bluuebunny/crossref_metadata_2025 huggingface dataset:
High resolution spatial map imaging of a gaseous target
Authors: Stei Martin , von Vangerow Johannes , Otto Rico , Kelkar Aditya H. , Carrascosa Eduardo , Best Thorsten , Wester Roland
Published: June 2013

Electrostatic ion imaging with the velocity map imaging mode is a widely used method in atomic and molecular physics and physical chemistry. In contrast, the spatial map imaging (SMI) mode has received very little attention, despite the fact that it has been proposed earlier [A. T. J. B. Eppink and D. H. Parker, Rev. Sci. Instrum. 68, 3477 (1997)]10.1063/1.1148310. Here, we present a detailed parametric characterization of SMI both by simulation and experiment. One-, two- and three-dimensional imaging modes are described. The influence of different parameters on the imaging process is described by means of a Taylor expansion. To experimentally quantify elements of the Taylor expansion and to infer the spatial resolution of our spectrometer, photoionization of toluene with a focused laser beam has been carried out. A spatial resolution of better than 4 μm out of a focal volume of several mm in diameter has been achieved. Our results will be useful for applications of SMI to the characterization of laser beams, the overlap control of multiple particle or light beams, and the determination of absolute collision cross sections.
On the construction of point processes in statistical mechanics
Authors: Nehring Benjamin , Poghosyan Suren , Zessin Hans
Published: June 2013

We present a new approach to the construction of point processes of classical statistical mechanics as well as processes related to the Ginibre Bose gas of Brownian loops and to the dissolution in \documentclass[12pt]{minimal}\begin{document}$\mathbb {R}^d$\end{document}Rd of Ginibre's Fermi-Dirac gas of such loops. This approach is based on the cluster expansion method. We obtain the existence of Gibbs perturbations of a large class of point processes. Moreover, it is shown that certain “limiting Gibbs processes” are Gibbs in the sense of Dobrushin, Lanford, and Ruelle if the underlying potential is positive. Finally, Gibbs modifications of infinitely divisible point processes are shown to solve a new integration by parts formula if the underlying potential is positive.
Towards an electro-magnetic field separation of deposited material implemented in an ion beam sputter process
Authors: Malobabic Sina , Jupé Marco , Ristau Detlev
Published: June 2013

Nowadays, Ion Beam Sputter (IBS) processes are very well optimized on an empirical basis. To achieve further progresses, a modification of the IBS process by guiding the coating material using an axial magnetic field and an additional electrical field has been studied. The electro-magnetic (EM) field leads to a significant change in plasma properties and deposition rate distributions, whereas an increase in deposition rate along the centerline of the axial EM field around 150% was observed. These fundamental studies on the prototype are the basis for the development of an applicable and workable design of a separation device.
The electronic states of pyridine-N-oxide studied by VUV photoabsorption andab initioconfiguration interaction computations
Authors: Palmer Michael H. , Hoffmann Søren Vrønning , Jones Nykola C. , Smith Elliott R. , Lichtenberger Dennis L.
Published: June 2013

The first vacuum-ultraviolet absorption spectrum of pyridine-N-oxide has been obtained, and has led to the identification of nearly 30 Rydberg states. These states were identified by use of the vibrational envelope (“footprint”) of the UV-photoelectron spectrum, and are based on the first to the third ionization energies (IE). The adiabatic IE order, central to the Rydberg state symmetry identification, is confirmed by multi-configuration SCF calculations as: 12B1 < 12B2 < 12A2 < 22B1. Several excited valence state equilibrium structures were determined by multi-configuration SCF and coupled cluster procedures. Multi-reference multi-root CI was used to calculate both Rydberg and valence state vertical excitation energies and oscillator strengths, which were correlated with the experimental measurements.
Interaction of the NO 3pπ Rydberg state with Ar: Potential energy surfaces and spectroscopy
Authors: Ershova Olga V. , Kłos Jacek , Harris Joe P. , Gardner Adrian M. , Tamé-Reyes Victor M. , Andrejeva Anna , Alexander Millard H. , Besley Nicholas A. , Wright Timothy G.
Published: June 2013

We present the experimental and simulated (2+1) REMPI spectrum of the $\tilde C\,^2 \Pi$C̃Π2 state of the NO–Ar complex, in the vicinity of the 3p Rydberg state of NO. Two Rydberg states of NO are expected in this energy region: the C2Π (3pπ) and D2Σ+ (3pσ) states, and we concentrate on the former here. When the C2Π (3pπ) state interacts with Ar at nonlinear orientations, the symmetry is lowered to Cs, splitting the degeneracy of the 2Π state to yield $\tilde C$C̃(2A″) and $\tilde C$C̃(2A′) states. For these two states of NO–Ar, we calculate potential energy surfaces using second order Møller-Plesset perturbation theory, exploiting a procedure to converge the reference Hartree-Fock wavefunction to describe the excited states, the maximum overlap method. The bound rovibrational states obtained from the surfaces are used to simulate the electronic spectrum, which is in excellent agreement with experiment, providing assignments for the observed spectral lines from the calculated rovibrational wavefunctions.
Pattern formation of anisotropic molecules on surfaces under non-equilibrium conditions as described by a minimum model
Authors: Heuer Andreas , Jana Pritam Kumar , Lied Fabian
Published: June 2013

