bluuebunny/crossref_metadata_2025 huggingface dataset:
Domain wall and periodic solutions of coupled asymmetric double well models
Authors: Khare Avinash , Saxena Avadh
Published: April 2007

Coupled asymmetric double well (aϕ2−bϕ3+cϕ4) one-dimensional potentials arise in the context of first order phase transitions both in condensed matter physics and field theory. Here we provide an exhaustive set of exact periodic solutions of such a coupled asymmetric model in terms of elliptic functions (domain wall arrays) and obtain single domain wall solutions in specific limits. We also calculate the energy and interaction between solitons for various solutions. Both topological (kinklike at T=Tc) and nontopological (pulselike for T≠Tc) domain wall solutions are obtained. We relate some of these solutions to domain walls in hydrogen bonded materials and also in the field theory context. As a by-product, we also obtain a new one parameter family of kink solutions of the uncoupled asymmetric double well model.
Stress and failure at mechanical contacts of microspheres under uniaxial compression
Authors: Chen Yun , Best Andreas , Haschke Thomas , Wiechert Wolfgang , Butt Hans-Jürgen
Published: April 2007

In order to study the failure mechanism of micron sized particles, ruby (α-Al2O3:Cr3+) spheres of R=75μm radius were compressed between two sapphire (α-Al2O3) plates. A confocal microscope was used to measure the local spectral shifts of the luminescence lines in the ruby sphere while slowly increasing the load up to failure at 6–7N. From the spectral shifts the local stress was calculated. The results show a steplike decrease of stress starting at a load of 4.3–4.7N. We interpret this as the formation of microcracks, which lead to a relaxation of stress. In the vicinity of the contact area luminescence spectra with multiple distinct peaks were observed. This indicates the presence of regions of homogeneous stress, which are mechanically decoupled and which are even smaller than the observation volume of ≈(2μm)3.
Influence of initial conditions on decaying two-dimensional turbulence
Authors: van Bokhoven L. J. A. , Trieling R. R. , Clercx H. J. H. , van Heijst G. J. F.
Published: April 2007

A numerical study of freely decaying two-dimensional turbulence is presented to show how the time evolution of characteristic flow quantities is influenced by the initial conditions. The numerical method adopted is a standard two-dimensional (2D) Fourier pseudospectral algorithm with Newtonian viscosity. Vortex statistics are extracted using a vortex census method. Several characteristic initial vorticity distributions analogous to those employed in previous laboratory experiments are considered. Some of the initial vorticity distributions have in common a dominant subset of vortices. Reliable statistics are obtained for each characteristic distribution by ensemble averaging. For the dominant subset, the time evolutions of the global enstrophy and the number density, respectively, are found to collapse confirming the self-similarity of 2D turbulence, one of the starting points for the scaling theory proposed by Carnevale et al. [Phys. Rev. Lett. 66, 2735 (1991)]. The relationship between the relevant scaling exponents as predicted by the scaling theory is not confirmed, however, and thus seems questionable within the considered parameter range. Furthermore, power-law exponents for both the number density and the global enstrophy are found to be affected by the initial number density and the initial vortex size distribution. Our results thus suggest that for experiments in shallow fluid layers, any agreement with a universal scaling exponent seems coincidental.
Copper diffusion and mechanical toughness at Cu-silica interfaces glued with polyelectrolyte nanolayers
Authors: Gandhi D. D. , Singh A. P. , Lane M. , Eizenberg M. , Ramanath G.
Published: April 2007

We demonstrate the use of polyallylamine hydrochloride (PAH)-polystyrene sulfonate (PSS) nanolayers to block Cu transport into silica. Cu/PSS-PAH/SiO2 structures show fourfold enhancement in device failure times during bias thermal annealing at 200 °C at an applied electric field of 2 MV/cm, when compared with structures with pristine Cu-SiO2 interfaces. Although the bonding at both Cu-PSS and PAH-SiO2 interfaces are strong, the interfacial toughness measured by the four-point bend tests is ∼2 Jm−2. Spectroscopic analysis of fracture surfaces reveals that weak electrostatic bonding at the PSS-PAH interface is responsible for the low toughness. Similar behavior is observed for Cu-SiO2 interfaces modified with other polyelectrolyte bilayers that inhibit Cu diffusion. Thus, while strong bonding at Cu-barrier and barrier-dielectric interfaces may be sufficient for blocking copper transport across polyelectrolyte bilayers, strong interlayer molecular bonding is a necessary condition for interface toughening. These findings are of importance for harnessing MNLs for use in future device wiring applications.
Growth of amorphous TeOx (2≤x≤3) thin film by radio frequency sputtering
Authors: Dewan Namrata , Gupta Vinay , Sreenivas K. , Katiyar R. S.
Published: April 2007

Thin films of Tellurium oxide TeOx over a wide range of x (2 to 3) were prepared by radio frequency diode sputtering at room temperature on corning glass and quartz substrate. The deposited films are amorphous in nature and IR spectroscopy reveals the formation of Te-O bond. X-ray photoelectron spectroscopy shows the variation in the stoichiometry of TeOx film from x=2 to 3 with an increase in oxygen percentage (25 to 100%) in processing sputtering gas composition. Raman spectroscopy depicts the formation of TeO3 trigonal pyramid besides TeO4 disphenoid in the amorphous TeOx film with increase in the value of x. The varying stoichiometry of TeOx thin film (x=2 to 3) was found to influence the optical, electrical, and elastic properties. The optical band gap of film increases from 3.8 to 4.2 eV with increasing x and is attributed to the decrease in density. The elastic constants (C11 and C44) of the deposited films are lower than the corresponding value reported for TeO2 single crystal.
Does the orbital degeneracy play any role in the high thermopower of lamellar cobaltites?
Authors: Pollet M. , Doumerc J. P. , Guilmeau E. , Grebille D. , Fagnard J. F. , Cloots R.
Published: April 2007

