The optical properties of GaN nanocolumn structures containing InGaN quantum disks are investigated by optical microphotoluminescence spectroscopy using pulsed lasers, and cathodo- luminescence. The results are analyzed in the context of current theories regarding an inho- mogeneous strain distribution in the disk which has been theorized to generate lateral charge separation in the disks by strain induced band bending, an inhomogeneous polarization field distribution, and Fermi surface pinning. Simulations of the strain distribution for the relevant materials and structures are also performed, and the results analysed. It is concluded from ex- perimental measurements that no extreme lateral separation of carriers occurs in the quantum disks under investigation. Internal field screening by an increased carrier density in the QDisks at higher excitation densities is observed via a blue-shift of the emission and a dynamically changing decay time. Other possible explanations for these effects are discussed and discounted. Microphotoluminescence studies are also carried out on a single GaN nanocolumn struc- ture that has been removed from its growth substrate and dispersed onto a patterned grid. An analysis of the dynamics of the carriers in the nanocolumn is presented. Suppression of the GaN luminescence from the area of the column in the vicinity of the InGaN QDisk in addition to a delayed emission from the QDisk relative to the GaN is observed. Time resolved spatial maps of the luminescence intensity from the column are also presented, illustrating the evolution of the carrier density in the system. Additional, albeit early-stage, work on novel structures based on the production of GaN nanocolumns, namely nanotubes and nanopyramids, is also presented.

In this work, Mn atoms are doped into GaN nanorods by two doping types, homogeneous and delta doping, and GaN nanorods are grown on Si (111) substrate using plasma-assisted MBE. The GaMnN nanorods are characterized by scanning electron microscopy (SEM), energy dispersive spectrometer (EDS), high-resolution x-ray diffraction (HR-XRD), Raman scattering, Transmission electron microscopy (TEM), superconducting quantum interference device (SQUID), and x-ray photoelectron spectroscopy (XPS). The Mn delta-doping GaN nanorods with Ga/Mn growth time ratio 20 are approximately 1500 nm in height, grown along the c-axis. The Mn concentration in nanorods is determined to be 0.83% by EDS, without secondary phase formation. The Mn atoms substitute Ga sites in the GaN wurtzite hexagonal structure and, according to the results of Raman, there is no observable Mn-N cluster formation existed. The delta-doping structure, without secondary phase inclusions, can be observed under TEM imaging of the nanorods. The nanorods appear to show ferromagnetic behavior at room temperature, as judged by the M-H with hysteresis curve, however the small the loops are. The delta-doping is adopted in this thesis work to fabricate GaMnN DMS nanorods without secondary phase formation.

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Táto práca sa zaoberá technikou výroby samousporiadaných nanoštruktúr pre elektrické aplikácie. Prototypy boli pripravené anodickou oxidáciou v dvoch dĺžkach a tromi rôznymi tepelnými úpravami. Štrukturálna charakterizácia bola spravená pomocou techniky SEM, TEM a EDX a vyhodnotenie nielen z štrukturálneho, ale aj z materiálového hľadiska. Jedinečná koreňová štruktúra samousporiadaných nanotyčiniek bola vyhodnotená a porovnaná po troch rôznych tepelných úpravách: po anodizácii, po vákuovom žíhaní, a po žíhaní vo vzduchu. Všetky prototypy obsahujú nanotyčinky s amorfnou štruktúrou, ale našli sa však aj nanokryštály pod koreňovými štruktúrami. Elektrická charakterizácia prototypov ukázala: odporové spínacie správanie (RS), diódové charakteristiky a charakteristiku podobnú pre diódy s kapacitorom. Aktívny povrch pre spínací mechanizmus je v hornej časti nanoštruktúr na rozhraní nanotyčiniek a zlatej elektródy. Výška Schottkyho bariéry na rozhraní Ti / TiO2 bola vypočítaná dvoma spôsobmi a pre všetky tri zariadenia bola nižšia ako 1,11 eV.

