Cavity Enhanced Organic Photodiodes with Charge Collection Narrowing

Color discrimination in photodetection is conventionally achieved using broadband-absorbing inorganic semiconductors with passive optical filters. Organicsemiconductors show promise to deliver narrowband spectral responses dueto their tunable optical properties. While achieving narrow-absorbing organicsemiconductors is an ongoing endeavor in the synthetic chemistry community,charge collection narrowing is introduced as a “material-agnostic” techniqueto realize narrowband spectral responses using broadband absorberssuch as blends of organic semiconductors, inorganic nanocrystals, and perovskitesin a photodiode architecture. Charge collection narrowing in organicsemiconductors demands photoactive junction thicknesses on the order ofa few micrometers causing fabrication difficulties and limitations in devicemetrics such as frequency bandwidth. In this work it is shown that electricalinversion can result in charge collection narrowing in organic photodiodeswith active layer thicknesses on the order of hundreds of nanometers and hencemuch easier to achieve via high throughput solution processing techniques.Additionally, it is shown that an indium tin oxide/gold electrode with modifiedwork function acts as a cavity mirror, further narrowing the spectral responseand at the same time delivering an extremely selective cathode, suppressingthe dark current dramatically. Nearly voltage independent detectivities of 1013Jones are achieved with an active sensing area of 0.2 cm2

Imagem aérea como representação pictórica da fotointerpretação topográfica da província de Bío-bío

The contemporary manifestations of Visual Arts suggest a broad language of communication between the creator, the process, the created work, and the spectator. They define the understanding of reality on the basis of aesthetic, symbolic and ideological stereotypes about the mechanisms that model the construction of beliefs related to the discourse of performances and installations, new technologies, hacktivism, digital art and Net Art , among other artistic manifestations. In this sense, Geomatics is directly related to contemporary art because, in its areas of specific knowledge, such as photogrammetry, topography and geographic information systems, they currently use images obtained by digital devices as support for research. In an interdisciplinary way, these devices allow the development of different mechanisms of visual, cognitive and emotional representation that condition our way of knowing, perceiving and experiencing reality. In this article, some guidelines of theoretical reflection are exposed as support of the RV30 project. Thus, this study adopts the model of research in artistic creation that guides the artist’s disciplinary development as a researcher and the fusion of a new format related to art and technology. Thus, the results of our creative process allow us to bring the public closer to knowing and using it. The project covers digital aerial photography within the parameters of photogrammetry from a two-dimensional perspective related to the creation and public exhibition of 12 paintings on an iconographic repertoire of the topography of the province of Biobío.Las manifestaciones contemporáneas de las Artes Visuales postulan un amplio lenguaje de comunicación entre el creador, el proceso, la obra creada y el espectador. Estas definen la comprensión de la realidad sobre la base de estereotipos estéticos, simbólicos e ideológicos acerca de los mecanismos que modelan la construcción de creencias relacionadas con el discurso de las performances e instalaciones, las nuevas tecnologías, el hacktivismo, el arte digital y el Net Art, entre otras manifestaciones. En este sentido, la Geomática posee directa relación con el arte contemporáneo porque en sus áreas de conocimiento específico como la fotogrametría, la topografía y los sistemas de información geográfica utiliza, en la actualidad, las imágenes obtenidas por dispositivos digitales como soporte para la investigación. De manera interdisciplinaria, estos permiten el desarrollo de diferentes mecanismos de representación visual, cognitivos y emocionales que condicionan nuestra manera de conocer, percibir y experimentar la realidad. En el presente artículo se exponen algunos lineamientos de reflexión teórica que fundamentan el proyecto RV30. Así, este estudio adopta el modelo de investigación en creación artística que orientan el desarrollo disciplinar del artista como investigador y la fusión de un nuevo formato relacionado con el arte y la tecnología. Los resultados de nuestro proceso creativo permiten acercar al público al conocimiento y utilización de esta última. El proyecto abarca la fotografía aérea digital dentro de los parámetros de la fotogrametría desde una perspectiva bidimensional relacionada con la creación y exhibición pública de 12 pinturas sobre un repertorio iconográfico de la topografía de la provincia del Biobío.As manifestações contemporâneas das Artes Visuais colocam uma ampla linguagem de comunicação entre o criador, o processo, a obra criada e o espectador. Estas definem a compreensão da realidade sobre a base de estereótipos estéticos, simbólicos e ideológicos acerca dos mecanismos que modelam a construção de crenças relacionadas com o discurso das performances e instalações, as novas tecnologias, o hacktivismo, a arte digital e a New Art, entre outras manifestações artísticas. Neste sentido, a Geomântica possui direta relação com a arte contemporânea porque em suas áreas do conhecimento específico, como a fotogrametria, a topografia e os sistemas de informação geográfica, utiliza na atualidade as imagens obtidas por dispositivos digitais como suporte para a pesquisa. De forma interdisciplinar, esses dispositivos permitem o desenvolvimento de diversos mecanismos de representação visual, cognitivos e emocionais, que condicionam nossa forma de conhecer, perceber e exprimir a realidade. No presente artigo expomos algumas linhas de reflexão teórica que fundamentam o projeto RV30. Assim, este estudo adota o modelo de pesquisa em criação artística que norteia o desenvolvimento disciplinar do artista como pesquisador e a fusão de um novo formato relacionado com a arte e a tecnologia. Os resultados de nosso processo criativo permitem aproximar o público ao conhecimento e à utilização de este. O projeto abrange a fotografia aérea bidimensional relacionada com a criação e exibição pública de 12 pinturas sobre um repertório iconográfico da topografia da província do Biobio

