bluuebunny/crossref_metadata_2025 huggingface dataset:
Magnetocapillary phenomenon affected by magnetic films
Authors: Lee Chiun-Peng , Chang Hsien-Chih , Lai Mei-Feng
Published: March 2011

Behaviors of magnetic fluid have been widely studied due to the potential for developing biochips and other micro devices. In this study, magnetic films are deposited on the capillary, and the influences of capillary gap distance and magnetic film thickness on the magnetocapillary phenomenon are investigated. It is observed that in a wider gap a larger liquid height drop occurs due to the stronger magnetic attraction in magnetic fluids. Film thickness is found to affect the solid-liquid interfacial tension, and it significantly influences the behavior of magnetic fluid in a capillary.
Positive magnetoresistance in Fe3Se4 nanowires
Authors: Li D. , Jiang J. J. , Liu W. , Zhang Z. D.
Published: March 2011

We report the magnetotransport properties of Fe3Se4 nanowire arrays in anodic aluminum oxide (AAO) porous membrane. The temperature dependence of resistance of Fe3Se4 nanowires at a zero field shows thermal activated behavior below 295 K. The exponential relationship in resistance is consistent with the model of strong localization with variable-range hopping (VRH) for a finite one-dimensional wire. Resistance versus magnetic field curves below 100 K show small positive magnetoresistance (MR). The field dependencies of log[R(H)/R(0)] explain the positive MR as the effect of magnetic field on the VRH conduction.
Electron doped Sr2IrO4−δ (0 ≤ δ ≤ 0.04): Evolution of a disordered Jeff = 1/2 Mott insulator into an exotic metallic state
Authors: Qi T. F. , Korneta O. B. , Chikara S. , Ge M. , Parkin S. , De Long L. E. , Schlottmann P. , Cao G.
Published: March 2011

Stoichiometric Sr2IrO4 is a ferromagnetic Jeff = [1/2] Mott insulator driven by strong spin-orbit coupling. Introduction of very dilute oxygen vacancies into single-crystal Sr2IrO4−δ with δ ≤ 0.04 leads to significant changes in lattice parameters and an insulator-to-metal transition at TMI = 105 K. The highly anisotropic electrical resistivity of the low-temperature metallic state for δ ≈ 0.04 exhibits anomalous properties characterized by non-Ohmic behavior and an abrupt current-induced transition in the resistivity at T* = 52 K, which separates two regimes of resistive switching in the nonlinear I-V characteristics. The novel behavior illustrates an exotic ground state and constitutes a new paradigm for devices structures in which electrical resistivity is manipulated via low-level current densities ∼ 10 mA/cm2 (compared to higher spin-torque currents ∼ 107–108 A/cm2) or magnetic inductions ∼ 0.1–1.0 T.
Micromagnetic studies on measurements of crystalline anisotropy and magnetostriction in disk media
Authors: Li Hongjia , Wei Dan
Published: March 2011

Measurements of intrinsic magnetic parameters are important in the study of magnetic devices. A micromagnetic model is set up for a perpendicular disk media, including a recording layer (RL, CoCrPt-SiO2, 6 nm), a 12-nm nonmagnetic interlayer and an amorphous soft underlayer (a-SUL, FeCo, 42 nm), in order to study the measurement methods of the crystalline anisotropy and magnetostriction constants in the RL. The effects of the a-SUL on the magnetic properties of the RL are studied by calculating the hysteresis loops. The contributions of the RL and a-SUL to the torque curves of the whole media are calculated respectively. If the intrinsic stress at the interface between the RL and interlayer is along one of the in-plane directions, the crystalline anisotropy constant K1 and magnetostriction field Hms can be determined simultaneously from the simulated in-plane torque curves.
Enhanced giant magnetoimpedance effect and field sensitivity in Co-coated soft ferromagnetic amorphous ribbons
Authors: Laurita Nicholas , Chaturvedi Anurag , Bauer Christopher , Jayathilaka Priyanga , Leary Alex , Miller Casey , Phan Manh-Huong , McHenry Michael E. , Srikanth Hariharan
Published: March 2011

A 50 nm-thick Co film has been grown either on the free surface (surface roughness, ∼6 nm) or on the wheel-side surface (surface roughness, ∼147 nm) of Co84.55Fe4.45Zr7B4 amorphous ribbons. A comparative study of the giant magnetoimpedance (GMI) effect and its field sensitivity (η) in the uncoated and Co-coated ribbons is presented. We show that the presence of the Co coating layer enhances both the GMI ratio and η in the Co-coated ribbons. Larger values for GMI ratio and η are achieved in the sample with Co coated on the free ribbon surface. The enhancement of the GMI effect in the Co-coated ribbons originates mainly from the reduction in stray fields due to surface irregularities and the enhanced magnetic flux paths closure. These findings provide good guidance for tailoring GMI in surface-modified soft ferromagnetic ribbons for use in highly sensitive magnetic sensors.
Spin transfer torque in MTJs with synthetic ferrimagnetic layers by the Keldysh approach
Authors: Ichimura M. , Hamada T. , Imamura H. , Takahashi S. , Maekawa S.
Published: March 2011

Based on the Keldysh Green’s function method within the tight-binding model, the spin transfer torque is analyzed in a magnetic tunnel junction with a synthetic ferrimagnetic (SyF) free layer in the ballistic regime. The spin transfer torque exerted on the magnetizations of ferromagnetic bilayers in the SyF free layer tends to rotate the magnetizations in the same direction as a combined motion of the SyF free layer regardless of the bias direction. This rotation causes a reduction of the critical current for the magnetization switching of the SyF free layer which is consistent with experimental observations.
Quantitative control of magnetic ordering in FeRh thin films using 30 keV Ga ion irradiation from a focused ion beam system
Authors: Aikoh K. , Kosugi S. , Matsui T. , Iwase A.
Published: March 2011

