bluuebunny/crossref_metadata_2025 huggingface dataset:
Analytical theory of low-frequency space charge oscillations in gyrotrons
Authors: Yan Ran , Antonsen T. M. , Nusinovich G. S.
Published: October 2008

Low-frequency oscillations attributed to reflected electrons bouncing adiabatically between the electron gun and the interaction space have been observed in many gyrotrons. An analytical model is considered which allows one to apply space-charge wave theory to the analysis of these oscillations. In the framework of the small-signal theory, the regions of low-frequency oscillations, the oscillation frequency and the temporal and spatial growth rates of low-frequency oscillations are determined in the relevant parameter space. The mode frequency is determined not only by the particle travel time, but by the travel time of charge waves on the reflected electron beam. This explains the existence of modes with noncommensurate frequencies.
Bipolar charge-carrier injection in semiconductor/insulator/conductor heterostructures: Self-consistent consideration
Authors: Yampolskii S. V. , Genenko Yu. A. , Melzer C. , Stegmaier K. , von Seggern H.
Published: October 2008

A self-consistent model of bipolar charge-carrier injection and transport processes in a semiconductor/insulator/conductor system is developed, which incorporates space-charge effects in the description of the injection process. The amount of charge carriers injected is strongly determined by the energy barrier emerging at the contact, but at the same time the electrostatic potential generated by the injected charge carriers modifies the height of this injection barrier itself. In our model, self-consistency is obtained by assuming continuity of the electric displacement and of the electrochemical potential all over the system. The constituents of the system are properly taken into account by means of their respective density of state distributions. The consequences resulting from our model are discussed on the basis of an indium tin oxide/organic semiconductor/conductor structure. The distributions of the charge carriers and the electric field through the electrodes and the organic layer are calculated. The recombination- and current-voltage characteristics are analyzed for different heights of injection barriers and varying values of the recombination rate and compared with the measured current-voltage dependences for an indium tin oxide/poly(phenylene vinylene)/Ca structure. The voltage dependences of the recombination efficiency for the different values of injection barriers and recombination rate reveal optimum conditions for the device performance.
Cytocompatibility of amorphous hydrogenated carbon nitride films deposited by CH4/N2 dielectric barrier discharge plasmas with respect to cell lines
Authors: Majumdar Abhijit , Schröder Karsten , Hippler Rainer
Published: October 2008

Special amorphous hydrogenated carbon nitride (a-H–CNx) films have been prepared on glass substrates for the investigation of adhesion and proliferation of different mammalian cell lines. CH4/N2 dielectric barrier discharge plasmas were applied to deposit a-H–CNx coatings at half of the atmospheric pressure. Film quality was modified by varying the CH4:N2 ratio and deposition duration. Chemical composition was determined by x-ray photoelectron spectroscopy and Fourier transformed infrared spectroscopy. The N/C ratio was in the range of 0.20–0.55. A very small surface roughness was verified by atomic force microscopy. Human embryonic kidney (HEK) and rat adrenal pheochromocytoma (PC12) cells were cultivated on the a-H–CNx films to investigate the cytocompatibility of these surfaces. The microscopic images show that both kinds of cells lines were unable to survive. The cells did not adhere to the surfaces, and most of the cells died after certain time spans. Increased amounts of nitrogen in the film induce an accelerated cell death. It is concluded, that the deposited CNx film behaves cytotoxic to HEK and PC12 cell lines.
Saturable and reverse saturable absorption in silver nanodots at 532 nm using picosecond laser pulses
Authors: Gurudas Ullas , Brooks Elijah , Bubb Daniel M. , Heiroth Sebastian , Lippert Thomas , Wokaun Alexander
Published: October 2008

Saturable absorption (SA) and reverse saturable absorption (RSA) at 532 nm were observed in Ag nanodots prepared by pulsed laser deposition. The real [Re χ(3)] and imaginary [Im χ(3)] parts of the third order nonlinearity of these films were measured using the Z-scan technique. At low input irradiances, the decrease in absorption near the focal point results from a negative Im χ(3) and yields SA. At higher input irradiance, RSA becomes dominant. The transition from SA to RSA suggests that there is a threshold irradiance at which additional nonlinear process(es) is (are) involved and become dominant. The recovery time of these nonlinear processes was measured by a degenerate pump-probe experiment. The effects are explained in terms of the electron dynamics in the excited states.
Length and thickness dependence of longitudinal flexural resonance frequency shifts of a piezoelectric microcantilever sensor due to Young’s modulus change
Authors: Shih Wan Y. , Zhu Qing , Shih Wei-Heng
Published: October 2008

For piezoelectric microcantilever sensors (PEMSs) whose resonance frequency shift during detection is due to Young’s modulus change in the piezoelectric layer, we showed that their detection longitudinal flexural resonance frequency shift, Δf, is inversely proportional to the square of the PEMS length, L2; their relative resonance frequency shift, Δf/f, inversely proportional to the PEMS thickness, t; and their mass detection sensitivity, Δf/Δm, inversely proportional to wL3 where w is the width. The resonance frequency shift caused by Young’s modulus change in the piezoelectric layer is more than 300 times larger than would be expected from the mass change.
Oxygen induced hysteretic current-voltage characteristics of iron-phthalocyanine thin films
Authors: Samanta Soumen , Singh Ajay , Debnath A. K. , Aswal D. K. , Gupta S. K. , Yakhmi J. V. , Singh S. , Basu S. , Deshpande S. K.
Published: October 2008

