Reduction of Thermal Conductivity by Nanoscale 3D Phononic Crystal
Yang, Lina; Yang, Nuo; Li, Baowen
2013-01-01
We studied how the period length and the mass ratio affect the thermal conductivity of isotopic nanoscale three-dimensional (3D) phononic crystal of Si. Simulation results by equilibrium molecular dynamics show isotopic nanoscale 3D phononic crystals can significantly reduce the thermal conductivity of bulk Si at high temperature (1000 K), which leads to a larger ZT than unity. The thermal conductivity decreases as the period length and mass ratio increases. The phonon dispersion curves show an obvious decrease of group velocities in 3D phononic crystals. The phonon's localization and band gap is also clearly observed in spectra of normalized inverse participation ratio in nanoscale 3D phononic crystal. PMID:23378898
Reduction of thermal conductivity by nanoscale 3D phononic crystal.
Yang, Lina; Yang, Nuo; Li, Baowen
2013-01-01
We studied how the period length and the mass ratio affect the thermal conductivity of isotopic nanoscale three-dimensional (3D) phononic crystal of Si. Simulation results by equilibrium molecular dynamics show isotopic nanoscale 3D phononic crystals can significantly reduce the thermal conductivity of bulk Si at high temperature (1000 K), which leads to a larger ZT than unity. The thermal conductivity decreases as the period length and mass ratio increases. The phonon dispersion curves show an obvious decrease of group velocities in 3D phononic crystals. The phonon's localization and band gap is also clearly observed in spectra of normalized inverse participation ratio in nanoscale 3D phononic crystal. PMID:23378898
Extreme low thermal conductivity in nanoscale 3D Si phononic crystal with spherical pores.
Yang, Lina; Yang, Nuo; Li, Baowen
2014-01-01
In this work, we propose a nanoscale three-dimensional (3D) Si phononic crystal (PnC) with spherical pores, which can reduce the thermal conductivity of bulk Si by a factor up to 10,000 times at room temperature. Thermal conductivity of Si PnCs depends on the porosity, for example, the thermal conductivity of Si PnCs with porosity 50% is 300 times smaller than that of bulk Si. The phonon participation ratio spectra demonstrate that more phonons are localized as the porosity increases. The thermal conductivity is insensitive to the temperature changes from room temperature to 1100 K. The extreme-low thermal conductivity could lead to a larger value of ZT than unity as the periodic structure affects very little the electric conductivity. PMID:24559126
Harvesting vibrations via 3D phononic isolators
NASA Astrophysics Data System (ADS)
Psarobas, Ioannis E.; Yannopapas, Vassilios; Matikas, Theodore E.
2016-05-01
We report on the existence of unidirectional phononic band gaps that may span over extended regions of the Brillouin zone and can find application in trapping elastic (acoustic) waves in properly designed multilayered 3D structures. Phononic isolators operate as a result of asymmetrical wave transmission through a slab of a crystallographic phononic structure with broken mirror symmetry. Due to the use of lossless materials in the crystal, the absorption rate is dramatically enhanced when the proposed isolator is placed next to a vibrational harvesting cell. xml:lang="fr"
El-Kady, Ihab F.; Olsson, Roy H.
2012-01-10
Phononic crystals that have the ability to modify and control the thermal black body phonon distribution and the phonon component of heat transport in a solid. In particular, the thermal conductivity and heat capacity can be modified by altering the phonon density of states in a phononic crystal. The present invention is directed to phononic crystal devices and materials such as radio frequency (RF) tags powered from ambient heat, dielectrics with extremely low thermal conductivity, thermoelectric materials with a higher ratio of electrical-to-thermal conductivity, materials with phononically engineered heat capacity, phononic crystal waveguides that enable accelerated cooling, and a variety of low temperature application devices.
NASA Astrophysics Data System (ADS)
Salehi, H.; Aryadoust, M.; Shoushtari, M. Zargar
2014-07-01
In this paper, the propagation of acoustic waves in the phononic crystal of 3D with rhombohedral(I) lattice is studied theoretically. The crystal composite constituted of nickel spheres embedded in epoxy. The calculations of the band structure and density of states are performed with the plane wave expansion method in the irreducible part of Brillouin zone. In the present work, we have investigated the effect of lattice angle on the band structure and width of the band gap rhombohedral(I) lattice in the irreducible part of the first Brillouin zone and its planes separately. The results show that more than one complete band gape are formed in the four planes of the irreducible part. The most complete band gaps are formed in the (111) plane and the widest complete band gap in (443) with an angle greater than 80. So, if the sound passes through the (111) and (443) planes for the lattice angle close to 90, the crystal phononic displays the excellent insulation behavior. Moreover, in the other planes, the lattice angle does not affect on the width and the number of band gaps. Also, for the filling fraction 5 %, the widest complete band gap is formed. These results are consistent with the effect of symmetry on the band gap width, because the (111) plane has the most symmetry.
Phonon manipulation with phononic crystals.
Kim Bongsang; Hopkins, Patrick Edward; Leseman, Zayd C.; Goettler, Drew F.; Su, Mehmet F.; El-Kady, Ihab Fathy; Reinke, Charles M.; Olsson, Roy H., III
2012-01-01
In this work, we demonstrated engineered modification of propagation of thermal phonons, i.e. at THz frequencies, using phononic crystals. This work combined theoretical work at Sandia National Laboratories, the University of New Mexico, the University of Colorado Boulder, and Carnegie Mellon University; the MESA fabrication facilities at Sandia; and the microfabrication facilities at UNM to produce world-leading control of phonon propagation in silicon at frequencies up to 3 THz. These efforts culminated in a dramatic reduction in the thermal conductivity of silicon using phononic crystals by a factor of almost 30 as compared with the bulk value, and about 6 as compared with an unpatterned slab of the same thickness. This work represents a revolutionary advance in the engineering of thermoelectric materials for optimal, high-ZT performance. We have demonstrated the significant reduction of the thermal conductivity of silicon using phononic crystal structuring using MEMS-compatible fabrication techniques and in a planar platform that is amenable to integration with typical microelectronic systems. The measured reduction in thermal conductivity as compared to bulk silicon was about a factor of 20 in the cross-plane direction [26], and a factor of 6 in the in-plane direction. Since the electrical conductivity was only reduced by a corresponding factor of about 3 due to the removal of conductive material (i.e., porosity), and the Seebeck coefficient should remain constant as an intrinsic material property, this corresponds to an effective enhancement in ZT by a factor of 2. Given the number of papers in literature devoted to only a small, incremental change in ZT, the ability to boost the ZT of a material by a factor of 2 simply by reducing thermal conductivity is groundbreaking. The results in this work were obtained using silicon, a material that has benefitted from enormous interest in the microelectronics industry and that has a fairly large thermoelectric power
Phononic crystal diffraction gratings
NASA Astrophysics Data System (ADS)
Moiseyenko, Rayisa P.; Herbison, Sarah; Declercq, Nico F.; Laude, Vincent
2012-02-01
When a phononic crystal is interrogated by an external source of acoustic waves, there is necessarily a phenomenon of diffraction occurring on the external enclosing surfaces. Indeed, these external surfaces are periodic and the resulting acoustic diffraction grating has a periodicity that depends on the orientation of the phononic crystal. This work presents a combined experimental and theoretical study on the diffraction of bulk ultrasonic waves on the external surfaces of a 2D phononic crystal that consists of a triangular lattice of steel rods in a water matrix. The results of transmission experiments are compared with theoretical band structures obtained with the finite-element method. Angular spectrograms (showing frequency as a function of angle) determined from diffraction experiments are then compared with finite-element simulations of diffraction occurring on the surfaces of the crystal. The experimental results show that the diffraction that occurs on its external surfaces is highly frequency-dependent and has a definite relation with the Bloch modes of the phononic crystal. In particular, a strong influence of the presence of bandgaps and deaf bands on the diffraction efficiency is found. This observation opens perspectives for the design of efficient phononic crystal diffraction gratings.
Manipulation of Phonons with Phononic Crystals
Leseman, Zayd Chad
2015-07-09
There were three research goals associated with this project. First, was to experimentally demonstrate phonon spectrum control at THz frequencies using Phononic Crystals (PnCs), i.e. demonstrate coherent phonon scattering with PnCs. Second, was to experimentally demonstrate analog PnC circuitry components at GHz frequencies. The final research goal was to gain a fundamental understanding of phonon interaction using computational methods. As a result of this work, 7 journal papers have been published, 1 patent awarded, 14 conference presentations given, 4 conference publications, and 2 poster presentations given.
Phonon-drag thermopower in 3D Dirac semimetals.
Kubakaddi, S S
2015-11-18
A theory of low-temperature phonon-drag thermopower S(g) in three-dimensional (3D) Dirac semimetals has been developed considering screened electron-phonon deformation potential coupling. Numerical investigations of S(g), in the boundary scattering regime for phonons, are made in 3D Dirac semimetal Cd3As2, as a function of temperature T and electron concentration n e. S(g) is found to increase rapidly for about T < 1 K and nearly levels off for higher T. It is also seen that S(g) increases (decreases) with decreasing n e at lower (higher) T (<2 K). A screening effect is found to be very significant, strongly affecting T and n e dependence for about <1 K and becoming negligible at higher temperature. In the Bloch-Gruneisen (BG) regime the power laws S(g) ~ T(8) (T(4)) and S(g) ~ n(e)(-5/3)(n(e)(-1/3) with (without) screening are obtained. These laws with respect to T and n e are, respectively, characteristics of 3D phonons and Dirac 3D electrons. Comparison with diffusion thermopower S(d) shows that S (g) dominates (and is much greater than) S(d) for about T > 0.2 K. Herring's law S(g) μ p ~ T (-1), relating phonon limited mobility μ p and S(g) in the BG regime, is shown to be valid in 3D Dirac semimetals. The results obtained here are compared with those in 3D semiconductors, low-dimensional semiconductor heterojunctions and graphene. We conclude that n e-dependent measurements, rather than T-dependent ones, provide a clearer signature of the 3D Dirac semimetal phase. PMID:26490643
Phonon-drag thermopower in 3D Dirac semimetals
NASA Astrophysics Data System (ADS)
Kubakaddi, S. S.
2015-11-01
A theory of low-temperature phonon-drag thermopower S g in three-dimensional (3D) Dirac semimetals has been developed considering screened electron-phonon deformation potential coupling. Numerical investigations of S g, in the boundary scattering regime for phonons, are made in 3D Dirac semimetal Cd3As2, as a function of temperature T and electron concentration n e. S g is found to increase rapidly for about T < 1 K and nearly levels off for higher T. It is also seen that S g increases (decreases) with decreasing n e at lower (higher) T (<2 K). A screening effect is found to be very significant, strongly affecting T and n e dependence for about <1 K and becoming negligible at higher temperature. In the Bloch-Gruneisen (BG) regime the power laws S g ~ T 8 (T 4) and S g ~ n\\text{e}-5/3 (n\\text{e}-1/3) with (without) screening are obtained. These laws with respect to T and n e are, respectively, characteristics of 3D phonons and Dirac 3D electrons. Comparison with diffusion thermopower S d shows that S g dominates (and is much greater than) S d for about T > 0.2 K. Herring’s law S g μ p ~ T -1, relating phonon limited mobility μ p and S g in the BG regime, is shown to be valid in 3D Dirac semimetals. The results obtained here are compared with those in 3D semiconductors, low-dimensional semiconductor heterojunctions and graphene. We conclude that n e-dependent measurements, rather than T-dependent ones, provide a clearer signature of the 3D Dirac semimetal phase.
Tunable Topological Phononic Crystals
NASA Astrophysics Data System (ADS)
Chen, Ze-Guo; Wu, Ying
2016-05-01
Topological insulators first observed in electronic systems have inspired many analogues in photonic and phononic crystals in which remarkable one-way propagation edge states are supported by topologically nontrivial band gaps. Such band gaps can be achieved by breaking the time-reversal symmetry to lift the degeneracy associated with Dirac cones at the corners of the Brillouin zone. Here, we report on our construction of a phononic crystal exhibiting a Dirac-like cone in the Brillouin zone center. We demonstrate that simultaneously breaking the time-reversal symmetry and altering the geometric size of the unit cell result in a topological transition that we verify by the Chern number calculation and edge-mode analysis. We develop a complete model based on the tight binding to uncover the physical mechanisms of the topological transition. Both the model and numerical simulations show that the topology of the band gap is tunable by varying both the velocity field and the geometric size; such tunability may dramatically enrich the design and use of acoustic topological insulators.
A wrinkly phononic crystal slab
NASA Astrophysics Data System (ADS)
Bayat, Alireza; Gordaninejad, Faramarz
2015-03-01
The buckling induced surface instability is employed to propose a tunable phononic crystal slab composed of a stiff thin film bonded on a soft elastomer. Wrinkles formation is used to generate one-dimensional periodic scatterers at the surface of a finitely thick slab. Wrinkles' pattern change and corresponding stress is employed to control wave propagation triggered by a compressive strain. Simulation results show that the periodic wrinkly structure can be used as a transformative phononic crystal which can switch band diagram of the structure in a reversible behavior. Results of this study provide opportunities for the smart design of tunable switch and elastic wave filters at ultrasonic and hypersonic frequency ranges.
Optically rewritable 3D liquid crystal displays.
Sun, J; Srivastava, A K; Zhang, W; Wang, L; Chigrinov, V G; Kwok, H S
2014-11-01
Optically rewritable liquid crystal display (ORWLCD) is a concept based on the optically addressed bi-stable display that does not need any power to hold the image after being uploaded. Recently, the demand for the 3D image display has increased enormously. Several attempts have been made to achieve 3D image on the ORWLCD, but all of them involve high complexity for image processing on both hardware and software levels. In this Letter, we disclose a concept for the 3D-ORWLCD by dividing the given image in three parts with different optic axis. A quarter-wave plate is placed on the top of the ORWLCD to modify the emerging light from different domains of the image in different manner. Thereafter, Polaroid glasses can be used to visualize the 3D image. The 3D image can be refreshed, on the 3D-ORWLCD, in one-step with proper ORWLCD printer and image processing, and therefore, with easy image refreshing and good image quality, such displays can be applied for many applications viz. 3D bi-stable display, security elements, etc. PMID:25361316
Ultrasonic and hypersonic phononic crystals
NASA Astrophysics Data System (ADS)
Khelif, A.; Hsiao, F.-L.; Benchabane, S.; Choujaa, A.; Aoubiza, B.; Laude, V.
2008-02-01
We report on the experimental and theoretical investigation two kinds of acoustic waves in two dimensional phononic crystal: bulk acoustic waves and surface acoustic waves. For bulk acoustic waves, the work focuses on the experimental observation of full acoustic band gaps in a two-dimensional lattice of steel cylinders immersed in water as well as deaf bands that cause strong attenuation in the transmission for honeycomb and triangular lattices. For surface acoustic waves, complete acoustic band gaps found experimentally in a two-dimensional square-lattice piezoelectric phononic crystal etched in lithium niobate will be presented. Propagation in the phononic crystal is studied by direct generation and detection of surface waves using interdigital transducers. The complete band gap extends from 203 to 226 MHz, in good agreement with theoretical predictions. Near the upper edge of the complete band gap, it is observed that radiation to the bulk of the substrate dominates. This observation is explained by introducing the concept of sound line.
Molding Phonon Flow with Symmetry: Rational Design of Hypersonic Phononic Crystals
NASA Astrophysics Data System (ADS)
Koh, Cheong Yang; Thomas, Edwin L.
2009-03-01
Phononic crystals structured at appropriate length scales allow control over the flow of phonons, leading to new possibilities in applications such as heat-management, sound isolation and even energy transfer and conversion. Symmetry provides a unified framework for the interpretation 1D to 3D phononic band structures, allowing utilization of a common set of principles for designing band structures of phononic crystals as well as actual purposeful defects such as waveguide location and boundary termination in finite devices. In this work, we explore the band structure properties of phononic crystals with non-symmorphic space groups, as well as those having quasi-crystalline approximants. We demonstrate gap opening abilities from both anti-crossing and Bragg scattering, as well as unique features like ``sticking'' bands. Symmetry concepts are also powerful means to tune the density of states of the structures. Importantly, we fabricate various theoretical designs and measure their experimental dispersion diagrams for comparison with theoretical calculation. This affords an elegant approach toward a design blueprint for fabricating phononic structures for applications such as opto-acoustic coupling.
Watching surface waves in phononic crystals.
Wright, Oliver B; Matsuda, Osamu
2015-08-28
In this paper, we review results obtained by ultrafast imaging of gigahertz surface acoustic waves in surface phononic crystals with one- and two-dimensional periodicities. By use of quasi-point-source optical excitation, we show how, from a series of images that form a movie of the travelling waves, the dispersion relation of the acoustic modes, their corresponding mode patterns and the position and widths of phonon stop bands can be obtained by temporal and spatio-temporal Fourier analysis. We further demonstrate how one can follow the temporal evolution of phononic eigenstates in k-space using data from phononic-crystal waveguides as an example. PMID:26217053
Phononic crystals and elastodynamics: Some relevant points
Aravantinos-Zafiris, N.; Sigalas, M. M.; Kafesaki, M.; Economou, E. N.
2014-12-15
In the present paper we review briefly some of the first works on wave propagation in phononic crystals emphasizing the conditions for the creation of acoustic band-gaps and the role of resonances to the band-gap creation. We show that useful conclusions in the analysis of phononic band gap structures can be drawn by considering the mathematical similarities of the basic classical wave equation (Helmholtz equation) with Schrödinger equation and by employing basic solid state physics concepts and conclusions regarding electronic waves. In the second part of the paper we demonstrate the potential of phononic systems to be used as elastic metamaterials. This is done by demonstrating negative refraction in phononic crystals and subwavelength waveguiding in a linear chain of elastic inclusions, and by proposing a novel structure with close to pentamode behavior. Finally the potential of phononic structures to be used in liquid sensor applications is discussed and demonstrated.
Acoustic superfocusing by solid phononic crystals
Zhou, Xiaoming; Assouar, M. Badreddine Oudich, Mourad
2014-12-08
We propose a solid phononic crystal lens capable of acoustic superfocusing beyond the diffraction limit. The unit cell of the crystal is formed by four rigid cylinders in a hosting material with a cavity arranged in the center. Theoretical studies reveal that the solid lens produces both negative refraction to focus propagating waves and surface states to amplify evanescent waves. Numerical analyses of the superfocusing effect of the considered solid phononic lens are presented with a separated source excitation to the lens. In this case, acoustic superfocusing beyond the diffraction limit is evidenced. Compared to the fluid phononic lenses, the solid lens is more suitable for ultrasonic imaging applications.
Refraction characteristics of phononic crystals
NASA Astrophysics Data System (ADS)
Nemat-Nasser, Sia
2015-08-01
Some of the most interesting refraction properties of phononic crystals are revealed by examining the anti-plane shear waves in doubly periodic elastic composites with unit cells containing rectangular and/or elliptical multi-inclusions. The corresponding band structure, group velocity, and energy-flux vector are calculated using a powerful mixed variational method that accurately and efficiently yields all the field quantities over multiple frequency pass-bands. The background matrix and the inclusions can be anisotropic, each having distinct elastic moduli and mass densities. Equifrequency contours and energy-flux vectors are readily calculated as functions of the wave-vector components. By superimposing the energy-flux vectors on equifrequency contours in the plane of the wave-vector components, and supplementing this with a three-dimensional graph of the corresponding frequency surface, a wealth of information is extracted essentially at a glance. This way it is shown that a composite with even a simple square unit cell containing a central circular inclusion can display negative or positive energy and phase velocity refractions, or simply performs a harmonic vibration (standing wave), depending on the frequency and the wave-vector. Moreover, that the same composite when interfaced with a suitable homogeneous solid can display: (1) negative refraction with negative phase velocity refraction; (2) negative refraction with positive phase velocity refraction; (3) positive refraction with negative phase velocity refraction; (4) positive refraction with positive phase velocity refraction; or even (5) complete reflection with no energy transmission, depending on the frequency, and direction and the wavelength of the plane-wave that is incident from the homogeneous solid to the interface. For elliptical and rectangular inclusion geometries, analytical expressions are given for the key calculation quantities. Expressions for displacement, velocity, linear momentum
Two-Dimensional Phononic Crystals: Disorder Matters.
Wagner, Markus R; Graczykowski, Bartlomiej; Reparaz, Juan Sebastian; El Sachat, Alexandros; Sledzinska, Marianna; Alzina, Francesc; Sotomayor Torres, Clivia M
2016-09-14
The design and fabrication of phononic crystals (PnCs) hold the key to control the propagation of heat and sound at the nanoscale. However, there is a lack of experimental studies addressing the impact of order/disorder on the phononic properties of PnCs. Here, we present a comparative investigation of the influence of disorder on the hypersonic and thermal properties of two-dimensional PnCs. PnCs of ordered and disordered lattices are fabricated of circular holes with equal filling fractions in free-standing Si membranes. Ultrafast pump and probe spectroscopy (asynchronous optical sampling) and Raman thermometry based on a novel two-laser approach are used to study the phononic properties in the gigahertz (GHz) and terahertz (THz) regime, respectively. Finite element method simulations of the phonon dispersion relation and three-dimensional displacement fields furthermore enable the unique identification of the different hypersonic vibrations. The increase of surface roughness and the introduction of short-range disorder are shown to modify the phonon dispersion and phonon coherence in the hypersonic (GHz) range without affecting the room-temperature thermal conductivity. On the basis of these findings, we suggest a criteria for predicting phonon coherence as a function of roughness and disorder. PMID:27580163
Synthetic thermoelectric materials comprising phononic crystals
El-Kady, Ihab F; Olsson, Roy H; Hopkins, Patrick; Reinke, Charles; Kim, Bongsang
2013-08-13
Synthetic thermoelectric materials comprising phononic crystals can simultaneously have a large Seebeck coefficient, high electrical conductivity, and low thermal conductivity. Such synthetic thermoelectric materials can enable improved thermoelectric devices, such as thermoelectric generators and coolers, with improved performance. Such synthetic thermoelectric materials and devices can be fabricated using techniques that are compatible with standard microelectronics.
Understanding Crystal Populations; Looking Towards 3D Quantitative Analysis
NASA Astrophysics Data System (ADS)
Jerram, D. A.; Morgan, D. J.
2010-12-01
In order to understand volcanic systems, the potential record held within crystal populations needs to be revealed. It is becoming increasingly clear, however, that the crystal populations that arrive at the surface in volcanic eruptions are commonly mixtures of crystals, which may be representative of simple crystallization, recycling of crystals and incorporation of alien crystals. If we can quantify the true 3D population within a sample then we will be able to separate crystals with different histories and begin to interrogate the true and complex plumbing within the volcanic system. Modeling crystal populations is one area where we can investigate the best methodologies to use when dealing with sections through 3D populations. By producing known 3D shapes and sizes with virtual textures and looking at the statistics of shape and size when such populations are sectioned, we are able to gain confidence about what our 2D information is telling us about the population. We can also use this approach to test the size of population we need to analyze. 3D imaging through serial sectioning or x-ray CT, provides a complete 3D quantification of a rocks texture. Individual phases can be identified and in principle the true 3D statistics of the population can be interrogated. In practice we need to develop strategies (as with 2D-3D transformations), that enable a true characterization of the 3D data, and an understanding of the errors and pitfalls that exist. Ultimately, the reproduction of true 3D textures and the wealth of information they hold, is now within our reach.
Honeycomb phononic crystals with self-similar hierarchy
NASA Astrophysics Data System (ADS)
Mousanezhad, Davood; Babaee, Sahab; Ghosh, Ranajay; Mahdi, Elsadig; Bertoldi, Katia; Vaziri, Ashkan
2015-09-01
We highlight the effect of structural hierarchy and deformation on band structure and wave-propagation behavior of two-dimensional phononic crystals. Our results show that the topological hierarchical architecture and instability-induced pattern transformations of the structure under compression can be effectively used to tune the band gaps and directionality of phononic crystals. The work provides insights into the role of structural organization and hierarchy in regulating the dynamic behavior of phononic crystals, and opportunities for developing tunable phononic devices.
Ionizing particle detection based on phononic crystals
Aly, Arafa H. E-mail: arafa.hussien@science.bsu.edu.eg; Mehaney, Ahmed; Eissa, Mostafa F.
2015-08-14
Most conventional radiation detectors are based on electronic or photon collections. In this work, we introduce a new and novel type of ionizing particle detector based on phonon collection. Helium ion radiation treats tumors with better precision. There are nine known isotopes of helium, but only helium-3 and helium-4 are stable. Helium-4 is formed in fusion reactor technology and in enormous quantities during Big Bang nucleo-synthesis. In this study, we introduce a technique for helium-4 ion detection (sensing) based on the innovative properties of the new composite materials known as phononic crystals (PnCs). PnCs can provide an easy and cheap technique for ion detection compared with conventional methods. PnC structures commonly consist of a periodic array of two or more materials with different elastic properties. The two materials are polymethyl-methacrylate and polyethylene polymers. The calculations showed that the energies lost to target phonons are maximized at 1 keV helium-4 ion energy. There is a correlation between the total phonon energies and the transmittance of PnC structures. The maximum transmission for phonons due to the passage of helium-4 ions was found in the case of making polyethylene as a first layer in the PnC structure. Therefore, the concept of ion detection based on PnC structure is achievable.
Ionizing particle detection based on phononic crystals
NASA Astrophysics Data System (ADS)
Aly, Arafa H.; Mehaney, Ahmed; Eissa, Mostafa F.
2015-08-01
Most conventional radiation detectors are based on electronic or photon collections. In this work, we introduce a new and novel type of ionizing particle detector based on phonon collection. Helium ion radiation treats tumors with better precision. There are nine known isotopes of helium, but only helium-3 and helium-4 are stable. Helium-4 is formed in fusion reactor technology and in enormous quantities during Big Bang nucleo-synthesis. In this study, we introduce a technique for helium-4 ion detection (sensing) based on the innovative properties of the new composite materials known as phononic crystals (PnCs). PnCs can provide an easy and cheap technique for ion detection compared with conventional methods. PnC structures commonly consist of a periodic array of two or more materials with different elastic properties. The two materials are polymethyl-methacrylate and polyethylene polymers. The calculations showed that the energies lost to target phonons are maximized at 1 keV helium-4 ion energy. There is a correlation between the total phonon energies and the transmittance of PnC structures. The maximum transmission for phonons due to the passage of helium-4 ions was found in the case of making polyethylene as a first layer in the PnC structure. Therefore, the concept of ion detection based on PnC structure is achievable.
Phononic subsurface: Flow stabilization by crystals
NASA Astrophysics Data System (ADS)
Hussein, Mahmoud I.; Biringen, Sedat; Bilal, Osama R.; Kucala, Alec
2015-11-01
Flow control is a century-old problem where the goal is to alter a flow's natural state to achieve improved performance, such as delay of laminar-to-turbulent transition or reduction of drag in a fully developed turbulent flow. Meeting this goal promises to significantly reduce the dependence on fossil fuels for global transport. In this work, we show that phonon motion underneath a surface interacting with a flow may be tuned to cause the flow to stabilize, or destabilize, as desired. This concept is demonstrated by simulating a fully developed plane Poiseuille (channel) flow whereby a small portion of an otherwise rigid wall is replaced with a one-dimensional phononic crystal. A Tollmien-Schlichting (TS) wave is introduced to the flow as an evolving disturbance. Upon tuning the frequency-dependent phase and amplitude relations of the surface of the phononic crystal that interfaces with the flow, the TS wave is shown to stabilize, or destabilize, as needed. A theory of subsurface phonons is presented that provides an accurate prediction of this behavior without the need for a flow simulation. This represents an unprecedented capability to passively synchronize wave propagation across a fluid-structure interface and achieve favorable, and predictable, alterations to the flow properties. National Science Foundation, Grant No. 1131802.
Tunable magneto-granular phononic crystals
NASA Astrophysics Data System (ADS)
Allein, F.; Tournat, V.; Gusev, V. E.; Theocharis, G.
2016-04-01
This paper reports on the study of the dynamics of 1D magneto-granular phononic crystals composed of a chain of spherical steel beads inside a properly designed magnetic field. This field is induced by an array of permanent magnets, located in a holder at a given distance from the chain. The theoretical and experimental results of the band gap structure are displayed, including all six degrees of freedom for the beads, i.e., three translations and three rotations. Experimental evidence of transverse-rotational modes of propagation is presented; moreover, by changing the strength of the magnetic field, the dynamic response of the granular chain is tuned. The combination of non-contact tunability with the potentially strong nonlinear behavior of granular systems ensures the suitability of magneto-granular phononic crystals as nonlinear, tunable mechanical metamaterials for use in controlling elastic wave propagation.
Registration of 3-D holograms of diamond crystals (Abstract Only)
NASA Astrophysics Data System (ADS)
Marchenko, S. N.; Smirnova, S. N.
1991-02-01
Registration of 3D ho1orarns broadens the possibility of using single-crystal tool for imagining and investigating inner inhomogeneities and dynamic stresses in top area of gem diamond, study of which by other techniques,e.g. polarization optics, is difficult or impossible. The difficulty is that the diamond with significant refractive index of 2.42 has comparatively small angle of total internal reflection of 24°50. As a result, with random illumination of the tops of octahedron diamond crystals, both smooth- faceted and with polycentric facets, illuminating light is successively reflected from different farets and absorbed in the crystal or comes out of it in a spot and direction that are difficult to calculate. Optimal schemes of illuminating crystals for recording 3D holograms of smooth faceted octahedron diamonds are given. Analysis of illumination of the crystal with polycentric facets shows that correction of light in the diamond is determined by directivity diagram the width of which depends in inhomogeneity size of the diamond. 3D holograms of diamonds with different reflectivity were produced. For the first time the possibility is shown for registration of holograms for studying stresses in diamond top using single-crystal tool.
Phonon heat conduction in layered anisotropic crystals
NASA Astrophysics Data System (ADS)
Minnich, A. J.
2015-02-01
The thermal properties of anisotropic crystals are of both fundamental and practical interest, but transport phenomena in anisotropic materials such as graphite remain poorly understood because solutions of the Boltzmann equation often assume isotropy. Here, we extend an analytic solution of the transient, frequency-dependent Boltzmann equation to highly anisotropic solids and examine its predictions for graphite. We show that this simple model predicts key results, such as long c -axis phonon mean free paths and a negative correlation of cross-plane thermal conductivity with in-plane group velocity, that were previously observed with computationally expensive molecular-dynamics simulations. Further, using our analytic solution, we demonstrate a method to reconstruct the anisotropic mean free path spectrum of crystals with arbitrary dispersion relations without any prior knowledge of their harmonic or anharmonic properties using observations of quasiballistic heat conduction. These results provide a useful analytic framework to understand thermal transport in anisotropic crystals.
Engineering thermal conductance using a two-dimensional phononic crystal
Zen, Nobuyuki; Puurtinen, Tuomas A.; Isotalo, Tero J.; Chaudhuri, Saumyadip; Maasilta, Ilari J.
2014-01-01
Controlling thermal transport has become relevant in recent years. Traditionally, this control has been achieved by tuning the scattering of phonons by including various types of scattering centres in the material (nanoparticles, impurities, etc). Here we take another approach and demonstrate that one can also use coherent band structure effects to control phonon thermal conductance, with the help of periodically nanostructured phononic crystals. We perform the experiments at low temperatures below 1 K, which not only leads to negligible bulk phonon scattering, but also increases the wavelength of the dominant thermal phonons by more than two orders of magnitude compared to room temperature. Thus, phononic crystals with lattice constants ≥1 μm are shown to strongly reduce the thermal conduction. The observed effect is in quantitative agreement with the theoretical calculation presented, which accurately determined the ballistic thermal conductance in a phononic crystal device. PMID:24647049
3D plasmonic crystal metamaterials for ultra-sensitive biosensing.
Aristov, Andrey I; Manousidaki, Maria; Danilov, Artem; Terzaki, Konstantina; Fotakis, Costas; Farsari, Maria; Kabashin, Andrei V
2016-01-01
We explore the excitation of plasmons in 3D plasmon crystal metamaterials and report the observation of a delocalized plasmon mode, which provides extremely high spectral sensitivity (>2600 nm per refractive index unit (RIU) change), outperforming all plasmonic counterparts excited in 2D nanoscale geometries, as well as a prominent phase-sensitive response (>3*10(4) deg. of phase per RIU). Combined with a large surface for bioimmobilization provided by the 3D matrix, the proposed sensor architecture promises a new important landmark in the advancement of plasmonic biosensing technology. PMID:27151104
3D plasmonic crystal metamaterials for ultra-sensitive biosensing
NASA Astrophysics Data System (ADS)
Aristov, Andrey I.; Manousidaki, Maria; Danilov, Artem; Terzaki, Konstantina; Fotakis, Costas; Farsari, Maria; Kabashin, Andrei V.
