bluuebunny/crossref_metadata_2025 huggingface dataset:
On the effect of 4f electrons on the structural characteristics of lanthanide trihalides: Computational and electron diffraction study of dysprosium trichloride
Authors: Lanza Giuseppe , Varga Zoltán , Kolonits Maria , Hargittai Magdolna
Published: February 2008

The molecular and electronic structure of dysprosium trichloride, DyCl3, was calculated by high-level quantum chemical methods in order to learn about the effect of the partially filled 4f subshell and of the possible spin-orbit coupling on them. High-temperature electron diffraction studies of DyCl3 were also carried out so that we could compare the computed geometry with the experimental one, after thermal corrections on the latter. Dysprosium monochloride, DyCl, and the dimer of dysprosium trichloride, Dy2Cl6, were also investigated by computation. We found that the electron configuration of the 4f subshell does not influence the geometry of the trichloride monomer molecule as the ground state and first excited state molecules have the same geometry. Nonetheless, taking the 4f electrons into account in the calculation, together with the 5s and 5p electrons, is important in order to get geometrical parameters consistent with the results from experiment. Based on electron diffraction and different levels of computation, the suggested equilibrium bond length (re) of DyCl3 is 2.443(14)Å, while the thermal average distance (rg) from electron diffraction is 2.459(11)Å. The molecule is trigonal planar in equilibrium. Although the ground electronic state splits due to spin-orbit coupling, the lowering of the total electronic energy is very small (about 0.025hartree) and the geometrical parameters are not affected. In contrast with the monomeric trichloride molecule, the bond angles of the dimer seem to be different for different electronic states, indicating the influence of the 4f electronic configuration on their structure. We carried out an anharmonic analysis of the out-of-plane vibration of the trichloride monomer and found that the vibration is considerably anharmonic at 39.5cm−1, compared with the 30.5cm−1 harmonic value.
Femtosecond pump-probe experiments on trapped flavin: Optical control of dissociation
Authors: Guyon Laurent , Tabarin Thibault , Thuillier Benoît , Antoine Rodolphe , Broyer Michel , Boutou Véronique , Wolf Jean-Pierre , Dugourd Philippe
Published: February 2008

Femtosecond pump-probe experiments are performed on flavin biomolecules isolated in an ion trap. Mass spectra of the photoinduced fragments show that the fragmentation pathways can be modified using two-color two-photon excitation. In particular, when an infrared probe pulse (810nm) is added subsequent to the first excitation step (excitation of the S1 state of flavin mononucleotide at 405nm), branching ratios between lumichrome and lumiflavin production are inverted relative to the single excitation case.
Cooperative motion of spheres arranged in periodic grids between two parallel walls
Authors: Bhattacharya Sukalyan
Published: February 2008

In this article, we analyze the collective motion of a two-dimensional periodic array of spheres in a slit-pore confined by two parallel planar walls. We determine the friction coefficient of the spheres when all particles move with the same velocity along a particular direction and cooperate with each other in their motion. In order to solve this many-body problem, we use Stokesian dynamics algorithm and resolve multiparticle hydrodynamic interactions in wall-bounded geometry. Apart from particle-particle interactions, we also recognize that the aforementioned collective motion of all particles creates a cumulative effect on the fluid medium. This effect is manifested as either a net induced flow for a periodic pressure field or an additional pressure gradient for quiescent fluid. In our analysis, we focus on both periodic pressure and no-flow conditions. For both cases, the hydrodynamic friction on the translating particles is calculated using our multiparticle Stokesian dynamics simulation. The simulation for the no-flow condition is relatively straightforward—we only need to compute the multiparticle hydrodynamic interactions in quiescent fluid. However, for the periodic pressure condition, the net induced flow dragged by the particles has to be evaluated also. We express this net induced flow in terms of an additional pressure-driven velocity field. We present the hydrodynamic friction as a function of the dimensions of the two-dimensional periodic lattice. For closely packed arrays, the results show a considerable reduction in friction coefficients that usually increase with interparticle distance. Hence, our work renders the theoretical justification for other recent findings that indicate the importance of interparticle mutual cooperation.
Energy level alignment at organic semiconductor/metal interfaces: Effect of polar self-assembled monolayers at the interface
Authors: Demirkan K. , Mathew A. , Weiland C. , Yao Y. , Rawlett A. M. , Tour J. M. , Opila R. L.
Published: February 2008

We determined the shifts in the energy levels of ∼15nm thick poly[2-methoxy-5-(2′-ethyl-hexyloxy)-1,4-phenylene vinylene] films deposited on various substrates including self-assembled monolayer (SAM) modified Au surfaces using photoelectron spectroscopy. As the unmodified substrates included Au, indium tin oxide, Si (with native oxide), and Al (with native oxide), a systematic shift in the detected energy levels of the organic semiconductor was observed to follow the work function values of the substrates. Furthermore, we used polar SAMs to alter the work function of the Au substrates. This suggests the opportunity to control the energy level positions of the organic semiconductor with respect to the electrode Fermi level. Photoelectron spectroscopy results showed that, by introducing SAMs on the Au surface, we successfully increased and decreased the effective work function of Au surface. We found that in this case, the change in the effective work function of the metal surface was not reflected as a shift in the energy levels of the organic semiconductor, as opposed to the results achieved with different substrate materials. Our study showed that when a substrate is modified by SAMs (or similarly by any adsorbed molecules), a new effective work function value is achieved; however, it does not necessarily imply that the new modified surface will behave similar to a different metal where the work function is equal to the effective work function of the modified surface. Various models and their possible contribution to this result are discussed.
Spin current studies in Fe∕Ag,Au∕Fe by ferromagnetic resonance and time-resolved magneto-optics
Authors: Kardasz B. , Mosendz O. , Heinrich B. , Liu Z. , Freeman M.
Published: February 2008

