Chalcogenide Glass-on-Graphene Photonics

Two-dimensional (2-D) materials are of tremendous interest to integrated photonics given their singular optical characteristics spanning light emission, modulation, saturable absorption, and nonlinear optics. To harness their optical properties, these atomically thin materials are usually attached onto prefabricated devices via a transfer process. In this paper, we present a new route for 2-D material integration with planar photonics. Central to this approach is the use of chalcogenide glass, a multifunctional material which can be directly deposited and patterned on a wide variety of 2-D materials and can simultaneously function as the light guiding medium, a gate dielectric, and a passivation layer for 2-D materials. Besides claiming improved fabrication yield and throughput compared to the traditional transfer process, our technique also enables unconventional multilayer device geometries optimally designed for enhancing light-matter interactions in the 2-D layers. Capitalizing on this facile integration method, we demonstrate a series of high-performance glass-on-graphene devices including ultra-broadband on-chip polarizers, energy-efficient thermo-optic switches, as well as graphene-based mid-infrared (mid-IR) waveguide-integrated photodetectors and modulators

Arsenic Trisulfide Inorganic Photoresist for Three-Dimensional Photolithography

The aim of this thesis is to investigate and develop a material that has both a high refractive index and spatially localizable photoluminescence while being processable like a conventional photoresist, so that it can be used with the 3D direct laser writing technique. The result obtained shows that this has been reduced to practice to enable the creation of 3D photonic crystals with full-photonic bandgaps, and the opportunity to incorporate photoluminescent guests at specific locations

The development of micropillars and two-dimensional nanocavities that incorporate an organic semiconductor thin film

Photonic crystals (PC) are periodic optical structures containing low and high refractive index layers that influence the propagation of electromagnetic waves. Photonic cavities can be created by inserting defects into a photonic crystal. Such structures have received significant attention due to their potential of confining light inside volumes (V) smaller than a cubic wavelength of light (λ/n)3 which can be used to enhance light-matter interaction. Cavity quality factor (Q) is useful for many applications that depend on the control of spontaneous emission from an emitter such quantum optical communication and low-threshold lasing. High Q/V values can also result in an enhancement of the radiative rates of an emitter placed on the surface of the cavity by means of the Purcell effect. This thesis concerns the fabrication and study of two types of optical cavity containing an organic-semiconductor material. The cavities explored are; (1) one-dimensional micropillar microcavities based on multilayer films of dielectric and organic materials, and (2) two-dimensional nanocavities defined into a photonic crystal slab. Firstly, light emission from a series of optical micropillar microcavities containing a thin fluorescent, red-emitting conjugated polymer film is investigated. The photoluminescence emission from the cavities is characterized using a Fourier imaging technique and it is shown that emission is quantised into a mode-structure resulting from both vertical and lateral optical confinement within the pillar. We show that optical-confinement effects result in a blue-shift of the fundamental mode as the pillar-diameter is reduced, with a model applied to describe the energy and distribution of the confined optical modes. Secondly, simulation, design, and analysis of two dimensional photonic crystal L3 nanocavities photonic crystal are presented. Nanocavities were then prepared from silicon nitride (SiN) as the cavity medium with the luminescence emitted from an organic material at red wavelengths that was coated on the cavity surface. To improve the quality factor of such structures, hole size, lattice constant and hole shift are systematically varied with their effect as cavity properties determined. Finite Difference Time Domain (FDTD) modelling is used to support the experimental work and predict the optimum design for such photonic crystal nanocavity devices. It is found that by fine-tuning the nearest neighbour air-holes close to the cavity edges, the cavity Q factor can be increased. As a result, we have obtained a single cavity mode having a Q-factor 938 at a wavelength of 652 nm. Here, the cavity Q factor then increases to 1100 at a wavelength of 687 nm as a result of coating a red-emitting conjugated polymer film onto the top surface of the nanocavity. We propose that this layer planarizes the dielectric surface and helps reduce optical losses as a result of scattering

Nanomechanical single-photon routing

The merger between integrated photonics and quantum optics promises new opportunities within photonic quantum technology with the very significant progress on excellent photon-emitter interfaces and advanced optical circuits. A key missing functionality is rapid circuitry reconfigurability that ultimately does not introduce loss or emitter decoherence, and operating at a speed matching the photon generation and quantum memory storage time of the on-chip quantum emitter. This ambitious goal requires entirely new active quantum-photonic devices by extending the traditional approaches to reconfigurability. Here, by merging nano-optomechanics and deterministic photon-emitter interfaces we demonstrate on-chip single-photon routing with low loss, small device footprint, and an intrinsic time response approaching the spin coherence time of solid-state quantum emitters. The device is an essential building block for constructing advanced quantum photonic architectures on-chip, towards, e.g., coherent multi-photon sources, deterministic photon-photon quantum gates, quantum repeater nodes, or scalable quantum networks.Comment: 7 pages, 3 figures, supplementary informatio

