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Journal of Applied Physics

Issue 16 • Date Apr 2014

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Displaying Results 1 - 25 of 94
  • Simulation and analysis of grating-integrated quantum dot infrared detectors for spectral response control and performance enhancement

    Page(s): 163101 - 163101-6
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    We propose and analyze a novel detector structure for pixel-level multispectral infrared imaging. More specifically, we investigate the device performance of a grating-integrated quantum dots-in-a-well photodetector under backside illumination. Our design uses 1-dimensional grating patterns fabricated directly on a semiconductor contact layer and, thus, adds a minimal amount of additional effort to conventional detector fabrication flows. We show that we can gain wide-range control of spectral response as well as large overall detection enhancement by adjusting grating parameters. For small grating periods, the spectral responsivity gradually changes with parameters. We explain this spectral tuning using the Fabry–Perot resonance and effective medium theory. For larger grating periods, the responsivity spectra get complicated due to increased diffraction into the active region, but we find that we can obtain large enhancement of the overall detector performance. In our design, the spectral tuning range can be larger than 1 μm, and, compared to the unpatterned detector, the detection enhancement can be greater than 92% and 148% for parallel and perpendicular polarizations. Our work can pave the way for practical, easy-to-fabricate detectors, which are highly useful for many infrared imaging applications. View full abstract»

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  • Numerical investigation of mid-infrared Raman soliton source generation in endless single mode fluoride fibers

    Page(s): 163102 - 163102-4
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    We numerically investigate Raman soliton generation in a fluoride photonic crystal fiber (PCF) pumped by 1.93 μm femtosecond fiber lasers in order to get widely tunable laser source in the mid-infrared region. The simulated results show that a continuously tunable range (1.93 ∼ 3.95 μm) over 2000 nm is achieved in 1-m-long fluoride PCF pumped by a 1.93 μm femtosecond fiber laser with a pulse width of 200 fs. The power conversion efficiency is also calculated and the maximum efficiency can be up to 84.27%. View full abstract»

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  • Experimental investigation of terahertz quantum cascade laser with variable barrier heights

    Page(s): 163103 - 163103-5
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    We report an experimental study of terahertz quantum cascade lasers with variable barrier heights based on the AlxGa1–xAs/GaAs material system. Two new designs are developed based on semiclassical ensemble Monte Carlo simulations using state-of-the-art Al0.15Ga0.85As/GaAs three-quantum-well resonant phonon depopulation active region design as a reference. The new designs achieved maximum lasing temperatures of 188 K and 172 K, as compared to the maximum lasing temperature of 191 K for the reference structure. These results demonstrate that terahertz quantum cascade laser designs with variable barrier heights provide a viable alternative to the traditional active region designs with fixed barrier composition. Additional design space offered by using variable barriers may lead to future improvements in the terahertz quantum cascade laser performance. View full abstract»

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  • Growth kinetics and mass transport mechanisms of GaN columns by selective area metal organic vapor phase epitaxy

    Page(s): 163104 - 163104-8
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    Three-dimensional GaN columns recently have attracted a lot of attention as the potential basis for core-shell light emitting diodes for future solid state lighting. In this study, the fundamental insights into growth kinetics and mass transport mechanisms of N-polar GaN columns during selective area metal organic vapor phase epitaxy on patterned SiOx/sapphire templates are systematically investigated using various pitch of apertures, growth time, and silane flow. Species impingement fluxes on the top surface of columns Jtop and on their sidewall Jsw, as well as, the diffusion flux from the substrate Jsub contribute to the growth of the GaN columns. The vertical and lateral growth rates devoted by Jtop, Jsw and Jsub are estimated quantitatively. The diffusion length of species on the SiOx mask surface λsub as well as on the sidewall surfaces of the 3D columns λsw are determined. The influences of silane on the growth kinetics are discussed. A growth model is developed for this selective area metal organic vapor phase epitaxy processing. View full abstract»

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  • Gain spectrum measurement using the segmented contact method with an integrated optical amplifier

