bluuebunny/crossref_metadata_2025 huggingface dataset:
Phase behaviors and ordering dynamics of diblock copolymer self-assembly directed by lateral hexagonal confinement
Authors: Xu Yuci , Xie Nan , Li Weihua , Qiu Feng , Shi An-Chang
Published: November 2012

The thermodynamics and kinetics of the self-assembly of cylinder-forming diblock copolymers directed by the lateral confinement of hexagons have been studied by the combination of self-consistent field theory (SCFT) calculation and time-dependent Ginzburg-Landau (TDGL) theory simulation. The SCFT calculations are used to determine the stability of candidate 2D and 3D equilibrium phases formed in small-size hexagons. Our phase diagram predicts the existence of stable phase regions with respect to the hexagonal size, which is centered around the optimal size with an extent of about a period, for the phases of perfect hexagonal cylinders. Our TDGL simulations reveal that the ordering event, in which the structure evolves toward the perfect state, occurs stochastically according to the Poisson distribution, and the ordering time grows roughly with a power-law relation of the hexagonal size. This prediction is helpful to estimate the annealing time for larger systems with the knowledge of the annealing time of a small system in experiments.
X-ray absorption from large molecules at metal surfaces: Theoretical and experimental results for Co-OEP on Ni(100)
Authors: Guo C. S. , Sun L. , Hermann K. , Hermanns C. F. , Bernien M. , Kuch W.
Published: November 2012

Metal octaethylporphyrins (M-OEP), M-N4C20H4(C2H5)8, adsorbed at a metallic substrate are promising candidates to provide spin dependent electric transport. Despite these systems having been studied extensively by experiment, details of the adsorbate geometry and surface binding are still unclear. We have carried out density functional theory calculations for cobalt octaethyl porphyrin (Co-OEP) adsorbate at clean and oxygen-covered Ni(100) surfaces as well as for the free Co-OEP molecule where equilibrium structures were obtained by corresponding energy optimizations. These geometries were then used in calculations of Co-OEP carbon and nitrogen 1s core excitations yielding theoretical excitation spectra to be compared with corresponding K-edge x-ray absorption fine structure (NEXAFS) measurements. The experimental NEXAFS spectra near the carbon K-edge of Co-OEP bulk material show large intensity close to the ionization threshold and a triple-peak structure at lower energies, which can be reproduced by the calculations on free Co-OEP. The experimental nitrogen K-edge spectra of adsorbed Co-OEP layers exhibit always a double-peak structure below ionization threshold, independent of the layer thickness. The peaks are shifted slightly and their separation varies with adsorbate-substrate distance. This can be explained by hybridization of N 2p with corresponding 3d contributions of the Ni substrate in the excited final state orbitals as a result of adsorbate-substrate binding via N–Ni bond formation.
Effect of electron correlation and shape resonance on photoionization from the S1 and S2 states of pyrazine
Authors: Suzuki Yoshi-Ichi , Suzuki Toshinori
Published: November 2012

In a previous study [T. Horio, T. Fuji, Y.-I. Suzuki, and T. Suzuki, J. Am. Chem. Soc. 131, 10392 (2009)10.1021/ja904780b], we demonstrated that the time–energy map of photoelectron angular anisotropy enables unambiguous identification of ultrafast S2(ππ*)–S1(nπ*) internal conversion in pyrazine. A notable characteristic of this map is that the forbidden ionization process of D0(n−1) ← S2(ππ*) gives a negative photoelectron anisotropy parameter. In the present study, we elucidate the mechanism of this process by calculating the photoionization transition dipole moments and photoelectron angular distribution using the first-order configuration interaction method and the continuum multiple scattering Xα approximation; these calculations at the S0 equilibrium geometry reproduce the observed anisotropy parameters for D0 ← S2 and D0 ← S1 ionizations, respectively. On the other hand, they do not reproduce the small difference in the photoelectron anisotropy parameters for the D1(π−1) ← S2 and D0 ← S1 ionizations, both of which correspond to removal of an electron from the same π* orbital in the excited states. We show that these ionizations are affected by the kag shape resonance and that the difference between their photoelectron anisotropy parameters originates from the difference in the molecular geometry in D1 ← S2 and D0 ← S1.
Growth of large domain epitaxial graphene on the C-face of SiC
Authors: Zhang Rui , Dong Yunliang , Kong Wenjie , Han Wenpeng , Tan Pingheng , Liao Zhimin , Wu Xiaosong , Yu Dapeng
Published: November 2012

Growth of epitaxial graphene on the C-face of SiC has been investigated. Using a confinement controlled sublimation (CCS) method, we have achieved well controlled growth and been able to observe propagation of uniform monolayer graphene. Surface patterns uncover two important aspects of the growth, i.e., carbon diffusion and stoichiometric requirement. Moreover, a new “stepdown” growth mode has been discovered. Via this mode, monolayer graphene domains can have an area of hundreds of square micrometers, while, most importantly, step bunching is avoided and the initial uniformly stepped SiC surface is preserved. The stepdown growth provides a possible route towards uniform epitaxial graphene in wafer size without compromising the initial flat surface morphology of SiC.
Two-current model of the composition dependence of resistivity in amorphous (Fe100−xCox)89−yZr7B4Cuy alloys using a rigid-band assumption
Authors: Shen S. , Ohodnicki P. R. , Kernion S. J. , McHenry M. E.
Published: November 2012