We investigated a low-energy ion-beam irradiation process for the magnetic modification of FeRh thin films using a focused ion beam system. Low-energy ion-beam irradiation induced ferromagnetic states in the FeRh thin films at low temperatures, that originally exhibited antiferromagnetism, as effectively as high-energy ion-beam irradiation. Because the energy deposited by the elastic collisions caused by the irradiation determined the magnetic properties of the samples, the magnetic state of the FeRh thin films could be quantitatively controlled. The low-energy ion-beam irradiation using a focused ion beam system is a potential technique to modify the magnetic properties of materials on the nano- and micro-scales, which may lead to a variety of novel spin devices and applications.
Effect of thermal strain on Jc and Tc in high density nano-SiC doped MgB2
Authors: Li W. X. , Zeng R. , Lu L. , Dou S. X.
Published: March 2011

The influences of lattice strain on the superconducting critical current density Jc and critical transition temperature Tc in pure MgB2 and a SiC-MgB2 composite made by the diffusion process are explored, based on the thermal expansion coefficients and the low temperature effects on Raman scattering. The strong thermal strain provides a strong flux pinning force for the supercurrents at the interfaces between SiC and MgB2. The high Tc of SiC-MgB2 is also discussed according to the expanded lattice and Raman characteristics.
Enhancement of current-perpendicular-to-plane giant magnetoresistance by insertion of Co50Fe50 layers at the Co2Mn(Ga0.5Sn0.5)/Ag interface
Authors: Hase N. , Nakatani T. M. , Kasai S. , Takahashi Y. K. , Hono K.
Published: March 2011

We have investigated the effect of the insertion of Co50Fe50 layers at ferromagnet/spacer interfaces on magnetoresistance (MR) properties in current-perpendicular-to-plane giant MR devices using Co2Mn(Ga0.5Sn0.5) Heusler alloy layers. The insertion of 1 nm thick Co50Fe50 layers led to a large enhancement of MR outputs with a large temperature dependence of MR. Smaller temperature dependences were observed for the insertion of Co50Fe50 layers of thicker than 2 nm, but only with less enhancement of MR outputs.
High frequency characteristics of FeCoAlO thin films combined the effects of stress and magnetic field
Authors: Zheng Fu , Wang Xuan , Li Xu , Bai Jianmin , Wei Dan , Liu Xiaoxi , Xie Wenhui , Wei Fulin
Published: March 2011

The soft magnetic FeCoAlO thin films with different response at high frequency were prepared by using RF magnetron sputtering. Two different configurations of the sputtering targets were used: the Al2O3 chips were placed on Fe70Co30 disk either uniformly dispersed on the sputtering area (Target-A) or dispersed on the half side of the sputtering area (Target-B). It was found that, although, the films deposited from both of Target A and B possessed good soft magnetic properties and in-plane uniaxial magnetic anisotropy, they showed different behaviors at high frequency. The films deposited by using Target-A have mean permeability of 500 and a cut-off frequency (fr) of around 780 MHz, while the films deposited by using Target-B have mean permeability of 200 and a fr of 3.4 GHz. The higher fr of the later corresponds to the higher uniaxial anisotropic field in the films deposited by using the Target-B, which due to an extra anisotropy induced by the stress resulted from gradient of the Al-O composition. By adjusting the configuration of Target-B, the permeability & fr can be tuned to satisfy the different requirements for certain industrial applications.
Magnetic control of breakdown: Toward energy-efficient hollow-cathode magnetron discharges
Authors: Baranov O. , Romanov M. , Kumar S. , Zhong X. X. , Ostrikov K.
Published: March 2011

Characteristics of electrical breakdown of a planar magnetron enhanced with an electromagnet and a hollow-cathode structure, are studied experimentally and numerically. At lower pressures the breakdown voltage shows a dependence on the applied magnetic field, and the voltage necessary to achieve the self-sustained discharge regime can be significantly reduced. At higher pressures, the dependence is less sensitive to the magnetic field magnitude and shows a tendency of increased breakdown voltage at the stronger magnetic fields. A model of the magnetron discharge breakdown is developed with the background gas pressure and the magnetic field used as parameters. The model describes the motion of electrons, which gain energy by passing the electric field across the magnetic field and undergo collisions with neutrals, thus generating new bulk electrons. The electrons are in turn accelerated in the electric field and effectively ionize a sufficient amount of neutrals to enable the discharge self-sustainment regime. The model is based on the assumption about the combined classical and near-wall mechanisms of electron conductivity across the magnetic field, and is consistent with the experimental results. The obtained results represent a significant advance toward energy-efficient multipurpose magnetron discharges.
Thermal conductivity and interfacial conductance of AlN particle reinforced metal matrix composites
Authors: Kida M. , Weber L. , Monachon C. , Mortensen A.
Published: March 2011