    Page(s): 163105 - 163105-5
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    The measurement of optical gain utilising a segmented contact and integrated optical amplifier is reported. We show that in a direct comparison of methods, the use of the integrated amplifier allows the gain spectrum to be deduced over wider spectral ranges and to lower carrier densities, as compared to the conventional segmented contact technique. View full abstract»

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  • Stark broadening for diagnostics of the electron density in non-equilibrium plasma utilizing isotope hydrogen alpha lines

    Page(s): 163106 - 163106-10
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    Two Stark broadening parameters including FWHM (full width at half maximum) and FWHA (full width at half area) of isotope hydrogen alpha lines are simultaneously introduced to determine the electron density of a pulsed vacuum arc jet. To estimate the gas temperature, the rotational temperature of the C2 Swan system is fit to 2500 ± 100 K. A modified Boltzmann-plot method with bi-factor is introduced to determine the modified electron temperature. The comparison between results of atomic and ionic lines indicates the jet is in partial local thermodynamic equilibrium and the electron temperature is close to 13 000 ± 400 K. Based on the computational results of Gig-Card calculation, a simple and precise interpolation algorithm for the discrete-points tables can be constructed to obtain the traditional ne-Te diagnostic maps of two Stark broadening parameters. The results from FWHA formula by the direct use of FWHM = FWHA and these from the diagnostic map are different. It can be attributed to the imprecise FWHA formula form and the deviation between FWHM and FWHA. The variation of the reduced mass pair due to the non-equilibrium effect contributes to the difference of the results derived from two hydrogen isotope alpha lines. Based on the Stark broadening analysis in this work, a corrected method is set up to determine ne of (1.10 ± 0.08) × 1021 m−3, the reference reduced mass μ0 pair of (3.30 ± 0.82 and 1.65 ± 0.41), and the ion kinetic temperature of 7900 ± 1800 K. View full abstract»

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  • Photoluminescence spectroscopy of YVO4:Eu3+ nanoparticles with aromatic linker molecules: A precursor to biomedical functionalization

    Page(s): 163107 - 163107-5
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    Photoluminescence spectra of YVO4:Eu3+ nanoparticles are presented, with and without the attachment of organic molecules that are proposed for linking to biomolecules. YVO4:Eu3+ nanoparticles with 5% dopant concentration were synthesized via wet chemical synthesis. X-ray diffraction and transmission electron microscopy show the expected wakefieldite structure of tetragonal particles with an average size of 17 nm. Fourier-transform infrared spectroscopy determines that metal-carboxylate coordination is successful in replacing native metal-hydroxyl bonds with three organic linkers, namely, benzoic acid, 3-nitro 4-chloro-benzoic acid, and 3,4-dihydroxybenzoic acid, in separate treatments. UV-excitation photoluminescence spectra show that the position and intensity of the dominant 5D07F2 electric-dipole transition at 619 nm are unaffected by the benzoic acid and 3-nitro 4-chloro-benzoic acid treatments. Attachment of 3,4-dihydroxybenzoic acid produces an order-of-magnitude quenching in the photoluminescence, due to the presence of high-frequency vibrational modes in the linker. Ratios of the dominant electric- and magnetic-dipole transitions confirm infrared measurements, which indicate that the bulk crystal of the nanoparticle is unchanged by all three treatments. View full abstract»

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  • The polarization trajectory of terahertz magnetic dipole radiation in (110)-oriented PrFeO3 single crystal

    Page(s): 163108 - 163108-4
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    By using the polarized terahertz (THz) time-domain spectroscopy, the macro-magnetization motion in (110)-oriented PrFeO3 single crystal was constructed. We emphasize that the trajectory of the emitted THz waveforms relies on not only the motion of macroscopic magnetization vector, but also the spin configuration in the ground state and the propagation of THz pulse. The azimuthal angle (the incident THz pulse polarization with respect to the crystal axes) enables us to control the polarization trajectories of the quasiferromagnetic and quasiantiferromagnetic mode radiations that can lead to further applications on multiple information storing and quantum processing. View full abstract»

