bluuebunny/crossref_metadata_2025 huggingface dataset:
Effect of rapid thermal annealing on microstructural, magnetic, and microwave properties of FeGaB alloy films
Authors: Shah Lubna R. , Fan X. , Kou X. , Wang W. G. , Zhang Y. P. , Lou J. , Sun N. X. , Xiao J. Q.
Published: May 2010

We have performed rapid thermal annealing (RTA) experiments on crystalline and amorphous (Fe70Ga30)1−xBx films in order to understand and reduce the linewidth of ferromagnetic resonance (FMR). In the absence of cubic anisotropy in amorphous films, the effective anisotropy is small, resulting in a narrow FMR linewidth. The FMR linewidth in both crystalline and amorphous films can be further reduced by RTA. In crystalline films, a minimum FMR linewidth can be achieved by annealing the samples at a relatively high temperature for a short time. The effect is attributed to the reduction in the uniaxial anisotropy. In amorphous films, the reduction in FMR linewidth is achieved at low temperature and short annealing time. Elevated temperatures and prolong time may crystallize the amorphous structure and introduce a much large cubic anisotropy, resulting in a large FMR linewidth.
Orthogonal fluxgate employing discontinuous excitation
Authors: Weiss Eyal , Paperno Eugene , Plotkin Anton
Published: May 2010

In this work, we suggest a new method for the reduction of the power consumption of an orthogonal fluxgate employing an amorphous wire. In order to reduce the power consumption, we introduce idle intervals in the fluxgate excitation. In fluxgates where the excitation current is applied directly to the wire core, the excitation wave form can easily be manipulated due to the very small impedance of the wire core. The resulted discontinuities in the excitation increase the fluxgate noise by a factor of about 3.5. In order to eliminate this excess noise, we simply discard the data related to the excitation idle intervals from the signal processing of the fluxgate output. As a result, we have reduced the fluxgate power consumption by a factor of 16, from 6.4 mW at 100% duty cycle down to 0.4 mW at 6.25% duty cycle. It is important to note that the reduction of power consumption is obtained without decreasing the fluxgate resolution.
Field-Programmable Gate Array-based fluxgate magnetometer with digital integration
Authors: Butta Mattia , Janosek Michal , Ripka Pavel
Published: May 2010

In this paper, a digital magnetometer based on printed circuit board fluxgate is presented. The fluxgate is pulse excited and the signal is extracted by gate integration. We investigate the possibility to perform integration on very narrow gates (typically 500 ns) by using digital techniques. The magnetometer is based on field-programmable gate array (FPGA) card: we will show all the advantages and disadvantages, given by digitalization of fluxgate output voltage by means of analog-to-digital converter on FPGA card, as well as digitalization performed by external digitizer. Due to very narrow gate, it is shown that a magnetometer entirely based on a FPGA card is preferable, because it avoids noise due to trigger instability. Both open loop and feedback operative mode are described and achieved results are presented.
Many-body design of highly strained GaInNAs electroabsorption modulators on GaInAs ternary substrates
Authors: Fujisawa Takeshi , Arai Masakazu , Kano Fumiyoshi
Published: May 2010

Electroabsorption in highly strained GaInAs and GaInNAs quantum wells (QWs) grown on GaInAs or quasi-GaInAs substrates is investigated by using microscopic many-body theory. The effects of various parameters, such as strain, barrier height, substrate composition, and temperature are thoroughly examined. It is shown that the value of the absorption coefficient strongly depends on the depth of the QWs under large bias electric field due to the small overlap integral of wave functions between the conduction and valence bands. The use of GaInNAs QWs makes the strain in the well layer very small. Further, the effective quantum-well depth is increased in GaInNAs QWs due to the anticrossing interaction between the conduction and N-resonant bands, making it possible to obtain larger absorption coefficient under large bias electric fields without using wide-band gap materials for barriers.
Giant magnetoelectric effect in the Jeff=1/2 Mott insulator Sr2IrO4
Authors: Chikara S. , Korneta O. , Crummett W. P. , DeLong L. E. , Schlottmann P. , Cao G.
Published: May 2010

Strong spin-orbit, crystal field, and Coulomb interactions compete to drive a narrow-gap Mott state in Sr2IrO4. Our study of the magnetic, thermal, and electrical properties of single-crystal Sr2IrO4 reveals a giant magnetoelectric effect (GME) arising from a frustrated magnetic/ferroelectric state below 240 K. The GME features (1) a strongly enhanced electric permittivity that peaks near a newly observed magnetic anomaly at 100 K, and (2) a large magnetodielectric shift (100%) near a metamagnetic transition.
Lifetimes of magnetic excitations in Fe and Co atoms and clusters on Pt(111)
Authors: Schuh T. , Balashov T. , Miyamachi T. , Takács A. F. , Suga S. , Wulfhekel W.
Published: May 2010

Investigations of single magnetic atoms on a Pt surface revealed giant magnetic anisotropies. Recently, scanning tunneling microscopy was used to probe single Fe and Co atoms, dimers, and trimers on Pt(111). The magnetic anisotropy and, additionally, the lifetimes of the magnetically excited states were measured by inelastic tunneling spectroscopy. The lifetimes are in the order of femtoseconds due to an effective electron-electron relaxation process caused by the strong hybridization of the impurity states and the substrate. The different lifetimes are explained by the quantum mechanical nature of Fe and Co on Pt(111). The measurements of an Fe dimer show besides the collinear excitation, a noncollinear excitation with two possible decaying channels: spin-flip and non-spin-flip. Thus information on the magnetization dynamics can be extracted from inelastic spectra.
Visualizing the propagation of volume magnetization in bulk ferromagnetic materials by neutron grating interferometry (invited)
Authors: Grünzweig C. , David C. , Bunk O. , Kohlbrecher J. , Lehmann E. , Lai Y. W. , Schäfer R. , Roth S. , Lejcek P. , Kopecek J. , Pfeiffer F.
Published: May 2010

