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Journal of Applied Physics

Issue 3 • Date Aug 1997

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Displaying Results 1 - 25 of 88
  • Issue Table of Contents

    Page(s): toc1
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    Freely Available from IEEE
  • The structural and luminescence properties of porous silicon

    Page(s): 909 - 965
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    A large amount of work world-wide has been directed towards obtaining an understanding of the fundamental characteristics of porous Si. Much progress has been made following the demonstration in 1990 that highly porous material could emit very efficient visible photoluminescence at room temperature. Since that time, all features of the structural, optical and electronic properties of the material have been subjected to in-depth scrutiny. It is the purpose of the present review to survey the work which has been carried out and to detail the level of understanding which has been attained. The key importance of crystalline Si nanostructures in determining the behaviour of porous Si is highlighted. The fabrication of solid-state electroluminescent devices is a prominent goal of many studies and the impressive progress in this area is described. © 1997 American Institute of Physics.   View full abstract»

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  • High-frequency response of atomic-force microscope cantilevers

    Page(s): 966 - 979
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    Recent advances in atomic-force microscopy have moved beyond the original quasistatic implementation into a fully dynamic regime in which the atomic-force microscope cantilever is in contact with an insonified sample. The resulting dynamical system is complex and highly nonlinear. Simplification of this problem is often realized by modeling the cantilever as a one degree of freedom system. This type of first-mode approximation (FMA), or point-mass model, has been successful in advancing material property measurement techniques. The limits and validity of such an approximation have not, however, been fully addressed. In this article, the complete flexural beam equation is examined and compared directly with the FMA using both linear and nonlinear examples. These comparisons are made using analytical and finite difference numerical techniques. The two systems are shown to have differences in drive-point impedance and are influenced differently by the interaction damping. It is shown that the higher modes must be included for excitations above the first resonance if both the low and high frequency dynamics are to be modeled accurately. © 1997 American Institute of Physics. View full abstract»

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  • Fast, high-resolution atomic force microscopy using a quartz tuning fork as actuator and sensor

    Page(s): 980 - 984
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    We report a new method of achieving tip–sample distance regulation in an atomic force microscope (AFM). A piezoelectric quartz tuning fork serves as both actuator and sensor of tip–sample interactions, allowing tip–sample distance regulation without the use of a diode laser or dither piezo. Such a tuning fork has a high spring constant so a dither amplitude of only 0.1 nm may be used to perform AFM measurements. Tuning-fork feedback is shown to operate at a noise level as low as that of a cantilever-based AFM. Using phase-locked-loop control to track excursions in the resonant frequency of a 32 kHz tuning fork, images are acquired at scan rates which are fast enough for routine AFM measurements. Magnetic force microscopy using tuning-fork feedback is demonstrated. © 1997 American Institute of Physics. View full abstract»

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  • Limits of different detection schemes used in the optical beam deflection method

    Page(s): 985 - 988
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    The theoretical performances of a split detector and a lateral effect detector used as a position sensitive device in the optical beam deflection method are compared. It is shown that the limit to the resolution in both cases is essentially equal. The possibility of improving the resolution in angle deflection by reflecting the beam from a cylindrical mirror, as was recently proposed by A. Yarai, Y. Fukunaga, K. Sakamoto, and T. Nakanishi [Jpn. J. Appl. Phys. 33, 3251 (1994)] is also explored. It is shown that using a cylindrical mirror does not result in a smaller theoretical limit to the resolution. However, it does improve the resolution in some cases and may have practical uses. © 1997 American Institute of Physics. View full abstract»

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  • Inversion in x-ray Bragg diffraction: A practical technique to compensate for dynamical scattering features

    Page(s): 989 - 993
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    A new numerical technique to compensate for the dynamical effects in experimental x-ray intensity profiles is proposed and implemented to enhance the crystal-lattice strain determination algorithm which is applicable to x-ray diffraction data collected from nearly perfect crystals. A practical procedure for the preliminary treatment of experimental data exhibiting dynamical features was tested using three sets of data representing different cases of near-surface distorted layers. It is shown that the influence of the substrate peak on the overall diffraction pattern can be removed by an iterative modification of the very vicinity of the Bragg region in experimental intensity profile. © 1997 American Institute of Physics. View full abstract»

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  • Refractive indices of rutile as a function of temperature and wavelength