Solution-processed semiconductors for next-generation photodetectors

Efficient light detection is central to modern science and technology.Current photodetectors mainly use photodiodes based on crystalline inorganic elementalsemiconductors, such as silicon, or compounds such as III–V semiconductors. Photodetectorsmade of solution-processed semiconductors — which include organic materials, metal-halideperovskites and quantum dots — have recently emerged as candidates for next-generation lightsensing. They combine ease of processing, tailorable optoelectronic properties, facile integrationwith complementary metal–oxide–semiconductors, compatibility with flexible substrates andgood performance. Here, we review the recent advances and the open challenges in the field ofsolution-processed photodetectors, examining the topic from both the materials and the deviceperspective and highlighting the potential of the synergistic combination of materials and deviceengineering. We explore hybrid phototransistorsand their potential to overcome trade-offsin noise, gain and speed, as well as the rapid advances in metal-halide perovskite photodiodesand their recent application in narrowband filterless photodetection

Seeing the Big Picture: System Architecture Trends in Endoscopy and LED-Based hyperspectral Subsystem Intergration

Early-stage colorectal lesions remain difficult to detect. Early development of neoplasia tends to be small (less than 10 mm) and flat and difficult to distinguish from surrounding mucosa. Additionally, optical diagnosis of neoplasia as benign or malignant is problematic. Low rates of detection of these lesions allow for continued growth in the colorectum and increased risk of cancer formation. Therefore, it is crucial to detect neoplasia and other non-neoplastic lesions to determine risk and guide future treatment. Technology for detection needs to enhance contrast of subtle tissue differences in the colorectum and track multiple biomarkers simultaneously. This work implements one such technology with the potential to achieve the desired multi-contrast outcome for endoscopic screenings: hyperspectral imaging. Traditional endoscopic imaging uses a white light source and a RGB detector to visualize the colorectum using reflected light. Hyperspectral imaging (HSI) acquires an image over a range of individual wavelength bands to create an image hypercube with a wavelength dimension much deeper and more sensitive than that of an RGB image. A hypercube can consist of reflectance or fluorescence (or both) spectra depending on the filtering optics involved. Prior studies using HSI in endoscopy have normally involved ex vivo tissues or xiv optics that created a trade-off between spatial resolution, spectral discrimination and temporal sampling. This dissertation describes the systems design of an alternative HSI endoscopic imaging technology that can provide high spatial resolution, high spectral distinction and video-rate acquisition in vivo. The hyperspectral endoscopic system consists of a novel spectral illumination source for image acquisition dependent on the fluorescence excitation (instead of emission). Therefore, this work represents a novel contribution to the field of endoscopy in combining excitation-scanning hyperspectral imaging and endoscopy. This dissertation describes: 1) systems architecture of the endoscopic system in review of previous iterations and theoretical next-generation options, 2) feasibility testing of a LED-based hyperspectral endoscope system and 3) another LED-based spectral illuminator on a microscope platform to test multi-spectral contrast imaging. The results of the architecture point towards an endoscopic system with more complex imaging and increased computational capabilities. The hyperspectral endoscope platform proved feasibility of a LED-based spectral light source with a multi-furcated solid light guide. Another LED-based design was tested successfully on a microscope platform with a dual mirror array similar to telescope designs. Both feasibility tests emphasized optimization of coupling optics and combining multiple diffuse light sources to a common output. These results should lead to enhanced imagery for endoscopic tissue discrimination and future optical diagnosis for routine colonoscopy

