jap banner
  • Volume/Page
  • Keyword
  • DOI
  • Citation
  • Advanced
   
 
 
 

Flickr Twitter UniPHY Group iResearch App Facebook

BROWSE VOLUMES

Year Range: 
Search Issue | RSS Feeds RSS
Next Issue

1 Jan 2012

Volume 111, Issue 1, Articles (01xxxx)

Issue Cover Spotlight Figure

J. Appl. Phys. 111, 014902 (2012); http://dx.doi.org/10.1063/1.3671672 (10 pages)

L. Combelles, S. Lorente, R. Anderson, and A. Bejan

Tree-shaped fluid flow and heat storage in a conducting solid

Enlarge Image | Read More
Page 1 of 6 Pages Next Page | Jump to Page
back to top
RSS Feeds
back to top Lasers, Optics, and Optoelectronics

Luminescent properties of LiBaPO4:RE (RE = Eu2+, Tb3+, Sm3+) phosphors for white light-emitting diodes

Jiayue Sun, Xiangyan Zhang, Zhiguo Xia, and Haiyan Du

J. Appl. Phys. 111, 013101 (2012); http://dx.doi.org/10.1063/1.3673331 (7 pages)

Online Publication Date: 4 January 2012

Full Text: Read Online (HTML) | Download PDF

Show Abstract
Multicolor emitting phosphors LiBaPO4:RE (RE = Eu2+, Tb3+, Sm3+) reported as interesting down-conversion luminescent materials in white light-emitting diodes (w-LEDs) have been prepared by a conventional solid-state reaction. The excitation and emission spectra indicate that these phosphors can be effectively excited by the near-UV light, and emit blue, green, and red light, respectively. The photoluminescence properties, decay times, and Commission Internationale de I’Eclairage (CIE) chromaticity indexes are determined for various concentrations of the activators Eu2+, Tb3+, and Sm3+ in LiBaPO4 host. Furthermore, the temperature-dependent luminescence of these phosphors was investigated. The emission intensities of Tb3+- and Sm3+-doped LiBaPO4 increased unexpectedly with increasing temperature. This interesting phenomenon is proposed to be the result of two ground states in the configurational coordination diagram. The present investigation suggests that LiBaPO4:RE (RE = Eu2+, Tb3+, Sm3+) were potential candidates for application in w-LEDs.
Show PACS
78.55.Hx Other solid inorganic materials
78.40.Ha Other nonmetallic inorganics

Spectroscopic features and laser performance at 1.06 μm of Nd3+-doped Gd1−xLuxCa4O(BO3)3 single crystal

C. Gheorghe, L. Gheorghe, P. Loiseau, and G. Aka

J. Appl. Phys. 111, 013102 (2012); http://dx.doi.org/10.1063/1.3673801 (7 pages)

Online Publication Date: 5 January 2012

Full Text: Read Online (HTML) | Download PDF

Show Abstract
High quality nonlinear optical Gd0.84Lu0.11Nd0.05Ca4O(BO3)3 (Nd: GdLuCOB) crystal has been grown by the Czochralski method. The high resolution and polarized spectroscopic data of Nd3+ in GdLuCOB crystal were carried out and analyzed in the framework of the Judd-Ofelt theory. The polarized emission cross-sections for the 4F3/2 → 4I9/2 and 4F3/2 → 4I11/2 Nd3+ transitions of special interest for laser application were determined. Near-infrared laser emission at 1061 nm was achieved under cw Ti: sapphire end pumping at 812 nm. For propagation along the Z-axis, laser emission polarized parallel to the Y-axis was obtained for the first time. This result offers the opportunity to achieve type I SFD of Nd3+ emission in the ZX plane which presents a non-linearity approximately three times larger than XY plane.
Show PACS
42.70.Hj Laser materials
78.30.Hv Other nonmetallic inorganics
81.10.Fq Growth from melts; zone melting and refining
78.55.Hx Other solid inorganic materials
42.60.By Design of specific laser systems
42.55.Rz Doped-insulator lasers and other solid state lasers

Experimental realization of the porous silicon optical multilayers based on the 1-s sequence

J. O. Estevez, J. Arriaga, A. Méndez-Blas, M. G. Robles-Cháirez, and D. A. Contreras-Solorio

J. Appl. Phys. 111, 013103 (2012); http://dx.doi.org/10.1063/1.3673598 (6 pages)

Online Publication Date: 6 January 2012

Full Text: Read Online (HTML) | Download PDF

Show Abstract
We report experimental results of the reflectance spectra of deterministic aperiodic multilayer structures fabricated with porous silicon. The refractive index of the layers forming the structures follows the values generated by the self-similar sequence called “the 1s-counting sequence.” We fabricated samples with 64, 128, and 256 layers with different thicknesses and porosities by controlling the applied current density and the etching time. The measured reflectance spectra exhibit properties of self-similarity, which are in good agreement with theoretical results reported previously.
Show PACS
61.43.Gt Powders, porous materials
68.65.-k Low-dimensional, mesoscopic, nanoscale and other related systems: structure and nonelectronic properties
78.20.Ci Optical constants (including refractive index, complex dielectric constant, absorption, reflection and transmission coefficients, emissivity)
81.65.Cf Surface cleaning, etching, patterning
Author Select

