bluuebunny/crossref_metadata_2025 huggingface dataset:
Electronic structure of TiS2 and its electric transport properties under high pressure
Authors: Liu Bao , Yang Jie , Han Yonghao , Hu Tingjing , Ren Wanbin , Liu Cailong , Ma Yanzhang , Gao Chunxiao
Published: March 2011

The electronic structure of TiS2 and its transport properties under high pressure have been studied using first-principles calculation and in situ transport parameters measurement. Both the theoretical and experimental results support the conclusion that TiS2 is a semimetal rather than a semiconductor and maintains its semimetallic behavior under high pressure. Although there is no significant change in density of state at Fermi level up to 20 GPa, the transport behavior change drastically at around 15 GPa, manifested by the change in the slope of resistivity and electronic concentration versus pressure curves. This pressure response of transport properties of TiS2 may be associated with conduction of pressure-induced ionization of impurity levels.
An atomically quantized hierarchy of shear transformation zones in a metallic glass
Authors: Ju J. D. , Jang D. , Nwankpa A. , Atzmon M.
Published: March 2011

Quasistatic measurements of room-temperature anelastic relaxation were used to characterize the properties of shear transformation zones (STZs) in amorphous Al86.8Ni3.7Y9.5 in the dilute limit. Using a combination of nanoindenter cantilever bending and mandrel bend relaxation techniques, anelastic relaxation was measured over times ranging from 1 s to 3 × 107 s. Direct spectrum analysis yields relaxation-time spectra, which display seven distinct peaks. The results were analyzed using a linear dashpot-and-spring model, combined with transition-state theory, to yield several STZ properties. These reveal a quantized hierarchy of STZs that differ from each other by one atomic volume. Potential STZs occupy a large volume fraction of the solid. They access their ergodic space, with the ratio of forward-to backward jump rates ranging from 1.03 to 4.3 for the range of stress values used.
Discrete breathers in nonlinear LiNbO3-type ferroelectrics
Authors: Giri Pradipta , Choudhary Kamal , Sengupta Arnab , Bandyopadhyay A. K. , Ray P. C.
Published: March 2011

Ferroelectric materials, such as lithium niobate, show interesting nonlinear hysteresis behavior that can be explained by a dynamical system analysis by using a nonlinear Klein- Gordon equation previously constructed from the Hamiltonian with Landau-Ginzburg two-well potential. In the discrete case [Phys. Rev. B 81, 064104 (2010)], the intrinsic localized modes were shown to exist above the linear modes. Nonlinearity and discreteness of domain structures in ferroelectrics slab domains arrayed in the x-direction lead to breather solutions under different values of controlling parameters, such as interaction between the domains and damping term mainly due to pinning effect. Different types of classical breather solution, namely Hamiltonian, dissipative and moving breather solutions are shown by numerical simulation with data on actual ferroelectric materials.
Probing the inter-tube transport in aligned and random multiwall carbon nanotubes
Authors: Bhatia Ravi , Prasad V. , Menon Reghu
Published: March 2011

The temperature and magnetic field dependence of conductivity has been used to probe the inter-tube transport in multiwall carbon nanotubes (MWNTs). The scanning electron microscopy images show highly aligned and random distribution of MWNTs. The conductivity in aligned carbon nanotube (ACNT) and random carbon nanotube (RCNT) samples at low temperature follows T1/2 (at T < 8 K) and T3/4 (at T > 8 K) dependence in accordance with the weak localization and electron-electron (e-e) interaction model. The values of diffusion coefficient in ACNT and RCNT are 0.25 × 10−2 and 0.71 × 10−2 cm2 s−1, respectively, indicating that larger number of inter-tube junctions in later enhances the bulk transport. The positive magnetoconductance (MC) data in both samples show that the weak localization contribution is dominant. However, the saturation of MC at higher fields and lower temperatures indicate that e-e interaction is quite significant in RCNT. The T−3/4 and T−1/2 dependence of inelastic scattering length (lin) in ACNT and RCNT samples show that the inelastic e-e scattering is more important in aligned tubes.
Plasmon hybridzation in coated metallic nanosphere
Authors: Zhang Yao , Fei Guang Tao , Zhang Li De
Published: March 2011

The plasmon frequencies of a general core/double-shell structure are studied by plasmon hybridization method, and three distinct plasmon modes (ω0, ω+, and ω−) are found, in which the value of ω0 is always stable, and ω+ as well as ω− is variable with the radius ratios. The influences of dielectric effect and permittivity difference between metallic core and outer-shell are also analyzed thoroughly. The origins of the stability and tunability of this core/double-shell structure are explored by comparing the charge densities and local field distributions at interfaces. Furthermore, our model can be simplified to different structures including metallic-core/dielectric-shell, dielectric-core/metallic-shell, metallic-core/metallic-shell and its complementary structures, of which the corresponding plasmon modes are also studied and compared with experimental results.
Synchronization of the bidirectionally coupled unified chaotic system via sum of squares method
Authors: Kim Cheol-Joong , Chwa Dongkyoung
Published: March 2011