2016-05-01
We explore the excitation of plasmons in 3D plasmon crystal metamaterials and report the observation of a delocalized plasmon mode, which provides extremely high spectral sensitivity (>2600 nm per refractive index unit (RIU) change), outperforming all plasmonic counterparts excited in 2D nanoscale geometries, as well as a prominent phase-sensitive response (>3*104 deg. of phase per RIU). Combined with a large surface for bioimmobilization provided by the 3D matrix, the proposed sensor architecture promises a new important landmark in the advancement of plasmonic biosensing technology.
3D plasmonic crystal metamaterials for ultra-sensitive biosensing
Aristov, Andrey I.; Manousidaki, Maria; Danilov, Artem; Terzaki, Konstantina; Fotakis, Costas; Farsari, Maria; Kabashin, Andrei V.
2016-01-01
We explore the excitation of plasmons in 3D plasmon crystal metamaterials and report the observation of a delocalized plasmon mode, which provides extremely high spectral sensitivity (>2600 nm per refractive index unit (RIU) change), outperforming all plasmonic counterparts excited in 2D nanoscale geometries, as well as a prominent phase-sensitive response (>3*104 deg. of phase per RIU). Combined with a large surface for bioimmobilization provided by the 3D matrix, the proposed sensor architecture promises a new important landmark in the advancement of plasmonic biosensing technology. PMID:27151104
Yudistira, D; Boes, A; Djafari-Rouhani, B; Pennec, Y; Yeo, L Y; Mitchell, A; Friend, J R
2014-11-21
We theoretically and experimentally demonstrate the existence of complete surface acoustic wave band gaps in surface phonon-polariton phononic crystals, in a completely monolithic structure formed from a two-dimensional honeycomb array of hexagonal shape domain-inverted inclusions in single crystal piezoelectric Z-cut lithium niobate. The band gaps appear at a frequency of about twice the Bragg band gap at the center of the Brillouin zone, formed through phonon-polariton coupling. The structure is mechanically, electromagnetically, and topographically homogeneous, without any physical alteration of the surface, offering an ideal platform for many acoustic wave applications for photonics, phononics, and microfluidics. PMID:25479504
3D holographic polymer photonic crystal for superprism application
NASA Astrophysics Data System (ADS)
Chen, Jiaqi; Jiang, Wei; Chen, Xiaonan; Wang, Li; Zhang, Sasa; Chen, Ray T.
2007-02-01
Photonic crystal based superprism offers a new way to design new optical components for beam steering and DWDM application. 3D photonic crystals are especially attractive as they could offer more control of the light beam based on the needs. A polygonal prism based holographic fabrication method has been demonstrated for a three-dimensional face-centered-cubic (FCC)-type submicron polymer photonic crystal using SU8 as the photo-sensitive material. Therefore antivibration equipment and complicated optical alignment system are not needed and the requirement for the coherence of the laser source is relaxed compared with the traditional holographic setup. By changing the top-cut prism structure, the polarization of the laser beam, the exposure and development conditions we can achieve different kinds of triclinic or orthorhombic photonic crystals on demand. Special fabrication treatments have been introduced to ensure the survivability of the fabricated large area (cm2) nano-structures. Scanning electron microscopy and diffraction results proved the good uniformity of the fabricated structures. With the proper design of the refraction prism we have achieved a partial bandgap for S+C band (1460-1565nm) in the [111] direction. The transmission and reflection spectra obtained by Fourier transform infrared spectroscopy (FTIR) are in good agreement with simulated band structure. The superprism effects around 1550nm wavelength for the fabricated 3D polymer photonic crystal have been theoretically calculated and such effects can be used for beam steering purpose.
Melting of Temperature-Sensitive 3D Colloidal Crystals
NASA Astrophysics Data System (ADS)
Alsayed, Ahmed; Han, Yilong; Yodh, Arjun
2006-03-01
We employ thermally responsive monodisperse microgel colloidal spheres to study the melting mechanisms of colloidal crystals [1]. The particle diameter decreases with increasing temperature and leads to volume fraction changes that drive phase-transitions. We will describe observations of a variety of phenomena. Premelting, the localized loss of crystalline order near defects (e.g. grain boundaries) at volume fractions above the bulk melting transition, is directly observed by video microscopy, and is characterized by monitoring the first peak position of the particle pair correlation function. We find the position of the first peak shifts toward smaller particle separations at the onset of premelting. After Delaunay triangulation, mean square rotational and translational fluctuations of bonds were measured close to and away from defects. The behavior of all such quantities exhibits increased disorder near the defects. By locally heating the material within a crystal domain, we also studied the superheating and melting of a perfect 3D crystal. Finally, the introduction of weak attractions between spheres reveals free-floating 3D crystal `blobs' which can be made to melt and recrystallize by tuning the temperature. [1] A. M. Alsayed, M. F. Islam, J. Zhang, P. J. Collings, A. G. Yodh, Science 309, 1207 (2005). This work was supported by grants from NSF (DMR-0505048 and MRSEC DMR05-20020) and NASA (NAG8-2172).
Hexagonal liquid crystal lens array for 3D endoscopy.
Hassanfiroozi, Amir; Huang, Yi-Pai; Javidi, Bahram; Shieh, Han-Ping D
2015-01-26
A liquid crystal lens array with a hexagonal arrangement is investigated experimentally. The uniqueness of this study exists in the fact that using convex-ring electrode provides a smooth and controllable applied potential profile across the aperture to manage the phase profile. We observed considerable differences between flat electrode and convex-ring electrode; in particular the lens focal length is variable in a wider range from 2.5cm to infinity. This study presents several noteworthy characteristics such as low driving voltage; 30 μm cell gap and the lens is electrically switchable between 2D/3D modes. We demonstrate a hexagonal LC-lens array for capturing 3D images by using single sensor using integral imaging. PMID:25835856
Large Area Printing of 3D Photonic Crystals
NASA Astrophysics Data System (ADS)
Watkins, James J.; Beaulieu, Michael R.; Hendricks, Nicholas R.; Kothari, Rohit
2014-03-01
We have developed a readily scalable print, lift, and stack approach for producing large area, 3D photonic crystal (PC) structures. UV-assisted nanoimprint lithography (UV-NIL) was used to pattern grating structures comprised of highly filled nanoparticle polymer composite resists with tune-able refractive indices (RI). The gratings were robust and upon release from a support substrate were oriented and stacked to yield 3D PCs. The RI of the composite resists was tuned between 1.58 and 1.92 at 800 nm while maintaining excellent optical transparency. The grating structure dimensions, line width, depth, and pitch, were easily varied by simply changing the imprint mold. For example, a 6 layer log-pile stack was prepared using a composite resist a RI of 1.72 yielding 72 % reflection at 900 nm. The process is scalable for roll-to-roll (R2R) production. Center for Hierarchical Manufacturing - an NSF Nanoscale Science and Engineering Center.
Remarkable reduction of thermal conductivity in phosphorene phononic crystal
NASA Astrophysics Data System (ADS)
Xu, Wen; Zhang, Gang
2016-05-01
Phosphorene has received much attention due to its interesting physical and chemical properties, and its potential applications such as thermoelectricity. In thermoelectric applications, low thermal conductivity is essential for achieving a high figure of merit. In this work, we propose to reduce the thermal conductivity of phosphorene by adopting the phononic crystal structure, phosphorene nanomesh. With equilibrium molecular dynamics simulations, we find that the thermal conductivity is remarkably reduced in the phononic crystal. Our analysis shows that the reduction is due to the depressed phonon group velocities induced by Brillouin zone folding, and the reduced phonon lifetimes in the phononic crystal. Interestingly, it is found that the anisotropy ratio of thermal conductivity could be tuned by the ‘non-square’ pores in the phononic crystal, as the phonon group velocities in the direction with larger projection of pores is more severely suppressed, leading to greater reduction of thermal conductivity in this direction. Our work provides deep insight into thermal transport in phononic crystals and proposes a new strategy to reduce the thermal conductivity of monolayer phosphorene.
Remarkable reduction of thermal conductivity in phosphorene phononic crystal.
Xu, Wen; Zhang, Gang
2016-05-01
Phosphorene has received much attention due to its interesting physical and chemical properties, and its potential applications such as thermoelectricity. In thermoelectric applications, low thermal conductivity is essential for achieving a high figure of merit. In this work, we propose to reduce the thermal conductivity of phosphorene by adopting the phononic crystal structure, phosphorene nanomesh. With equilibrium molecular dynamics simulations, we find that the thermal conductivity is remarkably reduced in the phononic crystal. Our analysis shows that the reduction is due to the depressed phonon group velocities induced by Brillouin zone folding, and the reduced phonon lifetimes in the phononic crystal. Interestingly, it is found that the anisotropy ratio of thermal conductivity could be tuned by the 'non-square' pores in the phononic crystal, as the phonon group velocities in the direction with larger projection of pores is more severely suppressed, leading to greater reduction of thermal conductivity in this direction. Our work provides deep insight into thermal transport in phononic crystals and proposes a new strategy to reduce the thermal conductivity of monolayer phosphorene. PMID:27033566
Broadband sound blocking in phononic crystals with rotationally symmetric inclusions.
Lee, Joong Seok; Yoo, Sungmin; Ahn, Young Kwan; Kim, Yoon Young
2015-09-01
This paper investigates the feasibility of broadband sound blocking with rotationally symmetric extensible inclusions introduced in phononic crystals. By varying the size of four equally shaped inclusions gradually, the phononic crystal experiences remarkable changes in its band-stop properties, such as shifting/widening of multiple Bragg bandgaps and evolution to resonance gaps. Necessary extensions of the inclusions to block sound effectively can be determined for given incident frequencies by evaluating power transmission characteristics. By arraying finite dissimilar unit cells, the resulting phononic crystal exhibits broadband sound blocking from combinational effects of multiple Bragg scattering and local resonances even with small-numbered cells. PMID:26428816
Finite element analysis of surface modes in phononic crystal waveguides
NASA Astrophysics Data System (ADS)
Guo, Yuning; Schubert, Martin; Dekorsy, Thomas
2016-03-01
The study of surface modes in phononic crystal waveguides in the hypersonic regime is a burgeoning field with a large number of possible applications. By using the finite element method, the band structure and the corresponding transmission spectrum of surface acoustic waves in phononic crystal waveguides generated by line defects in a silicon pillar-substrate system were calculated and investigated. The bandgaps are caused by the hybridization effect of band branches induced by local resonances and propagating modes in the substrate. By changing the sizes of selected pillars in the phononic crystal waveguides, the corresponding bands shift and localized modes emerge due to the local resonance effect induced by the pillars. This effect offers further possibilities for tailoring the propagation and filtering of elastic waves. The presented results have implications for the engineering of phonon dynamics in phononic nanostructures.
Low Frequency Thermal Conductivity in Micro Phononic Crystals
NASA Astrophysics Data System (ADS)
Anjos, Virgilio; Arantes, Alison
2015-03-01
We study theoretically the cumulative thermal conductivity of a micro phononic crystal at low temperature regime. The phononic crystal considered presents carbon microtubes inclusions arranged periodically in a two-dimensional square lattice embebed in soft elastic matrix. Moderate and high impedance mismatch are considered concerning the material composition. The low frequency phonon spectra (up to tens of GHz) are obtained solving the generalized wave equation for inhomogeneous media within the Plane Wave Expansion method. We consider low temperatures in order to increase the participation of GHz thermal phonons. We observed suppression in the cumulative thermal conductivity at the band gap region and thus a reduction of thermal conductivity of the phononic crystal when compared with the bulk matrix. The authors would like to thank the Brazilian agencies, National Council of Technological and Scientific Development (CNPq), Foundation for Research Support of Minas Gerais (FAPEMIG) and CAPES for their support.
NASA Astrophysics Data System (ADS)
Maasilta, I. J.; Puurtinen, T. A.; Tian, Y.; Geng, Z.
2016-07-01
We discuss two alternative and complementary means of controlling radial phonon conduction for bolometers in two dimensions: by using phononic crystals or by roughening the surface of the membranes (Casimir limit). For phononic crystals, we present new experiments with a modified geometry and a larger hole periodicity than before, achieving a low thermal conductance {˜ }2 pW/K at 150 mK. Calculations in the Casimir limit, on the other hand, show that for small detector dimensions thermal conductance below 1 fW/K seems achievable.
Investigating the existence of coherent phonon scattering in silicon using phononic crystals
NASA Astrophysics Data System (ADS)
Goettler, Drew
In silicon the majority of heat energy is transported by phonons, which are discrete lattice vibrations. Phonon scattering due to the presence of voids in silicon can further alter the material's thermal conductivity. There is a question about the possibility of some of this scattering being coherent rather than purely incoherent. Coherent phonon scattering is defined as constructive interference of phonons scattered from the inclusions in the phononic crystal. The intent of this work is to investigate the existence of coherent scattering in Si via phononic crystals. A phononic crystal is a periodic array of inclusions inside a host material. The inclusions could be a second material or a void. In this work five different supercell phononic crystals comprised of holes in silicon will be used to investigate the existence of coherent phonon scattering. Each of the supercells had nearly identical critical lengths in order to keep the amount of incoherent scattering equal among all of the PnCs. Porosity differences among the supercells were also minimized. All of the PnCs were fabricated with a focused ion beam (FIB). During fabrication a protective layer of Ti was used to protect the Si from unintentional Ga doping from the FIB. The Ti layer also helped generate voids with more vertical sidewalls. A set of experiments was performed to measure the thermal conductivity of each PnC. Thermal conductivity measurements were carried out on a silicon nitride suspended island platform with platinum resistance temperature detectors and coated with aluminum nitride. A silicon slab was concurrently measured with each PnC, and relative thermal conductivity values were determined. The addition of the PnC decreased Si's thermal conductivity to less than 22% of its original value. An analysis of the results shows there is a reduction in thermal conductivity beyond the effects of porosity and incoherent scattering. This enhanced reduction in thermal conductivity is due to coherent
3D crack tip fields for FCC single crystals
Cuitino, A.M.; Ortiz, M.
1995-12-31
Cracks in single crystals are of concern in a number of structural and non-structural applications, ranging form single-crystal turbine blades and rotors to metal interconnect lines in microcircuits. In this paper we present 3D numerical simulations of the crack-tip fields of a Cu single crystal, including stress, strain and slip activity patterns. The orientation of the crack tip is along the crystallographic orientation (101), while the crack plane is (010). A material model based on dislocation mechanics is used in these simulations. This model correctly predicts the observed behavior of Cu, including the basic hardening characteristics of single crystals, orientation dependence and stage I-II-III structure of the stress-strain curves, the observed levels of latent hardening and their variation with orientation and deformation in the primary system and slip activities and dislocation densities. We use the FEM within the context of finite deformation plasticity. In the figure below, we show the finite element mesh composed by 12-noded tetrahedrons with 6-noded triangular faces. The model simulates half of a beam, which is subjected to a concentrated load at 1/8 of total length from the support. Detailed results of the stress, deformation and slip activity are presented at different radii from crack tip and at different depths from the surface. In general, the results show a strong difference in the slip activity pattern form the interior to the exterior, while smaller differences are encountered in the stress and strain fields.
Phononic Crystal Waveguiding in GaAs
NASA Astrophysics Data System (ADS)
Azodi Aval, Golnaz
Compared to the much more common photonic crystals that are used to manipulate light, phononic crystals (PnCs) with inclusions in a lattice can be used to manipulate sound. While trying to propagate in a periodically structured media, acoustic waves may experience geometries in which propagation forward is totally forbidden. Furthermore, defects in the periodicity can be used to confine acoustic waves to follow complicated routes on a wavelength scale. Using advanced fabrication methods, we aim to implement these structures to control surface acoustic wave (SAW) propagation on the piezoelectric surface and eventually interact SAWs with quantum structures. To investigate the interaction of SAWs with periodic elastic structures, SAW interdigital transducers (IDTs) and PnC fabrication procedures were developed. GaAs is chosen as a piezoelectric substrate for SAWs propagation. Lift-off photolithography processes were used to fabricate IDTs with finger widths as low as 1.5 microns. PnCs are periodic structures of shallow air holes created in GaAs substrate by means of a wet-etching process. The PnCs are square lattices with lattice constants of 8 and 4 microns. To predict the behavior of a SAW when interacting with the PnC structures, an FDTD simulator was used to calculate the band structures and SAW wave displacement on the crystal surface. The bandgap (BG) predicted for the 8 micron crystal ranges from 180 MHz to 220 MHz. Simulations show a shift in the BG position for 4 microns crystals ranging from 391 to 439 MHz. Two main waveguide geometries were considered in this work: a simple line waveguide and a funneling entrance line waveguide. Simulations indicated an increase in acoustic power density for the funneling waveguides. Fabricated device evaluated with electrical measurements. In addition, a scanning Sagnac interferometer is used to map the energy density of the SAWs. The Sagnac interferometer is designed to measure the outward displacement of a surface due to
Phononic Crystal Tunable via Ferroelectric Phase Transition
NASA Astrophysics Data System (ADS)
Xu, Chaowei; Cai, Feiyan; Xie, Shuhong; Li, Fei; Sun, Rong; Fu, Xianzhu; Xiong, Rengen; Zhang, Yi; Zheng, Hairong; Li, Jiangyu
2015-09-01
Phononic crystals (PCs) consisting of periodic materials with different acoustic properties have potential applications in functional devices. To realize more smart functions, it is desirable to actively control the properties of PCs on demand, ideally within the same fabricated system. Here, we report a tunable PC made of Ba0.7Sr0.3Ti O3 (BST) ceramics, wherein a 20-K temperature change near room temperature results in a 20% frequency shift in the transmission spectra induced by a ferroelectric phase transition. The tunability phenomenon is attributed to the structure-induced resonant excitation of A0 and A1 Lamb modes that exist intrinsically in the uniform BST plate, while these Lamb modes are sensitive to the elastic properties of the plate and can be modulated by temperature in a BST plate around the Curie temperature. The study finds opportunities for creating tunable PCs and enables smart temperature-tuned devices such as the Lamb wave filter or sensor.
Sharp bends of phononic crystal surface modes
NASA Astrophysics Data System (ADS)
Cicek, Ahmet; Salman, Aysevil; Adem Kaya, Olgun; Ulug, Bulent
2015-12-01
Sharp bending of surface waves at the interface of a two-dimensional phononic crystal (PnC) of steel cylinders in air and the method of using a diagonally offset cylindrical scatterer are numerically demonstrated by finite-element method simulations. The radii of the diagonally offset scatterer and the cylinder at the PnC corner, along with the distance between them, are treated as optimization parameters in the genetic algorithm optimization of sharp bends. Surface wave transmittance of at most 5% for the unmodified sharp bend is significantly enhanced to approximately 75% as a result of optimization. A series of transmittance peaks whose maxima increase exponentially, as their widths reduce, with increasing frequency is observed for the optimized sharp bend. The transmittance peaks appear at frequencies corresponding to integer plus half-beat periods, depending on the finite surface length. The optimal parameters are such that the cylinder radius at the PnC corner is not significantly modified, whereas a diagonally offset scatterer having a diameter of almost two periods and a shortest distance of about 0.7 periods between them is required for the strongest transmittance peak. Utilization of PnC surface sharp bends as acoustic ring resonators is demonstrated.
The phononic crystals: An unending quest for tailoring acoustics
NASA Astrophysics Data System (ADS)
Kushwaha, Manvir S.
2016-07-01
Periodicity (in time or space) is a part and parcel of every living being: one can see, hear and feel it. Everyday examples are locomotion, respiration and heart beat. The reinforced N-dimensional periodicity over two or more crystalline solids results in the so-called phononic band gap crystals. These can have dramatic consequences on the propagation of phonons, vibrations and sound. The fundamental physics of cleverly fabricated phononic crystals can offer a systematic route to realize the Anderson localization of sound and vibrations. As to the applications, the phononic crystals are envisaged to find ways in the architecture, acoustic waveguides, designing transducers, elastic/acoustic filters, noise control, ultrasonics, medical imaging and acoustic cloaking, to mention a few. This review focuses on the brief sketch of the progress made in the field that seems to have prospered even more than was originally imagined in the early nineties.
Evolution of molecular crystal optical phonons near structural phase transitions
NASA Astrophysics Data System (ADS)
Michki, Nigel; Niessen, Katherine; Xu, Mengyang; Markelz, Andrea
Molecular crystals are increasingly important photonic and electronic materials. For example organic semiconductors are lightweight compared to inorganic semiconductors and have inexpensive scale up processing with roll to roll printing. However their implementation is limited by their environmental sensitivity, in part arising from the weak intermolecular interactions of the crystal. These weak interactions result in optical phonons in the terahertz frequency range. We examine the evolution of intermolecular interactions near structural phase transitions by measuring the optical phonons as a function of temperature and crystal orientation using terahertz time-domain spectroscopy. The measured orientation dependence of the resonances provides an additional constraint for comparison of the observed spectra with the density functional calculations, enabling us to follow specific phonon modes. We observe crystal reorganization near 350 K for oxalic acid as it transforms from dihydrate to anhydrous form. We also report the first THz spectra for the molecular crystal fructose through its melting point.
One-dimensional hypersonic phononic crystals.
Gomopoulos, N; Maschke, D; Koh, C Y; Thomas, E L; Tremel, W; Butt, H-J; Fytas, G
2010-03-10
We report experimental observation of a normal incidence phononic band gap in one-dimensional periodic (SiO(2)/poly(methyl methacrylate)) multilayer film at gigahertz frequencies using Brillouin spectroscopy. The band gap to midgap ratio of 0.30 occurs for elastic wave propagation along the periodicity direction, whereas for inplane propagation the system displays an effective medium behavior. The phononic properties are well captured by numerical simulations. The porosity in the silica layers presents a structural scaffold for the introduction of secondary active media for potential coupling between phonons and other excitations, such as photons and electrons. PMID:20141118
Phononic crystals of spherical particles: A tight binding approach
Mattarelli, M.; Secchi, M.; Dipartimento di Fisica, Università di Trento, Via Sommarive 14, 38123 Trento ; Montagna, M.
2013-11-07
The vibrational dynamics of a fcc phononic crystal of spheres is studied and compared with that of a single free sphere, modelled either by a continuous homogeneous medium or by a finite cluster of atoms. For weak interaction among the spheres, the vibrational dynamics of the phononic crystal is described by shallow bands, with low degree of dispersion, corresponding to the acoustic spheroidal and torsional modes of the single sphere. The phonon displacements are therefore related to the vibrations of a sphere, as the electron wave functions in a crystal are related to the atomic wave functions in a tight binding model. Important dispersion is found for the two lowest phonon bands, which correspond to zero frequency free translation and rotation of a free sphere. Brillouin scattering spectra are calculated at some values of the exchanged wavevectors of the light, and compared with those of a single sphere. With weak interaction between particles, given the high acoustic impedance mismatch in dry systems, the density of phonon states consist of sharp bands separated by large gaps, which can be well accounted for by a single particle model. Based on the width of the frequency gaps, tunable with the particle size, and on the small number of dispersive acoustic phonons, such systems may provide excellent materials for application as sound or heat filters.
Thermal energy transport in a surface phonon-polariton crystal
NASA Astrophysics Data System (ADS)
Ordonez-Miranda, Jose; Tranchant, Laurent; Joulain, Karl; Ezzahri, Younes; Drevillon, Jérémie; Volz, Sebastian
2016-01-01
We demonstrate that the energy transport of surface phonon polaritons can efficiently be observed in a crystal made up of a three-dimensional assembly of spheroidal nanoparticles of silicon carbide. The ultralow phonon thermal conductivity of this nanostructure, along with its high surface area-to-volume ratio, allows the predominance of the polariton energy over that generated by phonons. The polariton dispersion relation, propagation length, and thermal conductance are numerically determined as functions of the size, shape, and temperature of the nanoparticles. It is shown that the thermal conductance of a crystal with prolate nanoparticles at 500 K and a minor (major) axis of 50 nm (5 μ m ) is 0.5 nW K-1 , which is comparable to the quantum of thermal conductance of polar nanowires. We also show that a nanoparticle size dispersion of up to 200 nm does not change significantly the polariton energy, which supports the technological feasibility of the proposed crystal.
Bulk phonon scattering in perturbed quasi-3D multichannel crystallographic waveguide.
Rabia, M S
2008-11-19
In the present paper, we concentrate on the influence of local defects on scattering properties of elastic waves in perturbed crystalline quasi-three-dimensional nanostructures in the harmonic approximation. Our model consists of three infinite atomic planes, assimilated into a perfect waveguide in which different distributions of scatterers (or defects) are inserted in the bulk. We have investigated phonon transmission and conductance for three bulk defect configurations. The numerical treatment of the problem, based on the Landauer approach, resorts to the matching method initially employed for the study of surface localized phonons and resonances. We present a detailed study of the defect-induced fluctuations in the transmission spectra. These fluctuations can be related to Fano resonances and Fabry-Pérot oscillations. The first is due to the coupling between localized defect states and the perfect waveguide propagating modes whereas the latter results from the interference between incidental and reflected waves. Numerical results reveal the intimate relation between transmission spectra and localized impurity states and provide a basis for the understanding of conductance spectroscopy experiments in disordered mesoscopic systems. PMID:21693856
Phonon-enhanced crystal growth and lattice healing
Buonassisi, Anthony; Bertoni, Mariana; Newman, Bonna
2013-05-28
A system for modifying dislocation distributions in semiconductor materials is provided. The system includes one or more vibrational sources for producing at least one excitation of vibrational mode having phonon frequencies so as to enhance dislocation motion through a crystal lattice.
NASA Astrophysics Data System (ADS)
Iyer, Srikanth S.; Candler, Robert N.
2016-03-01
In this work, we determine the intrinsic mechanical energy dissipation limit for single-crystal resonators due to anharmonic phonon-phonon scattering in the Akhiezer (Ω τ ≪1 ) regime. The energy loss is derived using perturbation theory and the linearized Boltzmann transport equation for phonons, and includes the direction- and polarization-dependent mode-Grüneisen parameters in order to capture the strain-induced anharmonicity among phonon branches. This expression reveals the fundamental differences among the internal friction limits for different types of bulk-mode elastic waves. For cubic crystals, 2D-extensional modes have increased dissipation compared to width-extensional modes because the biaxial deformation opposes the natural Poisson contraction of the solid. Additionally, we show that shear-mode vibrations, which preserve volume, have significantly reduced energy loss because dissipative phonon-phonon scattering is restricted to pure-shear phonon branches, indicating that Lamé- or wineglass-mode resonators will have the highest upper limit on mechanical efficiency. Finally, we employ key simplifications to evaluate the quality factor limits for common mode shapes in single-crystal silicon devices, explicitly including the correct effective elastic storage moduli for different vibration modes and crystal orientations. Our expression satisfies the pressing need for a reliable analytical model that can predict the phonon-phonon dissipation limits for modern resonant microelectromechanical systems, where precise manufacturing techniques and accurate finite-element methods can be used to select particular vibrational mode shapes and crystal orientations.
Virtual and Printed 3D Models for Teaching Crystal Symmetry and Point Groups
ERIC Educational Resources Information Center
Casas, Lluís; Estop, Euge`nia
2015-01-01
Both, virtual and printed 3D crystal models can help students and teachers deal with chemical education topics such as symmetry and point groups. In the present paper, two freely downloadable tools (interactive PDF files and a mobile app) are presented as examples of the application of 3D design to study point-symmetry. The use of 3D printing to…
Phonons in Ultrathin Oxide Films: 2D to 3D Transition in FeO on Pt(111).
Spiridis, N; Zając, M; Piekarz, P; Chumakov, A I; Freindl, K; Goniakowski, J; Kozioł-Rachwał, A; Parliński, K; Ślęzak, M; Ślęzak, T; Wdowik, U D; Wilgocka-Ślęzak, D; Korecki, J
2015-10-30
The structural and magnetic properties of ultrathin FeO(111) films on Pt(111) with thicknesses from 1 to 16 monolayers (MLs) were studied using the nuclear inelastic scattering of synchrotron radiation. A distinct evolution of vibrational characteristics with thickness, revealed in the phonon density of states (PDOS), shows a textbook transition from 2D to 3D lattice dynamics. For the thinnest films of 1 and 2 ML, the low-energy part of the PDOS followed a linear ∝E dependence in energy that is characteristic for two-dimensional systems. This dependence gradually transforms with thickness to the bulk ∝E^{2} relationship. Density-functional theory phonon calculations perfectly reproduced the measured 1-ML PDOS within a simple model of a pseudomorphic FeO/Pt(111) interface. The calculations show that the 2D PDOS character is due to a weak coupling of the FeO film to the Pt(111) substrate. The evolution of the vibrational properties with an increasing thickness is closely related to a transient long-range magnetic order and stabilization of an unusual structural phase. PMID:26565477
Phonons in Ultrathin Oxide Films: 2D to 3D Transition in FeO on Pt(111)
NASA Astrophysics Data System (ADS)
Spiridis, N.; Zając, M.; Piekarz, P.; Chumakov, A. I.; Freindl, K.; Goniakowski, J.; Kozioł-Rachwał, A.; Parliński, K.; Ślezak, M.; Ślezak, T.; Wdowik, U. D.; Wilgocka-Ślezak, D.; Korecki, J.
2015-10-01
The structural and magnetic properties of ultrathin FeO(111) films on Pt(111) with thicknesses from 1 to 16 monolayers (MLs) were studied using the nuclear inelastic scattering of synchrotron radiation. A distinct evolution of vibrational characteristics with thickness, revealed in the phonon density of states (PDOS), shows a textbook transition from 2D to 3D lattice dynamics. For the thinnest films of 1 and 2 ML, the low-energy part of the PDOS followed a linear ∝E dependence in energy that is characteristic for two-dimensional systems. This dependence gradually transforms with thickness to the bulk ∝E2 relationship. Density-functional theory phonon calculations perfectly reproduced the measured 1-ML PDOS within a simple model of a pseudomorphic Fe O /Pt(1 1 1 ) interface. The calculations show that the 2D PDOS character is due to a weak coupling of the FeO film to the Pt(111) substrate. The evolution of the vibrational properties with an increasing thickness is closely related to a transient long-range magnetic order and stabilization of an unusual structural phase.
Template-Directed Directionally Solidified 3D Mesostructured AgCl-KCl Eutectic Photonic Crystals.
Kim, Jinwoo; Aagesen, Larry K; Choi, Jun Hee; Choi, Jaewon; Kim, Ha Seong; Liu, Jinyun; Cho, Chae-Ryong; Kang, Jin Gu; Ramazani, Ali; Thornton, Katsuyo; Braun, Paul V
2015-08-19
3D mesostructured AgCl-KCl photonic crystals emerge from colloidal templating of eutectic solidification. Solvent removal of the KCl phase results in a mesostructured AgCl inverse opal. The 3D-template-induced confinement leads to the emergence of a complex microstructure. The 3D mesostructured eutectic photonic crystals have a large stop band ranging from the near-infrared to the visible tuned by the processing. PMID:26177830
Cavity-type hypersonic phononic crystals
NASA Astrophysics Data System (ADS)
Sato, A.; Pennec, Y.; Yanagishita, T.; Masuda, H.; Knoll, W.; Djafari-Rouhani, B.; Fytas, G.
2012-11-01
We report on the engineering of the phonon dispersion diagram in monodomain anodic porous alumina (APA) films through the porosity and physical state of the material residing in the nanopores. Lattice symmetry and inclusion materials are theoretically identified to be the main factors which control the hypersonic acoustic wave propagation. This involves the interaction between the longitudinal and the transverse modes in the effective medium and a flat band characteristic of the material residing in the cavities. Air and filled nanopores, therefore, display markedly different dispersion relations and the inclusion materials lead to a locally resonant structural behavior uniquely determining their properties under confinement. APA films emerge as a new platform to investigate the rich acoustic phenomena of structured composite matter.
Topological Phononic Crystals with One-Way Elastic Edge Waves
NASA Astrophysics Data System (ADS)
Wang, Pai; Lu, Ling; Bertoldi, Katia
2015-09-01
We report a new type of phononic crystals with topologically nontrivial band gaps for both longitudinal and transverse polarizations, resulting in protected one-way elastic edge waves. In our design, gyroscopic inertial effects are used to break the time-reversal symmetry and realize the phononic analogue of the electronic quantum (anomalous) Hall effect. We investigate the response of both hexagonal and square gyroscopic lattices and observe bulk Chern numbers of 1 and 2, indicating that these structures support single and multimode edge elastic waves immune to backscattering. These robust one-way phononic waveguides could potentially lead to the design of a novel class of surface wave devices that are widely used in electronics, telecommunication, and acoustic imaging.