Optical and structural characterization of thermal oxidation effects of erbium thin films deposited by electron beam on silicon

Himani S. Kamineni, Vimal K. Kamineni, Richard L. Moore, Spyros Gallis, Alain C. Diebold, Mengbing Huang, and Alain E. Kaloyeros

J. Appl. Phys. 111, 013104 (2012); http://dx.doi.org/10.1063/1.3675278 (8 pages)

Online Publication Date: 6 January 2012

Full Text: Read Online (HTML) | Download PDF

Show Abstract
Thermal oxidation effects on the structural, compositional, and optical properties of erbium films deposited on silicon via electron beam evaporation were analyzed by x-ray diffraction, x-ray photoelectron spectroscopy, Auger electron spectroscopy, and spectroscopic ellipsometry. A gradual rise in oxidation temperature from 700 to 900 °C resulted in a transition from ErO- to Er2O3-rich phase. Additional increase in oxidation temperature above 1000°C led to the formation of erbium silicate due to further oxygen incorporation, as well as silicon out-diffusion from the substrate. A silicon oxide interfacial layer was also detected, with its thickness increasing with higher oxidation temperature. Additionally, film refractive index decreased, while its Tauc bandgap value increased from ∼5.2 eV to ∼6.4 eV, as the oxidation temperature was raised from 700 °C to above 900 °C. These transformations were accompanied by the appearance of an intense and broad absorption band below the optical gap. Thermal oxidation effects are discussed in the context of film structural characteristics and defect states.
Show PACS
78.66.Bz Metals and metallic alloys
81.05.Bx Metals, semimetals, and alloys
71.55.Ak Metals, semimetals, and alloys
78.20.Ci Optical constants (including refractive index, complex dielectric constant, absorption, reflection and transmission coefficients, emissivity)
79.60.Bm Clean metal, semiconductor, and insulator surfaces
81.15.Jj Ion and electron beam-assisted deposition; ion plating

A flexible Bloch mode method for computing complex band structures and impedances of two-dimensional photonic crystals

Felix J. Lawrence, Lindsay C. Botten, Kokou B. Dossou, R. C. McPhedran, and C. Martijn de Sterke

J. Appl. Phys. 111, 013105 (2012); http://dx.doi.org/10.1063/1.3674281 (8 pages)

Online Publication Date: 11 January 2012

Full Text: Read Online (HTML) | Download PDF

Show Abstract
We present a flexible method that can calculate Bloch modes, complex band structures, and impedances of two-dimensional photonic crystals from scattering data produced by widely available numerical tools. The method generalizes previous work which relied on specialized multipole and finite element method (FEM) techniques underpinning transfer matrix methods. We describe the numerical technique for mode extraction, and apply it to calculate a complex band structure and to design two photonic crystal antireflection coatings. We do this for frequencies at which other methods fail, but which nevertheless are of significant practical interest.
Show PACS
42.70.Qs Photonic bandgap materials
42.79.Wc Optical coatings

Depth measurements of drilled holes in bone by laser triangulation for the field of oral implantology

D. Quest, C. Gayer, and P. Hering

J. Appl. Phys. 111, 013106 (2012); http://dx.doi.org/10.1063/1.3676219 (5 pages)

Online Publication Date: 12 January 2012

Full Text: Read Online (HTML) | Download PDF

Show Abstract
Laser osteotomy is one possible method of preparing beds for dental implants in the human jaw. A major problem in using this contactless treatment modality is the lack of haptic feedback to control the depth while drilling the implant bed. A contactless measurement system called laser triangulation is presented as a new procedure to overcome this problem. Together with a tomographic picture the actual position of the laser ablation in the bone can be calculated. Furthermore, the laser response is sufficiently fast as to pose little risk to surrounding sensitive areas such as nerves and blood vessels. In the jaw two different bone structures exist, namely the cancellous bone and the compact bone. Samples of both bone structures were examined with test drillings performed either by laser osteotomy or by a conventional rotating drilling tool. The depth of these holes was measured using laser triangulation. The results and the setup are reported in this study.
Show PACS
87.63.lt Laser imaging
87.85.G- Biomechanics
87.19.R- Mechanical and electrical properties of tissues and organs
87.50.wp Therapeutic applications

Simulation of laser-generated longitudinal and shear ultrasonic waves in a diamond anvil cell by the finite element method

