bluuebunny/crossref_metadata_2025 huggingface dataset:
Investigation of the structure of a composite condensate for He-II at T=0
Authors: Tomchenko M.
Published: February 2006

The ground-state wave function of He-II is calculated in the “two sums over k” approximation, i.e. in the form of the Jastrow function and the first correction:lnΨ0=12!∑k≠0a2(k)ρkρ−k+13!1N∑k1,k2≠0k1+k2≠0a3(k1,k2)ρk1+k2ρ−k1ρ−k2,where the function a2(k) is found numerically from the Vakarchuk equation relating a2(k) and a3(k1,k2) with the structure factor. Knowing Ψ0, we calculated the amount of single- and two-particle condensates in He-II at T=0; this is the first derivation of a formula for a two-particle condensate in the “two sums” approximation. The model contains no adjustable parameters or functions. The results for the condensates are strongly dependent on the number of corrections an included in the expansion of lnΨ0: in the “single sum” approximation (a3=0) 27% of the atoms are in the single-particle condensate and about 53% of the atoms with momentum k>0 are in the two-particle condensate; in the more accurate “two sums” approximation (a3≠0) the percentages are 6% and 16%, respectively. For the “two sums” approximation we also found that the higher-order s-particle condensates (s⩾3) are absent in He-II at T=0.
Thin films of high-Tc YBCO with frozen strains
Authors: Yugay K. N. , Muravjev A. V. , Seropyan G. M. , Konovalenko K. B. , Huh Young
Published: February 2006

Strained YBa2Cu3O7−δ (YBCO) films of greater than the critical thickness are grown on LaAlO3 (100) substrates by the method of laser ablation. The strains are frozen in the films by rapid cooling after deposition. These films have an unusual temperature dependence of the critical current density: a characteristic minimum is observed in the temperature interval 55–57 K. The critical current density decreases from 106A∕cm2 at 77 K to 104A∕cm2 and lower. The films are stable against thermocycling from 300 K to the boiling point of liquid nitrogen. It is concluded on the basis of a scanning tunneling microscope study that a macroscopic structuring of the films occurs, with the formation of strain domains. The size of the domains decreases with increasing degree of strain of the films and is, on average, from 1 to 2.4μm. The penetration of magnetic field into a film with frozen strain differs from the penetration into single-crystal and granular films; this also suggests a macroscopic structuring in the strained films.
Development of most amplified wavelength Görtler vortices
Authors: Mitsudharmadi H. , Winoto S. H. , Shah D. A.
Published: February 2006

The development of most amplified wavelength Görtler vortices is studied by means of varying the spanwise spacing of thin vertical wires located upstream of the leading edge of a concave surface. The free-stream velocity is set so as to provide the value of the dimensionless parameter of that for the most amplified vortex wavelength. The resulting uniform vortex wavelengths were determined by the wire spacings and they were preserved downstream prior to turbulence. The spectrum study of the fluctuating velocity component was able to detect the fundamental frequency of the secondary instability mode with the streamwise wavelengths comparable to the wire spacing, which confirm that the wavelength of the vortices observed is the most amplified one. The intermittency study of the boundary layer flow in the presence of the most amplified wavelength Görtler vortices of 15.0 mm using Turbulent Energy Recognition Algorithm method shows the transition onset in the upwash regions, which coincides with the onset of the secondary instability obtained from the spectrum method. The intermittency factor distributions obtained agree with the single universal distribution with an error of about 5%. The transition Görtler number was also found within the range of that of the boundary layers in the presence of naturally developed Görtler vortices reported earlier.
Sum and difference frequency generation as diagnostics for leaky eigenmodes in two-dimensional photonic crystal waveguides
Authors: Bristow A. D. , Mondia J. P. , van Driel H. M.
Published: February 2006

We experimentally demonstrate how sum frequency generation (SFG) and difference frequency generation (DFG) of 150fs pulses can be enhanced and serve as diagnostics for leaky eigenmodes in a two-dimensional GaAs photonic crystal waveguide. SFG at 795nm is obtained in reflection from s-polarized 1900nm and p-polarized 1360nm pulses, with both input beams coupled to leaky eigenmodes; the SFG is enhanced by >350× compared to that from an untextured GaAs surface. We are able to detect Drude induced subnanometer blueshifts of the SFG, corresponding to refractive index changes of ⩽10−3. DFG of 1360nm light obtained in reflection from s-polarized 1900nm and p-polarized 793nm pulses displays an enhancement of >500× via three different leaky eigenmodes. As the 793nm beam polarization is varied from p polarized to right and left circularly polarized, the DFG remains essentially linearly polarized but with a reduced, albeit different, intensity for right and left circularly polarized 795nm pulses. Futhermore, the plane of polarization also rotates by different amounts for the left and right circularly polarized light, demonstrating interference of the components generated by s- and p-polarized 793nm pulses. Overall, our results demonstrate how enhanced DFG and SFG from leaky eigenmodes can be used to characterize their properties more precisely than linear optical techniques.
Deep traps in oxide-nitride-oxide stacks fabricated from hydrogen and deuterium containing precursors
Authors: Rosenman G. , Naich M. , Roizin Ya. , van Schaijk Rob
Published: February 2006