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  • Persistence of uranium emission in laser-produced plasmas

    Page(s): 163301 - 163301-8
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    Detection of uranium and other nuclear materials is of the utmost importance for nuclear safeguards and security. Optical emission spectroscopy of laser-ablated U plasmas has been presented as a stand-off, portable analytical method that can yield accurate qualitative and quantitative elemental analysis of a variety of samples. In this study, optimal laser ablation and ambient conditions are explored, as well as the spatio-temporal evolution of the plasma for spectral analysis of excited U species in a glass matrix. Various Ar pressures were explored to investigate the role that plasma collisional effects and confinement have on spectral line emission enhancement and persistence. The plasma-ambient gas interaction was also investigated using spatially resolved spectra and optical time-of-flight measurements. The results indicate that ambient conditions play a very important role in spectral emission intensity as well as the persistence of excited neutral U emission lines, influencing the appropriate spectral acquisition conditions. View full abstract»

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  • Towards a better understanding of dielectric barrier discharges in ferroelectrets: Paschen breakdown fields in micrometer sized voids

    Page(s): 163302 - 163302-5
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    Charged cellular polypropylene foams (i.e., ferro- or piezoelectrets) demonstrate high piezoelectric activity upon being electrically charged. When an external electric field is applied, dielectric barrier discharges (DBDs) occur, resulting in a separation of charges which are subsequently deposited on dielectric surfaces of internal micrometer sized voids. This deposited space charge is responsible for the piezoelectric activity of the material. Previous studies have indicated charging fields larger than predicted by Townsend's model of Paschen breakdown applied to a multilayered electromechanical model; a discrepancy which prompted the present study. The actual breakdown fields for micrometer sized voids were determined by constructing single cell voids using polypropylene spacers with heights ranging from 8 to 75 μm, “sandwiched” between two polypropylene dielectric barriers and glass slides with semi-transparent electrodes. Subsequently, a bipolar triangular charging waveform with a peak voltage of 6 kV was applied to the samples. The breakdown fields were determined by monitoring the emission of light due to the onset of DBDs using an electron multiplying CCD camera. The breakdown fields at absolute pressures from 101 to 251 kPa were found to be in good agreement with the standard Paschen curves. Additionally, the magnitude of the light emission was found to scale linearly with the amount of gas, i.e., the height of the voids. Emissions were homogeneous over the observed regions of the voids for voids with heights of 25 μm or less and increasingly inhomogeneous for void heights greater than 40 μm at high electric fields. View full abstract»

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  • Electrical characterization of the flowing afterglow of N2 and N2/O2 microwave plasmas at reduced pressure

    Page(s): 163303 - 163303-9
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    A cylindrical Langmuir probe was used to analyze the spatial distribution of the number density of positive ions and electrons as well as the electron energy distribution function (EEDF) in the flowing afterglow of a 6 Torr N2 and N2/O2 plasma sustained by a propagating electromagnetic surface wave in the microwave regime. In pure N2 discharges, ion densities were in the mid 1014 m−3 in the pink afterglow and in the mid 1012 m−3 early in the late afterglow. In both pink and late afterglows, the ion population was much higher than the electron population, indicating non-macroscopically neutral media. The EEDF was close to a Maxwellian with an electron temperature of 0.5 ± 0.1 eV, except in the pink afterglow where the temperature rose to 1.1 ± 0.2 eV. This latter behavior is ascribed to N2 vibration-vibration pumping in the pink afterglow that increases the concentration of high N2 vibrational states and thus rises the electron temperature by vibration-electron collisions. After addition of small amounts of O2 in the nominally pure N2 discharge, the charged particles densities and average electron energy first strongly increased and then decreased with increasing O2 concentration. Based on these data and the evolution of the N2+(B) band emission intensities, it is concluded that a significant change in the positive ion composition of the flowing afterglow occurs, going from N2+ in nominally pure N2 discharges to NO+ after addition of trace amounts of O2 in N2. View full abstract»

