bluuebunny/crossref_metadata_2025 huggingface dataset:
Electron-beam tip/sample heating device for a scanning tunneling microscopy
Authors: Ding H. F. , Pearson J. E. , Li Dongqi , Cheng Ruihua , Fradin F. Y. , Bader S. D.
Published: December 2005

We present an electron-beam heating device for a scanning tunneling microscopy (STM) that can be used for heating both the STM tip and the sample to 2200K. Mounted on a linear bellows with electrical feedthroughs, the device can be readily installed into the transfer path of a vacuum load lock. We demonstrate the heating capability of the device by flash cleaning Ru(0001) and Fe(001) crystals, and W tips. The flash-cleaned W tips are coated with Fe and further used for spin-polarized imaging of the Mn∕Fe(001) system.
A multiaxis stage configured for rapid observations of plane samples at multiple angles
Authors: Lamvik Michael , Grego Sonia
Published: December 2005

We describe a mechanical configuration that allows any point on a flat sample to be moved to any angle of tilt and rotation (within the limits of which the stage is capable) while maintaining the area of interest at a constant focus and within the field of view of a fixed optical system. We describe eight axes of movement required to obtain the desired stability of focus and view area. We demonstrate the proposed concept by assembling an instrument using mostly existing parts. This optical-microscope-based instrument allows sample tilts to 60° and unlimited rotation while maintaining the point of interest within better than 17μm in x, y, and z of the center of the field of view of a 100× optical system.
Small-volume, ultrahigh-vacuum-compatible high-pressure reaction cell for combined kinetic andin situIR spectroscopic measurements on planar model catalysts
Authors: Zhao Z. , Diemant T. , Häring T. , Rauscher H. , Behm R. J.
Published: December 2005

We describe the design and performance of a high-pressure reaction cell for simultaneous kinetic and in situ infrared reflection (IR) spectroscopic measurements on model catalysts at elevated pressures, between 10−3 and 103mbars, which can be operated both as batch reactor and as flow reactor with defined gas flow. The cell is attached to an ultrahigh-vacuum (UHV) system, which is used for sample preparation and also contains facilities for sample characterization. Specific for this design is the combination of a small cell volume, which allows kinetic measurements with high sensitivity under batch or continuous flow conditions, the complete isolation of the cell from the UHV part during UHV measurements, continuous temperature control during both UHV and high-pressure operation, and rapid transfer between UHV and high-pressure stage. Gas dosing is performed by a designed gas-handling system, which allows operation as flow reactor with calibrated gas flows at adjustable pressures. To study the kinetics of reactions on the model catalysts, a quadrupole mass spectrometer is connected to the high-pressure cell. IR measurements are possible in situ by polarization-modulation infrared reflection-absorption spectroscopy, which also allows measurements at elevated pressures. The performance of the setup is demonstrated by test measurements on the kinetics for CO oxidation and the CO adsorption on a Au∕TiO2∕Ru(0001) model catalyst film at 1–50 mbar total pressure.
A multiphoton laser scanning microscope setup for transcranial in vivo brain imaging on mice
Authors: Nase Gabriele , Helm P. Johannes , Reppen Trond , Ottersen Ole Petter
Published: December 2005

We describe a multiphoton laser scanning microscope setup for transcranial in vivo brain imaging in mice. The modular system is based on a modified industrial standard Confocal Scanning Laser Microscope (CSLM) and is assembled mainly from commercially available components. A special multifunctional stage, which is optimized for both laser scanning microscopic observation and preparative animal surgery, has been developed and built. The detection unit includes a highly efficient photomultiplier tube installed in a Peltier-cooled thermal box shielding the detector from changes in room temperature and from distortions caused by external electromagnetic fields. The images are recorded using a 12-bit analog–to–digital converter. Depending on the characteristics of the staining, individual nerve cells can be imaged down to at least 100μm below the intact cranium and down to at least 200μm below the opened cranium.
Remarkable impact of intermode couplings on multimode vibronic dynamics: the photoelectron spectrum of CH3F
Authors: Mahapatra S. , Vallet V. , Woywod C. , Köppel H. , Domcke W.
Published: December 2005

Electronic and nuclear motions on intersecting potential energy surfaces are often intricately mixed and the spectrum can become very complex. Here we choose the strongly coupled Jahn-Teller system CH3F+ as a prototype example, and establish the importance of intermode coupling terms on multimode vibronic dynamics. The theoretical approach consists of a full second-order diabatic vibronic Hamiltonian, constructed from high-quality electronic structure calculations. Our results compare amazingly well with the experimental data. This highlights the success of the present theoretical approach in explaining the complex structure of vibronic spectra, ubiquitous in molecular systems.
Anisotropy of magnetohydrodynamic turbulence at low magnetic Reynolds number
Authors: Vorobev Anatoliy , Zikanov Oleg , Davidson Peter A. , Knaepen Bernard
Published: December 2005

