bluuebunny/crossref_metadata_2025 huggingface dataset:
Improved Survival of Cardiac Transplantation Candidates with Implantable Cardioverter Defibrillator Therapy:
Authors: Ermis Cengiz , Zadeii Gino , Zhu Alan X. , Fabian William , Collins Joanne , Lurie Keith G. , Sakaguchi Scott , Benditt David G
Published: June 2003

Introduction:Survival in patients awaiting cardiac transplantation is poor due to the severity of left ventricular dysfunction and the susceptibility to ventricular arrhythmia. The potential role of implantable cardioverter defibrillators (ICDs) in this group of patients has been the subject of increasing interest. The aims of this study were to ascertain whether ICDs improve the survival rate of patients on the waiting list for cardiac transplantation and whether any improvement is independent of concomitant beta‐blocker or amiodarone therapy.

Methods and Results:Data comprised findings from 310 consecutive patients at a single center who were evaluated and deemed suitable for cardiac transplantation and placed on the waiting list. Kaplan‐Meier actuarial approach was used for survival analysis. Survival analysis censored patients at time of transplantation or death. Of the 310 patients, 111 (35.8%) underwent successful cardiac transplantation and 164 (52.9%) died while waiting; 35 patients remain on the waiting list. Fifty‐nine (19%) patients had ICD placement for ventricular arrhythmias prior to or after being listed. Twenty‐nine (49.1%) ICD patients survived until cardiac transplantation, 13 (22%) patients died, and 17 (28.8%) remain on the waiting list. Among non‐ICD patients, 82 (32.7%) received transplants, 151 (60.2%) died, and 18 (7.2%) remain on the waiting list. Survival rates at 6 months and 1, 2, 3, and 4 years were better for all ICD patients compared to non‐ICD patients (log‐rankx2, P = 0.0001). By multivariate analysis, ICD therapy and beta‐blocker treatment were the strongest predictors of survival. Further, ICD treatment was associated with improved survival independent of concomitant treatment with beta‐blocker or amiodarone. Among ICD and non‐ICD patients treated with a beta‐blocker or amiodarone, survivals at the 1 and 4 years were 93% vs 69% and 57% vs 32%, respectively (log‐rankx2, P = 0.003).

Conclusion:ICD therapy is associated with improved survival in high‐risk cardiac transplant candidates, and ICD benefit appears to be independent of concomitant treatment.(J Cardiovasc Electrophysiol, Vol. 14, pp. 578‐583, June 2003)
Clinical Outcome of Very Late Recurrence of Atrial Fibrillation after Catheter Ablation of Paroxysmal Atrial Fibrillation
Authors: Hsieh Ming‐Hsiung , Tai Ching‐Tai , TSAI Chin‐Feng , Lin Wei‐Shiang , Lin Yung‐Kuo , Tsao Hsuan‐Ming , Huang Jin‐Long , Ueng Kwo‐Chang , Yu Wen‐Chung , Chan Paul , Ding Yu‐An , Chang Mau‐Song , Chen Shih‐Ann
Published: June 2003

Introduction: High recurrence rate is still a major problem associated with ablation of paroxysmal atrial fibrillation (AF). Most of the recurrences occur within 6 months after ablation. The characteristics of very late recurrent AF (>12 months after ablation) have not been reported.

Methods and Results: Two hundred seven patients with drug‐refractory AF underwent successful focal ablation or isolation of AF foci. After the first ablation procedure, Holter monitoring and event recorders were used to evaluate symptomatic recurrent AF. A second ablation procedure was recommended if the antiarrhythmic drugs could not control recurrent AF. During long‐term follow‐up (mean

30 ± 11

months, up to 51 months), 70 patients had recurrent AF, including 13 patients (6%) with very late (>12 months) recurrent AF (group 1) and 57 patients (28%) with late (within 12 months after ablation) recurrent AF(group 2). Group 1 patients had a significantly lower incidence of multiple (≥2) AF foci

(23% vs 63%, P = 0.02)

than group 2 patients. In addition, the incidence of antiarrhythmic drugs use

(38% vs 84%, P = 0.001)

to maintain sinus rhythm after the first episode of recurrent AF was significantly lower in group 1 than group 2 patients, and the incidence of a second intervention procedure

(8% vs 35%, P = 0.051)

tended to be lower in group 1 than group 2 patients.

Conclusion: The incidence of very late recurrent AF after ablation of paroxysmal AF is very low, and the clinical outcome of patients with very late recurrent AF is benign.
(J Cardiovasc Electrophysiol, Vol. 14, pp. 598‐601, June 2003)
Extra‐Ostial Pulmonary Venous Isolation:
Authors: Reddy Vivek Y. , Neuzil Petr , Ruskin Jeremy N.
Published: June 2003

During catheter ablation of atrial fibrillation, ablation within the pulmonary veins is undesirable due to the risk of pulmonary venous stenosis and the possibility of leaving residual cuffs of arrhythmogenic tissue proximal to the ablation lesion set. An extra‐ostial pulmonary vein isolation strategy may circumvent these limitations, but achieving electrical isolation can be technically challenging, even with the use of saline‐irrigated radiofrequency energy technology. This report describes the successful use of epicardial radiofrequency ablation in a patient in whom endocardial irrigated radiofrequency ablation failed to achieve extra‐ostial pulmonary vein isolation.
(J Cardiovasc Electrophysiol, Vol. 14, pp. 663‐666, June 2003)
Slow relaxation of polar impurities in amorphous carbon thin films through capacitive spectroscopy
Authors: Bouzerar R. , Benlahsen M. , Racine B. , Picot J. C.
Published: June 2003

