bluuebunny/crossref_metadata_2025 huggingface dataset:
E-007 Y-Stenting for the treatment of basilar apex aneurysms
Authors: Albuquerque F , McDougall C
Published: December 2010

Introduction

Despite advances in surgical and endovascular treatment of intracranial aneurysms, the management of wide necked basilar tip aneurysms poses substantial treatment challenges. Y stenting, in which one stent is deployed through the side wall tines of a previously placed stent, is a feasible adjunct to coiling of these aneurysms. Case series describing this technique are small with limited follow-up. We describe our experience with the Y stent assisted, coil embolization of basilar tip aneurysms in the largest case series to date with medium term follow-up data.

Methods

A review of our prospectively maintained database from 2004 to 2009 was performed to assess technical factors associated with treatment, complications and radiographic follow-up of patients undergoing Y stenting for basilar apex aneurysms.

Results

11 patients with wide necked basilar tip aneurysms were treated. Average follow-up was 13 months. Post-procedure surveillance was carried out by MR angiography (n=6), cerebral angiogram (n=9) or CT angiography (n=1), with several patients undergoing multiple types of radiographic follow-up. All patients’ aneurysms were completely or nearly completely (>95%) occluded at the time of treatment. No patient required retreatment. One patient suffered an asymptomatic vertebral artery dissection that required stenting and another suffered a minor stroke but recovered completely.

Conclusion

Y stenting is a viable treatment modality for this complex subgroup of aneurysms. Our series demonstrated the safety of this technique, with no patients suffering permanent complications. While the efficacy of Y stenting has yet to be established, medium term radiographic follow-up suggests durable results.
E-009 What is the real risk of dislodging thrombi during endovascular revascularization of a proximal internal carotid artery occlusion?
Authors: Baik S , Jeon U , Choo K , Kim Y , Jeong H
Published: December 2010

Purpose

There is a theoretical concern that a thrombus may be dislodged distally when crossing the occluded segment during recanalization of a complete occlusion. In the present study, we assessed the immediate postprocedural brain diffusion weighted image (DWI) findings following endovascular recanalization using an embolic protection device for proximal internal carotid artery (ICA) occlusion.

Materials and methods

We retrospectively identified 12 patients who underwent stent implantation for sudden symptomatic occlusion of the proximal ICA. In eight patients, no additional intracranial occlusions were identified. In four patients, an additional intracerebral thrombus was detected in the middle cerebral artery. Distal protection devices were used in all cases. We evaluated the presence and amount of retrieved embolic fragments in the distal protection devices. The incidence and location of postprocedural emboli were determined using DWI.

Results

Recanalization of the proximal ICA was achieved in all patients. After complete occlusion of the proximal ICA was demonstrated, primary passage of the embolic protection device through the occluded ICA was gently navigated in seven patients. However, this was not possible in five patients. Three patients developed new lesions on postprocedural DWI. Of the 12 patients in which distal protection devices were used, debris was detected in seven patients.

Conclusion

In endovascular revascularization of proximal ICA occlusion, postprocedural emboli occur less frequently than reported in a systemic review of the DWI literature. The real risk of dislodging thrombi appears to derive from plaque fragment mobilization by angioplasty, rather than crossing an occluded segment.

Abstract E-009 Figure 1
Distributed temperature sensor based on Brillouin loss in an optical fibre for transient threshold monitoring
Authors: Bao X. , Webb D. J. , Jackson D. A.
Published: December 2010

A distributed temperature sensor for transient threshold monitoring with a 22 km sensing length, based on the Brillouin loss in standard communications fibre, is demonstrated. The system can be used for real-time monitoring of a preset temperature threshold. Good S/N ratios were achieved with only 8–16 sample averages giving a response time of 2 to 4 s with a temperature uncertainty of ±1 °C.
Inner-product theory calculations for some rational potentials in a three-dimensional system
Authors: Witwit M. R. M.
Published: December 2010

The energy levels of a three-dimensional system are calculated for the rational potentials,[Formula: see text]using the inner-product technique over a wide range of values of the perturbation parameters (λ, g) and for various eigenstates. The numerical results for some special cases agree with those of previous workers where available.
Black holes with regular horizons in Maxwell-scalar gravity
Authors: Turyshev Slava G.
Published: December 2010

A class of exact static spherically symmetric solutions of the Einstein–Maxwell gravity coupled to a massless scalar field is obtained in the harmonic coordinates of Minkowski space-time. For each value of the coupling constant a, these solutions are characterized by a set of three parameters, the physical mass μ0, the electric charge Q0 and the scalar-field parameter k. We find that the solutions for both gravitational and electromagnetic fields are not only affected by the scalar field, but also the nontrivial coupling with matter constrains the scalar field itself. In particular, we find that the constant k differs generically from ±1/2, falling into the interval [Formula: see text]. It takes these values only for black holes or in the case when a scalar field [Formula: see text] is totally decoupled from the matter. Our results differ from those previously obtained in that the presence of an arbitrary coupling constant a gives an opportunity to rule out the nonphysical horizons. In one of the special cases, the obtained solution corresponds to a charged dilatonic black hole with only one horizon μ+ and hence to the Kaluza–Klein case. The most remarkable property of this result is that the metric, the scalar curvature, and both the electromagnetic and scalar fields are all regular on this surface. Moreover, while studying the dilaton charge, we found that the inclusion of the scalar field in the theory resulted in a contraction of the horizon. The behavior of the scalar curvature was analysed.
Some analytical results for the scaled factorial moments
Authors: Huang Ding-Wei
Published: December 2010

