Phase-Space Properties of Two-Dimensional Elastic Phononic Crystals and Anharmonic Effects in Nano-Phononic Crystals
AuthorSwinteck, Nichlas Z.
Materials Science & Engineering
AdvisorDeymier, Pierre A.
MetadataShow full item record
PublisherThe University of Arizona.
RightsCopyright © is held by the author. Digital access to this material is made possible by the University Libraries, University of Arizona. Further transmission, reproduction or presentation (such as public display or performance) of protected items is prohibited except with permission of the author.
AbstractThis dissertation contains research directed at investigating the behavior and properties of a class of composite materials known as phononic crystals. Two categories of phononic crystals are explicitly investigated: (I) elastic phononic crystals and (II) nano-scale phononic crystals. For elastic phononic crystals, attention is directed at two-dimensional structures. Two specific structures are evaluated (1) a two-dimensional configuration consisting of a square array of cylindrical Polyvinylchloride inclusions in air and (2) a two-dimensional configuration consisting of a square array of steel cylindrical inclusions in epoxy. For the first configuration, a theoretical model is developed to ascertain the necessary band structure and equi-frequency contour features for the realization of phase control between propagating acoustic waves. In contrasting this phononic crystal with a reference system, it is shown that phononic crystals with equifrequency contours showing non-collinear wave and group velocity vectors are ideal systems for controlling the phase between propagating acoustic waves. For the second configuration, it is demonstrated that multiple functions can be realized of a solid/solid phononic crystal. The epoxy/steel phononic crystal is shown to behave as (1) an acoustic wave collimator, (2) a defect-less wave guide, (3) a directional source for elastic waves, (4) an acoustic beam splitter, (5) a phase-control device and (6) a k-space multiplexer. To transition between macro-scale systems (elastic phononic crystals) and nano-scale systems (nano-phononic crystals), a toy model of a one-dimensional chain of masses connected with non-linear, anharmonic springs is utilized. The implementation of this model introduces critical ideas unique to nano-scale systems, particularly the concept of phonon mode lifetime. The nano-scale phononic crystal of interest is a graphene sheet with periodically spaced holes in a triangular array. It is found through equilibrium molecular dynamics simulation techniques, that phonon-boundary collision effects and coherent phononic effects (band-folding) are two competing scattering mechanisms responsible for the reduction of acoustic and optical phonon lifetimes. Conclusions drawn about the lifetime of thermal phonons in phononic crystal patterned graphene are linked with the anharmonic, one-dimensional crystal model.
Degree ProgramGraduate College
Materials Science & Engineering
Degree GrantorUniversity of Arizona
Showing items related by title, author, creator and subject.
Tailoring k-Space Functionalities by Design in Phononic CrystalsDeymier, Pierre A; Bucay, Jaim; Deymier, Pierre A; Raghavan, Srini; Erdmann, Robert G (The University of Arizona., 2010)K-space functionalities in 2-D phononic crystals (PCs) were studied through the use of the finite difference time domain method (FDTD) as well as the plane wave expansion method (PWE) to solve for the propagation behavior of acoustic waves in these periodic structures. Each of these methods are fully explained in sections 2 and 3 in Appendix A. Characteristics of the various structures were found which aid in the design of the PC to obtain very specific and controlled propagation behavior.Various refractive behaviors were studied which included positive, negative, or zero-angle refraction depending on the angle of the incident wave. For all three cases of refraction, the transmitted beam underwent splitting upon exiting the crystal. These properties are analyzed theoretically as well as demonstrated experimentally. Band structures and equifrequency surfaces (EFSs) show that the observed properties result from the unique geometry of the PC's EFSs as compared to that of the incident media. These properties were extended to the applications of multiplexing and demultiplexing in which the separation of information carried by acoustic waves was attributed entirely to their differences in wave vector. To the best of our knowledge, this is the first report of a k-space multiplexing/demultiplexing device.Subwavelength resolution imaging capabilities of a flat lens composed of a phononic crystal (PC) were also studied. It was found that the image resolution of the PC flat lens beats the Rayleigh diffraction limit because bound modes in the lens can be excited by evanescent waves emitted by the source. These are modes that propagate only in the direction parallel to the lens surface. These modes resonantly amplify evanescent waves that contribute to the reconstruction of an image. The effect on the image resolution and focal point on various structural and operational parameters were studied. These parameters included source frequency, geometry of the lens, source position, and time. The mechanisms by which these factors affect resolution are discussed in terms of the competition between the contribution of propagative modes to focusing and the ability of the source to excite bound modes of the PC lens.
Phonon-assisted oscillatory exciton dynamics in monolayer MoSe2Chow, Colin M.; Yu, Hongyi; Jones, Aaron M.; Schaibley, John R.; Koehler, Michael; Mandrus, David G.; Merlin, R.; Yao, Wang; Xu, Xiaodong; Univ Arizona, Dept Phys (NATURE PUBLISHING GROUP, 2017-10-13)In monolayer semiconductor transition metal dichalcogenides, the exciton-phonon interaction strongly affects the photocarrier dynamics. Here, we report on an unusual oscillatory enhancement of the neutral exciton photoluminescence with the excitation laser frequency in monolayer MoSe2. The frequency of oscillation matches that of the M-point longitudinal acoustic phonon, LA(M), suggesting the significance of zone-edge acoustic phonons and hence the deformation potential in exciton-phonon coupling in MoSe2. Moreover, oscillatory behavior is observed in the steady-state emission linewidth and in time-resolved PLE data, which reveals variation with excitation energy in the exciton lifetime. These results clearly expose the key role played by phonons in the exciton formation and relaxation dynamics of two-dimensional van der Waals semiconductors.
Light-matter interaction: conversion of optical energy and momentum to mechanical vibrations and phononsMansuripur, Masud; Univ Arizona, Coll Opt Sci (SPIE-INT SOC OPTICAL ENGINEERING, 2016-02-13)Reflection, refraction, and absorption of light by material media are, in general, accompanied by a transfer of optical energy and momentum to the media. Consequently, the eigen-modes of mechanical vibration (phonons) created in the process must distribute the acquired energy and momentum throughout the material medium. However, unlike photons, phonons do not carry momentum. What happens to the material medium in its interactions with light, therefore, requires careful consideration if the conservation laws are to be upheld. The present paper addresses some of the mechanisms by which the electromagnetic momentum of light is carried away by mechanical vibrations.