Electrical transport has been investigated in amorphous and polycrystalline (α-phase) iron phthalocyanine (FePc) thin films grown by molecular beam epitaxy. Measurements carried out in the temperature range of 150–300 K showed hysteric current-voltage (I-V) characteristics at temperatures above 200 K. The I-V characteristics measured during the increasing voltage scan showed a transition from the Ohmic conduction to the trap controlled space charge limited conduction followed by a trap free conduction. During the decreasing voltage scan, trap free conduction was observed in full voltage range. The I-V hysteresis is attributed to the filling of deep surface traps created by chemisorbed oxygen. Amorphous films showed higher hysteresis as well as chemisorbed oxygen content.
Nonlinear scattering for a system of nonlinear Klein–Gordon equations
Authors: Hayashi Nakao , Naumkin Pavel I. , Wibowo Ratno Bagus Edy
Published: October 2008

We consider the initial value problem for systems of nonlinear Klein–Gordon equations with quadratic nonlinearities. We prove the existence of scattering states, namely, the asymptotic stability of small solutions in the neighborhood of the free solutions for small initial data in the weighted Sobolev space H4,3(R3)×H3,3(R3). If nonlinearities satisfy the strong null condition, then the same result is true in two space dimensions for small initial data in H5,4(R2)×H4,4(R2). A system of massive Dirac–massless Klein–Gordon equations in three space dimensions is also considered by our method.
Formation of a bimodal eutectic structure in Ti–Fe–Sn alloys with enhanced plasticity
Authors: Han J. H. , Kim K. B. , Yi S. , Park J. M. , Sohn S. W. , Kim T. E. , Kim D. H. , Das J. , Eckert J.
Published: October 2008

Microstructural investigations on a series of (Ti70.5Fe29.5)100−xSnx alloys with x=5, 7, and 9 reveal that Sn addition is effective in introducing both structural and spatial heterogeneities in ultrafine eutectic composites stemming from a large temperature difference between two eutectic temperatures upon solidification. The microstructural heterogeneities in these ultrafine eutectic composites strongly enhance the room temperature compressive plasticity up to ∼15.7%.
Optical properties of heavily boron-doped nanocrystalline diamond films studied by spectroscopic ellipsometry
Authors: Zimmer A. , Williams O. A. , Haenen K. , Terryn H.
Published: October 2008

The optical properties of heavily boron-doped nanocrystalline diamond films grown by microwave plasma enhanced chemical vapor deposition on silicon substrates are presented. The diamond films are characterized by spectroscopic ellipsometry within the midinfrared, visible, and near-ultraviolet regions. The ellipsometric spectra are also found to be best described by a four-phase model yielding access to the optical constants, which are found distinct from previous nanocrystalline diamond literature values. The presence of a subgap absorption yielding high extinction coefficient values defined clearly the boron incorporated films in comparison to both undoped and composite films, while refractive index values are relatively comparable.
Linear colloidal crystal arrays by electrohydrodynamic printing
Authors: Poon H. F. , Saville D. A. , Aksay I. A.
Published: October 2008

We use electrohydrodynamic jets of colloidal suspensions to produce arrays of colloidal crystalline stripes on surfaces. A critical factor in maintaining a stable jet is the distance of separation between the nozzle and the surface. Colloidal crystalline stripes are produced as two wetting lines of the deployed suspension merge during drying. To ensure that the two wetting lines merge, the “deployed-line-width” to “particle size” ratio is kept below a critical value so that the capillary forces overcome the frictional forces between the particles and the substrate.
Carbon-hydrogen bonding in near-frictionless carbon
Authors: Johnson J. A. , Woodford J. B. , Rajput D. , Kolesnikov A. I. , Schleuter J. A. , Eryilmaz O. L. , Erdemir A.
Published: October 2008

The uniquely low friction behavior of near-frictionless carbon (NFC) as compared to conventional diamondlike carbon (DLC) is determined by the bonding within the film. Inelastic neutron scattering (INS) and Fourier transform infrared (FTIR) spectroscopy were used to probe the bonding environment of carbon and hydrogen; both INS and FTIR can probe the whole sample. Previous work has focused on surface studies; the present results show that in the film as a whole the majority of the hydrogen is adjacent to sp3-bonded carbon. In addition this work has determined the absence of any molecular hydrogen in NFC.
Size effects on thin film ferroelectrics: Experiments on isolated single crystal sheets
Authors: Chang L. W. , McMillen M. , Morrison F. D. , Scott J. F. , Gregg J. M.
Published: October 2008

Thin lamellae were cut from bulk single crystal BaTiO3 using a focused ion beam microscope. They were then removed and transferred onto single crystal MgO substrates, so that their functional properties could be measured independent of the original host bulk ferroelectric. The temperature dependence of the capacitance of these isolated single crystal films was found to be strongly bulklike, demonstrating a sharp Curie anomaly, as well as Curie–Weiss behavior. In addition, the sudden change in the remanent polarization as a function of temperature at TC was characteristic of a first order phase change. The work represents a dramatic improvement on that previously published by Saad et al. [J. Phys.: Condens. Matter 16, L451 (2004)], as critical shortcomings in the original specimen geometry, involving potential signal contributions from bulk BaTiO3, have now been obviated. That the functional properties of single crystal thin film lamellae are comparable to bulk, and not like those of conventionally deposited heterogeneous thin film systems, has therefore been confirmed.
Hall magnetohydrodynamics in a strong magnetic field
Authors: Gómez Daniel O. , Mahajan Swadesh M. , Dmitruk Pablo
Published: October 2008

