Theses supervised by Prof. Dr. Hilmi Volkan Demir
26 theses · İhsan Doğramacı Bilkent University
Atomik olarak düz karmaşık nanokristal hetero yapıların koloidal sentetik yolları
Colloidal semiconductor nanocrystals (NCs) constitute one of the most important branches of nanoscience, with an increasingly high research interest, culminating with a Nobel Prize most recently. The nanometric size of these NCs allows for size-dependent optical properties, which provides an extra tool besides the composition to fine-tune these properties. Recent advancements in NC synthesis have been enabling important developments in the design and engineering of different shapes, compositions, and heterostructures of NCs. Accompanied by a deeper physical understanding and more sophisticated fabrication techniques, the NCs are now being integrated into many of the optoelectronic devices and are of prime importance for the next-generation optoelectronics. Despite all the progress, however, the full potential and synthesis dynamics of the NCs still need further investigation. Here, we addressed specifically four key aspects of the semiconductor NCs: shape engineering, electronic heterostructures, doping, and surface modification. In this thesis research, the synthesis dynamics, especially nucleation, growth and diffusion, were investigated in depth for different synthetic routes and conditions, and some of the important challenges were resolved. With the scarce number of proper emitters at longer wavelengths, in this thesis, a complex and thick heterostructure based on group II-VI nanoplatelets (NPLs) with relaxed quantum confinement was developed. The multi-shell design of the proposed NPLs helps overcome the unfavorable growth in the thickness direction, which, together with the cation dissolution/recrystallization and cation reorganization at high temperatures, relaxes the strain between the domains. The final NPLs, emitting in the deep-red region close to the bulk bandgap of CdSe, were used as an active layer in a light-emitting diode (LED) device and exhibited an exceptionally high external quantum efficiency (EQE) of 6.8% at electroluminescence peak wavelength of 701 nm, one of the best reported for colloids in this spectral range in the literature. Additionally, a novel heterostructure of multi-crown NPLs was designed and demonstrated, where several direct and indirect recombination pathways give rise to photoluminescence with both type-I and type-II characteristics. The design of these NPLs, especially the size of the domains, was shown to significantly impact the final optical properties that can activate/deactivate the recombination channels alongside the temperature. These multi-crown type-II NPLs exhibit an extremely high two-photon absorption cross-section with the highest value of 12.9 × 106 GM and low dark-bright exciton splitting energy critical for optoelectronic applications, including photodetectors, bioimaging and quantum devices. Next, we showed silver doping dynamics of core/shell NPLs, which previously proved challenging due to the self-purification after the shell growth. Here, the composition of the shell was shown to be an important factor in the destruction mechanism of the NPLs in the irreversible doping regime at high doping temperatures. The Ag:CdSe/CdZnS core/shell NPLs exhibit only dopant emission with superior paramagnetic properties compared to CdS-shelled NPLs thanks to better lattice preservation and higher dopant content. At last, a surface modification method was suggested and demonstrated for group I-III-VI NCs to enhance their electronic properties. Replacing the long-chain organic ligands with a S2- layer, injection of a negative charge and passivation of donor sites changed the behavior of the field-effect transistors (FETs) based on these NCs from p-type to n-type with more than a 105-fold enhancement in the carrier mobility. This method allowed fine-tuning of the optical properties of the NCs by the diffusion of the cations and shell formation. The findings of this thesis shine light on some of the important challenges in the field of semiconductor NCs while drawing a guideline for future research on the synthetic routes and optoelectronic properties. The thesis paves the way for future device integration of the developed NCs to fully realize their potential, while the demonstration of the more elaborated properties, including nonlinear absorption, paramagnetism and dark-bright exciton splitting, encourages further fundamental studies focusing on the physics of the semiconductor NCs.
Yarıiletken nanokristallerin koloidal fotoniği: Polarize renk dönüşümünden verimli güneş ışığı yoğunlaştırılmasına
Effective photon management is pivotal to the success of future photonic applications. The demand for high-performance electronic displays and solar light harvesters has been increasingly growing, ever with high expectations in advancing their power efficiencies. Semiconductor nanocrystals are highly promising for use in such advanced photonic applications. However, conventional device architectures and fabrication methods cannot fully exploit their potential. To address the need for their effective utilization, in this thesis, we proposed and demonstrated novel photon managing methods for colloidal nanocrystals to target polarized color conversion and efficient solar concentration. Nanocrystals possess an unmatched color purity for next-generation displays but color enrichment in displays suffers from the inherent random polarization in their photoluminescence. Instead of clipping the undesired polarization, we show a new class of v-shaped backlight unit (v-BLU) creating Fano resonances to enforce isotropic quantum emitters of the integrated color-conversion nanocrystals to emit polarized light. While enabling a front-panel configuration, the proposed v-BLU of nanocrystals allows for a strong modification of the density of optical states via resonance coupling. This control over the density of states for isotropic quantum dots empowers the realization of high polarization contrast ratios while sustaining their optical transmission. Similar to color conversion, colloidal nanocrystals are also instrumental to light harvesting, in particular using atomically flat nanocrystals with their step-like absorption profile making them potentially ideal candidates for luminescent solar concentrators (LSCs). Nevertheless, practically zero Stokes shift in their photoluminescence fundamentally limits their utilization. Here we overcame this limitation by proposing the doping of such colloidal quantum wells inducing a large Stokes shift with near-unity photoluminescence quantum efficiency. We developed and demonstrated high-performance LSC panels of the copper-doped quantum wells outperforming the LSCs of their undoped counterparts and doped quantum dots. The LSCs of such Cu-doped quantum wells offer record optical flux gain compared to other colloids. We believe that the findings presented in this thesis will advance the applications of colloidal nanocrystals boosting the performance of their next-generation photonic devices to unprecedented levels.