In this article we report on a neutron interferometry technique based on diffraction gratings which was used to visualize the geometry-dependent magnetization processes in bulk ferromagnetic materials. The contrast origin is based on the refraction of unpolarized neutrons at magnetic domain walls and the obtained image is termed neutron dark-field image (DFI). The magnetization process is imaged by measuring the spatially resolved domain wall density distribution of the sample. The sample under investigation was a polycrystalline steel plate where the magnetization process was imaged for different sample orientations. The DFI results of the magnetization processes were verified on the one hand by complementary neutron small angle scattering (SANS) experiments and on the other hand by finite element method (FEM) simulations. The obtained SANS and FEM results verify the same magnetization process behavior as observed in the DFI results.
Superconductivity in SmFe1−xCoxAsO (x=0.0–0.30)
Authors: Awana V. P. S. , Pal Anand , Vajpayee Arpita , Meena R. S. , Kishan H. , Husain Mushahid , Zeng R. , Yu S. , Yamaura K. , Takayama-Muromachi E.
Published: May 2010

We report synthesis, structural details, and magnetization of SmFe1−xCoxAsO with x ranging from 0.0 to 0.30. It is found that Co substitutes fully at Fe site in SmFeAsO in an isostructural lattice with slightly compressed cell. The parent compound exhibited known as the spin density wave (SDW) character is below at around 140 K. Successive doping of Co at Fe site suppressed the SDW transition for x=0.05 and later induced superconductivity for x=0.10, 0.15, and 0.20, respectively, at 14, 15.5, and 9 K. The lower critical field as seen from magnetization measurements is below 200 Oe. The appearance of bulk superconductivity is established by wide open isothermal magnetization M(H) loops. Superconductivity is not observed for higher content of Co, i.e., x≥0.30. Clearly the Co substitution at Fe site in SmFe1−xCoxAsO diminishes the Fe SDW character, introduces bulk superconductivity for x between 0.10 and 0.20 and finally becomes nonsuperconducting for x above 0.20. The Fe2+ site Co3+ substitution injects mobile electrons to the system and superconductivity appears; however direct substitution introduces simultaneous disorder in superconducting FeAs layer and thus superconductivity disappears for higher content of Co.
Superspin glass aging behavior in textured and nontextured frozen ferrofluid
Authors: Nakamae S. , Crauste-Thibierge C. , Komatsu K. , L’Hôte D. , Tahri Y. , Vincent E. , Dubois E. , Dupuis V. , Perzynski R.
Published: May 2010

The effect of magnetic anisotropy-axis alignment of individual nanoparticles on the collective aging behavior in the superspin glass state of a frozen ferrofluid has been investigated. The ferrofluid studied here consists of maghemite nanoparticles (γ-Fe2O3, mean diameter=8.6 nm) dispersed in glycerin at a volume fraction of ∼15%. The low temperature aging behavior has been explored through “zero-field cooled magnetization” (ZFCM) relaxation measurements using superconducting quantum interference device magnetometry. The ZFCM response functions were found to scale with effective age of the system in both textured and nontextured superspin glass states, but with markedly different scaling exponents, μ. The value of μ was found to shift from ∼0.9 in nontextured case to ∼0.6 in the textured case, despite the identical cooling protocol used in both experiments.
Hyperfine interaction study of CeRh2Si2 with perturbed γ-γ angular correlation spectroscopy using C111d and C140e probes
Authors: Cabrera-Pasca G. A. , Carbonari A. W. , Saxena R. N. , Bosch-Santos B.
Published: May 2010

The intermetallic compound CeRh2Si2 has been investigated by means of perturbed γ-γ angular correlation (PAC) spectroscopy using I111n(C111d) and L140a(C140e) probe nuclei. Measurements with C111d were carried out in the temperature range of 8–295 K. The results showed a highly distributed and almost temperature independent quadrupole interaction. No magnetic interaction was observed with this probe down to the lowest measured temperature. Measurements with L140a(C140e) probe were carried out in the temperature range of 8–36 K to determine the magnetic hyperfine field at Ce sites. A well defined magnetic interaction was observed at around 36 K. The PAC spectra below 25 K showed an additional magnetic interaction which was assigned to C140e probe substituting Ce positions with a different magnetic structure.
Zero field magnetic phase transitions and anomalous low temperature upturn in resistivity of single crystalline α-TmAlB4
Authors: Sung N. H. , Kreyssig A. , Kim H. , Tanatar M. A. , Rhyee J. S. , Kang B. Y. , Kim M. G. , Kim J. Y. , Canfield P. C. , Prozorov R. , Goldman A. I. , Cho B. K.
Published: May 2010

In this study, pure α-TmAlB4 (YCrB4 structure) single crystals were grown with no β-TmAlB4 (ThMoB4 structure) intergrowth, and zero magnetic field transitions were confirmed through specific heat capacity, magnetization, and electric resistivity measurements. The anomalous magnetic transition was found at approximately 6.2 K with long range antiferromagnetic transition at 5.6 K. The difference in field dependence between these two transitions indicates that they do not share a common magnetic origin. In addition, we investigated electrical resistivity down to 20 mK, and found upturn behavior at around 0.8 K. The low temperature upturn anomaly in resistivity was not found for other compounds of investigation for RAlB4 (R=rare earth elements), which suggests that an α-RAlB4 system has a significantly different ground state, compared to a β-RAlB4 system.
ac susceptibility of the quantum critical point mimicking series Lix[Mn1.96Li0.04]O4 (x=0.0,0.1,0.2,0.35,0.5,0.6,0.8,1.0)
Authors: Heitmann T. , Gaddy J. , Lamsal J. , Petrovic M. , Montfrooij W.
Published: May 2010