This paper considers the synchronization problem of the bidirectionally coupled unified chaotic system. Many previous works require the assumption that the states of the system are bounded and their range are known. This assumption may not hold for arbitrary controllers, and thus, it is not suitable to make this assumption beforehand. Accordingly, we propose the novel control method for bidirectionally coupled unified chaotic system via sum of squares method without this assumption. Numerical simulations show the validity and advantage of the proposed method.
O K-energy loss near-edge structure change induced by tantalum impurity in monoclinic hafnium oxide
Authors: Yang Mino , Baik Hionsuck , Ivanovskaya Viktoria , Colliex Christian , Benayad Anass
Published: March 2011

The present paper reports the energy loss near-edge structure (ELNES) study of monoclinic HfO2 (m-HfO2) and tantalum doped m-HfO2 (Ta0.1Hf0.9O2) thin films prepared by radio frequency magnetron co-sputtering method. A change in the O K-ELNES spectra was observed as the amount of dopant increases. In order to precise the common features and the differences as a function of Ta defect nature (substitutional or interstitial) in HfO2, the O K-ELNES were commented with respect to density functional theory calculations implemented in Vienna ab initio simulation package code. The calculated Ta doped HfO2 band structure showed that substitutional tantalum is the dominant defect and the spectral differences between doped and non-doped HfO2 are mainly originated from the change in the local cation distribution around the oxygen atoms.
Optical design of organic light emitting diodes
Authors: Wang Z. B. , Helander M. G. , Xu X. F. , Puzzo D. P. , Qiu J. , Greiner M. T. , Lu Z. H.
Published: March 2011

Out-coupling of light from organic light emitting diodes (OLEDs) is a significant challenge for the application of OLEDs in solid state lighting. Most of the light is trapped in the stratified thin film structure and the glass substrate. In this study, an optical model is developed to simulate the optical electrical field for OLEDs with a stratified structure based on the dipole source term and transfer matrix approach. The exciton distribution is also considered in the proposed model. OLEDs with weak microcavity are selected to evaluate the model. Calculation of the electroluminescence spectrum, device efficiency as well as the angular dependence is shown to have a good agreement with the experimental data. Moreover, by using the weak microcavity design, an OLED of more than 70% improved efficiency is achieved.
Deactivation of A549 cancer cells in vitro by a dielectric barrier discharge plasma needle
Authors: Huang Jun , Chen Wei , Li Hui , Wang Xing-Quan , Lv Guo-Hua , Khohsa M. Latif , Guo Ming , Feng Ke-Cheng , Wang Peng-Ye , Yang Si-Ze
Published: March 2011

An inactivation mechanism study on A549 cancer cells by means of a dielectric barrier discharge plasma needle is presented. The neutral red uptake assay provides a quantitative estimation of cell viability after plasma treatment. Experimental results show that the efficiency of argon plasma for the inactivation process is very dependent on power and treatment time. A 27 W power and 120 s treatment time along with 900 standard cubic centimeter per minute Ar flow and a nozzle-to-sample separation of 3 mm are the best parameters of the process. According to the argon emission spectra of the plasma jet and the optical microscope images of the A549 cells after plasma treatment, it is concluded that the reactive species (for example, OH and O) in the argon plasma play a major role in the cell deactivation.
Sol-gel synthesis and properties of tin-doped lanthanum manganites
Authors: Tovstolytkin A. I. , Polek T. I. , V’yunov O. I. , Solopan S. A. , Belous A. G. , Lozenko A. F. , Trotsenko P. A.
Published: March 2011

The crystallographic, magnetic, electrical, and magnetoresistive properties of samples of La0.775Sr0.225Mn1−xSnxO3 synthesized by the sol-gel method are studied. It is shown that introducing tin atoms, with their large size, into the manganese sublattice produces significant deformations of the crystal lattice and enhances the structural and magnetic inhomogeneity of the samples. It is discovered that increasing the tin content leads to a reduction in magnetization, a lowering of the Curie temperature, and an increase in the electrical resistivity. The way the crystallographic parameters change is found to correlate with the character of the changes in the magnetic parameters. It is shown that the low-temperature magnetoresistance increases with x, while the magnetoresistance around room temperature is a nonmonotonic function of the tin concentration and has a maximum at x=0.015.
Time-resolved shadowgraphic study of femtosecond laser ablation of aluminum under different ambient air pressures
Authors: Wu Zehua , Zhu Xiaonong , Zhang Nan
Published: March 2011

Femtosecond pulse laser ablation of aluminum under different ambient air pressures between 1 atm and 4 × 10−4 Pa is investigated using a femtosecond time-resolved shadowgraphic method. It is observed that as the ambient air pressure decreases, the contact front becomes more and more distinct for a certain pressure range, demonstrating that the confinement effect of the ambient air to the ablated target material can play a critically important role in the laser ablation process. It is also found that the concentric and semicircular stripe pattern, which results from the diffraction of the probe beam by the expanding plume of a specific material state and is typically observed in the shadowgraphs for 1–2 ns delay time, gradually blurs and disappears while the ambient air pressure decreases from 1 atm to 7000 Pa. If a prepulse or a relatively large pulse pedestal exists before the main pulse, however, the stripe pattern can still be observed even though the ambient air pressure is 5 × 10-4 Pa. It is thus inferred that what contributes to the formation of the unique stripe pattern is a mixture of the ejected target material and ionized background gas induced by the femtosecond laser ablation.
The channel mobility degradation in a nanoscale metal–oxide–semiconductor field effect transistor due to injection from the ballistic contacts
Authors: Riyadi Munawar A. , Arora Vijay K.
Published: March 2011

