bluuebunny/crossref_metadata_2025 huggingface dataset:
Direct evaluation of domain-wall and intrinsic contributions to the dielectric and piezoelectric response and their temperature dependence on lead zirconate-titanate ceramics
Authors: Zhang Q. M. , Wang H. , Kim N. , Cross L. E.
Published: July 2002

By making use of the fact that domain-wall motions do not produce volumetric changes, an experimental method is introduced to directly and quantitatively determine the domain-wall and intrinsic contributions to the piezoelectric and dielectric responses of a ferroelectric material. Utilizing this method, the contributions from the domain walls and intrinsic part as well as their temperature dependence for lead zirconate-titanate (PZT) 52/48 and PZT-500 ceramics are evaluated. The data show that at temperatures below 300 K, the large change in the dielectric and piezoelectric constants with temperature is due to the change in the domain-wall activities in the materials. The results confirm that most of the dielectric and piezoelectric responses at room temperature for the materials studied is from the domain-wall contributions. The data also indicate that in PZT-500, both 180° wall and non-180° walls are possibly active under a weak external driving field.
Thermodynamic modeling of reciprocating chillers
Authors: Gordon J. M. , Ng Kim Choon
Published: July 2002

A simple model for predicting the performance of reciprocating chillers is developed. The basic irreversibilities that mitigate against fast and slow cooling rates are accounted for. The model proposed here is consistent with real performance data for 30 chillers that span a range of cooling rates from 30 to 1300 kW and, with adjustable parameters that characterize a particular chiller, is shown to be capable of reproducing actual performance data to within better than experimental uncertainty.
Synthesis and characterization of Fe16N2 in bulk form
Authors: Huang M. Q. , Wallace W. E. , Simizu S. , Pedziwiatr A. T. , Obermyer R. T. , Sankar S. G.
Published: July 2002

Using molecular beam epitaxy and ion implantation, Japanese workers have formed Fe16N2 in thin Fe films. They report a large magnetic induction for this nitride, ≥2.8 T. In the present study, Fe16N2 has been prepared in bulk form by treating Fe powder with NH3/H2 gas mixtures at temperatures in the range 660–670 °C. The γ phase alloy, which forms under these conditions, was quenched to room temperature to form the α′-Fe-N phase and then heat treated at 120–150 °C to form the α″-Fe-N phase. The α′ phase has been prepared in 80% purity, the other phase being nonmagnetic γ-Fe-N. The α″ phase has been prepared in 50% purity, the impurity phases being α-Fe and γ-Fe-N. Magnetic measurements give saturation magnetizations at room temperature of 250±10 emu/g (2.6μB/Fe) for the α′ phase, 285±10 emu/g (2.9μB/Fe) for the α″ phase, and essentially zero for the γ phase. Mössbauer measurements confirm that nitrogen austenite is nonmagnetic. The anisotropy of Fe16N2 is small but detectable.
Real-time hot-stage high-voltage transmission electron microscopy precipitation of CdS nanocrystals in glasses: Experiment and theoretical analysis
Authors: Liu Li-Chi , Risbud Subhash H.
Published: July 2002

Hot-stage high-voltage (1.5 MeV) transmission electron microscopy was used to directly observe CdS nanocrystals precipitated in a silicate glass and a theoretical framework of nanocrystal coarsening kinetics more appropriate than the popularly used Lifshitz–Slyozov–Wagner theory was developed. Nanocrystallite nucleation and coarsening were monitored in situ by video taping of bright-field images of the edges of thin (less than 2 μm) glass fragments heated in the hot stage; crystallite size distribution was obtained from the taped experimental observations. The effects of electron-beam heating and diffusion out of the nanocrystals were included in developing the theoretical analysis of coarsening kinetics which were used, in turn, to interpret the experimental size distribution curves.
Properties of plasma-enhanced chemical-vapor-deposited a-SiNx:H by various dilution gases
Authors: Hsieh S. W. , Chang C. Y. , Lee Y. S. , Lin C. W. , Hsu S. C.
Published: July 2002

The effects of dilution gases on hydrogenated amorphous silicon nitride (a-SiNx:H) films were investigated. Silane and ammonia were used as the reactive species, while nitrogen, helium, hydrogen, and argon were used as the dilution gases in a plasma-enhanced chemical vapor-deposition system at a substrate temperature of 300 °C. The electrical, physical, and chemical properties of the a-SiNx:H films were found to be highly sensitive to the various kinds and flow rates of the carrier gases in the deposition. Additionally, the physical properties of growth rate, refractive index, and etching rate were also investigated. The hydrogen bonding configuration was explored by infrared spectroscopy. The total hydrogen concentrations for all a-SiNx:H films were observed to be smaller than 3.0×1022 cm−3. The electrical properties were characterized by I-V and C-V measurements in metal-insulator-semiconductor structures. The breakdown strength was determined at the current density of 3 mA/cm2; in addition, the dominant mode of electronic conduction would appear to be the Poole–Frenkel emission. The interface trap state density Dit which ranged from 3.4×1011 to 1.3×1012 cm−2 eV−1 was evaluated by the C-V characteristics. Finally, the influences of the gas dilution in the a-SiNx:H films, as applied to the devices, were investigated by using the hydrogenated amorphous silicon thin-film transistors (a-Si:H TFTs). Analyses of the transfer characteristics of the TFT devices revealed that the density of deep gap states is 4×1012 cm−2 eV−1 and the field-effect mobility μFE is changing from 0.37 to 1.45 cm2/V s.
Ejection of positive ions from plasmas induced by laser ablation of Si and Nd1.85Ce0.15CuO4
Authors: van Ingen R. P.
Published: July 2002