Koloidal kuantum kuyularının sentezi ve karakterizasyonu: Basit boyutları ayarlanabilir çekirdekliden karmaşık çoklu taçlı yapılara
As a new class of semiconductor nanocrystals, colloidal quantum wells (CQWs), also commonly known as nanoplatelets (NPLs), exhibit remarkable electronic and optical properties that will potentially find a wide range of use from nanophotonics to optoelectronics. NPLs feature step-like absorption profiles and discrete emission spectra with giant oscillator strength resulting in high recombination rates. All these features make these atomically-flat structures highly attractive for light-harvesting and -generating applications. In this thesis, to understand the size-tuned properties of their two-dimensional architecture, we conducted a systematic study on the core-only NPLs by using a set of 4 monolayer (ML) CdSe cores as our working model and carefully altered their aspect ratio while keeping their lateral area constant. In such a core-only NPL structure, electron and hole are both confined in the core resulting in type-I electronic band alignment. By decreasing the width of these NPLs to a value comparable to or less than their exciton Bohr radius, we observe additional confinement effects emerge. Subsequently, by growing CdSe1−xT ex alloyed crown around these starting 4 ML CdSe cores, we find type-II electronic band alignment is obtained. Thanks to their spatially indirect excitons, these core crown NPLs show extraordinarily long radiative lifetimes. Moreover, with the increased absorption cross-section owing to their added crown, high-performance optical gain is achieved via their core/crown heterostructure. However, in this form, their usage is limited since they are unstable in solution forming gels and they exhibit strong tendency to form stacks in films. To address this problem, here we proposed and developed a multi-crown architecture by additionally growing a CdS crown around the periphery of the typeII heterostructure, enabling excellent optical gain media with enhanced stability. The structural and optical characterizations of the synthesized multi-crown NPLs indicate that this complex architecture holds great promise for making devices in colloidal nanophotonics and optoelectronics.
Gümüş-katkılı cdse nanolevhaların kısmi katyon değişimi metodu ile kolloidal sentezi
Colloidal nanoplatelets (NPLs) exhibit strong one-dimensional quantum confinement in the vertical direction. This makes them a highly attractive host system for studying variable doping techniques and effects without variation in the quantum confinement effect. Earlier, core-only CdSe NPLs were converted into Cu2Se and HgSe NPLs, and also CdSe/CdS core/shell NPLs were transformed into Cu2Se/Cu2S, ZnSe/ZnS, and PbSe/PbS NPLs by using full cation exchange (CE) methods. Recently, core-only CdSe NPLs have been doped with Cu(I) ions using high-temperature nucleation doping and post-synthesis partial CE approaches. On the other hand, unlike Cu(I), such monovalent doping with Ag(I) ions has previously not been possible in NPLs as a host system, although silver doping had been widely studied in other host systems. Therefore, there has been no previous report on the doping of Ag(I) into CdSe NPLs to date. To address this gap, in this thesis, Ag(I) doping in CdSe NPLs by using a postsynthesis partial CE technique was developed. A systematic study was carried out to investigate the effects of dopant precursor reactivities, reaction timing, and temperature on the evolution of dopant-related emission as compared to the excitonic emission. In controlled experiments, the excitonic emission peak was eliminated and only dopant-related emission peak was successfully obtained. Finally, temperature-dependent emission kinetics of the as-synthesized Ag(I)-doped CdSe NPLs at varied temperatures ranging from 25 to 298 K were investigated. It was observed that both excitonic and dopant-related emission peaks were blue-shifted and their intensities were considerably increased with the decreasing temperature. As a new dopant-host system, these Ag(I)-doped CdSe NPLs hold a great promise for further systematic spectroscopic studies and possibly various optoelectronic applications.
Optik çınlaçlar içinde yakinen tümleştirilmiş koloidal yarıiletken kuantum kuyularının optik kazancı ve lazer eylemi
Colloidal semiconductor quantum wells, also known as nanoplatelets (NPLs), attract an increasingly greater deal of interest as a promising material platform for light-generating applications. The superior optical properties of NPLs including their ultra-large absorption cross-sections, purely homogeneous broadening, and suppressed Auger recombination make them highly attractive for solution-processable color convertors, LEDs and lasers. In this thesis, we studied the optical gain properties and performance levels of tailored heterostructures of such NPLs intimately integrated into various optical cavities. To do so, we systematically measured their amplified spontaneous emission under one- and two-photon absorption excitations. Also, with these hetero-NPLs as the gain media, we have proposed and demonstrated a new class of practical whispering gallery mode (WGM) NPL-fiber architecture with high stability and low lasing thresholds enabled by record low waveguide loss coefficients in its class. Moreover, we have developed a single-mode vertical-cavity surface-emitting laser (VCSEL) of these hetero-NPLs closely integrated into the wedge cavity of a pair of distributed Bragg reflectors, leading to a record low lasing threshold in its class. The findings obtained in these WGM NPL-laser and NPL-VCSEL structures indicate that these NPLs are excellent for high-performance colloidal lasing.
Koloidal atomik katman kaplama ve sıcak enjeksiyon kabuk kaplama yöntemlerinin birleşimiyle geliştirilen yarı iletken nanolevha heteroyapıları
One of the most promising families of semiconductor nanocrystals in colloidal optoelectronics and nanophotonics is considered to be colloidal quantum wells, also commonly referred to as nanoplatelets (NPLs). Possessing an atomically flat structure, NPLs feature unique properties including spectrally-resolved and tunable light-hole- and heavy-hole transitions accompanied by their respective giant oscillator strengths. CdSe, CdS and CdTe, making the first colloidal NPLs synthesized in core-only structure, portray distinct qualities necessary for light-harvesting and -generating applications. However, going beyond the core structure, there are many properties that are highly enhanced by growing crown and/or shell layers around core NPLs. While the crown growth takes place anisotropically in lateral directions, the shell layer covers the entire NPL surface, combinations of which enable NPL heterostructures in new architectures. Depending on the electronic alignment of parts of the NPL heterostructure and the resulting confinement of electron-hole wave functions, these hetero-NPLs can be type-I or type-II. In type-I electron-hole pairs are confined in the core-NPL and recombination occurs in a direct pathway. In type-II electron-hole wave function is separated into different semiconductor layers, resulting in spatially indirect recombination. In this thesis, we synthesized and showed thin- and thick-shell grown heterostructures of type-I CdSe/ZnS NPLs using hot-injection (HI) for the first time particularly for these semiconductor NPLs. Unlike the typical colloidal atomic layer deposition (c-ALD) technique, which produces NPL heterostructures with low quantum yield (QY) and low chemical and optical stability, our approach yields CdSe/ZnS NPLs of almost unity (100%) quantum yield (QY) and improved chemical stability, tested by washing the same samples rigorously up to 6 times with ethanol with little change observed in the QY. Additionally, unparalleled thermal and optical aging endurances is achieved in aging tests. These tests experimentally demonstrated that, elevated to 400 K, HI thick-shelled NPLs can retain up to 65% of their emission intensity in the colloidal form and 52% of that in the film. This level of high stability creates a great opportunity for employing these NPLs for high-temperature applications. Also, in the thesis, we synthesized and studied CdS/CdSe core/crown, CdS/CdZnS core/c-ALD shell-grown and CdS/CdSe/CdZnS core/crown/c-ALD shell-grown heterostructures of NPLs. Here the starting-template CdS NPLs are considered to be unique in terms of their emission in the blue region, which may open up new opportunities for NPL lasing in this spectral region. Nominally CdS NPLs are folded due to great lateral sizes. However, in this research work, when coated with crown and shell layer, these particles unfold. The unrolled CdS/CdSe core/crown NPLs are found to exhibit relatively higher QY up to 15-20% in its class of CdS core-seeded NPLs. The findings of this thesis reveal that such heterostructures of the NPLs are very rich in terms of variety of the quantum architectures one can achieve using them as working model systems.
