bluuebunny/crossref_metadata_2025 huggingface dataset:
Francium sources at Laboratori Nazionali di Legnaro: Design and performance
Authors: Stancari G. , Veronesi S. , Corradi L. , Atutov S. N. , Calabrese R. , Dainelli A. , Mariotti E. , Moi L. , Sanguinetti S. , Tomassetti L.
Published: March 2006

A facility for the production of radioactive francium is operating at the laboratories of the Istituto Nazionale di Fisica Nucleare (INFN) in Legnaro, Italy. The goal is to collect a cold sample of radioactive atoms in a magneto-optical trap for studies in atomic, nuclear, and particle physics. Production of francium is achieved via the fusion-evaporation reaction Au197(O18,kn)215−kFr generated by a ∼100-MeV O6+18 beam on a thick gold target. The production target is heated to ∼1200K and kept at a potential of +3kV to enhance Fr diffusion and surface desorption. Average production rates are 0.7×106ions∕s for Fr210 with a primary beam flux of 1012particles∕s, with peaks of 2×106ions∕s. Details are given on the design and construction of the production targets and on the measurements that characterize their performance.
Using design of experiments method to model beamlet properties
Authors: Peters J. H. , Tartz M. , Neumann H.
Published: March 2006

The design of experiments approach is used to build models of the extracted beamlet current and divergence in dependence on grid parameters and plasma density employing a beamlet simulation code. Appropriate polynomial degrees for the input parameters are determined which result in a mean deviation of the models from additional simulated data of less than 4%. The derived models are obtained at a low computational effort and are helpful in designing and optimizing ion source extraction systems.
Surface modification of Si(111) substrate by iron ion implantation: Growth of a thin β-FeSi2 layer
Authors: Ayache R. , Bouabellou A. , Eichhorn F. , Richter E. , Mücklich A.
Published: March 2006

The processes in the synthesis of a thin layer of the semiconducting iron silicide (β-FeSi2) on the surface of a single-crystal Si(111) substrate by implantation of 195 keV Fe ions with a dose of 8×1017cm−2 are investigated. Using Rutherford backscattering spectrometry, x-ray diffraction and cross-sectional transmission electron microscopy, the structure and the phase composition of the synthesized layers are studied. The infrared transmittance spectra show the absorption at 310cm−1 as an indication of the initial nucleation of β-FeSi2 precipitates during the implantation of iron into silicon substrate.
Microwave proton sources for the IUCF LENS project
Authors: Klyachko A. V. , Derenchuk V. P. , Bogdanov A. A. , Solberg K.
Published: March 2006

The Indiana University Cyclotron Facility (IUCF) has constructed and placed in operation a Low Energy Neutron Source using a 10mA, 7MeV proton beam incident on a beryllium target. A microwave ion source used for the IUCF cyclotrons was modified to work in this application. In parallel, a 150mA, 75keV injector, based on the same ion source technology, is under construction. This higher current injector will be used to inject beam into a new 100mA peak current linac that will be installed in 2006. The simulations of the 75keV injector are reported.
Development of a permanent magnet light ion source at CEA/Saclay
Authors: Gobin R. , Charruau G. , Delferrière O. , De Menezes D. , Gauthier Y. , Harrault F. , Leherissier P. , Pacquet J. Y.
Published: March 2006

In France, the Spiral 2 project dedicated to radioactive beam production is based on a 40MeV continuous wave (cw) deuteron Linac. This installation will allow extending the variety of accelerated particles to very heavy elements. Such beams will open research domains for the GANIL facility. To inject the requested 5mA deuteron beam into the Spiral 2 Linac, the performance of the high intensity light ion source (SILHI) allowed us to propose such an electron cyclotron resonance source. SILHI, developed at CEA/Saclay, regularly produces high intensity (over 100mA) proton or deuteron beams through a Φ 9mm aperture. So for this project, the main modifications of the source design concern the permanent magnets which provide the axial magnetic configuration and the Φ 3mm aperture. The source produced its first beam (proton) in 2004. This article will report the beam characterization while the source produced D+ beam with intensity as high as 7.0mA. Recently, this permanent magnet source has been equipped with the Φ 9mm plasma electrode. So high intensity proton beams reaching more than 100mA are now extracted from this source.
Generation of a boron ion beam in a modified ion source for semiconductor applications
Authors: Gushenets V. I. , Bugaev A. S. , Oks E. M. , Yushkov G. Yu. , Hershcovitch Ady , Johnson B. M. , Kulevoy T. V. , Poole H. J. , Swarovsky A. Ya.
Published: March 2006

Presented here are results of experimental studies on the production of intense beams of boron ions using a modified Bernas–Calutron ion source. Instead of using the conventional boron–trifluoride gas, a solid lithium–boron–tetrafluoride compound was heated to release boron–trifluoride. For optimum ion source parameters the measured 25–41mA of total ion beam current was composed of 70% singly charged and about 1% doubly charged boron ions.
Measurement of total ion current from vacuum arc plasma sources
Authors: Oks E. M. , Savkin K. P. , Yushkov G. Yu. , Nikolaev A. G. , Anders A. , Brown I. G.
Published: March 2006

