bluuebunny/crossref_metadata_2025 huggingface dataset:
Experimental gene interaction studies with SERT mutant mice as models for human polygenic and epistatic traits and disorders
Authors: Murphy D. L. , Uhl G. R. , Holmes A. , Ren‐Patterson R. , Hall F. S. , Sora I. , Detera‐Wadleigh S. , Lesch K.‐P.
Published: November 2003

Current evidence indicates that virtually all neuropsychiatric disorders, like many other common medical disorders, are genetically complex, with combined influences from multiple interacting genes, as well as from the environment. However, additive or epistatic gene interactions have proved quite difficult to detect and evaluate in human studies. Mouse phenotypes, including behaviors and drug responses, can provide relevant models for human disorders. Studies of gene–gene interactions in mice could thus help efforts to understand the molecular genetic bases of complex human disorders. The serotonin transporter (SERT, 5‐HTT, SLC6A4) provides a relevant model for studying such interactions for several reasons: human variants in SERT have been associated with several neuropsychiatric and other medical disorders and quantitative traits; SERT blockers are effective treatments for a number of neuropsychiatric disorders; there is a good initial understanding of the phenotypic features of heterozygous and homozygous SERT knockout mice; and there is an expanding understanding of the interactions between variations in SERT expression and variations in the expression of a number of other genes of interest for neuropsychiatry and neuropharmacology. This paper provides examples of experimentally–obtained interactions between quantitative variations in SERT gene expression and variations in the expression of five other mouse genes: DAT, NET, MAOA, 5‐HT1B and BDNF. In humans, all six of these genes possess polymorphisms that have been independently investigated as candidates for neuropsychiatric and other disorders in a total of > 500 reports. In the experimental studies in mice reviewed here, gene–gene interactions resulted in either synergistic, antagonistic (including ‘rescue’ or ‘complementation’) or more complex, quantitative alterations. These were identified in comparisons of the behavioral, physiological and neurochemical phenotypes of wildtype mice vs. mice with single allele or single gene targeted disruptions and mice with partial or complete disruptions of multiple genes. Several of the descriptive phenotypes could be best understood on the basis of intermediate, quantitative alterations such as brain serotonin differences. We discuss the ways in which these interactions could provide models for studies of gene–gene interactions in complex human neuropsychiatric and other disorders to which SERT may contribute, including developmental disorders, obesity, polysubstance abuse and others.
The utility of the non‐human primate model for studying gene by environment interactions in behavioral research
Authors: Barr C. S. , Newman T. K. , Becker M. L. , Parker C. C. , Champoux M. , Lesch K. P. , Goldman D. , Suomi S. J. , Higley J. D.
Published: November 2003

Variation in the serotonin transporter gene‐linked polymorphic region (5‐HTTLPR) has been associated with anxiety and harm avoidance and is weakly associated with a number of neuropsychiatric disorders, including Type II alcoholism, which has a high rate of comorbidity with antisocial personality disorder. Studies have also demonstrated interactions between 5‐HTTLPR variation and environmental stress on the incidence of depression. As in humans, there is a serotonin transporter gene promoter length polymorphism in rhesus macaques that produces similar decreases in transcriptional efficiency. Macaques with histories of early‐life stress have been shown to exhibit impulsive aggression, incompetent social behavior and increased behavioral and endocrine responsivity to stress. In this paper, we review studies performed previously in our lab and present preliminary data examininng interactions between early rearing and serotonin transporter gene promoter variation on the incidences of play behavior and aggression in infant rhesus macaques. The data presented here highlight the importance of considering gene‐environment interactions when studying childhood risk factors for aggression, anxiety and related neuropsychiatric disorders and support the use of the nonhuman primate for studing gene by environment interactions in behavioral research.
Scattering rings as a tool for birefringence measurements in porous silicon
Authors: Oton C. J. , Ghulinyan M. , Gaburro Z. , Bettotti P. , Pavesi L. , Pancheri L. , Gialanella S. , Capuj N. E.
Published: November 2003

We report measurements of angle-resolved light scattering in porous silicon films. Scattering rings were observed, and their aperture allowed to measure optical birefringence. These values are confirmed with other techniques. We study birefringence changes when pores are filled with liquids, after thermal annealing, and when the porous silicon layer is chemically etched in HF for different times. A decrease of optical anisotropy was observed in all cases.
Effect of Ru substitution for Re on the thermoelectric properties of AlPdRe icosahedral quasicrystals
Authors: Nagata T. , Kirihara K. , Kimura K.
Published: November 2003

The thermoelectric properties of the quaternary AlPdReRu icosahedral quasicrystals (i-AlPdReRu) obtained by replacing Re with Ru in AlPdRe icosahedral quasicrystals have been studied. In the middle of the substitution of Ru for Re, the electrical conductivity increases and the peak of Seebeck coefficient shifts to a higher temperature side. By Ru substitution for the AlPdRe quasicrystal, the dimensionless figure of merit (ZT) increases 1.5 times from 0.1 to 0.15. According to the result of two-band analysis, the effective mass has peaks at both the compositions of i-AlPdRe and i-AlPdReRu which reveal the peak ZT values. We ascribe the behavior of effective mass to the change in the bond strength of intra- and inter-Mackay icosahedral clusters.
Synchronization in a chain of nearest neighbors coupled oscillators with fixed ends
Authors: El-Nashar Hassan F. , Zhang Ying , Cerdeira Hilda A. , Ibiyinka A. Fuwape
Published: November 2003

