bluuebunny/crossref_metadata_2025 huggingface dataset:
Desorption of water cluster ions from the surface of solid rare gases
Authors: Tachibana T. , Miura T. , Arakawa I.
Published: December 2006

Electron or photon irradiation of H2O adsorbed on the surface of rare gas solids induces the desorption of protonated water clusters, (H2O)nH+. The yield and the size n distribution of cluster ions depend on the coverage, the deposition temperature of the water, and the thickness of the rare gas film. These results indicate that the (H2O)nH+ ions originate from the isolated water clusters, and the most important factor determining the size n distribution of desorbed (H2O)nH+ is the sizes of water islands on the rare gas solid. The measurement of kinetic energy distributions indicated that the desorbing energy of clusters depend on the rare gas species of the substrates and the cluster size. It is suggested that the (H2O)nH+ desorption is due to Coulomb repulsion between the ionic water cluster and the rare gas ion.
Origin of the near-band-edge photoluminescence emission in aqueous chemically grown ZnO nanorods
Authors: Bekeny Chegnui , Voss Tobias , Gafsi Houcem , Gutowski Jürgen , Postels Bianca , Kreye Marc , Waag Andreas
Published: November 2006

The optical properties of ZnO nanorods realized by an advanced low-temperature aqueous chemical growth on both silicon and plastic substrates are presented. Systematic photoluminescence investigations in the temperature range of 4–293K reveal strong and well-resolved near-band-edge emission even for rods on plastic substrate, and a weak deep-level emission. At intermediate temperatures phonon replicas of excitonic lines are observable. The optimum molar concentration range of the solution for obtaining nanorods of good optical quality is shown to lie between 0.025M and 0.075M. The large linewidth of the near-band-edge emission (∼10meV), its temperature dependence, and the absence of sharp excitonic transitions indicate that this emission is a result of transitions from a band of donor states.
Experimental modeling of sensor signal for electromagnetic flowmeter with sinusoidal excitation
Authors: Xu Ke-Jun , Wang Xiao-Fen
Published: November 2006

Since the interaction between the magnetic field and fluid field is complicated, the signal models of electromagnetic flowmeter under sinewave excitation cannot describe accurately the relationship among the sensor output, flow rate, and exciting signal now. The multiple regression method is adopted to build the signal models of electromagnetic flowmeter based on the experimental data in this article. The signal models not only express the action of flow rate but also reflect the effects of transformer and eddy current.
Temporal-coherence gain of superlens image with quasimonochromatic source
Authors: Jiang Xunya , Han Wenda , Yao Peijun , Li Wei
Published: November 2006

From numerical experiments, a dramatic observation of temporal-coherence gain of the image field is made for the negative-index superlens with a random quasimonochromatic source, even when there is almost no reflection and no frequency filtering effects. A single-parameter theory which can explain the phenomenon quantitatively is constructed based on the physical picture that signals propagating through the negative-index material on different paths have a different retardation time. The theoretical results agree excellently with the numerical ones.
Chemically gated AlGaN∕GaN heterostructure field effect transistors for polar liquid sensing
Authors: Song Junghui , Lu Wu
Published: November 2006

Al Ga N ∕ Ga N heterostructure field effect transistors are investigated to monitor the polarity of liquid molecules by exposing the unmetallized gate region between source and drain contacts to chemicals with dipole moments (μ) in the range of 1.6–3.96D. The results show that the channel current can be quantitatively modulated by the magnitude of μ of tested polar molecules. At room temperature, in comparison with the value in air, the channel current density drops from 13.9to7.15mA∕mm with chlorobenzene (μ=1.6D) or to 1.35mA∕mm with diemthyl sulfoxide (μ=3.96D) at a source-drain bias (VDS) of 10V. A linear fitting shows that the current slope is around −1.8mA∕(mmD). Dynamic response of the channel current indicates excellent reversibility of devices. The response time of devices is in the range of 0.1–16s for the chemicals tested in this work.
Rolled-up micro- and nanotubes from single-material thin films
Authors: Songmuang R. , Deneke Ch. , Schmidt O. G.
Published: November 2006

The authors fabricate well-positioned and size-scalable semiconductor micro- and nanotubes from single-material layers. The tubes form when a partially strain-relaxed film, grown at low substrate temperatures, is released from the substrate by selective underetching. The layer rolls downwards or upwards depending on whether it is initially tensile or compressively strained. They create silicon and indium-gallium-arsenide tubes with diameters accurately tunable by varying the layer thickness. They draw a simple model to describe the mechanism responsible for the tube formation from a single-material thin film. Moreover, the tube diameters are shown to scale with strain and layer thickness.
Achievement of ultrahigh quality factors in GaAs photonic crystal membrane nanocavity
Authors: Weidner Evelin , Combrié Sylvain , Tran Nguyen-Vi-Quynh , De Rossi Alfredo , Nagle Julien , Cassette Simone , Talneau Anne , Benisty Henri
Published: November 2006

The authors realized an ultrahigh quality factor nanocavity in a GaAs membrane with the highest loaded Q reported to date of 250 000 in a side-coupled cavity-waveguide system. This result could be obtained using an original aluminum-free material system combined with a carefully adjusted fabrication technology, yielding a device with small roughness and very good verticality of holes as well as small disorder. The authors show that the intrinsic Q factor is around 3.0×105 using a coupled-mode model.
Position sensitive x-ray spectrophotometer using microwave kinetic inductance detectors
Authors: Mazin Benjamin A. , Bumble Bruce , Day Peter K. , Eckart Megan E. , Golwala Sunil , Zmuidzinas Jonas , Harrison Fiona A.
Published: November 2006