Exciton-phonon interaction in crystals and quantum size structures
NASA Astrophysics Data System (ADS)
Yaremko, A. M.; Yukhymchuk, V. O.; Dzhagan, V. M.; Valakh, M. Ya; Baran, J.; Ratajczak, H.
2007-12-01
In this report, the problem of electron-phonon interaction (EPI) in bulk semiconductors and quantum dots (QDs) is considered. It is shown that the model of strong EPI developed for organic molecular crystals can be successfully applied to bulk and nano-sized semiconductors. The idea of the approach proposed is to describe theoretically the experimental Raman (IR) spectra, containing the phonon replicas, by varying the EPI constant. The main parameter of the theoretical expression (βS) is the ratio of EPI constant (χS) to the frequency of the corresponding phonon mode (ΩS). The theoretical results show that variation of the QD size can change the value of χS.
Generalized thermoelastic wave band gaps in phononic crystals without energy dissipation
NASA Astrophysics Data System (ADS)
Wu, Ying; Yu, Kaiping; Li, Xiao; Zhou, Haotian
2016-01-01
We present a theoretical investigation of the thermoelastic wave propagation in the phononic crystals in the context of Green-Nagdhi theory by taking thermoelastic coupling into account. The thermal field is assumed to be steady. Thermoelastic wave band structures of 3D and 2D are derived by using the plane wave expansion method. For the 2D problem, the anti-plane shear mode is not affected by the temperature difference. Thermoelastic wave bands of the in-plane x-y mode are calculated for lead/silicone rubber, aluminium/silicone rubber, and aurum/silicone rubber phononic crystals. The new findings in the numerical results indicate that the thermoelastic wave bands are composed of the pure elastic wave bands and the thermal wave bands, and that the thermal wave bands can serve as the low boundary of the first band gap when the filling ratio is low. In addition, for the lead/silicone rubber phononic crystals the effects of lattice type (square, rectangle, regular triangle, and hexagon) and inclusion shape (circle, oval, and square) on the normalized thermoelastic bandwidth and the upper/lower gap boundaries are analysed and discussed. It is concluded that their effects on the thermoelastic wave band structure are remarkable.
Self assembly of inorganic nanocrystals in 3D supra crystals: Intrinsic properties
NASA Astrophysics Data System (ADS)
Pileni, M. P.
2009-06-01
Here we describe how arrangements of nanocrystals can self-organize in 3D arrays called supra crystals. The 3D arrays can fall into the familiar categories of face centered cubic (fcc), hexagonal compact packing (hcp) crystals, and body centered (bcc) crystals. Intrinsic collective properties of these 3D arrangements are different from the properties of individual nanoparticles and from particles in bulk. We demonstrate by two various processes and with two types of nanocrystals (silver and cobalt) that when nanocrystals are self ordered in 3D superlattices, they exhibit a coherent breathing mode vibration of the supra crystal, analogous to a breathing mode vibration of atoms in a nanocrystal. Comparison between the approaches to saturation of the magnetic curve for supra crystals and disordered aggregates produced from the same batch of nanocrystals is similar to that observed with films or nanoparticles either highly crystallized or amorphous.
Optical phonon modes and crystal structure of NaLaF4 single crystals
NASA Astrophysics Data System (ADS)
Lage, Márcio Martins; Matinaga, Franklin Massami; Gesland, Jean-Yves; Moreira, Roberto Luiz
2006-03-01
Polarized Raman scattering and infrared reflectivity measurements have been used to investigate the crystal structure of Czochralski-grown NaLaF4 single crystals. The phonon symmetries, the simultaneous presence of polar modes in the infrared and Raman spectra, as well as the observation of piezoelectric resonance, helped us to identify the P6 group as the correct one for this crystal. This material belongs to a family of sodium lanthanide tetrafluorides (NaLnF4) crystals, whose photoluminescence efficiency is comparable to LiYF4. Therefore, NaLaF4 crystals may be important in the development of diode pumped up-conversion solid-state lasers. The number and behavior of the observed optical phonon modes were analyzed in terms of group theory predictions for the group symmetry found. A few anomalies in the phonon characteristics are discussed in terms of cationic disorder in the crystal lattice.
A full field, 3-D velocimeter for microgravity crystallization experiments
NASA Technical Reports Server (NTRS)
Brodkey, Robert S.; Russ, Keith M.
1991-01-01
The programming and algorithms needed for implementing a full-field, 3-D velocimeter for laminar flow systems and the appropriate hardware to fully implement this ultimate system are discussed. It appears that imaging using a synched pair of video cameras and digitizer boards with synched rails for camera motion will provide a viable solution to the laminar tracking problem. The algorithms given here are simple, which should speed processing. On a heavily loaded VAXstation 3100 the particle identification can take 15 to 30 seconds, with the tracking taking less than one second. It seeems reasonable to assume that four image pairs can thus be acquired and analyzed in under one minute.
Thermal transport in phononic crystals: The role of zone folding effect
NASA Astrophysics Data System (ADS)
Dechaumphai, Edward; Chen, Renkun
2012-04-01
Recent experiments [Yu et al., Nature Nanotech 5, 718 (2010); Tang et al., Nano Lett. 10, 4279 (2010); Hopkins etal., Nano Lett. 11, 107(2011)] on silicon based nanoscale phononic crystals demonstrated substantially reduced thermal conductivity compared to bulk Si, which cannot be explained by incoherent phonon boundary scattering within the Boltzmann Transport Equation (BTE). In this paper, partial coherent treatment of phonons, where phonons are regarded as either wave or particles depending on their frequencies, was considered. Phonons with mean free path smaller than the characteristic size of phononic crystals are treated as particles and the transport in this regime is modeled by BTE with phonon boundary scattering taken into account. On the other hand, phonons with mean free path longer than the characteristic size are treated as waves. In this regime, phonon dispersion relations are computed using the Finite Difference Time Domain (FDTD) method and are found to be modified due to the zone folding effect. The new phonon spectra are then used to compute phonon group velocity and density of states for thermal conductivity modeling. Our partial coherent model agrees well with the recent experimental results on in-plane thermal conductivity of phononic crystals. Our study highlights the importance of zone folding effect on thermal transport in phononic crystals.
Stress Wave Isolation by Purely Mechanical Topological Phononic Crystals
Chaunsali, Rajesh; Li, Feng; Yang, Jinkyu
2016-01-01
We present an active, purely mechanical stress wave isolator that consists of short cylindrical particles arranged in a helical architecture. This phononic structure allows us to change inter-particle stiffness dynamically by controlling the contact angles of the cylinders. We use torsional travelling waves to control the contact angles, thereby imposing a desired spatio-temporal stiffness variation to the phononic crystal along the longitudinal direction. Such torsional excitation is a form of parametric pumping in the system, which results in the breakage of the time-reversal symmetry. We report that, in quasi-static sense, the system shows topologically non-trivial band-gaps. However, in a dynamic regime where the pumping effect is significant, these band-gaps become asymmetric with respect to the frequency and wavenumber domains in the dispersion relationship. By using numerical simulations, we show that such asymmetry has a direct correspondence to the topological invariant, i.e., Chern number, of the system. We propose that this asymmetry, accompanied by selective inter-band transition, can be utilized for directional isolation of the stress wave propagating along the phononic crystal. PMID:27477236
Stress Wave Isolation by Purely Mechanical Topological Phononic Crystals
NASA Astrophysics Data System (ADS)
Chaunsali, Rajesh; Li, Feng; Yang, Jinkyu
2016-08-01
We present an active, purely mechanical stress wave isolator that consists of short cylindrical particles arranged in a helical architecture. This phononic structure allows us to change inter-particle stiffness dynamically by controlling the contact angles of the cylinders. We use torsional travelling waves to control the contact angles, thereby imposing a desired spatio-temporal stiffness variation to the phononic crystal along the longitudinal direction. Such torsional excitation is a form of parametric pumping in the system, which results in the breakage of the time-reversal symmetry. We report that, in quasi-static sense, the system shows topologically non-trivial band-gaps. However, in a dynamic regime where the pumping effect is significant, these band-gaps become asymmetric with respect to the frequency and wavenumber domains in the dispersion relationship. By using numerical simulations, we show that such asymmetry has a direct correspondence to the topological invariant, i.e., Chern number, of the system. We propose that this asymmetry, accompanied by selective inter-band transition, can be utilized for directional isolation of the stress wave propagating along the phononic crystal.
Stress Wave Isolation by Purely Mechanical Topological Phononic Crystals.
Chaunsali, Rajesh; Li, Feng; Yang, Jinkyu
2016-01-01
We present an active, purely mechanical stress wave isolator that consists of short cylindrical particles arranged in a helical architecture. This phononic structure allows us to change inter-particle stiffness dynamically by controlling the contact angles of the cylinders. We use torsional travelling waves to control the contact angles, thereby imposing a desired spatio-temporal stiffness variation to the phononic crystal along the longitudinal direction. Such torsional excitation is a form of parametric pumping in the system, which results in the breakage of the time-reversal symmetry. We report that, in quasi-static sense, the system shows topologically non-trivial band-gaps. However, in a dynamic regime where the pumping effect is significant, these band-gaps become asymmetric with respect to the frequency and wavenumber domains in the dispersion relationship. By using numerical simulations, we show that such asymmetry has a direct correspondence to the topological invariant, i.e., Chern number, of the system. We propose that this asymmetry, accompanied by selective inter-band transition, can be utilized for directional isolation of the stress wave propagating along the phononic crystal. PMID:27477236
Electrical manipulation of crystal symmetry for switching transverse acoustic phonons.
Jeong, H; Jho, Y D; Stanton, C J
2015-01-30
We experimentally explore the use of a novel device where lateral electric fields can be applied to break the translational symmetry within the isotropic plane and hence change the selection rules to allow normally forbidden transverse acoustic (TA) phonon generations. The ultrafast screening of the lateral electric field by the photocarriers relieves shear strain in the structure and switches on the propagating TA waves. The amplitude and on-state time of the TA mode can be modulated by the external field strength and size of the laterally biased region. The observed frequency shift with an external bias as well as the strong geometrical dependence confirm the role of the asymmetric potential distribution in electrically manipulating the crystal symmetry to control modal behavior of acoustic phonons. PMID:25679892
Electrical Manipulation of Crystal Symmetry for Switching Transverse Acoustic Phonons
NASA Astrophysics Data System (ADS)
Jeong, H.; Jho, Y. D.; Stanton, C. J.
2015-01-01
We experimentally explore the use of a novel device where lateral electric fields can be applied to break the translational symmetry within the isotropic plane and hence change the selection rules to allow normally forbidden transverse acoustic (TA) phonon generations. The ultrafast screening of the lateral electric field by the photocarriers relieves shear strain in the structure and switches on the propagating TA waves. The amplitude and on-state time of the TA mode can be modulated by the external field strength and size of the laterally biased region. The observed frequency shift with an external bias as well as the strong geometrical dependence confirm the role of the asymmetric potential distribution in electrically manipulating the crystal symmetry to control modal behavior of acoustic phonons.
Structural engineering of three-dimensional phononic crystals
NASA Astrophysics Data System (ADS)
Delpero, Tommaso; Schoenwald, Stefan; Zemp, Armin; Bergamini, Andrea
2016-02-01
Artificially-structured materials are attracting the research interest of a growing community of scientists for the possibility to develop novel materials with advantageous properties that arise from the ability to tailor the propagation of elastic waves, and thus energy, through them. In this work, we propose a three-dimensional phononic crystal whose unit cell has been engineered to obtain a strong wave-attenuation band in the middle of the acoustic frequency range. The combination of its acoustic properties with the dimensions of the unit cell and its static mechanical properties makes it an interesting material for possibly several applications in civil and mechanical engineering, for instance as the core of an acoustically insulating sandwich panel. A sample of this crystal has been manufactured and experimentally tested with respect to its acoustic transmissibility. The performance of the phononic crystal core is remarkable both in terms of amplitude reduction in the transmissibility and width of the attenuation band. A parametric study has been finally conducted on selected geometrical parameters of the unit cell and on their effect on the macroscopic properties of the crystal. This work represents an application-oriented example of how the macroscopic properties of an artificially-structured material can be designed, according to specific needs, by a conventional engineering of its unit cell.
Electron-phonon interaction in three-, two- and one-dimensional ternary mixed crystals
NASA Astrophysics Data System (ADS)
Hou, Junhua; Fan, Yunpeng
2016-05-01
The electron-phonon (e-p) interaction in three-dimensional (3D), two-dimensional (2D) and one-dimensional (1D) ternary mixed crystals is studied. The e-p interaction Hamiltonians including the unit cell volume variation in ternary mixed crystals are obtained by using the modified random-element-isodisplacement model and Born-Huang method. The polaronic self-trapping energy and renormalized effective mass of GaAsxSb1‑x, GaPxAs1‑x and GaPxSb1‑x compounds are numerically calculated. It is confirmed theoretically that the nonlinear variation of the self-trapping energy and effective mass with the composition is essential and the unit cell volume effects cannot be neglected except the weak e-p coupling. The dimensional effect cannot also be ignored.
Towards true 3D textural analysis; using your crystal mush wisely.
NASA Astrophysics Data System (ADS)
Jerram, D. A.; Morgan, D. J.; Pankhurst, M. J.
2014-12-01
The crystal cargo that is found in volcanic and plutonic rocks contains a wealth of information about magmatic mush processes, crystallisation history, crystal entrainment and recycling. Phenocryst populations predominantly record episodes of growth/nucleation and bulk geochemical changes within an evolving crystal-melt body. Ante- and xeno-crysts provide useful clues to the nature of mush interaction with wall rock and with principal magma(s). Furthermore, crystal evolutions (core to rim) record pathways through pressure, temperature and compositional space. These can often illustrate complex recycling within systems, describing the plumbing architecture. Understanding this architecture underpins our knowledge of how igneous systems can interact with the crust, grow, freeze, re-mobilise and prime for eruption. Initially, 2D studies produced corrected 3D crystal size distributions to help provide information about nucleation and residence times. It immediately became clear that crystal shape is an important factor in determining the confidence placed upon 3D reconstructions of 2D data. Additionally studies utilised serial sections of medium- to coarse-grain-size populations which allowed 3D reconstruction using modelling software to be improved, since size and shape etc. can be directly constrained. Finally the advent of textural studies using X-ray tomography has revolutionised the way in which we can inspect the crystal cargo in mushy systems, allowing us to image in great detail crystal packing arrangements, 3D CSDs, shapes and orientations etc. The latest most innovative studies use X-ray micro-computed tomography to rapidly characterise chemical populations within the crystal cargo, adding a further dimension to this approach, and implies the ability to untangle magmatic chemical components to better understand their individual and combined evolution. In this contribution key examples of the different types of textural analysis techniques in 2D and 3D
Numerical investigation of diffraction of acoustic waves by phononic crystals
NASA Astrophysics Data System (ADS)
Moiseyenko, Rayisa P.; Declercq, Nico F.; Laude, Vincent
2012-05-01
Diffraction as well as transmission of acoustic waves by two-dimensional phononic crystals (PCs) composed of steel rods in water are investigated in this paper. The finite element simulations were performed in order to compute pressure fields generated by a line source that are incident on a finite size PC. Such field maps are analyzed based on the complex band structure for the infinite periodic PC. Finite size computations indicate that the exponential decrease of the transmission at deaf frequencies is much stronger than that in Bragg band gaps.
Multiple beam splitting in elastic phononic crystal plates.
Lee, Hyuk; Oh, Joo Hwan; Kim, Yoon Young
2015-02-01
This work presents an experimental evidence for triple beam splitting in an elastic plate with an embedded elastic phononic crystal (PC) prism and elaborates on its working mechanism. While there were reports on negative refraction and double beam splitting with PCs, no experimental evidence on the splitting of triple or more ultrasonic elastic beams through PCs has been shown yet. After the experimental results are presented in case of triple beam splitting, further analysis is carried out to explain how triple or more beams can be split depending on elastic PC prism angles. PMID:25454094
Focusing of Rayleigh waves with gradient-index phononic crystals
NASA Astrophysics Data System (ADS)
Zhao, Jinfeng; Bonello, Bernard; Becerra, Loïc; Boyko, Olga; Marchal, Rémi
2016-05-01
We report on the subwavelength focusing of Rayleigh waves using gradient-index (GRIN) phononic crystals (PCs) made of air holes scatters in a thick silicon substrate. The subwavelength focusing is demonstrated both in the inner and in the silicon substrate behind the GRIN PCs by using a non-contact experimental technique. In both situations, the focal zone was observed at the position, which is in very good agreement with our theoretical predictions, at a frequency in the sound cone free of radiation into the substrate.
3D unsteady computer modeling of industrial scale Ky and Cz sapphire crystal growth
NASA Astrophysics Data System (ADS)
Demina, S. E.; Kalaev, V. V.
2011-04-01
In the present work, 3D features of melt convection during sapphire growth of 100 mm diameter Cz and of 200 mm diameter Ky crystals are studied. The approach accounting for radiative heat exchange with absorption and a specular reflection in the crystal, which we applied in 2D modeling [1-3], has been extended to 3D computational domains and coupled to 3D heat transfer in the melt, crystal, and crucible. 3D melt unsteady convection together with crystallization front formation are taken into account within the Direct Numerical Simulation (DNS) approach. Results of 3D modeling are discussed in detail and quantitatively compared to the previously reported data of 2D modeling and experiments [2,3]. It has been found that the features of unsteady melt convection during the "before seeding", "seeding", and "shouldering" growth stages are quite different from each other, which necessitates a flexible control of the radial and vertical temperature gradients in the crucible to provide optimal conditions for stable growth of high quality sapphire crystals.
Technology towards a SAW based phononic crystal sensor
NASA Astrophysics Data System (ADS)
Schmidt, Marc-Peter; Oseev, Aleksandr; Lucklum, Ralf; Hirsch, Soeren
2015-05-01
Phononic crystals (PnC) with a specifically designed defect have been recently introduced as novel sensor platform. Those sensors feature a band gap covering the typical input span of the measurand as well as a narrow transmission peak within the band gap where the frequency of maximum transmission is governed by the measurand. This innovative approach has been applied for determination of compounds in liquids [1]. Improvement of sensitivity requires higher probing frequencies around 100 MHz and above. In this range surface acoustic wave devices (SAW) provide a promising basis for PnC based microsensors [2]. The respective feature size of the PnC SAW sensor has dimensions in the range of 100 μm and below. Whereas those dimensions are state of the art for common MEMS materials, etching of holes and cavities in piezoelectric materials having an aspect ratio diameter/depth is challenging. In this contribution we describe an improved technological process to manufacture considerably deep and uniform phononic crystal structures inside of SAW substrates.
Raman phonons in multiferroic FeVO4 crystals
NASA Astrophysics Data System (ADS)
Zhang, An-Min; Liu, Kai; Ji, Jian-Ting; He, Chang-Zhen; Tian, Yong; Jin, Feng; Zhang, Qing-Ming
2015-12-01
Multiferroic materials are promising candidates for next-generation multi-functional devices, because of the coexistence of multi-orders and the coupling between the orders. FeVO4 has been confirmed to be a multiferroic compound, since it exhibits both ferroelectricity and antiferromagnetic ordering at low temperatures. In this paper, we have performed careful Raman scattering measurements on high-quality FeVO4 single crystals. The compound has a very rich phonon structure due to its low crystal symmetry (P - 1) and at least 47 Raman-active phonon modes have been resolved in the low and hightemperature spectra. Most of the observed modes are well assigned with aid of first-principles calculations and symmetry analysis. The present study provides an experimental basis for exploring spin-lattice coupling and the mechanism of multiferroicity in FeVO4 Project supported by the National Basic Research Program of China (Grant No. 2012CB921701), the National Natural Science Foundation of China (Grant Nos. 11174367 and 11004243), the China Postdoctoral Science Foundation, the Fundamental Research Funds for the Central Universities, and the Research Funds of Renmin University of China (Grant Nos. 10XNI038, 14XNLF06, and 14XNLQ03).
Temperature insensitive mass sensing of mode selected phononic crystal cavity
NASA Astrophysics Data System (ADS)
Li, Peng; Li, Feng; Liu, Yongshun; Shu, Fengfeng; Wu, Junfeng; Wu, Yihui
2015-12-01
Phononic crystal cavities with high quality (Q) factors are attractive in both signal processing and sensing applications. In this paper, 2D phononic crystal point defect cavities are fabricated on silicon slabs by micro electromechanical system (MEMS) technologies. An electrode design method is proposed to enhance displacements of the point defect modes. Then the method is applied to design MEMS resonators with different port numbers, among which Q factor as high as 21 300 is obtained in air. Multiport resonators with transmission measurements are proved to be advantageous over one-port resonators with impedance measurements in frequency resolution. A temperature insensitive resonant mass sensor is designed based on a two-port resonator. Two defect modes with strong responses in the two-port resonator are combined to compensate environmental temperature interference. The temperature compensation experiment reveals that temperature interference is effectively compensated from mass measurement and the mass sensitivity of the sensor is 5.4 Hz ng-1. The conclusion of mode selection or sensing mechanism will help to design resonators or sensors with high performances.
Blokh, M.D.
1988-01-01
The flux of nonequilibrium phonons excited by light in the near-surface domain of a crystal or a thin plate is investigated. An exact expression is obtained for the phonon energy flux for a crystal with a polar direction and its polarization dependence is analyzed. The magnitude of the energy flux can reach the incident light intensity. The temperature difference produced by the flux of nonequilibrium photo-excited phonons is found.
Nanoscale resolved infrared probing of crystal structure and of plasmon-phonon coupling.
Huber, A; Ocelic, N; Taubner, T; Hillenbrand, R
2006-04-01
We show that slight variations of a crystal lattice cause significant spectral modifications of phonon-polariton resonant near-field interaction between polar semiconductor crystals and a scanning metal tip. Exploiting the effect for near-field imaging a SiC polytype boundary, we establish infrared mapping of crystal structure and crystal defects at 20 nm spatial resolution (lambda/500). By spectroscopic probing of doped SiC polytypes, we find that phonon-polariton resonant near-field interaction is also sensitive to electronic properties due to plasmon-phonon coupling in the crystals. PMID:16608282
Wave propagation in single column woodpile phononic crystals: Formation of tunable band gaps
NASA Astrophysics Data System (ADS)
Kim, Eunho; Yang, Jinkyu
2014-11-01
We study the formation of frequency band gaps in single column woodpile phononic crystals composed of orthogonally stacked slender cylinders. We focus on investigating the effect of the cylinders' local vibrations on the dispersion of elastic waves along the stacking direction of the woodpile phononic crystals. We experimentally verify that their frequency band structures depend significantly on the bending resonant behavior of unit cells. We propose a simple theoretical model based on a discrete element method to associate the behavior of locally resonant cylindrical rods with the band gap formation mechanism in woodpile phononic crystals. The findings in this work imply that we can achieve versatile control of frequency band structures in phononic crystals by using woodpile architectures. The woodpile phononic crystals can form a new type of vibration filtering devices that offer an enhanced degree of freedom in manipulating stress wave propagation.
Hierarchical thermoelectrics: crystal grain boundaries as scalable phonon scatterers
NASA Astrophysics Data System (ADS)
Selli, Daniele; Boulfelfel, Salah Eddine; Schapotschnikow, Philipp; Donadio, Davide; Leoni, Stefano
2016-02-01
Thermoelectric materials are strategically valuable for sustainable development, as they allow for the generation of electrical energy from wasted heat. In recent years several strategies have demonstrated some efficiency in improving thermoelectric properties. Dopants affect carrier concentration, while thermal conductivity can be influenced by alloying and nanostructuring. Features at the nanoscale positively contribute to scattering phonons, however those with long mean free paths remain difficult to alter. Here we use the concept of hierarchical nano-grains to demonstrate thermal conductivity reduction in rocksalt lead chalcogenides. We demonstrate that grains can be obtained by taking advantage of the reconstructions along the phase transition path that connects the rocksalt structure to its high-pressure form. Since grain features naturally change as a function of size, they impact thermal conductivity over different length scales. To understand this effect we use a combination of advanced molecular dynamics techniques to engineer grains and to evaluate thermal conductivity in PbSe. By affecting grain morphologies only, i.e. at constant chemistry, two distinct effects emerge: the lattice thermal conductivity is significantly lowered with respect to the perfect crystal, and its temperature dependence is markedly suppressed. This is due to an increased scattering of low-frequency phonons by grain boundaries over different size scales. Along this line we propose a viable process to produce hierarchical thermoelectric materials by applying pressure via a mechanical load or a shockwave as a novel paradigm for material design.
Hierarchical thermoelectrics: crystal grain boundaries as scalable phonon scatterers.
Selli, Daniele; Boulfelfel, Salah Eddine; Schapotschnikow, Philipp; Donadio, Davide; Leoni, Stefano
2016-02-14
Thermoelectric materials are strategically valuable for sustainable development, as they allow for the generation of electrical energy from wasted heat. In recent years several strategies have demonstrated some efficiency in improving thermoelectric properties. Dopants affect carrier concentration, while thermal conductivity can be influenced by alloying and nanostructuring. Features at the nanoscale positively contribute to scattering phonons, however those with long mean free paths remain difficult to alter. Here we use the concept of hierarchical nano-grains to demonstrate thermal conductivity reduction in rocksalt lead chalcogenides. We demonstrate that grains can be obtained by taking advantage of the reconstructions along the phase transition path that connects the rocksalt structure to its high-pressure form. Since grain features naturally change as a function of size, they impact thermal conductivity over different length scales. To understand this effect we use a combination of advanced molecular dynamics techniques to engineer grains and to evaluate thermal conductivity in PbSe. By affecting grain morphologies only, i.e. at constant chemistry, two distinct effects emerge: the lattice thermal conductivity is significantly lowered with respect to the perfect crystal, and its temperature dependence is markedly suppressed. This is due to an increased scattering of low-frequency phonons by grain boundaries over different size scales. Along this line we propose a viable process to produce hierarchical thermoelectric materials by applying pressure via a mechanical load or a shockwave as a novel paradigm for material design. PMID:26815914
CMOS compatible fabrication of 3D photonic crystals by nanoimprint lithography
NASA Astrophysics Data System (ADS)
Eibelhuber, M.; Uhrmann, T.; Glinsner, T.
2015-03-01
Nanoimprinting techniques are an attractive solution for next generation lithography methods for several areas including photonic devices. A variety of potential applications have been demonstrated using nanoimprint lithography (NIL) (e.g. SAW devices, vias and contact layers with dual damascene imprinting process, Bragg structures, patterned media) [1,2]. Nanoimprint lithography is considered for bridging the gap from R and D to high volume manufacturing. In addition, it is capable to adapt to the needs of the fragmented and less standardized photonic market easily. In this work UV-NIL has been selected for the fabrication process of 3D-photonic crystals. It has been shown that UVNIL using a multiple layer approach is well suited to fabricate a 3D woodpile photonic crystal. The necessary alignment accuracies below 100nm were achieved using a simple optical method. In order to obtain sufficient alignment of the stacks to each other, a two stage alignment process is performed: at first proximity alignment is done followed by the Moiré alignment in soft contact with the substrate. Multiple steps of imprinting, etching, Si deposition and chemical mechanical polishing were implemented to create high quality 3D photonic crystals with up to 5 layers. This work has proven the applicability of nanoimprint lithography in a CMOS compatible process on 3D photonic crystals with alignment accuracy down to 100nm. Optimizing the processes will allow scaling up these structures on full wafers while still meeting the requirements of the designated devices.
Accidental degeneracy of double Dirac cones in a phononic crystal
Chen, Ze-Guo; Ni, Xu; Wu, Ying; He, Cheng; Sun, Xiao-Chen; Zheng, Li-Yang; Lu, Ming-Hui; Chen, Yan-Feng
2014-01-01
Artificial honeycomb lattices with Dirac cone dispersion provide a macroscopic platform to study the massless Dirac quasiparticles and their novel geometric phases. In this paper, a quadruple-degenerate state is achieved at the center of the Brillouin zone in a two-dimensional honeycomb lattice phononic crystal, which is a result of accidental degeneracy of two double-degenerate states. In the vicinity of the quadruple-degenerate state, the dispersion relation is linear. Such quadruple degeneracy is analyzed by rigorous representation theory of groups. Using method, a reduced Hamiltonian is obtained to describe the linear Dirac dispersion relations of this quadruple-degenerate state, which is well consistent with the simulation results. Near such accidental degeneracy, we observe some unique properties in wave propagating, such as defect-insensitive propagating character and the Talbot effect. PMID:24714512
Modification of phonon processes in nanostructured rare-earth-ion-doped crystals
NASA Astrophysics Data System (ADS)
Lutz, Thomas; Veissier, Lucile; Thiel, Charles W.; Cone, Rufus L.; Barclay, Paul E.; Tittel, Wolfgang
2016-07-01
Nano-structuring impurity-doped crystals affects the phonon density of states and thereby modifies the atomic dynamics induced by interaction with phonons. We propose the use of nano-structured materials in the form of powders or phononic bandgap crystals to enable or improve persistent spectral hole burning and coherence for inhomogeneously broadened absorption lines in rare-earth-ion-doped crystals. This is crucial for applications such as ultra-precise radio-frequency spectrum analyzers and optical quantum memories. As an example, we discuss how phonon engineering can enable spectral hole burning in erbium-doped materials operating in the convenient telecommunication band and present simulations for density of states of nano-sized powders and phononic crystals for the case of Y2SiO5 , a widely used material in current quantum memory research.
Edge waves and resonances in two-dimensional phononic crystal plates
Hsu, Jin-Chen Hsu, Chih-Hsun
2015-05-07
We present a numerical study on phononic band gaps and resonances occurring at the edge of a semi-infinite two-dimensional (2D) phononic crystal plate. The edge supports localized edge waves coupling to evanescent phononic plate modes that decay exponentially into the semi-infinite phononic crystal plate. The band-gap range and the number of edge-wave eigenmodes can be tailored by tuning the distance between the edge and the semi-infinite 2D phononic lattice. As a result, a phononic band gap for simultaneous edge waves and plate waves is created, and phononic cavities beside the edge can be built to support high-frequency edge resonances. We design an L3 edge cavity and analyze its resonance characteristics. Based on the band gap, high quality factor and strong confinement of resonant edge modes are achieved. The results enable enhanced control over acoustic energy flow in phononic crystal plates, which can be used in designing micro and nanoscale resonant devices and coupling of edge resonances to other types of phononic or photonic crystal cavities.
Coherent optical phonon oscillation and possible electronic softening in WTe2 crystals
He, Bin; Zhang, Chunfeng; Zhu, Weida; Li, Yufeng; Liu, Shenghua; Zhu, Xiyu; Wu, Xuewei; Wang, Xiaoyong; Wen, Hai-hu; Xiao, Min
2016-01-01
A rapidly-growing interest in WTe2 has been triggered by the giant magnetoresistance effect discovered in this unique system. While many efforts have been made towards uncovering the electron- and spin-relevant mechanisms, the role of lattice vibration remains poorly understood. Here, we study the coherent vibrational dynamics in WTe2 crystals by using ultrafast pump-probe spectroscopy. The oscillation signal in time domain in WTe2 has been ascribed as due to the coherent dynamics of the lowest energy A1 optical phonons with polarization- and wavelength-dependent measurements. With increasing temperature, the phonon energy decreases due to anharmonic decay of the optical phonons into acoustic phonons. Moreover, a significant drop (15%) of the phonon energy with increasing pump power is observed which is possibly caused by the lattice anharmonicity induced by electronic excitation and phonon-phonon interaction. PMID:27457385
Coherent optical phonon oscillation and possible electronic softening in WTe2 crystals
NASA Astrophysics Data System (ADS)
He, Bin; Zhang, Chunfeng; Zhu, Weida; Li, Yufeng; Liu, Shenghua; Zhu, Xiyu; Wu, Xuewei; Wang, Xiaoyong; Wen, Hai-Hu; Xiao, Min
2016-07-01
A rapidly-growing interest in WTe2 has been triggered by the giant magnetoresistance effect discovered in this unique system. While many efforts have been made towards uncovering the electron- and spin-relevant mechanisms, the role of lattice vibration remains poorly understood. Here, we study the coherent vibrational dynamics in WTe2 crystals by using ultrafast pump-probe spectroscopy. The oscillation signal in time domain in WTe2 has been ascribed as due to the coherent dynamics of the lowest energy A1 optical phonons with polarization- and wavelength-dependent measurements. With increasing temperature, the phonon energy decreases due to anharmonic decay of the optical phonons into acoustic phonons. Moreover, a significant drop (15%) of the phonon energy with increasing pump power is observed which is possibly caused by the lattice anharmonicity induced by electronic excitation and phonon-phonon interaction.