A few analytical results for the scaled factorial moments in high-energy collisions are presented. The characteristics of the observed features are discussed.
Supersymmetric modified Airy-function method and its application to the Schrödinger potential V(x) = x6 − 3x2
Authors: Sinha Anjana , Roychoudhury Rajkumar , Varshni Y. P.
Published: December 2010

A supersymmetric version of the modified Airy-function method is developed. Explicit calculations for eigenvalues are obtained for the Schrödinger potential V(x) = x6 − 3x2. Comparison is made with exact numerical results as well as those of the Wentzel–Kramers–Brillouin (WKB), supersymmetric WKB (SWKB), and modified Airy-function approximation methods.
Free-energy functional approximation for hard-sphere fluid
Authors: Lee Seung-Chan , Yoon Zi-Hong , Kim Soon-Chul
Published: December 2010

A free-energy functional approximation (FEFA) is extended up to the third-order term in the density expansion. The extended free-energy functional approximation (EFEFA) is applied to predict the density profiles of a hard-sphere fluid restricted by hard and permeable walls. For a hard-sphere fluid confined in hard walls and spherical cages, the EFEFA gives better results than the FEFA of Tarazona, and is comparable with computer simulations at even higher density. However, for a hard-sphere fluid restricted by permeable walls the FEFA of Tarazona shows better agreement than the EFEFA when compared with computer simulations. These results suggest that the structural properties of a hard-sphere fluid depend on the geometrical features of walls and wall potentials as well as the model approximations.
Improved finite-lattice method for estimating the zero-temperature properties of two-dimensional lattice models
Authors: Betts D. D. , Masui S. , Vats N. , Stewart G. E.
Published: December 2010

The well-known finite-lattice method for the calculation of the properties of quantum spin systems on a two-dimensional lattice at zero temperature was introduced in 1978. The method has now been greatly improved for the square lattice by including finite lattices based on parallelogram tiles as well as the familiar finite lattices based on square tiles. Dozens of these new finite lattices have been tested and graded using the [Formula: see text] ferromagnet. In the process new and improved estimates have been obtained for the XY model's ground-state energy per spin, ε0 = −0.549 36(30) and spontaneous magnetization per spin, m = 0.4349(10). Other properties such as near-neighbour, zero-temperature spin–spin correlations, which appear not to have been calculated previously, have been estimated to high precision. Applications of the improved finite-lattice method to other models can readily be carried out.
Structure of chemically reacting particles near a hard wall from integral equations and computer simulations
Authors: Trokhymchuk A. , Henderson D. , Sokołowski S.
Published: December 2010

We performed Monte-Carlo computer simulations of a fluid of chemically reacting, or overlapping, hard spheres near a hard wall. The model of the interparticle potential is that introduced by Cummings and Stell. This investigation is directed to the determination of the structure of the fluid at the wall, and the orientation of the dimers in particular. In addition, we applied the singlet Percus–Yevick, hypernetted chain and Born–Green–Yvon equations to calculate the total density profiles of the particles. A comparison with the Monte-Carlo data indicates that the singlet Percus–Yevick theory is superior and leads to results that are in reasonable agreement with simulations for all the parameters investigated. We also calculated the average numbers of dimers formed in the bulk part of the system and the results are compared with different theoretical predictions.
A study of multiple scattering in bubbly liquids by many-body theory
Authors: Ye Zhen , Ding Li
Published: December 2010

In this paper it is suggested that acoustic-wave propagation in bubbly liquids can be easily studied using the diagram method in many-body theory. The merit of this method is that it allows convenient inclusion of any higher order bubble interactions. In particular consideration is given to a higher order correction due to the mutual interaction of bubbles. It is shown that under certain circumstances, this correction could be rather significant. Other higher order interactions are also briefly discussed.
The derivation of 1/N equivalent potentials for the radial Schrödinger equation in N space dimensions
Authors: Papp E. , Micu C.
Published: December 2010

Proofs are given that SOq(N)-motivated q deformations of the expansion parameter of the 1/N method can be incorporated into symmetry transformations preserving the radial form of the Schrödinger equation. This opens the way to establish the q deformed energy and the corresponding 1/N equivalent potential. So far the number of space dimensions is subject of covariant transformations. An alternative derivation of the 1/N equivalent potential is also done by keeping this number invariant. In this latter case, the stability attributes of q-deformed power-law potentials are discussed in terms of the q > 1 choice.
Green Zn2SiO4:Mn thin-film electroluminescence on silicon substrates
Authors: Xiao T. , Liu G. , Adams M. , Kitai A. H.
Published: December 2010

Bright electroluminescence has been achieved on silicon substrates for the first time using Zn2SiO4:Mn thin films that were RF magnetron sputtered. A brightness of over 16 foot lambert (fL) was observed at 400 Hz and 260 V, with a steep brightness–voltage behaviour characteristic of ZnS electroluminescence. A multiplexed electroluminescent display is now feasible using Zn2SiO4:Mn.
Features of forward-backward multiplicity correlations in hadronic collisions
Authors: Tufail A. , Ahmad S. , Zafar M.
Published: December 2010

