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Semiconductor quantum dots are promising building blocks for quantum communication applications. Al- though deterministic, efficient, and coherent emission of entangled photons has been realized, implementing a practical quantum repeater remains outstanding. Here we explore the statistical limits for entanglement swapping with sources of polarization-entangled photons from the commonly used biexciton-exciton cascade. We stress the necessity of tuning the exciton fine structure, and explain why the often observed time evolution of photonic entanglement in quantum dots is not applicable for large quantum networks. We identify the critical, statistically distributed device parameters for entanglement swapping based on two sources. A numerical model for benchmarking the consequences of device fabrication, dynamic tuning techniques, and statistical effects is developed, in order to bring the realization of semiconductor-based quantum networks one step closer to reality. ©2022 American Physical Society

Medical micromotors have the potential to lead to a paradigm shift in future biomedicine, as they may perform active drug delivery, microsurgery, tissue engineering, or assisted fertilization in a minimally invasive manner. However, the translation to clinical treatment is challenging, as many applications of single or few micromotors require real-time tracking and control at high spatiotemporal resolution in deep tissue. Although optical techniques are a popular choice for this task, absorption and strong light scattering lead to a pronounced decrease of the signal-to-noise ratio with increasing penetration depth. Here, a highly reflective micromotor is introduced which reflects more than tenfold the light intensity of simple gold particles and can be precisely navigated by external magnetic fields. A customized optical IR imaging setup and an image correlation technique are implemented to track single micromotors in real-time and label-free underneath phantom and ex vivo mouse skull tissues. As a potential application, the micromotors speed is recorded when moving through different viscous fluids to determine the viscosity of diverse physiological fluids toward remote cardiovascular disease diagnosis. Moreover, the micromotors are loaded with a model drug to demonstrate their cargotransport capability. The proposed reflective micromotor is suitable as theranostic tool for sub-skin or organ-on-a-chip applications.

Hybrid interfaces between distinct quantum systems play a major role in the implementation of quantum networks. Quantum states have to be stored in memories to synchronize the photon arrival times for entanglement swapping by projective measurements in quantum repeaters or for entanglement purification. Here, we analyze the distortion of a single-photon wave packet propagating through a dispersive and absorptive medium with high spectral resolution. Single photons are generated from a single In(Ga)As quantum dot with its excitonic transition precisely set relative to the Cesium D1 transition. The delay of spectral components of the single-photon wave packet with almost Fourier-limited width is investigated in detail with a 200 MHz narrow-band monolithic Fabry-Pérot resonator. Reflecting the excited state hyperfine structure of Cesium, “slow light” and “fast light” behavior is observed. As a step towards room-temperature alkali vapor memories, quantum dot photons are delayed for 5 ns by strong dispersion between the two 1.17 GHz hyperfine-split excited state transitions. Based on optical pumping on the hyperfine-split ground states, we propose a simple, all-optically controllable delay for synchronization of heralded narrow-band photons in a quantum network.

In the last decades, additive manufacturing (AM), also called three-dimensional (3D) printing, has advanced micro/nano-fabrication technologies, especially in applications like lightweight engineering, optics, energy, and biomedicine. Among these 3D printing technologies, two-photon polymerization (TPP) offers the highest resolution (even at the nanometric scale), reproducibility and the possibility to create monolithically 3D complex structures with a variety of materials (e.g. organic and inorganic, passive and active). Such active materials change their shape upon an applied stimulus or degrade over time at certain conditions making them dynamic and reconfigurable (also called 4D printing). This is particularly interesting in the field of medical microrobotics as complex functions such as gentle interactions with biological samples, adaptability when moving in small capillaries, controlled cargo-release profiles, and protection of the encapsulated cargoes, are required. Here we review the physics, chemistry and engineering principles of TPP, with some innovations that include the use of micromolding and microfluidics, and explain how this fabrication schemes provide the microrobots with additional features and application opportunities. The possibility to create microrobots using smart materials, nano- and biomaterials, for in situ chemical reactions, biofunctionalization, or imaging is also put into perspective. We categorize the microrobots based on their motility mechanisms, function, and architecture, and finally discuss the future directions of this field of research.

Coupled whispering-gallery-mode (WGM) optical microcavities have been extensively explored to tune the resonant eigenfrequencies and spatial distributions of the optical modes, finding many unique photonic applications in a variety of fields, such as nonlinear optics, laser physics, and non-Hermitian photonics. As one type of WGM microcavities, microtube cavities with axial potential wells support 3D confined resonances by circulating light along the microtube cross-section and axis simultaneously, which offers a promising possibility to explore multidimensional and multichannel optical coupling. In this thesis, the optical coupling of 3D confined resonant modes is investigated in coupled microtube cavities fabricated by self-rolling of prestrained nanomembranes. In the first coupling system, multiple sets of 3D optical modes are generated in a single microtube cavity owing to nanogap induced resonant trajectory splitting. The large overlap of optical fields in the split resonant trajectories triggers strong optical coupling of the 3D confined resonant modes. The spectra anticrossing feature and changing-over of one group of coupled fundamental modes are demonstrated as direct evidence of strong coupling. The spatial optical field distribution of 3D coupling modes was experimentally mapped upon the strong coupling regime, which allows direct observation of the energy transfer process between two hybrid states. Numerical calculations based on a quasi-potential model and the mode detuning process are in excellent agreement with the experimental results. On this basis, monolithically integrated twin microtube cavities are proposed to achieve the collective coupling of two sets of 3D optical modes. Owing to the aligned twin geometries, two sets of 3D optical modes in twin microtubes are spectrally and spatially matched, by which both the fundamental and higher-order axial modes are respectively coupled with each other. Multiple groups of the coupling modes provide multiple effective channels for energy exchange between coupled microcavities, which are illustrated by the measured spatial optical field distributions. The spectral anticrossing and changing-over features of each group of coupled modes are revealed in experiments and calculations, indicating the occurrence of strong coupling. In addition, the simulated 3D mode profiles of twin microcavities confirm the collective strong coupling behavior, which is in good agreement with the experimental results. Our work provides a compact and robust scheme for realizing 3D optical coupling, which is of high interest for promising applications such as 3D non-Hermitian systems and multi-channel optical signal processing.

