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Ahmad, Nisar. "High-field transport in semiconducting material and devices." Thesis, Brunel University, 1990. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.258019.
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Kozawa, Daichi. "Behavior of photocarrier in atomically thin two-dimensional semiconducting materials for optoelectronics." Kyoto University, 2015. http://hdl.handle.net/2433/199420.
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Longhin, Mattia. "Semiconducting bolometric detectors : material optimization and device design for future room temperature THz imaging arrays." Paris 6, 2009. http://www.theses.fr/2009PA066076.
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L’application à grande échelle des technologies liées au rayonnement terahertz (THz) est encore aujourd’hui limitée par leur complexité et les coûts élevés. Dans ce mémoire, nous proposons des détecteurs bolométriques économiques fonctionnant à température ambiante pour application à l’imagerie THz. Dans ce contexte, nous avons tout d’abord étudié le dépôt de films minces de la phase semiconductrice de l’oxyde YBaCuO et optimisé les caractéristiques structurales et électriques des films minces pour les rendre compatibles avec une technologie CMOS. Nous avons ensuite initié et mis en œuvre de nouveaux procédés de technologie pour fabriquer des bolomètres à partir des films minces semiconducteurs. En particulier, nous nous sommes occupés du couplage entre l’antenne THz et l’élément sensible. Finalement, de premiers dispositifs correspondant à différentes configurations possibles du détecteur ont été réalisés et testés.
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CALASCIBETTA, ADIEL MAURO. "SUSTAINABLE SYNTHETIC METHODOLOGIES FOR THE PREPARATION OF ORGANIC SEMICONDUCTING MATERIALS: ORGANIC (OPTO)ELECTRONICS GROWING “GREEN”." Doctoral thesis, Università degli Studi di Milano-Bicocca, 2021. http://hdl.handle.net/10281/312085.
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The worldwide demand for energy-efficient and high-performing (opto)electronics, along with the increasing need for economically feasible and environmentally friendly chemistry, both require semiconducting materials that are both scalable and sustainable. The concern with waste generation and toxic/hazardous chemicals usage has already moulded many operations in chemical and manufacturing industries. To date, common syntheses to access organic semiconductors require the use of large quantities of toxic and/or flammable organic solvents, often involving reagents and by-products that are harmful to health and environment. Research in the field of organic electronics is now increasingly focusing on the development of new sustainable methodologies that allow to prepare active materials in a more efficiently way, caring further on safety and sustainability associated with production processes. The immediate approach applicable consist on the removal, or at least on the minimization, of harmful and toxic substances commonly employed within standard processes. The big elephant in the room in the synthesis of active materials is the amount of organic solvent employed, which could ideally be reduced by using aqueous solution of surfactants: in these nano/micro heterogeneous environments organic transformations can happen and often with unprecedent efficiency. Clearly, the process occur not through the dissolution of the reagents (starting materials and catalyst) but from their dispersion in water. Kwon as “micellar catalysis”, this strategy has proven to be highly effective on improving sustainability becoming a prominent topic in modern organic synthesis. In particular, the micellar catalysis strategy is compatible with the most common modern strategies employed for C-C and C-heteroatom bonds forming reactions and allow to perform reactions with high yields, in water and under very mild conditions. Nonetheless, the use of such method in the field of organic semiconductors is still limited, with only few relevant examples reported in literature concerning the preparation of π-conjugated molecular and polymeric materials.
This Thesis describes the importance of introducing sustainability in the synthesis of organic semiconductors, satisfying several principles of the green chemistry guidance. Our research purpose is not to provide an exhaustive list of examples of such chemistry, but rather to identify a few key developments in the field that seem especially suited to large-scale synthesis. Then, the discussion will consider the synthetic approaches typically employed to access semiconducting materials with extended π-conjugated structures. In particular, the discussion will involve the well-known Pd-catalysed cross-coupling techniques. Finally, the topic of the work will focus on micro-heterogeneous environments as a new tool for introducing sustainability in the preparation of active materials in water, satisfying several criteria relevant to green chemistry. On my opinion, the micellar catalysis approach constitute today the more promising method to lower the overall cost and environmental impact in the production of organic semiconductors without affecting yields, purity, and device performance.The worldwide demand for energy-efficient and high-performing (opto)electronics, along with the increasing need for economically feasible and environmentally friendly chemistry, both require semiconducting materials that are both scalable and sustainable. The concern with waste generation and toxic/hazardous chemicals usage has already moulded many operations in chemical and manufacturing industries. To date, common syntheses to access organic semiconductors require the use of large quantities of toxic and/or flammable organic solvents, often involving reagents and by-products that are harmful to health and environment. Research in the field of organic electronics is now increasingly focusing on the development of new sustainable methodologies that allow to prepare active materials in a more efficiently way, caring further on safety and sustainability associated with production processes. The immediate approach applicable consist on the removal, or at least on the minimization, of harmful and toxic substances commonly employed within standard processes. The big elephant in the room in the synthesis of active materials is the amount of organic solvent employed, which could ideally be reduced by using aqueous solution of surfactants: in these nano/micro heterogeneous environments organic transformations can happen and often with unprecedent efficiency. Clearly, the process occur not through the dissolution of the reagents (starting materials and catalyst) but from their dispersion in water. Kwon as “micellar catalysis”, this strategy has proven to be highly effective on improving sustainability becoming a prominent topic in modern organic synthesis. In particular, the micellar catalysis strategy is compatible with the most common modern strategies employed for C-C and C-heteroatom bonds forming reactions and allow to perform reactions with high yields, in water and under very mild conditions. Nonetheless, the use of such method in the field of organic semiconductors is still limited, with only few relevant examples reported in literature concerning the preparation of π-conjugated molecular and polymeric materials. This Thesis describes the importance of introducing sustainability in the synthesis of organic semiconductors, satisfying several principles of the green chemistry guidance. Our research purpose is not to provide an exhaustive list of examples of such chemistry, but rather to identify a few key developments in the field that seem especially suited to large-scale synthesis. Then, the discussion will consider the synthetic approaches typically employed to access semiconducting materials with extended π-conjugated structures. In particular, the discussion will involve the well-known Pd-catalysed cross-coupling techniques. Finally, the topic of the work will focus on micro-heterogeneous environments as a new tool for introducing sustainability in the preparation of active materials in water, satisfying several criteria relevant to green chemistry. On my opinion, the micellar catalysis approach constitute today the more promising method to lower the overall cost and environmental impact in the production of organic semiconductors without affecting yields, purity, and device performance.
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Fix, Aaron. "Synthesis and Properties of Indenofluorene and Diindenothiophene Derivatives for Use as Semiconducting Materials in Organic Electronic Devices." Thesis, University of Oregon, 2013. http://hdl.handle.net/1794/13444.
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Organic electronic devices are becoming commonplace in many academic and industrial materials laboratories, and commercial application of these technologies is underway. To maximize our fundamental understanding of organic electronics, a wide array of molecular frameworks is necessary, as it allows for a variety of optical and electronic properties to be systematically investigated. With the ability to further tune each individual scaffold via derivatization, access to a broad spectrum of interesting materials is possible. Of particular interest in the search for organic semiconducting materials are the cyclopenta-fused polyaromatic hydrocarbons, including those based on the fully conjugated indenofluorene (IF) system, which is comprised of five structural isomers. This dissertation represents my recent contributions to this area of research.
Chapter I serves as a historical perspective on early indenofluorene research and a review of more current research on their synthesis and applications in organic electronic devices. Chapters II and III cover our early work developing the synthesis of the fully-reduced indeno[1,2-b]fluorene scaffold, with the latter of these chapters showing the first example of its application in an organic electronic device, a field effect transistor. Chapter IV demonstrates the first syntheses of fully-reduced indeno[2,1-c]fluorene derivatives. Chapter V expands our research to encompass isoelectronic heteroatomic derivatives of that same scaffold, introducing the fully-reduced diindeno[2,1-b:1',2'-d]thiophene scaffold and showing that our synthetic methodology also can be used to produce a quinoidal thiophene core. Chapter VI concludes with a review of the similarities between the indeno[2,1-c]fluorene and diindeno[2,1-b:1',2'-d]thiophene molecular architectures and introduces benzo[a]indeno[2,1-b]fluorene derivatives, demonstrating the first example of a fully-reduced indenofluorene that possesses a non-quinoidal core, illustrating that the quinoidal core is not a prerequisite for the strong electron affinities seen across the families of fully-reduced indenofluorenes.
This dissertation encompasses previously published and unpublished co-authored material.2015-10-10
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Burwood, Ryan Paul. "Towards semiconducting hybrid framework materials." Thesis, University of Cambridge, 2013. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.648156.
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Zhang, Yu. "Fabrication, structural and spectroscopic studies of wide bandgap semiconducting nanoparticles of ZnO for application as white light emitting diodes." Thesis, Lyon, 2020. http://www.theses.fr/2020LYSEI046.
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La présente thèse étudie les nanoparticules de ZnO incorporées dans une matrice d'acide polyacrylique (PAA) mésosphérique synthétisée via un protocole d'hydrolyse. La structure hybride mésosphérique de ZnO / PAA a précédemment démontré son efficacité pour émettre de la lumière visible dans une large gamme, qui résulte des défauts intrinsèques de niveaux profonds dans les nanocristaux de ZnO. Pour modifier davantage le spectre de photoluminescence (PL) et améliorer le rendement quantique de PL (PL QY) du matériau, le ZnO dopé au métal et le ZnO / PAA revêtu de silice sont fabriqués indépendamment. Au niveau du ZnO dopé avec des éléments métalliques, la nature, la concentration, la taille et la valence du dopant affectent la formation des mésosphères et par conséquent la PL et le PL QY. Les ions plus grands que Zn2+ avec une valence plus élevée ont tendance à induire des mésosphères plus grandes et des nanoparticules de ZnO non incorporées. Le dopage conduit généralement à l'extinction de la PL, mais le spectre PL peut toujours être ajusté dans une large plage (entre 2,46 eV et 2,17 eV) sans dégrader le PL QY en dopant avec de petits ions à une faible concentration de dopage (0,1 %). Concernant le ZnO / PAA revêtu de silice, un revêtement optimal est obtenu, qui dépend corrélativement de la quantité de TEOS et d'ammoniac dans le processus de revêtement. La quantité de TEOS n'affecte pas la structure cristalline de ZnO ou le spectre PL du matériau, mais une concentration élevée d'ammoniac peut dégrader les mésosphères de PAA et épaissir la couche de silice. Une fine couche de silice qui n'absorbe pas trop de lumière d'excitation mais recouvre complètement les mésosphères s'avère être la plus efficace, avec une amélioration drastique du PL QY d’un facteur six. En ce qui concerne l'application, les matériaux souffrent d’une dégradation thermique à des températures élevées jusqu'à 100 °C, auxquelles les diodes électroluminescentes blanches (WLEDs) fonctionnent généralement. Cependant, le ZnO / PAA revêtu de silice induit une intensité d'émission plus élevée à température ambiante pour compenser la dégradation thermiqueThe present thesis studies ZnO nanoparticles embedded in a mesospheric polyacrylic acid (PAA) matrix synthesized via a hydrolysis protocol. The mesospheric ZnO/PAA hybrid structure was previously proved efficient in emitting visible light in a broad range, which results from the deep-level intrinsic defects in ZnO nanocrystals. To further tune the photoluminescence (PL) spectrum and improve the PL quantum yield (PL QY) of the material, metal-doped ZnO and silica-coated ZnO/PAA are fabricated independently. For ZnO doped with metallic elements, the nature, concentration, size and valence of the dopant are found to affect the formation of the mesospheres and consequently the PL and PL QY. Ions larger than Zn2+ with a higher valence tend to induce larger mesospheres and unembedded ZnO nanoparticles. Doping generally leads to the quenching of PL, but the PL spectrum can still be tuned in a wide range (between 2.46 eV and 2.17 eV) without degrading the PL QY by doping small ions at a low doping concentration (0.1 %). For silica-coated ZnO/PAA, an optimal coating correlatively depends on the amount of TEOS and ammonia in the coating process. The amount of TEOS does not affect the crystal structure of ZnO or the PL spectrum of the material, but high concentration of ammonia can degrade the PAA mesospheres and thicken the silica shell. A thin layer of silica that does not absorb too much excitation light but completely covers the mesospheres proves to be the most efficient, with a drastic PL QY improvement of six times. Regarding the application, the materials suffer from thermal quenching at temperatures high up to 100°C, at which white light emitting diodes (WLEDs) generally operates. However, silica-coated ZnO/PAA induces higher emission intensity at room temperature to make up for the thermal quenching
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Yang, Changduk. "Conjugated semiconducting organic materials for electronic applications." [S.l.] : [s.n.], 2006. http://deposit.ddb.de/cgi-bin/dokserv?idn=98159641X.