The forward–backward multiplicity correlations among the charged particles produced in the interactions of 24 and 400 GeV protons and 50 and 340 GeV pions with emulsion nuclei are being investigated. The results of hadron–nucleus interactions have been compared with those of hadron–hadron interactions. The variations of average values in the forward–backward hemisphere with the multiplicity in the opposite hemisphere have been studied by dividing the data into different ηc-intervals also.
Coulomb interaction energy including overlap effects for the ground state of RbCs beyond 7 Å
Authors: Hussein K.
Published: December 2010

We use a perturbative model based on a partition of the configuration space into four regions to calculate the Coulomb energy including charge-overlap effects (induction and dispersion terms) for the interaction between two atoms Rb(5s2S) and Cs(6s2S). Results for first-order electrostatic as well as second-order induction and dispersion energies will be presented in the range 13 < R < 25 a.u. The damping functions for the various dispersion terms varying as R−6, R−8, and R−10 in the range of large R have also been determined, and fitted analytical forms will be displayed for these terms. From comparison with accurate experimental results, the present method is seen to be valid for values of R beyond 7 Å (1 Å = 10−10 m).
One-loop effects in N = 4 supersymmetry
Authors: McKeon D. G. C.
Published: December 2010

It has been demonstrated that in massless supersymmetric theories, finite radiative corrections to the superpotential can occur (viz. the nonrenormalization theorems can be circumvented). In this paper, we examine the consequences of this in N = 4 supersymmetric Yang–Mills theory, a model in which the β function is known to be zero. It is shown that radiative corrections to the superpotential arise at one loop order in this theory contrary to the expectations of the nonrenormalization theorem, but that their form depends on which formulation of the model is used. When one uses a superfield formulation involving an N = 1 vector superfield and three N = 1 chiral superfields in conjunction with a supersymmetric (but not SU(4)) invariant gauge fixing, then at one-loop order, the radiative generation of terms in the superpotential means that the equality of the gauge and Yukawa couplings and indeed of different Yukawa couplings is lost. If one uses the component field formulation of the N = 4 model in the Wess–Zumino gauge with a covariant, SU(4) invariant (but not supersymmetric invariant) gauge fixing, then the SU(4) invariance is maintained, but the gauge and Yukawa couplings are no longer equal. We also consider computations in the component field formulation in the Wess–Zumino gauge using an N = 1 super Yang–Mills theory in ten dimensions, dimensionally reduced to four dimensions, with a ten-dimensional covariant gauge fixing condition. This formulation ensures that there is no distinction between gauge and Yukawa couplings and that SU(4) invariance is automatically preserved; however, supersymmetry is broken by the gauge fixing procedure.
Structural and optical properties of AlInAs/InP and GaPSb/InP type II interfaces
Authors: Sacilotti M. , Abraham P. , Pitaval M. , Ambri M. , Benyattou T. , Tabata A. , Perez M. A. Garcia , Motisuke P. , Landers R. , Morais J. , Corre A. Le , Loualiche S.
Published: December 2010

We present a study of type II interfaces between semiconducting materials. In this type of interface the lineup of the two semiconductor band gaps has a staggered shape. The band bending at the interface depends on the doping type and concentration of the two semiconductors involved. In most cases two triangular quantum wells appear at the interface, one for the electrons in the semiconductor having the lowest conduction band edge and one in the other material for holes. In such a case, when charges are injected, the electrons and holes are separated at the interface, so that the electron/hole recombination occurs through the interface. The main characteristic of type II interfaces is that their photoluminescent (PL) intensity is very high compared with each material forming the heterojunction. This high PL intensity can be used advantageously in optoelectronic device applications. We present semiconductor pairs for which it is possible to have type II interfaces and their optical properties. We will emphasize particularly the cases of AlInAs/InP and GaPSb/InP whose low-temperature interface recombination energies are 1.2 and 0.90 eV, respectively.
A meson-exchange isobar model for the π+d↔pp reaction
Authors: Canton L. , Cattapan G. , Dortmans P. J. , Pisent G. , Svenne J. P.
Published: December 2010

We calculated a broad set of observables for the π+d ↔ pp reaction with a relatively simple meson-exchange isobar model. The comparison between the calculated results and experimental data (including spin observables) shows that the model gives an overall phenomenologically acceptable description of the reaction around the Δ resonance. We also take into account the effects due to the inclusion of the Galilei invariant (pseudovector) recoil term in the πNN vertex, of relativistic corrections to the ρ-exchange component of the ΔN transition potential, and of NN final state interaction in the π+d → p + p process. Rescatterings via pion-nucleon interaction in the S–wave have also been included. The model is sufficiently simple to be extended to the case of pion absorption on other light nuclei, in particular 3He (or tritium).
Distorted wave calculation of the electron impact ionization cross section of the ground state of atomic hydrogen
Authors: Singh Th. Subodh Chandra , Singh N. Ranjit , Deb N. C. , Mukherjee S. C. , Babuyaima M. , Mazumdar P. S.
Published: December 2010

The total cross section and single differential cross section in energy for the electron impact ionization of the ground state of atomic hydrogen were computed using a distorted wave model. The incident electron energy range was 20–250 eV. The present results are compared with existing theoretical and experimental results.
Excitation of H2O+ in e–H2O collisions
Authors: Kuchenev A. N. , Smirnov Yu. M.
Published: December 2010