The dielectric properties of wide and small gap amorphous carbon thin films were probed through capacitive spectroscopy measurements. We report a long time evolution, ranging between a few hours and a few days, of the capacitive response of the films. The reported behavior suggests very different hypotheses, such as facilitated diffusion of polar impurities in porous films, or as slowly relaxing electronic states lying at the substrate/film interface and built-in stress relaxation. In the case of a contamination by polar impurities adsorbed on the voids surface, we develop a model predicting the correction to the capacitive response due to the contamination as a function of the density of impurities and their dynamical properties.
Laser-guided, intersecting discharge channels for the final beam transport in heavy-ion fusion
Authors: Niemann C. , Neff S. , Tauschwitz A. , Penache D. , Birkner R. , Constantin C. , Knobloch R. , Presura R. , Rosmej F. B. , Hoffmann D. H. H. , Yu S. S.
Published: June 2003

Ion-beam transport in space charge neutralizing discharge channels has been proposed for the final focus and chamber transport in a heavy-ion fusion reactor. A driver scenario with two-sided target illumination requires a system of two intersecting discharges to transport beams of the same charge from opposite sides towards the fusion target. In this article we report on experiments on the creation of free-standing, intersecting high-current discharge channels. The discharges are initiated in ammonia gas (NH3) in a metallic chamber by two perpendicular CO2-laser beams, which resonantly heat and subsequently rarefy the gas along the laser paths before the breakdown. These low density channels guide the discharges along the predefined paths and also around the 90° angles without any mechanical guiding structures. In this way stable X-, T-, and L-shaped discharges with currents in excess of 40 kA, at pressures of a few mbar were created with a total length of 110 cm. An 11.4 A MeV Ni+1258 beam from the UNILAC (Universal Linear Accelerator) linear accelerator was used to probe the line-integrated ion-optical properties of the central channel in a T-shaped discharge.
Micro-Raman study of electronic properties of inversion domains in GaN-based lateral polarity heterostructures
Authors: Park M. , Cuomo J. J. , Rodriguez B. J. , Yang W.-C. , Nemanich R. J. , Ambacher O.
Published: June 2003

The electronic properties of inversion domains in a GaN-based lateral polarity heterostructure were investigated using micro-Raman spectroscopy. The piezoelectric polarization of each domain was calculated from strain determined via Raman scattering. The free carrier concentration and electron mobility were deduced from the longitudinal optical phonon–plasmon coupled mode. The electron concentration in the N-face domain was slightly higher than that in the Ga-face domain. It appears that during growth, a larger number of donor impurities may have been incorporated into the N-face domain than into the Ga-face domain.
Evidence of threeDXcenters in Al0.28Ga0.72As:Si from Hall experiments
Authors: Triki A. , Rziga-Ouaja F. , Mejri H. , Selmi A.
Published: June 2003

In this article, we report the effect of cooling conditions on transport data in Si-doped AlxGa1−xAs. We show that a rapid cooling induces a freezing out of electrons similar to that observed after photoionization of the sample at low temperatures. By diving the sample in liquid nitrogen, we have evidenced a multicomponent structure with three resolved peaks on transport curves for a relatively low aluminum composition x=0.28. These peaks were assigned to the nonresonant 3 Al–, 2 Al—, and 1 Al–DX levels.
Electrical properties and phase transition of CoFe2O4 nanocrystals under pressure
Authors: Wu Zhenyu , Bao Zhongxing , Cao Li , Liu Cuixia , Li Qianshu , Xie Sishen , Zou Bingsuo
Published: June 2003

The electric resistance CoFe2O4 nanocrystals of different sizes, obtained by the coprecipitation method was investigated under pressure up to 20 GPa in a diamond anvil cell at ambient temperature. The experimental results indicate that the phase transition (from the spinel to a tetragonal structure) takes place at 7.5 and 12.5 GPa for 6 and 80 nm, nanocrystals, respectively, in agreement with the prediction of scaling theory of the phase transition of nanocrystals. The relatively low transition pressure for CoFe2O4 is related to the high d-electron coupling between magnetic ions and to the small band gap in CoFe2O4 as compared to the other spinel ferrites. These results are discussed in terms of decreasing band gap with increasing pressure. The smaller the size of nanocrystals, the higher the phase transition pressure. The resistance of CoFe2O4 nanocrystal decreases exponentially under pressure, according to R∝exp(−CP), where C=0.7634 GPa−1 for large nanocrystals (80 nm) and C=0.5124 GPa−1 for CoFe2O4 of 6 nm.
Physical and optical properties of sol-gel nano-silver doped silica film on glass substrate as a function of heat-treatment temperature
Authors: Li Wenyan , Seal Sudipta , Megan Edward , Ramsdell Jeff , Scammon Kirk , Lelong Gerald , Lachal Laurent , Richardson Kathleen A.
Published: June 2003