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Krishnamurthy, Rajesh. "Passivation of GaAs and GaInAsP semiconducting materials." Thesis, National Library of Canada = Bibliothèque nationale du Canada, 1998. http://www.collectionscanada.ca/obj/s4/f2/dsk2/tape17/PQDD_0005/NQ31174.pdf.
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Yang, Hui. "Modelling charge transport in organic semiconducting materials." Thesis, University College London (University of London), 2018. http://discovery.ucl.ac.uk/10062018/.
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Forming the active layers of organic light-emitting diodes (OLEDs), organic photovoltaics (OPVs) and organic field-effect transistors (OFETs), Organic semiconductors (OSs) have revolutionized the microelectronics industry. Compared with commonly used inorganic semiconductors, OSs combine many desirable properties: light-weight, flexible and relatively easy to produce from renewable resources. However, a drawback of OSs compared to inorganic semiconductors is their limited conductivity of electrical charges. In this thesis, I study charge transport properties of OSs in order to aid their material and structure design and to improve device efficiency. In this work, I evaluate the performance of a systematic and sophisticated computational tool for the prediction of charge mobilities in OSs. The method is based on the assumption that the charge carrier is localized, i.e. forms a small polaron that hops from one molecule to the next. Molecular dynamics simulation and first- principle calculations are used to calculate rate constants for each polaron hopping step and kinetic Monte Carlo simulations are carried out to compute the mobility from the set of hopping rate constants. The methodology is applied to hole hopping in single crystalline benzene, rubrene, pentacene, anthracene and electron hopping in C60. To find structure - property relations linking the morphology with the bulk charge carrier mobility, the methodology is further applied in few-layer thinfilm pentacene and amorphous pentacene.
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Sucharitakul, Sukrit. "2D ELECTRONIC SYSTEMS IN LAYERED SEMICONDUCTING MATERIALS." Case Western Reserve University School of Graduate Studies / OhioLINK, 2017. http://rave.ohiolink.edu/etdc/view?acc_num=case1491497351482802.
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Root, Samuel E. "Mechanical Properties of Semiconducting Polymers." Thesis, University of California, San Diego, 2018. http://pqdtopen.proquest.com/#viewpdf?dispub=10745535.
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Mechanical softness and deformability underpin most of the advantages offered by semiconducting polymers. A detailed understanding of the mechanical properties of these materials is crucial for the design and manufacturing of robust, thin-film devices such as solar cells, displays, and sensors. The mechanical behavior of polymers is a complex function of many interrelated factors that span multiple scales, ranging from molecular structure, to microstructural morphology, and device geometry. This thesis builds a comprehensive understanding of the thermomechanical properties of polymeric semiconductors through the development and experimental-validation of computational methods for mechanical simulation. A predictive computational methodology is designed and encapsulated into open-sourced software for automating molecular dynamics simulations on modern supercomputing hardware. These simulations are used to explore the role of molecular structure/weight and processing conditions on solid-state morphology and thermomechanical behavior. Experimental characterization is employed to test these predictions—including the development of simple, new techniques for rigorously characterizing thermal transitions and fracture mechanics of thin films.
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Mullins, J. T. "Properties of Tellurium-based II-VI semiconducting materials." Thesis, Durham University, 1990. http://etheses.dur.ac.uk/6004/.
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Opto-electronic devices operating as radiation detectors in the infra-red region of the electromagnetic spectrum are currently of interest. By operating in the infra-red, particularly in the 8-12 µm wavelength range, it is possible to detect the infra-red radiation emitted by objects at ordinary temperatures and so to image in darkness. Furthermore, at such wavelengths, vision is also possible in mist, fog or smoke. Semiconducting materials which have an energy gap corresponding to the photon energy of the radiation of interest are suitable for fabricating such devices. The growth and characterisation of two such materials both formed from elements in groups IIB and VIA of the periodic table and generally refered to as II-VI compounds, forms the subject matter of this thesis. The first of these materials is the ternary compound mercury cadmium telluride ((Hg,Cd)Te). This is a well established infra-red material and was grown for this work in thin film form by Metal Organic Vapour Phase Epitaxy (MOVPE) using the Inter- diffused Multilayer Process (IMP). The resulting layers were characterised optically and electrically and were shown to be of excellent compositional uniformity, an important consideration for infra-red devices, but to contain extremely high acceptor concentrations in the as grown state. These high acceptor concentrations were attributed to mercury vacancies present due to the inherent weakness of the material. Fitting of the electrical data obtained from p-type samples using a multicarrier/multilayer transport model suggested that the mercury vacancy concentrations were also highly non-uniform. A more novel alternative to (Hg(_1)Cd)Te is the HgTe:ZnTe superlattice system. By forming a superlattice from the two constituent binary compounds, rather than alloy, quantum confinement and strain effects may, in principle, be used to tailor the optical and electronic properties to some extent independently of the composition. The resulting material may also be structurally more stable than an equivalent alloy. Here the development of a thermal MOVPE growth process for this superlattice system is described and it is shown that such superlattices may be preferable to the equivalent alloys as they are easier to grow by MOVPE. Initial structural and optical studies and theoretical calculations have confirmed the suitability of MOVPE for the growth of this superlattice system and its applicability for infra-red applications.
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Yusoff, Rashid Bin Mohd. "Magnetic field effect in organic semiconducting materials and devices." reponame:Repositório Institucional da UFPR, 2011. http://hdl.handle.net/1884/26437.
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Resumo: O presente trabalho consiste transistores híbridos orgânicos/inorgânicos transistores de base permeável usando polianilina sulfonada como um terminal de base. Quatro emissores diferentes foram utilizados neste trabalho: Alq3, Alq3/C60, C60/Alq3 e C60/Alq3/C60. Foi observada uma forte influência de heteroestruturas da base/emissor sobre as características elétricas e magnéticas do transistor. Duas camadas de injecção diferentes foram utilizadas neste trabalho: Ca e V2O5. Os transistores estudados apresentam elétrons como portadores de carga majoritário. A caracterização elétrica foi realizada através medidas de dois e três terminais. A medida de três terminais consiste em dois modos de operação distintos: base comum e emissor comum. Além disso, as características dos transistores magnéticos foram medidas sequencialmente sob duas condições: (a) sem campo magnético externo aplicado (0 mT), e (b) com campo magnético externo aplicado (100 mT). Imagnes da superfície de filmes de polianilina sulfonada sobre silício foram feitas por microscopia de força atômica e microscopia óptica, a fim de verificar a morfologia da base. As influências da espessura da base e de vazios sobre as características de transistores elétricos e magnéticos foram estudadas.
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Gardecka, A. J. "Synthesis and characterisation of niobium doped TiO2 semiconducting materials." Thesis, University College London (University of London), 2016. http://discovery.ucl.ac.uk/1528770/.
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This thesis focuses on synthesis and characterisation of niobium doped TiO2 materials as thin films, nanorods and nanopowders and their applications as windows coatings, transparent conducting oxide (TCO) materials and anodes for lithium ion batteries. The first chapter gives an introduction to the TCO materials, TiO2 characterisation, application and doping methods. It also contains a brief description of the synthesis and analysis methods, used in the thesis. The second chapter describes the niobium doped anatase form of TiO2 thin films deposited via aerosol assisted chemical vapour deposition (AACVD) on silica coated glass. The as-deposited films were blue, largely transparent in the visible region, reflective in the IR region and electrically conductive. The doping progress and phase segregation propagation were analysed using high resolution transmission electron spectroscopy (HR-TEM) and X-ray absorption spectroscopy (XAS). In the third chapter, AACVD deposition of TiO2 and niobium doped TiO2 over a fluorine doped tin oxide (FTO) substrate in order to achieve the rutile form of TiO2 by templating the lattice structure is described. Depending on the synthesis precursors and temperatures used, the obtained films consisted of one to four different parts, varying from a metallic continuous tin film, mixture of rutile TiO2, FTO and metallic tin to layered FTO- anatase TiO2 thin films. In order to increase the photocatalytic properties of the anatase thin films described in the second chapter a silver layer was sputtered prior to the AACVD deposition of both pristine and niobium doped TiO2 thin films. While the Ag:TiO2 thin films remained electrically insulating, the Ag:NbTiO2 thin film displayed electrical conductivity. For both films the rate of photo degradation of Resazurin dye was lower than that of a Pilkington ActivTM standard. The fifth chapter describes the hydrothermal synthesis method of both rutile and anatase TiO2 powders, by changing the pH of the process. The successful substitutional doping of niobium into the TiO2 lattice was obtained at temperatures as low as 180 °C. The differences in phase segregation in rutile and anatase are described. Chapter six describes the hydrothermal synthesis of the Nb:TiO2 rutile free-standing film, 10 μm thick, with rutile rods creating a stable and merged structure, that maintains flexibility and can be shaped within a two minute exposure window to the air.
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He, Wei. "Ultrafast dynamics of photoexcited carriers in semiconducting nano materials." Thesis, University of Birmingham, 2015. http://etheses.bham.ac.uk//id/eprint/6064/.
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This thesis presents a systematic study on the characterising ultrafast dynamics of photo excited carriers in hydrogenated nano crystalline silicon (nc-Si:H) and porous silicon (PS) materials using the ultrafast optical pump probe spectroscopy approaches. The work involves the ground state optical property detection and optical model simulation, ultrafast time resolved pump probe measurements and pump probe data analysis processes. Applying the novel pump probe detection methods, the study explores the carriers concentration, carriers recombination property, scattering rate and conductivity of photo excited semiconducting nano materials.
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Liu, Qian. "Rational molecular design for multi-functional organic semiconducting materials." Thesis, Queensland University of Technology, 2021. https://eprints.qut.edu.au/208254/1/Qian_Liu_Thesis.pdf.