Micro-technology relies on a highly parallel fabrication of 2D electronic and/or microelectromechanical devices, where in most cases silicon wafers are used as substrates. In contrast 3D fabrication shows unique advantages, such as footprint reduction or the possibility to obtain additional functionalities. For example, in the case of a sensor, knowledge of the acceleration in all possible directions, the surrounding electric or magnetic field among other quantities can help to determine the exact position of an object in 3D space. To do that it is crucial to retrieve all components of a vector field, which requires at least one out of plane component. In other fields like integrated optics three dimensional structures can enhance the coupling efficiency with free space interactions. As such 3D micro-structures will be crucial for upcoming products and devices. A highly parallel fabrication is required to enable mass-adaption, self-assembly is an emerging technology that could deliver this purpose. Examples of 3D structures created by self-assembly include polyhedrons like cubes, pyramids or micro tubular structures such as tubes or spirals. Following a self assembly scheme, 3D devices would be created through the fabrication of standard 2D structures that are reshaped through a self-assembly step into a 3D object. In this thesis a novel dry release protocol was developed to roll-up strained nanomembranes from a silicon sacrificial layer employing dry fluorine chemistry. This way a wet release is totally circumvented thus preventing damage of the created structures due to turbulent flow or capillary forces. Additionally the developed process enabled the use of standard CMOS deposition and processing tools, leading to a high increase in yield and quality, with yields exceeding 99% for microtubes. Building on the developed technology various devices where fabricated, for example rolled-up micro capacitors at a wafer scale with an increased yield and a low spread of electrical characteristics. For the E12 industrial standard more than 90% of devices behaved within the required performance characteristics. Furthermore the yield and Q-factor of roll-up whispering gallery mode resonators was strongly improved, making it possible to self assemble 3D coupled photonic molecules, which showed a mode splitting exceeding the FSR, as well as hybrid supermodes at points of energy degeneracy.:Contents Bibliographic Record i List of Abbreviations vii List of Chemical Substances ix 1 Introduction 1 1.1 Microelectromechanical Systems 1 1.2 Strain Engineering 2 1.3 Rolled - Up Nanotechnology 3 1.4 Objective and Structure of the Thesis 5 2 Materials and Methods 9 2.1 Fabrication Techniques 9 2.1.1 Substrates 9 2.1.2 Plasma Enhanced Chemical Vapor Deposition 9 2.1.3 Dry Etching12 2.1.4 Deep Reactive Ion Etching 18 2.1.5 Atomic Layer Deposition 19 2.1.6 Lithography 20 2.2 Characterization Techniques 22 2.2.1 Strain Measurement 22 2.2.2 Ellipsometry 23 3 Dry Roll-Up of Strained Nanomembranes 25 3.1 Rolled - Up Nanotechnology 25 3.2 Fabrication 26 3.2.1 Release 29 3.3 Conclusions 33 4 Rolled-UpMicro Capacitors 35 4.1 Micro Capacitors 35 4.2 Fabrication 38 4.3 Characterization 39 4.4 Conclusion 41 5 Optical Micro-Cavities 43 5.1 Optical Micro Cavities 43 5.2 Theorectical Background 45 5.2.1 Quality - factor 49 5.2.2 FDTD 52 6 Optical Microtube Resonators 55 6.1 Optical Whispering Gallery Mode Microtube Resonators 55 6.2 Fabrication 57 6.3 Active Characterization 60 6.4 Conclusions 64 7 Photonic Molecules 65 7.1 Coupled Photonic Systems 65 7.2 Fabrication 68 7.3 Device Characterization 71 7.4 Multimode Waveguides 84 7.5 Conclusions 85 8 Conclusions and Outlook 87 8.1 Conclusions 87 8.2 Outlook 88 Bibliography 91 List of Figures 109 List of Tables 117 A Equipment 119 Cover Pages 121 Selbstständigkeitserklärung 123 Acknowledgements 125 List of Publications 127 List of Presentations 129 Curriculum Vitae 131

Miniaturization is a key technological approach in current times. The most prominent examples of miniaturization are personal computers and mobile phones, but we observe miniaturization in other aspects of life, with the most recent example being small portable corona test kits. In science a big part of miniaturization focuses on detectors: to make them portable, to make them integrable into bigger, multi-function systems or to enable detection of smaller and smaller samples. For many experimental techniques highly sensitive and compact devices are already available, one of the extreme examples being single photon detectors. Compared to that, miniaturization of nuclear magnetic resonance (NMR) has still a long way to go in terms of both size and sensitivity. Recently, the successful miniaturization of an NMR coil was presented: on top of a flat polymeric bilayer a metallic layout is patterned. In an aqueous solution, one polymer layer absorbs water and swells, which induces strain between the two polymeric layers. This strain is released by a self-rolling-up of the bilayer, and the metal layer transforms into a microcoil. Such microcoils were successfully used for impedimetric measurements, as antennas, and as mentioned for NMR, but their performance in the latter was far from optimal. This thesis focuses on the optimization of rolled-up microcoils (RUMs) for NMR spectroscopy, with the goal to produce high-resolution and, most importantly, high-sensitivity microcoils. The performance of the microcoil can be expressed in three parameters, namely the spectral linewidth, the (normalized) limit of detection and the damping of a nutation curve, which was not a key parameter for this thesis. Both the microcoil design and the roll-up process have an influence on the quality of a RUM. For an optimal roll-up process, the polymeric bilayer layout needed some adjustment. The rolling process itself was improved through an addition of supporting structures on top of the bilayer, which resulted in tightly rolled tubes with a well-defined diameter. The coil layout was selected from several simple layouts. This layout was then optimized with the help of experiments and simulations. For example, an improvement in resolution was achieved through a reduction of the susceptibility of the metal. Finally, the coil was embedded into a microfluidic chip. This chip allows an easy sample supply into the coil interior and protects the coil from damage. As a side effect, the chip has a positive influence on the resolution of the detector. The best RUMs have a volume of only 1.5 nl, show a linewidth of only 8 ppb and a normalized limit of detection of 0.6 nmol√Hz at 600 MHz. The achieved resolution and sensitivity allow to resolve a 1H ethanol spectrum fully in a single measurement of 6 s duration. Compared to a standard shimmed NMR detector, where the linewidth is 0.65 ppb and the nLOD 10 nmol√Hz, the RUMs linewidth still needs some improvement, but the limit of detection is already an order of magnitude smaller. Combined with the fact that the limit of detection improves with linewidth, this shows the far superior sensitivity of RUMs compared to standard setups. A comparison with literature is also very promising, where optimized RUMs compete with the best published microcoils. Additionally, RUMs can be produced en masse, with, at the moment, four coils fitting on a single 50 x 50 mm2 glass substrate, while the best other microcoils were all made for single, specific experiments one at a time. And finally, the here presented recipe for self-assembled, RUMs is easily adaptable to even smaller sample volumes and to other coil layouts. It can be used to produce matching gradient coil systems and is a guideline on how to combine NMR and other techniques while maintaining a high NMR performance.:Introduction Nuclear magnetic resonance 1 NMR principle 1.1 A single nucleus in a magnetic field 1.2 Multiple spins in external field 1.3 Spins in natura 1.4 Typical liquid state spectrum 1.5 Typical NMR setup 2 Properties of an NMR detector 2.1 Quality of rf-field 2.2 Resolution 2.3 Signal-to-noise ratio 2.4 How to optimize a microcoil 3 Existing microdetectors 3.1 Solenoids 3.2 Saddle coils 3.3 Flat coils 3.4 Striplines/Microslots 4 Comparing microdetectors 4.1 The limit of detection 4.2 Performance of published microcoils Self-assembly 5 What is self-assembly? 6 Self-assembly in microfabrication 6.1 Macroscopic self-assembly 6.2 Self-rolled tubes 7 Self-assembly of rolled-up microcoils 7.1 Working principle 7.2 Experimental methods for self-assembly 8 Encapsulating rolled-up tubes 8.1 Microfluidics 8.2 Microfluidic chip 8.3 Experimental methods for encapsulation Rolled-up microcoils 9 Fabrication 9.1 Bilayer 9.2 Coil geometry 9.3 Metal stack 9.4 Supporting elements 9.5 Rolling process 9.6 Final layout 9.7 Microfluidic integration 10 Reducing susceptibility-induced field distortions 10.1 Simulating field distortions 10.2 Influence of the coil shape 10.3 Susceptibility matching 11 NMR performance 11.1 Measurement setup 11.2 Quality of rf-field 11.3 Resolution and sensitivity 11.4 Comparison to published microcoils 12 Outlook 12.1 Further improvements to rf-field, FWHM and nLOD 12.2 New coil shapes 12.3 New applications Summary Appendix A Simulation and maths A.1 Filling factor and rf-homogeneity A.2 Nutation and rf-homogeneity A.3 FT of one-sided exponential A.4 DFT A.5 Programs B Protocols B.1 Polymeric platform B.2 Metal layers C Test protocols C.1 Wet etching D Calculations for nLODs