The energy spectrum of the traps and thermal stability of stored charge have been studied by the thermostimulated exoelectron emission method in hydrogenated H and deuterated D oxide-nitride-oxide (ONO) multilayer stacks of silicon-oxide-nitride-oxide-silicon (SONOS) nonvolatile memories. It is shown that the trap energies are identical for both types of ONO. The deep traps responsible for charge storage have an activation energy 1.7–1.8 eV and are attributed to complexes containing excess silicon with chemically bonded hydrogen or deuterium atoms. It was found that the stability of the deep traps in D-ONO stacks is much higher than in standard H-ONO. It is supposed that the observed isotopic effect is related to different vibration dynamics of hydrogen bonds compared with deuterium bonds.
Shock propagation through alumina observed at the mesoscale
Authors: Bourne N. K.
Published: February 2006

The shock response of 88% and 99.9% pure aluminas, chosen since they had been tested previously, was simulated at the mesoscale. Microstructures were investigated using electron microscopy and then digitized for use in simulation. These microstructural units were stacked to recover larger-scale structures generated randomly. These extended the length ranges in the simulations from the micrometer to the continuum scales. Modeling emphasized the inhomogeneity of the flow at this length scale and phenomena such as precursor decay were accentuated in the material with the greater impurities. The bulk composite behavior could be recovered from the properties of the individual phases by adopting simple expressions for the shock parameters. These behaviors include the profile of the stress histories and quantitative prediction of the Hugoniot elastic limits recovered using information derived purely on constituents.
Charging characteristics of Au nanocrystals embedded in metal-oxide-semiconductor structures
Authors: Wang Chen-Chan , Tseng Jiun-Yi , Wu Tai-Bor , Wu Lin-Jung , Liang Chun-Sheng , Wu Jenn-Ming
Published: February 2006

The charging characteristics of metal-oxide-semiconductor (p-type) structures containing Au nanocrystals in SiO2 gate oxide were studied. The Au nanocrystals of 2–3nm in diameter are self-assembled from the agglomeration of an ultrathin Au layer embedded in SiO2 matrix by annealing at 600°C. A large hysteresis loop is found in the capacitance-voltage (C-V) relation even at a low operating voltage (2V), indicating its significant charge storage effect. Different charging rates for two kinds of trapped carriers (electron and hole) were found from C-V measurement under various scan rates. The relatively stable retention characteristic for holes trapped in the Au nanocrystals at room temperature was also demonstrated.
Nucleation and growth study of atomic layer deposited HfO2 gate dielectrics resulting in improved scaling and electron mobility
Authors: Kirsch P. D. , Quevedo-Lopez M. A. , Li H. -J. , Senzaki Y. , Peterson J. J. , Song S. C. , Krishnan S. A. , Moumen N. , Barnett J. , Bersuker G. , Hung P. Y. , Lee B. H. , Lafford T. , Wang Q. , Gay D. , Ekerdt J. G.
Published: February 2006

HfO 2 films have been grown with two atomic layer deposition (ALD) chemistries: (a) tetrakis(ethylmethylamino)hafnium (TEMAHf)+O3 and (b) HfCl4+H2O. The resulting films were studied as a function of ALD cycle number on Si(100) surfaces prepared with chemical oxide, HF last, and NH3 annealing. TEMAHf+O3 growth is independent of surface preparation, while HfCl4+H2O shows a surface dependence. Rutherford backscattering shows that HfCl4+H2O coverage per cycle is l3% of a monolayer on chemical oxide while TEMAHf+O3 coverage per cycle is 23% of a monolayer independent of surface. Low energy ion scattering, x-ray reflectivity, and x-ray photoelectron spectroscopy were used to understand film continuity, density, and chemical bonding. TEMAHf+O3 ALD shows continuous films, density >9g∕cm3, and bulk Hf–O bonding after 15 cycles [physical thickness (Tphys)=1.2±0.2nm] even on H-terminated Si(100). Conversely, on H-terminated Si(100), HfCl4+H2O requires 50 cycles (Tphys∼3nm) for continuous films and bulk Hf–O bonding. TEMAHf+O3 ALD was implemented in HfO2∕TiN transistor gate stacks, over the range 1.2nm⩽Tphys⩽3.3nm. Electrical results are consistent with material analysis suggesting that at Tphys=1.2nm HfO2 properties begin to deviate from thick film properties. At Tphys=1.2nm, electrical thickness scaling slows, gate current density begins to deviate from scaling trendlines, and no hard dielectric breakdown occurs. Most importantly, n-channel transistors show improvement in peak and high field electron mobility as Tphys scales from 3.3 to 1.2nm. This improvement may be attributed to reduced charge trapping and Coulomb scattering in thinner films. Scaled HfO2 enables 1nm equivalent oxide thickness and 82% of universal SiO2 mobility.
Parallel arrays of individually addressable single-walled carbon nanotube field-effect transistors
Authors: Lastella Sarah , Mallick Govind , Woo Raymond , Karna Shashi P. , Rider David A. , Manners Ian , Jung Yung Joon , Ryu Chang Y. , Ajayan Pulickel M.
Published: February 2006

High-throughput field-effect transistors (FETs) containing over 300 disentangled, high-purity chemical-vapor-deposition-grown single-walled carbon nanotube (SWNT) channels have been fabricated in a three-step process that creates more than 160 individually addressable devices on a single silicon chip. This scheme gives a 96% device yield with output currents averaging 5.4mA and reaching up to 17mA at a 300mV bias. Entirely semiconducting FETs are easily realized by a high current selective destruction of metallic tubes. The excellent dispersity and nearly-defect-free quality of the SWNT channels make these devices also useful for nanoscale chemical and biological sensor applications.
Effect of polymer concentration on stabilized large-tilt-angle flexoelectro-optic switching
Authors: Broughton B. J. , Clarke M. J. , Morris S. M. , Blatch A. E. , Coles H. J.
Published: February 2006