The ballistic mobility degradation is shown to originate from nonstationary (transient) transport in response to the ohmic electric field. The source and drain reservoirs launch electrons into the channel with injection velocity transiting the channel with finite ballisticity defined as the probability of a collision-free flight. The distinction is made between the ballistic mean free path and that present in a long channel. The results are in excellent agreement with those obtained from Monte Carlo procedures and experiments.
Room-temperature spin photocurrent spectra at interband excitation and comparison with reflectance-difference spectroscopy in InGaAs/AlGaAs quantum wells
Authors: Yu J. L. , Chen Y. H. , Jiang C. Y. , Liu Y. , Ma H.
Published: March 2011

Spectra of the interband spin photocurrent due to Rashba and Dresselhaus spin splittings have been experimentally investigated in InGaAs/AlGaAs quantum wells at room temperature. The Rashba- and Dresselhaus-induced circular photogalvanic effect (CPGE) spectra are found to be quite similar in the spectral regions corresponding to the transitions 1e1hh (the first conduction to the first valence sub-band of heavy hole) and 1e2hh. The ratio of Rashba- and Dresselhaus-induced CPGE currents for the transition 1e1hh is estimated to be 4.95. The magnitude of the Rashba-induced CPGE current is up to several tens of nA/W for the transition 1e1hh, which is 1 order of magnitude larger than that obtained in GaN/AlGaN superlattices. Comparing the CPGE spectrum with reflectance-difference and photoreflectance spectra, we find that the large Rashba spin splitting is mainly induced by a large indium atom segregation effect and by the internal field in the quantum wells.
Phase transition and thermal expansion of hexafluoroethane
Authors: Klymenko N. A. , Galtsov N. N. , Prokhvatilov A. I.
Published: March 2011

X-ray studies of the lattice parameters of polycrystalline hexafluoroethane provide data on the linear and volume coefficients of thermal expansion in the low- and high-temperature phases for temperatures of 5–130K. The thermal expansion of the low-temperature monoclinic phase is found to be highly anisotropic. The expansion anisotropy is similar to that usually observed in laminar crystals. Strong damping of the diffraction pattern is observed in the high-temperature phase. It is proposed that this effect may be related to peculiarities in the lattice dynamics of C2F6 owing to a strong rotational-translational interaction. In this case, increased disorder associated with rising temperature, in both the orientational and translational subsystems of the crystal, becomes probable, as does the formation of a “dynamic glass” state at a certain time. A previously observed shift of the temperature of the orientational phase transition to 70K is explained. The contributions of the translational and rotational subsystems to the specific heat are analyzed thermodynamically. Indications of extremely strong disinhibition of torsional rotation of C2F6 are obtained, which ultimately leads to a structural phase transition. The temperature variation in the Grüneisen coefficient for the low-temperature phase of hexafluoroethane is found to be qualitatively similar to that observed for ethane and other simple molecular substances. This suggests that the lattice dynamics and scenarios for orientational disorder in the region of the phase transition are similar for these substances.
First-principles investigation of the adsorption of the 2,5-pyridine di-carboxylic acid onto the Cu(011) surface
Authors: Tranca D. C. , Keil F. J.
Published: March 2011

First-principles calculations within the density functional theory (DFT) framework have been performed in order to investigate various conformations of the 2,5-pyridine di-carboxylic acid (PDCA) molecule adsorbed onto the Cu(011) surface. By means of DFT calculations the adsorption geometry, the bond formation and the electronic properties of PDCA molecule conformations on the Cu(011) surface have been studied. The most important structural property is the orientation of the COOH H atom which can point either toward the aromatic ring or toward the vacuum. This H atom position determines the possible reactions in which the adsorbed molecule can get involved and also has a significant impact on the value of the Cu-molecule system work function. Thus, we find that simply by changing the H atom orientation (from up to down) the Cu-molecule system work function can be varied with more than 2.5 eV. This is a significant result as a lot of effort is put nowadays in finding efficient ways for the in situ variation of the systems work function. Scanning tunneling microscopy (STM) images, reflexion absorption infrared vibrational spectra (RAIRS) as well as various thermodynamic properties (adsorption entropies, enthalpies) have also been investigated in order to get a better insight into the system studied and to provide support to possible experimental studies (STM or RAIRS experiments).
Fiber optic probe hydrophone for the study of acoustic cavitation in water
Authors: Arvengas Arnaud , Davitt Kristina , Caupin Frédéric
Published: March 2011

We use focused ultrasound bursts to submit a liquid to mechanical tension. When the pressure in the sound wave reaches a sufficiently low value, vapor bubbles are nucleated in the bulk liquid. According to nucleation theory, increasing the ultrasound frequency increases the cavitation threshold by a calculable amount. To check this, we have built a fiber optic probe hydrophone based on one originally proposed by Staudenraus and Eisenmenger [Ultrasonics 31, 267 (1993)]. We have adapted the pressure calibration and data analysis of this tool to make it appropriate for precise measurements of tension in liquids. We are able to resolve the fractional change in the pressure threshold for cavitation in water that results from a twofold increase in the frequency. This provides a test of nucleation theory in general.
The isotropic remnant of the CO2 near-fully depolarized Raman 2ν3 overtone
Authors: Chrysos M. , Verzhbitskiy I. A. , Rachet F. , Kouzov A. P.
Published: March 2011