Coherent optical phonon oscillation and possible electronic softening in WTe2 crystals.
He, Bin; Zhang, Chunfeng; Zhu, Weida; Li, Yufeng; Liu, Shenghua; Zhu, Xiyu; Wu, Xuewei; Wang, Xiaoyong; Wen, Hai-Hu; Xiao, Min
2016-01-01
A rapidly-growing interest in WTe2 has been triggered by the giant magnetoresistance effect discovered in this unique system. While many efforts have been made towards uncovering the electron- and spin-relevant mechanisms, the role of lattice vibration remains poorly understood. Here, we study the coherent vibrational dynamics in WTe2 crystals by using ultrafast pump-probe spectroscopy. The oscillation signal in time domain in WTe2 has been ascribed as due to the coherent dynamics of the lowest energy A1 optical phonons with polarization- and wavelength-dependent measurements. With increasing temperature, the phonon energy decreases due to anharmonic decay of the optical phonons into acoustic phonons. Moreover, a significant drop (15%) of the phonon energy with increasing pump power is observed which is possibly caused by the lattice anharmonicity induced by electronic excitation and phonon-phonon interaction. PMID:27457385
NASA Astrophysics Data System (ADS)
Bagheri Nouri, Mohammad; Moradi, Mehran
2016-05-01
In this paper, a new heterostructure phononic crystal is introduced. The new heterostructure is composed of square and rhombus phononic crystals. Using finite difference method, a displacement-based algorithm is presented to study elastic wave propagation in the phononic crystal. In contrast with conventional finite difference time domain method, at first by using constitutive equations and strain-displacement relations, elastic wave equations are derived based on displacement. Then, these forms are discretized using finite difference method. By this technique, components of stress tensor can be removed from the updating equations. Since the proposed method needs less elementary arithmetical operations, its computational cost is less than that of the conventional FDTD method. Using the presented displacement-based finite difference time domain algorithm, square phononic crystal, rhombus phononic crystal and the new heterostructure phononic crystal were analyzed. Comparison of transmission spectra of the new heterostructure phononic crystal with those creating lattices, showed that band gap can be extended by using the new structure. Also it was observed that by changing the angular constant of rhombus lattice, a new extended band gap can be achieved.
Rigorous analysis of an electric-field-driven liquid crystal lens for 3D displays
NASA Astrophysics Data System (ADS)
Kim, Bong-Sik; Lee, Seung-Chul; Park, Woo-Sang
2014-08-01
We numerically analyzed the optical performance of an electric field driven liquid crystal (ELC) lens adopted for 3-dimensional liquid crystal displays (3D-LCDs) through rigorous ray tracing. For the calculation, we first obtain the director distribution profile of the liquid crystals by using the Erickson-Leslie motional equation; then, we calculate the transmission of light through the ELC lens by using the extended Jones matrix method. The simulation was carried out for a 9view 3D-LCD with a diagonal of 17.1 inches, where the ELC lens was slanted to achieve natural stereoscopic images. The results show that each view exists separately according to the viewing position at an optimum viewing distance of 80 cm. In addition, our simulation results provide a quantitative explanation for the ghost or blurred images between views observed from a 3D-LCD with an ELC lens. The numerical simulations are also shown to be in good agreement with the experimental results. The present simulation method is expected to provide optimum design conditions for obtaining natural 3D images by rigorously analyzing the optical functionalities of an ELC lens.
Theory of rigid-plane phonon modes in layered crystals
NASA Astrophysics Data System (ADS)
Michel, K. H.; Verberck, B.
2012-03-01
The lattice dynamics of low-frequency rigid-plane modes in metallic (graphene multilayers, GML) and in insulating (hexagonal boron-nitride multilayers, BNML) layered crystals is investigated. The frequencies of shearing and compression (stretching) modes depend on the layer number N and are presented in the form of fan diagrams. The results for GML and BNML are very similar. In both cases, only the interactions (van der Waals and Coulomb) between nearest-neighbor planes are effective, while the interactions between more distant planes are screened. A comparison with recent Raman scattering results on low-frequency shear modes in GML [Tan , Nat. Mater., in press, doi:10.1038/nmat3245, (2012)] is made. Relations with the low-lying rigid-plane phonon dispersions in the bulk materials are established. Master curves, which connect the fan diagram frequencies for any given N, are derived. Static and dynamic thermal correlation functions for rigid-layer shear and compression modes are calculated. The results might be of use for the interpretation of friction force experiments on multilayer crystals.
Tunable ultrasonic phononic crystal controlled by infrared radiation
Walker, Ezekiel; Neogi, Arup E-mail: arup@unt.edu; Reyes, Delfino; Rojas, Miguel Mayorga; Krokhin, Arkadii; Wang, Zhiming E-mail: arup@unt.edu
2014-10-06
A tunable phononic crystal based ultrasonic filter was designed by stimulating the phase of the polymeric material embedded in a periodic structure using infrared radiation. The acoustic filter can be tuned remotely using thermal stimulation induced by the infrared radiation. The filter is composed of steel cylinder scatterers arranged periodically in a background of bulk poly (N-isopropylacrylamide) polymer hydrogel. The lattice structure creates forbidden bands for certain sets of mechanical waves that cause it to behave as an ultrasonic filter. Since the bandstructure is determined by not only the arrangement of the scatterers but also the physical properties of the materials composing the scatterers and background, modulating either the arrangement or physical properties will alter the effect of the crystal on propagating mechanical waves. Here, the physical properties of the filter are varied by inducing changes in the polymer hydrogel using an electromagnetic thermal stimulus. With particular focus on the k{sub 00}-wave, the transmission of ultrasonic wave changes by as much as 20 dBm, and band widths by 22% for select bands.
NASA Astrophysics Data System (ADS)
Üpping, J.; Bielawny, A.; Fahr, S.; Rockstuhl, C.; Lederer, F.; Steidl, L.; Zentel, R.; Beckers, T.; Lambertz, A.; Carius, R.; Wehrspohn, R. B.
2010-05-01
A 3D photonic intermediate reflector for textured micromorph silicon tandem solar cells has been investigated. In thin-film silicon tandem solar cells consisting of amorphous and microcrystalline silicon with two junctions of a-Si/c-Si, efficiency enhancements can be achieved by increasing the current density in the a-Si top cell providing an optimized current matching at high current densities. For an ideal photon-management between top and bottom cell, a spectrally-selective intermediate reflective layer (IRL) is necessary. We present the first fully-integrated 3D photonic thin-film IRL device incorporated on a planar substrate. Using a ZnO inverted opal structure the external quantum efficiency of the top cell in the spectral region of interest could be enhanced. As an outlook we present the design and the preparation of a 3D self organized photonic crystal structure in a textured micromorph tandem solar cell.
Nomura, Masahiro; Kage, Yuta; Müller, David; Moser, Dominik; Paul, Oliver
2015-06-01
Electrical and thermal properties of polycrystalline Si thin films with two-dimensional phononic patterning were investigated at room temperature. Electrical and thermal conductivities for the phononic crystal nanostructures with a variety of radii of the circular holes were measured to systematically investigate the impact of the nanopatterning. The concept of phonon-glass and electron-crystal is valid in the investigated electron and phonon transport systems with the neck size of 80 nm. The thermal conductivity is more sensitive than the electrical conductivity to the nanopatterning due to the longer mean free path of the thermal phonons than that of the charge carriers. The values of the figure of merit ZT were 0.065 and 0.035, and the enhancement factors were 2 and 4 for the p-doped and n-doped phononic crystals compared to the unpatterned thin films, respectively, when the characteristic size of the phononic crystal nanostructure is below 100 nm. The greater enhancement factor of ZT for the n-doped sample seems to result from the strong phonon scattering by heavy phosphorus atoms at the grain boundaries.
3D position determination in monolithic crystals coupled to SiPMs for PET
NASA Astrophysics Data System (ADS)
Etxebeste, Ane; Barrio, John; Muñoz, Enrique; Oliver, Josep F.; Solaz, Carles; Llosá, Gabriela
2016-05-01
The interest in using continuous monolithic crystals in positron emission tomography (PET) has grown in the last years. Coupled to silicon photomultipliers (SiPMs), the detector can combine high sensitivity and high resolution, the two main factors to be maximized in a positron emission tomograph. In this work, the position determination capability of a detector comprised of a 12× 12× 10 mm3 LYSO crystal coupled to an 8× 8 -pixel array of SiPMs is evaluated. The 3D interaction position of γ-rays is estimated using an analytical model of the light distribution including reflections on the facets of the crystal. Monte Carlo simulations have been performed to evaluate different crystal reflectors and geometries. The method has been characterized and applied to different cases. Intrinsic resolution obtained with the position estimation method used in this work, applied to experimental data, achieves sub-millimetre resolution values. Average resolution over the detector surface for 5 mm thick crystal is ∼0.9 mm FWHM and ∼1.2 mm FWHM for 10 mm thick crystal. Depth of interaction resolution is close to 2 mm FWHM in both cases, while the FWTM is ∼5.3 mm for 5 mm thick crystal and ∼9.6 mm for 10 mm thick crystal.
3D position determination in monolithic crystals coupled to SiPMs for PET.
Etxebeste, Ane; Barrio, John; Muñoz, Enrique; Oliver, Josep F; Solaz, Carles; Llosá, Gabriela
2016-05-21
The interest in using continuous monolithic crystals in positron emission tomography (PET) has grown in the last years. Coupled to silicon photomultipliers (SiPMs), the detector can combine high sensitivity and high resolution, the two main factors to be maximized in a positron emission tomograph. In this work, the position determination capability of a detector comprised of a [Formula: see text] mm(3) LYSO crystal coupled to an [Formula: see text]-pixel array of SiPMs is evaluated. The 3D interaction position of γ-rays is estimated using an analytical model of the light distribution including reflections on the facets of the crystal. Monte Carlo simulations have been performed to evaluate different crystal reflectors and geometries. The method has been characterized and applied to different cases. Intrinsic resolution obtained with the position estimation method used in this work, applied to experimental data, achieves sub-millimetre resolution values. Average resolution over the detector surface for 5 mm thick crystal is ∼0.9 mm FWHM and ∼1.2 mm FWHM for 10 mm thick crystal. Depth of interaction resolution is close to 2 mm FWHM in both cases, while the FWTM is ∼5.3 mm for 5 mm thick crystal and ∼9.6 mm for 10 mm thick crystal. PMID:27119737
Coherent heat transport in 2D phononic crystals with acoustic impedance mismatch
NASA Astrophysics Data System (ADS)
Arantes, A.; Anjos, V.
2016-03-01
In this work we have calculated the cumulative thermal conductivities of micro-phononic crystals formed by different combinations of inclusions and matrices at a sub-Kelvin temperature regime. The low-frequency phonon spectra (up to tens of GHz) were obtained by solving the generalized wave equation for inhomogeneous media with the plane wave expansion method. The thermal conductivity was calculated from Boltzmann transport theory highlighting the role of the low-frequency thermal phonons and neglecting phonon-phonon scattering. A purely coherent thermal transport regime was assumed throughout the structures. Our findings show that the cumulative thermal conductivity drops dramatically when compared with their bulk counterpart. Depending on the structural composition this reduction may be attributed to the phonon group velocity due to a flattening of the phonon dispersion relation, the extinction of phonon modes in the density of states or due to the presence of complete band gaps. According to the contrast between the inclusions and the matrices, three types of two dimensional phononic crystals were considered: carbon/epoxy, carbon/polyethylene and tungsten/silicon, which correspond respectively to a moderate, strong and very strong mismatch in the mechanical properties of these materials.
Bloch wave deafness and modal conversion at a phononic crystal boundary
NASA Astrophysics Data System (ADS)
Laude, Vincent; Moiseyenko, Rayisa P.; Benchabane, Sarah; Declercq, Nico F.
2011-12-01
We investigate modal conversion at the boundary between a homogeneous incident medium and a phononic crystal, with consideration of the impact of symmetry on the excitation of Bloch waves. We give a quantitative criterion for the appearance of deaf Bloch waves, which are antisymmetric with respect to a symmetry axis of the phononic crystal, in the frame of generalized Fresnel formulas for reflection and transmission at the phononic crystal boundary. This criterion is used to index Bloch waves in the complex band structure of the phononic crystal, for directions of incidence along a symmetry axis. We argue that within deaf frequency ranges transmission is multi-exponential, as it is within frequency band gaps.
Band gap in tubular pillar phononic crystal plate.
Shu, Fengfeng; Liu, Yongshun; Wu, Junfeng; Wu, Yihui
2016-09-01
In this paper, a phononic crystal (PC) plate with tubular pillars is presented and investigated. The band structures and mode displacement profiles are calculated by using finite element method. The result shows that a complete band gap opens when the ratio of the pillar height to the plate thickness is about 1.6. However, for classic cylinder pillar structures, a band gap opens when the ratio is equal or greater than 3. A tubular pillar design with a void room in it enhances acoustic multiple scattering and gives rise to the opening of the band gap. In order to verify it, a PC structure with double tubular pillars different in size (one within the other) is introduced and a more than 2times band gap enlargement is observed. Furthermore, the coupling between the resonant mode and the plate mode around the band gap is characterized, as well as the effect of the geometrical parameters on the band gap. The behavior of such structure could be utilized to design a pillar PC with stronger structural stability and to enlarge band gaps. PMID:27376841
Acoustic scattering from phononic crystals with complex geometry.
Kulpe, Jason A; Sabra, Karim G; Leamy, Michael J
2016-05-01
This work introduces a formalism for computing external acoustic scattering from phononic crystals (PCs) with arbitrary exterior shape using a Bloch wave expansion technique coupled with the Helmholtz-Kirchhoff integral (HKI). Similar to a Kirchhoff approximation, a geometrically complex PC's surface is broken into a set of facets in which the scattering from each facet is calculated as if it was a semi-infinite plane interface in the short wavelength limit. When excited by incident radiation, these facets introduce wave modes into the interior of the PC. Incorporation of these modes in the HKI, summed over all facets, then determines the externally scattered acoustic field. In particular, for frequencies in a complete bandgap (the usual operating frequency regime of many PC-based devices and the requisite operating regime of the presented theory), no need exists to solve for internal reflections from oppositely facing edges and, thus, the total scattered field can be computed without the need to consider internal multiple scattering. Several numerical examples are provided to verify the presented approach. Both harmonic and transient results are considered for spherical and bean-shaped PCs, each containing over 100 000 inclusions. This facet formalism is validated by comparison to an existing self-consistent scattering technique. PMID:27250192
Viewing zone duplication of multi-projection 3D display system using uniaxial crystal.
Lee, Chang-Kun; Park, Soon-Gi; Moon, Seokil; Lee, Byoungho
2016-04-18
We propose a novel multiplexing technique for increasing the viewing zone of a multi-view based multi-projection 3D display system by employing double refraction in uniaxial crystal. When linearly polarized images from projector pass through the uniaxial crystal, two possible optical paths exist according to the polarization states of image. Therefore, the optical paths of the image could be changed, and the viewing zone is shifted in a lateral direction. The polarization modulation of the image from a single projection unit enables us to generate two viewing zones at different positions. For realizing full-color images at each viewing zone, a polarization-based temporal multiplexing technique is adopted with a conventional polarization switching device of liquid crystal (LC) display. Through experiments, a prototype of a ten-view multi-projection 3D display system presenting full-colored view images is implemented by combining five laser scanning projectors, an optically clear calcite (CaCO_{3}) crystal, and an LC polarization rotator. For each time sequence of temporal multiplexing, the luminance distribution of the proposed system is measured and analyzed. PMID:27137284
Phonons in two-dimensional colloidal crystals with bond-strength disorder
NASA Astrophysics Data System (ADS)
Gratale, Matthew D.; Yunker, Peter J.; Chen, Ke; Still, Tim; Aptowicz, Kevin B.; Yodh, A. G.
2013-05-01
We study phonon modes in two-dimensional colloidal crystals composed of soft microgel particles with hard polystyrene particle dopants distributed randomly on the triangular lattice. This experimental approach produces close-packed lattices of spheres with random bond strength disorder, i.e., the effective springs coupling nearest neighbors are very stiff, very soft, or of intermediate stiffness. Particle tracking video microscopy and covariance matrix techniques are then employed to derive the phonon modes of the corresponding “shadow” crystals with bond strength disorder as a function of increasing dopant concentration. At low frequencies, hard and soft particles participate equally in the phonon modes, and the samples exhibit Debye-like density of states behavior characteristic of crystals. For mid- and high-frequency phonons, the relative participation of hard versus soft particles in each mode is found to vary systematically with dopant concentration. Additionally, a few localized modes, primarily associated with hard particle motions, are found at the highest frequencies.
High-resistance liquid-crystal lens array for rotatable 2D/3D autostereoscopic display.
Chang, Yu-Cheng; Jen, Tai-Hsiang; Ting, Chih-Hung; Huang, Yi-Pai
2014-02-10
A 2D/3D switchable and rotatable autostereoscopic display using a high-resistance liquid-crystal (Hi-R LC) lens array is investigated in this paper. Using high-resistance layers in an LC cell, a gradient electric-field distribution can be formed, which can provide a better lens-like shape of the refractive-index distribution. The advantages of the Hi-R LC lens array are its 2D/3D switchability, rotatability (in the horizontal and vertical directions), low driving voltage (~2 volts) and fast response (~0.6 second). In addition, the Hi-R LC lens array requires only a very simple fabrication process. PMID:24663563
Bottom-up Fabrication of Multilayer Stacks of 3D Photonic Crystals from Titanium Dioxide.
Kubrin, Roman; Pasquarelli, Robert M; Waleczek, Martin; Lee, Hooi Sing; Zierold, Robert; do Rosário, Jefferson J; Dyachenko, Pavel N; Montero Moreno, Josep M; Petrov, Alexander Yu; Janssen, Rolf; Eich, Manfred; Nielsch, Kornelius; Schneider, Gerold A
2016-04-27
A strategy for stacking multiple ceramic 3D photonic crystals is developed. Periodically structured porous films are produced by vertical convective self-assembly of polystyrene (PS) microspheres. After infiltration of the opaline templates by atomic layer deposition (ALD) of titania and thermal decomposition of the polystyrene matrix, a ceramic 3D photonic crystal is formed. Further layers with different sizes of pores are deposited subsequently by repetition of the process. The influence of process parameters on morphology and photonic properties of double and triple stacks is systematically studied. Prolonged contact of amorphous titania films with warm water during self-assembly of the successive templates is found to result in exaggerated roughness of the surfaces re-exposed to ALD. Random scattering on rough internal surfaces disrupts ballistic transport of incident photons into deeper layers of the multistacks. Substantially smoother interfaces are obtained by calcination of the structure after each infiltration, which converts amorphous titania into the crystalline anatase before resuming the ALD infiltration. High quality triple stacks consisting of anatase inverse opals with different pore sizes are demonstrated for the first time. The elaborated fabrication method shows promise for various applications demanding broadband dielectric reflectors or titania photonic crystals with a long mean free path of photons. PMID:27045887
NASA Technical Reports Server (NTRS)
Scalapino, D. J.; Sugar, R. L.; White, S. R.; Bickers, N. E.; Scalettar, R. T.
1989-01-01
Numerical simulations on the half-filled three-dimensional Hubbard model clearly show the onset of Neel order. Simulations of the two-dimensional electron-phonon Holstein model show the competition between the formation of a Peierls-CDW state and a superconducting state. However, the behavior of the partly filled two-dimensional Hubbard model is more difficult to determine. At half-filling, the antiferromagnetic correlations grow as T is reduced. Doping away from half-filling suppresses these correlations, and it is found that there is a weak attractive pairing interaction in the d-wave channel. However, the strength of the pair field susceptibility is weak at the temperatures and lattice sizes that have been simulated, and the nature of the low-temperature state of the nearly half-filled Hubbard model remains open.
Electron crystallography of ultrathin 3D protein crystals: atomic model with charges.
Yonekura, Koji; Kato, Kazuyuki; Ogasawara, Mitsuo; Tomita, Masahiro; Toyoshima, Chikashi
2015-03-17
Membrane proteins and macromolecular complexes often yield crystals too small or too thin for even the modern synchrotron X-ray beam. Electron crystallography could provide a powerful means for structure determination with such undersized crystals, as protein atoms diffract electrons four to five orders of magnitude more strongly than they do X-rays. Furthermore, as electron crystallography yields Coulomb potential maps rather than electron density maps, it could provide a unique method to visualize the charged states of amino acid residues and metals. Here we describe an attempt to develop a methodology for electron crystallography of ultrathin (only a few layers thick) 3D protein crystals and present the Coulomb potential maps at 3.4-Å and 3.2-Å resolution, respectively, obtained from Ca(2+)-ATPase and catalase crystals. These maps demonstrate that it is indeed possible to build atomic models from such crystals and even to determine the charged states of amino acid residues in the Ca(2+)-binding sites of Ca(2+)-ATPase and that of the iron atom in the heme in catalase. PMID:25730881
Electron crystallography of ultrathin 3D protein crystals: Atomic model with charges
Yonekura, Koji; Kato, Kazuyuki; Ogasawara, Mitsuo; Tomita, Masahiro; Toyoshima, Chikashi
2015-01-01
Membrane proteins and macromolecular complexes often yield crystals too small or too thin for even the modern synchrotron X-ray beam. Electron crystallography could provide a powerful means for structure determination with such undersized crystals, as protein atoms diffract electrons four to five orders of magnitude more strongly than they do X-rays. Furthermore, as electron crystallography yields Coulomb potential maps rather than electron density maps, it could provide a unique method to visualize the charged states of amino acid residues and metals. Here we describe an attempt to develop a methodology for electron crystallography of ultrathin (only a few layers thick) 3D protein crystals and present the Coulomb potential maps at 3.4-Å and 3.2-Å resolution, respectively, obtained from Ca2+-ATPase and catalase crystals. These maps demonstrate that it is indeed possible to build atomic models from such crystals and even to determine the charged states of amino acid residues in the Ca2+-binding sites of Ca2+-ATPase and that of the iron atom in the heme in catalase. PMID:25730881
2D and 3D Histioid Disclination Networks in Liquid Crystals
NASA Astrophysics Data System (ADS)
Jiang, Miao; Guo, Yubing; Lavrentovich, Oleg; Wei, Qi-Huo
Topological defects and disclination lines are of both fundamental interest and practical importance. In this paper, we will show that periodic/non-periodic 2D/3D networks of disclination lines can be created in nematic liquid crystal cells by setting well-designed alignment patterns at the top and bottom substrate surfaces. The desired complex patterns of liquid crystal molecular alignments at the substrates are obtained using a projection photoalignment technique based on plasmonic metamasks. The designs of alignment patterns and their resulting disclination line networks will be presented. These designable topological networks represent a new kind of artificial materials which could be of useful for directing colloidal and molecular assembly. National Science Foundation CMMI-1436565.
Shaping of light beams by 3D direct laser writing on facets of nonlinear crystals.
Lightman, Shlomi; Gvishi, Raz; Hurvitz, Gilad; Arie, Ady
2015-10-01
We demonstrate experimentally spatial-mode conversions of light beams generated in a quadratic nonlinear process by micron-scale structures placed on the facets of nonlinear crystals. These structures were printed on the crystal facets using a three-dimensional (3D) direct laser writing system. The functional structures were designed to modify the phase of the beam at specific wavelengths, thereby enabling conversion of a fundamental Gaussian laser beam into different high-order Hermite-Gaussian modes, Laguerre-Gaussian modes, and zeroth-order Bessel beams of the second harmonic. This facet functionalization opens exciting new opportunities for robust and compact beam shaping in a nonlinear interaction without compromising the conversion efficiency. PMID:26421556
Fabrication of 3D polymer photonic crystals for near-IR applications
NASA Astrophysics Data System (ADS)
Yao, Peng; Qiu, Liang; Shi, Shouyuan; Schneider, Garrett J.; Prather, Dennis W.; Sharkawy, Ahmed; Kelmelis, Eric
2008-02-01
Photonic crystals[1, 2] have stirred enormous research interest and became a growing enterprise in the last 15 years. Generally, PhCs consist of periodic structures that possess periodicity comparable with the wavelength that the PhCs are designed to modulate. If material and periodic pattern are properly selected, PhCs can be applied to many applications based on their unique properties, including photonic band gaps (PBG)[3], self-collimation[4], super prism[5], etc. Strictly speaking, PhCs need to possess periodicity in three dimensions to maximize their advantageous capabilities. However, many current research is based on scaled two-dimensional PhCs, mainly due to the difficulty of fabrication such three-dimensional PhCs. Many approaches have been explored for the fabrication of 3D photonic crystals, including layer-by-layer surface micromachining[6], glancing angle deposition[7], 3D micro-sculpture method[8], self-assembly[9] and lithographical methods[10-12]. Among them, lithographic methods became increasingly accepted due to low costs and precise control over the photonic crystal structure. There are three mostly developed lithographical methods, namely X-ray lithography[10], holographic lithography[11] and two-photon polymerization[12]. Although significant progress has been made in developing these lithography-based technologies, these approaches still suffer from significant disadvantages. X-ray lithography relies on an expensive radiation source. Holographic lithography lacks the flexibility to create engineered defects, and multi-photon polymerization is not suitable for parallel fabrication. In our previous work, we developed a multi-layer photolithography processes[13, 14] that is based on multiple resist application and enhanced absorption upon exposure. Using a negative lift-off resist (LOR) and 254nm DUV source, we have demonstrated fabrication of 3D arbitrary structures with feature size of several microns. However, severe intermixing problem
A 3D parallel simulator for crystal growth and solidification in complex alloy systems
NASA Astrophysics Data System (ADS)
Nestler, Britta
2005-02-01
A 3D parallel simulator is developed to numerically solve the evolution equations of a new non-isothermal phase-field model for crystal growth and solidification in complex alloy systems. The new model and the simulator are capable to simultaneously describe the diffusion processes of multiple components, the phase transitions between multiple phases and the development of the temperature field. Weak and facetted formulations of both, surface energy and kinetic anisotropies are incorporated in the phase-field model. Multicomponent bulk diffusion effects including interdiffusion coefficients as well as diffusion in the interfacial region of phase or grain boundaries are considered. We introduce our parallel simulator that is based on a finite difference discretization including effective adaptive strategies and multigrid methods to reduce computation time and memory usage. The parallelization is realized for distributed as well as shared memory computer architectures using MPI libraries and OpenMP concepts. Applying the new computer model, we present a variety of simulated crystal structures such as dendrites, grains, binary and ternary eutectics in 2D and 3D. The influence of anisotropy on the microstructure evolution shows the formation of facets in preferred crystallographic directions. Phase transformations and solidification processes in a real multi-component alloy can be described by incorporating the physical data (e.g. surface tensions, kinetic coefficients, specific heat, heat and mass diffusion coefficients) and the specific phase diagram (in particular latent heats and melting temperatures) into the diffuse interface model via the free energies.
Broadband evolution of phononic-crystal-waveguide eigenstates in real- and k-spaces.
Otsuka, P H; Nanri, K; Matsuda, O; Tomoda, M; Profunser, D M; Veres, I A; Danworaphong, S; Khelif, A; Benchabane, S; Laude, V; Wright, O B
2013-01-01
Control of sound in phononic band-gap structures promises novel control and guiding mechanisms. Designs in photonic systems were quickly matched in phononics, and rows of defects in phononic crystals were shown to guide sound waves effectively. The vast majority of work in such phononic guiding has been in the frequency domain, because of the importance of the phononic dispersion relation in governing acoustic confinement in waveguides. However, frequency-domain studies miss vital information concerning the phase of the acoustic field and eigenstate coupling. Using a wide range of wavevectors k, we implement an ultrafast technique to probe the wave field evolution in straight and L-shaped phononic crystal surface-phonon waveguides in real- and k-space in two spatial dimensions, thus revealing the eigenstate-energy redistribution processes and the coupling between different frequency-degenerate eigenstates. Such use of k-t space is a first in acoustics, and should have other interesting applications such as acoustic-metamaterial characterization. PMID:24284621
Broadband evolution of phononic-crystal-waveguide eigenstates in real- and k-spaces
Otsuka, P. H.; Nanri, K.; Matsuda, O.; Tomoda, M.; Profunser, D. M.; Veres, I. A.; Danworaphong, S.; Khelif, A.; Benchabane, S.; Laude, V.; Wright, O. B.
2013-01-01
Control of sound in phononic band-gap structures promises novel control and guiding mechanisms. Designs in photonic systems were quickly matched in phononics, and rows of defects in phononic crystals were shown to guide sound waves effectively. The vast majority of work in such phononic guiding has been in the frequency domain, because of the importance of the phononic dispersion relation in governing acoustic confinement in waveguides. However, frequency-domain studies miss vital information concerning the phase of the acoustic field and eigenstate coupling. Using a wide range of wavevectors k, we implement an ultrafast technique to probe the wave field evolution in straight and L-shaped phononic crystal surface-phonon waveguides in real- and k-space in two spatial dimensions, thus revealing the eigenstate-energy redistribution processes and the coupling between different frequency-degenerate eigenstates. Such use of k-t space is a first in acoustics, and should have other interesting applications such as acoustic-metamaterial characterization. PMID:24284621
Raman study of phonon modes in ErVO4 single crystals
NASA Astrophysics Data System (ADS)
Guedes, I.; Hirano, Y.; Grimsditch, M.; Wakabayashi, N.; Loong, C.-K.; Boatner, L. A.
2001-08-01
The phonon modes of a pure ErVO4 crystal were determined at room temperature using Raman scattering methods, and the observed frequencies were assigned according to group theory in terms of the internal modes of the VO43- ions and the external modes of the Er(VO4) lattice. The assignments of the phonon modes match well with the overall phonon systematics of the rare-earth orthovanadate series, and the results presented here reinforce the general trend of bonding strength in the zircon series of RVO4, RAsO4, and RPO4 materials.
Complete band gaps and deaf bands of triangular and honeycomb water-steel phononic crystals
NASA Astrophysics Data System (ADS)
Hsiao, Fu-Li; Khelif, Abdelkrim; Moubchir, Hanane; Choujaa, Abdelkrim; Chen, Chii-Chang; Laude, Vincent
2007-02-01
Phononic crystals with triangular and honeycomb lattices are investigated experimentally and theoretically. They are composed of arrays of steel cylinders immersed in water. The measured transmission spectra reveal the existence of complete band gaps but also of deaf bands. Band gaps and deaf bands are identified by comparing band structure computations, obtained by a periodic-boundary finite element method, with transmission simulations, obtained using the finite difference time domain method. The appearance of flat bands and the polarization of the associated eigenmodes is also discussed. Triangular and honeycomb phononic crystals with equal cylinder diameter and smallest spacing are compared. As previously obtained with air-solid phononic crystals, it is found that the first complete band gap opens for the honeycomb lattice but not for the triangular lattice, thanks to symmetry reduction.
Dexterous acoustic trapping and patterning of particles assisted by phononic crystal plate
Wang, Tian; Ke, Manzhu Xu, Shengjun; Feng, Junheng; Qiu, Chunyin; Liu, Zhengyou
2015-04-20
In this letter, we present experimental demonstration of multi-particles trapping and patterning by the artificially engineered acoustic field of phononic crystal plate. Polystyrene particles are precisely trapped and patterned in two dimensional arrays, for example, the square, triangular, or quasi-periodic arrays, depending on the structures of the phononic crystal plates with varying sub-wavelength holes array. Analysis shows that the enhanced acoustic radiation force, induced by the resonant transmission field highly localized near the sub-wavelength apertures, accounts for the particles self-organizing. It can be envisaged that this kind of simple design of phononic crystal plates would pave an alternative route for self-assembly of particles and may be utilized in the lab-on-a-chip devices.
Photonic liquid crystal fibers tuning by four electrode system produced with 3D printing technology
NASA Astrophysics Data System (ADS)
Ertman, Slawomir; Bednarska, Karolina; Czapla, Aleksandra; Woliński, Tomasz R.
2015-09-01
Photonic liquid crystal fiber has been intensively investigated in last few years. It has been proved that guiding properties of such fibers could be tuned with an electric field. In particular efficient tuning could be obtained if multi-electrode system allowing for dynamic change of not only intensity of the electric field, but also its direction. In this work we report a simple to build four electrode system, which is based on a precisely aligned four cylindrical microelectrodes. As an electrodes we use enameled copper wire with diameter adequate to the diameter of the fiber to be tuned. To ensure uniform and parallel alignment of the wires a special micro-profiles has been designed and then produced with filament 3D printer. The possibility of the dynamic change of the electric field direction in such scalable and cost effective electrode assembly has been experimentally confirmed.
