The aim of this project was to improve the imaging performance of planar superlenses for evanescent near-field lithography. An experimental investigation of the performance of superlenses with reduced surface roughness was proposed. Such an investigation poses significant requirements in regards to process control in thin film deposition of silver onto dielectric substrates. Thin film deposition of silver films, onto silicon dioxide substrates, achieved films with root mean square surface roughness as low as 0.8 nm. While these experiments provided good understanding of the deposition process, significant variability of the surface roughness parameter remained an issue. The diffculty of achieving consistent control of surface roughness led to a finite element method simulation study where this parameter could be readily controlled. An improved understanding of how surface roughness affects superlens imaging performance was obtained from the results of this investigation. Furthermore, it was shown that in order to conduct an experimental investigation to verify the simulation results, it would be necessary to improve the imaging capability of super-resolution lithography protocols to achieve 3σ line edge roughness (LER) of <20 nm. Resist-scheme optimisation was identied as an important factor in this regard. Thus, a novel calixarene-based photoresist was formulated and characterised. The resist demonstrated superior imaging capabilities through interference lithography and evanescent near-field optical lithography, capable of resolving 250-nm period half-pitch line gratings with 3σ LER below 10 nm. The development of this novel photoresist will enable future lithographical investigations to be conducted with improved resolution and imaging fidelity.

Thesis advisor: Krzysztof Kempa / Though nature provides a plethora of materials to work with, their properties are very much restricted, forcing severe limitations on the devices that are built from them. A huge portion of current technology stands to be significantly advanced and even revolutionized by the emergence of a new class of “configurable” materials. This class, generally referred to as metamaterials, has become more feasible than ever due to advancements in nanotechnology and fabrication techniques. Notable among nature’s limitations is an ever-positive index of refraction. This barrier has only recently been broken, and the known paths to negative refraction are few and limited. This paper introduces two distinct three-dimensional crystals capable of all-angle negative refraction. One uses the familiar photonic band, while the other is the first of its kind to rely on polaritonic waves. Their mode structures are examined and a set of parameters are chosen at which a negative effective index of refraction can be harnessed for unrestricted sub-wavelength lensing, demonstrated via numerical simulation. This work is expected to enable experimental observation of polaritonic negative refraction and sub-wavelength lensing at microwave frequencies. / Thesis (BS) — Boston College, 2009. / Submitted to: Boston College. College of Arts and Sciences. / Discipline: College Honors Program. / Discipline: Physics.

Novel wave phenomena in two- and three-dimensional (2D and 3D) phononic crystals were investigated experimentally using ultrasonic techniques. Resonant tunneling of ultrasonic waves was successfully observed for the first time by measuring the transmission of ultrasound pulses through a double barrier consisting of two 3D phononic crystals separated by a cavity. This effect is the classical analogue of resonant tunneling of a quantum mechanical particle through a double potential barrier, in which transmission reaches unity at resonant frequencies. For phononic crystals, the tunneling peak was found to be less than unity, an effect that was explained by absorption. The dynamics of resonant tunneling was explored by measuring the group velocities of the ultrasonic pulses. Very slow and very fast velocities were found at frequencies close to and at the resonance, respectively. These extreme values are less than the speed of sound in air and greater than the speed of sound in any of the crystal’s constituent materials. Negative refraction and focusing effects in 2D phononic crystals were also observed. Negative refraction of ultrasound was demonstrated unambiguously in a prism-shaped 2D crystal at frequencies in the 2nd pass band where the wave vector and group velocity are opposite. The Multiple Scattering Theory and Snell’s law allowed theoretical predictions of the refraction angles. Excellent agreement was found between theory and experiment. The negative refraction experiments revealed a mechanism that can be used to focus ultrasound using a flat phononic crystal, and experiments to demonstrate the focusing of ultrasound emitted by several point sources were successfully carried out. The importance of using phononic crystals with circular equifrequency contours, as well as matching the size of the contours inside and outside the crystal, was established. Both conditions were satisfied by a flat phononic crystal of steel rods, in which the liquid inside the crystal (methanol) was different from the outside medium (water). The possibility of achieving subwavelength resolution using this phononic crystal was investigated with a subwavelength line source (a miniature strip-shaped transducer, approximately lambda/5 wide, where lambda is sound wavelength in water). A resolution of 0.55lambda was found, which is just above the diffraction limit lambda/2. / October 2007