In a recent paper [M. Chrysos, I. A. Verzhbitskiy, F. Rachet, and A. P. Kouzov, J. Chem. Phys. 134, 044318 (2011)], we showed that, in CO2, the 2ν3 transition generates a Raman line spectrum that is 98% depolarized, a property in agreement with general symmetry rules. Here, we present an extensive analysis, experimental and theoretical, of the isotropic remnant of this overtone. The isotropic spectrum turned out to be 45 times less intense than its anisotropic counterpart and to have a moment that is 350 times smaller than the moment of the anisotropic spectrum, in excellent agreement with theoretical predictions. Once the measured intensity (along with other data exclusively experimental) was fed back into the formula of the moment, a value for the CO2 mean-polarizability asymmetric stretch derivative \documentclass[12pt]{minimal}\begin{document}$\partial ^{2}\bar{\alpha }/\partial q_{3}^{2}$\end{document}∂2α¯/∂q32 was returned that matches the best ab initio prediction to better than 4%. Agreement, in order of magnitude, was found between the intensity reported herein and that reported in the sole prior study of this overtone [G. Tejeda, B. Mat, and S. Montero, J. Chem. Phys. 103, 568 (1995)].
Evaluation of horizontal surface solar radiation levels in southern Nigeria
Authors: Dike V. N. , Chineke T. C. , Nwofor O. K. , Okoro U. K.
Published: March 2011

Solar energy, which is inexhaustible and abundant, has become an economically viable and environmentally preferable alternative to fossil fuels. There is the inherent advantage of solar energy in mitigation of climate change, generation of employment, and reduction of poverty, as well as increased energy security and supply. It is therefore important to continue to evaluate the global solar radiation levels in countries such as Nigeria with considerably high solar energy potential. In this paper, we report such evaluation for southern Nigeria; in particular, the correlations of meteorological estimates from National Aeronautics and Space Administration (NASA) and calculated Hargreaves estimates for this region of Nigeria (latitude of 4.75°–7.77°N and longitude of 3.33°–8.32°E) are carried out and the results show a good agreement in all the sites, thereby strengthening the case we make for decentralized renewable energy investments in the region.
Electron dynamics in the presence of an active medium incorporated in a Penning trap
Authors: Schächter Levi
Published: March 2011

Based on an idealized 1D model we demonstrate that electrons oscillating in a Penning trap may get bunched, at the resonant frequency of the active medium. During multiple round trips in the trap, the bunched electrons gain energy and, therefore, they may escape the trap forming a low energy optical injector.
Phase diagram and ferroelectric behaviors of BaTiO3 nanowires
Authors: Qiu J. H. , Ding J. N. , Yuan N. Y. , Cao H. X. , Wang X. Q. , Zhou Y.
Published: March 2011

A modified Landau-Ginzburg-Devonshire theory is developed to investigate the “diameter-temperature” phase diagram and the ferroelectric behaviors of BaTiO3 nanowires. Four phases, such as the Cubic phase, the Tetragonallike phase, the Orthorhombic phase, and the Monoclinic phase, are obtained. The ferroelectric phase transition temperatures are all depressed as the diameter decreases. A temperature-dependent critical diameter below which the polarization disappears is 0.8 nm at 0 K. Moreover, the magnitude and the direction of the polarization are strongly dependent on the diameter as well as the dielectric behaviors. Therefore, it can generate a specific direction of the polarization by controlling the diameter of the nanowires which may optimize the physical properties.
The polarizable embedding coupled cluster method
Authors: Sneskov Kristian , Schwabe Tobias , Kongsted Jacob , Christiansen Ove
Published: March 2011

We formulate a new combined quantum mechanics/molecular mechanics (QM/MM) method based on a self-consistent polarizable embedding (PE) scheme. For the description of the QM region, we apply the popular coupled cluster (CC) method detailing the inclusion of electrostatic and polarization effects into the CC Lagrangian. Also, we consider the transformations required to obtain molecular properties from the linear and quadratic response functions and provide an implementation for the calculation of excitation energies, one- and two-photon absorption properties, polarizabilities and hyperpolarizabilities all coupled to a polarizable MM environment. In the process, we identify CC densitylike intermediates that allow for a very efficient implementation retaining a computational low cost of the QM/MM terms even when the number of MM sites increases. The strengths of the new implementation are illustrated by property calculations on different systems representing the frontier of the capabilities of the CC/MM method. We combine our method with a molecular dynamics sampling scheme such that statistical averages of different excited state solvated properties may be obtained. Especially, we systematically investigate the relative importance of multipoles and polarizabilities in the description of two-photon absorption activity for formamide in aqueous solution. Also, we demonstrate the strengths of the CC hierarchies by incorporating correlation effects both at the CC2, CCSD, and at the triples level in the so-called PE-CCSDR(3) model. Finally, we utilize the presented method in the description of a full protein by investigating the shift of the intense electronic excitation energy of the photoactive yellow protein due to the surrounding amino acids.
Adsorption of CF4 on graphite preplated with a monolayer of CF3Cl
Authors: Thomas Petros , Velazquez Daniel , Hess George B.
Published: March 2011