We investigate a system of coupled phase oscillators with nearest neighbors coupling in a chain with fixed ends. We find that the system synchronizes to a common value of the time-averaged frequency, which depends on the initial phases of the oscillators at the ends of the chain. This time-averaged frequency decays as the coupling strength increases. Near the transition to the frozen state, the time-averaged frequency has a power law behavior as a function of the coupling strength, with synchronized time-averaged frequency equal to zero. Associated with this power law, there is an increase in phases of each oscillator with 2π jumps with a scaling law of the elapsed time between jumps. During the interval between the full frequency synchronization and the transition to the frozen state, the maximum Lyapunov exponent indicates quasiperiodicity. Time series analysis of the oscillators frequency shows this quasiperiodicity, as the coupling strength increases.
Ferromagnetic resonance experiments in an obliquely deposited FeCo–Al2O3 film system
Authors: Lesnik N. A. , Oates C. J. , Smith G. M. , Riedi P. C. , Kakazei G. N. , Kravets A. F. , Wigen P. E.
Published: November 2003

Granular cermet films (Fe50Co50)x–(Al2O3)1−x fabricated using the electron-beam coevaporation technique at oblique incidence of FeCo and alumina atom fluxes have been found to exhibit both oblique and in-plane uniaxial magnetic anisotropy. This anisotropy first appears just below the percolation threshold due to a magnetic coupling of particles taking place at a certain stage of their growth and coalescence. The FeCo content x varied from 0.07 to 0.49. A simple model of the film microstructure is presented based on the results of magnetization measurements and ferromagnetic resonance at intermediate (9.4 GHz) and high (94 GHz) frequencies. At 94 GHz the concentration dependence of the effective anisotropy field follows the solid solution law, since then the magnetic field is sufficient to magnetize the films close to saturation. The 9.4 GHz data points deviate from the solid solution line below the percolation threshold due to both modification of the resonance fields by intergranular interactions in nonsaturated films and the reduction of the average magnetization of granules, comparing to the saturation magnetization, at room temperature. Different mechanisms of line broadening observed at frequencies used in experiments are also discussed.
Influence of oxygen plasma on electrical and physical parameters of Au–oxide–n-InP structures
Authors: Touhami R. , Ravelet S. , Yagoub M. C. E. , Baudrand H.
Published: November 2003

This article reports on the electrical properties of Au–oxide–n-InP structures obtained by oxygen plasma oxidation and its influence on the conduction mechanism. A discussion on the evolution of the electrical and physical parameters according to the oxidation conditions is presented. We observed that the treatment time and the plasma power strongly influence the parameters, namely, the tuning coefficient, the barrier height at 0 K, the barrier lowering at zero bias, the correct value of the Richardson constant, the dielectric constant, the oxide capacitance, and the oxide thickness. Moreover, in accordance with the current–voltage–temperature measurements, the electrical and physical parameters describing the Au–oxide–n-InP structures depend significantly on the treatment parameters characterizing the oxygen plasma. The results obtained establish the relationships between the parameters of the conduction mechanism and oxidation conditions.
High-temperature annealing of AlGaN: Stress, structural, and compositional changes
Authors: Rajasingam S. , Sarua A. , Kuball M. , Cherodian A. , Miles M. J. , Younes C. M. , Yavich B. , Wang W. N. , Grandjean N.
Published: November 2003

The effect of high-temperature annealing on stress in AlxGa1−xN in different ambients and at different temperatures was studied using ultraviolet micro-Raman spectroscopy. Low (x=0.08) and high (x=0.31 and x=0.34) composition AlGaN, grown by metalorganic chemical vapor deposition (MOCVD) and molecular-beam epitaxy (MBE), were compared. Compositional and morphological changes were monitored using Auger electron spectroscopy (AES) and atomic force microscopy (AFM), respectively. The Raman results demonstrate that all samples exhibit maximum stress changes in the compressive direction when annealed in an air ambient. AES confirms this to be due to higher oxygen incorporation after annealing in the air ambient, and shows higher oxygen incorporation in the vicinity of cracks and defects. MOCVD and MBE samples of a similar composition were found to reach the same biaxial stress, despite differences in initial stress and growth temperature. Relaxation of a parabolic intercrack stress profile to homogeneous stress was observed with annealing in all ambients for cracked samples. AFM results on cracked samples show an increase in width of the primary cracks along the 〈21̄1̄0〉 directions, and the formation of secondary cracks along the 〈11̄00〉 directions.
Phase-locking in a nonuniform array of tunnel junctions
Authors: Nezlobin Nikolai A. , Kiehl Richard A.
Published: November 2003

A nonuniform, one-dimensional tunnel junction array that is designed to promote phase-locking to an ac pump signal is proposed and theoretically investigated for possible information processing applications. The tunnel resistances of the junctions in one part of the array are tailored to provide phase restoration for electrons tunneling in the array, while the tunnel resistances in the other part of the array are designed to provide a time delay with minimal jitter. It is shown that phase-locking of the tunneling is possible at the fundamental and at the one-half subharmonic of the pump frequency. While the required parameter ranges and the necessary degree of control of this design are not practical for tunneling phase logic based on conventional tunnel junction technologies, the proposed design could potentially be realized in a molecular system.
How we hear what is not there: A neural mechanism for the missing fundamental illusion
Authors: Chialvo Dante R.
Published: November 2003

