1,720,967 research outputs found
Analysis and synthesis of plasmonic devices and metamaterials at optical and terahertz frequencies
Full text linkFabrication technologies have played a major role ever since the ‘60s to the rapid growth of information processing, and to the information revolution we are living today; in the electronic industry, by scaling down the size of devices, it has been possible to improve performance, functionality and reliability, all while reducing cost and increasing the production volume of the devices. Industrial success has given more impetus to further research microfabrication and nanofabrication [1 - 3], which has not only propelled more success, but has also opened to scientists and engineers a new array of physical phenomena to study and apply [4]. Over the last decades, the same fabrication apparatus and approach have allowed significant development in the field of optics, plasmonics, metamaterials, microfluidics and even mechanics [5 - 7]; those are still being extensively researched, sometimes in conjunction, for key applications such as: creation of novel materials, increase in volume of computation and communication, precise medical operations, and sensors for chemistry, biology and telecommunication [8 - 10].
As an example, we can take the plasmonics, where the discovering of a subwavelength confinements [11], coupled to the research of new nano-metamaterials [12, 13], has contributed to different families of the nanodevices with unprecedented functionalities, such as subwavelength waveguides [14, 15], optical nanoantennas [16 – 18], superlenses [19, 20], optical invisibility cloaks [21, 22], hyperlenses [23, 24], planar magnifying hyperlens and light concentrators [25, 26].
In this thesis, I present my research activity as a PhD student which encompasses various projects. My main objective has been the analysis and synthesis of plasmonic filters based on metamaterials; I have also worked on a waveguiding systems and gratings-sensors supporting long range surface plasmon polaritons. The activities were focused mainly on optical frequencies, but some devices worked on THz regime.
In the first part of my PhD, I have studied devices working in plasmonic optical frequencies. In order to perform the analysis and design, I have used numerical instruments such as the finite-difference time-domain method (FDTD) included in the software Lumerical FDTD; with the aim to have a numerical comparison for the Lumerical’s results I have also used the Finite Element Method (FEM) present in the Comsol Multyphisics software. The post-processing of the simulation’s results were performed by using Matlab. I could use these tools in the S.B.A.I. (Basic and Applied Sciences for Engineering at Sapienza University of Rome) department and in the LabCEm2 laboratory of the D.I.E.T. (Department of Information Engineering, Electronics and Telecommunications at Sapienza University of Rome).
To complete and then expand the analysis performed with numerical instruments in the second part of my PhD I have worked on the fabrication of the devices. With the gradual reduction of the devices’ dimension, various challenges have been encountered: as can be seen in later chapters, while research on nano-optics and metamaterials may be mature from an analytical and numerical point of view, there are still many challenges on the actual fabrication of the devices, because of non-ideality of geometrical shapes, materials and chemical composition; sometimes, even the characterization poses as a limiting factor. Thus, a good part of the activities has been the study of compromises between feasibility and performance of the devices: study on the fabrication tolerances and optimum fabrication dosages.
As already told, I have used the same fabrication approach of microelectronics field, which is defined “top down”: externally controlled tools are used to depose, etch, and shape materials (litography) into the desired shape. In contrast, the bottom-up approach the devices are fabricated by using the auto-assembly of molecular components through their chemical bonds; these methods are widely used today to manufacture a large variety of useful chemicals such as pharmaceuticals or commercial polymers.
