. M. , Nunes L. A. O.
Published: July 2002

The presence of hydrogen in HF solutions at a silicon substrate surface is shown to be sufficient to produce a photoluminescent porous silicon layer. The photoluminescence measurements of bubbled and anodized samples show similar spectra when illuminated with UV radiation. This is strong evidence that the hydrogen produced by the anodic silicon dissolution reaction is also responsible for the formation of nanostructures.
Laser magnetometer measurement of the natural remanent magnetization of rocks
Authors: Cotteverte Jean-Charles , Poirson Jérôme , Le Floch Albert , Bretenaker Fabien , Chauvin Annick
Published: July 2002

The ability of a laser magnetometer to measure the natural remanent magnetization of rocks is experimentally investigated. It is shown that the performance of such a magnetometer permits the rapid measurement of rock magnetizations of less than 1 A m−1 in a laboratory without the need of any magnetic shielding or cryogenic facilities. Moreover, the laser magnetometer is experimentally shown to be able to measure the distribution of magnetization in spatially inhomogeneous samples.
The origin of gallium desorption transients during AlGaAs/GaAs heterointerface formation by molecular beam epitaxy
Authors: Mahalingam K. , Dorsey D. L. , Evans K. R. , Venkat Rama
Published: July 2002

A Monte Carlo simulation study is performed to investigate the Ga desorption behavior at AlGaAs/GaAs heterointerfaces during growth by molecular beam epitaxy. The transients in Ga desorption rate upon opening/closing the Al shutter arise due to both the change in V/III flux ratio and the Al–Ga surface exchange mechanism. It is shown that the desired “steplike” variation in Ga desorption rate at each interface can be attained by a growth procedure employing a constant V/III flux ratio.
Stability of far fields in double heterostructure and multiple quantum well InAsSb/InPAsSb/InAs midinfrared lasers
Authors: Yi H. , Rybaltowski A. , Diaz J. , Wu D. , Lane B. , Xiao Y. , Razeghi M.
Published: July 2002

Far fields in perpendicular direction to the junction are investigated in double heterostructure (DH) and multiple quantum well (MQW) midwave-infrared InAsSb/InPAsSb/InAs lasers (λ=3.2–3.6 μm). Strong broadening of the far fields in the DH lasers was observed with increases in temperature and/or current. On the contrary, MQW lasers with otherwise identical structure exhibit very stable far fields as narrow as 23° for all the operating conditions investigated. Our experiment and theoretical modeling suggest that these different behaviors of far fields in DH and MQW lasers are attributed to the refractive index fluctuation in the InAsSb laser active region.
Detecting squeezed phonons through an indirect radiative transition
Authors: Müstecaplıoǧlu Ö. E. , Shumovsky A. S.
Published: July 2002

A model of the effect of the longitudinal optical phonon number distribution on the Rabi oscillations of the photons involved in the associated indirect transition in a semiconductor is presented. It is shown that a faster cavity photon revival rate is obtained given an initial squeezed thermal phonon state. This is the result of pairwise correlations of phonons due to squeezing and also holds true when phonons are in squeezed vacuum or in squeezed number states. It may be possible to use this effect to detect squeezing in phonons.
Observation of a new class of crystal sonoluminescence at piezoelectric crystal surface
Authors: Ostrovskii I. V. , Das P.
Published: July 2002

Ultrasonic vibrations of a single-piezoelectric crystal of LiNbO3 and CdS can excite luminescence of gas near the crystal surface. Light excitation starts at ultrasonic intensity above a certain threshold. This threshold lies in the range 3–10 W/cm2 and corresponds to the unpinning of dislocations and beginning of their reversible motion in the piezoelectric crystal. The effects constitute a new class of acousto-optic and dislocation phenomena having the main feature of energy transformation from ultrasound in solid to luminescence of gas at normal atmospheric pressure. The unpinning of dislocations is shown to be critical for sonoluminescence excitation.
Low threshold continuously tunable vertical-cavity surface-emitting lasers with 19.1 nm wavelength range
Authors: Sugihwo Fred , Larson Michael C. , Harris J. S.
Published: July 2002