This article investigates the role of the CoO6 octahedron distortion on the electronic properties and more particularly on the high value of the Seebeck coefficient in the BiCaCoO lamellar cobaltites. Our measurements provide clues indicating that the t2g orbital degeneracy lifting has to be considered to account for the observed high temperature limit of the thermopower. They also provide experimental arguments for locating the a1g and eg′ orbitals levels on the energy scale, through the compression of the octahedron. These results are in agreement with recent ab initio calculation including the electronic correlations and concluding for the inversion of these levels as compared to the expectation from the crystal field theory.
Electrical and optical characterization of SiONC dielectric thin film deposited by polymer-source chemical vapor deposition
Authors: Oulachgar El Hassane , Aktik Cetin , Scarlete Mihai , Dostie Starr , Sowerby Rob , Gujrathi Subhash
Published: April 2007

The electro-optical properties of SiONC dielectric thin films deposited by polymer-source chemical vapor deposition using an organosilane precursor has been investigated as a function of oxygen concentration in the films. SiONC thin films were characterized using capacitance-voltage (C-V), conductance-voltage (G-V), ellipsometry, and ultraviolet visible (UV-Vis) photospectroscopy. These measurements showed that the electro-optical properties of the films are greatly influenced by the atomic concentration of oxygen. The high frequency C-V measurement revealed a nearly ideal metal-oxide-semiconductor (MOS) structure behavior at high atomic concentration of oxygen (35 at. %). A relative dielectric constant as high as 6 is obtained at 10 kHz for samples with about 5 at. % of oxygen, which corresponds to high-k dielectric material. The interface trap density extracted from G-V measurement using Hill-Coleman method is as low as 3.2×1010 (cm−2 eV−1), making these films a viable high-k dielectric alternative to SiO2 and SiON in MOS devices. The refractive index measured by ellipsometry at a wavelength of 632.8 nm shows a linear variation with atomic concentration of oxygen from 1.58 to 1.69. The optical energy band gap extracted from UV-Vis absorption spectra was found to vary between 4.40 and 5.25 eV.
Mechanism of mark deformation in phase-change media tested in an accelerated environment
Authors: Hirotsune Akemi , Terao Motoyasu , Miyauchi Yasushi , Tokushuku Nobuhiro , Tamura Reiji
Published: April 2007

Increased jitter caused by recording marks becoming deformed in an accelerated environmental test was investigated and a model where the change in the speed of crystallization is affected by passive oxidation on the amorphous surface of the recording layer was devised. The model clarified the mechanism by which deformation in the marks caused increased jitter in the accelerated environmental test. Adding nitrogen into the gas when sputtering the protective layer adjacent to the recording film was investigated. It was confirmed that a prototype disk with this protective layer has decreased jitter after a 500 h accelerated test and superior power margins.
Optical and other physical properties of semiconducting cadmium vanadate glasses
Authors: Ghosh Aloka , Bhattacharya S. , Ghosh A.
Published: April 2007

The optical and other physical properties of semiconducting xV2O5−(1−x)CdO glasses have been reported in this article. The changes in both density and molar volume indicate structural modification of crystalline V2O5 due to addition of CdO. The glass transition temperatures are observed to decrease with an increase in V2O5 content in the compositions. It has been observed from the analysis of Fourier-transform infrared spectra that the network structure strongly depends upon the V2O5 content in the glass compositions. Introduction of CdO into the V2O5 matrix changes the two-dimensional layer structure of the crystalline V2O5 into a more complicated three-dimensional structure. The fundamental absorption edge for all the glasses is analyzed in terms of the theory proposed by Davis and Mott [E. A. Davis and N. F. Mott, Philos. Mag. 22, 903 (1970)]. The position of absorption edge and, hence, the value of the optical band gap are found to depend on the V2O5 content in the glass compositions.
Mechanisms of enhancement of light emission in nanostructures of II–VI compounds doped with manganese
Authors: Godlewski M. , Yatsunenko S. , Ivanov V. Yu. , Drozdowicz-Tomsia K. , Goldys E. M. , Phillips M. R. , Klar P. J. , Heimbrodt W.
Published: April 2007

Intra-shell transitions of transition metal and rare earth ions are parity forbidden processes. For Mn2+ ions this is also a spin forbidden process, i.e., light emission should be inefficient. Surprisingly, it has been reported that in nanostructures of ZnMnS the T14 to A16 intra-shell transition of Mn2+ results in a bright photoluminescence characterized by a short PL decay time. The model of a quantum confined atom was introduced to explain the observed experimental results. It was later claimed that this model is incorrect. Based on the results of our photoluminescence, photoluminescence kinetics, time-resolved photoluminescence, electron spin resonance, and optically detected magnetic resonance investigations, we confirm photoluminescence enhancement and decrease of photoluminescence lifetime and relate these effects to spin dependent magnetic interactions between localized spins of Mn2+ ions and spins/magnetic moments of free carriers. This mechanism is active in both bulk and in low-dimensional structures, but is significantly enhanced in nanostructure samples.
Orbital-optimized opposite-spin scaled second-order correlation: An economical method to improve the description of open-shell molecules
Authors: Lochan Rohini C. , Head-Gordon Martin
Published: April 2007

