By Topic

Journal of Applied Physics

Issue 9 • Date May 1999

Filter Results

Displaying Results 1 - 25 of 108
  • Issue Table of Contents

    Page(s): toc1
    Save to Project icon | PDF file iconPDF (60 KB)  
    Freely Available from IEEE
  • Semi-insulating semiconductor heterostructures: Optoelectronic properties and applications

    Page(s): 6259 - 6289
    Save to Project icon | PDF file iconPDF (618 KB)  

    This review covers a spectrum of optoelectronic properties of and uses for semi-insulating semiconductor heterostructures and thin films, including epilayers and quantum wells. Compensation by doping, implantation, and nonstoichiometric growth are described in terms of the properties of point defects and Fermi level stabilization and pinning. The principal optical and optoelectronic properties of semi-insulating epilayers and heterostructures, such as excitonic electroabsorption of quantum-confined excitons, are described, in addition to optical absorption by metallic or semimetallic precipitates in these layers. Low-temperature grown quantum wells that have an arsenic-rich nonstoichiometry and a supersaturated concentration of grown-in vacancies are discussed. These heterostructures experience transient enhanced diffusion and superlattice disordering. The review discusses the performance of optoelectronic heterostructures and microcavities that contain semi-insulating layers, such as buried heterostructure stripe lasers, vertical cavity surface emitting lasers, and optical electroabsorption modulators. Short time-scale applications arise from the ultrashort carrier lifetimes in semi-insulating materials, such as in photoconductors for terahertz generation, and in saturable absorbers for mode-locking solid state lasers. This review also comprehensively describes the properties and applications of photorefractive heterostructures. The low dark-carrier concentrations of semi-insulating heterostructures make these materials highly sensitive as dynamic holographic thin films that are useful for adaptive optics applications. The high mobilities of free carriers in photorefractive heterostructures produce fast dielectric relaxation rates that allow light-induced space-charge gratings to adapt to rapidly varying optical fringe patterns, canceling out environmental noise during interferometric detection in laser-based ultrasound, and in optical coherence tomography. They ar- e also the functional layers in high-sensitivity dynamic holographic materials that replace static holograms in Fourier imaging systems and in experimental Tbit/s optical systems. Semi-insulating heterostructures and their applications have attained a degree of maturity, but many critical materials science issues remain unexplored. © 1999 American Institute of Physics. View full abstract»

    Full text access may be available. Click article title to sign in or learn about subscription options.
  • Constant height scanning tunneling spectroscopy using an alternating voltage signal

    Page(s): 6290 - 6294
    Save to Project icon | PDF file iconPDF (103 KB)  

    A method of performing scanning tunneling spectroscopy (STS) at a constant height while maintaining feedback control is described. By using sinusoidal voltage oscillations the ac tunneling current can be separated from the displacement current present in current–voltage (i–V) measurements. The method allows statistically well averaged spectra spanning both occupied and unoccupied states of the sample to be obtained from a continuous set of i–V curves. The unoccupied π* state on graphite is observed using the technique described, and the utility of the technique is further demonstrated by the detection of several bulk states on NiTe2 and PdTe2, two transition metal dichalcogenides. A weighting towards k perpendicular states is seen in the STS spectra. These results show that the fast alternating current form of STS is suitable for probing low amplitude electron states on metal surfaces within 2 eV of the Fermi level. © 1999 American Institute of Physics. View full abstract»

    Full text access may be available. Click article title to sign in or learn about subscription options.
  • Investigation on phase jump in a differential interferometer

    Page(s): 6295 - 6302
    Save to Project icon | PDF file iconPDF (211 KB)  

    This article presents a new phase jump phenomenon in a differential heterodyne interferometer. When the intensity of one arm of an interferometer changes from greater to less (or less to greater) than that of another, a phase jump of 180° will take place if the phase difference between two arms is prefixed at π. We call this phenomenon phase jump. To demonstrate phase jump, a modified differential heterodyne interferometer has been setup. The intensity of one arm is modulated as the arm is scanning across an edge. Both theoretical and experimental investigations are conducted in detail. The theoretical and experimental results indicate that the phase slope of the phase jump is infinite and the amplitude of output signal is zero when a phase jump occurs. Meanwhile the position of phase jump is very sensitive to the displacement. Therefore, both phase and amplitude signals of phase jump are suitable for precise position index and may find wide potential applications in the fields of edge detection, alignment, optical storage, and so on. © 1999 American Institute of Physics. View full abstract»