A precessing magnetization within a magnetic double layer acts as a peristaltic spin pump which transports spin momentum but no net electric charge. Crystalline Fe single layers Au∕12Fe∕GaAs(001) and double layers Fe12∕(Au,Ag)∕Fe16∕GaAs(001) were prepared by molecular beam epitaxy, where the integers represent the number of Fe atomic layers, and (Au,Ag) represents a set of gold and silver layers of different thicknesses. Ferromagnetic resonance (FMR) was used to investigate spin diffusion in thick Au layers in Au∕12Fe∕GaAs(001) samples. Time-resolved magneto-optical Kerr effect (TRMOKE) measurements are an ideal tool for investigating the propagation of spin currents in these structures. Spin currents generated by the bottom 16Fe layer propagated across the normal metal spacer and resulted in rf excitations in the top 12Fe film. Landau-Lifshitz-Gilbert equations of motion modified by spin pump and spin sink effects were used to interpret the FMR and TRMOKE measurements. The spin diffusion lengths in Au were Ag were found 34 and 170nm, respectively.
Magnetic properties of a metal-organic porous network [Ni2(BODC)2(TED)]
Authors: Yuen Tan , Danilovic D. , Li Kunhao , Li Jing
Published: February 2008

A new material [Ni2(BODC)2(TED)], (BODC=4,4′-bicyclo[2.2.2]octane dicarboxylate and TED=triethylene-4,4′-diamine), which is a guest-free, porous metal-organic coordination network, has been successfully synthesized. The crystal structure of this compound is tetragonal with the space group P4∕mmm. It is a three-dimensional network that can be deconstructed into rectangular gridlike layers along ab planes. These planes are formed by BODC and Zn2O4 paddle-wheel-like clusters, and the TED ligands from the axial directions of the paddle-wheels connect the layers into a three-dimesional structure. There are no guest molecules found in the pores. The shortest Ni–Ni distance within the paddle wheel is found to be 2.613Å. Magnetic susceptibility χ(T)=M(T)∕H and isothermal magnetization M(H) measurements have been measured on powder samples of this compound. The results of χ(T) show that there is a rapid increase in the susceptibility below 20K due to a spontaneous ordering of the Ni2+ moments. The effective moment μeff of Ni2+ is about 2.20μB at room temperature. The M(H) result at 1.8K shows a clear hysteresis with a coercivity of Hcoe≈1700G. The behavior of this compound is discussed in terms of Ni–Ni coupling within the Ni dimers and dimer chains.
Adaptive model-following control for slim voice coil motor type optical image stabilization actuator
Authors: Yu Hsing-Cheng , Liu T. S.
Published: February 2008

An autofocusing optical image stabilization actuator (AFOISA) will become standard equipment quickly in megapixel resolution mobile phone cameras (MPCs). A slim AFOISA composed of two orthogonal directions has been developed based on magnetic analysis and it is an effective solution to address image quality of a charged coupled device to compensate 10–20Hz hand jitter in taking photos. However, environmental disturbance often occur irregular shake, such as when a photographer holds a MPC while walking or in a vehicle. Therefore, this paper develops an adaptive model-following control (AMFC) law including two proportional-integral-derivative controllers with position and speed feedback control, which is shown to be able to compensate for irregular shake of MPCs and to obtain fast response. Although irregular environmental shake cause parameter variation, an adaptation mechanism synthesizes an auxiliary input signal to assure that an AFOISA plant exactly behaves as a reference model. The time response by utilizing AMFC includes 30ms settling time and 5μm steady state error without any overshoot. Furthermore, a compensatory force can quickly cancel irregular disturbance. As a result, the present slim AFOISA satisfies the optical demands of MPCs.
Third harmonic generation of a short pulse laser in a plasma density ripple created by a machining beam
Authors: Liu C. S. , Tripathi V. K.
Published: February 2008

An intense machining laser beam, impinged on a gas jet target, causes space periodic ionization of the gas and heats the electrons. The nonuniform plasma pressure leads to atomic density redistribution. When, after a suitable time delay, a second more intense laser pulse is launched along the periodicity wave vector q⃗, a plasma density ripple nq is instantly created, leading to resonant third harmonic generation when q=4ωp2∕(3ωcγ0), where ωp is the plasma frequency, ω is the laser frequency, and γ0 is the electron Lorentz factor. The third harmonic is produced through the beating of ponderomotive force induced second harmonic density oscillations and the quiver velocity of electrons at the fundamental. The relativistic mass nonlinearity plays no role in resonant coupling. The energy conversion efficiency scales as the square of plasma density and square of depth of density ripple, and is ∼0.2% for normalized laser amplitude ao∼1 in a plasma of 1% critical density with 20% density ripple. The theory explains several features of a recent experiment.
Electroluminescence imaging and microstructure of organic light-emitting field-effect transistors
Authors: Zaumseil Jana , Kline R. Joseph , Sirringhaus Henning
Published: February 2008