Coupled-cluster methods based on Brueckner orbitals are well known to resolve the problems of symmetry breaking and spin contamination that are often associated with Hartree-Fock orbitals. However, their computational cost is large enough to prevent application to large molecules. Here the authors present a simple approximation where the orbitals are optimized with the mean-field energy plus a correlation energy taken as the opposite-spin component of the second-order many-body correlation energy, scaled by an empirically chosen parameter (recommended as 1.2 for general applications). This “optimized second-order opposite-spin” (abbreviated as O2) method requires fourth-order computation on each orbital iteration. O2 is shown to yield predictions of structure and frequencies for closed-shell molecules that are very similar to scaled second-order Møller-Plesset methods. However, it yields substantial improvements for open-shell molecules, where problems with spin contamination and symmetry breaking are shown to be greatly reduced.
Jahn–Teller effect and lattice shear strain in Zn1−xMxSe
Authors: Sokolov V. I. , Lonchakov A. T. , Podgornykh S. M. , Dubinin S. F. , Teploukhov S. G. , Parkhomenko V. D. , Gurzdev N. B.
Published: April 2007

The structural states of the semiconductors Zn1−xNixSe (x=0.0025) and Zn1−xCrxSe (x=0.0029) are investigated by the method of thermal neutron diffraction. Large-scale shear displacements of the atoms of the ZnSe lattice are observed, presumably brought on by the Jahn-Teller ions Cr2+ and Ni2+. The results of a study of the impurity heat capacity of the solid solutions Zn1−xMxSe (M=Cr2+,Ni2+) in the temperature interval 1.8–20K are presented. A heat-capacity method for determining the energy of intracenter transitions in these systems is described and employed. The role of the Jahn–Teller effect in the formation of the low-energy excited states of 3d ions in ZnSe is discussed.
Low-temperature effects of resonance electronic states at transition-element impurities in the kinetic, magnetic, and acoustic properties of semiconductors
Authors: Okulov V. I. , Govorkova T. E. , Gudkov V. V. , Zhevstovskikh I. V. , Korolyev A. V. , Lonchakov A. T. , Okulova K. A. , Pamyatnykh E. A. , Paranchich S. Yu.
Published: April 2007

New research results on phenomena due to the existence of electronic resonance energy levels and hybridized states at impurities of transition elements in semiconductors are presented. The data show that the thermal conductivity and ultrasonic parameters of mercury selenide containing iron impurities have resonance anomalies due to the influence of these impurities. A consistent and detailed interpretation is offered for the set of observed effects of hybridized states in mercury selenide with iron impurities. The proposed interpretation of the data obtained on other systems is discussed.
Analysis of self-organization processes among the hole states in cuprates and the features of their manifestation in YBa2Cu3O6+δ
Authors: Mitin A. V.
Published: April 2007

A string model proposed previously, based on the concept of quasi-one-dimensional correlations in the overlapping 2p shells of the oxygen sublattice, is used to analyze the influence of self-organization processes in the hole community on the evolution of the electronic properties of cuprates as the doping level is increased. The proposed scenario implies, in particular, that the formation of bosonic stripes within bunches of fermion-like hole excitations in the cuprates should be reflected in their electron spectra, first in the form of bulges and then in the form of coherent peaks adjacent to humps of incoherent origin on the low-energy side. In light of the approaches developed, the central thrust is to ascertain the specifics of the ordering of hole states in the compounds YBa2Cu3O6+δ, where, owing to alignment of the basal oxygen into chains, more favorable conditions can be created for the formation of a frustrated network of superconducting nanochannels consisting of second-rank bosonic stripes, which can maintain stability at temperatures up to 1200K at δ≈0.22. It is shown that the theoretical results, calculated without recourse to adjustable parameters, are in good agreement with the results of measurements for the main characteristics of the electron spectra of the cuprates.
Influence of magnetic interactions on the activation energy of the polaron hopping conductivity in the paramagnetic phase of single-crystal manganite Eu0.6Sr0.4MnO3
Authors: Neifeld E. A. , Arkhipov V. E. , Ugryumova N. A. , Korolyov A. V. , Mukovsky Ya. M.
Published: April 2007

Experimental results are presented on the resistivity, thermopower, magnetization, and magnetic susceptibility of single-crystal doped europium manganite Eu0.6Sr0.4MnO3 in the paramagnetic phase. In the temperature interval 80–400K in the resistivity ρ(T) of the sample is observed to grow monotonically by approximately 6 orders of magnitude, a comparative analysis of the experimental dependence of ρ(T) and the theoretical models used for description of the activation conductivity of manganites is carried out. The behavior of ρ(T) is most accurately described by a hopping polaron model in which the hops of adiabatic small polarons occur between nearest neighbors, but the activation energy decreases with decreasing temperature. A qualitative explanation of the observed temperature dependence of the activation energy is offered, based on a fluctuation model of phase separation with the magnetic contribution to the activation energy proposed by L. P. Gor’kov and co-authors taken into account.
Acquisition of low-frequency signals immersed in noise by random sampling and finite impulse response filters
Authors: Carrica Daniel O. , Petrocelli Roberto , Benedetti Mario , Funes Marcos A.
Published: April 2007