For a plasma embedded in a strong external magnetic field, the spatial structures tend to develop fine scales preferentially across the field, rather than along the parallel direction. This feature, which allowed a major simplification in the theoretical structure of one-fluid magnetohydrodynamics (leading to reduced magnetohydrodynamics), is exploited here to derive what may be called the reduced Hall magnetohydrodynamic equations (RHMHD) reflecting two-fluid effects such as the Hall current and the electron pressure. These physical effects, which can be relevant in astrophysical environments and also in fusion plasmas, allow for the propagation of circularly polarized normal modes such as whistlers and shear/ion-cyclotron waves. In this paper, the RHMHD system of equations is integrated numerically, to investigate externally driven turbulence.
Influence of the material parameters on quantum cascade devices
Authors: Benveniste E. , Vasanelli A. , Delteil A. , Devenson J. , Teissier R. , Baranov A. , Andrews A. M. , Strasser G. , Sagnes I. , Sirtori C.
Published: October 2008

An experimental investigation on the influence of the material systems on the optical properties of quantum cascade structures is presented. Three electroluminescent quantum cascade devices have been grown using GaAs∕AlGaAs, GaInAs∕AlInAs, and InAs∕AlSb heterostructures. The devices emit at 10μm and are based on a similar bandstructure design. Our results verify that the optical quantum efficiency has the predicted dependence on the electron effective mass. We also demonstrate that the shape of the electroluminescence spectra is independent from the particular material parameters and mainly depends on the tunnel coupling between the injector state and the upper state of the radiative transition.
Observation of individual dopants in a thin silicon layer by low temperature Kelvin Probe Force Microscope
Authors: Ligowski Maciej , Moraru Daniel , Anwar Miftahul , Mizuno Takeshi , Jablonski Ryszard , Tabe Michiharu
Published: October 2008

Detection of individual dopants in the thin silicon layer using Kelvin Probe Force Microscopy is presented. The analysis of the surface potential images taken at low temperatures (13K) on n-type and p-type samples reveals local potential fluctuations that can be attributed to single phosphorus and boron atoms, respectively. Results are confirmed by simulation of surface potential induced by dopants and by the back gate voltage dependence of the measured potential.
Quartz microbalance device for transfer into ultrahigh vacuum systems
Authors: Stavale F. , Niehus H. , Achete C. A.
Published: October 2008

An uncomplicated quartz microbalance device has been developed which is transferable into ultrahigh vacuum (UHV) systems. The device is extremely useful for flux calibration of different kinds of material evaporators. Mounted on a commercial specimen holder, the device allows fast quartz microbalance transfer into the UHV and subsequent positioning exactly to the sample location where subsequent thin film deposition experiments shall be carried out. After backtransfer into an UHV sample stage, the manipulator may be loaded in situ with the specimen suited for the experiment. The microbalance device capability is demonstrated for monolayer and submonolayer vanadium depositions with an achieved calibration sensitivity of less the 0.001 ML coverage.
A flexible, highly stable electrochemical scanning probe microscope for nanoscale studies at the solid-liquid interface
Authors: Stieg A. Z. , Rasool H. I. , Gimzewski J. K.
Published: October 2008

This work describes the design, fabrication, and application of an ultrastable scanning probe microscope for nanoscale studies at the solid-liquid interface, specifically in electrolyte environments. Quantification of system noise limits in the tunneling mode, mechanical drift rates, and lowest mechanical resonance provided values of ≤10 pA/Hz1/2, 2 nm/min (XY) and 0.15 nm/min (Z), and 7.9 kHz, respectively. Measurement of the closed-loop transfer function in the tunneling condition demonstrated linear feedback responses up to 4.2 and 2.5 kHz in ambient and electrochemical conditions. Atomic and molecular resolution imagings have been achieved in ambient, in situ, and electrochemical imaging environments at scan rates up to 80 lines/s. A modular design approach has produced a highly flexible microscope capable of imaging and spectroscopy in tunneling, tapping force [amplitude modulation atomic force microscopy (AFM)], and noncontact force (frequency modulation-AFM) modes.
Intersubband linewidths in quantum cascade laser designs
Authors: Wittmann A. , Bonetti Y. , Faist J. , Gini E. , Giovannini M.
Published: October 2008

We present a model to a priori calculate the temperature and field dependent intersubband linewidth of the optical transition in quantum cascade laser designs. Besides intra- and intersubband lifetime broadening, it comprises interface roughness scattering based on the approach of Tsujino et al. [Appl. Phys. Lett. 86, 062113 (2005)]. We verified our model with experimental data of quantum cascade lasers having different linewidths. Excellent agreement with the experiment was found for the two-phonon resonance design. Linewidths are slightly overestimated in the bound-to-continuum design. Differential gain and threshold current density are in excellent agreement for the two-phonon resonance design. Although the slope efficiency is somewhat underestimated at low temperatures, there is still reasonable agreement with the experiment.
Current-perpendicular-to-plane transport properties of polycrystalline Fe3O4/α-Fe2O3 heterostructures
Authors: Mi W. B. , Jiang E. Y. , Bai H. L.
Published: October 2008