The effect of morphology and microstructure on the emission characteristics of ambipolar light-emitting field-effect transistors is studied using the polyfluorene copolymer F8BT [poly(9,9-di-n-octylfluorene-alt-benzothiadiazole)] as a model system. Different intensity distributions of the emission zones of amorphous, polycrystalline, and aligned F8BT films are demonstrated. Electroluminescence maps of the channel region are produced by overlaying a series of images recorded during gate voltage sweeps. They show a correlation to the microcrystalline structure of the F8BT and are assumed to visualize the current density distribution within the transistor channel.
Stacked triangular XY antiferromagnets: End of a controversial issue on the phase transition
Authors: Ngo V. Thanh , Diep H. T.
Published: February 2008

In this paper, we show, by using the Wang–Landau flat-histogram Monte Carlo method, that the phase transition in the XY stacked triangular antiferromagnet is clearly of first order, confirming results from latest Monte Carlo simulation and from a nonperturbative renormalization group, putting an end to a long-standing controversial issue.
Atomistic molecular dynamics simulations of model C36 fullerite
Authors: Abramo Maria C. , Caccamo C.
Published: February 2008

We report atomistic molecular dynamics investigations of a model C36 fullerite in which the fullerene molecules are modeled as rigid cages over which the carbon atoms occupy fixed interaction sites, distributed in space according to the experimentally known atomic positions in the molecule. Carbon sites belonging to different molecules are assumed to interact via a 12-6 Lennard–Jones–type potential; the parameters of the latter are employed in the framework of a molecular dynamics fitting procedure, through which the ambient condition physical quantities characterizing the hcp structure of solid C36 are eventually reproduced. We discuss applications of the adopted modelization to the C36 phases in a temperature range spanning from 300to1500K, and compare the obtained results to the available data for C36 and other fullerenes, and to the predictions of the well known Girifalco central potential modelization of interactions in fullerenes, as applied to the C36 case.
On the inviscid neutral curve of rotating Poiseuille pipe flow
Authors: Heaton C. J.
Published: February 2008

This paper concerns linear instabilities of incompressible flow along a rotating pipe when the disturbances are inviscid. The inviscid spectrum comprises an infinite number of eigenmodes, and significant complications arise from (i) switching in the identity of the most unstable mode and (ii) the existence of distinguished parameter limits in which some or all of the modes acquire special scalings. Nevertheless, we show that in one sense all the instabilities form a single ordered family, which we term a center-mode family, by applying an asymptotic theory recently developed for the trailing line vortex flow. We give complete computed neutral curves (stability boundaries) over a wide range of Rossby numbers, as well as contour plots of maximum growth rate. We find that the numerical calculations are in good agreement with the asymptotic theory and correctly recover previous results, including the limits of very large and very small Rossby number. There is some disagreement, however, with published results on the neutral curve at finite Rossby number. We show that this disagreement results from the intricate nature of the spectrum, which possesses two different types of neutral mode with two distinguished scalings.
Aliovalent B-site modification on three- and four-layer Aurivillius intergrowth
Authors: Wang Wei , Shan Dan , Sun Jia-bao , Mao Xiang-yu , Chen Xiao-bing
Published: February 2008

Electrical properties of Nb-, V-, and W-doped Bi4Ti3O12–MBi4Ti4O15 (BIT-MBTi) (M=Ca,Sr) compounds were investigated. The remanent polarization (2Pr) and piezoelectric coefficient (d33) of BIT-MBTi are greatly increased by such donor doping. W-doped and Nb-doped BIT-SBTi exhibited the greatest enlargement in 2Pr and d33, respectively. Nb doping also increases 2Pr and d33 of BIT-CBTi though not that much as in the BIT-SBTi case. BIT-CBTi thin film shows a high 2Pr value of 39μC∕cm2. The enhanced properties are thought to stem from the reduced concentration and weakened mobility of oxygen vacancies. Increased activation energy of conduction further confirmed the restraint of oxygen vacancies. The different optimal V-doping content for 2Pr and d33 in BIT-SBTi might be related to the fact that V doping could affect the structure and density of domain more apparently than the concentration of oxygen vacancies. The thermal variation of dielectric constant of BIT-CBTi shows a distinctive double anomaly at 658 and 728°C. The first dielectric anomaly is related to the regulation of BIT parts, and the second one corresponds to the ferroelectric-paraelectric phase transition.
First-principles study of the effect of nitrogen vacancies on the decomposition pattern in cubic Ti1−xAlxN1−y
Authors: Alling B. , Karimi A. , Hultman L. , Abrikosov I. A.
Published: February 2008

The effect of nitrogen substoichiometry on the isostructural phase stabilities of the cubic Ti1−xAlxN1−y system has been investigated using first-principles calculations. The preferred isostructural decomposition pattern in these metastable solid solutions was predicted from the total energy calculations on a dense concentration grid. Close to the stoichiometric Ti1−xAlxN1 limit, N vacancies increase the tendency for phase separation as N sticks to Al while the vacancies prefers Ti neighbors. For nitrogen depleated conditions, N sticks to Ti forming TiNδ (0<δ<1) while Al tends to form nitrogen-free fcc-Al or Al–Ti alloys.
One- and two-photon Absorptions in asymmetrically substituted free-base porphyrins: A density functional theory study
Authors: Chandra Jha Prakash , Minaev Boris , Ågren Hans
Published: February 2008