The surface impedance of a superconductor changes when energy is absorbed and Cooper pairs are broken to produce single electron (quasiparticle) excitations. This change may be sensitively measured using a thin-film resonant circuit called a microwave kinetic inductance detector (MKID). The practical application of MKIDs for photon detection requires a method of efficiently coupling the photon energy to the MKID. The authors present results on position sensitive x-ray detectors made by using two aluminum MKIDs on either side of a tantalum photon absorber strip. Diffusion constants, recombination times, and energy resolution are reported. MKIDs can easily be scaled into large arrays.
A velocity map imaging study of the one and two photon dissociations of state-selected DCl+ cations
Authors: Webb Alexander D. , Nahler N. Hendrik , Dixon Richard N. , Ashfold Michael N. R.
Published: November 2006

D Cl + ( X Π 3 ∕ 2 2 , v + ″ = 0 ) cations have been prepared by 2+1 resonance enhanced multiphoton ionization, and their subsequent fragmentation following excitation at numerous wavelengths in the range of 240–350nm studied by velocity map imaging of the resulting Cl+ products. This range of excitation wavelengths allows selective population of AΣ+2 state levels with all vibrational (v+′) quantum numbers in the range 0⩽v+′⩽15. Image analysis yields wavelength dependent branching ratios and recoil anisotropies of the various D+Cl+ (PJ3, D1, and S1) product channels. Levels with 10⩽v+′⩽15 have sufficient energy to predissociate, forming D+Cl+(PJ3) products with perpendicular recoil anisotropies—consistent with the AΣ+2←XΠ2 parent excitation and subsequent fragmentation on a time scale that is fast compared with the parent rotational period. Branching into the various spin-orbit states of the Cl+(PJ3) product is found to depend sensitively upon v+′ and, in the case of the v+′=13 level, to vary with the precise choice of excitation wavelength within the AΣ+2←XΠ2(13,0) band. Such variations have been rationalized qualitatively in terms of the differing contributions made to the overall predissociation rate of DCl+(A,v+′) molecules by coupling to repulsive states of Π4, Σ−4, and Σ−2 symmetries, all of which are calculated to cross the outer limb of the AΣ+2 state potential at energies close to that of the v+′=10 level. Cl+(PJ3) fragments are detected weakly following excitation to AΣ+2 state levels with v+′=0 or 1, Cl+(D1) fragments dominate the ion yield when exciting via 2⩽v+′⩽6 and via v+′=9, while Cl+(S1) fragments dominate the Cl+ images obtained when exciting via levels with v+′=7 and 8. Analysis of wavelength resolved action spectra for forming these Cl+ ions and of the resulting Cl+ ion images shows that (i) these ions all arise via two photon absorption processes, resonance enhanced at the one photon energy by the various A(v+′<10) levels, (ii) the first AΣ+2←XΠ2 absorption step is saturated under the conditions required to observe significant two photon dissociation, and (iii) the final absorption step from the resonance enhancing A(v+′) level involves a parallel transition.
On electro-osmotic flows through microchannel junctions
Authors: Yossifon G. , Frankel I. , Miloh T.
Published: November 2006

We study the electro-osmotic flow through a T-junction of microchannels whose dielectric walls are weakly polarizable. The present global analysis thus extends earlier studies in the literature concerning the local flow of an unbounded electrolyte solution around nearly insulated wedges. The velocity field is obtained via superposition of an irrotational part associated with the equilibrium zeta potential and the induced-charge electro-osmotic flow originating from the interaction of the externally applied electric field and the charge cloud it induces owing to field leakage through the polarizable dielectric channel walls. Along the channel walls the latter component gives rise to fluid velocities converging toward the corner which dominate the flow in its immediate vicinity. Recent experimental observations in the literature regarding the appearance and subsequent expansion of flow reversal and vortices downstream (initially) and upstream (subsequently) of the junction, are both rationalized in terms of the growing relative importance of this induced contribution to the global velocity field with increasing intensity of the externally applied electric field.
Silicon-based nanoelectronic field-effect pH sensor with local gate control
Authors: Chen Yu , Wang Xihua , Erramilli Shyamsunder , Mohanty Pritiraj , Kalinowski Agnieszka
Published: November 2006

The authors demonstrate the operation of a nanoscale field-effect pH sensor engineered from a functionalized silicon nanowire. With this nanofabricated pH sensor, the change in the hydrogen ion concentration or the pH value of a solution can be detected by the corresponding change in the nanowire differential conductance with a resolution of ±5nS∕pH. Fabrication of selective side gates on the nanowire sensor allows field-effect control of the surface charge on the nanowire by controlling the accumulation of charge carriers with the side-gate voltage. A simple physical model is used to analyze the observed data and to quantify the dependence of the conductance on pH. The development of a nanoscale sensor with physically engineered gates offers the possibility of highly parallel labeling and detection of chemical and biological molecules with selective control of individual array elements.
The scaling laws of transport properties for fractal-like tree networks
Authors: Xu Peng , Yu Boming
Published: November 2006

