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Journal of Applied Physics

Issue 3 • Date Aug 1994

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Displaying Results 1 - 25 of 110
  • Issue Table of Contents

    Page(s): toc1
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    Freely Available from IEEE
  • Large‐band‐gap SiC, III‐V nitride, and II‐VI ZnSe‐based semiconductor device technologies

    Page(s): 1363 - 1398
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    In the past several years, research in each of the wide‐band‐gap semiconductors, SiC, GaN, and ZnSe, has led to major advances which now make them viable for device applications. The merits of each contender for high‐temperature electronics and short‐wavelength optical applications are compared. The outstanding thermal and chemical stability of SiC and GaN should enable them to operate at high temperatures and in hostile environments, and also make them attractive for high‐power operation. The present advanced stage of development of SiC substrates and metal‐oxide‐semiconductor technology makes SiC the leading contender for high‐temperature and high‐power applications if ohmic contacts and interface‐state densities can be further improved. GaN, despite fundamentally superior electronic properties and better ohmic contact resistances, must overcome the lack of an ideal substrate material and a relatively advanced SiC infrastructure in order to compete in electronics applications. Prototype transistors have been fabricated from both SiC and GaN, and the microwave characteristics and high‐temperature performance of SiC transistors have been studied. For optical emitters and detectors, ZnSe, SiC, and GaN all have demonstrated operation in the green, blue, or ultraviolet (UV) spectra. Blue SiC light‐emitting diodes (LEDs) have been on the market for several years, joined recently by UV and blue GaN‐based LEDs. These products should find wide use in full color display and other technologies. Promising prototype UV photodetectors have been fabricated from both SiC and GaN. In laser development, ZnSe leads the way with more sophisticated designs having further improved performance being rapidly demonstrated. If the low damage threshold of ZnSe continues to limit practical laser applications, GaN appears poised to become the semiconductor of choice for short‐wavele- ngth lasers in optical memory and other applications. For further development of these materials to be realized, doping densities (especially p type) and ohmic contact technologies have to be improved. Economies of scale need to be realized through the development of larger SiC substrates. Improved substrate materials, ideally GaN itself, need to be aggressively pursued to further develop the GaN‐based material system and enable the fabrication of lasers. ZnSe material quality is already outstanding and now researchers must focus their attention on addressing the short lifetimes of ZnSe‐based lasers to determine whether the material is sufficiently durable for practical laser applications. The problems related to these three wide‐band‐gap semiconductor systems have moved away from materials science toward the device arena, where their technological development can rapidly be brought to maturity. View full abstract»

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  • Free‐electron laser intracavity light as a source of hard x‐ray production by Compton backscattering

    Page(s): 1399 - 1404
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    In this paper we consider the x‐ray production by Compton backscattering of intracavity visible free‐electron laser (FEL) radiation. We discuss the interplay between the build‐up of the laser in the cavity and the backscattered signal including the effects of the e‐beam degradation (energy spread) induced by the FEL interaction. View full abstract»

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  • Estimation of direct current bias and drift of Ti:LiNbO3 optical modulators

    Page(s): 1405 - 1408
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    The dc drift data of Ti:LiNbO3 optical modulators are well fitted to an exponential equation, describing the relaxation phenomena of the dielectric materials. The relaxation time and the saturation voltage ratio, which are necessary to estimate the dc bias follow‐up control, can be obtained from simple dc drift measurements. View full abstract»

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  • Efficient Raman conversion of high repetition rate, 193 nm picosecond laser pulses

    Page(s): 1409 - 1412
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    Efficient generation of Stokes lines has been obtained in H2, CH4, N2, and O2 by 10 ps, 300 Hz, 193 nm laser pulses. A 60% energy conversion efficiency was recorded for the first Stokes of H2 and 40% in CH4. For the pressure range 1–30 atm the conversion efficiency did not change with pump pulse repetition rate up to 300 Hz. The higher order Stokes observed were generated mainly by means of four wave mixing. View full abstract»