Wen Feng, Dexing Yang, Xiangchao Zhu, Yuning Guo, and Wei Liao

J. Appl. Phys. 111, 013107 (2012); http://dx.doi.org/10.1063/1.3676253 (6 pages)

Online Publication Date: 12 January 2012

Full Text: Read Online (HTML) | Download PDF

Show Abstract
Based on the thermoelastic theory, a numerical model of ultrasonic displacement field induced by a vertical incident pulsed laser in an aluminum film in a diamond anvil cell (DAC) is established by using the finite element method (FEM). After precisely calculating the transient temperature field distributions, the bulk ultrasonic waveforms on the rear surface of the film and the characteristics of ultrasonic displacement field with time are obtained. Then directivity patterns of laser-generated longitudinal and shear ultrasonic waves are analyzed in details. The numerical results indicate that the thermoelastic force source and the characteristics of ultrasonic directivity are strongly affected by the diamond window. The energy of longitudinal wave is concentrated near the laser incident direction, and the one of shear wave is concentrated between 30° and 60° that deflected from the laser incident direction to the excited source. These characteristics in DAC system are different from the results of free surface in thermoelastic effect, while are similar to the results of free surface in ablation effect.
Show PACS
68.60.Bs Mechanical and acoustical properties
81.40.Jj Elasticity and anelasticity, stress-strain relations
62.20.D- Elasticity
79.20.Eb Laser ablation
43.35.-c Ultrasonics, quantum acoustics, and physical effects of sound

Time dynamics of self-pumped reflection gratings in a photorefractive polymer

P. P. Banerjee, S. H. Buller, C. M. Liebig, S. A. Basun, G. Cook, D. R. Evans, P.-A. Blanche, J. Thomas, C. W. Christenson, and N. Peyghambarian

J. Appl. Phys. 111, 013108 (2012); http://dx.doi.org/10.1063/1.3672832 (4 pages)

Online Publication Date: 12 January 2012

Full Text: Read Online (HTML) | Download PDF

Show Abstract
The time dynamics of self-pumped reflection gratings in a commonly used photorefractive polymer PDCST:PVK:ECZ-BBP:C60 with no additional electron sources or traps is investigated. While holes are normally the mobile charges and responsible for grating formation, our experimental observations, analyzed using multi-exponential fitting curves, show evidence of electrons in addition to holes as charge carriers, particularly above an applied field of 40 V/μm. The dependence of effective carrier mobilities on the applied electric field, deduced from experimental results, show stronger field dependence of electron mobility at high electric fields. At an applied field of 70 V/μm, electron and hole mobilities become approximately equal, and the contribution of electrons on grating formation becomes significant.
Show PACS
42.70.Jk Polymers and organics
42.79.Dj Gratings

Modeling upconversion of erbium doped microcrystals based on experimentally determined Einstein coefficients

Stefan Fischer, Heiko Steinkemper, Philipp Löper, Martin Hermle, and Jan Christoph Goldschmidt

J. Appl. Phys. 111, 013109 (2012); http://dx.doi.org/10.1063/1.3674319 (13 pages) | Cited 2 times

Online Publication Date: 13 January 2012

Full Text: Read Online (HTML) | Download PDF


See Also: Publisher's Note | Publisher's Note

Show Abstract
The upconversion of infrared photons is a promising possibility to enhance solar cell efficiency by producing electricity from otherwise unused sub-band-gap photons. We present a rate equation model and the relevant processes in order to describe the upconversion of near-infrared photons. The model considers stimulated and spontaneous processes, multi-phonon relaxation, and energy transfer between neighboring ions. The input parameters for the model are experimentally determined for the material system, β-NaEr0.2Y0.8F4. The determination of the transition probabilities, also known as the Einstein coefficients, is the focus of the parameterization. The influence of multi-phonon relaxation and energy transfer on the upconversion are evaluated and discussed in detail. Since upconversion is a non-linear process, the irradiance dependence of the simulations is investigated and compared to the experimental data of quantum efficiency measurements. The results are very promising and indicate that upconversion is reasonably physically described by the rate equations. Therefore, the presented model will be the basis for further simulations concerning various applications of upconversion, such as in combination with plasmon resonances in metal nanoparticles.
Show PACS
78.55.Hx Other solid inorganic materials
61.46.Df Structure of nanocrystals and nanoparticles ("colloidal" quantum dots but not gate-isolated embedded quantum dots)
back to top Plasmas and Electrical Discharges

Stability and properties of stationary state of one dimensional space charge limited current