The self-organization of lipophilic chain molecules on surfaces in vacuum deposition experiments has been recently studied by Monte Carlo simulations of a coarse grained microscopic model system. Surprisingly, the final potential energy depends in a non-monotonous way on the chosen flux and the surface temperature. Here we introduce a schematic model which contains the relevant physical ingredients of the microscopic model and which elucidates the origin of this anomalous non-equilibrium effect. Intra-cluster effects, reflecting the chain arrangement within one cluster, and inter-cluster effects, based on the distribution of chains among the different formed clusters, are taken into account. This schematic model is solved numerically as well as via analytical means. From the analytical solutions, it is possible to understand quantitatively for which interaction parameters the observed anomalies can indeed be observed. The generality of the observed phenomena is stressed. It is related to the concept of kinetic trapping, which often occurs during self-assembly.
Determining the bending modulus of a lipid membrane by simulating buckling
Authors: Hu Mingyang , Diggins Patrick , Deserno Markus
Published: June 2013

The force needed to buckle a thin elastic surface is proportional to its bending rigidity. This fact suggests using a buckling setup to measure the bending modulus of lipid membranes. Extending the work of Noguchi [Phys. Rev. E 83, 061919 (2011)10.1103/PhysRevE.83.061919], we systematically derive highly accurate analytical expressions for the forces along and perpendicular to the buckle, and we elucidate some of their counterintuitive properties using the framework of a surface stress tensor. Furthermore, we estimate the corrections to buckling forces due to thermal fluctuations and find them significant only for stresses along the ridges. We then apply this buckling protocol to four different lipid membrane models, which widely differ in their level of resolution and the treatment of solvent, and show that in all cases buckling is a reliable and accurate means for measuring their rigidity. Finally, we show that monitoring both stresses and energies during a simulation offers additional insights into the thermodynamics of curvature elasticity and permits one to predict the bending rigidity for a range of temperatures around the actual simulation temperature.
Path-integral simulations with fermionic and bosonic reservoirs: Transport and dissipation in molecular electronic junctions
Authors: Simine Lena , Segal Dvira
Published: June 2013

We expand iterative numerically exact influence functional path-integral tools and present a method capable of following the nonequilibrium time evolution of subsystems coupled to multiple bosonic and fermionic reservoirs simultaneously. Using this method, we study the real-time dynamics of charge transfer and vibrational mode excitation in an electron conducting molecular junction. We focus on nonequilibrium vibrational effects, particularly, the development of vibrational instability in a current-rectifying junction. Our simulations are performed by assuming large molecular vibrational anharmonicity (or low temperature). This allows us to truncate the molecular vibrational mode to include only a two-state system. Exact numerical results are compared to perturbative Markovian master equation calculations demonstrating an excellent agreement in the weak electron-phonon coupling regime. Significant deviations take place only at strong coupling. Our simulations allow us to quantify the contribution of different transport mechanisms, coherent dynamics, and inelastic transport, in the overall charge current. This is done by studying two model variants: The first admits inelastic electron transmission only, while the second one allows for both coherent and incoherent pathways.
Excitons and polaritons in quasi-molecular eigenbasis of the excitation hopping system interacting with a photon field
Authors: Hong Suc-Kyoung , Yoon Jae Seok , Nam Seog Woo
Published: June 2013

We report studies of excitons and polaritons in the quasi-molecular eigenbasis of a nano-aggregate, in the model of excitation transfer with, or without, photon-exciton coupling. We evaluate the effective interaction between quasi-molecular subsystems in quasi-molecular eigenbasis representation, with its eigenenergies and eigenstates. From the analysis of the effective interaction Hamiltonian in the quasi-molecular eigenbasis representation, we see that the effective interaction between subsystems in quasi-molecular eigenbasis representation gives fertile points of view to understand the given system, and the dynamics of excitons and polaritons becomes simpler to understand, or to deal with, depending on the division of the whole system into specified subsystems.
Subdiffusive exciton motion in systems with heavy-tailed disorder
Authors: Vlaming S. M. , Malyshev V. A. , Eisfeld A. , Knoester J.
Published: June 2013

We study the transport of collective excitations (Frenkel excitons) in systems with static disorder in the transition energies, not limiting ourselves to Gaussian transition energy distributions. Instead, we generalize this model to the wider class of Lévy stable distributions, characterized by heavy tails. Phonon-assisted scattering of excitons, localized by the disorder, leads to thermally activated exciton motion. The time evolution of the second moment of the exciton distribution is shown to be sublinear, thus indicating that the exciton dynamics in such systems is not diffusive, but rather subdiffusive instead. The heavier the tail in the transition energy distribution is, the larger are the deviations from the diffusive regime. This from fluctuations of site energies larger than the exciton band width (outliers). We show that the occurrence of subdiffusive transport for heavy-tailed disorder distributions can be understood from the scattering rate distributions, which possess a (second) peak at zero scattering rate.
Optimization of nonlinear optical localization using electromagnetic surface fields (NOLES) imaging
Authors: Jarrett Jeremy W. , Chandra Manabendra , Knappenberger Kenneth L.
Published: June 2013