How the brain estimates the pitch of a complex sound remains unsolved. Complex sounds are composed of more than one tone. When two tones occur together, a third lower pitched tone is often heard. This is referred to as the “missing fundamental illusion” because the perceived pitch is a frequency (fundamental) for which there is no actual source vibration. This phenomenon exemplifies a larger variety of problems related to how pitch is extracted from complex tones, music and speech, and thus has been extensively used to test theories of pitch perception. A noisy nonlinear process is presented here as a candidate neural mechanism to explain the majority of reported phenomenology and provide specific quantitative predictions. The two basic premises of this model are as follows: (I) The individual tones composing the complex tones add linearly producing peaks of constructive interference whose amplitude is always insufficient to fire the neuron (II): The spike threshold is reached only with noise, which naturally selects the maximum constructive interferences. The spacing of these maxima, and consequently the spikes, occurs at a rate identical to the perceived pitch for the complex tone. Comparison with psychophysical and physiological data reveals a remarkable quantitative agreement not dependent on adjustable parameters. In addition, results from numerical simulations across different models are consistent, suggesting relevance to other sensory modalities.
Superior radiation resistance of In1−xGaxN alloys: Full-solar-spectrum photovoltaic material system
Authors: Wu J. , Walukiewicz W. , Yu K. M. , Shan W. , Ager J. W. , Haller E. E. , Lu Hai , Schaff William J. , Metzger W. K. , Kurtz Sarah
Published: November 2003

High-efficiency multijunction or tandem solar cells based on group III–V semiconductor alloys are applied in a rapidly expanding range of space and terrestrial programs. Resistance to high-energy radiation damage is an essential feature of such cells as they power most satellites, including those used for communications, defense, and scientific research. Recently we have shown that the energy gap of In1−xGaxN alloys potentially can be continuously varied from 0.7 to 3.4 eV, providing a full-solar-spectrum material system for multijunction solar cells. We find that the optical and electronic properties of these alloys exhibit a much higher resistance to high-energy (2 MeV) proton irradiation than the standard currently used photovoltaic materials such as GaAs and GaInP, and therefore offer great potential for radiation-hard high-efficiency solar cells for space applications. The observed insensitivity of the semiconductor characteristics to the radiation damage is explained by the location of the band edges relative to the average dangling bond defect energy represented by the Fermi level stabilization energy in In1−xGaxN alloys.
Metal content of multicrystalline silicon for solar cells and its impact on minority carrier diffusion length
Authors: Istratov A. A. , Buonassisi T. , McDonald R. J. , Smith A. R. , Schindler R. , Rand J. A. , Kalejs J. P. , Weber E. R.
Published: November 2003

Instrumental neutron activation analysis was performed to determine the transition metal content in three types of silicon material for cost-efficient solar cells: Astropower silicon-film sheet material, Baysix cast material, and edge-defined film-fed growth (EFG) multicrystalline silicon ribbon. The dominant metal impurities were found to be Fe (6×1014 cm−3 to 1.5×1016 cm−3, depending on the material), Ni (up to 1.8×1015 cm−3), Co (1.7×1012 cm−3 to 9.7×1013 cm−3), Mo (6.4×1012 cm−3 to 4.6×1013 cm−3), and Cr (1.7×1012 cm−3 to 1.8×1015 cm−3). Copper was also detected (less than 2.4×1014 cm−3), but its concentration could not be accurately determined because of a very short decay time of the corresponding radioactive isotope. In all samples, the metal contamination level would be sufficient to degrade the minority carrier diffusion length to less than a micron, if all metals were in an interstitial or substitutional state. This is a much lower value than the actual measured diffusion length of these samples. Therefore, most likely, the metals either formed clusters or precipitates with relatively low recombination activity or are very inhomogeneously distributed within the samples. No significant difference was observed between the metal content of the high and low lifetime areas of each material. X-ray microprobe fluorescence spectrometry mapping of Astropower mc-Si samples confirmed that transition metals formed agglomerates both at grain boundaries and within the grains. It is concluded that the impact of metals on solar cell efficiency is determined not only by the total metal concentration, but also by the distribution of metals within the grains and the chemical composition of the clusters formed by the metals.
Time-domain simulation of quantum spin
Authors: Sullivan Dennis M. , Citrin D. S.
Published: November 2003

There have been many recent advances in the fields of spintronics and quantum computing. However, because these fields are grounded in quantum mechanics, there is an increasing need for simulation methods to handle the more complicated interactions. To date, only model calculations have been carried out in the time domain. There is a need for more realistic time-domain simulation of the spatial and spin dynamics. In this article, the explicit implementation of spin into a formulation of the finite-difference time-domain method in the unrestricted Hartree–Fock approximation is presented. Examples are given to show the ability of the method to model basic spin phenomena, such as spin flip and precession. Some suggestions are also presented for the implementation of quantum-based logic gates.
Sputtering growth and optical properties of [100]-oriented tetragonal SnO2 and its Mn alloy films
Authors: Park Young Ran , Kim Kwang Joo
Published: November 2003