A. Rokhlenko and J. L. Lebowitz

J. Appl. Phys. 111, 013301 (2012); http://dx.doi.org/10.1063/1.3665875 (7 pages) | Cited 1 time

Online Publication Date: 3 January 2012

Full Text: Read Online (HTML) | Download PDF

Show Abstract
A linear stability analysis of the planar one dimensional space charge limited flow shows that the classical Child’s solution is stable in time. Small perturbations of the flow are accompanied by high frequency oscillations that decay exponentially. These oscillations should appear when the flow regime changes rapidly, and they might be detectable experimentally by their electromagnetic radiation. We also study the stationary state of more general space charge limited flow and obtain a relation between the current density and the electric field at the emitter surface for arbitrary emission laws and a fixed non-zero initial speed of electrons. In such a case there is the possibility of creation of electrostatic barriers for the emission and stationary flow regimes in this simple model.
Show PACS
77.22.Jp Dielectric breakdown and space-charge effects

X-band microwave generation caused by plasma-sheath instability

Y. Bliokh, J. Felsteiner, and Ya. Z. Slutsker

J. Appl. Phys. 111, 013302 (2012); http://dx.doi.org/10.1063/1.3675178 (8 pages)

Online Publication Date: 6 January 2012

Full Text: Read Online (HTML) | Download PDF

Show Abstract
It is well known that oscillations at the electron plasma frequency may appear due to instability of the plasma sheath near a positively biased electrode immersed in plasma. This instability is caused by transit-time effects when electrons, collected by this electrode, pass through the sheath. Such oscillations appear as low-power short spikes due to additional ionization of a neutral gas in the electrode vicinity. Herein we present first results obtained when the additional ionization was eliminated. We succeeded in prolonging the oscillations during the whole time a positive bias was applied to the electrode. These oscillations could be obtained at much higher frequency than previously reported (tens of GHz compared to few hundreds of MHz) and power of tens of mW. These results in combination with presented theoretical estimations may be useful, e.g., for plasma diagnostics.
Show PACS
52.40.Kh Plasma sheaths
52.70.Gw Radio-frequency and microwave measurements
52.25.Fi Transport properties
52.35.Fp Electrostatic waves and oscillations (e.g., ion-acoustic waves)
52.35.Qz Microinstabilities (ion-acoustic, two-stream, loss-cone, beam-plasma, drift, ion- or electron-cyclotron, etc.)

Numerical simulations of runaway electron generation in pressurized gases

D. Levko, S. Yatom, V. Vekselman, J. Z. Gleizer, V. Tz. Gurovich, and Ya. E. Krasik

J. Appl. Phys. 111, 013303 (2012); http://dx.doi.org/10.1063/1.3675527 (9 pages) | Cited 2 times

Online Publication Date: 6 January 2012

Full Text: Read Online (HTML) | Download PDF

Show Abstract
The results of a numerical simulation of the generation of runaway electrons in pressurized nitrogen and helium gases are presented. It was shown that runaway electrons generation occurs in two stages. In the first stage, runaway electrons are composed of the electrons emitted by the cathode and produced in gas ionization in the vicinity of the cathode. This stage is terminated with the formation of the virtual cathode, which becomes the primary source of runaway electrons in the second stage. Also, it was shown that runaway electrons current is limited by both the shielding of the field emission by the space charge of the emitted electrons and the formation of a virtual cathode. In addition, the influence of the initial conditions, such as voltage rise time and amplitude, gas pressure, and the type of gas, on the processes that accompany runaway electrons generation is presented.
Show PACS
52.80.Tn Other gas discharges
52.65.Rr Particle-in-cell method
02.60.Cb Numerical simulation; solution of equations

Effect of explosive emission on runaway electron generation

D. Levko, S. Yatom, V. Vekselman, J. Z. Gleizer, V. Tz. Gurovich, and Ya. E. Krasik

J. Appl. Phys. 111, 013304 (2012); http://dx.doi.org/10.1063/1.3676198 (7 pages) | Cited 1 time

Online Publication Date: 11 January 2012

Full Text: Read Online (HTML) | Download PDF

Show Abstract
The results of numerical simulations of the generation of runaway electrons in a nitrogen-filled coaxial diode with electron emission governed by field emission that transfers to explosive emission with a variable time delay are presented. It is shown that the time when the explosive emission turns on influences significantly the generation of runaway electrons. Namely, an explosive emission turn-on prior to the formation of the virtual cathode leads to an increase in the current amplitude of the runaway electrons and a decrease in its duration. Conversely, an explosive emission turn-on after the formation of the virtual cathode and during the high-voltage pulse rise time does not influence the generation of runaway electrons significantly. When the explosive emission turns on during the fall of the high-voltage pulse and after the virtual cathode formation, one obtains additional runaway electron generation. Finally, a comparison between electron energy distributions obtained with and without explosive emission turn-on showed that the former increases the number of electrons in the high-energy tail and the electrons’ largest energy. The comparison of both the simulated electron energy distributions with the experimentally obtained electron spectrum has shown that the best fit is obtained when the explosive emission is considered in the simulation.
Show PACS
79.70.+q Field emission, ionization, evaporation, and desorption
02.60.-x Numerical approximation and analysis