The scaling laws of transport properties are very important for understanding the transport mechanisms of the fractal-like tree networks, which have received extensive attention recently. In this paper, we analyze the transport properties including electrical conductivity, heat conduction, convective heat transfer, laminar flow, and turbulent flow in the networks and also derive the scaling exponents of the transport properties in the networks. We show that the scaling laws are different for different transport processes and the scaling exponents are sensitive to microstructures of the networks. The models and results we present here may shed light on the transport mechanisms of the networks such as the natural systems, nanotube networks, microelectronic cooling networks, organisms, fracture networks in oil/water reservoirs, seepage flow in porous networks/media, etc., and might provide guidance for design of composites with the tree structures.
Light-emitting organic field-effect transistor using an organic heterostructure within the transistor channel
Authors: De Vusser Stijn , Schols Sarah , Steudel Soeren , Verlaak Stijn , Genoe Jan , Oosterbaan Wibren D. , Lutsen Laurence , Vanderzande Dirk , Heremans Paul
Published: November 2006

The authors have realized a light-emitting organic field-effect transistor. Excitons are generated at the interface between a n-type and a p-type organic semiconductor heterostructure inside the transistor channel. The dimensions and the position of the p-n heterostructure are defined by photolithography. The p-n heterostructure is at a distance of several microns from the metal electrodes. Therefore, the exciton and photon quenching in this device is reduced. Numerical simulations fit well with the experimental data and show that the light-emitting zone can move within the transistor channel.
Impedance spectroscopy characterization of resistance switching NiO thin films prepared through atomic layer deposition
Authors: You Yil-Hwan , So Byung-Soo , Hwang Jin-Ha , Cho Wontae , Lee Sun Sook , Chung Taek-Mo , Kim Chang Gyoun , An Ki-Seok
Published: November 2006

To understand electrical/dielectric phenomena and the origins of bistable resistive switching, impedance spectroscopy was applied to NiO thin films prepared through atomic layer deposition. The dc current-voltage characteristics of the NiO thin films were also determined. Frequency-dependent characterizations indicated that the switching and memory phenomena in NiO thin films did not originate from the non-Ohmic effect at the electrode/NiO interfaces but from the bulk-related responses, i.e., from an electrocomposite where highly conducting components are distributed in the insulating NiO matrix. Low dielectric constants and bias-independent capacitance appeared to corroborate the bulk-based responses in resistive switching in NiO thin films.
High reflectivity high-Q micromechanical Bragg mirror
Authors: Böhm H. R. , Gigan S. , Blaser F. , Zeilinger A. , Aspelmeyer M. , Langer G. , Bäuerle D. , Hertzberg J. B. , Schwab K. C.
Published: November 2006

The authors report on the fabrication and characterization of a micromechanical oscillator consisting only of a freestanding dielectric Bragg mirror with high optical reflectivity and high mechanical quality. The fabrication technique is a hybrid approach involving laser ablation and dry etching. The mirror has a reflectivity of 99.6%, a mass of 400ng, and a mechanical quality factor Q of approximately 104. Using this micromirror in a Fabry-Pérot cavity, a finesse of 500 has been achieved. This is an important step towards designing tunable high-Q high-finesse cavities on chip.
Confinement of nonequilibrium plasmas in microcavities with diamond or circular cross sections: Sealed arrays of Al∕Al2O3/glass microplasma devices with radiating areas above 20cm2
Authors: Park S.-J. , Kim K. S. , Chang A. Y. , Hua L. Z. , Asinugo J. C. , Mehrotra T. , Spinka T. M. , Eden J. G.
Published: November 2006

Arrays of Al∕Al2O3/glass microplasma devices with microcavities having diamond or circular cross-sectional geometries and radiating (active) areas >20cm2 have been operated sealed-off in Ne, Ar, and Ar∕D2 gas mixtures. Microcavities are fabricated in only one of the two electrodes, and the thickness of the completed package is ∼170μm (excluding the quartz output window). Excited by a sinusoidal 20kHz voltage wave form, arrays with active areas of 4.5×3cm2 exhibit ignition voltages as low as 110±5V rms for Ne pressures of 400–700Torr. Mixtures of 1% D2 in Ar at a total pressure of 300Torr produce wavelength-integrated (λ∼250–400nm) intensities of ∼1mWcm−2 over a 25cm2 area. Optical micrographs show the operation of the microplasmas in two well-defined modes. For current densities below a threshold value (∼53mAcm−2 for 250μm dia. cavities and pNe=400Torr), diffuse uniform plasma is produced in each cavity but, with higher currents, a positive column having near-cylindrical geometry appears, as evidenced by the generation of intense emission localized in the region of weak electric field gradient near the axis of symmetry.
Improving photovoltaic response of poly(3-hexylthiophene)/n-Si heterojunction by incorporating double walled carbon nanotubes
Authors: Somani Savita P. , Somani Prakash R. , Umeno M. , Flahaut E.
Published: November 2006

Poly(3-hexylthiophene)/n-Si heterojunction solar cells were studied with and without incorporation of double walled carbon nanotubes (DWCNs) in the polymer layer. Performance of the device improves by manyfold by incorporation of DWCN. The authors report power conversion efficiency, open circuit voltage, short-circuit current density, and fill factor of 0.026%, 0.446V, 0.3398mA∕cm2, and 0.17, respectively, for an unoptimized cell containing DWCN. Reference cells without DWCNs show much lower performance. DWCN incorporation yields better hole transport, easy exciton splitting, and suppression of charge recombination, thereby improving photovoltaic action. DWCN seems promising materials for improving hole transport in organic solar cells.
Rectifying I-V characteristic of LiNbO3∕Nb-doped SrTiO3 heterojunction
Authors: Guo S. M. , Zhao Y. G. , Xiong C. M. , Lang P. L.
Published: November 2006