Continuous wavelength tuning of 19.1 nm is reported for vertical-cavity surface-emitting lasers. Stress-matched dielectric mirror stacks are added to the micromachined deformable-membrane top mirror to enhance reflectance, resulting in devices with 6.5% quantum efficiency and threshold current as low as 0.34 mA. The laser operates in single mode near 968 nm with 24 dB mode suppression ratio and tuning voltages are below 18 V.
The growth of AlGaAs–InGaAs quantum-well structures by molecular beam epitaxy: Observation of critical interdependent effects
Authors: Bicknell-Tassius Robert N. , Lee Kyeong , Brown April S. , Dagnall Georgianna , May Gary
Published: July 2002

Critical interdependent effects have been observed in the growth of AlGaAs/InGaAs quantum-well structures by molecular beam epitaxy. It is shown that statistical experimental design is an effective method for quickly optimizing complex device structures. This technique is very useful for the optimization of processes with a large number of interdependent parameters, and allows for the clear visualization and separation of complex interwoven effects. In the present work, we show the importance of the oxide desorption process for the optimal growth of AlGaAs-containing structures.
Nonequilibrium hydrogen temperatures under diamond chemical vapor deposition conditions
Authors: Sinkovits Robert S.
Published: July 2002

Direct simulation Monte Carlo calculations indicate that significant differences can exist between the translational, rotational, and vibrational temperatures of molecular hydrogen under diffusion-dominated diamond chemical vapor deposition conditions. For hydrogen confined in a 1 cm gap between an activating source and a diamond substrate, the largest discrepancies between the translational and rotational temperatures of H2 occur at a pressure of approximately 2 Torr, but measurable differences persist for pressures exceeding 20 Torr. The observed trends are due to the inefficiency of intermolecular collisions at exciting the internal modes of H2.
Evolution of subsurface hydrogen from boron-doped Si(100)
Authors: Hess G. , Parkinson P. , Gong B. , Xu Z. , Lim D. , Downer M. , John S. , Banerjee S. , Ekerdt J. G. , Jo S. K.
Published: July 2002

The reactions of atomic hydrogen with boron-doped Si(100) were studied using temperature programmed desorption (TPD). In addition to adsorbing at surface sites, hydrogen penetrates into boron-doped Si(100) samples and gets trapped by forming subsurface boron–hydrogen complexes. H2-TPD spectra, taken after exposure to atomic hydrogen, showed, in addition to the well known dihydride (680 K) and monohydride (795 K) desorption features, two peaks at 600 and 630 K due to decomposition of subsurface boron–hydrogen complexes. Increasing total hydrogen uptake with increasing dosing temperature (1.7 ML at 300 K, 4.2 ML at 500 K), suggests an activation barrier for subsurface hydrogen uptake. A quantitative correlation between boron concentration and subsurface hydrogen uptake is shown.
Effects of electron–hole energy transfer on the nonlinear gain coefficients in the small-signal modulation response of semiconductor lasers
Authors: Tsai Chin-Yi , Shih Fang-Ping , Chen Chih-Hsiung , Wu Tsu-Yin , Sung Tien-Li , Tsai Chin-Yao
Published: July 2002

The effects of energy transfer between electrons and holes on the small-signal modulation response of semiconductor lasers are theoretically investigated. We calculate the electron energy relaxation time due to electron–hole scattering from the first principle. We show that its value is comparable to the electron energy relaxation time due to the electron–LO phonon scattering with the effect of nonequilibrium LO phonons. In such a case, the nonlinear gain coefficient due to carrier heating defined in the small-signal modulation response of semiconductor lasers is no longer a simple sum of the term due to electron heating and that due to hole heating.
Direct atomic flux measurement of electron-beam evaporated yttrium with a diode-laser-based atomic absorption monitor at 668 nm
Authors: Wang Weizhi , Hammond R. H. , Fejer M. M. , Arnason S. , Beasley M. R. , Bortz M. L. , Day T.
Published: July 2002