Nano-silver doped silica films were deposited on glass slides using a sol-gel process and heat-treated at different temperatures. The films were characterized by ultraviolet-visible spectroscopy, x-ray photoelectron spectroscopy (XPS), atomic force microscopy (AFM), Rutherford backscattering spectrometry (RBS), and transmission electron microscopy for their optical, chemical, and structural properties. The absorption peak of silver colloids (wavelength from 400 to 460 nm) was present and a blueshift and intensity reduction of the absorption peak was observed during heat-treatment. Particle size reduction and surface morphology changes in the films were observed by AFM as a function of varying heat treatment temperatures. Silver nanoparticles were formed through spontaneous reduction of silver ions. The oxidation of silver occurs during heat-treatment, causing a reduction of absorption intensity. An interdiffusion between the Ag in the film and Na in the substrate glass was observed by XPS and RBS. Sodium in the coating likely increased the stability of silver oxide at high temperature treated samples.
Comment on “(Ta1−xNbx)2O5 films produced by atomic layer deposition: Temperature dependent dielectric spectroscopy and room-temperature I–V characteristics” [J. Appl. Phys. 90, 4532 (2001)]
Authors: Brazis R. , Pipinys P.
Published: June 2003

Experimental results on the I–V characteristics of Ta2O5 and mixed Ta–Nb oxide films at room temperature, reported by Strømme et al. [J. Appl. Phys. 90, 4532 (2001)], are reinterpreted in terms of multiphonon-assisted electron tunneling from traps. Electron-phonon coupling constant and trap depth values are elucidated. Multiphonon-assisted electron tunneling theory eliminates ambiguities in the values of the dielectric constant and other basic parameters deduced from the Poole–Frenkel, Fowler–Nordheim, or Schottky models. Only in the low-field range must the Frenkel emission be taken into account.
Probing local electric field distribution of nanotube arrays using electrostatic force microscopy
Authors: Ba Long , Shu Jian , Lu Zuhong , Li Juntao , Lei Wei , Wang Baoping , Li Waisang
Published: June 2003

The local electric field distribution of nanotube arrays has been studied by using the electrostatic force microscopy (EFM) technique. The nanotube arrays were fabricated using the anodic alumina template method. Good electric contact has been proofed using contact mode conductive atomic force microscopy. The experiment shows that the EFM can provide a quantitative mapping tool to measure three-dimensional distribution of local electric field with resolution down to several nanometers. The finite difference method has been applied to calculate the electric field distribution near the surface of the nanotube array induced by a conductive tip. The results show that the field decays in a power law with exponent varies for nanotubes of different packing environments as the tip was lifted away from the top of nanotubes. The protrusion of nanotubes causes a much higher enhanced field than packing geometry. Medium packing density may enable the maximum collective emission current for such nanotube arrays of narrow diameter and height diversity.
Be diffusion in molecular beam epitaxy-grown GaAs structures
Authors: Mosca R. , Bussei P. , Franchi S. , Frigeri P. , Gombia E. , Carnera A. , Peroni M.
Published: June 2003

Beryllium diffusion is considered in heavily doped p-type GaAs structures grown by molecular beam epitaxy (MBE). Secondary ion mass spectrometry (SIMS) measurements performed on samples which underwent rapid thermal processing (RTP) experiments at 850 °C for 30 s show that (i) Be diffusion is faster in p/p+/p structures than in p/p+ ones and (ii) an increase of the As4/Ga flux ratio during the MBE growth affects Be diffusion only in p/p+ structures. These results are discussed by modeling Be diffusion according to a substitutional–interstitial diffusion mechanism where Be transition from substitutional to interstitial takes place by a kick-out process. The modeling procedure, which has been previously used to simulate Be and Zn diffusion in GaAs and in other related compounds, has been modified in order to account for the lacking of equilibrium in the initial concentration of Ga interstitials. It is shown that when the lacking of equilibrium is accounted for at the beginning of the annealing experiment, a satisfactory description of the SIMS results has been achieved in both p/p+ and p/p+/p structures, also considering samples grown by different As4/Ga flux ratios. The modeling results allow us to conclude that in the p/p+/p structures the concentration of point defects (e.g., IGa) in the regions cladding the base layer affects, to a major extent, Be diffusion during RTP, so that an efficient reduction of Be diffusivity is expected only when the whole structure is grown by high V/III flux ratios.
Characteristics of hard x-ray emission from laser-induced vacuum spark discharges
Authors: Ohzu Akira , Ito Kazunori
Published: June 2003

An experimental study of the characteristics of hard x-ray emission in laser-induced vacuum spark discharges has been carried out. The spark discharge is performed in a gap (10 mm) of pin electrodes using a Marx generator and a laser pulse to produce Au plasma on the tip of an anode. When spark discharge with charge voltage of 150 kV occurred simultaneously with the incidence of a laser pulse, an x-ray pulse made of a short (∼20 ns) x-ray spike pulse and a long (∼400 ns) pulse was emitted with high intensity (∼10 mR per shot). The two pulses appeared at the beginning and at the latter part of discharge. The effective photon energy was around 150 and 80 keV, respectively. The results show that the x-ray intensity strongly depends on the timing of the onset of the discharge with respect to the laser irradiation, the laser intensity, and the charge voltage. The mechanisms responsible for the x-ray emission are discussed in terms of the results observed.
Diffusion and electrical activation of indium in silicon
Authors: Scalese S. , Italia M. , La Magna A. , Mannino G. , Privitera V. , Bersani M. , Giubertoni D. , Barozzi M. , Solmi S. , Pichler P.
Published: June 2003

