bluuebunny/crossref_metadata_2025 huggingface dataset:
Submicrosecond beam notching at low energy
Authors: Moehs D. P.
Published: March 2006

A technique for creating a burst of 100ns notches (beam extinctions) in a H− beam at 454kHz has been developed at ⩽20keV utilizing a magnetron ion source with a slit extraction system and a split extractor. Each half of the extractor is treated as part of a 50Ω transmission line which can be pulsed at ±700V, creating a 1400V gradient across the extractor. A beam current reduction of better than 95% has been observed at the end of the Fermilab 400MeV linac. Notched multiturn charge-exchange injection into the booster, a 400MeV–8GeV synchrotron, has been demonstrated with a charge reduction in the resulting beam gap of 83%. Presently, the trailing edge of the notch may be adversely affected by space charge resulting in a beam recovery with two different time constants. Efforts to minimize this effect are discussed.
Direct calculation of coupled diabatic potential-energy surfaces for ammonia and mapping of a four-dimensional conical intersection seam
Authors: Nangia Shikha , Truhlar Donald G.
Published: March 2006

We used multiconfiguration quasidegenerate perturbation theory and the fourfold-way direct diabatization scheme to calculate ab initio potential-energy surfaces at 3600 nuclear geometries of NH3. The calculations yield the adiabatic and diabatic potential-energy surfaces for the ground and first electronically excited singlet states and also the diabatic coupling surfaces. The diabatic surfaces and coupling were fitted analytically to functional forms to obtain a permutationally invariant 2×2 diabatic potential-energy matrix. An analytic representation of the adiabatic potential-energy surfaces is then obtained by diagonalizing the diabatic potential-energy matrix. The analytic representation of the surfaces gives an analytic representation of the four-dimensional conical intersection seam which is discussed in detail.
Kinetic properties of particle-in-cell simulations compromised by Monte Carlo collisions
Authors: Turner M. M.
Published: March 2006

The particle-in-cell method with Monte Carlo collisions is frequently used when a detailed kinetic simulation of a weakly collisional plasma is required. In such cases, one usually desires, inter alia, an accurate calculation of the particle distribution functions in velocity space. However, velocity space diffusion affects most, perhaps all, kinetic simulations to some degree, leading to numerical thermalization (i.e., relaxation of the velocity distribution toward a Maxwellian), and consequently distortion of the true velocity distribution functions, among other undesirable effects. The rate of such thermalization can be considered a figure of merit for kinetic simulations. This article shows that, contrary to previous assumption, the addition of Monte Carlo collisions to a one-dimensional particle-in-cell simulation seriously degrades certain properties of the simulation. In particular, the thermalization time can be reduced by as much as three orders of magnitude. This effect makes obtaining strictly converged simulation results difficult in many cases of practical interest.
Emittance studies with an Allison scanner
Authors: Stockli M. P. , Welton R. F. , Keller R. , Leitner M.
Published: March 2006

The Spallation Neutron Source H− source on the ion source test stand is being used to study the emittance of the H−-ion beam injected into the SNS radiofrequency quadrupole (RFQ). The emittance measurements are performed with a LBNL Allison scanner that underwent several modifications. The slit width was optimized to improve the signal-to-noise ratio. In addition, the electric deflector plates were replaced with plates featuring a staircased surface. This modification is shown to suppress over 99% of ghost signals generated by the beam hitting the deflector plates. Both modifications, combined with noise suppression measures and a self-consistent analysis, yield highly accurate results. Measured emittances are presented as a function of the ion-beam current.
Method for the calculation of electrical field in laser-generated plasma for ion stream production
Authors: Torrisi L. , Gammino S.
Published: March 2006

Ion streams are produced by hot plasmas laser generated at INFN-LNS of Catania by using a 9ns Nd:YAG laser which irradiates heavy element targets (Ta and Au) placed in vacuum. The ion emission from the plasma was measured with an electrostatic ion energy analyzer either for the energy-to-charge ratio or for the ion energy distributions. The ion emission occurs mainly along the normal to the target surface; the ion stream has a maximum charge state of 10+; the ions’ kinetic energy ranges from hundreds of eV up to values of about 6keV. In order to evaluate the production and acceleration processes a theoretical framework was defined and cross-checked with experimental results. The ion energy distributions can be fitted with Boltzmann-Coulomb-shifted functions giving the ion plasma temperature, the thermal velocity, the adiabatic expansion velocity of the plasma, and the Coulomb velocity. The ion energy distribution increased with the charge state (about 600eV/charge state). This result and the emission normal to the target surface indicate the presence of an electrical field inside the plasma which can be calculated by the method described hereinafter. Assuming that the electrical field acts for a distance comparable with the Debye length, the calculated electrical field is of the order of 5MV∕cm, in good agreement with the literature data. Measurements and calculation will be presented and discussed in detail.
Optimization of negative ion sources for a heavy-ion-beam probe
Authors: Nishiura M. , Ido T. , Shimizu A. , Kato S. , Tsukada K. , Nishizawa A. , Hamada Y. , Matsumoto Y. , Mendenilla A. , Wada M.
Published: March 2006