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This thesis demonstrates a comprehensive study of multifunctional applications of low-cost solution-processable organic semiconducting materials. It presents a series of rationally designed predominantly dye based innovative soft semiconductors with their generic optoelectronic properties. The performance of these materials’ application in various devices, including transistors, solar cells, memory devices and displays, are evaluated through world class collaboration to establish the structure-property relationship. In doing so, we not only developed several high-performance materials but also found that fused ring incorporation into the conjugated backbone is an effective strategy to construct multifunctional semiconductors towards flexible and printed electronics.
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Dusastre, Vincent Jean-Marie. "Semiconducting oxide gas-sensitive resistors." Thesis, University College London (University of London), 1998. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.300516.
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Avelas, Resende Joao. "Copper-based p-type semiconducting oxides : from materials to devices." Thesis, Université Grenoble Alpes (ComUE), 2017. http://www.theses.fr/2017GREAI072/document.
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L'absence d'oxydes semi-conducteurs de type p de haute performance retarde le développement de d’électronique transparente et du photovoltaïque à base d’oxydes. Dans le groupe des composés semi-conducteurs, les oxydes à base de cuivre présentent des caractéristiques électriques, optiques et de fabrication prometteuses qui établissent cette famille de matériaux comme bien adaptés aux applications semi-conductrices de type p. Dans ce travail, nous nous concentrons sur la croissance de films minces d’une part de Cu2O dopée par des cations et d’autre part de CuCrO2, visant à améliorer leurs propriétés optiques et électriques. De plus, nous avons mis en œuvre ces films d'oxyde dans des dispositifs de jonction pn tels que des cellules solaires et des photodétecteurs UV.Dans le travail sur Cu2O, nous avons réalisé l'incorporation de magnésium jusqu'à 17% dans des films minces par dépôt chimique en phase vapeur assisté par aérosol, entraînant des changements de morphologie. La résistivité électrique a été réduite jusqu’à des valeurs de 6,6 ohm.cm, en raison de l'augmentation de la densité de porteur de-charges jusqu'à 10^18 cm-3. L'incorporation du magnésium a en outre eu un impact sur la stabilité de la phase Cu2O. En effet la transformation du Cu2O en CuO en conditions oxydantes est considérablement retardée par la présence de Mg dans les films, en raison de l'inhibition de la formation d’un type particulier de lacune de cuivre (split vacancy). L'intégration dans les jonctions pn a été réalisée avec succès en utilisant uniquement des voies de dépôt chimique en phase vapeur, en combinaison avec le ZnO de type n. Néanmoins, l'application de Cu2O dopé au Mg dans les cellules solaires présente un effet photovoltaïc très faible, loin des meilleures valeurs de l’état de l’art.Dans le travail sur CuCrO2, nous démontrons la première fabrication d'hétérostructures de nanofils en configuration cœur/coquille ZnO/CuCrO2 utilisant des techniques de dépôt chimique adaptées pour des grandes surface, à faible coût, facilement implémentées à des températures modérées et leur intégration dans des photodétecteurs UV auto-alimentés. Une coquille conforme de CuCrO2 avec la phase de delafossite et avec une uniformité élevée a été élaborée par un dépôt chimique en phase vapeur assisté par aérosol sur un réseau de nanofils ZnO alignés verticalement, obtenu par dépôt par bain chimique. Les hétérostructures ZnO/CuCrO2 coeur-coquille présentent un comportement rectificatif significatif, avec un ratio de rectification maximal de 5500 à ± 1V, ce qui est bien meilleur que les dispositifs 2D similaires rapportés dans la littérature, ainsi qu'une absorption élevée supérieure à 85% dans la région UV. Lorsqu'ils sont appliqués en tant que photodétecteurs UV auto-alimentés, les hétérojonctions optimisées présentent une réponse maximale de 187 μA / W sous une polarisation nulle à 374 nm ainsi qu'une sélectivité élevée avec un ratio de rejet entre l’UV-et le visible (374-550 nm) de 68 sous irradiance de 100 mW/cm2The lack of a successful p-type semiconductor oxides delays the future implementation of transparent electronics and oxide-based photovoltaic devices. In the group semiconducting compounds, copper-based oxides present promising electrical, optical and manufacturing features that establish this family of materials suitable for p-type semiconductor applications. In this work, we focused on the growth of cation doped Cu2O and intrinsic CuCrO2 thin films, aiming for enhancements of their optical and electrical response. Furthermore, we implemented these oxide films into pn junction devices, such as solar cells and UV photodetectors.In the work on Cu2O, we achieved the incorporation of magnesium up to 17% in thin films by aerosol-assisted chemical vapor deposition, resulting in morphology changes. Electrical resistivity was reduced down to values as low as 6.6 ohm.cm, due to the increase of charge-carrier density up to 10^18 cm-3. The incorporation of magnesium had additionally an impact on the stability of the Cu2O phase. The transformation of Cu2O into CuO under oxidizing conditions is significantly postponed by the presence of Mg in the films, due to the inhibition of copper split vacancies formation. The integration into pn junctions was successfully achieved using only chemical vapor deposition routes, in combination with n-type ZnO. Nevertheless, the application of Mg-doped Cu2O in solar cells present a meager photovoltaic performance, far from the state-of-the-art reports.In the work on CuCrO2, we demonstrate the first fabrication of ZnO/CuCrO2 core-shell nanowire heterostructures using low-cost, surface scalable, easily implemented chemical deposition techniques at moderate temperatures, and their integration into self-powered UV photodetectors. A conformal CuCrO2 shell with the delafossite phase and with high uniformity is formed by aerosol-assisted chemical vapor deposition over an array of vertically aligned ZnO nanowires grown by chemical bath deposition. The ZnO/CuCrO2 core-shell nanowire heterostructures present a significant rectifying behavior, with a maximum rectification ratio of 5500 at ±1V, which is much better than similar 2D devices, as well as a high absorption above 85% in the UV region. When applied as self-powered UV photodetectors, the optimized heterojunctions exhibit a maximum responsivity of 187 µA/W under zero bias at 374 nm as well as a high selectivity with a UV-to-visible (374-550 nm) rejection ratio of 68 under an irradiance of 100 mW/cm2
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Teng, Teng. "Semiconducting Materials Based on Donor/Acceptor Units for Optoelectronic Applications." Electronic Thesis or Diss., Sorbonne université, 2018. https://accesdistant.sorbonne-universite.fr/login?url=https://theses-intra.sorbonne-universite.fr/2018SORUS452.pdf.
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Les semi-conducteurs cristaux liquides et les matériaux à faible gap sont deux familles de matériaux intéressants pour des applications dans le domaine de l’optoélectronique. Ils peuvent être utilisés dans de nombreux dispositifs électroniques différents tels que les cellules solaires organiques (OPV), les diodes électroluminescentes organiques (OLED) et les transistors organiques à effet de champ (OFET). Dans ce travail, nous nous sommes concentrés sur la conception et la synthèse de nouveaux matériaux semi-conducteurs constitués d’architectures donneur / accepteur qui présentent soit des propriétés de photoluminescence et de transport de charge élevées, soit un gap énergétique fable pour viser des matériaux ambipolaires. Les premières séries de matériaux sont des molécules organiques cristal liquides basées sur un cœur accepteur de benzothiadiazole et des groupes donneurs de type alcoxyphényle, avant de développer des structures plus complexes de type diade et triade. Les molécules à faible gap sont quant à elles constituées d’un cœur naphtalène diimide substitué par des unités comportant le benzothiadiazole. L'objectif était d'étudier leurs propriétés photophysiques, leurs propriétés de transport de charge et de corréler ces propriétés avec les propriétés structurelles des matériaux développés. Sur la base de nos résultats, nous avons démontré que ces molécules luminescentes possèdent des propriétés cristal liquide avec des structures lamellaires ou multilamellaires constituées de couches alternées d'unités fluorescentes ? Ces matériaux possèdent également une capacité élevée à transporter des charges, ce qui indique que ces composés ont un potentiel intéressant pour des applications en optoélectronique et en particulier pour des dispositifs type OFET. D’autre part, il a été démontré que les deux molécules à faible gap possèdent des propriétés de transport de charge de type n ou de type ambipolaireLiquid crystalline semiconductors and narrow bandgap materials are two kinds of interesting materials for optoelectronic applications. They can be used in several type of organic electronic devices such as organic solar cells (OPV), Organic Light Emitting Diodes (OLED) and Organic Field Effect transistors (OFET). In this work, we focused on designing and synthesizing novel semiconducting materials based on donor/acceptor architectures which present either high photoluminescence and charge transport properties, or a narow bandgap for ambipolar charge transport. These materials are liquid crystalline molecules based on a benzothiadiazole acceptor core and alkoxyphenyl donor groups. The narrow bandgap molecules are based on a naphthalene diimide core and in this case flanked by benzothiadiazole units. The objective was to study their photophysical properties, charge transport properties, and to correlate this to the structural properties of the materials developed. Based on our results, we demostrated that these luminescent molecules possess liquid crystal properties with lamellar or multi-lamellar structures consisting of alternating layers of fluorescent units and high charge transport moieties. The charge transport properties measured of these compounds indicate that they have a potential for optoelectronic applications such as OFET devices. In addition, the two narrow bandgap molecules developed were found to exhibt n-type, and ambipolar charge transport properties
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Mattocks, Philip. "Scanning tunnelling microscopy and atomic force microscopy of semiconducting materials." Thesis, University of Manchester, 2012. https://www.research.manchester.ac.uk/portal/en/theses/scanning-tunnelling-microscopy-and-atomic-force-microscopy-of-semiconducting-materials(9bc10301-2c4d-4dfb-a374-f65ee37ae23a).html.
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Michael Faraday first documented semiconducting behaviour in 1833 whenhe observed that the resistance of silver sulphide decreased with temperature,contrary to the behaviour of normal conducting materials. Up untilthe middle of the twentieth century, semiconductors were used as photodetectors,thermisters and rectifiers. In 1947 the invention of the transistor byBardeen and Brattain lead to the integrated circuit and paved the way formodern electronics. The need to produce smaller and faster transistors hasdriven research into new semiconductors. This thesis will first introduce the physics of semiconductors, followed bya description of the experimental techniques employed; scanning tunnellingmicroscopy (STM) and atomic force microscopy (AFM). Chapter 3 is concernedwith explaining anomalous scanning tunnelling spectroscopy resultsobtained for Si(100) and GaAs(110). To this end, a one-dimensional planarmodel, in which surface states affect the charge distribution and tunnellingin the system is proposed. Graphene, a novel two-dimensional material,is introduced in Chapter 4. Scanning tunnelling microscopy measurementsof graphene suspended on a metal grid are presented in this chapter. Finally,Indium antimonide Schottky contacts are investigated using conductingatomic force microscopy in Chapter 5.
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Ferlauto, Laura. "Correlation between structural and electrical properties of organic semiconducting materials." Thesis, Strasbourg, 2015. http://www.theses.fr/2015STRAF009/document.