    Full text access may be available. Click article title to sign in or learn about subscription options.
  • Xenon–neon gas proportional scintillation counters: Experimental and simulation results

    Page(s): 6303 - 6312
    Save to Project icon | PDF file iconPDF (213 KB)  

    When gas proportional scintillation counters (GPSC) are used to detect very low energy x rays, the addition of the light noble gas neon to the usual xenon filling improves the collection of primary electrons that originate near the detector window. However, xenon–neon mixtures have lower electroluminescence yields than pure xenon. Increasing the scintillation electric field jeopardizes the energy resolution because of the additional fluctuations introduced by electron multiplication. In this work we investigate the effect of a limited amount of charge multiplication on the electroluminescence yield and the energy resolution R of a xenon–neon GPSC using both Monte Carlo simulation and experimental measurements. We consider xenon–neon mixtures with 5%, 10%, 20%, 30%, 40%, 50%, 70%, 90%, and 100% Xe at a total pressure of 800 Torr. Comparing the experimental and Monte Carlo data for 5.9 keV x rays, we conclude that optimum value of R is reached in a region of weak ionization with a charge gain of less than 2. By extrapolating the experimental results for R to infinite light yield we obtain the intrinsic energy resolution Rint for 5.9 keV x rays in all mixtures. From these results we can predict Fw values, where F is the relative variance in the number of primary electrons (the Fano factor) and w is the mean energy required to produce a primary electron. From a comparison between Monte Carlo and experimental electroluminescence yields, F and w values are estimated for 5.9 keV x rays in the various mixtures. © 1999 American Institute of Physics. View full abstract»

    Full text access may be available. Click article title to sign in or learn about subscription options.
  • Two-plane focusing of high-space-charge sheet electron beams using periodically cusped magnetic fields

    Page(s): 6313 - 6322
    Save to Project icon | PDF file iconPDF (210 KB)  

    Numerical and theoretical analyses show that stable, two-plane focusing of finite width, elliptical cross section, sheet electron beams with high space charge (low voltage, high current density) can be accomplished using periodically cusped-magnetic (PCM) fields. Magnetic field strength requirements for focusing high-space-charge sheet beams are within technological capabilities of modern permanent magnet technology. Both an offset-pole PCM stack and a PCM stack combined with a periodic quadrupole magnet (PQM) edge array are shown to be effective for two-plane sheet beam confinement. The PCM-PQM hybrid configuration offers inherent advantages for independent adjustment of confinement fields to achieve beam matching (minimum ripple) in both transverse dimensions. The offset-pole configuration offers the advantage of open-side access for applications such as vacuum electronic microwave devices. It is also shown that PCM-focused sheet beam envelope stability obeys criteria equivalent to that previously identified for round-cross-section electron beams in periodic permanent magnet focusing. © 1999 American Institute of Physics. View full abstract»

    Full text access may be available. Click article title to sign in or learn about subscription options.
  • Noise and coupling in magnetic super-resolution media for magneto-optical readout

    Page(s): 6323 - 6330
    Save to Project icon | PDF file iconPDF (456 KB)  

    Interfacial magnetic coupling, transient thermal response, and carrier and noise levels are investigated for two central aperture detection magnetic super-resolution disks. In one of the disks, the two magnetic layers are exchange-coupled, while in the other the coupling is of magneto-static nature. For the exchange-coupled disk, the coupling between the two magnetic layers is fairly strong, and the Kerr loop of the readout layer does not have a square shape. For the magneto-statically coupled disk, the strength of coupling depends on the nonuniformity of the magnetization of the storage layer. The readout layer has a square Kerr loop, but its perpendicular magnetization in the hot region under the focused spot has random orientation if the stray field from the storage layer is weak. This random orientation of magnetization within the readout layer gives rise to a high level of noise during readout. © 1999 American Institute of Physics. View full abstract»