In this work we investigate the diffusion and the electrical activation of In atoms implanted into silicon with energies ranging from 40 to 360 keV and doses of 5×1012 and 5×1013 In/cm2 during rapid thermal processing. Our investigation shows a clear dependence of In outdiffusion and electrical activation on the implant depth. For a fixed dose, the electrical activation was found to increase with the implant energy. We propose that the data can be explained by considering the balance between the local In concentration and the C background. The occurrence of coupling between the C present in the substrate and the implanted In, depending on the C/In ratio, may in fact give rise to significant formation of C–In complexes. Such complexes play a role in the enhanced electrical activation due to the shallower level they introduce into the Si band gap (Ev+0.111 eV), with respect to the rather deep level (Ev +0.156 eV) of In alone [R. Baron et al., Appl. Phys. Lett. 30, 594 (1977); R. Baron et al., ibid. 34, 257 (1979)]. The interaction of In atoms with the C background inside the silicon substrate has been, therefore, identified as the most likely origin of this behavior. In and C coimplantation has also been studied in this work, in order to further investigate the key role of C in the increase of electrical activation. A large increase of electrical activation has been detected in the coimplanted samples, up to a factor of about 8 after annealing at 900 °C. However, C precipitation occurs at 1100 °C, and has dramatic effects on the carrier concentration that falls by even two orders of magnitude. This limits the maximum thermal budget that can be used for In activation in C coimplanted material.
Hysteresis curve of magnetic nanocrystals monolayers: Influence of the structure
Authors: Russier V. , Petit C. , Pileni M. P.
Published: June 2003

We calculate the magnetization curve at vanishing temperature of a monolayer of spherical single domain magnetic nanocrystals in terms of the structure of the monolayer. The magnetization curve of a square lattice of particles is compared to those of disordered monolayers. The particles on the disordered monolayers are either distributed isotropically on the surface or organized in chains, which are either linear and or totally flexible. A strong effect of the structure is found only in the case of linear chains and when the magnetization is measured along the chains direction. In the experimental part a monolayer of cobalt nanoparticles organized in a chainlike structure is elaborated by applying a magnetic field during the evaporation of a ferrofluid on a substrate. The change of the magnetization curve due to the chainlike structure is compared to that of the model.
High pressure behavior of titanium–silicon carbide (Ti3SiC2)
Authors: Jordan J. L. , Sekine T. , Kobayashi T. , Li X. , Thadhani N. N. , El-Raghy T. , Barsoum M. W.
Published: June 2003

The dynamic high-pressure behavior and phase stability of titanium–silicon carbide (Ti3SiC2), a unique ceramic having metal-like properties, was investigated in this study. Time-resolved measurements of the Hugoniot equation of state, employing a plate impact geometry, were conducted on the Ti3SiC2 samples in the pressure range of 50–120 GPa using a two stage light gas gun. At pressures around 90–120 GPa, Ti3SiC2 was found to transform to a more compressed state. Shock-recovery experiments were also performed on Ti3SiC2 powders at impact velocities of 1.5–2 km/s using a single capsule geometry, with and without the addition of copper powder to vary the shock-loading pressure (calculated to be 22–58 GPa) and temperature (calculated to be up to 3250 °C) in the sample. No evidence of shock-induced decomposition was observed in these recovery experiments performed on the Ti3SiC2 powders.
Macroporosity free aluminum alloy weldments through numerical simulation of keyhole mode laser welding
Authors: Zhao H. , DebRoy T.
Published: June 2003

A transport phenomena-based numerical model is developed to predict the keyhole geometry and temperature profiles in the weldment during laser welding. The model can be used to prevent macroporosity formation during laser welding of aluminum alloys. The experimental results show that the weld metal contains large pores when the welding mode changes from conduction to keyhole mode or vice versa due to changes in welding variables. Based on this observation, the mathematical model predicts macroporosity formation when welding is conducted under conditions where small changes in welding parameters lead to a change in the welding mode. The model has been used to predict the geometry of the keyhole and the fusion zone, and the weldment temperature field for laser beam welding of aluminum alloys 5182 and 5754. The calculated weld pool depth, width, and shape for different welding speeds agreed well with the experimental results. The calculations showed that the keyhole profiles for high-speed welding were asymmetric. Negative beam defocusing resulted in a deeper keyhole than that obtained with positive beam defocusing. The transition from keyhole to conduction mode was more abrupt for negative beam defocusing. The model could predict the formation of macroporosity during laser welding of aluminum alloys 5182 and 5754. The results provide hope that transport phenomena-based models can be useful to prevent the formation of macroporosity during keyhole mode laser welding of aluminum alloys.
A semiclassical approach to Coulomb scattering of conduction electrons on ionized impurities in nondegenerate semiconductors
Authors: Poklonski N. A. , Vyrko S. A. , Yatskevich V. I. , Kocherzhenko A. A.
Published: June 2003