SnO 2 and its Mn alloy thin films have been grown on Al2O3(0001) substrates by reactive radio-frequency magnetron sputtering performed in the presence of O2 gas. The prepared films showed preferred orientation in the [100] direction of the rutile structure of SnO2. The O2/Ar gas-flow ratio maintained during the sputtering was found to significantly affect the crystalline quality and stoichiometry of the films. The optical constants of the SnO2 and Sn1−xMnxO2 (x⩽0.27) films were measured by spectroscopic ellipsometry in the 2–5 eV photon energy region. The band-gap energy of SnO2 is determined to be 3.86 eV and that of Sn1−xMnxO2 increases for x⩽0.11 and then decreases for the higher x, exhibiting a negative bowing. The initial increase of the band-gap energy is attributable to the hybridization between localized Mn d states located near the band gap and O p-like valence bands. The decrease of the band-gap energy is interpreted as due to the SnO2–MnO2 alloying effects.
Dynamics of a barrier discharge at high overvoltage
Authors: Khudik V. N. , Nagorny V. P. , Shvydky A.
Published: November 2003

The dynamics of a strong barrier discharge is investigated analytically in the simplest model that still keeps the essential discharge features. It is shown that at high overvoltage, the discharge develops into the ionizing wave moving from the anode toward the cathode. The velocity of this wave is found to be controlled mainly by the charge production rate in the cathode fall region and can considerably exceed the characteristic ion velocity. The influence of the capacitor formed by the dielectric layers on the discharge dynamics is analyzed. It is shown that, depending on the magnitude of the capacitance, two qualitatively different charging regimes exist.
Electron-beam-induced current and cathodoluminescence characterization of InGaAs strain-balanced multiquantum well photovoltaic cells
Authors: Tundo Stefania , Mazzer Massimo , Nasi Lucia , Lazzarini Laura , Salviati Giancarlo , Rohr Carsten , Abbott Paul , Bushnell David B. , Barnham Keith W. J. , Clarke Graham , Peng Ruwen
Published: November 2003

In x Ga 1−x As/In y Ga 1−y As strain-balanced quantum well cells (QWCs) have been shown to be beneficial for photovoltaic applications in particular to extend the light absorption edge of a single-junction cell toward the near infrared with a lower reduction of the open-circuit voltage compared to a single band-gap cell. The strain-balancing condition ensures that the multi-quantum well as a whole does not relax. However, if the mismatch between wells and barriers exceeds a critical limit, the structure becomes vulnerable to morphological or compositional fluctuations, which can lead to a local structural breakdown with the generation of extended defects of a completely different nature from misfit dislocations. In this work, we investigated a series of strain-balanced InGaAs QWCs grown on InP for thermophotovoltaic applications by means of electron-beam-induced current (EBIC) and cathodoluminescence (CL) measurements. Despite being electrically active, these defects appear to have a minor impact on the dark current of the cells but cause a drop of the photocurrent at relatively low forward bias voltage. The higher carrier collection efficiency revealed both by EBIC and CL at the boundaries of the defects suggests that a notch in the valence band edge limits the collection of holes generated in the MQW and the energy states, induced by the defects inside the energy gap, assist the tunneling of holes through the notch. At zero bias, the overall reduction of the collection efficiency is of the order of a few percent but the rate of recombination of photogenerated carriers increases dramatically with increasing forward-bias voltage as the junction built-in field drops more rapidly where the density of in-gap states is higher.
Analysis of interfacial adhesion based on electrical contact resistance measurements
Authors: Kogut L. , Komvopoulos K.
Published: November 2003

An analytical approach for determining the adhesion force and adhesion energy at contact interfaces from electrical contact resistance measurements is presented for isotropic, conductive, and rough surfaces. The method is especially suitable for in situ measurement of adhesion forces in lightly loaded contacts, and because it accounts for the real contact area, it yields more accurate estimates of the adhesion energy than traditional methods based on the apparent contact area of microcantilever beams partially adhered to substrates. The advantage of obtaining adhesion measurements in the case of plastically deformed contacts is demonstrated by the wide range of the electrical contact resistance achieved with this method. The relation between adhesion force and electrical contact resistance is shown to be independent of the surface topography when the asperities deform plastically. For this situation, the present method is especially suitable for adhesion measurements in dynamic systems, where the interfacial topography changes with contact cycles due to irreversible deformation of the asperity microcontacts. Analytical results are presented for the adhesion force and adhesion energy at rough contact interfaces in terms of electrical contact resistance and surface topography parameters. The present analytical approach also provides a means of determining the interfacial surface energy of contacting bodies with known surface energies or the surface energy of two identical contacting surfaces.
Photoemission spectral analysis of fullerene films polymerized by argon plasma treatment
Authors: Maruyama Ryuichiro
Published: November 2003

Photoemission spectral analysis was carried out on plasma polymerized fullerene (C60) films prepared by sublimating C60 under an argon plasma. In the photoemission analysis, the overall distribution of the shallow valence band states of the plasma-treated C60 was compared with pristine C60. These changes suggest that the pi conjugation of the shallow valence band states of two C60 molecules is induced by polymerization during the plasma treatment. To investigate the changes in the onset of the shallow valence band states brought about by polymerization, the orbital energy levels in C60 dimers were examined using the semiempirical AM-1 method. Calculations showed that the highest occupied molecular orbital levels of the dimers were shallower than that of C60.
Structure and magnetic properties of Gd nanoparticles and carbon coated Gd/GdC2 nanocapsules
Authors: Si P. Z. , Škorvánek I. , Kováč J. , Geng D. Y. , Zhao X. G. , Zhang Z. D.
Published: November 2003