The deterministic generation and manipulation of quantum states has attracted much interest ever since the rise of quantum mechanics. Large-scale, distributed quantum states are the basis for novel applications such as quantum communication, quantum remote sensing, distributed quantum computing or quantum voting protocols. The necessary infrastructure will be provided by distributed quantum networks, allowing for quantum bit processing and storage at single nodes. Quantum states of light then allow for inter-node transmission of quantum information. Transmission losses in optical fibers may be overcome by quantum repeaters, the quantum equivalent of classical signal amplifiers. The fragility of quantum superposition states makes building such networks very challenging. Hybrid solutions combine the strengths of different physical systems: Efficient quantum memories can be realized using alkali atoms such as rubidium. Leading in the deterministic generation of single photons and polarization entangled photon pairs are semiconductor InAs/GaAs quantum dots grown by the Stranski-Krastanov method. Despite remarkable progress in the last twenty years, complex quantum optical protocols could not be realized due to low degree of entanglement, low brightness and broad wavelength distribution. In this work, an emerging family of epitaxially grown GaAs/AlGaAs quantum dots obtained by droplet etching and nanohole infilling is studied. Under pulsed resonant two-photon excitation, they emit single pairs of entangled photons with high purity and unprecedented degree of entanglement. Entanglement fidelities up to f = 0.94 are observed, which are only limited by the optical setup or a residual exciton fine structure. The samples exhibit a very narrow wavelength distribution at rubidium memory transitions. Strain tuning is applied via piezoelectric actuators to allow for reversible fine-tuning of the emission frequency. In a next step, active feedback is employed to stabilize the frequency of single photons emitted by two separate quantum dots to an atomic rubidium standard. The transmission of a rubidium-based Faraday filter serves as the error signal for frequency stabilization. A residual frequency deviation of < 30MHz is achieved, which is less than 1.5% of the quantum dot linewidth. Long-term stability is demonstrated by Hong-Ou-Mandel interference between photons from the two quantum dots. Their internal dephasing limits the expected visibility to V = 40%. For frequency-stabilized dots, V = (41 ± 5)% is observed as opposed to V = (31 ± 7)% for free-running emission. This technique reaches the maximally expected visibility for the given system and therefore facilitates quantum networks with indistinguishable photons from distributed sources. Based on the presented techniques and improved emission quality, pivotal quantum communication protocols can now be implemented with quantum dots, such as transferring entanglement between photon pairs. Embedding quantum dots in a dielectric antenna ensures a bright emission. For the first time, entanglement swapping between two pairs of photons emitted by a single quantum dot is realized. A joint Bell measurement heralds the successful generation of the Bell state Ψ+ with a fidelity of up to (0.81 ± 0.04). The state's nonlocal nature is confirmed by violating the CHSH-Bell inequality with S = (2.28 ± 0.13). The photon source is tuned into resonance with rubidium transitions, facilitating implementation of hybrid quantum repeaters. This work thus represents a major step forward for the application of semiconductor based entangled photon sources in real-world scenarios.

Micromotors – untethered, motile, microscopic devices – are implemented in this dissertation for two applications in the field of assisted reproductive technology. First, as synthetic motor units for individual sperm cells, representing a novel approach to counteract sperm immotility (asthenozoospermia), which is one of the most prevalent causes of male infertility. Second, as synthetic carriers of fertilized oocytes (zygotes) towards the realization of non-invasive intrafallopian transfer, representing a novel alternative to the current keyhole surgery (laparoscopy) approach to achieve early embryo transfer after in vitro fertilization. In both applications, magnetically actuated micromotors are utilized to capture, transport, and deliver individual cells in a reproducible, controllable manner. In comparison with established in vitro fertilization routines, the crucial advantage of employing micromotors for the manipulation of gametes, i.e. sperm and (fertilized) oocytes, lies in the potential transfer of decisive steps of the fertilization process back to its natural environment – the fallopian tube of the female patient – taking advantage of the untethered, non-invasive motion and manipulation capabilities of magnetic micromotors. When sperm motility can be restored with magnetic micromotors, sperm can travel to the oocyte under external actuation and control, and the oocyte does not need to be explanted for in vitro fertilization. However, if in vitro fertilization was necessary, fertilized oocytes can be transferred back to the fallopian tube by micromotors in a non-invasive manner, to undergo early embryo development in the natural environment. These novel concepts of micromotor-assisted reproduction are presented and investigated in this thesis, and their potential is analyzed on the basis of proof-of-concept experiments.:1 Introduction 6 1.1 Background and Motivation 6 1.2 Objectives and Structure of this Dissertation 9 2 Fundamentals 11 2.1 Micromotors Definition and Concept 11 2.2 Micromotors for Biomedical Applications 13 2.3 Magnetic Micropropellers 15 2.3.1 Theory 15 2.3.2 Implementation 20 2.4 Microfabrication: Direct Laser Writing 21 2.5 Assisted Reproductive Technology 23 2.5.1 In vitro Fertilization and Intracytoplasmic Sperm Injection 24 2.5.2 Embryo Transfer and Zygote Intrafallopian Transfer 25 2.5.3 The Sperm Cell and the Oocyte 26 2.6 Towards Micromotor-Assisted Reproduction 28 3 Materials and Methods 30 3.1 Fabrication of Microfluidic Channel Platforms 30 3.1.1 Tailored Parafilm Channels 30 3.1.2 Polymer Channels Cast from Micromolds 31 3.1.3 Tubular Channels to Mimic In vivo Ducts 32 3.2 Fabrication of Magnetic Micropropellers 32 3.2.1 Direct Laser Writing of Polymeric Resin 33 3.2.1.1 Design and Programming 33 3.2.1.2 Exposure and Development 35 3.2.1.3 In Situ Direct Laser Writing 35 3.2.2 Critical Point Drying 35 3.2.3 Magnetic Metal Coatings 36 3.2.4 Surface Functionalization 37 3.3 Sample Characterization 38 3.3.1 Optical Microscopy 38 3.3.2 Scanning Electron Microscopy 38 3.4 Cell Culture and Analysis 39 3.4.1 Sperm Cells 39 3.4.2 Oocytes 39 3.4.3 In vitro Fertilization 41 3.4.4 Hypoosmotic Swelling Test 44 3.4.5 Cell Viability Assays 44 3.5 Magnetic Actuation 45 3.5.1 Modified Helmholtz Coil Setup 46 3.5.2 MiniMag Setup 47 3.5.3 Experimental Procedure 48 3.5.3.1 Micromotor Performance Evaluation 48 3.5.3.2 Cell Transport Experiments 49 3.5.3.3 Cell Transfer Experiments 50 4 Micromotor-assisted Sperm Delivery 51 4.1 Micromotor Design and Fabrication 51 4.2 Actuation and Propulsion Performance 53 4.3 Capture, Transport, and Release of Sperm 56 4.4 Delivery to the Oocyte 59 4.5 Sperm Viability and the Ability to Fertilize 61 5 Micromotor-assisted Zygote Transfer 68 5.1 Micromotor Design and Fabrication 68 5.2 Actuation and Propulsion Performance 70 5.3 Capture, Transport, and Release of Zygotes 76 5.4 Transfer between Separate Environments 80 5.5 Zygote Viability and Further Development 82 6 Conclusions and Prospects 85 Appendix 87 Bibliography 93 List of Figures and Tables 108 List of Abbreviations and Terms 109 Theses 111 Selbstständigkeitserklärung 112 Acknowledgments 113 List of Publications 115 Curriculum Vitae 116