Aluminum nitride (AlN) particle reinforced metal-matrix-composites produced by pressure infiltration are characterized in terms of their thermal conductivity. The composites are designed to cover a wide range of phase contrast between the dispersed particles and the matrix; this is achieved by changing the matrix conductivity using Cu, Al, Sn, and Pb as the matrix. The interface thermal conductance (hc) between AlN and the matrix metals is determined by varying the size of the AlN particles using the Hasselman–Johnson approach and the differential effective medium (DEM) model to calculate hc from measured composite conductivity values. In addition, hc is measured directly at the AlN/Al interface using the transient thermoreflectance (TTR) method on thin aluminum layers deposited on flat AlN substrates to find good agreement with the value derived directly from Al/AlN composites of variable particle size and thus confirm the approach used here to measure hc. Data from the study show that hc at AlN-metal interfaces increases with the metal/AlN Debye temperature ratio; however, the increase is much less than predicted by currently accepted models.
Transport and separation of micron sized particles at isotachophoretic transition zones
Authors: Goet Gabriele , Baier Tobias , Hardt Steffen
Published: March 2011

Conventionally, isotachophoresis (ITP) is used for separation of ionic samples according to their electrophoretic mobilities. We demonstrate that the scope of ITP applications may be extended toward particle concentration and separation. Owing to the distributions of electrolyte concentration and electric field inside a transition zone between two electrolytes, a number of different forces act on a small particle. As far as possible, we provide estimates for the order of magnitude of these forces and analyze their scaling with the particle size and the electric-field strength. Furthermore, we experimentally demonstrate that polymer beads of 5 μm diameter dispersed in a high mobility “leading” electrolyte are picked up and carried along by an ITP transition zone which is formed with a low mobility “trailing” electrolyte. By studying the particle positions and trajectories, we show that impurities in the electrolytes play a significant role in the experiments. Additionally, it is experimentally shown that different types of beads can be separated at an ITP transition zone. In particular, beads of 1 μm diameter are not carried along with the transition zone, in contrast to the 5 μm beads. The presented technique thus adds to the portfolio of electrokinetic transport, concentration, and separation methods in microfluidics.
Study of roughness evolution and layer stacking faults in short-period atomic layer deposited HfO2/Al2O3 multilayers
Authors: de Pauli M. , Malachias A. , Westfahl H. , Bettini J. , Ramirez A. , Huang G. S. , Mei Y. F. , Schmidt O. G.
Published: March 2011

In this work we study the evolution of roughness in interfaces of HfO2/Al2O3 multilayers by x-ray reflectivity. It was found that, besides the reduced adatom surface mobility during atomic layer deposition, an improvement of the interface quality can be achieved upon the stacking of several layers. Although the low roughness of the initial surface could not be recovered, there was a considerable improvement of surface/interface quality along the deposition process. In particular, variations on the growth temperature were not able to tailor the surface quality, if compared to the stacking process. Finally, transmission electron microscopy analysis has shown that local defects can take place among nearly perfect interfaces. Such effect must be taken into account for nanometer-scale device fabrication.
Multiple-photon peak generation near the ˜10 μm range in quantum dot infrared photodetectors
Authors: Degani Marcos H. , Maialle Marcelo Z. , Farinas Paulo F. , Studart Nelson , Pires Mauricio P. , Souza Patricia L.
Published: March 2011

We present results from simulations of the photocurrent observed in recently fabricated InAs quantum dot infrared photodetectors that respond with strong resonance peaks in the ∼10μm wavelength range. The results are in good agreement with experimental data generated earlier. Multiphoton scattering of electrons localized in the quantum dots are not only in accordance with the observed patterns, but are also necessary to explain the photocurrent spectrum obtained in the calculations.
Magnetic properties and recording performances of patterned media fabricated by nitrogen ion implantation
Authors: Hinoue Tatsuya , Ito Kenichi , Hirayama Yoshiyuki , Ono Toshinori , Inaba Hiroshi
Published: March 2011

Nitrogen ion implantation was performed on CoCrPt–SiO2 perpendicular media with a resist mask to fabricate patterned media. Signal amplitude and autocorrelation signal-to-noise ratio of the preamble pattern were measured to evaluate the quality of the pattern fabricated by the ion implantation. The signal-to-noise ratio and the jitter were closely related to the saturation magnetization of the ion-implanted area. The remained magnetization of the ion-implanted area probably affects edge roughness of the magnetic pattern. Larger reduction of the saturation magnetization at the ion-implanted area is important for obtaining higher signal quality. Off-track profiles and 747 curves were measured for 76-nm-pitch discrete track fabricated by ion implantation. The results show that discrete track recording had advantages over recording on continuous magnetic film, which indicates that the fabricated patterns were successfully isolated. The nitrogen ion implantation was effective in fabricating isolated magnetic tracks or isolated magnetic dots for the patterned media.
Giant coercivity of dense nanostructured spark plasma sintered barium hexaferrite
Authors: Mazaleyrat F. , Pasko A. , Bartok A. , LoBue M.
Published: March 2011

Due to the limited rare-earth elements resources, ferrite magnets need to be improved drastically. Ideally, for a true hard magnet, the coercive field should be larger than the saturation magnetization, which is not yet realized for ferrites. Thus, an alternative can be found in making very fine grain ferrite magnets, but it is usually impossible to get small grains and dense material together. In this paper, it is shown that the spark plasma sintering method is able to produce approximately 80% of dense material with crystallites smaller than 100 nm. The as-prepared bulk sintered anisotropic magnets exhibits coercive field of 0.5 T which is approximately 60% of the theoretical limit and only a few percentage below that of loose nanopowders. As a result, the magnets behave nearly ideal (−1.18 slope in the BH plane second quadrant) and the energy product reaches 8.8 kJ m−3, the highest value achieved in the isotropic ferrite magnet to our knowledge.
Changes in the bioluminescence of firefly under pulsed and static magnetic fields
Authors: Iwasaka M. , Miyashita Y. , Barua A. G. , Kurita S. , Owada N.
Published: March 2011