The development of plasma-sputter-type negative ion sources is underway for the heavy-ion-beam probe system as plasma diagnostic beams of the large helical device (LHD) for potential and fluctuation field measurements. Our purpose is to increase the doubly charged exchanged Au+ beam intensity to enhance the detection signal after passing through the plasmas of the LHD. For this purpose, the characterization of the Au− ion source and the beam optics has been carried out both experimentally and numerically. Based on these results, a new plasma-sputter-type negative ion source is designed and tested.
Chemical investigations of isotope separation on line target units for carbon and nitrogen beams
Authors: Frånberg H. , Ammann M. , Gäggeler H. W. , Köster U.
Published: March 2006

Radioactive ion beams (RIBs) are of significant interest in a number of applications. Isotope separation on line (ISOL) facilities provide RIB with high beam intensities and good beam quality. An atom that is produced within the ISOL target will first diffuse out from the target material. During the effusion towards the transfer line and into the ion source the many contacts with the surrounding surfaces may cause unacceptable delays in the transport and, hence, losses of the shorter-lived isotopes. We performed systematic chemical investigations of adsorption in a temperature and concentration regime relevant for ISOL targets and ion source units, with regard to COx and NOx on Al2O3 and SiO2. These materials are potential construction materials for the above-mentioned areas. Off-line and on-line tests have been performed using a gas thermochromatography setup with radioactive tracers. The experiments were performed at the production of tracers for atmospheric chemistry (PROTRAC) facility at the Paul Scherrer Institute in Villigen, Switzerland.
Investigation of a rf inductively coupled plasma ion source capable of highly uniform and collimated ion-beam generation
Authors: Kanarov V. , Hayes A. , Yevtukhov R. , Kameyama I. , Siegfried D. , Wåhlin E.
Published: March 2006

In accordance with advanced data storage device fabrication requirements, we have evaluated a new broad-beam rf ion source for ion beam etching and deposition application. This source utilizes a novel reentrant shaped plasma inductively coupled plasma generator for improved radial plasma density uniformity and a dynamic magnetic field for improved static etch uniformity. It has the capability of reproducibly generating extremely uniform ion beams from 500to1500eV with divergence angle <3° and high directionality [Kanarov et al. (patent pending)]. For a 150mm diameter wafer, an etch uniformity of <1% σ/mean in static condition or <0.5% with wafer rotation is obtained over an ion incident angle range of 0°–65°. Recently, we have investigated extending the operation of this source to the critical low energy range, 100–500eV, required for fabricating thin film magnetic head sensors. It was found that, under optimum operating conditions, excellent static etch uniformity (1%–1.5% σ/mean) could be obtained at high ion beam current densities, up to 0.5mA∕cm2, over the entire low-energy range while still achieving low divergence angles (<5°) and high beam directionality. The ion beam performance was consistent with results obtained by simulation and by experiment using a 19-hole array ion optic test stand with scanning ion probe [E. Wåhlin (unpublished)]. In this article we will describe the design of the ion source and then present the experimental performance data including plasma density distribution measured by an array of flat Langmuir probes, beam divergence distribution obtained by a “pepper-pot” etch measurement technique, and etching rate distributions.
Conformational entropy of a pseudoknot polymer
Authors: Sheng Yu-Jane , Mou You-Chin , Tsao Heng-Kwong
Published: March 2006

The thermodynamics and kinetics of ABAB pseudoknot formation owing to reversible intrachain reactions are investigated for a flexible polymer based on the off-lattice Monte Carlo simulations. The polymer is made of N hard spheres tethered by inextensible bonds and consists of two reactive pairs AA and BB with binding energies −ε1 and −ε2, respectively, and three loop lengths (ℓ1, ℓ2, and ℓ3). Although two intermediate states, loops A and B, may be formed, the folding path goes mainly through the intermediate loop whose free energy reduction associated with coil-to-loop crossover is greater. The conformational entropy loss is found to follow ΔS=αlnN+G, where α≃2.48 for coil-loop crossover and α≃2.43 for loop-pseudoknot crossover. The constant G depends on the three loop lengths and the two end-to-reactive site lengths (L1 and L2). For a given total loop length, G is maximum when the three loop lengths are equal (ℓ1=ℓ2=ℓ3). When ℓ1=ℓ3, the entropy loss is minimum if ℓ2=0. However, the condition ℓ1≠ℓ3 makes G even smaller. This consequence indicates that asymmetry in loop lengths is thermodynamically favorable and this fact is consistent with observations of pseudoknotted RNA structures.
Markov property and strong additivity of von Neumann entropy for graded quantum systems
Authors: Moriya Hajime
Published: March 2006

The quantum Markov property is equivalent to the strong additivity of von Neumann entropy for graded quantum systems. The additivity of von Neumann entropy for bipartite graded systems implies the statistical independence of states. However, the structure of Markov states for graded systems is different from that for tensor-product systems which have trivial grading. For three-composed graded systems we have U(1)-gauge invariant Markov states whose restriction to the marginal pair of subsystems is nonseparable.
Laser spectroscopic studies of several Rydberg states of MgO
Authors: Wang Jinjin , Breckenridge W. H.
Published: March 2006

We report extensive spectroscopic measurements of rovibronic transitions from the MgO XΣ+1 ground state to the high-energy EΣ+1, FΠ11, and GΠ11 Rydberg states. Perturbations in the EΣ+1 and GΠ11 states were observed. The Rydberg molecular orbital character of the three states is examined, given ab initio calculations by Thummel et al. [Chem. Phys. 129, 417 (1989)]. It is concluded that the EΣ+1 and GΠ11 states consist primarily of the MgO+XΠ2 ionic core, surrounded by 3pπ and 3pσ Rydberg electron clouds, respectively, and that the FΠ11 state consists primarily of the MgO+AΣ+2 ionic core surrounded by a 3pπ Rydberg electron cloud. Spectroscopic characterizations of some unassigned vibrational levels of analogous MgOΠ23 states in this energy region are also reported.
Free energy landscape analysis of two-dimensional dipolar solvent model at temperatures below and above the rotational freezing point
Authors: Suzuki Yohichi , Tanimura Yoshitaka
Published: March 2006