Inelastic collisions, between electrons of low and medium energies and H2O molecules, that give rise to the appearance of optical radiation were studied. An experiment was performed with a gas-filled cell using an extended beam of monokinetic electrons to excite the molecules. A spectrum appearing in the visible region was identified as belonging to H2O+. About 430 excitation cross sections attributed to 10 subbands of the [Formula: see text] system were measured. For a number of lines, measurements were made of the optical excitation functions in the range of energies from the excitation threshold to 200 eV.
Diffusion analysis of the GLE (ground-level enhancement) of September 29, 1989
Authors: Koning C. A. de , Mathews T.
Published: December 2010

On September 29, 1989, neutron monitors and muon telescopes around the world recorded a significant increase in their count rate. This ground-level enhancement affords a unique opportunity to study the rigidity dependence of the interplanetary scattering mean free path, [Formula: see text]. By fitting the well-known diffusion model to worldwide neutron monitor and muon telescope data, we calculate the value of [Formula: see text] observed by each station. A plot of [Formula: see text] observed by each station versus the mean rigidity of solar flare particles observed by each station (which ranges from 3–16 GV) clearly indicates that [Formula: see text] is rigidity dependent. If we assume that [Formula: see text] for P > 3 GV, where the power-law index q is a measure of the deviation from isotropic scattering (q = 1), then we find that q = 0.86 ± 0.03 at the time of this ground-level enhancement.
Localization of the 4f wave-function in cesium
Authors: Onwuagba B. N.
Published: December 2010

The local spin density approximation is used in the study of the localization of the 4f wave function in cesium, by superimposing the radial part of the kinetic-energy term on the self-consistent field potential VSCF(r). The results obtained show a collapsed 4f wave function in Cs+, but not in neutral Cs, which compares favourably with the previous findings and provide good insight into the understanding of the collapsed 4f wave function in cesium.
Analysis of the excitation function of alpha-particle-induced reactions on natural silver
Authors: Patel H. B. , Gadkari M. S. , Dave Bhruna , Singh N. L. , Mukherjee S.
Published: December 2010

Excitation functions of the reactions 107Ag[(α, n); (α, 2n); (α, αn); (α, α2n)] and,109Ag[(α, 2n); (α, 3n); (α, 4n); (α, α3n); (α, α4n)] were investigated up to 70 MeV by the stacked foil activation technique and Ge(Li) gamma-ray spectroscopy method. Since the natural silver used as the target has two odd mass stable isotopes of abundance 51.83% (107Ag) and 48.17% (109Ag), their activation in some cases gives the same residual nucleus through different reaction channels, but with very different Q values. In such cases, the individual reaction cross sections are separated with the help of the ratio of theoretical cross sections. The experimental cross sections were compared with the predictions of a pre-equilibrium hybrid model. The (α, xn) reactions are fairly well reproduced with initial exciton number n0 = 4(4p0h), whereas (α, αxn) reactions are underestimated in magnitude by a factor of five to six.
Sine-Gordon model in (1 + 1)-dimensional curved space: Schrödinger picture approach
Authors: Sinha Anjana , Roychoudhury Rajkumar
Published: December 2010

The effective potential for the sine-Gordon model in a curved space-time, given by [Formula: see text], has been calculated using the Schrödinger picture formalism. It has been shown that when α(x) → 1 our method reproduces the flat-space results. To show the effect of the curvature term, the effective potential Veff has been calculated numerically for several values of the parameter M, where α(x) has been taken to be of the form [Formula: see text].
Energy-dependent effects in coherent pion production
Authors: Deutchman P. A.
Published: December 2010

Theoretical calculations have been done for the coherent production of pions in the exclusive reaction 12C + 12 C → 12 C (15.11 MeV) + 12C + π0 at 100 and 250 MeV/nucleon. An analysis is made on how three-body kinematics and other energy dependencies affect the various factors that enter the calculation for the pion differential cross section. Momentum and momentum-transfer diagrams are constructed that show pictorially how projectile- and target-generated pions differ in their intermediate states, even though they lead to the same final states. It is shown how three-body kinematics affect the exchange-process amplitudes that account for projectile- and target-generated pions. Also, the energy dependencies found in the delta width and phase-space factors are assessed as to their relative importance. Momentum robbing and kickback effects to the final-state nuclei from the produced pion are discussed. These effects are shown to give an asymmetry in the pion angular distribution. The study of three-body kinematics and its associated energy dependencies under the Born approximation is considered to be an important first step in the understanding of coherent pion production in heavy-ion collisions, before the complicating features of absorption and distortion are introduced. Even though the pion is much lighter than either of the two equal-mass, final-state nuclei, observable asymmetries are seen in the pion angular distribution that are caused by the produced pion.
Multiplicity characteristics of 12C-nucleus interactions at 4.5 A GeV c−1
Authors: Khan M. Saleem , Khushnood H. , Ansari A. R.
Published: December 2010