Composition dependence of resistivity is studied in amorphous (Fe100−xCox)89−yZr7B4Cuy (0 ≤ x ≤ 50, y = 0, 1) alloys. The two-current model proposed by Mott for crystalline materials is extended to a disordered amorphous system where s-d scattering is dominant in electron conduction. A rigid-band assumption is made due to the small atomic number difference between Fe and Co. Band structures with a constant density of states (DOS), parabolic distributed DOS, and Gaussian distributed DOS were investigated to fit experimental data. The Gaussian distributed DOS was found to simulate the resistivity maximum and magnetic moment maximum in the Fe-rich region. The basic concepts presented here can potentially provide insight into the optimization of FeCo-based HITPERM alloys for applications at increased frequencies.
Time-resolved emission of dye probes in a shock-compressed polymer
Authors: Brown Kathryn E. , Fu Yuanxi , Shaw William L. , Dlott Dana D.
Published: November 2012

Simultaneous impact velocity and time-resolved emission measurements are made on shocked poly-methylmethacryalate doped with rhodamine 640 (R640) dye. Planar single-stage shocks in the 0-16 GPa range are produced using a laser-driven flyer plate apparatus. This method allows for reproducible measurements of the time-resolved dye emission intensity, redshift, and spectral width monitored with 1 ns time resolution. The redshift is used to probe the shock front, which has a two-part viscoelastic structure. The maximum dye emission redshift under shock loading stops increasing above ∼6 GPa. In static high-pressure measurements, the redshift continues to increase up to at least 10 GPa. The smaller redshift seen in shock experiments is not an effect of the shock temperature increase, and it is attributed to incomplete polymer configurational relaxation frustrated by the short duration (<15 ns) of the shock. The viscous relaxation behind the shock front has a part whose rate increases with increasing shock pressure and a part that does not. It is this latter part that causes the shock-induced emission redshift to stop increasing above 6 GPa, and the differences between the two types of relaxation are explained in the context of the free-energy needed to surmount configurational barriers.
Boundary effect on the plasticity and stress of lithiated silicon: First-principles calculations
Authors: Lv H. Y. , Jiang H. , Liu H. J. , Shi J.
Published: November 2012

Silicon anode experiences large volumetric change (∼400%) during lithiation in lithium ion batteries, which induces fracture and plasticity. In this paper, the boundary effect of silicon nanofilms on the structural evolution, plasticity, stress, and strain during lithiation is studied by first-principles calculations. It is found that rigid boundary induces compression stress and structural disruption during lithiation, as well as voids and plastic deformation during delithiation. In contrast, free boundary allows silicon to expand freely and release the stress during lithiation. Moreover, the volume expansion of the lithiated Si is totally recoverable during delithiation and thus the deformation is entirely elastic.
Cluster size resolving analysis of CH3F-(ortho-H2)n in solid para-hydrogen using FTIR absorption spectroscopy at 3 μm region
Authors: Miyamoto Yuki , Momose Takamasa , Kanamori Hideto
Published: November 2012

Infrared absorption spectra of methyl fluoride with ortho-hydrogen (ortho-H2) clusters in a solid para-hydrogen (para-H2) crystal at 3.6 K were studied in the C-H stretching fundamental region (∼3000 cm−1) using an FTIR spectrometer. As shown previously, the ν3 C-F stretching fundamental band of CH3F-(ortho-H2)n (n = 0, 1, 2, …) clusters at 1040 cm−1 shows a series of n discrete absorption lines, which correspond to different-sized clusters. We observed three unresolved broad peaks in the C-H stretching region and applied this cluster model to them assuming the same intensity distribution function as the ν3 band. A fitting analysis successfully gave us the linewidth and lineshift of the components in each vibrational band. It was found that the separately determined linewidth, matrix shift of the band origin, and cluster shift are dependent on the vibrational mode. From the transition intensities of the monomer component derived from the fitting analysis, we discuss the mixing ratio of the vibrational modes due to Fermi resonance.
Low loading of carbon nanotubes to enhance acoustical properties of poly(ether)urethane foams
Authors: Basirjafari Sedigheh , Malekfar Rasoul , Esmaielzadeh Khadem Siamak
Published: November 2012

The aim of this paper is to fabricate a sound absorber flexible semi-open cell polymeric foam based on polyether urethane (PEU) with carboxylic functionalized multi-walled carbon nanotubes (COOH-MWCNTs) as an energy decaying filler at low loadings up to 0.20 wt. %. This paper provides the relationship between the mentioned foam microstructure via field emission scanning electron microscopy and different acoustical and non-acoustical properties of PEU/COOH-MWCNT composites. Addition of just 0.05 wt. % COOH-MWCNTs enhanced the sound absorption coefficient of the mentioned nanocomposite foam over the entire frequency range. Raman spectra revealed the better dispersion of COOH-MWCNTs in the PEU matrix leading to more stress transfer between them to cause a significant dissipation of energy.
Consideration of the electron energy distribution function shape in a Ar and N2 global model
Authors: Kang Namjun , Gaboriau Freddy , Oh Soo-Ghee
Published: November 2012

This paper presents a method to compensate the effects of the electron energy distribution function (EEDF) shape on plasma characteristics when using global models to describe Ar and N2 inductively coupled discharges. A non-Maxwellian global model is developed for the pressure range 1-1000 mTorr by using an user-friendly Boltzmann equation solver to calculate the EEDF. The calculated EEDFs are compared with the measurements performed with a single Langmuir probe in the same conditions. We also compare the calculated results by using the Boltzmann equation solver with the results by assuming a Maxwellian EEDF and point out the influence of both methods on the contribution of the multi-step process on ionization. Finally, to take into account the shape of the EEDF in global models, abacuses are presented as a function of the absorbed power density and the pressure for typical Ar and N2 planar ICP discharges.
Magnetic and electrical properties of PbTiO3/Mn-Zn ferrite multiphase nanotube arrays by electro-deposition
Authors: Guo Limin , Wang Xiaohui , Nan Cewen , Li Longtu
Published: November 2012