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Cette thèse présents plusieurs techniques de caractérisation appliqués à diverses matières organiques dans le but de démêler leur structure-propriétés relation once encapsulés comme matériaux actifs dans les dispositifs de OFET. Un soin particulier est alors dédié aux méthodes de caractérisation structurale (2D-GIXRD, XRR et XRD) à la fois de source de laboratoire classique et de rayonnement de synchrotron. Divers matériaux polymères organiques, compris de p- et n-type de petites molécules et polymères en solution ou déposés par sublimation sous vide sont étudiées. En particulier, l'étude de OFET basée sur deux fonctionnalisés isomères péryléne ne différant que par la forme des alkyle côté chaînes démontre comment la nature ramifié et asymétrique des chaînes peut conduire à une amélioration de la performance électrique avec un simple traitement thermique post-dépôt, tandis que la fabrication de dispositifs ambipolaire polymères au moyen de la technique Langmuir-Schaefer souligne l'importance de la méthode de dépôt sur l'agencement de la matière sur la surface du substrat. Une approche inhabituelle, nommé enquête structurelle in_situ et en temps réel, est aussi présenté pour évaluer les modifications structurelles dans les films minces organiques subissent un processus particulier. Plus précisément, la réponse de la structure des films minces de pentacene à l’application de VSG et VSD au OFET et des films minces dérivés de TTF à la variation d’humidité ont été étudiésThis thesis presents multiple characterization techniques applied to various organic materials with the ultimate goal of unraveling their structure-properties relationship once encapsulated as active materials in OFETs devices. Particular care is then dedicated to the structural characterization methods (2D-GIXRD, XRR and XRD) both from classical laboratory source and from synchrotron radiation. Various organic materials, comprising p- and n-type small molecules and polymers deposited from solution or by vacuum sublimation are investigated. In particular, the study on OFETs based two functionalized perylene isomers differing only in the shape of the alkyl side-chians demonstrates how the branched and asymmetric nature of the chains can lead to an improvement of the electrical performance with a simple post-deposition thermal treatment, while the fabrication of ambipolar polymeric devices by means of Langmir-Schaefer technique highligts the importance of the deposition method on the arrangement of the material on the substrate surface. A more unusual approach, named in-situ and real-time structural investigation, is also presented to evaluate structural modifications in organic thin films undergoing a particular process. Specifically, the structural responce of pentacene thin films to the application of VSG and VSD to the OFET and of TTF derivatives thin films to the variation of humidty were investigated
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FERLAUTO, Laura. "CORRELATION BETWEEN STRUCTURAL AND ELECTRICAL PROPERTIES OF ORGANIC SEMICONDUCTING MATERIALS." Doctoral thesis, Università degli studi di Ferrara, 2015. http://hdl.handle.net/11392/2389073.
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Decataldo, Francesco <1992>. "Semiconducting Polymers for Electronic Biosensors and Biological Interfaces." Doctoral thesis, Alma Mater Studiorum - Università di Bologna, 2020. http://amsdottorato.unibo.it/9344/1/PhD_Thesis_Complete_Decataldo.pdf.
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Bioeletronics aims at the direct coupling of biomolecular function units with standard electronic devices. The main limitations of this field are the material needed to interface soft living entities with hard inorganic devices. Conducting polymers enabled the bridging between these two separate worlds, owing to their biocompatibility, soft nature and the ability to be tailored according to the required application. In particular, the intrinsically conductive poly(3,4-ethylenedioxythiophene):poly(styrenesulfonic acid) (PEDOT:PSS) is one of the most promising polymers, having an excellent chemical and thermal stability, reversible doping state and high conductivity.
This thesis relies on the use of PEDOT:PSS as semiconducting material for biological interfaces and biosensors.
In detail, OECTs were demonstrated to be able to real-time monitor growth and detachment of both strong-barrier and no-barrier cells, according to the patterning of the device active area and the selected geometry. Thus, these devices were employed to assess silver nanoparticles (AgNPs) toxicity effects on cell lines, allowing further insights on citrate-coated AgNPs uptake by the cells and their toxic action, while demonstrating no cytotoxic activity of EG6OH-coated AgNPs.
Moreover, PEDOT:PSS OECTs were proved to be capable of detecting oxygen dissolved in KCl or even cell culture medium, in the oxygen partial pressure range of 0-5%.
Furthermore, PEDOT:PSS OECTs were biofunctionalized to impart specificity on the device sensing capabilities, through a biochemical functionalization strategy, electrically characterized. The resulting devices showed a proof of concept detection of a fundamental cytokine for cells undergoing osteogenic differentiation.
Finally, PEDOT:PSS thickness-controlled films were employed as biocompatible, low-impedance and soft interfaces between the animal nerve and a gold electrode. The introduction of the plasticizer polyethylene glycol (PEG) enhanced the elasticity of the polymer, while keeping good conductivity and low-impedance properties. An in-vivo, chronic recording of the renal sympathetic nerve activity in rats demonstrated the efficiency of the device.
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Hsu, Ching-Ming. "High resolution SIMS analysis using a chemical bevelling technique." Thesis, Imperial College London, 1996. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.243823.
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Flatten, Lucas Christoph. "Quantum electrodynamics of semiconducting nanomaterials in optical microcavities." Thesis, University of Oxford, 2017. http://ora.ox.ac.uk/objects/uuid:a5f4797f-ea23-49e4-bd1e-2483154508d6.
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Semiconducting nanocrystals in open-access microcavities are promising systems in which enhanced light-matter interactions lead to quantum effects such as the modulation of the spontaneous emission process and exciton-polariton formation. In this thesis I present improvements of the open cavity platform which serves to confine the electromagnetic field with mode volumes down to the λ3 regime and demonstrate results in both the weak and strong coupling regimes of cavity quantum electrodynamics with a range of different low-dimensional materials. I report cavity fabrication details allowing a peak finesse of 5 × 104 and advanced photonic structures such as coupled cavities in the open cavity geometry. By incorporating two-dimensional materials and nanoplatelets in the cavity I demonstrate the strong coupling regime of light-matter interaction with the formation of exciton-polaritons, quasi-particles composed of both photon and exciton, at room temperature. In the perturbative weak coupling regime I show pronounced modulation of the single-photon emission from CdSe/ZnS quantum dots and the two-dimensional material WSe2 and demonstrate Purcell enhancement of the spontaneous emission rate by factors of 2 at room temperature and 8 at low temperature. The findings presented in this thesis pave the way to establish open microcavities as a platform for a wide range of applications in nanophotonics and quantum information technologies.
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Schneck, Jude Robert. "Femtosecond electronic dephasing and population relaxation of some novel semiconducting materials." Thesis, Boston University, 2012. https://hdl.handle.net/2144/34692.
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Thesis (Ph.D.)--Boston UniversityPLEASE NOTE: Boston University Libraries did not receive an Authorization To Manage form for this thesis or dissertation. It is therefore not openly accessible, though it may be available by request. If you are the author or principal advisor of this work and would like to request open access for it, please contact us at open-help@bu.edu. Thank you.
The dissipation of energy by excited carriers in semiconductors is crucial to device development. In particular, the carrier relaxation mechanisms are strongly modified by the degree of disorder introduced into the lattice via the growth process. The pump probe spectroscopic technique is ideally suited to monitor the energy dissipation process and elucidate the relaxation mechanisms contributing to the carrier decay. Additionally, phase breaking interactions of optical transitions, as measured via the photon echo spectroscopic technique, provides insight into the different homogeneous relaxation mechanisms contributing to the optical resonance. When compared to high quality semiconducting materials, the fundamental homogeneous relaxation mechanisms depend strongly on the disorder inherent in the material. The photon echo technique is ideal for quantifying the strength of these interactions. Femtosecond pump-probe responses of a GaN thin film excited above and below the UV band gap were measured to determine the kinetic relaxation pathways of carriers. A number of fluence dependent decay processes were identified, including carrier-carrier scattering, exciton decay, trapping to defect states, and hole state recovery. The characteristic timescales of these mechanisms ranged from <50 fs to >600 ps. In other measurements on GaN, two-pulse photon echoes due to the strongly dipole coupled excitons were observed as a function of temperature (1 0 - 295K). A biexponential decay of the dephasing rate was found from these measurements and attributed to free and bound excitons. The dynamics of the E22 transition of (6,5) single walled carbon nanotubes was studied over a range of fluences via pump-probe spectroscopy. A fluence dependent dephasing rate was deduced from an analysis of the pump-probe signal intensity at a fixed short delay time allowing an effective cross section for exciton-exciton interactions to be determined. The relaxation kinetics of optically excited E22 excitons was revealed by pump fluence dependent fits to the observed pump-probe responses. The model includes both Auger recombination from the E11 and E22 states due to exciton-exciton annihilation and a stretched exponential decay from E11 to the valence band. E11 and E22 diffusion coefficients and the defect density were determined from this analysis.
2031-01-01
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Worch, Joshua Charles. "Well-Defined Semiconducting Materials with Stabilized Molecular Orbitals: Thiaphospholes to Polythiophenes." Research Showcase @ CMU, 2016. http://repository.cmu.edu/dissertations/1029.
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The development of organic semiconductors for device applications has been intensely pursued over the past four decades. The active layer in such devices consists of both hole transporting (p– type) semiconductors and electron transporting (n–type) semiconductors. The development of p– type materials has progressed rapidly while n–type systems are relatively underdeveloped, primarily due to stability issues. Perhaps the most salient feature of electron transport materials is a low reduction potential, resulting from the stabilization of the lowest unoccupied molecular orbital (LUMO). Thus, current research is largely focused on molecular design strategies to reduce LUMO energy levels. An extension of the π–system (i.e. conjugated polymers) normally results in a lowering of the LUMO while simultaneously raising the highest occupied molecular orbital (HOMO), reducing the ambient stability. The incorporation of π-accepting functional groups is a convenient manner through which to stabilize molecular orbitals (HOMO and LUMO) and their incorporation into conjugated polymers should lead to materials with improved stability. This thesis explains our efforts to synthesize well-defined conjugated polymers that incorporate π- accepting functional groups. Moreover, heteroatom substitution also has a profound impact on the optoelectronic properties of semiconducting materials and the insertion of main group elements into conjugated organic scaffolds is another established approach to accomplish LUMO stabilization. Specifically, phosphorus is an attractive element to incorporate into organic semiconductors because of its inimitable bonding versatility. This thesis also highlights our efforts to synthesize aromatic phosphorus heterocycles for electron transport. Chapter 1 provides a general introduction into organic semiconductors as well as efforts to manipulate the molecular orbitals of π–conjugated materials. The focus is on both small molecules and polymeric materials with specific attention paid to main group substitution and functional group incorporation and how these strategies can be applied to create n-type materials. Chapter 2 describes a series of bench-stable 2-aryl-1,3-benzothiaphospholes synthesized from 1-mercapto-2-phosphinobenzene and a variety of acid chlorides. The structure of 2-phenyl-1,3- benzothiaphosphole was established using X-ray diffraction. The electrochemical and photophysical properties of each benzothiaphosphole are reported and some of these molecules exhibit reversible 1–electron reductions due to the LUMO stabilization afforded by incorporation of P=C moiety. The reduction potentials show a defined pattern: becoming incrementally more positive as the electron deficiency of the 2-aryl substituent increases and enhances LUMO stabilization. DFT calculations corroborate the electrochemical data elucidating the more pronounced effect of electron deficient groups on reduction by showing significantly more participation of those substituents in the LUMO. Chapter 3 discusses the synthesis and functionalization of the parent 1,3-benzothiaphosphole. The phosphole could not be isolated, but the compound could be manipulated in solution to produce several new phosphorus compounds. Metallation of the 2–position using lithium diisopropylamide proceeded smoothly according to 31P NMR spectroscopy, and quenching with trimethylsilyl chloride resulted in the desired 2-(trimethylsilyl)-1,3-benzothiaphosphole. However, functional substrates for cross-coupling could not be isolated using this approach. The P=C bond of the thiaphosphole was also explored as a dienophile, owing to its low lying LUMO, in Diels- Alder reactions with isoprene, 2,3-dimethylbutadiene, 2,3-dibenzylbutadiene and cyclopentadiene. The fused ring structures were fully characterized and a solid-state molecular structure of the 2,3- dimethylbutadiene cycloadduct was obtained. Chapter 4 highlights our initial efforts to expand the functional group scope of conjugated polymers. Controlled synthesis of conjugated polymers with functional side chains is of great importance, affording well–defined optoelectronic materials possessing enhanced stability and tunability as compared to their alkyl substituted counterparts. A chain–growth Suzuki polycondensation of an ester–functionalized thiophene is described using commercially available nickel precatalysts. Model compound studies were used to identify suitable catalysts, and these experiments provided guidance for the polymerization of the ester–substituted monomer. This is the first report of nickel–catalyzed Suzuki cross-coupling for catalyst–transfer polycondensation (CTP) and to further illustrate the versatility of this method, block and alternating copolymers with 3-hexylthiophene were synthesized. This Suzuki protocol should serve as an entry point into the controlled synthesis of other electron-deficient polymers and donor-acceptor copolymers. Chapter 5 describes further application of our nickel–catalyzed Suzuki CTP protocol. Ni(dppp)Cl2 was used to polymerize an amide–functionalized polythiophene – a monomer that is structurally similar to the prominent thiophene diimide electron–acceptor. Polymer molecular weights could be modulated according to catalyst loading, thus indicating a chain–growth process. Alternating and block copolymers were also prepared with reasonable polydispersities. Cyano– functionalized dimeric and trimeric monomers were explored using the Suzuki CTP protocol, however the resultant polymers were found to be highly insoluble. Chapter 6 provides a general outlook for CTP regarding state of the art conjugated polymers. The development of new catalysts for mild cross-coupling strategies should significantly enhance the monomer scope for CTP. Next generation conjugated polymers will be synthesized by CTP protocols providing control over topology, microstructure, and composition. Specifically, sequence controlled conjugated polymers should provide a major advancement to the field of organic electronics.