Current-perpendicular-to-plane transport properties of sputtered polycrystalline Fe3O4/α-Fe2O3 heterostructures were investigated. A rectifying behavior was observed. The voltage shift increases linearly with temperature and turns from negative to positive at 230 K. The current-dependent magnetoresistance (MR) changes from negative to positive in the temperature range of 230–260 K. The largest negative MR is −32% at 230 K, and the positive MR at 305 K reaches 80% at 1.0 mA. The characteristic MR is thought to be caused by the rectifying effect and band structure at the Fe3O4/α-Fe2O3 interface.
Fabrication of nanoelectrodes and nanojunction hydrogen sensor
Authors: Mubeen Syed , Yoo Bongyoung , Myung Nosang V.
Published: October 2008

A simple method to fabricate nanoelectrodes with controllable gap was demonstrated by local electrical melting of nickel nanowire. The width of nanogap was tuned by diameter of nanowire and the gap distance was controlled by voltage sweep rate. These nanoelectrodes were then electrochemically backfilled with palladium to fabricate hydrogen nanojunction sensor. Sensors showed excellent sensing performance (dynamic range from 0.1% to 4% H2 and <1 min response time for H2 concentration >2%) at room temperature. Our method of electrochemically backfilling a nanogap opens up a possibility to create various nanojunction devices in a cost-effective matter.
Local work function measurements of epitaxial graphene
Authors: Filleter T. , Emtsev K. V. , Seyller Th. , Bennewitz R.
Published: October 2008

The work function difference between single layer and bilayer graphene grown epitaxially on 6H-SiC(0001) has been determined to be 135±9 meV by means of the Kelvin probe force microscopy. Bilayer films are found to increase the work function as compared to single layer films. This method allows an unambiguous distinction between interface layer, single layer, and bilayer graphene. In combination with high-resolution topographic imaging, the complex step structure of epitaxial graphene on SiC can be resolved with respect to substrate and graphene layer steps.
Low-voltage C60 organic field-effect transistors with high mobility and low contact resistance
Authors: Zhang X.-H. , Kippelen B.
Published: October 2008

State-of-the-art C60 organic transistors are reported here by engineering the essential electrode/semiconductor and dielectric/semiconductor interfaces. By using calcium (Ca) as the source and drain electrodes, the width-normalized contact resistance (RCW) at the electrode/semiconductor interface could be reduced to a constant value of 2 kΩ cm at a gate-source voltage (VGS) of 2.6 V, for devices with channel lengths ranging from 25 to 200 μm. Channel transconductance is observed to follow channel length scaling, and charge mobility average value of 2.5 cm2/Vs at VGS<5 V is found independent of channel length within the studied range.
Gigahertz modulation of tunable terahertz radiation from photomixers driven at telecom wavelengths
Authors: Martin M. , Mangeney J. , Crozat P. , Chassagneux Y. , Colombelli R. , Zerounian N. , Vivien L. , Blary K.
Published: October 2008

Here, we report the gigahertz-rate modulation of a tunable terahertz carrier. Terahertz radiation, tunable from 300 GHz to 1.2 THz, is generated by mixing two telecom lasers with an offset frequency in an ultrafast In0.53Ga0.47As photoconductive device coupled to a broadband antenna. The microwave modulation applied to the telecom lasers is directly transferred to the terahertz carrier. A maximum modulation rate of 20 GHz has been achieved, and the bandwidth is independent of the carrier frequency.
Degradation studies on high-voltage-driven organic light-emitting device using in situ on-operation method with scanning photoelectron microscopy
Authors: Lee J. , Sohn S. , Yun H. J. , Shin H. J.
Published: October 2008

We investigated the degradation behavior of a high-voltage-driven organic light-emitting device (OLED) by operating the device in an ultrahigh-vacuum environment. In situ on-operation method provided the initial degradation process when the OLED was biased inside an analysis chamber. The degraded area was probed by scanning photoelectron microscopy (SPEM) using synchrotron. SPEM showed that the degradation was accompanied by a local drift of indium tin oxide (anode) toward Al (cathode) and that the heat from the degraded area separated the cathode from the Alq3 layer, forming large bubbles. These results also indicate that microbubbles were formed under the Alq3, implying, before popping, the existence of local high-temperature degradation spots.
Process induced mechanical stress in InP ridge waveguides fabricated by inductively coupled plasma etching
Authors: Avella M. , Jiménez J. , Pommereau F. , Landesman J. P. , Rhallabi A.
Published: October 2008

Inductively coupled plasma (ICP) etching is suitable for producing semiconductor structures with a high aspect ratio. While the morphology of the structures is very satisfactory, less is known about other aspects related to the process, but with potential influence in the optical performance of the devices. We present herein a study of the mechanical stresses produced by the ICP process in the fabrication of ridge waveguides in InP. Stresses purely induced by the process are revealed by the spectral analysis of the cathodoluminescence. A dependence of the stress distribution on the aspect ratio of the waveguides is demonstrated.
Observation of magnetoelectric coupling in Bi0.7Dy0.3FeO3 thin films at room temperature
Authors: Palkar V. R. , Prashanthi K.
Published: October 2008

Spatial coexistence of ferroelectric and magnetic domains in micrometer scale is confirmed by multimode scanning probe microscopy of pulsed laser deposited Bi0.7Dy0.3FeO3 thin films. The observed change in ferroelectric polarization with applied magnetic field proves the coupling between magnetic and ferroelectric order parameters. Moreover, the alignment of magnetic domains with externally applied electric field further confirms the presence of coupling in this system. Remarkably, the effect persists even after the electric field is removed, thereby implying an electric field induced magnetic hysteresis phenomenon in the magnetic domain structure. The results suggest an in-principle usability of this system for multifunctional applications.
Fluorescence enhancement by a photonic crystal with a nanorod-structured high index layer
Authors: Zhang Wei , Cunningham Brian T.
Published: October 2008