Ionic solvation in a polar solvent is modeled by a central charge surrounded by dipolar molecules posted on two-dimensional distorted lattice sites with simple rotational dynamics. Density of states is calculated by applying the Wang-Landau algorithm to both the energy and polarization states. The free energy landscapes of solvent molecules as a function of polarization are depicted to explore the competition between the thermal fluctuation and solvation energy. Without a central charge, for temperatures higher than the energy scale of the dipole-dipole interactions, the energy landscape for the small polarization region exhibits a parabolic shape as predicted by Marcus [Rev. Mod. Phys. 65, 599 (1993)] for electron transfer reaction, while there is an additional quartic contribution to the landscape for the large polarization region. When the temperature drops, the simulated free energy landscapes are no longer smooth due to the presence of multiple local minima arising from the frustrated interaction among the dipoles. The parabolic contribution becomes negligible and the energy landscape becomes quartic in shape. For a strong central charge, the energy landscape exhibits an asymmetric profile due to the contributions of linear and cubic terms that arise from the charge-dipole interactions.
Lower Rydberg series of methane: A combined coupled cluster linear response and molecular quantum defect orbital calculation
Authors: Velasco A. M. , Pitarch-Ruiz J. , Sánchez de Merás Alfredo M. J. , Sánchez-Marín J. , Martin I.
Published: March 2006

Vertical excitation energies as well as related absolute photoabsorption oscillator strength data are very scarce in the literature for methane. In this study, we have characterized the three existing series of low-lying Rydberg states of CH4 by computing coupled cluster linear response (CCLR) vertical excitation energies together with oscillator strengths in the molecular-adapted quantum defect orbital formalism from a distorted Cs geometry selected on the basis of outer valence green function calculations. The present work provides a wide range of data of excitation energies and absolute oscillator strengths which correspond to the Rydberg series converging to the three lower ionization potential values of the distorted methane molecule, in energy regions for which experimentally measured data appear to be unavailable.
Coherent exciton transport in dendrimers and continuous-time quantum walks
Authors: Mülken Oliver , Bierbaum Veronika , Blumen Alexander
Published: March 2006

We model coherent exciton transport in dendrimers by continuous-time quantum walks. For dendrimers up to the second generation the coherent transport shows perfect recurrences when the initial excitation starts at the central node. For larger dendrimers, the recurrence ceases to be perfect, a fact which resembles results for discrete quantum carpets. Moreover, depending on the initial excitation site, we find that the coherent transport to certain nodes of the dendrimer has a very low probability. When the initial excitation starts from the central node, the problem can be mapped onto a line which simplifies the computational effort. Furthermore, the long time average of the quantum mechanical transition probabilities between pairs of nodes shows characteristic patterns and allows us to classify the nodes into clusters with identical limiting probabilities. For the (space) average of the quantum mechanical probability to be still or to be again at the initial site, we obtain, based on the Cauchy-Schwarz inequality, a simple lower bound which depends only on the eigenvalue spectrum of the Hamiltonian.
Study of intense femtosecond laser propagation into a dense Ar gas and cluster jet
Authors: Caillaud T. , Blasco F. , Bonté C. , Dorchies F. , Mora P.
Published: March 2006

The propagation of an intense (up to 1017W∕cm2) and short laser pulse (down to 40fs) is studied through a well characterized high density Ar cluster jet obtained at the output of a supersonic nozzle. The x-ray emission from the irradiated clusters is measured as a function of the focusing depth inside the jet, with a spatial resolution of the emitting plasma. A strong refraction of the laser pulse is observed, limiting the interaction at the entrance of the jet and decreasing the effective laser intensity on clusters. Calculations indicate that it is due to the ionization of the residual gaseous phase present in the cluster jet. As the focal volume is modified, this effect should be considered for any quantitative analysis of the laser-cluster interaction.
The ionization instability and resonant acoustic modes suppression by charge space effects in a dusty plasma
Authors: Conde L.
Published: March 2006

The large wavenumber suppression of unstable modes by space charge effects of the ionization instability in a weakly ionized and unmagnetized dusty plasma is investigated. The charge losses in the initial equilibrium state are balanced by electron impact ionizations originated by both the thermal electron populations and an additional monoenergetic electron beam. The multifluid dimensionless equations are deduced by using the time and length scales for elastic collisions between ions and neutral atoms and the Poisson equation relates the plasma potential fluctuations with charged particle densities instead of the quasineutral approximation. A general dimensionless dispersion relation is obtained from the linearized transport equations, where the ratios between the characteristic velocities, as the dust ion acoustic (IA), dust acoustic (DA), ion sound, and thermal speeds permits us to evaluate the weight of the different terms. In the long wavelength limit the results obtained using the quasineutral approximation are recovered. The differences found between roots of both dispersion equations are discussed, as well as those of previous models. The unstable mode of the linear ionization instability is originated by the imbalance between ion and electron densities in the rest state caused by the negative charging of dust grains. Contrary to dust free plasmas, the unstable mode exists, even in the absence of the ionizing electron beam. The numerical calculations of the roots of the full dispersion equation present a maximum unstable wavenumber not predicted by the quasineutral approximation, which is related with the minimum allowed length for space charge fluctuations within a fluid model. This upper limit of unstable wave numbers hinders the predicted resonant coupling in the long wavenumber regime between the DA and DIA waves.
Experimental and theoretical determination of the dipole-quadrupole and dipole-octopole polarizabilities of the group IV tetrachlorides TiCl4, ZrCl4, and HfCl4
Authors: Hohm Uwe , Maroulis G.
Published: March 2006