This article presents a method for digital acquisition of low-frequency signals immersed in high-frequency noise when noise frequency is higher than the sampling one. This method uses no antialiasing filters, but random sampling and filtering instead. Its formulation is developed for JRS (jitter random sampling) and finite impulse response (FIR) filters. The proposed method is experimentally tested on three FIR filters: moving average, windowed linear phase, and constrained least square.
Synthesis and optical properties of V2O5 nanorods
Authors: Wang Yuquan , Li Zhengcao , Sheng Xing , Zhang Zhengjun
Published: April 2007

A two-step method was proposed in synthesizing V2O5 nanorods on planar substrates, i.e., depositing a V2O3 thin film at ∼220°C (by heating a pure sheet of vanadium in a rough vacuum) and then heating it in air at ∼400°C. The V2O5 nanorods produced by this technique are single crystalline and could emit intense visible light at room temperature, possibly due to some defects such as oxygen vacancies which got involved during growth. This study provides a simple and low-substrate-temperature route in fabricating V2O5 nanorods on planar substrates, which might be also applicable to other metal oxides.
Field emission properties of N-doped capped single-walled carbon nanotubes: A first-principles density-functional study
Authors: Qiao L. , Zheng W. T. , Xu H. , Zhang L. , Jiang Q.
Published: April 2007

The geometrical structures and field emission properties of pristine and N-doped capped (5,5) single-walled carbon nanotubes have been investigated using first-principles density-functional theory. The structures of N-doped carbon nanotubes are stable under field emission conditions. The calculated work function of N-doped carbon nanotube decreases drastically when compared with pristine carbon nanotube, which means the enhancement of field emission properties. The ionization potentials of N-doped carbon nanotubes are also reduced significantly. The authors analyze the field emission mechanism in terms of energy gap between the lowest unoccupied molecular orbital and the highest occupied molecular orbital, Mulliken charge population, and local density of states. Due to the doping of nitrogen atom, the local density of states at the Fermi level increases dramatically and donor states can be observed above the Fermi level. The authors’ results suggest that the field emission properties of carbon nanotubes can be enhanced by the doping of nitrogen atom, which are consistent with the experimental results.
Excited state absorption spectrum of chlorophyll a obtained with white-light continuum
Authors: De Boni L. , Correa D. S. , Pavinatto F. J. , dos Santos D. S. , Mendonça C. R.
Published: April 2007

The study of excited state properties of chlorophyll a is a subject of foremost interest, given that it plays important roles in biological process and has also been proposed for applications in photonics. This work reports on the excited state absorption spectrum of chlorophyll a solution from 460to700nm, obtained through the white-light continuum Z-scan technique. Saturation of absorption was observed due to the ground state depletion, induced by the white-light continuum region that is resonant with the Q band of chlorophyll a. The authors also observed reverse saturation of absorption related to the excitation from the first excited state to a higher energy level for wavelengths below 640nm. An energy-level diagram, based on the electronic states of chlorophyll a, was employed to interpret their results, revealing that more states than the ones related to the Q and B bands participate in the excited state absorption of this molecule.
Low retaining force optical viewport seal
Authors: Kaltenhäuser Bernd , Kübler Harald , Chromik Andreas , Stuhler Jürgen , Pfau Tilman
Published: April 2007

We report on the experimental realization of an ultrahigh vacuum (UHV) indium sealing between a conflat knife edge and an optical window. The sealing requires a very low clamping force and thus allows for the use of very thin and fragile windows.
A statistical quasiclassical trajectory model for atom-diatom insertion reactions
Authors: Aoiz F. J. , Sáez Rábanos V. , González-Lezana T. , Manolopoulos D. E.
Published: April 2007

A statistical model based on the quasiclassical trajectory method is presented in this work for atom-diatom insertion reactions. The basic difference between this and the corresponding statistical quantum model (SQM) lies in the fact that trajectories instead of wave functions are propagated in the entrance and exit channels. Other than this the two formulations are entirely similar. In particular, it is shown that conservation of parity can be taken into account in a natural and precise way in the statistical quasiclassical trajectory (SQCT) model. Additionally, the SQCT model complies with the principle of detailed balance and overcomes the problem of the zero point energy in the products. As a test, the model is applied to the H3+ and H+D2 exchange reactions. The excellent agreement between the SQCT and SQM results, especially in the case of the differential cross sections, indicates that the effect of tunneling through the centrifugal barrier is negligible. The effect of ignoring quantum mechanical parity conservation is also investigated.
Stacking heterogeneity: A model for the sequence dependent melting cooperativity of duplex DNA
Authors: Grigoryan A. V. , Mamasakhlisov E. Sh. , Buryakina T. Yu. , Tsarukyan A. V. , Benight A. S. , Morozov V. F.
Published: April 2007

A microscopic Potts-like one-dimensional model with many particle interactions [referred as the generalized model of polypeptide chains (GMPCs)] is developed to investigate cooperativity of DNA sequence dependent melting. For modeling sequence, regular homogeneous sequences were arranged in heterogeneous blocks of various lengths. Within the framework of the GMPC the authors show that the inclusion of stacking interaction heterogeneity relative to homogeneous hydrogen bond interactions leads to an unexpected and quite remarkable increase in melting cooperativity for small blocks. In some cases this tendency persists for long blocks having sharp sequence heterogeneity.
Midinfrared photoreflectance study of InAs-rich InAsSb and GaInAsPSb indicating negligible bowing for the spin orbit splitting energy
Authors: Cripps S. A. , Hosea T. J. C. , Krier A. , Smirnov V. , Batty P. J. , Zhuang Q. D. , Lin H. H. , Liu Po-Wei , Tsai G.
Published: April 2007