The use of plasmon amplification of nonlinear optical wave-mixing signals to generate optical images in which the position of the scattering point source can be determined with nanometer accuracy is described. Solid gold nanosphere dimers were used as a model system for the nonlinear medium, which converted the Ti:sapphire fundamental to its second harmonic frequency. Matching the fundamental wave energy to the localized surface plasmon resonance of the electromagnetically coupled nanospheres was critical for achieving the high localization accuracy. Our technique, named Nonlinear Optical Localization using Electromagnetic Surface fields (NOLES) imaging, routinely yielded nonlinear optical images with 1-nm localization accuracy at rates ≥2 fps and can also be used as a photo-switching localization contrast method. This high level of accuracy in pinpointing the signal point source position exceeded that made possible using conventional diffraction-limited far-field methods by 160×. The NOLES technique, with its high temporal resolution and spatial accuracy that far surpass the performance typical of fluorescence-based imaging, will be relevant for imaging dynamic chemical, biological, and material environments.
Heterogeneity in binary mixtures of dimethyl sulfoxide and glycerol: Fluorescence correlation spectroscopy
Authors: Chattoraj Shyamtanu , Chowdhury Rajdeep , Ghosh Shirsendu , Bhattacharyya Kankan
Published: June 2013

Diffusion of four coumarin dyes in a binary mixture of dimethyl sulfoxide (DMSO) and glycerol is studied using fluorescence correlation spectroscopy (FCS). The coumarin dyes are C151, C152, C480, and C481. In pure DMSO, all the four dyes exhibit a very narrow (almost uni-modal) distribution of diffusion coefficient (Dt). In contrast, in the binary mixtures all of them display a bimodal distribution of Dt with broadly two components. One of the components of Dt corresponds to the bulk viscosity. The other one is similar to that in pure DMSO. This clearly indicates the presence of two distinctly different nano-domains inside the binary mixture. In the first, the micro-environment of the solute consists of both DMSO and glycerol approximately at the bulk composition. The other corresponds to a situation where the first layer of the solute consists of DMSO only. The burst integrated fluorescence lifetime (BIFL) analysis also indicates presence of two micro-environments one of which resembles DMSO. The relative contribution of the DMSO-like environment obtained from the BIFL analysis is much larger than that obtained from FCS measurements. It is proposed that BIFL corresponds to an instantaneous environment in a small region (a few nm) around the probe. FCS, on the contrary, describes the long time trajectory of the probes in a region of dimension ∼200 nm. The results are explained in terms of the theory of binary mixtures and recent simulations of binary mixtures containing DMSO.
Studies on antimony telluride thin films as buffer layer for solar cell applications
Authors: Sonawane Shivaji M. , Chaure N. B.
Published: June 2013

Antimony telluride (Sb2Te3) is binary p-type compound of narrow band gap (0.3 eV) semiconductor, which has application in solar cell to make low resistive ohmic contact. Sb2Te3 acts as a diffusion barrier and may improve the ohmic contact due to top doping on CdTe surface. We have synthesized antimony telluride thin films by electrodeposition technique and studied their various properties. Three-electrode system was employed for the electrodeposition of Sb2Te3 thin films on fluorine tin oxide coated glass substrates. Sb2O3 and TeO2 were used as an ionic source for Sb and Te ions, whereas tartaric acid was used as complexing agent and also supportive electrolyte. The electrochemical parameters were optimized by slow scan cyclic voltammetry (CV) experiment. The effects of deposition potential on morphology, structure, and composition have been studied. Various properties of Sb2Te3 film were studied by X-ray diffraction, atomic force microscopy (AFM), and energy dispersive X-ray analysis. Prominent (015) peak of Sb2Te3 was attributed at 2θ = 28.36° for as-deposited and heat treated samples. After heat treatment, crystallinity of the film was improved. The electrical properties of as-deposited and annealed films were studied by two probe method. Growth potential dependent I-V characteristics of FTO/Sb2Te3/Au diode were studied and found to be Schottky barrier diode. Compact, uniform, and void free films surface morphology is observed by AFM. The effect of deposition potentials on morphology, structure, and composition of Sb2Te3 thin films were studied.
Measurement of transmission efficiency for 400 MeV proton beam through collimator at Fermilab MuCool Test Area using Chromox-6 scintillation screen
Authors: Jana M. R. , Chung M. , Freemire B. , Hanlet P. , Leonova M. , Moretti A. , Palmer M. , Schwarz T. , Tollestrup A. , Torun Y. , Yonehara K.
Published: June 2013

The MuCool Test Area (MTA) at Fermilab is a facility to develop the technology required for ionization cooling for a future Muon Collider and/or Neutrino Factory. As part of this research program, feasibility studies of various types of RF cavities in a high magnetic field environment are in progress. As a unique approach, we have tested a RF cavity filled with a high pressure hydrogen gas with a 400 MeV proton beam in an external magnetic field (B = 3 T). Quantitative information about the number of protons passing through this cavity is an essential requirement of the beam test. The MTA is a flammable gas (hydrogen) hazard zone. Due to safety reasons, no active (energized) beam diagnostic instrument can be used. Moreover, when the magnetic field is on, current transformers (toroids) used for beam intensity measurements do not work due to the saturation of the ferrite material of the transformer. Based on these requirements, we have developed a passive beam diagnostic instrumentation using a combination of a Chromox-6 scintillation screen and CCD camera. This paper describes details of the beam profile and position obtained from the CCD image with B = 0 T and B = 3 T, and for high and low intensity proton beams. A comparison is made with beam size obtained from multi-wires detector. Beam transmission efficiency through a collimator with a 4 mm diameter hole is measured by the toroids and CCD image of the scintillation screen. Results show that the transmission efficiency estimated from the CCD image is consistent with the toroid measurement, which enables us to monitor the beam transmission efficiency even in a high magnetic field environment.
In situ “artificial plasma” calibration of tokamak magnetic sensors
Authors: Shiraki D. , Levesque J. P. , Bialek J. , Byrne P. J. , DeBono B. A. , Mauel M. E. , Maurer D. A. , Navratil G. A. , Pedersen T. S. , Rath N.
Published: June 2013