The dipole-quadrupole and dipole-octopole polarizabilities A and E of TiCl4, ZrCl4, and HfCl4 have been determined from collision-induced light-scattering experiments. Our respective experimental results for ∣A∣ are (165±10), (110±30), and (140±20) e2a03Eh−1, whereas ∣E∣ is determined to be (675±125), (750±200), and (670±400) e2a04Eh−1. Theory predicts values convincingly close to experiment, as A=(181.4±9.1), (167.6±8.4), and (139.8±7.0) e2a03Eh−1, and E=(−671±67), (−688±69), and (−574±57) e2a04Eh−1. In addition our quantum chemical ab initio calculations give reliable values for the dipole polarizability α, as well as for the octopole and hexadecapole moments Ω and Φ for all three substances.
Symmetry-dependent vibrational excitation in N 1s photoionization of N2: Experiment and theory
Authors: Ehara M. , Nakatsuji H. , Matsumoto M. , Hatamoto T. , Liu X.-J. , Lischke T. , Prümper G. , Tanaka T. , Makochekanwa C. , Hoshino M. , Tanaka H. , Harries J. R. , Tamenori Y. , Ueda K.
Published: March 2006

We have measured the vibrational structures of the N 1s photoelectron mainline and satellites of the gaseous N2 molecule with the resolution better than 75meV. The gerade and ungerade symmetries of the core-ionized (mainline) states are resolved energetically, and symmetry-dependent angular distributions for the satellite emission allow us to resolve the Σ and Π symmetries of the shake-up (satellite) states. Symmetry-adapted cluster-expansion configuration-interaction calculations of the potential energy curves for the mainline and satellite states along with a Franck-Condon analysis well reproduce the observed vibrational excitation of the bands, illustrating that the theoretical calculations well predict the symmetry-dependent geometry relaxation effects. The energies of both mainline states and satellite states, as well as the splitting between the mainline gerade and ungerade states, are also well reproduced by the calculation: the splitting between the satellite gerade and ungerade states is calculated to be smaller than the experimental detection limit.
Vibrational Feshbach resonances in uracil and thymine
Authors: Burrow P. D. , Gallup G. A. , Scheer A. M. , Denifl S. , Ptasinska S. , Märk T. , Scheier P.
Published: March 2006

Sharp peaks in the dissociative electron attachment (DEA) cross sections of uracil and thymine at energies below 3eV are assigned to vibrational Feshbach resonances (VFRs) arising from coupling between the dipole bound state and the temporary anion state associated with occupation of the lowest σ* orbital. Three distinct vibrational modes are identified, and their presence as VFRs is consistent with the amplitudes and bonding characteristics of the σ* orbital wave function. A deconvolution method is also employed to yield higher effective energy resolution in the DEA spectra. The site dependence of DEA cross sections is evaluated using methyl substituted uracil and thymine to block H atom loss selectively. Implications for the broader issue of DNA damage are briefly discussed.
Apparatus for solution jet beam deposition of organic thin films and in situ ultraviolet photoelectron spectroscopy
Authors: Okabayashi Y. , Kanai K. , Ouchi Y. , Seki K.
Published: March 2006

We report an instrument with the combination of solution jet beam deposition method and ultraviolet photoelectron spectroscopy (UPS). The solution jet beam method is a novel technique to fabricate organic thin films in vacuum, where solution of the organic material is sprayed in vacuum. This method can be applied to organic materials which cannot be vacuum evaporated due to thermal decomposition, e.g., ionic organic solids such as cyanine dyes. The present instrument combines this method with UPS, which is a powerful method for investigating the electronic structure of solids. Using this instrument, the UPS spectra of cyanine dye films deposited by the solution jet beam method were measured without exposure to air. The observed spectra were clearer than those of spin-coated films exposed to air.
Pendulum for precision force measurement
Authors: Fujii Yusaku
Published: March 2006

A pendulum and a method for correcting the restoring force of the pendulum are proposed for realizing an instrument based on the levitation mass method without the use of pneumatic linear bearings. As an example a material tester using the pendulum, which evaluates the mechanical response of general objects against impact forces, is developed. The characteristics of the restoring force are accurately determined using the same instrument under the free-swing condition without the object under test. To demonstrate the high performance of the developed instrument, the impact response of a gel block is accurately determined. The possible applications of the developed method are discussed.
Contact-mode scanning tunneling microscopy experimental technique employed for tunneling magnetoresistance measurements
Authors: Podgursky V. , Adam R. , Teske M. , Krämer M. , Franchy R.
Published: March 2006