Li Nb O 3 ∕ Nb -doped SrTiO3 heterojunction was fabricated by pulsed laser deposition. The current-voltage curve of this heterojunction shows good rectifying property and changes with temperature dramatically. For the forward bias, the conduction mechanism changes from Ohmic-like for the low bias voltages to space charge limited current for the high bias voltages. While for the reverse bias, it changes from Schottky emission to avalanche breakdown with increasing bias voltage. The results were explained by considering the band structures of the junction. This work demonstrates that ferroelectric materials, combined with other oxides, can lead to some interesting property which may have potential applications.
Amorphous lanthanum lutetium oxide thin films as an alternative high-κ gate dielectric
Authors: Lopes J. M. J. , Roeckerath M. , Heeg T. , Rije E. , Schubert J. , Mantl S. , Afanas’ev V. V. , Shamuilia S. , Stesmans A. , Jia Y. , Schlom D. G.
Published: November 2006

Lanthanum lutetium oxide thin films were grown on (100) Si by pulsed laser deposition. Rutherford backscattering spectrometry, atomic force microscopy, x-ray diffraction, and x-ray reflectometry were employed to investigate the samples. The results indicate the growth of stoichiometric and smooth LaLuO3 films that remain amorphous up to 1000°C. Internal photoemission and photoconductivity measurements show a band gap width of 5.2±0.1eV and symmetrical conduction and valence band offsets of 2.1eV. Capacitance and leakage current measurements reveal C-V curves with a small hysteresis, a dielectric constant of ≈32, and low leakage current density levels.
Hybrid-type temperature sensor for in situ measurement
Authors: Iuchi Tohru , Hiraka Kensuke
Published: November 2006

A hybrid-type surface temperature sensor combines the contact and noncontact methods, which allows us to overcome the shortcomings of both methods. The hybrid-type surface thermometer is composed mainly of two components: a metal film sheet that makes contact with an object and a radiometer that is used to detect the radiance of the rear surface of the metal film, which is actually a modified radiation thermometer. Temperature measurement using the hybrid-type thermometer with a several tens micrometer thick Hastelloy sheet, a highly heat and corrosion resistant alloy, is possible with a systematic error of −0.5K and random errors of ±0.5K, in the temperature range from 900to1000K. This thermometer provides a useful means for calibration of in situ temperature measurement in various processes, especially in the silicon semiconductor industry. This article introduces the basic idea of the hybrid-type surface sensor, presents experimental results and discussions, and finally describes some applications.
Large-scale fabrication of single-phase Er2SiO5 nanocrystal aggregates using Si nanowires
Authors: Suh Kiseok , Shin Jung H. , Seo Seok-Jun , Bae Byeong-Soo
Published: November 2006

Single-phase Er2SiO5 nanocrystal aggregates were produced on a large scale using Si nanowire (Si-NW) arrays as templates. A dense array of Si-NWs was grown by vapor-liquid-solid mechanism using Au catalyst on Si (111) substrate. Afterwards, ErCl3∙6H2O dissolved ethanol solution was spin coated and annealed first at 900°C for 4min in a flowing N2∕O2 environment and then at 1200°C in a flowing Ar environment for 3min. X-ray diffraction, scanning electron microscope, and high-resolution transmission electron microscope measurements indicate that due to the use of Si-NWs, such a short annealing procedure is sufficient to completely transform the Er-coated Si-NWs into a thick, large-area aggregate of pure, single-phase to Er2SiO5 oxyorthosilicate nanocrystals. The crystalline nature of Er2SiO5 film and the loose nature of the aggregate result in an atomlike Er3+ spectrum with a very narrow luminescence linewidth at 1.53μm, which together with a complete lack of temperature quenching of Er3+ luminescence and a high Er concentration indicate a viability of this method to fabricate efficient, high-gain Si-based optical material for Si photonics.
Magnetic anisotropy of vertically aligned α-Fe2O3 nanowire array
Authors: Kim Chang Hyun , Chun Hye Jin , Kim Dae Sung , Kim Shin Young , Park Jeunghee , Moon Je Yong , Lee Gangho , Yoon Jungbum , Jo Younghun , Jung Myung-Hwa , Jung Seung Il , Lee Cheol Jin
Published: November 2006

Vertically aligned Fe2O3 nanowire arrays were synthesized by the thermal oxidation of Fe foil. They consist of single-crystalline rhombohedral α-Fe2O3 nanocrystals grown along the [112¯0] direction. Most of the nanowires have a sharp tip (diameter=50nm) and beltlike base. The magnetization measurement reveals a Morin temperature of 125K and unique magnetic anisotropy due to the easy axis of the magnetocrystalline anisotropy perpendicular to the nanowire axis.
Pump-probe spectroscopy of molecules driven by infrared field in both ground and excited electronic states
Authors: Guimarães F. F. , Gel’mukhanov F.
Published: November 2006

Pump-probe spectra of molecules driven by strong infrared (IR) field in both ground and excited states are studied theoretically. The role of the final state interaction becomes important when pump and probe pulses overlap, and the Rabi frequency is comparable with the lifetime broadening of the excited state and the duration of the pump pulse. Our theoretical approach is applied to x-ray absorption of nitrogen molecule and valence photoionization of carbon monoxide. It is shown that IR–x-ray pump-probe spectroscopy can directly evidence the delocalization of core hole.
The free energy landscape of small peptides as obtained from metadynamics with umbrella sampling corrections
Authors: Babin Volodymyr , Roland Christopher , Darden Thomas A. , Sagui Celeste
Published: November 2006