We report the design and characterization of a one-dimensional photonic crystal slab incorporating a nanorod-structured TiO2 high index layer. The photonic crystal is designed to function as an optical resonator at the wavelength of a laser used to excite fluorescence emission and the highly porous TiO2 film, not only increases the surface area of the device but more importantly allows fluorophores to penetrate into the most intense region of the resonance-enhanced near electric fields. The design shows an enhancement of 193-fold in fluorescence intensity for the detection of cyanine 5-labeled streptavidin in comparison to an unpatterned glass slide.
Numerical and theoretical study of Bernstein modes in a magnetized quantum plasma
Authors: Eliasson Bengt , Shukla Padma K.
Published: October 2008

A numerical and theoretical study is presented for the propagation of electron Bernstein modes in a magnetized quantum plasma. The dispersion relation for electrostatic waves is derived, using a semiclassical Vlasov model for Fermi–Dirac distributed electrons. The dispersion relation is checked numerically with direct Vlasov simulations, where the wave energy is concentrated to the Bernstein modes as well as to the zero-frequency convective mode. Dispersion relations in the long wavelength limit are derived, including the upper hybrid dispersion relation for a degenerate quantum plasma.
Fast computation of magnetostatic fields by nonuniform fast Fourier transforms
Authors: Kritsikis Evaggelos , Toussaint Jean-Christophe , Fruchart Olivier , Szambolics Helga , Buda-Prejbeanu Liliana
Published: October 2008

The bottleneck of micromagnetic simulations is the computation of the long-ranged magnetostatic fields. This can be tackled on regular N-node grids with fast Fourier transforms in time N log N, whereas the geometrically more versatile finite element methods (FEMs) are bounded to N4/3 in the best case. We report the implementation of a nonuniform fast Fourier transform algorithm, which brings a N log N convergence to FEM, with no loss of accuracy in the results.
Bandgap engineering of tunnel oxide with multistacked layers of Al2O3/HfO2/SiO2 for Au-nanocrystal memory application
Authors: Lo Yun-Shan , Liu Ke-Chih , Wu Jyun-Yi , Hou Cheng-Hao , Wu Tai-Bor
Published: October 2008

Charge storage characteristics of metal-oxide-semiconductor (MOS) structure containing Au nanocrystals on tunnel oxide composed of triply stacked SiO2, HfO2, and Al2O3 layers were studied. Significantly high charge injection and detrapping efficiency for program and erase operations along with a satisfactory long-term charge retention were obtained from the above MOS structure. It is attributed to the bandgap engineering of tunnel oxide with a multistacked concave barrier, from which the effective thickness of the tunneling barrier can be greatly reduced under a moderate bias, while a thick and high barrier is retained for charge retention.
Three dimensional characterization of dopant distribution in polycrystalline silicon by laser-assisted atom probe
Authors: Inoue K. , Yano F. , Nishida A. , Tsunomura T. , Toyama T. , Nagai Y. , Hasegawa M.
Published: October 2008

Dopant distribution in polycrystalline Si of n-type metal-oxide-semiconductor field effect transistor was measured by laser-assisted three dimensional atom probe. Segregation of As and P atoms to grain boundaries and at the interface between gate and gate oxide, resulting from different mechanisms, i.e., volume diffusion in the bulk and grain boundary diffusion at the interface, was clearly observed. Concentration profiles that show such clear segregation were directly obtained by atomic-resolution measurement.
Zener tunneling in plasmonic metal gap waveguide superlattices
Authors: Lin Weihua , Gu Yang , Wang Guo Ping
Published: October 2008

We report the zener tunneling (ZT) in plasmonic metal gap waveguide superlattices. Two types of plasmonic cavities are introduced into the structures for producing two plasmonic minibands separated by a narrow minigap, and a geometric thickness gradient is employed for creating two plasmonic Wannier–Stark ladders. Theoretical calculation by the transfer matrix method reveals that at a certain gradient, the transmission spectrum of surface plasmon polaritons (SPPs) shows an enhanced transmission peak, indicating the occurrence of resonant ZT between the two minibands. Finite-difference time-domain simulation on the time evolution of SPP propagation in the superlattices demonstrates the analytical prediction.
Absolute atomic oxygen density profiles in the discharge core of a microscale atmospheric pressure plasma jet
Authors: Knake Nikolas , Niemi Kari , Reuter Stephan , Schulz-von der Gathen Volker , Winter Jörg
Published: October 2008

The micro atmospheric pressure plasma jet is an rf driven (13.56 MHz, ∼20 W) capacitively coupled discharge producing a homogeneous plasma at ambient pressure when fed with a gas flow of helium (1.4 slm) containing small admixtures of oxygen (∼0.5%). The design provides excellent optical access to the plasma core. Ground state atomic oxygen densities up to 3×1016 cm−3 are measured spatially resolved in the discharge core by absolutely calibrated two-photon absorption laser-induced fluorescence spectroscopy. The atomic oxygen density builds up over the first 8 mm of the discharge channel before saturating at a maximum level. The absolute value increases linearly with applied power.
A percolation model for insulator-metal transition in polymer-conductor composites
Authors: Yang Q. Q. , Liang J. Z.
Published: October 2008