In this thesis, we focus on the generation of entangled photon pair from III-V quantum dots. The achievements mainly consists of two aspects: one is the wavelength tunability of these entangled photon pairs, which is enabled by on-chip strain engineering; the other is the brightness enhancement with an optical-broadband antenna to boost the extraction of entangled photons from the material matrix where quantum dots are embedded in.

Asymmetrically sandwiched ferromagnetic thin films display a large number of spin-orbit effects, including the Dzyaloschinsii-Moriya interaction (DMI), spin-orbit torques (SOT) and magnetoresistance (MR) effects. Their concurrence promises the implementation of interesting magnetic structures like skyrmions in future memory and logic devices. The complex interplay of various effects originating from the spin-orbit coupling and their dependencies on the microstructural details of the material system mandates a holistic characterization of its properties. In this PhD thesis, a comprehensive study of the spin-orbit effects in a chromium oxide/cobalt/platinum trilayer sample series is presented. The determination of the complete micromagnetic parameter set is based on a developed measurement routine that utilizes quasistatic methods. The unambiguous quantification of all relevant constants is crucial for the modeling of the details of magnetic structures in the system. In this context the necessity of a strict distinction of magnetic objects, that are stabilized by magnetostatics or the DMI, was revealed. Furthermore, a sample layout was developed to allow for the simultaneous quantification of the magnitudes of SOTs and MR effects from nonlinear magnetotransport measurements. In conjunction with a structural characterization, the dominating dependence of the effect magnitudes on microstructural details of the systems is concluded. Precisely characterized systems establish a solid groundwork for further investigations that are needed for viable skyrmion-based devices.:1 Introduction 2 Fundamentals 2.1 Towards new devices 2.2 Spin-orbit effects 2.2.1 Spin-current sources 2.2.2 Magnetoresistanceeffects 2.2.3 Spin-orbit torques 2.2.4 Harmonic analysis 2.3 Micromagnetic model 2.3.1 Dzyaloshinskii-Moriya interaction (DMI) 2.3.2 Consequences of the DMI for magnetic structures 2.3.3 Interface-induced DMI in asymmetrically stacked ferromagnets 2.3.4 Quantification of the interface-induced DMI 2.3.5 Levy-Fert three-site model including roughness 3 The CrOx/Co/Pt sample system 3.1 Experimental techniques 3.2 Structural characterization 4 Complete micromagnetic characterization 4.1 Magnetometry 4.1.1 Static investigation 4.1.2 Ferromagnetic resonance 4.2 DMI quantification 4.2.1 Field-driven domain wall creep motion 4.2.2 Asymmetric domain growth 4.2.3 Winding pair stability 4.3 Determination of the exchange parameter 4.3.1 Generation of circular magnetic objects 4.3.2 Homochiral magnetic bubble domains 4.4 Results 5 Magnetotransport measurements 5.1 Measurement setup 5.2 Magnetoresistance effects 5.3 Spin-orbit torque quantification 5.4 Results 6 Discussion 6.1 Structural predomination of the DMI strength 6.2 Ultra-thin limit exchange parameter reduction 6.3 Magnetotransport properties 6.4 Magneticstructures in //CrOx/Co/Pttrilayers 7 Conclusion and Outlook A Appendix A.1 Calculation of the skyrmion diameter A.2 Micromagnetic simulation of the winding pair stability Bibliography Acknowledgements

Rechargeable lithium-ion batteries are now attracting great attention for applications in portable electronic devices and electrical vehicles, because of their high energy density, long cycle and great convenience. For new generations of rechargeable lithium-ion batteries, they applied not only to consumer electronics but also especially to clean energy storage and hybrid electric vehicles. Therefore, further breakthroughs in electrode materials that open up a new important avenue are essential. Graphite, the most commonly used commercial anode material, has a limited reversible lithium intercalation capacity (372 mAh g-1). In this regard, tremendous efforts have been made towards even further improving high capacity, excellent rate capability, and cycling stability by developing advanced anode materials. This work focuses on the lithium storage properties of nickel oxide (NiO) and germanium (Ge) nanomembranes anodes mainly fabricated by electron-beam evaporation. Specifically, NiO is selected for conversion-type material because of high theoretical specific capacity of 718 mAh g-1 and easily obtained material. The resultant curved NiO nanomembranes anodes exhibit ultrafast power rate of 50 C (1 C = 718 mA g-1) and good capacity retention (721 mAh g-1, 1400 cycles). Remarkably, multifunctional Ni/NiO hybrid nanomembranes were further fabricated and investigated. Benefiting from the advantages of the intrinsic architecture and the electrochemical catalysis of metallic nickel, the hybrid Ni/NiO anodes could be tested at an ultrahigh rate of ~115 C. With Ge as active alloying-type material (1624 mAh g-1), the effect of the incorporated oxygen to the lithium storage properties of amorphous Ge nanomembranes is well studied. The oxygen-enabled Ge (GeOx) nanomembranes exhibit improved electrochemical properties of highly reversible capacity (1200 mAh g-1), and robust cycling performance.