Turbulent fluctuations in magnetohydrodynamic flows are known to become anisotropic under the action of a sufficiently strong magnetic field. We investigate this phenomenon in the case of low magnetic Reynolds number using direct numerical simulations and large eddy simulations of a forced flow in a periodic box. A series of simulations is performed with different strengths of the magnetic field, varying Reynolds number, and two types of forcing, one of which is isotropic and the other limited to two-dimensional flow modes. We find that both the velocity anisotropy (difference in the relative amplitude of the velocity components) and the anisotropy of the velocity gradients are predominantly determined by the value of the magnetic interaction parameter. The effects of the Reynolds number and the type of forcing are much weaker. We also find that the anisotropy varies only slightly with the length scale.
Light-induced properties of ruthenium-doped Bi4Ge3O12 crystals
Authors: Marinova Vera , Lin Shiuan Huei , Hsu Ken Yuh
Published: December 2005

The influence of ruthenium addition at different doping concentrations on the optical properties and holographic behavior of Bi4Ge3O12 crystals is investigated. Doped Bi4Ge3O12 single crystals are grown by using the Czochralski technique. The distribution coefficient of each crystal is measured to determine the concentration of a doped ruthenium element. Holographic experiments are performed. Ruthenium is found to make Bi4Ge3O12 sensitive in the red spectral range. Thermal annealing and ultraviolet exposure have been used to modify the defect structure and corresponding absorption band of each crystal such that the holographic recording has been influenced. The diffraction efficiency increases with increasing of ruthenium content, especially after irradiation by ultraviolet light.
Effect of metal liner on electromigration in Cu Damascene lines
Authors: Hu C.-K. , Gignac L. M. , Liniger E. , Detavernier C. , Malhotra S. G. , Simon A.
Published: December 2005

Electromigration in Cu single Damascene lines capped with amorphous a-SiCxNyHz and fabricated with various Ta-based liners is investigated. The Ta-based liner layers were deposited using atomic layer and physical vapor deposition techniques. The crystallographic phases of the Ta liners were determined using x-ray and transmission electron diffraction. Although the Cu electromigration lifetimes are determined by % resistance increase failure criteria that are dependent on the liner resistance, the Cu void growth rate was found to be insensitive to the phases of Ta. This result is consistent with the dominant diffusion path being along the Cu∕a-SiCxNyHz interface in these samples. The activation energy for Cu along Cu∕a-SiCxNyHz interface diffusion was found to be 1.0±0.04eV.
An unusual nonlinearity in current-voltage curves of a bidimensional electron gas at low temperatures
Authors: Khlil R. , El Hdiy A. , Cavanna A. , Laruelle F. , Jin Y.
Published: December 2005

Electrical characterization of a bidimensional electron gas transport has been investigated. Three AlGaAs∕GaAs heterostructures have been used for the study. Hall measurements have been performed at 4.2K and current-voltage characteristics at fixed temperatures between 4.2 and 300K. Measurements have been made using a four-point probe method. A saturation of the current at weak electric fields was observed in the range of low temperatures (<100K). The channel conductivity, the contact resistance, the electron mobility and the bidimensional electron gas density were determined. Electron drift velocities were deduced from current-voltage curves at the beginning of the saturation regime at 4.2K and compared with those found in the literature. The saturation, giving weak velocity, is related to impurity and alloy scatterings. Drift velocities close to the Fermi velocity are related to the Gunn effect. A Schottky effect has been observed at low temperatures (<100K) when the electron transport is perpendicular to the direction leading to the saturation of the current. This Schottky behavior indicates degradation of Ohmic contacts in the Au∕Ni∕Ge structure constituting the source and the drain.
Physics-based simulation of buffer-trapping effects on slow current transients and current collapse in GaN field effect transistors
Authors: Horio Kazushige , Yonemoto Ken , Takayanagi Hiroki , Nakano Hiroyuki
Published: December 2005

Two-dimensional transient analyses of GaN metal-semiconductor field effect transistors (MESFETs) are performed in which a three level compensation model is adopted for a semi-insulating buffer layer, where a shallow donor, a deep donor, and a deep acceptor are included. Quasipulsed current-voltage (I-V) curves are derived from the transient characteristics and are compared with steady-state I-V curves. It is shown that when the drain voltage VD is raised abruptly, the drain current ID overshoots the steady-state value, and when VD is lowered abruptly, ID remains at a low value for some periods, showing drain-lag behavior. These are explained by the deep donor’s electron capturing and electron emission processes quantitatively. The drain lag could be a major cause of current collapse, although some gate lag is also seen due to the buffer layer. The current collapse is shown to be more pronounced when the deep-acceptor density in the buffer layer is higher and when an off-state drain voltage is higher, because the change of ionized deep-donor density becomes larger and hence the trapping effects become more significant. It is suggested that to minimize the current collapse in GaN-based FETs, an acceptor density in a semi-insulating layer should be made low, although the current cutoff behavior may be degraded.
Lattice bending, disordering, and amorphization induced plastic deformation in a SiC nanowire
Authors: Han X. D. , Zhang Y. F. , Liu X. Q. , Zhang Z. , Hao Y. J. , Guo X. Y.
Published: December 2005

The plastic deformation features of intrinsic brittle-featured SiC nanowires by high resolution electron microscopy have been investigated. Strong plastic deformation strain fields were observed in a bent SiC nanowire. The achieved localized strain reaches about 1.5%. Localized lattice bending, atomic lattice disordering, and amorphization are contribution factors to achieve the plastic deformation. The projected Si–Si bonding angle distribution on the (110) atomic plane demonstrates the disordering features of the bent SiC nanowire. Buckling is found at the compressive side of the bent SiC nanowire. Growth bending can be achieved through {111} twinning and phase transformation from 3C to 2H.
Electronic properties of InN nanowires
Authors: Cheng Guosheng , Stern Eric , Turner-Evans Daniel , Reed Mark A
Published: December 2005