Gd nanoparticles and carbon coated Gd/GdC2 nanocapsules have been prepared by means of arc discharge in argon and methane, respectively. In the Gd nanoparticles, gadolinium oxide was detected by x-ray diffraction, while the presence of metallic gadolinium was proved by oxygen analysis and x-ray photoelectron spectra. In the nanocapsules, the existence of GdC2 and Gd was detected by x-ray diffraction. Shell/core structures were observed for either the nanoparticles (with diameters larger than 20 nm) or the nanocapsules. The magnetization data above 25 K, when scaled as a function of μ0H/T, fall on a universal curve while the deviation of the magnetization curves at 4.2 K from the universal curves was ascribed to the superparamagnetism–ferromagnetism transition of small Gd particles. The temperature dependence of magnetization supports the theoretical predictions for very tiny Gd nanoparticles. The presence of metallic Gd in these nanocapsules results in comparatively high magnetization of about 60.5 A m2/kg at 4.2 K, compared with the carbon-coated gadolinium carbide nanocapsules without the metallic Gd core. The possibility of the existence of the spin-glass-like state is discussed for Gd(O) nanoparticles and Gd(C) nanocapsules.
Investigation of the direct electromigration term for Al nanodots within the depletion zone of a pn junction
Authors: Young Park Jeong , Phaneuf R. J.
Published: November 2003

We have investigated the effect of the large field produced within the depletion region of a pn junction on the shapes and positions of aluminum nanodots. Dots of 10–60 nm diameter were fabricated by the application of voltage pulses between an Al-coated scanning tunneling microscopy tip and the Si substrate. Reverse bias conditions produce an intense field (104–105 V/cm), but the current density is quite small (∼10−2 A/cm2). This electric field dominated configuration provides a unique model system for the separation of the two components of electromigration, direct and wind forces. We find that even after several tens of hours the observed motion of Al is confined to small changes in dot shape, with no evident motion of the dots as a whole. Our observations are consistent with a strong adhesion between the dots and the underlying substrate and a dominant direct force term.
Noise modeling in HgCdTe heterostructure devices
Authors: Józwikowski Krzysztof , Sewell Richard , Musca Charles , Dell John , Faraone Lorenzo
Published: November 2003

A numerical method to analyze noise generation in semiconductor devices and based on “transport equations for fluctuations” is presented. The spectral intensity of temperature fluctuations, fluctuations of background illumination, fluctuations of thermal g–r processes (including Auger, radiative, and S–R mechanisms) as well as fluctuations of electron and hole mobility were taken into account. Noise spectra of midwavelength HgCdTe heterostructure photoconductors were measured over a wide temperature range, and the numerical model was fitted to these data. The results of the numerical model show the spatial distributions and the relative contributions of each source of fluctuation to the total noise measured in the devices.
Spherical cavity expansion in densifying material
Authors: Xin Kai , Lambropoulos John C.
Published: November 2003

When subjected to sufficiently large compressive stresses, amorphous silica glass densifies permanently. Such densification is facilitated by shear stresses. It also exhibits some unique features upon grinding, which are associated with the plastic behavior of amorphous silica under constrained compression. To describe the effect of densification, a constitutive law proposed by Lambropoulos et al. [J. Am. Ceram. Soc. 79, 1441 (1996)] is used to model plastic deformation of silica. A densification parameter is introduced as a material parameter. Analytic solution of cavity expansion is presented here for this constitutive law. Both associated and nonassociated flow theories are studied. The range of values of the densification parameter for amorphous silica is estimated. For amorphous silica, the cavity expansion model shows that, based on the induced stress distribution, densification contributes to lower removal rate and less subsurface damage.
Electrical isolation of n- and p-In0.53Ga0.47As epilayers using ion irradiation
Authors: Carmody C. , Tan H. H. , Jagadish C.
Published: November 2003

A study of the evolution of sheet resistance of p- and n-type In0.53Ga0.47As epilayers during O, C, Li, and H irradiation was conducted. The threshold dose at which the material becomes highly resistive increased upon decreasing the mass of the implanted ion, was higher for n-InGaAs as compared to p-InGaAs and was greater for samples with a higher initial free carrier concentration. Implantation with H+ yielded isolation behavior that was different from that for implantation with the three medium-mass ions. The thermal stability of defects induced by implantation was also investigated by cumulative annealing, and was found to be slightly higher in n-InGaAs as compared to p-InGaAs. Shallow donor production in the InGaAs epilayer during implantation played a crucial role in determining the electrical characteristics of the samples.
Coupling effects for counterpropagating light beams in lithium niobate crystals studied by grating translation technique for extremely high external electric fields
Authors: Luennemann M. , Buse K. , Sturman B.
Published: November 2003