The authors report on midinfrared photoreflectance measurements of the band gap (E0) and spin-orbit splitting energies (Δ0) in InAs-rich InAsSb and GaInAsPSb samples for varying antimony contents ⩽22.5%. The E0 behavior as a function of Sb content is consistent with the literature value bowing parameter of ∼670meV. However, Δ0 does not exhibit the positive bowing of +1170meV quoted in the literature: rather, a best fit to their data tentatively suggests a negative bowing of −225meV. This result is likely to have strong impact due to the importance of the Δ0 parameter in governing InAsSb-based device performance.
Effect of gate-source and gate-drain Si3N4 passivation on current collapse in AlGaN∕GaN high-electron-mobility transistors on silicon
Authors: Arulkumaran S. , Ng G. I. , Liu Z. H.
Published: April 2007

The effects of gate-source (GS) and gate-drain (GD) region passivation on the drain current (ID) collapse in AlGaN∕GaN high-electron-mobility transistors (HEMTs) were studied. Electrical stresses were applied to the GS and GD regions of HEMTs, (1) unpassivated (device A), (2) fully passivated (device B), (3) GD passivated only (device C), and (4) device C with additional full passivation (device D). An increase of ID density and the extrinsic transconductance was observed in devices with full Si3N4 passivation. Due to the increase of gate leakage current by Si3N4 passivation, breakdown voltage decreases. Device A exhibited severe (96%) ID collapse when it was electrically stressed in both the GS and GD regions. Devices C and D have suppressed only 14% of ID collapse after passivation. However, HEMTs with full Si3N4 passivation (device B) have suppressed more than 80% of the ID collapse. Full passivation is required to suppress the ID collapse effectively for AlGaN∕GaN HEMTs. The remaining ID collapse (19%) of device B is affected primarily by bulk/buffer related traps rather than surface related traps.
Huge positive magnetoresistance in an InN film
Authors: Liang C.-T. , Sun Zhi-Hao , Hsiao Ching-Lien , Hsu M. Z. , Tu Li-Wei , Lin Jyun-Ying , Chen Jing-Han , Chen Y. F. , Wu Chien Ting
Published: April 2007

The authors report on magnetoresistance measurements on an InN film grown by molecular beam epitaxy. The application of a low magnetic field (B≈0.15T) perpendicular to their InN film causes striking huge positive magnetoresistance (PMR) of up to ∼106%. This PMR shows a strong temperature dependence and therefore their device can also be used as a temperature sensor. The authors’ experimental data pave the way for integrating magnetic sensors with optoelectronic devices using the same nonmagnetic material system which is not susceptible to ferromagnetic noise.
High efficiency phosphorescent organic light emitting diodes using triplet quantum well structure
Authors: Kim Sung Hyun , Jang Jyongsik , Hong Jae-Min , Lee Jun Yeob
Published: April 2007

Light emission in phosphorescent quantum well structure which can confine excitons within an emitting layer was investigated. A multilayer quantum well structure which has a narrow triplet band gap host material sandwiched between wide triplet band gap host materials was designed, and device performances were studied. The multilayer emitting structure gave high efficiency of 47cd∕A compared with 11cd∕A of standard green devices.
Nanocarbon counterelectrode for dye sensitized solar cells
Authors: Ramasamy Easwaramoorthi , Lee Won Jae , Lee Dong Yoon , Song Jae Sung
Published: April 2007

Nanosize carbon powders were deposited on conducting glass substrate for counterelectrode application in dye sensitized solar cell (DSSC). Electrochemical impedance measurement shows that charge transfer resistance of carbon electrode in liquid electrolyte is 0.74Ωcm−2, which is two times less than that of screen printed platinum. Using such counterelectrode and dye sensitized TiO2 working electrode, DSSC was fabricated. Under one sun illumination (AM1.5, Pin of 100mWcm−2), carbon counterelectrode DSSC shows 6.73% overall energy conversion efficiency with good stability.
Dipole formation at direct-contact HfO2∕Si interface
Authors: Abe Yasuhiro , Miyata Noriyuki , Shiraki Yasuhiro , Yasuda Tetsuji
Published: April 2007

Direct-contact HfO2∕Si interfaces, which have virtually no interfacial SiO2 layer, exhibit characteristic interface-charge distribution. The authors report that direct-contact interfaces demonstrate a negative flatband-voltage shift that is reduced by the insertion of a ∼0.5-nm-thick Si-oxide layer. The authors propose that the observed flatband-voltage shift is mainly caused by an electrostatic dipole (∼0.5V) formed at the HfO2∕Si interface rather than fixed charges. The effects of the dipole on leakage current are also discussed.
Thermal reversal of exchange spring composite media in magnetic fields
Authors: Goll D. , Macke S. , Bertram H. N.
Published: April 2007

For exchange coupled composite particles composed of a soft and a hard magnetic layer, the minimum energy paths between equilibrium states of the hysteresis loops are calculated using a path approach based on the nudged elastic band method. From the minimum energy paths the energy barriers for thermal reversal are determined as a function of the applied magnetic field. The field dependence of the energy barrier can be described approximately by power laws. Until reaching the saddle point for thermal reversal a domain wall is nucleated and compressed to the width of a wall propagating through a hard magnetic reference particle.
Additive color mixture of emission from InGaN∕GaN quantum wells on structure-controlled GaN microfacets
Authors: Ueda M. , Kondou T. , Hayashi K. , Funato M. , Kawakami Y. , Narukawa Y. , Mukai T.
Published: April 2007