Fabrication of 3-D Photonic Band Gap Crystals Via Colloidal Self-Assembly
NASA Technical Reports Server (NTRS)
Subramaniam, Girija; Blank, Shannon
2005-01-01
The behavior of photons in a Photonic Crystals, PCs, is like that of electrons in a semiconductor in that, it prohibits light propagation over a band of frequencies, called Photonic Band Gap, PBG. Photons cannot exist in these band gaps like the forbidden bands of electrons. Thus, PCs lend themselves as potential candidates for devices based on the gap phenomenon. The popular research on PCs stem from their ability to confine light with minimal losses. Large scale 3-D PCs with a PBG in the visible or near infra red region will make optical transistors and sharp bent optical fibers. Efforts are directed to use PCs for information processing and it is not long before we can have optical integrated circuits in the place of electronic ones.
Polymorphism, crystal nucleation and growth in the phase-field crystal model in 2D and 3D.
Tóth, Gyula I; Tegze, György; Pusztai, Tamás; Tóth, Gergely; Gránásy, László
2010-09-15
We apply a simple dynamical density functional theory, the phase-field crystal (PFC) model of overdamped conservative dynamics, to address polymorphism, crystal nucleation, and crystal growth in the diffusion-controlled limit. We refine the phase diagram for 3D, and determine the line free energy in 2D and the height of the nucleation barrier in 2D and 3D for homogeneous and heterogeneous nucleation by solving the respective Euler-Lagrange (EL) equations. We demonstrate that, in the PFC model, the body-centered cubic (bcc), the face-centered cubic (fcc), and the hexagonal close-packed structures (hcp) compete, while the simple cubic structure is unstable, and that phase preference can be tuned by changing the model parameters: close to the critical point the bcc structure is stable, while far from the critical point the fcc prevails, with an hcp stability domain in between. We note that with increasing distance from the critical point the equilibrium shapes vary from the sphere to specific faceted shapes: rhombic dodecahedron (bcc), truncated octahedron (fcc), and hexagonal prism (hcp). Solving the equation of motion of the PFC model supplied with conserved noise, solidification starts with the nucleation of an amorphous precursor phase, into which the stable crystalline phase nucleates. The growth rate is found to be time dependent and anisotropic; this anisotropy depends on the driving force. We show that due to the diffusion-controlled growth mechanism, which is especially relevant for crystal aggregation in colloidal systems, dendritic growth structures evolve in large-scale isothermal single-component PFC simulations. An oscillatory effective pair potential resembling those for model glass formers has been evaluated from structural data of the amorphous phase obtained by instantaneous quenching. Finally, we present results for eutectic solidification in a binary PFC model. PMID:21386517
Polymorphism, crystal nucleation and growth in the phase-field crystal model in 2D and 3D
NASA Astrophysics Data System (ADS)
Tóth, Gyula I.; Tegze, György; Pusztai, Tamás; Tóth, Gergely; Gránásy, László
2010-09-01
We apply a simple dynamical density functional theory, the phase-field crystal (PFC) model of overdamped conservative dynamics, to address polymorphism, crystal nucleation, and crystal growth in the diffusion-controlled limit. We refine the phase diagram for 3D, and determine the line free energy in 2D and the height of the nucleation barrier in 2D and 3D for homogeneous and heterogeneous nucleation by solving the respective Euler-Lagrange (EL) equations. We demonstrate that, in the PFC model, the body-centered cubic (bcc), the face-centered cubic (fcc), and the hexagonal close-packed structures (hcp) compete, while the simple cubic structure is unstable, and that phase preference can be tuned by changing the model parameters: close to the critical point the bcc structure is stable, while far from the critical point the fcc prevails, with an hcp stability domain in between. We note that with increasing distance from the critical point the equilibrium shapes vary from the sphere to specific faceted shapes: rhombic dodecahedron (bcc), truncated octahedron (fcc), and hexagonal prism (hcp). Solving the equation of motion of the PFC model supplied with conserved noise, solidification starts with the nucleation of an amorphous precursor phase, into which the stable crystalline phase nucleates. The growth rate is found to be time dependent and anisotropic; this anisotropy depends on the driving force. We show that due to the diffusion-controlled growth mechanism, which is especially relevant for crystal aggregation in colloidal systems, dendritic growth structures evolve in large-scale isothermal single-component PFC simulations. An oscillatory effective pair potential resembling those for model glass formers has been evaluated from structural data of the amorphous phase obtained by instantaneous quenching. Finally, we present results for eutectic solidification in a binary PFC model.
NASA Astrophysics Data System (ADS)
Ponge, Marie-Fraise; Dubus, Bertrand; Granger, Christian; Vasseur, Jérôme; Thi, Mai Pham; Hladky-Hennion, Anne-Christine
Piezoelectric phononic crystals with periodic short-circuit conditions exhibit Bragg band gaps. They are used to design a Fabry-Perot cavity. The design of the device enables a modification of cavity length by a spatial shift of electrical boundary conditions. The resonator is thus tunable and a frequency shift is obtained. An analytical model based on a transfer matrix formalism is used to model longitudinal wave propagation inside the structure. Cavity length, phononic crystal and transducer position are optimized to increase resonance and antiresonance frequency shifts as well as coupling coefficient. Numerical and experimental results are presented and discussed.
Vibration energy harvesting using a phononic crystal with point defect states
NASA Astrophysics Data System (ADS)
Lv, Hangyuan; Tian, Xiaoyong; Wang, Michael Yu; Li, Dichen
2013-01-01
A vibration energy harvesting generator was studied in the present research using point-defect phononic crystal with piezoelectric material. By removing a rod from a perfect phononic crystal, a resonant cavity was formed. The elastic waves in the range of gap frequencies were all forbidden in any direction, while the waves with resonant frequency were localized and enhanced in the resonant cavity. The collected vibration energy was converted into electric energy by putting a polyvinylidene fluoride film in the middle of the defect. This structure can be used to simultaneously realize both vibration damping and broad-distributed vibration energy harvesting.
Tunable phononic crystals based on piezoelectric composites with 1-3 connectivity.
Croënne, Charles; Ponge, Marie-Fraise; Dubus, Bertrand; Granger, Christian; Haumesser, Lionel; Levassort, Franck; Vasseur, Jérôme O; Lordereau, Albert; Pham Thi, Mai; Hladky-Hennion, Anne-Christine
2016-06-01
Phononic crystals made of piezoelectric composites with 1-3 connectivity are studied theoretically and experimentally. It is shown that they present Bragg band gaps that depend on the periodic electrical boundary conditions. These structures have improved properties compared to phononic crystals composed of bulk piezoelectric elements, especially the existence of larger band gaps and the fact that they do not require severe constraints on their aspect ratios. Experimental results present an overall agreement with the theoretical predictions and clearly show that the pass bands and stop bands of the device under study are easily tunable by only changing the electrical boundary conditions applied on each piezocomposite layer. PMID:27369154
Research on the large band gaps in multilayer radial phononic crystal structure
NASA Astrophysics Data System (ADS)
Gao, Nansha; Wu, Jiu Hui; Guan, Dong
2016-04-01
In this paper, we study the band gaps (BGs) of new proposed radial phononic crystal (RPC) structure composed of multilayer sections. The band structure, transmission spectra and eigenmode displacement fields of the multilayer RPC are calculated by using finite element method (FEM). Due to the vibration coupling effects between thin circular plate and intermediate mass, the RPC structure can exhibit large BGs, which can be effectively shifted by changing the different geometry values. This study shows that multilayer RPC can unfold larger and lower BGs than traditional phononic crystals (PCs) and RPC can be composed of single material.
Interface nano-confined acoustic waves in polymeric surface phononic crystals
Travagliati, Marco; Nardi, Damiano; Giannetti, Claudio; Ferrini, Gabriele; Banfi, Francesco; Gusev, Vitalyi; Pingue, Pasqualantonio; Piazza, Vincenzo
2015-01-12
The impulsive acoustic dynamics of soft polymeric surface phononic crystals is investigated here in the hypersonic frequency range by near-IR time-resolved optical diffraction. The acoustic response is analysed by means of wavelet spectral methods and finite element modeling. An unprecedented class of acoustic modes propagating within the polymer surface phononic crystal and confined within 100 nm of the nano-patterned interface is revealed. The present finding opens the path to an alternative paradigm for characterizing the mechanical properties of soft polymers at interfaces and for sensing schemes exploiting polymers as embedding materials.
Simulation of light transport in scintillators based on 3D characterization of crystal surfaces
Cherry, Simon R.
2013-01-01
In the development of positron emission tomography (PET) detectors, understanding and optimizing scintillator light collection is critical for achieving high performance, particularly when the design incorporates depth-of-interaction (DOI) encoding or time-of-flight information. Monte-Carlo simulations play an important role in guiding research in detector designs and popular software such as GATE now include models of light transport in scintillators. Although current simulation toolkits are able to provide accurate models of perfectly polished surfaces, they do not successfully predict light output for other surface finishes, for example those often used in DOI-encoding detectors. The lack of accuracy of those models mainly originates from a simplified description of rough surfaces as an ensemble of micro-facets determined by the distribution of their normal, typically a Gaussian distribution. The user can specify the standard deviation of this distribution, but this parameter does not provide a full description of the surface reflectance properties. We propose a different approach based on 3D measurements of the surface using atomic force microscopy (AFM). Polished and rough (unpolished) crystals were scanned to compute the surface reflectance properties. The angular distributions of reflectance and reflected rays were computed and stored in look-up tables (LUTs). The LUTs account for the effect of incidence angle and were integrated in a light transport model. Crystals of different sizes were simulated with and without reflector. The simulated maximum light output and the light output as a function of DOI showed very good agreement with experimental characterization of the crystals, indicating that our approach provides an accurate model of polished and rough surfaces and could be used to predict light collection in scintillators. This model is based on a true 3D representation of the surface, makes no assumption about the surface and provides insight on the
NASA Astrophysics Data System (ADS)
Mizoguchi, K.; Morishita, R.; Oohata, G.
2013-02-01
The detection-energy dependence of a coherent phonon in a (001) CdTe crystal, generated by ultrashort laser pulses with the center energy transparent or opaque to the sample, is investigated using a spectrally resolved pump-probe method. At the excitation in the transparent region, the detection-energy dependence of the phonon amplitude has two peaks at the energy shifted by one times the phonon energy of CdTe from the center energy of the probe pulses. On the other hand, the amplitude in the opaque region shows two peaks at the energy shifted by about two times the phonon energy. This difference occurs even though the observed energies of the coherent phonons in both regions are the same as that of the longitudinal optical phonon of CdTe. The energy shifts in the detection-energy dependence imply that the emission and absorption of one phonon and two phonons in the transparent and opaque regions, respectively, are implicated in coherent phonon generation. In this study, the detection-energy dependence is examined from the viewpoint of the third-order nonlinear susceptibility based on the impulsive stimulated Raman scattering process under nonresonant and resonant conditions.
NASA Astrophysics Data System (ADS)
Gu, Chunlong; Jin, Feng
2016-05-01
Point defect modes in a 2D phononic crystal with giant magnetostrictive material tuned by a magnetic field and compressive stress are investigated theoretically in this study. The 3D magnetostrictive constitutive model proposed by Liu and Zheng (2005 Acta Mech. Sin. 21 278-85) is adopted to develop effective elastic, piezomagnetic, and magnetic permeability constants. The finite element method, in combination with a supercell technique, is then applied to obtain the band structures and transmission spectra of the point defect modes in a 2D phononic crystal composed of Terfenol-D rods of circular cross section embedded in a polymethyl methacrylate matrix with a square lattice. The magnetic field not only enlarges the first band gap (FBG) but also opens up a new band gap of XY modes. New point defect modes are simultaneously trapped in the band gaps. The width of the FBG and the frequencies of the point defects of the Z mode decrease as the magnetic field increases.
Formation of Bragg band gaps in anisotropic phononic crystals analyzed with the empty lattice model
Wang, Yan -Feng; Maznev, Alexei; Laude, Vincent
2016-05-11
Bragg band gaps of phononic crystals generally, but not always, open at Brillouin zone boundaries. The commonly accepted explanation stems from the empty lattice model: assuming a small material contrast between the constituents of the unit cell, avoided crossings in the phononic band structure appear at frequencies and wavenumbers corresponding to band intersections; for scalar waves the lowest intersections coincide with boundaries of the first Brillouin zone. However, if a phononic crystal contains elastically anisotropic materials, its overall symmetry is not dictated solely by the lattice symmetry. We construct an empty lattice model for phononic crystals made of isotropic andmore » anisotropic materials, based on their slowness curves. We find that, in the anisotropic case, avoided crossings generally do not appear at the boundaries of traditionally defined Brillouin zones. Furthermore, the Bragg "planes" which give rise to phononic band gaps, are generally not flat planes but curved surfaces. Lastly, the same is found to be the case for avoided crossings between shear (transverse) and longitudinal bands in the isotropic case.« less
NASA Astrophysics Data System (ADS)
Yin, J.; Zhang, S.; Zhang, H. W.; Chen, B. S.
2015-10-01
A fast scheme based on the multi-level substructure technique is proposed for the band structure and transmission characteristics calculation of phononic crystals uniformly. The main idea is that finite element models of phononic crystals are divided into several domains by a special multi-level decomposition. For the band structure calculation, the upscaling calculation is employed to condense the internal stiffness matrix of the unit cell into the Bloch boundary. Due to the internal stiffness matrix does not change along with reduced wave vectors in an iteration process, the scheme can reduce the computational scale and improve the efficiency greatly, meanwhile it does not introduce approximation into the traditional finite element model. For the transmission characteristics calculation, the unit cell of the phononic crystal is periodic which is taken as a substructure with the same coefficient matrix. Moreover, the downscaling calculation of internal displacements can be selected flexibly. Some closely watched examples of the three-dimensional locally resonant, defect state of Lamb wave and Bragg waveguide are analyzed. Numerical results indicate that the proposed scheme is efficient and accurate, which may widely be applicable and suitable for complex phononic crystal problems, and provides a reliable numerical tool to optimize and design crystal devices.
Switchable 3D liquid crystal grating generated by periodic photo-alignment on both substrates.
Nys, I; Beeckman, J; Neyts, K
2015-10-21
A planar liquid crystal (LC) cell is developed in which two photo-alignment layers have been illuminated with respectively a horizontal and a vertical diffraction pattern of interfering left- and right-handed circularly polarized light. In the bulk of the cell, a complex LC configuration is obtained with periodicity in two dimensions. Remarkably, the period of the structure is larger than the period of the interference pattern, indicating that lowering of the symmetry allows a reduction in the elastic energy. The liquid crystal configuration depends on the periodicity of the alignment but also on the thickness of the cell. By applying a voltage over the electrodes, the power going into the different diffracted orders can be tuned. Finite element (FE) simulations based on Q-tensor theory are used to find the 3D equilibrium director distribution, which is used to simulate the near-field transmission profile based on the Jones calculus. A 2D Fourier transform is performed for both the x- and y-component of the transmitted wave to find the diffraction efficiency. PMID:26313442
Roll, Mark F.; Kampf, Jeffrey W.; Laine, Richard M.
2011-05-10
We report here the Diels–Alder reaction of octa(diphenylacetylene)silsesquioxane [DPA₈OS] with tetraphenylcyclopentadienone or tetra(p-tolyl)cyclopentadienone to form octa(hexaphenylbenzene)octasilsesquioxane, (Ph₆C₆)₈OS, or octa(tetratolyldiphenylbenzene)octasilsesquioxane, (p-Tolyl₄Ph₂C₆)₈OS. Likewise, tetra(p-tolyl)cyclopentadienone reacts with octa(p-tolylethynylphenyl)OS to form octa(pentatolylphenylbenzene)octasilsesquioxane (p-Tolyl₅PhC₆)₈OS. These compounds, with molecular weights of 4685–5245 Da, were isolated and characterized using a variety of analytical methods. The crystal structure of DPA₈OS offers a 3 nm³ unit cell with Z = 1. The crystal structure of (Ph₆C₆)₈OS was determined to have a triclinic unit cell of 11 nm³ with Z = 1. The latter structure is believed to be the largest discrete molecular structure reported with 330 carbons. Efforts to dehydrogenatively cyclize (Scholl reaction) the hexaarylbenzene groups to form 3-D octgraphene compounds are described.
Ultra-wide acoustic band gaps in pillar-based phononic crystal strips
Coffy, Etienne Lavergne, Thomas; Addouche, Mahmoud; Euphrasie, Sébastien; Vairac, Pascal; Khelif, Abdelkrim
2015-12-07
An original approach for designing a one dimensional phononic crystal strip with an ultra-wide band gap is presented. The strip consists of periodic pillars erected on a tailored beam, enabling the generation of a band gap that is due to both Bragg scattering and local resonances. The optimized combination of both effects results in the lowering and the widening of the main band gap, ultimately leading to a gap-to-midgap ratio of 138%. The design method used to improve the band gap width is based on the flattening of phononic bands and relies on the study of the modal energy distribution within the unit cell. The computed transmission through a finite number of periods corroborates the dispersion diagram. The strong attenuation, in excess of 150 dB for only five periods, highlights the interest of such ultra-wide band gap phononic crystal strips.
Dynamic response of a tunable phononic crystal under applied mechanical and magnetic loadings
NASA Astrophysics Data System (ADS)
Bayat, Alireza; Gordaninejad, Faramarz
2015-06-01
The dynamic response of a tunable phononic crystal consisting of a porous hyperelastic magnetoelastic elastomer subjected to a macroscopic deformation and an external magnetic field is theoretically investigated. Finite deformations and magnetic induction influence phononic characteristics of the periodic structure through geometrical pattern transformation and material properties. A magnetoelastic energy function is proposed to develop constitutive laws considering large deformations and magnetic induction in the periodic structure. Analytical and finite element methods are utilized to compute the dispersion relation and band structure of the phononic crystal for different cases of deformation and magnetic loadings. It is demonstrated that magnetic induction not only controls the band diagram of the structure but also has a strong effect on preferential directions of wave propagation.
Long-Lived, Coherent Acoustic Phonon Oscillations in GaN Single Crystals
Wu, S.; Geiser, P.; Jun, J.; Karpinski, J.; Park, J.-R.; Sobolewski, R.
2006-01-31
We report on coherent acoustic phonon (CAP) oscillations studied in high-quality bulk GaN single crystals with a two-color femtosecond optical pump-probe technique. Using a far-above-the-band gap ultraviolet excitation (~270 nm wavelength) and a near-infrared probe beam (~810 nm wavelength), the long-lived, CAP transients were observed within a 10 ns time-delay window between the pump and probe pulses, with a dispersionless (proportional to the probe-beam wave vector) frequency of ~45 GHz. The measured CAP attenuation corresponded directly to the absorption of the probe light in bulk GaN, indicating that the actual (intrinsic) phonon-wave attenuation in our crystals was significantly smaller than the measured 65.8 cm^-1 value. The velocity of the phonon propagation was equal to the velocity of sound in GaN.
Ultra-wide acoustic band gaps in pillar-based phononic crystal strips
NASA Astrophysics Data System (ADS)
Coffy, Etienne; Lavergne, Thomas; Addouche, Mahmoud; Euphrasie, Sébastien; Vairac, Pascal; Khelif, Abdelkrim
2015-12-01
An original approach for designing a one dimensional phononic crystal strip with an ultra-wide band gap is presented. The strip consists of periodic pillars erected on a tailored beam, enabling the generation of a band gap that is due to both Bragg scattering and local resonances. The optimized combination of both effects results in the lowering and the widening of the main band gap, ultimately leading to a gap-to-midgap ratio of 138%. The design method used to improve the band gap width is based on the flattening of phononic bands and relies on the study of the modal energy distribution within the unit cell. The computed transmission through a finite number of periods corroborates the dispersion diagram. The strong attenuation, in excess of 150 dB for only five periods, highlights the interest of such ultra-wide band gap phononic crystal strips.
Observation of superconductivity induced by a point contact on 3D Dirac semimetal Cd3As2 crystals.
Wang, He; Wang, Huichao; Liu, Haiwen; Lu, Hong; Yang, Wuhao; Jia, Shuang; Liu, Xiong-Jun; Xie, X C; Wei, Jian; Wang, Jian
2016-01-01
Three-dimensional (3D) Dirac semimetals, which possess 3D linear dispersion in the electronic structure as a bulk analogue of graphene, have lately generated widespread interest in both materials science and condensed matter physics. Recently, crystalline Cd3As2 has been proposed and proved to be a 3D Dirac semimetal that can survive in the atmosphere. Here, by using point contact spectroscopy measurements, we observe exotic superconductivity around the point contact region on the surface of Cd3As2 crystals. The zero-bias conductance peak (ZBCP) and double conductance peaks (DCPs) symmetric around zero bias suggest p-wave-like unconventional superconductivity. Considering the topological properties of 3D Dirac semimetals, our findings may indicate that Cd3As2 crystals under certain conditions could be topological superconductors, which are predicted to support Majorana zero modes or gapless Majorana edge/surface modes in the boundary depending on the dimensionality of the material. PMID:26524129
From Modal Mixing to Tunable Functional Switches in Nonlinear Phononic Crystals
NASA Astrophysics Data System (ADS)
Ganesh, R.; Gonella, S.
2015-02-01
We introduce a paradigm for spatial and modal wave manipulation based on nonlinear phononic crystals and explore its potential for engineering wave control systems with tunable, adaptive, and multifunctional characteristics. Our approach exploits nonlinear mechanisms to stretch the frequency signature of the wave response and distribute it over multiple modes, thereby activating a mixture of modal characteristics and enabling functionalities associated with high-frequency optical modes, even while operating in the low-frequency regime. To elucidate the versatility of this approach, we consider different granular crystal configurations that span the available landscape of crystal topologies and wave control functionalities. The ability to switch between complementary functionalities allows rethinking nonlinear phononic crystals as programmable acoustic ports that form the building blocks of a new structural logic framework enabled by nonlinearity.
From modal mixing to tunable functional switches in nonlinear phononic crystals.
Ganesh, R; Gonella, S
2015-02-01
We introduce a paradigm for spatial and modal wave manipulation based on nonlinear phononic crystals and explore its potential for engineering wave control systems with tunable, adaptive, and multifunctional characteristics. Our approach exploits nonlinear mechanisms to stretch the frequency signature of the wave response and distribute it over multiple modes, thereby activating a mixture of modal characteristics and enabling functionalities associated with high-frequency optical modes, even while operating in the low-frequency regime. To elucidate the versatility of this approach, we consider different granular crystal configurations that span the available landscape of crystal topologies and wave control functionalities. The ability to switch between complementary functionalities allows rethinking nonlinear phononic crystals as programmable acoustic ports that form the building blocks of a new structural logic framework enabled by nonlinearity. PMID:25699446
Mechanism of the Reduced Thermal Conductivity of Fishbone-Type Si Phononic Crystal Nanostructures
NASA Astrophysics Data System (ADS)
Nomura, M.; Maire, J.
2015-06-01
The mechanism of the reduced thermal conductivity of fishbone-type phononic crystal (PnC) nanostructures, in which ballistic phonon transport is dominant, was investigated with consideration of both the wave and particle nature of phonons. Phononic band diagrams were calculated for an Si nanowire and a fishbone-type PnC structure with a period of 100 nm, and a clear reduction of the group velocity of phonons, because of a zone-folding effect, was shown. Air-suspended Si nanowires and fishbone-type PnC structures were fabricated by electron beam (EB) lithography, and their thermal conductivities were measured by use of the originally developed micro time-domain thermoreflectance method. The PnC structure had a much lower thermal conductivity. We measured the thermal conductivity of a variety of PnC structures with different fin widths to investigate the mechanism of the reduced thermal conductivity observed. The result indicates that the increase of the phonon traveling distance. as a result of the fins, also results in reduced thermal conductivity.
Mechanism of the Reduced Thermal Conductivity of Fishbone-Type Si Phononic Crystal Nanostructures
NASA Astrophysics Data System (ADS)
Nomura, M.; Maire, J.
2014-09-01
The mechanism of the reduced thermal conductivity of fishbone-type phononic crystal (PnC) nanostructures, in which ballistic phonon transport is dominant, was investigated with consideration of both the wave and particle nature of phonons. Phononic band diagrams were calculated for an Si nanowire and a fishbone-type PnC structure with a period of 100 nm, and a clear reduction of the group velocity of phonons, because of a zone-folding effect, was shown. Air-suspended Si nanowires and fishbone-type PnC structures were fabricated by electron beam (EB) lithography, and their thermal conductivities were measured by use of the originally developed micro time-domain thermoreflectance method. The PnC structure had a much lower thermal conductivity. We measured the thermal conductivity of a variety of PnC structures with different fin widths to investigate the mechanism of the reduced thermal conductivity observed. The result indicates that the increase of the phonon traveling distance. as a result of the fins, also results in reduced thermal conductivity.
Raman study of phonon dynamics in PMN crystal
NASA Astrophysics Data System (ADS)
Svitelskiy, O.; Toulouse, J.; Ye, Z.-G.
2002-03-01
PMN is a model system for lead relaxors.Despite much effort,the origin of the relaxor behavior remains a puzzle.Difficulties arise from the coexistence of several phases at the same temperature.We have carried out a new detailed Raman study of PMN in a wide temperature range of 100-1000K.The entire acquired spectra have been analyzed using multiple peak decomposition.A comparison with neutron scattering data[1] suggests that strong Raman line at 45 cm_-1 is dominated by scattering from a distribution of TA phonons near the zone boundary.The fine structure of the line can be explained by interaction with TO1 and LA phonons.Lowering the temperature leads to the gradual appearance of the rhombohedral phase and to the growth and splitting of lines associated with it (as in KTN[2]): TO2,TO3,TO4.None of the lines exhibit a characteristic ferroelectric behavior.No Raman analogue of the neutron scattering waterfall[3] have been observed Thanks for support to DOE#DE-FG02-00ER45842 1.A.Naberezhnov et al,Eur.Phys.J.B11,13(1999) 3.P.DiAntonio et al,Phys.Rev.B,47,5629(1993) 2.P.Gehring et al.,accepted to PRL
Light-directing chiral liquid crystal nanostructures: from 1D to 3D.
Bisoyi, Hari Krishna; Li, Quan
2014-10-21
Endowing external, remote, and dynamic control to self-organized superstructures with desired functionalities is a principal driving force in the bottom-up nanofabrication of molecular devices. Light-driven chiral molecular switches or motors in liquid crystal (LC) media capable of self-organizing into optically tunable one-dimensional (1D) and three-dimensional (3D) superstructures represent such an elegant system. As a consequence, photoresponsive cholesteric LCs (CLCs), i.e., self-organized 1D helical superstructures, and LC blue phases (BPs), i.e., self-organized 3D periodic cubic lattices, are emerging as a new generation of multifunctional supramolecular 1D and 3D photonic materials in their own right because of their fundamental academic interest and technological significance. These smart stimuli-responsive materials can be facilely fabricated from achiral LC hosts by the addition of a small amount of a light-driven chiral molecular switch or motor. The photoresponsiveness of these materials is a result of both molecular interaction and geometry changes in the chiral molecular switch upon light irradiation. The doped photoresponsive CLCs undergo light-driven pitch modulation and/or helix inversion, which has many applications in color filters, polarizers, all-optical displays, optical lasers, sensors, energy-saving smart devices, and so on. Recently, we have conceptualized and rationally synthesized different light-driven chiral molecular switches that have very high helical twisting powers (HTPs) and exhibit large changes in HTP in different states, thereby enabling wide phototunability of the systems by the addition of very small amounts of the molecular switches into commercially available achiral LCs. The light-driven chiral molecular switches are based on well-recognized azobenzene, dithienylcyclopentene, and spirooxazine derivatives. We have demonstrated high-resolution and lightweight photoaddressable displays without patterned electronics on
Propagation of Electromagnetic Waves in 3D Opal-based Magnetophotonic Crystals
NASA Astrophysics Data System (ADS)
Pardavi-Horvath, Martha; Makeeva, Galina S.; Golovanov, Oleg A.; Rinkevich, Anatolii B.
2013-03-01
Opals, a class of self-organized 3D nanostructures, are typical representatives of photonic bandgap structures. The voids inside of the opal structure of close packed SiO2 spheres can be infiltrated by a magnetic material, creating magnetically tunable magnetophotonic crystals with interesting and potentially useful properties at GHz and THz frequencies. The propagation of electromagnetic waves at microwave frequencies was investigated numerically in SiO2 opal based magnetic nanostructures, using rigorous mathematical models to solve Maxwell's equations complemented by the Landau-Lifshitz equation with electrodynamic boundary conditions. The numerical approach is based on Galerkin's projection method using the decomposition algorithm on autonomous blocks with Floquet channels. The opal structure consists of SiO2 nanospheres, with inter-sphere voids infiltrated with nanoparticles of Ni-Zn ferrites. Both the opal matrix and the ferrite are assumed to be lossy. A model, taking into account the real structure of the ferrite particles in the opal's voids was developed to simulate the measured FMR lineshape of the ferrite infiltrated opal. The numerical technique shows an excellent agreement when applied to model recent experimental data on similar ferrite opals.
Probing the intrinsic optical Bloch-mode emission from a 3D photonic crystal.
Hsieh, Mei-Li; Bur, James A; Du, Qingguo; John, Sajeev; Lin, Shawn-Yu
2016-10-14
We report experimental observation of intrinsic Bloch-mode emission from a 3D tungsten photonic crystal at low thermal excitation. After the successful removal of conventional metallic emission (normal emission), it is possible to make an accurate comparison of the Bloch-mode and the normal emission. For all biases, we found that the emission intensity of the Bloch-mode is higher than that of the normal emission. The Bloch-mode emission also exhibits a slower dependence on [Formula: see text] than that of the normal emission. The observed higher emission intensity and a different T-dependence is attributed to Bloch-mode assisted emission where emitters have been located into a medium having local density of states different than the isotropic case. Furthermore, our finite-difference time-domain (FDTD) simulation shows the presence of localized spots at metal-air boundaries and corners, having intense electric field. The enhanced plasmonic field and local non-equilibrium could induce a strong thermally stimulated emission and may be the cause of our unusual observation. PMID:27606574
Manipulating the temperature dependence of the thermal conductivity of graphene phononic crystal
NASA Astrophysics Data System (ADS)
Hu, Shiqian; An, Meng; Yang, Nuo; Li, Baowen
2016-07-01
By using non-equilibrium molecular dynamics simulations, modulating the temperature dependence of thermal conductivity of graphene phononic crystals (GPnCs) is investigated. It is found that the temperature dependence of thermal conductivity of GPnCs follows ∼T ‑α behavior. The power exponents (α) can be efficiently tuned by changing the characteristic size of GPnCs. The phonon participation ratio spectra and dispersion relation reveal that the long-range phonon modes are more affected in GPnCs with larger holes (L 0). Our results suggest that constructing GPnCs is an effective method to manipulate the temperature dependence of thermal conductivity of graphene, which would be beneficial for developing GPnC-based thermal management and signal processing devices.
Manipulating the temperature dependence of the thermal conductivity of graphene phononic crystal.
Hu, Shiqian; An, Meng; Yang, Nuo; Li, Baowen
2016-07-01
By using non-equilibrium molecular dynamics simulations, modulating the temperature dependence of thermal conductivity of graphene phononic crystals (GPnCs) is investigated. It is found that the temperature dependence of thermal conductivity of GPnCs follows ∼T (-α) behavior. The power exponents (α) can be efficiently tuned by changing the characteristic size of GPnCs. The phonon participation ratio spectra and dispersion relation reveal that the long-range phonon modes are more affected in GPnCs with larger holes (L 0). Our results suggest that constructing GPnCs is an effective method to manipulate the temperature dependence of thermal conductivity of graphene, which would be beneficial for developing GPnC-based thermal management and signal processing devices. PMID:27196392
Zhong, Kuo; Li, Jiaqi; Van Cleuvenbergen, Stijn; Clays, Koen
2016-09-21
Direct reactive ion etching (RIE) of hollow SiO2 sphere colloidal crystals (HSCCs) is employed as a facile, low-cost method to fabricate complex three-dimensional (3D) hierarchical nanostructures. These multilayered structures are gradually transformed into nanostructures of increasing complexity by controlling the etching time, without complicated procedures (no mask needed). The resulting 3D topologies are unique, and cannot be obtained through traditional approaches. The formation mechanism of these structures is explained in detail by geometrical modeling during the different etching stages, through shadow effects of the higher layers. SEM images confirm the modeled morphological changes. The nanostructures obtained by our approach show very fine features as small as ∼30 nm. Our approach opens new avenues to directly obtain complex 3D nanostructures from colloidal crystals and can find applications in sensing, templating, and catalysis where fine tuning the specific surface might be critical. PMID:27545098
Combined global 2D-local 3D modeling of the industrial Czochralski silicon crystal growth process
NASA Astrophysics Data System (ADS)
Jung, T.; Seebeck, J.; Friedrich, J.