The total ion current generated by a vacuum arc plasma source was measured. The discharge system investigated allowed ion collection from the arc plasma streaming through a hemispherical mesh anode with geometric transparency of 72%. A range of different cathode materials was investigated, and the arc current was varied over the range of 50–500A. We find that the normalized ion current (Iion∕Iarc) depends on the cathode material, with values in the range from 5% to 19% and generally greater for elements of low cohesive energy. The application of a strong axial magnetic field in the cathode and arc region leads to increased normalized ion current, but only by virtue of enhanced ion charge states formed in a strong magnetic field.
Dresden electron beam ion trap: Status report and next developments
Authors: Zschomack G. , Heller R. , Kreller M. , Landgraf S. , Grossmann F. , Kentsch U. , Ovsyannikov V. P. , Schmidt M. , Ullmann F.
Published: March 2006

The Dresden EBIT is a room-temperature EBIT producing highly charged ions for x-ray spectroscopy as well as for materials modifications and other applications. In the past we have demonstrated the production of ions such as Ar18+, Fe26+, Kr35+, Xe46+, and Ir67+. Here we give a report on the further development of this ion source to increase the electric trap capacity involving the production of a greater amount of highly charged ions.
Design of a modular and versatile interlock system for ultrahigh vacuum machines: A crossed molecular beam setup as a case study
Authors: Guo Ying , Gu Xibin , Kawamura Ed , Kaiser Ralf I.
Published: March 2006

The design of a modular, versatile interlock system for ultrahigh vacuum machines is presented. This system can monitor the pressure (ultrahigh vacuum and high vacuum), the status of the power (power failure, power fluctuations, and scheduled power outages), the operation mode of the pumps (operation versus failure), the flow of cooling water, the humidity and temperature levels in the laboratory, as well as the concentration of toxic gases. If any of the set points is triggered, the vacuum machine is protected fully automatically. The interlock system is also interfaced to an automated paging system, thus transmitting a pager signal to the person on duty. Since the interlock system is modular in nature, it can be expanded and be adapted stepwise to incorporate additional safety and monitoring functions as needed.
High-order correlation effects on dynamic hyperpolarizabilities and their geometric derivatives: A comparison with density functional results
Authors: Pecul Magdalena , Pawłowski Filip , Jørgensen Poul , Köhn Andreas , Hättig Christof
Published: March 2006

Second harmonic generation hyperpolarizabilities and their geometric derivatives have been calculated for HF, HCl, CO, and LiF, using the coupled cluster hierarchies, CCS, CC2, CCSD, CC3, and large correlation-consistent basis sets. The full configuration interaction results have been used to test the accuracy of the coupled cluster results. The CCS and CC2 methods do not improve on the Hartree-Fock results while CCSD is robust and gives significant improvements compared to CCS and CC2. The effects of triples in CC3 are in some cases substantial. Higher order correlation effects are significant for LiF. Including core-valence correlation effects is required only if high accuracy is desired. The coupled cluster results have been used as benchmarks for the results obtained by means of density functional theory using various exchange-correlation functionals. For the hyperpolarizability B3LYP was found to perform best, i.e., to give the results closest to the CC3 ones, while for the geometric derivatives none of the considered functionals was able to give a consistent description for all the considered molecules.
Critical angle laser refractometer
Authors: Castrejón-Pita J. R. , Morales A. , Castrejón-García R.
Published: March 2006

A simple laser refractometer based on the detection of the critical angle for liquids is presented. The calibrated refractometer presents up to 0.000 11 of uncertainty when the refractive index is in the range between 1.300 00 and 1.340 00. The experimental setup is easy to construct and the material needed is available at most optics laboratories. The calibration method is simple and can be used in other devices. The refractive index measurements in aqueous solutions of sodium chloride were carried out to test the device and a linear dependence between the refractive index and the salt concentration was found.
1
kW
imaging furnace with in situ measurement of surface temperature
Authors: Guesdon Christine , Alxneit Ivo , Tschudi Hans Rudolf , Wuillemin Daniel , Sturzenegger Marcel
Published: March 2006

This article describes the development and characterization of a 1kW imaging furnace that allows to investigate materials such as sulfides at ultrahigh temperatures under controlled atmosphere. Peak flux densities up to (15.37±0.66)×106Wm−2 corresponding to a maximum stagnation temperature of 3090K can be reached in the center of the heating zone of 3mm diameter (full width at half height). Individual sample holders can be mounted on a generic sample stage that is aligned in three axes. Together they define an experiment. Experiments can thus be easily interchanged without requiring any realignment. The use of a specific sample holder is reported where the sample rests on a water-cooled tip to avoid contamination by crucible material and where a protective glass dome can be mounted to allow the study of samples releasing condensable or corrosive gases. With the dome in place the peak flux density decreases to a value of (13.59±0.45)×106Wm−2 (Tstag=2980K). The surface temperature of the sample and the average irradiance can be measured simultaneously by the pyrometric method flash assisted multiwavelength pyrometry. The irradiance on the sample and, thus, the temperature reached can be controlled by adjusting the position of the sample. This is effected by a computer controlled fork lift with a resolution of 0.05mm.
Noninvasive system for the simultaneous stabilization and control of magnetic field strength and gradient
Authors: Botti Laura , Buffa Roberto , Bertoldi Andrea , Bassi Davide , Ricci Leonardo
Published: March 2006

We report on the realization and characterization of a system for the simultaneous stabilization and control of magnetic field strength and gradient in a region of 35mm and along a given direction. The system is based on two magnetometers, each providing a field readout every 10μs, and a control unit, which real-time processes the readouts and controls the currents flowing into two compensation coils. Attenuations of 30dB for the field strength and 20dB for the gradient have been achieved, along with feedback loop bandwidths of 450 and 620Hz, respectively. The method can be extended in order to noninvasively control the field strength and gradient along all three directions as well as higher-order multipole terms.
Ultrasonic instrumentation for measurements in high magnetic fields. I. Continuous magnetic fields
Authors: Suslov A. , Sarma Bimal K. , Feller J. , Ketterson J.
Published: March 2006