A direct measurement of atomic flux in e-beam evaporated yttrium has been demonstrated with a diode-laser-based atomic absorption (AA) monitor at 668 nm. Atomic number density and velocity were measured through absorption and Doppler shift measurements to provide the atomic flux. The AA-based deposition rates were compared with independent quartz crystal monitors showing agreement between the two methods.
Pressure-induced intra-4f luminescence in GaAs:Er,O
Authors: Takarabe K. , Mizushima T. , Minomura S. , Hogg R. A. , Taguchi A. , Takahei K.
Published: July 2002

In metalorganic chemical vapor deposition grown GaAs:Er,O samples, at ambient pressure, only the ErGa−2O center is excited by above band gap host photoexcitation (host excitation) and shows a sharp infrared luminescence spectra due to intra-4f transitions in the Er3+ ion. It is found, at high pressure, that at least two other Er centers become optically active by host excitation. One of these pressure-induced centers is assigned to a specific Er center having slightly different atomic configuration than the ErGa−2O center by comparing the pressure-induced photoluminescence (PL) spectra with the site-selective PL spectra.
Extended platelets on {111} in GaAs created by He-ion implantation followed by low temperature annealing
Authors: Nomachi T. , Muto S. , Hirata M. , Kohno H. , Yamasaki Jun , Takeda S.
Published: July 2002

We have found that the extremely extended platelets of about 1 μm in diameter are formed in GaAs by He-ion implantation and subsequent annealing at 250 and 300 °C for the short period of 180–300 s. We have shown that the platelets are extended not on the most easily cleavaged {110}-type planes but on {111}-type planes. The platelets give rise to the extra transmission electron diffraction spots. The analysis of the diffraction, combined with electron microscopy data, has shown that unreconstructed interior {111} surfaces, oppositely bent, are created in GaAs.
Stress relaxation in tungsten films by ion irradiation
Authors: Snoeks E. , Boutros K. S. , Barone J.
Published: July 2002

Tungsten films, grown by plasma-enhanced chemical vapor deposition for very large scale integration interconnect applications, suffer from a high internal tensile stress that leads to contact failure. We show with wafer curvature measurements that the stress can be relaxed via viscous flow at room temperature by irradiating the films with energetic ions after deposition. Transmission electron microscopy does not indicate significant structural changes in the W films during irradiation. We varied the irradiation conditions (from 140 keV B ions to 400 keV P ions) and find that the flow rate scales with the nuclear stopping power. Similarities and differences with beam-induced mixing and diffusion are discussed.
High temperature superconducting Josephson junctions in a stacked bicrystal geometry
Authors: Li H. Q. , Ono R. H. , Vale L. R. , Rudman D. A. , Liou S. H.
Published: July 2002

Bicrystal grain boundary Josephson junctions were fabricated in a stack of two layers of YBa2Cu3Ox separated by epitaxial SrTiO3. Weak link behavior was observed in the bridges formed in both layers that had similar shunted-junction characteristics but significantly different critical currents. Characteristic voltages up to 1.9 mV were measured at 4.5 K. The resonant structure was seen in the current–voltage characteristics of the upper-layer junctions, and interactions between junctions in the two layers were evident.
Measurement of interdiffusion by high angle hollow cone illumination
Authors: Ewert J. C. , Hartung F. , Schmitz G.
Published: July 2002

High angle hollow cone darkfield or Z-contrast imaging is used to supress dynamical contributions like bend or extinction contours to electron imaging. Using a multiple scattering model it is possible to interpret image intensities quantitatively and to analyze specimen composition on a nanometer scale without specialized detectors like energy-energy-loss spectroscopy or energy dispersive spectroscopy. This method is practically tested on the interdiffusion of Cu-Au couples. Measured thin film interdiffusion coefficents, are comparable to literature data of the bulk diffusion coefficent in this system.
A microfabricated tip for simultaneous acquisition of sample topography and high-frequency magnetic field
Authors: Agrawal V. , Neuzil P. , van der Weide D. W.
Published: July 2002