2013-04-01
A global, axisymmetric thermal model of a Czochralski furnace is coupled to an external, local, 3D, time-dependent flow model of the melt via the inclusion of turbulent heat fluxes, extracted from the 3D melt model, into the 2D furnace model. Boundary conditions of the 3D model are updated using results from the 2D model. In the 3D model the boundary layers are resolved by aggressive mesh refinement towards the walls, and the Large Eddy Simulation approach is used to model the turbulent flow in the melt volume on a relatively coarse mesh to minimize calculation times. It is shown that by using this approach it is possible to reproduce fairly good results from Direct Numerical Simulations obtained on much finer meshes, as well as experimental results for interface shape and oxygen concentration in the case of growth of silicon crystals with 210 mm diameter for photovoltaics by the Czochralski method.
Electrical conduction mechanisms in PbSe and PbS nano crystals 3D matrix layer
NASA Astrophysics Data System (ADS)
Arbell, Matan; Hechster, Elad; Sarusi, Gabby
2016-02-01
A simulation study and measurements of the electrical conductance in a PbSe and PbS spherical Nano-crystal 3D matrix layer was carried out focusing on its dependences of Nano-crystal size distribution and size gradient along the layer thickness (z-direction). The study suggests a new concept of conductance enhancement by utilizing a size gradient along the layer thickness from mono-layer to the next mono-layer of the Nano-crystals, in order to create a gradient of the energy levels and thus improve directional conductance in this direction. A Monte Carlo simulation of the charge carriers path along the layer thickness of the Nano-crystals 3D matrix using the Miller-Abrahams hopping model was performed. We then compared the conductance characteristics of the gradual size 3D matrix layer to a constant-sized 3D matrix layer that was used as a reference in the simulation. The numerical calculations provided us with insights into the actual conductance mechanism of the PbSe and PbS Nano-crystals 3D matrix and explained the discrepancies in actual conductance and the variability in measured mobilities published in the literature. It is found that the mobility and thus conductance are dependent on a critical electrical field generated between two adjacent nano-crystals. Our model explains the conductance dependents on the: Cathode-Anode distance, the distance between the adjacent nano-crystals in the 3D matrix layer and the size distribution along the current direction. Part of the model (current-voltage dependence) was validated using a current-voltage measurements taken on a constant size normal distribution nano-crystals PbS layer (330nm thick) compared with the predicted I-V curves. It is shown that under a threshold bias, the current is very low, while after above a threshold bias the conductance is significantly increased due to increase of hopping probability. Once reaching the maximum probability the current tend to level-off reaching the maximal conductance
Convergence of the phonon energy in two-dimensional atomic crystal of lead
NASA Astrophysics Data System (ADS)
Yan, Jia-An
2015-03-01
Accurate phonon energies are important for the study of two-dimensional (2D) atomic crystals. Using the 2D honeycomb lattice of lead (Pb) as a model system, we studied the convergence of the phonon energies on several important parameters in supercell calculations based on the density-functional perturbation theory as implemented in Quantum Espresso code. These parameters include the plane wave cut-off energy, the vacuum space size, the charge density cut-off, and FFT grid. The tested pseudopotentials (PPs) include the widely used Troullier-Martin (TM), Hartwigsen-Goedeker-Hutter (HGH), Projector Augmented-Wave (PAW), and ultrasoft pseudopotential (USPP), with the same PBE exchange-correlation functional. Surprisingly, the phonon energies calculated using these PPs exhibit quite distinct dependence on those parameters. Specifically, for both TM and USPP PPs, the phonon energies at the Brillouin zone center exhibit oscillations and even large negative phonon modes with the increase of the vacuum size. In contrast, the HGH and PAW PPs show fast and stable convergence with the same settings. The origin of these oscillation will be discussed. Supported by the Towson University Faculty Development and Research Committee (Grant OSPR # 140269), and the Fisher College of Science and Mathematics Fisher General Endowment.
Phonon probe of local strains in SnSxSe2-x mixed crystals
NASA Astrophysics Data System (ADS)
Hadjiev, V. G.; De, D.; Peng, H. B.; Manongdo, J.; Guloy, A. M.
2013-03-01
We present a combined Raman spectroscopy and density functional perturbation theory (DFPT) study of phonon variation with composition x in the mixed crystals SnSxSe2-x. The experimentally observed two-mode behavior of the A1g and Eg vibrations involving Se(S) atoms is shown to arise from the lack of overlapping of the corresponding phonon dispersion bands in SnS2 and SnSe2. This offers a unique opportunity to assess local distortions of the trigonal Sn3Se pyramids in SnSxSe2-x as no Se and S mode mixing is involved. The dependence of local height and base length of Sn3Se pyramids with x is derived by a procedure that uses the measured A1g (Se) and Eg (Se) phonons in SnSxSe2-x, those calculated by DFPT for SnSe2 at different hydrostatic pressure, DFPT phonon dispersion, and the contribution from mass-disorder induced phonon self-energy.
Li, J.; Guan, J. Y.; Zhang, S. F.; Ban, S. L.; Qu, Y.
2014-04-21
Within the framework of dielectric continuum and Loudon's uniaxial crystal models, existence conditions dependent on components and frequencies for optical phonons in wurtzite nitride core-shell nanowires (CSNWs) are discussed to obtain dispersion relations and electrostatic potentials of optical phonons in In{sub x}Ga{sub 1−x}N/GaN CSNWs. The results show that there may be four types of optical phonons in In{sub x}Ga{sub 1−x}N/GaN CSNWs for a given ternary mixed crystal (TMC) component due to the phonon dispersion anisotropy. This property is analogous to wurtzite planar heterojunctions. Among the optical phonons, there are two types of quasi-confined optical (QCO) phonons (named, respectively, as QCO-A and QCO-B), one type of interface (IF) phonons and propagating (PR) phonons existing in certain component and frequency domains while the dispersion relations and electrostatic potentials of same type of optical phonons vary with components. Furthermore, the size effect on optical phonons in CSNWs is also discussed. The dispersion relations of IF and QCO-A are independent of the boundary location of CSNWs. Meanwhile, dispersion relations and electrostatic potentials of QCO-B and PR phonons vary obviously with size, especially, when the ratio of a core radius to a shell radius is small, and dispersion relation curves of PR phonons appear to be close to each other, whereas, this phenomenon disappears when the ratio becomes large. Based on our conclusions, one can further discuss photoelectric properties in nitride CSNWs consisting of TMCs associated with optical phonons.
Phonon dispersion in acene molecular crystals using van der Waals density functionals
NASA Astrophysics Data System (ADS)
Brown-Altvater, Florian; Rangel, Tonatiuh; Neaton, Jeffrey B.
Much progress has been made of late in understanding the fundamental processes in optoelectronic materials. An ongoing challenge is the accurate inclusion of nuclear motion and to go beyond the Born-Oppenheimer approximation. Especially in materials like molecular crystals, where van der Waals (vdW) forces dominate the cohesive energy and the electronic structure is very sensitive to intermolecular geometry, phonons can be an important facilitator and dissipation mechanism. Thus there is a need to assess and understand the efficacy of existing approaches for phonon dispersions in vdW-bound solids. In this work we use a vdW density functional to calculate the phonon dispersion of members of the acene family. We establish the accuracy of the method using naphthalene, obtaining excellent agreement with experimental results, and in a further step, we explore the strength of the electron-phonon coupling across the Brillouin zone. Taken all together, our calculations illustrate the potential for quantitative prediction of vibrational properties of weakly-bound organic crystals over the entire Brillouin zone from first principles.
Elastic filter based on coupled resonator waveguides in phononic crystal slabs
NASA Astrophysics Data System (ADS)
Khelif, Abdelkrim; Mohammadi, Saeed; Eftekhar, Ali; Adibi, Ali; Aoubiza, Boujemaa
2010-02-01
In this paper we demonstrate the possibility of forming a new elastic filter structure based on the coupled resonator waveguides in phononic crystal slabs (CRAW) with superior performance over the conventional filters. The structures are made by etching a honeycomb array of holes in a free standing slab. This phononic slab structure exhibits an absolute phononic band gap for all polarizations of guided waves inside the slab including the Lamb and Love waves. We present an analysis of a different family of waveguides in phononic-crystal slabs, and illustrate the considerations that must be applied to achieve single-mode guided bands in these structures. Consequently, an unusual family of selective elastic filters composed of several single resonators that are coupled periodically through evanescent waves is obtained. The elastic energy is localized in the extended defect formed by the collective coupled resonators. The frequencies of the filters are sensitive to the geometrical parameters and to the separation distance between the indiviual resonators. Numerical simulations are performed using the finite element method and considering Zinc-Oxide slab.
Bulk crystal growth and electronic characterization of the 3D Dirac semimetal Na{sub 3}Bi
Kushwaha, Satya K.; Krizan, Jason W.; Cava, R. J.; Feldman, Benjamin E.; Gyenis, András; Randeria, Mallika T.; Xiong, Jun; Xu, Su-Yang; Alidoust, Nasser; Belopolski, Ilya; Liang, Tian; Zahid Hasan, M.; Ong, N. P.; Yazdani, A.
2015-04-01
High quality hexagon plate-like Na{sub 3}Bi crystals with large (001) plane surfaces were grown from a molten Na flux. The freshly cleaved crystals were analyzed by low temperature scanning tunneling microscopy and angle-resolved photoemission spectroscopy, allowing for the characterization of the three-dimensional (3D) Dirac semimetal (TDS) behavior and the observation of the topological surface states. Landau levels were observed, and the energy-momentum relations exhibited a linear dispersion relationship, characteristic of the 3D TDS nature of Na{sub 3}Bi. In transport measurements on Na{sub 3}Bi crystals, the linear magnetoresistance and Shubnikov-de Haas quantum oscillations are observed for the first time.
Zou, Guo-Dong; Zhang, Gui-Gang; Hu, Bing; Li, Jian-Rong; Feng, Mei-Ling; Wang, Xin-Chen; Huang, Xiao-Ying
2013-11-01
A 3D organic-inorganic hybrid compound, (2-MepyH)3[{Fe(1,10-phen)3}3][{Pr4Sb12O18(OH)Cl(11.5)}(TDC)(4.5)({Pr4Sb12O18(OH)Cl(9.5)} Cl)]·3(2-Mepy)·28H2O (1; 2-Mepy=2-methylpyridine, 1,10-phen=1,10-phenanthroline, H2TDC=thiophene-2,5-dicarboxylic acid), was hydrothermally synthesized and structurally characterized. Unusually, two kinds of high-nuclearity clusters, namely [(Pr4Sb12O18(OH)Cl11)(COO)5](5-) and [(Pr4Sb12O18(OH)Cl9)Cl(COO)5](4-), coexist in the structure of compound 1; two of the latter clusters are doubly bridged by two μ2-Cl(-) moieties to form a new centrosymmetric dimeric cluster. An unprecedented spontaneous and reversible single-crystal-to-single-crystal transformation was observed, which simultaneously involved a notable organic-ligand movement between the metal ions and an alteration of the bridging ion in the dimeric cluster, induced by guest-release/re-adsorption, thereby giving rise to the interconversion between compound 1 and the compound (2-MepyH)3[{Fe(1,10-phen)3}3][{Pr4Sb12O18(OH)Cl(11.5)}(TDC)4({Pr4Sb12O18Cl(10.5)(TDC)(0.5)(H2O)(1.5)}O(0.5))]·25H2O (1'). The mechanism of this transformation has also been discussed in great detail. Photocatalytic H2-evolution activity was observed for compound 1' under UV light with Pt as a co-catalyst and MeOH as a sacrificial electron donor. PMID:24114981
Potemkin, F V; Mareev, E I; Khodakovskii, N G; Mikheev, P M
2013-08-31
The dynamics of coherent phonons in fluorine-containing crystals was investigated by pump-probe technique in the plasma production regime. Several phonon modes, whose frequencies are overtones of the 0.38-THz fundamental frequency, were simultaneously observed in a lithium fluoride crystal. Phonons with frequencies of 1 and 0.1 THz were discovered in a calcium fluoride crystal and coherent phonons with frequencies of 1 THz and 67 GHz were observed in a barium fluoride crystal. Furthermore, in the latter case the amplitudes of phonon mode oscillations were found to significantly increase 15 ps after laser irradiation. (interaction of laser radiation with matter)
NASA Astrophysics Data System (ADS)
Liu, Yifei; Manjubala, Inderchand; Roschger, Paul; Schell, Hanna; Duda, Georg N.; Fratzl, Peter
2010-10-01
Callus tissue formed during bone fracture healing is a mixture of different tissue types as revealed by histological analysis. But the structural characteristics of mineral crystals within the healing callus are not well known. Since two-dimensional (2D) scanning small-angle X-ray scattering (sSAXS) patterns showed that the size and orientation of callus crystals vary both spatially and temporally [1] and 2D electron microscopic analysis implies an anisotropic property of the callus morphology, the mineral crystals within the callus are also expected to vary in size and orientation in 3D. Three-dimensional small-angle X-ray scattering (3D SAXS), which combines 2D SAXS patterns collected at different angles of sample tilting, has been previously applied to investigate bone minerals in horse radius [2] and oim/oim mouse femur/tibia [3]. We implement a similar 3D SAXS method but with a different way of data analysis to gather information on the mineral alignment in fracture callus. With the proposed accurate yet fast assessment of 3D SAXS information, it was shown that the plate shaped mineral particles in the healing callus were aligned in groups with their predominant orientations occurring as a fiber texture.
Switching band-gaps of a phononic crystal slab by surface instability
NASA Astrophysics Data System (ADS)
Bayat, Alireza; Gordaninejad, Faramarz
2015-07-01
High-amplitude wrinkle formation is employed to propose a one-dimensional phononic crystal slab consists of a thin film bonded to a thick compliant substrate. Buckling induced surface instability generates a wrinkly structure triggered by a compressive strain. It is demonstrated that a surface periodic pattern and corresponding stress can control elastic wave propagation in the low thickness composite slab. Simulation results show that the periodic wrinkly structure can be used as a transformative phononic crystal that can switch the band diagram of the structure in a reversible manner. The results of this study provide opportunities for the smart design of tunable switches and frequency filters at ultrasonic and hypersonic frequency ranges.
NASA Astrophysics Data System (ADS)
Tsai, Chia-Nien; Chen, Lien-Wen
2016-07-01
Self-collimation is wave propagation in straight path without diffraction. The performance is evaluated by bandwidth, angular collimating range and straightness of equi-frequency contours. The present study aims to manipulate the self-collimated beam in square-array phononic crystals by means of orientated rectangular inclusions. Finite element simulations are performed to investigate the effects of the aspect ratio and orientation angle of rectangular inclusions on the self-collimated beam. The simulation results show that the proposed design successfully achieves all-angle self-collimation phenomenon. In addition, it also shows that the propagation direction of a self-collimated beam can be effectively manipulated by varying the orientation angle of inclusions. Numerical simulation result of the S-shaped bend demonstrates that acoustic collimated beam can be steered with negligible diffraction. Overall, the proposed design has significant potential for the realization of applications such as collimators, acoustic waveguides and other phononic crystals-based systems.
Acoustic beam splitting in two-dimensional phononic crystals using self-collimation effect
Li, Jing; Wu, Fugen Zhong, Huilin; Yao, Yuanwei; Zhang, Xin
2015-10-14
We propose two models of self-collimation-based beam splitters in phononic crystals. The finite element method is used to investigate the propagation properties of acoustic waves in two-dimensional phononic crystals. The calculated results show that the efficiency of the beam splitter can be controlled systematically by varying the radius of the rods or by changing the orientation of the square rods in the line defect. The effect of changing the side length of the square rods on acoustic wave propagation is discussed. The results show that the total transmission/reflection range decreases/increases as the side length increases. We also find that the relationship between the orientation of the transflective point and the side length of the square rods is quasi-linear.
Acoustic beam splitting in two-dimensional phononic crystals using self-collimation effect
NASA Astrophysics Data System (ADS)
Li, Jing; Wu, Fugen; Zhong, Huilin; Yao, Yuanwei; Zhang, Xin
2015-10-01
We propose two models of self-collimation-based beam splitters in phononic crystals. The finite element method is used to investigate the propagation properties of acoustic waves in two-dimensional phononic crystals. The calculated results show that the efficiency of the beam splitter can be controlled systematically by varying the radius of the rods or by changing the orientation of the square rods in the line defect. The effect of changing the side length of the square rods on acoustic wave propagation is discussed. The results show that the total transmission/reflection range decreases/increases as the side length increases. We also find that the relationship between the orientation of the transflective point and the side length of the square rods is quasi-linear.
Interface-guided mode of Lamb waves in a two-dimensional phononic crystal plate
NASA Astrophysics Data System (ADS)
Huang, Ping-Ping; Yao, Yuan-Wei; Wu, Fu-Gen; Zhang, Xin; Li, Jing; Hu, Ai-Zhen
2015-05-01
We investigate the interface-guided mode of Lamb waves in a phononic crystal heterostructures plate, which is composed of two different semi-infinite phononic crystal (PC) plates. The interface-guided modes of the Lamb wave can be obtained by the lateral lattice slipping or by the interface longitudinal gliding. Significantly, it is observed that the condition to generate the interface-guided modes of the Lamb wave is more demanding than that of the studied fluid-fluid system. The interface-guided modes are strongly affected not only by the relative movement of the two semi-infinite PCs but also by the thickness of the PC plate. Project supported by the National Natural Science Foundation of China (Grant Nos. 11374068 and 11374066), the Science & Technology Star of Zhujiang Foundation of Guangzhou, China (Grant No. 2011J2200013), and the Natural Science Foundation of Guangdong, China (Grant No. S2012020010885).
NASA Astrophysics Data System (ADS)
Wang, T.; Ke, M.; Qiu, C.; Liu, Z.
2016-06-01
We present the design for an acoustic system that can achieve particle trapping and transport using the acoustic force field above a phononic crystal plate. The phononic crystal plate comprised a thin brass plate with periodic slits alternately embedded with two kinds of elastic inclusions. Enhanced acoustic transmission and localized acoustic fields were achieved when the structure was excited by external acoustic waves. Because of the different resonant frequencies of the two elastic inclusions, the acoustic field could be controlled via the working frequency. Particles were transported between adjacent traps under the influence of the adjustable acoustic field. This device provides a new and versatile avenue for particle manipulation that would complement other means of particle manipulation.
Control of elastic wave propagation in one-dimensional piezomagnetic phononic crystals.
Ponge, Marie-Fraise; Croënne, Charles; Vasseur, Jérôme O; Bou Matar, Olivier; Hladky-Hennion, Anne-Christine; Dubus, Bertrand
2016-06-01
Two ways of controlling the acoustic waves propagation by external inductance or capacitance in a one-dimensional (1-D) piezomagnetic phononic crystal are investigated. The structure is made of identical bars, constituted of a piezomagnetic material, surrounded by a coil and connected to an external impedance. A model of propagation of longitudinal elastic waves through the periodic structure is developed and the dispersion equation is obtained. Reflection and transmission coefficients are derived from a 2 × 2 transfer matrix formalism that also allows for the calculation of elastic effective parameters (density, Young modulus, speed of sound, impedance). The effect of shunting impedances is numerically investigated. The results reveal that a connected external inductance tunes the Bragg band gaps of the 1-D phononic crystal. When the elements are connected via a capacitance, a hybridization gap, due to the resonance of the LC circuit made of the piezomagnetic element and the capacitance, coexists with the Bragg band gap. The value of the external capacitance modifies the boundaries of both gaps. Calculation of the effective characteristics of the phononic crystal leads to an analysis of the physical mechanisms involved in the wave propagation. When periodically connected to external capacitances, a homogeneous piezomagnetic stack behaves as a dispersive tunable metamaterial. PMID:27369153
Gutmann, Matthias J.; Graziano, Gabriella; Mukhopadhyay, Sanghamitra; Refson, Keith; von Zimmerman, Martin
2015-01-01
Direct phonon excitation in a neutron time-of-flight single-crystal Laue diffraction experiment has been observed in a single crystal of NaCl. At room temperature both phonon emission and excitation leave characteristic features in the diffuse scattering and these are well reproduced using ab initio phonons from density functional theory (DFT). A measurement at 20 K illustrates the effect of thermal population of the phonons, leaving the features corresponding to phonon excitation and strongly suppressing the phonon annihilation. A recipe is given to compute these effects combining DFT results with the geometry of the neutron experiment. PMID:26306090
Lai, Chun-Feng; Hsieh, Cheng-Liang; Wu, Chia-Jung
2013-09-15
This study presents the light-spectrum modification of warm white-light-emitting diodes (w-WLEDs) with 3D colloidal photonic crystals (3D CPhCs) to approximate candlelight. The study measures the angular-resolved transmission properties of the w-WLEDs with CPhCs, which exhibit photonic stop bands based on the CPhC photonic band structures. The w-WLEDs with 3D CPhCs produce a low correlated color temperature of 1963 K, a high color-rendering index of 85, and a luminous flux of 22.8 lm (four times that of a candle). This study presents the successful development of a novel low-cost technique to produce candlelight w-WLEDs for use as an indoor light source. PMID:24104827
Zhu, Jun; Chen, Weiqiu; Yang, Jiashi
2014-09-01
We study the propagation of thickness-twist (TT) waves in a crystal plate of AT-cut quartz with periodically varying, piecewise constant thickness. The scalar differential equation by Tiersten and Smythe is employed. The problem is found to be mathematically equivalent to the motion of an electron in a periodic potential field governed by Schrodinger's equation. An analytical solution is obtained. Numerical results show that the eigenvalue (frequency) spectrum of the waves has a band structure with allowed and forbidden bands. Therefore, for TT waves, plates with periodically varying thickness can be considered as phononic crystals. The effects of various parameters on the frequency spectrum are examined. PMID:24924785
Novel and simple route to fabricate 2D ordered gold nanobowl arrays based on 3D colloidal crystals.
Rao, Yanying; Tao, Qin; An, Ming; Rong, Chunhui; Dong, Jian; Dai, Yurong; Qian, Weiping
2011-11-01
In this study, we present a new method to fabricate large-area two-dimensionally (2D) ordered gold nanobowl arrays based on 3D colloidal crystals by wet chemosynthesis, which combines the advantages of a very simple preparation and an applicability to "real" nanomaterials. By combination of in situ growth of gold nanoshell (GNSs) arrays based on three-dimensional (3D) colloidal silica crystals, a monolayer ordered reversed GNS array (2D ordered GNS array) was conveniently manufactured by an acrylic ester modified biaxial oriented polypropylene (BOPP). 2D ordered gold nanobowl array with adjustable periodic holes, good stability, reproducibility, and repeatability could be obtained when the silica core was etched by HF solution. The surface-enhanced Raman scattering (SERS) enhancement factor (EF) of this 2D ordered gold nanobowl array could reach 1.27 × 10(7), which shows high SERS enhancing activity and can be used as a universal SERS substrate. PMID:21932785
NASA Astrophysics Data System (ADS)
Yan, C. L.; Bao, J.; Yan, Z. W.
2016-03-01
The surface and interface phonon-polaritons in freestanding rectangular quantum well wire systems consisting of polar ternary mixed crystals are investigated in the modified random-element-isodisplacement model and the Born-Huang approximation, based on the Maxwell's equations with the boundary conditions. The numerical results of the surface and interface phonon-polariton frequencies as functions of the wave-vector, geometric structure, and the composition of the ternary mixed crystals in GaAs/AlxGa1-xAs and ZnxCd1-xSe/ZnSe quantum well wire systems are obtained and discussed. It is shown that there are 10 and 8 branches of surface and interface phonon-polaritons in the two quantum well wire systems respectively. The effects of the "two-mode" and "one-mode" behaviors of the ternary mixed crystals on the surface and interface phonon-polariton modes are shown in the dispersion curves.
Nanostructured TTT(TCNQ)2 Organic Crystals as Promising Thermoelectric n-Type Materials: 3D Modeling
NASA Astrophysics Data System (ADS)
Sanduleac, Ionel; Casian, Anatolie
2016-03-01
The thermoelectric properties of quasi-one-dimensional TTT(TCNQ)2 organic crystals have been investigated to assess the prospect of using this type of compound as an n-type thermoelectric material. A three-dimensional (3D) physical model was elaborated. This takes into account two of the most important interactions of conduction electrons with longitudinal acoustic phonons—scattering of the electrons' by neighboring molecular chains and scattering by impurities and defects. Electrical conductivity, thermopower, power factor, electronic thermal conductivity, and thermoelectric figure of merit in the direction along the conducting molecular chains were calculated numerically for different crystal purity. It was shown that in stoichiometric compounds the thermoelectric figure of merit ZT remains small even after an increase of crystal perfection. The thermoelectric properties may be significantly enhanced by simultaneous increases of crystal perfection and electron concentration. The latter can be achieved by additional doping with donors. For less pure crystals, the interaction with impurities dominates the weak interchain interaction and the simpler one-dimensional (1D) physical model is applicable. When the impurity scattering is reduced, the interchain interaction begins to limit carrier mobility and use of the 3D physical model is required. The optimum properties enabling prediction of ZT ˜ 1 were determined.
Stone, Adam; Jain, Himanshu; Dierolf, Volkmar; Sakakura, Masaaki; Shimotsuma, Yasuhiko; Miura, Kiyotaka; Hirao, Kazuyuki; Lapointe, Jerome; Kashyap, Raman
2015-01-01
Direct three-dimensional laser writing of amorphous waveguides inside glass has been studied intensely as an attractive route for fabricating photonic integrated circuits. However, achieving essential nonlinear-optic functionality in such devices will also require the ability to create high-quality single-crystal waveguides. Femtosecond laser irradiation is capable of crystallizing glass in 3D, but producing optical-quality single-crystal structures suitable for waveguiding poses unique challenges that are unprecedented in the field of crystal growth. In this work, we use a high angular-resolution electron diffraction method to obtain the first conclusive confirmation that uniform single crystals can be grown inside glass by femtosecond laser writing under optimized conditions. We confirm waveguiding capability and present the first quantitative measurement of power transmission through a laser-written crystal-in-glass waveguide, yielding loss of 2.64 dB/cm at 1530 nm. We demonstrate uniformity of the crystal cross-section down the length of the waveguide and quantify its birefringence. Finally, as a proof-of-concept for patterning more complex device geometries, we demonstrate the use of dynamic phase modulation to grow symmetric crystal junctions with single-pass writing. PMID:25988599
Stone, Adam; Jain, Himanshu; Dierolf, Volkmar; Sakakura, Masaaki; Shimotsuma, Yasuhiko; Miura, Kiyotaka; Hirao, Kazuyuki; Lapointe, Jerome; Kashyap, Raman
2015-01-01
Direct three-dimensional laser writing of amorphous waveguides inside glass has been studied intensely as an attractive route for fabricating photonic integrated circuits. However, achieving essential nonlinear-optic functionality in such devices will also require the ability to create high-quality single-crystal waveguides. Femtosecond laser irradiation is capable of crystallizing glass in 3D, but producing optical-quality single-crystal structures suitable for waveguiding poses unique challenges that are unprecedented in the field of crystal growth. In this work, we use a high angular-resolution electron diffraction method to obtain the first conclusive confirmation that uniform single crystals can be grown inside glass by femtosecond laser writing under optimized conditions. We confirm waveguiding capability and present the first quantitative measurement of power transmission through a laser-written crystal-in-glass waveguide, yielding loss of 2.64 dB/cm at 1530 nm. We demonstrate uniformity of the crystal cross-section down the length of the waveguide and quantify its birefringence. Finally, as a proof-of-concept for patterning more complex device geometries, we demonstrate the use of dynamic phase modulation to grow symmetric crystal junctions with single-pass writing. PMID:25988599
Abernathy, Douglas L.; Ma, Jie; Yan, Jiaqiang; Delaire, Olivier A.; Chen, Xi; Weathers, Annie; Mukhopadhyay, Saikat; Shi, Li
2015-04-15
A variety of crystals contain quasi-one-dimensional substructures, which yield distinctive electronic, spintronic, optical and thermoelectric properties. There is a lack of understanding of the lattice dynamics that influences the properties of such complex crystals. Here we employ inelastic neutron scatting measurements and density functional theory calculations to show that numerous low-energy optical vibrational modes exist in higher manganese silicides, an example of such crystals. These optical modes, including unusually low-frequency twisting motions of the Si ladders inside the Mn chimneys, provide a large phase space for scattering acoustic phonons. A hybrid phonon and diffuson model is proposed to explain the low and anisotropic thermal conductivity of higher manganese silicides and to evaluate nanostructuring as an approach to further suppress the thermal conductivity and enhance the thermoelectric energy conversion efficiency. This discovery offers new insights into the structure-property relationships of a broad class of materials with quasi-one-dimensional substructures for various applications.
Wu, Yuchen; Feng, Jiangang; Su, Bin; Jiang, Lei
2016-03-01
Arrays of unidirectional dewetting behaviors can be generated by using 3D-wettability-difference micropillars, yielding highly ordered organic single-crystalline belt arrays. These patterned organic belts show an improved mobility record and can be used as flexible pressure sensors with high sensitivity. PMID:26823061
Design of quasi-one-dimensional phononic crystal cavity for efficient photoelastic modulation
NASA Astrophysics Data System (ADS)
Kim, Ingi; Iwamoto, Satoshi; Arakawa, Yasuhiko
2016-08-01
We propose and design a phononic crystal (PnC) cavity for efficient photoelastic modulation. A strongly confined acoustic field in the cavity enhances light-sound interaction, which results in efficient phase modulation of light. As one of the possible configurations, an acoustic cavity formed in a quasi-one-dimensional (quasi-1D) PnC was investigated. By carefully tuning geometrical parameters, we successfully designed a high-Q cavity mode for a longitudinal wave within a complete phononic band gap. The acoustic Q was calculated to be as high as 9.5 × 104. This enables efficient optical modulation by a factor of 2.5 compared with a bar-type structure without PnCs.
Band gap structures in two-dimensional super porous phononic crystals.
Liu, Ying; Sun, Xiu-zhan; Chen, Shao-ting
2013-02-01
As one kind of new linear cellular alloys (LCAs), Kagome honeycombs, which are constituted by triangular and hexagonal cells, attract great attention due to the excellent performance compared to the ordinary ones. Instead of mechanical investigation, the in-plane elastic wave dispersion in Kagome structures are analyzed in this paper aiming to the multi-functional application of the materials. Firstly, the band structures in the common two-dimensional (2D) porous phononic structures (triangular or hexagonal honeycombs) are discussed. Then, based on these results, the wave dispersion in Kagome honeycombs is given. Through the component cell porosity controlling, the effects of component cells on the whole responses of the structures are investigated. The intrinsic relation between the component cell porosity and the critical porosity of Kagome honeycombs is established. These results will provide an important guidance in the band structure design of super porous phononic crystals. PMID:23089223
Observation of superconductivity induced by a point contact on 3D Dirac semimetal Cd3 As2 crystals
NASA Astrophysics Data System (ADS)
Wang, He; Wang, Huichao; Liu, Haiwen; Lu, Hong; Yang, Wuhao; Jia, Shuang; Liu, Xiongjun; Xie, Xincheng; Wei, Jian; Wang, Jian
The 3D Dirac semimetal state is located at the topological phase boundary and can potentially be driven into other topological phases including topological insulator, topological metal and the long-pursuit topological superconductor states. Crystalline Cd3As2 has been proposed and proved to be one of 3D Dirac semimetals which can survive in atmosphere. By precisely controlled point contact (PC) measurements, we observe the exotic superconductivity in the vicinity of the point contact region on the surface of Cd3As2 crystal, which might be induced by the local pressure in the out-of-plane direction from the metallic tip for PC. The observation of zero bias conductance peak (ZBCP) and double conductance peaks (DCPs) symmetric to zero bias further reveals p-wave like unconventional superconductivity in Cd3As2. Considering the special topological property of the 3D Dirac semimetal, our findings may indicate that the Cd3As2 crystal under certain conditions is a candidate of topological superconductor, which is predicted to support Majorana zero modes or gapless Majorana edge/surface modes on the boundary depending on the dimensionality of the material. This work was financially supported by the National Basic Research Program of China (Greanted Nos. 2012CB927400).