    Page(s): 994 - 997
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    The ordinary and extraordinary refractive indices of rutile (TiO2) have been measured as a function of temperature and wavelength within the ranges 30–160 °C and 454–1330 nm, respectively, by using a prism coupling reflectivity setup. The measurements have been done with regard to the accurately known indices of a congruent LiNbO3 substrate. The index values are given with the same accuracy as that of the substrate taken as reference, i.e., ±0.001 at room temperature and ±0.003 at 160 °C. The room temperature values are coincident with those previously published by other workers. Sellmeier-like equations which include wavelength and temperature as variables within the studied ranges are given for both indices. © 1997 American Institute of Physics. View full abstract»

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  • High intensity illumination effects in LiNbO3 and KTiOPO4 waveguides

    Page(s): 998 - 1005
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    Quasi-phase-matched waveguides are known to degrade when generating high intensity short wavelength light. Photoinduced changes in the refractive indices can lead to reduced efficiency by broadening phase-matching curves or inducing power dependent losses. In this work a pump-probe technique was used to investigate photorefractive effects in nonlinear optical waveguides. A strong two photon photorefractive effect in single domain and Ti-poled LiNbO3 was found that is considerably reduced in electric field periodically poled LiNbO3 and is absent in Rb-exchanged KTiOPO4. © 1997 American Institute of Physics. View full abstract»

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  • Photorefractive effect in LiNbO3 crystals enhanced by stoichiometry control

    Page(s): 1006 - 1009
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    LiNbO3 single crystals with a composition close to stoichiometry are grown by using a double crucible Czochralski method equipped with an automatic powder supply system. The photorefractive properties are compared with those of LiNbO3 crystals grown from the congruent composition melt. Two beam coupling experiments show that both nondoped and Fe-doped stoichiometric crystals exhibit stronger photorefractive effect than the Fe-doped congruent crystals.© 1997 American Institute of Physics. View full abstract»

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  • Relationship between refractive indices and hydrogen concentration in proton exchanged LiNbO3 waveguides

    Page(s): 1010 - 1017
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    Proton-exchanged LiNbO3 optical waveguides (HxLi1-xNbO3) exhibit very complex structural behavior which is different from that known for their powders. Seven crystallographic phases have been identified in the HxLi1-xNbO3 layers. A method to determine the proton concentration in different phases has been proposed. Correlation between the crystal structure, hydrogen concentration, and the ordinary and extraordinary refractive indices has been experimentally determined allowing one to explain some optical phenomena observed and to predict the characteristics of a great variety of proton exchanged waveguides. © 1997 American Institute of Physics. View full abstract»

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  • Modeling of pyrolytic laser direct writing: Noncoherent structures and instabilities

    Page(s): 1018 - 1025
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    Three-dimensional simulations of pyrolytic laser direct writing from gas-phase precursors are presented. They are based on a fast method for the calculation of temperature distributions induced by an energy beam in deposits of arbitrary shape. Analytical approximations, fast Fourier transform, and the multigrid technique are combined in the algorithm. Temperature dependences of the absorptivities and heat conductivities of the deposit and the substrate have been taken into account. Self-consistent modeling of the growth process allows one to explain oscillations in the height and width of lines caused by the feedback between the shape of the deposit, the temperature distribution, and the growth rate. For the deposition of W from an admixture of WCl6+H2 and a-SiO2 substrates, the oscillations originate from a sharp increase in the absorptivity of the deposit with temperature. With the deposition of Si from SiH4, or C from CH4, C2H2, and C2H4, onto a-SiO2, the oscillations are related to the large ratio of height/width of the deposit and the increase in temperature on its upper surface. This increase also explains the transition from line-type to fiber-type growth. The hysteresis of this transition with respect to laser power and scanning velocity is explained as well. The same algorithm can be used in the modeling of pyrolytic etching and e-beam microprocessing when the feedback between the temperature distributions and changes in the- processing geometry is important. © 1997 American Institute of Physics. View full abstract»

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  • Second-harmonic generation accompanying nonlinear reflection of shear waves in an isotropic layered structure

    Page(s): 1026 - 1030
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    A theory is proposed for solving second-harmonic generation accompanying nonlinear reflection of shear (SH) waves. An analysis is presented for the resonant second-harmonic generation in a layered structure consisting of an isotropic layer and two semi-infinite isotropic solids. The result reveals that the effect of second-harmonic cumulative growth will occur once the component of incident SH-wave vector along the boundary equals the magnitude of the longitudinal wave vector of the elastic medium of the solid layer. Moreover, we have formally obtained the analytical expressions for the resonant second-harmonic generation in each region of the layered structure which yields physical insight into the process of the second-harmonic generation not previously available. © 1997 American Institute of Physics. View full abstract»