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Nakamura, Tomoya. "Molecular Orientation Control of Organic Semiconducting Materials for Thin Film Electronics." Kyoto University, 2019. http://hdl.handle.net/2433/242523.
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Blanagulu, B. "Novel nanoscopic molecular materials as precursors for metal and semiconducting nanoparticles." Thesis(Ph.D.), CSIR-National Chemical Laboratory, Pune, 2016. http://dspace.ncl.res.in:8080/xmlui/handle/20.500.12252/2066.
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Ciavatti, Andrea <1986>. "Transport Properties and Novel Sensing Applications of Organic Semiconducting Crystals." Doctoral thesis, Alma Mater Studiorum - Università di Bologna, 2015. http://amsdottorato.unibo.it/6769/1/ciavatti_andrea_tesi.pdf.
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The present thesis is focused on the study of Organic Semiconducting Single Crystals (OSSCs) and crystalline thin films. In particular solution-grown OSSC, e.g. 4-hdroxycyanobenzene (4HCB) have been characterized in view of their applications as novel sensors of X-rays, gamma-rays, alpha particles radiations and chemical sensors.
In the field of ionizing radiation detection, organic semiconductors have been proposed so far mainly as indirect detectors, i.e. as scintillators or as photodiodes.
I first study the performance of 4HCB single crystals as direct X-ray detector i.e. the direct photon conversion into an electrical signal, assessing that they can operate at room temperature and in atmosphere, showing a stable and linear response with increasing dose rate.
A dedicated study of the collecting electrodes geometry, crystal thickness and interaction volume allowed us to maximize the charge collection efficiency and sensitivity, thus assessing how OSSCs perform at low operating voltages and offer a great potential in the development of novel ionizing radiation sensors.
To better understand the processes generating the observed X-ray signal, a comparative study is presented on OSSCs based on several small-molecules: 1,5-dinitronaphthalene (DNN), 1,8-naphthaleneimide (NTI), Rubrene and TIPS-pentacene.
In addition, the proof of principle of gamma-rays and alpha particles has been assessed for 4HCB single crystals.
I have also carried out an investigation of the electrical response of OSSCs exposed to vapour of volatile molecules, polar and non-polar.
The last chapter deals with rubrene, the highest performing molecular crystals for electronic applications. We present an investigation on high quality, millimeter-sized, crystalline thin films (10 – 100 nm thick) realized by exploiting organic molecular beam epitaxy on water-soluble substrates. Space-Charge-Limited Current (SCLC) and photocurrent spectroscopy measurements have been carried out. A thin film transistor was fabricated onto a Cytop® dielectric layer. The FET mobility exceeding 2 cm2/Vs, definitely assess the quality of RUB films.
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Ciavatti, Andrea <1986>. "Transport Properties and Novel Sensing Applications of Organic Semiconducting Crystals." Doctoral thesis, Alma Mater Studiorum - Università di Bologna, 2015. http://amsdottorato.unibo.it/6769/.
Full textAbstract:
The present thesis is focused on the study of Organic Semiconducting Single Crystals (OSSCs) and crystalline thin films. In particular solution-grown OSSC, e.g. 4-hdroxycyanobenzene (4HCB) have been characterized in view of their applications as novel sensors of X-rays, gamma-rays, alpha particles radiations and chemical sensors.
In the field of ionizing radiation detection, organic semiconductors have been proposed so far mainly as indirect detectors, i.e. as scintillators or as photodiodes.
I first study the performance of 4HCB single crystals as direct X-ray detector i.e. the direct photon conversion into an electrical signal, assessing that they can operate at room temperature and in atmosphere, showing a stable and linear response with increasing dose rate.
A dedicated study of the collecting electrodes geometry, crystal thickness and interaction volume allowed us to maximize the charge collection efficiency and sensitivity, thus assessing how OSSCs perform at low operating voltages and offer a great potential in the development of novel ionizing radiation sensors.
To better understand the processes generating the observed X-ray signal, a comparative study is presented on OSSCs based on several small-molecules: 1,5-dinitronaphthalene (DNN), 1,8-naphthaleneimide (NTI), Rubrene and TIPS-pentacene.
In addition, the proof of principle of gamma-rays and alpha particles has been assessed for 4HCB single crystals.
I have also carried out an investigation of the electrical response of OSSCs exposed to vapour of volatile molecules, polar and non-polar.
The last chapter deals with rubrene, the highest performing molecular crystals for electronic applications. We present an investigation on high quality, millimeter-sized, crystalline thin films (10 – 100 nm thick) realized by exploiting organic molecular beam epitaxy on water-soluble substrates. Space-Charge-Limited Current (SCLC) and photocurrent spectroscopy measurements have been carried out. A thin film transistor was fabricated onto a Cytop® dielectric layer. The FET mobility exceeding 2 cm2/Vs, definitely assess the quality of RUB films.
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Brewster, Megan Marie. "The interplay of structure and optical properties in individual semiconducting nanostructures." Thesis, Massachusetts Institute of Technology, 2011. http://hdl.handle.net/1721.1/69662.
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Thesis (Ph. D.)--Massachusetts Institute of Technology, Dept. of Materials Science and Engineering, 2011.This electronic version was submitted by the student author. The certified thesis is available in the Institute Archives and Special Collections.
Cataloged from PDF version of thesis. Vita.
Includes bibliographical references (p. 163-174).
Semiconductor nanostructures exhibit distinct properties by virtue of nano-scale dimensionality, allowing for investigations of fundamental physics and the improvement of optoelectronic devices. Nanoscale morphological variations can drastically affect overall nanostructure properties because the investigation of nanostructure assemblies convolves nanoscale fluctuations to produce an averaged result. The investigation of individual nanostructures is thus paramount to a comprehensive analysis of nanomaterials. This thesis focuses on the study of individual GaAs, AlGaAs, and ZnO nanostructures to understand the influence of morphology on properties at the nanoscale. First, the diameter-dependent exciton-phonon coupling strengths of individual GaAs and AlGaAs nanowires were investigated by resonant micro-Raman spectroscopy near their direct bandgaps. The one-dimensional nanowire architecture was found to affect exciton lifetimes through an increase in surface state population relative to volume, resulting in Fröhlich coupling strengths stronger than any previously observed. Next, ZnO nanowire growth kinetics and mechanisms were found to evolve by altering precursor concentrations. The cathodoluminescence of nanowires grown by reaction-limited kinetics were quenched at the nanowire tips, likely due to point defects associated with the high Zn supersaturation required for reaction-limited growth. Further, cathodoluminescence was quenched in the vicinity of Au nanoparticles, which were found on nanowire sidewalls due to the transition in growth mechanism, caused by excited electron transfer from the ZnO conduction band to the Au Fermi level. Finally, ZnO nanowalls were grown by significantly increasing precursor flux and diffusion lengths over that of the ZnO nanowire growth. Nanowall growth began with the Au-assisted nucleation of nanowires, whose growth kinetics was a combination of Gibbs- Thomson-limited and diffusion-limited, followed by the domination of non-assisted film growth to form nanowalls. Nanoscale morphological variations, such as thickness variations and the presence of dislocations and Au nanoparticles, were directly correlated with nanoscale variations in optical properties. These investigations prove unequivocally that nanoscale morphological variations have profound consequences on optical properties on the nanoscale. Studies of individual nano-objects are therefore prerequisite to fully understanding, and eventually employing, these promising nanostructures.
by Megan Marie Brewster.
Ph.D.
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Jones, Eric James Ph D. Massachusetts Institute of Technology. "Nanoscale quantification of stress and strain in III-V semiconducting nanostructures." Thesis, Massachusetts Institute of Technology, 2015. http://hdl.handle.net/1721.1/98578.
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Thesis: Ph. D., Massachusetts Institute of Technology, Department of Materials Science and Engineering, 2015.This electronic version was submitted by the student author. The certified thesis is available in the Institute Archives and Special Collections.
Cataloged from student-submitted PDF version of thesis.
Includes bibliographical references (pages 142-149).
III-V semiconducting nanostructures present a promising platform for the realization of advanced optoelectronic devices due to their superior intrinsic materials properties including direct band gap energies that span the visible light spectrum and high carrier mobilities. Additionally, the inherently high surface-to-volume ratio of nanostructures allows for the efficient relaxation of stress enabling the realization of defect free heterostructures between highly mismatched materials. As a result, nanostructures are being investigated as a route towards the direct integration of III-V materials on silicon substrates and as platforms for the fabrication of novel heterostructures not achievable in a thin film geometry. Due to their small size, however, many of the methods used to calculate stress and strain in 2D bulk systems are no longer valid as free surface effects allow for relaxation creating more complicated stress and strain fields. These inhomogeneous strain fields could have significant impacts on both device fabrication and operation. Therefore, it will be vital to develop techniques that can accurately predict and measure the stress and strain in individual nanostructures. In this thesis, we demonstrate how the combination of advanced transmission electron microscopy (TEM) and continuum modeling techniques can provide a quantitative understanding of the complex strain fields in nanostructures with high spatial resolutions. Using techniques such as convergent beam electron diffraction, nanobeam electron diffraction, and geometric phase analysis we quantify and map the strain fields in top-down fabricated InAlN/GaN high electron mobility transistor structures and GaAs/GaAsP core-shell nanowires grown by a particle-mediated vapor-liquid-solid mechanism. By comparing our experimental results to strain fields calculated by finite element analysis, we show that these techniques can provide quantitative strain information with spatial resolutions on the order of 1 nm. Our results highlight the importance of nanoscale characterization of strain in nanostructures and point to future opportunities for strain engineering to precisely tune the behavior and operation of these highly relevant structures.
by Eric James Jones.