We employed contact-mode scanning tunneling microscopy technique to perform systematic measurements of micrometer-sized Co∕Al2O3∕Co magnetic tunnel junctions (MTJs). Magnetic multilayer was grown by means of magnetron sputtering, followed by patterning of MTJ on top of FeMn antiferromagnetic bias layer into an array of rectangular mesa structures by standard photolithography. The maximum of 12.5% tunneling magnetoresistance at room temperature was measured for up to 40×40μm2 test MTJs.
Epitaxial growth of AlN on single-crystal Ni(111) substrates
Authors: Kim Tae-Won , Matsuki N. , Ohta J. , Fujioka H.
Published: March 2006

We grew AlN thin films on Ni(111) at room temperature using pulsed laser deposition. In situ reflection high-energy electron diffraction observations showed sharp streak patterns, revealing that the AlN films grew epitaxially and were of high quality, even when grown at room temperature. Electron backscatter diffraction measurements showed that the in-plane epitaxial relationship between the film and Ni was AlN[11-20]∥Ni[01-1] with no 30° rotational domains. Grazing incidence angle x-ray reflectivity measurements determined that the interfacial layer was less than 1.2nm thick, if present. This indicates that the heterointerface between the AlN film and Ni substrate is atomically abrupt and that the AlN films serve as an excellent barrier layer for Ni atoms. Furthermore, the refractive index of a 60-nm-thick AlN film was 2.15 at 3.1eV and 2.08 at 1.6eV. These results demonstrate that the AlN films grown on Ni substrates at room temperature are of high quality from the perspective of their structural and optical properties.
Field-effect control of protein transport in a nanofluidic transistor circuit
Authors: Karnik Rohit , Castelino Kenneth , Majumdar Arun
Published: March 2006

Electrostatic interactions play an important role in nanofluidic channels when the channel size is comparable to the Debye screening length. Electrostatic fields have been used to control concentration and transport of ions in nanofluidic transistors. Here, we report a transistor-reservoir-transistor circuit that can be used to turn “on” or “off” protein transport using electrostatic fields with gate voltages of ±1V. Our results suggest that global electrostatic interactions of the protein were dominant over other interactions in the nanofluidic transistor. The fabrication technique also demonstrates the feasibility of nanofluidic integrated circuits for the manipulation of biomolecules in picoliter volumes.
External cavity InAs∕InP quantum dot laser with a tuning range of 166nm
Authors: Ortner G. , Allen C. Ni. , Dion C. , Barrios P. , Poitras D. , Dalacu D. , Pakulski G. , Lapointe J. , Poole P. J. , Render W. , Raymond S.
Published: March 2006

We have studied the tuning behavior of an external cavity laser in Littrow configuration using antireflection/high-reflection coated InAs∕InGaAsP∕InP quantum dot laser diodes as the amplifying element. Adding the coatings improves the performance of the setup, and the tunability of the external cavity laser output has been increased up to 166nm. Detailed investigations have revealed that laser diode length and width influence the magnitude of the tuning range. Furthermore, the external differential quantum efficiency is systematically increasing as the external cavity laser wavelength is decreasing. These characteristics are discussed in terms of energy levels available in the inhomogeneous broadening of the self-assembled quantum dots.
Low-voltage varistors from ZnO+CaMnO3 ceramics
Authors: Vijayanandhini K. , Kutty T. R. N.
Published: March 2006

Varistors prepared from ZnO with CaMnO3 perovskite as the only forming additive, exhibit voltage-limiting current-voltage characteristics with nonlinearity coefficient α up to 380 at low voltages of 1.8–12V∕mm. High nonlinearity is observed only with a suitable combination of processing parameters. The most crucial of them are (i) initial formulation of ceramics and (ii) the sintering temperature and conditions of post-sinter annealing. An electrically active intergranular phase is formed between ZnO grains with the composition ranging from Ca4Mn6Zn4O17 to Ca4Mn8Zn3O19, which creates the n-p-n heterojunctions. The low-voltage nonlinearity originates as a result of higher concentration of Mn(III)∕Mn(IV) present at the grain boundary layer regions, being charge compensated by zinc vacancies. Under the external electric field, the barrier height is lowered due to the uphill diffusion of holes mediated by the acceptor states. Above the turn-on voltages, the unhindered transport of charge carriers between grains generates high current density associated with large nonlinearity.
Experimental evidence for the role of Xe2+ in pumping the Ar–Xe infrared laser
Authors: Apruzese J. P. , Giuliani J. L. , Wolford M. F. , Sethian J. D. , Petrov G. M. , Hinshelwood D. D. , Myers M. C. , Ponce D. M. , Hegeler F. , Petrova Ts.
Published: March 2006

In a series of experiments on the Naval Research Laboratory's Electra generator, we have measured the dependence of the laser output in the principal (1.733μm) transition of the Ar–Xe laser upon both initial gas temperature and Xe concentration. The data show that the laser output is less sensitive to gas temperature when the laser gas contains more Xe. The destruction rate of the molecular ion ArXe+ increases rapidly with gas temperature, but that of Xe2+ does not. Interpreted with a kinetics model, these data indicate that both Xe2+ and ArXe+ contribute to the pumping of the ArXe laser.
Properties of photoluminescence in type-II ZnTe∕ZnSe quantum dots
Authors: Lin T. Y. , Lyu D. Y. , Chang J. , Shen J. L. , Chou W. C.
Published: March 2006