A unique in situ calibration technique has been used to spatially calibrate and characterize the extensive new magnetic diagnostic set and close-fitting conducting wall of the High Beta Tokamak-Extended Pulse (HBT-EP) experiment. A new set of 216 Mirnov coils has recently been installed inside the vacuum chamber of the device for high-resolution measurements of magnetohydrodynamic phenomena including the effects of eddy currents in the nearby conducting wall. The spatial positions of these sensors are calibrated by energizing several large in situ calibration coils in turn, and using measurements of the magnetic fields produced by the various coils to solve for each sensor's position. Since the calibration coils are built near the nominal location of the plasma current centroid, the technique is referred to as an “artificial plasma” calibration. The fitting procedure for the sensor positions is described, and results of the spatial calibration are compared with those based on metrology. The time response of the sensors is compared with the evolution of the artificial plasma current to deduce the eddy current contribution to each signal. This is compared with simulations using the VALEN electromagnetic code, and the modeled copper thickness profiles of the HBT-EP conducting wall are adjusted to better match experimental measurements of the eddy current decay. Finally, the multiple coils of the artificial plasma system are also used to directly calibrate a non-uniformly wound Fourier Rogowski coil on HBT-EP.
Non-contact data access with direction identification for industrial differential serial bus
Authors: Xie Kai , Li Xiaoping , Zhang Hanlu , Yang Ming , Ye Yinghao
Published: June 2013

We propose a non-contact method for accessing data in industrial differential serial bus applications, which could serve as an effective and safe online testing and diagnosing tool. The data stream and the transmission direction are reconstructed simultaneously from the near-field emanations of a twisted pair, eliminating direct contact with the actual conductors, and avoiding damage to the insulation (only the outer sheathing is removed). A non-contact probe with the ability to sense electric and magnetic fields is presented, as are theories for data reconstruction, direction identification, and a circuit implementation. The prototype was built using inexpensive components and then tested on a standard RS-485 industrial serial bus. Experimental results verified the validity of the proposed scheme.
Compact high-flux source of cold sodium atoms
Authors: Lamporesi G. , Donadello S. , Serafini S. , Ferrari G.
Published: June 2013

We present a compact source of cold sodium atoms suitable for the production of quantum degenerate gases and versatile for a multi-species experiment. The magnetic field produced by permanent magnets allows to simultaneously realize a Zeeman slower and a two-dimensional magneto-optical trap (MOT) within an order of magnitude smaller length than standard sodium sources. We achieve an atomic flux exceeding 4 × 109 atoms/s loaded in a MOT, with a most probable longitudinal velocity of 20 m/s, and a brightness larger than 2.5 × 1012 atoms/s/sr. This atomic source allows us to produce pure Bose-Einstein condensates with more than 107 atoms and a background pressure limited lifetime of 5 min.
A novel construction of complex-valued Gaussian processes with arbitrary spectral densities and its application to excitation energy transfer
Authors: Chen Xin , Cao Jianshu , Silbey Robert J.
Published: June 2013

The recent experimental discoveries about excitation energy transfer (EET) in light harvesting antenna (LHA) attract a lot of interest. As an open non-equilibrium quantum system, the EET demands more rigorous theoretical framework to understand the interaction between system and environment and therein the evolution of reduced density matrix. A phonon is often used to model the fluctuating environment and convolutes the reduced quantum system temporarily. In this paper, we propose a novel way to construct complex-valued Gaussian processes to describe thermal quantum phonon bath exactly by converting the convolution of influence functional into the time correlation of complex Gaussian random field. Based on the construction, we propose a rigorous and efficient computational method, the covariance decomposition and conditional propagation scheme, to simulate the temporarily entangled reduced system. The new method allows us to study the non-Markovian effect without perturbation under the influence of different spectral densities of the linear system-phonon coupling coefficients. Its application in the study of EET in the Fenna-Matthews-Olson model Hamiltonian under four different spectral densities is discussed. Since the scaling of our algorithm is linear due to its Monte Carlo nature, the future application of the method for large LHA systems is attractive. In addition, this method can be used to study the effect of correlated initial condition on the reduced dynamics in the future.
Detecting ZnSe secondary phase in Cu2ZnSnSe4 by room temperature photoluminescence
Authors: Djemour Rabie , Mousel Marina , Redinger Alex , Gütay Levent , Crossay Alexandre , Colombara Diego , Dale Phillip J. , Siebentritt Susanne
Published: June 2013

Secondary phases, such as ZnSe, occur in Cu2ZnSnSe4 and can be detrimental to the resulting solar cell performance. Therefore, it is important to have simple tools to detect them. We introduce subband gap defect excitation room temperature photoluminescence of ZnSe as a practical and non-destructive method to discern the ZnSe secondary phase in the solar cell absorber. The PL is excited by the green emission of an Ar ion laser and is detected in the energy range of 1.2–1.3 eV. A clear spatial correlation with the ZnSe Raman signal confirms this attribution.
Low spin-wave damping in amorphous Co40Fe40B20 thin films
Authors: Conca A. , Greser J. , Sebastian T. , Klingler S. , Obry B. , Leven B. , Hillebrands B.
Published: June 2013