Ph. D.
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Buccheri, Alexander. "Modelling the optical properties of semiconducting nanostructures." Thesis, University of Oxford, 2016. https://ora.ox.ac.uk/objects/uuid:67d66b15-c5b1-4bb1-806c-6cc22d0eb482.
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In this thesis we describe the development of a real-space implementation of the Bethe-Salpeter equation (BSE) and use it in conjunction with a semi-empirical tight-binding model to investigate the optoelectronic properties of colloidal quantum- confined nanostructures. This novel implementation exploits the limited radial extent and small size of the atomic orbital basis to treat finite systems containing up to ∼4000 atoms in a fully many-body framework. In the first part of this thesis our tight-binding model is initially benchmarked on zincblende CdSe nanocrystals, before subsequently being used to investigate the electronic states of zincblende CdSe nanoplatelets as a function of thickness. The band-edge electronic states are found to show minimal variation for a range of thicknesses and the results of our tight-binding model show good agreement with those predicted using a 14-band k·p model for a nanoplatelet of 4 monolayers (ML) in thickness. Optical absorption spectra were also computed in the independent-particle approximation. While the results of the tight-binding model show good agreement with those of the 14-band k·p model in the low-energy region of the spectrum, agreement with experiment was poor. This reflects the need for a many-body treatment of optical absorption in nanoplatelet systems. In the second part of this thesis we apply our tight-binding plus BSE model to study the excitonic properties of CdSe nanocrystals and nanoplatelets. Simulations performed on CdSe nanocrystals examined an approximation of the BSE equivalent to configuration interaction singles (CIS), and found that both the optical gap and the low-energy spectral features were unaffected by the approximation. A comparison of exciton binding energies with those predicted by CIS demonstrates the sensitivity of results to the exact treatment of dielectric screening and the decision of whether or not to screen exchange. Our model predicts optical gaps that are in strong agreement with average experimental data for all but the smallest diameters, but was not able to reproduce low-energy spectral features that were fully consistent with experiment. This was attributed to the absence of the spin-orbit interaction in the model. Simulations performed on CdSe nanoplatelets investigate the optical gaps and exciton binding energies as a function of thickness. Exciton binding energies were found to reach ∼200 meV for the thinnest system, however, optical gaps were slightly overestimated in comparison to experiment. This is attributed to the reduced lateral dimensions used in our simulations and our bulk treatment of dielectric screening. A two-dimensional treatment of dielectric screening is expected to further increase binding energies. Calculations of the excitonic absorption spectrum reproduce the characteristic spectral features observed in experiment, and show strong agreement with the spectra of nanoplatelets, with thicknesses ranging from 3 ML to 5 ML.
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Carroli, Marco. "Novel materials for direct X-ray detectors based on semiconducting organic polymers." Master's thesis, Alma Mater Studiorum - Università di Bologna, 2015. http://amslaurea.unibo.it/9345/.
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Conventional inorganic materials for x-ray radiation sensors suffer from several drawbacks, including their inability to cover large curved areas, me- chanical sti ffness, lack of tissue-equivalence and toxicity. Semiconducting organic polymers represent an alternative and have been employed as di- rect photoconversion material in organic diodes. In contrast to inorganic detector materials, polymers allow low-cost and large area fabrication by sol- vent based methods. In addition their processing is compliant with fexible low-temperature substrates. Flexible and large-area detectors are needed for dosimetry in medical radiotherapy and security applications. The objective of my thesis is to achieve optimized organic polymer diodes for fexible, di- rect x-ray detectors. To this end polymer diodes based on two different semi- conducting polymers, polyvinylcarbazole (PVK) and poly(9,9-dioctyluorene) (PFO) have been fabricated. The diodes show state-of-the-art rectifying be- haviour and hole transport mobilities comparable to reference materials. In order to improve the X-ray stopping power, high-Z nanoparticle Bi2O3 or WO3 where added to realize a polymer-nanoparticle composite with opti- mized properities. X-ray detector characterization resulted in sensitivties of up to 14 uC/Gy/cm2 for PVK when diodes were operated in reverse. Addition of nanoparticles could further improve the performance and a maximum sensitivy of 19 uC/Gy/cm2 was obtained for the PFO diodes. Compared to the pure PFO diode this corresponds to a five-fold increase and thus highlights the potentiality of nanoparticles for polymer detector design. In- terestingly the pure polymer diodes showed an order of magnitude increase in sensitivity when operated in forward regime. The increase was attributed to a different detection mechanism based on the modulation of the diodes conductivity.
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Khalil, Mahmoud. "Investigation and optimization of semiconducting chromium disilicide based materials for thermoelectric applications." Thesis, Montpellier, 2015. http://www.theses.fr/2015MONTS165.
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Depuis les années 90, dans le contexte de la pénurie annoncée d'énergies fossiles et de modifications climatiques, un regain d'intérêt s'est fait sentir pour les énergies renouvelables et, parmi elles, pour la thermoélectricité. Cette dernière permettant la conversion directe entre énergies thermique et électrique devrait permettre la récupération de l'énergie perdue sous forme de chaleur, durant les processus industriels. Cependant, à l'heure actuelle, l'efficacité de la conversion thermoélectrique, évaluée à partir du facteur de mérite, ZT, n'est pas suffisante pour des applications à grande échelle. Cependant, pour évaluer l'impact potentiel de la thermoélectricité, il est nécessaire de prendre en compte d'autres critères que celui de l'efficacité relativement faible de la thermoélectricité, qui la cantonne dans des niches spécifiques, et tels que la faible toxicité des matières premières, leur abondance, leur faible coût et leur facilité de mise en œuvre. Diverses familles de matériaux répondent à ces critères parmi lesquelles les plus favorables sont les siliciures pour les matériaux inorganiques et les polymères conducteurs pour les composés organiques. Dans ce travail de thèse, nous nous sommes intéressés au disiliciure de chrome (CrSi2) et au polymère PEDOT:PSS.Parmi les siliciures, CrSi2 est un candidat prometteur mais sa grande conductivité thermique est un handicap par rapport aux matériaux conventionnels. Elle peut cependant être réduite par nanostructuration. Nous présentons une étude CrSi2 nanostructurés (10-15 nm) obtenus soit par four à arc suivie d'un broyage mécanique, soit par mécanosynthèse. Ces poudres sont chimiquement stables jusqu'à 1073 K. A plus hautes températures, des phases secondaires apparaissent, notamment CrSi. Grâce à la technique SPS, CrSi2 a pu être densifié jusqu'à 94% en maintenant une taille nanométrique (30-45 nm) ce qui a conduit à une réduction de la conductivité thermique d'un facteur 2 par rapport au composé CrSi2 massif. Malheureusement, le facteur de mérite ZT n'a pas été amélioré en raison de l'accroissement de la résistivité électrique.Guidés par des calculs DFT, nous avons explorés de nouvelles voies de dopage pour améliorer les propriétés thermoélectriques de CrSi2. Des alliages Cr1-xTixSi2, Cr1-xZrxSi2 et Cr1-xMoxSi2 ont ainsi été synthétisés et nous avons étudié leurs propriétés thermoélectriques. A Tamb, le dopage au Ti semblerait de ne pas significativement améliorier le facteur de puissance (PF) pour une porosité de 11% par rapport à nano-CrSi2. Par contre, pour 2% Zr, PF a été amélioré d'un facteur 1.7 pour une porosité de 30%. En plus, il semblerait que le PF de Cr0.98Zr0.02Si2 avec une porosité de 0% est amélioré d'un factuer 1.9 par rapport au CrSi2 massif. Néanmoins, à hautes températures il existe encore un potentiel d'amélioration pour le dopage au Ti. Bien qu'il soit métastable, l'alliage Cr1-xZrxSi2 a pu être obtenu jusqu'à 5% Zr. Une optimisation supplémentaire est encore nécessaire pour les alliages dopés au Ti et Zr. L'alliage Cr1-xMoxSi2 est le plus prometteur avec une amélioration significative du facteur de Mérite (ZTmax > 0.2) pour 10% et 20% de Mo entre 500 et 700 K. Ces valeurs sont supérieures à celle du massif bien que toujours du même ordre de grandeur que le meilleur ZT obtenu pour CrSi2.Enfin, nous avons élaboré des composites à base de CrSi2 associé à du Polypyrrole (PPy) ou du PEDOT:PSS. Aucune amélioration significative n'a été obtenue pour le composite PPy-CrSi2. Dans le cas du PEDOT:PSS, nous avons testé la fonctionnalisation de CrSi2 pour améliorer sa dispersion dans le polymère. Nous avons montré qu'un agent de fonctionnalisation avec un groupement phosphonique réagissant avec Cr est le plus efficace. Cette étape est très prometteuse car il s'agit de la première étude de ce type effectuée dans le cas de l'élaboration de composites à base de siliciures intermétalliques pour des applications thermoélectriquesIn the context of renewable energies, which is related to the shortage of fossil energies and climate change, thermoelectricity has regained interest in recent years (1990s). The concept of this technology is the direct conversion between thermal and electrical energies. This can contribute to a progress in the industrial sector. However, the efficiency of the thermoelectric materials, denoted ZT (figure of merit), is not sufficient for large scale applications. Nevertheless, thermoelectricity can be found in the niche market sector where other criteria are taken into account such as the abundance of the raw elements, their price and toxicity. Several families meet these criteria with the silicides as inorganics materials and conductive polymers as organics materials being the most favorable. The objective of this dissertation was to investigate the chromium disilicide (CrSi2) and PEDOT:PSS.Among the silicides, CrSi2 stands as a promising candidate for thermoelectric applications. However, its relatively high thermal conductivity compared to the conventional materials is considered as a drawback. Therefore, we were interested in nanostructuration in order to reduce this thermal conductivity. Nanostructured CrSi2 is synthesized by arc melting followed by mechanical milling or mechanical alloying with a grain size of 10-15 nm. These powders have a good chemical stability up to 1073 K. Above this temperature, secondary phases, such as CrSi, are formed. SPS processing permits to efficiently densify our pellets up to 94% while maintaining nanometric grain size (30-45 nm). This leads to a reduction of the thermal conductivity by a factor of 2 compared to bulk CrSi2. However, the Figure of merit (ZT) does not improve as the electrical resistivity increases.DFT calculations predict that some doping elements have potentiality to improve CrSi2 electronic structure. Therefore, Cr1-xTixSi2, Cr1-xZrxSi2 et Cr1-xMoxSi2 alloys are synthesized in order to enhance the thermoelectric properties of CrSi2. At RT, The power factor of Cr0.9Ti0.1Si2 seems not to be improved compared to nano-CrSi2 for a porosity of 11%. On the other hand, 2% Zr doping improved the power factor by 1.7 at RT for a porosity of 30%. It also seems that for 0% porosity, the power factor of Cr0.98Zr0.02Si2 is improved by a factor 1.9 compared to bulk CrSi2. Nevertheless, an improvement could be predicted at high temperatures for Cr0.9Ti0.1Si2. Although Cr1-xZrxSi2 alloy is metastable, we were able to synthesize it by mechanical alloying up to 5%. Further optimization is needed for improving the thermoelectric performances of Ti and Zr- doped CrSi2 . On the other hand, Cr1-xMoxSi2 alloys seem to be the most promising as an increase of the Figure of merit is observed with a ZTmax reaching values larger than 0.2 for Cr0.9Mo0.1Si2 and Cr0.8Mo0.2Si2 in the temperature range of 500-700 K. These values are higher compared to the bulk but still in the same order of magnitude as for the highest ZT value report for CrSi2.We then elaborated CrSi2 based composites with Polypyrrole (PPy) and PEDOT :PSS. No significant enhancement was observed for PPy-CrSi2 composites. In order to improve the dispersion of CrSi2 in the PEDOT :PSS, we have tested the functionnalization. Preliminary tests show that grafting agents with phosphonic acid group is the most efficient by reacting with Cr. This step is very promising as no study till date reported the functionnalization approach for the elaboration of silicides based composites, especially for thermoelectric applications
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Fratelli, Ilaria <1992>. "Novel Semiconducting Materials and Thin Film Technologies for High Energy Radiation Detection." Doctoral thesis, Alma Mater Studiorum - Università di Bologna, 2021. http://amsdottorato.unibo.it/9560/1/tesi_ilariaFratelli.pdf.