Numerical simulation of runaway electrons generation in sulfur hexafluoride

D. Levko and Ya. E. Krasik

J. Appl. Phys. 111, 013305 (2012); http://dx.doi.org/10.1063/1.3676256 (5 pages)

Online Publication Date: 12 January 2012

Full Text: Read Online (HTML) | Download PDF

Show Abstract
The results of the numerical simulation of the generation of runaway electrons in sulfur hexafluoride are presented. It is shown that the emission of the runaway electrons occurs from the cathode and its vicinity. The generation of these electrons is terminated because of the formation primarily by negative ions of a virtual cathode which causes the field emission to be screened. The simulations showed that the virtual cathode consists mainly of negative ions and cannot be an effective source of runaway electrons. In addition, the results of the simulations showed that the parameters of the runaway electrons depend on the amplitude and rise-time high-voltage pulse and gas pressure.
Show PACS
79.70.+q Field emission, ionization, evaporation, and desorption
02.60.-x Numerical approximation and analysis

Numerical simulation of the pre-ionization processes during nanosecond-pulse discharge in nitrogen

D. Levko, V. Tz. Gurovich, and Ya. E. Krasik

J. Appl. Phys. 111, 013306 (2012); http://dx.doi.org/10.1063/1.3675439 (4 pages) | Cited 1 time

Online Publication Date: 13 January 2012

Full Text: Read Online (HTML) | Download PDF

Show Abstract
The pre-ionization of nitrogen gas by high-voltage nanosecond pulse discharges is studied using one-dimensional particle-in-cell numerical simulations. The comparison between the various mechanisms of pre-ionization, i.e., by runaway electrons, x-rays, and ultraviolet radiation, is presented. It is shown that runaway electrons produce a much higher number of electron-ion pairs than those generated by x-rays, which accompany the process of runaway electron generation. Also, results of simulations showed that among photo-ionization mechanisms the most significant gas pre-ionization is caused by x-rays generated in the process of impact ionization of the K-shell of nitrogen atoms.
Show PACS
52.25.Os Emission, absorption, and scattering of electromagnetic radiation
52.80.-s Electric discharges
52.25.Jm Ionization of plasmas
52.65.Rr Particle-in-cell method
back to top Structural, Mechanical, Thermodynamic, and Optical Properties of Condensed Matter

Photoluminescence decay of direct and indirect transitions in Ge/SiGe multiple quantum wells

A. Giorgioni, E. Gatti, E. Grilli, A. Chernikov, S. Chatterjee, D. Chrastina, G. Isella, and M. Guzzi

J. Appl. Phys. 111, 013501 (2012); http://dx.doi.org/10.1063/1.3673271 (4 pages) | Cited 1 time

Online Publication Date: 3 January 2012

Full Text: Read Online (HTML) | Download PDF

Show Abstract
We present a detailed experimental study of the photoluminescence decay of direct Γ-Γ and indirect L-Γ transitions in compressively strained Ge/Si0.15Ge0.85 type I multiple quantum wells. The lifetime of the fundamental L-Γ indirect-gap related transition is in the 6 to 13 ns range at the lattice temperature of 14 K. These values are just one order of magnitude higher than those typical of type-I direct gap III-V quantum wells and are significantly shorter than those characteristic of type-II indirect gap SiGe/Si quantum wells. The measured decay times show a clear dependence on the quantum well width and lattice temperature. The decay of the Γ-Γ direct-gap related transition is dominated by the ultrafast electron scattering from Γ-type to L-type states of the conduction band.
Show PACS
78.67.De Quantum wells
68.65.-k Low-dimensional, mesoscopic, nanoscale and other related systems: structure and nonelectronic properties

Photoluminescence and secondary ion mass spectrometry investigation of unintentional doping in epitaxial germanium thin films grown on III-V compound by metal-organic chemical vapor deposition