Portable, superheterodyne, ultrasonic interferometers have been constructed for use with the continuous and pulsed magnetic field facilities of the National High Magnetic Field Laboratory sites at Tallahassee, FL and Los Alamos, NM. The instrumentation operates in the frequency range from 10 to 1000 MHz and enables precise measurements of changes in the ultrasonic velocity and attenuation in solids using the pulse-echo technique. In this first of a two part article we describe a basic ultrasonic system intended for measurements in quasicontinuous fields.
The rovibrational distribution of H2 and HD formed on a graphite surface at 15–50 K
Authors: Creighan Susan C. , Perry James S. A. , Price Stephen D.
Published: March 2006

The rotational distributions of H2 and HD formed on a highly oriented pyrolitic graphite surface at temperatures of 15–50 K have been measured using laser spectroscopy. The population of the rovibrational levels ν=1, J=0–4 and ν=2,J=0–4 has been observed and the average rotational temperatures of the nascent H2 and HD molecules have been determined. We find that the average rotational temperature of the newly formed molecules is much higher than the surface temperature on which they have formed. We compare our results with other recent experimental data and theoretical calculations.
Quantum transport through C48N12 based atomic devices
Authors: Xu Yan , Wang Jian , Xu Shijie
Published: March 2006

We report numerical calculations on the quantum transport through C48N12 based devices from first principles. We find that the transport properties are very sensitive to orientations of the molecules to the electrode. Different orientations can give rise to semiconducting to metallic behaviors. Our results show that the charge transfer which can be tuned by the gate voltage plays an important role in determining the transport properties. By varying the gate voltages, the transport properties can be changed from semiconducting to metallic behaviors and thereby magnifying effect can be achieved.
Selective adsorption, bound states, and potential parameters for He, Ne, and Ar interacting with a Cu(110) surface
Authors: Andersson T. , Linde P. , Hassel M. , Andersson S.
Published: March 2006

Using nozzle beams of He, Ne, and Ar, we have measured diffractive selective adsorption resonances from a Cu(110) surface kept at 20 K. Bound state energies of the atom-surface potentials have been determined from plots of the measured resonance energies versus incident angle and their fits to calculated kinematical dispersion relations. For He3 and He4 we have found a unique level assignment that is compatible with a single gas-surface potential curve with a well depth of 6.05 meV of the He–Cu(110) potential. This value is about 10% larger than the prediction of 5.55 meV from the current physisorption theory. The Ne and Ar data reveal a large number of closely spaced levels with level separations and estimated van der Waals coefficients that are compatible with available theoretical data.
Observation of octahedral cation coordination on the {111} surfaces of iron oxide nanoparticles
Authors: Lovely G. R. , Brown A. P. , Brydson R. , Kirkland A. I. , Meyer R. R. , Chang L. , Jefferson D. A. , Falke M. , Bleloch A.
Published: March 2006

High-resolution (scanning) transmission electron micrographs taken on both aberration corrected and uncorrected microscopes, and indirect reconstructed images of mixed phase magnetite—maghemite nanoparticles all show the presence of {111} facets that terminate with enhanced contrast. This enhanced contrast is shown to be a real effect caused by the presence of additional octahedrally coordinated iron cations occupying the {111} terminating layers of these nanoparticle surfaces.
Time- and frequency-domain analyses of fluorescence lifetime for temperature sensing
Authors: Rosso L. , Fernicola V. C.
Published: March 2006

Fluorescence lifetime detection is widely used for sensing physical and chemical quantities. The measurement accuracy of fluorescence lifetime-based sensing systems, either in time or frequency domain relies on their capability of detection and analysis of low level signal superimposed to noise. In this work a quantitative assessment of several data processing and analysis methods for the estimation of the fluorescence lifetime was carried out by using an experimental arrangement based on a fiber optic temperature sensor system. A comparison between the various methods was performed using actual signals from an optical sensing medium. The basic principles of time- and frequency-domain lifetime measurements were also reviewed and discussed in order to point out the limit of the cw frequency-domain approach and to suggest a way to overcome it. The investigated lifetime interval was from 200 to about 2200μs, corresponding to a temperature span of the sensor of about 300 °C. The results showed that in time domain (such as with Marquardt, integration, and log-fit algorithms) a good agreement, with relative differences from 0.2% to 0.5%, can be reached. Frequency-domain results based on an N-point fast Fourier transform (FFT) compare favorably with the previous ones in the long lifetime region (resulting in relative differences lower than 0.2%) with larger differences for short lifetimes. For each data processing method, the uncertainty associated with lifetime estimation was evaluated. Sampling and harmonics effects on the estimation accuracy for N-point FFTs were also investigated to trade-off between speed and accuracy of the algorithm in view of its application in real-time detection systems.
van der Waals interactions and dipole polarizabilities of lanthanides: Tm(F2)–He and Yb(S1)–He potentials
Authors: Buchachenko Alexei A. , Szczȩśniak Małgorzata M. , Chałasiński Grzegorz
Published: March 2006