Wu, Songtao; Zhu, Gaohua; Zhang, Jin S; Banerjee, Debasish; Bass, Jay D; Ling, Chen; Yano, Kazuhisa
2014-05-21
We report anisotropic expansion of self-assembled colloidal polystyrene-poly(dimethylsiloxane) crystals and its impact on the phonon band structure at hypersonic frequencies. The structural expansion was achieved by a multistep infiltration-polymerization process. Such a process expands the interplanar lattice distance 17% after 8 cycles whereas the in-plane distance remains unaffected. The variation of hypersonic phonon band structure induced by the anisotropic lattice expansion was recorded by Brillouin measurements. In the sample before expansion, a phononic band gap between 3.7 and 4.4 GHz is observed; after 17% structural expansion, the gap is shifted to a lower frequency between 3.5 and 4.0 GHz. This study offers a facile approach to control the macroscopic structure of colloidal crystals with great potential in designing tunable phononic devices. PMID:24691556
NASA Astrophysics Data System (ADS)
Maier, S.; Port, H.
1987-11-01
Photoexcitation spectra of triplet (T1← S0) zero-phonon lines and phonon sidebands in different anthracene electron donor-acceptor (EDA) complex crystals (A-PMDA, A-TCNB, A-TCPA) have been analyzed between 1.3 K and 50 K at high spectral resolution. From the electron-phonon coupling strength at T = 0 K values of the charge-transfer (CT) character in the range between 6% and 10% are calculated. The differences in these values are found to be correlated with the energetic positions of the triplet state, which are explained within the framework of the Mulliken theory.
Self-consistent phonon theory of the crystallization and elasticity of attractive hard spheres.
Shin, Homin; Schweizer, Kenneth S
2013-02-28
We propose an Einstein-solid, self-consistent phonon theory for the crystal phase of hard spheres that interact via short-range attractions. The approach is first tested against the known behavior of hard spheres, and then applied to homogeneous particles that interact via short-range square well attractions and the Baxter adhesive hard sphere model. Given the crystal symmetry, packing fraction, and strength and range of attractive interactions, an effective harmonic potential experienced by a particle confined to its Wigner-Seitz cell and corresponding mean square vibrational amplitude are self-consistently calculated. The crystal free energy is then computed and, using separate information about the fluid phase free energy, phase diagrams constructed, including a first-order solid-solid phase transition and its associated critical point. The simple theory qualitatively captures all the many distinctive features of the phase diagram (critical and triple point, crystal-fluid re-entrancy, low-density coexistence curve) as a function of attraction range, and overall is in good semi-quantitative agreement with simulation. Knowledge of the particle localization length allows the crystal shear modulus to be estimated based on elementary ideas. Excellent predictions are obtained for the hard sphere crystal. Expanded and condensed face-centered cubic crystals are found to have qualitatively different elastic responses to varying attraction strength or temperature. As temperature increases, the expanded entropic solid stiffens, while the energy-controlled, fully-bonded dense solid softens. PMID:23464163
NASA Astrophysics Data System (ADS)
Schubert, M.; Korlacki, R.; Knight, S.; Hofmann, T.; Schöche, S.; Darakchieva, V.; Janzén, E.; Monemar, B.; Gogova, D.; Thieu, Q.-T.; Togashi, R.; Murakami, H.; Kumagai, Y.; Goto, K.; Kuramata, A.; Yamakoshi, S.; Higashiwaki, M.
2016-03-01
We derive a dielectric function tensor model approach to render the optical response of monoclinic and triclinic symmetry materials with multiple uncoupled infrared and far-infrared active modes. We apply our model approach to monoclinic β -Ga2O3 single-crystal samples. Surfaces cut under different angles from a bulk crystal, (010) and (2 ¯01 ), are investigated by generalized spectroscopic ellipsometry within infrared and far-infrared spectral regions. We determine the frequency dependence of 4 independent β -Ga2O3 Cartesian dielectric function tensor elements by matching large sets of experimental data using a point-by-point data inversion approach. From matching our monoclinic model to the obtained 4 dielectric function tensor components, we determine all infrared and far-infrared active transverse optic phonon modes with Au and Bu symmetry, and their eigenvectors within the monoclinic lattice. We find excellent agreement between our model results and results of density functional theory calculations. We derive and discuss the frequencies of longitudinal optical phonons in β -Ga2O3 . We derive and report density and anisotropic mobility parameters of the free charge carriers within the tin-doped crystals. We discuss the occurrence of longitudinal phonon plasmon coupled modes in β -Ga2O3 and provide their frequencies and eigenvectors. We also discuss and present monoclinic dielectric constants for static electric fields and frequencies above the reststrahlen range, and we provide a generalization of the Lyddane-Sachs-Teller relation for monoclinic lattices with infrared and far-infrared active modes. We find that the generalized Lyddane-Sachs-Teller relation is fulfilled excellently for β -Ga2O3 .
Crystal structure and phonon softening in Ca3Ir4Sn13
NASA Astrophysics Data System (ADS)
Mazzone, D. G.; Gerber, S.; Gavilano, J. L.; Sibille, R.; Medarde, M.; Delley, B.; Ramakrishnan, M.; Neugebauer, M.; Regnault, L. P.; Chernyshov, D.; Piovano, A.; Fernández-Díaz, T. M.; Keller, L.; Cervellino, A.; Pomjakushina, E.; Conder, K.; Kenzelmann, M.
2015-07-01
We investigated the crystal structure and lattice excitations of the ternary intermetallic stannide Ca3Ir4Sn13 using neutron and x-ray scattering techniques. For T >T*≈38 K, the x-ray diffraction data can be satisfactorily refined using the space group P m 3 ¯n . Below T*, the crystal structure is modulated with a propagation vector of q ⃗=(1 /2 ,1 /2 ,0 ) . This may arise from a merohedral twinning in which three tetragonal domains overlap to mimic a higher symmetry, or from a doubling of the cubic unit cell. Neutron diffraction and neutron spectroscopy results show that the structural transition at T* is of a second-order, and that it is well described by mean-field theory. Inelastic neutron scattering data point towards a displacive structural transition at T* arising from the softening of a low-energy phonon mode with an energy gap of Δ (120 K)=1.05 meV. Using density functional theory, the soft phonon mode is identified as a "breathing" mode of the Sn12 icosahedra and is consistent with the thermal ellipsoids of the Sn2 atoms found by single-crystal diffraction data.
Low-frequency spatial wave manipulation via phononic crystals with relaxed cell symmetry
Celli, Paolo; Gonella, Stefano
2014-03-14
Phononic crystals enjoy unique wave manipulation capabilities enabled by their periodic topologies. On one hand, they feature frequency-dependent directivity, which allows directional propagation of selected modes even at low frequencies. However, the stellar nature of the propagation patterns and the inability to induce single-beam focusing represent significant limitations of this functionality. On the other hand, one can realize waveguides by defecting the periodic structure of a crystal operating in bandgap mode along some desired path. Waveguides of this type are only activated in the relatively high and narrow frequency bands corresponding to total bandgaps, which limits their potential technological applications. In this work, we introduce a class of phononic crystals with relaxed cell symmetry and we exploit symmetry relaxation of a population of auxiliary microstructural elements to achieve spatial manipulation of elastic waves at very low frequencies, in the range of existence of the acoustic modes. By this approach, we achieve focusing without modifying the default static properties of the medium and by invoking mechanisms that are well suited to envision adaptive configurations for semi-active wave control.
Sun, Shuhui; Zhang, Gaixia; Geng, Dongsheng; Chen, Yougui; Banis, Mohammad Norouzi; Li, Ruying; Cai, Mei; Sun, Xueliang
2010-01-18
A newly designed and fabricated novel three dimensional (3D) nanocomposite composed of single-crystal Pt nanowires (PtNW) and a coaxial nanocable support consisting of a tin nanowire and a carbon nanotube (Sn@CNT) is reported. This nanocomposite is fabricated by the synthesis of Sn@CNT nanocables by means of a thermal evaporation method, followed by the direct growth with PtNWs through a facile aqueous solution approach at room temperature. Electrochemical measurements demonstrate that the PtNW--Sn@CNT 3D electrode exhibits enhanced electrocatalytic performance in oxygen reduction reaction (ORR) for polymer electrolyte membrane fuel cells (PEMFCs), methanol oxidation (MOR) for direct methanol fuel cells (DMFCs), and CO tolerance compared with commercial ETEK Pt/C catalyst made of Pt nanoparticles. PMID:20024993
Surface acoustic waves in two dimensional phononic crystal with anisotropic inclusions
NASA Astrophysics Data System (ADS)
Ketata, H.; Hédi Ben Ghozlen, M.
2012-06-01
An analysis is given to the band structure of the two dimensional solid phononic crystal considered as a semi infinite medium. The lattice includes an array of elastic anisotropic materials with different shapes embedded in a uniform matrix. For illustration two kinds of phononic materials are assumed. A particular attention is devoted to the computational procedure which is mainly based on the plane wave expansion (PWE) method. It has been adapted to Matlab environment. Numerical calculations of the dispersion curves have been achieved by introducing particular functions which transform motion equations into an Eigen value problem. Significant improvements are obtained by increasing reasonably the number of Fourier components even when a large elastic mismatch is assumed. Such approach can be generalized to different types of symmetry and permit new physical properties as piezoelectricity to be added. The actual semi infinite phononic structure with a free surface has been shown to support surface acoustic waves (SAW). The obtained dispersion curves reveal band gaps in the SAW branches. It has been found that the influence, of the filling factor and anisotropy on their band gaps, is different from that of bulk waves.
Planar modes free piezoelectric resonators using a phononic crystal with holes.
Aragón, J L; Quintero-Torres, R; Domínguez-Juárez, J L; Iglesias, E; Ronda, S; Montero de Espinosa, F
2016-09-01
By using the principles behind phononic crystals, a periodic array of circular holes made along the polarization thickness direction of piezoceramic resonators are used to stop the planar resonances around the thickness mode band. In this way, a piezoceramic resonator adequate for operation in the thickness mode with an in phase vibration surface is obtained, independently of its lateral shape. Laser vibrometry, electric impedance tests and finite element models are used to corroborate the performances of different resonators made with this procedure. This method can be useful in power ultrasonic devices, physiotherapy and other external medical power ultrasound applications where piston-like vibration in a narrow band is required. PMID:27387418
Omnidirectional refractive devices for flexural waves based on graded phononic crystals
Torrent, Daniel Pennec, Yan; Djafari-Rouhani, Bahram
2014-12-14
Different omnidirectional refractive devices for flexural waves in thin plates are proposed and numerically analyzed. Their realization is explained by means phononic crystal plates, where a previously developed homogenization theory is employed for the design of graded index refractive devices. These devices consist of a circular cluster of inclusions with a properly designed gradient in their radius. With this approach, the Luneburg and Maxwell lenses and a family of beam splitters for flexural waves are proposed and analyzed. Results show that these devices work properly in a broadband frequency region, being therefore an efficient approach for the design of refractive devices specially interesting for nano-scale applications.
Wave transmission in time- and space-variant helicoidal phononic crystals
NASA Astrophysics Data System (ADS)
Li, F.; Chong, C.; Yang, J.; Kevrekidis, P. G.; Daraio, C.
2014-11-01
We present a dynamically tunable mechanism of wave transmission in one-dimensional helicoidal phononic crystals in a shape similar to DNA structures. These helicoidal architectures allow slanted nonlinear contact among cylindrical constituents, and the relative torsional movements can dynamically tune the contact stiffness between neighboring cylinders. This results in cross-talking between in-plane torsional and out-of-plane longitudinal waves. We numerically demonstrate their versatile wave mixing and controllable dispersion behavior in both wavenumber and frequency domains. Based on this principle, a suggestion toward an acoustic configuration bearing parallels to a transistor is further proposed, in which longitudinal waves can be switched on and off through torsional waves.
Hybrid phononic crystal plates for lowering and widening acoustic band gaps.
Badreddine Assouar, M; Sun, Jia-Hong; Lin, Fan-Shun; Hsu, Jin-Chen
2014-12-01
We propose hybrid phononic-crystal plates which are composed of periodic stepped pillars and periodic holes to lower and widen acoustic band gaps. The acoustic waves scattered simultaneously by the pillars and holes in a relevant frequency range can generate low and wide acoustic forbidden bands. We introduce an alternative double-sided arrangement of the periodic stepped pillars for an enlarged pillars' head diameter in the hybrid structure and optimize the hole diameter to further lower and widen the acoustic band gaps. The lowering and widening effects are simultaneously achieved by reducing the frequencies of locally resonant pillar modes and prohibiting suitable frequency bands of propagating plate modes. PMID:24996255
Schellenberger, Pascale; Demangeat, Gérard; Lemaire, Olivier; Ritzenthaler, Christophe; Bergdoll, Marc; Oliéric, Vincent; Sauter, Claude; Lorber, Bernard
2011-05-01
The small icosahedral plant RNA nepovirus Grapevine fanleaf virus (GFLV) is specifically transmitted by a nematode and causes major damage to vineyards worldwide. To elucidate the molecular mechanisms underlying the recognition between the surface of its protein capsid and cellular components of its vector, host and viral proteins synthesized upon infection, the wild type GFLV strain F13 and a natural mutant (GFLV-TD) carrying a Gly₂₉₇Asp mutation were purified, characterized and crystallized. Subsequently, the geometry and volume of their crystals was optimized by establishing phase diagrams. GFLV-TD was twice as soluble as the parent virus in the crystallization solution and its crystals diffracted X-rays to a resolution of 2.7 Å. The diffraction limit of GFLV-F13 crystals was extended from 5.5 to 3 Å by growth in agarose gel. Preliminary crystallographic analyses indicate that both types of crystals are suitable for structure determination. Keys for the successful production of GFLV crystals include the rigorous quality control of virus preparations, crystal quality improvement using phase diagrams, and crystal lattice reinforcement by growth in agarose gel. These strategies are applicable to the production of well-diffracting crystals of other viruses and macromolecular assemblies. PMID:21352920
Image forces on 3d dislocation structures in crystals of finite volume
El-Azab, A.
1999-07-01
The present work aims at studying the image stress and image Peach-Koehler force fields for three-dimensional dislocation configurations in a single crystal of finite volume. It is shown that the image stress field is significant within the entire crystal volume, and that the image Peach-Koehler force can be of the same order of magnitude as the direct interaction force calculated from the infinite domain solution. The results demonstrate that image stress gives rise to long-range interaction forces that are important in meso-scale dynamics of dislocation structures.
Image Forces on 3-D Dislocation Structures in Crystals of Finite Volume
El-Azab, Anter ); V.V. Bulatov
1999-01-01
The present work aims at studying the image stress and image Peach-Koehler force fields for three-dimensional dislocation configurations in a single crystal of finite volume. It is shown that the image stress field is significant within the entire crystal volume, and that the image Peach-Koehler force can be of the same order of magnitude as the direct interaction force calculated from the infinite domain solution. The results demonstrate that image stress gives rise to long-range interaction forces that are important in meso-scale dynamics of dislocation structures.
Application of liquid crystal polymer films for photolithographic fabrication of 3D structures
NASA Astrophysics Data System (ADS)
Fox, Anna E.; Fontecchio, Adam K.
2008-02-01
In this paper, we demonstrate a silicon etching application of a holographically formed polymer dispersed liquid crystal (H-PDLC) photomask. H-PDLC is a periodically nanostructured material consisting of stratified layers of polymer and liquid crystal. Due to the natural random alignment of the liquid crystal axes with respect to the polymer layers, an index of refraction mismatch exists and a reflection occurs. Application of bias across the film aligns the liquid crystals and eliminates the index mismatch causing the film to become transparent. H-PDLC films have been shown to sufficiently attenuate the UV exposure dose in the photolithographic process when in the unbiased state, and can be electrically controlled to modulate the amount of UV transmission when electric field is applied. We show etch depth profiles of patterns masked on a silicon substrate using the H-PDLC photomask device compared with etch profiles of similar structures patterned with more conventional ink jet printed photomasks and chrome on quartz glass photomasks. We investigate reactive ion etching technique and potassium hydroxide wet etch technique.
NASA Astrophysics Data System (ADS)
Abou Diwan, E.; Royer, F.; Kekesi, R.; Jamon, D.; Blanc-Mignon, M. F.; Neveu, S.; Rousseau, J. J.
2013-05-01
In this paper, we present the synthesis and the optical properties of 3D magneto-photonic structures. The elaboration process consists in firstly preparing then infiltrating polystyrene direct opals with a homogeneous solution of sol-gel silica precursors doped by cobalt ferrite nanoparticles, and finally dissolving the polystyrene spheres. Scanning Electron Microscopy (SEM) images of the prepared samples clearly evidence a periodic arrangement. Using a home-made polarimetric optical bench, the transmittance as a function of the wavelength, the Faraday rotation as a function of the applied magnetic field, and the Faraday ellipticity as a function of the wavelength and as a function of the applied magnetic field were measured. The existence of deep photonic band gaps (PBG), the unambiguous magnetic character of the samples and the qualitative modification of the Faraday ellipticity in the area of the PBG are evidenced.
Zhou, Changjiang; Sai, Yi; Chen, Jiujiu
2016-09-01
This paper theoretically investigates the band gaps of Lamb mode waves in two-dimensional magnetoelastic phononic crystal slabs by an applied external magnetostatic field. With the assumption of uniformly oriented magnetization, an equivalent piezomagnetic material model is used. The effects of magnetostatic field on phononic crystals are considered carefully in this model. The numerical results indicate that the width of the first band gap is significantly changed by applying the external magnetic field with different amplitude, and the ratio between the maximum and minimum gap widths reaches 228%. Further calculations demonstrate that the orientation of the magnetic field obviously affects the width and location of the first band gap. The contactless tunability of the proposed phononic crystal slabs shows many potential applications of vibration isolation in engineering. PMID:27281285
Khazanov, E. N. Taranov, A. V.; Gainutdinov, R. V.; Akchurin, M. Sh.; Basiev, T. T.; Konyushkin, V. A.; Fedorov, P. P.; Kuznetsov, S. V.; Osiko, V. V.
2010-06-15
The methods of optical, electron, and atomic force microscopy (AFM) are applied to the study of the real structure of optical lithium fluoride ceramic obtained by hot deformation of single crystals. A comparative analysis is carried out of the scattering mechanisms of weakly nonequilibrium thermal phonons at liquid helium temperatures in LiF single crystals and ceramics. It is demonstrated that the phonon scattering in the original single crystals is determined by the forced vibrations of dislocations in the stress field of an elastic plane wave (a phonon), i.e., by the flutter mechanism. As the degree of deformation of the original material increases, the ceramics exhibit a change in the plastic deformation mechanisms, which leads to a decrease in the average size of grains and to an ordered structure. In this case, the dominant scattering is that by intergrain boundaries. The thickness and the acoustic impedance of these boundaries are evaluated.
Zhao, J.; Boyko, O.; Bonello, B.
2014-12-15
This work deals with an analytical and numerical study of the focusing of the lowest order anti-symmetric Lamb wave in gradient index phononic crystals. Computing the ray trajectories of the elastic beam allowed us to analyze the lateral dimensions and shape of the focus, either in the inner or behind the phononic crystal-based acoustic lenses, for frequencies within a broad range in the first band. We analyzed and discussed the focusing behaviors inside the acoustic lenses where the focalization at sub-wavelength scale was achieved. The focalization behind the gradient index phononic crystal is shown to be efficient as well: we report on FMHM = 0.63λ at 11MHz.
Multilayer-split-tube resonators with low-frequency band gaps in phononic crystals
NASA Astrophysics Data System (ADS)
Jing, Li; Wu, Jiu Hui; Guan, Dong; Gao, Nansha
2014-09-01
In this paper, low-frequency band gaps in two-dimensional Helmholtz resonant phononic crystals (PCs) composed of multilayer-split-tube resonators are investigated. The band structures, transmission spectra, and pressure field of the acoustic modes of these PCs are calculated by using a finite element method (FEM). The numerical results show that the first band gap of the structure is from 88 to 140 Hz. The transmission spectra are in accordance with those of the dispersion relation calculations. The acoustic modes of the bands are analyzed to reveal the nature of this phenomenon. It is found that the interaction between the local resonance and the traveling wave modes in proposed structure is responsible for the formation of the first band gap. The influences of the structural parameters on the band gaps are investigated by using FEM and the electrical circuit analogy. Numerical results show that the band gaps can be modulated in an even wider frequency range by changing the structural parameters, such as the rotation angle, the number of tubes, and the radius of the outer tube. The structural design results provide an effective way for phononic crystals to obtain the low-frequency band gaps, which have potential application in the low-frequency noise reduction.
Phononic crystal surface mode coupling and its use in acoustic Doppler velocimetry.
Cicek, Ahmet; Salman, Aysevil; Kaya, Olgun Adem; Ulug, Bulent
2016-02-01
It is numerically shown that surface modes of two-dimensional phononic crystals, which are Bloch modes bound to the interface between the phononic crystal and the surrounding host, can couple back and forth between the surfaces in a length scale determined by the separation of two surfaces and frequency. Supercell band structure computations through the finite-element method reveal that the surface band of an isolated surface splits into two bands which support either symmetric or antisymmetric hybrid modes. When the surface separation is 3.5 times the lattice constant, a coupling length varying between 30 and 48 periods can be obtained which first increases linearly with frequency and, then, decreases rapidly. In the linear regime, variation of coupling length can be used as a means of measuring speeds of objects on the order of 0.1m/s by incorporating the Doppler shift. Speed sensitivity can be improved by increasing surface separation at the cost of larger device sizes. PMID:26565078
Evanescent coupling between surface and linear-defect guided modes in phononic crystals
NASA Astrophysics Data System (ADS)
Cicek, Ahmet; Salman, Aysevil; Adem Kaya, Olgun; Ulug, Bulent
2016-01-01
Evanescent coupling between surface and linear-defect waveguide modes in a two-dimensional phononic crystal of steel cylinders in air is numerically demonstrated. When the ratio of scatterer radii to the lattice constant is set to 0.47 in the square phononic crystal, the two types of modes start interacting if there is one-row separation between the surface and waveguide. Supercell band structure computations through the Finite Element Method suggest that the waveguide band is displaced significantly, whereas the surface band remains almost intact when the waveguide and surface are in close proximity. The two resultant hybrid bands are such that the coupling length, which varies between 8 and 22 periods, initially changes linearly with frequency, while a much sharper variation is observed towards the top of the lower hybrid band. Such small values facilitate the design of compact devices based on heterogeneous coupling. Finite-element simulations demonstrate bilateral coupling behaviour, where waves incident from either the surface or waveguide can efficiently couple to the other side. The coupling lengths calculated from simulation results are in agreement with the values predicted from the supercell band structure. The possible utilisation of the coupling scheme in sensing applications, especially in acoustic Doppler velocimetry, is discussed.
NASA Astrophysics Data System (ADS)
Gao, Nansha; Wu, Jiu Hui; Yu, Lie; Hou, Hong
2016-06-01
This paper investigates ultralow frequency acoustic properties and energy recovery of tetragonal folding beam phononic crystal (TFBPC) and its complementary structure. The dispersion curve relationships, transmission spectra and displacement fields of the eigenmodes are studied with FEA in detail. Compared with the traditional three layer phononic crystal (PC) structure, this structure proposed in this paper not only unfold bandgaps (BGs) in lower frequency range (below 300 Hz), but also has lighter weight because of beam structural cracks. We analyze the relevant physical mechanism behind this phenomenon, and discuss the effects of the tetragonal folding beam geometric parameters on band structure maps. FEM proves that the multi-cell structures with different arrangements have different acoustic BGs when compared with single cell structure. Harmonic frequency response and piezoelectric properties of TFBPC are specifically analyzed. The results confirm that this structure does have the recovery ability for low frequency vibration energy in environment. These conclusions in this paper could be indispensable to PC practical applications such as BG tuning and could be applied in portable devices, wireless sensor, micro-electro mechanical systems which can recycle energy from vibration environment as its own energy supply.
NASA Astrophysics Data System (ADS)
Li, Yinggang; Chen, Tianning; Wang, Xiaopeng; Yu, Kunpeng; Chen, Weihua
2014-02-01
In this paper, we theoretically investigate the propagation characteristics of Lamb waves in one-dimensional radial phononic crystal plates with periodic corrugations. The dispersion relations, the power transmission spectra, and the displacement fields of the eigenmodes are calculated by using the finite element method based on two-dimensional axial symmetry models in cylindrical coordinates. The axial symmetry model is validated by three-dimensional finite element model in rectangular coordinates. The effects of the geometrical parameters on the band gaps are further explored numerically. Numerical results show that several complete band gaps with a variable bandwidth exist for Lamb waves in the proposed structures. The formation mechanism of opening the acoustic band gaps is attributed to the coupling between the Lamb modes and the corrugation mode. The band gaps are significantly dependent upon the geometrical parameters such as the corrugation height, the corrugation width, and the plate thickness. Significantly, as the increase of corrugation height, band width shifts, new band gaps appear, the bands become flat, and the corrugation mode plays a more prominent role in the opening of Lamb wave band gaps. These properties of Lamb waves in the radial phononic crystal plates can potentially be applied to optimize band gaps, generate filters, and design acoustic devices.
Morvan, B.; Tinel, A.; Sainidou, R.; Rembert, P.; Vasseur, J. O.; Hladky-Hennion, A.-C.; Swinteck, N.; Deymier, P. A.
2014-12-07
Phononic crystals (PC) can be used to control the dispersion properties of acoustic waves, which are essential to direct their propagation. We use a PC-based two-dimensional solid/solid composite to demonstrate experimentally and theoretically the spatial filtering of a monochromatic non-directional wave source and its emission in a surrounding water medium as an ultra-directional beam with narrow angular distribution. The phenomenon relies on square-shaped equifrequency contours (EFC) enabling self-collimation of acoustic waves within the phononic crystal. Additionally, the angular width of collimated beams is controlled via the EFC size-shrinking when increasing frequency.
NASA Astrophysics Data System (ADS)
Lim, Chae Young; Choi, Eunpyo; Park, Youngkyu; Park, Jungyul
2013-05-01
In this paper, we propose a new technique for protein detection by using the enhancement of intensity in quantum dots (Qdot) whose emission is guided by 3D photonic crystal (PC) structures. For easy to use, we design the emitted light from the sensor can be recovered, when the chemical antibody (aptamer) conjugated with guard DNA (g-DNA) labeled with a quencher (Black FQ) hybridizes with the target proteins. In detail, we synthesis a Qdot-aptamer complex and then immobilize these complex on the PC surfaces. Next, we perform the hybridization of the Qdot-aptamer complex with g-DNA labeled with the quencher. It induces the quenching effect of fluoresce intensity in the Qdot-aptamer. In presence of target protein (thrombin), the Qdot-aptamer complex prefers to form the thrombin-aptamer complex: this results in the release of Black FQ-g-DNA and the quenched light intensity recovers into the original high intensity with Qdot. The intensity recovery varies quantitatively according to the level of the target protein concentration. This proposed sensor shows much higher detection sensitivity than the general fluorescent detection mechanism, which is functionalized on the flat surfaces because of the light guiding effect from 3D photonic crystal structures.
Design of a 3D Digital Liquid Crystal Particle Thermometry and Velocimetry (3DDLCPT/V) System
NASA Astrophysics Data System (ADS)
Grothe, Rob; Rixon, Greg; Dabiri, Dana
2007-11-01
A novel 3D Digital Liquid Crystal Particle Thermometry and Velocimetry (3DDLCPT/V) system has been designed and fabricated. By combining 3D Defocusing Particle Image Velocimetry (3DDPIV) and Digital Particle Image Thermometry (DPIT) into one system, this technique provides simultaneous temperature and velocity data using temperature-sensitive liquid crystal particles (LCP) as flow sensors. A custom water-filled prism corrects for astigmatism caused by off-axis imaging. New optics equations are derived to account for multi-surface refractions. This redesign also maximizes the use of the CCD area to more efficiently image the volume of interest. Six CCD cameras comprise the imaging system, with three allocated for velocity measurements and three for temperature measurements. The cameras are optically aligned to sub-pixel accuracy using a precision grid and high-resolution translation stages. Two high-intensity custom-designed xenon flashlamps provide illumination. Temperature calibration of the LCP is then performed. These results and proof-of-concept experiments will be discussed in detail.
Tao, Yulun; Shen, Yuhua; Yang, Liangbao; Han, Bin; Huang, Fangzhi; Li, Shikuo; Chu, Zhuwang; Xie, Anjian
2012-06-21
While the number of man-made nano superstructures realized by self-assembly is growing in recent years, assemblies of conductive polymer nanocrystals, especially for superlattices, are still a significant challenge, not only because of the simplicity of the shape of the nanocrystal building blocks and their interactions, but also because of the poor control over these parameters in the fabrication of more elaborate nanocrystals. Here, we firstly report a facile and general route to a new generation of 3D layered superlattices of polyaniline doped with CSA (PANI-CSA) and show how PANI crystallize and self-assemble, in a suitable single solution environment. In cyclohexane, 1D amorphous nanofibers transformed to 1D nanorods as building blocks, and then to 2D single-crystal nanosheets with a hexagonal phase, and lastly to 3D ordered layered superlattices with the narrowest polydispersity value (M(w)/M(n) = 1.47). Remarkably, all the instructions for the hierarchical self-assembly are encoded in the layered shape in other non-polar solvents (hexane, octane) and their conductivity in the π-π stacking direction is improved to about 50 S cm(-1), which is even higher than that of the highest previously reported value (16 S cm(-1)). The method used in this study is greatly expected to be readily scalable to produce superlattices of conductive polymers with high quality and low cost. PMID:22609947
Clusters, molecular layers, and 3D crystals of water on Ni(111)
Thürmer, Konrad; Nie, Shu; Bartelt, Norman C.; Feibelman, Peter J.
2014-11-14
We examined the growth and stability of ice layers on Ni(111) up to ∼7 molecular layers (ML) thick using scanning tunneling microscopy. At low coverage, films were comprised of ∼1 nm wide two-dimensional (2D) clusters. Only above ∼0.5 ML did patches of continuous 2D layers emerge, coexisting with the clusters until the first ML was complete. The structure of the continuous layer is clearly different from that of the 2D clusters. Subsequently, a second molecular layer grew on top of the first. 3D crystallites started to form only after this 2nd ML was complete. 2D clusters re-appeared when thicker films were partially evaporated, implying that these clusters represent the equilibrium configuration at low coverage. Binding energies and image simulations computed with density functional theory suggest that the 2D clusters are partially dissociated and surrounded by H adatoms. The complete 2D layer contains only intact water molecules because of the lack of favorable binding sites for H atoms. We propose molecular structures for the 2D layer that are composed of the same pentagon-heptagon binding motif and water density observed on Pt(111). The similarity of the water structures on Pt and Ni suggests a general prescription for generating low-energy configurations on close-packed metal substrates.
Fabrication of fully undercut ZnO-based photonic crystal membranes with 3D optical confinement
NASA Astrophysics Data System (ADS)
Hoffmann, Sandro Phil; Albert, Maximilian; Meier, Cedrik
2016-09-01
For studying nonlinear photonics, a highly controllable emission of photons with specific properties is essential. Two-dimensional photonic crystals (PhCs) have proven to be an excellent candidate for manipulating photon emission due to resonator-based effects. Additionally, zinc oxide (ZnO) has high susceptibility coefficients and therefore shows pronounced nonlinear effects. However, in order to fabricate such a cavity, a fully undercut ZnO membrane is required, which is a challenging problem due to poor selectivity of the known etching chemistry for typical substrates such as sapphire or ZnO. The aim of this paper is to demonstrate and characterize fully undercut photonic crystal membranes based on a thin ZnO film sandwiched between two layers of silicon dioxide (SiO2) on silicon substrates, from the initial growth of the heterostructure throughout the entire fabrication process. This process leads to a fully undercut ZnO-based membrane with adjustable optical confinement in all three dimensions. Finally, photonic resonances within the tailored photonic band gap are achieved due to optimized PhC-design (in-plane) and total internal reflection in the z-direction. The presented approach enables a variety of photon based resonator structures in the UV regime for studying nonlinear effects, including photon-exciton coupling and all-optical switching.
Inverted Yablonovite-like 3D photonic crystals fabricated by laser nanolithography
NASA Astrophysics Data System (ADS)
Shishkin, Ivan I.; Samusev, Kirill B.; Rybin, Mikhail V.; Limonov, Mikhail F.; Kivshar, Yuri S.; Gaidukeviciute, Arune; Kiyan, Roman V.; Chichkov, Boris N.