Electronic spectra and structures of a new family of free-base porphyrin (H2P) derivatives with 4-(diphenylamino)stilbene (DPAS) or 4,4′-bis-(diphenylamino)stilbene (BDPAS) asymmetric substituents, recently synthesized and studied by Drobizhev et al. [J. Phys. Chem. B 110, 9802 (2006)] are investigated by density functional theory (DFT) using modern density functionals and the 6-31G* basis set. The time-dependent DFT technique is applied for calculations of one- and two-photon absorption spectra, electric and magnetic dipole moments, and for prediction of electronic circular dichroism for these chiral molecules. The four-band absorption spectrum of the H2P molecule (Qx, Qy, 0-0 and 1-0 bands) is enhanced in single-bond-linked DPAS. This enhancement is explained by hyperconjugation of the almost orthogonal π systems and by small charge-transfer admixtures. The effect is much stronger for the double-bond- and triple-bond-linked DPAS and BDPAS substituents where absorption in the Q region transforms into a two-band spectrum. These molecules with ethenyl and ethynyl bonding of the porphyrin and donor substituent show very strong two-photon absorption in the near-infrared region. DFT calculations explain this by more efficient conjugation between the H2P and DPAS (BDPAS) chromophores, since they are almost coplanar: “Gerade” states of the H2P molecule occur in the Soret region and transform into charge-transfer states with nonzero transition moments. They are responsible for the strong two-photon absorption effects. Mixing of excitations in both chromophores explains the broadening of the Soret band. Though the calculated two-photon absorption cross sections are overestimated, the qualitative trends are reproduced and help understanding the whole genesis of spectra of these asymmetrically substituted H2P derivatives.
Highly collimated laser emission from a peanut-shaped microcavity
Authors: Shang Lei , Liu Liying , Xu Lei
Published: February 2008

Highly collimated laser emission from a largely deformed microcavity laser (peanut-shaped microcavity laser) was observed. Emission divergence of 2° was achieved. The microcavity laser was found to be operated on a hybrid lasing mode that formed with a combination of whispering gallery orbit and multiple-bouncing orbit.
High-frequency characterization of Permalloy nanosized strips using network analyzer ferromagnetic resonance
Authors: Kuanr Bijoy K. , Lopusnik Radek , Malkinski Leszek M. , Wenger Matt , Yu Minghui , Scherer Donald , Camley R. E. , Celinski Z.
Published: February 2008

We report on the dynamic properties of Permalloy nanostrips at gagahertz frequencies. The thickness of the strips is 100nm, strip width is 300nm, strip spacing is 1μm, and length is 0.3–100μm; aspect ratios are 1:1, 1:2, 1:3, 1:5, 1:10, and 1:333. The dynamic behavior was studied by network analyzer ferromagnetic resonance (FMR) using Permalloy strips on a coplanar waveguide in flip-chip geometry. The FMR mode frequencies (fr) can be controlled by the aspect ratio as well as by the applied magnetic field (H). In longer strips (1:10 and 1:333), the excitation frequencies show a soft mode behavior (Heff=990Oe) when the field is along the hard axis. However, along the easy axis (along the strip length), fr increases with applied field. At a field of 3kOe, fr values are almost independent of aspect ratio along the easy axis except for the 1:1 strip. Along the hard axis, the frequencies are strongly dependent upon the aspect ratio. We also observed that the frequency linewidths of the strips are dependent on the aspect ratio.
Synthesis and room-temperature ferromagnetism of Zn0.96Mn0.04O∕ZnO coaxial nanocable and Zn0.96Mn0.04O film
Authors: Wang D. F. , Park S. Y. , Lee Y. S. , Lee Y. P. , Li J. C. , Liu C.
Published: February 2008

Zn 0.96 Mn 0.04 O ∕ Zn O coaxial nanocable and Zn0.96Mn0.04O film were prepared by two-step method and magnetron sputtering, respectively. The x-ray diffraction analysis reveals that Mn is incorporated well into the wurtzite ZnO without formation of Mn or Mn oxide. The high resolution transmission electron microscopy image and the selected-area electron diffraction pattern demonstrate that both ZnO and Zn0.96Mn0.04O layers are single crystalline and an epitaxial growth is achieved between Zn0.96Mn0.04O and ZnO in the coaxial nanocable. The magnetic property measurements show that both Zn0.96Mn0.04O∕ZnO nanocable and Zn0.96Mn0.04O film are ferromagnetic at room temperature. Moreover, the saturated magnetization and the coercive field of Zn0.96Mn0.04O∕ZnO coaxial nanocable are larger than those of Zn0.96Mn0.04O film.
Characteristics of organic light-emitting diodes with conducting polymer anodes on plastic substrates
Authors: Huh Jin Woo , Kim Young Min , Park Young Wook , Choi Jin Hwan , Lee Jin Woo , Lee Jong Woo , Yang Jae Woong , Ju Sung Hoo , Paek Kyeong Kap , Ju Byeong Kwon
Published: February 2008

The fabrication of conducting polymer films by a screen-printing method and characterization of an organic light-emitting diode (OLED) implemented using these films as an anode on plastic substrates are reported. Organic transparent electrode materials containing poly(3,4-ethylenedioxythiophene) (PEDOT) doped with poly(styrenesulfonic acid) (PSS) (PEDOT:PSS) were used after the modification by a unique nanoparticle binder design. The electro-optical properties as well as mechanical stabilities of these films were measured. The OLED performances when employing these films were comparable to that of OLEDs using indium tin oxide (ITO) despite their relatively poor conductivity. An external quantum efficiency of the OLED using this anode is ∼3.5%, which is about twice as that of OLEDs using ITO. These results show that the organic transparent electrode of a conducting polymer film patterned by the screen-printing method is a potential candidate for an electrode of the flexible OLED.
Simultaneous three-wavelength depolarization measurements of clouds and aerosols using a coherent white light continuum
Authors: Somekawa Toshihiro , Yamanaka Chihiro , Fujita Masayuki , Galvez Maria Cecilia
Published: February 2008