In this letter, the uniform lying helix (ULH) liquid crystal texture, required for the flexoelectro-optic effect, is polymer stabilized by the addition of a small percentage of reactive mesogen to a high-tilt-angle (ϕ>60°) bimesogenic chiral nematic host. The electro-optic response is measured for a range of reactive mesogen concentration mixtures, and compared to the large-tilt-angle switch of the pure chiral nematic mixture. The optimum concentration of reactive mesogen, which is found to provide ample stabilization of the texture with minimal impact on the electro-optic response, is found to be approximately 3%. Our results indicate that polymer stabilization of the ULH texture using a very low concentration of reactive mesogen is a reliable way of ruggedizing flexoelectro-optic devices without interfering significantly with the electro-optics of the effect, negating the need for complicated surface alignment patterns or surface-only polymerization. The polymer stabilization is shown to reduce the temperature dependence of the flexoelectro-optic response due to “pinning” of the chiral nematic helical pitch. This is a restriction of the characteristic thermochromic behavior of the chiral nematic. Furthermore, selection of the temperature at which the sample is ultraviolet cured allows the tilt angle to be optimized for the entire chiral nematic temperature range. The response time, however, remains more sensitive to operating temperature than curing temperature. This allows the sample to be cured at low temperature and operated at high temperature, providing simultaneous optimization of these two previously antagonistic performance aspects.
Breakdown-induced polarization buildup in porous fluoropolymer sandwiches: a thermally stable piezoelectret
Authors: Hu Z. , von Seggern H.
Published: February 2006

The buildup of air-breakdown-induced polarization in a one-side-metallized three-layer sandwich structure consisting of fluorinated ethylene propylene copolymer (FEP) / expanded polytetrafluoroethylene (ePTFE) / FEP has been studied utilizing a corona triode for voltage application. The FEP layers form structurally and electrically dense layers, whereas the ePTFE layer consists of 91% air and 9% fibrous PTFE. Upon negative corona charging, breakdown sets in within the pores of the ePTFE, as soon as the electric field strength exceeds the Paschen breakdown value of air. The resulting ion-plasma then separates in the strong electric field of the corona-deposited surface charges whereby ions of the two polarities drift towards opposite FEP layers, where they are trapped, and macroscopic dipoles are formed. These dipoles are responsible for a strong piezoelectricity. It will be demonstrated by thermally stimulated discharge currents that when poling is performed at elevated temperatures, for example, 150°C, the polarization is temperature stable, and consequently so is the piezoelectric d33 coefficient. The d33 coefficients, however, decay from 800 to 400pC∕N under atmospheric pressures within six days, and repeated loading also shows a similar loss of piezoelectricity, related to mechanical relaxation of the highly porous ePTFE.
Magnetic properties of the singlet antiferromagnet KTb(WO4)2
Authors: Loginov A. A. , Khatsko E. N. , Cherny A. S. , Baumer B. N. , Rykova A. I. , Kalinin P. S. , Sulpis A.
Published: February 2006

X-ray studies of the magnet KTb(WO4)2 have shown that this compound belongs to the monoclinic class C2∕c with a chain structure. The susceptibility and magnetization of KTb(WO4)2 single crystals are investigated experimentally in the temperature region 0.4–100 K and at magnetic fields up to 2 T. The angular dependence of the susceptibility shows that at low temperatures a purely Ising anisotropy is realized in this compound: there exists but one component of the moment, along the b axis. The temperature dependence of the susceptibility has a maximum at T=1.2K, and the M(H) curve obtained at 0.5 K exhibits substantial nonlinearity at low fields, as is characteristic of an ordered state. Analysis of the experimental data in the mean field approximation suggests that this state is a singlet Ising antiferromagnet with TN≈0.7K, a value determined from the susceptibility data. At extremely low temperatures a collinear antiferromagnetic structure with equivalent sublattices is realized in the sample, according to estimates made. The high-temperature behavior of the susceptibility is evidence of the presence of an excited quasi-doublet in the vicinity of 35 K.
Stabilizing effect of a harmonized field on the magnetic resonance position
Authors: Ivanchenko E. A. , Tolstoluzhsky A. P.
Published: February 2006

An effect wherein the magnetic resonance position is stabilized by a magnetic-field modulation periodic in time is investigated in a two-level system in the density-matrix formalism. An exact solution for the density matrix at resonance is found. It is shown that at resonance the spin-flip transition probability is independent of the shape of the field, i.e., the fundamental resonance is stabilized against a matched variation of the longitudinal and transverse magnetic fields. A differential equation for the transition probability is obtained. The dependence of the time-averaged spin-flip probability an normalized Larmor frequency is investigated numerically for different model parameters with allowance for dissipation and decoherence. It is shown that the resonance linewidths increase substantially with increasing dissipation and decoherence. The position of the fundamental resonance is independent of the field deformation and the dissipation; only the width of the resonance varies. The odd parametric (multiphoton) resonance transitions are investigated. The static magnetization induced by a harmonized field is examined. This study may find application for analysis of interference experiments, refinement of the design of magnetic spectrometers, and manipulation of qubits.
Ultrahigh transverse strain and piezoelectric behavior in (1−x)Pb(Mg1∕3Nb2∕3)O3–xPbTiO3 crystals
Authors: Luo Laihui , Wang Haixia , Tang Yanxue , Zhao Xiangyong , Feng Zuyong , Lin Di , Luo Haosu
Published: February 2006