Angle-resolved time-of-flight distributions of Si+ ions and of O+, Cu+, and Nd+ ions originating from laser ablation of Si and Nd1.85Ce0.15CuO4, respectively, were measured using a quadrupole mass spectrometer. From these distributions angle-resolved yield distributions of the ions were obtained. The time-of-flight distributions did not change with the detection angle; consequently, neither did the associated yields. The degrees of ionization of the laser-induced plasmas appeared to be about 5×10−7. However, it is argued that only a fraction of the order of 5×10−4 of the total number of ions could have been detected and that thus the actual degrees of ionization were of the order of 1×10−3. All these observations are explained in terms of ambipolar diffusion of the ions (and electrons) from the sheaths, with thicknesses of the Debye shielding distance, of the laser-induced plasmas in their initial stages. The results obtained indicate that in the case of the Si+ ions the main ionization mechanisms were collisional ionization and multiphoton ionization.
Experimental investigation of dichroism sum rules for V, Cr, Mn, Fe, Co, and Ni: Influence of diffuse magnetism
Authors: O’Brien W. L. , Tonner B. P. , Harp G. R. , Parkin S. S. P.
Published: July 2002

Uncertainties in the application of the 〈Lz〉/〈Sz〉 sum rule to experimental spectra of V, Cr, Mn, Fe, Co, and Ni are discussed. An important contribution to these uncertainties is the possible presence of dichroism due to diffuse magnetic moments, which are known to exist in Fe, Co, and Ni.
Phase equilibria in the Fe-rich corner of the Nd-Fe-Ti ternary alloy system at 1100 °C
Authors: Margarian A. , Dunlop J. B. , Day R. K. , Kalceff W.
Published: July 2002

High-temperature phase relations in the Fe-rich corner of the Nd-Fe-Ti ternary alloy system have been investigated and an equilibrium phase diagram has been constructed at 1100 °C. Arc-melted and annealed alloys of systematically varying compositions were characterized utilizing scanning electron microscopy, an energy dispersive x-ray microanalysis system (EDS), x-ray diffraction, and optical metallography. Three major phases have been identified, the well known Nd(Fe,Ti)12 ‘‘1:12’’ (ThMn12-type structure) and Nd2(Fe,Ti)17 ‘‘2:17’’ (Th2Zn17-type structure) compounds, and a phase with approximate composition Nd2(Fe,Ti)19 ‘‘2:19.’’ The crystal structure of the latter phase has very recently been solved, and the ‘‘ideal’’ composition shown to be Nd3(Fe,Ti)29 ‘‘3:29.’’ Quantitative EDS data has been used to identify the compositional limits for the three major phases. Annealing the ‘‘1:12’’ and ‘‘3:29’’ ternary phases at 900 °C results in a slow decomposition into Nd2(Fe,Ti)17, Fe2Ti, and α-Fe(Ti).
Preparation and microwave characterization of spherical and monodisperse Co20Ni80 particles
Authors: Viau G. , Ravel F. , Acher O. , Fiévet-Vincent F. , Fiévet F.
Published: July 2002

Spherical and monodisperse Co20Ni80 particles were prepared, in the micrometer and submicrometer size range, by the polyol process. X-ray diffraction showed crystalline particles with a fcc structure. From electron probe microanalysis a fairly homogeneous distribution of both elements within each particle was observed. Microwave properties of metal particles dielectric matrix composites were studied in the 0.1–18 GHz range for different filler concentrations. The intrinsic permeability of the metal powders was obtained using the Bruggeman effective medium theory. The control of the particle size allowed the study of its effect upon dynamic permeability. Whereas micrometer size particle permeability presents a single resonance band at low frequencies which can be correlated to the low magnetocrystalline anisotropy of the particles, submicrometer size particle permeability exhibits an original behavior, never reported before, with several resonance bands.
Evolution of electrical activity and structure of nickel precipitates with the treatment temperature of a Σ=25 silicon bicrystal
Authors: Rizk R. , Ihlal A. , Portier X.
Published: July 2002

Experiments of deep-level transient spectroscopy and transmission electron microscopy (TEM) observations have been carried out on heat-treated Σ=25 silicon bicrystals precontaminated with nickel before being heat treated at various temperatures Ta. For the lowest Ta value (600 °C), the electronic interface states were found to be shared between two overlapping narrow continua around Ec−0.63 eV and Ec−0.52 eV. Upon increasing Ta, these states shift toward shallow positions and exhibit a marked tendency to shrink and to turn into a unique trap level. While the annealing at 900 °C has led to a single state at Ec−0.50 eV, this later moved to Ec−0.48 eV for 1000 °C and then to Ec−0.44 eV for 1100 °C, with an accompanying consistent lowering in the barrier height (BH). TEM observations demonstrated the formation of pure type-B NiSi2 platelets for 800 °C, but indicated an increasingly important growth of type A for increasingly higher Ta values. While the existence of a unique trap level at high Ta could be explained, like previous findings, by some ‘‘uniform’’ coverage of the boundary by the precipitates, the displacement of the interface state(s) toward shallower positions, together with the reduction of the potential barrier, are interpreted in terms involving the increasing contribution of A-type plates with their low BH in addition to that of B-type silicides with their high BH.
Measurement of optical nonlinearities using an elliptic Gaussian beam
Authors: Mian S. M. , Wicksted J. P.
Published: July 2002