Özdizili kuantum kuyusu üstyapılarının koloidal optoelektroniği
Advances in the colloidal nanocrystal synthesis enabled creation of quasi two-dimensional colloidal quantum wells (CQWs) in the last decade. These CQWs possess similar properties to those of epitaxially grown quantum wells while at the same time offering the benefits of low-cost synthesis and solubility in various solvents. Their atomically precise thickness and one-dimensional quantum confinement grant them favorable properties such as narrow emission linewidth, reduced inhomogeneous broadening and giant oscillator strength. In addition, due to their quasi two-dimensional shape, they display intrinsic anisotropy. Because of this anisotropy, the particle interactions in closely packed films depend greatly on the orientation of these CQWs. To fully utilize the interaction of CQWs with each other or with other particles in their proximity, we develop a self-assembly technique, which is used to deposit highly uniform thin CQW films onto various solid substrates. This self-assembly technique allows us to deposit CQWs as a continuous monolayer while at the same time controlling their orientation throughout the substrate, thereby modifying their packing factor as well as near-field dipole-dipole interactions. This self-assembly technique is also employed to create large-are CQW films of any desired thickness, simply by applying the same deposition technique on the same substrate as many times as desired. We use these self-assembled CQW films to study the two main aspects of nanocrystal optoelectronics, namely, Förster resonance energy transfer (FRET) and optical gain, with CQWs. By using the orientation-controlled CQW monolayers, we show that the rate of FRET from colloidal quantum dots (QDs) to a monolayer of CQWs can be tuned via dipole-dipole interactions between QDs and CQWs. We use Förster's theory of nonradiative energy transfer while taking into account the anisotropy of the excitonic CQW excitonic state as well as its delocalization throughout the CQW to account for our results. Next, we show that our multilayered CQW films display optical gain in uncharacteristically low thicknesses (as small as 40 nm) due to the tight packing and extremely uniform deposition of the CQWs. We furthermore study systematically the observed threshold of amplified spontaneous emission (ASE) in these CQW multilayers as a function of the film thickness (i.e. the number of monolayers), and demonstrate that the gain threshold drops with increasing thickness, accompanied by the red-shift of the ASE peak. These trends can be explained by the varying degree of optical mode confinement, which is a function of both the film thickness as well as the wavelength of propagating mode. Our self-assembly technique allows to study and make use of the favorable properties of the CQWs including anisotropy and enhanced optical gain. Since this technique enables us to produce large-area films displaying excellent homogeneity, it can be a benchmark building block for creating device-scale 2- or 3-dimensional superstructures from CQWs as well as from other types of colloidal nanocrystals to be utilized in both in- and out-of-plane optical applications.
Yakın-alan komşu-bağlaşımlı hücresiz metayüzey doku ve uygulamaları
Metasurfaces are subwavelength-thick artificial structures with engineered responses, designed to provide functionalities that do not exist in the natural domain. Their application areas are broad and vary in both functionality and operation regime. Across all functionalities and regimes, the fundamental purpose behind the metasurfaces is to manipulate the surrounding electromagnetic landscape to form devices with superior sensitivity and efficiency. With conventional design routines and available high-index materials, this was achieved across longer wavelengths in the past decade. However, the lack of suitable materials in the higher frequencies limit the design space for the mainstream approaches that discretize the phase surface with the help of independent nanostructures, dubbed as "meta-cells" or alternatively "meta-atoms". With increasing frequencies, the discrepancy between a smoothly-changing effective index surface and a discretized step-index surface increase, resulting in unwanted scattering. Additionally, the methodology behind the uncoupled scatterers breaks up as the meta-atoms act collectively in sufficiently small scales, resulting in topology-induced errors in the generated phase response. In this thesis, a new class of highly efficient metasurfaces relying on the near-field coupling of identical scatterers in a continuous fabric is proposed. Contrary to the conventional approach, which sees the inter-cell coupling as phase distortions, our proposed methodology utilizes near-field coupling between the nearest neighbors, enabling lattice generation schemes applicable at broad scales that are insusceptible to topological errors. Owing to these, this methodology offers opportunities in further miniaturization of optical consumer products. One of the functionalities high in demand from metasurfaces is efficient and achromatic focusing with compact devices in the visible range, core to contact lenses and smartphone cameras. However, the examples in the literature are not sufficient in terms of either broadband performance or efficiency. Our proposed phase acquisition scheme effectively eliminates inhomogeneous scattering while reducing the design procedure to the tiling of the phase surface, subject to a function of the nearest-neighbor distances. Here, with this methodology, one cylindrical and one circular achromatic metasurface lenses (metalenses) with near-diffraction-limit focusing operating across the whole visible spectrum are demonstrated as a proof of concept. The validity of the utilized approach is confirmed via both waveguide solutions and full electromagnetic computations. Both structures proved to be highly efficient, with the cylindrical one having superior efficiency in its preferred polarization, whereas the circular one is highly efficient while operating independent of polarization. These findings prove the applicability of our near-field inter-coupled cell-less metasurface fabrics as a compact and efficient optical device generation framework.