A characterization of the magnetic properties of amorphous Co40Fe40B20 thin films, developed for low damping applications in magnon spintronics, using vector network analyzer ferromagnetic resonance (VNA-FMR) and the magneto-optical Kerr effect is presented. Our films show a very weak uniaxial anisotropy and a low Gilbert damping parameter (α=0.0042). The saturation magnetization MS extracted from the FMR measurements is 1250 kA/m. The frequency dependence of the first perpendicular standing spin waves mode on the applied magnetic field is used to determine the exchange constant A for this alloy resulting in a value of 1.5×10−11 J/m. These values are discussed in comparison to literature values for different CoFeB compositions and other related alloys.
Possible unified model for the Hooge parameter in inversion-layer-channel metal-oxide-semiconductor field-effect transistors
Authors: Omura Yasuhisa
Published: June 2013

This paper proposes a possible unified model for the Hooge parameter by considering the impact of transport dimensionality on the Hooge parameter behavior of various inversion-layer-channel metal-oxide-semiconductor field-effect transistors. Past experiments show that the Hooge parameter has a couple of peculiar behaviors. Based on a phenomenological consideration, the original mobility-based model for the Hooge parameter is shown to provide only a partial understanding of the results. It is also observed that, in contrast to past models, the interpretation of some aspects of the Hooge parameter strongly depends on how the two fluctuation modes, the carrier-density fluctuation and the mobility fluctuation, correlate. The phenomenological model proposed here gives a fundamental physical basis that allows important aspects of the Hooge parameter to be interpreted; the model also introduces three basic parameters (the Hooge parameter elements for the carrier-density fluctuation, the mobility fluctuation, and the cross-correlation component). Theoretical expressions for the three basic Hooge parameters are given by merging the fundamental Hooge model, Handel's theory, statistical physics, and quantum-mechanical transport physics. The gate voltage dependence of the Hooge parameter can be explained reasonably well by stating that the screening length rules the dielectric function and that the mobility fluctuation and carrier density fluctuation are correlated. Finally, the theoretical models are examined against the results of past experiments.
Far infrared reflection spectra of InAsxSb1−x (x = 0-0.4) thin films
Authors: Huang L. , Li Z. F. , Chen P. P. , Zhang Y. H. , Lu W.
Published: June 2013

A series of InAsxSb1−x ternary thin films (x = 0-0.4) has been studied in a far-infrared reflection experiment over the range of 50-4000 cm−1 at room temperature. The obtained spectra are fitted using a multi-oscillator model. Two types of lattice vibration modes, InSb-like and InAs-like, plus one plasmon mode have been identified in x > 0 samples. The lattice vibration in these ternary alloy films shows a typical two-mode behavior. Within the studied fraction range, the InSb transverse-optical (TO) phonon frequency decreases with x, while the InAs TO frequency increases. A random-element-isodisplacement model has been employed to describe the phonon frequency changes. The fitted plasmon parameters have been used to extract the carrier concentrations and mobility. The carrier concentration increases monotonously with the increase of As fraction and is attributed to the bandgap narrowing effect. The mobility decreases with x, indicating an increased scattering.
Nd3+-doped Ca3Ga2Ge3O12 garnet: A new optical pressure sensor
Authors: Rodríguez-Mendoza U. R. , León-Luis S. F. , Muñoz-Santiuste J. E. , Jaque D. , Lavín V.
Published: June 2013

A pressure-induced shift of the emission spectrum corresponding to the near infrared 4F3/2 → 4I9/2 transition of Nd3+ ions in a calcium gadolinium germanium garnet was obtained in the interval from ambient conditions up to 23 GPa in order to test its suitability as an optical pressure sensor. Although several Nd3+ non-equivalent centers are present in this garnet, which complicates the assignation of the optical transitions, the R1,R2 → Z5 transitions are unequivocally characterised and fit the requirements of an ideal optical pressure sensor. Results obtained for these emission peaks indicate large pressure coefficients of −8.8 and −10.8 cm−1 GPa−1; meanwhile, the rest of the R1,R2 → Z1−4 emissions remain almost unchanged under pressure. This behaviour is ascribed to the influence of the crystal-field at high pressure on the Z5 Stark level of the ground state and can be easily reproduced exclusively by varying the cubic term of fourth rank of the crystal-field Hamiltonian, which accounts for the Nd3+ ions and is related to medium Nd3+-oxygen distances. These coefficients are larger than those found for the R-lines of Cr3+ in ruby, −7.56 cm−1 GPa−1, suggesting that this system may be a good candidate for a luminescence pressure sensor.
Study of poly(3-hexylthiophene)/cross-linked poly(vinyl alcohol) as semiconductor/insulator for application in low voltage organic field effect transistors
Authors: Benvenho Adriano R. V. , Machado Wagner S. , Cruz-Cruz Isidro , Hümmelgen Ivo A.
Published: June 2013

In this work we study the cross-linked poly(vinyl alcohol)/poly(3-hexylthiophene) interfacial properties of an organic field effect transistor. We use cross-linked poly(vinyl alcohol) prepared with different ammonium dichromate:poly(vinyl alcohol) proportions, ranging from 0% to 35%, as insulator. Using admittance spectroscopy, we show that the interfacial properties change when the ammonium dichromate concentration is altered. The interfacial properties and the better insulation are responsible for the improvement of the device performance in these organic field effect transistors, achieving best performance in the blend with ammonium dichromate:poly(vinyl alcohol) proportion of 0.25:1.
Enhanced fluorescence emission using a photonic crystal coupled to an optical cavity
Authors: Pokhriyal Anusha , Lu Meng , Chaudhery Vikram , George Sherine , Cunningham Brian T.
Published: June 2013