Indium nitride nanowires (NWs) grown by a catalyst-free, vapor-solid method are shown to be high-purity, single-crystal hexagonal wurtzite and intrinsic n type with uniform diameters that range from 70to150nm and lengths that vary between 3 and 30μm. Single NWs were fabricated into field-effect transistors and the electronic material parameters of the wires were extracted and are found to be identical to comparable bulk InN.
Stark shift of the A2Π1∕2 state in YbF174
Authors: Condylis P. C. , Hudson J. J. , Tarbutt M. R. , Sauer B. E. , Hinds E. A.
Published: December 2005

We have measured the Stark shift of the A2Π1∕2–X2Σ+ transition in YbF. We use a molecular beam triple resonance method, with two laser transitions acting as pump and probe, assisted by an rf transition that tags a single hyperfine transition of the X state. After subtracting the known ground state Stark shift, we obtain a value of 70.3(1.5)Hz∕(V∕cm)2 for the static electric polarizability of the state A2Π1∕2(J=12,f) by fitting our data to a purely quadratic Stark shift in the interval 0–5kV∕cm. A more exact analysis that does not assume a perfectly quadratic Stark effect yields the value μe=2.48(3)D for the electric dipole moment of the A2Π1∕2(v=0) state.
Mixed donor-acceptor molecular heterojunctions for photovoltaic applications. II. Device performance
Authors: Xue Jiangeng , Rand Barry P. , Uchida Soichi , Forrest Stephen R.
Published: December 2005

We demonstrate efficient organic photovoltaic cells employing a photoactive region composed of a mixed donor-acceptor molecular layer, the properties of which were introduced in the preceding paper (Part I) [Rand et al., J. Appl. Phys. 98, 124902 (2005)]. The hybrid planar-mixed heterojunction (PM-HJ) device architecture consists of a film mixture of donor and acceptor molecules inserted between layers of pure donor and acceptor composition. Using the donor, copper phthalocyanine, and the acceptor, C60, we demonstrate a hybrid PM-HJ cell with a maximum power conversion efficiency of (5.0±0.3)% under 1–4suns simulated AM1.5 solar illumination. The current-voltage characteristics of the PM-HJ cell are described using a model based on the field-dependent charge collection length.
Field emission and photoluminescence of SnO2 nanograss
Authors: Wang B. , Yang Y. H. , Wang C. X. , Xu N. S. , Yang G. W.
Published: December 2005

Two-dimensional SnO2 nanograsses were synthesized on single-crystal Si substrates by catalyst-assisted thermal evaporation. The photoluminescence spectra from the products revealed multipeaks consistent with previous reports, with the exception of a new peak at 574 nm. The large field emission current from SnO2 nanograss was observed at a high turn-on voltage, which is attributed to a shorter length and a wide emitter radius. The formation of SnO2 nanograsses at the low temperature was pursued on the basis of the vapor-liquid-solid mechanism.
Micromagnetic modeling with eddy current and current-induced spin torque effect
Authors: Wadhwa P. , Jalil M. B. A. , Tan S. G.
Published: December 2005

We present a micromagnetic model which incorporates eddy current and spin transfer torque effects due to the passage of a spin-polarized current in the current-perpendicular-to-plane (CPP) geometry. Eddy current effects are modeled by solving Faraday’s and Poisson’s equations self-consistently with the Landau-Lifshitz-Gilbert (LLG) equation, whereas spin transfer torque is modeled by including the Slonczewski spin torque term in the LLG equation. We consider a 50 nm cubic Co element, which forms the free layer of a pseudo-spin-valve structure. With a typical damping parameter of α=0.5, the eddy currents act to accelerate the magnetic reversal process. The spin torque effect can also assist the reversal process but at high current densities exceeding Jext=108A∕cm2 onwards. At these current densities, spin transfer torque also causes a substantial reduction in the coercivity.
Discrete model analysis of the critical current-density measurements in superconducting thin films by a single-coil inductive method
Authors: Aurino M. , Di Gennaro E. , Di Iorio F. , Gauzzi A. , Lamura G. , Andreone A.
Published: December 2005

The critical current density of a superconducting film can be easily determined by an inductive and contactless method. Driving a sinusoidal current in a single coil placed in front of a superconducting sample, a nonzero third-harmonic voltage V3 is induced in it when the sample goes beyond the Bean critical state. The onset of V3 marks the value of current beyond which the sample response to the magnetic induction is no more linear. To take into account, in a realistic way, the magnetic coupling between the film and the coil, we have developed a discrete model of the inducing and induced currents distribution. In the framework of this model the magnetic-field profile on the sample surface and the coefficient linking the current flowing in the coil and the critical current density JC of superconducting thin films are evaluated. The numerical results are checked by measuring JC of several thin films of YBa2Cu3O7−δ of known superconducting properties, used as a control material.
Nonlinear effects of lower hybrid wave absorption on location of power deposition in the HL-2A reversed-shear plasma
Authors: Gao Qingdi , Zhang Jinhua
Published: December 2005