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  • Spectroscopy and green upconversion laser emission of Er3+‐doped crystals at room temperature

    Page(s): 1413 - 1422
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    The spectroscopic parameters of Er3+‐doped crystals were determined with regard to the upconversion laser parameters of the green transition 4S3/24I15/2. The influence of excited‐state absorption on this laser channel was determined. Furthermore, upconversion pump mechanisms using ground‐state and excited‐state absorption around 810 and 970 nm were investigated by direct measurements of excited‐state absorption. The spectroscopic results confirm the pulsed room‐temperature laser experiments on the 4S3/24I15/2 transition. The lasers based on Er:LiYF4, Er:Y3Al5O12, and Er:Lu3Al5O12 were directly excited into the upper laser level by an excimer laser pumped dye laser in the blue spectral range. In Er:LiYF4, Er:KYF4, and Er:Y3Al5O12, laser action was achieved with two‐step upconversion pumping by a Ti:sapphire laser and a krypton ion laser. In the case of the fluorides, the additional pumping with the krypton ion laser was not necessary. The laser emission wavelengths were 551 nm for Er:LiYF4, 561 nm for Er:Y3Al5O12 and Er:Lu3Al5O12, and 562 nm for Er:KYF4. In addition, green quasi‐cw laser emission of Er:LiYF4 pumped with an argon‐ion laser was realized at room temperature. View full abstract»

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  • Linewidth calculations of Si11+ and Mg9+ resonance lines and application to photoresonant x‐ray laser pumping

    Page(s): 1423 - 1430
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    The linewidths of the 2p‐3d line of lithium‐like silicon (Si11+) and of the 2s‐3p, 2p‐3d, 2s‐4p, 2p‐4d, 2s‐5p, 2p‐5d lines of lithium‐like magnesium (Mg9+) have been calculated in a range of electron densities and temperatures typical of laser‐produced plasmas. The implications of these results for the realization of photoresonantly pumped soft x‐ray lasers are discussed.   View full abstract»

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  • Field‐induced tuning of the optical properties of nonlinear composites near resonance

    Page(s): 1431 - 1435
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    The bulk effective dielectric function of metal‐dielectric composites has a series of poles in the vicinity of which it is extremely sensitive to small changes in the properties of the components. It is possible to induce such a change in the nonlinear component of a composite, containing at least one nonlinear component, by applying an external electric field at a similar frequency. This causes a tuning of the effective dielectric function and a continuous alteration of the optical properties of the medium. We propose a general framework for calculating this effect in two component composites and also calculate it in a few three component microgeometries. It is found that the optical transmittance of a thin film of this kind can be changed from zero up to 80% using moderate electric fields. View full abstract»

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  • Gas dynamics resulting from laser vaporization of metals in one dimension. I

    Page(s): 1436 - 1446
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    A mathematical model for the transient gas dynamics in one dimension resulting from laser vaporization of metals in the presence of an ambient atmosphere (air) is presented. The gas dynamics is analyzed by considering four regions: a transition zone between the melt surface and the bulk vaporized metal (known as the Knudsen layer), the bulk vaporized metal, the disturbed, and the undisturbed air. The ratios of the temperature and density across the Knudsen layer are modeled by constructing a velocity distribution which is a sum of two variably weighted Maxwellian distributions. The formation of a shock front is considered, and where appropriate the shock front location and velocity are included in the boundary conditions. Profiles in space and time for the velocity, temperature, pressure, and density are determined in a mathematically consistent way by appropriate matching across the Knudsen layer, the vapor/air interface, and the interface between the disturbed and undisturbed air (which may or may not be a shock front). The specific case of homentropic flow, in which the specific entropy in each region is constant, is taken up. The gas dynamics was completely determined by the ambient atmospheric conditions and the velocity νK of the vapor exiting the Knudsen layer, and relations were obtained for thermodynamic parameters in terms of the velocity and specific entropy. It was found that the specific entropy varied with νK, but slowly enough so that the change was perturbative over a reasonably large range of exit velocities. Results of some calculations are presented for a commercially available material. It is estimated that the homentropic model is applicable to vaporization due to laser beams in which the change in intensity is ≲0.1 MW/cm2. The model can be applied to relatively low intensity irradiation such as occurs during welding and slow drilling, and is valid near the center line of a laser beam, or in- deep holes being drilled in which the sidewalls prevent lateral flow of vaporized material. View full abstract»