There is considerable interest in developing methodologies for the accurate evaluation of free energies, especially in the context of biomolecular simulations. Here, we report on a reexamination of the recently developed metadynamics method, which is explicitly designed to probe “rare events” and areas of phase space that are typically difficult to access with a molecular dynamics simulation. Specifically, we show that the accuracy of the free energy landscape calculated with the metadynamics method may be considerably improved when combined with umbrella sampling techniques. As test cases, we have studied the folding free energy landscape of two prototypical peptides: Ace-(Gly)2-Pro-(Gly)3-Nme in vacuo and trialanine solvated by both implicit and explicit water. The method has been implemented in the classical biomolecular code AMBER and is to be distributed in the next scheduled release of the code.
Surface enhanced Raman scattering imaging of carbon onions with a silver nanoparticle immobilized tip
Authors: Kodama Takashi , Ohtani Hiroyuki
Published: November 2006

In this study, the authors developed the silver nanoparticle immobilized tip as an apertureless near-field scanning optical microscope probe. Also, they developed experimental technique to obtain the surface enhanced Raman scattering (SERS) image of samples over wide range. As a result, the SERS spectra of individual carbon onions could be detected by the homemade tip with a high sensitivity. The results revealed that the intensity of D band varied according to the presence of the defect of the carbon ring in the contact area. Also, carbon rings could be visualized with the maximum scan area of 5μm2.
Metal gate-HfO2 metal-oxide-semiconductor capacitors on n-GaAs substrate with silicon/germanium interfacial passivation layers
Authors: Kim Hyoung-Sub , Ok Injo , Zhang Manhong , Lee Tackhwi , Zhu Feng , Yu Lu , Lee Jack C.
Published: November 2006

In this letter, the authors present the capacitance-voltage and current-voltage characteristics of TaN∕HfO2∕n-GaAs metal-oxide-semiconductor capacitors with thin silicon and germanium interfacial passivation layers (IPLs). Physical vapor deposition high-k dielectric films and silicon/germanium IPLs were deposited on GaAs substrate which has been cleaned with HCl and (NH4)2S solutions. Equivalent oxide thickness (EOT) of 12.5Å and dielectric leakage current density of 2.0×10−4A∕cm2 at ∣VG−VFB∣=1V with low capacitance-voltage frequency dispersion have been obtained. The results indicate that the use of a thin silicon/germanium IPL assists in scaling EOT below 13Å, while improving the quality of the interface.
Magnetization reversal in europium sulfide nanocrystals
Authors: Redígolo Marcela L. , Koktysh Dmitry S. , Rosenthal Sandra J. , Dickerson James H. , Gai Zheng , Gao Lan , Shen Jian
Published: November 2006

The authors report the observation of the reversal in the magnetization hysteresis curve of europium sulfide nanocrystals. This phenomenon was investigated through the temperature-dependent magnetization of two classes of nanomaterials, nanocrystalline (2.0nm⩽dNCs⩽100nm) and quantum confined (dNCs⩽2.0nm), where dNCs is the diameter of the nanomaterial. The effect of the size of the nanomaterial on the magnetization is attributed to the competition between the magnetic properties of strained surface atoms and unstrained core atoms. Superconducting quantum interference device probed the magnetic response. Electron microscopy and X-ray diffraction spectroscopy revealed the crystallinity and monodispersivity of the nanomaterials.
Single domain strain relaxed PrScO3 template on miscut substrates
Authors: Folkman C. M. , Das R. R. , Eom C. B. , Chen Y. B. , Pan X. Q.
Published: November 2006

The authors have grown strain relaxed epitaxial template of a rare-earth scandate, PrScO3, on miscut (001) SrTiO3 and (001) (LaAlO3)0.3–(Sr2AlTaO3)0.7 substrates by pulsed laser deposition of PrScO3 buffer layers followed by postannealing and overlayer growth. X-ray diffraction exhibits that the PrScO3 is a single domain with bulk lattice parameters and the out-of-plane crystalline quality is comparable with SrTiO3 single crystals. Cross-sectional transmission electron microscopy micrographs show dislocation-free overlayers containing boundaries with very small in-plane misalignment. The growth of strain relaxed rare-earth scandate templates with controlled lattice parameters offers strain and domain engineering of epitaxial multifunctional oxide thin films.
Nonlinear inverse scattering and three-dimensional near-field optical imaging
Authors: Panasyuk George Y. , Markel Vadim A. , Scott Carney P. , Schotland John C.
Published: November 2006

The nonlinear inverse scattering problem for electromagnetic fields with evanescent components is considered. A solution to this problem is obtained in the form of a functional series expansion. The first term in the expansion corresponds to the pseudoinverse solution to the linearized inverse problem. The higher order terms represent nonlinear corrections to this result. Applications to the problem of three-dimensional optical imaging with subwavelength resolution are described and illustrated with numerical simulations.
Ti
O
2
anatase nanolayer on TiN thin film exhibiting high-speed bipolar resistive switching
Authors: Fujimoto Masayuki , Koyama Hiroshi , Konagai Masashi , Hosoi Yasunari , Ishihara Kazuya , Ohnishi Shigeo , Awaya Nobuyoshi
Published: November 2006

The surface oxidized layer of a TiN barrier metal thin film grown on a Pt electrode was used as a resistive switching material. The fabricated memory cell shows bipolar resistive switching on a nanosecond order. A TiO2 anatase layer of about 2.5nm thick on TiN thin film was characterized by high-resolution scanning transmission electron microscopy. The results suggested that the high-speed resistive change was derived from the Mott transition in the TiO2 anatase nanolayer, and the obtained results could relate to the formation of filament paths previously reported in binary transition metal oxide thin films exhibiting resistive switching.
Separation of electric charge flow mechanisms in conducting polymer networks under hydrostatic pressure
Authors: Papathanassiou A. N. , Sakellis I. , Grammatikakis J.
Published: November 2006