We have investigated optical nonlinearities using a beam that has a transverse elliptic Gaussian profile. The popular single-beam technique known as Z-scan complimented with optical limiting experiments are analyzed in this study. A geometric optics model including both nonlinear refraction and absorption is developed in the aberration-free approximation. We have found good agreement between theory and experimental data taken from a lead silicate glass where the elliptic beam had an eccentricity of about 0.98.
Coupled defect-level recombination: Theory and application to anomalous diode characteristics
Authors: Schenk Andreas , Krumbein Ulrich
Published: July 2002

We calculated the steady-state recombination rate for two coupled defect levels and implemented the model into a device simulator. This model generalizes the familiar single-level Shockley–Read–Hall (SRH) formula. If the intercenter transition probability vanishes, it reduces to the sum of two individual SRH rates, which are only linked via the band occupancies. The cases, where one of the levels or even both behave like traps in carrier capture, and the case of a rate-limiting intercenter transition are derived from the general expression. The important feature of the model is a possible increased field effect which might lead to large excess currents. The field effect is discussed in terms of tunnel-assisted multiphonon capture or direct tunneling into the levels, respectively. We show by means of numerical simulation that the large ideality factors found for liquid phase epitaxy grown diodes with weak intrinsic fields can be the result of a rapid direct charge transfer between donors and acceptors and the high probability of tunneling into the hydrogenic states.
Controlling chaos in a model of thermal pulse combustion
Authors: Rhode M. A. , Rollins R. W. , Markworth A. J. , Edwards K. D. , Nguyen K. , Daw C. S. , Thomas J. F.
Published: July 2002

We describe methods for automating the control and tracking of states within or near a chaotic attractor. The methods are applied in a simulation using a recently developed model of thermal pulse combustion as the dynamical system. The controlled state is automatically tracked while a parameter is slowly changed well beyond the usual flame-out point where the chaotic attractor ceases to exist because of boundary crisis. A learning strategy based on simple neural networks is applied to map-based proportional feedback control algorithms both with and without a recursive term. Adaptive recursive proportional feedback is found to track farther beyond the crisis (flame-out) boundary than does the adaptive non-recursive map-based control. We also found that a continuous-time feedback proportional to the derivative of a system variable will stabilize and track an unstable fixed point near the chaotic attractor. The positive results suggest that a pulse combustor, and other nonlinear systems, may be suitably controlled to reduce undesirable cyclic variability and extend their useful operating range.
High-temperature thermoelectric properties of (Zn1−xAlx)O
Authors: Ohtaki Michitaka , Tsubota Toshiki , Eguchi Koichi , Arai Hiromichi
Published: July 2002

A mixed oxide (Zn1−xAlx)O exhibits promising thermoelectric properties attaining a dimensionless figure of merit ZT of 0.30 at 1000 °C, which value is much superior to other oxides and quite comparable to conventional state-of-the-art thermoelectric materials. The addition of a small amount of Al2O3 to ZnO results in a large power factor of 10–15×10−4 W/mK2, showing a marked increase in the electrical conductivity while retaining moderate thermoelectric power. A large product of the carrier mobility and density of states would be responsible for the favorable electrical properties of the present oxide. A figure of merit Z=0.24×10−3 K−1 is attained by (Zn0.98Al0.02)O at 1000 °C, even with a high thermal conductivity. A predominant proportion of the phonon thermal conductivity promises a further improvement in the thermoelectric performance by selective enhancement of phonon scattering.
Kinetics of transformation with nucleation and growth mechanism: Two- and three-dimensional models
Authors: Yu Ge , Lai J. K. L.
Published: July 2002

Theoretical results on the kinetics of transformations with nucleation and growth mechanisms in homogeneous systems during isothermal annealing are reported. The present derivations start from a probability calculation in a finite discrete assembly. In the simplest case with a constant growth rate the results of the formulation agree with the classical Avrami equation for two- and three-dimensional systems. Furthermore, by calculating the survival probability step by step for separate occurrences, the relationships between interfering processes and the effects of neighboring nuclei are revealed. In particular, the distribution of nuclei pairs with distance is determined. Various cases of preferred nucleation in specialized regions, such as linear zones (e.g., dislocations), planar areas (e.g., grain boundaries), or three-dimensional partial volumes, are analytically solved and these solutions can be directly used for the interpretation and evaluation of experimental measurements.
Control of the axis of chemical ordering and magnetic anisotropy in epitaxial FePt films
Authors: Farrow R. F. C. , Weller D. , Marks R. F. , Toney M. F. , Cebollada A. , Harp G. R.
Published: July 2002