Lidar (light detection and ranging) depolarization measurements were performed simultaneously at three wavelengths using a coherent white light continuum. The white light continuum ranging from the ultraviolet to the infrared region was generated by a focused 0.5 TW/100 fs pulse in a krypton gas cell at the atmospheric pressure. The lidar system consisted of three depolarization channels at 450, 550, and 800 nm. The observed depolarization ratios for each wavelength showed differences for clouds. These depolarization features in wavelength are discussed in terms of particle size and shape using T-matrix computations. The depolarization ratios at three wavelengths can be used to infer information on the size of the particles in clouds, assuming an ice crystal shape a priori. Also, the obtained size distributions from the three-wavelength depolarization ratios correspond with the changes in particle size indicated by changes in the Angstrom coefficient obtained by multiwavelength lidar techniques. This study demonstrated that the three-wavelength depolarization ratios provided additional information about the size and shape of clouds and aerosols.
First-order ferromagnetic to helimagnetic transition in MgMn6Ge6
Authors: Mazet T. , Ihou-Mouko H. , Malaman B.
Published: February 2008

The magnetic and magnetocaloric properties of the new HfFe6Ge6-type (P6/mmm) MgMn6Ge6 compound have been studied by magnetic measurements and powder neutron diffraction experiments. MgMn6Ge6 magnetically orders at TC∼345 K in a ferromagnetic easy-plane arrangement. At TAF∼235 K, it undergoes a first-order transition to a helical structure, characterized by a temperature dependent propagation vector k=⟨0,0,qz⟩ (qz∼0.116 reciprocal lattice units at 1.4 K), without structural modification. The Mn atoms carry a magnetic moment of about 2 μB. A metamagnetic transition with a low critical field (Hcr<1 T) is observed below TAF. At low temperature, both magnetic and magnetocaloric data strongly suggest that some kinds of intermediate noncollinear ferromagnetic arrangements are stabilized above the critical field while the pure ferromagnetic state is obtained for significantly higher magnetic fields (H>5 T). The magnitude of the magnetic entropy change at TC (−ΔSM∼20.5 mJ cm−3 K−1 for ΔH=5 T) is about 25% that of Gd metal. The magnetocaloric effect at the order-order transition is of opposite sign and of lower magnitude.
Charged particle stopping power effects on ignition: Some results from an exact calculation
Authors: Singleton Robert L.
Published: February 2008

A completely rigorous first-principles calculation of the charged particle stopping power has recently been performed by Brown, Preston, and Singleton (BPS). This calculation is exact to leading and next-to-leading order in the plasma number density, including an exact treatment of two-body quantum scattering. The BPS calculation is therefore extremely accurate in the plasma regime realized during the ignition and burn of an inertial confinement fusion capsule. For deuterium-tritium fusion, the 3.5MeV alpha particle range tends to be 20%–30% longer than most models in the literature have predicted, and the energy deposition into the ions tends to be smaller. Preliminary numerical simulations indicate that this increases the ρR required to achieve ignition.
Band structure built from oligomer calculations
Authors: Pomogaeva Anna , Kirtman Bernard , Gu Feng Long , Aoki Yoriko
Published: February 2008

A method to build accurate band structures of polymers from oligomer calculations has been developed. This method relies on systematic procedures for (i) assigning k values, (2) eliminating strongly localized molecular orbitals, and (iii) connecting bands across the entire Brillouin zone. Illustrative calculations are carried out at the HF/STO-3G level for trans-polyacetylene (PA), poly(para-phenylene) (PPP), and water chains. More stringent tests at several different levels are reported for polydiacetylene/polybutatriene.
A microfluidic refractive index sensor based on an integrated three-dimensional photonic crystal
Authors: Wu Jing , Day Daniel , Gu Min
Published: February 2008

We present the concept of using three-dimensional photonic crystals for refractive index sensing in a microfluidic channel. The sensors are based on a three-dimensional void channel photonic crystal fabricated by femtosecond laser writing in a polymer substrate. It is demonstrated that a change in the refractive index of the fluid in the microchannel results in a shift in the band gap or band gap defect position of the photonic crystal. According to Fourier transform infared spectroscopy of the photonic crystal sensor, a change of 6×10−3 in the refractive index of the fluid can be detected.
Deep level photothermal spectroscopy: Physical principles and applications to semi-insulating GaAs band-gap multiple trap states
Authors: Mandelis Andreas , Xia Jun
Published: February 2008