Composite nanotube (NT) array layers incorporating PbTiO3 and Mn-Zn ferrite were prepared by electrophoretic deposition and hydrothermal method using TiO2 NT arrays as templates. Crystal structure and micrograph of the hybrid NTs were characterized by x-ray diffraction and field-emission scanning electron microscopy. The samples showed multiphase of tetragonal PbTiO3 and spinel Mn-Zn ferrite structure. Temperature depended magnetic properties of the layers were studied when the applied field paralleled the NT's channel axis. Temperature increasing caused an increase in magnetization by the enhanced shape anisotropy at higher temperatures. Good ferroelectricity and piezoelectricity were well remained in the hybrid NT layers. A maximum displacement of 0.3 nm and d33* of 55 pm V−1 was observed in the layers.
Electronic structure of buried Co-Cu interface studied with photoemission spectroscopy
Authors: Banik Soma , Barman Sonali , Rai S. K. , Phase D. M. , Srivastava A. K. , Das G. P. , Deb S. K.
Published: November 2012

Depth profiling type of measurement has been performed on the Co(100 Å)/Cu(50 Å) bilayer thin film. Valence band photoemission spectra were recorded at 50 eV photon energy as a function of sputtering time. The motivation of the present work is to understand the electronic structure of the buried Co/Cu interface and the nature of intermixing in the Co and Cu layers. X-ray reflectivity and transmission electron microscopy corroborate with the photoemission results and shows a very broad intermixed Co-Cu interface. The valence band of intermixed Co/Cu interface shows the Co and Cu 3d states which are considerably shifted towards higher and lower binding energy, respectively, as compared to the bulk elemental Co and Cu 3d states. The experimental observations are explained with the help of calculations based on projected augmented wave pseudopotential method using density functional theory. The origin and the shift of feature in the valence band of the Co-Cu interface are mainly due to the formation of two different Co and Co-Cu mixed nanoclusters.
Unusual Urbach tail in TlGaSe2 ferroelectric-semiconductor with incommensurate phase
Authors: Seyidov МirHasan Yu. , Suleymanov Rauf A. , Şale Yasin
Published: November 2012

An analysis of temperature behavior of optical absorption edge is performed for TlGaSe2 ferroelectric-semiconductor with incommensurate phase. Unusual behavior of the Urbach tail manifested by the shift of the absorption edge toward the higher energies with increasing temperature was observed. It was shown that such behavior is due to the specific temperature interval where Urbach energy decreases with the temperature. This interval corresponds to the incommensurate phase-commensurate phase transition region. Unusual behavior of the Urbach energy can be explained interpreting the incommensurate phase as some type of disordered state, and TlGaSe2 crystal as a disordered semiconductor with controllable disorder.
Characterization of defect evolution in ultrathin SiO2 layers under applied electrical stress
Authors: Bonifacio Cecile S. , van Benthem Klaus
Published: November 2012

The structural evolution of ultrathin dielectric SiO2 layers within a Co-silicide/poly-Si/SiO2/Si multilayer system was studied by in situ transmission electron microscopy (TEM). The interface structure represents a model system for field effect transistors with a SiO2 dielectric layer. Electrical bias was applied across the interfaces of cross sectional TEM samples using a scanning tunneling microscopy (STM) tip. Atomic structure modifications of the dielectric layer due to the applied electrical field were observed by this in situ STM-TEM technique. Constant bias (+5.0 V) and ramped bias (+3.0 to +10.5 V) stresses applied to the CoSi2 gate electrode resulted in a loss in capacitance of the dielectric layer consistent with descriptions of soft dielectric breakdown (SBD) and hard dielectric breakdown (HBD). It was found that SBD events are characterized by fluctuations within uniform current step increase of 21 nA and increased roughness of the SiO2 film due to oxygen vacancy percolation. HBD, however, was found to be preceded by multiple SBD events between +6.5 V and +10 V, cobalt atom migration into the dielectric layer, partial crystallization of the amorphous gate dielectric (dielectric breakdown induced epitaxy), and significant diffusion of oxygen from the SiO2 layer into the silicon substrate through a reduction-oxidation reaction of the Si/SiO2 interface. Experimental results demonstrate the feasibility of in situ STM-TEM experiments for studying time-dependent dielectric breakdown behaviors to obtain a direct correlation of individual defect structures and their corresponding electrical signatures. Experimental limitations of this new technique are critically discussed.
Dielectric spectra broadening as a signature for dipole-matrix interaction. III. Water in adenosine monophosphate/adenosine-5′-triphosphate solutions
Authors: Puzenko Alexander , Levy Evgeniya , Shendrik Andrey , Talary Mark S. , Caduff Andreas , Feldman Yuri
Published: November 2012