Growth of epitaxial films of the L10 phase of FePt, with the tetragonal c axis along either the film normal or in-plane, is described. Films were grown by coevaporation of Fe and Pt, under ultrahigh vacuum conditions, onto a seed film of Pt grown on MgO or SrTiO3 substrates. The perpendicular or in-plane orientation of the c axis was controlled by selecting the (001) or (110) substrate plane, respectively. Nearly complete chemical ordering was achieved for growth at 500 °C for both orientations. Magnetic and magneto-optical characterization of these films confirmed the huge magnetic anisotropy expected for this phase. In the most highly ordered films, anisotropy fields in excess of 120 kOe were measured.
Influence of laser energy density on the plasma expansion dynamics and film stoichiometry during laser ablation of BiSrCaCuO
Authors: Gonzalo J. , Afonso C. N. , Perrière J.
Published: July 2002

The plasma expansion dynamics and the composition of films deposited during laser ablation of BiSrCaCuO at laser energy densities in a broad interval (1–6 J/cm2) have been studied by means of spatially resolved real time optical emission spectroscopy and Rutherford backscattering and nuclear reactive analysis, respectively. In vacuum, the velocity of the ejected species is found to increase as the energy density increases whereas the compositional and angular distribution of the deposited films remain unchanged. When an oxygen pressure of 10−1 mbar is applied, the film composition and angular distribution depend on the laser energy density. The results are analyzed in the frame of a collisional mechanism between the ejected and gas species, the effect of increasing the laser energy density being similar to that of decreasing the oxygen pressure. Finally, this competitive influence of the oxygen pressure and the energy density is discussed within the adiabatic expansion model.
The influence of Thomson effect on the maximum power output and maximum efficiency of a thermoelectric generator
Authors: Chen Jincan , Yan Zijun , Wu Liqing
Published: July 2002

Considering a thermoelectric generator as a heat engine cycle, the general differential equations of the temperature field inside thermoelectric elements are established by means of nonequilibrium thermodynamics. These equations are used to study the influence of heat leak, Joule’s heat, and Thomson heat on the performance of the thermoelectric generator. New expressions are derived for the power output and the efficiency of the thermoelectric generator. The maximum power output is calculated and the optimal matching condition of load is determined. The maximum efficiency is discussed by a representative numerical example. The aim of this research is to provide some novel conclusions and redress some errors existing in a related investigation.
Growth of giant magnetoresistance spin valves using Pb and Au as surfactants
Authors: Egelhoff W. F. , Chen P. J. , Powell C. J. , Stiles M. D. , McMichael R. D. , Lin C.-L. , Sivertsen J. M. , Judy J. H. , Takano K. , Berkowitz A. E.
Published: July 2002

We have investigated the use of Pb and Au as surfactants in an attempt to achieve smoother and sharper interfaces in three types of giant magnetoresistance (GMR) spin valve multilayers: symmetric spin valves, bottom spin valves, and top spin valves. The coupling fields are reduced by a factor of 10 for symmetric and bottom spin valves and by a factor of 3 for top spin valves, presumably by suppressing roughness and interdiffusion at the Co/Cu/Co interfaces, when ∼1 monolayer of Pb is deposited in the early stages of spin valve growth. The Pb has a strong tendency to float out or segregate to the surface during deposition of the spin valve leaving the GMR largely unaltered. Au is almost as effective as Pb, however the Au tends to be left behind in the spin valve, and the GMR is reduced slightly. Attempts to use Hg as a surfactant were unsuccessful. The coupling field increased, and the GMR decreased sharply.
P and N compensation in diamond molecular orbital theory
Authors: Anderson Alfred B. , Kostadinov Lubomir N.
Published: July 2002

Cluster models and the atom superposition and electron delocalization molecular orbital theory calculations lead to an explanation for the ability of nitrogen to cause phosphorous incorporation in low pressure grown diamond films as observed recently by Cao and coworkers. The theory shows that substitutional N compensates substitutional P, creating stable P+–N− disubstitutional pairs. These ionized systems are calculated to be deep donors, which explains the absence of measurable electrical conductivity or phosphorous induced luminescence. The possibility of creating donor P defects by the annealing reaction P–N+N→P+N–N is discussed. The issues of atom size and electronegativity and their influence on donor capability are addressed. It is shown that the difference between substitutional P, a shallow donor, and substitutional N, a deep donor, is predominantly due to the larger size of P; its lower electronegativity makes a relatively small contribution.
Influence of ion energy and substrate temperature on the optical and electronic properties of tetrahedral amorphous carbon (ta-C) films
Authors: Chhowalla M. , Robertson J. , Chen C. W. , Silva S. R. P. , Davis C. A. , Amaratunga G. A. J. , Milne W. I.
Published: July 2002

The properties of amorphous carbon (a-C) deposited using a filtered cathodic vacuum arc as a function of the ion energy and substrate temperature are reported. The sp3 fraction was found to strongly depend on the ion energy, giving a highly sp3 bonded a-C denoted as tetrahedral amorphous carbon (ta-C) at ion energies around 100 eV. The optical band gap was found to follow similar trends to other diamondlike carbon films, varying almost linearly with sp2 fraction. The dependence of the electronic properties are discussed in terms of models of the electronic structure of a-C. The structure of ta-C was also strongly dependent on the deposition temperature, changing sharply to sp2 above a transition temperature, T1, of ≈200 °C. Furthermore, T1 was found to decrease with increasing ion energy. Most film properties, such as compressive stress and plasmon energy, were correlated to the sp3 fraction. However, the optical and electrical properties were found to undergo a more gradual transition with the deposition temperature which we attribute to the medium range order of sp2 sites. We attribute the variation in film properties with the deposition temperature to diffusion of interstitials to the surface above T1 due to thermal activation, leading to the relaxation of density in context of a growth model.
The thermodynamics of amorphous phases in immiscible systems: The example of sputter-deposited Nb–Cu alloys
Authors: Michaelsen C. , Gente C. , Bormann R.
Published: July 2002