We report a study of the adsorption of CF4 on graphite preplated with a monolayer of CF3Cl, using infrared reflection absorption spectroscopy combined with ellipsometry. The saturated vapor pressure of CF3Cl is nearly 3 orders of magnitude smaller than that of CF4 at the same temperature, so the main control variables are the temperature and the pressure (or chemical potential) of CF4, together with the initial coverage of CF3Cl. The temperature range covered is 60–105 K. We find that, if the initial monolayer of CF3Cl is liquid, CF4 continuously displaces CF3Cl by substitution in the monolayer. If the initial monolayer of CF3Cl is solid, due to either lower temperature or compression, CF4 condenses as a second layer on the top of the CF3Cl layer, with only slight mixing with the original layer. This behavior persists to multiple layers of CF4.
End-growth/evaporation living polymerization kinetics revisited
Authors: Semenov A. N. , Nyrkova I. A.
Published: March 2011

End-growth/evaporation kinetics in living polymer systems with “association-ready” free unimers (no initiator) is considered theoretically. The study is focused on the systems with long chains (typical aggregation number N ≫ 1) at long times. A closed system of continuous equations is derived and is applied to study the kinetics of the chain length distribution (CLD) following a jump of a parameter (T-jump) inducing a change of the equilibrium mean chain length from N0 to N. The continuous approach is asymptotically exact for t ≫ t1, where t1 is the dimer dissociation time. It yields a number of essentially new analytical results concerning the CLD kinetics in some representative regimes. In particular, we obtained the asymptotically exact CLD response (for N ≫ 1) to a weak T-jump (ε = N0/N − 1 ≪ 1). For arbitrary T-jumps we found that the longest relaxation time tmax  = 1/γ is always quadratic in N (γ is the relaxation rate of the slowest normal mode). More precisely tmax ∝4N2 for N0 < 2N and tmax ∝NN0/(1 − N/N0) for N0 > 2N. The mean chain length Nn is shown to change significantly during the intermediate slow relaxation stage t1 ≪ t ≪ tmax . We predict that $N_n(t)-N_n(0)\propto \sqrt{t}$Nn(t)−Nn(0)∝t in the intermediate regime for weak (or moderate) T-jumps. For a deep T-quench inducing strong increase of the equilibrium Nn (N ≫ N0 ≫ 1), the mean chain length follows a similar law, $N_n(t)\propto \sqrt{t}$Nn(t)∝t, while an opposite T-jump (inducing chain shortening, N0 ≫ N ≫ 1) leads to a power-law decrease of Nn: Nn(t)∝t−1/3. It is also shown that a living polymer system gets strongly polydisperse in the latter regime, the maximum polydispersity index r = Nw/Nn being r* ≈ 0.77N0/N ≫ 1. The concentration of free unimers relaxes mainly during the fast process with the characteristic time tf ∼ t1N0/N2. A nonexponential CLD dominated by short chains develops as a result of the fast stage in the case of N0 = 1 and N ≫ 1. The obtained analytical results are supported, in part, by comparison with numerical results found both previously and in the present paper.
Interaction of single-walled carbon nanotubes with poly(propyl ether imine) dendrimers
Authors: Jayamurugan G. , Vasu K. S. , Rajesh Y. B. R. D. , Kumar S. , Vasumathi V. , Maiti P. K. , Sood A. K. , Jayaraman N.
Published: March 2011

We study the complexation of nontoxic, native poly(propyl ether imine) dendrimers with single-walled carbon nanotubes (SWNTs). The interaction was monitored by measuring the quenching of inherent fluorescence of the dendrimer. The dendrimer–nanotube binding also resulted in the increased electrical resistance of the hole doped SWNT, due to charge-transfer interaction between dendrimer and nanotube. This charge-transfer interaction was further corroborated by observing a shift in frequency of the tangential Raman modes of SWNT. We also report the effect of acidic and neutral pH conditions on the binding affinities. Experimental studies were supplemented by all atom molecular dynamics simulations to provide a microscopic picture of the dendrimer–nanotube complex. The complexation was achieved through charge transfer and hydrophobic interactions, aided by multitude of oxygen, nitrogen, and n-propyl moieties of the dendrimer.
Unusual mechanism for H3+ formation from ethane as obtained by femtosecond laser pulse ionization and quantum chemical calculations
Authors: Kraus Peter M. , Schwarzer Martin C. , Schirmel Nora , Urbasch Gunter , Frenking Gernot , Weitzel Karl-Michael
Published: March 2011