In the simulations of the reversed-shear plasma of the HL-2A tokamak [Q. Gao et al., Nucl. Fusion 40, 1897 (2000)], the absorption of the lower hybrid (LH) wave is weak and makes many passes through the plasma until the initial launched wave spectrum is sufficiently broadened to be absorbed. As the constraint imposed by the wave propagation condition limits the maximum allowed n‖ upshift, the LH wave absorption is bounded in the region defined by the strong Landau-damping limit and the boundary of the wave propagation domain. This mechanism of the LH wave absorption causes interplay of the distribution of the LH wave driven current with the modification of the plasma configuration, which constitutes nonlinearity in the LH wave deposition. Due to the nonlinear coupling between the LH power deposition and the profiles of both pressure and current, the LH wave deposition position changes spontaneously, generating two distinct quasistationary reversed magnetic shear (RS) configurations in a single discharge without changing the discharge condition. Therefore, the feedback control of the plasma current profile through controlling the externally driven current by the LH wave is a challenge in the RS plasma regimes for steady-state high performance tokamak operations.
Enhanced stability of light-emitting performances of phosphors under low energy electrons
Authors: Bukesov Sergey A. , Jeon Duk Y. , Lee Burtrand I.
Published: December 2005

Here we demonstrate the experimental evidence of an unusually high stability of emission characteristics of phosphor screens by the intensive bombardment by low-energy electrons. The explanation of the observed emission stability is based on the assumption that the low-energy electrons enhanced the electrical conductivity of the phosphor which initiated the improvement of the light-emitting performances.
Framework for potential systems and nonlocal symmetries: Algorithmic approach
Authors: Bluman George , Cheviakov Alexei F.
Published: December 2005

An algorithmic framework is presented to find an extended tree of nonlocally related systems for a given system of differential equations (DEs). Each system in an extended tree is equivalent in the sense that the solution set for any system in a tree can be found from the solution set for any other system in the tree. Useful conservation laws play an essential role in the construction of an extended tree. A useful conservation law yields potential variables and equivalent nonlocally related potential systems and subsystems for any given system. Nonlocal symmetries for a given system of DEs can arise from any system in its extended tree. We construct extended trees for the systems of planar gas dynamics and nonlinear telegraph equations, and in both cases obtain new nonlocal symmetries. More importantly, due to the equivalence of solution sets, any coordinate-independent method of analysis (qualitative, numerical, perturbation, etc.) can be applied to any system within the tree, and may yield simpler computations and/or results that cannot be obtained when the method is directly applied to the given system.
Quantitative estimates on the enhanced binding for the Pauli-Fierz operator
Authors: Barbaroux Jean-Marie , Linde Helmut , Vugalter Semjon
Published: December 2005

For a quantum particle interacting with a short-range potential, we estimate from below the shift of its binding threshold, which is due to the particle interaction with a quantized radiation field.
Extensive ground state entropy in supersymmetric lattice models
Authors: van Eerten Hendrik
Published: December 2005

We present the result of calculations of the Witten index for a supersymmetric lattice model on lattices of various type and size. Because the model remains supersymmetric at finite lattice size, the Witten index can be calculated using row-to-row transfer matrices and the calculations are similar to calculations of the partition function at negative activity −1. The Witten index provides a lower bound on the number of ground states. We find strong numerical evidence that the Witten index grows exponentially with the number of sites of the lattice, implying that the model has extensive entropy in the ground state.
Dynamic response of binders; teflon, estane™ and Kel-F-800™
Authors: Bourne N. K. , Gray G. T.
Published: December 2005

It is important to understand the mechanical behavior of polymeric materials that have a range of industrial and defence applications. In particular, several are used as the binder phase in plastic bonded explosives and propellants. Binder materials used in energetics need to be understood first to ensure their long-term, high-temperature stability when cycled during service, and second to ensure that the accidental loading of such materials leaves the explosives crystals within safe to handle. This work presents experimental data on equation-of-state and shock-induced damage evolution of the polymers teflon, estane™ and Kel-F-800™. The tensile (spall) strength at high rate was quantified using real-time laser interferometric techniques on each polymer as a function of impact stress. Measurements were made of the lateral stress under impact using manganin gauges, which, when combined with longitudinal data, allowed investigation of the shear strength of each polymer. An increase of shear strength, determined in this manner, was noted for two polymers and comparisons are drawn with others investigated using the same technique. A discussion of the mechanical response of these polymers is presented.
Photoconduction in Alq3
Authors: Ray Debdutta , Patankar Meghan P. , Periasamy N. , Narasimhan K. L.
Published: December 2005

Photoelectronic properties of Alq3 were studied by photoconductivity (PC) measurements in thin film, sandwich (indium-tin-oxide/Alq3∕LiF∕Al) devices. We find that the photocurrent is dominated by bulk generation of carriers for incident photon energies greater than 2.75eV. The quantum efficiency of photocarrier generation has been measured from carrier collection measurements to be about 10%. The quantum efficiency is largely independent of electric field. This enables a direct measurement of the electric field dependence of mobility using photoconductivity measurements, which is used for quantitative analysis of the dark forward current in these devices. PC measurements were also used to obtain (μ0nτn) product which can be used as a measure of material quality. For Alq3, we find that the value of (μ0nτn) product was between 3×10−15cm2∕V to 8×10−15cm2∕V for different samples. In forward bias, at high field the photocurrent shows saturation accompanied by a phase shift. These effects are attributed to space charge effects in the device.
Optical properties of thin films of [Ru(bpy)3][NaCr(ox)3] polymeric networks
Authors: Rabaste Sebastien , Amstutz Nahid , Hauser Andreas , Pillonnet Anne
Published: December 2005