The effects of a pulsed train magnetic field (PMF) and 10-T order of static magnetic fields on firefly bioluminescence were investigated on two species, Luciola cruciata and Luciola lateralis. Strong static magnetic field exposure experiments were carried out with a time-resolved spectroscopy, and the firefly bioluminescence spectrum showed a redshift in the range of 540–580nm when the firefly emitted pulses under the 10-T magnetic field. Separately from this effect, a transient decrease in the firefly’s emission intensity was observed right after being exposed to the static magnetic fields of up to 10 T. On the other hand, the utilized PMFs stimulated and enhanced the bioluminescence of Luciola cruciata. The PMF with 250–325 T/s at 1.3–10 Hz increased both the firefly’s pulsed density and frequency. It was speculated that the magnetically induced current inside the firefly affected its nervous system or the photochemical processes in the light producing organ, while the diamagnetic torque forces, which were induced by the 10 T order of the static field, had an inhibitory effect on the bioluminescence system.
Nuclear magnetic resonance study of Gd-based nanoparticles to tag boron compounds in boron neutron capture therapy
Authors: Corti M. , Bonora M. , Borsa F. , Bortolussi S. , Protti N. , Santoro D. , Stella S. , Altieri S. , Zonta C. , Clerici A. M. , Cansolino L. , Ferrari C. , Dionigi P. , Porta A. , Zanoni G. , Vidari G.
Published: March 2011

We report the investigation of new organic complexes containing a magnetic moment (Gd-based molecular nanomagnets), which can serve the double purpose of acting as boron neutron capture therapy (BNCT) agents, and at the same time act as contrast agents to detect the molecule in the tissue by a proton magnetic resonance imaging (MRI). We also explore the possibility of monitoring the concentration of the BNCT agent directly via proton and boron NMR relaxation. The absorption of 10B-enriched molecules inside tumoral liver tissues has been shown by NMR measurements and confirmed by α spectroscopy. A new molecular Gd-tagged nanomagnet and BNCT agent (GdBPA) has been synthesized and characterized measuring its relaxivity R1 between 10 kHz and 66 MHz, and its use as a contrast agent in MRI has been demonstrated. The NMR-based evidence of the absorption of GdBPA into living tumoral cells is also shown.
Simulation and visualization of attosecond stimulated x-ray Raman spectroscopy signals in trans-N-methylacetamide at the nitrogen and oxygen K-edges
Authors: Healion Daniel , Wang Haitao , Mukamel Shaul
Published: March 2011

The stimulated Raman component of the pump-probe spectrum of trans-N-methylacetamide obtained in response to two soft x-ray pulses is calculated by treating the core excitations at the Hartree–Fock static-exchange level. The signal reveals the dynamics of valence-electron wave packets prepared and detected in the vicinity of a selected atom (either nitrogen or oxygen). The evolving electronic charge density as well as electronic coherence of the doorway and the window created by the two pulses are visualized using a time-dependent basis set of natural orbitals, which reveals that the wave packets consist of several entangled valence particle–hole pairs.
Protein stability at a carbon nanotube interface
Authors: Vaitheeswaran S. , Garcia A. E.
Published: March 2011

The interactions of proteins with solid surfaces occur in a variety of situations. Motivated by the many nanoengineering applications of protein-carbon nanotube hybrids, we investigate the conformational transitions of hen egg white lysozyme adsorbed on a carbon nanotube. Using a Cα structure-based model and replica exchange molecular dynamics, we show how the folding/unfolding equilibrium of the adsorbed protein varies with the strength of its coupling to the surface. The stability of the native state depends on the balance between the favorable entropy and unfavorable enthalpy change on adsorption. In the case of a weakly attractive surface when the former dominates, the protein is stabilized. In this regime, the protein can fold and unfold while maintaining the same binding fraction. With increasing surface attraction, the unfavorable enthalpic effect dominates, the native state is destabilized, and the protein has to extensively unbind before changing states from unfolded to folded. At the highest surface coupling, the entropic penalty of folding vanishes, and a folding intermediate is strongly stabilized. In this intermediate state, the α-domain of lysozyme is disrupted, while the β-sheet remains fully structured. We rationalize the relative stability of the two domains on the basis of the residue contact order.
Carrier dynamics of InxGa1−xN quantum disks embedded in GaN nanocolumns
Authors: Holmes Mark J. , Park Young S. , Wang Xu , Chan Christopher C. S. , Jarjour Anas F. , Taylor Robert A. , Warner Jamie H. , Luo Jun , El-Ella H. A. R. , Oliver R. A.
Published: March 2011

Time-integrated and time-resolved microphotoluminescence studies have been performed on Inx Ga1−xN quantum disks at the tips of GaN nanocolumns. The results are analyzed in the context of current theories regarding an inhomogeneous strain distribution in the disk which is theorized to generate lateral charge separation in the disks by strain induced band bending, an inhomogeneous polarization field distribution, and Fermi surface pinning. It is concluded that no lateral separation of carriers occurs in the quantum disks under investigation. Internal field screening by an increased carrier density in the QDisks at higher excitation densities is observed via a blue-shift of the emission and a dynamically changing decay time. Other possible explanations for these effects are discussed and discounted. Cathodoluminescence studies have also been carried out on the nanocolumns to provide insight into the physical origin of the luminescence.
Stable optical-signal emitter based on a semiconductor photonic dot
Authors: Zhang Yongyou , Zou Bingsuo , Jin Guojun
Published: March 2011