In this, the third part of our series on the dielectric spectrum symmetrical broadening of water, we consider the nucleotide aqueous solutions. Where in Parts I [E. Levy et al., J. Chem. Phys. 136, 114502 (2012)10.1063/1.3687914] and II [E. Levy et al., J. Chem. Phys. 136, 114503 (2012)10.1063/1.3691183], the dipole–dipole or ion–dipole interaction had a dominant feature, now the interplay between these two types of dipole–matrix interactions will be considered. We present the results of high frequency dielectric measurements of different concentrations of adenosine monophosphate/adenosine-5′-triphosphate aqueous solutions. We observed the Cole-Cole broadening of the main relaxation peak of the solvent in the solutions. Moreover, depending on the nucleotide concentration, we observed both types of dipole–matrix interaction. The 3D trajectory approach (described in detail in Part I) is applied in order to highlight the differences between the two types of interaction.
Nuclear magnetic resonance study on rotational dynamics of water and benzene in a series of ionic liquids: Anion and cation effects
Authors: Kimura Hiroshi , Yasaka Yoshiro , Nakahara Masaru , Matubayasi Nobuyuki
Published: November 2012

The rotational correlation times (τ2R) for polar water (D2O) molecule and apolar benzene (C6D6) molecule were determined in ionic liquids (ILs) by means of the 2H (D) NMR spin-lattice relaxation time (T1) measurements. The solvent IL was systematically varied to elucidate the anion and cation effects separately. Five species, bis(trifluoromethylsulfonyl)imide (TFSI−), trifluoromethylsulfonate (TfO−), hexafluorophosphate (PF6−), chloride (Cl−), and formate (HCOO−), were examined for the anion effect against a fixed cation species of 1-butyl-3-methyl-imidazolium (bmim+). Four species, bmim+, N-methyl-N-butylpyrrolidinium (bmpy+), N,N,N-trimethyl-N-propylammonium (N1,1,1,3+), and P,P,P-trihexyl-P-tetradecylphosphonium (P6,6,6,14+), were employed for the cation effect against a fixed anion species of TFSI−. The τ2R ratio of water to benzene, expressed as τW/B, was used as a probe to characterize the strength of Coulombic solute-solvent interaction in ILs beyond the hydrodynamic limit based on the excluded-volume effect. The τW/B value was found to strongly depend on the anion species, and the solute dynamics are sensitive not only to the size but also to the chemical structure of the component anion. The cation effect was rather weak, in contrast. The largest and most hydrophobic P6,6,6,14+ cation was exceptional and a large τW/B was observed, indicating a unique solvation structure in [P6,6,6,14+]-based ILs.
Pyroelectric current measurements on PbZr0.2Ti0.8O3 epitaxial layers
Authors: Bhatia B. , Karthik J. , Tong T. , Cahill David G. , Martin L. W. , King W. P.
Published: November 2012

We report pyroelectric current measurements on 150 nm thick PbZr0.2Ti0.8O3 (PZT) epitaxial films using frequency-domain thermal measurements over the range 0.02 Hz–1.3 MHz. The measured pyroelectric currents are proportional to the rate of temperature change, from ∼10−5 A/m2 to ∼103 A/m2 over the range 10−2 to 106 K/s. The film temperature oscillation is controlled using either a hotplate, microfabricated heater, or modulated laser, and the pyroelectric current is measured from a microelectrode fabricated onto the film. The measured pyroelectric coefficient of the PZT films is nearly constant across the entire frequency range at ≈−200 μC/m2K.
One step synthesis of pure cubic and monoclinic HfO2 nanoparticles: Correlating the structure to the electronic properties of the two polymorphs
Authors: Rauwel P. , Rauwel E. , Persson C. , Sunding M. F. , Galeckas A.
Published: November 2012

Hafnium dioxide is a wide band-gap, high-κ material, and Hafnium based compounds have already been integrated into micro-electronic devices. The pure cubic HfO2 phase is promising as it presents a higher permittivity (κ > 25), but needs to be stabilized by addition of divalent or trivalent dopants, which in turn modify the electronic properties of HfO2. Here, we employ a one-pot synthesis approach to produce undoped cubic and monoclinic HfO2 nanoparticles by choice of solvent alone. The average size of these nanoparticles from transmission electron microscopy studies was estimated to be around 2.6 nm. We present a study of the morphology and microstructure and also demonstrate the presence of a strong visible photoluminescence linked to the nanosize of the particles. Furthermore, the synthesis in equivalent conditions of these two phases of HfO2 provides means for direct comparison of the chemical composition and electronic structures of the two polymorphs. This has therefore allowed us to experimentally elucidate similarities and differences in the valence band, band gap states, and conduction band of these pure phases seconded by first principles calculations within the density functional theory.
Enhanced microwave dielectric properties of Ba0.4Sr0.6TiO3 ceramics doping by metal Fe powders
Authors: Zhang Qiwei , Zhai Jiwei , Ben Qianqian , Yu Xian , Yao Xi
Published: November 2012

Ba0.4Sr0.6TiO3 ceramics by adding mental Fe powders have been fabricated via the solid-state reaction method. The microstructures and optical properties of samples are systematically studied in order to establish the effects of Fe powder additives on microwave dielectric properties of Ba0.4Sr0.6TiO3 ceramics by x-ray diffraction, x-ray photoelectron spectroscopy, and optical reflective spectrum. The results show the coexistence of Fe2+ and Fe3+ in Ba0.4Sr0.6TiO3 ceramics, the decrease of O vacancy concentrations, and their incorporation into the B-site (Ti) of the Ba0.4Sr0.6TiO3 host lattice give rise to excellent microwave dielectric properties. All samples have a higher Q value above 290 while maintaining relatively high tunability above 16.6%. In particular, the sample with the composition of x = 0.035 mol has the dielectric constant of 889, Q × f value of 826 (at 1.370 GHz), and tunability of 24%, which are very promising for high power tunable devices. In comparison, Fe2O3 oxide doped Ba0.4Sr0.6TiO3 ceramics with the same molar ratios of Fe exhibit inferior microwave properties. It indicates that additives of the metal Fe powders can more effectively improve dielectric properties of BaxSr1-xTiO3 system than Fe2O3 oxide.
Enthalpy change in the magnetocaloric effect
Authors: Quintero M. , Ghivelder L. , Gomes A. M. , Sacanell J. , Parisi F.
Published: November 2012