The present work elucidates the series of magnetic phase transitions present in the series of spinel compounds Lix[Mn1.96Li0.04]O4 (x=0.0,0.1,0.2,0.35,0.5,0.6,0.8,1.0). These systems display dynamical scaling originating from the presence of magnetic clusters that form below ∼70 K. This scaling is similar to what has been observed in the 122 quantum critical point materials containing intrinsic disorder. We study this system using ac susceptibility in order to understand how disorder leads to fragmentation of the magnetic lattice. The Li doped system’s antiferromagnetic (AF) ordering sets in below ∼70 K; however, for x=1 this ordering is limited to clusters of Mn4+ ions that are weakly coupled to each other. For the intermediate Li concentrations we observe the formation of individual spin clusters consistent with neutron scattering experiments and we find evidence for the coaligning of these clusters for T≲20 K. A maximum in the peak of the susceptibility versus Li content between x=0.5 and x=0.35 indicates a crossover from a regime dominated by the cluster dynamics to one in which the long-range order of the delithiated λ-MnO2 phase begins to emerge. We discuss the magnetic phase diagram pertaining to short-range order in relationship to the dynamic response of these systems as measured by inelastic neutron scattering experiments.
Giant magneto-optical Faraday effect in GaP epilayers containing MnP magnetic nanoclusters
Authors: Monette Gabriel , Lacroix Christian , Lambert-Milot Samuel , Boucher Vincent , Ménard David , Francoeur Sébastien
Published: May 2010

We report a giant magneto-optical (MO) effect in a GaP(011) epilayer with embedded MnP nanoclusters (GaP:MnP) grown on a GaP(011) substrate using metal-organic vapor phase epitaxy. The MO effect exhibits a hysteretic behavior when sweeping the applied magnetic field, thereby indicating a clear dependence upon the magnetization of the sample. The measured Faraday rotation per unit length is 60 times higher in the epilayer than that of GaP at room temperature. The role of the magnetization in the MO effect makes it possible to increase this factor even further by lowering the temperature well below the Curie point (TC) of 292 K for those samples. We observed an increase of the Faraday rotation at longer wavelengths, indicating that those GaP:MnP epilayers could potentially be useful for enhanced MO effects in the visible and infrared regions of the electromagnetic spectrum.
The research of equivalent circuit of left-handed coplanar-waveguide transmission line element
Authors: Fu Jia-Hui , Wu Qun , Zhang Kuang , Yang Guo-Hui , Meng Fan-Yi
Published: May 2010

In this paper, a new type of left-handed (LH) transmission line is proposed. It is composed of a parallel embedded inductance and a series interdigital capacitor based on a coplanar-waveguide (CPW) transmission line. According to medium theory, the effective permittivity and permeability of LH CPW transmission line have been extracted. The characteristics of LH transmission line have been verified by calculating β parameter of the CPW transmission line. Then, an equivalent circuit model of LH CPW transmission line is extracted and the validity of the model is demonstrated by full-wave simulation.
Reduction in the planar Hall resistance amplitude in the reversal process of Fe film with biaxial easy axes
Authors: Lee Hakjoon , Chung Sunjae , Yoo Taehee , Lee Sanghoon , Liu X. , Furdyna J. K.
Published: May 2010

The magnetization reversal process of ferromagnetic Fe film with biaxial easy axes has been investigated using magnetotransport measurements. In addition to the change in the planar Hall resistance (PHR) between the positive and negative values depending on the direction of magnetization, we have noticed that the amplitude of the PHR strongly depends on the applied field direction. Specifically, when the external field direction is near the easy axis, the amplitude of the PHR is significantly reduced in the field scan data. This phenomenon was understood by the presence of multidomains with three different directions of magnetizations.
Reversible alternation between bipolar and unipolar resistive switching in polycrystalline barium strontium titanate thin films
Authors: Shen Wan , Dittmann Regina , Waser Rainer
Published: May 2010

The alternation from bipolar to unipolar resistive switching was observed in perovskite Ba0.7Sr0.3TiO3 thin films. By controlling the switching voltage, either bipolar or unipolar switching was obtained. When the switching voltage is higher than a threshold voltage, the device exhibits unipolar switching while if the switching voltage is lower than a threshold voltage, the device shows bipolar switching behavior. The bipolar-to-unipolar alternation is dynamically repeatable and may be related to the local modification of broken filaments by oxygen vacancy movement.
First-principles study of iron segregation into silicon ∑5 grain boundary
Authors: Shi T. T. , Li Y. H. , Ma Z. Q. , Qu G. H. , Hong F. , Xu F. , Yan Yanfa , Wei Su-Huai
Published: May 2010

Using ab initio density function theory total energy calculations, we have investigated the mechanism of Fe segregation into Si ∑5⟨310⟩ grain boundary (GB). We find that the segregation is site selective at the GB—Fe will only segregate to specific sites. We further find that the choice of the segregation site is determined by the segregation-induced stress and effective crystal-field-induce splitting of Fe d orbital at that site. Our results suggest that the revealed mechanism of Fe segregation into the GB should be general for other 3d transition metals with partially filled 3d orbits and for other grain boundaries.
Theoretical proposal for a biosensing approach based on a linear array of immobilized gold nanoparticles
Authors: Rafsanjani S. M. Hashemi , Cheng T. , Mittler S. , Rangan C.
Published: May 2010