A coupled transport-rate theory of free photoexcited carrier densities and band-gap trap states in direct-gap semiconductors with fast band-to-band recombination rates is presented. The rate equations are decoupled and solved analytically by means of an adiabatic principle which leads to time gating of photothermal emission and capture transport processes between trap states and bandedges occurring with time constants much longer than the recombination lifetime. This theory exploits the adiabatic character of photoexcitation of nonequilibrium excess free carriers which attains steady-state distribution at times very short compared to trap emission and capture effects induced by thermal transport to and from the bandedges of the semiconductor. The theory accounts for the absorption of a sub-band-gap probe laser beam by free carriers (both electrons and holes) photogenerated by a super-band-gap laser beam, as well as absorption by nonequilibrium trapped carriers in the band-gap states due to thermal emission and capture events. The theory forms the basis of a new two-laser-beam deep level photothermal spectroscopy (DLPTS). The latter was implemented and tested on semi-insulating (SI)-GaAs. DLPTS and photocarrier radiometric signals were used to validate the theory. The generated experimental temperature-scanned photothermal spectra and time-resolved transients were fitted with the multiple-trap theory and yielded superpositions of energy levels and capture cross sections. It was found that the one-trap theory commonly used in conventional deep level transient spectroscopy based techniques, such as photoinduced transient spectroscopy, does not give a good fit to the experimental DLPTS spectrum. The methodology encompassing the adiabatic theory and combined DLPTS time-scanned transients and temperature-scanned spectra amounts to an analytical quantitative photothermal spectroscopy capable of noncontact all-optical probing of band-gap defect/impurity state energy distributions and capture cross sections in direct-gap semiconductors, and SI-GaAs in particular.
Influence of film thickness on texture and electrical and optical properties of room temperature deposited nanocrystalline V2O5 thin films
Authors: Singh Preetam , Kaur Davinder
Published: February 2008

Nanocrystalline V2O5 thin films have been grown at low temperature on glass substrates by dc magnetron sputtering using a vanadium metal target. Film thickness was found to have a great impact on the orientation, shape, and size of the crystallites of these films. X-ray diffraction (XRD) patterns of the films with a thickness of 110nm show a strong c-axis orientated crystal structure with a preferred (001) orientation, while those with a thickness of 315nm show mixed orientations (a-axis+c-axis). With further increase in film thickness, an a-axis orientation with predominant (200) reflection was observed in the XRD pattern. The shape of the crystallite changes from a rodlike to a bricklike structure with change in crystallographic orientation from (001) to (200). Atomic force microscopy results were also in agreement with the field emission scanning electron microscopy and XRD results. A direct correlation has been established between the semiconductor to metal transformation of V2O5 films and their crystallite size and orientation. The optical measurement also revealed a systematic band gap variation (from 2.50to2.20eV) with variation in film thickness.
Destruction of dimethyl methylphosphonate using a microwave plasma torch
Authors: Uhm Han S. , Cho Soon C. , Hong Yong C. , Park Yang G. , Park Ju S.
Published: February 2008

A microwave plasma torch with a microwave power of 1.2kW destroys dimethyl methylphosphonate (DMMP) with a destruction rate of 1.14l∕h, demonstrating a safe removal capability of stockpiled chemical weapons. The FTIR spectra of the discharge gas from DMMP destruction indicates near perfect elimination of DMMP when the proper amount of oxygen gas is added. This can be confirmed by the gas chromatography spectra, which show the disappearance of even intermediary compounds. The compactness and light weight of the microwave plasma torch provide an effective means of on-site removal of the chemical warfare agents found on a battlefield.
Giant stability enhancement of rare-earth implanted SiO2 light emitting devices by an additional SiON protection layer
Authors: Sun J. M. , Rebohle L. , Prucnal S. , Helm M. , Skorupa W.
Published: February 2008

The electrical stability of rare-earth implanted SiO2 light emitting devices was improved by using a SiON dielectric buffer layer in an indium tin oxide/SiON∕SiO2:Tb∕Si device structure. At the expense of a small increase of the electroluminescence threshold voltage, a large increase of the breakdown electric field from 7.5to10.5MV∕cm was obtained in the SiO2:Tb layer, and the maximum injection current density was increased by three orders of magnitude from 4mA∕cm2to4A∕cm2. The operation time of the electroluminescence devices was increased by more than three orders of magnitude at an injection current density of ∼4mA∕cm2. Our experimental results are consistent with a theoretical model proposed for designing a stable and efficient thin-film light emitting device containing double-stacked dielectric layers.
Photoluminescence enhancement in quaternary III-nitrides alloys grown by molecular beam epitaxy with increasing Al content
Authors: Fernández-Garrido S. , Pereiro J. , González-Posada F. , Muñoz E. , Calleja E. , Redondo-Cubero A. , Gago R.
Published: February 2008

Room temperature photoluminescence and optical absorption spectra have been measured in wurtzite InxAlyGa1−x−yN (x∼0.06, 0.02<y<0.27) layers grown by molecular beam epitaxy. Photoluminescence spectra show both an enhancement of the integrated intensity and an increasing Stokes shift with the Al content. Both effects arise from an Al-enhanced exciton localization revealed by the S- and W-shaped temperature dependences of the photoluminescence emission energy and bandwidth, respectively. Present results point to these materials as a promising choice for the active region in efficient light emitters. An In-related bowing parameter of 1.6eV was derived from optical absorption data.
Epitaxial Ni–Mn–Ga films deposited on SrTiO3 and evidence of magnetically induced reorientation of martensitic variants at room temperature
Authors: Heczko O. , Thomas M. , Buschbeck J. , Schultz L. , Fähler S.
Published: February 2008

Epitaxial Ni–Mn–Ga films were grown on SrTiO3 by sputter deposition. The films deposited at 673K are ferromagnetic and martensitic at room temperature. Pole figure measurements indicate that the twinned orthorhombic martensite microstructure of the film has a lower symmetry compared to bulk. Magnetically induced reorientation or magnetic shape memory effect is indicated by magnetization curve measurements. Though the overall extension of the film is constrained by a rigid substrate, the reorientation is possible due to the additional degree of freedom in the orthorhombic phase.
Effect of dc bias on pressure-induced depolarization of Pb(Nb,Zr,Sn,Ti)O3 ceramics
Authors: Dai Zhonghua , Xu Zhuo , Yao Xi
Published: February 2008

