Modelling of graded photonic and plasmonic crystals in metamaterial regime

U ovoj tezi su istraˇzeni elektromagnetski kompozitni materijali u cilju realizacije sredina sa elektromagnetskim osobinama koje ne postoje u prirodnim materijalima. Istraˇzivani kompoziti su jednodimenzionalni i dvodimenzionalni fotonski i plazmonski kristali. Jednodimenzionalne strukture se sastoje od slojeva odgovaraju´ceg oblika, dok se dvodimenzionalne strukture sastoje od ˇstapi´ca u vazduhu ili cilindriˇcnih rupa u dielektriku. Pored struktura sa periodiˇcnim ponavljanjem jediniˇcnih ´celija, razmatraju se i gradirane strukture dobijene prostornom promenom geometrije ili dielektriˇcne permitivnosti jediniˇcnih ´celija. Fotonski kristali se sastoje iskljuˇcivo od dielektrika, dok su plazmonski kristali kombinacija dielektriˇcnih i plazmonskih materijala, metala ili poluprovodnika. Posebna klasa razmotrenih kompozitnih struktura su planarni plazmonski kristali koji se sastoje od paralelnih traka od plazmonskih materijala na dielektriˇcnom substratu. Sve kompozitne strukture se razmatraju u reˇzimu metamaterijala gde veliˇcina jedini ˇcne ´celije nije zanemarljiva u odnosu na talasnu duˇzinu svetlosti, ali se efektivni parametri ipak mogu definisati. I jednodimenzionalne i dvodimenzionalne strukture su homogenizovane pomo´cu Maksvel Garnetove teorije. Planarni plazmonski kristali nisu opisani efektivnim parametrima, nego se razmatraju kao nizovi istih i podtalasnih rezonatora sa definisanim plazmonskim rezonancijama tako da rezonantne karakteristike plazmonskih kristala predstavljaju kolektivni odziv svih rezonatora. Posebna paˇznja je posve´cena izboru odgovaraju´cih materijala u kompozitima. Strukture namenjene vodenju elektromagnetskog polja treba da imaju ˇsto manje gubitke tako da u ovom sluˇcaju strukture treba da budu iskljuˇcivo dielektriˇcne. Plazmonski materijali kao ˇsto su metali i poluprovodnici se moraju koristiti u slede´cim sluˇcajevima: u realizaciji visoke anizotropije dielektriˇcne permitivnosti i u realizaciji rezonantnih struktura. Prvi metod koji je istraˇzivan za vodenje elektromagnetskog polja je transformaciona optika. U ovom metodu, prave linije polja u slobodnom prostoru se na odgovaraju´ci naˇcin transformiˇsu u linije polja sa ˇzeljenim oblikom. Maksvelove jednaˇcine su invarijantne prilikom koordinatnih transformacija dok se materijalni parametri menjaju u skladu sa primenjenom transformacijom. Dobijeni materijalni parametri su opisani anizotropnom i prostorno nehomogenom dielektriˇcnom permitivno ˇs´cu i magnetskom peremabilnoˇs´cu u opˇstem sluˇcaju. Ovde je data procedura kojom se nalaze jednostavniji materijalni parametri pomo´cu koncepta redukovanih parametara pri ˇcemu se zadrˇzava ista disperzija ili pomo´cu koncepta transformacija sa jediniˇcnim Jakobijanom. Kao rezultat primenjenih procedura, pokazuje se da je mogu´ce realizovati uredaje na bazi transformacione optike pomo´cu anizotropne i prostorno nehomogene dielektriˇcne permitivnosti. Anizotropija je onda realizovana slojevima ploˇca, dok se nehomogenost moˇze realizovati odgovaraju´com gradacijom debljine ili permitivnosti ploˇca.parametri menjaju u skladu sa primenjenom transformacijom. Dobijeni materijalni parametri su opisani anizotropnom i prostorno nehomogenom dielektriˇcnom permitivno ˇs´cu i magnetskom peremabilnoˇs´cu u opˇstem sluˇcaju. Ovde je data procedura kojom se nalaze jednostavniji materijalni parametri pomo´cu koncepta redukovanih parametara pri ˇcemu se zadrˇzava ista disperzija ili pomo´cu koncepta transformacija sa jediniˇcnim Jakobijanom. Kao rezultat primenjenih procedura, pokazuje se da je mogu´ce realizovati uredaje na bazi transformacione optike pomo´cu anizotropne i prostorno nehomogene dielektriˇcne permitivnosti. Anizotropija je onda realizovana slojevima ploˇca, dok se nehomogenost moˇze realizovati odgovaraju´com gradacijom debljine ili permitivnosti ploˇca.parametri menjaju u skladu sa primenjenom transformacijom. Dobijeni materijalni parametri su opisani anizotropnom i prostorno nehomogenom dielektriˇcnom permitivno ˇs´cu i magnetskom peremabilnoˇs´cu u opˇstem sluˇcaju. Ovde je data procedura kojom se nalaze jednostavniji materijalni parametri pomo´cu koncepta redukovanih parametara pri ˇcemu se zadrˇzava ista disperzija ili pomo´cu koncepta transformacija sa jediniˇcnim Jakobijanom. Kao rezultat primenjenih procedura, pokazuje se da je mogu´ce realizovati uredaje na bazi transformacione optike pomo´cu anizotrparametri menjaju u skladu sa primenjenom transformacijom. Dobijeni materijalni parametri su opisani anizotropnom i prostorno nehomogenom dielektriˇcnom permitivnoˇs´cu i magnetskom peremabilnoˇs´cu u opˇstem sluˇcaju...In this thesis we investigate electromagnetic composite materials in order to realize media with the electromagnetic properties not achievable in the nature. The investigated composites are one dimensional and two dimensional photonic and plasmonic crystals. One dimensional structures consist of appropriately shaped slabs, whereas two dimensional structures consist of rods in air or cylindrical holes in a dielectric host. Beside the structures with the periodic arrangement of the unit cells, we consider graded structures obtained by a spatial variation of either cells’ geometry or dielectric permittivity. Photonic crystals are all dielectric structures whereas the plasmonic crystals are combination of dielectric and plasmonic materials, metals or semiconductors. Special class of the composite structures are the planar plasmonic crystals which consist of parallel ribbons made from plasmonic material on a dielectric substrate. All composites are considered in the metamaterial regime where unit cell size of the composites are not negligible in comparison to light wavelength, but the effective parameters can be still well defined. Homogenization of both one and two dimensional structures are done within the framework of Maxwell Garnett theory. Planar plasmonic crystals are not described by effective parameters, but they are considered as arrays of the same and subwavelength resonators with well defined plasmonic resonances so the resonant behaviour of the plasmonic crystals is the collective response of all resonators. Special attention is devoted to the choice of appropriate materials in the composites. The structures aimed for guiding of electromagnetic field should have as low as possible losses so the structures built form dielectrics only are the most preferably in this case. The plasmonic materials such as metals or semiconductors have to be used in the following cases: in the realization of extreme anisotropy in the dielectric permittivity and in the realization of resonant structures. The first method investigated for guiding of electromagnetic field is transformation optics. In this method, straight field trajectories in free space are appropriately transformed into the desired field trajectories. Maxwell equations are invariant under the applied coordinate transformations while the material parameters are scaled accordingly. The obtained material parameters are described with anisotropic and spatially inhomogeneous dielectric permittivity and magnetic permeability in a general case..