Altering the mask geometry controls the apparent emission color from InGaN∕GaN quantum wells (QWs) grown on GaN microfacets formed by regrowth on SiO2 mask stripes over a wide spectral range, including white. The mask stripes are along the ⟨11¯00⟩ direction and the microfacet structure is composed of the (0001) and {112¯2} planes. With a large occupancy of the mask opening within a period, both facets simultaneously appear and emit different colors. For example, the {112¯2} facet QWs emit blue and the (0001) facet QWs emit green. On the other hand, with a small occupancy of the mask opening, the {112¯2} facets become dominant and a greenish-blue light is emitted. To synthesize these spectra, the mask patterns are designed so that two different microfacet structures are included within a period. Hence, the macroscopically observed emission color, which depends on the pattern design, can change from green to purple through white due to the additive color mixture.
Polymer thin film transistors with self-aligned gates fabricated using ink-jet printing
Authors: Li S. P. , Newsome C. J. , Kugler T. , Ishida M. , Inoue S.
Published: April 2007

Polymer thin film transistors (TFTs) with self-aligned gates have been fabricated by using a one step prepatterning technique in combination with ink-jet printing. The TFTs the authors show here are of the bottom gate configuration, whereby the gate electrode dimensions are defined by microembossing a polymer film which is supported by another polymer layer acting as a buffer. The deposition of the aluminium gates into the depressions of the embossed film was realized by thermal evaporation and subsequent lift-off technique. The buffer layer was then etched by using the gate electrodes as mask to create a thickness contrast. By taking the advantage of this thickness contrast a self-assembled molecule monolayer was applied by soft-contact printing on a spin coated dielectric layer to generate a series of banks with a sufficiently high wetting contrast for subsequent ink-jet deposition of the source and drain electrodes. Self-aligned bottom gated TFTs with channel lengths from several to several tens of micrometers have been fabricated. For TFTs with poly(9,9-dioctylfluorene-co-bithiophene) as an active layer, a hole mobility of 4.5×10−3cm2V−1s−1 and an on/off current ratio of 104 was achieved. By using a similar process TFTs with self-aligned top gates have also been fabricated.
Unveiling the morphology of buried In(Ga)As nanostructures by selective wet chemical etching: From quantum dots to quantum rings
Authors: Ding Fei , Wang Lijuan , Kiravittaya Suwit , Müller Elisabeth , Rastelli Armando , Schmidt Oliver G.
Published: April 2007

The three-dimensional morphology of In(Ga)As nanostructures embedded in a GaAs matrix is investigated by combining atomic force microscopy and removal of the GaAs cap layer by selective wet etching. This method is used to investigate how the morphology of In(Ga)As quantum dots changes upon GaAs capping and subsequent in situ etching with AsBr3. A wave function calculation based on the experimentally determined morphologies suggests that quantum dots transform into quantum rings during in situ etching.
Use of an asymmetric pulse profile for higher crystalline volumes from excimer laser crystallization of amorphous silicon
Authors: Adikaari A. A. D. T. , Mudugamuwa N. K. , Silva S. R. P.
Published: April 2007

An excimer laser is used to crystallize amorphous silicon on glass to nanocrystalline silicon, yielding higher crystalline volumes than reported earlier, by modifying the laser pulse profile used for crystallization at a given energy density. An asymmetric, shorter pulse profile, as opposed to the conventional Gaussian profile retains the desirable gradual leading edge of the Gaussian pulse for controlled evolution of hydrogen, while increasing the peak energy. The resultant films show an increased surface roughness along with higher crystalline volumes, which may be beneficial for photovoltaics and electron field emission cold cathodes.
Synthesis of Mn-doped zinc blende CdSe nanocrystals
Authors: Kwak Woo-Chul , Sung Yun-Mo , Kim Tae Geun , Chae Won-Seok
Published: April 2007

CdSe colloidal nanocrystals (∼3.7nm) with zinc blende structure were synthesized at a low temperature via an inverse micelle technique. They were successfully doped with ∼4at.% Mn, which was examined using inductively coupled plasma atomic emission spectroscopy. In spite of larger particle size (∼4.1nm), the Mn-doped CdSe nanocrystals showed an apparent blueshift in the UV-visible spectroscopy light absorption peaks. Considering the nanoparticle size and the effective energy band gap, the increase in the bulk energy band gap was estimated in the Mn-doped CdSe nanocrystals, which provides an obvious evidence of true Mn doping in the CdSe lattices.
Ring waveguide resonator on surface acoustic waves
Authors: Biryukov S. V. , Martin G. , Weihnacht M.
Published: April 2007

A simple regular electrode structure for surface acoustic wave (SAW) devices is proposed. The structure consists of an interdigital transducer in the form of a ring placed on the Z cut of a hexagonal piezoelectric crystal. Finite thickness electrodes produce the known slowing effect for a SAW in comparison with this SAW on a free surface. The closed “slow” electrode region with the “fast” surrounding region forms an open waveguide resonator structure with the acoustic field concentrated in the electrode region. If the radius of the structure is large enough for a given wavelength, an acceptable level of radiation losses can be reached. The electrical admittance of such resonator does not have sidelobes.
Improved hole-injection contact for top-emitting polymeric diodes
Authors: Li Juo-Hao , Huang Jinsong , Yang Yang
Published: April 2007