In order to reveal the important influence of the aggregate structure of conductive component to the percolation behavior of polymer-conductor composites, a percolation model, which is based on the percolation theory and the equivalent sphere of aggregate that acts as a basic cell, is proposed. A formula, describing the relationship of the conductivity and the volume fraction of conductive component, and an expression, estimating percolation threshold of the composites, are derived. Based on these expressions, the electrical conductivity and percolation threshold of some composites are predicted. The results show that the predictions are reasonably consistent with the experimental data.
Observation of a high negative spin polarization at the Fe/MgO(100) surface oxidized at room temperature
Authors: Kurahashi M. , Sun X. , Entani S. , Yamauchi Y.
Published: October 2008

Spin polarization of an Fe/MgO(100) surface oxidized at room temperature has been analyzed with a spin-polarized metastable helium beam, which is an extremely surface sensitive spin probe, under high magnetic fields (0–50 kOe). The spin polarization of the Fe surface, although it initially decays with oxygen exposure, increases at >20 L (1 L=10−6 Torr sec) and becomes comparable to that observed for a clean Fe surface at >100 L. The polarization is negative and especially high at around the Fermi level. This may be understood if we assume the formation of Fe3O4.
On the possibility of ferromagnetism in carbon-doped anatase TiO2
Authors: Yang Kesong , Dai Ying , Huang Baibiao , Whangbo Myung-Hwan
Published: October 2008

To see if ferromagnetism can occur in C-doped anatase TiO2, we performed first-principles calculations for a number of C-doped structures in which C atoms substitute O atoms. Our study shows that each C has spin-polarized 2p states in the band gap generating a magnetic moment of 2.0μB. The magnetic coupling between doped C atoms is substantial leading to either antiferromagnetism or ferromagnetism when the C⋯C distance lies between 3–4Å. A strong ferromagnetic coupling occurs when the two C atoms form a slightly bent C–Ti–C unit by replacing two oxygen atoms at the opposite vertices of a TiO6 octahedron.
Electrical properties of aggregated detonation nanodiamonds
Authors: Bevilacqua Mose , Patel Sameer , Chaudhary Aysha , Ye Haitao , Jackman Richard B.
Published: October 2008

Nanometer-scale diamonds formed using a detonation process are an interesting class of diamond materials. Commercially supplied material is highly aggregated with ∼5nm diamond crystals forming particles with micron sizes. Previous models have suggested that nondiamond carbon is incorporated between the crystals, which would reduce the electrical and chemical usefulness of this form of diamond. However, using impedance spectroscopy we have shown that at temperatures below 350°C the form of detonation nanodiamond being studied is a near to ideal dielectric, implying a full sp3 form. At temperatures above this the surfaces of the diamond crystals may support some nondiamond carbon.
Conducting polymer/carbon nanotube composite as counter electrode of dye-sensitized solar cells
Authors: Fan Benhu , Mei Xiaoguang , Sun Kuan , Ouyang Jianyong
Published: October 2008

This letter reports dye-sensitized solar cells with a thin film of multiwall carbon nanotube/conducting poly(3,4-ethylenedioxythiophene):poly(styrenesulfonate) composite as the counterelectrode. The composite thin film was prepared by spin coating the aqueous solution of the composite. The devices exhibited high performance with the energy conversion efficiency of 6.5%, short-circuit current of 15.5mAcm−2, open-circuit voltage of 0.66V, and fill factor of 0.63. This performance is close to the devices using conventional platinum as the counterelectrode and is significantly higher than the ones using a thin film of multiwall carbon nanotube/poly(styrenesulfonate acide) composite as the counterelectrode.
Nanotip formation on a carbon nanotube pillar array for field emission application
Authors: Rai Padmnabh , Mohapatra Dipti R. , Hazra K. S. , Misra D. S. , Tiwari S. P.
Published: October 2008

The field emission of a carbon nanotube (CNT) pillar array has been improved significantly by plasma treatment in a mixture of hydrogen and nitrogen gases. The plasma treatment for 30s on a pillar array decreased the turn-on electric field from 0.48to0.37V∕μm and increased the field enhancement factor from 6200 to 6900. The emission current density increased by a factor of ≈40. We report in this letter the technique of generating nanotips on CNT pillars with an enormous potential to become a tool for the control and manipulation of CNTs and nanostructures.
Electron scatterings in selectively doped n-AlGaAs∕GaAs heterojunctions with high density self-assembled InAlAs antidots
Authors: Kawazu Takuya , Sakaki Hiroyuki
Published: October 2008

The scattering processes of two-dimensional electrons are studied in selectively doped n-AlGaAs∕GaAs heterojunctions where high density InAlAs anti dots are embedded in the vicinity of the GaAs channel. Mobilities μ are measured as a function of the electron concentrations Ns in two samples where the In1−xAlxAs antidots are grown with different Al contents (x∼0.75 and 0.5). It is found that the Ns dependence of μ is strongly dependent on the Al content x of the embedded InAlAs dots, although their shapes and densities are almost same. The experimental data are well explained by theoretical models based on the surface profiles of the InAlAs dot layers.
High quality ultraviolet AlGaN∕GaN multiple quantum wells with atomic layer deposition grown AlGaN barriers
Authors: Li Zhen-Yu , Lo Ming-Hua , Hung C. T. , Chen Shih-Wei , Lu Tien-Chang , Kuo Hao-Chung , Wang Shing-Chung
Published: October 2008