Novel wave phenomena in two- and three-dimensional (2D and 3D) phononic crystals were investigated experimentally using ultrasonic techniques. Resonant tunneling of ultrasonic waves was successfully observed for the first time by measuring the transmission of ultrasound pulses through a double barrier consisting of two 3D phononic crystals separated by a cavity. This effect is the classical analogue of resonant tunneling of a quantum mechanical particle through a double potential barrier, in which transmission reaches unity at resonant frequencies. For phononic crystals, the tunneling peak was found to be less than unity, an effect that was explained by absorption. The dynamics of resonant tunneling was explored by measuring the group velocities of the ultrasonic pulses. Very slow and very fast velocities were found at frequencies close to and at the resonance, respectively. These extreme values are less than the speed of sound in air and greater than the speed of sound in any of the crystal’s constituent materials. Negative refraction and focusing effects in 2D phononic crystals were also observed. Negative refraction of ultrasound was demonstrated unambiguously in a prism-shaped 2D crystal at frequencies in the 2nd pass band where the wave vector and group velocity are opposite. The Multiple Scattering Theory and Snell’s law allowed theoretical predictions of the refraction angles. Excellent agreement was found between theory and experiment. The negative refraction experiments revealed a mechanism that can be used to focus ultrasound using a flat phononic crystal, and experiments to demonstrate the focusing of ultrasound emitted by several point sources were successfully carried out. The importance of using phononic crystals with circular equifrequency contours, as well as matching the size of the contours inside and outside the crystal, was established. Both conditions were satisfied by a flat phononic crystal of steel rods, in which the liquid inside the crystal (methanol) was different from the outside medium (water). The possibility of achieving subwavelength resolution using this phononic crystal was investigated with a subwavelength line source (a miniature strip-shaped transducer, approximately lambda/5 wide, where lambda is sound wavelength in water). A resolution of 0.55lambda was found, which is just above the diffraction limit lambda/2.

Novel wave phenomena in two- and three-dimensional (2D and 3D) phononic crystals were investigated experimentally using ultrasonic techniques. Resonant tunneling of ultrasonic waves was successfully observed for the first time by measuring the transmission of ultrasound pulses through a double barrier consisting of two 3D phononic crystals separated by a cavity. This effect is the classical analogue of resonant tunneling of a quantum mechanical particle through a double potential barrier, in which transmission reaches unity at resonant frequencies. For phononic crystals, the tunneling peak was found to be less than unity, an effect that was explained by absorption. The dynamics of resonant tunneling was explored by measuring the group velocities of the ultrasonic pulses. Very slow and very fast velocities were found at frequencies close to and at the resonance, respectively. These extreme values are less than the speed of sound in air and greater than the speed of sound in any of the crystal’s constituent materials. Negative refraction and focusing effects in 2D phononic crystals were also observed. Negative refraction of ultrasound was demonstrated unambiguously in a prism-shaped 2D crystal at frequencies in the 2nd pass band where the wave vector and group velocity are opposite. The Multiple Scattering Theory and Snell’s law allowed theoretical predictions of the refraction angles. Excellent agreement was found between theory and experiment. The negative refraction experiments revealed a mechanism that can be used to focus ultrasound using a flat phononic crystal, and experiments to demonstrate the focusing of ultrasound emitted by several point sources were successfully carried out. The importance of using phononic crystals with circular equifrequency contours, as well as matching the size of the contours inside and outside the crystal, was established. Both conditions were satisfied by a flat phononic crystal of steel rods, in which the liquid inside the crystal (methanol) was different from the outside medium (water). The possibility of achieving subwavelength resolution using this phononic crystal was investigated with a subwavelength line source (a miniature strip-shaped transducer, approximately lambda/5 wide, where lambda is sound wavelength in water). A resolution of 0.55lambda was found, which is just above the diffraction limit lambda/2.

La propagation des ondes ultrasonores à travers des cristaux phononiques CP à deux dimensions 2D constitués de diffuseurs solides dans des matrices solide et fluide est ici étudiée, ainsi que la caractérisation de ces milieux et leur application à l’imagerie acoustique. Les techniques expérimentales utilisées permettent une mesure complète des champs transmis à travers les cristaux. Les études sont menées dans des bandes fréquentielles autorisant les effets de réfraction négative indispensables à l’obtention d’une résolution inférieure à la limite de diffraction (super-résolution). De manière à compléter les analyses, différents outils théoriques sont exploités Décomposition en Ondes Planes et Eléments Finis, notamment.La première partie du document concerne la réalisation et la caractérisation de cristaux phononiques possédant des propriétés nécessaires à la réalisation de systèmes d’imagerie acoustique réfraction négative, contours équi-fréquences circulaires, accord d’indice, accord d’impédance. Cette première étude est menée sur un cristal à matrice solide, elle met en relief la possibilité de générer différents modes de Bloch au cours de la propagation. L’accord d’indice avec l’eau n’étant cependant pas obtenu, la seconde partie porte sur la réfraction négative et la focalisation des ondes à travers un CP à matrice fluide. Les propriétés du CP déterminées, le dernier chapitre s’attache à évaluer les performances des systèmes d’imagerie développés : dynamique et résolution. / This investigation deals with wave propagation in two dimensional phononic crystals (PC) made of solid scatterers embedded in solid or fluid matrices. After characterizing such composite materials, their application to acoustic imaging is brought to the forth. The ultrasonic techniques used in the experiments allow the complete measurement of the acoustic transmitted fields and the investigations concern frequency bandwidth able to exhibit negative refraction allowing Oie super-resolution effects. In order to complete the analysis, different theoretical tools are used: Plane Wave Expansion (PWE) and Finite Elements Method (FEM).The first part of this work deals with the realization and characterization of PC to be introduced into acoustic imaging devices (lenses) based on negative refraction. Special attention is given to characteristics such as circular equi-frequency contours, or index and impedance matching. However, during the acoustic wave propagation in a solid PC immersed in water, the presence of different Bloch modes contributing to the transmission of ultrasound is revealed and the index matching was not possible to obtain. Therefore the second part of the manuscript deals with negative refraction and waves focusing through a PC filled with a fluid. After determining the crystal properties, last chapter is devoted to the evaluation of the performances of acoustic imaging systems based on phononic lens.