The grating translation technique (GTT), which employs a momentary shift of light fringes during holographic recording, is a powerful tool for characterization of nonlinear materials. Earlier, it was used in the transmission geometry. We formulate the main relations of GTT for the reflection case. These allow us to determine in situ the real and imaginary parts of the coupling strength and to detect the formation of refractive-index and absorption gratings. We apply GTT to determine the photorefractive characteristics of two-wave coupling in z-cut iron-doped lithium niobate crystals for an extremely small grating spacing (Λ≃105 nm) and extremely large externally applied electric fields (up to 650 kV/cm). Stabilization of the light fringes, crucially important in the reflection geometry, has been achieved with the use of an electronic feedback loop. We prove that the feedback introduces a frequency detuning between the light beams and modifies strongly the nonlinear response.
Relaxing melt and plasma bubbles in laser-pulsed metals
Authors: Dömer H. , Bostanjoglo O.
Published: November 2003

Melting and ablation of aluminum, chromium, and nickel films by nanosecond laser pulses with fluences of 2.4–13 J/cm2 were tracked by high-speed transmission electron microscopy and selected area (20 μmø) diffraction. Electron exposure time was 8 ns. At fluences causing no detected evaporation, short-range order in the melt, as probed by diffraction, shows up with a time lag of nanoseconds. At lower “evaporating” fluences, the material is ablated by exploding gas bubbles nucleating all over the melt within 5 ns. At sufficiently high laser fluences, a plasma is produced with an ionization degree >20%, varying on the micrometer scale, as revealed by dark-field imaging.
Investigation of a hollow anode with an incorporated ferroelectric plasma source for generation of high-current electron beams
Authors: Gleizer J. Z. , Krokhmal A. , Krasik Ya. E. , Felsteiner J.
Published: November 2003

We report experimental results of operation of a high-current hollow anode (HA) with a BaTi ferroelectric plasma source (FPS) incorporated in it. It is shown that the application of the FPS allows one to significantly decrease the HA surface area, thus providing a compact electron source. Use of this HA as an electron source in a high-voltage diode for generation of high-current electron beams is described as well. It was found that the FPS allows reliable ignition and sustaining of the HA discharge with current amplitude ⩽1.2 kA and pulse duration ⩽2×10−5 s at N2 gas pressure of (1–3)×10−4 Torr. Also, it was found that the operation of the HA is characterized by plasma formation with density of ∼4×1012 cm−3, electron temperature of ∼5 eV, and that the plasma acquires a positive potential of ∼10 V with respect to the anode and of 50–70 V with respect to the autobiased HA output grid. It is shown that the autobiased HA output grid prevents plasma penetration towards the accelerating gap if the grid half-cell size has approximately the same value as the thickness of the double layer formed between the plasma and the grid wires. Generation and characterization of a high-current electron beam with current amplitude of ∼1.2 kA was achieved under an accelerating pulse amplitude ⩽300 kV and ∼400 ns pulse duration.
Electric-field-induced insulator–metal transition in Pr0.5Ca0.5MnO3 thin films in ramp-type junctions
Authors: Murakami T. , Sakai J. , Imai S.
Published: November 2003

A large decrease in the electrical resistance of the junction was observed with an applied voltage of several volts in small area ramp-type junctions, YBa2Cu3O7−δ/Pr0.5Ca0.5MnO3−z/SrRuO3. The lowest resistivity of the Pr0.5Ca0.5MnO3−z barrier layer attained was ∼100 Ω cm, which is much lower than the previously observed resistivities in the electric-field-induced metallic states in a single crystal of Pr0.7Ca0.3MnO3 or in stacked junctions with a Pr0.5Ca0.5MnO3−z barrier. The lowest resistivity is still much larger than that of the fully ferromagnetic metallic states induced by a magnetic field. However, it was found that the lowest resistivity is not intrinsic and that it is limited by a series resistance caused by the SrRuO3 electrode, including contact resistances. The lower resistivity can be reached using an electrode with a lower resistance.
Light-emitting devices based on ruthenium(II)(4,7-diphenyl-1,10-phenanthroline)3: Device response rate and efficiency by use of tris-(8-hydroxyquinoline) aluminum
Authors: Yang Jihua , Gordon Keith C. , Zidon Yigal , Shapira Yoram
Published: November 2003

Light-emitting devices based on ruthenium(II)(4,7-diphenyl-1,10-phenanthroline)3 ([Ru(dphphen)3]2+) as emitter have been fabricated. The effect of an electron transport layer of tris-(8-hydroxyquinoline) aluminum (Alq3) on device performance has been investigated. The emission, peaking at 630 nm, for the indium–tin–oxide (ITO)glass/[Ru(dphphen)3]2+/Ag device reaches maximum luminance after about 15 min at a turn on voltage of 2.5 V. The use of an ITO/[Ru(dphphen)3]2+/Alq3/Ag device reduces this response time to about 120 s at a turn on voltage of 7 V. A maximum brightness of 1300 cd/m2 can be obtained at 15 V within 2 s, with a luminous efficiency of 0.27 cd/A. Based on the charge transporting characteristics of [Ru(dphphen)3]2+ and Alq3 films determined by surface photovoltage spectroscopy, the improved device response time and efficiency are attributed to the enhanced electron injection at [Ru(dphphen)3]2+/Alq3 interface.
Preparation of high coercivity magnetic FePt nanoparticles by liquid process
Authors: Iwaki Toru , Kakihara Yasuo , Toda Toshiyuki , Abdullah Mikrajuddin , Okuyama Kikuo
Published: November 2003