    Full text access may be available. Click article title to sign in or learn about subscription options.
  • Laser-frequency mixing in a scanning tunneling microscope at 1.3 μm

    Page(s): 6331 - 6336
    Save to Project icon | PDF file iconPDF (237 KB)  

    The radiation of two single-mode diode lasers at 1.3 μm is focused into the tunneling junction of a scanning tunneling microscope, and gigahertz difference-frequency signals radiated from the tip are detected. Simultaneous measurements of the bias-voltage dependence of the mixing signal and the tunneling current for different surface samples show that the mixing process is due to the nonlinearity of the static current–voltage characteristic of the tunneling junction. The coupling of the laser radiation into the junction conforms to antenna theory. The experimental results are compared with previous measurements at a laser wavelength of 9.3 μm. Surface images produced by means of the difference-frequency signal show the chemical contrast between micron-sized Au islands and a graphite substrate. © 1999 American Institute of Physics.   View full abstract»

    Full text access may be available. Click article title to sign in or learn about subscription options.
  • Near-field optical microscopy of thin photonic crystal films

    Page(s): 6337 - 6342
    Save to Project icon | PDF file iconPDF (594 KB)  

    Near-field optical microscopy is used to image the light propagating in a Si3N4-on-silica film with a strip of deeply etched submicron holes in the center. Fringe patterns created by interference between incident and diffracted guided modes are observed in the smooth waveguide surrounding the large air-hole photonic film. Observation of the fields in the photonic crystal regions indicates that out-of-plane scattering at the smooth/periodic transitions and leakage caused by grating coupling play major roles. The effects of different air-hole sizes and lattice pitches are also explored. © 1999 American Institute of Physics. View full abstract»

    Full text access may be available. Click article title to sign in or learn about subscription options.
  • Ultrasonic pulse compression with one-bit time reversal through multiple scattering

    Page(s): 6343 - 6352
    Save to Project icon | PDF file iconPDF (257 KB)  

    We present experimental results that demonstrate the feasibility of one-bit time reversal even through high-order multiple scattering. A short ultrasonic pulse is transmitted and propagates through a random set of steel rods. The scattered waves are recorded on a 128-channel array, time reversed, and retransmitted through the same medium. The time-reversal mirror takes advantage of multiple scattering to compress the scattered waves into a pulse and focus it back onto the source. Paradoxically, we show that the results are even better when the scattered signals are digitized over one bit. Both temporal and spatial resolutions remain unchanged, while the compressed pulse is amplified by 12 dB, and the signal-to-noise ratio is lowered by 1.2 dB. A statistical model is developed, and its predictions are found to be in good agreement with the experimental results. © 1999 American Institute of Physics. View full abstract»

    Full text access may be available. Click article title to sign in or learn about subscription options.
  • Detection efficiency of microparticles in laser breakdown water analysis

    Page(s): 6353 - 6357
    Save to Project icon | PDF file iconPDF (163 KB)  

    Polystyrene and silica particles in pure water were successfully detected to a size as small as 0.04 μm by the laser breakdown method. In conventional experimental conditions, detection efficiency has been extremely low, since breakdown occurs only when a particle happens to be present in a narrow focal region during a short laser pulse duration. Through the use of a long focal length lens, which expanded the high power density region without inducing water breakdown around the focal point, efficiency was notably enhanced. Ultrasonic aggregation of particles was also observed to enhance efficiency. © 1999 American Institute of Physics. View full abstract»

    Full text access may be available. Click article title to sign in or learn about subscription options.
  • Ion energy distributions in inductively coupled radio-frequency discharges in argon, nitrogen, oxygen, chlorine, and their mixtures

    Page(s): 6358 - 6365
    Save to Project icon | PDF file iconPDF (163 KB)  