In this letter, an efficient hole-injection contact was achieved for the top-emitting polymeric light-emitting diodes (PLEDs). The anode has a structure of metal/molybdenum oxide/poly(3,4-ethylenedioxythiophene) poly(styrenesulfonate) (PEDOT:PSS). It has been found that hole injection was significantly improved by inserting a thin layer of MoO3 between aluminum and PEDOT:PSS. An ultraviolet photoelectron spectroscopy (UPS) was used to investigate the change of work function, and photovoltaic measurement confirmed that the improved hole injection is due to the reduction of barrier height, resulted from the addition of transition metal oxide. PEDOT:PSS layer was found necessary in anode structure to further enhance the hole injection and electroluminance efficiency. A peak power efficiency of 11.42lm∕W was achieved at current density of 1.2mA∕cm2 for the white emission top-emitting PLEDs.
Ce
3
+
∕
Eu
2
+
codoped Ba2ZnS3: A blue radiation-converting phosphor for white light-emitting diodes
Authors: Yang Woan-Jen , Chen Teng-Ming
Published: April 2007

The Ce3+∕Eu2+ codoped Ba2ZnS3 phosphor shows intense blue absorption and tunable green-to-red emission. The energy transfer from Ce3+ to Eu2+ in this phosphor has been demonstrated to be a resonant type via an electric dipole-dipole mechanism. The Ba2ZnS3:Ce3+,Eu2+ phosphor would be the great potential application as a blue radiation-converting phosphor for white light-emitting diodes.
Gas sensing using electrostatic force potentiometry
Authors: Koley G. , Qazi M. , Lakshmanan L. , Thundat T.
Published: April 2007

A highly sensitive potentiometric technique generally applicable for detection of gases utilizing adsorption-induced changes in surface work function is demonstrated. This technique is applied to sense hydrogen based on work function change of a Pt thin film. The surface work function changes of Pt upon exposure to pure and 1000ppm hydrogen were found to be ∼900 and ∼270mV, respectively. These work function changes are much higher than corresponding changes in the Schottky barrier height in Pt-semiconductor based amperometric sensor devices for similar hydrogen concentration. Using this technique, detection down to 8ppm hydrogen concentration is demonstrated.
Large scale microcomponents assembly using an external magnetic array
Authors: Ramadan Qasem , Uk Yoon Seung , Vaidyanathan Kripesh
Published: April 2007

Assembly of 2500 microcomponents has been accomplished in 5min with assembly yield of 97% by combining magnetic force, shape recognition, and vibration. The host substrate has been patterned with physical cavities having the shape of the target chip and positioned on top of a master substrate which is an 8in. wafer having array of magnets embedded in it. The chip has been modified by depositing a soft magnetic film (CoNiP) on its back side. By the competition between the magnetic force and the mechanical force, microcomponents have been assembled with their active side facing up.
Deterministic plasma-aided synthesis of high-quality nanoislanded nc-SiC films
Authors: Cheng Qijin , Xu S. , Long Jidong , Ostrikov Kostya (Ken)
Published: April 2007

Despite major advances in the fabrication and characterization of SiC and related materials, there has been no convincing evidence of the synthesis of nanodevice-quality nanoislanded SiC films at low, ultralarge scale integration technology–compatible process temperatures. The authors report on a low-temperature (400°C) plasma-assisted rf magnetron sputtering deposition of high-quality nanocrystalline SiC films made of uniform-size nanoislands that almost completely cover the Si(100) surface. These nanoislands are chemically pure, highly stoichiometric, have a typical size of 20–35nm, and contain small (∼5nm) nanocrystalline inclusions. The properties of nanocrystalline SiC films can be effectively controlled by the plasma parameters.
Scaling of dissipation in megahertz-range micromechanical diamond oscillators
Authors: Imboden Matthias , Mohanty Pritiraj , Gaidarzhy Alexei , Rankin Janet , Sheldon Brian W.
Published: April 2007

The authors report frequency and dissipation scaling laws for doubly clamped diamond resonators. The device lengths range from 10to19μm corresponding to frequency and quality-factor ranges of 17to66MHz and 600–2400, respectively. The authors find that the resonance frequency scales as 1∕L2 confirming the validity of the thin-beam approximation. The dominant dissipation comes from two sources: for the shorter beams, clamping loss is the dominant dissipation mechanism, while for the longer beams, surface losses provide a significant source of dissipation. The authors compare and contrast these mechanisms with other dissipation mechanisms to describe the data.
Long-term automated monitoring of the distribution of small carnivores
Authors: King C. M. , McDonald R. M. , Martin R. D. , Tempero G. W. , Holmes S. J.
Published: April 2007

A new automated monitoring device for small carnivores, the Scentinel®, is a ‘smart’ tracking tunnel. It records time, date, weight and a digital photograph of every animal visiting it, and stores the data to be downloaded on command. This paper describes a field trial aiming, first, to verify the Scentinel’s species identifications against those given by footprint tracking papers, and then to compare the efficacy of routine monitoring with the Scentinel against standard tunnel tracking methods. In February–April 2005 we identified to species 98% of 1559 visiting animals, mainly hedgehogs (Erinaceus europaeus), ferrets (Mustela furo), cats (Felis catus) and rats (Rattus rattus and R. norvegicus) in 1718 Scentinel-nights. In May–June 2005 we set up three monitoring lines 1 km apart, each with 10 tracking tunnels and two Scentinels. We recorded 656 visits by ship rats (Rattus rattus), 88% of them on only one of the three lines, in 198 Scentinel-nights (over 5 weeks). The 30 footprint tracking tunnels set intermittently (360 trap-nights) recorded high (70–100%) tracking rates on all lines. The presence of a stoat (Mustela erminea) was detected by both methods, but earlier by Scentinels than by tracking tunnels. These results confirm that it is possible to use automated devices to record detailed monitoring data on small carnivores in remote areas over long periods, unaffected by interference or bait loss from common non-target species.
Resource selection by grazing herbivores on post-fire regrowth in a West African woodland savanna
Authors: Klop Erik , van Goethem Janneke , de Iongh Hans H.
Published: April 2007