In the proposed model of mobility, the time of electron–ion interaction equals the time taken by the conduction electron to pass a spherical region, corresponding to one impurity ion in crystal, and the minimum scattering angle is determined after Conwell–Weisskopf. We consider the acts of electron scattering on ions as independent and incompatible events. It is shown in the approximation of quasimomentum relaxation time, that for nondegenerate semiconductors, the mobility μi, limited by the elastic scattering by impurity ions with the concentration Ni, is proportional to T/Ni2/3; the Hall factor equals 1.4. The calculated dependences of the mobility of the majority charge carriers upon their concentration for different temperatures T agree well with known experimental data. It is shown, that the Brooks–Herring formula μBH∝T3/2/Ni gives overestimated values of mobility. Comparison of the calculations of mobility in degenerate semiconductors with experimental data also yields μi<μBH.
Spectroscopic ellipsometry of thin film and bulk anatase (TiO2)
Authors: Jellison G. E. , Boatner L. A. , Budai J. D. , Jeong B.-S. , Norton D. P.
Published: June 2003

Spectroscopic ellipsometry (SE) measurements were made on thin-film and single-crystal TiO2 anatase using a two-modulator generalized ellipsometer. The TiO2 films were epitaxially stabilized on a LaAlO3 substrate in the anatase crystal structure using reactive sputter deposition. The films were highly crystalline, possessing a “stepped surface” morphology indicative of atomic layer-by-layer growth. The SE results for the anatase film indicate that the material is essentially oriented with the c axis perpendicular to the substrate, but there is some anisotropy near the interface and the surface. Corrugations of the film surface, as observed using atomic force microscopy, are consistent with a surface structure needed to create cross polarization. Accurate values of the optical functions of crystalline anatase were obtained above and below the band edge using SE. Above the band edge, both the ordinary and extraordinary complex dielectric functions exhibited two critical points.
Minority carriers recombination in n-InP single crystals
Authors: Tsimberova I. , Rosenwaks Y. , Molotskii M.
Published: June 2003

We present a comprehensive study of minority carrier lifetime and recombination mechanisms in n-InP single crystals. The study is based on steady state and time-resolved photoluminescence measurements in a wide temperature range (15–300 K). Various recombination and trapping mechanisms are analyzed and compared in order to assess their influence on the effective hole lifetime. It was found that two main processes govern the hole lifetime: radiative band-to-band recombination at temperatures >100 K and nonradiative trapping in unintentional induced acceptor centers at low temperatures (<100 K). A fit of the measured effective bulk lifetime to a recombination model based on these two processes enabled us to extract the rate constant for the radiative band-to-band recombination, and the density of the acceptor-like trapping centers.
Electronic and positron properties of zinc-blende structure of GaN, AlN, and their alloy Ga1−xAlxN
Authors: Al-Douri Yarub
Published: June 2003

Electronic and positron band structures and charge densities of GaN, AlN, and their alloy Ga0.5Al0.5N in zinc-blende structure using the empirical pseudopotential method are investigated. For the ternary alloy Ga1−xAlxN, the virtual crystal approximation is coupled with the pseudopotential method. The energies along Γ, X, and L of Ga1−xAlxN alloy as a function of the alloy concentration are calculated. Angular correlation of positron annihilation radiation along different crystallographic directions in GaN, AlN, and Ga0.5Al0.5N is calculated. Other quantities such as ionicity character and bulk modulus by means of recent models with respect to the alloy concentration are discussed.
Least action principle for the estimation of the slowness and the attenuation of pseudo surface acoustic waves
Authors: Laude Vincent , Wilm Mikael , Ballandras Sylvain
Published: June 2003

The estimation of the slowness and of the attenuation of pseudo surface acoustic waves (PSAWs) has been addressed by many authors, but still represents a challenge because of the intrinsic difficulty to provide a physically consistent representation of their characteristics. In this work, we propose an alternative approach to the popular use of complex slownesses along the propagation direction. We introduce in the standard harmonic model an optimal source term exactly compensating for the energy lost by leakage, by analogy with the problem of the reflection of a bulk acoustic wave on the surface. This leads us to the minimization of a function whose minimum is the PSAW slowness and whose minimum value gives the attenuation. The method is found to be stable and reliable compared to previously published data, without requiring any change in the partial wave selection rule, and further does not require one to consider waves with increasing energy in the depth of the substrate, which generally does not correspond to the observed phenomena.
Surface acoustic wave propagation characteristics of aluminum nitride thin films grown on polycrystalline diamond
Authors: Iriarte G. F.
Published: June 2003

Diamond has the highest surface acoustic wave (SAW) velocity among all materials and thus provides substantial advantages for the fabrication of high-frequency SAW devices when combined with a piezoelectric thin film. The properties of layered film structures consisting of a piezoelectric material layer, aluminum nitride (AlN), and a polycrystalline diamond layer grown on a silicon substrate have been examined. Highly textured AlN thin films have been sputter-deposited onto polycrystalline diamond substrates at room temperature. X-ray diffraction analysis of the multilayer structure as well as atomic force microscope images of the AlN surface indicate that the deposited AlN films were c-axis oriented with a full width at half maximum of the rocking curve of the AlN-002-peak of 2.1°. The thickness of the AlN layer was of 4.3 μm, whereas the diamond layer was 50 μm thick and resting on a 3-in Si wafer. Standard one-port SAW resonators with aluminum (Al) metallization have been subsequently fabricated and evaluated. Experimental results indicate that the fundamental as well as higher Rayleigh SAW modes are excited. Thus, the phase velocities of the first, second, third, and fourth mode are found to be 6.850, 10.000, 11.800, and 14.450 m/s respectively. A very good out-of-band rejection of −50 dB was obtained.
Photonic crystal polarizers and polarizing beam splitters
Authors: Solli D. R. , McCormick C. F. , Chiao R. Y. , Hickmann J. M.
Published: June 2003