Electric-field-induced transverse strain behavior of (1−x)Pb(Mg1∕3Nb2∕3)O3-xPbTiO3 (PMNT∕x) crystals with different cuts and compositions was investigated for using as electromechanical actuators. High transverse strain with low hysteresis was achieved for rhombohedral crystals near morphotropic phase boundary (28⩽x⩽30). Optimum crystallographic cut was found to be pseudocubic [001]L×[1¯10]W×[110]T for rhombohedral crystals, exhibiting high transverse strain S1∼−0.33% with hysteresis ∼8% and ultrahigh piezoelectric coefficient (d31)∼−3100pC∕N. When E field <6kV∕cm, the strain versus E-field curve is approximately linear, without obvious hysteresis. negative E field of −1.5kV∕cm can be applied to PMNT∕x crystals with minimal hysteresis. However, strain behavior of PMNT∕x crystals cut into [01¯1]L×[2¯11]W×[111]T or [100]L×[010]W×[001]T did not exhibit excellent properties as we expected. High transverse strain with low hysteresis makes PMNT∕x crystals promising candidates for high-performance strain actuators.
A maximum entropy approach to optimal mixing in a pulsed source–sink flow
Authors: Stremler Mark A. , Cola Baratunde A.
Published: February 2006

Fluid mixing in a Hele–Shaw cell can be accomplished by periodically pulsing pairs of sources and sinks. The mixing efficiency of this system depends largely on the volume of fluid that is injected (and extracted) during each pulse. In this paper, the authors use a two-dimensional potential flow model to find the pulse volumes that optimize mixing in a rectangular domain containing two source–sink pairs, a system of current interest in DNA microarray analysis. Optimal mixing protocols are identified by determining maximum entropy using an analysis of chaotic advection.
Energy band shape of monolayer metal/organic/metal structures as determined by the capacitance-voltage method
Authors: Cvikl B. , Koželj M. , Korošak D. , Jecl R.
Published: February 2006

The room-temperature differential capacitance of monolayer metal/organic-semiconductor/metal structures was derived. The derivation was based on two basic assumptions: (a) the rectifying metal/organic-semiconductor junction is characterized by the bias-dependent net excess charge density, induced at the interface, and (b) the charge flow within the organic layer is represented by the space-charge-limited current. The predictions of the derivations were compared to C-U data on an ionized cluster beam Ag-deposited 3,4,9,10-perylenetetracarboxylic dianhydride (PTCDA) on indium-tin-oxide (ITO), Ag∕PTCDA∕ITO, sample obtained at 1 kHz and at room temperature. In addition, thorough analyses of published, room-temperature capacitance-voltage data for Al∕pentacene(60nm)∕ITO, poly(phenylene vinylene) Al∕PPV(200nm)∕ITO, poly[2-methoxy, 5-(2′-ethyl-hexyloxy)-1,4-phenylene vinylene], Ca∕MEH-PPV(40nm)∕Au, tris-(8-hydroxyquinoline) aluminum, Al∕Alq3(60nm)∕ITO, Ca∕Alq3(60nm)∕ITQ, and Ca∕Alq3(120nm)∕ITO organic-semiconductor structures were made, and, in all cases, a good agreement with the predictions was obtained. The quantitative and qualitative values of the interfacial charge density, the internal electric field originating from populated traps, and the nature of the current in these monolayer structures were identified. The parameters deduced from fitting to the Al∕PPV(200nm)∕ITO capacitance-voltage measurements of Meier et al. [J. Appl. Phys. 82, 1961 (1997)] were used to show, assuming Fermi-level alignment, that the energy bands of this structure, as well as all other samples investigated in this work, are well described in terms of a quadratic function of the coordinate, as measured from the cathode/organic junction.
The effect of external magnetic field on mark size in heat-assisted probe recording on CoNi∕Pt multilayers
Authors: Zhang Li , Bain James A. , Zhu Jian-Gang , Abelmann Leon , Onoue Takahiro
Published: February 2006

A method of heat-assisted magnetic recording potentially suitable for probe-based storage systems is characterized. In this work, field-emission current from a scanning tunneling microscope tip is used as the heating source. Pulse voltages of 2–7 V were applied to a CoNi∕Pt multilayered film. During heating, various external magnetic fields were applied. Experimental results show that a positive magnetic field increases mark size while a negative field decreases mark size, compared to the case of writing without an external field in which an average mark size of 170 nm was achieved. In addition, a positive field reduces the threshold voltage of writing as well. A synthesized model is built to quantitatively simulate the experimental results. It includes the model of emission current, heat transfer, and dynamics of magnetic domains in the film. Simulation results show that the calculated mark size in various cases is consistent with experimental results. Based on this model, we will be able to figure out the proposals to achieve small marks for the goal of 1Tbit∕in.2 recording density.
X-ray-diffraction study of crystalline Si nanocluster formation in annealed silicon-rich silicon oxides
Authors: Comedi D. , Zalloum O. H. Y. , Irving E. A. , Wojcik J. , Roschuk T. , Flynn M. J. , Mascher P.
Published: February 2006