Yu Bai (白煜), Mayank T. Bulsara, and Eugene A. Fitzgerald

J. Appl. Phys. 111, 013502 (2012); http://dx.doi.org/10.1063/1.3673538 (8 pages)

Online Publication Date: 3 January 2012

Full Text: Read Online (HTML) | Download PDF

Show Abstract
High quality epitaxial germanium (Ge) thin films grown on lattice matched and mismatched III-V compound may lead to development of new electronic and optoelectronic devices. Understanding the doping and electronic properties of these Ge thin films is the first step in this development. In this paper, we report on high-quality epitaxial Ge thin films grown on GaAs and AlAs by metal-organic chemical vapor deposition. Cross-sectional transmission electron microscopy and atomic force microscopy reveal the high structural quality of the Ge thin films. Using photoluminescence, secondary ion mass spectrometry, and spreading resistance analysis, we investigated the unintentional doping characteristics of the fabricated Ge-on-III-V thin films. We found that arsenic (n-type doping) concentration is determined by the background partial pressure of volatile As-species (e.g., As2 and As4), which incorporate into the Ge thin films via gas phase transport during the growth. Group III element (p-type doping) incorporation in the Ge thin films occurs during the growth through a surface exchange process. There exists a trade-off between Ge film structural quality and group III element “auto-doping.” III-V compound surfaces that are group III element-rich facilitate the initiation of Ge thin films with high crystalline quality and low surface roughness. However, the group-III-rich surfaces also result in high group III element (p-type doping) concentrations in the Ge thin films.
Show PACS
78.66.Db Elemental semiconductors and insulators
81.15.Gh Chemical vapor deposition (including plasma-enhanced CVD, MOCVD, ALD, etc.)
61.72.uf Ge and Si
68.55.ag Semiconductors
73.61.Cw Elemental semiconductors
78.55.Ap Elemental semiconductors

First-principles study of pressure-induced phase transition and electronic property of PbCrO3

Bao-Tian Wang, Wen Yin, Wei-Dong Li, and Fangwei Wang

J. Appl. Phys. 111, 013503 (2012); http://dx.doi.org/10.1063/1.3673865 (7 pages)

Online Publication Date: 3 January 2012

Full Text: Read Online (HTML) | Download PDF

Show Abstract
We have performed a systematic first-principles investigation to calculate the structural, electronic, and magnetic properties of PbCrO3, CrPbO3 as well as their equiproportional combination. The local density approximation (LDA) + U and the generalized gradient approximation + U theoretical formalisms have been used to account for the strong on-site Coulomb repulsion among the localized Cr 3d electrons. By choosing the Hubbard U parameter around 4 eV within LDA + U approach, ferromagnetic, and/or antiferromagnetic ground states can be achieved and our calculated volumes, bulk moduli, and equation of states for PCO-CPO in R3 phase and PCO in Pmmathm or R3c phases are in good agreement with recent experimental Phase I and Phase II [W. Xiao etal., PNAS 107, 14026 (2010)], respectively. Under pressure, phase transitions of R3 PCO-CPO to Pmmathm PCO at 1.5 GPa and R3 PCO-CPO to R3c PCO at −6.7 GPa have been predicted. The abnormally large volume and compressibility of Phase I are due to the content of CrPbO3 in the experimental sample and the transition of PbO6/2 octahedron to CrO6/2 upon compression. Our electronic structure study showed that there will occur an insulator-metal transition upon the phase transitions. Clear hybridization of Cr 3d and O 2p orbitals in wide energy range has been observed.
Show PACS
64.70.kg Semiconductors
61.66.Fn Inorganic compounds
75.50.Ee Antiferromagnetics
75.50.Dd Nonmetallic ferromagnetic materials
71.15.Mb Density functional theory, local density approximation, gradient and other corrections
71.30.+h Metal-insulator transitions and other electronic transitions

Stress tensor dependence of the polarized Raman spectrum of tetragonal barium titanate

Giuseppe Pezzotti, Keisuke Okai, and Wenliang Zhu

J. Appl. Phys. 111, 013504 (2012); http://dx.doi.org/10.1063/1.3672833 (16 pages)

Online Publication Date: 4 January 2012

Full Text: Read Online (HTML) | Download PDF

Show Abstract
The stress tensor dependence of the polarized Raman spectrum of the barium titanate (BaTiO3) tetragonal structure has been theoretically elucidated and the phonon deformation potential (PDP) constants of its A1(TO) and E(TO) vibrational modes measured by means of a spectroscopic analysis of single-crystalline samples under controlled stress fields. Two types of stress field were employed: (i) A uniaxial (compressive) stress field generated with loading along different crystallographic axes and (ii) a biaxial (tensile) stress field stored at the tip of a surface crack propagated across the a-plane of the crystal. This latter stress field enabled us unfolding the full set of PDP values for the E(TO) vibrational mode. However, the highly graded (multiaxial) stress field stored at the crack tip required both rationalizing the dependence of oblique phonons on crystal orientation and applying a spatial deconvolution routine based on the three-dimensional response of the Raman probe. According to a combination of experimental and computational procedures, we quantitatively uncoupled the effects of crystallographic orientation and spatial convolution from the locally collected Raman spectra. Uniaxial compression and biaxial tensile stress calibrations led to consistent PDP values, thus allowing the establishment of a working algorithm for stress analysis in the technologically important class of perovskitic material. Finally, as an application of the newly developed procedure, a tensor-resolved stress analysis was performed to evaluate the unknown (elastic) magnitude of the residual stress components and the extent of the plastic deformation zone generated around a Vickers indentation print in BaTiO3 single crystal. The present findings open the way to tensor resolved Raman analysis of the complex strain fields stored in advanced ferroelectric devices.
Show PACS
78.30.Hv Other nonmetallic inorganics
63.20.D- Phonon states and bands, normal modes, and phonon dispersion
81.40.Np Fatigue, corrosion fatigue, embrittlement, cracking, fracture, and failure
62.20.mt Cracks
81.40.Lm Deformation, plasticity, and creep
62.20.F- Deformation and plasticity