Anisotropic dipole polarizabilities of Tm(F2),Tm+2(F2), and Yb(S1) are calculated using the finite-field multireference averaged quadratic coupled cluster (MR-AQCC) (Tm and Tm+2) and RCCSD(T) (Yb) methods with small-core relativistic pseudopotentials ECP28MWB combined with the augmented ANO basis sets. The lanthanide atoms are strongly polarizable with the scalar part originating from the 6s electrons and the tensorial part from the open 4f shells. The adiabatic interaction potentials Σ+2,Π2,Δ2, and Φ2 of Tm(F2)–He and Tm+2(F2)–He were examined by the multireference approaches, multireference configuration interaction and MR-AQCC, using the basis sets designed in the polarizability calculations. A closed-shell lanthanide system Yb(S1)–He was included for comparison. The Tm–He Σ+2,Π2,Δ2, and Φ2 interaction potentials are very shallow and nearly degenerate (within 0.01cm−1), with the well depths in the range of 2.35–2.36cm−1 at R=6.17Å. The basis-set saturated well depths are expected to be larger by ca. 25%, as estimated using the bond-function augmented basis set. The interactions of lanthanide atoms with He are one order of magnitude less anisotropic than those involving first-row transition metal atoms. The suppression of anisotropy is chiefly attributed to the screening effected by the 6s shell. When these electrons are removed as in the di-cation complex Tm+2(F2)–He, the potentials deepen to a thousand wave number range and their anisotropy is enhanced 500-fold.
Field induced anisotropy of charged magnetic colloids: A rescaled mean spherical approximation study
Authors: Wagner Joachim , Fischer Birgit , Autenrieth Tina
Published: March 2006

The liquidlike structure of colloidal suspensions with both electrostatic and magnetic interactions is investigated by means of small angle x-ray scattering (SAXS) dependent on an external magnetic field. For weak magnetic interactions, without external field, the magnetic dipoles are randomly oriented. Under this condition, isotropic structures are observed. In an external field, however, the magnetic momenta arrange parallel to the external field and induce anisotropic liquidlike structures. For weak magnetic interactions, the structure factor can be described within the framework of the rescaled mean spherical approximation. Due to the high experimental accuracy of synchrotron SAXS, from the anisotropic distortion of liquidlike structures, interparticle forces smaller than 10−15N can easily be detected.
Tetrahertz near-field electro-optic probe based on a microresonator
Authors: Mitrofanov Oleg
Published: March 2006

Electro-optic detection of tetrahertz (THz) pulses typically requires a long nonlinear crystal to accumulate a measurable electro-optic phase shift. The large crystal size prevents application of the method in high-resolution THz near-field microscopy. An electro-optic microresonator that enhances the electro-optic phase shift in a small volume is proposed as a near-field probe for THz microscopy. Frequency response of the microresonator probe is evaluated for different resonator designs.
Tip-enhanced near-field Raman spectroscopy probing single dye-sensitized TiO2 nanoparticles
Authors: Pan Duohai , Klymyshyn Nick , Hu Dehong , Lu H. Peter
Published: March 2006

The correlated metallic tip-enhanced Raman spectroscopy and atomic force microscopy (AFM) technique was used to characterize dye-sensitized titanium oxide (TiO2) nanoparticles. We have obtained the near-field Raman spectra that are associated with the photo-induced charge transfer reaction in Ru(4,4’-dicarboxy-2,2’-bipyridine)2(NCS)2-sensitized TiO2 single nanoparticles. This method demonstrates that tip-enhanced near-field Raman spectroscopy is an effective approach for understanding inhomogeneous interfacial electron transfers with nanoscale spatial resolution.
The influence of the quencher concentration on the rate of simple bimolecular reaction: Molecular dynamics study. II
Authors: Litniewski Marek
Published: March 2006

In this paper new results of the simulations [M. Litniewski, J. Chem. Phys. 123, 124506 (2005)] on the influence of the quencher concentration on the reaction A+B→C+B for the identical soft sphere system are presented. The problem is generalized by considering also the case when the spheres are immersed in the Brownian medium. A significant difference between simple deterministic systems and the Brownian ones is found: the excess in the rate coefficient for the Brownian system is constant and positive, except for very short times. The reaction has been simulated for a very long time, but any tendency to decrease the excess has not been noted. It is also shown that the relative excess in the surviving probability is a universal quadratic function of the quencher concentration for the range of time much longer than the result from the previous simulations. A very strong correlation between the excess in the relative value of spatial correlations between the reagents and the excess in the rate coefficient is shown. It is also shown that the A-A and A-C interactions have some influence on the excess values. A simple model for this effect is presented.
Coexistence of MA and MC phases in Pb(Mg1∕3Nb2∕3)0.68Ti0.32O3 single crystals
Authors: Bao Peng , Yan Feng , Lu Xiaomei , Zhu Jinsong , Shen Huimin , Wang Yening , Luo Haosu
Published: March 2006

The coexistence of MA (space group Cm) and MC (space group Pm) phases in as-grown Pb(Mg1∕3Nb2∕3)0.68Ti0.32O3 (PMNT32) single crystals is observed at room temperature under polarization microscopy. Laminar MA and MC domains normal to ⟨110⟩cub direction appear alternately in PMNT32 single crystals. In the heating run, the MA domains show a phase transition sequence of MA-MC-cubic, while the MC domains show only a phase transition of MC to cubic. In the cooling run, the phase transition sequence of cubic-MC-MA can be observed in the whole sample. It is suggested that the internal stress in the as-grown PMNT crystals is the main reason for the coexistence of the MA and MC phases.
Improved density of states Monte Carlo method based on recycling of rejected states
Authors: Chopra Manan , de Pablo J. J.
Published: March 2006