The polarization and depolarization of antiferroelectric Pb(Nb,Zr,Sn,Ti)O3 (PNZST) ceramics under a dc bias were studied in a hydraulic pressure from 0to250MPa. It is found that the antiferroelectric ceramic can be induced to a metastable ferroelectric state and that the ceramic at this ferroelectric state can be switched to the antiferroelectric state using hydraulic pressure. The hydraulic pressure to induce the transition from the ferroelectric to the antiferroelectric states increases with the positive and decreases with the negative dc bias. Based on the results, the pressure–electric field phase diagram for polarized PNZST ceramics was established.
Broad-stripe, single-mode, mid-IR interband cascade laser with photonic-crystal distributed-feedback grating
Authors: Kim C. S. , Kim M. , Bewley W. W. , Lindle J. R. , Canedy C. L. , Nolde J. A. , Larrabee D. C. , Vurgaftman I. , Meyer J. R.
Published: February 2008

We have demonstrated an electrically pumped photonic-crystal distributed-feedback laser with an interband cascade active region emitting at 3.3μm. At 78K, the stripe of width 400μm emits up to 67mW of cw power into a single spectral mode with side-mode suppression ratio ≈27dB. The full width at half maximum of the far-field divergence angle is ≈0.5°, which combined with the near-field profile yields an effective M2 of 1.7–2.0.
Designing liquid crystal alignment surfaces
Authors: Kitson S. C. , Edwards E. G. , Geisow A. D.
Published: February 2008

We have previously shown that tilted micron-scale posts can be used to generate uniform liquid crystal alignment. By considering the geometry and symmetry of individual surface features in more detail, we have been able to demonstrate finer control of alignment, eliminate the need for tilted structures, and show multidomain alignment.
Polarization beam splitting through an anisotropic metamaterial slab realized by a layered metal-dielectric structure
Authors: Zhao Junming , Chen Yan , Feng Yijun
Published: February 2008

We report a polarization beam splitter (PBS) utilizing the anomalous reflection and transmission of an anisotropic metamaterial slab. By properly design of the constitutive tensors of the slab, PBS is achieved with little dependence on incident angle and slab thickness. The realization of the proposed PBS in the optical range is achieved by layered metal-dielectric nanostructured system, which could be modeled as an effective anisotropic metamaterial with the desired constitutive tensors. The full-wave electromagnetic simulation has confirmed the optical polarization splitting with an extinction ratio of over 20dB by a slab of an alternating silver and silicon carbide multilayer.
Over 40% transverse Kerr effect from Ni80Fe20
Authors: Allwood D. A. , Seem P. R. , Basu S. , Fry P. W. , Gibson U. J. , Cowburn R. P.
Published: February 2008

We show how mixed s- and p-polarized light incident on a ferromagnetic surface yields large transverse magneto-optical Kerr effect (MOKE) signals. Fractional MOKE signals of over 40% could be achieved from transverse magnetization changes in 35nm thick Ni80Fe20, an increase of over two orders of magnitude compared with the standard MOKE configuration. Transverse MOKE signals from patterned structures were also improved by an order of magnitude. Calculations of the magneto-optical interaction show how changing the incident polarization controls the Kerr rotation and reflected beam intensity for opposite magnetization orientations.
Structural, elastic, and electronic properties of Fe3C from first principles
Authors: Jiang C. , Srinivasan S. G. , Caro A. , Maloy S. A.
Published: February 2008

Using first-principles calculations within the generalized gradient approximation, we predicted the lattice parameters, elastic constants, vibrational properties, and electronic structure of cementite (Fe3C). Its nine single-crystal elastic constants were obtained by computing total energies or stresses as a function of applied strain. Furthermore, six of them were determined from the initial slopes of the calculated longitudinal and transverse acoustic phonon branches along the [100], [010], and [001] directions. The three methods agree well with each other; the calculated polycrystalline elastic moduli are also in good overall agreement with experiments. Our calculations indicate that Fe3C is mechanically stable. The experimentally observed high elastic anisotropy of Fe3C is also confirmed by our study. Based on electronic density of states and charge density distribution, the chemical bonding in Fe3C was analyzed and was found to exhibit a complex mixture of metallic, covalent, and ionic characters.
Spirobifluorene molecular films investigated by means of near infrared-vacuum ultraviolet spectroscopic ellipsometry
Authors: Silaghi Simona D. , Spehr Till , Cobet Christoph , Saragi Tobat P. I. , Werner Christoph , Salbeck Josef , Esser Norbert
Published: February 2008

Thin films of spirobifluorene-type materials, namely, spiro-octo1 and spiro-octo2, were investigated by means of spectroscopic ellipsometry in a broad spectral range from near-infrared to vacuum ultraviolet. The optical response of the amorphous organic films was described by an isotropic layer model based on Tauc–Lorentz functions. The dielectric functions of both types of organic films were determined. The strongest light absorption occurs around 6eV for both types of organic films. The more effective π-conjugation of spiro-octo2 redshifts by 160meV the absorption edge compared to Spiro-Octo1.
Crystal rotation in Cu single crystal micropillars: In situ Laue and electron backscatter diffraction
Authors: Maaß R. , Van Petegem S. , Grolimund D. , Van Swygenhoven H. , Kiener D. , Dehm G.
Published: February 2008