An attempt is made to study the multiplicity distributions of different charged secondaries, the dispersions of their distributions, and intercorrelations between them in 12C-nucleus reactions at 4.5 GeV per nucleon. The results reveal that the value of [Formula: see text] does not depend on the projectile mass. The constancy of [Formula: see text] shows that, irrespective of the amount of average energy imparted to the target nuclei for their excitation, the temperature of the residual nucleus never exceeds some critical temperature. However, the value of [Formula: see text] is found to increase with increasing mass of the projectile. This observation is in accord with the prediction of the fireball model. The angular distribution of charged shower particles in terms of the pseudorapidity variable, η, was also investigated. The results suggest that there are different degrees of stopping for different thicknesses of the nuclear matter traversed by the projectile. In general, our results are similar to those obtained for hadronic interactions. The results are also compared with those obtained in hadron–nucleus collisions in the energy range ~6−400 GeV.
The Riccati–Padé quantization method for one-dimensional quantum-mechanical models
Authors: Fernández Francisco M. , Tipping R. H.
Published: December 2010

We improve on a previously developed method for the calculation of accurate eigenvalues and eigenfunctions of separable models in quantum mechanics. It consists of the approximation of the logarithmic derivative of the eigenfunction by means of a rational function or Padé approximant. Here we modify the approach by the separation of the function just mentioned into its odd and even parts, thus making the procedure more efficient for treating asymmetric one-dimensional potentials. We obtain the ground-state eigenvalue of anharmonic oscillators with one and two wells and the lowest resonances of anharmonic oscillators that support only continuum states.
Extremely low threshold current density InGaAs/GaAs/AIGaAs strained SQW laser grown by MBE with As2
Authors: Dion M. , Wasilewski Z. R. , Chatenoud F. , Gupta V. K. , Pratt A. R. , Williams R. L. , Norman C. E. , Fahy M. R. , Marinopoulou A.
Published: December 2010

In this report, we present data on an InGaAs/GaAs strained single quantum well laser with the lowest reported threshold current density to date, namely 44 A cm−2 for a 3 mm cavity length. This was grown by solid-source molecular-beam epitaxy with the arsenic dimer, As2. The structure is that of a graded-index, separate-confinement heterostructure with a single strained InGaAs quantum well, sandwiched between GaAs barrier layers and AlGaAs cladding layers. The wavelength of the lasers was around 985 nm, and the internal efficiency and losses were 69% and 0.70 cm−1, respectively. In addition, data on the uniformity of our lasers, which are grown on rotating 2 in substrates (1 in = 2.54 cm), show drops in photoluminescence emission wavelength and layer thickness of less than 4 nm and 4%, respectively, from the centre to the edge of the wafer and very little compositional change.
Slow-wave electrodes on GaAs for integrated electro-optic modulators
Authors: Rahmatian Farnoosh , Kato Hiroshi , Jaeger Nicolas A. F. , James Robert , Berolo Ezio
Published: December 2010

Slow-wave electrodes that are suitable for use in integrated-optics, electro-optic modulators were fabricated and tested. Measurements of the microwave indices on a number of these electrodes show that sufficient slowing can be obtained to match the velocities of modulating microwaves to optical waves in graded-index AlxGa1−xAs waveguides for a wide range of mole fraction, x. Calculations based on the measured losses, for integrated-optics, electro-optic modulators in which the velocity-match condition has been achieved, indicate that devices having optical bandwidths >100 GHz should be possible using the electrodes presented.
Laser-micromachining silicon three-dimensional structures, tunnels, and cavities
Authors: Shen B. , Allard M. , Boughaba S. , Izquierdo R. , Meunier M.
Published: December 2010

A laser-micromachining technique has been developed to make tunnels and cavities in Si under SiO2 or Si3N4 films. Based on the laser-induced Cl2 etching of Si, and high chlorine Si/SiO2 and Si/Si3N4 etch-rate ratios, tunnels with length of up to 3 mm and cavities of 100 × 100 μm2 were successfully fabricated in SiO2/Si bilayered samples. Similarly, cavities of 50 × 50 μm2 were also fabricated in Si3N4/Si samples.
Tailoring of low-temperature MBE-grown GaAs for ultrafast photonic devices
Authors: Benjamin S. D. , Loka H. S. , Smith P. W. E.
Published: December 2010

In this paper, we review recent work on ultrafast nonlinear optical effects in low-temperature MBE-grown GaAs, and describe a rate-equation formalism that can be used to model the dynamic behaviour of the nonlinear absorption and refractive index. We show that under suitable conditions, this material exhibits the behaviour required for an ultrafast all-optical switch, and demonstrate how the material characteristics can be tailored for such applications by suitable control of growth and annealing conditions.
Electrical characterization of fluorine-implanted gate oxide structures
Authors: Nguyen T. K. , Landsberger L. M. , Logiudice V. , Jean C.
Published: December 2010

In the ongoing quest for thinner and more reliable gate dielectrics for microelectronics, fluorination of gate oxide structures has emerged as a leading technique. In this work, the fluorine is implanted into the polysilicon gate before the poly etch. After the subsequent poly etch and anneal, the samples are not sent through the remainder of the process, but are subjected to electrical reliability stressing by two methods: constant-current Fowler–Nordheim tunnelling stress, and constant-voltage stress (J–t analysis). Two different fluorination cases (doses and implant energies) are studied, along with unimplanted controls. In the fluorinated cases, improvement vs. controls is found in device reliability indicators: mid-gap Dit, Qf, and ΔVth. J–t analysis corroborates the improvement, and the combination of techniques is found to offer a more, comprehensive view of complex variations in fluorinated oxide properties.
Modification of the GalnAsP(100) surface by oxidation and sulfur passivation
Authors: Rajesh K. , Huang L. J. , Lau W. M. , Bruce R. , Ingrey S. , Landheer D.
Published: December 2010