Amorphous metallic alloys, frequently observed to occur in systems with large negative heats of mixing, are much less common in systems which are immiscible in the equilibrium solid state, such as Nb–Cu. However, amorphous Nb–Cu alloys can be produced over a wide composition range by sputtering. Using isothermal and nonisothermal differential scanning calorimetry, both the kinetics and the thermodynamics of these amorphous Nb–Cu alloys were characterized quantitatively. It was found that the formation enthalpies of the amorphous alloys amounted to only 4.5–7.6 kJ/g atom. These data were combined with a modeling of the thermodynamic functions of the system. The unexpected low enthalpies and Gibbs energies of the amorphous phase demonstrate the thermodynamic stabilization of the liquid phase which develops with undercooling. This is connected with a change of sign in the heat of mixing of the liquid phase, which is positive at high temperatures and negative at low temperatures.
Voltage dependence of the magnetoresistance and the tunneling current in magnetic tunnel junctions (abstract)
Authors: Marley A. C. , Parkin S. S. P.
Published: July 2002

Magnetic tunnel junctions (MTJ), structures consisting of two ferromagnetic layers separated by a thin barrier of Al2O3, have recently been shown to exhibit large magnetoresistance (MR) at room temperature. The possible use of these structures in devices requires a thorough characterization and understanding of the transport properties of MTJs, which has motivated the present work. The junctions studied here were fabricated via dc sputtering on silicon substrates at room temperature with a series of contact masks to define the junction area (80×80 μm2), and plasma oxidation to produce the insulating barrier. A long standing problem of MTJs is the sensitivity of their MR to bias voltage. For example, in a recent work1 it was reported that the peak MR of 11% exhibited by a CoFe/Al2O3/Co junction was decreased by half at a bias voltage of <200 mV. In this work, we will show a significant improvement of the MR voltage dependence, with peak MR values of 20%–25% near zero bias decreasing to half these values for 300–500 mV. The voltage falloff is typically asymmetric with regard to the sign of the applied voltage. For example, the peak MR of a Co/Al2O3/Ni85Fe15 MTJ, in which the Co is exchange biased with Mn54Fe46, decreases by half at a positive bias of 300 mV but requires a negative bias of 500 mV to attain the same MR decrease. There is significant structure in the resistance versus bias voltage curves with distinct differences at high and low magnetic fields for which the moments of the Co and Ni85Fe15 layers are parallel and antiparallel, respectively. A decrease in MR at high bias levels is found in all junctions independent of their resistance and the composition of the magnetic layers. However, the detailed dependence of MR on bias voltage varies with the detailed structure of the MTJ. Results will be presented for a wide range of magnetic materials and for junction resistances varying from 1 to 10 000 Ω. Possible explanations for this phenomena will be offered.
Prediction of mechanical stress effects on the iron loss in electrical machines
Authors: Ali K. , Atallah K. , Howe D.
Published: July 2002

Iron losses can account for a significant portion of the total loss in electrical machines. Nevertheless, although analytical and numerical techniques have been developed for predicting the iron loss density distribution and the total iron loss of various types of machine under any operating load condition, to date these have neglected the effect of mechanical stress. However, during the manufacture of many electrical machines, a significant radial compressive stress can be imposed on the stator lamination stack, by shrink fitting/pressing an outer frame, for example. This paper describes a technique that has been developed for predicting the effect of compressive stress on the iron loss density in lamination materials, and demonstrates its use in calculating the iron loss of a permanent magnet brushless dc motor.
Iron detection in polished and epitaxial silicon wafers using generation lifetime measurements
Authors: Obermeier Guenther , Huber Diethard
Published: July 2002

For iron detection in silicon, minority carrier diffusion length measurements are often used. These methods analyze only the bulk properties of the wafer and therefore failed in the case of epitaxial wafers due to the disturbing influence of the highly doped substrate. A technique is presented for the determination of the iron content in epitaxial as well as in polished wafers using generation lifetime measurements on metal-oxide-silicon capacitors. The influence of interstitial iron and iron-boron pairs on generation lifetime was investigated for samples diffused with iron in boron-doped silicon. The difference in reciprocal generation lifetime before and after a thermal anneal of 200 °C for three minutes was calibrated using deep level transient spectroscopy to detect the iron-boron pair concentration. For a typical metal-oxide-silicon capacitor fabrication process this means a detectability limit for iron-boron concentrations of about 8×1010 at/cm3. The advantage of this method is that it detects iron in a surface near region in contrast to the often used diffusion length measurements. This gives us the opportunity of controlling the iron content in epitaxial wafers as well as in wafers after an internal gettering process. In addition, the iron-boron pairing reaction was investigated in the temperature range between 21 and 50 °C. The activation energy for this reaction was determined to be 0.70 eV.
Off-axis electron holography of epitaxial FePt films
Authors: McCartney M. R. , Smith David J. , Farrow R. F. C. , Marks R. F.
Published: July 2002