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  • Experimental investigation on a vectorized aerodynamic dielectric barrier discharge plasma actuator array

    Page(s): 163304 - 163304-12
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    The Electro-Hydro-Dynamics (EHD) interaction, induced in atmospheric pressure still air by a surface dielectric barrier discharge (DBD) actuator, had been experimentally studied. A plasma aerodynamic actuator array, able to produce a vectorized jet, with the induced airflow oriented toward the desired direction, had been developed. The array was constituted by a sequence of single surface DBD actuators with kapton as dielectric material. An ac voltage in the range of 0–6 kV peak at 15 kHz had been used. The vectorization had been obtained by feeding the upper electrodes with different voltages and by varying the electrical connections. The lower electrodes had been connected either to ground or to the high voltage source, to produce the desired jet orientation and to avoid plasma formation acting in an undesired direction. Voltage and current measurements had been carried out to evaluate waveforms and to estimate the active power delivered to the discharge. Schlieren imaging allowed to visualize the induced jet and to estimate its orientation. Pitot measurements had been performed to obtain velocity profiles for all jet configurations. A proportional relation between the jet deflection angle and the applied voltage had been found. Moreover, a linear relation had been obtained between the maximum speed in the jet direction and the applied voltage. The active power of the discharge is approximated by both a power law function and an exponential function of the applied voltage. View full abstract»

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  • Plasma generation for controlled microwave-reflecting surfaces in plasma antennas

    Page(s): 163305 - 163305-7
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    The idea of replacing metal antenna elements with equivalent plasma objects has long been of interest because of the possibility of switching the antenna on and off. In general, two kinds of designs have so far been reported: (a) Separate plasma “wires” which are thin glass tubes filled with gas, where plasma appears due to discharge inside. (b) Reflecting surfaces, consisting of tightly held plasma wires or specially designed large discharge devices with magnetic confinement. The main disadvantages of these antennas are either large weight and size or too irregular surfaces for proper reflection. To design a microwave plasma antenna in the most common radar wavelength range of 1–3 cm with a typical gain of 30 dB, a smooth plasma mirror having a 10–30 cm diameter and a proper curvature is required. The plasma density must be 1012–1014 cm−3 in order to exceed the critical density for the frequency of the electromagnetic wave. To achieve this we have used a ferromagnetic inductively coupled plasma (FICP) source, where a thin magnetic core of a large diameter is fully immersed in the plasma. In the present paper, we show a way to adapt the FICP source for creating a flat switchable microwave plasma mirror with an effective diameter of 30 cm. This mirror was tested as a microwave reflector and there was found no significant difference when compared with a copper plate having the same diameter. View full abstract»

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  • Defect study in molecular beam epitaxy-grown HgCdTe films with activated and unactivated arsenic

    Page(s): 163501 - 163501-7
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    A defect study was performed on molecular beam epitaxy-grown HgCdTe films in situ doped with arsenic. Doping was performed from either effusion cell or cracker cell, and studied were both as-grown samples and samples subjected to arsenic activation annealing. Electrical properties of the films were investigated with the use of ion milling as a means of “stirring” defects in the material. As a result of the study, it was confirmed that the most efficient incorporation of electrically active arsenic occurs at the cracking zone temperature of 700 °C. Interaction between arsenic and tellurium during the growth was observed and is discussed in the paper. View full abstract»

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  • Exploring the behavior of molybdenum diboride (MoB2): A high pressure x-ray diffraction study

    Page(s): 163502 - 163502-4
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    Investigation of the equation of state of molybdenum diboride (MoB2) has been performed to 24.1 GPa using synchrotron radiation angle-dispersive x-ray diffraction techniques (ADXRD) in a diamond anvil cell (DAC) at room temperature. Rietveld refinement of the X-ray powder diffraction data reveals that the rhombohedral structure MoB2 is stable up to 24.1 GPa. The ADXRD data yield a bulk modulus K0 = 314(11) GPa with a pressure derivative K0 = 6.4(1.5). The experimental data are discussed and compared to the results of first-principles calculations. In addition, the compressibility of the unit cell axes (a and c axes) of MoB2 demonstrates an anisotropic property with pressure increasing. View full abstract»