The optical properties of a thin film of the [Ru(bpy)3][NaCr(ox)3] network structure obtained by pulsed laser deposition are described. The luminescence shows the characteristic doublet of R lines at 14400cm−1 of the spin-forbidden ligand field transition E2(t2g3)→A24(t2g3) of the [Cr(ox)3]3− chromophore. The resonant energy migration within the R1 line shows that the three-dimensional crystallographic structure is preserved during the coating process. The observation of the R lines of [Cr(bpy)3]3+ at 13710cm−1 indicates that a small fraction of Cr3+ ions migrate from the oxalate network to the tris-bipyridine cation site in the cavities of the network.
Nanoindentation of HgCdTe prepared by molecular beam epitaxy
Authors: Martyniuk M. , Sewell R. H. , Musca C. A. , Dell J. M. , Faraone L.
Published: December 2005

Nanoindentation has been used to investigate the elastoplastic behavior of Hg0.7Cd0.3Te prepared by molecular beam epitaxy. It was found that Hg0.7Cd0.3Te had a modulus of elasticity of ∼50GPa and hardness of ∼0.66GPa. The HgCdTe response to nanoindentation was found to be purely elastic for low loads and developed into ∼10% elastic and ∼90% plastic response for higher-load indentation exhibiting significant amounts of creep. The onset of plasticity has been observed to be marked by discontinuities or “pop-in” events in the indenter load-penetration curves at sheer stresses of ∼1.8GPa, and has been correlated with the homogeneous nucleation and propagation of dislocations.
Two-staged sorption isotherm of a nanoporous energy absorption system
Authors: Surani Falgun B. , Kong Xinguo , Qiao Yu
Published: December 2005

To selectively absorb impact energy, the profiles of sorption isotherms of protection systems must be adjusted in a broad spectrum. In this article, a N-Lauroylsarcosine sodium salt (sarcosyl) of intermediate molecular size is used to control the pressure induced infiltration of a nanoporous silica. The experimental result shows that the infiltration plateau of this system is two-staged; that is, not only the activation pressure but also the infiltration volume can be modified. It is noticed that the sarcosyl molecule demands a “free volume” to enter a nanopore. The free volume size decreases nearly linearly as the sarcosyl concentration increases.
Underdoped cuprate antiferromagnet as a two-dimensional antiferromagnetic metal
Authors: Sergeeva G. G.
Published: December 2005

An approach to describing the pseudogap state as a two-dimensional antiferromagnetic metal with non-Fermi charge carriers is developed for quasi-two-dimensional underdoped HTSC cuprates with one CuO2 plane. The model of local closed Varma currents is extended to holes of the ion Cu3+ surrounded by four ionic complexes Cu↑2+O42− (or Cu↓2+O42−). It is shown that taking account of the electron-vibrational interactions results in vibronic transitions from a nondegenerate state of the Cu3+ ion into doubly degenerate Cu↑2+ (or Cu↓2+) with splitting of the energy band for two types of quasilocal states of a “copper-oxygen” hole (vortex or antivortex), each of which moves in its own magnetic sublattice. The transfer of the vortex current from the “molecule” Cu3+O42− to the complex Cu↓2+O42− with the copper ion from the same magnetic sublattice creates the dynamical effect of a displacement of a Cu3+ ion to the site of a Cu↓2+ ion and a transition of the “molecule” Cu3+O42− into the complex Cu↓2+O42−.
Detection of fluctuation effects near the phase separation temperature of concentrated He3−He4 solid solutions
Authors: Antsygina T. N. , Grigor’ev V. N. , Maidanov V. A. , Penzev A. A. , Rubets S. P. , Rudavskii E. Ya. , Rybalko A. S. , Syrnikov E. V. , Chishko K. A.
Published: December 2005

A precision barometric study has revealed unusual behavior of the pressure of He3−He4 solid solutions with a concentration of around 30% He3: in the pre-separation region the pressure increases with decreasing temperature long before the start of the phase transition. It is established that such an anomaly is due to correlation effects in the impurity subsystem which give rise to large-scale fluctuations of the impurity concentration, and the fluctuation contribution to the pressure is much greater than the phonon contribution. Quantitative agreement between the experimental data and the proposed theory is obtained, and it is shown that the observed temperature dependence of the pressure in the pre-separation and metastable regions can be explained only when the long-range character of the interaction between impurities is taken into account.
Influence of the character of electron reflection from a surface on the electric properties of a cylindrical particle
Authors: Zavitaev É. V. , Yushkanov A. A.
Published: December 2005

The cross section for the absorption of electromagnetic radiation in a cylindrical metallic particle is calculated. Specular-diffuse reflection of electrons from the inner surface of the particle is taken as the boundary condition for the problem. Limiting cases are studied, and the results obtained are discussed.
Relaxation of the magnetization of superconducting YBCO samples in weak magnetic fields
Authors: Timofeev V. P. , Omel’yanchuk A. N. , Petrusenko Yu. T.
Published: December 2005