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Nowadays the development of real-time ionizing radiation detection system operating over large areas is crucial. Increasing quest for flexible, portable, low cost and low power consumption sensors pushed the scientific community to look for alternative materials and technologies able to fulfill these new requirements. In this thesis the potentiality of organic semiconductors and metal oxides as material platforms for novel ionizing radiation sensors is demonstrated. In particular, organic semiconductors are human tissue-equivalent and this represents a unique and desirable property for the development of dosimeters to be employed in the medical field. The ionizing radiation sensors described in this thesis have been designed, fabricated and characterized during my PhD research and are realized onto polymeric foils leading to flexible devices operating at low voltages, in ambient condition and able to directly detect X-rays, gamma-rays and protons. Following the study of the properties and of the mechanisms of interaction between the radiation and the active layers of the sensors, several strategies have been adopted to enhance the efficiency of these detectors. X-rays dosimeters based on organic semiconductors have been realized presenting record sensitivity values compared with the state of the art for large area radiation detection. The unprecedentedly reported performance led to the possibility to testing these devices in actual medical environments. Moreover, the proof-of-principle demonstration of a dosimetric detection of proton beams by organic-based sensors is reported. Finally, a new sensing platform based on metal oxides is introduced. Combining the advantages of amorphous high mobility oxide semiconductors with a multilayer dielectric, novel devices have been designed, capable of providing a sensitivity one order of magnitude higher than the one shown by the standard RADFETs. Thanks to their unique properties, these sensors have been integrated with a wireless readout system based on a commercial RFID tag and its assessment is presented.
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SIBILIA, MIRTA. "Organic semiconducting single crystal growth on naostructured matrices." Doctoral thesis, Università degli Studi di Trieste, 2017. http://hdl.handle.net/11368/2908140.
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In recent years, the development of the organic electronics has led to the employment of organic materials as the basis for many electronic devices, such as organic light emitting diodes, organic field effect transistors, organic solar cells and radiation sensors. As regards radiation sensors, the studies reported in literature mainly refer to devices based on thin film organic semiconductors, which, however, present problems due to instability, degradation and low reproducibility. Organic single crystals overcame most of the major limitations inherent to thin film-based detectors.
In this experimental work, a starting plethora of commercially available compounds has been crystallized and evaluated in terms of both overall crystallizability and applicability as direct X-ray detectors. This first step of work allow to select only those structures capable to provide single-crystals with good morphological properties and electronic properties suitable for X-ray detections.
A careful screening of some thermodynamic variables affecting the growth has been carried out and the obtained results suggest applicability of the present approach to achieve the control of size, quality and crystal habit. Indeed, single crystals with dimensional and morphological properties suitable to the application as X-ray detector have been prepared.
Single-crystals have been physically attached to Au electrodes deposited on a thin film of polyethylennaphthalate – via the functionalization of the electrode with different self-assembled monolayers (SAMs), chemically and structurally similar to the molecule constituting the selected crystal. In particular, two of the explored SAMs showed very promising results in the first qualitative adhesion tests.
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Golea, Mostefa. "AB(2)C(4) semiconducting compounds crystal growth, intrinsic defects and optical properties." Thesis, University of Ottawa (Canada), 1988. http://hdl.handle.net/10393/5374.
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Sirota, Benjamin. "Investigation into the Semiconducting and Device Properties of MoTe2 and MoS2 Ultra-Thin 2D Materials." Thesis, University of North Texas, 2018. https://digital.library.unt.edu/ark:/67531/metadc1157626/.
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The push for electronic devices on smaller and smaller scales has driven research in the direction of transition metal dichalcogenides (TMD) as new ultra-thin semiconducting materials. These ‘two-dimensional' (2D) materials are typically on the order of a few nanometers in thickness with a minimum all the way down to monolayer. These materials have several layer-dependent properties such as a transition to direct band gap at single-layer. In addition, their lack of dangling bonding and remarkable response to electric fields makes them promising candidates for future electronic devices. For the purposes of this work, two 2D TMDs were studied, MoS2 and MoTe2. This dissertation comprises of three sections, which report on exploration of charge lifetimes, investigation environmental stability at elevated temperatures in air, and establishing feasibility of UV laser annealing for large area processing of 2D TMDs, providing a necessary knowledge needed for practical use of these 2D TMDs in optoelectronic and electronic devices.
(1) A study investigating the layer-dependence on the lifetime of photo-generated electrons in exfoliated 2D MoTe2 was performed. The photo-generated lifetimes of excited electrons were found to be strongly surface dependent, implying recombination events are dominated by Shockley-Read-Hall effects (SRH). Given this, the measured lifetime was shown to increase with the thickness of exfoliated MoTe¬2; in agreement with SRH recombination. Lifetimes were also measured with an applied potential bias and demonstrated to exhibit a unique voltage dependence. Shockley-Read-Hall recombination effects, driven by surface states were attributed to this result. The applied electric field was also shown to control the surface recombination velocity, which lead to an unexpected rise and fall of measured lifetimes as the potential bias was increased from 0 to 0.5 volts.
(2) An investigation into the environmental stability of exfoliated 2D MoTe2 was conducted using a passivation layer of amorphous boron nitride as a capping layer for back-gated MoTe2 field effect transistor (FET) devices. A systematic approach was taken to understand the effects of heat treatment in air on the performance of FET devices. Atmospheric oxygen was shown to negatively affect uncoated MoTe2 devices while BN-covered FETs showed remarkable chemical and electronic characteristic stability. Uncapped MoTe2 FET devices, which were heated in air for one minute, showed a polarity switch from n- to p-type at 150 °C, while BN-MoTe2 devices switched only after 200 °C of heat treatment. Time-dependent experiments at 100 °C showed that uncapped MoTe2 samples exhibited the polarity switch after 15 min of heat treatment while the BN-capped device maintained its n-type conductivity. X-ray photoelectron spectroscopy (XPS) analysis suggests that oxygen incorporation into MoTe2 was the primary doping mechanism for the polarity switch.
(3) The feasibility of UV laser annealing as a post-process technique to sinter 2D crystal structures from sputtered amorphous MoS2 was explored. Highly crystalline materials are sought after for their use in electron and opto-electronic devices. Sputtered MoS2 has the advantage of potential for large area deposition and high scalability, however, it requires high temperatures (>350 °C) for their crystalline growth. Which creates difficulty for devices grown on polymer substrates. Low-temperature and room temperature deposition results in amorphous films which is detrimental for electric devices. A one-step lase annealing procedure was developed to provide amorphous to crystalline conversion of nanometer thin MoS2 films. Samples were annealed using an unfocused laser beam from a KrF (248 nm) excimer source. The power density was found to be 1.04 mJ/mm2. Raman analysis of laser annealed MoS2 was shown to exhibit a significant improvement of the 2D MoS2 crystallinity compared to as-deposited films on both SiO2/Si, as well as polydimethylsiloxane (PDMS) substrates. Annealed samples showed improvement of their conductivity on an order of magnitude. A top-gated FET device was fabricated on flexible PDMS substrates using Al2O3 as a gate oxide. Measured field effect mobility of annealed samples showed significant improvement over as-deposited devices.
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Villalpando, Páez Federico. "Raman spectroscopy of double walled carbon nanotubes with different metallic and semiconducting configurations." Thesis, Massachusetts Institute of Technology, 2010. http://hdl.handle.net/1721.1/59238.
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Thesis (Ph. D.)--Massachusetts Institute of Technology, Dept. of Materials Science and Engineering, 2010.Includes bibliographical references (p. 117-125).
A double-walled carbon nanotube (DWNT) provides the simplest system to study the interaction between concentric tubes in carbon nanotubes. The inner and outer walls of a DWNT can be metallic (M) or semiconducting (S), and each of the four possible configurations (MUM, M©S, SUS, S©M) has different electronic properties. We analyze the Raman spectra from undoped and boron-doped chemical vapor deposition-derived DWNT bundles (CVD-DWNTs) that exhibit the "coalescence inducing mode" (CIM) as they are heat treated at temperatures between 12000C and 2000'C. We then report, for the first time, detailed Raman spectroscopy experiments carried out on individual DWNTs, where both concentric tubes of the same DWNT are measured under resonance conditions. A technique is developed that combines tunable Raman spectroscopy with Raman mapping procedures and electron beam lithography to enable the acquisition of Raman spectra from the individual constituents of the same isolated DWNT. By using the technique mentioned above, we measure resonant Raman scattering from 11 individual C60-derived double wall carbon nanotubes all having inner semiconducting (6,5) tubes and various outer metallic tubes. We report that in an individual DWNT an increase in the RBM frequency of the inner tube is related to an increase in the RBM frequency of the outer tube due to a decrease in the wall to wall distance. Finally, we use 40 laser excitation energies to analyze the differences in the Raman spectra from chemical vapor deposition-derived DWNT bundles (CVD-DWNTs), fullerene-derived DWNT bundles (C₆₀-DWNTs) and individual fullerene-derived DWNTs with inner type I and type II semiconducting tubes paired with outer metallic tubes.
by Federico Villalpando Páez.
Ph.D.
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Lu, Chih-Yuan. "Group III-selenides : new silicon compatible semiconducting materials for phase change memory applications /." Thesis, Connect to this title online; UW restricted, 2007. http://hdl.handle.net/1773/10610.
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Bhandari, Srijana. "AN ELECTRONIC STRUCTURE APPROACH TO UNDERSTAND CHARGE TRANSFERAND TRANSPORT IN ORGANIC SEMICONDUCTING MATERIALS." Kent State University / OhioLINK, 2020. http://rave.ohiolink.edu/etdc/view?acc_num=kent1606836665551399.