Off-axis electron holography at the nanometer level has been used to investigate the magnetic microstructure of thin epitaxial FexPt1−x (x∼0.5) ordered alloy films. High-resolution electron microscopy in cross section showed high quality epitaxial growth but also revealed some widely spaced regions with structural defects. Lorentz microscopy and off-axis electron holography in field-free conditions established conclusively that similar defective areas were associated with local perturbations of the in-plane magnetic field within the thin films. Further holographic observations with the FePt[001] axis parallel to the film normal revealed variations in phase shifts in the vacuum outside the sample which indicated flux leakage along the film normal. Overall, the results demonstrate that off-axis electron holography is a highly useful technique for mapping local variations of the in-plane magnetic structure associated with defective thin films.
Kinetics of transformation with nucleation and growth mechanism: Diffusion-controlled reactions
Authors: Yu Ge , Lai Y. K. L. , Zhang W.
Published: July 2002

Kinetics of phase transformations controlled by the diffusion of solute atoms has been studied by using a newly developed method based on probability theory. It is demonstrated that an exact solution considering the redistribution of the solute atoms can be achieved for a homogeneous one-dimensional system with all nuclei simultaneously generated at the beginning of the transformation. If the growth rate of the individual grains is not strongly correlated and obeys the square-root rule up to the very late stage, the equation describing the rate of the transformation as a function of time can be derived. The effect of the overlapping diffusion zones is discussed by numerically solving the diffusion function for the model systems. It can be concluded that the “soft impingement,” which is frequently argued in the works on the diffusion-controlled reaction, plays a role only in the final stage of the transformation and generally cannot cause bending of the curve in the Avrami-type plots.
Attenuation of Love waves in low-loss media
Authors: Kiełczyński P.
Published: July 2002

A theory of Love waves propagating in a viscoelastic surface layer deposited on a perfect elastic substrate was considered. In the case of low losses (ωη44/μB0≪1) an analytical formula relating the attenuation coefficient of the Love wave and the viscoelastic parameters of the waveguide structure was established. This makes it possible to apply the obtained analytical formula in nondestructive testing for determining the rheological parameters of viscoelastic bodies. The established theory of Love waves in viscoelastic media can also be applied in seismology and integrated optics.
Influence of mixed particle size on electrorheological response
Authors: Wu C. W. , Conrad H.
Published: July 2002

Two sizes (6 and 100 μm average diameter) glass spheres suspended in silicone oil (volume fraction φ=0.3) were used to investigate the influence of particle size on electrorheological response at a shear rate 2 s−1. The larger particles gave a higher shear yield stress but a lower current density at zero shear than the smaller ones. When the two particle sizes were mixed together, the shear yield stress decreased, reaching a minimum when the volume fraction of the small particles equals that of the large particles. The minimum in the current density occurred when the ratio of the volume of small to large particles was ∼1/3.
Optical constants of CdxZn1−xSe ternary alloys
Authors: Suzuki Ken-ichi , Adachi Sadao
Published: July 2002

A simple model is presented for the complex dielectric function, ε(E)=ε1(E)+iε2(E), of CdxZn1−xSe alloy. The effects of alloy composition are properly taken into consideration in the calculation. The model is applicable over the entire range of photon energies, below and above the lowest band gap, and is in relatively good agreement with the existing experimental data. Dielectric-function-related optical constants, such as the real refractive index (n), extinction coefficient (k), and high-frequency dielectric constant (ε∞), of this alloy system have also been presented. The present results can be used in the design and analysis of various optoelectronic devices using this alloy system.
Deep energy levels in CdTe and CdZnTe
Authors: Castaldini A. , Cavallini A. , Fraboni B. , Fernandez P. , Piqueras J.
Published: July 2002

The deep levels present in semiconducting CdTe and semi-insulating CdTe:Cl and Cd0.8Zn0.2Te have been investigated by means of cathodoluminescence, deep level transient spectroscopy (DLTS), photo-induced current transient spectroscopy, and photo-DLTS. The latter two methods, which can be applied to semi-insulating materials, allow to characterize the deep traps located up to midgap and can determine whether they are hole or electron traps. We have identified 12 different traps, some common to all the investigated samples, some peculiar to one of them. A comparison of the results obtained from the various materials is given and the status of defect models is reviewed.
Second-harmonic generation of femtosecond high-intensity Ti:sapphire laser pulses
Authors: Mori Kurumi , Tamaki Yusuke , Obara Minoru , Midorikawa Katsumi
Published: July 2002

The second-harmonic generation (SHG) of ultrashort Ti:sapphire laser pulses in potassium dihydrogen phosphate crystal in type-I phase-matching geometry has been investigated theoretically, including the effects of cubic nonlinearity. It is found that the phase mismatch due to the broad bandwidth associated with the short pulse width limits the maximum conversion efficiency to less than 60%, and the temporal shape of the converted pulse has an intensity modulation at an incident intensity of 100 GW/cm2 for a 100 fs pulse. In order to increase the energy conversion efficiency and improve the temporal pulse shape, a new SHG geometry using two antiparallel tilted crystals is discussed.
High-strain-rate deformation and comminution of silicon carbide
Authors: Shih C. J. , Nesterenko V. F. , Meyers M. A.
Published: July 2002