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  • Anomalous behaviour of leaky surface waves for stiffening layer near cutoff

    Page(s): 1031 - 1035
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    The propagation of surface acoustic waves has been investigated for a layered system (water-isotropic layer-isotropic substrate) where the layer is faster than the substrate. It has been found that when the velocity of the surface wave reaches the velocity of the shear wave of the substrate (cutoff) the behaviour of the attenuation has an anomalous character. Attenuation drops down towards zero below cutoff and increases abruptly beyond cutoff. Acoustic microscopy measurements on aluminum coated with oxalic oxide film were in coincidence with theory.© 1997 American Institute of Physics. View full abstract»

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  • A study of ion velocity distribution functions in processing plasmas produced by electron cyclotron resonance discharges

    Page(s): 1036 - 1041
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    Ion velocity distribution functions were measured using Doppler-shifted laser-induced fluorescence spectroscopy in an electron cyclotron resonance discharge in argon. The influence of the magnetic field configuration on the distributions was studied by making measurements with different magnetic field configurations. Results of a two-dimensional hybrid model of the discharge were used to help interpret the measured data. The results from the experiment and the simulation indicated that the magnetic field configuration had a strong influence on the ion velocity distribution functions. From the simulation it was concluded that the magnetic field configuration determined the axial distributions of plasma potential and electron density, and how these plasma parameters determined the ion velocity distribution function in the downstream region of the discharge.© 1997 American Institute of Physics. View full abstract»

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  • Implantation-induced disordering of CuPtB-ordered GaInP

    Page(s): 1042 - 1052
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    In this article, a comprehensive treatment of the implantation-induced disordering (IID) of CuPtB-ordered GaInP with regard to microstructuring is presented. Ion implantation reduces the thermal stability of the crystal, so that disordering occurs at temperatures smaller than 800 °C for which the ordered phase normally is stable. It is shown that IID is mediated by implantation defects and can be described quantitatively by a model based on defect annealing. From the temperature dependence of the disordering process an activation energy of 2.15 eV has been evaluated, which is supposed to be the migration enthalpy of group III vacancies. Lateral order/disorder structures were achieved by masked implantation using high resolution electron beam lithography for the definition of wire and dot implantation masks down to 35 nm width. These structures were examined using photoluminescence and transmission electron microscopy. Both methods show that the spatial resolution is determined by implantation straggling, whereas defect diffusion can be neglected. This is also confirmed by extracting the defect diffusion length from the disordering model. © 1997 American Institute of Physics. View full abstract»

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  • Ion-beam annealing of electron traps in n-type Si by post-H+ implantation

    Page(s): 1053 - 1057
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    The effects of post-H+ implantation on electron traps that are induced by P+ implantation (300 keV, 1×109cm-2) has been studied by deep-level transient spectroscopy. H+ implantation is performed at room temperature to a dose of 2×1010cm-2 in the range 30–120 keV. The post-H+ implantation partly decreases the concentration of the electron traps induced by P+ implantation, although it increases the concentrations around the projected range of H+. The annealing effect is ascribed to the reaction of preexisting defects with point defects induced by postimplantation. Peaks are observed in the reduction ratio profiles of the preexisted trap concentrations versus the distance from the projected ranges of postimplantation. The highest values of the reduction ratios in each postimplantation tend to decrease with increasing distance between the projected ranges of P+ and H+. This is due to the decrease of the supply of point defects caused by postimplantation with increasing distance. We compare the reduction ratio profiles of the dominant three electron traps (Ec-0.12, 0.15, and 0.39 eV). © 1997 American Institute of Physics. View full abstract»

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  • A model for ion-irradiation induced hydrogen loss from organic materials

    Page(s): 1058 - 1064
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    In the study of interfacial diffusion processes in polymer light-emitting diodes, the use of high-energy ion-scattering techniques can be of great value due to the possibility of quantitative elemental depth profiling. However, ion irradiation of polymers is known to cause various degradation effects, including the loss of hydrogen. Since the hydrogen loss determines the accuracy of depth profiling, it is an interesting subject for study in order to define experimental conditions in which the degradation is suppressed. The loss of hydrogen from porphyrins (organic solar cells) has been measured by means of elastic recoil detection analysis with 2, 4, and 7.6 MeV He+ beams. A theoretical model is proposed in which the hydrogen loss is described through the formation and recombination of free hydrogen radicals. A distinct difference is introduced between direct recombination processes and the diffusion of radicals out of the ion track. © 1997 American Institute of Physics. View full abstract»