We report a combined μm-level topography and high-frequency magnetic field probe, a 6 μm loop defined on a scanning-force microscope cantilever. Since it functions as a near-zone antenna, it can be used with any suitable detector, and can probe both active and passive samples. We demonstrate its performance by scanning a coplanar waveguide sample at 10 GHz using a microwave network analyzer. With this instrument, the device noise at this frequency is ∼2μΦ0/Hz1/2 at T=300 K, comparable to that found for a superconducting quantum interference device (SQUID) at DC. Unlike the SQUID, however, the thermally limited minimum-detectable field of this system scales with frequency.
Nanometer-scale germanium islands on Si(111) surface windows formed in an ultrathin silicon dioxide film
Authors: Shklyaev Alexander A. , Shibata Motoshi , Ichikawa Masakazu
Published: July 2002

Three-dimensional Ge islands between 15 and 200 nm in size were found to grow only on Si(111) surface windows in ultrathin SiO2 film after Ge deposition and subsequent SiO2 decomposition. The size of Ge islands gradually decreased as the Ge thickness decreased. Pseudomorphic two-dimensional Ge layers with the 5×5 structure formed in surrounding areas of the windows. The windows were produced by selective thermal SiO2 decomposition induced by focused electron beam irradiation. These results suggest a new technique for nanometer-scale Ge island fabrication at given points on Si surfaces.
Anisotropic grain noise in eddy current inspection of noncubic polycrystalline metals
Authors: Blodgett Mark , Nagy Peter B.
Published: July 2002

This letter discusses the role electrical anisotropy plays in the structural integrity assessment of polycrystalline titanium alloys from the standpoint of fatigue crack detection and the related issue of microstructural noise. In eddy current inspection of noncubic crystallographic classes of polycrystalline metals the electric anisotropy of individual grains produces an inherent microstructural variation or noise that is very similar to the well-known acoustic noise produced by the elastic anisotropy of both cubic and noncubic materials in ultrasonic characterization. The presented results demonstrate that although the electrical grain noise is clearly detrimental in eddy current nondestructive testing for small flaws, it can be also exploited for characterization of the microstructure in noncubic polycrystalline materials such as titanium alloys in the same way acoustic grain noise is used for ultrasonic characterization of the microstructure in different materials.
Decoupling the structural and magnetic phase transformations in magneto-optic MnBi thin films by the partial substitution of Cr for Mn
Authors: Bandaru Prabhakar R. , Sands Timothy D. , Kubota Yukiko , Marinero Ernesto E.
Published: July 2002

The first-order nature of the magnetic phase transformation at 360 °C and the presence of a Bi-rich eutectic at 265 °C have inhibited the application of MnBi thin films for high density magneto-optical data storage. It is suggested that partial substitution of Cr for Mn should both lower the Curie temperature, Tc, and decouple the lattice and magnetic transitions so as to allow reversible Curie point writing. It is found experimentally that 10% substitution of Cr for Mn reduces the apparent Tc to ∼250 °C while retaining a Kerr rotation angle greater than 1° at 633 nm, as measured through the silica glass substrate. Observations of increasing Hc with temperature in both MnBi and (Mn,Cr)Bi thin films suggest that the low-temperature phase is ferrimagnetic.
Magnetic domain structures of Co22Ag78 granular films observed by magnetic force microscopy
Authors: Chen Y. J. , Cheung W. Y. , Wilson I. H. , Ke N. , Wong S. P. , Xu J. B. , Sang H. , Ni G.
Published: July 2002

A magnetic force microscope (MFM) was used to image the topography and magnetic microstructures of Co22Ag78 granular films. The observed morphology shows isolated nanometer-scale cobalt particles (granules) embedded in the silver matrix. Stripe magnetic domains with much larger size (typically of ∼100 nm wide) than that of cobalt particles are resolved clearly on MFM micrographs for the annealed samples. It is demonstrated that the domain width and the relative magnetic force strength first increases and then decreases with annealing temperature with a maximum at about 600 K. We suggest that the appearance of the stripe domains is attributed to magnetic correlation among many of the isolated single-domain cobalt particles and is dependent on the microstructure of the samples.
Plasma-assisted pulsed laser deposition of SrBi2Ta2O9 thin films of improved ferroelectric and crystalline properties
Authors: Rastogi A. C. , Tirumala S. , Desu S. B.
Published: July 2002