The quaternary III–V compound semiconductor (GaInAsP) is one of the important materials for optoelectronic devices such as long-wavelength semiconductor lasers. Understanding its surface chemistry, which is subjected to oxidation, and sulphur passivation, a widely used passivation technique, is of importance for its use for device fabrication. In this study, modification of the quaternary GaInAsP(100) surfaces was performed by UV/ozone and wet chemical oxidation, dilute HF etching, and sulfur passivation. The surface chemistry and composition of the oxidized, oxide-free, and the sulfur-passivated surfaces were measured by X-ray photoemission spectroscopy (XPS). It was found that oxidation by wet chemical etching resulted in preferential oxidation while, oxidation by ozone exposure formed multiple oxide phases of all the constituent elements. Both the HF etch and sulfur-passivation treatment were effective in generating surfaces having no oxide. Preliminary data on surface Fermi-level changes induced by the above surface treatments indicated that both the HF etch and sulfur-passivation treatment reduced the surface-state density on an oxidized surface.
CO2 laser-assisted particle removal from silicon surfaces
Authors: Héroux J. B. , Boughaba S. , Sacher E. , Meunier M.
Published: December 2010

A CO2 laser particle removal system was built that enables the removal of 0.1 μm alumina particles from silicon substrates. This system has raster scan capabilities to clean large surfaces, which were analysed using a particle counter. After deposition and removal of 0.1 μm alumina particles, the final concentration is less than 25 particles cm−2 for particle clusters between 0.1 and 10 μm. The efficiency of particle removal is nearly independent of the laser fluence between 0.65 and 2.9 J cm−2 and drops suddenly below 0.65 J cm−2.
Characteristics of dual-gate thin-film transistors for applications in digital radiology
Authors: Waechter D. , Huang Z. , Zhao W. , Blevis I. , Rowlands J. A.
Published: December 2010

A large-area flat-panel detector for digital radiology is being developed. The detector uses an array of dual-gate thin-film transistors (TFTs) to read out X-ray-generated charge produced in an amorphous selenium (a-Se) layer. The TFTs use CdSe as the semiconductor and use the bottom gate for row selection. The top gate can be divided into a "deliberate" gate, covering most of the channel length, and smaller "parasitic" gates that consist of (i) overlap of source or drain metal over the top-gate oxide, and (ii) gap regions in the metal that are covered only by the a-Se. In this paper we present the properties of dual-gate TFTs and examine the effect of both the deliberate and parasitic gates on the detector operation. Various options for controlling the top-gate potential are analyzed and discussed.
A floating-gate MOSFET gamma dosimeter
Authors: Peters C. J. , Tarr N. G. , Shortt K. , Thomson I. , Mackay G. F.
Published: December 2010

A novel MOSFET-based dosimeter that uses a floating polysilicon gate to trap radiation-generated charge is reported. As in previous MOSFET dosimeters, absorbed dose is inferred from changes in threshold voltage. High sensitivity is obtained by extending the floating gate over the field oxide. Prototype devices have been fabricated in a conventional 5 μm nMOS integrated-circuit technology, and show sensitivities up to 280 mV Gy−1 when irradiated with a 60Co gamma source.
A micro-integrated Peltier heat pump for localized on-chip temperature control
Authors: Shafai C. , Brett M. J.
Published: December 2010

A thin-film Peltier heat pump was fabricated using standard semiconductor patterning and etching techniques. The device consisted of chrome–gold and bismuth telluride metallization to form the thermoelectric junctions. The device achieved a maximum heat-pumping rate of −24 μW at a current of 0.89 mA when operating in the cooling mode. These values were less than expected primarily due to excessive contact resistance at the Au–Bi2Te3 junctions of the Peltier device. Thermal isolation of the Peltier device on a 2.4 μm thick oxide bridge was used to enhance device performance. Complete etching of the silicon surrounding this oxide bridge was not possible, due to resultant damage of the bismuth telluride thin film. The silicon remaining increased thermal losses, resulting in the Peltier device lowering the temperature of the oxide bridge only 0.23 °C below ambient.
Simulation and physical response of negative temperature coefficient of resistance polysilicon micromachined structures
Authors: Shen Bing , Hu Ming , Yu Bing , Robinson A. M. , Lawson R. , Allegretto Walter
Published: December 2010

We present experimental and simulation results for polysilicon micromachined devices with a negative temperature coefficient of resistance. These were fabricated by a CMOS process with a customized sheet resistance for the second polysilicon layer. We first obtained an expression for the device resistivity, and then employed our simulation procedure to analyze both the steady-state and the time-varying response. The thermal efficiency is also examined. Explicit comparisons between simulation and experimental results show excellent agreement.
Location and quantification of the interface defects in stressed LDD NMOSFETs using a combination of floating-gate and transconductance techniques, and charge-pumping methods
Authors: Kwan W. S. , Raychaudhuri A. , Deen M. J.
Published: December 2010