The preference of grazing herbivores to feed on grass regrowth following savanna fires rather than on unburnt grass swards is widely recognised. However, there is little information on which factors govern patterns of resource selection within burnt areas. In this study, we attempted to disentangle the effects of different habitat and grass sward characteristics on the utilisation of post-fire regrowth by nine species of ungulates in a fire-dominated woodland savanna in north Cameroon. We used resource-selection functions based on logistic regression. Overall, the resource-selection functions identified the time elapsed since burning as the most influential parameter in determining probability of use by ungulates, as most species strongly selected swards that were recently burned. This pattern might be related to nutrient levels in the grass sward. In addition, most species selected areas with high grass cover and avoided grass swards with high amounts of dead stem material. This is likely to increase bite mass and, hence, intake rates. The avoidance of high tree cover by some species may suggest selection for open areas with good visibility and, hence, reduced risk of predation. Body mass seemed to have no effect on differential selection of post-fire regrowth, irrespective of feeding style.
Bait consumption by, and 1080-based control of, feral pigs in the Mediterranean climatic region of south-western Australia
Authors: Twigg Laurie E. , Lowe Tim , Martin Gary
Published: April 2007

The consumption of five non-toxic, grain-based baits, and the effectiveness of the preferred baits when treated with 1080 in reducing pig numbers, were determined for feral pigs (Sus scrofa) in several areas in the Mediterranean agricultural region of Western Australia. Fermented wheat with added blood and bone proved an effective attractant for feral pigs, and for determining areas of pig activity. Wheat and malted barley were the preferred baits, there was a variable response to lupins, and commercial pig pellets were consumed least. Malted barley, barley, and wheat treated with 1080 gave good reductions in pig numbers at the localised scale. Where pigs would eat lupins, 1080-treated lupins were usually effective in reducing pig abundance. In some instances, further evidence of feral pig activity was not seen on several sites for several months after poison-baiting occurred. The addition of a small amount of unpoisoned grain to mask the presence of 1080 did not increase the take of treated bait (P < 0.05). Although finding poisoned pigs was difficult owing to the terrain and the presence of bush remnants, the poisoned pigs found (n = 90) were often within 200 m of active bait stations. 1080-poisoned pigs included both adult (≥25 kg) and non-adult pigs of both sexes. Body mass of these pigs ranged from 4 to 90 kg. In all, 42% of poisoned adults found (n = 50) were 50 kg or more. There was minimal evidence of bait take by non-target species, and, where this occurred, it generally involved the consumption of the fermented wheat attractant by kangaroos (Macropus spp.) and foxes (Vulpes vulpes). Six foxes were known to have been poisoned with 1080-treated grain (4 with malted barley, 2 with wheat). Excluding foxes, no other non-target animals, including native species, were found dead during the intensive searches for poisoned pigs.
Demonstration of artificial visual percepts generated through thalamic microstimulation
Authors: Pezaris John S. , Reid R. Clay
Published: April 2007

Electrical stimulation of the visual system might serve as the foundation for a prosthetic device for the blind. We examined whether microstimulation of the dorsal lateral geniculate nucleus of the thalamus can generate localized visual percepts in alert monkeys. To assess electrically generated percepts, an eye-movement task was used with targets presented on a computer screen (optically) or through microstimulation of the lateral geniculate nucleus (electrically). Saccades (fast, direct eye movements) made to electrical targets were comparable to saccades made to optical targets. Gaze locations for electrical targets were well predicted by measured visual response maps of cells at the electrode tips. With two electrodes, two distinct targets could be independently created. A sequential saccade task verified that electrical targets were processed not in motor coordinates, but in visual spatial coordinates. Microstimulation produced predictable visual percepts, showing that this technique may be useful for a visual prosthesis.
Transmembrane protein Sun2 is involved in tethering mammalian meiotic telomeres to the nuclear envelope
Authors: Schmitt Johannes , Benavente Ricardo , Hodzic Didier , Höög Christer , Stewart Colin L. , Alsheimer Manfred
Published: April 2007

Dynamic repositioning of telomeres is a unique feature of meiotic prophase I that is highly conserved among eukaryotes. At least in fission yeast it was shown to be required for proper alignment and recombination of homologous chromosomes. On entry into meiosis telomeres attach to the nuclear envelope and transiently cluster at a limited area to form a chromosomal bouquet. Telomere clustering is thought to promote chromosome recognition and stable pairing of the homologs. However, the molecular basis of telomere attachment and movement is largely unknown. Here we report that mammalian SUN-domain protein Sun2 specifically localizes to the nuclear envelope attachment sites of meiotic telomeres. Sun2–telomere association is maintained throughout the dynamic movement of telomeres. This association does not require the assembly of chromosomal axial elements or the presence of A-type lamins. Detailed EM analysis revealed that Sun2 is part of a membrane-spanning fibrillar complex that interconnects attached telomeres with cytoplasmic structures. Together with recent findings in fission yeast, our study indicates that the molecular mechanisms required for tethering meiotic telomeres and their dynamic movements during bouquet formation are conserved among eukaryotes.