Low dislocation density ultraviolet (UV) AlGaN∕GaN multiple quantum well (MQW) structure was grown using atomic layer deposition (ALD) technique. The AlGaN∕GaN MQW grown on the sapphire substrate consisted of three GaN QWs and four AlGaN barriers formed by ALD grown AlN∕GaN superlattices. The as-grown sample showed smooth surface morphology with a root-mean-square roughness value of only 0.35nm, and no surface cracks were found. The dislocation density was estimated to be as low as 3.3×107cm−2. X-ray and transmission electron microscope data showed the MQW had sharp interfaces with good periodicity. The sample had an UV photoluminescence emission at 334nm (3.71eV) with a very narrow linewidth of 47meV at 13K. The cathodoluminescence image revealed a fairly uniform luminescence pattern at room temperature. The AlGaN∕GaN MQW grown by ALD technique should be useful for providing high crystalline quality for fabrication of various optical devices.
Suppression of the subband parasitic peak by 1nm i-AlN interlayer in AlGaN deep ultraviolet light-emitting diodes
Authors: Zhang J. C. , Zhu Y. H. , Egawa T. , Sumiya S. , Miyoshi M. , Tanaka M.
Published: October 2008

The origin and suppression of the subband parasitic peak in AlGaN deep ultraviolet light-emitting diodes have been studied. The parasitic peak is clarified to come from a p-AlGaN cladding layer and to be related to Mg dopants. By using 1nm i-AlN as an interlayer between the active region and the p-AlGaN cladding layer, this peak is suppressed efficiently. The devices with such an interlayer show improved output power by a factor of 4 at injection current density of 20A∕cm2, except that the series resistance and turn-on voltage are slightly increased.
Epitaxial ferromagnetic Fe3Si∕Si(111) structures with high-quality heterointerfaces
Authors: Hamaya K. , Ueda K. , Kishi Y. , Ando Y. , Sadoh T. , Miyao M.
Published: October 2008

To develop silicon-based spintronic devices, we have explored high-quality ferromagnetic Fe3Si/silicon (Si) structures. Using low-temperature molecular beam epitaxy at 130°C, we realize the epitaxial growth of ferromagnetic Fe3Si layers on Si(111) with an abrupt interface, and the grown Fe3Si layer has the ordered DO3 phase. Measurements of magnetic and electrical properties for the Fe3Si∕Si(111) yield a magnetic moment of ∼3.16μB∕f.u. at room temperature and a rectifying Schottky-diode behavior with the ideality factor of ∼1.08, respectively.
Marketing the Self: The Politics of Aspiration among Middle-Class Silicon Valley Youth
Authors: Davidson Elsa
Published: October 2008

I explore a contemporary politics of social reproduction among middle-class youth in Silicon Valley during the economic downturn subsequent to the tech boom of the 1990s. Drawing on ethnographic data collected at a public high school serving middle-class and affluent youth, I examine the relationship of the school and community environment to students' styles of self-cultivation and aspiration. In particular, I explore values and notions of success—such as freedom of expression, the pursuit of authentic passions, and conventional markers of academic and social achievement—that shape students' forms of self-discipline, self-definition, and aspiration. While arguing that young people's styles of self-cultivation suggest an entitled orientation toward work and life that may promote class privilege, I suggest that they also reflect a neoliberal politics of citizenship-shaping processes of social reproduction through schooling for middle-class youth. This politics of citizenship obligates middle-class youth to ‘package’ or market authentic personal traits to showcase their exceptional qualities, well-roundedness, and authentic originality, and to frame such acts in terms of personal choice. Linking such processes of subjectification to political–economic and social conditions, I ultimately argue that middle-class youth bear increasing responsibility for middle-class status. Moreover, I suggest that the pressures resulting from this burden and the ways in which young people negotiate them suggest a domestic politics of ‘hyper-vigilance’ that may transform young people's self-perceptions, attitudes towards schooling, and aspirations, while also potentially posing risks to youth.
Relaunching Regional Economic-Development Policy and Planning for Auckland: Remaking the State and Contingent Governance under Neoliberalism
Authors: Wetzstein Steffen
Published: October 2008

Neoliberalisation in New Zealand has been driven further as a political project than in most other countries. After two decades of neoliberal economic policy, it is possible to examine how political-economic actors in subnational spaces have responded to vastly new conditions. I provide an account on how regional economic-development policy and planning has reappeared in Auckland in the postrestructuring period. By deploying relational – institutional and poststructural perspectives in the examination of key policy initiatives that coconstituted an emerging regional economic intervention trajectory, I discuss how economic governance has been assembled, assess its structural coherence and directionality, and analyse the role of the state. I argue that regional governance processes are characterised by contingencies, patterns of institutional experimentation, and, increasingly, the work of central state actors. What is not known to date, however, is whether new regulatory structures are having any major material effects on the course of New Zealand's largest regional economy.
‘Wicked’, ‘Messy’, and ‘Clumsy’: Long-Term Frameworks for Sustainability
Authors: Frame Bob
Published: October 2008