Coordinate transformation based design of confined metamaterial structures

The coordinate transformation method is applied to bounded domains to design metamaterial devices for steering spatially confined electromagnetic fields. Both waveguide and free-space beam applications are considered as these are analogous within the present approach. In particular, we describe devices that bend the propagation direction and squeeze confined electromagnetic fields. Two approaches in non-magnetic realization of these structures are examined. The first is based on using a reduced set of material parameters, and the second on finding non-magnetic transformation media. It is shown that transverse-magnetic fields can be bent or squeezed to an arbitrary extent and without reflection using only dielectric structures.Comment: The previous version has been revised and considerably expande

Comparative studies on osmosis based encapsulation of sodium diclofenac in porcine and outdated human erythrocyte ghosts

The objective of our study was to develop controlled drug delivery system based on erythrocyte ghosts for amphiphilic compound sodium diclofenac considering the differences between erythrocytes derived from two readily available materials - porcine slaughterhouse and outdated transfusion human blood. Starting erythrocytes, empty erythrocyte ghosts and diclofenac loaded ghosts were compared in terms of the encapsulation efficiency, drug releasing profiles, size distribution, surface charge, conductivity, surface roughness and morphology. The encapsulation of sodium diclofenac was performed by an osmosis based process - gradual hemolysis. During this process sodium diclofenac exerted mild and delayed antihemolytic effect and increased potassium efflux in porcine but not in outdated human erythrocytes. FTIR spectra revealed lack of any membrane lipid disorder and chemical reaction with sodium diclofenac in encapsulated ghosts. Outdated human erythrocyte ghosts with detected nanoscale damages and reduced ability to shrink had encapsulation efficiency of only 8%. On the other hand, porcine erythrocyte ghosts had encapsulation efficiency of 37% and relatively slow drug release rate. More preserved structure and functional properties of porcine erythrocytes related to their superior encapsulation and release performances, define them as more appropriate for the usage in sodium diclofenac encapsulation process