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  • Structural and electronic characterization of 355 nm laser-crystallized silicon: Interplay of film thickness and laser fluence

    Page(s): 163503 - 163503-6
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    We present a detailed study of the laser crystallization of amorphous silicon thin films as a function of laser fluence and film thickness. Silicon films grown through plasma-enhanced chemical vapor deposition were subjected to a Q-switched, diode-pumped solid-state laser operating at 355 nm. The crystallinity, morphology, and optical and electronic properties of the films are characterized through transmission and reflectance spectroscopy, resistivity measurements, Raman spectroscopy, X-ray diffraction, atomic force microscopy, and optical and scanning-electron microscopy. Our results reveal a unique surface morphology that strongly couples to the electronic characteristics of the films, with a minimum laser fluence at which the film properties are optimized. A simple scaling model is used to relate film morphology to conductivity in the laser-processed films. View full abstract»

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  • Effect of Mg doping on the structural and free-charge carrier properties of InN films

    Page(s): 163504 - 163504-10
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    We present a comprehensive study of free-charge carrier and structural properties of two sets of InN films grown by molecular beam epitaxy and systematically doped with Mg from 1.0 × 1018 cm−3 to 3.9 × 1021 cm−3. The free electron and hole concentration, mobility, and plasmon broadening parameters are determined by infrared spectroscopic ellipsometry. The lattice parameters, microstructure, and surface morphology are determined by high-resolution X-ray diffraction and atomic force microscopy. Consistent results on the free-charge carrier type are found in the two sets of InN films and it is inferred that p-type conductivity could be achieved for 1.0 × 1018 cm−3 ≲ [Mg] ≲ 9.0 × 1019 cm−3. The systematic change of free-charge carrier properties with Mg concentration is discussed in relation to the evolution of extended defect density and growth mode. A comparison between the structural characteristics and free electron concentrations in the films provides insights in the role of extended and point defects for the n-type conductivity in InN. It further allows to suggest pathways for achieving compensated InN material with relatively high electron mobility and low defect densities. The critical values of Mg concentration for which polarity inversion and formation of zinc-blende InN occurred are determined. Finally, the effect of Mg doping on the lattice parameters is established and different contributions to the strain in the films are discussed. View full abstract»

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  • Strengthening and toughening metallic glasses: The elastic perspectives and opportunities

    Page(s): 163505 - 163505-11
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    There exist general conflicts between strength and toughness in crystalline engineering materials, and various strengthening and toughening strategies have been developed from the dislocation motion perspectives. Metallic glasses (MGs) have demonstrated great potentials owing to their unique properties; however, their structural applications are strictly limited. One of the key problems is that the traditional strengthening and toughening strategies and mechanisms are not applicable in MGs due to the absence of dislocations and crystalline microstructures. Here, we show that the strength and toughness, or equivalently the shear modulus and Poisson's ratio, are invariably mutually exclusive in MGs. Accordingly, the MGs can be categorized into four groups with different levels of integrated mechanical properties. It is further revealed that the conflicts originate fundamentally from the atomic bonding structures and the levels of strength-toughness combinations are indeed dominated by the bulk modulus. Moreover, we propose novel strategies for optimizing the mechanical properties of MGs from the elastic perspectives. We emphasize the significance of developing high bulk modulus MGs to achieve simultaneously both high strength and good toughness and highlight the elastic opportunities for strengthening and toughening materials. View full abstract»

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  • Phase transformation of ZnMoO4 by localized thermal spike