Society requires new forms of science and technology to productively accommodate the intrinsic value-laden judgments needed to manage the high uncertainties and considerable long-term impacts of sustainable urban planning. Responses to these ‘wicked’ problems include the development of postnormal science in the early 1990s. In subsequent literature on postnormal sustainability technologies, multiactor approaches to decision making are beginning to emerge. I examine an example: the development in New Zealand of a 100-year vision: the Auckland Sustainability Framework. Developed over fifteen months through ‘messy’ consultation across stakeholders, it has provided a clumsy’ outcome, namely one which enabled multiple viewpoints to be expressed and responded to by others. The process adopted offers evidence in support of the development of sustainability frameworks over much longer timescales than the current norm in local authorities, and indications of how such processes may unfold.
Mass Transport and Flow Dispersion in the Compartments of a Modular 10 Cell Filter-Press Stack
Authors: Ponce-de-León Carlos , Whyte Ian , Reade Gavin W. , Male Stewart E. , Walsh Frank C.
Published: October 2008

Flow dispersion, pressure drop, and averaged mass transport measurements have been made to characterize the reaction environment in an industrial scale electrochemical reactor. The 10 cell filter-press stack was operated with a relatively low mean linear velocity in the range 0.6 to 6.2 cm s–1. Flow dispersion was studied by a perturbation–response technique by electrolyte conductivity measurements at the reactor outlet. Mass transport coefficients were evaluated from the first order reaction decay of dissolved bromine (Br3–) which was anodically generated from 1 mol dm–3 NaBr (aq). Each cell consisted of two 0.72 m2 projected area electrodes separated by a cationic membrane, and each electrolyte compartment contained a high-density polyolefin turbulence promoter. The electrodes consisted of a carbon/polyethylene core with a layer of an activated carbon–poly(vinylidene difluoride) composite on each side. Comparison is made with the mass transport characteristics of a similar system that contains five bipolar cells.
Two Novel Triazole-Based Metal - Organic Frameworks Consolidated by a Flexible Dicarboxylate Co-ligand: Hydrothermal Synthesis, Crystal Structure, and Luminescence Properties
Authors: Yang En-Cui , Liang Qing-Qing , Wang Xiu-Guang , Zhao Xiao-Jun
Published: October 2008

To explore the effects of a co-ligand on the construction of mixed-ligand metal–organic frameworks (MOFs), two new triazole-based complexes with a flexible dicarboxylate as a co-ligand, {[Zn4(trz)4(gt)2(H2O)2](H2O)2}n 1 and {[Cd2(trz)2(gt)(H2O)2](H2O)4}n 2 (Htrz = 1,2,4-triazole; H2gt = glutaric acid), were synthesized and their structures were fully characterized by elemental analyses, IR spectroscopy, and single-crystal X-ray crystallography. Their thermal stability and luminescence emissions were further investigated to establish their structure–property relationship. Crystal structure determination showed that 1 is a neutral two-dimensional pillared-bilayer network consisting of 14-membered hydrophobic channels, whereas 2 is an infinite three-dimensional framework constructed from tetranuclear [Cd4(trz)4]4+ subunits. Interestingly, the overall structure of both MOFs can be solely supported by ZnII/CdII and trz anions, and were further consolidated by the introduction of a flexible gt co-ligand. In addition, the carboxylate groups in the co-ligand can also serve as a weak O–H···O hydrogen-bond acceptor to capture guest water molecules. The synchronous weight-loss behaviour of trz and gt anions presented by thermogravometric curves suggest their cooperative contributions to the thermal stability of the MOFs. In contrast, the fluorescence emissions of two complexes are significantly dominated by the core trz ligand, rather than the gt co-ligand and metal ions.
Antiviral Agents. I. Synthesis and Antiviral Evaluation of Trimeric Naphthoquinone Analogues of Conocurvone
Authors: Crosby Ian T. , Rose Mark L. , Collis Maree P. , de Bruyn Paula J. , Keep Philip L. C. , Robertson Alan D.
Published: October 2008

Conocurvone, a novel natural product isolated from the endemic Australian shrub Conosperum sp. (Proteaceae), exhibits anti-HIV activity but is a highly lipophilic compound, which suggests that there may be problems with its aqueous solubility and bioavailability. A general and convenient synthesis of trimeric naphthoquinones using the condensation of 2-hydroxynaphthoquinones and 2,3-dihaloquinones is described. The application of this method to the synthesis of a series of simpler and less lipophilic trimeric naphthoquinone simple analogues of conocurvone is also reported together with their anti-HIV activity.
Spatial and temporal patterns of habitat use by three estuarine species of mysid shrimp
Authors: Taylor Matthew D.
Published: October 2008

The mysids Rhopalopthalmus egregius, Haplostylus dakini and Doxomysis australiensis are abundant yet unstudied omnivorous crustaceans in Australian estuaries. Habitat use and population dynamics were investigated for these species over spring and summer in the Tweed River, Australia, to explore their ecological role in estuarine ecosystems. Overall, mysids were concentrated in shallow unvegetated and deep unvegetated estuarine habitats. H. dakini were most abundant in shallow and deep bare habitats at night, whereas R. egregius were most abundant in deep bare habitats during the night. D. australiensis were present across all habitats in the night, but negligible numbers were present during the day. Significantly greater numbers of R. egregius and D. australiensis were sampled during the new moon, compared with the full moon. Significantly larger R. egregius and D. australiensis individuals were present in benthic habitats at night, indicating possible partitioning of habitat for juvenile and adult subpopulations. Adaptive foraging strategies and habitat use facilitates the coexistence of sympatric mysid species, H. dakini and R. egregius, and within-species habitat partitioning allowed juvenile R. egregius to avoid interaction with adult R. egregius. The observed dynamics minimize inter- and intra-specific predation between mysids, and by other predators, while optimizing access to key trophic resources.