All fluorescent assays would benefit from greater signal-to-noise ratios (SNRs), which enable detection of disease biomarkers at lower concentrations for earlier disease diagnosis and detection of genes that are expressed at the lowest levels. Here, we report an approach to enhance fluorescence in which surface adsorbed fluorophore-tagged biomolecules are excited on a photonic crystal surface that is coupled to an underlying Fabry-Perot type cavity through a gold mirror reflector beneath the photonic crystal. This approach leads to 6× increase in signal-to-noise ratio of a dye labeled polypeptide compared to ordinary photonic crystal enhanced fluorescence.
Electrical conductivity of thermally hydrogenated nanodiamond powders
Authors: Kondo Takeshi , Neitzel Ioannis , Mochalin Vadym N. , Urai Junichi , Yuasa Makoto , Gogotsi Yury
Published: June 2013

Electrical properties of detonation diamond nanoparticles (NDs) with individual diameters of ∼5 nm are important for many applications. Although diamond is an insulator, it is known that hydrogen-terminated bulk diamond becomes conductive when exposed to water. We show that heating ND in hydrogen gas at 600–900 °C resulted in a remarkable decrease in resistivity from 107 to 105 Ω cm, while the resistivity was essentially unchanged after treatment at 400 °C and lower temperatures. Fourier Transform Infrared Spectroscopy and X-ray photoelectron spectroscopy (XPS) studies revealed that hydrogenation of ND occurs at 600–900 °C, suggesting that the decrease in resistivity is based on transfer doping at the hydrogenated ND surface. Oxidation of the hydrogenated sample at 300 °C recovers resistivity to its original value. The resistivity of treated ND as a function of the O/C atomic ratio showed a transition from resistive (O/C ratio > 0.033) to conductive (O/C ratio < 0.033) state. This is consistent with the idea that the change in the resistivity is caused by the shift of the valence band maximum to above the Fermi level due to the dipole of the C-H bonds leading to transfer doping.
Absorption and diffusion of beryllium in graphite, beryllium carbide formation investigated by density functional theory
Authors: Ferro Yves , Allouche Alain , Linsmeier Christian
Published: June 2013

The formation of beryllium carbide from beryllium and graphite is here investigated. Using simple models and density functional theory calculations, a mechanism leading to beryllium carbide is proposed; it would be (i) first diffusion of beryllium in graphite, (ii) formation of a metastable beryllium-intercalated graphitic compound, and (iii) phase transition to beryllium carbide. The growth of beryllium carbide is further controlled by defects' formations and diffusion of beryllium through beryllium carbide. Rate limiting steps are the formation of defects in beryllium carbide, with estimated activation energies close to 2 eV.
Competition between uncatalyzed and catalyzed growth during the plasma synthesis of Si nanowires and its role on their optical properties
Authors: Garozzo C. , La Magna A. , Mannino G. , Privitera V. , Scalese S. , Sberna P. M. , Simone F. , Puglisi R. A.
Published: June 2013

In this paper, we study the metal-catalyzed synthesis of Si nanowires (Si-NWs) in a plasma based chemical vapor deposition system. In these deposition systems due to the high efficiency of precursor molecule dissociation, both uncatalyzed and catalyzed growth mechanisms can take place. The first one gives rise to the formation of the quasi one-dimensional (1D) Si-NWs, while the second one to a continuous two-dimensional (2D) Si layer over the substrate or on the nucleated Si-NWs. The Si-NWs formation is then the result of the competition between these two processes. The control parameters ruling these two contributions are here explored. Samples with different weights of 1D and 2D growth are deposited and characterized by using a plasma based chemical vapor deposition apparatus operating at T < 400 °C. It is found that the main control parameter of these processes is the plasma power through the distribution of the precursor dissociation products. By properly tuning the power, Si-NWs with 1 × 1010 cm−2 of density, up to 1 μm long and without uncatalyzed growth are obtained. The optical functionality of the samples, grown with different 1D/2D contributions, is investigated and it is demonstrated that the uncatalyzed layer produces a total reflectance as high as ∼40%, similar to that found in a planar Si wafer, while the highly dense Si-NWs, without the uncatalyzed deposition, produce a total reflectance of ∼15%.
Constant-pitch microprism-array optical device for beam condensers in hard x-ray synchrotron radiation beamlines
Authors: Kagoshima Y. , Takano H. , Takeda S.
Published: June 2013

A constant-pitch microprism-array optical device has been developed. It is a modified version of the previously reported quasi-Fresnel lens [Kagoshima et al., Appl. Phys. Lett. 101, 163102 (2012)]. The modification eases the fabrication of the lens, although it degrades some of the focusing performance. It consists of twenty 50-μm-wide right-angle microprisms, whose slope angles gradually increase to 67.8° at the outer side. By inclining the array, the aspect ratio of the microprisms becomes large enough for X-ray use. The effective slope angle can be enlarged to 86.4° at an inclination angle of 80.5°. A 10-keV synchrotron beam with a size of 680 μm (V) × 660 μm (H) was two-dimensionally condensed to 130 μm (V) × 380 μm (H) with a photon flux density gain of ∼3. We also show that the microprism array is suitable for practical use below the critical radiation dose rate.
Microstructure evolution during the isostructural decomposition of TiAlN—A combined in-situ small angle x-ray scattering and phase field study
Authors: Knutsson A. , Ullbrand J. , Rogström L. , Norrby N. , Johnson L. J. S. , Hultman L. , Almer J. , Johansson Jöesaar M. P. , Jansson B. , Odén M.
Published: June 2013