Laminated piezoelectric phononic crystal with imperfect interfaces

Man Lan and Peijun Wei

J. Appl. Phys. 111, 013505 (2012); http://dx.doi.org/10.1063/1.3672404 (9 pages)

Online Publication Date: 5 January 2012

Full Text: Read Online (HTML) | Download PDF

Show Abstract
Dispersive characteristics of elastic waves propagating through laminated piezoelectric phononic crystal with imperfect interfaces are studied in this paper. First, the transfer matrix method and the Bloch theorem are used to derive the dispersion equation. Next, the imperfect interfaces with the jump of mechanical quantity across interface are considered. In the spring model of imperfect interface, the tractions are continuous, but displacements are discontinuous across the interface. In the mass model of imperfect interface, displacements are continuous, but tractions are discontinuous. In the spring-mass model, both traction and displacement are discontinuous. The effect of imperfect interface is introduced by inserting an additional interface transfer matrix in the calculation of total transfer matrix. Finally, the dispersion equation is solved numerically and the dispersive curves are shown in the Brillouin zone. Band gaps of phononic crystal with imperfect interface are compared with that of phononic crystal with perfect interface. The influences of the imperfect interface on the dispersive curves and the band gaps of periodic laminated piezoelectric composite are discussed.
Show PACS
63.20.D- Phonon states and bands, normal modes, and phonon dispersion
77.65.-j Piezoelectricity and electromechanical effects
71.20.-b Electron density of states and band structure of crystalline solids
62.30.+d Mechanical and elastic waves; vibrations

Second order nonlinear properties of monoclinic single crystal BaTeMo2O9

Qingxia Yu, Zeliang Gao, Shaojun Zhang, Weiguo Zhang, Shanpeng Wang, and Xutang Tao

J. Appl. Phys. 111, 013506 (2012); http://dx.doi.org/10.1063/1.3673249 (4 pages)

Online Publication Date: 5 January 2012

Full Text: Read Online (HTML) | Download PDF

Show Abstract
The second order nonlinear optical properties of BaTeMo2O9 were studied by means of Maker fringe technology and the phase matching method. The value and relative sign of the second order nonlinear optical coefficients were obtained, with the largest being d31 = 9.88 pm/V. At 1064 nm, the crystal can support noncritical phase-matching, and the effective nonlinear coefficient is 10.3 pm/V for phase matching II at (90°, 62.8°) in the x0y plane. The relation between the second order nonlinear properties and the crystal structure is also discussed. All the results show that BaTeMo2O9 is a good candidate for nonlinear optical applications.
Show PACS
78.20.Ci Optical constants (including refractive index, complex dielectric constant, absorption, reflection and transmission coefficients, emissivity)
61.66.-f Structure of specific crystalline solids

High pressure transport, structural, and first principles investigations on the fluorite structured intermetallic, PtAl2

Alka B. Garg, P. Modak, and V. Vijayakumar

J. Appl. Phys. 111, 013507 (2012); http://dx.doi.org/10.1063/1.3673522 (5 pages)

Online Publication Date: 5 January 2012

Full Text: Read Online (HTML) | Download PDF

Show Abstract
Phase stability of intermetallic PtAl2 at high pressure and ambient temperature has been investigated using synchrotron based angle dispersive x-ray diffraction technique, electrical transport (resistance and thermoelectric power) measurements, and first principles electronic structure calculations. The electrical resistance falls approximately by 15% near 4.5 GPa. This feature is also reflected in the thermoelectric power measurements as a dip in the same pressure region. Consistent with these observations, the x-ray diffraction data show a structural phase transition from ambient cubic phase to an orthorhombic phase with a 5% volume reduction. Beyond 7.2 GPa, the diffraction peaks are broadened indicating the presence of disorder at high pressure. Ab initio structural relaxations and total energy calculations predict the cubic to orthorhombic phase transitions at 6.2 GPa.
Show PACS
62.50.-p High-pressure effects in solids and liquids
64.70.kd Metals and alloys
71.15.-m Methods of electronic structure calculations
71.20.Eh Rare earth metals and alloys
72.15.Eb Electrical and thermal conduction in crystalline metals and alloys
72.15.Jf Thermoelectric and thermomagnetic effects