We report a study of the magnetocaloric effect in magnetic systems by extracting the temperature change from the enthalpy difference between the high and the low magnetic field phases. To evaluate this alternative approach, we compare the results extracted from the proposed model with direct measurements of the adiabatic temperature change. Results obtained in the manganite compound Pr0.5Sr0.41Ca0.09MnO3 are used to show that this method is valid and useful to evaluate the magnetocaloric effect in different solid state systems, and to follow the heat dynamic of the system while a magnetic first order phase transition takes place.
Modeling of helium plasma jets emerged into ambient air: Influence of applied voltage, jet radius, and helium flow velocity on plasma jet characteristics
Authors: Naidis G. V.
Published: November 2012

Simulation of guided positive streamers propagating along helium jets emerged into ambient air is performed, in the framework of a standard two-dimensional streamer model, for various values of parameters (applied voltage, helium flow velocity, and jet radius) governing the streamer dynamics and structure. Obtained dependencies of the streamer velocity, radius, and propagation length on the governing parameters are compared with available results of observations.
Strong quantum size effects in transition metal silicide ultrathin films: Critical role of Fermi surface nesting
Authors: Li Meng , Wang Fei , Li Chenhui , Li Chong , Sun Qiang , Wang Songyou , Jia Yu
Published: November 2012

Using first-principles calculations based on density functional theory, the quantum size effects (QSEs) of CoSi2 ultrathin films with different thickness have been studied. Our results confirm that both the stability and the interlayer relaxation of CoSi2(111) films oscillate in a tri-trilayers by tri-trilayers mode, with a beating period of 16 trilayers. We also predict that the stability of CoSi2(100) films oscillate in a bi-bilayers by bi-bilayers mode, with a beating period of 9 bilayers. Such thickness-depend oscillation of stability and relaxation can be attributed to the QSEs associated with the very flat Fermi surface along the growth direction, resulting in a strong nesting of Fermi sheet. The match of the calculated Fermi wave length and the interlayer space explains the oscillation period well, and the beating period could also be deduced from the electronic structure. Our theoretical research uncovers the underlying mechanisms of the electronic growth of transition metal silicides films reported in the previous experimental work.
Atomistic simulations of pH-dependent self-assembly of micelle and bilayer from fatty acids
Authors: Morrow Brian H. , Koenig Peter H. , Shen Jana K.
Published: November 2012

Detailed knowledge of the self-assembly and phase behavior of pH-sensitive surfactants has implications in areas such as targeted drug delivery. Here we present a study of the formation of micelle and bilayer from lauric acids using a state-of-the-art simulation technique, continuous constant pH molecular dynamics (CpHMD) with conformational sampling in explicit solvent and the pH-based replica-exchange protocol. We find that at high pH conditions a spherical micelle is formed, while at low pH conditions a bilayer is formed with a considerable degree of interdigitation. The mid-point of the phase transition is in good agreement with experiment. Preliminary investigation also reveals that the effect of counterions and salt screening shifts the transition mid-point and does not change the structure of the surfactant assembly. Based on these data we suggest that CpHMD simulations may be applied to computational design of surfactant-based nano devices in the future.
Spectrally resolved analysis of fluorescence blinking of single dye molecules in polymers at low temperatures
Authors: Orlov S. V. , Naumov A. V. , Vainer Yu. G. , Kador Lothar
Published: November 2012

We present a method for the spectrally resolved analysis of fluorescence blinking of single quantum emitters. It is based on the well-known technique of repeated recording of single-molecule (SM) fluorescence excitation spectra. The potential of our approach is presented for the example of single tetra-tert-butylterrylene molecules in an amorphous polymer matrix (polyisobutylene), which exhibit fluorescence blinking at cryogenic temperatures. Measuring the spectral dependence of the blinking statistics improves the possibility to clarify the microscopic nature of the dark state(s) of the emitters. We demonstrate how the blinking statistics can be definitely attributed to conformational changes in the local environment of a SM and how the parameters of the corresponding elementary excitations can be measured. The analysis of the blinking statistics as a function of the optical excitation frequency allows us to discriminate between photo-induced and spontaneous transitions into a dark state.
Vapor–liquid nucleation in two dimensions: On the intriguing sign switch of the errors of the classical nucleation theory
Authors: Loeffler Troy D. , Henderson David E. , Chen Bin
Published: November 2012