Propagation of a Gaussian beam in a layered periodic structure is studied analytically, numerically, and experimentally. It is demonstrated that for a special set of parameters the acoustic beam propagates without diffraction spreading. This propagation is also accompanied by negative refraction of the direction of phase velocity of the Bloch wave. In the study of two-dimensional viscous phononic crystals with asymmetrical solid inclusions, it was discovered that acoustic transmission is nonreciprocal. The effect of nonreciprocity in a static viscous environment is due to broken PT symmetry of the system as a whole. The difference in transmission is caused by the asymmetrical transmission and dissipation. The asymmetrical transmission is caused solely by broken mirror symmetry and could appear even in a lossless system. Asymmetrical dissipation of sound is a time-irreversible phenomenon that arises only if both energy dissipation and broken parity symmetry are present in the system. The numerical results for both types of phononic crystals were verified experimentally. Proposed devices could be exploited as collimation, rectification, and isolation acoustic devices.

Quelle que soit la nature des ondes utilisées et des milieux traversés, le contrôle de la propagation ondes est d'un intérêt majeur pour de nombreuses applications. D'une part, la complexité du milieu peut être exploitée en exerçant un contrôle cohérent du front d’onde incident. D'autre part, on peut forcer une onde à se propager suivant un chemin désiré en concevant soi-même le milieu de propagation. Dans cette thèse, nous étudions ces deux aspects à partir d'expériences ultrasons-laser mettant en jeu la propagation d'ondes de Lamb dans des plaques.La propagation des ondes à travers un milieu diffusant est tout d’abord étudiée à partir de sa matrice de diffusion. Une prédiction théorique importante est l’existence de canaux de propagation totalement ouverts ou fermés. Une première partie de ces travaux consiste à démontrer expérimentalement ce résultat en mettant en évidence la possibilité de transmettre totalement une onde à travers un milieu désordonné. Dans un second temps, la mesure d’une matrice des temps de vol nous permet d’étudier ces canaux dans le domaine temporel. Ceux-ci donnent lieu à des paquets d’onde dont la cohérence spatiale et temporelle est conservée tout au long de leur propagation dans le milieu.Le second volet de cette thèse consiste à tirer profit des phénomènes de réflexion et réfraction négative afin de contrôler la propagation des ondes de Lamb. D’une part, la réflexion négative est mise à profit pour réaliser une conjugaison de phase passive des ondes de Lamb. D’autre part, le concept des milieux complémentaires est exploré afin d’annuler la diffraction des ondes et ainsi camoufler certaines zones du milieu de propagation. / Whatever their nature or the propagation medium, controlling the propagation of waves is of fundamental interest for many applications. On the one hand, one can tame wave-fields in order to take advantage of the complexity of the medium. On the other hand, one can force waves along desired paths through a careful design of manmade materials. In this thesis, we study those two aspects on the basis of laser-ultrasonic experiments involving the propagation of Lamb waves in elastic plates.The control of wave propagation through complex systems is first investigated by means of the scattering matrix approach. In diffusive media, theorists have demonstrated the existence of propagation channels either closed or open through which the wave can travel. The first part of this work present a direct experimental evidence of this result as well as the ability to fully transmit a wave through a disordered medium. In a second part, the measurement of the time-delay matrix allows the study of such channels in the time domain. They are shown to give rise to particle-like wave packets that remain focused in time and space throughout their trajectory in the medium.The second part of this thesis consists in studying the concepts of negative reflection and refraction for the manipulation of Lamb wave propagation. On the one hand, negative reflection is taken advantage of to perform a passive phase conjugation of Lamb waves. On the other hand, the notion of complementary media is investigated in order to cancel the diffraction of waves and cloak some areas of the plate.