To distinguish between different electric charge flow mechanisms in conducting polymer networks, the authors performed ac conductivity and complex permittivity measurements in conducting polypyrrole at various hydrostatic pressure values. Pressure influences capacitive coupling of chains or conducting grains. The measurement of ac conductivity and complex permittivity in the frequency domain at different hydrostatic pressures seems to be a tool for resolving different conductivity modes in conjugated polymer networks and understanding electric signal propagation in random networks.
Piezoelectricity in ZnO nanowires: A first-principles study
Authors: Xiang H. J. , Yang Jinlong , Hou J. G. , Zhu Qingshi
Published: November 2006

Hexagonal [0001] nonpassivated ZnO nanowires with diameters up to 2.8nm are studied with density functional calculations. The authors find that ZnO nanowires have larger effective piezoelectric constant than bulk ZnO due to their free boundary. For ZnO nanowires with diameters larger than 2.8nm, the effective piezoelectric constant is almost a constant. Surprisingly, the effective piezoelectric constant in small ZnO nanowires does not depend monotonically on the radius due to two competitive effects. Moreover, the quantum confinement effect results in larger band gaps of bare ZnO nanowires compared to that of bulk ZnO.
Resolution limitation in superconducting transition edge photon detectors due to downconversion phonon noise
Authors: Kozorezov A. G. , Wigmore J. K. , Martin D. , Verhoeve P. , Peacock A.
Published: November 2006

The authors have identified an important source of line broadening in transition edge sensors used as optical photon detectors. It arises through the loss of high energy phonons into the substrate during the initial photon energy downconversion stage. Because of the relatively small number of phonons involved, the loss rate is subjected to large fluctuations due to the statistical nature of the energy exchange processes. They show that the resulting noise may represent a significant limitation to the resolving power of current detectors.
Deep ultraviolet detection dynamics of AlGaN based devices
Authors: Mazzeo G. , Conte G. , Reverchon J.-L. , Dussaigne A. , Duboz J.-Y.
Published: November 2006

The photoconductive response of AlGaN based UV detectors to 193nm excimer laser radiation is presented. Two devices have been tested: a metal-semiconductor-metal (MSM) planar structure and a Schottky diode. The transient response of the MSM device closely follows the laser pulses, with a photoconductive decay time constant shorter than 3ns. Conversely, the Schottky diode shows a slower photoconductive rise and decay kinetics due to the material series resistance coupled with the junction capacitance. Moreover, a longer time constant tail is also evident in this case with a characteristic time of about 40ns, due to the presence of trap states localized at 0.2–0.3eV from the band edge. The detection dynamics has been evaluated by changing the beam energy density between 2×10−5 and 0.2mJ∕mm2. The signal increases linearly in the case of the MSM device up to 0.001mJ∕mm2, whereas, for a further intensity rise, the response shows a sublinear behavior. On the contrary, the Schottky diode showed a linear trend inside the reduced 2×10−3–1.5×10−2mJ∕mm2 range.
Determination of vibrational modes in electron energy loss spectroscopy of polycrystalline diamond surfaces by isotopic exchange
Authors: Michaelson Sh. , Hoffman A. , Lifshitz Y.
Published: November 2006

The high resolution electron energy loss spectrum of polycrystalline diamond films deposited from various isotopic gas mixtures, C12H4+H2, C12D4+D2, and C13H4+H2, are reported. Three types of peaks were unambiguously identified: (1) Pure C–C related peaks (a diamond C–C stretch at ∼150meV and its overtones at 300, 450, and 600meV), (2) pure C–H related peaks (C–H bend at ∼150meV and C–H stretch of sp3 carbon at 360meV), and (3) coupling of C–H and C–C peaks (∼510meV peak due to coupling of the C–H stretch at 360meV with either the C–C stretch or the C–H bend at ∼150–155meV).
Molecular monolayer modification of the cathode in organic light-emitting diodes
Authors: Lee Tae-Woo , Hsu Julia W. P.
Published: November 2006

The effects of alkanethiol self-assembled monolayers (SAMs) attached to the gold cathode of organic light-emitting diodes made by soft contact lamination are investigated. In spite of reported work function lowering by alkanethiol SAMs, the results from this work showed that their primary effect in carrier transport is to act as a thin insulating layer, causing current reduction. At the same time, the luminescence efficiency was enhanced because the SAMs reduce exciton quenching by the metal cathode. A two-order-of-magnitude enhancement at light emission onset was observed for a hexadecanethiol modified device.
Time resolved photoluminescence spectroscopy of surface-plasmon-enhanced light emission from conjugate polymers
Authors: Neal Terrell D. , Okamoto Koichi , Scherer Axel , Liu Michelle S. , Jen Alex K.-Y.
Published: November 2006

The authors have experimentally verified that the light emission from conjugated polymers can be enhanced through the use of surface plasmon coupling layers. Carrier dynamics of such plasmon-enhanced organic light emitters were studied and a recombination rate increase due to surface plasmon polaritons was experimentally observed. Internal quantum efficiency data from the polyfluorenes studied follow the trend supported by the time resolved photoluminescence measurements.
Magnetic field-induced entropy change in phase-separated manganites
Authors: Liu G. J. , Sun J. R. , Wang J. Z. , Shen B. G.
Published: November 2006