In sub-micrometre LDD NMOSFETs we were able to correlate an evolution of hot-carrier-induced gate currents obtained from floating-gate measurements with corresponding evolution of saturation transconductances. With this correlation, additional substrate current measurements, and the help of a 2D device simulation framework, we find that negative oxide-trapped charges of magnitude 2.5 × 1018 cm−3 are responsible for the experimental observations. This damage is located in the oxide at the edge of the gate over 100 Å (1 Å = 10−10 m) above the oxide–silicon interface, which is deep into the LDD structure and difficult to probe with the existing methods. Then we demonstrate how the in-channel interface states density can be profiled using a lateral-profiling charge-pumping technique. The coupling of the techniques mentioned above leads to the characterization of the entire oxide–silicon interface along the length of the gate. This is essential for the proper understanding of the directions for process improvements and the mechanisms of defect generation.
The use of multiple-gated MOSFETs in a simple application
Authors: Bradford T. , McAlister S. P.
Published: December 2010

We describe the design and simulation of the use of neuron MOSFETs in a simple application — that of a parallel-carry adder circuit. The neuron MOSFETs are multigated MOSFETs where the multiple coupling to a MOSFET's gate is made capacitatively. By using such devices a multilevel logic is achieved that allows functions in a circuit to be achieved with fewer transistors than in a conventional CMOS design.
Modelling of bonding pads and their effect on the high-frequency-noise figure of polysilicon emitter bipolar junction transistors
Authors: Deen M. J. , Ilowski J.
Published: December 2010

This paper presents detailed experimental results on the input impedance of bonding pads, and a simple electrical model that accurately describes the impedances of these pads as a function of frequency for five different types of pad structures. It also describes the effects of the bonding pads on the minimum high-frequency-noise figure (NFMIN) of polysilicon emitter npn bipolar junction transistors as functions of collector current density and emitter areas. It was found that for devices with larger emitter areas (AE > 48 μm2) and relatively low base resistance (RB < 30 Ω), the effects of the same bonding pads on the noise figure was not as pronounced as for the smaller area devices with larger base resistances. For a device with AE = 3.2 μm2 operating at 1 GHz, biased with a collector density of 0.15 mA μm−2, neglect of the effects of the bonding pads results in too low NFMIN (by 1–2 dB) when calculated values were compared to measurements. Finally, for devices with the same emitter areas, bonding pads with smaller impedance results in a larger NFMIN compared to measurements on similar transistors with pads of larger impedances.
Demonstration of device conductance modulation by electrostatic control of the electron phase
Authors: Gould C. , Sachrajda A. , Feng Y. , Delage A. , Kelly P. , Coleridge P. T.
Published: December 2010

In this paper we describe a novel effect observed in a quantum wire containing two parallel "artificial" (i.e., electrostatically defined antidots) impurities. At low magnetic fields we observe a series of resistance peaks. These occur at magnetic fields for which classical electron trajectories are commensurate with the device geometry. The resistance peaks are modulated by periodic oscillations that can be observed both as a function of the applied magnetic field or the gate voltage, which controls the size of the impurities. These oscillations are analyzed in terms of the classical action of ballistic electrons on closed trajectories, the related phase gained along these trajectories, and the resulting quantum interference effect. We show that these oscillations when observed as a function of gate voltage are consistent with changes of the electron wavelength along part of the electron trajectory. The device conductance is thus being modulated by the electrostatic control of the electron phase.
Optical identification of the exciton–polariton in epitaxial InAs
Authors: Lacroix Y. , Tran C. A. , Watkins S. P. , Thewalt M. L. W.
Published: December 2010

We report optical identification of the exciton–polariton in epitaxial InAs by combined photoluminescence, reflectance, and transmittance spectroscopy. The photoluminescence of these samples showed identifiable spectral lines a thousand times narrower than previously published results from other groups. The measurements were made at 1.4 K and at magnetic fields up to 7 T. Contrary to what is observed in other III–V semiconductors such as GaAs or InP, the free exciton (polariton) is nearly invisible in the photoluminescence spectrum without the application of a magnetic field. We believe that the relatively large residual donor concentration coupled with the large spatial extent of the exciton wave function in this material inhibit the existence of unbound excitonic recombination. Reflectance and transmittance spectroscopy provide very strong evidence that our identification is correct, and the magnetic field dependence yielded values of the electron effective mass and g-factor of (0.026 + 0.002)m0 and −15.3 ± 0.2, respectively, based on this assignment.
Temperature dependence of ultrasharp luminescence lines in AlyIn1−yAs/AlxGa1−xAs self-assembled quantum dots
Authors: Raymond S. , Fafard S. , Charbonneau S.
Published: December 2010

Ensembles of~600 AlyIn1−yAs/AlxGa1−xAs self-assembled quantum dots (QDs) are investigated using photoluminescence (PL) and time-resolved PL in the visible. At very low excitation intensities, the PL spectrum shows multiple ultranarrow luminescence lines (FWHM ~200 μeV), which are attributed to the ground-state transition of a few dots (4 or less). The temperature and intensity evolution of these sharp lines is then monitored. The temperature-dependent measurements show that the line width and lifetime of the narrow lines remain constant up to the onset of thermionic, emission. Intensity-dependent measurements show that for high excitation density the collective background, emitted by the ensemble of QDs, is enhanced relative to the amplitude of individual ultranarrow lines.
Doping effects on carrier capture in a single quantum well by ensemble Monte Carlo
Authors: Reid B. , Abou-Khalil M. , Maciejko R.
Published: December 2010