We propose a sensing mechanism for detection of analytes that can specifically recognized. The sensor is based on closely-spaced chains of functionalized gold nanoparticles (NPs) immobilized on a waveguide surface, with the signal detected by evanescent waveguide absorption spectroscopy. The localized surface plasmon spectrum of a linear array of closely-spaced, hemispherical gold NPs is calculated using the discrete dipole approximation. The plasmon band is found to broaden to a nanowirelike spectrum when a dielectric coating is put on the particles, and the light polarization is along the NP chain. The origin of this broadening is shown to be the polarization-dependent overlap of the evanescent fields of adjacent NPs upon application of the dielectric coating. These features suggests a mechanism for biosensing with an improved sensitivity compared with traditional NP biosensor methods.
The critical current density, irreversibility line, and flux pinning properties of Ba2CaCu2O4(O,F)2 high-Tc superconductor
Authors: Shirage P. M. , Tanaka Y. , Iyo A.
Published: May 2010

The high-Tc superconductor of Ba2CaCu2O4(O,F)2 (F-0212) is an appealing material for application as it has a simple crystal structure with a highest Tc of 108 K. We have derived the intragrain critical current density (Jc), irreversibility field (Birr), flux pinning properties, etc., for the polycrystalline samples from under doping (Tc=82 K) to slightly-over doping (Tc=106 K) from the dc magnetization hysteresis loops. The Jc and Birr properties were found to improve rapidly as the doping state changes from under doping to slightly-over doping. Here we show that property of the spacing is crucial to enhance Birr as well as its thickness. An anisotropy factor for under doped Ba2CaCu2O4F2 was reckoned to 118 from a three-dimensional-two-dimensional crossover field of about 0.28 T. The double logarithmic plot of irreversibility field versus [1−(T/Tc)] analysis hints that the flux line melting model is adopted. Analysis of the normalized pinning force reveals that a surface pinning mechanism is dominant and reduced magnetic field bmax=0.2 agree with surface pinning mechanism with closely spaced pins.
Hysteresis switching loops in Ag-manganite memristive interfaces
Authors: Ghenzi N. , Sánchez M. J. , Gomez-Marlasca F. , Levy P. , Rozenberg M. J.
Published: May 2010

Multilevel resistance states in silver-manganite interfaces are studied both experimentally and through a realistic model that includes as a main ingredient the oxygen vacancies diffusion under applied electric fields. The switching threshold and amplitude studied through hysteresis switching loops are found to depend critically on the initial state. The associated vacancy profiles further unveil the prominent role of the effective electric field acting at the interfaces. While experimental results validate main assumptions of the model, the simulations allow to disentangle the microscopic mechanisms behind the resistive switching in metal-transition metal oxide interfaces.
Luminescence properties of ZnO/Zn1−xCdxO/ZnO double heterostructures
Authors: Lange M. , Dietrich C. P. , Czekalla C. , Zippel J. , Benndorf G. , Lorenz M. , Zúñiga-Pérez J. , Grundmann M.
Published: May 2010

We report on luminescence properties from T=2 K up to room temperature of ZnO/Zn1−xCdxO/ZnO double heterostructures grown by pulsed-laser deposition on a-plane sapphire substrates. Depending on the growth conditions, the spectral position of the Zn1−xCdxO related maximum has been tuned from 3.19 to 3.056 eV, corresponding approximately to Cd contents between 2.1% and 5.6%. Independent of x we observe intense phonon replicas of the photoluminescence (PL) maximum. The quenching of the luminescence intensity indicates the presence of two thermal activation energies, one of them being assigned to the delocalization of excitons from donors. The temperature-dependent PL spectra exhibit the so-called “S-shape” behavior as function of temperature for the Zn1−xCdxO due to the superposition of the usual S-shape, caused by the alloy, and a change in the peak character from donor-bound exciton to free exciton.
Experimental investigation on thermal conductivity of nanofluids containing graphene oxide nanosheets
Authors: Yu Wei , Xie Huaqing , Chen Wei
Published: May 2010

Nanofluids containing graphene oxide nanosheets have substantially higher thermal conductivities than the base fluids. The thermal conductivity enhancement ratios with the loading 5.0 vol % are up to 30.2%, 62.3%, and 76.8%, when the base fluids are distilled water, propyl glycol and liquid paraffin, respectively. The enhancement ratios of the nanofluids are almost constant with the tested temperature varying, and they are reduced with the increasing thermal conductivity of the base fluids. Heat transport along the graphene oxide plane is proposed to be the major contributions to the increase in the thermal conductivity.
Noninvasive probing of persistent conductivity in high quality ZnCdSe/ZnSe quantum wells using surface acoustic waves
Authors: Fuhrmann D. A. , Krenner H. J. , Wixforth A. , Curran A. , Prior K. A. , Warburton R. J. , Ebbecke J.
Published: May 2010