In this paper a new algorithm is presented that improves the efficiency of Wang and Landau algorithm or density of states (DOS) Monte Carlo simulations by employing rejected states. The algorithm is shown to have a performance superior to that of the original Wang-Landau [F. Wang and D. P. Landau, Phys. Rev. Lett. 86, 2050 (2001)] algorithm and the more recent configurational temperature DOS algorithm. The performance of the method is illustrated in the context of results for the Lennard-Jones fluid.
Diameter-selective near-field Raman analysis and imaging of isolated carbon nanotube bundles
Authors: Yano Taka-aki , Verma Prabhat , Kawata Satoshi , Inouye Yasushi
Published: March 2006

Tip-enhanced near-field Raman scattering has been utilized to demonstrate the measurement of the distribution of single-walled carbon nanotubes (SWNTs) with a spatial resolution far beyond the diffraction limit of the probing light. This was done by measuring the radial breathing mode (RBM) of SWNTs in the near-field Raman spectra, which corresponded to the diameters of various SWNTs in the immediate vicinity of the tip. Further, near-field Raman imaging of the RBM provided a super-resolved color mapping corresponding to the diameter distribution of SWNTs within a bundle, which is not possible to realize by conventional topographic imaging methods.
The generalized Ricci flow for three-dimensional manifolds with one Killing vector
Authors: Gegenberg J. , Kunstatter G.
Published: March 2006

We consider three-dimensional (3D) flow equations inspired by the renormalization group (RG) equations of string theory with a three-dimensional target space. By modifying the flow equations to include a U(1) gauge field, and adding carefully chosen De Turck terms, we are able to extend recent two-dimensional results of Bakas to the case of a 3D Riemannian metric with one Killing vector. In particular, we show that the RG flow with De Turck terms can be reduced to two equations: the continual Toda flow solved by Bakas, plus its linearizaton. We find exact solutions which flow to homogeneous but not always isotropic geometries.
A note on the Zassenhaus product formula
Authors: Scholz Daniel , Weyrauch Michael
Published: March 2006

We provide a simple method for the calculation of the terms cn in the Zassenhaus product ea+b=ea∙eb∙∏n=2∞ecn for noncommuting a and b. This method has been implemented in a computer program. Furthermore, we formulate a conjecture on how to translate these results into nested commutators. This conjecture was checked up to order n=17 using a computer.
Layer-resolved study of magnetic interaction effects in heterostructure dot arrays
Authors: Choi Y. , Lee D. R. , Freeland J. W. , Srajer G. , Metlushko V.
Published: March 2006

Using polarized x rays we have studied magnetic interactions in a series of patterned single-layer (NiFe and Co) and multilayer (NiFe∕Co and NiFe∕Cu∕Co) heterostructures. Extraction of layer-specific magnetic hysteresis loops from an array of 1-μm dots allows us to separate the influence of inter- and intralayer interactions. Double layer (NiFe∕Co) dots show evidence of identical vortex formation in both layers while with the spacer layer the direct coupling between the two magnetic layers is removed, and dipolar field contribution becomes significant so that the vortex formation in both layers is suppressed.
Influence of grain boundaries on the glass-transition behavior in C60 films
Authors: Wu Jian , Gu Min , Bao Peng , Feng Duan , Tang Tong Bor , Yang Senzu
Published: March 2006

Two batches of C60 films were prepared via sublimation on Ag (111) at two different growth rates. X-ray diffraction revealed in them a preferential (111) orientation and substantial stacking faults. Their dielectric spectra at various temperatures between 80 and 300K showed broad and asymmetric loss peaks attributable to some orientational glass transition. The nominal activation energies evaluated for the two batches are 344 and 305meV, respectively, larger than the value of 280meV for bulk C60. Applying Ngai’s correlated-state model, we determine the real activation energy, which then agrees well with the bulk value. We propose that, under the ac field, molecular volume changes accompany orientational “jumps” and cause local alternating stresses at grain boundaries, which correlate with the dipole reorientations. This correlation explains the deviation from Debye relaxation behavior and the increase in apparent activation energy.
A combined drop/suction-casting machine for the manufacture of bulk-metallic-glass materials
Authors: Wall J. J. , Fan C. , Liaw P. K. , Liu C. T. , Choo H.
Published: March 2006

The development of a machine with the capability to manufacture bulk-amorphous metal-alloy castings with a wide range of geometries and dimensions is described. The design utilizes a method of melting and alloying elemental metals and subsequently quench casting while controlling relative pressures to facilitate both drop and suction castings within an ultrahigh purity environment(∼1appm oxygen). The focus of this design was to improve the capabilities and simplicity of existing laboratory-scale metallic-glass casting machines, as well as to combine two major casting processes currently being utilized for the fabrication of bulk-metallic glasses (BMGs). Processing experiments on the glass-forming alloy Vitrelloy-105 (Zr52.5Cu17.9Ni14.6Al10Ti5) are discussed. The design is presented in a conceptual format, which will allow future units to be developed and, subsequently, utilized for their unique capabilities. It is believed that this document should be of interest to anyone who would like to develop the capability to produce BMGs on the laboratory scale.
Composite dipolar recoupling: Anisotropy compensated coherence transfer in solid-state nuclear magnetic resonance
Authors: Khaneja Navin , Kehlet Cindie , Glaser Steffen J. , Nielsen Niels Chr.
Published: March 2006