    We report ion energy distributions, relative ion intensities, and absolute total ion current densities at the grounded electrode of an inductively coupled Gaseous Electronics Conference radio-frequency reference cell for discharges generated in pure argon, nitrogen, oxygen, and chlorine, and in mixtures of argon with N2, O2, and Cl2. Measured current densities are significantly greater for pure argon and for mixtures containing argon than for pure N2, O2, and Cl2. For all three molecular gases, the ratio of molecular ions to the fragment ions decreases when argon is added to the molecular gas discharges. A possible destruction mechanism for the molecular ions involving metastable argon is discussed. © 1999 American Institute of Physics. View full abstract»

    Full text access may be available. Click article title to sign in or learn about subscription options.
  • Ion energy distributions in pulsed large area microwave plasma

    Page(s): 6366 - 6372
    Save to Project icon | PDF file iconPDF (139 KB)  

    The energy and the flux of ions impinging on surfaces exposed to low pressure plasmas are important factors which determine the chemical structure and the physical properties of the surfaces and of the thin films. In the present work, we use a large area microwave (MW) plasma reactor in which a grounded sample holder is exposed to a MW (2.45 GHz) discharge excited in different gases, such as Ar, N2, and He, at a pressure ranging from 50 to 200 mTorr. A three-grid, differentially pumped ion energy analyzer is used to measure the ion energy distribution functions (IEDF). The use of a pulsed plasma gives rise to a structured IEDF in which the mean ion energy values vary between 2 and 10 eV. The pulse frequency and the duty cycle were found to strongly affect the IEDF and the ion flux. The evolution of the IEDF is analyzed in terms of the pulsed plasma global model, used to derive the characteristic time constants of plasma ignition and plasma decay. It is shown that the ions in the low energy portion of the IEDF originate from the time period between the individual power pulses, and their relative contribution increases with decreasing the duty time. Controlled pulsing thus allows one to selectively adjust the ion energy, and thereby the surface phenomena in materials processing which are primarily influenced by ion bombardment. © 1999 American Institute of Physics. View full abstract»

    Full text access may be available. Click article title to sign in or learn about subscription options.
  • Numerical analysis of shroud gas effects on air entrainment into thermal plasma jet in ambient atmosphere of normal pressure

    Page(s): 6373 - 6380
    Save to Project icon | PDF file iconPDF (348 KB)  

    A numerical analysis of the influence of air entrainment into the plasma jet on the thermal plasma characteristics is performed to provide a design basis for nontransferred plasma torches operated in an ambient air of atmospheric pressure along with shroud gas injection. The assumption of steady-state, axisymmetric, local thermodynamic equilibrium, and optically thin plasma is adopted in a two-dimensional modeling of thermal plasma flow with an annular shroud gas shell. A control volume method and a modified semi-implicit pressure linked equations revised algorithm (known as SIMPLER) are used for solving the governing equations, i.e., the conservation equations of mass, momentum, and energy along with the equations describing the so-called K–Є model for flow turbulent kinetic energy (K) and its dissipation rate (Є), and the mass fraction equations for gas mixing. The two-dimensional distributions of temperature and flow velocity of the thermal plasma jet as well as the air mole fraction mixed with the plasma are found in an exterior jet expanding region outside the torch, and they are compared for the two cases with and without shroud gas injection. As a result of calculations, the flow rate of the injected shroud gas and the location of its injector turn out to be major parameters for controlling ambient air entrainment. The calculations also reveal that the annular injection of shroud gas surrounding the plasma jet reduces air entrainment into the plasma jet remarkably while it does not significantly affect the plasma temperature and velocity. The present numerical modeling suggests the optimum design and operating values of an argon shroud gas injector for minimizing air entrainment into the thermal plasma flame ejected from the nontransferred plasma torch operated at normal pressure in the ambient atmosphere. © 1999 American Institute of Physics. View full abstract»

    Full text access may be available. Click article title to sign in or learn about subscription options.
  • Computed electron oscillation inside the duct of a vacuum arc source

    Page(s): 6381 - 6384
    Save to Project icon | PDF file iconPDF (101 KB)  