The formation and subsequent growth of crystalline silicon nanoclusters (Si-ncs) in annealed silicon-rich silicon oxides (SRSOs) were studied by glancing angle x-ray diffraction. SRSO samples with Si concentrations (y) of 0.40, 0.42, and 0.45 were grown by inductively coupled plasma-enhanced chemical-vapor deposition (PECVD). Samples with y=0.42 grown by electron-cyclotron-resonance PECVD were also studied. Annealing treatments were performed at temperatures (T) of 900, 1000, and 1100 °C for times (t) between 0.5 and 3 h in flowing Ar. As-grown SRSO films did not present signs of Si clusters (amorphous or crystalline); however, (111), (220), and (311) Bragg peaks corresponding to c-Si were clearly seen after annealing at 900 °C for the y=0.45 sample, but only barely seen for the y=0.42 and undetected for the y=0.40 samples. For T=1000°C, all studied SRSO samples clearly showed the c-Si diffraction peaks, which became narrower with increasing t and T. From the width of the Si (111) peaks, the mean size of Si-ncs and their dependence on T and t was determined. Activation energies were deduced from the T dependence by fitting the results to two growth models of Si precipitates in an a-SiO2 matrix reported in the literature. The activation energies qualitatively agree with values deduced from transmission electron microscopy studies of annealed SRSO reported in the literature. However, they are significantly lower than Si diffusion activation energies available in the literature for SiO2 with low excess Si. A broad feature is also observed in the x-ray diffractograms for as-grown samples with low y, which shifts to the peak position corresponding to a-SiO2 with increasing T. This behavior is explained by the formation of a well-defined a-SiO2 phase with increasing T, where mixed Si–O4−nSin (n=1,2,3) tetrahedra in the as-grown alloy are gradually converted into Si–O4 and Si–Si4 as phase separation of Si and SiO2 proceeds. From the measured Si (111) peak positions, small Si-ncs are found to be tensilely strained by as much as ∼0.8%. This effect becomes insignificant as Si-ncs become larger with increasing y or T.
Nanoscale phase changes in crystalline Ge2Sb2Te5 films using scanning probe microscopes
Authors: Satoh H. , Sugawara K. , Tanaka K.
Published: February 2006

Nanoscale amorphous marks have been produced in crystalline Ge2Sb2Te5 films using an atomic-force microscope (AFM) and a scanning-tunneling microscope (STM) through electrical phase changes. Voltage pulses with duration of 5–100 ns applied by metal probes of the AFM and the STM can produce, respectively, high-resistance regions and deformations, the smallest sizes being ∼10 and ∼100 nm in diameter. Raman-scattering spectra demonstrate that these marks are amorphous. The AFM mark can be erased by applying longer pulses. Formation processes of the marks are considered from electrothermal and thermodynamic aspects.
Modeling of lubricant spreading on a solid substrate
Authors: Li Xin , Hu Yuanzhong , Wang Hui
Published: February 2006

The spreading of nonfunctional or functional perfluoropolyether (PFPE) on a solid substrate is important for the service durability and reliability of computer head-disk devices. Molecular-dynamics simulations based on a coarse-grained, bead-spring model have been adopted to investigate the spreading process. For nonfunctional PFPE, molecules in the fluid interface region of the droplet will flow down to form a cap structure on the substrate. Simultaneously molecules at the liquid front will diffuse along the substrate to form a precursor film, and molecules above the diffusion layer will move downward to fill the cavities created by diffusion. For functional PFPE, interactions between end beads, and between end beads and the substrate complicate the spreading process, giving rise to a hat structure with a vertical step and a precursor film with slower flux.
Sb surfactant-mediated SiGe graded layers for Ge photodiodes integrated on Si
Authors: Liu J. L. , Yang Z. , Wang K. L.
Published: February 2006

High-quality SiGe and Ge thin films were grown on Si substrates by molecular-beam epitaxy using a technique that combines SiGe composition grading and Sb surfactant mediation. Both transmission electron microscopy and Schimmel defect etch measurements show that the Sb surfactant-mediated SiGe graded buffer layers have lower dislocation densities than those without an Sb surfactant. A systematic study of Sb surfactant-mediated graded buffers was carried out. The relationship between the threading dislocation densities and the grading rates of the Sb surfactant-mediated SiGe buffer layers was investigated. Moreover, p-i-n Ge photodiodes were fabricated on Si substrates using Sb surfactant-mediated SiGe graded buffer layers. These photodiodes exhibit very low dark current densities of about 0.15mA∕cm2 at the reverse bias of 1 V and high quantum efficiencies of 50%–72%.
Structural characterization of a-plane Zn1−xCdxO (⩽x⩽0.085) thin films grown by metal-organic vapor phase epitaxy
Authors: Zúñiga-Pérez J. , Muñoz-Sanjosé V. , Lorenz M. , Benndorf G. , Heitsch S. , Spemann D. , Grundmann M.
Published: February 2006

Zn 1 − x Cd x O ( 11 2 ¯ 0 ) films have been grown on (011¯2) sapphire (r–plane) substrates by metal-organic vapor phase epitaxy. A 800-nm-thick ZnO buffer, deposited prior to the alloy growth, helps to prevent the formation of pure CdO. A maximum uniform Cd incorporation of 8.5 at. % has been determined by Rutherford backscattering spectrometry. Higher Cd contents lead to the coexistence of Zn1−xCdxO alloys of different compositions within the same film. The near band-edge photoluminescence emission shifts gradually to lower energies as Cd is incorporated and reaches 2.93 eV for the highest Cd concentration (8.5 at. %). The lattice deformation, due to Cd incorporation, has been described using a new reference frame in which the lattice distortions are directly related to the a-plane surface structure. Cd introduction does not affect the c lattice parameter but expands the lattice along the two perpendicular directions, [112¯0] and [1¯100], resulting in a quadratic volume increase.
First-principles calculations of the electronic band structure of In4Sn3O12 and In5SnSbO12
Authors: Ren Chung-Yuan , Chiou Shan-Haw , Choisnet J.
Published: February 2006