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  • Ultraviolet-induced densification in fused silica

    Page(s): 1065 - 1071
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    Ultraviolet-induced densification in fused silica is investigated using birefringence measurements to detect compaction-induced strain. This technique is capable of measuring compaction in the 10 parts per billion range in cm-sized specimens. A universal relation describing ultraviolet-induced compaction is discovered in which, using the total energy absorbed from two-photon absorption as the dose parameter, density changes equal a material dependent constant times the dose parameter to a power of about 0.65. This dose dependence is consistent with past compaction studies using electron beam and gamma radiation. Moreover, the density change per ionization “event” is found to be consistent for all radiation types. By comparing density measurements to refractive index change measurements found with interferometry, polarizability changes from ultraviolet-induced densification are extracted and compared with previous results using other radiation sources and inelastic densification methods. © 1997 American Institute of Physics. View full abstract»

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  • Dependence of the third-order coefficients in Landau free energies for bcc→fcc structural transition on hydrogen concentration in zirconium hydrides

    Page(s): 1072 - 1079
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    Young’s modulus E and the modulus of rigidity G of zirconium hydrides ZrHx(0.9≤x≤1.65) at 941 and 1001 K have been obtained as a function of hydrogen concentration c by measuring resonance frequencies for bending and torsion vibrations of a polycrystalline wire. As c increases, observed E and G increase in the bcc β phase, slightly increase linearly in the β+δ phase, and then decrease in the fcc δ phase. On the basis of a phenomenological free energy in terms of strain components taking account of space group symmetry, two types of Landau expansion of the free energies for the β phase in terms of the strain components which play an important role in the structural phase transition between the β and the δ phases are examined. The observed E and G are assumed to be the same as the second-order coefficients of the free energy for the Bain distortions, which occur at the structural phase transition. The dependence of the third-order coefficients on c permits the expanded free energies to describe the fact that the β phase is more stable than the δ phase at low c. © 1997 American Institute of Physics. View full abstract»

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  • Coherent Raman spectroscopy of nanoshocks

    Page(s): 1080 - 1087
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    A new technique is described, where picosecond laser pulses generate and probe 4.2 GPa nanoshocks in polymeric and polycrystalline solids at a high repetition rate of ∼100/s. The term nanoshock refers to the short duration (a few ns) of the shock pulse and the very small shocked volume (a few ng). The nanoshock wave form is characterized by the shock front risetime, shock falltime, peak pressure, and velocity. Coherent Raman spectroscopy during nanoshock propagation in a 700-nm-thick layer of polycrystalline anthracene, called an optical nanogauge, is used to determine these quantities. A powerful method of analysis, singular value decomposition (SVD), is applied to Raman spectroscopy of shock waves for the first time. Using SVD analysis, the risetime of the nanoshock pulses is found to be less than 25 ps, and the velocity of the shock front in the nanogauge is monitored in real time. Some possible applications of nanoshock technology in the areas of shock-induced material transformation and shock-induced mechanical deformation processes, are discussed briefly. © 1997 American Institute of Physics. View full abstract»

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  • Crack softening damage model for ceramic impact and its application within a hydrocode

    Page(s): 1088 - 1092
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    A physically based crack softening damage model has been developed and used in a non-linear transient dynamic computer code (AUTODYN-2D). It is assumed that there is a finite number of orientated pre-existing flaws within the ceramic target. The mode I and mode II stress intensity factors are calculated in compression and tension and the strain energy release rate is then estimated and compared to a critical dynamic strain energy release rate. At initiation, a tension crack propagates at a velocity dependent on the mode I stress intensity factor and failure occurs in a computational cell when two neighbouring microcracks coalesce. The model was used to simulate two different plate impact experiments of alumina on alumina with encouraging results. The model was also used to analyze the impact of a steel sphere on alumina and shows strong correlation between experimental and predicted results. © 1997 American Institute of Physics. View full abstract»

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  • Speckle photography during dynamic impact of an energetic material using laser-induced fluorescence

    Page(s): 1093 - 1099
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    Laser and white light speckle photography have been used to observe surface displacement in a number of materials and over a varied range of strain rates. However, each suffers from limitations. We have developed a novel application of speckle photography in very difficult environments by using laser-induced fluorescence to generate the speckle pattern. This permits confinement of the free surface without undue degradation of the correlation upon which speckle methods are based. We have applied this method to measure the surface displacement of a reactive material during dynamic deformation at moderate strain rates. Conventional methods were tried but were unsuccessful, necessitating a novel approach. To the best of our knowledge, neither high-speed laser nor white light speckle photography has been performed using energetic materials. These measurements are very difficult because of the low material strength (yield strength ∼8–80 MPa), and because significant out-of-plane motion and surface disruption occur during fracture, and early during the deformation process. We report results from experiments in which these major problems have been overcome. © 1997 American Institute of Physics. View full abstract»