    Page(s): 163506 - 163506-5
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    We show that ZnMoO4 remains in stable phase under thermal annealing up to 1000 °C, whereas it decomposes to ZnO and MoO3 under transient thermal spike induced by 100 MeV Ag irradiation. The transformation is evidenced by X-ray diffraction (XRD), Raman spectroscopy, and X-ray photoelectron spectroscopy (XPS). Thin films of ZnMoO4 were synthesized by thermal evaporation and subsequent annealing in oxygen ambient at 600 °C for 4 h. XRD results show that as the irradiation fluence increases, the peak related to ZnMoO4 decreases gradually and eventually disappear, whereas peaks related to ZnO grow steadily up to fluence of 3 × 1012 ions/cm2 and thereafter remain stable till highest fluence. This indicates that polycrystalline ZnMoO4 film has transformed to polycrystalline ZnO thin film. The Raman lines related to ZnMoO4 are observed to have disappeared with increasing irradiation fluence. XPS results show modification in bonding and depletion of Mo from near surface region after the ion irradiation. Cross-sectional transmission electron microscopy result shows the formation of ion track of diameter 12–16 nm. These results demonstrate that ion beam methods provide the means to control phase splitting of ZnMoO4 to ZnO and MoO3 within nanometric dimension along the ion track. The observation of phase splitting and Mo loss are explained in the framework of ion beam induced thermal spike formalism. View full abstract»

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  • On the notch sensitivity of CuZr nanoglass

    Page(s): 163507 - 163507-5
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    Recently, nanoglass (NG) was found to exhibit a surprising homogeneous superplastic deformation behavior. However, how the presence of notch affects its mechanical properties remains unexplored. Here, we perform molecular dynamics simulations on a superplastic Cu50Zr50 NG containing a pre-existing notch under tensile loading, with focus on the notch sensitivity. Our results show that when the notch size is smaller than or comparable to the average grain size (d), the NG still exhibits a superplastic deformation and shows notch-insensitivity. When the notch size is larger than d, however, the NG fails by localized shear banding emanating from the notch root and shows notch-sensitivity. The origin of this transition arises from the competition between the shear band nucleation induced by the stress concentration at the notch root and the growth of shear transformation zones distributed in the glass-glass interfaces. Our results provide useful guidelines for the design and engineering of NG with notch for structural applications. View full abstract»

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  • Thermodynamic model of coherent island formation on vicinal substrate

    Page(s): 163508 - 163508-5
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    A thermodynamic model has been proposed to address the formation of coherent island on the vicinal substrate. The morphological transition from square based island to elongated based one with various substrate misorientations is described. The initial stage of nucleation and growth process of islands in Stranski–Krastanow system is studied by taking into account the elastic deformations and the change of energy in the case of two-dimensional growth mode. The theoretical analysis shows the minimum nucleation barrier of island is on the decrease with increment of substrate misorientation, which means the nucleation of island on vicinal substrate is more favorable than that on flat substrate. By using the fitting data of experimental results done by Persichetti et al., [Phys. Rev. Lett. 104, 036104 (2010) and Phys. Rev. B 82, 121309(R) (2010)], we provide a meaningful explanation of the experimental observations. View full abstract»

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  • Strain-induced phase transformation under compression in a diamond anvil cell: Simulations of a sample and gasket

    Page(s): 163509 - 163509-14
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    Combined high pressure phase transformations (PTs) and plastic flow in a sample within a gasket compressed in diamond anvil cell (DAC) are studied for the first time using finite element method. The key point is that phase transformations are modelled as strain-induced, which involves a completely different kinetic description than for traditional pressure-induced PTs. The model takes into account, contact sliding with Coulomb and plastic friction at the boundaries between the sample, gasket, and anvil. A comprehensive computational study of the effects of the kinetic parameter, ratio of the yield strengths of high and low-pressure phases and the gasket, sample radius, and initial thickness on the PTs and plastic flow is performed. A new sliding mechanism at the contact line between the sample, gasket, and anvil called extrusion-based pseudoslip is revealed, which plays an important part in producing high pressure. Strain-controlled kinetics explains why experimentally determined phase transformation pressure and kinetics (concentration of high pressure phase vs. pressure) differ for different geometries and properties of the gasket and the sample: they provide different plastic strain, which was not measured. Utilization of the gasket changes radial plastic flow toward the center of a sample, which leads to high quasi-homogeneous pressure for some geometries. For transformation to a stronger high pressure phase, plastic strain and concentration of a high-pressure phase are also quasi-homogeneous. This allowed us to suggest a method of determining strain-controlled kinetics from experimentation, which is not possible for weaker and equal-strength high-pressure phases and cases without a gasket. Some experimental phenomena are reproduced and interpreted. Developed methods and obtained results represent essential progress toward the understanding of PTs under compression in the DAC. This will allow one optimal design of experiments and conditions for synthesis of new- high pressure phases. View full abstract»