2012-06-01
We report on the fabrication of inverted Yablonovite-like three-dimensional photonic crystals by nonlinear optical nanolithography based on two-photon polymerization of a zirconium propoxide hybrid organic-inorganic material with Irgacure 369 as photo-initiator. Advantage of this material is ultra-low shrinkage that guaranty high fabrication fidelity. Images of the fabricated structure are obtained with a scanning electron microscope. The photonic crystal consists of three sets of nearly cylindrical structural elements directed along the three lattice vectors of the fcc lattice and cross each other at certain angles to produce inverted Yablonovite geometry. To investigate photonic properties of the inverted Yablonovite structures, we calculate the photonic band structure for ten lowest-frequency electromagnetic modes. In contrast to the direct Yablonovite structure that has a complete photonic band gap between the second and third bands, we find no complete photonic band gaps in the inverted Yablonovite lattice. This situation is opposite to the case of fcc lattice of close-packed dielectric spheres in air that has a complete photonic band gap only for the inverted geometry.
Nishizawa, Seizi; Tsumura, Naoki; Kitahara, Hideaki; Wada Takeda, Mitsuo; Kojima, Seiji
2002-11-01
A new instrument for terahertz time-domain spectroscopy (THz-TDS) has been developed. It consists of a composite THz-TDS system and a high throughput (Martin-Puplett) interferometer. The instrument is for use in the qualitative study of optoelectronic constants of materials. The spectral transmission intensity and phase shift related to phonon-polariton dispersion have been measured between 100 cm(-1) and 3 cm(-1) on ferroelectric crystals of industrial interest. These include bismuth titanate Bi4Ti3O12 (a key material for FeRAM), lithium niobate LiNbO3 (a typical nonlinear crystal for parametric oscillator applications) and lithium heptagermanate Li2Ge7O15 for surface elastic wave filter applications. The complex dielectric constants are well reproduced by the phonon-polariton dispersion relation based on the Kurosawa formula. The instrument details and phonon-polariton dispersion results are described. PMID:12452567
3D visualization of XFEL beam focusing properties using LiF crystal X-ray detector
NASA Astrophysics Data System (ADS)
Pikuz, Tatiana; Faenov, Anatoly; Matsuoka, Takeshi; Matsuyama, Satoshi; Yamauchi, Kazuto; Ozaki, Norimasa; Albertazzi, Bruno; Inubushi, Yuichi; Yabashi, Makina; Tono, Kensuke; Sato, Yuya; Yumoto, Hirokatsu; Ohashi, Haruhiko; Pikuz, Sergei; Grum-Grzhimailo, Alexei N.; Nishikino, Masaharu; Kawachi, Tetsuya; Ishikawa, Tetsuya; Kodama, Ryosuke
2015-12-01
Here, we report, that by means of direct irradiation of lithium fluoride a (LiF) crystal, in situ 3D visualization of the SACLA XFEL focused beam profile along the propagation direction is realized, including propagation inside photoluminescence solid matter. High sensitivity and large dynamic range of the LiF crystal detector allowed measurements of the intensity distribution of the beam at distances far from the best focus as well as near the best focus and evaluation of XFEL source size and beam quality factor M2. Our measurements also support the theoretical prediction that for X-ray photons with energies ~10 keV the radius of the generated photoelectron cloud within the LiF crystal reaches about 600 nm before thermalization. The proposed method has a spatial resolution ~ 0.4-2.0 μm for photons with energies 6-14 keV and potentially could be used in a single shot mode for optimization of different focusing systems developed at XFEL and synchrotron facilities.
3D visualization of XFEL beam focusing properties using LiF crystal X-ray detector.
Pikuz, Tatiana; Faenov, Anatoly; Matsuoka, Takeshi; Matsuyama, Satoshi; Yamauchi, Kazuto; Ozaki, Norimasa; Albertazzi, Bruno; Inubushi, Yuichi; Yabashi, Makina; Tono, Kensuke; Sato, Yuya; Yumoto, Hirokatsu; Ohashi, Haruhiko; Pikuz, Sergei; Grum-Grzhimailo, Alexei N; Nishikino, Masaharu; Kawachi, Tetsuya; Ishikawa, Tetsuya; Kodama, Ryosuke
2015-01-01
Here, we report, that by means of direct irradiation of lithium fluoride a (LiF) crystal, in situ 3D visualization of the SACLA XFEL focused beam profile along the propagation direction is realized, including propagation inside photoluminescence solid matter. High sensitivity and large dynamic range of the LiF crystal detector allowed measurements of the intensity distribution of the beam at distances far from the best focus as well as near the best focus and evaluation of XFEL source size and beam quality factor M(2). Our measurements also support the theoretical prediction that for X-ray photons with energies ~10 keV the radius of the generated photoelectron cloud within the LiF crystal reaches about 600 nm before thermalization. The proposed method has a spatial resolution ~0.4-2.0 μm for photons with energies 6-14 keV and potentially could be used in a single shot mode for optimization of different focusing systems developed at XFEL and synchrotron facilities. PMID:26634431
3D visualization of XFEL beam focusing properties using LiF crystal X-ray detector
Pikuz, Tatiana; Faenov, Anatoly; Matsuoka, Takeshi; Matsuyama, Satoshi; Yamauchi, Kazuto; Ozaki, Norimasa; Albertazzi, Bruno; Inubushi, Yuichi; Yabashi, Makina; Tono, Kensuke; Sato, Yuya; Yumoto, Hirokatsu; Ohashi, Haruhiko; Pikuz, Sergei; Grum-Grzhimailo, Alexei N.; Nishikino, Masaharu; Kawachi, Tetsuya; Ishikawa, Tetsuya; Kodama, Ryosuke
2015-01-01
Here, we report, that by means of direct irradiation of lithium fluoride a (LiF) crystal, in situ 3D visualization of the SACLA XFEL focused beam profile along the propagation direction is realized, including propagation inside photoluminescence solid matter. High sensitivity and large dynamic range of the LiF crystal detector allowed measurements of the intensity distribution of the beam at distances far from the best focus as well as near the best focus and evaluation of XFEL source size and beam quality factor M2. Our measurements also support the theoretical prediction that for X-ray photons with energies ~10 keV the radius of the generated photoelectron cloud within the LiF crystal reaches about 600 nm before thermalization. The proposed method has a spatial resolution ~ 0.4–2.0 μm for photons with energies 6–14 keV and potentially could be used in a single shot mode for optimization of different focusing systems developed at XFEL and synchrotron facilities. PMID:26634431
The properties of optimal two-dimensional phononic crystals with different material contrasts
NASA Astrophysics Data System (ADS)
Liu, Zong-Fa; Wu, Bin; He, Cun-Fu
2016-09-01
By modifying the spatial distribution of constituent material phases, phononic crystals (PnCs) can be designed to exhibit band gaps within which sound and vibration cannot propagate. In this paper, the developed topology optimization method (TOM), based on genetic algorithms (GAs) and the finite element method (FEM), is proposed to design two-dimensional (2D) solid PnC structures composed of two contrasting elastic materials. The PnCs have the lowest order band gap that is the third band gap for the coupled mode, the first band gap for the shear mode or the XY 34 Z band gap for the mixed mode. Moreover, the effects of the ratios of contrasting material properties on the optimal layout of unit cells and the corresponding phononic band gaps (PBGs) are investigated. The results indicate that the topology of the optimal PnCs and corresponding band gaps varies with the change of material contrasts. The law can be used for the rapid design of desired PnC structures.
Rotational modes in a phononic crystal with fermion-like behavior
NASA Astrophysics Data System (ADS)
Deymier, P. A.; Runge, K.; Swinteck, N.; Muralidharan, K.
2014-04-01
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.
NASA Astrophysics Data System (ADS)
Rudevics, A.; Muiznieks, A.; Ratnieks, G.; Riemann, H.
2005-06-01
In the modern industrial floating zone (FZ) silicon crystal growth process by the needle-eye technique, the high frequency (HF) electromagnetic (EM) field plays a crucial role. The EM field melts a rotating poly silicon feed rod and maintains the zone of molten silicon, which is held by the rotating single crystal. To model such a system, the 2D axi-symmetric models can be used, however, due to the system's asymmetry (e.g., the asymmetry of the HF inductor) the applicability of such models is restricted. Therefore, the modeling of FZ process in three dimensions (3D) is necessary. This paper describes a new complex 3D mathematical model of the FZ crystal growth and a correspondingly developed software package Shape3D. A 3D calculation example for the realistic FZ system is also presented. Figs 25, Refs 9.
NASA Astrophysics Data System (ADS)
Rutowska, Monika S.; Garcia Gunning, Fatima C.; Kivlehan, Francine; Moore, Eric; Brennan, Des; Galvin, Paul; Ellis, Andrew D.
2010-09-01
In this paper, we demonstrate the integration of a 3D hydrogel matrix within a hollow core photonic crystal fibre (HC-PCF). In addition, we also show the fluorescence of Cy5-labelled DNA molecules immobilized within the hydrogel formed in two different types of HC-PCF. The 3D hydrogel matrix is designed to bind with the amino groups of biomolecules using an appropriate cross-linker, providing higher sensitivity and selectivity than the standard 2D coverage, enabling a greater number of probe molecules to be available per unit area. The HC-PCFs, on the other hand, can be designed to maximize the capture of fluorescence to improve sensitivity and provide longer interaction lengths. This could enable the development of fibre-based point-of-care and remote systems, where the enhanced sensitivity would relax the constraints placed on sources and detectors. In this paper, we will discuss the formation of such polyethylene glycol diacrylate (PEGDA) hydrogels within a HC-PCF, including their optical properties such as light propagation and auto-fluorescence.
NASA Astrophysics Data System (ADS)
Vattré, A.; Devincre, B.; Feyel, F.; Gatti, R.; Groh, S.; Jamond, O.; Roos, A.
2014-02-01
A unified model coupling 3D dislocation dynamics (DD) simulations with the finite element (FE) method is revisited. The so-called Discrete-Continuous Model (DCM) aims to predict plastic flow at the (sub-)micron length scale of materials with complex boundary conditions. The evolution of the dislocation microstructure and the short-range dislocation-dislocation interactions are calculated with a DD code. The long-range mechanical fields due to the dislocations are calculated by a FE code, taking into account the boundary conditions. The coupling procedure is based on eigenstrain theory, and the precise manner in which the plastic slip, i.e. the dislocation glide as calculated by the DD code, is transferred to the integration points of the FE mesh is described in full detail. Several test cases are presented, and the DCM is applied to plastic flow in a single-crystal Nickel-based superalloy.
Modeling the crystal distribution of lead-sulfate in lead-acid batteries with 3D spatial resolution
NASA Astrophysics Data System (ADS)
Huck, Moritz; Badeda, Julia; Sauer, Dirk Uwe
2015-04-01
For the reliability of lead-acid batteries it is important to have an accurate prediction of its response to load profiles. A model for the lead-sulfate growth is presented, which is embedded in a physical-chemical model with 3D spatial resolution is presented which is used for analyzing the different mechanism influencing the cell response. One import factor is the chemical dissolution and precipitation of lead-sulfate, since its dissolution speed limits the charging reaction and the accumulation of indissolvable of lead-sulfate leads to capacity degradation. The cell performance/behavior is not only determined by the amount of the sulfate but also by the radii and distribution of the crystals. The presented model can be used to for an improved understanding of the interaction of the different mechanisms.
NASA Astrophysics Data System (ADS)
Torres-Lazos, Faraon
Photonic crystals (PhC) have recently become of great interest because of their potential as replacement of electronics and/or supplement to semiconductors technology. The PhC's capability to make compact integrated optical circuits has already made possible the laboratory manufacture of an array of different types of optical waveguides, cavities and filters. The work presented here aimed to simultaneously fabricate a 3D-PhC templates employing six-beam holographic lithography. The basic procedures included recording gratings using interference field of laser sources in a photoresist coating on a glass substrate. The manufacturing method utilized only one optical element, a phasemask, drastically reducing the complexity of fabrication by eliminating the need multiple mirrors and beam splitters. Using this approach, a template can be created with a single exposure to laser source and just varying exposure times, increasing reproducibility.
NASA Astrophysics Data System (ADS)
Tao, Yulun; Shen, Yuhua; Yang, Liangbao; Han, Bin; Huang, Fangzhi; Li, Shikuo; Chu, Zhuwang; Xie, Anjian
2012-05-01
While the number of man-made nano superstructures realized by self-assembly is growing in recent years, assemblies of conductive polymer nanocrystals, especially for superlattices, are still a significant challenge, not only because of the simplicity of the shape of the nanocrystal building blocks and their interactions, but also because of the poor control over these parameters in the fabrication of more elaborate nanocrystals. Here, we firstly report a facile and general route to a new generation of 3D layered superlattices of polyaniline doped with CSA (PANI-CSA) and show how PANI crystallize and self-assemble, in a suitable single solution environment. In cyclohexane, 1D amorphous nanofibers transformed to 1D nanorods as building blocks, and then to 2D single-crystal nanosheets with a hexagonal phase, and lastly to 3D ordered layered superlattices with the narrowest polydispersity value (Mw/Mn = 1.47). Remarkably, all the instructions for the hierarchical self-assembly are encoded in the layered shape in other non-polar solvents (hexane, octane) and their conductivity in the π-π stacking direction is improved to about 50 S cm-1, which is even higher than that of the highest previously reported value (16 S cm-1). The method used in this study is greatly expected to be readily scalable to produce superlattices of conductive polymers with high quality and low cost.While the number of man-made nano superstructures realized by self-assembly is growing in recent years, assemblies of conductive polymer nanocrystals, especially for superlattices, are still a significant challenge, not only because of the simplicity of the shape of the nanocrystal building blocks and their interactions, but also because of the poor control over these parameters in the fabrication of more elaborate nanocrystals. Here, we firstly report a facile and general route to a new generation of 3D layered superlattices of polyaniline doped with CSA (PANI-CSA) and show how PANI crystallize and
Hajj Hussein, R; Pagès, O; Polian, A; Postnikov, A V; Dicko, H; Firszt, F; Strzałkowski, K; Paszkowicz, W; Broch, L; Ravy, S; Fertey, P
2016-05-25
Near-forward Raman scattering combined with ab initio phonon and bond length calculations is used to study the 'phonon-polariton' transverse optical modes (with mixed electrical-mechanical character) of the II-VI ZnSe1-x S x mixed crystal under pressure. The goal of the study is to determine the pressure dependence of the poorly-resolved percolation-type Zn-S Raman doublet of the three oscillator [1 × (Zn-Se), 2 × (Zn-S)] ZnSe0.68S0.32 mixed crystal, which exhibits a phase transition at approximately the same pressure as its two end compounds (~14 GPa, zincblende → rocksalt), as determined by high-pressure x-ray diffraction. We find that the intensity of the lower Zn-S sub-mode of ZnSe0.68S0.32, due to Zn-S bonds vibrating in their own (S-like) environment, decreases under pressure (Raman scattering), whereas its frequency progressively converges onto that of the upper Zn-S sub-mode, due to Zn-S vibrations in the foreign (Se-like) environment (ab initio calculations). Ultimately, only the latter sub-mode survives. A similar 'phonon freezing' was earlier evidenced with the well-resolved percolation-type Be-Se doublet of Zn1-x Be x Se (Pradhan et al 2010 Phys. Rev. B 81 115207), that exhibits a large contrast in the pressure-induced structural transitions of its end compounds. We deduce that the above collapse/convergence process is intrinsic to the percolation doublet of a short bond under pressure, at least in a ZnSe-based mixed crystal, and not due to any pressure-induced structural transition. PMID:27114448
Abernathy, Douglas L.; Ma, Jie; Yan, Jiaqiang; Delaire, Olivier A.; Chen, Xi; Weathers, Annie; Mukhopadhyay, Saikat; Shi, Li
2015-04-15
A variety of crystals contain quasi-one-dimensional substructures, which yield distinctive electronic, spintronic, optical and thermoelectric properties. There is a lack of understanding of the lattice dynamics that influences the properties of such complex crystals. Here we employ inelastic neutron scatting measurements and density functional theory calculations to show that numerous low-energy optical vibrational modes exist in higher manganese silicides, an example of such crystals. These optical modes, including unusually low-frequency twisting motions of the Si ladders inside the Mn chimneys, provide a large phase space for scattering acoustic phonons. A hybrid phonon and diffuson model is proposed to explain themore » low and anisotropic thermal conductivity of higher manganese silicides and to evaluate nanostructuring as an approach to further suppress the thermal conductivity and enhance the thermoelectric energy conversion efficiency. This discovery offers new insights into the structure-property relationships of a broad class of materials with quasi-one-dimensional substructures for various applications.« less
Design of acoustic beam aperture modifier using gradient-index phononic crystals
Lin, Sz-Chin Steven; Tittmann, Bernhard R.; Huang, Tony Jun
2012-01-01
This article reports the design concept of a novel acoustic beam aperture modifier using butt-jointed gradient-index phononic crystals (GRIN PCs) consisting of steel cylinders embedded in a homogeneous epoxy background. By gradually tuning the period of a GRIN PC, the propagating direction of acoustic waves can be continuously bent to follow a sinusoidal trajectory in the structure. The aperture of an acoustic beam can therefore be shrunk or expanded through change of the gradient refractive index profiles of the butt-jointed GRIN PCs. Our computational results elucidate the effectiveness of the proposed acoustic beam aperture modifier. Such an acoustic device can be fabricated through a simple process and will be valuable in applications, such as biomedical imaging and surgery, nondestructive evaluation, communication, and acoustic absorbers. PMID:22807585
Broadband and wide-angle negative reflection at a phononic crystal boundary
Zhao, Degang; Zhu, Xuefeng Yi, Lin; Ye, Yangtao; Xu, Shengjun
2014-01-27
We have theoretically and experimentally demonstrated the anomalous negative reflection at the boundary of a well-designed two-dimensional phononic crystal. This exotic phenomenon is attributed to the selective enhancement of −1st order diffraction mode with the zero-order diffraction mode being dramatically suppressed. After material and structural optimization, the negative reflection can be maintained in a broadband of frequencies and for a wide incident angle range. Our system can be employed to design Littrow configuration to realize perfect broadband and wide-angle blazing. The study gives a possibility to achieve greater flexibility and stronger effects in manipulating reflected acoustic waves, which has potential applications in underwater communication, medical ultrasonics, etc.
Thermal tuning of omnidirectional reflection bands in one-dimensional finite phononic crystals
NASA Astrophysics Data System (ADS)
Chen, Zhaojiang
2015-03-01
This study investigates the temperature-tuned omnidirectional reflection (ODR) bands in a one-dimensional (1D) finite phononic crystal (PnC), formed by alternating layers of nitinol and epoxy. An analytical model, based on the transfer matrix method, is developed to study reflection and transmission characteristics of the acoustic waves including shear and compressional waves in a 1D PnC. Existence criteria and the sensitive and continuous temperature-tunability of ODR bands in the nitinol/epoxy PnC are demonstrated using the analyses of projected-band structures and reflection spectra. The width and location of the ODR bands shift markedly with temperature variations of nitinol across the phase transition from martensite to austenite. The effects of temperature, filling fraction of nitinol layers, and the Si clad layer on ODR bands are considered. The results will be of benefit in the design and optimization of thermal tuning of omnidirectional acoustic mirrors.
Nardi, Damiano; Travagliati, Marco; Siemens, Mark E; Li, Qing; Murnane, Margaret M; Kapteyn, Henry C; Ferrini, Gabriele; Parmigiani, Fulvio; Banfi, Francesco
2011-10-12
High-frequency surface acoustic waves can be generated by ultrafast laser excitation of nanoscale patterned surfaces. Here we study this phenomenon in the hypersonic frequency limit. By modeling the thermomechanics from first-principles, we calculate the system's initial heat-driven impulsive response and follow its time evolution. A scheme is introduced to quantitatively access frequencies and lifetimes of the composite system's excited eigenmodes. A spectral decomposition of the calculated response on the eigemodes of the system reveals asymmetric resonances that result from the coupling between surface and bulk acoustic modes. This finding allows evaluation of impulsively excited pseudosurface acoustic wave frequencies and lifetimes and expands our understanding of the scattering of surface waves in mesoscale metamaterials. The model is successfully benchmarked against time-resolved optical diffraction measurements performed on one-dimensional and two-dimensional surface phononic crystals, probed using light at extreme ultraviolet and near-infrared wavelengths. PMID:21910426
NASA Astrophysics Data System (ADS)
Li, FengLian; Wang, YueSheng; Zhang, ChuanZeng
2016-06-01
A boundary element method (BEM) is presented to compute the transmission spectra of two-dimensional (2-D) phononic crystals of a square lattice which are finite along the x-direction and infinite along the y-direction. The cross sections of the scatterers may be circular or square. For a periodic cell, the boundary integral equations of the matrix and the scatterers are formulated. Substituting the periodic boundary conditions and the interface continuity conditions, a linear equation set is formed, from which the elastic wave transmission can be obtained. From the transmission spectra, the band gaps can be identified, which are compared with the band structures of the corresponding infinite systems. It is shown that generally the transmission spectra completely correspond to the band structures. In addition, the accuracy and the efficiency of the boundary element method are analyzed and discussed.
2011-01-01
High-frequency surface acoustic waves can be generated by ultrafast laser excitation of nanoscale patterned surfaces. Here we study this phenomenon in the hypersonic frequency limit. By modeling the thermomechanics from first-principles, we calculate the system’s initial heat-driven impulsive response and follow its time evolution. A scheme is introduced to quantitatively access frequencies and lifetimes of the composite system’s excited eigenmodes. A spectral decomposition of the calculated response on the eigemodes of the system reveals asymmetric resonances that result from the coupling between surface and bulk acoustic modes. This finding allows evaluation of impulsively excited pseudosurface acoustic wave frequencies and lifetimes and expands our understanding of the scattering of surface waves in mesoscale metamaterials. The model is successfully benchmarked against time-resolved optical diffraction measurements performed on one-dimensional and two-dimensional surface phononic crystals, probed using light at extreme ultraviolet and near-infrared wavelengths. PMID:21910426
Gradient-index phononic crystal lens-based enhancement of elastic wave energy harvesting
NASA Astrophysics Data System (ADS)
Tol, S.; Degertekin, F. L.; Erturk, A.
2016-08-01
We explore the enhancement of structure-borne elastic wave energy harvesting, both numerically and experimentally, by exploiting a Gradient-Index Phononic Crystal Lens (GRIN-PCL) structure. The proposed GRIN-PCL is formed by an array of blind holes with different diameters on an aluminum plate, where the blind hole distribution is tailored to obtain a hyperbolic secant gradient profile of refractive index guided by finite-element simulations of the lowest asymmetric mode Lamb wave band diagrams. Under plane wave excitation from a line source, experimentally measured wave field validates the numerical simulation of wave focusing within the GRIN-PCL domain. A piezoelectric energy harvester disk located at the first focus of the GRIN-PCL yields an order of magnitude larger power output as compared to the baseline case of energy harvesting without the GRIN-PCL on the uniform plate counterpart.
Dirac-like point at the high symmetric M point in a square phononic crystal
NASA Astrophysics Data System (ADS)
Gao, Han-Feng; Zhang, Xin; Wu, Fu-Gen; Yao, Yuan-Wei; Li, Jing
2016-05-01
Using the accidental degeneracy of a doubly degenerate state and a single state, a new Dirac-like point was constructed at the high symmetric M point in a two-dimensional phononic crystal (PnC) that consists of a square array of square rods in water. When a plane wave at a frequency near the Dirac-like point impinges on the PnC slab from the left, the spatial phase experiences a minor change in the regions located near the incident interface, but this phase remains uniform in the far field. We also demonstrate two important properties that are correlated to these special field patterns: acoustic cloaking and wavefront reshaping.
Effects of periodicity perturbations on the transmission by underwater phononic crystals.
Zong, K; Franklin, H; Lenoir, O; Predoi, M V
2012-10-01
The effects of periodicity perturbations in underwater phononic crystal layers composed of noninterpenetrating rows of identical shells are investigated. The results for one row are obtained by using a multiple scattering method between shells. Then, taking into account the multiple reflections and transmissions between two adjacent rows, a Debye series method is used to calculate the reflection and transmission coefficients by a finite number of rows. The paper focuses on three kinds of perturbations: (i) variation of the inner radius of shells from row to row, (ii) increase in the spacing from row to row and of the number of rows, and (iii) substitution of simple steel rows by steel-polyethylene bilayers. It is shown by studying the transmission coefficient that the case (i) permits the insertion of narrow pass bands in the stop band while the two other cases (ii) and (iii) widen the stop band. The study intends to model simple underwater acoustic filters. PMID:23039549
Carrier scattering processes and low energy phonon spectroscopy in hybrid perovskites crystals
NASA Astrophysics Data System (ADS)
Even, Jacky; Paofai, Serge; Bourges, Philippe; Letoublon, Antoine; Cordier, Stéphane; Durand, Olivier; Katan, Claudine
2016-03-01
Despite the wealth of research conducted the last three years on hybrid organic perovskites (HOP), several questions remain open including: to what extend the organic moiety changes the properties of the material as compared to allinorganic (AIP) related perovskite structures. To ultimately reach an answer to this question, we have recently introduced two approaches that were designed to take the stochastic molecular degrees of freedom into account, and suggested that the high temperature cubic phase of HOP and AIP is an appropriate reference phase to rationalize HOP's properties. In this paper, we recall the main concepts and discuss more specifically the various possible couplings between charge carriers and low energy excitations such as acoustic and optical phonons. As available experimental or simulated data on low energy excitations are limited, we also present preliminary neutron scattering and ultrasonic measurements obtained and freshly prepared single crystals of CH3NH3PbBr3.
Körsgen, Martin; Pelster, Andreas; Dreisewerd, Klaus; Arlinghaus, Heinrich F
2016-02-01
The analytical sensitivity in matrix-assisted laser desorption/ionization mass spectrometry (MALDI-MS) is largely affected by the specific analyte-matrix interaction, in particular by the possible incorporation of the analytes into crystalline MALDI matrices. Here we used time-of-flight secondary ion mass spectrometry (ToF-SIMS) to visualize the incorporation of three peptides with different hydrophobicities, bradykinin, Substance P, and vasopressin, into two classic MALDI matrices, 2,5-dihydroxybenzoic acid (DHB) and α-cyano-4-hydroxycinnamic acid (HCCA). For depth profiling, an Ar cluster ion beam was used to gradually sputter through the matrix crystals without causing significant degradation of matrix or biomolecules. A pulsed Bi3 ion cluster beam was used to image the lateral analyte distribution in the center of the sputter crater. Using this dual beam technique, the 3D distribution of the analytes and spatial segregation effects within the matrix crystals were imaged with sub-μm resolution. The technique could in the future enable matrix-enhanced (ME)-ToF-SIMS imaging of peptides in tissue slices at ultra-high resolution. Graphical Abstract ᅟ. PMID:26419771
NASA Astrophysics Data System (ADS)
Körsgen, Martin; Pelster, Andreas; Dreisewerd, Klaus; Arlinghaus, Heinrich F.
2016-02-01
The analytical sensitivity in matrix-assisted laser desorption/ionization mass spectrometry (MALDI-MS) is largely affected by the specific analyte-matrix interaction, in particular by the possible incorporation of the analytes into crystalline MALDI matrices. Here we used time-of-flight secondary ion mass spectrometry (ToF-SIMS) to visualize the incorporation of three peptides with different hydrophobicities, bradykinin, Substance P, and vasopressin, into two classic MALDI matrices, 2,5-dihydroxybenzoic acid (DHB) and α-cyano-4-hydroxycinnamic acid (HCCA). For depth profiling, an Ar cluster ion beam was used to gradually sputter through the matrix crystals without causing significant degradation of matrix or biomolecules. A pulsed Bi3 ion cluster beam was used to image the lateral analyte distribution in the center of the sputter crater. Using this dual beam technique, the 3D distribution of the analytes and spatial segregation effects within the matrix crystals were imaged with sub-μm resolution. The technique could in the future enable matrix-enhanced (ME)-ToF-SIMS imaging of peptides in tissue slices at ultra-high resolution.
Yan, Zhi-Hao; Li, Xiao-Yu; Liu, Li-Wei; Yu, Si-Qi; Wang, Xing-Po; Sun, Di
2016-02-01
A new 3D Ag(I)-based coordination network, [Ag2(pz)(bdc)·H2O]n (1; pz = pyrazine and H2bdc = benzene-1,3-dicarboxylic acid), was constructed by one-pot assembly and structurally established by single-crystal X-ray diffraction at different temperatures. Upon cooling from 298 to 93 K, 1 undergo an interesting single-crystal to single-crystal phase transition from orthorhombic Ibca (Z = 16) to Pccn (Z = 32) at around 148 K. Both phases show a rare 2-fold-interpenetrated 4-connected lvt network but incorporate different [Ag2(COO)2] dimeric secondary building units. It is worth mentioning that complex 1 shows red- and blue-shifted luminescences in the 290-170 and 140-80 K temperature ranges, respectively. The variable-temperature single-crystal X-ray crystallographic studies suggest that the argentophilic interactions and rigidity of the structure dominated the luminescence chromism trends at the respective temperature ranges. Upon being mechanically ground, 1 exhibits a slight mechanoluminescence red shift from 589 to 604 nm at 298 K. PMID:26828950
Phonon interference and thermal conductance reduction in atomic-scale metamaterials
NASA Astrophysics Data System (ADS)
Han, Haoxue; Potyomina, Lyudmila G.; Darinskii, Alexandre A.; Volz, Sebastian; Kosevich, Yuriy A.
2014-05-01
We introduce and model a three-dimensional (3D) atomic-scale phononic metamaterial producing two-path phonon interference antiresonances to control the heat flux spectrum. We show that a crystal plane partially embedded with defect-atom arrays can completely reflect phonons at the frequency prescribed by masses and interaction forces. We emphasize the predominant role of the second phonon path and destructive interference in the origin of the total phonon reflection and thermal conductance reduction in comparison with the Fano-resonance concept. The random defect distribution in the plane and the anharmonicity of atom bonds do not deteriorate the antiresonance. The width of the antiresonance dip can provide a measure of the coherence length of the phonon wave packet. All our conclusions are confirmed both by analytical studies of the equivalent quasi-1D lattice models and by numerical molecular dynamics simulations of realistic 3D lattices.
NASA Astrophysics Data System (ADS)
Lacis, K.; Muiznieks, A.; Ratnieks, G.
2005-06-01
A system of three-dimensional numerical models is described to analyse the melt hydrodynamics in the floating zone crystal growth by the needle-eye technique under a rotating magnetic field for the production of high quality silicon single crystals of large diameters big( 100dots 200 mm big). Since the pancake inductor has only one turn, the high frequency (HF) electromagnetic (EM) field and the distribution of heat sources and EM forces on the melt free surface have distinct asymmetric features. This asymmetry together with the displacement of the crystal and feed rod axis and crystal rotation manifests itself as three dimensional hydrodynamic, thermal and dopant concentration fields in the molten zone and causes variations of resistivity in the grown single crystal, which are known as the so-called rotational striations. Additionally, the rotating magnetic field can be used to influence the melt hydrodynamics and to reduce the flow asymmetry. In the present 3D model system, the shape of the molten zone is obtained from symmetric FZ shape calculations. The asymmetric HF EM field is calculated by the 3D boundary element method. The low-frequency rotating magnetic field and a corresponding force density distribution in the melt are calculated by the 3D finite element method. The obtained asymmetric HF field power distribution on the free melt surface, the corresponding HF EM forces and force density of the rotating magnetic field are used for the coupled calculation of 3D steady-state hydrodynamic and temperature fields in the molten zone on a body fitted structured 3D grid by a commercial program package with a control volume approach. Beside the EM forces, also the buoyancy and Marangoni forces are considered. After HD calculations a corresponding 3D dopant concentration field is calculated and used to derive the variations resistivity in the grown crystal. The capability of the system of models is illustrated by a calculation example of a realistic FZ system
NASA Astrophysics Data System (ADS)
Yahya, I.; Kusuma, J. I.; Harjana; Kristiani, R.; Hanina, R.
2016-02-01
This paper emphasizes the influence of tubular shaped microresonators phononic crystal insertion on the sound absorption coefficient of profiled sound absorber. A simple cubic and two different bodies centered cubic phononic crystal lattice model were analyzed in a laboratory test procedure. The experiment was conducted by using transfer function based two microphone impedance tube method refer to ASTM E-1050-98. The results show that sound absorption coefficient increase significantly at the mid and high-frequency band (600 - 700 Hz) and (1 - 1.6 kHz) when tubular shaped microresonator phononic crystal inserted into the tested sound absorber element. The increment phenomena related to multi-resonance effect that occurs when sound waves propagate through the phononic crystal lattice model that produce multiple reflections and scattering in mid and high-frequency band which increases the sound absorption coefficient accordingly