This paper describes details of the spinodal decomposition and coarsening in metastable cubic Ti0.33Al0.67N and Ti0.50Al0.50N coatings during isothermal annealing, studied by in-situ small angle x-ray scattering, in combination with phase field simulations. We show that the isostructural decomposition occurs in two stages. During the initial stage, spinodal decomposition, of the Ti0.50Al0.50N alloy, the phase separation proceeds with a constant compositional wavelength of ∼2.8 nm of the AlN- and TiN-rich domains. The time for spinodal decomposition depends on annealing temperature as well as alloy composition. After the spinodal decomposition, the coherent cubic AlN- and TiN-rich domains coarsen. The coarsening rate is kinetically limited by diffusion, which allowed us to estimate the diffusivity and activation energy of the metals to 1.4 × 10−6 m2 s−1 and 3.14 eV at−1, respectively.
Time-dependent ferroelectric transition in Pb(1−x)(Zr0.4Ti0.6)(1−x/4)O3 − xLa system
Authors: Sun Zhimin , Xue Dezhen , Wu Haijun , Ji Yuanchao , Ding Xiangdong , Wang Dong , Yang Yaodong , Ren Xiaobing
Published: June 2013

Ferroelectric transition involves tiny shift of ions within unit cell, thus being intrinsically a very fast process without apparent time-dependence. Contrary to this conventional wisdom, here we report a time-dependent ferroelectric transition, which occurs in hours. The system studied was Pb(1−x)(Zr0.4Ti0.6)(1−x/4)O3 − xLa system with relaxor-forming dopant La3+. The time-dependent ferroelectric transition occurs at the ferroelectric/relaxor crossover composition range of 0.09 < x ≤ 0.16. In these compositions, in situ Raman spectroscopy and transmission electron microscopy reveal very slow growth of ferroelectric phase. Dielectric measurement shows isothermal kinetics of the transition. The slow ferroelectric transition can be understood as being caused by the slowing-down of the otherwise fast growth of polar nano-domains due to the random local field caused by La3+, so that long time is needed to achieve long-range order macroscopic ferroelectric phase.
Minimization of ion micromotion using ultracold atomic probes
Authors: Härter A. , Krükow A. , Brunner A. , Hecker Denschlag J.
Published: June 2013

We report on a sensitive method to minimize excess micromotion of an ion in a Paul trap. The ion is placed in an ultracold cloud of neutral Rb atoms in which ionic micromotion induces atomic losses and heating. Micromotion is minimized by applying static electric offset fields such that both loss and heating are minimized. We achieve a compensation on the level of the most precise compensation methods to date. In contrast to these methods, our scheme is applicable even for ions that cannot be optically probed. Furthermore, it avoids the formation of temporary patch charges which are a main issue for the long-term stability of micromotion minimization.
Formation of uniformly sized gold nanoparticles over graphene by MeV electron beam irradiation for transparent conducting films
Authors: Kim Yooseok , Song Wooseok , Lee Su-il , Youb Lee Seung , Cha Myoung-Jun , Sung Jung Dae , Park Chong-Yun
Published: June 2013

Highly flexible, transparent, and conducting sheet was fabricated by decoration of uniformly sized gold nanoparticles (Au NPs) with high-density on large-area graphene by MeV electron beam irradiation (MEBI) at room temperature under ambient conditions. The Au NPs with an average size of 13.6 ± 3.5 nm were clearly decorated on the graphene after MEBI with an irradiation energy of 1.0 MeV. The sheet resistances of the Au NPs/graphene significantly decreased. For the Au NPs/trilayer graphene, the sheet resistance reached to ∼45 Ω/sq, and the optical transmittance was ∼90.2% which is comparable to that of conventional indium tin oxide film.
Coherent monochromatic phonons in highly purified semiconducting single-wall carbon nanotubes
Authors: Honda Yuki , Maret Elizabeth , Hirano Atsushi , Tanaka Takeshi , Makino Kotaro , Hase Muneaki
Published: June 2013

We have used a femtosecond pump-probe impulsive Raman technique to explore the polarization dependence of coherent optical phonons in highly purified and aligned semiconducting single-wall carbon nanotubes (SWCNTs). Coherent phonon spectra for the radial breathing modes (RBMs) exhibit a different monochromatic frequency between the film and solution samples, indicating the presence of differing exciton excitation processes. By varying the polarization of the incident pump beam on the aligned SWCNT film, we found that the anisotropy of the coherent RBM excitation depends on the laser wavelength, which we consider to be associated with the resonant and off-resonant behavior of RBM excitation.
Symmetry breaking and other nonlinear elastic responses of metallic glasses subject to uniaxial loading
Authors: Wang Hao , Li Mo
Published: June 2013

Topologically disordered metallic glasses (MGs) are known for exceedingly high elastic limit (2%–3%) and large local deformation at the onset of yielding in the form of shear banding. However, the manifestation of the large elastic deformation has not been taken into consideration in understanding the overall mechanical responses. By applying a finite deformation theory to initially isotropic solids under uniaxial loading, we investigate the nonlinear elastic behavior and its effects on mechanical properties. We take bulk metallic glass (BMG) Zr52.5Ti5Cu17.9Ni14.6Al10 as an example which is the only system by far with the experimentally measured nonlinear elastic constants up to the fourth order available for our theory. We show that the uniaxial loading breaks the isotropic symmetry of the MG and makes it transversely isotropic. We also predict the strain dependence of Poisson's ratio, Young's modulus, and anisotropic coefficients of the amorphous solids. Our work also gives the first estimate of the theoretical stress-strain relations and the elastic stability conditions under uniaxial loading from which we obtain the maximum tensile and compressive strengths and intrinsic deformation modes at the corresponding maximum stresses. Although depicting ideal scenarios, the theoretical results provide a useful reference for understanding mechanical response of MGs at large deformation.
Low rank approximation method for efficient Green's function calculation of dissipative quantum transport
Authors: Zeng Lang , He Yu , Povolotskyi Michael , Liu XiaoYan , Klimeck Gerhard , Kubis Tillmann
Published: June 2013