A nucleation study of a two-dimensional (2D) Lennard-Jones (LJ) system is done using the aggregation-volume-bias Monte Carlo with umbrella sampling method. The results obtained from this simulation study was compared to those predicted by the classical nucleation theory (CNT). It was found that the nucleation free energy obtained for this 2D LJ system was underestimated by CNT; however, this result is significantly different from that found for the 3D LJ system where CNT overestimates the free energy. These results are generally in agreement with previous studies on these systems. While both errors can be traced to the incorrect description of the smallest clusters by the theory, structural analysis reveals striking differences between 2D and 3D clusters, leading to a possible source for this observed sign switch. In particular, the radius of gyration data indicates that for the 3D LJ system, clusters formed at the beginning are fractal and the cluster growth is accompanied by an increase of the dimensionality, whereas clusters in 2D show little sign of this dimensionality transition.
Lateral resolution improvement in scanning nonlinear dielectric microscopy by measuring super-higher-order nonlinear dielectric constants
Authors: Chinone N. , Yamasue K. , Hiranaga Y. , Honda K. , Cho Y.
Published: November 2012

Scanning nonlinear dielectric microscopy (SNDM) can be used to visualize polarization distributions in ferroelectric materials and dopant profiles in semiconductor devices. Without using a special sharp tip, we achieved an improved lateral resolution in SNDM through the measurement of super-higher-order nonlinearity up to the fourth order. We observed a multidomain single crystal congruent LiTaO3 (CLT) sample, and a cross section of a metal-oxide-semiconductor (MOS) field-effect-transistor (FET). The imaged domain boundaries of the CLT were narrower in the super-higher-order images than in the conventional image. Compared to the conventional method, the super-higher-order method resolved the more detailed structure of the MOSFET.
Quantum dynamical study of the electronic nonadiabaticity in the D + DBr → Br(Br*) + D2 reaction on new diabatic potential energy surfaces
Authors: Zhang Ai-Jie , Zhang Pei-Yu , Chu Tian-Shu , Han Ke-Li , He Guo-Zhong
Published: November 2012

A set of diabatic potential energy surfaces, that describe the D + DBr → Br(P1/2,3/2) + D2 reaction, is constructed based on MRCI/aug-cc-pV5Z calculations at 29 526 grid points. Time-dependent wave packet calculations are performed for ground-state DBr initially with collision energies up to 2.0 eV to investigate possible electronic nonadiabaticity in this reaction. Reaction probabilities and integral cross sections are calculated. The results show negligible nonadiabatic effects for the title reaction in the energy range considered here, confirming experimental work of Zare and co-workers. In addition, the calculated thermal rate constants are in good agreement with experimental ones.
Core and valence excitations in resonant X-ray spectroscopy using restricted excitation window time-dependent density functional theory
Authors: Zhang Yu , Biggs Jason D. , Healion Daniel , Govind Niranjan , Mukamel Shaul
Published: November 2012

We report simulations of X-ray absorption near edge structure (XANES), resonant inelastic X-ray scattering (RIXS) and 1D stimulated X-ray Raman spectroscopy (SXRS) signals of cysteine at the oxygen, nitrogen, and sulfur K and \documentclass[12pt]{minimal}\begin{document}$\textrm {L}_{2,3}$\end{document}L2,3 edges. Comparison of the simulated XANES signals with experiment shows that the restricted window time-dependent density functional theory is more accurate and computationally less expensive than the static exchange method. Simulated RIXS and 1D SXRS signals give some insights into the correlation of different excitations in the molecule.
Effects of the surface charge screening and temperature on the vortex domain patterns of ferroelectric nanodots
Authors: Wu C. M. , Chen W. J. , Ma D. C. , Woo C. H. , Zheng Yue
Published: November 2012

Based on the phase field simulations, effects of the surface charge screening and temperature on the vortex domain structure of the ferroelectric nanodot have been investigated. Our calculations show that the ferroelectric nanodot adopts a rhombohedral vortex domain pattern under an ideal open-circuit boundary condition. With the increase of the surface charge screening, the dipole vortex gradually rotates and appears rhombohedral-orthorhombic-tetragonal transformation. By adjusting the surface charge screening, the polar single domain and multi-vortices domain patterns with zero toroidal moment have been obtained near the phase transition temperature. More importantly, temperature and charge screening “T-C” phase diagram has been summarized, which indicates an effective method to control the vortex domain structure in the low-dimensional ferroelectric nanostructures.
In situ x-ray diffraction of solution-derived ferroelectric thin films for quantitative phase and texture evolution measurement
Authors: Nittala Krishna , Mhin Sungwook , Jones Jacob L. , Robinson Douglas S. , Ihlefeld Jon F. , Brennecka Geoff L.
Published: November 2012

An in situ measurement technique is developed and presented, which utilizes x-rays from a synchrotron source with a two-dimensional detector to measure thin film microstructural and crystallographic evolution during heating. A demonstration experiment is also shown wherein the measured diffraction patterns are used to describe phase and texture evolution during heating and crystallization of solution-derived thin films. The diffraction images are measured sequentially while heating the thin film with an infrared lamp. Data reduction methodologies and representations are also outlined to extract phase and texture information from the diffraction images as a function of time and temperature. These techniques and data reduction methods are demonstrated during crystallization of solution-derived lead zirconate titanate ferroelectric thin films heated at a rate of 30 °C/min and using an acquisition time of 8 s. During heating and crystallization, a PtxPb type phase was not observed. A pyrochlore phase was observed prior to the formation and growth of the perovskite phase. The final crystallized films are observed to have both 111 and 100 texture components. The in situ measurement methodology developed in this work allows for acquiring diffraction images in times as low as 0.25 s and can be used to investigate changes during crystallization at faster heating rates. Moreover, the experiments are shown to provide unique information during materials processing.
Dispersion of effective refractive indices of mid-infrared quantum cascade lasers
Authors: Yang Q. , Kinzer M. , Aidam R. , Driad R. , Bronner W. , Hugger S. , Ostendorf R. , Fuchs F. , Wagner J.
Published: November 2012