The efficiency of dipole-dipole coupling driven coherence transfer experiments in solid-state nuclear magnetic resonance (NMR) spectroscopy of powder samples is limited by dispersion of the orientation of the internuclear vectors relative to the external magnetic field. Here we introduce general design principles and resulting pulse sequences that approach full polarization transfer efficiency for all crystallite orientations in a powder in magic-angle-spinning experiments. The methods compensate for the defocusing of coherence due to orientation dependent dipolar coupling interactions and inhomogeneous radio-frequency fields. The compensation scheme is very simple to implement as a scaffold (comb) of compensating pulses in which the pulse sequence to be improved may be inserted. The degree of compensation can be adjusted and should be balanced as a compromise between efficiency and length of the overall pulse sequence. We show by numerical and experimental data that the presented compensation protocol significantly improves the efficiency of known dipolar recoupling solid-state NMR experiments.
Mirror that does not change the phase of reflected waves
Authors: Fedotov V. A. , Rogacheva A. V. , Zheludev N. I. , Mladyonov P. L. , Prosvirnin S. L.
Published: March 2006

We report that electromagnetic wave reflected from a flat metallic mirror superimposed with a planar wavy metallic structure with subwavelength features that resemble “fish scales” reflects like a conventional mirror without diffraction, but shows no phase change with respect to the incident wave. Such unusual behavior resembles a reflection from a hypothetical zero refractive index material, or “magnetic wall”. We also discovered that the structure acts as a local field concentrator and a resonant “amplifier” of losses in the underlying dielectric.
Polymer translocation through a nanopore under an applied external field
Authors: Luo Kaifu , Huopaniemi Ilkka , Ala-Nissila Tapio , Ying See-Chen
Published: March 2006

We investigate the dynamics of polymer translocation through a nanopore under an externally applied field using the two-dimensional fluctuating bond model with single-segment Monte Carlo moves. We concentrate on the influence of the field strength E, length of the chain N, and length of the pore L on forced translocation. As our main result, we find a crossover scaling for the translocation time τ with the chain length from τ∼N2ν for relatively short polymers to τ∼N1+ν for longer chains, where ν is the Flory exponent. We demonstrate that this crossover is due to the change in the dependence of the translocation velocity v on the chain length. For relatively short chains v∼N−ν, which crosses over to v∼N−1 for long polymers. The reason for this is that with increasing N there is a high density of segments near the exit of the pore, which slows down the translocation process due to slow relaxation of the chain. For the case of a long nanopore for which R‖, the radius of gyration Rg along the pore, is smaller than the pore length, we find no clear scaling of the translocation time with the chain length. For large N, however, the asymptotic scaling τ∼N1+ν is recovered. In this regime, τ is almost independent of L. We have previously found that for a polymer, which is initially placed in the middle of the pore, there is a minimum in the escape time for R‖≈L. We show here that this minimum persists for weak fields E such that EL is less than some critical value, but vanishes for large values of EL.
Polarization and experimental configuration analyses of sum frequency generation vibrational spectra, structure, and orientational motion of the air/water interface
Authors: Gan Wei , Wu Dan , Zhang Zhen , Feng Ran-ran , Wang Hong-fei
Published: March 2006

Here we report a detailed study on spectroscopy, structure, and orientational distribution, as well as orientational motion, of water molecules at the air/water interface, investigated with sum frequency generation vibrational spectroscopy (SFG-VS). Quantitative polarization and experimental configuration analyses of the SFG data in different polarizations with four sets of experimental configurations can shed new light on our present understanding of the air/water interface. Firstly, we concluded that the orientational motion of the interfacial water molecules can only be in a limited angular range, instead of rapidly varying over a broad angular range in the vibrational relaxation time as suggested previously. Secondly, because different vibrational modes of different molecular species at the interface has different symmetry properties, polarization and symmetry analyses of the SFG-VS spectral features can help the assignment of the SFG-VS spectra peaks to different interfacial species. These analyses concluded that the narrow 3693cm−1 and broad 3550cm−1 peaks belong to C∞v symmetry, while the broad 3250 and 3450cm−1 peaks belong to the symmetric stretching modes with C2v symmetry. Thus, the 3693cm−1 peak is assigned to the free OH, the 3550cm−1 peak is assigned to the singly hydrogen-bonded OH stretching mode, and the 3250 and 3450cm−1 peaks are assigned to interfacial water molecules as two hydrogen donors for hydrogen bonding (with C2v symmetry), respectively. Thirdly, analysis of the SFG-VS spectra concluded that the singly hydrogen-bonded water molecules at the air/water interface have their dipole vector directed almost parallel to the interface and is with a very narrow orientational distribution. The doubly hydrogen-bonded donor water molecules have their dipole vector pointing away from the liquid phase.
Field emission of doped carbon nanotubes
Authors: Ahn Hyo-Shin , Lee Kwang-Ryeol , Kim Doh-Yeon , Han Seungwu
Published: March 2006

We calculated field-emission currents from nitrogen- and boron-doped single-walled (5,5) carbon nanotubes by integrating time-dependent Schrödinger equations. Nitrogen doping increased the emission current owing to a shift in the energy level of a localized state to the Fermi level, and the creation of coupled states that have characteristics of both localized and extended states. On the other hand, boron doping had an opposite effect on the electronic structure by increasing the energy level of the localized state. The calculated emission currents of the boron-doped carbon nanotube fluctuated depending on the doping site and the external electric field.
Selective plasma etching of ZrOx to Si using inductively coupled BCl3∕C4F8 plasmas
Authors: Park S. D. , Lim J. H. , Oh C. K. , Lee H. C. , Yeom G. Y.
Published: March 2006