    A three-dimensional numerical model has been developed to simulate the motion of electrons inside the duct of a vacuum arc metal source. It is found that electrons will travel back and forth along the center axis inside the duct tube. This phenomenon of electron oscillation can be explained by the combined effects of the electric and magnetic fields. The electron oscillation will increase the charge state of the positive ions and the ions will gain more energy. Due to the influence of electron oscillation, the plasma throughput of the duct will be different from that of a duct under the influence of only the magnetic field. This finding should be taken into account when designing metal arc sources and optimizing their performance. © 1999 American Institute of Physics. View full abstract»

    Full text access may be available. Click article title to sign in or learn about subscription options.
  • The effect of magnetic field configuration on plasma beam profiles in curved magnetic filters

    Page(s): 6385 - 6391
    Save to Project icon | PDF file iconPDF (733 KB)  

    Curved magnetic filters are commonly used with cathodic vacuum arcs to remove macroparticles from the plasma stream, making it suitable for the preparation of smooth, dense, and defect free films. Although a variety of filters have been investigated experimentally, the influence of the magnetic field configuration on the shape and position of the plasma beam at the filter exit has not been recognized. In this work the magnetic field configurations for a wide range of filter designs have been calculated and compared with measured beam profiles. The results show that the field configurations can be used to predict the dimensions of the plasma beam and in-plane off-axis shifts at the filter exit, as well as identifying regions of high loss. Magnetic field configuration calculations are shown to be a valuable design and optimization tool for curved magnetic field filters of various designs. © 1999 American Institute of Physics. View full abstract»

    Full text access may be available. Click article title to sign in or learn about subscription options.
  • Does plastic deformation proceed near thermodynamic equilibrium? The case made for shear-strained lamellar diblock copolymers

    Page(s): 6392 - 6399
    Save to Project icon | PDF file iconPDF (774 KB)  

    Observations on kink bands in lamellar diblock copolymers (SEP 40–70), caused by unidirectional or oscillatory shear strain, are interpreted in terms of the low-energy structure (LES) hypothesis, to wit: “In a material subject to mechanical stresses, that structure will be approached which has the lowest free energy among all structures which are in equilibrium with the tractions and are accessible to the system.” This is the generalization of the low-energy dislocation structure (LEDS) hypothesis applicable to dislocation structures in crystalline materials. In agreement with the LES hypothesis, moderate fatigue cycling of initially disordered material establishes an order such that the plane of the lamellae is parallel to the plane of shear stress application, being the orientation of lowest shear modulus and, hence, for fixed fatigue amplitude, of lowest strain energy. At fatigue strain amplitudes above about 40% the material develops kink bands on account of the compressive stress along the body diagonal of the samples. The geometry of these kink bands shows that the plane parallel to the lamellae serves as preferred slip plane with the lowest resistance against sliding among all possible directions. Also the kink band morphology conforms with the LES hypothesis. Specifically, on average the ratio of kink band length (L) to the square of kink band width (W), i.e., L/W2, is nearly constant as expected from the minimization of kink band boundary energy and the elastic strain energy on account of the strain discontinuity at the ends of the bands. Subsequent experiments on a different copolymer in a range of temperatures additionally verify the LES hypothesis through establishing that, throughout, large-amplitude cycling causes the lamella orientation of lowest shear modulus. © 1999 American Institute of Physics. View full abstract»

    Full text access may be available. Click article title to sign in or learn about subscription options.
  • Amorphization of Zr–Al solid solutions under mechanical alloying at different temperatures

    Page(s): 6400 - 6407
    Save to Project icon | PDF file iconPDF (419 KB)  

    The effects of temperature on the amorphization of Zr–Al solid solutions have been investigated by ball milling Zr100-xAlx powder blends at different temperatures. At low milling temperatures, the Zr–Al solid solutions amorphized under the polymorphic constraint imposed by intensive external forcing. At elevated temperatures, the solid solution and the amorphous phases coexisted in an obvious two-phase region, signaling a transition approaching two-phase metastable equilibrium. The Al concentration needed for the complete amorphization of Zr–Al increased with increasing milling temperature. These observations, and in particular, the apparent reentrant liquidus, can be explained in terms of the temperature dependence of the external forcing effects brought in by the nonequilibrium milling process in this dynamic driven system. © 1999 American Institute of Physics. View full abstract»