Verbesserung der Anwendbarkeit von organischen Leuchtdioden durch integrierte Nanostrukturen

The organic light-emitting diode (OLED) is a promising technology for a variety of applications, such as displays, large-area lighting, integrated sensing, smart packaging, and signage. OLEDs are thin-film devices comprising organic semiconductors, which allow for cost-efficient high-volume manufacturing using solution-based fabrications methods and therefore hold great potential towards disposable and recyclable electronic products. In this thesis, three different approaches to improve the applicability of OLEDs through integrated nanostructures are explored. Nanostructuring the carrier substrate's outside surface provides a way to enhance light extraction as well as customize tactile and visual device perception. Here, a polymer coating containing tetrapodal zinc oxide nanoparticles and color pigments is investigated with respect to surface roughness characteristics and optical properties. Electrical device properties can be altered by integrating nanostructures directly into the OLED semiconductor stack. In this work, periodic nanopatterning of a metal electrode is shown to improve charge injection into the organic semiconductor layer of a single-carrier device through local electric field enhancements. A current increase of up to 300 % is observed, exceeding the planar current injection limit and indicating a local transition to space charge limited operation. Integration of a photonic crystal slab into the waveguide formed by the OLED can also lead to resonant light outcoupling. Here, a fabrication method is presented to create two-dimensional nanogratings with variable grating designs in the commonly used electrode material indium tin oxide. Furthermore, a novel device structure is investigated in which a fluorescent nanopatterned waveguide is placed outside the OLED for directional light emission leading to sharp angle-dependent outcoupling peaks in the emission spectra