In this study, the etch characteristics of ZrOx and the etch selectivity to Si were investigated using BCl3∕C4F8 plasmas. The etching mechanism was also investigated. Increasing the C4F8 percentage to 4% formed a C–F polymer layer on the silicon surface due to the increased flux ratio of CFx∕F to the substrate, while no such C–F polymer was formed on the ZrOx surface due to the removal of carbon from CFx by the oxygen in ZrOx. By using 3–4% C4F8 in the BCl3∕C4F8 mixture, infinite etch selectivity of ZrOx to silicon and photoresist could be obtained while maintaining the ZrOx etch rate above 400Å∕min.
All-solid-state, narrow linewidth, wavelength-agile terahertz-wave generator
Authors: Guo Ruixiang , Akiyama Koichi , Minamide Hiroaki , Ito Hiromasa
Published: March 2006

An all-solid-state, narrow linewidth, wavelength-agile THz-wave parametric generator was developed. The THz-wave frequency can be set randomly or tuned rapidly and smoothly over the range from 0.6to2.4THz with a narrow linewidth of 50MHz. Using this THz-wave parametric generator, accurate and rapid measurements were made of the absorption spectrum of water vapor, with a wide frequency range from 0.8to2.1THz, from a single scan of the THz-wave frequencies. These results demonstrate that this THz-wave parametric generator is a powerful tool with practical applications in THz-wave spectroscopy.
Helical instability in metal halide lamps under micro and hypergravity conditions
Authors: Stoffels W. W. , Hout F. van den , Kroesen G. M. W. , Haverlag M. , Keijser R.
Published: March 2006

The onset and rotation frequency of a helical instability in a metal halide lamp is studied for gravity conditions varying from microgravity to 1.8g during parabolic flights and at microgravity in the International Space Station. The results show that gravity-induced convection seriously alters the onset and behavior of the instability. Hypergravity and low lamp power increase the rotation frequency of the instability, which seems independent of the arc pressure. At microgravity conditions, only arc bending and no rotation has been observed. The arc bending increases with lamp power, allowing one to monitor the driving and damping forces of the instability.
Calculation of deep carrier traps in a divacancy in germanium crystals
Authors: Coutinho J. , Torres V. J. B. , Jones R. , Carvalho A. , Öberg S. , Briddon P. R.
Published: March 2006

We present an ab initio density functional study on the electronic structure and electrical properties of divacancies in Ge. Although suffering essentially different Jahn-Teller distortions when compared to the analogous defect in Si, the relative location of the electrical levels in the gap does not differ radically in both materials. We propose a V2 model that is responsible for a donor level at Ev+0.03eV, a first acceptor state at Ev+0.3eV, and a second acceptor level at Ec−0.4eV. The latter is only 0.1eV deeper than an electron trap that has been recently linked to a divacancy in proton implanted material.
Multiband GaNAsP quaternary alloys
Authors: Yu K. M. , Walukiewicz W. , Ager J. W. , Bour D. , Farshchi R. , Dubon O. D. , Li S. X. , Sharp I. D. , Haller E. E.
Published: March 2006

We have synthesized GaNxAs1−yPy alloys (x∼0.003−0.01 and y=0–0.4) using nitrogen (N) ion implantation into GaAsP epilayers followed by pulsed laser melting and rapid thermal annealing techniques. As predicted by the band anticrossing model, the incorporation of N splits the conduction band of the GaAs1−yPy substrate, and strong optical transitions from the valence band to the lower (E−) and upper (E+) conduction subbands are observed. The relative strengths of the E− and E+ transition change as the localized N level EN emerges from the conduction band forming narrow intermediate band for y>0.3. The results show that GaNxAs1−x−yPy alloys with y>0.3 is a three band semiconductor alloy with potential applications for high-efficiency intermediate band solar cells.
Estimation of carrier recombination and electroluminescence emission regions in organic light-emitting field-effect transistors using local doping method
Authors: Oyamada Takahito , Sasabe Hiroyuki , Oku Yoshiaki , Shimoji Noriyuki , Adachi Chihaya
Published: March 2006

To elucidate the electroluminescence (EL) mechanism of organic light-emitting field-effect transistors (OLEFETs), we determined the carrier recombination and EL emission regions using the local doping method. We demonstrated that the local doping method is a useful technique for estimating the width of these regions in OLEFETs. We inserted an ultrathin rubrene doped 1,3,6,8-tetraphenylpyrene (TPPy) layer (d=10nm) as a sensing layer in a TPPy layer (80nm) and measured the luminance-drain current-drain voltage characteristics and the EL spectra depending on the position of the sensing layer. We confirmed that the EL emission region expanded almost to the height (h≃40nm) of the source-drain electrodes and was independent of the gate bias voltage (Vg). Further, we observed that the EL external quantum efficiency (ηext) significantly decreased as Vg increased, suggesting that excitons generated in a TPPy host layer by carrier recombination are quenched by the application of Vg.
Unambiguous observation of electronic couplings between InGaAs∕InGaAsP quantum dots emitting at 1.5μm
Authors: Jang Y. D. , Lee E. G. , Yim J. S. , Lee D. , Jeong W. G. , Pyun S. H. , Jang J. W.
Published: March 2006