We have experimentally demonstrated polarizers and polarizing beam splitters based on microwave-scale two-dimensional photonic crystals. Using polarized microwaves within certain frequency bands, we have observed a squared-sinusoid (Malus) transmission law when using the photonic crystal as a polarizer. The photonic crystal also functions as a polarizing beamsplitter; in this configuration it can be engineered to split incident polarizations in either order and in any direction, making it more versatile than conventional, Brewster-angle beamsplitters.
Laser-induced decompression shock development in fused silica
Authors: Wang Junlan , Weaver Richard L. , Sottos Nancy R.
Published: June 2003

Laser-induced weak shock formation in fused silica is studied using standard wave mechanics and applied to thin-film laser spallation experiments. Due to the negative nonlinear elasticity of fused silica, a laser-induced Gaussian stress pulse evolves into a shock after traveling a certain distance in a fused silica substrate. Experimental observations confirm theoretical predictions of shock development. A decompression shock forms and greatly enhances interfacial failure of a thin film deposited on the substrate. The effects of laser fluence and substrate thickness (attenuation) on shock development are also investigated.
Response of a Pt-polyyne membrane in surface acoustic wave sensors: Experimental and theoretical approach
Authors: Caliendo Cinzia , Fratoddi Ilaria , Russo Maria Vittoria , Lo Sterzo Claudio
Published: June 2003

A surface acoustic wave (SAW) sensor, based on a polymeric sensitive membrane, has been realized for sensor applications and materials characterization. A platinum-containing rigid-rod organometallic polymer [-Pt(PPh3)2(-C≡C-pC6H2(2,5-OC16H33)2-C≡C-)]n (Pt–P–HDOB), obtained by the reaction of cis-[Pt(PPh3)2Cl2] with 1,4-diethynyl-2,5-dihexadeciloxybenzene (HDOB) by means of the recently assessed “Extended one pot” polymerization route, was here studied. The chemical structure and chain length of Pt–P–HDOB polymer were defined by spectroscopic techniques and gel permeation chromatography measurements. The acoustic characterization of the Pt–P–HDOB film was developed with the aid of the perturbation theory applied to different polymer-coated-piezoelectric substrates and the shear modulus of Pt–P–HDOB film have been estimated. A SAW delay line has been implemented on ZnO/Si substrate and a thin polymeric film has been spin deposited on the device surface to realize a chemical sensor. The sensor has been exposed to different chemicals and its response has been measured for different chemical concentrations. High sensitivity and reproducibility of the sensor response to relative humidity and methanol vapors were found.
Carrier-type reversal in metal modified chalcogenide glasses: Results of thermal transport measurements
Authors: Rajesh R. , Philip J.
Published: June 2003

It is known that chalcogenide glasses, in general, are p-type semiconductors. This is attributed to the following two reasons. (i) The number of electrons excited above the conduction band mobility edge is smaller than the number of holes excited below the valence band mobility edge. (ii) The lifetime of the free holes excited from positive defect states is higher than the lifetime of free electrons excited from negative defect states. Moreover, chalcogenide glasses are rather insensitive to impurity doping because their Fermi levels are pinned near the middle of the band gap by valence alternation pairs. However, it is found that the chemical modification of certain chalcogenide glasses by metallic elements such as lead and bismuth changes the conduction to n type at specific metal concentrations. This phenomenon, called carrier-type reversal (CTR), is explained in terms of the unpinning of the Fermi level and the consequent enhancement in electron concentration in the medium. In this work we report the results of our measurement of the thermal properties-thermal diffusivity, effusivity, conductivity and heat capacity—on four glass systems that are known to undergo CTR at specific metal concentrations. The photopyroelectric technique has been used to make these measurements on bulk samples prepared by melt quenching. Four series of glasses, PbxGe42−xSe58 (x=0-20), Pb20GeySe80−y (y=17-24), BixGe20Se80−x (x=2-12) and PbxIn25−xSe75 (x=0-15) which are known to undergo CTR at specific metal concentrations, have been subjected to the investigations reported in this work. It is found that all the above thermal properties show anomalous variations at the metal concentrations at which CTR occurs. The results are explained in terms of the enhancement in electron concentration during CTR in the material.
Large magnetic entropy change in the metallic antiperovskite Mn3GaC
Authors: Yu Ming-Hui , Lewis L. H. , Moodenbaugh A. R.
Published: June 2003

A large positive magnetic entropy change ΔSM is observed in the metallic antiperovskite Mn3GaC near its first-order metamagnetic transition temperature 159 K where the stoichiometric compound transforms from an antiferromagnetic to a canted ferromagnetic state accompanied by a discontinuous volume change of −0.46% without change of symmetry. The unusual field dependence of the ΔSM of Mn3GaC shows a very rapid linear increase from zero to a saturation value within a field interval smaller than 1 T. The broadening of the peak of ΔSM to low temperature with increasing field change creates an ΔSM plateau in the temperature dependence of the MCE, which is of significance for practical application of these materials in the Ericsson-cycle magnetic refrigerator.
Influence of water molecule coordination on the magnetic properties of polyamine copper dinitrate complexes
Authors: Guskos N. , Glenis S. , Likodimos V. , Typek J. , Fuks H. , Wabia M. , Szymczak R. , Lin C. L. , Perkowska T. A.
Published: June 2003