Kolloidal yarıiletken kuantum kuyuları ışıma kinetiklerinin iyi kontrol edilebilen değişikliği
Colloidal quantum wells (CQWs) belong to an important quasi-2-dimensional sub-family of semiconductor nanocrystals. Thanks to their uniquely tight quantum confinement of only few monolayers extending across their vertical thickness, CQWs possess giant oscillator strength, substantially increasing their absorption cross-section along with their large lateral size expanded over tens to hundreds of nm's on one side. These together make CQWs excellent candidates for light-harvesting applications. In this thesis, to utilize CQWs' superior light-harvesting capability, we investigated the alteration and control of photoluminescence decay lifetimes of the CQWs in a variety of hybrid absorbing systems. In particular, we proposed and demonstrated the nonradiative energy transfer from strongly-absorbing CQWs to indirect-bandgap bulk semiconductors as weak absorbers, e.g., bulk silicon. To this end, we systematically studied and showed the well-controlled modification of the emission kinetics of these CQWs that are self-assembled into a single-layer all-face-down oriented ensemble in the vicinity of silicon with a fine-tuned dielectric separator (of thickness d). We found the Förster resonance energy transfer (FRET) to be the chief underlying mechanism for the observed modifications in the emission kinetics of the CQWs, which we further modeled and explained using full electromagnetic solutions. We showed that the rate of the resultant energy transfer from these CQWs to the bulk silicon scales slowly with d^-1 in space. Finite element method (FEM) based computation revealed that this inverse relationship is caused by the delocalization of the electric field in the CQW layer and the substrate due to strong in-plane dipoles present in the CQWs. To address the shortcomings of silicon-based photo-detecting platforms, in a proof-of-concept hybrid device we fabricated, we experimentally demonstrated that the photosensitization using such a single-layer CQW-film enhances the photocurrent collected in the silicon by up to 3-folds. The findings in this thesis are expected to help further exploit the amazing light-harvesting potential of CQWs in optoelectronic applications.
Tek katmanlı koloidal kuantum kuyularından yapılan çözelti bazlı ışık yayan diyotlar
Semiconductor colloidal quantum wells (CQWs) make an exciting quasi-2D class of nanocrystals thanks to their unique properties emerging from their atomically-flat vertically-thin geometry including highly anisotropic optical transition dipole moment (TDM), giant oscillator strength, and extraordinarily high absorption cross-section. This regular shape of the CQWs enables them to assemble on the surface of a liquid with a high degree of packing, which creates an almost fully uniform monolayer film with the desired orientation. Nearly all of the emission in a single CQW, again because of its geometry, comes from in-plane (IP) transition dipole moments (TDMs). Thus, an assembled film of such CQWs with an all-face-down orientation may show a highly anisotropic and directional emission. Using such a film in an emissive layer (EML) of an electroluminescent device, in this thesis work our intention is therefore to substantially boost photon outcoupling efficiency in a light-emitting device of oriented monolayer of CQWs. Thus far, research efforts have been conducted to investigate the properties of the deposited film of CQWs with self-assembly. However, in all of the previous studies, the property of CQW monolayer has been investigated only in a passive film; therefore, investigation of the self-assembled film in an active device is lacking. In this thesis, we developed and demonstrated an all-solution-processed colloidal quantum well light-emitting diodes (CQW-LEDs) using a single all-face-down oriented self-assembled monolayer (SAM) film of CQWs that enables a high level of IP TDMs of 92%. This film significantly enhances the outcoupling efficiency of LEDs from 22% (of standard randomly-oriented emitters) to 34% (of face-down oriented emitters). As a result of the outcoupling efficiency increased by 1.55 times, along with the enhanced charge injection and reduced reabsorption in the case of using a single SAM of CQWs, the external quantum efficiency reaches a record high level of 18.1% for the solution-processed type of CQW-LEDs, putting their efficiency performance on par with those of the hybrid organic-inorganic evaporation-based CQW-LEDs and all other best solution-processed LEDs. This EQE value is 65% higher than that in the devices fabricated by spin-coating with the same procedure and structure. Also, the SAM-CQW-LED architecture enables a high maximum brightness of 19,800 cd/m2 with a long operational lifetime of 247 h at 100 cd/m2, as well as a stable saturated deep-red emission (651 nm) with a low turn-on voltage of 1.7 eV and a high J90 of 99.58 mA/cm2. These findings indicate the effectiveness of oriented self-assembly of CQWs as electrically-driven emissive layers in improving outcoupling and external quantum efficiencies in the CQW-LEDs.
Mikro-3D şekillendirilmiş metayapılar
Today three-dimensional (3D) printers are highly popular and find use in a vast range of applications thanks to their capability to construct complex 3D structures. However, 3D-printing vertical structures with a high aspect ratio of height to width remains a pending challenge especially when a high lateral resolution is required in large footprints. In this thesis, we propose and demonstrate micro-3D sculptured metastructures using the idea of constructing deep trenches to erect their high aspect ratio metal lines along long strips. To generate such deep-trenched 3D-patterns, our construction relies on nonlinear absorption process, enabling the two-photon polymerization (2PP). In our fabrication, the 2PP process requires optical trajectory optimization, followed by electroplating thick metal film and dry etching seed layer. To test the developed process flow of 2PP, we built three-dimensional RF metastructures showcasing the depth effect as a third dimension. Based on our systematic numerical and experimental studies, our designed metastructure resonators are found to fall within a targeted specific operating resonance frequency range, with their resonance frequency being controlled and shifted and their quality factor (Q-factor) tuned as a function of their cross-sectional aspect ratio. In the thesis, with these proof-of-concept demonstrations, we show that such 2PP-defined high aspect ratio RF resonators highly benefit in terms of tunability of their resonance frequencies, along with increased Q-factor and reduced footprint. The findings of this thesis indicate that the proposed fabrication method of producing deep trenches via 3D-printing provides rich opportunities to implement high aspect ratio, complex structures that are highly miniaturized. Keywords: Deep trenches, three-dimensional printing, two-photon polymerization, electroplating, RF metastructures, RF resonators
Koloidal kuantum kuyuları tabanlı ışık yayan dalga kılavuzları
Micro/nanoscale semiconductor light-emitting devices of colloidal nanocrystals offer low-cost solutions while delivering high performance in ambient lighting systems, displays, and photonic circuits. Colloidal quantum wells (CQWs) are excellent candidates as active materials for these optoelectronic devices owing to their superior properties including suppressed Auger recombination, large absorption cross-section, and narrow emission linewidth. In this thesis, as our first study, we proposed and demonstrated dual-color lasing using heterostructures of CQWs as the gain media in an all-solution-processed dual-color optical cavity for the first time. Here, a multilayered waveguide architecture consisting of green- and red-emitting CQWs, separated with a transparent low refractive index colloidal spacing layer of silica nanoparticles (NPs) suppressing otherwise detrimental nonradiative energy transfer between them, enabled amplified spontaneous emission (ASE) simultaneously in two colors at the threshold level of ~17 µJ/cm2. We further adapted this multilayer waveguide configuration to a whispering-gallery-mode (WGM) cavity by fabricating a microdisk structure directly out of these layered CQWs-NPs-CQWs colloids. The resulting device showed dual-color multimode lasing both at 569 and 648 nm at the same time with the threshold of ~106 µJ/cm2. Then, as the second study of this thesis, we developed a colloidal waveguide light-emitting diode (LED) structure of CQWs that changes the direction of light from the surface to the edge of the device by combining the active CQW region with a slit-shaped waveguide architecture that confines the light within the emissive layer and guides it through the lateral axis. Driving this LED waveguide of 900 µm in length by 150 µm in width at a current density level of 5.6 A/cm2, we observed the output emission reached a luminance level of ~20,400 cd/m2. These unique waveguiding architectures integrated into the light-emitting devices of CQWs hold great promise for on-chip photonic applications including CQW dual-color excitation for biological imaging and CQW LED-based photonic integrated circuits.