Die vorliegende Arbeit beschäftigt sich mit der Leistungssteigerung organischer Solarzellen durch Änderung der Geometrie an der Donor-Akzeptor Grenzfläche und dem Einstellen der elektronischen Eigenschaften von Grenzflächen durch molekulares p-Dotieren. Kristalline und gleichmäßige Nanosäulen aus dem organischen Halbleiter Pentazen wurden durch glancing angle deposition (GLAD) hergestellt, die einen ineinandergreifenden Heteroübergang zu Methanofulleren [6,6]-Phenyl-C61-Butansäure Methylester (PCBM) als Akzeptor ermöglichten. Die Kurzschlussspannung der nanosäulenbasierten Solarzellen war signifikant erhöht im Vergleich zu planaren Heteroübergängen zwischen denselben Materialien. Die Leistungssteigerung der Solarzellen konnte maßgebend der vergrößerten Grenzfläche zugewiesen werden, wegen des verringerten Einflusses der kurzen Exciton Diffusionslänge. Molekulares p-Dotieren mit Tetrafluorotetracyanoquinodimethan (F4TCNQ) als Dotand in polyfuranbasierten Solarzellen wurde für verschiede Dotierkonzentrationen untersucht. Ultraviolettphotoelektronenspektroskopie wurde verwendet, um die Veränderungen der Energieniveaus mit zunehmender Dotierkonzentration zu analysieren, welche zu einer Vergrößerung der 0,2 V Kurzschlussspannung auf bis zu 0,4 V führte. Nach Kombination dieser Beobachtung mit Ergebnissen an dotierten Polymerfilmen, insbesondere bezüglich deren Morphologie und Absorptionsverhalten, wurde vorgeschlagen, dass ein resultierender Dipol an der Donor-Akzeptorgrenzfläche präsent ist. Zusammenfassend zeigt die vorliegende Arbeit das Potential sowohl der GLAD Technik als auch des molekularen, elektrischen Dotierens für die Leistungsverbesserung organischer Solarzellen. / The present work mainly focuses on improving the performance of OPVCs by tailoring the donor-acceptor interface geometry and by tuning the electrical properties of interfaces with p-type molecular doping. Crystalline and uniform nanocolumns of pentacene (PEN) and diindenoperylene (DIP) were fabricated by glancing angle deposition (GLAD), forming an interdigitated donor/acceptor heterojunction with [6,6]-phenyl-C61-butyric acid methyl ester (PCBM) and/or fullerene as the electron acceptor. The short circuit current of nanocolumn-based OPVCs increased significantly compared to planar heterojunction OPVCs made from the same materials. The performance improvement of OPVCs had been verified to be contributed decisively by the donor-acceptor interface area enlargement because of reduced impact of short exciton diffusion length in organic materials. P-type molecular doping as applied in polyfuran (PF) based OPVCs was investigated by using tetrafluorotetracyanoquinodimethane (F4-TCNQ) as the dopant for various doping ratios. Ultraviolet photoelectron spectroscopy (UPS) was applied to analyze the energy level shift with increasing doping ratio leading to the enlargement of the open circuit voltage in OPVCs, from 0.2 V to close to 0.4 V. Combining this observation with the results of doped polymer films, their morphology and absorption behavior, a net dipole pointing towards the donor material at the donor-acceptor interface of OPVCs is proposed. Overall, this work demonstrates the potential of both the GLAD technique and molecular electrical doping for improving the performance of OPVCs.

La microscopie optique stochastique de reconstruction (STORM) contourne la limite de diffraction en enregistrant des signaux monomoléculaires spatialement et temporellement séparés, atteignant une résolution de ~10-40 nm. Dans mon étude, j'ai développé une stratégie d'imagerie et d'analyse de données dSTORM bicolore afin d'étudier l'ultrastructure des synapses inhibitrices mixtes. Mes résultats ont montré que les GlyRs, les GABAARs, la géphyrine et RIM1/2 présentent une organisation intra-synaptique hétérogène et forment des domaines sous-synaptiques (SSDs). Les GlyR et les GABAAR ne sont pas complètement mélangés, mais peuvent occuper des espaces différents à la densité post-synaptique (PSD). De plus, les SSD de géphyrine postsynaptique sont alignées avec les SSD de RIM1/2 pré-synaptiques, formant des nanocolonnes trans-synaptiques. Au cours d'une activité neuronale élevée par traitement 4-AP, la corrélation spatiale entre les GlyRs, les GABAARs et la géphyrine a augmentée au PSD. De plus, la corrélation spatiale des GlyRs et RIM1/2 a également augmenté, tandis que celle des GABAARs et RIM1/2 n'a pas changé. Le nombre de SSD par synapse pour ces protéines synaptiques n'est pas modifié par 4-AP. Cette étude fourni un nouvel angle de compréhension des mécanismes sous-jacents à la co-transmission GABAergique/glycinergique. / Stochastic optical reconstruction microscopy (STORM) bypasses the diffraction limit by recording spatially and temporally separated single molecule signals, achieving a resolution of ~10-40 nm. In my study, I have developed a two-color dSTORM imaging and data analysis strategy, in order to investigate the ultrastructure of mixed inhibitory synapses. My results show that GlyRs, GABAARs, gephyrin and RIM1/2 exhibit a heterogeneous intra-synaptic organization and form sub-synaptic domains (SSDs). GlyRs and GABAARs were not fully intermingled, but sometimes occupied different spaces at the post-synaptic density (PSD). In addition, post-synaptic gephyrin SSDs were aligned with pre-synaptic RIM1/2 SSDs, forming trans-synaptic nanocolumns. During elevated neuronal activity by 4-AP treatment, the spatial correlation between GlyRs, GABAARs and gephyrin was increased at the PSD. Moreover, the spatial correlation of GlyRs and RIM1/2 was also increased, while that of GABAARs and RIM1/2 did not change. The number of SSDs per synapse for these synaptic proteins was not changed by 4-AP. My study thus provides a new angle for understanding the mechanisms underlying GABAergic/glycinergic co-transmission.