FePt nanoparticles have been synthesized using a liquid process, by mixing two precursor liquids: ferric acetyl ferric acetyl acetonate, Fe(acac)3, and platinum acetyl acetonate, Pt(acac)2 in polyol solution of sodium hydroxide at high temperatures. To avoid the agglomeration of the produced particle, aminoethoxy ethanol has been used. The particle size was monodisperse and non- agglomerating. The fraction of Fe in FexPt(100−x) was a linear function of Fe(acac)3 molar fraction. The highest room temperature coercivity (up to 10 kOe) was observed in Fe53Pt47 sample after annealed at 580 °C, which also exhibited the most ordered fct structure.
Geometric resonance in a periodic waveguide
Authors: Pogrebnyak V. A.
Published: November 2003

The geometric resonance has been predicted in a planar periodically corrugated waveguide. It is shown that for a change in thickness of the waveguide, at some of its values, one of the cutoff frequencies splits into two, separated by the forbidden gap, while other cutoff frequencies experience only slight shifts due to the periodicity. This resonant splitting causes the creation of an additional mode in the electromagnetic spectrum of the waveguide with the negative group velocity.
Structure of germanium nanoparticles prepared by evaporation method
Authors: Yamada Susumu
Published: November 2003

The structural characteristics of crystalline germanium nanoparticles prepared by an evaporation method were investigated by transmission electron microscopy and electron energy-loss spectroscopy. Fivefold multiply twinned particles with diameters as fine as 7 nm were found; the misfit angle caused by symmetry is compensated by lattice distortion without introducing lattice defects. It is clarified that both the quantum size effect and lattice distortion occur in particles with 12–20 nm diameter. Due to distortion, the unit cell volume of these particles is compressed to 94% of that for bulk, on average. It was also found that the diamond structure is stable when the particle diameter is as small as approximately 2 nm.
Elastic anisotropy and incohesive bond of chemical-vapor-deposition diamond film: Acoustic resonance measurements and micromechanics modeling
Authors: Nakamura Nobutomo , Ogi Hirotsugu , Ichitsubo Tetsu , Hirao Masahiko , Tatsumi Natsuo , Imai Takahiro , Nakahata Hideaki
Published: November 2003

This article studies elastic anisotropy of chemical vapor deposition (CVD) polycrystalline diamond films using acoustic spectroscopy and micromechanics modeling. CVD diamond films often exhibit elastic anisotropy between the film-growth direction and in-plane direction and show five independent elastic constants. They are denoted by C11, C33, C13, C44, and C66 when the x3 axis lies along the film-growth direction. Measurements of thickness resonance frequencies and free-vibration resonance frequencies of the diamond film deduce four independent elastic constants among them, including C44 and C66, with which the elastic anisotropy is discussed. The anisotropy between the shear moduli is 5%–10%. The elastic constants are remarkably smaller than those of an isotropic polycrystalline diamond. We attribute the anisotropy and small elastic constants of the CVD diamond film to local incomplete cohesion. This view is supported by a micromechanics calculation.
Shock response of tantalum: Lateral stress and shear strength through the front
Authors: Gray G. T. , Bourne N. K. , Millett J. C. F.
Published: November 2003

Lateral stresses generated by shock loading in tantalum have been determined using manganin stress gauges. These have been used in combination with the measured longitudinal impact stresses to determine the shear strength behind the shock. Results show that with an increase in impact stress, the shear strength in tantalum also increases. Analysis shows that during shock loading the lateral stress in tantalum increases behind the shock front. Since the longitudinal stress is nominally constant until arrival of the release, this implies that the shear strength is reducing behind the shock front. The shock-wave response of tantalum is discussed in the context of a previous weak-shock wave-profile analysis of tantalum, and in terms of the defect generation and storage response of pure face-centered- versus body-centered-cubic metals.
Field emission from amorphous-carbon nanotips on copper
Authors: Huang C. J. , Chih Y. K. , Hwang J. , Lee A. P. , Kou C. S.
Published: November 2003

Amorphous-carbon (a-C) nanotips were directly grown on copper substrates by microwave plasma-enhanced chemical-vapor deposition. The length of a typical a-C nanotip is ∼250 nm and its tip diameter is ∼25 nm. The in-plane correlation length La, equivalent to the size of the sp2 clusters, is determined to be 1.2 nm through the intensity ratio of the D and G peaks in the Raman spectrum, which is about in the optimum range for field emission. A low turn-on field of 1.6 V/μm at 10 μA/cm2, a threshold field of 3.8 V/μm at 10 mA/cm2, and a high current density of 32.42 mA/cm2 at 4.0 V/μm are achieved. The field emission characteristics of a-C nanotips are close to those of carbon nanotubes, and much better than what has been reported for flat diamond-like carbon or a-C:H coated cathodes. The roles of the sp2 cluster size, electron confinement and conductivity in the field emission of a-C nanotips are discussed.
Tensile behavior of electrorheological fluids under direct current electric fields
Authors: Tian Yu , Zou Qian , Meng Yonggang , Wen Shizhu
Published: November 2003