Compact microscopy systems with non-conventional optical techniques

This work has been motivated by global efforts to decentralize high performance imaging systems through frugal engineering and expansion of 3D fabrication technologies. Typically, high resolution imaging systems are confined in clinical or laboratory environment due to the limited means of producing optical lenses on the demand. The use of lenses is an essential mean to achieve high resolution imaging, but conventional optical lenses are made using either polished glass or molded plastics. Both are suited for highly skilled craftsmen or factory level production. In the first part of this work, alternative low-cost lens-making process for generating high quality optical lenses with minimal operator training have been discussed. We evoked the use of liquid droplets to make lenses. This unconventional method relies on interfacial forces to generate curved droplets that if solidified can become convex-shaped lenses. To achieve this, we studied the droplet behaviour (Rayleigh-Plateau phenomenon) before creating a set of 3D printed tools to generate droplets. We measured and characterized the fabrication techniques to ensure reliability in lens fabrication on- demand at high throughput. Compact imaging requires a compact optical system and computing unit. So, in the next part of this work, we engineered a deconstructed microscope system for field-portable imaging. Still a core limitation of all optical lenses is the physical size of lens aperture – which limits their resolution performance, and optical aberrations – that limit their imaging quality performance. In the next part of this work, we investigated use of computational optics-based optimization approaches to conduct in situ characterization of aberrations that can be digitally removed. The computational approach we have used in this work is known as Fourier Ptychography (FP). It is an emerging computational microscopic technique that combines the use of synthetic aperture and iterative optimization algorithms, offering increased resolution, at full field-of-view (FOV) and aberration-removal. In using FP techniques, we have shown measurements of optical distortions from different lenses made from droplets only. We also, investigated the limitations of FP in aberration recovery on moldless lenses. In conclusion, this work presents new opportunities to engineer high resolution imaging system using modern 3D printing approaches. Our successful demonstration of FP techniques on moldless lenses will usher new additional applications in digital pathology or low-cost mobile health

Skin Texture as a Source of Biometric Information

Traditional face recognition systems have achieved remarkable performances when the whole face image is available. However, recognising people from partial view of their facial image is a challenging task. Face recognition systems' performances may also be degraded due to low resolution image quality. These limitations can restrict the practicality of such systems in real-world scenarios such as surveillance, and forensic applications. Therefore, there is a need to identify people from whatever information is available and one of the possible approaches would be to use the texture information from available facial skin regions for the biometric identification of individuals. This thesis presents the design, implementation and experimental evaluation of an automated skin-based biometric framework. The proposed system exploits the skin information from facial regions for person recognition. Such a system is applicable where only a partial view of a face is captured by imaging devices. The system automatically detects the regions of interest by using a set of facial landmarks. Four regions were investigated in this study: forehead, right cheek, left cheek, and chin. A skin purity assessment scheme determines whether the region of interest contains enough skin pixels for biometric analysis. Texture features were extracted from non-overlapping sub-regions and categorised using a number of classification schemes. To further improve the reliability of the system, the study also investigated various techniques to deal with the challenge where the face images may be acquired at different resolutions to that available at the time of enrolment or sub-regions themselves be partially occluded. The study also presented an adaptive scheme for exploiting the available information from the corrupt regions of interest. Extensive experiments were conducted using publicly available databases to evaluate both the performance of the prototype system and the adaptive framework for different operational conditions, such as level of occlusion and mixture of different resolution skin images. Results suggest that skin information can provide useful discriminative characteristics for individual identification. The comparison analyses with state-of-the-art methods show that the proposed system achieved a promising performance