Yeni nesil optoelektronik teknolojileri için koloidal nanokristallerin eksitonik özelliklerinin anlaşılması
Owing to the tremendous progress in the past decade, semiconductor nanocrystals that are grown by low-temperature solution-phase epitaxy have evolved into highly promising material systems for optoelectronics with ever increasing interest from the industry. However, fundamental challenges exist in conventional nanocrystals hampering their energy-efficient optoelectronic devices. In this thesis, we addressed important scientific problems and overcome various technological hurdles through optical physics discoveries and innovative nanomaterial processing. Specifically, we have proposed, designed and developed next generation of nanocrystals that exhibit superior optical and material properties than those of the conventional nanocrystals. Mastering intra- and inter-particle excitonic processes in these nanocrystals and their hybrids empowered us to control and tailor the desired photonic response. Our key achievements include demonstration of record high modal gain coefficients and giant nonlinear absorption cross-section in atomically-flat nanocrystals, ultralow-threshold all-solution processed quantum dot lasers and unprecedentedly strong exciton transport in self-assembled nanocrystals.
Yarı iletken kuantum noktacıkları ve konjüge polimer nanoparçacıkların yenilikçi ışık yayan aygıtları
Starting with the modern times, lighting has become an essential part of our lives. Today, its share of the total energy consumption reaching 15% should not surprise us. This share further increases when the energy demand for display backlighting is taken into account. Therefore, increasing the efficiency of the lighting sources is of significant importance for decreasing the carbon footprint for a sustainable environment. At this point, light-emitting diodes (LEDs)step forward as the most important candidate for revolutionizing the existing lighting systems; however, the current conventional technologies, which typically employ rare-earth ion based broad-band emitters, are plagued with low photometric efficiency, lack of light quality, and incapability of the spectrum design for application-specific performance. As a remedy to these problems, in this thesis we study light-emitting diodes of quantum dots that are efficient narrow-band emitters as opposed to phosphors. These colloidal quantum dots allow for the achievement of the light source performance specific to each application. By employing this strength, we first present our design of quantum dot integrated LED display backlight for reducing the adverse effects of the displays on the human biological rhythm while maximizing the color definition. Here we also addressed the need for light sources exhibiting polarization anisotropy for display backlights by hybridizing self-assembled magnetic nanowires and quantum dots. To solve the emission stability problem of the quantum dots in solid-films, we demonstrated the incorporation of the quantum dots within crystalline matrices that act as a barrier against oxygen and humidity and substantially increase their emission stability. Another important strength of this technique has been the preservation of the dispersion quantum efficiencies of the quantum dots in powder form and in solid-films. By employing these material systems, we designed and successfully demonstrated a warm white LED exhibiting successful color rendition capability and large spectral overlap with the human eye sensitivity function. We also showed that embedding quantum dots into crystalline matrices offers a robust platform to study the excitonic and plasmonic interactions, both of which we utilized for increasing the efficiencies of the quantum dots in crystalline matrices. To meet the need for non-toxic color converter enabling color tuning, we also employed conjugated polymer nanoparticles and studied their near-field interaction with epitaxially grown quantum well nanopillars to boost their emission intensity. We believe that the materials and light sources that we presented in this thesis will enable to reach the targets for realizing high-efficiency but also high-quality light sources for general lighting and displays.
0, 2 ve 3 boyutlu malzemelerin oluşturduğu karmaşık yapılarda ışınımsız enerji transferinin fiziği
Quantum-confined colloidal nanostructures with strong excitonic properties have emerged as promising light harvesting components in photonics and optoelectronics over the past 20 years. With their favorable photophysical characteristics, three-dimensional-confined colloidal quantum dots and 2D-confined colloidal quantum wells have garnered great attention in the fields ranging from biology and chemistry to physics and engineering. It is technologically significant to utilize the key characteristics of these brightly luminescent nanomaterials through hybridizing and/or interfacing with various technological materials including 3D bulk silicon, graphene based 2D structures such as graphene oxide and reduced graphene oxide, and 2D layered transition metal dichalcogenides such as molybdenum disulphide. Compelling partnership of these appealing materials can be achieved through the nonradiative energy transfer (NRET), which is a phenomenon involving both the exciton and charge transfer mechanisms. Along with the hybrids of low dimensional particles with the conventional bulk materials, the closely interacting structures of these colloidal and layered nanomaterials have widespread interest at both the fundamental science and application levels. From these physical and technological points of view, in this thesis, we addressed important scientific problems and proposed innovative solutions including both the experimental and theoretical approaches in interfacing complex media of 0D, 2D and 3D materials and showing strong NRET interactions. Our key achievements include high excitonic enhancement in silicon and graphene based materials with the integration of nanoparticles, comprehensive photophysical investigation of the newly emerging nanomaterials and successful tailoring of the colloidal nanostructures to the next-generation optoelectronic applications.