We point out the difference between the two mostly used methods for calculating the effective refractive index of mid-infrared quantum cascade lasers, namely by solving the Maxwell's wave equation and by analyzing the frequency spacing of the longitudinal modes of the Fabry-Perot cavity. The effective refractive indices obtained by these methods are shown to be different, as one refers to the phase effective refractive index while the other refers to the group effective refractive index, respectively. Dispersion relationships for these two effective refractive indices are deduced for mid-infrared quantum cascade lasers, which show an increase in group refractive index and a decrease in phase refractive index with wavelength. Experiments are conducted to obtain the group effective refractive indices of quantum cascade lasers emitting at various wavelengths, and good agreement has been achieved between the experimental data and theory.
Interatomic potential to predict the favored and optimized compositions for ternary Cu-Zr-Hf metallic glasses
Authors: Luo S. Y. , Cui Y. Y. , Dai Y. , Li J. H. , Liu B. X.
Published: November 2012

Under the framework of smoothed and long range second-moment approximation of tight-binding, a realistic interatomic potential was first constructed for the Cu-Zr-Hf ternary metal system. Applying the constructed potential, Monte Carlo simulations were carried out to compare the relative stability of crystalline solid solution versus its disordered counterpart over the entire composition triangle of the system (as a function of alloy composition). Simulations not only reveal that the origin of metallic glass formation but also determine, in the composition triangle, a quadrilateral region, within which metallic glass formation is energetically favored. It is proposed to define the energy differences between the crystalline solid solutions and disordered states as the driving force for amorphization and the corresponding calculations pinpoint an optimized composition locating at an composition of Cu55Zr10Hf35, around which the driving force for metallic glass formation reaches its maximum, suggesting that the ternary Cu-Zr-Hf metallic glasses designed to have the compositions around Cu55Zr10Hf35 could be more stable than other alloys in the system. Moreover, for the Cu55Zr10Hf35 metallic glass, the Voronoi tessellation calculations reveal some interesting features of its atomic configurations and coordination polyhedra distribution.
Platinum nanostructures formed by femtosecond laser irradiation in water
Authors: Huo Haibin , Shen Mengyan
Published: November 2012

Platinum nanostructures with various morphologies, such as spike-like, ripple-like and array-like structures, have been fabricated by 400 nm and 800 nm femtosecond laser irradiation in water. Different structures can be formed on the surfaces as a function of the laser wavelength, the fluence and scan methods. The reflectance measurements of these structures show much larger absorption on the irradiated surfaces than untreated platinum surfaces.
Magnetic and electric properties of Ru-substituted CoFe2O4 thin films fabricated by pulsed laser deposition
Authors: Iwamoto Fujiyuki , Seki Munetoshi , Tabata Hitoshi
Published: November 2012

Epitaxial thin films of Ru-substituted CoFe2O4 with a cubic spinel structure were fabricated on α-Al2O3 (001) substrates using pulsed laser deposition, and their magnetic and electric properties were investigated. The films showed room temperature ferrimagnetic behavior with hard magnetic features similar to those of non-Ru-substituted cobalt ferrite films. The electrical conductivity of the films was dramatically enhanced by the substitution of Ru. The anomalous Hall effect was observed in all films even at 300 K suggesting that carriers in the films are highly spin-polarized at room temperature as expected from a first-principles calculation.
Voltage generation of piezoelectric cantilevers by laser heating
Authors: Hsieh Chun-Yi , Liu Wei-Hung , Chen Yang-Fang , Shih Wan Y. , Gao Xiaotong , Shih Wei-Heng
Published: November 2012

Converting ambient thermal energy into electricity is of great interest in harvesting energy from the environment. Piezoelectric cantilevers have previously been shown to be an effective biosensor and a tool for elasticity mapping. Here we show that a single piezoelectric (lead-zirconate titanate (PZT)) layer cantilever can be used to convert heat to electricity through pyroelectric effect. Furthermore, piezoelectric-metal (PZT-Ti) bi-layer cantilever showed an enhanced induced voltage over the single PZT layer alone due to the additional piezoelectric effect. This type of device can be a way for converting heat energy into electricity.
Atomistic simulations of shock induced melting of bicrystal copper with twist grain boundary
Authors: He A. M. , Duan Suqing , Shao Jian-Li , Wang Pei , Qin Chengsen
Published: November 2012

We investigate the shock induced melting of Cu bicrystals with [001] twist grain boundary (GB) under various shock intensities using atomistic dynamics simulations. Two representative types of twist GBs are studied: ∑=5/(001)/36.87° and ∑=181/(001)/6.03° with relatively high and low GB energies, respectively. The properties of the shocked GB region evolving with time are characterized in terms of order parameters and mean-squared displacement. In the case of ∑=5/(001)/36.87°, it is found that prior to the homogeneous melting of the whole sample, continuous partial melting with considerable premelting of the shocked GB region precedes bulk melting with negligible superheating of GB, while solid state disordering may precede the partial melting. In contrast, for ∑=181/(001)/6.03°, the melting process is analogous to that of a shocked perfect crystal except that a limited superheated partial melting state occurs before homogeneous melting of the whole bicrystal.
Ultrahigh arsenic sorption using iron oxide-graphene nanocomposite supercapacitor assembly
Authors: Mishra A. K. , Ramaprabhu S.
Published: November 2012