Effects of photonic confinement on the emission from CdTe quantum dots

The thesis describes phenomena related to the control of the spontaneous emission from excitons in CdTe/ZnTe quantum dots (QDs). It describes development of ZnTe-based planar and micropillar cavities followed by the demonstration of modification of various aspects of QDs spontaneous emission. In the first step basic optical properties of the microcavities were investigated. The experiments were conducted on structures with a large spectral density of quantum dot emission lines in the range of energies close to the energies of photonic modes. Thus, QDs acted as probes for the photonic characteristics of the structures. We determined energy of microcavity modes together with their Q-factors. We performed mode mapping of micropillar cavities and measured angular distribution of the emission originating from planar microcavity. In further experiments micropillars with single QDs emission lines in the vicinity of the fundamental modes were investigated. The method of tuning the energy difference between an excitonic state and a cavity mode by a variation of the temperature of the sample was used. In the step we measured the intensity of emission related to quantum dot and cavity mode. This experiment shoed, that the emission from the mode is funneled from the emission of spectraly closest QD transition. In the next experiment we investigated time-resolved photoluminescence of the system. We measured the decay time of QDs placed inside micropillars for varied cavity mode - QD detuning. Additionally, we measeured decay time for QDs embedded in standard semiconductor matrix. This demonstrated enhancement of the decay rate of spontaneous emission from the micropillars if the emission is resonant. an Purcell-factor above 5 was demonstrated, in agreement with the model simulations Next topic covered by the thesis is related to the development of the micropillars with an enhanced radial confinement. This project was realized in collaboration with the University of Leipzig, where an additional radial Bragg reflector was deposited on the micropillars. In the obtained structures we observed decrease of spontaneous emission rate of QDs detunde from the cavity mode by factor more than~3. This demonstrates, that the coupling of QD emission into the undesired continuum of radial decay channels has been successfully decreased. Finally, the last part of the thesis describes the development of epitaxial growth of ZnTe-based nanostructures on GaSb substrates. A series of samples with both quantum wells and distributed Bragg reflectors were grown by the molecular beam epitaxy. The photoluminescence and reflectivity of samples was characterized. The crystal quality and lattice constant was measured using High Resolution X-ray diffraction.Praca poświęcona jest poprawie sterowania spontaniczną emisją fotonów z kropek kwantowych wytworzonych z materiałów typu II-VI: z tellurku kadmu (CdTe) osadzonych w tellurku cynku (ZnTe). W tym celu zastosowano mikrownęki optyczne wykorzystujące opracowane niedawno rozproszone zwierciadła Braggowskie o stałej sieci ZnTe. Badania mikrownęk optycznych dla materiałów typu II-VI uzasadniony są istnieniem dojrzałej technologii półprzewodników półmagnetycznych tego typu, świetnymi własnościami optycznymi heterostruktur zawierających (Cd,Mn)Te (takich jak np. kropki kwantowe), oraz dobrą znajomością oddziaływań i stałych materiałowych. Te własności w połączeniu z wlasnosciami mikrownek optycznych pozwalają uzyskać systemy o unikatowych własnościach magneto-optycznych. Bazując na planarnych mikrownękach wytworzono mikrownęki filarowe charakteryzujące się związaniem fotonicznym we wszystkich kierunkach przestrzeni. Własności optyczne mikrownęk filarowych zawierających kropki kwantowe zostały zbadane przy użyciu fotoluminescencji niskotemperaturowej. W pierwszym kroku wyznaczono energie fotonowych modów własnych mikrownęk filarowych oraz dobroć tych rezonatorów. Wykazano również modyfikacje widma emisji omawianych kropek kwantowych. Następnie zbadano szczegółowe własności modów własnych takich mikrownęk. Dokonano mapowania rozkładu przestrzennego emisji mikrownęk filarowych oraz zmierzono rozkład kątowy emisji mikrownęk planarnych w zależności od energii fotonu. Zbadano również aspekty polaryzacyjne emisji obu rodzajów mikrownęk. Stwierdzono, iż mod podstawowy składa się z dwóch niezdegenerowanych energetycznie modów własnych o wzajemnie prostopadłych polaryzacjach. Wyniki pomiarów energii modów własnych dla różnych średnic mikrownęk filarowych porównano z symulacjami wykonanymi przy użyciu rozszerzonej metody macierzy transferu. Uzyskano dobrą zgodność wyników symulacji z wynikami eksperymentalnymi. Czynnik Purcella opisuje przyśpieszenie spontanicznej emisji dla emitera we wnęce optycznej względem emitera w przestrzeni. Metodą macierzy transferu obliczono również efektywne objętości modów, co w połączeniu ze znajomością dobroci rezonatorów pozwoliło wyznaczyć spodziewaną zależność czynnika Purcella od średnicy mikrwonęki filarowej. Eksperymentalnie ustalono, iż największe przyśpieszenie emisji związane z efektem Purcella uzyskuje się dla mikrownęk o średnicy poniżej 2 mikrometrów. W eksperymentach z rozdzielczością czasową wykazano skrócenie czasu życia ekscytonu uwięzionego w kropce kwantowej będącego w rezonansie z modem fotonicznym mikrownęki filarowej o średnicy 1,5 mikrona. Uzyskany współczynnik Purcella o wartości 5,7 jest zgodny z wartością wyznaczoną dzięki symulacjom i pomiarom dobroci rezonatora. W następnej kolejności zbadane zostały mechanizmy relaksacji wzbudzenia eks\-cy\-to\-no\-wego do fotonicznych modów własnych mikrownęki poprzez oddziaływanie z siecią krystaliczną materiału półprzewodnikowego, z którego zrobiona jest kropka kwantowa. Pomiary te są wykonywane dla zmieniajęcej się w sposób kontrolowany temperatury próbki. Daje to możliwość sprzęgania wybranych stanów ekscytonowych z modami fotonicznymi, gdyż energie obu tych zmieniają się w różnym tempie w zależności od temperatury. Zbadno intensywności emisji kropki kwantowej i modu własnego mikrownęki przy zmianie ich dostrojenia energetycznego. Pozwoliło to wykazać, iż emisja modu zasilana jest z najbliższej spektralnie linii kropki kwantowej. Eksperyment ten wykazał również ukierunkowanie emisji kropki kwantowej poprzez sprzężenie jej z modem własnym mikrownęki, który to mod jest emitowany kierunkowo. Dysponując dobrze poznanym systemem mikrownęk filarowych z kropkami kwantowymi CdTe/ZnTe opracowano nowatorskie mikrownęki filaorwe z dodatkowymi radialnymi rozproszonymi zwierciadłami Bragga. Dla takich mikrownęk wykazano, iż tempo rekombinacji promienistej w przypadku emiterów odstrojonych od modów własnych mikrownęki może zostać wydłużone o czynik co najmniej 3. W zakresie badań technologicznych przeprowadzono również optymalizację wzrostu kropek kwantowych CdTe/ZnTe oraz zwierciadeł Bragga o stałej sieci ZnTe w komorze do epitaksji z wiązki molekularnej poprzez użycie nowego rodzaju podłoży z antymonku galu (GaSb). Dzięki lepszemu dopasowaniu stałej sieci krystalicznej w takim podłożu zmniejszła się gęstość defektów w wyhodowanych na nich strukturach. Dzięki wytworzeniu wydajnych mikrownęk fotonicznych opartych na ZnTe badania kropek kwantowych CdTe w ZnTe zyskują nowe narzędzie do badania fizyki procesów w nich zachodzących. Własności materiałów II-VI, takie jak wysoka stabilność temperaturowa emisji i świecenie w widzialnym zakresie widma fal elektromagnetycznych, stawiają je jako dobre źródła pojedynczych fotonów na żądanie. Te ostatnie są kluczowym elementem informatyki i kryptografii kwantowej