Temperature and time evolution of the photoluminescence (PL) intensity of bimodal ZnTe∕ZnSe type-II quantum dots (QDs) were investigated. A particular temperature dependence of PL was observed in large QDs. PL decay of small QDs is composed of a faster initial component and a slower tail component whereas PL decay of large QDs simply comprises a fast component. All phenomena could be understood consistently by considering charge carrier transfer mechanism, band-bending effect, and the existence of nonradiative centers in the bimodal type-II QD array. We show that excitons play an important role in the emission properties of a self-assembled type-II QD system.
Electron-beam deposited SiO2 investigated by scanning capacitance microscopy
Authors: Brezna W. , Fischer M. , Wanzenboeck H. D. , Bertagnolli E. , Smoliner J.
Published: March 2006

The quality of electron-beam deposited, few nanometers thick, SiO2 layers on silicon substrates was investigated by scanning capacitance microscopy and spectroscopy. Rapid thermal annealing had to be applied prior to the capacitance versus voltage [C(V)] measurements to obtain typical metal-oxide-semiconductor behavior, and it was found that the total oxide charge is negative on the deposited oxide layers. Higher annealing temperatures resulted in an overall reduction of the number of oxide charges. This opens up the possibility to use electron-beam deposited SiO2 as a dielectric material in metal-oxide-semiconductor prototyping applications.
Determination of the thermal expansion of Cr3+ sites in glasses
Authors: Calas Georges , Majérus Odile , Galoisy Laurence , Cormier Laurent
Published: March 2006

High temperature optical spectra of Cr3+ in glasses show a systematic linear redshift of crystal-field transitions in the 300–800K range, giving them thermochromic properties. Linear thermal expansion coefficients of Cr3+ in glasses of about 15×10−6K−1 are derived from the spectroscopic data, using a point charge model. The values obtained are independent on glass composition and greater than the macroscopic thermal expansion coefficients of the glasses investigated. These observations help understand the structural evolution of glasses at high temperatures by a better comparison between thermal expansion processes in glasses and crystals.
Improvement of the emission current from a cesiated metal-oxide-semiconductor cathode
Authors: Mimura H. , Neo Y. , Shimawaki H. , Abe Y. , Tahara K. , Yokoo K.
Published: March 2006

We have reduced the work function of the gate electrode of a metal-oxide-semiconductor tunneling cathode by cesiation. After cesiation, there was a considerable increase in the emission current and a large number of electrons were detected at energies lower than the original vacuum level of the poly-Si gate electrode. These results indicate that almost all the tunneling electrons have energies lower than the original vacuum level of the gate electrode, and that after cesiation electrons initially prevented from being emitted by the original vacuum level were emitted, because of the reduced work function due to cesiation.
Photoluminescence of Ge∕Si structures grown on oxidized Si surfaces
Authors: Shklyaev A. A. , Nobuki S. , Uchida S. , Nakamura Y. , Ichikawa M.
Published: March 2006

Ge ∕ Si structures grown on oxidized Si surfaces are studied by means of photoluminescence (PL). High-temperature annealing of the structures leads to the increase of their PL intensity by at least one order of magnitude at energies around 0.82eV. It is suggested that relaxation of strain, existing in our structures due to the Ge∕Si lattice mismatch, occurs through the formation of defects such as interstitial clusters in the Si layer capping the layer of Ge islands. These defects in conjunction with oxygen complexes of the rest of the Si oxide film provide the intense PL in the D1 range.
Influence of growth temperature on order within silicon films grown by ultrahigh-vacuum evaporation on silica
Authors: Tay Li-Lin , Lockwood David J. , Baribeau Jean-Marc , Noël Mario , Zwinkels Joanne C. , Orapunt Farida , O’Leary Stephen K.
Published: March 2006

We study the role that the growth temperature plays in determining the amount of order present within silicon films deposited on fused silica substrates through ultrahigh-vacuum evaporation at growth temperatures ranging from 98 to 572°C. Through measurements of the Raman and optical absorption spectra, we quantitatively determine how the growth temperature influences the order present within 11 such films. We employ three disparate measures of order for the purposes of this study: the breadth of the transverse-optic phonon Raman peak, this being related to the amount of short-range order present; the area under the transverse-acoustic Raman peak divided by the area under the corresponding transverse-optic peak, this being related to the amount of intermediate-range order present; and the breadth of the optical absorption tail, which is a general measure of the overall amount of order present. All three measures of order indicate a dramatic increase in the amount of order present for growth temperatures above 400°C.
Activation of a photosensitive pharmaceutical agent by a triboluminescent material
Authors: Yuen Stacey , Schreyer Magdalena , Finlay W. H. , Löbenberg R. , Moussa W.
Published: March 2006

Given the recent emphasis on applications of triboluminescent materials, we investigate the ability of a triboluminescent material to activate a photosensitive pharmaceutical agent. Using compressed sucrose doped with wintergreen, which luminesces when fractured, we demonstrate the activation of riboflavin (vitamin B2), a photosensitizer. A product of activation is the highly reactive singlet oxygen. We add ascorbic acid (vitamin C), an antioxidant, and measure the amount of ascorbic acid oxidation to correlate with the amount of riboflavin activation. Up to 17% ascorbic acid oxidation is observed, indicating triboluminescence is worth exploring as a mechanism for activation of photosensitizers in photodynamic therapy.
Thermophysical properties of Mo liquids growing into spherical single crystals via containerless electrostatic levitation
Authors: Sung Y. S. , Bae D. S. , Song T. K. , Kim M. H. , Takeya H. , Hirata K. , Togano K.
Published: March 2006