Magnetic field-induced entropy change has been experimentally studied for phase-separated manganites Eu0.55Sr0.45MnO3 and La0.27Nd0.40Ca0.33 MnO3. The entropy derived from the measured heat capacity exhibits a significant decrease under applied field in a broad temperature range below Curie temperature, and the maximum change is ∼8J∕kgK for Eu0.55Sr0.45MnO3 and is ∼4.2J∕kgK for La0.27Nd0.40Ca0.33MnO3 for a field change of 0–5T. In comparison with the calorimetric technique, Maxwell relation fails to give a proper description for the entropy change. It underestimates the entropy reduction in the low temperature range and even anticipates an entropy increase for Eu0.55Sr0.45MnO3. Failures of the Maxwell relation could be ascribed to the coexistence of two phases in the compound and to the variation of the proportion of each phase with applied field.
Strain sensitivity enhancement of thin metal film strain gauges on polymer microscale structures
Authors: Engel J. , Chen J. , Liu C.
Published: November 2006

Arrays of identical polyimide cantilever beams have been fabricated with nickel-chrome strain gauges covering an increasing portion of the beam. In contrast to accepted beam models, testing showed that gauge factor increased 136% for polyimide beams as the strain gauge extended over a larger length of the beam. This effect is due to the high modulus of the thin film strain gauges relative to the polymer beams, a hypothesis supported by duplicate experiments with silicon nitride beams that showed a 65% reduction in gauge factor. Comparison with an analytical model and finite element analysis is also made, giving good agreement.
Multiple transmission bands through metal films perforated with two periodic arrays of apertures
Authors: Ye Yong-Hong , Wang Zhi-Bing , Yan Desheng , Zhang Jia-Yu
Published: November 2006

The authors report experimental results of optical transmission through metal films perforated with two periodic arrays of subwavelength holes in the middle-infrared region. Multiple transmission bands can be achieved by such single-layer structured metal film, and their locations were controlled independently by the periodicities of the individual hole arrays. The coupling between surface plasmon polaritons in the cascaded structure is also studied.
Magnetic field dependent evolution of band structure in La1−xCaxMnO3 (x=0.18 and 0.30)
Authors: Zhou T. F. , Li G. , Qian T. , Li X. G.
Published: November 2006

Probing of the evolution of electronic structure in magnetic field is a key issue for the design and realization of manganite-based devices. Here, the shift of the maximum (or minimum) position in unusual magnetoresistance (MR) versus V curves of the heterojunctions composed of La1−xCaxMnO3 (LCMO, x=0.18 and 0.3) and 0.5wt% Nb-doped SrTiO3 (SNTO) was used to investigate the change of band gaps of LCMO with magnetic field. Negative and positive MRs which depend on temperature, bias current (or voltage), and Ca concentration observed in these heterojunctions are directly determined by the band structure at the LCMO-SNTO interface.
Observation of random lasing in gold-silica nanoshell/water solution
Authors: Kang Jin U.
Published: November 2006

The author reports experimental observation of resonant surface plasmon enhanced random lasing in gold-silica nanoshells in de-ionized water. The gold-silica nanoshell/water solution with concentration of 8×109particles∕ml was pumped above the surface plasmon resonance frequency using 514nm argon-krypton laser. When pumping power was above the lasing threshold, sharp random lasing peaks occurred near and below the plasmon peak from 720to860nm with a lasing linewidth less than 1nm.
In situ probing mechanical properties of individual tungsten oxide nanowires directly grown on tungsten tips inside transmission electron microscope
Authors: Liu K. H. , Wang W. L. , Xu Z. , Liao L. , Bai X. D. , Wang E. G.
Published: November 2006

The mechanical properties of individual tungsten oxide (WO3) nanowires, directly grown onto tungsten scanning tunneling microscopy tips, have been investigated by a custom-built in situ transmission electron microscopy (TEM) measurement system. Young’s modulii (E) of the individual WO3 nanowires were measured with the assistance of electric-induced mechanical resonance. The results indicate that E basically keeps constant at diameter larger than 30nm, while it largely increases with decreasing diameter when diameter becomes smaller than 30nm. This diameter dependence is attributed to the lower defect density in nanowires with smaller diameter, as imaged by in situ TEM.
Polarization-induced Rashba spin-orbit coupling in structurally symmetric III-nitride quantum wells
Authors: Litvinov V. I.
Published: November 2006

The effective linear coupling coefficient and the total spin splitting are calculated in Ga- and N-face InGaN quantum wells. The sign of structural inversion asymmetry spin-orbit coupling coefficient depends on an internal electric field in the well that results in different signs for Ga-face and N-face III-nitride structures. The effective linear coupling coefficient is always positive because of the Dresselhaus-type contribution that is a major one in quantum wells under consideration. The magnitude of the spin splitting is comparable with that experimentally observed in III-nitrides and III-V zinc-blende structures.
Method based on atomic photoionization for spot-size measurement on focused soft x-ray free-electron laser beams
Authors: Sorokin A. A. , Gottwald A. , Hoehl A. , Kroth U. , Schöppe H. , Ulm G. , Richter M. , Bobashev S. V. , Domracheva I. V. , Smirnov D. N. , Tiedtke K. , Düsterer S. , Feldhaus J. , Hahn U. , Jastrow U. , Kuhlmann M. , Nunez T. , Plönjes E. , Treusch R.
Published: November 2006

A method has been developed and applied to measure the beam waist and spot size of a focused soft x-ray beam at the free-electron laser FLASH of the Deutsches Elektronen-Synchrotron in Hamburg. The method is based on a saturation effect upon atomic photoionization and represents an indestructible tool for the characterization of powerful beams of ionizing electromagnetic radiation. At the microfocus beamline BL2 at FLASH, a full width at half maximum focus diameter of (15±2)μm was determined.
Stability and structure of oligomers and polymers made of xenon and hydrocarbons: Theoretical predictions
Authors: Sheng Li , Gerber R. Benny
Published: November 2006