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  • Gas dynamics resulting from laser vaporization of metals in one dimension. II

    Page(s): 1447 - 1454
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    A mathematical model for the transient gas dynamics in one dimension resulting from laser vaporization of metals is presented. The model treats the case of inviscid isentropic (the material derivative of the specific entropy vanishes) flow. A general solution is obtained for the flow velocity and thermodynamic parameters as functions of time and position. The flow field is determined in terms of the time dependence of the velocity νK, which is the velocity of the vapor exiting a transition zone between the melt surface and the bulk vapor flow (known as the Knudsen layer). It was found that the stagnation parameters c0, p0, ρ0, and T0 (the sound speed, pressure, density, and temperature for the field when the flow velocity vanishes) were functions only of the specific entropy s and thus their material derivatives also vanish. The general solution is applied to a specific case in which νK is taken to be linear in time. The isentropic results are compared with the homentropic results using a quasisteady approximation. It was found that for reasonably small variations in νK, comparison of isentropic and homentropic results show them to be consistent. Thermodynamics relations derived and used to test the results are not satisfied by the quasisteady homentropic calculations but are satisfied by the isentropic results. It is concluded that the specific entropy varies with νK and the isentropic model extends the range of applicability of the flow model to all subsonic flow situations.   View full abstract»

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  • Velocity surface measurements for ZnO films over {001}‐cut GaAs

    Page(s): 1455 - 1461
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    A potential application for a piezoelectric film deposited on a GaAs substrate is the monolithic integration of surface acoustic wave (SAW) devices with GaAs electronics. Knowledge of the SAW properties of the filmed structure is critical for the optimum design of such devices. In this article, the measurements of the velocity surface, which directly affects the SAW diffraction, on the bare and metallized ZnO/SiO2 or Si3N4/GaAs {001}‐cut samples are reported using two different techniques: (1) knife‐edge laser probe, (2) line‐focus‐beam scanning acoustic microscope. Comparisons, such as measurement accuracy and tradeoffs, between the former (dry) and the latter (wet) method are given. It is found that near the 〈110〉 propagation direction the autocollimating SAW property of the bare GaAs changes into a noncollimating one for the layered structure, but a reversed phenomenon exists near the 〈100〉 direction. The passivation layer of SiO2 or Si3N4 (≪0.2 μm thick) and the metallization layer change the relative velocity but do not significantly affect the velocity surface. On the other hand, the passivation layer reduces the propagation loss by 0.5–1.3 dB/μs at 240 MHz depending upon the ZnO film thickness. Our SAW propagation measurements agree well with theoretical calculations. We have also obtained the anisotropy factors for samples with ZnO films of 1.6, 2.8, and 4.0 μm thickness. Comparisons concerning the piezoelectric coupling and acoustic loss between dc triode and rf magnetron sputtered ZnO films are provided.   View full abstract»

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  • Thermal diffusivity measurements in opaque solids by the mirage technique in the temperature range from 300 to 1000 K