Low-friction, wear-resistant, and electrically homogeneous multilayer graphene grown by chemical vapor deposition on molybdenum

Chemical vapour deposition (CVD) is a promising method for producing large-scale graphene (Gr). Nevertheless, microscopic inhomogeneity of Gr grown on traditional metal substrates such as copper or nickel results in a spatial variation of Gr properties due to long wrinkles formed when the metal substrate shrinks during the cooling part of the production cycle. Recently, molybdenum (Mo) has emerged as an alternative substrate for CVD growth of Gr, mainly due to a better matching of the thermal expansion coefficient of the substrate and Gr. We investigate the quality of multilayer Gr grown on Mo and the relation between Gr morphology and nanoscale mechanical and electrical properties, and spatial homogeneity of these parameters. With atomic force microscopy (AFM) based scratching, Kelvin probe force microscopy, and conductive AFM, we measure friction and wear, surface potential, and local conductivity, respectively. We find that Gr grown on Mo is free of large wrinkles that are common with growth on other metals, although it contains a dense network of small wrinkles. We demonstrate that as a result of this unique and favorable morphology, the Gr studied here has low friction, high wear resistance, and excellent homogeneity of electrical surface potential and conductivity.This is peer-reviewed version of the artcle: B. Vasić, U. Ralević, K.C. Zobenica, M.M. Smiljanić, R. Gajić, M. Spasenović, S. Vollebregt, Low-friction, wear-resistant, and electrically homogeneous multilayer graphene grown by chemical vapor deposition on molybdenum, Appl. Surf. Sci. (2019) 144792. [https://doi.org/10.1016/j.apsusc.2019.144792]Published version: [http://cer.ihtm.bg.ac.rs/handle/123456789/3347

Nanoscale electrical and mechanical control of resistive switching in iridates and manganites

Resistive switching (RS) is an electrically induced change of the resistance of various thin metal-oxide films [1]. Research on RS is mainly motivated by possible applications in new data storage devices. In addition, RS can be induced by strain engineering [2] which does not depend on film thickness, while biasing is not needed. In this talk the main focus will be on the nanoscale RS induced and characterized by atomic force microscopy (AFM) based methods. In the first part, the relation between the electrically induced RS in semimetallic SrIrO3 thin films and metal-insulator transition (MIT) triggered by film thickness reduction will be discussed [3]. It is shown that thin films are insulating and characterized by hysteretic I-V curves. The threshold voltage indicating the transition from high- (HRS) to low-resistance state (LRS) is well defined due to a band gap opening as a result of MIT. On the other hand, thicker films are semimetallic, while the transition from HRS to LRS is characterized with a smooth increase of the current without a threshold voltage. In the second part, mechanically induced switching of surface electrical properties of La0.67Sr0.33MnO3 (LSMO) thin films covered by magnetic nanoparticles is discussed [4]. The local pressure applied by AFM tip leads to a drop of the electrical conductivity, finally inducing an electrically insulating state for high enough normal load as shown in Fig. 1. Subsequent electrical characterization suggests that the RS is mainly governed by the flexoelectric field induced at the sample surface

Sub-micrometer parallel surface structures induced by femtosecond laser beam in forensics

Један од ефеката интеракције ултра-кратког ласерског снопа са материјалима је формирање паралелних структура на површини (laser-induced parallel surface structures - LIPSS), чији је период мањи од таласне дужине снопа. Уколико се ради о вишеслојним танким филмовима метала, квалитет формираних структура је бољи. Узорак од пет двослојних танких филмова Al и Ti на супстрату Si смо изложили фемтосекундном снопу и запазили формирање две врсте структура које се разликују по облику. Обе су врсте вероватно узроковане појавом површинског плазмонаполаритона на површини најгорњег слоја. Појава плазмона поларитона на површини танких металних филмова и наночестица може да ограничи простирање електромагнетног поља и да појача флуоресцентни сигнал из молекула хемикалије на површини. У зависности од структуре интерфејса за одређивање циљне хемикалије на металној површини флуоресценција побољшана плазмоном (plasmon-enhanced fluorescence, PEF) је привлачан метод за скраћење времена и појачање осетљивости разних аналитичких технологија које се користе у форензици.One of the effects of the interaction of ultrashort laser beam with materials is the forming of laser-induced parallel surface structures (LIPSS), with period less than beam wavelength. For multilayer thin metal films, the quality of formed structures is better. The sample of five bilayers of Al and Ti on Si substrate was exposed to femtosecond beam and noticed the forming of of two types of structures different in shape. Both are most probably the product of surface Plasmon polariton on the surface of most top layer. The occurrence of Plasmon polariton on the surface of thin metal layers and nanoparticles can confine the propagation of electromagnetic field and to amplify the fluorescent signal from molecules of the chemical compound on the surface. Depending on the interface structure for determining the target chemical on metal surface, Plasmon enhanced fluorescence is an attractive method for shortening the time of detection and increasing the sensitivity of various analytical technologies used in forensics