In situ microdiffraction experiments were conducted on focused ion beam machined single crystal Cu pillars oriented for double slip. During deformation, the crystal undergoes lattice rotation on both the primary and critical slip system. In spite of the initial homogeneous microstructure of the Cu pillar, rotation sets in already at yield and is more important at the top of the pillar than at the bottom, demonstrating the inhomogeneous stress state during a microcompression experiment. The rotation results are confirmed by electron backscatter diffraction measurements.
Electric-field tuning s-d exchange interaction in quantum dots
Authors: Li X. J. , Chang Kai
Published: February 2008

We investigate theoretically the electron-hole pair states in CdTe quantum dot (QD) containing a single Mn2+ ion by the magneto-optical spectrum tuned by the electric field. It is shown that the electric field does not only tune the spin splitting via the sp-d exchange interaction but also affect significantly the anticrossing behavior in the photoluminescence spectrum. This anticrossing is caused by the s-d exchange interaction and/or the hole mixing effect, which depends sensitively on the shape of the QD.
Deposition of controllable preferred orientation silicon films on glass by inductively coupled plasma chemical vapor deposition
Authors: Li Junshuai , Wang Jinxiao , Yin Min , Gao Pingqi , He Deyan , Chen Qiang , Li Yali , Shirai Hajime
Published: February 2008

An inductively coupled plasma (ICP) system with the adjustable distance between the inductance coil and substrates was designed to effectively utilize the spatial confinement of ICP discharge, and then control the gas-phase transport process. The effects of the gas phase processes on the crystallinity and preferred orientation of silicon films deposited on glass were systematically investigated. The investigation was conducted in the ICP-chemical vapor deposition process with the precursor gas of a SiH4∕H2 mixture at a substrate temperature of 350°C. Highly crystallized silicon films with different preferred orientations, (111) or (220), could be selectively deposited by adjusting the SiH4 dilution ratio [R=[SiH4]∕([SiH4]+[H2])] or total working pressure. When the total working pressure is 20Pa, the crystallinity of the silicon films increases with the increase of the SiH4 dilution ratio, while the preferred orientation was changed from (111) to (220). In the case of the fixed SiH4 dilution (10%), the silicon film with I(220)∕I(111) of about 3.5 and Raman crystalline fraction of about 89.6% has been deposited at 29.7nm∕min when the total working pressure was increased to 40Pa. At the fixed SiH4 partial pressure of 2Pa, the film crystallinity decreases and the preferred orientation is always (111) with increasing the H2 partial pressure from 18to58Pa. Atomic force microscope reveals that the film deposited at a relatively high H2 partial pressure has a very rough surface caused by the devastating etching of H atoms to the silicon network.
Safer heterosex: perspectives from young men in Ireland
Authors: Hyde Abbey , Drennan Jonathan , Howlett Etaoine , Brady Dympna
Published: February 2008

Background: Existing research indicates that large numbers of people do not consistently use condoms when embarking on sexual relationships and instead use unreliable social cues to determine whether a potential partner is likely to have a sexually transmissible infection. This article reports on an aspect of the first major piece of qualitative research that explored young people’s perspectives on sexuality in Ireland, and focuses on how young men made sense of risk when it came to sexual behaviour. Methods: Seventeen focus group interviews (collectively comprising 124 young men) were conducted with male secondary school pupils in Ireland, whose ages ranged from 14 to 19 years. Results: The data are structured around three themes that capture how study participants made sense of sexual safety. These themes are: (i) rumour, local hearsay and ‘knowing’ a potential partner; (ii) the social construction of the ‘slut’ category; and (iii) women as ‘bearers of disease’. Young women in the young men’s social group tended to acquire a specific sexual identity, not necessarily through any definitive evidence of their sexual history, but rather through their normative behaviours – dress, presentation, appearance and so forth. It was on this basis that the sexual status of a young woman was judged. Conclusions: Based on participants’ accounts, we conclude that notions of safer sex are not merely established in individual discussions between a couple embarking on a sexual relationship, but rather are produced discursively in the wider social setting beyond the sexual encounter.
The Clathrin Adaptor Gga2p Is a Phosphatidylinositol 4-phosphate Effector at the Golgi Exit
Authors: Demmel Lars , Gravert Maike , Ercan Ebru , Habermann Bianca , Müller-Reichert Thomas , Kukhtina Viktoria , Haucke Volker , Baust Thorsten , Sohrmann Marc , Kalaidzidis Yannis , Klose Christian , Beck Mike , Peter Matthias , Walch-Solimena Christiane
Published: February 2008

Phosphatidylinositol 4-phosphate (PI(4)P) is a key regulator of membrane transport required for the formation of transport carriers from the trans-Golgi network (TGN). The molecular mechanisms of PI(4)P signaling in this process are still poorly understood. In a search for PI(4)P effector molecules, we performed a screen for synthetic lethals in a background of reduced PI(4)P and found the gene GGA2. Our analysis uncovered a PI(4)P-dependent recruitment of the clathrin adaptor Gga2p to the TGN during Golgi-to-endosome trafficking. Gga2p recruitment to liposomes is stimulated both by PI(4)P and the small GTPase Arf1p in its active conformation, implicating these two molecules in the recruitment of Gga2p to the TGN, which ultimately controls the formation of clathrin-coated vesicles. PI(4)P binding occurs through a phosphoinositide-binding signature within the N-terminal VHS domain of Gga2p resembling a motif found in other clathrin interacting proteins. These data provide an explanation for the TGN-specific membrane recruitment of Gga2p.