Therefore, I created a nanofabrication procedure following the top-down approach and by using the classics microelectronic processes and techniques: Spin Coating followed by Hot plate for the deposition of polymer materials; Vacuum Evaporator and Sputtering for the deposition of metals and Electron Beam Lithography to imprint the desired geometry to the devices in nano-fabrication; while, for imprint geometry in micro-fabrication field, I used the standard UV-Lithography. I have performed the processes described above in collaboration with the CNR-IMM (Institute for Microelectronics and Microsystem) of Rome and I could use the FESEM Zeiss Auriga system who is kept in the Sapienza’s C.N.I.S. (Centro di Ricerca per le Nanotecnologie Applicate all’Ingegneria) laboratory in order to perform the EBL technique. The characterization of the manufactured samples are finally carried out in collaboration with the CNR-Nanotech institute of nanotechnology and Univesity of Palermo
Multilayer optical routing by means of vertical directional coupler with long range surface plasmons
No full textNumerical evaluation of irradiation diagram by plasmonic gratings and slit apertures
No full textWe describe a fast method to evaluate the far-field profile of a generic planar disposition of plasmonic gratings and
slit apertures, based on the ideal decomposition of the structure into a linear array of distinct scattering elements
and provided an accurate description of their plasmonic and radiating behaviors. This approach allows for a fast
calculation of the irradiation diagram, and has general validity for any kind of surface defects and for multiple set
of gratings and slit apertures
Analysis on vertical directional couplers with long range surface plasmons for multilayer optical routing
No full textNems-technology based nanogripper for mechanic manipulation in space exploration missions
No full textWe present the first prototype of a new concept grasping device whose overall size has been reduced as much as permitted by a new NEMS-based fabrication procedure. The fabrication processes used are compatible with rigid or flexible substrates and the materials employed are biocompatible and chemically inert. The jaws lumen size is adequate to the mechanical manipulation of micro- and sub-microscaled objects and organic matter like bacteria. The proposed device represents a promising solution for pick-transport-place operation and biological experiments for future space exploration missions
Dose influence on the PMMA e-resist for the development of high-aspect ratio and reproducible sub-micrometric structures by electron beam lithography
Full text linkIn this work, a statistical process control method is presented showing the accuracy and the reliability obtained with of PMMA E-resist AR-P 672, using an Elphy Quantum Electron Beam Lithography module integrated on a FE-SEM Zeiss Auriga instrument. Reproducible nanostructures with an high aspect ratio between e-resist thickness and width of written geometric structure are shown. Detailed investigation of geometry features are investigated with dimension in the range of 200nm to 1-m. The adopted method will show how tuning the Area Dose factor and the PMMA thickness it was possible to determine the correct and reproducible parameters that allows to obtain well defined electron-beam features with a 4:1 aspect ratio. Such high aspect ratio opens the possibility to realize an electron-beam lithography lift-off process by using a standard e-beam resist. © 2016 Author(s)
Numerical tailoring of linear response from plasmonicnano-resonators grown on a layer of polystyrene spheres
No full textWe developed a geometrical method to reproduce the morphology of hybrid structures composed by self-ordered dielectric nanospheres covered by anisotropic plasmonic structures. Numerical analysis allowed to investigate the optical response of the considered system, and to identify the relevant parameters to achieve efficient and versatile light manipulation. In particular, we show that the overall structure, acting as a hybrid plasmonic-photonics meta-surface, can be engineered in order to maximize its linear and circular dichroic behavior at optical frequencie
Going Beyond Counting First Authors in Author Co-citation Analysis
Full text linkThe present study examines one of the fundamental aspects of author co-citation analysis (ACA) - the way co-citation
counts are defined. Co-citation counting provides the data on which all subsequent statistical analyses and mappings
are based, and we compare ACA results based on two different types of co-citation counting - the traditional type that
only counts the first one among a cited work's authors on the one hand and a non-traditional type that takes into
account the first 5 authors of a cited work on the other hand. Results indicate that the picture produced through this non-traditional author co-citation counting contains more coherent author groups and is therefore considerably clearer. However, this picture represents fewer specialties in the research field being studied than that produced through the traditional first-author co-citation counting when the same number of top-ranked authors is selected and analyzed. Reasons for these effects are discussed
Variations on the Author
Full text link“Variations on the Author” discusses two of Eduardo Coutinho’s recent films (Um Dia na Vida, from 2010, and Últimas Conversas, posthumously released in 2015) and their contribution to the general question of documentary authorship. The director’s filmography is characterized by a consistent yet self-effacing form of authorial self-inscription: Coutinho often features as an interviewer that rather than express opinions propels discourses; an interviewer that is good at listening. This mode of self-inscription characterizes him as an author who is not expressive but who is nonetheless markedly present on the screen. In Um Dia na Vida, however, Coutinho is completely absent form the image, while Últimas Conversas, on the contrary, includes a confessional prologue that moves the director from the margins to the center of his films. This article examines the ways in which these works stand out in the filmography of a director who offers new insights into the notion of cinematic authorship
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