Attenuation of a surface acoustic wave is used as a highly sensitive and noninvasive probe of persistent photoconductivity effects in ZnCdSe/ZnSe quantum wells. These effects are observed over long time-scales exceeding several minutes at low temperatures. By varying the optical excitation energy and power and temperature we show that these effects arise from carriers photogenerated by interband excitation which are trapped in random potential fluctuations in the quantum wells related to compositional fluctuations. Effects related to defect levels in the band gap can be excluded and a transition of the conduction mechanism with temperature from a hopping to a percolation regime is observed. The transition temperature observed for our quantum well material is strongly reduced compared to bulk crystals. This indicates a superior structural quality giving rise to only weak potential fluctuation of ≲3 meV.
Electric-field control of strain-mediated magnetoelectric random access memory
Authors: Hu Jia-Mian , Li Zheng , Wang Jing , Nan C. W.
Published: May 2010

A strain-mediated magnetoelectric random access memory with electric-field-writing is presented, which consists of a magnetic tunnel junction (MTJ) in intimate contact with a ferroelectric (FE) layer. The calculations show that the magnetization vector in the free layer of the MTJ unit can switch in-plane by 90° upon applying an appropriate electric field to the FE layer, as compared to the common 180° reversal induced by magnetic field or spin-current. A perfect interface between the FE layer and the MTJ is assumed. The free layers used for illustration include either (001)-oriented or polycrystalline magnetic films of Fe–Co alloy, CoFe2O4 (CFO), Ni, and Fe3O4. Among them, the (001)-oriented FeCo and CFO films with positive magnetocrystalline anisotropy constant (i.e., K1>0) show an abrupt magnetization switching, while a gradual magnetization switching takes place in the (001)-oriented Ni and Fe3O4 films with K1<0 as well as the polycrystalline films. Such electric-field-induced in-plane magnetization switching can result in a remarkable change in the MTJ’s electric resistance. In particular, hysteretic dependence of the device resistance on the applied electric field is obtained for the cases of the (001)-oriented FeCo and CFO free layers that exhibit the abrupt magnetization switching, whereby a nonvolatile information storage process can be achieved. The influence of the shape of the free layer on both magnetization and resistance switching features is discussed.
Formation of core-shell structured silicon nanoparticles during pulsed laser ablation
Authors: Umezu Ikurou , Nakayama Yusuke , Sugimura Akira
Published: May 2010

We performed pulsed laser ablation of Si target in nitrogen background gas and found that core-shell structured nanoparticles can be prepared without postsurface treatment. The predominant ejected species from the target at free expansion region is Si, and N related species appears at the point blast region. The core-shell structure and plume expansion dynamics suggest that nuclei of the Si nanodroplets are formed in early stage followed by growth of nanodroplets and nitraidation at the surfaces region of the nanodroplets. Formation of core shell structure is a result of nonequilibrium high energy pulsed ejection of Si species.
Strain-induced semiconducting-metallic transition for ZnO zigzag nanoribbons
Authors: Si H. , Pan B. C.
Published: May 2010

Using first-principles calculations, we investigate structures and electronic properties of ZnO nanoribbons with different widths. By loaded strain along the periodic axis the ZnO zigzag nanoribbons are transformed into new ground state featuring square lattice. We find that this new ground state is semiconducting, which is completely different from the initial zigzag nanoribbons having metallic behavior. Such a metallic-semiconducting phase transition might allow ZnO nanoribbons to have potential applications in nanoswitch.
Analyzing real-time surface modification of operating semiconductor laser diodes using cross-sectional scanning tunneling microscopy
Authors: Cobley R. J. , Rees P. , Teng K. S. , Wilks S. P.
Published: May 2010

Cross-sectional scanning tunneling microscopy (STM) has been used to study in-operation changes that occur at the active region of clean-cleaved semiconductor laser diodes. A tunneling model that allows the inclusion of tip-induced band bending and surface defect states has been used to study the origin of the surface changes which give rise to the observed modification. Low-doped layers close to the active region are found to undergo both a reduction in doping concentration and an increase in the surface defect state density as the lasers are operated. These changes ultimately lead to device failure. Under different tunneling modes STM can be sensitive to one effect or the other, and the importance of modeling the changes to confirm which are occurring is emphasized.
Patterning of dielectric nanoparticles using dielectrophoretic forces generated by ferroelectric polydomain films
Authors: Mokrý P. , Marvan M. , Fousek J.
Published: May 2010

A theoretical study of a dielectrophoretic force, i.e., the force acting on an electrically neutral particle in the inhomogeneous electric field, which is produced by a ferroelectric domain pattern, is presented. It has been shown by several researchers that artificially prepared domain patterns with given geometry in ferroelectric single crystals represent an easy and flexible method for patterning dielectric nanoobjects using dielectrophoretic forces. The source of the dielectrophoretic force is a strong and highly inhomogeneous (stray) electric field, which exists in the vicinity of the ferroelectric domain walls at the surface of the ferroelectric film. We analyzed dielectrophoretic forces in the model of a ferroelectric film of a given thickness with a lamellar 180° domain pattern. The analytical formula for the spatial distribution of the stray field in the ionic liquid above the top surface of the film is calculated including the effect of free charge screening. The spatial distribution of the dielectrophoretic force produced by the domain pattern is presented. The numerical simulations indicate that the intersection of the ferroelectric domain wall and the surface of the ferroelectric film represents a trap for dielectric nanoparticles in the case of so called positive dielectrophoresis. The effects of electrical neutrality of dielectric nanoparticles, free charge screening due to the ionic nature of the liquid, domain pattern geometry, and the Brownian motion on the mechanism of nanoparticle deposition and the stability of the deposited pattern are discussed.
Characterization of Si volume- and delta-doped InGaAs grown by molecular beam epitaxy
Authors: Fedoryshyn Y. , Beck M. , Kaspar P. , Jaeckel H.
Published: May 2010