Granular flow of comminuted ceramics governs the resistance for penetration of ceramic armor under impact. To understand the mechanism of the granular flow, silicon carbide was subjected to high-strain, high-strain-rate deformation by radial symmetric collapse of a thick-walled cylinder by explosive. The deformation, under compressive stresses, was carried out in two stages: the first stage prefractured the ceramic, while a large deformation was accomplished in the second stage. The total tangential strain (−0.23) was accommodated by both homogeneous deformation (−0.10) and shear localization (−0.13). Three microstructures, produced by different processing methods, were investigated. The microstructural differences affected the microcrack propagation: either intergranular or transgranular fracture was observed, depending on the processing conditions. Nevertheless, the spacing between shear bands and the shear displacement within the shear bands were not significantly affected by the microstructure. Within the shear bands, the phenomenon of comminution occurred, and the thickness of the shear bands increased gradually with the shear strain. A bimodal distribution of fragments developed inside the shear bands. The comminution proceeded through the incorporation of fragments from the shear-band interfaces and the erosion of fragments inside the shear band. Outside the shear bands, an additional comminution mechanism was identified: localized bending generated comminution fronts, which transformed the fractured material into the comminuted material. The observed features of high-strain-rate deformation of comminuted SiC can be used for validation of computer models for penetration process.
Influence of temperature on the electromechanical and fatigue behavior of piezoelectric ceramics
Authors: Wang Donny , Fotinich Yevgeniy , Carman Greg P.
Published: July 2002

This paper presents research results on the electro–thermomechanical behavior of piezoelectric ceramics for use in actuator applications with an emphasis on ferroelectric fatigue. The material being investigated is a lead zirconate titanate piezoelectric ceramic with the composition PbZr0.53Ti0.47O3 (PZT-5H). Results presented in this paper include an augmented constitutive model that accounts for the temperature-dependent piezoelectric properties. Using this model, nonlinear effects measured at one temperature can be extrapolated to other temperatures with good accuracy. Experimental studies into 180° and 90° polarization switching of PZT-5H indicate that the dielectric flux to dipole the material appears to be an adequate criterion for predicting this nonlinear switching behavior. Fatigue studies show that material degradation is strongly influenced by temperature and by the magnitude of the applied electric field. Above a critical temperature, PZT-5H no longer fatigues in the presence of large electric fields due to changes in the electromechanical properties such as the depolarization strain. Using a finite element model incorporating the proposed constitutive relations along with a domain switching criterion, this paper suggests that fatigue degradation is primarily caused by mechanical stresses in the material resulting from spatially variant electric fields causing preferential domain wall motion. The large stress mismatches induce mechanical damage in the form of cracks.
Photoinduced transformations in amorphous Se75Ge25 thin film by XeCl excimer-laser exposure
Authors: Lee Hyun-Yong , Park Soo-Ho , Chun Jin-Young , Chung Hong-Bay
Published: July 2002

The scalar photoinduced changes of the optical absorption edge and the optical constants in amorphous Se75Ge25 chalcogenide thin film have been studied using XeCl excimer laser light with a wavelength of 306 nm. The glass transition temperature (Tg) of this material is evaluated to be approximately 220 °C, at which the as-deposited film is initially annealed. The optical energy gaps Eop of as-deposited and initially annealed Se75Ge25 thin films are 1.90 and 1.84 eV, respectively. When initially annealed films are exposed to a 4.05 eV excimer laser (≫Eop) with energy densities of 100, 120 and 180 mJ/cm2, a photodarkening effect that exhibits a decrease in the optical transmittance (Top) and Eop and an increase of the refractive index n and the extinction coefficient k in the vicinity of the absorption edge (1.4–3.0 eV) is observed. In particular, in the case of a thin film exposed by 120 mJ/cm2, Eop and n+ik measured at 673.7 nm(1.84 eV), i.e., an absorption edge of initially annealed thin film, are 160 eV and 2.680+i0.118 and the changes of ΔEop and Δn+iΔk are 0.24 eV and 0.215+i0.100, respectively. Furthermore, these photodarkened thin films recovered (bleached) to the initial annealed state by re-annealing at Tg. As a result of the x-ray diffraction analysis, we can conclude that these changes are due to an amorphous to amorphous transition. Therefore, considering that these large changes in Se75Ge25 thin film lead to its structural changes, we could expect high etch selectivity in using this film as a deep ultraviolet lithography resist.
Mercury annealing of reactive ion etching induced p- to n-type conversion in extrinsically doped p-type HgCdTe
Authors: Smith E. P. G. , Siliquini J. F. , Musca C. A. , Antoszewski J. , Dell J. M. , Faraone L. , Piotrowski J.
Published: July 2002

Mercury annealing of reactive ion etching (RIE) induced p- to n-type conversion in extrinsically doped p-type epitaxial layers of HgCdTe (x=0.31) has been used to reconvert n-type regions created during RIE processing. For the RIE processing conditions used (400 mT, CH4/H2, 90 W), p- to n-type conversion was observed using laser beam induced current (LBIC) measurements. After a sealed tube mercury anneal at 200 °C for 17 h, LBIC measurements clearly indicated that no n-type converted region remained. Subsequent Hall measurements confirmed that the material consisted of a uniform p-type layer, with electrical properties equivalent to that of the initial as-grown wafer (NA−ND=2×1016 cm−3, μ=350 cm2 V−1 s−1).
Removal of laser-melted material with an assist gas
Authors: Farooq K. , Kar A.
Published: July 2002