The first investigations are performed of the magnetization and isothermal relaxation of the magnetization of high-temperature superconducting samples with different crystal structure in very weak constant fields (H⩽0.5 Oe) at temperatures close to the critical value. It is shown that the twinning boundaries in YBCO single crystals strongly influence the relaxation rate of the magnetization. The collective pinning model is used to estimate the effective pinning potential under these conditions. This estimate can be used to characterize the degree to which artificially produced point defects affect the critical currents of MgB2 samples.
Dust-particle transport in tokamak edge plasmas
Authors: Pigarov A. Yu. , Krasheninnikov S. I. , Soboleva T. K. , Rognlien T. D.
Published: December 2005

Dust particulates in the size range of 10nm–100μm are found in all fusion devices. Such dust can be generated during tokamak operation due to strong plasma∕material-surface interactions. Some recent experiments and theoretical estimates indicate that dust particles can provide an important source of impurities in the tokamak plasma. Moreover, dust can be a serious threat to the safety of next-step fusion devices. In this paper, recent experimental observations on dust in fusion devices are reviewed. A physical model for dust transport simulation and a newly developed code DUSTT are discussed. The DUSTT code incorporates both dust dynamics due to comprehensive dust-plasma interactions as well as the effects of dust heating, charging, and evaporation. The code tracks test dust particles in realistic plasma backgrounds as provided by edge-plasma transport codes. The results are presented for dust transport in current and next-step tokamaks. The effect of dust on divertor plasma profiles and core plasma contamination is examined.
Strain-facilitated process for the lift-off of a Si layer of less than 20 nm thickness
Authors: Shao Lin , Lin Yuan , Swadener J. G. , Lee J. K. , Jia Q. X. , Wang Y. Q. , Nastasi M. , Thompson Phillip E. , Theodore N. David , Alford T. L. , Mayer J. W. , Chen Peng , Lau S. S.
Published: December 2005

We report a process for the lift-off of an ultrathin Si layer. By plasma hydrogenation of a molecular-beam-epitaxy-grown heterostructure of Si∕Sb-doped-Si∕Si, ultrashallow cracking is controlled to occur at the depth of the Sb-doped layer. Prior to hydrogenation, an oxygen plasma treatment is used to induce the formation of a thin oxide layer on the surface of the heterostructure. Chemical etching of the surface oxide layer after hydrogenation further thins the thickness of the separated Si layer to be only 15 nm. Mechanisms of hydrogen trapping and strain-facilitated cracking are discussed.
Effect of two-temperature trapped electrons to nonlinear dust-ion-acoustic solitons
Authors: Moslem Waleed M. , El-Taibany W. F.
Published: December 2005

Propagation of three-dimensional dust-ion-acoustic solitons is investigated in a dusty plasma consisting of positive ions, negatively variable-charged dust particles, and two-temperature trapped electrons. We use the reductive perturbation theory to reduce the basic set of fluid equations to one evolution equation called damped modified Kadontsev-Petviashivili equation. Exact solution of this equation is not possible, so we obtain the time evolution solitary wave form approximate solution. It is found that only compressive soliton can propagate in this system. We develop a theoretical estimate condition under which the solitons can propagate. It is found that this condition is satisfied for Saturn’s F ring. It is found also that low electron temperature has a role on the behavior of the soliton width, i.e., for lower (higher) range of low electron temperature the soliton width decreases (increases). However, high electron temperature decreases the width. The trapped electrons have no effect on the soliton width. The ratio of free low (high) to trapped low (high) electron temperatures increases the soliton amplitude. Also, the amplitude increases with free low and free high electron temperatures. To investigate the stabilty of the waves, we used a method based on energy consideration to obtain a condition for stable solitons. It is found that this condition depends on dust charge variation, streaming velocity, directional cosine of the wave vector k along the x axis, and temperatures of dust particles, ions, and free electrons.
On the negative mass flows in evaporation and condensation problems
Authors: Onishi Yoshimoto
Published: December 2005

One of the features in evaporation and condensation problems would be the existence of the so-called negative mass flow phenomenon in the sense that the direction of the mass flows due to evaporation and condensation processes may become opposite to what one would usually expect to be. This phenomenon, which surely manifests itself in particular situations in which the latent heat parameter is quite small under the existence of some degree of rarefaction of the gas phase, was first noticed by Sone and Onishi in their asymptotic analysis for steady gas flows of a general type based on the linearized kinetic equation. The detailed discussion on this phenomenon, however, is not yet given. The present paper, paying particular attention to cases with small Knudsen numbers, aims to clarify the effects of the relevant parameters involved on the existence and the magnitude of this negative mass flow by taking up a two-surface problem of evaporation and condensation, one of the simple and typical problems to study motions of a vapor, transient to steady, caused by evaporation and condensation processes occurring at the condensed phases placed in parallel.
Identification method for vortex sheet structures in turbulent flows
Authors: Horiuti Kiyosi , Takagi Youhei
Published: December 2005