We propose a polariton hyperparametric oscillator (PHO) based on a semiconductor photonic dot at the micro/nano scale. By theoretical derivations and numerical calculations, we find that the PHO not only amplify weak signals like general large-planar polariton amplifiers, but also depress strong signals unusually. The coexistence of such signal amplification and depression can cause a stable signal emission being almost independent of the excitation instabilities in the strong-excitation regime. It has been verified that the instability of the signal emission, increasing with the increase of the excitation instabilities, is only about one to two percent deviation from its average intensity even under strong instable excitations. Hence, the PHO can serve as a stable optical-signal emitter in micro/nano optical systems.
Contactless electroreflectance of AlGaN/GaN heterostructures deposited on c-, a-, m-, and (20.1)-plane GaN bulk substrates grown by ammonothermal method
Authors: Kudrawiec R. , Rudziński M. , Gladysiewicz M. , Janicki L. , Hageman P. R. , Strupiński W. , Misiewicz J. , Kucharski R. , Zając M. , Doradziński R. , Dwiliński R.
Published: March 2011

Room temperature contactless electroreflectance (CER) has been applied to study optical transitions and the distribution of the built-in electric field in AlGaN/GaN heterostructures grown on c-, a-, m-, and (20.1)-plane GaN substrates obtained by the ammonothermal method. It has been clearly shown that polarization effects in the AlGaN/GaN heterostructures grown on the c-plane lead to a strong built-in electric field in the AlGaN layer. The aforementioned field was determined to be ∼0.43 MV/cm from the period of Franz–Keldysh oscillations (FKOs). In addition, polarization effects lead to the formation of a two dimensional electron gas at the AlGaN/GaN interface, which screens the band bending modulation in the GaN buffer layer, and, therefore, GaN-related excitonic transitions are not observed for this heterostructure. Such features/effects are also not observed in the AlGaN/GaN heterostructures grown on nonpolar and semipolar GaN substrates because any strong polarization effects are not expected in this case. For these heterostructures, very strong and sharp GaN excitonic resonances are clearly visible in CER spectra. The resonances are very similar to the excitonic transitions observed for the GaN epilayers deposited on nonpolar and semipolar substrates. Moreover, there is a very weak AlGaN-resonance without FKO for nonpolar and semipolar heterostructures instead of the strong AlGaN-related FKO, which is typical of polar AlGaN/GaN heterostructures.
Laser treatment of plasma-hydrogenated silicon wafers for thin layer exfoliation
Authors: Ghica Corneliu , Nistor Leona Cristina , Teodorescu Valentin Serban , Maraloiu Adrian , Vizireanu Sorin , Scarisoreanu Nae Doinel , Dinescu Maria
Published: March 2011

We have studied by transmission electron microscopy the microstructural effects induced by pulsed laser annealing in comparison with thermal treatments of RF plasma hydrogenated Si wafers aiming for further application in the smart-cut procedure. While thermal annealing mainly produces a slight decrease of the density of plasma-induced planar defects and an increase of the size and number of plasma-induced nanocavities in the Si matrix, pulsed laser annealing of RF plasma hydrogenated Si wafers with a 355 nm wavelength radiation results in both the healing of defects adjacent to the wafer surface and the formation of a well defined layer of nanometric cavities at a depth of 25–50 nm. In this way, a controlled fracture of single crystal layers of Si thinner than 50 nm is favored.
Transport properties and barrier height evaluation in Ni/InAlN/GaN Schottky diodes
Authors: Donoval D. , Chvála A. , Šramatý R. , Kováč J. , Morvan E. , Dua Ch. , DiForte-Poisson M. A. , Kordoš P.
Published: March 2011

The current-voltage characteristics of the Ni/InAlN/GaN Schottky diodes were measured at various temperatures in the range of 300–820 K. The experimental data were analyzed considering different current-transport mechanisms, such as thermionic emission, generation-recombination, tunneling and leakage currents. From the fitting of experimental data it follows that the tunneling current dominates in whole temperature range. The thermionic emission becomes comparable to the tunneling current only at highest temperatures used. The barrier height of the Ni/InAlN/GaN Schottky diodes, evaluated from the thermionic emission current, shows a slightly negative temperature coefficient and its value at 300 K is 1.47 eV. Lower barrier heights were reported before, which follow from an incorrect evaluation of measured data without separation of individual current components. The dislocation density of about 2×109 cm−2 is obtained assuming dislocation governed tunneling current mechanism.
Formation and emission of gold and silver carbide cluster ions in a single ${\rm C}^{-}_{60}$C60− surface impact at keV energies: Experiment and calculations
Authors: Cohen Y. , Bernshtein V. , Armon E. , Bekkerman A. , Kolodney E.
Published: March 2011