Tensile behavior of electrorheological (ER) fluids based on zeolite and silicone oil under different applied dc voltages has been experimentally investigated. Five types of tensile behavior have been observed and described. The different behaviors were reasonably explained by the structural evolution of particle chains and the decreasing field effect during their elongation. The experimental results also revealed that the tensile yield strength was proportional to the electric field to the power of 1.58 for voltages ranging between 0.2 and 1.0 kV, 2.11 for voltages between 1.0 and 2.5 kV, and 1.17 at voltages between 2.5 and 3.5 kV. The exponent of 2.11 is higher than the square relationship predicted by traditional polarization models. At higher voltages, the limitation of the interaction between the ER fluids and the electrodes caused the exponent to decrease. Also, the tensile behavior of ER fluids was compared with the elongation of metal bars that determined the tensile strength of metal materials, to assist in understanding the structural strengthening effect and other behaviors of ER fluids under elongation. Finally, current density was also simultaneously tested to verify the structure evolution during elongation.
Scattering matrix method for modeling acoustic waves in piezoelectric, fluid, and metallic multilayers
Authors: Reinhardt Alexandre , Pastureaud Thomas , Ballandras Sylvain , Laude Vincent
Published: November 2003

Many ultrasonic devices, among which are surface and bulk acoustic wave devices and ultrasonic transducers, are based on multilayers of heterogeneous materials, i.e., piezoelectrics, dielectrics, metals, and conducting or insulating fluids. We introduce metal and fluid layers and half spaces into a numerically stable scattering matrix model originally proposed for solving the problem of plane wave propagation in piezoelectric and dielectric multilayers. The method is stable for arbitrary thicknesses of the layers. We discuss how the surface Green’s functions can be computed for an arbitrary stack of homogeneous materials with plane interfaces. Aditionnally, we set up a backscattering algorithm to compute the distribution of electromechanical fields at any point in the stack. The model is assessed by considering some well-known examples.
Oxygen doping of TiO2/poly(phenylene–vinylene) bilayer solar cells
Authors: van der Zanden Barbara , Goossens Albert
Published: November 2003

The change in electronic properties of poly[2-methoxy-5-(3,7dimethyloctyloxy), paraphenylene–vinylene] (MDMO–PPV) in oxygen-saturated SnO2:F/TiO2/MDMO–PPV/Hg cells caused by optical irradiation is the subject of the present study. During preparation, the samples are exposed to air with exclusion of light, or in a glovebox in the presence of light. When these samples are subjected to a well-controlled light dose in ambient atmosphere, their current–voltage behavior changes. If open-circuit conditions prevail during irradiation, the dark forward and reverse currents increase. However, when the cells are shorted during irradiation, in ambient atmosphere, virtually no change in the I–V response occurs. The changes in the I–V response are reversible and are not related to photodegradation. These findings can be accounted for by the occurrence of oxygen doping. When oxygen is present it can interact with electrons in the lowest occupied molecular orbital (LUMO) band of the polymer to form a charge transfer complex. Due to this electron transfer, holes are generated in the MDMO–PPV highest occupied molecular orbital band. This type of oxygen doping takes place upon illumination under open-circuit conditions, since in this case LUMO-band electrons are not transferred to TiO2. When cells are short circuited, the photogenerated electrons are injected into the conduction band of TiO2 and quickly escape from the interface. In this case the electron transfer to oxygen is inhibited. To evaluate the oxygen-doping effect quantitatively, capacitance–voltage scans have been recorded. From these scans the increase of the acceptor density due to the light dose is determined. It is found that soon after the onset of irradiation the acceptor density becomes so high that tunneling of electrons through the barrier at the TiO2/MDMO–PPV interface becomes possible.
Buckling suppression of SiGe islands on compliant substrates
Authors: Yin Haizhou , Huang R. , Hobart K. D. , Liang J. , Suo Z. , Shieh S. R. , Duffy T. S. , Kub F. J. , Sturm J. C.
Published: November 2003

A cap layer was used to suppress buckling during the relaxation of compressively strained 30 nm Si0.7Ge0.3 islands on borophosphorosilicate glass. The lateral expansion and buckling of a bilayer structure made of SiGe and a cap layer were studied by both modeling and experiment. Both epitaxial silicon and amorphous silicon dioxide (SiO2) caps were investigated. Caps stiffen the islands to reduce buckling and accelerate the lateral relaxation, so that larger, flat, relaxed SiGe islands can be achieved. Using a 31 nm silicon cap, flat Si0.7Ge0.3 islands up to 200 μm×200μm were achieved. However, germanium diffusion in the SiGe/Si structure took place during relaxation anneals and lowered the germanium fraction of the final fully relaxed SiGe film. Silicon dioxide caps, which are not prone to germanium diffusion, allowed suppression of SiGe buckling without lowering the germanium percentage. Full relaxation of SiGe islands was achieved by a controlled multicycle silicon dioxide removal and anneal procedure. Large, fully relaxed, smooth SiGe islands obtained using cap layers indicate that this approach could be of potential use for electronic device applications.
Effects of oxidation on band edge states in H-covered ultrasmall Si quantum boxes: Calculations of electronic states and oscillator strengths
Authors: Nishida Masahiko
Published: November 2003

Electronic state calculations are performed by the extended Hückel-type nonorthogonal tight-binding method for a Si dihydride backbonded to oxygen on the hydrogen-covered (001) surface of ultrasmall Si 5×5×Nz (Nz=5,9,13, etc.) quantum boxes (QBs) with (100) planes. It is found that the backbond oxidation clearly induces surfacelike electronic states at the conduction-band edge and downshifts the band gaps. Calculated oscillator strengths in the oxidized QBs are about three orders of magnitude higher than those in the unoxidized counterparts, explaining luminescence enhancement due to oxidation observed in porous Si.