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  • Rotational modes in a phononic crystal with fermion-like behavior

    Page(s): 163510 - 163510-9
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    The calculated band structure of a two-dimensional phononic crystal composed of stiff polymer inclusions in a soft elastomer matrix is shown to support rotational modes. Numerical calculations of the displacement vector field demonstrate the existence of modes whereby the inclusions and the matrix regions between inclusions exhibit out of phase rotations but also in phase rotations. The observation of the in-phase rotational mode at low frequency is made possible by the very low transverse speed of sound of the elastomer matrix. A one-dimensional block-spring model is used to provide a physical interpretation of the rotational modes and of the origin of the rotational modes in the band structure. This model is analyzed within Dirac formalism. Solutions of the Dirac-like wave equation possess a spinor part and a spatio-temporal part. The spinor part of the wave function results from a coupling between the senses (positive or negative) of propagation of the wave. The wave-number dependent spinor-part of the wave function for two superposed waves can impose constraints on the integral of the spatio-temporal part that are reflected in a fermion-like lifting of degeneracy in the phonon band structure associated with in-phase rotations. View full abstract»

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  • Investigations on residual strains and the cathodoluminescence and electron beam induced current signal of grain boundaries in silicon

    Page(s): 163511 - 163511-8
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    Cathodoluminescence (CL) and electron beam induced current (EBIC) measurements were used to investigate the optical behavior and electrical activity of grain boundaries (GBs) in coarsely grained silicon. Electron backscatter diffraction (EBSD) was applied for a comprehensive characterization of the structural properties of the high angle and low angle GBs (HAGBs and LAGBs) in the sample. It was found that not only the EBIC but also the panchromatic (pan) CL contrast of Σ3 HAGBs strongly depends on the hkl-type of the boundary plane. At room temperature coherent Σ3 GBs exhibit no significant contrast in the CL or EBIC images, whereas at low temperatures the pan-CL contrast is strong. For incoherent Σ3 GBs, a strong pan-CL and EBIC contrast was observed in the entire temperature range. Only on a LAGB (misorientation angle 4.5°) CL investigations at low temperatures revealed a line with peak position at about (0.82 ± 0.01) eV, usually related to the dislocation associated D1 transition. Cross-correlation EBSD was applied to analyze the strain fields of Σ3 HAGBs as well as of the LAGB. All the components of the local strain tensors were quantitatively determined. The relationship between the extension of the strain field at the LAGB and the spatial D1 intensity distribution is discussed. View full abstract»

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  • Thermal rectification in pristine-hydrogenated carbon nanotube junction: A molecular dynamics study

    Page(s): 163512 - 163512-5
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    Using non-equilibrium molecular dynamics method, we investigate thermal rectification (TR) in hybrid pristine carbon nanotube (PCNT) and hydrogenated carbon nanotube (HCNT) structures. The interface thermal resistance of the junction is dependent on the direction of thermal transport, leading to TR. We show that by selecting nanotubes of smaller diameters, and/or increasing the hydrogen coverage of HCNT, the TR can be amplified. The observed TR does not decrease by increasing the system length, which presents PCNT/HCNT system as a promising thermal rectifier at room temperature. 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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P. James Viccaro
Argonne National Laboratory