Nanofabrication

We face many challenges in the 21st century, such as sustainably meeting the world's growing demand for energy and consumer goods. I believe that new developments in science and technology will help solve many of these problems. Nanofabrication is one of the keys to the development of novel materials, devices and systems. Precise control of nanomaterials, nanostructures, nanodevices and their performances is essential for future innovations in technology. The book "Nanofabrication" provides the latest research developments in nanofabrication of organic and inorganic materials, biomaterials and hybrid materials. I hope that "Nanofabrication" will contribute to creating a brighter future for the next generation

Lasing action in dye-doped thin films coupled with 2D plasmonic nanoarrays

In the last few years, due to the great advances in nanotechnology the peculiar properties of the matter at the nanometric scale have been widely investigated. These properties can be exploited for many innovative applications involving several fields, and, in particular, in nanophotonics, where plasmonic nanolasers gather growing interest. These devices are coherent light sources that can support ultrafast dynamics and ultrasmall mode volume below the diffraction limit. Nowadays, the photonic band-edge lasers that are widely used for many applications have various drawbacks, such as low modulation speeds and diffraction-limited mode confinement. Plasmonic nanolasers can potentially overcome these limits and replace the actual light source technology in many fields from integrated photonic circuits and optical communications to high-performance biosensors. The purpose of the present Master thesis is the synthesis and characterisation of a novel plasmonic-based nanolaser device operating in the near infrared-region. In particular, the attention has been focused on plasmonic nanostructures composed of an array of 2D nanoparticles that act as field enhancer for the lasing of the gain medium. The fabrication of the plasmonic nanoarray was substantially different from the usual approach based on electron beam lithography (EBL). On the contrary, the NanoSphere Lithography (NSL) technique adopted in the present thesis is a highthroughput and cost-effective way to manufacture nanoparticle arrays with a highquality order, obtaining defectless domains of several hundreds of square micrometers. The nanostructure adopted in a this work is two-dimensional hexagonal lattice of nanodomes which is fabricated by gold deposition (carried out by magnetron sputtering) over an ordered array of polystyrene (PS) nanospheres (NSs) obtained using NSL. A gain medium layer was then deposited over the metallic array, and it consists of an organic dye, specifically Styryl 9M (LDS 821), embedded in a polymeric matrix. In order to maximise the efficiency and the throughput of the nanolaser, a match between the uorescence emission of the selected dye and the plasmonic resonance of the nanostructure is needed. To this aim, the domes geometry has been optimised by varying metal thickness and the PS nanosphere radius (while keeping the array lattice parameter) by reactive ion etching (RIE). The deposition process for the gain medium has been achieved by embedding the dye molecules in a PMMA matrix, which is then deposited upon the nanodome array to form a solid film of a hundred of micrometers. The nanostructures have been characterised morphologically by atomic force microscopy (AFM) and scanning electron microscopy (SEM) techniques and optically by re ection measurements. The absorption and uorescence spectra that characterise the dye were measured by a UV-VIS-NIR spectrophotometry. As a result, samples supporting lasing action were fabricated and characterised: the emission features of the obtained device were investigated by photoluminescence (PL) measurements to determine the main properties of the laser, including the lasing wavelength, linewidth, threshold, beam divergence and emission angle, showing how, when a coupling between the plasmonic resonance of the nanodome array and the dye emission wavelength is obtained, interesting lasing properties arise and the lasing threshold can be decreased by at least one order of magnitude