    Page(s): 1462 - 1468
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    A method to measure the thermal diffusivity of solid samples as a function of temperature is presented. The measurement technique is based on the mirage effect and in its linear zero‐crossing relation for the transverse deflection, whose slope directly gives the diffusivity of the material. A 3D theoretical model has been developed in order to include both the effects of the radiative and convective heat transfers between the sample and its surroundings, and the temperature dependence of the refractive index and thermal diffusivity of the gas. The model also incorporates the effects introduced by the mirage parameters (sizes of the pump and probe beams, and probe beam height). The samples studied are opaque and thermally thick, and the applicability of the method is restricted to materials with diffusivity ≳1 mm2/s. Two experimental mirage setups are presented, one with the sample being heated in an open environment, and the other with the sample heated within a furnace. In the first case the range of measurable temperatures goes from ambient to ∼500 K, whereas in the second the upper limit is ∼1000 K. A comparison of the experimental results obtained with this method with those from the literature on calibrated samples of pure nickel, pure cobalt, and an AISI‐302 alloy of low thermal diffusivity, confirm the validity of the model and method proposed.   View full abstract»

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  • Investigation of the Paschen curve of nitrogen via the application of nanosecond pulsed electromagnetic radiation

    Page(s): 1469 - 1475
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    The Paschen curve of nitrogen from pressures of 0.336 to 685 Torr via the application of nanosecond pulsed electromagnetic radiation has been investigated. Breakdown of the gas was achieved via pumping by short electromagnetic pulses and verified through the use of an optical multichannel analyzer. Adjustments for the short pulse nature of this investigation have been derived and are applied to the Paschen curve. The experiments were conducted utilizing a pulser with machine parameters of 1 J delivered during 1.375 ns FWHM into a 50 Ω coaxial line, at a peak power of 1 GW. Investigation of this region has yielded data in the region of the relativistic Paschen curve as hypothesized by Graham and Roussel‐Dupré. Experimental results yield no observable relativistic effects under the conditions of this experiment. Additionally, the collisional frequency limit has been experimentally identified.   View full abstract»

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  • Effect of plasma‐surface interactions on the radial variation of H atom density in a hydrogen radio frequency discharge

    Page(s): 1476 - 1479
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    The effect of plasma surface interactions on the radial variation of H atom density has been measured in a low pressure pure H2 rf discharge by two‐photon (electric quadrupole and magnetic dipole) allowed laser induced fluorescence using a standard reference cell. Measurements were made in the pressure range from 0.5 to 7 Torr and at a rf power of 35 W into the plasma. The influence of different electrode materials on the H atom density close to the electrode surface and in the discharge volume was measured. The data shows that the radial density distribution, under our discharge conditions, is primarily determined by the plasma‐surface interactions and not by the discharge current uniformity (or nonuniformity). We have clearly demonstrated the ability of this measurement technique to monitor in situ, plasma induced surface property changes. View full abstract»

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  • Time‐integrated optical emission studies of plumes generated from laser ablated germania glass

    Page(s): 1480 - 1486
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    The optical emission from plumes induced by ArF laser irradiation of GeO2 was characterized as a function of laser fluence, distance from the target surface, and ambient O2 pressure. Dispersion of the light emitted by the plume in a vacuum revealed emission from both neutral and singly ionized Ge atoms as well as neutral O atoms. The spatial variation showed that the ion concentration decreased exponentially from the target surface while the neutral atom number density reached peak intensities at distances of ≊1.5–2.5 cm from the target surface. Interactions between the plume constituents and the ambient molecular oxygen increased the excited Ge atom and Ge ion populations in the plume and, most notably, significantly enlarged the excited O atom concentration over that produced directly from the ablation process.   View full abstract»

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  • Two‐photon laser induced fluorescence and amplified spontaneous emission atom concentration measurements in O2 and H2 discharges

    Page(s): 1487 - 1493
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    Multiphoton laser‐induced fluorescence (LIF) and amplified spontaneous emission (ASE) are used to detect ground‐state atoms in oxygen and hydrogen glow discharge plasmas. Experimental results and modeling are analyzed to establish the validity criteria for the use of LIF and ASE as diagnostic probes in the measurements of ground‐state atom concentrations. An absolute calibration of the LIF signals is obtained by vacuum ultraviolet absorption experiments, either on the 130 nm resonant line of the atomic oxygen, or the 125 nm resonant line of the hydrogen atom. Under typical operating conditions of dc glow discharges, that is, for gas pressure between 0.5 and 5.0 Torr and discharge current from 1 to 50 mA, the densities of the atomic species are measured in the range 1013 cm-3–1015 cm-3. Under the same conditions the hydrogen atom temperature varies from (336±43) K to (1580±90) K. View full abstract»