The formation of H3+ from saturated hydrocarbon molecules represents a prototype of a complex chemical process, involving the breaking and the making of chemical bonds. We present a combined theoretical and experimental investigation providing for the first time an understanding of the mechanism of H3+ formation at the molecular level. The experimental approach involves femtosecond laser pulse ionization of ethane leading to H3+ ions with kinetic energies on the order of 4 to 6.5 eV. The theoretical approach involves high-level quantum chemical calculation of the complete reaction path. The calculations confirm that the process takes place on the potential energy surface of the ethane dication. A surprising result of the theoretical investigation is, that the transition state of the process can be formally regarded as a H2 molecule attached to a C2H42+ entity but IRC calculations show that it belongs to the reaction channel yielding C2H3+ + H3+. Experimentally measured kinetic energies of the correlated H3+ and C2H3+ ions confirm the reaction path suggested by theory.
Fabrication and magnetic properties of patterned NiFeMo films electrodeposited in self-assembled nanosphere templates
Authors: Zhou Quanguo , Heard Peter J. , Schwarzacher Walther
Published: March 2011

Large area patterned NiFeMo thin films possessing long-range order were fabricated by electrodeposition through a template consisting of a self-assembled close-packed monolayer of polystyrene nanospheres of diameter 390 nm. Unlike many methods, this process generates films possessing both two-dimensional in-plane periodicity and features of varying cross-section in the growth direction. As a consequence, the magnetic properties of the patterned NiFeMo films depend strongly on film thickness. Inhomogeneous magnetization reversal that can be explained by different regions having different effective in-plane coercivities was observed for films with thickness greater than the nanosphere radius, but not for films with lesser thickness. We also observed oscillations in the in-plane coercivity as a function of the film thickness with a period significantly different to that reported for NiFe and Co films prepared by a similar method [A. A. Zhukov et al., Appl. Phys. Lett. 88, 062511 (2006)].
Generation of plane shocks using intense heavy ion beams: Application to Richtmyer–Meshkov instability growth studies
Authors: Tahir N. A. , Shutov A. , Zharkov A. P. , Piriz A. R. , Stöhlker Th.
Published: March 2011

A design of a novel experiment that allows the generation of a well defined, steady, and strong plane shock wave employing an intense uranium ion beam that is incident on a wedge shaped compound target is presented. This technique will open up the possibility of carrying out unique high energy density physics experiments using these shock waves. One such experiment is to study the growth of Richtmyer–Meshkov instability in fluids as well as in solids, both in the linear and nonlinear regimes, as shown by detailed numerical simulations presented in this paper. The ion beam parameters used in this study correspond to those that will be available at the Facility for Antiprotons and Ion Research (FAIR) at Darmstadt.
Elastic stiffness of L1 FePt thin film studied by picosecond ultrasonics
Authors: Nakamura N. , Uranishi A. , Wakita M. , Ogi H. , Hirao M. , Nishiyama M.
Published: March 2011

The elastic stiffness of epitaxial and polycrystalline L10 FePt films is studied by picosecond ultrasonics coupled with x-ray reflectivity analysis, and we find that C33 of L10 FePt is 309 GPa. The morphology of FePt films shows dependence on the film thickness; as the film thickness increases the mazelike structure changes to a continuous film. The elastic stiffness correlates with the morphology change, and it increases as the film thickness increases. When the film thickness exceeds 40 nm, the elastic stiffness becomes independent of the film thickness, and we define the saturated value as C33 of L10 FePt.
Wavelength-sized GaAs optomechanical resonators with gigahertz frequency
Authors: Ding L. , Baker C. , Senellart P. , Lemaitre A. , Ducci S. , Leo G. , Favero I.
Published: March 2011

We report on wavelength-sized GaAs optomechanical disk resonators showing ultrastrong optomechanical interaction. We observe optical transduction of a disk mechanical breathing mode with 1.4 GHz frequency and effective mass of ∼2 pg. The measured vacuum optomechanical coupling rate reaches g0=0.8 MHz, with a related differential optomechanical coupling factor gom=485 GHz/nm. The disk Brownian motion is optically resolved with a sensitivity of 10−17 m/√Hz at room temperature and pressure.
New ab initio potential energy surface for BrH2 and rate constants for the H + HBr → H2 + Br abstraction reaction
Authors: Jiang Bin , Xie Changjian , Xie Daiqian
Published: March 2011

A global potential energy surface (PES) for the electronic ground state of the BrH2 system was constructed based on the multireference configuration interaction (MRCI) method including the Davidson's correction using a large basis set. In addition, the spin–orbit correction were computed using the Breit–Pauli Hamiltonian and the unperturbed MRCI wavefunctions in the Br + H2 channel and the transition state region. Adding the correction to the ground state potential, the lowest spin–orbit correlated adiabatic potential was obtained. The characters of the new potential are discussed. Accurate initial state specified rate constants for the H + HBr → H2 + Br abstraction reaction were calculated using a time-dependent wave packet method. The predicted rate constants were found to be in excellent agreement with the available experimental values and much better than those obtained from a previous PES.
Investigating the switching dynamics and multilevel capability of bipolar metal oxide resistive switching memory
Authors: Yu Shimeng , Wu Yi , Wong H.-S. Philip
Published: March 2011

HfO x / AlO x bilayer resistive switching devices were fabricated for the study of the switching dynamics of the metal oxide memory. An exponential voltage-time relationship was experimentally observed as follows: the programming pulse widths need for switching exponentially decreased with the increase in the programming pulse amplitudes. Two following programming schemes were proposed to modulate the high resistance state values: (1) exponentially increase the programming pulse width; (2) linearly increase the programming pulse amplitude. Although both of these schemes were effective to achieve the target resistance, the transient current response measurements suggest the second scheme consumes considerably less energy in the programming. A field-driven oxygen ions migration model was utilized to elucidate the above experimentally observed phenomenon.
Cloaking of a phase object in ghost imaging
Authors: Gan Shu , Zhang Su-Heng , Zhao Ting , Xiong Jun , Zhang Xiangdong , Wang Kaige
Published: March 2011