The electronic band structures of M7O12 rhombohedral In4Sn3O12 and In5SnSbO12 are studied using the projector-augmented-wave method based upon the density-functional theory within the generalized gradient approximation. The cation ordering in both materials, as determined by means of ab initio self-consistent total-energy calculations, confirms the results of previous structural studies. It is found that the valence-band maximum states of these two materials are mainly formed by O 2p states hybridized with In 5d characters whereas the bottoms of conduction bands are due primarily to Sn 5s electrons at M2 sites. The present study shows that the introduction of antimony into In4Sn3O12 broadens the splitting of the conduction band, which is presumably related to the substantial change in electrical conductivity observed in In5SnSbO12.
The ordered thin-film growth of organic semiconductor on Ag(110)
Authors: Han Huang , Hanjie Zhang , Botters Bernhard , Qiao Chen , Hongying Mao , Bin Lu , Haiyang Li , Pimo He , Shining Bao
Published: February 2006

Growth of ordered perylene thin films on the Ag(110) surface has been investigated with scanning tunneling microscope. By saturating the surface with a monolayer of perylene molecules, two kinds of ordered structures are simultaneously formed with flat-lying perylene molecules on the Ag(110) surface, in which one is commensurate relative to the Ag substrate with a periodicity of (−2322) while the other is commensurate with a periodicity of (−2724). There is one molecule within the former unit cell with a surface coverage of 0.1 molecule per Ag atom, while there are two molecules within the latter unit cell, which gives a slightly lower surface coverage of 0.091 molecule per Ag atom. Ab initio calculations have been carried out to identify the adsorption geometry and bonding sites.
Angular distributions of H-induced HD and D2 desorptions from the Si(100) surfaces
Authors: Inanaga S. , Kiyonaga T. , Rahman F. , Khanom F. , Namiki A. , Lee J.
Published: February 2006

We measured angular distributions of HD and D2 molecules desorbed via the reactions H+D∕Si(100)→HD [abstraction (ABS)] and H+D∕Si(100)→D2 [adsorption-induced-desorption (AID)], respectively. It was found that the angular distribution of HD molecules desorbed along ABS is broader than that of D2 molecules desorbed along AID, i.e., the former could be fit with cos2.0±0.2θ, while the latter with cos5.0±0.5θ. This difference of the angular distributions between the two reaction paths suggests that their dynamic mechanisms are different. The observed cos2θ distribution for the ABS reaction was reproduced by the classical trajectory calculations over the London-Eyring-Polanyi-Sato potential-energy surfaces. The simulation suggests that the HD desorption along the ABS path takes place along the direction of Si–D bonds, but the apparent angular distribution is comprised of multiple components reflecting the different orientations of D-occupied Si dimers in the (2×1) and (1×2) double domain structures.
Experimental study of inclined film flow along periodic corrugations: The effect of wall steepness
Authors: Argyriadi K. , Vlachogiannis M. , Bontozoglou V.
Published: February 2006

Gravity-driven film flow along an inclined periodic wall with transverse rectangular corrugations is studied experimentally. The effect of corrugation steepness (=height∕length) is considered in detail and an interesting contrast emerges between properties of the flow that are apparently independent of corrugation steepness and properties that are strongly affected by it. The steady interaction between the wall and the flow leads to a statically deformed free surface, whose amplitude is independent of the corrugation heights tested. Beyond the maximum steady free-surface amplitude, a three-dimensional pattern is established (consisting of transverse arrays of depressions along corrugation valleys), again at conditions independent of corrugation height. On the contrary, steep corrugations expand significantly the stable region of steady flow. Also, fully developed traveling waves (emerging from ambient noise under unsteady conditions) are significantly larger and more regular than under the same conditions along a flat wall. This difference is attributed to the continuous interaction of traveling pulses with the steadily deformed substrate.
Benchmarking two-photon absorption with CC3 quadratic response theory, and comparison with density-functional response theory
Authors: Paterson Martin J. , Christiansen Ove , Pawłowski Filip , Jørgensen Poul , Hättig Christof , Helgaker Trygve , Sałek Paweł
Published: February 2006

We present a detailed study of the effects of electron correlation on two-photon absorption calculated by coupled cluster quadratic response theory. The hierarchy of coupled cluster models CCS, CC2, CCSD, and CC3 has been used to investigate the effects of electron correlation on the two-photon absorption cross sections of formaldehyde (CH2O), diacetylene (C4H2), and water (H2O). In particular, the effects of triple excitations on two-photon transition cross sections are determined for the first time. In addition, we present a detailed comparison of the coupled cluster results with those obtained from Hartree-Fock and density-functional response theories. We have investigated the local-density approximation, the pure Becke-Lee-Yang-Parr (BLYP) functional, the hybrid Becke-3-parameter-Lee-Yang-Parr (B3LYP), and the Coulomb-attenuated B3LYP (CAM-B3LYP) functionals. Our results show that the CAM-B3LYP functional, when used in conjuction with a one-particle basis-set containing diffuse functions, has much promise; however, care must still be exercised for diffuse Rydberg-type states.
Flow regime analysis of non-Newtonian duct flows
Authors: Speetjens Michel , Rudman Murray , Metcalfe Guy
Published: February 2006