We have unambiguously estimated the vertical and lateral electronic couplings between quantum dots (QDs) by comparing the carrier lifetimes at different energy positions inside the ground state band. InGaAs∕InGaAsP QDs on InP(100) substrate give photoluminescence around 1.55μm and have the dot density over 1011∕cm2. The measured carrier lifetimes are almost the same across the entire photoluminescence band, indicating negligible lateral electronic coupling between QDs at this high dot density. However, for a QD sample with the 15nm barrier spacing between QD layers the lifetime increases with increasing wavelength, clearly indicating the significant vertical electronic coupling between QDs.
Polarization splitting and terahertz oscillations from a single planar Fabry-Pérot microcavity
Authors: Gehlhaar R. , Swoboda M. , Sudzius M. , Hoffmann M. , Fröb H. , Lyssenko V. G. , Leo K. , Wendrock H.
Published: March 2006

We report the experimental observation of polarization splitting at normal incidence and terahertz oscillations of transmitted light from a single planar microcavity. Optical anisotropy in the SiO2∕TiO2-dielectric mirrors leads to two perpendicularly polarized transmission modes. We ascribe the anisotropy to oblique columnar structures in the dielectrics resulting from off-axial growth of the microcavity structure. We apply an up-conversion setup for temporally and spectrally resolved measurements and obtain a corresponding beating of 1.25THz. Time resolved measurements yield a cavity photon lifetime of 0.65ps, corresponding to a Q value of 1600. To explain our observations we introduce a Fourier-transform based analytical model.
Quality factor control of Si-based two-dimensional photonic crystals with a Bragg mirror
Authors: Li X. , Boucaud P. , Checoury X. , El Kurdi M. , David S. , Sauvage S. , Yam N. , Fossard F. , Bouchier D. , Fédéli J. M. , Salomon A. , Calvo V. , Hadji E.
Published: March 2006

We have investigated the coupling between two-dimensional photonic crystals and a distributed Bragg reflector by fabricating silicon-based photonic crystals on top of a one-dimensional Bragg mirror. The two-dimensional photonic crystals contain Ge∕Si self-assembled islands as an internal source covering the 1.1–1.6μm spectral range. We show that we can control the quality factor of Bloch modes by varying the thickness of the silicon layer on top of the Bragg mirror. Quality factors up to 2200 are obtained for optical radiative modes collected from the surface for a photonic crystal with a square lattice pattern. The variation of the quality factor as a function of the thickness of the upper layer is confirmed by three-dimensional finite-difference time domain calculations of the investigated structures.
Van Hove singularities in intersubband transitions in multiquantum well photodetectors
Authors: Le Rouzo Judikaël , Ribet-Mohamed I. , Guérineau N. , Haïdar R. , Tauvy M. , Rosencher E. , Chuang S. L.
Published: March 2006

Photocurrent spectra of quantum well infrared photodetector (QWIP) devices have been studied over more than three orders of magnitude, revealing features which have been largely overlooked before. Electric field assisted tunneling and, more surprisingly, Van Hove singularities at the miniband edges are shown to play an important role in the low and high energy parts of the QWIP photocurrent spectra, respectively. The photoresponse of QWIPs away from their peak responsivity is found to be non-negligible (>1% in the 3–5μm for a 8–12μm detector), which has to be taken into consideration when optimizing multispectral devices.
Temperature dependence of noise equivalent temperature change of Pt∕Si∕p-Si composites in the 3–5μm wavelength range
Authors: Bates Clayton W. , Hendricks Alphonso J. , Bankman Isaac N. , Thomas Michael E. , Prendergast Daniel T.
Published: March 2006

The temperature dependence of noise equivalent temperature change (NEΔT) in Kelvin was obtained for Pt∕Si∕p-Si planar Schottky diodes for temperatures from 50 to 150K. Over this range NEΔT is 0.2K at 120K, remaining below 1K up to about 130K assuming a typical quantum efficiency of 1%, due essentially to the large leakage current from the metal into the semiconductor. A calculation assuming recently measured values of the transport properties for a Pt∕Si∕p-Si composite system shows that a NEΔT of less than 0.2K is attainable at 300K for a film thickness of 0.5μm, with PtSi particle sizes of 3nm with a 15% volume fraction and a 1% quantum efficiency. The leakage here is determined by charge transfer between the metallic grains. At higher efficiencies it is possible to produce a wider range of particle sizes and volume fractions with NEΔT's smaller than 0.5K.
Supercritical-carbon dioxide-assisted cyclic deposition of metal oxide and metal thin films
Authors: Barua Dipak , Gougousi Theodosia , Young Erin D. , Parsons Gregory N.
Published: March 2006

Thin films of aluminum oxide and palladium were deposited on silicon at low temperatures (70–120°C) by a cyclic adsorption/reaction processes using supercritical CO2 solvent. Precursors included Al(hfac)3, Al(acac)3, and Pd(hfac)2, and aqueous H2O2, tert-butyl peracetate, and H2 were used as the oxidants or reductants. For the precursors studied, growth proceeds through a multilayer precursor adsorption in each deposition cycle, and film thickness increased linearly with the number of growth cycles.
On-chip microfluidic tuning of an optical microring resonator
Authors: Levy Uriel , Campbell Kyle , Groisman Alex , Mookherjea Shayan , Fainman Yeshaiahu
Published: March 2006

We describe the design, fabrication, and operation of a tunable optical filter based on a bus waveguide coupled to a microring waveguide resonator located inside a microchannel in a microfluidic chip. Liquid flowing in the microchannel constitutes the upper cladding of the waveguides. The refractive index of the liquid controls the resonance wavelengths and strength of coupling between the bus waveguide and the resonator. The refractive index is varied by on-chip mixing of two source liquids with different refractive indices. We demonstrate adjustment of the resonance by 2nm and tuning the filter to an extinction ratio of 37dB.