Memristor, defined as a two-terminal device which exhibits a pinched hysteresis loop in the current-voltage characteristics, is a main component of the resistive random access memory. Both memristor and memristive phenomena, known also as resistive switching (RS), have been thoroughly investigated in the past nearly two decades. This dissertation investigates YMnO3 thin films and explores a new concept concerning utilization of multiferroic properties for activation and/or enhancement of RS. It is hypothesized that the charged domain walls and/or vortex cores in YMnO3 thin films can act as an effective nanoscale features which support formation of the conductive filaments and, in consequence, enable development of an electroforming-free memristive structure. Results of the electrical characterization of YMnO3-based metal-insulator-metal structures indicate that hexagonal YMnO3 films deposited on metal-coated oxide substrate exhibit electroforming-free unipolar resistive switching (URS) while orthorhombic YMnO3 films grown on the doped oxide substrate show bipolar resistive switching (BRS). Observed URS is assigned to the formation and rupture of conductive, metallic-like filaments induced by the thermo-chemical phenomena. Results of polarity-dependent studies reveal that formation of conductive filaments proceeds in the electrostatic discharge event which is followed by their irreversible rupture during the reset process. Main properties of the observed URS include very good retention of programmed states, large memory window (between 10E+2 and 10E+4), high voltage and current required for set and reset, respectively, and low endurance. BRS is attributed to the complementary electronic and ionic processes within the p-n junction formed at the interface between p-YMnO3 and n-type oxide substrate. Results of ferroelectric characterization reveal that resistively switching YMnO3 films do not exhibit ferroelectric properties. Therefore, observed RS in YMnO3-based structures can not be directly related to the presence of charged domain walls and/or multiferroic vortex cores. Prospective functionality extension of YMnO3-based memristive devices is developed and presented on the example of photodetecting properties of metal-YMnO3-insulator-semiconductor stacks. Studies conducted within the framework of this doctoral dissertation investigate the resistive switching behaviour of YMnO3-based junctions. Obtained results contribute to the better understanding of the resistive switching and failure mechanisms in ternary oxides, and provide hints toward device engineering. Der Memristor ist definiert als eine Zweipol-Vorrichtung, die eine hysteretische Strom-Spannungs-Charakteristik aufweist. Memristoren sind nichtflüchtige Widerstandsspeicher, deren elektrischer Widerstand mittels elektrischer Spannungspulse verändert werden kann. Sowohl Memristoren als auch memristive Widerstandsschalter (RS) werden seit mehr als zwei Jahrzehnten intensiv untersucht. Diese Dissertation untersucht YMnO3-Dünnschichten mit zirkularen Vorderseiten-Elektroden und unstrukturierten Rückseiten-Elektroden und erforscht ein neues Konzept über die Nutzung der multiferroischen Eigenschaften für die Aktivierung und/oder Verbesserung des memristiven Verhaltens. Es wird angenommen, dass die geladenen Domänenwände und/oder Vortices in YMnO3-Dünnschichten die Bildung leitfähiger Filamente wirksam unterstützt und folglich die Entwicklung eines neuartigen, formierungs-freiem Widerstandsspeichersermöglicht. Die Ergebnisse der elektrischen Charakterisierung von YMnO3-basierten Widerstandsschalter zeigen unipolares RS (URS), wenn eine metallische Rückseitenelektrode verwendet wird und bipolares RS (BRS), wenn als Rückseitenelektrode ein metallisch leitendes Oxid-Substrat verwendet werden. Das URS wird als thermochemisches RS klassifiziert und mit der Bildung und Auflösung metallisch leitender Filamente korreliert. Das BRS wird auf das Einfangen/Freigeben von Defekten in der Raumladungszone des YMnO3 im pn-Übergang von p-YMnO3/n-Nb:SrTiO3-Strukturen zurückgeführt. Die wichtigsten Eigenschaften des formierungsfreien URS sind die sehr gute Retention der programmiertenWiderstandszustände, große Speicherfenster (zwischen 10E+2 und 10E+4), die hohe Schreibspannung für den Set-Prozess und der hohe Schreibstrom für den Reset-Prozess. Die Endurance ist aufgrund der Degradation des Vorderseiten-Elektrode gering. Die Ergebnisse des polaritätsabhängigen Widerstandsschaltens zeigen, dass der Set-Prozess mit elektrostatischer Entladung einhergeht. Die ferroelektrische Charakterisierung zeigt, dass die YMnO3–Dünnfilme keine ferroelektrischen Eigenschaften aufweisen. Daher kann das beobachtete URS nicht direkt auf die Anwesenheit von geladenen Domänenwände und Vortices zurückgeführt werden. Darüberhinaus wurden die photodetektierenden Eigenschaften von Metall-YMnO3-Isulator-Halbleiter-Stacks als potenzielle Erweiterung der Funktionalität von YMnO3-basierten memristiven Bauelementen vorgestellt und vorgeschlagen. Im Rahmen der vorliegenden Dissertation wurde das Widerstandsschalten von multiferroischen, YMnO3-basierten Widerstandsschaltern untersucht. Die erhaltenen Ergebnisse tragen zu einem besseren Verständnis des Widerstandsschaltens von multiferroischen Materialien bei.

Confronted with the global demographic changes and the increasing pressure on modern healthcare system, there has been a surge of developing new technology platforms in the past decades. Droplet microfluidics is a prominent example of such technology platforms, which offers an efficient format for massively parallelized screening of a large number of samples and holds great promise to boost the throughput and reduce the costs of modern biomedical activities. Despite recent achievements, the realization of a compact and generic screening system which is suited for resource-limited settings and point-of-care applications remains elusive. To address the above challenges, the dissertation focuses on the development of a compact multifunctional droplet micro-magnetofluidic system by exploring the advantages of magnetic in-flow detection principles. The methodologies behind a novel technique for biomedical applications, namely, magnetic in-flow cytometry have been put forth, which encompass magnetic indexing schemes, quantitative multiparametric analytics and magnetically-activated sorting. A magnetic indexing scheme is introduced and intrinsic to the magnetofluidic system. Two parameters characteristic of the magnetic signal when detecting magnetically functionalized objects, i.e. signal amplitude and peak width, providing information which is necessary to perform quantitative analysis in the spirit of optical cytometry has been proposed and realized. Magnetically-activated sorting is demonstrated to actively select individual droplets or to purify a population of droplets of interest. Together with the magnetic indexing scheme and multiparametric analytic technique, this functionality synergistically enables controlled synthesis, quality administration and screening of encoded magnetic microcarriers, which is crucial for the practical realization of magnetic suspension arrays technologies. Furthermore, to satisfy the needs of cost-efficient fabrication and high-volume delivery, an approach to fabricate magnetofluidic devices on flexible foils is demonstrated. The resultant device retains high performance of its rigid counterpart and exhibits excellent mechanical properties, which promises long-term stability in practical applications.