Molten material is removed in many laser applications such as laser grooving and laser cutting. An assist gas is usually used to remove the molten material from the laser material interaction zone. The effect of assist gas pressure on the material removal rate is investigated in this article for laser cutting and grooving applications. The model for melt depth is based on the overall energy balance, and the cut depth is obtained by considering the effect of the assist gas. The model for kerf width is based on the modified Rosenthal solution taking into account the melting effect. The cut depths reach a constant value beyond a critical pressure if the kerf width is of the order of nozzle width and through cuts are assumed. Most of the molten material is removed by the assist gas at pressures below this critical pressure. The model predicts on the basis of the Prandtl or Meyer relation that the cutting speed decreases when the assist gas pressure exceeds a critical value if the kerf dimensions are smaller than the nozzle dimensions.
Pressure induced reversal of the volume expansion caused by interstitial nitrogen in Nd2Fe17N3
Authors: Marasinghe G. K. , James W. J. , Ezekwenna P. C. , Luo H. , Yelon W. B. , Zhao Y. , Von Dreele R. B. , Ellouze M. , l’Héritier Ph.
Published: July 2002

Crystallographic properties of Nd2Fe17N3 have been investigated using powder neutron diffraction techniques at pressures up to 7.3 GPa. With increasing pressure, the unit cell volume of Nd2Fe17N3 decreases almost linearly at a rate of 6.1 Å3/GPa without undergoing a phase transformation or expelling the interstitial nitrogen atoms. The observed rate of contraction corresponds to a bulk modulus of 1.4×1011 N/m2 for Nd2Fe17N3. The unit cell volume of Nd2Fe17N3 at 7.3 GPa is approximately equal to that of Nd2Fe17 at atmospheric pressure. Even though the unit cell of Nd2Fe17 expands anisotropically due to nitrogenation, contraction of the Nd2Fe17N3 unit cell under pressure appears to be isotropic with lattice parameters a and c decreasing by approximately 1.8% as the sample pressure increases from ambient to 7.3 GPa.
Field emission from chemical vapor deposited diamond and diamond-like carbon films: Investigations of surface damage and conduction mechanisms
Authors: May Paul W. , Höhn Stefan , Ashfold Michael N. R. , Wang Wang N. , Fox Neil A. , Davis Tim J. , Steeds J. W.
Published: July 2002

Field emission properties of undoped chemical vapor deposited diamond and diamond-like carbon films have been measured for a variety of different deposition conditions. The nature and appearance of the damage site after testing has been investigated with scanning electron microscopy and laser Raman mapping. These observations, together with the mathematical form of the observed current–voltage relations, are correlated with the conductivity of the film. The results are consistent with a model for the overall emission current that combines conduction mechanisms through the bulk of the film with Fowler–Nordheim tunneling.
Soft x-ray emission of laser-produced plasmas using a low-debris cryogenic nitrogen target
Authors: Lebert R. , Schriever G. , Wilhein T. , Niemann B.
Published: July 2002

Laser-produced nitrogen plasmas (LPPs) are intense narrow-band emitters in the “water window” spectral range which is suited for x-ray microscopy of biological samples. Frozen gases as target materials are predicted to have low debris precipitated onto laser or x-ray optics arranged inside the vacuum chamber. Gaseous nitrogen is frozen onto a metal surface at a temperature of 16 K. The solid nitrogen is illuminated with nanosecond pulsed laser radiation with intensities of 1.3×1013 W/cm2 and the emission characteristics of laser-produced nitrogen plasmas are investigated with a calibrated imaging spectrograph. The x-ray emission in the water window region is compared to the radiation of a LPP with a solid boron nitride target at the same laser parameters.
Recrystallization kinetics of electroplated Cu in damascene trenches at room temperature
Authors: Lingk C. , Gross M. E.
Published: July 2002

Cu metallization for sub-0.25 μm interconnects marks not only a change in metallurgy from Al and a change in architecture from subtractive to damascene but also a major shift in deposition technology from sputtering to electroplating. A remarkable feature of electroplated Cu films is the recrystallization or grain growth process that takes place at room temperature over a period of hours to weeks after plating. While this phenomenon has been described for blanket films, the influence of substrate topography on the kinetics of recrystallization has not previously been reported. Using focused ion beam imaging we demonstrate that recrystallization of the small grained as-plated Cu is initiated at the upper corners of damascene trenches and grains continue to grow laterally, eventually transforming the entire film. Removal of overlying Cu by chemical mechanical polishing before the transformation leads to incomplete recrystallization of the Cu left in the trenches. The kinetics of the recrystallization process for trench widths of 0.3, 0.5, 0.8, 2, and 5 μm reveal a minimum time for recrystallization for the 0.8 μm trenches. An acceleration of the room temperature recrystallization rates for all trench widths is observed if the films are first cycled to −78 °C immediately after plating, and a more pronounced minimum time for recrystallization is observed for the 0.8 μm trenches. These observations lead us to propose that the initiation of this process at the upper corners of the trenches and the trench width dependence of the recrystallization rate are related to higher stress or dislocation densities.