Ce mémoire de thèse est consacré à l'étude, la fabrication et la caractérisation de métamatériaux en vue d'applications dans le domaine millimétrique et submillimétrique. Dans un premier temps, nous avons tenu à rappeler les propriétés remarquables ainsi que les processus physiques mis en jeux par cette nouvelle génération de matériaux. Le manuscrit regroupe essentiellement des résultats issus d’études réalisées sur différentes structures en microondes et en terahertz : métamatériaux composites, métamatériaux entièrement diélectriques à base de résonances de Mie, ouvertures sublongueur d’ondes basés sur la transmission extraordinaire assistée par plasmons de surface. Nos investigations ont permis d’ouvrir la voie à de multiples applications dans les domaines des capteurs et des télécommunications. / This PhD dissertation is dedicated to the study, fabrication and characterization of metamaterials for millimeter and submillimeter applications. First of all we proposed to remind the extraordinary properties and physical processes involving within this new generation of materials. The manuscript contains results obtained from studies performed on different categories of metamaterials at microwave and terahertz frequencies: composite metamaterials, all dielectric metamaterials based on Mie resonances, subwavelength apertures based on the extraordinary transmission assisted by surface Plasmon polaritons. Our investigations have contributed to open the path to multiple potential applications in the field of sensors and telecommunications.

Metamaterials are artificial structures, which periodically arranged to exhibit fascinating electromagnetic properties, not existing in nature. A great deal of research in the field of metamaterial was conducted in a linear regime, where the electromagnetic responses are independent of the external electric or magnetic fields. Unfortunately, in linear regime the desired properties of metamaterials have only been achieved within a narrow bandwidth, around a fixed frequency. Therefore, nonlinearity is introduced into metamaterials by merging meta-atoms with well-known nonlinear materials. Nonlinear metamaterials are exploited in this dissertation to introduce and develop applications in microwave frequency with broadband responses. The nonlinearity was achieved via embedding varactor diode on to split ring resonator (SRR) design, which demonstrates tunability in resonance frequency and phase of the transmission signal. SRR exhibits power and frequency dependent broadband tunability and it is realized for external electro-magnetic signals. More importantly, the nonlinear SRR shows bi-stability with distinct transmission levels, where the transition between bi-states is controlled by the impulses of pump signal and it can be used as a switching device in microwave regime. In order to increase its functionality in other frequencies, a new design, double split ring resonator (DSRR) is introduced with two rings, which has two distinct resonance frequencies. The double split ring resonator also demonstrate similar behavior as the SRR but it is broadband. Furthermore, by designing the structure such that the inner ring has a frequency twice as outer ring resonance frequency; we observed the enhancement of harmonic generation. We exhibit enhancement in second harmonic generation and methods that can use to increase the harmonic signal power. Arranging the unit cells in an array and particular orientation further increases the harmonic power. In addition, we show that using a back plate to create a cavity will help to increase harmonic power. Furthermore, we have demonstrated that applying an external DC voltage can be used to tune resonance frequency as well as phase of the signal. Exploring these ideas in THz frequency regime is also important. So simulation results were obtained with advanced designs to achieve non-linearity in terahertz frequency regime to realize tunability, hysteresis and bi-stable states. A negative refractive index can be realized in metamaterials consisting of strong magnetic and electric resonators with responses at the same frequency band. However, high loss and narrow bandwidth resulting from strong resonances have impeded negative index optical components and devices from reaching expected functionalities (e.g. perfect lens). Here, we demonstrate experimentally and numerically that a 2D helical chiral metamaterial exhibits broadband negative refractive index with extremely low loss. With Drude-like dispersion, its permittivity leads to zero-index, and broadband chirality further brings the index to negative values for left-handed circularly polarized light in the entire range below the plasma frequency. Non-resonant architecture results in very low loss (<2% per layer) and an extremely high Figure-of-merit (>90). Tunable THz metamaterials has shown great potential to solve the material challenge due to the so-called “THz gap”. However, the tunable mechanism of current designs relies on using semiconductors insertions, which inevitably results in high Ohmic loss, and thereby significantly degrades the performance of metamaterials. In this work, we demonstrate a novel tunable mechanism based on polymeric microactuators. Our metamaterials are fabricated on the surface of patterned pillar array of flexible polymers embedded with magnetic nanoparticles. The transmission spectrum of the metamaterial can be tuned as the pillars are mechanically deformed though applied magnetic field. We observed and measured several type of deformation including bending, twisting and compressing when the applied magnetic field is polarized along different direction with respected to the axis of the magnetic particles. Compared to previous semiconductor based tunable mechanism, our structure has shown much lower loss. We demonstrate using simulations and experimentally that with an external magnetic field, we can achieve phase modulation using magnetic polymeric micro-actuators.