Significant effect of the introduction of O2-plasma discharge during pulsed laser ablative deposition of SrBi2Ta2O9 (SBT) films on improving the crystallite orientation and ferroelectric properties has been described. O2-plasma assists in the formation of highly crystalline films at a low 700 °C temperature over (111) oriented Pt films coated Si(100) single crystal substrates at a nominal pressure of 200 mTorr. Plasma excitation potential, applied at an auxiliary ring electrode placed near the substrate, has a profound effect on surface morphology, crystallite orientation, and remnant polarization, Pr values. At −350 V, SBT growth at 700 °C with predominant (a-b) orientation showing high Pr∼6.5 μC/cm2 in the as-deposited state has been obtained. In comparison, SBT films deposited identically but without the plasma show a low Pr of ∼1.7 μC/cm2. Ionized cationic species along with ionic and atomic oxygen present in the plasma improve thermodynamic stability of the film growth through enhanced chemical reactivity and thus eliminates the need for any severe postgrowth crystallization anneal step in the synthesis of SBT films. Impingement of energetic O2 ions and atomic oxygen helps lower the nucleation barrier for the growth of (a-b) crystallites and changes the c-axis orientation from normal to near parallel to the film plane. Quality of the film declines with the plasma excitation potential as enhanced kinetic energy of impinging O2 ions introduce defects and reduce nucleation density by resputtering from the substrate.
Evolution of the energy levels in quantum dot ensembles with different densities
Authors: Fafard S. , Wasilewski Z. R. , Spanner M.
Published: July 2002

Ensembles of self-assembled InAs/GaAs quantum dots (QDs) have been obtained with different densities by molecular beam epitaxy. The evolution of the structural and optical properties with coverage shows that lateral interactions are present for QD spacings of hundreds of nanometers (coverage>∼109 QDs/cm2). Clear evidence for transfer of InAs from the wetting layer to the QDs is observed at the onset of the Stranski–Krastanow’s island formation for 1.83 monolayers (MLs). QDs with sharp electronic shell structures are observed by state-filling spectroscopy for the low density ensembles (1.83–1.91 ML). A decrease in the photoluminescence intensity is observed for more than 1.96 ML and is associated with the coalescence of the islands.
Ab initio study of 180° domain wall energy and structure in PbTiO3
Authors: Pöykkö S. , Chadi D. J.
Published: July 2002

We have calculated the electronic and atomic structures for 180° domain walls in PbTiO3 using a first-principles total energy method. Domain walls are found to be Pb centered and extremely narrow with a width of only about two lattice constants. The energy density of a domain wall is calculated to be 0.1–0.2 J/m2.
Realization of numerical aperture 2.0 using a gallium phosphide solid immersion lens
Authors: Wu Qiang , Feke G. D. , Grober Robert D. , Ghislain L. P.
Published: July 2002

We report a study of a gallium phosphide, hemispherical, solid immersion lens through the imaging of 40-nm-diam fluorescent dye balls. A spatial resolution as small as 139 nm has been achieved at a wavelength of 560 nm, which is equivalent to a diffraction-limited system of numerical aperture 2.0. This resolution is a 33% improvement over conventional oil immersion objectives and previously reported solid immersion lenses, which typically have a numerical aperture around 1.5.
Energy transfer upconversion in Er-doped LiTaO3
Authors: Kostritskii S. M. , Maring D. B. , Tavlykaev R. F. , Ramaswamy R. V.
Published: July 2002