Ghost imaging is a nonlocal imaging technique in which the image or diffraction pattern of an object can be observed through the intensity correlation measurement other than the intensity itself. Here, we report the experimental observation of invisibility cloaking in ghost imaging with thermal light. We show that when two identical phase-modulated objects are placed at equal distances from the thermal light source, they are offset completely in ghost imaging. The experimental results can be understood through the phase conjugation established by the intensity correlation of thermal light.
Note: Fast, small, accurate 90° rotator for a polarizer
Authors: Shelton David P. , O’Donnell William M. , Norton James L.
Published: March 2011

A permanent magnet stepper motor is modified to hold a dichroic polarizer inside the motor. Rotation of the polarizer by 90° ± 0.04° is accomplished within 80 ms. This device is used for measurements of the intensity ratio for two orthogonal linear polarized components of a light beam. The two selected polarizations can be rapidly alternated to allow for signal drift compensation, and the two selected polarizations are accurately orthogonal.
The formation of an intense filament controlled by interference of ultraviolet femtosecond pulses
Authors: Wang Yongdong , Zhang Yisan , Chen Peng , Shi Liping , Lu Xin , Wu Jian , Ding Liang’en , Zeng Heping
Published: March 2011

We experimentally investigated the formation of a wavelength-scale photonic plasma grating induced by interference-assisted coalescence of two noncollinear ultraviolet femtosecond laser pulses. The period of the created plasma grating decreased with the crossing angle of the interacting laser pulses. For a proper small crossing angle, the noncollinear ultraviolet filaments were coalesced and an intense single ultraviolet filament was formed with a diameter of 5 μm which was below the focused limitation. This may provide a way to control ultraviolet femtosecond filamentation.
Relativistic multireference calculation of photodissociation of o-, m-, and p-bromofluorobenzene
Authors: Li Wen-Zuo , Chen Shu-Feng , Liu Ya-Jun
Published: March 2011

Quantum chemical calculations with relativistic effects were performed on the photodissociation of o-, m-, and p-bromofluorobenzene (o-, m-, and p-BrFPh) at 266 nm. The method of multistate second-order multiconfigurational perturbation theory in conjunction with spin–orbit interaction through complete active space state interaction was employed to calculate the potential energy curves for the ground and low-lying excited states of o-, m-, and p-BrFPh along their photodissociation reaction coordinates. The dissociation mechanisms with products of Br(2P3/2) and Br*(2P1/2) states were clarified with the computed potential energy curves and the surface crossings. The current calculations augmented previous theoretical investigations by including relativistic effects and resolved some differences of experimental assignment regarding the dissociation channels of o-, m-, and p-BrFPh.
Atomistic mechanisms of rapid energy transport in light-harvesting molecules
Authors: Ohmura Satoshi , Koga Shiro , Akai Ichiro , Shimojo Fuyuki , Kalia Rajiv K. , Nakano Aiichiro , Vashishta Priya
Published: March 2011

Synthetic supermolecules such as π-conjugated light-harvesting dendrimers efficiently harvest energy from sunlight, which is of significant importance for the global energy problem. Key to their success is rapid transport of electronic excitation energy from peripheral antennas to photochemical reaction cores, the atomistic mechanisms of which remains elusive. Here, quantum-mechanical molecular dynamics simulation incorporating nonadiabatic electronic transitions reveals the key molecular motion that significantly accelerates the energy transport based on the Dexter mechanism.
Surface reactions as carbon removal mechanism in deposition of silicon dioxide films at atmospheric pressure
Authors: Reuter R. , Ellerweg D. , von Keudell A. , Benedikt J.
Published: March 2011

The deposition of thin SiOxCyHz or SiOxHy films by means of an atmospheric pressure microplasma jet with helium/hexamethyldisiloxane (HMDSO)/O2 mixtures and the surface reactions involving oxygen have been studied. It is shown, that the carbon content in the film can be controlled by choosing the right O2/HMDSO ratio in the gas mixture. The microplasma jet geometry and localization of the deposition at a spot of few square millimeters allows studying the role of oxygen in the deposition process. This is done by alternating application of He/HMDSO plasma and He/O2 plasma to the same deposition area, here achieved by a treatment of a rotating substrate by two jets with above mentioned gas mixtures. It is shown that carbon-free SiOxHy film can be deposited in this way and that surface reaction with oxygen is the main loss mechanism of carbon from the film.
Enhanced Sb incorporation in InAsSb nanowires grown by metalorganic vapor phase epitaxy
Authors: Borg B. Mattias , Dick Kimberly A. , Eymery Joël , Wernersson Lars-Erik
Published: March 2011