Impact of fullerene ions (${\rm C}^{-}_{60}$C60−) on a metallic surface at keV kinetic energies and under single collision conditions is used as an efficient way for generating gas phase carbide cluster ions of gold and silver, which were rarely explored before. Positively and negatively charged cluster ions, ${\rm Au}_{\rm n}{\rm C}_{\rm m}^{+}$ Au nCm+ (n = 1–5, 1 ≤ m ≤ 12), ${\rm Ag}_{\rm n}{\rm C}_{\rm m}^{+}$ Ag nCm+ (n = 1–7, 1 ≤ m ≤ 7), ${\rm Au}_{\rm n}{\rm C}_{\rm m}^{-}$ Au nCm− (n = 1–5, 1 ≤ m ≤ 10), and ${\rm Ag}_{\rm n}{\rm C}_{\rm m}^{-}$ Ag nCm− (n = 1–3, 1 ≤ m ≤ 6), were observed. The ${\rm Au}_{3}{\rm C}_{2}^{+}$ Au 3C2+ and ${\rm Ag}_{3}{\rm C}_{2}^{+}$ Ag 3C2+ clusters are the most abundant cations in the corresponding mass spectra. Pronounced odd/even intensity alternations were observed for nearly all ${\rm Au}_{\rm n}{\rm C}_{\rm m}^{+/-}$ Au nCm+/− and ${\rm Ag}_{\rm n}{\rm C}_{\rm m}^{+/-}$ Ag nCm+/− series. The time dependence of signal intensity for selected positive ions was measured over a broad range of ${\rm C}^{-}_{60}$C60− impact energies and fluxes. A few orders of magnitude immediate signal jump instantaneous with the ${\rm C}^{-}_{60}$C60− ion beam opening was observed, followed by a nearly constant plateau. It is concluded that the overall process of the fullerene collision and formation/ejection of the carbidic species can be described as a single impact event where the shattering of the incoming ${\rm C}^{-}_{60}$C60− ion into small Cm fragments occurs nearly instantaneously with the (multiple) pickup of metal atoms and resulting emission of the carbide clusters. Density functional theory calculations showed that the most stable configuration of the ${\rm Au}_{\rm n}{\rm C}_{\rm m}^{+}$ Au nCm+ (n = 1, 2) clusters is a linear carbon chain with one or two terminal gold atoms correspondingly (except for a bent configuration of Au2C+). The calculated AuCm adiabatic ionization energies showed parity alternations in agreement with the measured intensity alternations of the corresponding ions. The ${\rm Au}_{3}{\rm C}_{2}^{+}$ Au 3C2+ ion possesses a basic Au2C2 acetylide structure with a π-coordinated third gold atom, forming a π-complex structure of the type [Au(π-Au2C2)]+. The calculation shows meaningful contributions of direct gold–gold bonding to the overall stability of the ${\rm Au}_{3}{\rm C}_{2}^{+}$ Au 3C2+ complex.
Compression behavior and phase transition of cubic In2O3 nanocrystals
Authors: Qi J. , Liu J. F. , He Y. , Chen W. , Wang C.
Published: March 2011

High-pressure behaviors of bixbyite-type cubic In2O3 nanocrystals with an average grain size of 6.0 nm and bulk In2O3 samples were investigated by in situ high-pressure synchrotron radiation x-ray diffraction measurements up to 40 GPa at ambient temperature. It was found that nanosized and bulk samples began to transform from cubic into hexagonal structure at about 15–25 GPa and extended up to 40 GPa. Both cubic and hexagonal phases remained after pressure release. Below the onset transition pressure, the nanosized samples were harder to compress with a larger bulk modulus of 296.06 GPa than the bulk samples with a bulk modulus of 178.87 GPa.
The rectifying performance of the multibiphenyl with different end groups: A density functional study
Authors: Deng Xiaoqing , Zhang Zhenhua , Zhou Jicheng , Tang Guiping
Published: March 2011

We investigated the rectifying properties of the multibiphenyl connected to two Au electrodes based on the nonequilibrium Green’s function method combined with the density functional theory. It has been found that the number of benzenes and the type of end groups have distinct influences on rectifying performance of such devices. For the four (five)-benzene system connected with Au electrodes by S–Au bond, we can observe the rectifying performance. While for the six-benzene system, the rectifying behavior is more obvious. When the left end benzene is replaced by pyrimidine, the rectifying effect is weakened. When this substitute is pyridine, however, the rectifying behavior changes clearly as compared with the previous two cases. The detailed analysis demonstrates that the highest occupied molecular orbital resonance changing with the applied bias contributes to the obvious asymmetry of current-voltage characteristics.
Apparatus for processing of samples at high pressures and high temperatures in a fast quenching-rate regime and synthesis of polyacetylene by pulsed laser heating of confined carbon thin films
Authors: Andreazza M. L. , Perottoni C. A. , da Jornada J. A. H.
Published: March 2011

The pulsed laser heating of confined samples followed by ultrafast cooling constitutes an interesting route to explore the production of new phases and compounds. Indeed, in some cases the ultrafast cooling allows retaining at ambient conditions species that were produced under extreme conditions. The experimental setup described in this work allows the heating of thin film samples to temperatures ranging from 1400 to 5500 K, in a controlled and measurable way, with estimated cooling rates in excess of 1011 K·s−1. In this paper, we show that the pulsed laser heating of thin amorphous carbon films deposited on copper substrates leads to the formation of polyacetylene in peak temperatures ranging from 1400 to 2600 K and static pressures between 0.8 and 1.1 GPa. The probable source of hydrogen was tracked to the small amount of water physically adsorbed at the carbon film/copper gasket interface. Because of the fast heating and cooling rate in these experiments, the hydrogen formed by water dissociation at high temperatures does not have enough time to diffuse out of the reaction cell. The results here reported strongly suggest that the evolution and stability of carbon-rich species produced by pulsed-laser heating at high pressure and high temperature critically depends on the capability of hydrogen retention in the reactional system.
L1 FePt(111)/glassy CoFeTaB bilayered structure for patterned media
Authors: Sharma Parmanand , Kaushik Neelam , Makino Akihiro , Esashi Masayoshi , Inoue Akihisa
Published: March 2011