    Full text access may be available. Click article title to sign in or learn about subscription options.
  • Simulation of void and oxygen precipitation processes during high temperature annealing of silicon wafers

    Page(s): 6408 - 6414
    Save to Project icon | PDF file iconPDF (145 KB)  

    The kinetics for dissolution/growth of defects in Czochralski silicon wafers during a 1 h high temperature annealing at 1100 °C has been investigated. The size and distribution of point defects such as vacancy, self-interstitial and oxygen interstitial, are simulated for oxygen and hydrogen ambient annealing. The boundary conditions are analyzed separately for hydrogen and oxygen annealing. A deterministic homogeneous model is used for describing the defect kinetics. The self-interstitial injection rate during oxide annealing is calculated from the Deal-Grove model. Simulated void and oxygen size distributions are compared to B- and C-mode capacitor failure distribution functions. Experimental and theoretical data show that voids can be dissolved during either oxygen or hydrogen annealing, while oxygen precipitates are dissolved during hydrogen annealing and only partially dissolved during oxygen annealing. © 1999 American Institute of Physics. View full abstract»

    Full text access may be available. Click article title to sign in or learn about subscription options.
  • Effects of laser mode and scanning direction on melt pool shape

    Page(s): 6415 - 6420
    Save to Project icon | PDF file iconPDF (195 KB)  

    A three-dimensional quasi-steady-state mathematical model is presented for laser heating with a multimode beam. The effects of laser beam scanning direction on the melt pool shape are investigated through the conduction analysis without phase change. The maximum temperature is found to be behind the center of the focal spot due to advection. The isotherms ahead of the focal spot bunch together and spread apart behind the focal spot on the surface of the workpiece due to the same effect. The temperature profile shows four distinct peaks as a result of four intensity peaks. Scanning direction affects the melt pool shape which needs to be considered for high precision cutting applications such as integrated circuit cutting. The melt pool shape is found to be symmetric about the x axis in the x-y plane and z axis in the y-z plane for the scanning angles Φs=0° and -90°, however it is asymmetric for other scanning angles. © 1999 American Institute of Physics. View full abstract»

    Full text access may be available. Click article title to sign in or learn about subscription options.
  • Measurement of elastic modulus, Poisson ratio, and coefficient of thermal expansion of on-wafer submicron films

    Page(s): 6421 - 6424
    Save to Project icon | PDF file iconPDF (85 KB)  

    A bending beam method has been developed to measure the elastic modulus E, the coefficient of thermal expansion (CTE) and the Poisson ratio ν for on-wafer dielectric films with thicknesses in the submicron range. The method was demonstrated for 0.5 μm thick silicon dioxide films made from tetraethylorthosilane (TEOS). First, the biaxial elastic modulus E/(1-ν) and CTE were measured on blanket TEOS on Si and GaAs substrates and found to be 77 GPa and 1.0 ppm/°C, respectively. The Poisson ratio ν was determined by combining the finite element calculation and the experimental result of the thermal stresses of TEOS fine lines on the Si substrate. The Poisson ratio of TEOS was determined to be 0.24 and, as a consequence, the Young’s modulus was 59 GPa. Fourier transform infrared spectra were obtained for TEOS films on the Si and GaAs substrates to ensure that the chemical structure of the film is independent of the substrate. © 1999 American Institute of Physics. View full abstract»

    Full text access may be available. Click article title to sign in or learn about subscription options.
  • Feasibility of stimulated emission to measure R-line shifts in shock compressed ruby

    Page(s): 6425 - 6429
    Save to Project icon | PDF file iconPDF (95 KB)  