Yenilikçi hibrit kompozit nanomalzemeler
Digital lighting and bio-imaging are two emerging crucial research fields. Nanotechnology stands in the center of these applications by providing nano-scale particles possessing large surface-to-volume ratios, high efficiency, and low toxicity while allowing for functionalization, efficient quality lighting and improved biocompatible bio-imaging. Some of the frequently employed nanoparticles in optoelectronics and imaging are colloidal semiconductor quantum dots, colloidal conjugated polymer nanoparticles, and colloidal iron oxide nanoparticles, all of which we have studied using colloidal approaches to make hybrid composites for lighting and imaging in this thesis. Fluorescent inorganic nanoparticles of colloidal quantum dots (QDs) attract significant interest for many optoelectronic and biomedical applications. Although they possess numerous advantages including broad absorption band, high quantum yield, and narrow emission spectrum, there are serious concerns on their recycling due to their cadmium-based composition. Alternatively, relatively low toxic organic uorescent polymer nanoparticles or oligomer nanoparticles have stepped forward. However, their reduced emission efficiency and stability in solid state is an important limitation for their use in wide-spread solid-state lighting applications. To address these problems, in the first part of this thesis, we proposed and demonstrated the design of new hybrid composite material systems of oligomer nanoparticles to be used in solid-state lighting. We first showed that the emission efficiency and stability of the oligomer nanoparticles in solid state are significantly improved based on our proposed crystallization technique. Here, using this simple and low-cost approach, oligomer nanoparticle monoliths were obtained from the powders of these crystals. Despite the disadvantages of using QDs, their high quantum efficiency and narrow-band emission still make them a valuable asset for solid-state lighting. However, the decrease in solid-film efficiencies is still an important issue to be addressed. With this perspective, in this thesis we utilized the incorporation of QDs into crystalline matrices allowing for the nonradiative energy transfer (NRET) to improve the emission capability of the nano-emitters. Since it is an interesting crystalline semiconductor organic molecule, we employed anthracene as the host donor medium and incorporated the quantum dots being exciton acceptors. Here, we systematically investigated the NRET from each anthracene emission peak to QDs and demonstrated the use of this composite system on LEDs as color converters and the polarization ratio change of quantum dots within this crystal system. Magnetic resonance imaging (MRI), for which we also developed colloidal contrast agents using nanoparticles (NPs) as the second part of this thesis, is a powerful diagnostic tool providing good soft tissue contrast and high spatial resolution. It produces T1- and T2-weighted images, in which the region of interest is observed as brighter and darker contrast, respectively. Superparamagnetic iron oxide (IO) NPs are an important member of T2-weighted contrast agents possessing low toxicity. However, they suffer from poor anatomic details due to their darker contrast. Therefore, combining T1- and T2-weighted features in a single IO NP (dual-modal contrast) is a major step for improving MRI contrast. In order to meet the requirement for dual-modal contrast agents, which possess both T1-and T2-weighted imaging capability, in this thesis we synthesized highly monodisperse superparamagnetic cubic IO NPs. Magnetic characterizations along with in vivo MRI experiments demonstrated that these nanoparticles hold great promise for dual-modal imaging. This increased dual-modal effect without paramagnetic material doping or decreasing the size of nanoparticles smaller than 5 nm directed us to understand the relation of the T1 and T2 relaxations depending on the IO NP size and shape. Here, we showed the presence of intrinsic paramagnetic phase in magnetite IO NPs. Moreover, we demonstrated that this contribution is higher in IO NPs possessing cubic shape compared to the spherical counterparts, which explains the increased dual-modal effect in the monodisperse superparamagnetic nanocubes. Keywords: Oligomer nanoparticles, quantum dots, light-emitting diodes (LEDs), nonradiative energy transfer, superparamagnetic iron oxide nanoparticles (SPIONs), magnetic resonance imaging (MRI).
Çok yüksek verimlilikte indüktif ısıtma ve otomatik metal algılama için yenilikçi modüler ve dizi bobin sistemleri
Induction systems have become increasingly more important and popular in our modern world and their application areas have widely expanded because of their high levels of safety and controllability. Today one important application of these induction systems is the inductive heating, which now finds use not only in conventional applications of point-source heating but also in new areas including all-surface heating with some degree of flexibility in localization. The efficiency of such emerging systems, especially in planar structures across an entire surface, however, has thus far been limited compared to conventional inductive heating. In this thesis, to address these problems, we show a new class of strongly coupled planar coils that enhance magnetic coupling in square lattice stacking by design and with phase difference application in operation. These coils can be tiled in two-dimensional arrays in a modular fashion or to cover an arbitrarily large continuous surface. In a proof-of-concept realization, we experimentally demonstrated that these proposed outer squircle-inner circular coils outperform the conventional coils of circular shape. Using square-arrayed coil architecture, here we also present all-surface induction systems achieving uniform and enhanced heating speed for all loading positions no matter what the misalignment of the heated vessel with respect to the coils is. In addition, to solve the problems of automatically detecting metals over the whole surface together with determining their exact positions, we introduce a new method that relies on simultaneous wireless measurement and tracking of inductance-resistance of the coils at multiple frequencies to identify those coupled with the metal targets to be detected in the system. While pinpointing the location of the targeted metals, the proposed technique also identifies their material types. For future ubiquitous all-surface systems, this approach allows for automated sensing of metal vessels and powering the loaded coils for the highest possible performance independent of the specific location of each vessel with respect to coils. These findings indicate that the proposed innovative modular and arrayed coils enable, for the first time, full degree of flexibility in localized inductive heating with space-invariance in all-surface heating.
Metayüzey mikrolens odak düzlem matrisleri ve aynaları
Lenses, mirrors and focal plane arrays (FPAs) are among the key components affecting the functionality, performance and cost of electro-optical (EO) systems. Conventional lenses rely on phase accumulation mechanism for bending wavefront of light. This mechanism and the scarcity of transparent materials result in high-complexity, high-cost and bulky EO systems. Conventional mirrors, on the other hand, are limited by the electromagnetic properties of metals and cannot be used in certain EO systems. Also, conventional FPAs suffer the fundamental tradeoff between the optical resolution and optical crosstalk. Metasurfaces, relying on the concept of abrupt phase shifts, can be used to built a new class of optical components. However, for realizing metasurfaces, optical resonators should cover a full 0-to-2π phase shift response with close to uniform amplitude response. In this thesis, to develop these metasurface optical components, nanoantennas that act as unit cell optical resonators were designed and modeled. A design methodology for building and optimizing these metasurfaces using the designed nanoantennas was developed. After obtaining the metasurfaces, we successfully addressed the problems of optical crosstalk in mid-wavelength infrared (MWIR) FPAs and weak field localization in mirror contacts. Full-wave simulations confirmed major crosstalk suppression of the microlens arrays to achieve ≤ 1% optical crosstalk in the proposed metasurface FPAs, which outperforms all other types of MWIR FPAs reported to date. However, due to intrinsic absorption losses in metals, the resulting device efficiency was low (≤ 10%). To solve this problem, metallic nanoantennas were replaced by dielectric nanoantennas and the focusing efficiency was dramatically increased to 80%. This is the first account of high-efficiency low-crosstalk metasurface MWIR FPAs. Full-wave simulations also confirmed the strong field localization of metasurface mirrors that can impose a phase shift response close to 0◦. The findings of this thesis indicate that metasurface FPAs and mirrors are highly promising for future EO systems.