Reoriented duct flows of generalized Newtonian fluids are an idealization of non-Newtonian fluid flow in industrial in-line mixers. Based on scaling analysis and computation we find that non-Newtonian duct flows have several limit behaviors, in the sense that such flows can become (nearly) independent of one or more of the rheological and dynamical control parameters, simplifying the general flow and mixing problem. These limit flows give several levels of modeling complexity to the full problem of non-Newtonian duct flow. We describe the sets of simplified flow models and their corresponding regions of validity. This flow-model decomposition captures the essential rheological and dynamical characteristics of the reoriented duct flows and enables a more efficient and systematic study and design of flow and mixing of non-Newtonian fluids in ducts. Key aspects of the flow-model decomposition are demonstrated via a specific, but representative, duct flow.
Particle diffusion in a field-guided microfluidic channel
Authors: Helseth L. E. , Wen H. Z. , Fischer T. M.
Published: February 2006

If an ensemble of particles is squeezed together in a trap that is suddenly removed, one may anticipate that they obey the normal Fickian diffusion equation, which predicts that the width of the system increases proportionally to the square root of the elapsed time t. Here we show that for a finite one-dimensional system composed of particles which interact via dipolar forces, this is no longer correct. Instead, our measurements using colloidal particles in a removable magnetic trap suggest that the system size increases as t1∕5, which may be of importance for the transport of interacting particles in microfluidic channels.
Classification of transition temperature behavior in ferroelectric PbTiO3–Bi(Me′Me″)O3 solid solutions
Authors: Stringer C. J. , Shrout T. R. , Randall C. A. , Reaney I. M.
Published: February 2006

The ferroelectric transition temperature (Tc) behavior of perovskite solid solutions based on PbTiO3–Bi(Me′Me″)O3 (Me′=Fe3+, Zn2+, Sc3+, In3+, Mg2+, Ni2+, etc., and Me″=Ti4+, Nb5+, W6+) was considered. Trends in the Tc compositional dependence near the PbTiO3 end member could be described with a geometrical polynomial expression. Three main cases were observed: Case 1, a continued increase in transition temperature above the end member PbTiO3 (495°C); case 2, an increase and then decrease of the transition temperature; and case 3, a continuous decrease in the transition temperature with Bi(Me′Me″)O3 additions. It was noted that for all case 2 examples the enhancement of ΔTc=Tc(max)−Tc(PT) increased as the distribution of B-site ionic radii increased. A correlation was therefore proposed between the maximum enhancement in transition temperature and the spread of tolerance factor (Δt) and∕or variance in B-site ionic radius (σ2). Finally, it was proposed that these observations are consistent with random-field effects created by local strain-field fluctuations within the perovskite lattice.
Aggregation of blood components on a surface in a microfluidic environment
Authors: Tsai F.-K. , Lauer J. L. , Shohet J. L.
Published: February 2006

The aggregation of blood components on the blood-contacting surface of a medical device will reduce its reliability and lifetime. Such aggregations are known to be generated by sheared-flow activation of blood components which themselves are greatly influenced by flow patterns. This is especially important in the case of a microfluidic system. A numerical simulation was conducted to evaluate the flow parameters in a microminiature blood circulation loop to determine those flow factors that promote the aggregation of blood components and their potential deposition on the blood-contacting surface. The local geometry of the system was found to be the most important factor that affects the evolution of the flow field. Based on these results, the predicted locations of aggregation of blood components for the circulating blood-loop system were compared with experimental results.
Deposition of vertically oriented carbon nanofibers in atmospheric pressure radio frequency discharge
Authors: Nozaki Tomohiro , Goto Tomoya , Okazaki Ken , Ohnishi Kuma , Mangolini Lorenzo , Heberlein Joachim , Kortshagen Uwe
Published: February 2006

Deposition of vertically oriented carbon nanofibers (CNFs) has been studied in an atmospheric pressure radio frequency discharge without dielectric barrier covering the metallic electrodes. When the frequency is sufficiently high so that ions reside in the gap for more than one rf cycle (“trapped ions”), the operating voltage decreases remarkably and the transition from a uniform glow discharge to an arc discharge is suppressed even without dielectric barriers. More importantly, the trapped ions are able to build up a cathodic ion sheath. A large potential drop is created in the sheath between the bulk plasma and the electrode, which is essential for aligning growing CNFs. At the same time, the damage to CNFs due to ion bombardment can be minimized at atmospheric pressure. The primary interest of the present work is in identifying the cathodic ion sheath and investigating how it influences the alignment of growing CNFs in atmospheric pressure plasma-enhanced chemical-vapor deposition. Spectral emission profiles of He (706nm), Hα (656nm), and CH (432nm) clearly showed that a dark space is formed between the cathode layer and the heated bottom electrode. However, increasing the rf power induced the transition to a nonuniform γ-mode discharge which creates intense plasma spots in the dark space. Aligned CNFs can be grown at moderate input power during the initial stage of the deposition process. Catalyst particles were heavily contaminated by precipitated carbon in less than 5min. Alignment deteriorates as CNFs grow and deposition was virtually terminated by the deactivation of catalyst particles.
Magnetostriction and microstructure of the melt-spun Fe83Ga17 alloy
Authors: Zhang M. C. , Jiang H. L. , Gao X. X. , Zhu J. , Zhou S. Z.
Published: February 2006

The ribbons with different thicknesses of Fe83Ga17 alloy were prepared by melt spun. The maximum magnetostriction of −2100ppm has been obtained in the ribbon with the thickness of 75μm. The microstructures of the ribbons were determined by x-ray diffraction. It was found that DO3 structure emerges in those ribbons melt spun at a higher cooling rate. This special DO3 structure is favorable to the enhancement of magnetostriction. It is considered that more short-range ordering of Ga atoms appeared when liquid alloy was solidified with a certain extreme cooling rate. Such short-range ordering of Ga atoms brings a local stress and results in the giant magnetostriction. The large demagnetizing magnetic energy in the normal direction of the ribbons causes the magnetic moments parallel to the ribbon plane. When an applied magnetic field is perpendicular to the ribbon plane, the magnetic moments turn 90° and generate giant magnetostriction.
Analysis of particle transport in a magnetophoretic microsystem
Authors: Furlani E. P.
Published: February 2006