Bulk InGaAs layers were grown at 400 °C lattice-matched to InP semi-insulating substrates by molecular beam epitaxy. Si doping of the layers was performed by applying volume- and delta-doping techniques. The samples were characterized by capacitance-voltage, van der Pauw–Hall, secondary ion mass spectroscopy and photoluminescence measurements. Good agreement in terms of dependence of mobility and Burstein–Moss shift shift on doping concentration in samples doped by the two different techniques was obtained. Amphoteric behavior of Si was observed at doping concentrations higher than ∼2.9×1019 cm−3 in both delta- and volume-doped samples. Degradation of InGaAs crystalline quality occurred in samples with Si concentrations higher than ∼4×1019 cm−3.
Magnetism in a Mn modulation-doped InAs/InGaAs heterostructure with a two-dimensional hole system
Authors: Rupprecht B. , Krenner W. , Wurstbauer U. , Heyn Ch. , Windisch T. , Wilde M. A. , Wegscheider W. , Grundler D.
Published: May 2010

For an InAs quantum well which is modulation-doped with Mn we measure directly and simultaneously the magnetization and magnetic anisotropy of, both, the two dimensional hole system (2DHS) and Mn dopants. Using highly sensitive micromechanical torque magnetometry at 400 mK we observe the de Haas-van Alphen effect of the 2DHS in a magnetic field B up to 14 T. Around B=0 we find a magnetic hysteresis which we attribute to the spontaneous ordering of magnetic moments in the interacting Mn-hole system. Tilted field experiments suggest a uniaxial magnetic anisotropy with the easy axis in (001) growth direction.
Effect of germanium doping on the annealing characteristics of oxygen and carbon-related defects in Czochralski silicon
Authors: Londos C. A. , Andrianakis A. , Sgourou E. N. , Emtsev V. , Ohyama H.
Published: May 2010

This paper is devoted to the annealing studies of defects produced in carbon-rich Ge-doped Czochralski-grown Si (Cz-Si) by 2 MeV electron irradiation. The annealing temperature of vacancy-oxygen (VO) complexes, carbon interstitial-oxygen interstitial (CiOi), and carbon interstitial-carbon substitutional (CiCs) pairs as well as the formation temperature of vacancy-two oxygen (VO2) complexes are monitored as a function of Ge concentration. It has been established that the annealing of CiOi and CiCs defects remains practically unaffected by the Ge presence, whereas the annealing temperature of VO defects and the formation temperature of VO2 complexes are substantially lowered at Ge concentrations larger than 1×1019 cm−3. The hydrostatic component of elastic strains introduced by Ge atoms in the Si crystal lattice was calculated. It appears to be very small, at least insufficient to exert a pronounced effect upon the annealing behavior of radiation-produced defects. This conclusion is in line with what is observed for the CiOi and CiCs species. In the case of VO, whose annealing process in Cz-Si is concurrently conducted by two reaction paths VO+Oi→VO2 and VO+SiI→Oi, we suggest that the latter reaction in Ge-doped Cz-Si is enhanced by emitting self-interstitials (SiI) from loosely bound self-interstitial clusters predominantly formed around Ge impurity atoms. As a result, the liberation of self-interstitials at lower annealing temperatures leads to an enhanced annealing of VO defects. An enhanced formation of VO2 complexes at lower temperatures is also discussed in terms of other reactions running in parallel with the reaction VO+SiI→Oi.
Silver catalyzed ultrathin silicon nanowires grown by low-temperature chemical-vapor-deposition
Authors: Wittemann Joerg V. , Münchgesang Wolfram , Senz Stephan , Schmidt Volker
Published: May 2010

In this work we demonstrate the synthesis of monocrystalline silicon nanowire using silver particles as catalysts at temperatures of less than 500 °C by means of ultrahigh vacuum chemical vapor deposition. The nanowires were grown epitaxially on silicon substrates and had diameters of about 10 nm. We furthermore show that the silver remnants can be wet chemically removed with potassium ferricyanide and sodium thiosulfate.
Radiation fields of a uniformly accelerating point source in the framework of Stueckelberg’s manifestly covariant relativistic dynamics
Authors: Aharonovich I. , Horwitz L. P.
Published: May 2010

In this paper we explore the problem of fields generated by a source undergoing hyperbolic motion in the framework of Stueckelberg manifestly covariant relativistic dynamics. The resulting gauge fields are computed numerically using Green-Functions which are retarded in the Stueckelberg absolute time τ, and qualitatively compared with Maxwell fields generated by the same motion. The gauge invariant field equations are second order in this parameter as well as in space-time, resulting in identification of a five-dimensional manifold for the gauge fields. We find that although the zero mode of all fields coincides with the corresponding Maxwell fields, the generalized Lorentz force (necessarily involving a fifth component of the gauge field) depends on the nonzero modes as well, which affects the motion of particles subject to these forces.
Effects of surface diffusional anisotropy on the current-driven surface morphological response of stressed solids
Authors: Tomar Vivek , Gungor M. Rauf , Maroudas Dimitrios
Published: May 2010