Using a bipolar ensemble Monte Carlo coupled with a Poisson equation solver, we simulate, for the first time, carrier capture with both types of carriers in an InGaAs/InP-doped single quantum well, following femtosecond light-pulse excitation. We show that Coulomb interaction between electrons and holes is very efficient in keeping the capture ambipolar for a long time. However, for short times, the capture is unipolar. Our results indicate that for these kinds of experiments, Monte Carlo simulations with only one type of carrier give questionable results.
Monitoring of the formation and removal of bulk, surface, and interfacial carrier traps on silicon(100)
Authors: Li Hongjun , Ogryzlo Elmer A.
Published: December 2010

An RF probe was used to monitor the steady-state photo-generated carrier concentration in silicon with and without an oxide layer. The changes in this steady-state concentration during exposure to gaseous molecular and atomic species such as He, H2, O2, H, and O at temperatures between 25 and 450 °C are interpreted in terms of changes in the bulk silicon, interface, and exposed surface. The initial experiments established the relationship between the carrier concentration and the RF-probe signal, and distinguished between changes in the bulk, and on silicon surfaces and interfaces. It was found that in the case of hydrogen, bulk passivation and depassivation by H2 can be observed only at elevated temperatures, with or without an oxide layer. H-atom depassivation can be observed at all temperatures and is irreversible at room temperature. The formation of an oxide layer by exposure to O atoms at 25 and 450 °C was followed, and the oxides formed were then treated in an attempt to create an SiO2/Si interface with an acceptable density of interfacial states.
A comparison of the dc and rf characteristics of single and double InP/InGaAs heterojunction bipolar transistors
Authors: McKinnon W. R. , McAlister S. P. , Abid Z. , Guzzo E. E. , Laframboise S.
Published: December 2010

The dc and rf characteristics for InP/InGaAs heterojunction bipolar transistors having a single heterojunction design were measured and compared with those for double heterojunction devices that employ a composite collector. Although the composite-collector design improves the breakdown characteristics of our devices the rf performance was not as good. This we partially attribute to the collector heterojunction, which causes "current blocking".
Optical absorption, disorder, and hydrogen in amorphous silicon
Authors: O'Leary Stephen K. , Sidhu Lakhbeer S. , Zukotynski Stefan , Perz John M.
Published: December 2010

We study how bonded hydrogen influences the optical absorption spectrum of amorphous silicon. We use a model for optical absorption in which the local form of the joint density of states is averaged over a Gaussian distribution of energy-gap fluctuations, this distribution being characterized by a mean energy gap and a standard deviation about this mean. We then fit this model to optical absorption data, and study how the modeling parameters vary with the bonded hydrogen concentration. We find that for the group of samples that we have considered, for bonded-hydrogen concentrations less than 10 at.%, we can adequately fit the data with a constant mean energy gap and a variable standard deviation that decreases with increasing bonded-hydrogen concentration. This suggests that bonded hydrogen plays a significant role in decreasing the amount of disorder in amorphous silicon.
STRUCTURAL, ELECTRONIC AND OPTICAL PROPERTIES OF THE TETRAGONAL PHASE OFCaSiO3PEROVSKITE UNDER PRESSURE: FIRST-PRINCIPLES CALCULATIONS
Authors: LIU ZI-JIANG , ZHANG CAI-RONG , SUN XIAO-WEI , WANG LU , SONG TING , QI JIAN-HONG
Published: December 2010

First principles studies of structural, elastic, electronic and optical properties of tetragonal CaSiO3perovskite under pressure are reported using the pseudopotential plane wave method within the local density approximation (LDA). The calculated equilibrium lattice is in good agreement with the available experimental data. The elastic constants and their pressure dependence are calculated using the static finite strain technique. A linear pressure dependence of the elastic stiffnesses is found. Band structures show that tetragonal CaSiO3perovskite is a direct band gap material. In order to understand the optical properties of tetragonal CaSiO3perovskite, the dielectric function, absorption coefficient, optical reflectivity, refractive index, extinction coefficient, and electron energy loss are calculated for radiation up to 40 eV. This is the first quantitative theoretical prediction of the elastic, electronic and optical properties of tetragonal CaSiO3perovskite, and it still awaits experimental confirmation.
MAGNETIC CLUSTERS DEVELOPMENT IN OXIDIZEDCeNi5POWDER
Authors: REDNIC LIDIA , COLDEA MARIN , DEAC IOSIF GRIGORE , REDNIC VASILE , ALDEA NICOLAE , NEUMANN MANFRED
Published: December 2010

Synthesis, X-ray diffraction (XRD), transmission electron microscopy (TEM), X-ray photoelectron spectroscopy (XPS), Raman spectroscopy and magnetic measurements at low temperature of Ni metallic clusters covered by NiO , Ce2O3and CeO2, obtained from CeNi5powder oxidized in air at different temperatures up to 800°C, are reported. The average crystallite size of Ni core and the thickness of NiO oxide formed at the surface increase with temperature due to recrystallization processes, from 34 nm at 300°C to 77 nm at 800°C and from 9 nm to 19 nm, respectively. Ni metallic component was detected both in XPS valence bands and core levels spectra only after sputtering. The hysteresis loop presents a small shift towards negative magnetic fields which confirms the presence of ferromagnetic Ni /antiferromagnetic NiO interfaces.