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The Cold-Electron Bolometer (CEB) is a sensitive detector of millimeter-wave radiation, in which tunnel junctions are used as temperature sensors of a nanoscale normal metal strip absorber. The absorber is fed by an antenna via two Superconductor-Insulator-Normal metal (SIN) tunnel junctions, fabricated at both ends of the absorber. Incoming photons excite electrons, heating the whole electron system. The incoming RF power is determined by measuring the tunneling current through the SIN junctions. Since electrons at highest energy levels escape the absorber through the tunnel junctions, it causes cooling of the absorber. This electron cooling provides electro-thermal feedback that makes the saturation power of a CEB well above that of other types of millimeter-wave receivers. The key features of CEB detectors are high sensitivity, large dynamic range, fast response, easy integration in arrays on planar substrates, and simple readout. The high dynamic range allows the detector to operate under relatively high background levels. In this thesis, we present the development and successful operation of CEB, focusing on the fabrication technology and different implementations of the CEB for efficient detection of electromagnetic signals. We present the CEB detector integrated across a unilateral finline deposited on a planar substrate. We have measured the finline-integrated CEB performance at 280-315 mK using a calibrated black-body source mounted inside the cryostat. The results have demonstrated strong response to the incoming RF power and reasonable sensitivity. We also present CEB devices fabricated with advanced technologies and integrated in log-periodic, double-dipole and cross-slot antennas. The measured CEB performance satisfied the requirements of the balloon-borne experiment BOOMERANG and could be considered for future balloon-borne and ground-based instruments. In this thesis we also investigated a planar phase switch integrated in a back-to-back finline for modulating the polarization of weak electromagnetic signals. We examine the switching characteristics and demonstrate that the switching speed of the device is well above the speed required for phase modulation in astronomical instruments. We also investigated the combination of a detector and a superconducting phase switch for modulating the polarization of electromagnetic radiation.

Organic solar cells have great potential for cost-effective and large area electricity production, but their applicability is limited by the relatively low efficiency. In this dissertation I report investigations of novel materials and the underlying principles of organic solar cells, carried out at the University of St Andrews between 2011 and 2015. Key results of this investigation: • The charge carrier mobility of organic semiconductors in the active layer of polymer solar cells has a rather small influence on the power conversion efficiency. Cooling solar cells of the polymer:fullerene blend PTB7:PC₇₁BM from room temperature to 77 K decreased the hole mobility by a factor of thousand but the device efficiency only halved. • Subphthalocyanine molecules, which are commonly used as electron donor materials in vacuum-deposited active layers of organic solar cells, can, by a slight structural modification, also be used as efficient electron acceptor materials in solution-deposited active layers. Additionally these acceptors offer, compared to standard fullerene acceptors,advantages of a stronger light absorption at the peak of the solar spectrum. • A low band-gap polymer donor material requires a careful selection of the acceptor material in order to achieve efficient charge separation and a maximum open circuit voltage. • Metal structures in nanometer-size can efficiently enhance the electric field and light absorption in organic semiconductors by plasmonic resonance. The fluorescence of a P3HT polymer film above silver nanowires, separated by PEDOT:PSS, increased by factor of two. This could be clearly assigned to an enhanced absorption as the radiative transition of P3HT was identical beside the nanowires. • The use of a processing additive in the casting solution for the active layer of organic solar cells of PTB7:PC₇₁BM strongly influences the morphology, which leads not only to an optimum of charge separation but also to optimal charge collection.

Geschichtete bzw. 2D Materialien bieten interessante Eigenschaften für Halbleiteranwendungen, wie Photonik durch direkte Bandlücken und Miniaturisierung durch atomar dünne Schichten. Diese Arbeit behandelt die Isolierung von 2D-Materialien und die Kontrolle über ionische Modulation in den resultierenden Bauteilen. Im ersten Kapitel wird eine silbervermittelte Exfoliation für MoS₂ eingeführt, die Monolagen mit großer Fläche liefert. Diese Technik ist ebenso leistungsfähig wie goldvermittelte Prozesse und erfordert nur einen einfachen Heizschritt, was zukünftige Exfoliationen erleichtern könnte. Die folgenden Kapitel befassen sich mit Funktionen, die durch kontrolliertes ionisches Gating ermöglicht werden. Im zweiten Kapitel wird die kontrollierte Li-Interkalation in LixZrNCl genutzt, um Supraleitung bei niedriger Ladungsträgerdichte zu untersuchen (BCS-BEC-Übergang). Durch Steuerung der Li-Menge wurden Veränderungen in der Vortex-Dynamik aufgedeckt, z.B. ein Vorzeichenwechsel im Vortex-Hall-Effekt, was auf eine Veränderung der Vortex-Flussdynamik in BEC-ähnlicher Supraleitung zurückgeführt wurde. Diese Erkenntnisse sind relevant für die Entwicklung von Supraleitern. Das dritte Kapitel wechselt zu Bauteilen auf Basis der elektrochemischen Doppelschicht (EDL). Ein 2D MoS₂-synaptischer Transistor wurde demonstriert, wobei gezeigt wurde, dass die Hysterese auf Ionenretention an der EDL zurückzuführen ist. Diese Kombination eines 2D-Materials mit einem Polymerelektrolyten emuliert synaptische Lernprozesse wie gepaarte Puls-Fazilitation und arbeitet energieeffizient. Das letzte Kapitel verlagert das ionische Gating auf das Substrat mittels Li-Ionen-leitender Keramiken für operando-Messungen an 2D-Materialien. Zusammenfassend demonstriert diese Arbeit neben der Exfoliation die vielfältigen Funktionen, die durch kontrolliertes ionisches Gating verfügbar sind, einschließlich Supraleitung bei niedriger Ladungsträgerdichte, neuromorphe Bauteile und operando-Plattformen. / Layered materials and their 2D single-layer forms offer interesting properties for semiconductor applications, such as photonics due to direct band gaps and miniaturization through atomically thin layers. This work addresses the isolation of 2D materials and the control via ionic modulation in the resulting devices. In the first chapter, a silver-mediated exfoliation for MoS₂ is introduced, yielding large-area monolayers. This technique is as effective as gold-mediated processes and requires only a simple heating step, potentially simplifying future exfoliations. The following chapters explore functions enabled by controlled ionic gating. The second chapter utilizes controlled Li intercalation in LixZrNCl to investigate superconductivity at low charge carrier densities to investigate superconductivity within the BCS-BEC crossover. By adjusting the Li content, changes in vortex dynamics were revealed, such as a sign reversal in the vortex Hall effect, attributed to altered vortex flow in increasingly BEC-like superconductivity. These findings are relevant for the development of future superconductors. The third chapter shifts to devices based on the electric double layer (EDL). A 2D MoS₂ synaptic transistor was demonstrated, showing that hysteresis and hence the short-term memory effect stems from ion retention in the EDL formed at the 2D material electrolyte interface. This combination of a 2D material with a polymer electrolyte emulates synaptic learning processes like paired-pulse facilitation and operates in an energy-efficient manner. The final chapter translates the ionic gating to the substrate using Li-ion-conducting ceramics for operando measurements on 2D materials in “open-hood” devices. In summary, besides exfoliation, this work demonstrates the diverse functions achievable through controlled ionic gating applied to 2D and layered materials, including superconductivity at low charge carrier densities, neuromorphic devices, and operando platforms.