Shock-induced consolidation and spallation of Cu nanopowders

L. Huang, W. Z. Han, Q. An, W. A. Goddard, III, and S. N. Luo

J. Appl. Phys. 111, 013508 (2012); http://dx.doi.org/10.1063/1.3675174 (6 pages)

Online Publication Date: 5 January 2012

Full Text: Read Online (HTML) | Download PDF

Show Abstract
A useful synthesis technique, shock synthesis of bulk nanomaterials from nanopowders, is explored here with molecular dynamics simulations. We choose nanoporous Cu (∼11 nm in grain size and 6% porosity) as a representative system, and perform consolidation and spallation simulations. The spallation simulations characterize the consolidated nanopowders in terms of spall strength and damage mechanisms. The impactor is full density Cu, and the impact velocity (ui) ranges from 0.2 to 2 km s−1. We present detailed analysis of consolidation and spallation processes, including atomic-level structure and wave propagation features. The critical values of ui are identified for the onset plasticity at the contact points (0.2 km s−1) and complete void collapse (0.5 km s−1). Void collapse involves dislocations, lattice rotation, shearing/friction, heating, and microkinetic energy. Plasticity initiated at the contact points and its propagation play a key role in void collapse at low ui, while the pronounced, grain-wise deformation may contribute as well at high ui. The grain structure gives rise to nonplanar shock response at nanometer scales. Bulk nanomaterials from ultrafine nanopowders (∼10 nm) can be synthesized with shock waves. For spallation, grain boundary (GB) or GB triple junction damage prevails, while we also observe intragranular voids as a result of GB plasticity.
Show PACS
81.16.-c Methods of micro- and nanofabrication and processing
81.07.Wx Nanopowders
62.50.Ef Shock wave effects in solids and liquids
81.05.Bx Metals, semimetals, and alloys
81.40.Lm Deformation, plasticity, and creep
62.20.fq Plasticity and superplasticity

Elastic, anelastic, and piezoelectric coefficients of GaN

N. Nakamura, H. Ogi, and M. Hirao

J. Appl. Phys. 111, 013509 (2012); http://dx.doi.org/10.1063/1.3674271 (6 pages)

Online Publication Date: 6 January 2012

Full Text: Read Online (HTML) | Download PDF

Show Abstract
We report elastic, anelastic, and piezoelectric coefficients of wurtzite GaN measured by resonant-ultrasound spectroscopy coupled with laser-Doppler interferometry. Five rectangular parallelepiped specimens, measuring 6.5 × 2.0 × 4.0 mm3, cut from two single crystals were used. Our values of elastic and piezoelectric coefficients were C11 = 359.4 GPa, C12 = 129.2 GPa, C13 = 92.0 GPa, C33 = 389.9 GPa, C44 = 98.0 GPa, e15 = 0.10 C/m2, e31 = 0.17 C/m2, and e33 = 0.29 C/m2. In anelastic coefficients, anisotropy was observed between Q11−1 and Q33−1.
Show PACS
81.40.Jj Elasticity and anelasticity, stress-strain relations
62.40.+i Anelasticity, internal friction, stress relaxation, and mechanical resonances
77.84.Bw Elements, oxides, nitrides, borides, carbides, chalcogenides, etc.
77.65.Bn Piezoelectric and electrostrictive constants
62.20.dq Other elastic constants

On the effective thermoelectric properties of layered heterogeneous medium

Y. Yang, S. H. Xie, F. Y. Ma, and J. Y. Li

J. Appl. Phys. 111, 013510 (2012); http://dx.doi.org/10.1063/1.3674279 (7 pages)

Online Publication Date: 6 January 2012

Full Text: Read Online (HTML) | Download PDF

Show Abstract
The effective thermoelectric behavior of layered heterogeneous medium is studied, with the distribution of temperature, electric potential, and heat flux solved rigorously from the governing equations, and the effective thermoelectric properties defined through an equivalency principle. It is discovered that the effective thermoelectric figure of merit of a composite medium can be higher than all of its constituents even in the absence of size and interface effects, in contrast to previous studies. This points toward a new route for high figure of merit thermoelectric materials.
Show PACS
72.20.Pa Thermoelectric and thermomagnetic effects
61.46.-w Structure of nanoscale materials
Page 1 of 6 Pages Next Page | Jump to Page
Close

Google Calendar

ADVERTISEMENT

Your Recent History Recent History Help

Recently Viewed

  1. A simple method for direct observation of the converse magnetoelectric effect in magnetic/ferroelectric composite thin films
  2. Adaptive oxide electronics: A review
  3. On the solubility of yttrium in RuO2
  4. Will we exceed 50% efficiency in photovoltaics?
  5. First-principles study of field emission from carbon nanotubes and graphene nanoribbons
Go to AIP Home
Copyright © American Institute of Physics
close