We demonstrate metalorganic vapor phase epitaxy of InAs1−xSbx nanowires (x=0.08–0.77) for applications in high-speed electronics and long-wavelength optical devices. The composition of the InAsSb nanowires and InAsSb epilayers on the same sample is independently determined using lab-setup high resolution x-ray diffraction, by making use of the size-dependent in-plane broadening of the nanowire Bragg peak. We find that the incorporation of Sb into the nanowires is significantly higher than for planar epitaxy under the same growth conditions. Thermodynamic calculations indicate that this is due to a dramatically decreased effective V/III ratio at the particle/nanowire interface.
Ultrathin body InAs tunneling field-effect transistors on Si substrates
Authors: Ford Alexandra C. , Yeung Chun Wing , Chuang Steven , Kim Ha Sul , Plis Elena , Krishna Sanjay , Hu Chenming , Javey Ali
Published: March 2011

An ultrathin body InAs tunneling field-effect transistor on Si substrate is demonstrated by using an epitaxial layer transfer technique. A postgrowth, zinc surface doping approach is used for the formation of a p+ source contact which minimizes lattice damage to the ultrathin body InAs compared to ion implantation. The transistor exhibits gated negative differential resistance behavior under forward bias, confirming the tunneling operation of the device. In this device architecture, the ON current is dominated by vertical band-to-band tunneling and is thereby less sensitive to the junction abruptness. The work presents a device and materials platform for exploring III–V tunnel transistors.
Mechanism of Cs2CO3 as an n-type dopant in organic electron-transport film
Authors: Cai Y. , Wei H. X. , Li J. , Bao Q. Y. , Zhao X. , Lee S. T. , Li Y. Q. , Tang J. X.
Published: March 2011

The electronic structures of cesium carbonate (Cs2CO3) doped 4,7-diphenyl-1,10-phenanthroline (BPhen) films with various doping concentration are characterized by in situ ultraviolet and x-ray photoelectron spectroscopies, in an attempt to understand the mechanism of electron-transport enhancement in Cs2CO3-doped organic electron-transport layer for organic optoelectronic devices. The n-type electrical doping effect is evidenced by the Fermi level shift in the Cs2CO3-doped BPhen films toward unoccupied molecular states with increasing doping concentration, leading to increase in electron concentration in the electron-transport layer and reduction in electron injection barrier height. These findings originate from energetically favorable electron transfer from Cs2CO3 to BPhen.
Adhesion determines resonance response of piezoelectric cantilever sensors
Authors: Sharma Harsh , Mutharasan Raj
Published: March 2011

The response of resonant-mode cantilever sensors depends on the binding strength of analyte mass to the sensor surface. Comparison of cantilever response to attachment of three macrosized pieces: quartz [300 and 600 μg, water contact angle (Φ)=10°], silanized quartz (300 μg, Φ=99°), and polytetrafluoroethylene (1.5 mg, Φ=85°), with water and ethanol films indicates that the resonance frequency decrease is larger for higher liquid surface tension and lower contact angle. For example, quartz piece (1×1×0.160 mm3, L×W×H) weighing 300 μg caused a 1987±214 Hz (n=22) decrease in the resonance frequency with a water film while the hydrophobic silanized quartz caused a significantly lower frequency shift of 1218±187 Hz (n=22).
Surface orientation dependent band alignment for CuInSe2–ZnSe–ZnO
Authors: Hofmann Andreas , Pettenkofer Christian
Published: March 2011

The interface formation and band-lineup between ZnO and epitaxial CuInSe2 substrates is investigated with photoelectron spectroscopy. ZnO films prepared by a metal-organic molecular beam epitaxy process lead to the formation of an intrinsic ZnSe buffer layer. The effect of substrate orientation on the band alignment is studied for the orientations (112) and (001). We found a weak dependence of the interfacial dipole on orientation. Together with our findings for CuInS2 films, we suggest a ubiquitous CuInX2–ZnX–ZnO (X=Se, S) structure with an ultra-thin ZnX buffer layer for ZnO growth on chalcopyrites at elevated temperatures.
An experimental test of the toxicity of cereal pellets containing brodifacoum to the snails of Henderson Island, South Pacific
Authors: Brooke M. de L. , Cuthbert R. J. , Mateo R. , Taggart M. A.
Published: March 2011

Context
Cereal pellets containing the anti-coagulant poison brodifacoum at 20 ppm are routinely used to rid islands of invasive rodents. The impact, if any, of the poison on invertebrates is not well understood. This is problematic because many of the islands targeted for treatment harbour endemic invertebrate species, including snails where available information about brodifacoum impact is equivocal.

Aims
Combining field tests and subsequent laboratory analysis, the present study investigated the effect of brodifacoum on the snails of Henderson Island, South Pacific.

Methods
In the field, we housed snails in plastic boxes for up to 10 days to compare the survival of those kept with and without access to brodifacoum cereal pellets. Subsequently, we analysed brodifacoum levels in those kept with access to poisoned pellets, according to whether they survived or died.

Key results
There were no detectable differences in the survival between the captive snails kept with and those kept without access to brodifacoum. Among those with access, there were no significant differences in brodifacoum concentrations between the minority that died and the majority that survived. In fact, brodifacoum was detected in only a few samples.

Conclusions
Brodifacoum appears not to pose a risk to the snails of Henderson Island.

Implications
Although it would be prudent to test the impact of brodifacoum on the resident snails before proceeding with a rodent eradication on other islands, we suspect the Henderson results can be extended to other sites.