The thermophysical ratio of constant pressure heat capacity to hemispherical total emissivity cP(T)∕ϵT(T) of liquid Mo (Tm=2895K) was analytically estimated from the radiative cooling curve measured during containerless melting and solidification via electrostatic levitation. cP(T) and ϵT(T) were then derived to describe the temperature-dependent cooling behavior of liquid Mo before nucleation. Spherical Mo liquids by surface tension kept their spherical shapes during containerless solidification becoming single crystals confirmed by the truncated octahedron bound by eight {111} planes exposed by preferential macroetching and the spotty Laue patterns by backreflection.
Formation of nanoscale liquid menisci in electric fields
Authors: Garcia-Martin Antonio , Garcia Ricardo
Published: March 2006

Nanometer-sized menisci of polar and nonpolar liquids are used to confine chemical reactions. Electric fields applied between two surfaces a few nanometers apart allow the formation and manipulation of three-dimensional nanoscale liquid bridges. At low fields, two stable shapes coexist: one represents a small liquid protrusion underneath the strongest field lines while the other is a nanoscale liquid contact bridging both surfaces. The formation of a nanoscale liquid meniscus requires the application of a threshold voltage to overcome the energy barrier between stable configurations. The bridge formation is accompanied by a drastic reduction of the electrical field at the solid-liquid interface.
Erbium luminescence imaging of infrared surface plasmon polaritons
Authors: Verhagen E. , Tchebotareva A. L. , Polman A.
Published: March 2006

We demonstrate a new technique to spatially map the propagation and damping of infrared surface plasmon polaritons (SPPs) on metal films using optically active erbium ions as a probe of the SPP field. The bound SPP mode propagating along the Ag/glass interface of a 96nm thick Ag film on glass is excited by illuminating a subwavelength hole array in the metal with 1.49μm light. By imaging the 1.53μm photoluminescence of Er ions positioned in the glass at a distance of 60nm from the Ag/glass interface in a confocal microscope, a SPP beam was observed to propagate along a broad stripe waveguide, with a characteristic propagation length of 76μm. This technique provides a useful tool to study the characteristics of SPP modes at metal-dielectric interfaces in a wide range of geometries.
Experimental characterization of the sensor effect in ferromagnetic shape memory Ni–Mn–Ga
Authors: Sarawate N. , Dapino M.
Published: March 2006

The characterization of a commercial Ni–Mn–Ga alloy for use as a deformation sensor is addressed. The experimental determination of flux density as a function of strain loading and unloading at various fixed magnetic fields gives the bias field needed for maximum recoverable flux density change. This bias field is shown to mark the transition from irreversible (quasiplastic) to reversible (pseudoelastic) stress-strain behavior. A reversible flux density change of 145mT is observed over a range of 5.8% strain and 4.4MPa stress at a bias field of 368kA∕m. The alloy investigated shows potential as a high-compliance, high-displacement deformation sensor.
Effective hydraulic conductivity and diffusivity of randomly heterogeneous porous solids with compressible constituents
Authors: Müller Tobias M. , Gurevich Boris
Published: March 2006

Inhomogeneous fluid-saturated porous materials are often probed with diffusion waves to estimate their effective hydraulic conductivity and diffusivity. Analysis of diffusion wave fields in randomly inhomogeneous poroelastic structures provides new insight into how fluctuations of the compressible constituents affect the effective diffusivity. Based on the method of statistical smoothing an effective wave number of the coherent diffusion wave field is computed. From this wave number both an effective hydraulic conductivity and diffusivity are identified. These transport properties are frequency dependent. The correspondence between this conductivity and that estimated from unsteady flow through porous media based on Darcy’s law is elucidated.
Photoluminescence decay characteristics of an oxide-confined vertical-cavity surface-emitting laser
Authors: Recoleto Florencio D. , Mateo Jennette N. , Dimamay Mariel Grace S. , Somintac Armando S. , Estacio Elmer S. , Salvador Arnel A.
Published: March 2006

Room temperature time-resolved photoluminescence (TRPL) decay measurements are performed on oxidized and unoxidized vertical-cavity surface-emitting lasers (VCSELs). The oxidized device shows faster photoluminescence (PL) decay time (370ps) compared to the unoxidized device (1200ps). The oxidation of the AlAs layers reduces the aperture area and causes a blueshift in the cavity resonance wavelength, relative to that of the unoxidized device. The faster decay time can be attributed to better optical field confinement inside the microcavity which results in an increase in the transition probability of electron-hole recombination.
Atomic structure and electronic properties of c-Si∕a-Si:H heterointerfaces
Authors: Yan Yanfa , Page M. , Wang T. H. , Al-Jassim M. M. , Branz Howard M. , Wang Qi
Published: March 2006

The atomic structure and electronic properties of crystalline-amorphous interfaces in silicon heterojunction solar cells are investigated by high-resolution transmission electron microscopy, atomic-resolution Z-contrast imaging, and electron energy-loss spectroscopy. With these combined techniques, we directly observe abrupt and flat transition from crystalline Si to hydrogenated amorphous Si at the interface of Si heterojunction solar cells. We find that high-quality hydrogenated amorphous Si layers can be grown abruptly by hot-wire chemical vapor deposition on 200°C (100) Si substrates after a two-step pretreatment of the substrate, comprised of exposure to hot-wire decomposed H2-diluted NH3 followed by atomic H etching.
1.9
THz
quantum-cascade lasers with one-well injector
Authors: Kumar Sushil , Williams Benjamin S. , Hu Qing , Reno John L.
Published: March 2006