A new identification method was proposed for an eduction of vortex sheet structures in turbulent flows. This method took advantage of a prominent feature of a sheet, i.e., comparable dominance of both strain rate and vorticity and their strong correlation. The effectiveness of the proposed method was presented in the assessment using direct numerical simulation data for homogeneous isotropic turbulence. Both strain rate and vorticity were indeed large and correlated in the region identified using the proposed method. As a result, intense dissipation took place in the educed region. The relationship between the eigenvalue solution used in the present method and the invariants of fourth-order moments of velocity gradients was discussed. It was shown that the proposed method performed better than other invariants and previous identification methods for educing the vortex sheets.
Spin-coatable inorganic gate dielectric for organic thin-film transistors
Authors: Han Keon-kook , Park S. Young , Kim M. Joon , Lee Hong H.
Published: December 2005

Polymer gate dielectrics have been used for organic thin-film transistors (OTFTs) primarily because of wet processability. An inorganic dielectric, if it is wet processable, can remedy many problems associated with a polymer dielectric. A siloxane-based spin-on glass is used to show that it can lead to better device performance than the best polymer dielectric known, thus paving the way to replacing the polymer dielectric for OTFTs, except in flexible device applications.
Single-ionized-oxygen-vacancy-related dielectric relaxation in Bi3.25La0.75Ti3O12 ferroelectric films
Authors: Zhong N. , Okamura S. , Uchiyama K. , Shiosaki T.
Published: December 2005

The dielectric and conductive properties of Bi3.25La0.75TiO3 ferroelectric films were investigated in the temperature range of 25°C–600°C. A dielectric peak with a relaxation-type characteristic was observed around 400°C. This peak can be greatly suppressed or eliminated by high sintering temperature or annealing in an oxygen atmosphere (O2), and induced again by annealing in a reducing atmosphere (N2). The activation energy of dielectric relaxation and the characteristic relaxation time are estimated to be 1.89eV and 1.08×10−14s, respectively. In the corresponding temperature region, activation energy of conductivity is 0.65eV. The mechanism of this dielectric anomaly is discussed.
High-quality nanothickness single-crystal Sc2O3 film grown on Si(111)
Authors: Hong M. , Kortan A. R. , Chang P. , Huang Y. L. , Chen C. P. , Chou H. Y. , Lee H. Y. , Kwo J. , Chu M.-W. , Chen C. H. , Goncharova L. V. , Garfunkel E. , Gustafsson T.
Published: December 2005

High-quality single-crystal Sc2O3 films a few nanometer thick have been grown epitaxially on Si (111) despite a huge lattice mismatch. The films were electron-beam evaporated from a Sc2O3 target. Structural and morphological studies were carried out by x-ray diffraction and reflectivity, atomic force microscopy, high-resolution transmission electron microscopy, and medium-energy ion scattering, with the initial epitaxial growth monitored by in situ reflection high-energy electron diffraction. The films have the cubic bixbyite phase with a remarkably uniform thickness and high structural perfection. The film surfaces are very smooth and the oxide/Si interfaces are atomically sharp with a low average roughness of 0.06nm. The films are well aligned with the Si substrate with an orientation relationship of Si(111)‖Sc2O3(111), and an in-plane expitaxy of Si[1¯10]‖Sc2O3[1¯01].
Electron energy-loss spectrometry studies of bonding in nanoscale Ni–SiO2 multilayers
Authors: Taylor Seth T. , Gronsky Ronald
Published: December 2005

Electron energy-loss spectrometry in the transmission electron microscope is used to directly assess the nature of bonding at interfaces formed during alternating deposition of nanoscale Ni and SiO2 multilayers. Interfacial Ni–O bond formation near the interface is revealed by energy-loss near-edge structure preceding the OK edge threshold, indicating hybridization of O2p with Ni3d orbitals, and by characteristic white line structure associated with the NiL2,3 edge. Interface spectra are compared to reference NiO spectra, verifying local Ni–O bonding at the Ni∕SiO2 interface.
Giant negative thermal expansion in Ge-doped anti-perovskite manganese nitrides
Authors: Takenaka K. , Takagi H.
Published: December 2005

We report the discovery of a large negative thermal expansion (NTE) up to α=−25×10−6K−1 (α: coefficient of linear thermal expansion) in Ge-doped anti-perovskite manganese nitrides Mn3AN (A=Cu,Zn,Ga). This gigantic NTE is several to ten times higher than that of commercially available NTE materials. The discontinuous lattice expansion seen in pure Mn3AN is broadened by Ge substitution over a wide temperature window, at widest ΔT∼100K, around room temperature. Such a large, isotropic and nonhysteretic NTE is desirable for practical applications.
Annealing effect on the structural and magnetic properties of La0.7Sr0.3MnO3 films
Authors: Li Tong , Wang Bo , Dai Hongyun , Du Yongsheng , Yan Hui , Liu Yanpin
Published: December 2005

The effects of annealing on the structural and magnetic properties of La0.7Sr0.3MnO3 (LSMO) films sputtered on the (100) LaAlO3 substrate at 600°C, have been studied by using x-ray diffraction, Raman spectroscopy, and superconducting quantum interference device magnetometers. After annealing at high temperatures, a lattice contraction attributed to the oxygen absorption was observed. The procedure was accompanied by the lattice ordering and the vanishing of Jahn-Teller (JT) distortion evidenced by Raman spectra. As a result, both the magnetic moment and Curie temperature (Tc) were enhanced and the coercivity was dramatically reduced in the annealed LSMO films.
Magnetization reversal phenomena in (Cr0.70Ti0.30)5S6
Authors: Hashimoto Satoshi , Matsuda Yuji , Sato Tetsuya , Anzai Shuichiro
Published: December 2005