The magnetic properties of two biogenic polyamine copper complexes were investigated by dc magnetization and electron paramagnetic resonance (EPR) measurements. The variation in temperature of the low field magnetization reveals that the absence or presence of water molecules in the copper coordination sphere results, respectively, in the enhancement or suppression of antiferromagnetic interactions between Cu2+ ions. Analysis of the EPR spectra shows considerable temperature dependence of both the g values and EPR linewidths that persist in the paramagnetic regime for both complexes. Such variation of EPR parameters is attributed to the interplay of demagnetizing field effects, pertinent to the purely paramagnetic compound, and to the presence of short-range magnetic order that applies to the antiferromagnetic polyamine complex.
Formation of interfacial layer during reactive sputtering of hafnium oxide
Authors: Tsui Bing-Yue , Chang Hsiu-Wei
Published: June 2003

Hafnium oxide is one of the most promising high dielectric constant materials to replace silicon dioxide as the gate dielectric. To take the advantages of high dielectric constant of HfO2 thoroughly, the relatively low dielectric constant interfacial layer must be controlled carefully. In this work, the formation of an interfacial SiO2 layer at the HfO2/Si interface was studied comprehensively. It is observed that during reactive sputtering deposition of the HfO2 layer, a very thick interfacial SiO2 layer, thicker than 3 nm, would be grown. O-radical signals, instead of O2-radicl signals, are detected in the sputtering chamber. An O-radical enhanced oxidation model is proposed to explain such an unusual thick SiO2 layer. The adoption of a two-step deposition method, the thickness of interfacial SiO2 layer can be reduced only if the bottom Hf layer is thicker than 5 nm. However, the reduction of effective oxide thickness would be limited. Reoxidation of Hf film sounds a better choice. A 1.0–1.5-nm-thick interfacial SiO2 layer is still observed. This implies that the traced oxygen in the sputtering chamber plays a critical role on the formation of the interfacial layer. It is thus concluded that reactive sputtering is not a suitable method to prepare a HfO2 layer with a negligible interfacial SiO2 layer. Reoxidation of Hf film is a better choice, but the oxygen content in the sputtering chamber must be well controlled.
Abatement of perfluorinated compounds using microwave plasmas at atmospheric pressure
Authors: Kabouzi Y. , Moisan M. , Rostaing J. C. , Trassy C. , Guérin D. , Kéroack D. , Zakrzewski Z.
Published: June 2003

Microwave plasmas sustained at atmospheric pressure, for instance by electromagnetic surface waves, can be efficiently used to abate greenhouse-effect gases such as perfluorinated compounds. As a working example, we study the destruction and removal efficiency (DRE) of SF6 at concentrations ranging from 0.1% to 2.4% of the total gas flow where N2, utilized as a purge gas, is the carrier gas. O2 is added to the mixture at a fixed ratio of 1.2–1.5 times the concentration of SF6 to ensure full oxidation of the SF6 fragments, providing thereby scrubbable by-products. Fourier-transform infrared spectroscopy has been utilized for identification of the by-products and quantification of the residual concentration of SF6. Optical emission spectroscopy was employed to determine the gas temperature of the nitrogen plasma. In terms of operating parameters, the DRE is found to increase with increasing microwave power and decrease with increasing gas flow rate and discharge tube radius. Increasing the microwave power, in the case of a surface-wave discharge, or decreasing the gas flow rate increases the residence time of the molecules to be processed, hence, the observed DRE increase. In contrast, increasing the tube radius or the gas-flow rate increases the degree of radial contraction of the discharge and, therefore, the plasma-free space close to the tube wall: this comparatively colder region favors the reformation of the fragmented SF6 molecules, and enlarging it lowers the destruction rate. DRE values higher than 95% have been achieved at a microwave power of 6 kW with 2.4% SF6 in N2 flow rates up to 30 standard l/min.
Dynamical analysis of relaxation luminescence in ZnS:Er3+ thin film devices
Authors: Wang Yu-Jiang , Wu Chen-Xu , Chen Mou-Zhi , Huang Mei-Chun
Published: June 2003

The relaxation luminescence of ZnS:Er3+ thin film devices fabricated by thermal evaporation with two boats is studied. The dynamical processes of the luminescence of Er3+ in ZnS are described in terms of a resonant energy transfer model, assuming that the probability of collision excitation of injected electrons with luminescence centers is expressed as a Gaussian function. It is found that the frequency distribution depends on the Lorentzian function by considering the emission from excited states as a damped oscillator. Taking into consideration the energy storing effect of traps, an expression is obtained to describe a profile that contains multiple relaxation luminescence peaks using the convolution theorem. Fitting of experimental results shows that the relaxation characteristics of the electroluminescence are related to the carriers captured by bulk traps as well as by interface states. The numerical calculation carried out agrees well with the dynamical characteristics of relaxation luminescence obtained by experiments.
Low frequency noise in GaN/AlGaN heterostructure field effect transistors in non-ohmic region
Authors: Rumyantsev S. L. , Pala N. , Shur M. S. , Levinshtein M. E. , Asif Khan M. , Simin G. , Yang J.
Published: June 2003