The fluorescence spectrum of Er-indiffused LiTaO3 was measured and revealed strong anti-Stokes fluorescence (ASF) with upconverted green and red emissions when the F9/24 manifold of an Er3+ ion was pumped by either a 632.8 or a 647 nm laser. Investigation into the dependence of fluorescence intensity on pump intensity and depth profiling of the Stokes and anti-Stokes fluorescences revealed that the ASF is attributed mainly to energy transfer upconversion within Er3+ cluster sites. Postindiffusion processing in molten LiNO3 was found to be effective in suppressing the upconversion via decrease of the cluster site concentration.
Traveling plumes generated within a double-diffusive interface between counter shear flows
Authors: Nishimura Tatsuo , Sakura Soshun , Gotoh Kuniaki , Morega Alexandru M.
Published: July 2002

A two-layer, salt-stratified NaCl–H2O system destabilized and mixed by lateral heating and cooling is considered in this paper. Flow visualizations are performed to examine the structure of the diffusive interface that separates the convection layers. Simultaneous temperature measurement and flow visualization technique reveal the existence of a regular, three-dimensional flow structure consisting of time-periodic buoyant plumes within the interface, which are due to instabilities of diffusive type. The plumes aligned in the spanwise direction travel toward the hot wall above the interface and toward the cold wall below the interface, respectively, and there is a phase shift of a half plume spacing between the upper and lower ones. Consequently, temperature and concentration oscillations are periodically observed in the paths of plumes.
On the appearance of swirl in a confined sink flow
Authors: Fernandez-Feria R. , Sanmiguel-Rojas E.
Published: July 2002

Radial and swirl velocity components in an axisymmetric sink flow inside a cylindrical container of variable aspect ratio H/R are measured using laser-Doppler anemometry. It is shown that a vortex, superimposed to the meridional sink flow, is formed when the Reynolds number based on the sink flow rate is above a critical value. Both clockwise and counterclockwise directions of rotation are found.
X-ray photoelectron spectroscopy of low surface concentration mass-selected Ag clusters
Authors: O’Shea James N. , Schnadt Joachim , Andersson Staffan , Patthey Luc , Rost Steffen , Giertz Annika , Brena Barbara , Forsell Jan-Olof , Sandell Anders , Björneholm Olle , Brühwiler Paul A. , Mårtensson Nils
Published: July 2002

We have developed an experimental setup for the study of small mass-selected clusters delivered by soft landing to a model oxide support. An automated deposition system to achieve accurately quantified homogeneous surfaces is described which also overcomes beam instability. Finally we present some recent photoelectron spectroscopic data from the analysis of mass-selected Agn+ clusters deposited on a Xe covered Al2O3 surface. Large core-level binding energy shifts are observed as a function of deposited cluster size and diffusion/agglomeration within the noble gas layer.
Activation of the CH stretching vibrations in CH4–OH entrance channel complexes: Spectroscopy and dynamics
Authors: Tsiouris Maria , Wheeler Martyn D. , Lester Marsha I.
Published: July 2002

The vibrational spectroscopy and decay dynamics of CH4–OH reactant complexes have been studied in the CH4 symmetric and antisymmetric stretching regions (ν1 and ν3). The vibrational spectra have been obtained using both infrared and stimulated Raman excitation with ultraviolet probe laser-induced fluorescence detection. Stimulated Raman excitation of CH4–OH in the symmetric stretching region reveals two blended Q branch features at 2912.5 and 2911.8 cm−1. An extremely weak infrared spectrum is also seen in the CH4 symmetric stretching region, which is induced by the presence of the nearby OH partner. Infrared excitation in the asymmetric stretching region results in an intense, yet enormously broad spectrum centered at 3020 cm−1 that extends over 40 cm−1. The appearance of the spectra in the ν1 and ν3 regions has been explained in terms of a model in which the CH4 unit undergoes internal rotation within the CH4–OH complex. The ν1 features are attributed to transitions involving two different nuclear spin states of CH4. In the ν3 region, the CH4–OH complex can undergo a multitude of allowed transitions, each associated with a rovibrational transition of free methane, which give rise to the enormous span of the spectrum. The vibrational spectra also exhibit extensive homogeneous broadening (⩾1 cm−1) arising from the rapid decay of vibrationally activated CH4–OH complexes due to vibrational predissociation and possibly reaction. The OH fragments are produced with minimal rotational excitation, indicating that the dominant inelastic decay channel involves near-resonant vibrational energy transfer within the CH4 unit from the initially prepared CH stretch to an overtone bend (2ν4) state.
Flux quantization in stationary and nonstationary states in long Josephson junctions
Authors: Yugay K. N. , Blinov N. V. , Shirokov I. V.
Published: July 2002