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  • Unsteady plane smooth wave fronts of combined growing-attenuating type

    Page(s): 1100 - 1112
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    Unsteady plane smooth wave fronts of a combined growing-attenuating type, where the peak of each strain wave is growing, are derived by a qualitative analysis. There are three different modes in this combined type: In mode I, the peak of a particle velocity wave is growing, but that of a stress wave is attenuating; in mode II, the former is attenuating, but the latter is growing; in mode III, both are attenuating. Three possible wave fronts belong to mode I, five to mode II, and three to mode III. Five new elementary waves are found in these eleven wave fronts. The wave fronts near the impacted surface of sandstone detected by the previous quantitative analysis [Sano, J. Appl. Phys. 73, 118 (1993)] are identified with some of the eleven possible wave fronts. As a result, the theoretical existence of several new wave fronts and a new elementary wave is verified. The equation for the stress at the impacted surface indicates that strain acceleration is responsible for the formation of the wave fronts of the combined type, which cause an anomalous response, and hence it should be included in the constitutive relations which describe the response. © 1997 American Institute of Physics. View full abstract»

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  • Shock-induced chemical reactions in titanium–silicon powder mixtures of different morphologies: Time-resolved pressure measurements and materials analysis

    Page(s): 1113 - 1128
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    The response of porous titanium (Ti) and silicon (Si) powder mixtures with small, medium, and coarse particle morphologies is studied under high-pressure shock loading, employing postshock materials analysis as well as nanosecond, time-resolved pressure measurements. The objective of the work was to provide an experimental basis for development of models describing shock-induced solid-state chemistry. The time-resolved measurements of stress pulses obtained with piezoelectric polymer (poly-vinyl-di-flouride) pressure gauges provided extraordinary sensitivity for determination of rate-dependent shock processes. Both techniques showed clear evidence for shock-induced chemical reactions in medium-morphology powders, while fine and coarse powders showed no evidence for reaction. It was observed that the medium-morphology mixtures experience simultaneous plastic deformation of both Ti and Si particles. Fine morphology powders show particle agglomeration, while coarse Si powders undergo extensive fracture and entrapment within the plastically deformed Ti; such processes decrease the propensity for initiation of shock-induced reactions. The change of deformation mode between fracture and plastic deformation in Si powders of different morphologies is a particularly critical observation. Such a behavior reveals the overriding influence of the shock-induced, viscoplastic deformation and fracture response, which controls the mechanochemical nature of shock-induced solid-state chemistry. The present work in conjunction with our prior studies, demonstrates that the initiation of chemical reactions in shock compression of powders is controlled by solid-state mechanochemical processes, and cannot be qualitatively or quantitatively described by thermochemical models. © 1997 American Institute of Physics. View full abstract»

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  • Assessment of the theoretical basis of the Rule of Additivity for the nucleation incubation time during continuous cooling

    Page(s): 1129 - 1137
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    The rule of additivity was first proposed by Scheil and Steinberg for predicting the incubation time for nucleation of solid phases during continuous-cooling phase transformations, and has since been widely used for both the nucleation incubation and the entire process of phase transformation. While having been successfully used to calculate the transformed volume fraction during continuous cooling in many steel alloy systems, there is experimental evidence that shows rule of additivity to be invalid for describing the incubation time for nucleation. Attempts to prove the validity of the rule of additivity for the incubation time have not met with much success, and much confusion still exists about its applicability to the incubation time. This article investigates the additivity of the consumption of the incubation time for nucleation during continuous cooling through an analysis based upon classical nucleation theory. It is rigorously demonstrated that the rule of additivity is invalid for the incubation time for nucleation. However, in practice, the relative error caused by using the rule of additivity could be very small in many cases due to the resolution limit of current experimental techniques. The present theory provides an explanation for the failure of the rule of additivity in predicting the incubation time for nucleation during continuous cooling. © 1997 American Institute of Physics. View full abstract»

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Aims & Scope

Journal of Applied Physics is the American Institute of Physics' (AIP) archival journal for significant new results in applied physics

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Editor
P. James Viccaro
Argonne National Laboratory