    In previous studies, ruby R-line shifts under shock compression and tension have been measured using the spontaneous luminescence from optically pumped samples. The signal intensities obtained are limited by the short time duration of the experiments in comparison to the long lifetime of the luminescence. We have investigated the use of stimulated emission for measuring R-line shifts in shocked ruby crystals. Experiments were performed both at ambient conditions and under shock compression to 6 GPa using an experimental configuration similar to that used for time resolved ruby luminescence measurements in previous shock wave studies. Signal gain due to stimulated emission was observed, with gains ranging from 1.1 to 3.4, in agreement with calculations performed for the particular experimental configuration used. The present results make a good case for incorporating this technique into the measurement of shock induced R-line shifts in ruby. © 1999 American Institute of Physics. View full abstract»

    Full text access may be available. Click article title to sign in or learn about subscription options.
  • Using Fourier transform infrared grazing incidence reflectivity to study local vibrational modes in GaN

    Page(s): 6430 - 6433
    Save to Project icon | PDF file iconPDF (77 KB)  

    Both Fourier transform infrared (FTIR) grazing incidence reflectivity and FTIR transmission methods have been used to study GaN films grown on α-Al2O3 (0001) substrates by atmospheric pressure metal-organic chemical vapor deposition and low pressure metal-organic chemical vapor deposition. The results show that in the frequency range from 400 to 3500 cm-1 the signal-to-noise ratio of the FTIR grazing incidence measurement is far higher than that of the FTIR transmission measurement. Some new vibrational structures appearing in the former measurement have been discussed. The features around 1460 and 1300 cm-1 are tentatively assigned to scissoring and wagging local vibrational modes of CH2 in GaN, respectively. © 1999 American Institute of Physics. View full abstract»

    Full text access may be available. Click article title to sign in or learn about subscription options.
  • Glassy dynamics of the incommensurate–commensurate phase transition in Zr0.98Hf0.02TiO4 ceramics

    Page(s): 6434 - 6439
    Save to Project icon | PDF file iconPDF (129 KB)  

    The complex dielectric constants of Zr0.98Hf0.02TiO4 ceramics are reported in the frequency range 10-3–1010 Hz for the temperature range 830 °C≤T≤860 °C, just above the commensurate-incommensurate phase transition temperature, Tc. The disappearance of x-ray satellite reflections at 825 °C was used to determine Tc experimentally. The dielectric measurements show that a relatively narrow distribution of relaxation times is present in the ceramics, which broadens as the temperature approaches Tc from above. By analyzing the temperature at which the dielectric constant is a maximum as a function of frequency using the Vogel-Fulcher relationship, an activation energy of 550±15 kb,where kb is the Boltzmann constant, and an effective freezing temperature, Tf, of 825 °C have been determined, confirming that, to within experimental error, Tf coincided with Tc. The experimental results for Zr0.98Hf0.02TiO4 are interpreted in terms of a possible dipole-glass-like phase that has been proposed for relaxor systems. © 1999 American Institute of Physics. View full abstract»

    Full text access may be available. Click article title to sign in or learn about subscription options.
  • Fractional contributions of microscopic diffusion mechanisms for common dopants and self-diffusion in silicon

    Page(s): 6440 - 6446
    Save to Project icon | PDF file iconPDF (121 KB)  

    An identical set of thermal oxidation and nitridation experiments has been performed for four common dopants and self-diffusion in Si. Selectively perturbing the equilibrium point-defect concentrations by these surface reactions is a powerful tool for identifying the relative importance of the various atomic-scale diffusion mechanisms. We obtain bounds on the fractional contributions of the self-interstitial, vacancy, and concerted exchange mechanisms for arsenic, boron, phosphorus, antimony, and self-diffusion in Si at temperatures of 1100 and 1000 °C. These bounds are found by simultaneously solving a system of equations making only very conservative assumptions. The validity of common approximations found in previous work and their effects on the results are also analyzed in detail. We find that B and P diffuse by a self-interstitial mechanism, whereas Sb diffusion is almost exclusively vacancy mediated. As and self-diffusion, on the other hand, exhibit evidence for a dual vacancy-interstitial mechanism with the possibility of some concerted exchange component. © 1999 American Institute of Physics. View full abstract»

    Full text access may be available. Click article title to sign in or learn about subscription options.

Aims & Scope

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

Full Aims & Scope

Meet Our Editors

Editor
P. James Viccaro
Argonne National Laboratory