Magnetization reversal phenomena (MRP) along magnetic order-order transitions have recently been reported on impurity-doped magnetic systems. Because imperfect long-range magnetic order exists in these systems, it is expected that a systematic investigation of MRP will give physical information on thermomagnetic processes of magnetic systems in the range from the micro- to nanoscales. As a typical order-order transition (a state doubly modulated by helical and canting orders to a collinear ferrimagnetic state) has been known to occur on Cr5S6 at a transition temperature Tt, we investigate the magnetizations of (Cr0.70Ti0.30)5S6 on heating and cooling runs in various magnetic fields. At 20Oe, the field-cooled magnetization just below the Curie temperature has a positive sign; the sign turns negative below the compensation temperature TCM (first step) and finally returns to positive below Tt (second step). The first-step MRP observed in this system is explained by the potential barriers resulting from anisotropy energy when the preferred direction of collinear ferrimagnetic moment reverses. The proposed mechanism for second-step MRP is the pinning effect caused by the impurity atoms (Ti) in the helical long-range-order chains. Comparing other examples of MRPs, we discuss the roles of local impurity centers in the thermomagnetic process in magnetic order-order transitions.
Effects of heat treatment and magnetoannealing on nanocrystalline Co-ferrite powders
Authors: Wang Y. C. , Ding J. , Yin J. H. , Liu B. H. , Yi J. B. , Yu S.
Published: December 2005

This work consists of three parts: the effects of heat treatment (slow cooling and quenching), magnetoannealing, and postannealing of samples with induced anisotropy. It has been found that noncomplete inverse spinel structure was the result after annealing at higher temperature and quenching. Our Mössbauer spectroscopy study confirmed noncomplete inverse structure after quenching, while inverse spinel structure was formed after slow cooling. The kinetics of the formation of induced anisotropy during magnetoannealing has been investigated in this study. Reduction of crystalline magnetic anisotropy was observed, as coercivity decreased after magnetoannealing. The change of remanence ratio and coercivity followed the expected equations for ion diffusion. A relative large anisotropy in magnetization was evident. A postannealing resulted in the conversion into the initial isotropic stage. The process could be well described using the equations of ion diffusion.
Low-frequency flute instabilities of self-pinched ion beams
Authors: Uhm Han S. , Davidson Ronald C.
Published: December 2005

The stability properties of the low-frequency flute instabilities in a self-pinched ion beam propagating through a preformed plasma channel are investigated for long-wavelength and low-frequency perturbations. Consistent with the flute instabilities, the stability analysis is restricted to the surface perturbations on the ion beam. A closed algebraic dispersion relation of the flute instabilities for Bennett [Phys. Rev. 45, 890 (1934)] density profile is obtained, by making use of the energy group model. From the analytical and numerical calculations of the dispersion relation for highly collisional plasma, we find the necessary condition for instability in terms of the fractional current neutralization f. Threshold values of the fractional current neutralization for instability are tabulated for each azimuthal mode number ℓ.
Design and characterization of late-mixing flash pyrolytic reactor molecular-beam source
Authors: Kim Hahkjoon , Dooley Kristin S. , Johnson Elizabeth R. , North Simon W.
Published: December 2005

We report on the design and characterization of an intense pulsed beam source for the generation of expansion-cooled radical species. The source combines both dual pulsed valve late mixing for coexpansion of reactive gases with a pyrolytic end nozzle as a flash kinetic reactor. As a demonstration of the source we present evidence of BrO and ClO radical production and subsequent photodissociation studies of these species using velocity map ion imaging. The radicals are characterized by a rotational temperature of 150±40K although substantially lower temperatures should be possible.
Temperature-controlled autocollimator with ultrahigh angular measuring precision
Authors: Yuan Jie , Long Xingwu , Yang Kaiyong
Published: December 2005

A temperature-controlled autocollimator with ultrahigh angular measuring precision is proposed in this article, which is different from our previous publication [J. Yuan and X. W. Long, Rev. Sci. Instrum. 74, 1362 (2003)]. The autocollimator consists of a zoom lens illuminating a charge-coupled device (CCD). This design provides a compact size and increased stability without compromising precision. Moreover, this design makes it possible to detect a target mirror with either plane reflectors or spherical reflectors. Devices for shock absorption and heat insulation were implemented to diminish external interferences. A special temperature-control system for the autocollimator is designed to control the temperature of the autocollimator. The temperature of the autocollimator fluctuates less than ±0.01°C. The CCD camera’s noise is a fatal obstacle that prevents us from achieving an ultrahigh angular measuring precision. In this article, the influence of the CCD camera’s noise on the measuring resolution is analyzed theoretically in detail. Based on the analysis, some special noise-suppressing methods to eliminate the influence of the CCD camera’s noise are proposed. Both the influence of the CCD camera’s noise and the noise-suppressing methods have not been discussed in our previous publication [J. Yuan and X. W. Long, Rev. Sci. Instrum. 74, 1362 (2003)]. By using the methods mentioned above, the measuring precision of the autocollimator has been greatly improved and the requirements on the external condition have been greatly reduced. The method is proved to be reliable by a prototype experiment. Two-axis angular displacement can be measured simultaneously and a measuring precision of 0.005arcsec has been achieved, which is currently the highest measuring precision in the world.