This thesis addresses the development of materials, technologies and circuits applied for the fabrication of a new class of microelectronic devices that are relying on a three-dimensional shape variation namely shapeable microelectronics. Shapeable microelectronics has a far-reachable future in foreseeable applications that are dealing with arbitrarily shaped geometries, revolutionizing the field of neuronal implants and interfaces, mechanical prosthetics and regenerative medicine in general. Shapeable microelectronics can deterministically interface and stimulate delicate biological tissue mechanically or electrically. Applied in flexible and printable devices shapeable microelectronics can provide novel functionalities with unmatched mechanical and electrical performance. For the purpose of shapeable microelectronics, novel materials based on metallic multilayers, photopatternable organic and metal-organic polymers were synthesized. Achieved polymeric platform, being mechanically adaptable, provides possibility of a gentle automatic attachment and subsequent release of active micro-scale devices. Equipped with integrated electronic the platform provides an interface to the neural tissue, confining neural fibers and, if necessary, guiding the regeneration of the tissue with a minimal impact. The self-assembly capability of the platform enables the high yield manufacture of three-dimensionally shaped devices that are relying on geometry/stress dependent physical effects that are evolving in magnetic materials including magentostriction and shape anisotropy. Developed arrays of giant magnetoimpedance sensors and cuff implants provide a possibility to address physiological processes locally or distantly via magnetic and electric fields that are generated deep inside the organism, providing unique real time health monitoring capabilities. Fabricated on a large scale shapeable magnetosensory systems and nanostructured materials demonstrate outstanding mechanical and electrical performance. The novel, shapeable form of electronics can revolutionize the field of mechanical prosthetics, wearable devices, medical aids and commercial devices by adding novel sensory functionalities, increasing their capabilities, reducing size and power consumption.

On demand single-photon and entangled-photon sources are key building-blocks for many proposed photonic quantum technologies. For practical device applications, epitaxially grown quantum dots (QDs) are of increasing importance due to their bright photon emission with sharp line width. Particularly, they are solid-state systems and can be easily embedded within a light-emitting diode (LED) to achieve electrically driven sources. Therefore, one would expect a full-fledged optoelectronic quantum network that is running on macroscopically separated, QD-based single- and entangled-photon devices. An all-electrically operated wavelength-tunable on demand single-photon source (SPS) is demonstrated first. The device consists of a LED in the form of self-assembled InGaAs QDs containing nanomembrane integrated onto a piezoelectric crystal. Triggered single photons are generated via injection of ultra-short electrical pulses into the diode, while their energy can be precisely tuned over a broad range of about 4.8 meV by varying the voltage applied to the piezoelectric crystal. High speed operation of this single-photon emitting diode up to 0.8 GHz is demonstrated. In the second part of this thesis, a fast strain-tunable entangled-light-emitting diode (ELED) is demonstrated. It has been shown that the fine structure splitting of the exciton can be effectively overcome by employing a specific anisotropic strain field. By injecting ultra-fast electrical pulses to the diode, electrically triggered entangled-photon emission with high degree of entanglement is successfully realized. A statistical investigation reveals that more than 30% of the QDs in the strain-tunable quantum LED emit polarization-entangled photon-pairs with entanglement-fidelities up to f+ = 0.83(5). Driven at the highest operation speed ever reported so far (400 MHz), the strain-tunable quantum LED emerges as unique devices for high-data rate entangled-photon applications. In the end of this thesis, on demand and wavelength-tunable LH single-photon emission from strain engineered GaAs QDs is demonstrated. Fourier-transform spectroscopy is performed, from which the coherence time of the LH single-photon emission is studied. It is envisioned that this new type of LH exciton-based SPS can be applied to realize an all-semiconductor based quantum interface in the foreseeable distributed quantum networks.

Vertically rolled-up microcavities are fabricated using differentially strained nanomembranes by employing rate and temperature gradients during electron beam evaporation of SiO2. The geometry of the rolled-up tubes is defined by a photo-lithographically patterned polymer sacrificial layer beneath the SiO2 layers that is dissolved to start the rolling. Rolled-up tubes support resonances formed by constructive interference of light propagating along the circumference. Optical studies are performed in the visible spectral range using a micro-photoluminescence (µPL) setup to excite and detect optical modes. Record high quality factors (Q factors) of 5400 for rolled-up resonators probed in PL-emission mode are found and their limits are theoretically investigated. Axial modes can also be supported when an increased winding number in the center is realized by appropriate pattern designs. In addition, higher order radial modes can be confined when atomic layer deposition (ALD) coatings are applied. Both types of modes are identified using polarization and spatially resolved µPL maps. Evanescent-wave coupling by tapered fibers and tubes on substrates is the second method used to study light confinement and to demonstrate frequency filtering in ALD coated rolled-up microcavities. Scans are performed by monitoring light from a tunable laser in the range of 1520-1570 nm after transmission through the tapered fiber. Dips in the spectrum are found and attributed to fundamental and axial resonant modes. Moreover, by coupling two tapered fibers to a lifted rolled-up microcavity, a four-port add-drop filter is demonstrated as a future component for vertical resonant light transfer in on-chip optical networks. Simulations show that the subwavelength tube wall thickness limits the Q factor at infrared wavelengths and ALD coatings are necessary to enhance the light confinement. After coating, two linear polarization states are found in experiment and fundamental and axial modes can be selectively excited by coupling the fiber to different positions along the tube axis. Spatially and polarization resolved transmission maps reveal a polarization dependent axial mode distribution which is verified theoretically. The results of this thesis are important for lab-on-chip applications where rolled-up microcavities are employed as high resolution optofluidic sensors as well as for future uses as waveguide coupled components in three-dimensional multi-level optical data processing units to provide resonant interlayer signal transfer.

This work is devoted to investigate light confinement in rolled-up microtubular cavities and their optofluidic applications. The microcavities are fabricated by a roll-up mechanism based on releasing pre-strained silicon-oxide nanomembranes. By defining the shape and thickness of the nanomembranes, the geometrical tube structure is well controlled. Micro-photoluminescence spectroscopy at room temperature is employed to study the optical modes and their dependence on the structural characteristics of the microtubes. Finite-difference-time-domain simulations are performed to elucidate the experimental results. In addition, a theoretical model (based on a wave description) is applied to describe the optical modes in the tubular microcavities, supporting quantitatively and qualitatively the experimental findings. Precise spectral tuning of the optical modes is achieved by two post-fabrication methods. One method employs conformal coating of the tube wall with Al2O3 monolayers by atomic-layer-deposition, which permits a mode tuning over a wide spectral range (larger than one free-spectral-range). An average mode tuning to longer wavelengths of 0.11nm/ Al2O3-monolayer is obtained. The other method consists in asymmetric material deposition onto the tube surface. Besides the possibility of mode tuning, this method permits to detect small shape deformations (at the nanometer scale) of an optical microcavity. Controlled confinement of resonant light is demonstrated by using an asymmetric cone-like microtube, which is fabricated by unevenly rolling-up circular-shaped nanomembranes. Localized three-dimensional optical modes are obtained due to an axial confinement mechanism that is defined by the variation of the tube radius and wall windings along the tube axis. Optofluidic functions of the rolled-up microtubes are explored by immersing the tubes or filling their core with a liquid medium. Refractive index sensing of liquids is demonstrated by correlating spectral shift of the optical modes when a liquid interacts with the resonant light of the microtube. In addition, a novel sensing methodology is proposed by monitoring axial mode spacing changes. Lab-on-a-chip methods are employed to fabricate an optofluidic chip device, allowing a high degree of liquid handling. A maximum sensitivity of 880 nm/refractive-index-unit is achieved. The developed optofluidic sensors show high potential for lab-on-a-chip applications, such as real-time bio/chemical analytic systems.