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  • Electron emission from pseudospark cathodes

    Page(s): 1494 - 1502
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    The pseudospark cathode has the remarkable property of macroscopically homogeneous electron emission at very high current density (≳1 kA/cm2) over a large area (some cm2). The model of electron emission presented here is based on the assumption that the pseudospark microscopically utilizes explosive arc processes, as distinct from earlier models of ‘‘anomalous emission in superdense glow discharges.’’ Explosive emission similar to vacuum are cathode spots occurs rapidly when the field strength is sufficiently high. The plasma remains macroscopically homogeneous since the virtual plasma anode adapts to the cathode morphology so that the current is carried by a large number of homogeneously distributed cathode spots which are similar to ‘‘type 1’’ and ‘‘type 2’’ spots of vacuum arc discharges. The net cathode erosion is greatly reduced relative to ‘‘spark gap‐type’’ emission. At very high current levels, a transition to highly erosive spot types occurs, and this ‘‘arcing’’ leads to a significant reduction in device lifetime. Assuming vacuum‐arc‐like cathode spots, the observed current density and time constants can be easily explained. The observed cathode erosion rate and pattern, recent fast‐camera data, laser‐induced fluorescence, and spectroscopic measurements support this approach. A new hypothesis is presented explaining current quenching at relatively low currents. From the point of view of electron emission, the ‘‘superdense glow’’ or ‘‘superemissive phase’’ of pseudosparks represents an arc and not a glow discharge even if no filamentation or ‘‘arcing’’ is observed. View full abstract»

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  • Structural, optical, and electrical properties of epitaxial chalcopyrite CuIn3Se5 films

    Page(s): 1503 - 1510
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    Single crystal CuIn3Se5 epitaxial films have been synthesized on GaAs(001) by a hybrid sputtering and evaporation technique. The microstructure, microchemistry, and selected electrical and optical properties of the films have been investigated by scanning electron microscopy, energy dispersive x‐ray spectroscopy, transmission electron microscopy, cathodoluminescence, optical absorption and reflection, and four‐point probe resistivity measurements. The results showed that the CuIn3Se5 crystals have an ordered point defect structure, a band gap of ≥1.18 eV, an optical absorption coefficient of about 15 000 cm-1 at a photon energy of 1.35 eV, and a film resistivity of ≳105 Ω cm. The results suggest the presence of band tails giving rise to subgap radiative recombination and absorption. Antiphase domain boundaries, stacking faults, and nanotwins were observed in the epitaxial layers and were reduced in number by rapid thermal annealing. View full abstract»

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  • Theoretical analysis of dopant redistribution in silicon after implantation through an SiO2 mask

    Page(s): 1511 - 1514
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    The redistribution after annealing in silicon of dopant implanted through a silicon oxide mask is discussed. The conditions which are essential to analyze diffusion profiles by simple Gaussian function are presented. The finite thickness of the oxide mask is taken into consideration. Experimental data of implanted P are compared with the exact and approximated solutions and it is shown that the use of the Gaussian approximation is within of ∼12% accuracy of the exact solution.   View full abstract»

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  • Influence of neutron irradiation on the thermal conductivity of vapor‐deposited diamond

    Page(s): 1515 - 1517
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    The influence of neutron irradiation on the thermal conductivity κ of diamond films fabricated by hot filament (HF) and microwave plasma assisted (MPA) deposition has been studied. The additional thermal resistivity induced by irradiation is similar to that found in single crystal diamond and is due mainly to the formation of clusters of disordered carbon material. Despite a significant difference in κ prior to irradiation, the thermal conductivity of the HF and MPA films is almost the same after a cumulative dose of 2.7×1017 neutrons cm-2. View full abstract»