Formation d'image : estimation du champ lumineux et matrice de filtres couleurs

Dans ce mémoire de maîtrise de type recherche, nous discutons essentiellement de la formation d’image. Dans un premier chapitre, nous décrivons les modèles classiques de formation d'image. Nous commençons par une description de la lumière voyageant dans la scène pour arriver à l'image formée sur le capteur. Ensuite, nous critiquons ces modèles sur le fait que le capteur entraine une perte d’informations sur la structure de la scène. De plus, pour un point donné du plan image, tous les rayons provenant de la scène ne sont pas pris en compte pour la formation d'une image. Nous essayons alors de combler ces défauts en introduisant la notion de champ lumineux dans le deuxième chapitre. Nous décrivons le modèle des champs lumineux d'une scène. Ce dernier permet alors d'estimer le champ lumineux à partir d'une image à l'aide de deux méthodes : la méthode des moindres carrés et une méthode variationnelle. Celles-ci sont présentées dans le troisième chapitre. Enfin, dans un quatrième chapitre, nous abordons un autre aspect de la formation d'image. En effet, nous travaillons sur une nouvelle matrice de filtres couleurs (color filter arrays, CFA) que nous nommons CFA de Burtoni. Dans ce chapitre, nous comparons, selon une mesure d'aliasing et de résolution, ce CFA avec d'autres CFAs existant dans la littérature, sans faire appel au démosaïquage. Afin d'effectuer ces comparaisons, nous introduisons également des classes d'images correspondantes à différents contenus comme les textures, les zoneshomogènes et les lignes

Engineering Tunable Colloidal Nanostructures for Light Energy Harvesting

Colloidal nanomaterials, such as semiconductor quantum dots and plasmonic metal nanoparticles, are of interest for various optoelectronic applications due to their size-tunable optical properties, unique electronic structures, and low-cost fabrication techniques. As the physical footprint of emerging optoelectronic device components continues to shrink, colloidal nanomaterials have the potential to enable advances in fields such as low-power computing, renewable energy generation and storage, and biosensing and medicine, due to their small size, earth-abundance, and novel functionality. This thesis focuses on engineering these nanostructures for energy harvesting technologies, such as solar cells, photodetectors and photocatalysts. This is achieved by combining modeling, nanofabrication, and advanced optical and electrical characterization techniques. The study is implemented in three sections. The first involves engineering these nanostructures for solution processed solar cells. Using optimization algorithms combined with thin film interference modeling, we developed a method for producing arbitrary spectral profiles in solar cells structures for potential applications in building- and window-integrated power generation. Similarly, by using photonic band engineering in strongly absorbing materials, we developed and analyzed a new strategy for tuning the spectral selectivity of optoelectronic films. Additionally we critically evaluate the prospects for plasmonic enhancements in solution-processed thin-film solar cells by developing an intuitive effective medium model for embedded plasmonic nanostructures in photovoltaic thin films. The next section involves investigating these nanostructures for photon detection applications. One study involves using a one-step solution-based growth technique to grow antimony selenide nanowires. This enables the growth of high-quality antimony selenide nanostructures from a molecular ink directly on flexible substrates for high-performance near-infrared photodetectors thus providing a route for low-cost, flexible, and broadband photon detection. The other study demonstrates high responsivity visible blind photodetectors based on nanoheterojunction films, thus representing a viable path for building UV cost-effective optoelectronic devices Finally, the last section includes designing, developing and characterizing new plasmonic-catalytic systems based on earth-abundant and cost-effective nanomaterials such as aluminum. We present the first photophysical characterization of plasmonic aluminum nanoparticles, and identify tuning strategies such as surface modifications for various niche applications. These three sections culminate in creating a sustainable route to building both an energy-efficient and scalable-materials platform for the next generation of nanotechnology-based optoelectronic devices for energy applications