A comprehensive analysis is presented of the effects of surface diffusional anisotropy on the morphological stability of planar surfaces of stressed crystalline solids under the simultaneous action of an electric field. The analysis is based on self-consistent dynamical simulations of driven surface morphological evolution in conjunction with linear stability theory. Results are reported of a systematic study of the effects on the surface morphological response of varying surface diffusional anisotropy parameters; these include the direction of the applied electric field with respect to fast surface diffusion directions, the surface crystallographic orientation, and the strength of the anisotropy that increases with decreasing temperature. For face-centered cubic crystalline solids under stress, we find that there exists a preferred direction for the applied electric field that optimizes their surface morphological response. In addition, we find that for these solids under given surface electromigration conditions, the morphological response of their ⟨111⟩-oriented surfaces is superior to that of their ⟨100⟩-oriented and ⟨110⟩-oriented surfaces. Furthermore, we demonstrate that increasing the strength of the surface diffusional anisotropy in these materials has beneficial effects on their surface morphological stability under the simultaneous action of an electric field. Our predictions can provide guidance for experimental studies of surface morphological response to the combined action of electric fields and mechanical stresses, as well as for tailoring operating conditions to improve the mechanical reliability of thin films in service.
Integration of atomic force microscopy and a microfluidic liquid cell for aqueous imaging and force spectroscopy
Authors: Schoenwald K. , Peng Z. C. , Noga D. , Qiu S. R. , Sulchek T.
Published: May 2010

We have designed and built a microfluidic liquid cell capable of high-resolution atomic force microscope (AFM) imaging and force spectroscopy. The liquid cell was assembled from three molded poly(dimethylsiloxane) (PDMS) pieces and integrated with commercially purchased probes. The AFM probe was embedded within the assembly such that the cantilever and tip protrude into the microfluidic channel. This channel is defined by the PDMS assembly on the top, a PDMS gasket on all four sides, and the sample substrate on the bottom, forming a liquid-tight seal. Our design features a low volume fluidic channel on the order of 50 nl, which is a reduction of over 3–5 orders of magnitude compared to several commercial liquid cells. This device facilitates testing at high shear rates and laminar flow conditions coupled with full AFM functionality in microfluidic aqueous environments, including execution of both force displacement curves and high resolution imaging.
Strong magnetohydrodynamic turbulence with cross helicity
Authors: Perez Jean Carlos , Boldyrev Stanislav
Published: May 2010

Magnetohydrodynamics (MHD) provides the simplest description of magnetic plasma turbulence in a variety of astrophysical and laboratory systems. MHD turbulence with nonzero cross helicity is often called imbalanced, as it implies that the energies of Alfvén fluctuations propagating parallel and antiparallel the background field are not equal. Recent analytical and numerical studies have revealed that at every scale, MHD turbulence consists of regions of positive and negative cross helicity, indicating that such turbulence is inherently locally imbalanced. In this paper, results from high resolution numerical simulations of steady-state incompressible MHD turbulence, with and without cross helicity are presented. It is argued that the inertial range scaling of the energy spectra (E±) of fluctuations moving in opposite directions is independent of the amount of cross helicity. When cross helicity is nonzero, E+ and E− maintain the same scaling, but have differing amplitudes depending on the amount of cross helicity.
Optical scattering lengths in large liquid-scintillator neutrino detectors
Authors: Wurm M. , von Feilitzsch F. , Göger-Neff M. , Hofmann M. , Lachenmaier T. , Lewke T. , Undagoitia T. Marrodán , Meindl Q. , Möllenberg R. , Oberauer L. , Potzel W. , Tippmann M. , Todor S. , Traunsteiner C. , Winter J.
Published: May 2010

For liquid-scintillator neutrino detectors of kiloton scale, the transparency of the organic solvent is of central importance. The present paper reports on laboratory measurements of the optical scattering lengths of the organic solvents phenylxylylethane, linear alkylbenzene (LAB), and dodecane, which are under discussion for next-generation experiments such as SNO+ (Sudbury Neutrino Observatory), HanoHano, or LENA (Low Energy Neutrino Astronomy). Results comprise the wavelength range of 415–440 nm. The contributions from Rayleigh and Mie scattering as well as from absorption/re-emission processes are discussed. Based on the present results, LAB seems to be the preferred solvent for a large-volume detector.
Analysis of efficiency and optimization of plasmon energy coupling into nanofocusing metal wedges
Authors: Tan Shiaw Juen , Gramotnev Dmitri K.
Published: May 2010

In this paper, we investigate theoretically and numerically the efficiency of energy coupling from a plasmon generated by a grating coupler at one of the interfaces of a metal wedge into the plasmonic eigenmode (i.e., symmetric or quasisymmetric plasmon) experiencing nanofocusing in the wedge. Thus the energy efficiency of energy coupling into metallic nanofocusing structure is analyzed. Two different nanofocusing structures with the metal wedge surrounded by a uniform dielectric (symmetric structure) and with the metal wedge enclosed between a substrate and a cladding with different dielectric permittivities (asymmetric structure) are considered by means of the geometrical optics (adiabatic) approximation. It is demonstrated that the efficiency of the energy coupling from the plasmon generated by the grating into the symmetric or quasisymmetric plasmon experiencing nanofocusing may vary between ∼50% to ∼100%. In particular, even a very small difference (of ∼1%–2%) between the permittivities of the substrate and the cladding may result in a significant increase in the efficiency of the energy coupling (from ∼50% up to ∼100%) into the plasmon experiencing nanofocusing. Distinct beat patterns produced by the interference of the symmetric (quasisymmetric) and antisymmetric (quasiantisymmetric) plasmons are predicted and analyzed with significant oscillations of the magnetic and electric field amplitudes at both the metal wedge interfaces. Physical interpretations of the predicted effects are based upon the behavior, dispersion, and dissipation of the symmetric (quasisymmetric) and antisymmetric (quasiantisymmetric) film plasmons in the nanofocusing metal wedge. The obtained results will be important for optimizing metallic nanofocusing structures and minimizing coupling and dissipative losses.
Growth, electromechanical, and electro-optic properties of tungsten bronze (Ca0.28Ba0.72)0.25(Sr0.6Ba0.4)0.75Nb2O6 single crystal
Authors: Gao W. L. , Zhang H. J. , Yin X. , Song H. L. , Wang J. Y. , Jiang M. H. , Boughton R. I.
Published: May 2010