We report on the use of CoFeTaB metallic glass thin film as a soft magnetic underlayer which promotes the growth of L10 FePt along the preferred (111) crystallographic direction. The preferred oriented phase of L10 FePt is obtained by either in situ deposition upon a heated CoFeTaB/SiO2/Si or at room temperature (FePt/CoFeTaB/SiO2/Si) followed by annealing at 400–450 °C for 15 min. The latter process is shown to be advantageous in terms of the fabrication of patterned media. Pattern sizes ranging from 25–100 nm made from L10 FePt (111)/glassy CoFeTaB were fabricated by photo/electron beam lithography. The structural and magnetic characterizations strongly suggest the applicability of the present bilayered structure in the fabrication of high density bit-patterned magnetic recording media.
Materials and electrical characterization of physical vapor deposited LaxLu1−xO3 thin films on 300 mm silicon
Authors: Edge L. F. , Vo T. , Paruchuri V. K. , Iijima R. , Bruley J. , Jordan-Sweet J. , Linder B. P. , Kellock A. J. , Tsunoda T. , Shinde S. R.
Published: March 2011

La x Lu 1 − x O 3 thin films were deposited on 300 mm silicon wafers by physical vapor deposition and fabricated into field-effect transistors using a gate-first process flow. The films were characterized using transmission electron microscopy, Rutherford backscattering spectrometry, and synchrotron x-ray diffraction. The results show the films remain amorphous even at temperatures of 1000 °C. The dielectric properties of LaxLu1−xO3 (0.125≤x≤0.875) thin films were evaluated as a function of film composition. The amorphous LaxLu1−xO3 thin films have a dielectric constant (K) of 23 across the composition range. The inversion thickness (Tinv) of the LaxLu1−xO3 thin films was scaled to <1.0 nm.
Size dependence of exciton-phonon coupling in sol-gel ZnMgO powders
Authors: Chia C. H. , Chen J. N. , Han T. C. , Chiou J. W. , Lin Y. C. , Hsu W. L. , Chou W. C.
Published: March 2011

We found that the exciton-phonon coupling in the Zn1−xMgxO powders (0.01 ≦ x ≦ 0.07) is greatly influenced by the crystalline-size. Two well-resolved photoluminescence (PL) bands due to recombination of free exciton and its longitudinal optical (LO)-phonon replicas enable us to analyze the relative intensities among free excitons, one-LO-phonon replicas, and two-LO-phonon replicas. As crystalline size increases, a larger enhancement of the PL-intensity ratio of a free exciton to its LO-phonon replicas was found compared to that of two LO-phonon replica to one-LO-phonon replica.
Effect of the substrate on the insulator–metal transition of vanadium dioxide films
Authors: Kovács György J. , Bürger Danilo , Skorupa Ilona , Reuther Helfried , Heller René , Schmidt Heidemarie
Published: March 2011

Single-phase vanadium dioxide films grown on (0001) sapphire and (001) silicon substrates show a very different insulator–metal electronic transition. A detailed description of the growth mechanisms and the substrate–film interaction is given, and the characteristics of the electronic transition are described by the morphology and grain boundary structure. (Tri-)epitaxy-stabilized columnar growth of VO2 takes place on the sapphire substrate, whereas on silicon the expected Zone II growth is identified. We have found that in the case of the Si substrate the reasons for the broader hysteresis and the lower switching amplitude are the formation of an amorphous insulating VOx (x > 2.6) phase coexisting with VO2 and the high vanadium vacancy concentration of the VO2. These phenomena are the result of the excess oxygen during the growth and the interaction between the silicon substrate and the growing film.
Surface segregation effects of erbium in GaAs growth and their implications for optical devices containing ErAs nanostructures
Authors: Crook Adam M. , Nair Hari P. , Bank Seth R.
Published: March 2011

We report on the integration of semimetallic ErAs nanoparticles with high optical quality GaAs-based semiconductors, grown by molecular beam epitaxy. Secondary ion mass spectrometry and photoluminescence measurements provide evidence of surface segregation and incorporation of erbium into layers grown with the erbium cell hot, despite the closed erbium source shutter. We establish the existence of a critical areal density of the surface erbium layer, below which the formation of ErAs precipitates is suppressed. Based upon these findings, we demonstrate a method for overgrowing ErAs nanoparticles with III-V layers of high optical quality, using subsurface ErAs nanoparticles as a sink to deplete the surface erbium concentration. This approach provides a path toward realizing optical devices based on plasmonic effects in an epitaxially-compatible semimetal/semiconductor system.
Magnetism and superconductivity in MxFe1+yTe1–zSez (M = Cr, Mn, Co, Ni, Cu, and Zn) single crystals
Authors: Zhang Z. T. , Yang Z. R. , Li L. , Zhang C. J. , Pi L. , Tan S. , Zhang Y. H.
Published: March 2011

High-quality single crystals with nominal composition M0.05Fe0.95Te0.8Se0.2 (M = Cr, Mn, Co, Ni, Cu, and Zn) have been grown, through which the doping effect on magnetism and superconductivity is studied. Elementary analysis reveals that Cu, Co, and Ni, with smaller ionic radii for valence state 2+, can substitute effectively for Fe with doping levels near 5%. In contrast, the solid solution of Cr, Mn, and Zn in the host system is low. Magnetic and electronic investigations show that the substitution of Co, Ni, or Cu for Fe leads to the formation of spin-glass state and suppression of superconductivity. The superconductivity is partly suppressed by Co doping, while completely destroyed by Ni and Cu doping. Compared with Cu- and Ni-doped samples, the Co-doped sample has the smallest lattice constant, indicating that the superconductivity might be also modulated by the changes of microstructure.
Asymmetric pulsing for reliable operation of titanium/manganite memristors
Authors: Gomez-Marlasca F. , Ghenzi N. , Stoliar P. , Sánchez M. J. , Rozenberg M. J. , Leyva G. , Levy P.
Published: March 2011