An analytical analysis is presented of the transport and capture of magnetic micro/nanoparticles in a magnetophoretic microsystem that consists of an array of integrated soft-magnetic elements embedded beneath a microfluidic channel. The elements, which are polarized by a bias field, produce a nonuniform field distribution that gives rise to a force on magnetic particles within the microchannel. The equations governing particle motion are derived using analytical expressions for the dominant magnetic and fluidic forces. The magnetic force is obtained using an analytical expression for the field distribution in the microchannel combined with a linear magnetization model for the magnetic response of the particles. The theory takes into account particle size and material properties, the bias field, the dimensions of the microchannel, the fluid properties, and the flow velocity. The equations of motion are solved to study particle transport and capture. The analysis indicates that the particles exhibit an oscillatory motion as they traverse the microsystem, and that a high capture efficiency can be obtained in practice.
Distribution of optical emission between guided modes and free space in a semiconductor nanowire
Authors: Maslov A. V. , Bakunov M. I. , Ning C. Z.
Published: February 2006

We study the distribution of the emitted power between the free-space modes and guided modes in a semiconductor nanowire. We analyze all possible dipole orientations and nanowire radii in the range from very small to comparable to the wavelength. Our theoretical approach is based on the Fourier transform technique and equivalent to the construction of Green’s function for a dipole at an arbitrary location inside the nanowire. We show that the total emitted power can exhibit rather pronounced oscillations as a function of the frequency and radius. The far-field pattern is also very sensitive to the frequency and radius, especially in the regime when leaky (or whispering gallery) modes with finite axial wave numbers are excited. We discuss the enhancement of emission into guided modes due to formation of Fabry-Pérot cavity in a finite length nanowire. Our results yield directly the extraction efficiencies and angular distribution of radiation of light-emitting diodes made of nanowires.
Submicron-sized magnetic tunnel junctions in field programmable logic gate arrays
Authors: Meyners D. , Rott K. , Brückl H. , Reiss G. , Wecker J.
Published: February 2006

We experimentally demonstrate the feasibility of reprogrammable logic gate arrays with lateral dimensions down to 10×10μm2. The gates are based on magnetic tunnel junctions which are elliptically patterned by e-beam lithography with sizes down to 200×100nm2. The junctions are realized with different tunneling systems and are investigated magnetically and electrically, where the magnetization reversal of the junctions’ soft magnetic layer is done via currents in conducting lines. The switching currents could be reduced by a factor of about 2 by introducing an additional NiFe layer on top of the lines. Thus it is possible to use these gate arrays within a highly integrated environment.
Crystallization of Zr41Ti14Cu12.5Ni10Be22.5 bulk metallic glass under high pressure examined by in situ synchrotron radiation x-ray diffraction
Authors: Yang C. , Wang W. K. , Liu R. P. , Zhan Z. J. , Sun L. L. , Zhang J. , Jiang J. Z. , Yang L. , Lathe C.
Published: February 2006

Crystallization of Zr41Ti14Cu12.5Ni10Be22.5 bulk metallic glass under high temperature and high pressure has been investigated by in situ synchrotron radiation x-ray diffraction. The onset temperature of crystallization was found to increase with pressure, but with a sudden drop at about 5.6GPa. Though the primarily precipitated phase is the same at different pressures, the sequences of the following phase precipitation are different.
A simple natural orbital mechanism of “pure” van der Waals interaction in the lowest excited triplet state of the hydrogen molecule
Authors: Gritsenko Oleg , Baerends Evert Jan
Published: February 2006

A treatment of van der Waals (vdW) interaction by density-matrix functional theory requires a description of this interaction in terms of natural orbitals (NOs) and their occupation numbers. From an analysis of the configuration-interaction (CI) wave function of the Σu+3 state of H2 and the exact NO expansion of the two-electron triplet wave function, we demonstrate that the construction of such a functional is straightforward in this case. A quantitative description of the vdW interaction is already obtained with, in addition to the standard part arising from the Hartree-Fock determinant ∣1σg(r1)1σu(r2)∣, only two additional terms in the two-electron density, one from the first “excited” determinant ∣2σg(r1)2σu(r2)∣ and one from the state of Σu+3 symmetry belonging to the (1πg)1(1πu)1 configuration. The potential-energy curve of the Σu+3 state calculated around the vdW minimum with the exact density-matrix functional employing only these eight NOs and NO occupations is in excellent agreement with the full CI one and reproduces well the benchmark potential curve of Kolos and Wolniewicz [J. Chem. Phys. 43, 2429 (1965)]. The corresponding terms in the two-electron density ρ2(r1,r2), containing specific products of NOs combined with prefactors that depend on the occupation numbers, can be shown to produce exchange-correlation holes that correspond precisely to the well-known intuitive picture of the dispersion interaction as an instantaneous dipole-induced dipole (higher multipole) effect. Indeed, (induced) higher multipoles account for almost 50% of the total vdW bond energy. These results serve as a basis for both a density-matrix functional theory of van der Waals bonding and for the construction of orbital-dependent functionals in density-functional theory that could be used for this type of bonding.