A calcium strontium barium niobate (Ca0.28Ba0.72)0.25(Sr0.60Ba0.40)0.75Nb2O6 (CSBN25) single crystal has been grown using the Czochralski technique. The point group and space group of CSBN25 were determined by x-ray powder diffraction analysis to be tetragonal 4 mm and P4bm, respectively. The complete set of dielectric, piezoelectric, and elastic constants of CSBN25 have been determined by resonance techniques and impedance analysis at room temperature, and the relevant constants have been obtained and discussed. The relative dielectric constants are ε11=343, and ε33=502. Our results show that CSBN25 has excellent piezoelectric properties with d33=94.3, d31=−31.1, and d15=16.6 pC/N. The elastic compliance constants are s11=5.1, s12=−4, s13=1.4, s33=5.1, s55=13.2, and s66=19 pm2/N. The linear electro-optic coefficients of CSBN25 also have been measured by using an interferometric method. The results obtained are γ33=140, γ13=18, γ51=18, and γc=108.7 pm/V.
Frequency response of magnetoelectric 1–3-type composites
Authors: Lam K. H. , Lo C. Y. , Chan H. L. W.
Published: May 2010

A three-phase magnetoelectric (ME) composite consisting of Pb(Zr,Ti)O3 rods embedded in a matrix of Terfenol-D/epoxy (TDE) pseudo 1–3 composites has been fabricated. Besides the large ME effect, its frequency response under a magnetic bias field has been studied. It was found that the resonance shifts to lower frequency with increasing bias field. Due to the magnetomechanical characteristics of the TDE pseudo 1–3 medium, the composite shows a similar trend in ME performance. Magnetic-field dependence of the frequency shift provides a means to tune the performance of ME sensors based on the composite.
An analysis of temperature-dependent photocurrent-spectra in photoconductive CuGaSe2 layers
Authors: Yun S. Y. , Hong K. J. , Jeong T. S. , Youn C. J.
Published: May 2010

The photocurrent (PC) variation in photoconductive CuGaSe2 (CGS) layers had been investigated as a function of temperature. Three peaks A, B, and C of the PC spectra were associated with the band-to-band transitions. Thus, the parameters of the crystal-field splitting (Δcr) and spin-orbit splitting (Δso) were directly acquired through the PC measurement. The Δcr and Δso were 0.0903 eV and 0.2130 eV at 10 K, respectively. From the relations of peak position and temperature, the temperature dependence of the band-gap energy is well described by Eg(T)=Eg(0)−(8.63×10−4)T2/(336+T). Also, the Eg(0) is estimated to be 1.7952, 1.8855, and 2.0985 eV at the valence-band states of Γ7(A), Γ6(B), and Γ7(C), respectively. However, the behavior of the PC was different from that generally observed in other semiconductors, the PC intensities decreased with decreasing temperature. From the relation of log Jph versus 1/T, where Jph is the PC density, two dominant levels were observed, one at high temperature and the other at low temperature. By comparing the results of the PC and photoluminescence, we confirmed that the activation energy of 82.7 meV at high temperatures is related to the dissociation energy of donor level due to Se vacancies. Consequently, we suggest that in photoconductive CGS layers, the trapping center due to native defects and impurities limits the PC signal with decreasing temperature.
Single donor induced negative differential resistance in silicon n-type nanowire metal-oxide-semiconductor transistors
Authors: Bescond M. , Lannoo M. , Raymond L. , Michelini F.
Published: May 2010

This work presents a theoretical study of the influence of a single donor on the transport properties of silicon nanowire transistors. Using a three-dimensional self-consistent nonequilibrium Green’s function approach we find that the donor states induce transitions from resonant to antiresonant Breit–Wigner interferences when increasing the gate or drain voltages. Numerical and analytical calculations demonstrate that these interferences strongly degrade the transistor performances but can also generate a remarkable negative differential resistance behavior. The robustness of this phenomenon with respect to a change of the defect position in the channel is an opportunity to develop novel device properties.
Influence of 190 MeV Ag+15 ion irradiation on electrical transport and magnetic properties of LaFe1−xNixO3 (x=0.3 and 0.4) thin films
Authors: Khan M. Wasi , Khan M. A. Majeed , Alhoshan Mansour , AlSalhi M. S. , Aldwayyan A. S. , Kumar Ravi , Husain Shahid
Published: May 2010

In the present work we have studied the effect of 190 MeV Ag ion irradiation on the structural, electrical, and magnetic properties of LaFe1−xNixO3 (x=0.3 and 0.4) thin films. The films were grown on LaAlO3 ⟨001⟩ oriented substrates using pulsed laser deposition technique. The pristine and irradiated samples were investigated using x-ray diffraction, temperature dependent resistivity, and magnetic measurements. The x-ray diffraction patterns of the irradiated films show that the lattice of the composition strain relaxed with enhanced c-axis orientation. The temperature dependence of the resistivity indicates that all the films (pristine and irradiated) exhibit semiconducting behavior for entire studied temperature range (80–300 K). The pristine and irradiated samples show the activated variable range hopping behavior throughout the studied temperature range. The magnetization hysteresis measurements show ferromagnetic behavior at 300 K for all samples. The results are explained on the basis of the close interplay between the electrical and the magnetic properties.