Understanding thermal transport in nanoscale is important for developing nanostructured thermolelectric materials and for heat management in nanoelectronic devices. This dissertation is devoted to understand thermal transport through SiGe based superlattices. First, we systematically studied the cross-plane thermal conductivity of SiGe superlattices by varying the thickness of Si(Ge) spacers thickness. The observed additive character of thermal resistance of the SiGe nanodot/planar layers allows us to engineer the thermal conductivity by varying the interface distance down to ~1.5 nm. Si-Ge intermixing driven by Ge surface segregation is crucial for achieving highly diffusive phonon scattering at the interfaces. By comparing the thermal conductivity of nanodot Ge/Si superlattices with variable nanodot density and superlattices with only wetting layers, we find that the effect of nanodots is comparable with that produced by planar wetting layers. This is attributed to the shallow morphology and further flattening of SiGe nanodots during overgrowth with Si. Finally, the experiments show that the interface effect on phonon transport can be weakened and even eliminated by reducing the interface distance or by enhancing Si-Ge intermixing around the interfaces by post-growth annealing. The results presented in this dissertation are expected to be relevant to applications requiring optimization of thermal transport for heat management and for the development of thermoelectric materials and devices based on superlattice structures. Verständnis des thermischen Transport auf Nanoskala ist sowohl grundlegend für die Entwicklung nanostrukturierter Materialien, als auch für Temperaturkontrolle in nanoelektronischen Bauteilen. Diese Dissertation widmet sich der Erforschung des thermischen Transports durch SiGe basierenden Übergittern. Variationen, der Si(Ge) Schichtdicken, wurden zur systematischen Untersuchung der Normalkomponente zur Wachstumsrichtung der Wärmeleitfähigkeit, von SiGe Übergittern, genutzt. Die Beobachtung des additiven Charakters, des thermischen Widerstands, der SiGe Schichten, mit oder ohne Inselwachstum, ermöglicht die Erstellung von Strukturen mit bestimmter Wärmeleitfähigkeiten durch die Variation der Schichtdicken bis zu einer Minimaldistanz zweier Schichtübergänge von ~1.5nm. Die Ge Segregation führt zu einer Vermischung, von Si und Ge, welche eine essentielle Rolle zur diffusen Phononenstreuung spielt. Unsere Untersuchungen, von planaren Übergittern und Übergittern mit variabler Inseldichte, zeigen, dass Inseln und planare Schichten zu einer vergleichbaren Reduktion, der Wärmeleitfähigkeit, führen. Diese Beobachtung lässt sich, sowohl auf die flache Morphologie als auch die Abplattung der SiGe Inseln, aufgrund der Überwachsung mit Si, zurückführen. Die Experimente zeigen außerdem, dass sich der Barriereneffekt, der Schichtgrenzen, durch Reduktion der Schichtabstände und durch verstärkte Vermischung im Bereich der Schichtgrenzen, durch Erhitzung, eliminieren lässt. Die präsentierten Messungen sind sowohl, für die Entwicklung jener Bauteile, die eine Optimierung des thermischen Transports oder Temperaturmanagment erfordern, als auch von thermoelektrischen Matieralien und Bauteilen, basierend auf Übergittern, relevant.

Over the past two decades, organic semiconductors played a growing part as active layers in several electronic systems such as sensors, field‑effect transistors or light emitting diodes to cite a few. In fact, organic materials offer a high versatility and flexibility. However, pure organic systems often lack stability and robustness, which can be overcome by combining them with inorganic scaffolds. In this work, a conducting polymer, polypyrrole (PPy) is employed to create new sensor elements based on the combination of both inorganic and organic layers. Electrical measurements, infrared spectroscopy and current sensing atomic force microscopy provides a better understanding of the polymer behavior upon immersion in aqueous solutions. The observed discharge in water leads to a straightforward application of the device as an in‑flow sensor for several acids like HCl, H2SO4 and H3PO4. The wide range of sensing concentrations as well as the low detection limit place the present detector among the best reported so far in the literature. In a further step to turn towards lab‑in‑a‑tube devices, tubular‑shaped‑integrated microelectrodes are developed by using the rolled‑up technology. As a proof of concept, the successful integration of PPy as an active layer and its use as a gas sensor for volatile organic compounds (VOCs) is demonstrated. Finally, by adapting the rolled‑up top electrodes, as developed by Bof Bufon et al. for self‑assembled monolayers (SAMs), thin PPy films (

Polarization entangled photon pairs on demand are considered to be an important building block of quantum communication technology. It has been demonstrated that semiconductor quantum dots (QDs), which exhibit a certain spatial symmetry, can be used as a triggered, on-chip source of polarization entangled photon pairs. Due to limitations of the growth, the as-grown QDs usually do not exhibit the required symmetry, making the availability of post-growth tuning techniques essential. In this work first the QD-morphology of hundreds of QDs is correlated with the optical emission of neutral excitons confined in GaAs/AlGaAs QDs. It is presented how elastic anisotropic stress can be used to partially restore the symmetry of self-assembled GaAs/AlGaAs and InGaAs/GaAs QDs, making them as candidate sources of entangled photon pairs. As a consequence of the tuning of the QD-anisotropy we observe a rotation of the polarization of the emitted light. The joint modification of polarization orientation and QD anisotropy can be described by an anticrossing of the so-called bright excitonic states. Furthermore, it is demonstrated that anisotropic stress can be used to tune the purity of the hole states of the QDs by modifying the degree of heavy and light hole mixing. This ability might be interesting for applications using the hole spin as a so-called quantum bit.

By implementing the rolled-up microfabrication method based on strain engineering, several systems are investigated within the contents of this thesis. The structural morphing of planar geometries into three-dimensional structures opens up many doors for the creation of unique material configurations and devices. An exploration into several novel microsystems, encompassing various scientific subjects, is made and methods for on-chip integration of these devices are presented. The roll-up of a metal and oxide allows for a cylindrical hollow-core structure with a cladding layer composed of a multilayer stack, plasmonic metamaterial. This structure can be used as a platform for a number of optical metamaterial devices. By guiding light radially through this structure, a theoretical investigation into the system makeup of a rolled-up hyperlens, is given. Using the same design, but rather propagating light parallel to the cylinder, a novel device known as a metamaterial optical fiber is defined. This fiber allows light to be guided classically and plasmonically within a single device. These fibers are developed experimentally and are integrated into preexisting on-chip structures and characterized. A system known as lab-in-a-tube is introduced. The idea of lab-in-a-tube combines various rolled-up components into a single all-encompassing biosensor that can be used to detect and monitor single bio-organisms. The first device specifically tailored to this system is developed, flexible split-wall microtube resonator sensors. A method for the capturing of embryonic mouse cells into on-chip optical resonators is introduced. The sensor can optically detect, via photoluminescence, living cells confined within the resonator through the compression and expansion of a nanogap built within its walls. The rolled-up fabrication method is not limited to the well-investigated systems based on the roll-up from semiconductor material or from a photoresist layer. A new approach, relying on the delamination of polymers, is presented. This offers never-before-realized microscale structures and configurations. This includes novel magnetic configurations and flexible fluidic sensors which can be designed for on-chip and roving detector applications.