We report terahertz quantum-cascade lasers operating predominantly at 1.90THz with side modes as low as 1.86THz (λ≈161μm, ℏω≈7.7meV). This is the longest wavelength to date of any solid-state laser that operates without assistance of a magnetic field. Carriers are injected into the upper radiative state by using a single quantum-well injector, which resulted in a significant reduction of free-carrier losses. The laser operated up to a heat-sink temperature of 110K in pulsed mode, 95K in continuous wave (cw) mode, and the threshold current density at 5K was ∼140A∕cm2.
Elimination of AlGaN epilayer cracking by spatially patterned AlN mask
Authors: Sarzyński Marcin , Kryśko Marcin , Targowski Grzegorz , Czernecki Robert , Sarzyńska Agnieszka , Libura Adam , Krupczyński Wiktor , Perlin Piotr , Leszczyński Michał
Published: March 2006

The inherent problem in III-nitride technology is the cracking of AlGaN layers that results from lattice mismatch between AlGaN and GaN. In case of thin substrates (30–90μm), such as, bulk GaN grown by the high-pressure/high-temperature method, the bowing of AlGaN∕GaN strained structures becomes an additional problem. To eliminate cracking and bowing, AlGaN layers were grown on GaN substrates with an AlN mask patterned to form 3–15μm wide windows. In the 3μm window, the AlGaN layer was not cracked, although its thickness and Al composition exceeded critical values for growth on nonpatterned substrates. Dislocation density in the windows was of 5×106∕cm2.
A formula on phase velocity of waves and application
Authors: Chen Z. , Ho Y. K. , Wang P. X. , Kong Q. , Xie Y. J. , Wang W. , Xu J. J.
Published: March 2006

Phase velocity plays a key role in wave-matter interactions where phase matching is essential. Laser acceleration of electrons is a good example. We have derived an exact formula with two deductions of the phase velocity for a monochromatic wave field in homogeneous medium from the fundamental wave equation. The core of these formulae is that the phase velocity is sufficiently determined in terms of the wave amplitude with no explicit reference to the phase. We applied these formulae to make out the phase velocity distribution of a Gaussian laser beam and compared with the traditional method.
Lowering the ignition voltage by the dual microhollow cathode configuration for multichannel flat panel lamp
Authors: Lee Tae Il , Park Ki Wan , Lee Sung Won , Baik Hong Koo
Published: March 2006

We have developed a dual microhollow cathode configuration, employing one power supply circuit with a resistor that is suitable for lamp starting without additional power supplier. We also investigated their electrical characteristics and photo images, varying the applied voltage. The electrical and optical measurements showed that the discharge passed through four distinct stages: no discharges, the first microhollow cathode discharges, the both of the first and second microhollow cathode discharges, and finally the main discharge. As a result, the Vs and Es∕p of a dual microhollow configuration were lower by a factor of about 2 than those of a diode at 40Torr. We have also observed that the parallel operation can be possible with a single resistor in nine channels flat panel lamp.
Room-temperature short-wavelength (λ∼3.7–3.9μm) GaInAs∕AlAsSb quantum-cascade lasers
Authors: Yang Quankui , Manz Christian , Bronner Wolfgang , Köhler Klaus , Wagner Joachim
Published: March 2006

We discuss the possible limitations on realizing short-wavelength GaInAs∕AlAsSb quantum-cascade lasers and consequently demonstrate room-temperature (Tmax=310K) short-wavelength (λ∼3.7–3.9μm) GaInAs∕AlAsSb quantum-cascade lasers based on triple-well vertical-transition active regions. For a device with the size of 14μm×3.0mm with as-cleaved facets, the maximum peak powers per facet are around 31mW at 300K and 17mW at 310K. The characteristic temperature of the laser is 170K in the temperature range between 220 and 310K.
Field enhancement by surface plasmon polariton in self-assembling nanopatterned media
Authors: Matsuyama Tsuyoshi , Kawata Yoshimasa
Published: March 2006

We present the fabrication of nanodot arrays on metal films by self-assembly of diblock copolymer. The nanodots are uniform and aligned regularly with hexagonal close-packed structure on both gold film and glass. Gold is specifically a good candidate as the metal film excites surface plasmon polariton in the near-field optical media. Surface plasmon polariton is excited with the Kretschmann configuration at the gold-nanodot interface. We found that the intensity at the interface was enhanced 53.8 times to that of the incident light. It is expected to improve the carrier-to-noise ratio of the readout signal in the case of nanopatterned near-field optical data storage under collection mode.
Electrical breakthrough effect for end pointing in 90 and 45nm node circuit edit
Authors: Liu Kun , Soskov Alex , Scipioni Larry , Bassom Neil , Sijbrandij Sybren , Smith Gerald
Published: March 2006

The interaction between high-energy Ga+ ions and condensed matter is studied for circuit edit applications. A new “electrical breakthrough effect” due to charging of, and Ga+ penetration/doping into, dielectrics is discovered. This new effect is proposed for end pointing in 90 and 45nm node circuit edits where integrated circuit device dimensions are of a few hundred nanometers. This new end point approach is very sensitive, reliable, and precise. Most importantly, it is not sensitive to device dimensions. A series of circuit edits involving milling holes of high aspect ratio (5–30) and small cross-section area (0.01–0.25μm2) on real chips has been successfully performed using the electrical breakthrough effect as the end point method.