Calculations at B3LYP level predict the existence of three carbon chain oligomers containing HXeCC branches: C7H8Xe2, C11H12Xe3, and C15H16Xe4. The geometries and NBO charges of the HXeCC groups in the species are similar to those of the experimental known HXeCCH molecule, and are insensitive to the length of the carbon chain. The structures of the xenon oligomers are very similar to their hydrocarbon precursors. The energetics for C11H12Xe3 is calculated to assess the stability of these polymers. Similar to HXeCCH, C11H12Xe3 is kinetically stable and protected by a high barrier of 2.47eV against dissociation to C11H12Xe2+Xe, and is energetically more stable by 1.30eV than the C11H11Xe2+Xe+H products, which strongly supports the existence of the molecule. Extrapolation of the results for the oligomers suggests the existence of an extended [−CH2CH(CCXeH)−]n polymer. A strategy for preparation is proposed.
Density functional theory for the recognition of polymer at nanopatterned surface
Authors: Chen Houyang , Ye Zhencheng , Peng Changjun , Liu Honglai , Hu Ying
Published: November 2006

The recognition of homopolymer at nanopatterned surface has been investigated by density functional theory (DFT). Chain conformation and pattern transfer parameter predicted from the DFT are in good agreement with Monte Carlo simulation results. The theory describes satisfactorily the transition from depletion at low packing fractions to adsorption and double-layer adsorption at high packing fractions and also accounts for the crucial effect of the segment-wall interaction. It is found that homopolymer is better recognized at a low bulk density and a stronger interaction with the surface. The polymer can not only recognize the surface but also invert the surface at high bulk densities. The chain in the solution-wall interface exhibits a typical “brush” conformation with a length approximated by half the length of polymer chain.
Nanoliter droplet coalescence in air by directional acoustic ejection
Authors: Lee Chuang-Yuan , Yu Hongyu , Kim Eun Sok
Published: November 2006

This letter presents a controlled coalescence of nanoliter liquid droplets in air by acoustic directional ejections. An asymmetrical electric field is created within a piezoelectric transducer to produce lopsided acoustic waves, which are focused (through a lens based on the innate impedance mismatch between solid and gas) onto a spot on the liquid surface. The focused acoustic beam is shown to obliquely eject 80-μm-diameter droplets at a traveling speed of 2.3m∕s. Up to four such obliquely ejected droplets coalesce in air into a single droplet, which then continue to travel, rotating at 16000rad∕s and producing effective micromixing in air.
Fabrication of 5,6,11,12 -tetraphenyl-naphthacene doped 4-bis(2,2-diphenylvinyl)-1,1-biphenyl white organic light-emitting device
Authors: Pode R. B. , Lee C. J. , Han J. I. , Moon D. G.
Published: November 2006

Using a blue emitting material, 4-bis(2,2-diphenylvinyl)-1,1-biphenyl and orange dopant 5,6,11,12-tetraphenyl-naphthacene, white organic light-emitting devices have been fabricated. An insignificant variation in Commission Internationale de l’Eclairage color index with the applied voltage is reported. Transient electroluminescence measurements show a delay time in the microsecond range (<26μs). The authors propose a device configuration for the white light emission, having a color stability and low delay time.
Transport properties of single-crystal CdS nanoribbons
Authors: Jie J. S. , Zhang W. J. , Jiang Y. , Lee S. T.
Published: November 2006

The transport properties of single-crystal CdS nanoribbons were studied by evaluating the characteristics of field-effect transistors made of individual CdS nanoribbons. The nanoribbon transistors exhibited typical normally off n-channel characteristics with an on-off ratio as high as 104 in dark and in air. A barrier of 0.55eV at the metal-semiconductor contact was deduced from the temperature-dependent conductance. The CdS nanoribbons were highly sensitive to visible light and to adsorbed oxygen molecules. The transistor showed substantial improvement in performance under light irradiation and in vacuum.
Magnetic phase diagram of the semi-Heusler alloys from first principles
Authors: Şaşıoğlu E. , Sandratskii L. M. , Bruno P.
Published: November 2006

The magnetic phase diagram of the Mn-based semi-Heusler alloys is determined at T=0 using first-principles calculations in conjunction with the frozen-magnon approximation. The authors show that the magnetism in these systems strongly depends on the number of conduction electrons, their spin polarization, and the position of the unoccupied Mn 3d states with respect to Fermi energy. Various magnetic phases are obtained depending on these characteristics. The conditions leading to diverse magnetic behavior are identified. The obtained results are in very good agreement with the available experimental data.
Self-assembly vicinal surface of Mo(001) grown on Al2O3(11¯02)
Authors: Lai J. H. , Tu C. L. , Su S. H. , Kuo C. C. , Huang J. C. A.
Published: November 2006

The structure and surface morphology of self-assembly vicinal surfaces (SAVSs) of Mo epitaxially grown on Al2O3(11¯02) substrates have been investigated by reflective high energy electron diffraction and scanning tunneling microscopy. The terrace edges for the Mo(001) SAVS are mainly arranged along [11¯0]Mo‖[112¯0]Al2O3 with a narrow distribution terrace width. The structural analyses show that the formation of the SAVS is due to a tilt growth of Mo(001) plane with respect to Al2O3(11¯02) substrate. By a simple geometric model, the tilt growth and SAVS of Mo(001) can be attributed to the asymmetric lattice mismatch between Mo(001) and Al2O3(11¯02) surfaces.