In this work, the low rank approximation concept is extended to the non-equilibrium Green's function (NEGF) method to achieve a very efficient approximated algorithm for coherent and incoherent electron transport. This new method is applied to inelastic transport in various semiconductor nanodevices. Detailed benchmarks with exact NEGF solutions show (1) a very good agreement between approximated and exact NEGF results, (2) a significant reduction of the required memory, and (3) a large reduction of the computational time (a factor of speed up as high as 150 times is observed). A non-recursive solution of the inelastic NEGF transport equations of a 1000 nm long resistor on standard hardware illustrates nicely the capability of this new method.
Study of structural properties of cubic InN films on GaAs(001) substrates by molecular beam epitaxy and migration enhanced epitaxy
Authors: Casallas-Moreno Y. L. , Pérez-Caro M. , Gallardo-Hernández S. , Ramírez-López M. , Martínez-Velis I. , Escobosa-Echavarría A. , López-López M.
Published: June 2013

InN epitaxial films with cubic phase were grown by rf-plasma-assisted molecular beam epitaxy (RF-MBE) on GaAs(001) substrates employing two methods: migration-enhanced epitaxy (MEE) and conventional MBE technique. The films were synthesized at different growth temperatures ranging from 490 to 550 °C, and different In beam fluxes (BEPIn) ranging from 5.9 × 10−7 to 9.7 × 10−7 Torr. We found the optimum conditions for the nucleation of the cubic phase of the InN using a buffer composed of several thin layers, according to reflection high-energy electron diffraction (RHEED) patterns. Crystallographic analysis by high resolution X-ray diffraction (HR-XRD) and RHEED confirmed the growth of c-InN by the two methods. We achieved with the MEE method a higher crystal quality and higher cubic phase purity. The ratio of cubic to hexagonal components in InN films was estimated from the ratio of the integrated X-ray diffraction intensities of the cubic (002) and hexagonal (101¯1) planes measured by X-ray reciprocal space mapping (RSM). For MEE samples, the cubic phase of InN increases employing higher In beam fluxes and higher growth temperatures. We have obtained a cubic purity phase of 96.4% for a film grown at 510 °C by MEE.
Magnetism of ultrathin Fe films in MgO/Fe/MgO in epitaxial structures probed by nuclear resonant scattering of synchrotron radiation
Authors: Kozioł-Rachwał A. , Giela T. , Matlak B. , Matlak K. , Ślęzak M. , Ślęzak T. , Zając M. , Rüffer R. , Korecki J.
Published: June 2013

Nuclear resonant scattering (NRS) of synchrotron radiation was used to investigate the magnetic anisotropy of iron films in MgO/Fe(t)/MgO(001) structures for t = (4–10) Å. The low-temperature NRS spectra were analyzed using a static magnetization model involving two interface-like components and a bulk-like component. We confirmed the existence of perpendicular magnetic anisotropy in MgO/Fe/MgO structures at 10 K with an increasing in-plane component of the magnetization for t > 8 Å over the entire thickness of the Fe film. The evolution of the magnetic structure with increasing temperature was studied for an Fe film thickness of 8.8 Å, and the temperature dependence of superparamagnetic fluctuations with characteristic frequencies ranging over tens of MHz was interpreted in terms of a spin reorientation transition. We showed that interfacial magnetic moments are less sensitive to thermal excitations than the magnetic moments in the film center, which was attributed to the spin pinning at the interface.
Tuning the mechanical behaviour of structural elements by electric fields
Authors: Di Lillo Luigi , Raither Wolfram , Bergamini Andrea , Zündel Manuel , Ermanni Paolo
Published: June 2013

This work reports on the adoption of electric fields to tune the mechanical behaviour of structural elements. A mechanical characterization procedure, consisting of double lap joint and 3-point bending tests, is conducted on copper-polyimide laminates while applying electric fields of varying intensity. Field dependence and, thus, adaptability of shear strength and bending stiffness are shown as a function of the overlapping length and interfaces number, respectively. Further, the impact of remaining charges is investigated in both testing configurations. The findings herein lay the foundation for the implementation of electro-adaptive components in structural applications.
High-gain wavelength-stabilized 1.55 μm InAs/InP(100) based lasers with reduced number of quantum dot active layers
Authors: Sichkovskyi V. I. , Waniczek M. , Reithmaier J. P.
Published: June 2013

The effect of the number of InAs/InP quantum dot layers (QDLs) on the static parameters of 1.55 μm emitting lasers was studied in the range of 1–3 QDLs. Due to the high modal gain of Γg0 ≥ 15.5 cm−1 per QDL ground state lasing of lasers with only a single QDL could be achieved with 11 mW total output power. By optimizing the QDLs number and the cavity length, the temperature dependence of the emission wavelength can be intrinsically stabilized resulting in an ultra-low emission wavelength shift of 0.078 nm/K for a 590 μm long laser with 2 QDLs.