In response to the increasing water demand, electro-sorption method has shown promise in context of high removal efficiency of metals with less energy consumption. Here, we report for the first time ultrahigh sorption capacity of iron oxide-graphene (Fe3O4-HEG) nanocomposite supercapacitor assembly for both inorganic arsenic species (arsenate and arsenite). Graphene has been synthesized by hydrogen induced exfoliation of graphitic oxide and decorated with iron oxide (Fe3O4) nanocrystals by chemical route. Electrochemical sorption behavior of nanocomposite electrodes for arsenic has been examined by cyclic voltammetry and kinetic studies. Adsorption isotherm models have been tested to calculate the maximum adsorption capacities (using Langmuir isotherm) for arsenate and arsenite and found to be nearly 172.1 and 180.3 mg/g, respectively, using supercapacitor assembly. These values are higher than other adsorbents for arsenic.
Study of interfacial tension between an organic solvent and aqueous electrolyte solutions using electrostatic dissipative particle dynamics simulations
Authors: Mayoral E. , Nahmad-Achar E.
Published: November 2012

The study of the modification of interfacial properties between an organic solvent and aqueous electrolyte solutions is presented by using electrostatic dissipative particle dynamics (DPD) simulations. In this article, the parametrization for the DPD repulsive parameters aij for the electrolyte components is calculated considering the dependence of the Flory-Huggins χ parameter on the concentration and the kind of electrolyte added, by means of the activity coefficients. In turn, experimental data were used to obtain the activity coefficients of the electrolytes as a function of their concentration in order to estimate the χ parameters and then the aij coefficients. We validate this parametrization through the study of the interfacial tension in a mixture of n-dodecane and water, varying the concentration of different inorganic salts (NaCl, KBr, Na2SO4, and UO2Cl2). The case of HCl in the mixture n-dodecane/water was also analyzed and the results presented. Our simulations reproduce the experimental data in good agreement with previous work, showing that the use of activity coefficients to obtain the repulsive DPD parameters aij as a function of concentration is a good alternative for these kinds of systems.
A mathematical proof of the zeroth “law” of thermodynamics and the nonlinear Fourier “law” for heat flow
Authors: Evans Denis J. , Williams Stephen R. , Rondoni Lamberto
Published: November 2012

What is now known as the zeroth “law” of thermodynamics was first stated by Maxwell in 1872: at equilibrium, “Bodies whose temperatures are equal to that of the same body have themselves equal temperatures.” In the present paper, we give an explicit mathematical proof of the zeroth “law” for classical, deterministic, T-mixing systems. We show that if a body is initially not isothermal it will in the course of time (subject to some simple conditions) relax to isothermal equilibrium where all parts of the system will have the same temperature in accord with the zeroth “law.” As part of the derivation we give for the first time, an exact expression for the far from equilibrium thermal conductivity. We also give a general proof that the infinite-time integral, of transient and equilibrium autocorrelation functions of fluxes of non-conserved quantities vanish. This constitutes a proof of what was called the “heat death of the Universe” as was widely discussed in the latter half of the 19th century.
Valence and diffuse-bound anions of noble-gas complexes with uracil
Authors: Streit Lívia , Dolgounitcheva O. , Zakrzewski V. G. , Ortiz J. V.
Published: November 2012

Valence-bound (VB) and diffuse-bound (DB) anions of noble-gas (Ar, Kr, and Xe) complexes with uracil have been studied with ab initio methods. MP2 optimizations revealed minima corresponding to anions of both kinds in each case. Coupled-cluster singles and doubles with perturbative triples, CCSD(T), and electron propagator single-point calculations were performed in order to assess vertical and adiabatic electron detachment energies of these complexes. Ab initio electron propagator calculations employed the outer valence Green's function and partial third-order approximations, and the algebraic diagrammatic construction in third order. Basis set effects have been systematically examined. DB anions of all three complexes were adiabatically bound, with calculated adiabatic electron attachment energies below 0.06 eV. Corresponding vertical electron detachment energies were below 0.1 eV. As to VB anions, only the Xe complex had a positive adiabatic electron detachment energy, of 0.01 eV, with a corresponding vertical electron detachment energy of 0.6 eV. These computational findings are consistent with the interpretation of results previously obtained experimentally by Hendricks et al.
Electrical potential measurement in plasma columns of atmospheric plasma jets
Authors: Cho Gunagsup , Kim Junghyun , Kang Hanlim , Kim Yunjung , Kwon Gi-Chung , Uhm Han S.
Published: November 2012

The electrical potential of plasma generated from an atmospheric plasma jet device with Ar or He gas is measured with a high voltage probe in a plasma column inside a tube as well as in the plasma ejected through the open end of the tube. When the double plasma jet devices with Ar-gas are operated by the opposite polarities of an ac voltage with a few kV at both ends of a glass tube, the electrical potential of plasma column is high at both ends of the column, while the electrical potential in the middle of the plasma column is a few tens of volts. When the plasma column is formulated with the double plasma jets of a high voltage electrode at one end of the glass tube and a grounded electrode at the other end of the tube, the plasma column potential decreases linearly from a high voltage to a very low value, as the measurement position moves from the side of high voltage to the grounded location. In the double plasma jets of He-gas operated by high voltages in opposite polarities, the ejected plasma jets are attractive to each other at the intersection, merging together and having the electrical potential of a few tens of volts. On the other hand, if the two plasma jet columns are operated by high voltages of same polarity the ejected plasma jets are repulsive to each other at the intersection, having the electrical potential of a few hundreds of volts and causing an electrical shock.