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Ma, Yingqiao. "A Two-dimensional Semiconducting GaN-based Ferromagnetic Monolayer." Ohio University / OhioLINK, 2018. http://rave.ohiolink.edu/etdc/view?acc_num=ohiou1541513207541646.
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Andy, Andre Sarker. "Design, analysis, and applications of optically-activated antennas and dielectric lenses using photosensitive semiconducting materials." Thesis, Queen Mary, University of London, 2018. http://qmro.qmul.ac.uk/xmlui/handle/123456789/41784.
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The primary objective of the research is to investigate photosensitive semiconducting materials, mainly organic, and utilise them in antenna front-end systems and dynamic lenses for sub-THz applications. Mechanisms such as phase-shifting and photo-conductive switching are introduced in EM-devices to alter the antenna performance and behaviour. Using such mechanisms the devices are able to attain frequency, radiation pattern and polarisation reconfigurability. The common inorganic semiconductor, Si, and organic semiconductors such as poly 3-hexylthiophene (P3HT), [6,6]-Phenyl C61 butyric acid methyl ester (PCBM) have been extensively studied and used in the exemplar EM-devices developed for this thesis. In this research, novelty is deployed with the use of photosensitive semiconductors as a means of 'tuning' dielectrics to control the propagation of the emerging beam-field of an antenna. Both organic and inorganic photosensitive semiconductors have been implemented in this work. The research begins by exploring the physical properties of such photosensitive semiconductors at microwave frequencies. Medium-resistivity Si was characterised using a conventional microstrip transmission line and the conductivity of the Si piece in dark and active states were estimated by matching its transmission characteristics with the modelled Si in CST Studio Suite. Thereafter the modelled Si was used in an antenna design to estimate the reconfigurability of the device. However, inorganic semiconductors are being replaced with organic semiconductors because of their inflexibility in device fabrication. Organic polymers, on the other hand, are light in weight, can be cast onto any surface, when blended with an organic solvent, and also photo-excited using white light. Organic polymer heterojunction 95% P3HT: 5% PCBM was characterised and changes in the real and imaginary parts of the complex dielectric constant of the organic blend are measured in the range of -0.05 to -0.55 and +0.01 to +0.52 respectively, over the sub-THz frequency-domain. In order to demonstrate EM-control of a wave using a photo-sensitive material, a two-element patch antenna array using organic polymer P3HT-PCBM is fabricated and the functionality for antenna beam steering examined. Non-optimum illumination of the organic layer on the antenna patches, led to an asymmetric and perturbed beam steer. Hence, a novel optically triggered antenna has been proposed at S-Band (2 - 4 GHz), where sodalime glass is being used as lower substrate, ITO (Indium Tin Oxide), transparent to white-light, as the ground plane and transmission lines along with patches are modelled onto the upper substrate layer (P3HT:PCBM). The estimates of the dielectric changes in the organic polymer blend due to optical excitation were used as inputs in the modelled device to show the proof-of-concept for beam steering with such a phase-shifting device. In addition, the antenna design also demonstrated that with a small change in the real part of the permittivity of the substrate it is possible to generate a maximum beam steer of 5°, using an effective phase-shifting design in CST Studio Suite. At millimetre-wave or sub-terahertz frequencies, small changes in the dielectric with excitation-region depth comparable to the wavelength are plenty to manipulate the emerging wave of an antenna or lens. Hence, an optically-activated dynamic lens is proposed and designed to dynamically control millimetre-wave transmission using optical illumination. The lens acts as a graduated gateway for phase transmission by adjusting the spatial permittivity across the lens. A nearfield measurement system is used to analyse the performance of the lens over the WR-10 (75 - 110 GHz) waveband. The phase distribution of the electric field across the face of the plane organic lens shows a similar pattern in the spatial phase-distribution of the lens plane in the active state as that projected by the illuminating source, allowing for projection-angle-induced cosine errors. Hence the dynamic operation of the lens can be beneficial for beam controlling applications in imaging, surveillance and remote sensing in the mm-wave frequency-domain.
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Martinez-Morales, Alfredo Adolfo. "Synthesis, characterization and applications of novel nanomaterial systems and semiconducting nanowires." Diss., [Riverside, Calif.] : University of California, Riverside, 2010. http://proquest.umi.com/pqdweb?index=0&did=2019838541&SrchMode=2&sid=2&Fmt=2&VInst=PROD&VType=PQD&RQT=309&VName=PQD&TS=1273864032&clientId=48051.
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Thesis (Ph. D.)--University of California, Riverside, 2010.Includes abstract. Available via ProQuest Digital Dissertations. Title from first page of PDF file (viewed May 14, 2010). Includes bibliographical references. Also issued in print.
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Huang, Lanqi. "Synthesis and characterization of benzodithiophene- and quinoxalinedithienothiophene-based semiconducting materials for organic solar cells." HKBU Institutional Repository, 2019. https://repository.hkbu.edu.hk/etd_oa/608.
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Organic semiconducting materials have been attracted considerable attention as a promising technology for the next generation flexible electronic devices, such as solar cells and field-effect transistors because of their advantages of low-cost, structural versatility and flexibility. Many organic semiconducting materials have been developed in recent years. In this thesis, four pi-conjugated building blocks based on benzodithiophene and quinoxalinedithienothiophene were applied to develop novel photovoltaic materials, including donor-acceptor alternating copolymers as a donor material for polymer solar cells, photosensitizers for dye sensitized solar cells, small molecule hole transporting materials for perovskite solar cells and small molecule acceptors for organic solar cells. A comprehensive review of current development of organic photovoltaic materials was presented in Chapter 1. In Chapter 2, a series of D-A copolymers (PBB-n) based on 4,7-di(thiophen-2-yl)benzo[c][1,2,5]thiadiazole and 4,5-bis((2-ethylhexyl)oxy)benzo[2,1-b:3,4-b'] dithiophene attached with different solubilizing side-chains were designed, synthesised and characterized. In general, PBB-n polymers showed good absorption in the region of visible light and UV region, indicating such polymers are a promising light harvester. Also, PBB-n exhibited suitable energy levels, suggesting that they could be applied as the donor materials in polymer solar cells. PBB-n also exhibited various extent of aggregation behaviour. Chapter 3 described syntheses and the fluorination effect of two series of fluoro-substituted PBB-n copolymers, namely PfBB-n and PffBB-n on optical, electrochemical, and optoelectronic properties. Among them, PfBB-n series was characterized with photovoltaic performance. The champion devices fabricated from PfBB-12 showed a PCE as high as 9.7%, with a Voc of 0.92 V, a Jsc of 16.60 mA/cm-2 and a FF of 63.49%. Cells fabricated from other PfBB-n copolymers also exhibited good PV performance with PCE ranging from 7.4 - 8.5%. For PffBB-n polymers, temperature-dependent aggregation behaviour was exploited by modulating the coating temperature during device fabrication. PSC devices based on PffBB-n exhibited good PV performance with PCE ranging from 7.4% to 9.9%. Among which, PffBB-14 provided the most promising PV performance with PCE of 9.9%, a Voc of 0.92 V, a Jsc of 16.8 mA/cm-2 and a FF of 64.36%. Electron deficient conjugated structure was seldom used as the π-bridge in metal-free photosensitizers. In Chapter 4, four novel organic photosensitizers, namely QC5-m and PC5-n were designed with an electron deficient π-bridge. Typical sandwich-structured DSSCs based on the newly developed photosensitizers exhibited promising photovoltaic performance with PCE ranging from 5.23 - 7.77 %, with a maximum Jsc as high as 15.63 mA cm-2. These results suggest that the use of electron deficient π-bridge provides alternative approach to construct efficient organic photosensitizers. Chapter 5 and Chapter 6 described the design, synthesis and investigation of novel hole-transporting materials and electron acceptor materials based on benzo[2,1-b:3,4-b']dithiophene-4,5-dione derived building blocks as potential organic photovoltaic materials for solar cell applications. Keywords: organic photovoltaic materials, photosensitizers, polymer solar cell, electron acceptor, hole-transporting materials.
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Miller, Derek. "Advancing electronic structure characterization of semiconducting oxide nano-heterostructures for gas sensing." The Ohio State University, 2017. http://rave.ohiolink.edu/etdc/view?acc_num=osu1492639729205609.
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Dey, Prasenjit. "Exciton Dynamics and Many Body Interactions in Layered Semiconducting Materials Revealed with Non-linear Coherent Spectroscopy." Thesis, University of South Florida, 2016. http://pqdtopen.proquest.com/#viewpdf?dispub=10076073.
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Atomically thin, semiconducting transition metal dichalogenides (TMDs), a special class of layered semiconductors, that can be shaped as a perfect two dimensional material, have garnered a lot of attention owing to their fascinating electronic properties which are achievable at the extreme nanoscale. In contrast to graphene, the most celebrated two-dimensional (2D) material thus far; TMDs exhibit a direct band gap in the monolayer regime. The presence of a non-zero bandgap along with the broken inversion symmetry in the monolayer limit brands semiconducting TMDs as the perfect candidate for future optoelectronic and valleytronics-based device application. These remarkable discoveries demand exploration of different materials that possess similar properties alike TMDs. Recently, III-VI layered semiconducting materials (example: InSe, GaSe etc.) have also emerged as potential materials for optical device based applications as, similar to TMDs, they can be shaped into a perfect two-dimensional form as well as possess a sizable band gap in their nano-regime. The perfect 2D character in layered materials cause enhancement of strong Coulomb interaction. As a result, excitons, a coulomb bound quasiparticle made of electron-hole pair, dominate the optical properties near the bandgap. The basis of development for future optoelectronic-based devices requires accurate characterization of the essential properties of excitons. Two fundamental parameters that characterize the quantum dynamics of excitons are: a) the dephasing rate, γ, which represents the coherence loss due to the interaction of the excitons with their environment (for example- phonons, impurities, other excitons, etc.) and b) excited state population decay rate arising from radiative and non-radiative relaxation processes. The dephasing rate is representative of the time scale over which excitons can be coherently manipulated, therefore accurately probing the source of exciton decoherence is crucial for understanding the basic unexplored science as well as creating technological developments. The dephasing dynamics in semiconductors typically occur in the picosecond to femtosecond timescale, thus the use of ultrafast laser spectroscopy is a potential route to probe such excitonic responses.
The focus of this dissertation is two-fold: firstly, to develop the necessary instrumentation to accurately probe the aforementioned parameters and secondly, to explore the quantum dynamics and the underlying many-body interactions in different layered semiconducting materials. A custom-built multidimensional optical non-linear spectrometer was developed in order to perform two-dimensional spectroscopic (2DFT) measurements. The advantages of this technique are multifaceted compared to regular one-dimensional and non-linear incoherent techniques. 2DFT technique is based on an enhanced version of Four wave mixing experiments. This powerful tool is capable of identifying the resonant coupling, probing the coherent pathways, unambiguously extracting the homogeneous linewidth in the presence of inhomogeneity and decomposing a complex spectra into real and imaginary parts. It is not possible to uncover such crucial features by employing one dimensional non-linear technique.
Monolayers as well as bulk TMDs and group III-VI bulk layered materials are explored in this dissertation. The exciton quantum dynamics is explored with three pulse four-wave mixing whereas the phase sensitive measurements are obtained by employing two-dimensional Fourier transform spectroscopy. Temperature and excitation density dependent 2DFT experiments unfold the information associated with the many-body interactions in the layered semiconducting samples.