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  • Solute trapping of group III, IV, and V elements in silicon by an aperiodic stepwise growth mechanism

    Page(s): 1518 - 1529
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    With rapid solidification following pulsed laser melting, we have measured the dependence on interface orientation of the amount of solute trapping of several group III, IV, and V elements (As, Ga, Ge, In, Sb, Sn) in Si. The aperiodic stepwise growth model of Goldman and Aziz accurately fits both the velocity and orientation dependence of solute trapping of all of these solutes except Ge. The success of the model implies a ledge structure for the crystal/melt interface and a step‐flow mechanism for growth from the melt. In addition, we have observed an empirical inverse correlation between the two free parameters (‘‘diffusive speeds’’) in this model and the equilibrium solute partition coefficient of a system. This correlation may be used to estimate values of these free parameters for other systems in which solute trapping has not or cannot be measured. The possible microscopic origin of such a correlation is discussed. View full abstract»

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  • Shock‐induced amorphization of q‐GeO2

    Page(s): 1530 - 1534
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    Polycrystalline samples of the α‐quartz phase of GeO2 (q‐GeO2), recovered from peak shock compressions of 5, 6.8, and 10 GPa, have been examined by x‐ray diffraction, thermoluminescence, and Raman techniques. The measurements show that q‐GeO2 irreversibly amorphizes above 6.8 GPa. The estimates of the shear band temperature suggest that the mechanism of shock‐induced amorphization in q‐GeO2 is a solid‐solid one, in contrast to that in SiO2 quartz which has both solid‐solid and fusion‐quenched components. View full abstract»

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  • Growth of voids in porous ductile materials at high strain rate

    Page(s): 1535 - 1542
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    A hollow‐sphere model, with temperature‐dependent viscoplastic material response, is developed to investigate the inertial and thermal effects on dynamic growth of voids in ductile materials. Theoretical analysis indicates that the inertial effect (kinetic energy of void growth) mainly dominates the behavior of the void growth in temperature‐dependent and high‐strain‐rate cases. Otherwise, the viscoplastic effect dominates and the inertial effect can be neglected. The rate of the dynamic growth of voids increases when the thermal effect is considered. An expression of the threshold stress for the void growth is obtained, which depends on the initial porosity, the porosity, the yield strength, the density of surface energy of voids, the initial temperature, and the melting temperature. View full abstract»

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  • On the shear strength of shock loaded brittle solids

    Page(s): 1543 - 1546
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    We propose a new approach to analyze the response of brittle materials to shock loading. Our analysis is based on assuming that these materials obey Griffith’s criterion for failure under pressure. This criterion leads to an explicit relationship between the shear strength of the shocked solid and the pressure behind the shock front. The agreement between this relation and direct measurements of shear strength, on shock loaded titanium‐diboride, is very good. Moreover, several discrepancies between different sets of data, concerning shock loaded alumina, are removed by applying the new interpretation for the response of brittle solids to shock waves. View full abstract»

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  • Determination of bending stress of Si wafer using concentrated load

    Page(s): 1547 - 1551
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    The technique of concentrated load with a simple O‐ring supporter is used to measure the deflection of Si wafers. The load varies so that the ratio of the deflection to the wafer thickness changes from 0 to 1. For some samples, this ratio goes up to 1.4 at which the samples are fractured. It is observed in the experiment that the stress of the wafer can be described by the linear deflection theory for small deflection. However, when the deflection is larger than 1/5 of the wafer thickness, nonlinear deflection theory should be used and the stress in the middle plane cannot be ignored anymore. The total stress for large deflection is approximately equal to the sum of the stress of a linear elastic plate and the stress in the middle plane. The experiment also shows that the bending strength of the Si wafer strongly depends on the surface conditions. Mirror finishing surface gives high mechanical strength. 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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Meet Our Editors

Editor
P. James Viccaro
Argonne National Laboratory