Beam Steering Efficiency in Resonant Reflective Metasurfaces

Beam steering is one of the prevailing functions performed by electromagnetic metasurfaces. Its efficiency depends on a large number of physical parameters associated with resonant elements comprising the metasurface and is thus notoriously difficult to optimize. Here we formulate a theoretical model for evaluating the diffraction efficiency of an array of lossy resonant elements whose spectral response is dominated by the coupling between a leaky eigenmode and a single incoming/outgoing channel. We use it to deduce a formula for the maximum attainable diffraction efficiency and the gradient parameter profile for which it is achieved. The optimization procedure is demonstrated on the example of an electrically tunable liquid-crystal terahertz beam steering metasurface. Finally, the proposed model is benchmarked against rigorous metasurface simulations. © 1995-2012 IEEE

Resistive Switching of SrIrO3 thin films in the vicinity of a Metal Insulator Transition

The relation between Metal Insulator Transitions (MIT) and Resistive Switching (RS) is important from the fundamental point of view, but also highly relevant because of the possible applications of RS based devices in non-volatile memories [1]. We studied RS of 5d SrIrO3 thin films in the vicinity of a MIT triggered by the reduction of thickness [2]. RS was studied for two characteristic cases: 1. in a thick film which behaves like a semimetal, and 2. in a very thin film which has undergone the MIT and is in an insulating state (see Figure 1). Local electrical properties were measured by means of Conductive Atomic Force Microscopy (C-AFM). In the case of very thin and initially insulating films, I/V curves presented an abrupt increase of the current intensity only for high enough sample voltage indicating a sharp transition into low resistance state (LRS). On the other hand, in the case of initially semimetallic films, this transition was less pronounced without clear threshold voltage for the switching into LRS (see Figure 2). As a result, such different behavior indicates that the MIT has indeed a high impact on the RS. Possible mechanisms of RS in both samples involving oxygen vacancies will be discuss

Resistive switching in Strontium iridate based thin films

We report on the local electrical properties, measured by conductive atomic force microscopy, of the Iridate-based Srn+1IrnO3n+1 family of thin films, in particular by comparing the n = 1, Sr2IrO4, and the n = ∞, SrIrO3, phases. We analyze the different resistive switching behavior as a function of the pristine electronic properties of the films. We will show that, for films exhibiting insulating behavior, i.e., films of the n = 1 phase or films below 3 nm of thickness for the n = ∞ phase, hysteretic I–V curves with a sharp transition into a low resistance state (LRS), i.e. an abrupt increase of the current intensity, is detected above a well-defined threshold voltage. This suggests a resistive switching behavior associated to the jump between two resistance states that may be correlated to the activation energy, Δ, obtained by fitting the temperature dependence of the resistivity to a thermal activated Arrhenius law, ρ (T) ~ ρ0exp(−Δ/kBT). On the other hand, thicker samples of the n = ∞ phase exhibit a semimetallic character and I–V curves show progressive changes of the local resistance without a clearly defined threshold voltage. Kelvin Probe Force Microscopy based measurements confirmed that, concomitantly to the resistive switching, an evolution of the electronic states at the surface takes place that may be associated to the migration of oxygen vacancies promoted by the electrical fields under the AFM tip.We acknowledge financial support from the Spanish Ministry of Science, Innovation and Universities through Severo Ochoa Program (SEV-2015-04969), MAT2015-71664-R (HETEROCS) and RTI2018-099960-B-I00 (SPINCURIOX) and funding from the European Union’s Horizon 2020 research and innovation program under the Marie Sklodowska-Curie grant agreement No. 645658 (DAFNEOX Project) and FEDER Program. B.V. and Z.K. acknowledge the support of the Serbian Ministry of Education, Science and Technological Development (Projects No. OI171005 and III45018). A.P., V.F. and Z.K. thank Senzor-INFIZ (Serbia) for the cooperation provided during their respective secondments.Peer reviewe