The combination of modern self-assembly techniques with well-established top-down processing methods pioneered in the electronics industry is paving the way for increasingly sophisticated devices in the future[1]. Nanomembranes, made from a variety of materials, can provide the necessary framework for a diverse range of device structures incorporating wrinkling, buckling, folding, and rolling of thin films[2, 3]. Over the past decade, an elegant symbiosis of bottom-up and top-down methods has been developed, allowing the fabrica- tion of hybrid layer systems via the controlled release and rearrangement of inherently strained layers [4]. Self-assembled rolled-up structures[4, 5] have become increasingly at- tractive in a number of fields including micro/nano uidics[6], optics[7](including metama- terial optical fibers[8]), Lab on a Chip applications[9], and micro- and nanoelectronics[10]. The use of such structures for microelectronic applications has been driven by the versatility in contacting geometries and the abundance of material combinations that these devices offer. By allowing devices to expand in the third dimension, certain obstacles that inhibit 2D structuring can be overcome in elegant ways. Similarly, recent progress in nanostructured superconducting electronic structures has been receiving increased attention[11]. The advancement of such devices has been mo- tivated by their use in quantum computation[12], high sensitivity radiation sensors[13], precision voltage standards[14] and superconducting spintronics[15] to name a few. Combining semiconductor with superconductor materials to create new hybrid geometries is advantageous because it adds the functionalities of the semiconductor, including high charge carrier mobilities, gating possibilities, and refined processing technologies. The main focus of the work presented in this thesis is the development of new methods for controlling strain behavior and its applications toward novel semiconduc- tor/superconductor heterostructures based on nanomembranes. More specifically, the goal is to integrate inherently strained semiconductor layer structures with superconducting materials to create innovative electronic devices by the controlled releasing and rearrangement of thin films. By rolling up pre-patterned semiconductor/superconductor layers, device geometries have been realized that are not feasible using any other technique. In this way, superconducting hybrid junctions, or Josephson junctions, have been created and their basic properties investigated. The Josephson effect, and junctions displaying this quantum coherent behavior, have found many essential uses in diverse areas of science and technology. Many research groups around the world are involved in finding new materials and fabrication methods to tune the properties and structure of such Josephson devices further[11]. The inclusion of semi- conductors, for example, allows for a greater control of the charge carrier density within the junction area, thus allowing for "transistor-like" behavior in these superconducting devices. By rolling up the superconductor contacts using a strained semiconductor as scaffolding, the fabrication of hybrid nano-junctions is simplified drastically, removing the need for complicated processing steps such as electron-beam or nano-imprint lithography. Furthermore, the technique allows many nanometer-sized devices to be created in parallel on a single chip which has the advantage that it can be scaled up to full-wafer processing. First, post-growth processing techniques of epitaxial layers are developed in order to extend the control of hybrid device fabrication. Here, three unique concepts for controlling the rolling behavior of strained semiconductor nanomembranes are presented. First an optical method for inhibiting the rolling of the strained layers is described. Next, a selective etching method for destroying the inherent strain within the semiconductor layer is introduced. Finally, a method by which the strain gradient across a trilayer stack is altered in situ during rolling is presented. Next, the fabrication of a hybrid nanomembrane-based superconducting device is presented. Various experimental details of the fabrication process are analyzed, and the electronic properties of the completed device are investigated. The devices created here highlight the fabrication process in which nanometer-sized structures are created using self-assembly techniques and standard microelectronics fabrication methods, presenting a new method to circumvent more complicated processing techniques. References [1] G. M. Whitesides and B. Grzybowski. Self-assembly at all scales. Science 295, 2418{2421 (2002). [2] Y. G. Sun, W. M. Choi, H. Q. Jiang, Y. G. Y. Huang and J. A. Rogers. Controlled buckling of semiconductor nanoribbons for stretchable electronics. Nature Nanotechnology 1, 201{207 (2006). [3] O. G. Schmidt and K. Eberl. Nanotechnology - Thin solid films roll up into nanotubes. Nature 410, 168 (2001). [4] O. G. Schmidt, C. Deneke, Y. Nakamura, R. Zapf-Gottwick, C. Mller and N. Y. Jin-Phillipp. Nanotechnology { Bottom-up meets top-down. Advanced Solid State Physics 42, 231 (2002). [5] V. Ya. Prinz, V. A. Seleznev, A. K. Gutakovsky, A. V. Chehovskiy, V. V. Preobrazhenskii, M. A. Putyato and T. A. Gavrilova. Free-standing and overgrown InGaAs/GaAs nanotubes, nanohelices and their arrays. Physica E 6, 828 (2000). [6] D. J. Thurmer, C. Deneke, Y. F. Mei and O. G. Schmidt. Process integration of microtubes for uidic applications. Applied Physics Letters 89, 223507 (2006). [7] R. Songmuang, A. Rastelli, S. Mendach and O. G. Schmidt. SiOx/Si radial superlattices and microtube optical ring resonators. Applied Physics Letters 90, 091905 (2007). [8] E. J. Smith, Z. W. Liu, Y. F. Mei and O. G. Schmidt. Combined surface plasmon and classical waveguiding through metamaterial fiber design. Nano Letters 10, 1{5 (2010). [9] G. S. Huang, Y. F. Mei, D. J. Thurmer, E. Coric and O. G. Schmidt. Rolled-up transparent microtubes as two-dimensionally confined culture scaffolds of individual yeast cells. Lab on a Chip 9, 263{268 (2009). [10] C. C. B. Bufon, J. D. C. Gonzalez, D. J. Thurmer, D. Grimm, M. Bauer and O. G. Schmidt. Self-assembled ultra-compact energy storage elements based on hybrid nanomembranes. Nano Letters 10, 2506{2510 (2010). [11] G. Katsaros, P. Spathis, M. Stoffel, F. Fournel, M. Mongillo, V. Bouchiat, F. Lefloch, A. Rastelli, O. G. Schmidt and S. De Franceschi. Hybrid superconductor-semiconductor devices made from self-assembled SiGe nanocrystals on silicon. Nature Nanotechnology 5, 458{464 (2010). [12] Y. J. Doh, J. A. van Dam, A. L. Roest, E. P. A. M. Bakkers, L. P. Kouwenhoven and S. De Franceschi. Tunable supercurrent through semiconductor nanowires. Science 309, 272{275 (2005). [13] F. Giazotto, T. T. Heikkila, G. P. Pepe, P. Helisto, A. Luukanen and J. P. Pekola. Ultrasensitive proximity Josephson sensor with kinetic inductance readout. Applied Physics Letters 92, 162507 (2008). [14] S. P. Benz. Superconductor-normal-superconductor junctions for programmable voltage standards. Applied Physics Letters 67, 2714{2716 (1995). [15] Y. C. Tao and J. G. Hu. Superconducting spintronics: Spin-polarized transport in superconducting junctions with ferromagnetic semiconducting contact. Journal of Applied Physics 107, 041101 (2010).