We present a pulsing protocol that significantly increases the endurance of a titanium-manganite interface used as a binary memory cell. The core of this protocol is an algorithm that searches for the proper values for the set and reset pulses, canceling the drift in the resistance values. A set of experiments show the drift-free operation for more than 105 switching cycles, as well as the detrimental effect by changing the amplitude of pulses indicated by the protocol. We reproduced the results with a numerical model, which provides information on the dynamics of the oxygen vacancies during the switching cycles.
Monte Carlo study of the molecular mechanisms of surface-layer protein self-assembly
Authors: Horejs Christine , Mitra Mithun K. , Pum Dietmar , Sleytr Uwe B. , Muthukumar Murugappan
Published: March 2011

The molecular mechanisms guiding the self-assembly of proteins into functional or pathogenic large-scale structures can be only understood by studying the correlation between the structural details of the monomer and the eventual mesoscopic morphologies. Among the myriad structural details of protein monomers and their manifestations in the self-assembled morphologies, we seek to identify the most crucial set of structural features necessary for the spontaneous selection of desired morphologies. Using a combination of the structural information and a Monte Carlo method with a coarse-grained model, we have studied the functional protein self-assembly into S(surface)-layers, which constitute the crystallized outer most cell envelope of a great variety of bacterial cells. We discover that only few and mainly hydrophobic amino acids, located on the surface of the monomer, are responsible for the formation of a highly ordered anisotropic protein lattice. The coarse-grained model presented here reproduces accurately many experimentally observed features including the pore formation, chemical description of the pore structure, location of specific amino acid residues at the protein–protein interfaces, and surface accessibility of specific amino acid residues. In addition to elucidating the molecular mechanisms and explaining experimental findings in the S-layer assembly, the present work offers a tool, which is chemical enough to capture details of primary sequences and coarse-grained enough to explore morphological structures with thousands of protein monomers, to promulgate design rules for spontaneous formation of specific protein assemblies.
Pattern formation in dielectric barrier discharges with different dielectric materials
Authors: Dong L. F. , Fan W. L. , Wang S. , Ji Y. F. , Liu Z. W. , Chen Q.
Published: March 2011

The influence of dielectric material on the bifurcation and spatiotemporal dynamics of the patterns in dielectric barrier discharge in argon/air at atmospheric pressure is studied. It is found that pattern bifurcation sequences are different with different dielectric materials. The spatiotemporal dynamics of the hexagonal pattern in dielectric barrier discharge depends on the dielectric material. The hexagon pattern with glass dielectric is an interleaving of two rectangular sublattices appearing at different moments. The hexagon pattern with quartz dielectric is composed of one set of hexagonal lattice discharging twice in one half cycle of the applied voltage, one is at the rising edge and the other at the falling edge. It results in that the accumulation of wall charges in individual microdischarges in a hexagon pattern with quartz dielectric is greater than that with glass dielectric, which is in agreement with the electron density measurement by Stark broadening of Ar I 696.54 nm.
Compact very low temperature scanning tunneling microscope with mechanically driven horizontal linear positioning stage
Authors: Suderow H. , Guillamon I. , Vieira S.
Published: March 2011

We describe a scanning tunneling microscope for operation in a dilution refrigerator with a sample stage which can be moved macroscopically in a range up to a cm and with an accuracy down to the tens of nm. The position of the tip over the sample as set at room temperature does not change more than a few micrometers when cooling down. This feature is particularly interesting for work on micrometer sized samples. Nanostructures can be also localized and studied, provided they are repeated over micrometer sized areas. The same stage can be used to approach a hard single crystalline sample to a knife and cleave it, or break it, in situ. In situ positioning is demonstrated with measurements at 0.1 K in nanofabricated samples. Atomic resolution down to 0.1 K and in magnetic fields of 8 T is demonstrated in NbSe2. No heat dissipation nor an increase in mechanical noise has been observed at 0.1 K when operating the slider.
On the thermal force acting on dust grain in fully ionized plasma
Authors: Stepanenko A. A. , Smirnov R. D. , Zhdanov V. M. , Krasheninnikov S. I.
Published: March 2011

The expressions for ion and electron thermal forces and electron friction force acting on a spherical dust grain from plasma embedded into a magnetic field are found. The electron and ion distribution functions were considered by using 21 moments Grad approximation. Dust grain with a radius much smaller than ion and electron gyroradii was assumed to be either negatively or relatively weakly positively charged. The forces found in this paper can be important, particularly for dust dynamics in fusion plasmas with stagnated plasma flow.
Note: Diagnosing femtosecond laser-solid interactions with monochromatic K
α imager and x-ray pinhole camera
Authors: Lin X. X. , Li Y. T. , Liu F. , Liu B. C. , Du F. , Wang S. J. , Chen L. M. , Zhang L. , Zheng Y. , Liu X. , Liu X. L. , Wang Z. H. , Ma J. L. , Wei Z. Y. , Zhang J.
Published: March 2011

An x-ray pinhole camera and a monochromatic Kα imager are used to measure the interactions of intense femtosecond laser pulses with Cu foil targets. The two diagnostics give different features in the spot size and the laser energy scaling, which are resulted from different physical processes. Under our experimental conditons, the Kα emission is mainly excited by the fast electrons transporting inside the cold bulk target. In contrast, the x-ray pinhole signals are dominated by the broadband thermal x-ray emission from the hot plasma at the front target surface.