Dynamical chaos and the stability of states in long Josephson junctions are investigated from the standpoint of flux quantization. It is shown that the stationary Meissner and fluxon states having integer numbers of fluxons are stable. Stationary antifluxon states also having integer numbers of flux quanta and all other states with half-integer numbers of flux quanta are unstable. Transitions between all states — Meissner states and states having integer and half-integer numbers of flux quanta — take place in the nonstationary case, and all these states are dynamically equivalent, but the number of flux quanta is an irregular time-dependent function for the chaotic states and a regular one for the regular states.
Stability of N- and Ga-polarity GaN surfaces during the growth interruption studied by reflection high-energy electron diffraction
Authors: Shen X. Q. , Ide T. , Cho S. H. , Shimizu M. , Hara S. , Okumura H.
Published: July 2002

GaN films with N- and Ga-polarity were grown on sapphire (0001) substrates using different buffer layers by plasma-assisted molecular-beam epitaxy. The surface stability of each lattice-polarity film during the growth interruption was studied by reflection high-energy electron diffraction (RHEED). It was found that the surface of N-polarity film was unstable against the exposure to the nitrogen plasma flux, while that of Ga-polarity one was stable. This provides a method to clarify the lattice polarity by the in situ RHEED observation directly. A model is proposed to explain the observed phenomenon, where the origin of the phenomenon is mainly attributed to the differences in surface dynamics processes and morphologies between the two kinds of lattice-polarity films.
Fine structure of coherent twin boundaries in metals
Authors: Mazilova T. I. , Mikhailovskij I. M. , Lygovskaja E. I.
Published: July 2002

The oscillatory features of the atomic relaxation on coherent twin boundary in tungsten are studied by the methods of molecular dynamics. A nonmonotonic character of the variation of the atomic density in the near-boundary region is established. It is shown that the relaxation near twin boundaries can be described satisfactorily in the framework of a continuum model of linearly distributed surface forces.
On the features of the polarization of the bielectronic absorption spectra of the cryocrystal δ-O2
Authors: Loktev V. M.
Published: July 2002

The possible form of the absorption spectrum of the δ phase of oxygen in polarized light is analyzed by proceeding from the known crystal structure of this phase.
Arrangement of nitrogen atoms in GaAsN alloys determined by scanning tunneling microscopy
Authors: McKay H. A. , Feenstra R. M. , Schmidtling T. , Pohl U. W.
Published: July 2002

The pair distribution function of nitrogen atoms in GaAs0.983N0.017 has been determined by scanning tunneling microscopy. Nitrogen atoms in the first and third planes relative to the cleaved (11̄0) surface are imaged. A modest enhancement in the number of nearest-neighbor pairs particularly with [001] orientation is found, although at larger separations the distribution of N pair separations is found to be random.
Crossover criticality in ionic solutions
Authors: Gutkowski K. , Anisimov M. A. , Sengers J. V.
Published: July 2002

To examine the nature of criticality in ionic fluids we have analyzed experimental liquid–liquid coexistence and susceptibility data for various ionic solutions. We show that ionic fluids generally exhibit crossover or, at least, a tendency to crossover from Ising behavior asymptotically close to the critical point to mean-field behavior upon increasing distance from the critical point. This crossover is governed by two physical parameters: a rescaled coupling constant which reflects the strength and range of intermolecular interactions and a “cutoff” length. We conclude that the crossover critical behavior in ionic fluids is primarily governed by the cutoff length, which emerges as a new length scale that cannot be identified with the effective molecular-interaction range. An analogy between crossover critical phenomena in ionic fluids and in polymer solutions is discussed.