Experimental data on the low-frequency noise in GaN/AlGaN heterostructure field effect transistors show that the spectral noise density of the drain current fluctuations, SI, close to the saturation voltage increases faster than the square of the drain voltage Vd. At drain voltages higher than the saturation voltage, SI decreases with a further increase in drain voltage. A model of noise behavior below saturation based on the tunneling mechanism of noise is in a good agreement with the data measured.
Effects of a resonant shallow state on the electrical properties of Te-doped AlxGa1−xSb
Authors: Ghezzi C. , Magnanini R. , Parisini A. , Gombia E. , Mosca R.
Published: June 2003

In AlxGa1−xSb, the Te impurity originates a simple donor state (D level), whose occupancy equilibrates rapidly with the conduction band; it coexists with a DX state which is responsible for the persistent photoconductivity effect. The D level is linked to the L conduction band minima and becomes resonant with the conduction band for x<0.20. Under these conditions, occupancy variations in the D level give rise to a nonomonotonic temperature dependence of the nH Hall density which is not attributable to mixed conduction effects. The role of the D level was investigated in samples of different alloy compositions (x<0.20) and doping levels (1016–1018 cm−3) and analyzed using a simplified model. The analysis confirmed the role of the occupancy variations in the D level in determining the temperature dependence of nH and the linkage of the level to the L conduction band edge.
Low-temperature conductance measurements on single molecules
Authors: Reichert J. , Weber H. B. , Mayor M. , Löhneysen H. v.
Published: June 2003

An experimental protocol which allows to perform conductance spectroscopy on organic molecules at low temperatures (T≈30 K) has been developed. This extends the method of mechanically controlled break junctions which has recently demonstrated to be suitable to contact single molecules at room temperature. The conductance data obtained at low T with a conjugated sample molecule show a highly improved data quality with a higher stability, narrower linewidth, and substantially reduced noise. Thus, the comparability of experimental data with other measurements as well as with theoretical simulations is considerably improved.
Effects of Ag and In addition on the optical properties and crystallization kinetics of eutectic Sb70Te30 phase-change recording film
Authors: Her Yung-Chiun , Chen Hung , Hsu Yung-Sung
Published: June 2003

Adding specific foreign elements into the eutectic Sb70Te30 fast-growth material is expected to be an effective way to increase its thermal stability for blue laser recording. We have studied the effects of Ag and In addition on the optical properties and crystallization kinetics of the eutectic Sb70Te30 recording film. The results showed that the addition of Ag and In increased the refractive index and decreased the extinction coefficient of amorphous Sb70Te30 film and decreased both the refractive index and extinction coefficient of crystalline Sb70Te30 film. The archival stability of the eutectic SbTe alloy could be effectively improved by adding Ag and In elements, however, the addition of Ag and In also made the initialization of the as-deposited eutectic SbTe film more difficult. During the isothermal crystallization process, the incubation time was extended, crystallization speed was reduced, and the crystallization process became more grain-growth dominated as Ag and In were added. All these effects were further enhanced by increasing the concentration of In element.
Computer simulations of magnetization switching of elongated magnetic particles with shape defects
Authors: Endo Hiraku , Uesaka Yasutaro , Nakatani Yoshinobu , Hayashi Nobuo , Fukushima Hiroshi
Published: June 2003

The switching fields of elongated magnetic particles with various shape defects were investigated by means of computer simulations. The magnetic particles were approximated by rectangular parallelepipeds that have groove or chip defects. We modeled 13 types of particle shape defects for two particle sizes. The particle sizes used were “small particle” 10 nm×10 nm×50 nm and “large particle” 40 nm×40 nm×200 nm. The magnetocrystalline anisotropy field in the magnetic particles was set to zero. The switching fields of the small and large particles were found to decrease with the number of groove defects, but they were independent of the total number of chip defects. The magnetic moments of all of the small particles rotated almost coherently. The switching fields of the small particles almost coincided with the average of the difference between the demagnetizing fields in all cells along two directions: An easy-axis direction and one of the hard-axis directions. That is, we obtained the switching fields with various shapes from the demagnetizing fields even when the particles were deformed by defects. On the other hand, the magnetic moments of all the large particles rotated incoherently. The magnetic moments began to switch at particular planes that include the cell with the lowest difference between the demagnetizing fields in the easy-axis direction and one of the hard-axis directions.
Geometrical modeling of surface profile formation during laser ablation of materials
Authors: Vatsya S. R. , Bordatchev E. V. , Nikumb S. K.
Published: June 2003

Recent advances in laser machining technology have made it possible to fabricate parts and features with high accuracy and precision, using high-powered, short-pulsed, Q-switched lasers. To determine the machining parameters to obtain the desired geometrical quality, an understanding of the relationship between the process parameters and the resulting surface profile is necessary. In the present study, we adopt a geometrical approach which, coupled with the material properties and machining process parameters, yields a method to determine the surface profile of the material ablated by a laser pulse. It is reasoned that the energy incident upon an infinitesimal area of the surface at a given time is transferred in the outward normal direction to the surface, and the volume of ablation, centered about the normal, is determined by the laser–material interaction and the process parameters. The direction and depth of ablation determine the modified surface profile an infinitesimal time later, yielding a nonlinear partial differential equation, which is then integrated starting with the initial known surface to determine the profile at an arbitrary time. Theoretical predictions and the experimental results are compared for a test case of metals. The agreement between the two is satisfactory indicating the adequacy of the approach.