Algılama ve işaretleme için kablosuz ince-film mikrodalga rezonatörler
Rapid progress in wireless microwave technology has attracted increasing interest for high-performance wireless devices. The thin- lm microwave technology is now evolving into the mainstream of applications but signi cant advances are required in resonator architectures and processing for operation in the desired frequency ranges. This dissertation studies the thin- lm microwave technology to develop wireless resonators and describes the core elements that give rise to resonators for high performance in wireless sensing and marking. Speci c to wireless sensing, we proposed and developed a novel wireless microwave resonator scheme that enables telemetric strain sensing avoiding the need for calibration at di erent interrogation distances. In this work, we showed that by using both the proposed sensor architecture and wireless measurement method, strain can be successfully extracted independent of the interrogation distance for the rst time. The experimental results indicate high sensitivity and linearity for the proposed system. This approach enables mobile wireless sensing with varying interrogation distance. For wireless marking, we investigated an ultra-thin, exible, passive radio frequency (RF) based resonator compatible with magnetic resonance imaging (MRI) that successfully was tested in clinic. The ultra-thin and exible architecture of the device o ers an e ective and safe MR visualization and improves the feasibility and reliability of anatomic marking at various surfaces of the body. Results show that, at low background ip angles, the proposed structure enables precise and rapid visibility with high marker-to-background contrast as well as high signal-to-noise ratio (SNR). Also clinical studies have led to a successful biopsy procedure using marking functionality of our device. In another work related to marking, we proposed a new method to enhance local SNR and resolution without disturbing the B1- eld. Here we used our passive RF resonator in the inductively uncoupled mode for endocavity MR imaging. T1- and T2-weighted sequences were employed for phantom and in vivo experiments. The obtained images show the feasibility of the proposed technique to improve the SNR and the resolution in the vicinity of the device. These ndings will allow for new possibilities in applications using wireless sensing and marking approaches shown in this thesis.
Koloidal yarıiletken kuantum kuyularının heteroyapıları: Sentezlenmesi, karakterizasyonu ve uygulamaları
Colloidal semiconductor quantum wells, also known as nanoplatelets (NPLs), have recently emerged as a new class of colloidal semiconductor nanocrystals enabling fascinating excitonic properties. With their quasi two-dimensional structure resembling epitaxially-grown quantum wells, these atomically-flat nanoplatelets exhibit narrow emission linewidths, giant linear and nonlinear absorption cross-sections, and ultrafast fuorescence lifetimes when compared to other classes of semiconductor nanocrystals. These appealing features have led to achievement of low lasing thresholds and high color purity by using simple heterostructures of these NPLs. To further exploit the benefits of these solution-processed NPLs and develop next-generation colloidal optoelectronic devices, novel heterostructures of NPLs with superior excitonic properties are in high demand. In this thesis, to address these needs, we proposed and demonstrated novel heterostructured NPLs. This thesis includes the rational design and systematic synthesis and characterization of these hetero-NPLs. To overcome the lower photoluminescence quantum yield (PL-QY) and stability issues of core/shell NPLs, we successfully synthesized CdSe/CdS/CdS core/crown/shell NPLs resembling platelet-in-a-box. With this advanced architecture, we accomplished substantially enhanced PL-QY and absorption crosssection as well as stability, allowing for the achievement of low-threshold optical gain. However, due to the pure vertical confinement observed in these NPLs,these exciting excitonic features of NPLs suffered from the limited spectral tunability. By developing homogenously alloyed CdSexS1-x NPLs together with their alloyed core/crown and alloyed core/shell heterostructures, we succeeded in obtaining highly tunable excitonic features and further extending tunability of the optical gain from these NPLs. In addition to the NPLs having Type-I electronic structure, we demonstrated the highly uniform growth of CdSe/CdTe core/crown NPLs having Type-II electronic structure exhibiting unique excitonic properties. Additionally, to realize the evolution of Type-II electronic structure, we synthesized CdSe/CdSe1-xTex core/crown NPLs by precisely tailoring the composition of the crown region. Without changing their vertical thicknesses, we achieved again highly tunable excitonic features and near-unity PL-QY from these hetero-NPLs. Based on the proposed architectures of these heteronanoplatelets, we believe the findings of this thesis provide important guidelines and inspiration for the synthesis of highly e fficient and stable heterostructured NPLs to construct high-performance colloidal optoelectronic devices, possibly challenging their conventional epitaxially-grown counterparts.
MRG için implant edilebilir kablosuz cm-altı çınlaçlar: Devre teorisinden tıbbi görüntülemeye
Making implantable wireless resonators having small footprints is fundamentally challenging when using conventional designs that are subject to the inherent tradeoff between their size and the achievable range of quality-factors (Q-factors). For clinical magnetic resonance imaging (MRI) frequencies (e.g., about 127 MHz for 3 T), conventional resonators either require a diameter of about 20 cm in chip size or off-the-chip lumped elements for successful operation, both of which practically prevent their use as implantable devices. At least two orders-of-magnitude reduction in footprint area is necessary to make on-chip resonators suitable for in-vivo applications. However, decreasing the size of such a conventional resonator chip comes at the expense of substantially decreased Q-factor. Thus, achieving high Q-factors with reduced footprints simultaneously entails a novel approach in implantable electronics. In this thesis work, to address this problem, we proposed, designed and demonstrated a new class of sub-wavelength, thin-film loaded helical metamaterial structures for in-vivo applications including field localization and signal-to-noise ratio (SNR) improvement in MRI. This implantable wireless architecture, implemented fully on chip with partially overlaid helicals on both sides of the chip interconnected by a through-chip-via, enables a wide range of resonant radio frequencies tunable on chip by design while achieving an extraordinarily small footprint area (<< 1 cm2) and ultra-thin geometry (< 30 µm). The miniaturization of such microwave circuits to sub-cm range, together with their high Q-factors exceeding 30 in lossy soft tissues, allows for their use in vivo. The fabricated devices correspond to 1/1500th of their operating wavelength in size, rendering them deep sub-wavelength. For the proposed wireless resonant devices, equivalent circuit models were developed to understand their miniaturization property and the resulting high Q-factors are well explained by using these models. Additionally, full-wave numerical solutions of the proposed geometries were systematically carried out to verify the findings of the developed equivalent circuit models. All of these theoretical and numerical studies were found in excellent agreement with the experimental RF characterization of the microfabricated devices. Retrieval analyses of the proposed architectures showed that these geometries lead to both negative relative permittivity and permeability simultaneously at their operating frequencies, which do not naturally exist together in nature, making these structures true metamaterials. These fabricated wireless devices were further shown to be promising for the in-vivo application of subdural electrode marking, along with SNR improvement and field localization without causing excessive heating in MRI. MR images support that the proposed circuitry is also suitable for MRI marking of implants, high-resolution MR imaging and electric field confinement for lossy medium. Although our demonstrations were for the purpose of marking subdural electrodes, RF characterization results suggest that the proposed device is not limited to MRI applications. Utilizing the same class of structures enabling strong field localization, numerous wireless applications seem feasible, especially where miniaturization of the wireless devices is required and/or improving the performance of conventional structures is necessary. The findings of this thesis indicate that the proposed implantable sub-cm wireless resonators will open up new possibilities for the next-generation implants and wireless sensing systems.
Kalın nanolevhaların kolloidal katkılanması
Semiconductor nanoplatelets (NPLs) make an interesting group of nanocrystals with unique optical properties as a result of their quasi 2-dimensional (2D) electronic structure. Such emerging fascinating optical features of NPLs include high absorption cross-section, narrow emission linewidths, and reduced Auger recombination, making them a superior choice compared to conventional semiconductor nanocrystals for optoelectronic applications. Doping of these materials with transition metals, such as silver and copper, provides great opportunities to modify and tune the electronic structure of these NPLs for various devices including light-emitting diodes and luminescent solar concentrators. Such doping with transition metals allows for manipulation of the photoluminescence from these NPLs, control of the recombination processes of the photogenerated carriers in these NPLs, and observation of the giant Zeeman effect as a result of exchange interactions between the dopants and carriers in these NPLs. Previously, CdSe NPLs have been doped with copper and silver only up to vertical thickness of 5 monolayers (ML). However, doping of thicker NPLs has not been possible to date. In this thesis work, we successfully doped thick CdSe NPLs having 7 ML in thickness with silver and copper using partial cation exchange to obtain large Stokes-shifted emission in the near-infrared (NIR) region. Here, the effect of precursor ratio and reaction temperature were systematically studied to tune the resulting emission. For both copper and silver dopants, we successfully quenched fully the band-edge emission, and purely dopant-induced emission was obtained. We also co-doped these NPLs with silver and copper, and we successfully obtained both copper- and silver-induced emissions from these NPLs. We further grew the CdZnS shell on 7 ML CdSe core by hot injection method and doped the resulting CdSe/CdZnS core/shell NPLs with silver and copper to push their emission further towards longer wavelengths in the NIR region. These thick doped-NPLs with large Stokes shift and emission in the NIR region present a promising platform for light-emitting and -harvesting applications.
Tek katman kalınlığında yönlendirilmiş koloidal kuantum kuyuları tabanlı ışığa duyarlı nanokristal yüzeyleri
Colloidal quantum wells (CQWs), a two-dimensional member of semiconductor nanocrystals, featuring very tight vertical quantum confinement, possess giant oscillator strengths. Also, CQWs exhibit remarkably large absorption cross-sections, thanks to their oscillator strengths combined with their laterally large geometries. Additionally, as a powerful tool of fabrication, CQWs lend themselves to be conveniently self-assembled into monolayer-thick films in a single orientation of our choice: either face-down (lying down on their large lateral surfaces and side by side leaving no large gap between them similar to a mosaic pattern) or edge-up (standing up on their thin edges and facing each other in a very dense superstructure formation of repeating chains). In this thesis, to make use of the attractive absorption properties of CQWs and leverage on our ability to construct their orientation-controlled self-assemblies, we show the first account of monolayer-thick light-sensitive nanocrystal skins (LS-NS) that employ self-oriented CQWs as their active absorptive layer. These CQW LS-NS devices operate on the principle of strong optical absorption of the monolayered assembly of CQWs and the subsequent photogenerated potential build-up across their strongly capacitive thin device for sensing in the visible to ultraviolet. Such oriented CQWs in the LS-NS device architecture yield profoundly reduced surface roughness in their monolayer-thick films, essential to high device performance. Here, specifically, we developed and demonstrated two groups of LS-NS devices: one group consisting of all face-down oriented CQWs and the other, of all edge-up ones. We systematically studied their photocharging effect, spectral sensitivity and decay times. We observed in all LS-NS devices that the spectral sensitivity complies with the first (heavy-hole) and second (light hole) excitonic peaks of the absorption of the CQWs. We also found that, as the excitation power is increased, the peak photovoltage readout increases while the sensitivity decreases. The photocharging effect was further observed as the excitation was turned off. Finally, using the edge-up orientation, we identified a profound peak photovoltage signal enhancement. These findings of the thesis indicate that the proposed LS-NS devices of the orientation-controlled CQW monolayers hold great promise for applications in photos-sensing facades over larger surfaces.
Koloidal yarıiletken nanokristallerin sıvı-arayüzey yönlendirmeli öz-dizilimi ve uygulamaları
Over the past, different techniques have been used for the self-assembly of nanocrystals (NCs). Recently, the orientation control over the assembly of anisotropic NCs has been achieved using liquid-interface self-assembly, which is a simple yet vastly applicable technique. Here, we propose and show the first account of the application of this method to assemble multi-layered alternating orientation NC films, with distinct orientation control of our choice over the NCs in each layer. Being laterally atomically flat, these anisotropic NCs belong to a class of quasi-two-dimensional nanocrystals with one confined dimension. Exhibiting extraordinarily large absorption cross-sections, ultra-narrow emission linewidths, and intrinsic structural anisotropy, these nanoplatelets (NPLs) possess characteristics comparable to those of epitaxially grown quantum wells, though while offering low-cost solution-based synthesis and processability at the same time. Due to this anisotropy, the emission of these NPLs is directional with mostly in-plane transition dipole moments, making them favorable for a variety of optoelectronic active media with orientation control over their deposited films. To achieve this, we have assembled the NPL films with one defined orientation and successfully attained their orientation control using macroscopic parameters, including the evaporation rate of the solvent and subphase selection to be used as the active layers for a number of optoelectronic devices. We demonstrated different multi-layered structures of these NPLs with varying orientations. The resulting surface roughness in all these films was successfully kept, on average, with Sq smoother than 2 nm. We further extended this self-assembly technique to different classes of nanocrystals, including large hexagonal NPLs (with around 100 nm in lateral dimensions) and cubic quantum dots (with around 15 nm on each side) to show the versatility of our method. The findings of this thesis indicate that our orientation-dictated self-assembly approach holds great promise for constructing complex colloidal structures made of these oriented nanocrystals as the building blocks.