Charakterisierung funktionaler Nanomaterialien für biomagnetische Sensoren und Atemanalyse

The presented thesis is covering materials aspects for the development of magnetoelectric sensors for biomagnetic sensing and solid state sensors for breath monitoring. The electrophysiological signals of the human body and especially their irregularities provide extremely valuable information about the heart, brain or nerve malfunction in medical diagnostics. Similar and even more detailed information is contained in the generated biomagnetic fields which measurement offers improved diagnostics and treatment of the patients. A new type of room temperature operable magnetoelectric composite sensors is developed in the framework of the CRC1261 Magnetoelectric Sensors: From Composite Materials to Biomagnetic Diagnostics. This thesis focuses on the individual materials structure-property relations and their combination in magnetoelectric composite sensors studied by electron beam based techniques, at lengths scales ranging from micrometers to atomic resolution. The first part of this thesis highlights selected studies on the structural and analytic aspects of single phase materials and their composites using TEM as the primary method of investigation. With respect to the piezoelectric phase, alternatives to AlN have been thoroughly investigated to seek for improvement of specific sensor approaches. In this context, the alloying of Sc into the AlN matrix has been demonstrated to yield high quality films with improved piezoelectric and unprecedented ferroelectric properties grown under the control of deposition parameters. Lead-free titanate films with large piezo-coefficients at the verge of the morphotropic phase boundary as alternative to PZT films have been investigated in terms of crystal symmetry, defect structure and domains of cation ordering. New morphologies of ZnO and GaN semiconductors envisioned for a piezotronic-based sensor approach were subject of in-depth defect and analytical studies describing intrinsic defects and lattice strains upon deposition as well as hollow composite structures. When the dimensions of a materials are reduced, novel exciting properties such as in-plane piezoelectricity can arise in planar transition-metal dichalcogenides. Here, the turbostratic disorder in a few-layered MoSe2 film has been investigated by nanobeam electron diffraction and Fast Fourier Transformations. From the perspective of magnetic materials, the atomic structure of magnetostrictive multilayers of FeCo/TiN showing stability up to elevated temperatures has been analyzed in detail regarding the crystallographic relationship of heteroepitaxy in multilayer composites exhibiting individual layer thicknesses below 1 nm. Further, magnetic hard layers have been investigated in the context of exchange spring concepts and ME composites based on shape memory alloy substrates have been studied regarding structural changes implied by different annealing processes. The second part of this thesis introduces materials aspects and sensor studies on gas detection in the clinical context of breath analysis. The detection of specific vapors in the human breath is of medical relevance, since certain species can be enriched depending on the conditions and processes within the human body. Hence, they can be regarded as biomarkers for the patients condition of health. The selection of suitable materials and the gas measurement working principle are considered and selected studies on solid state sensors with different surface functionalization or targeted application on basis of ZnO or CuO-oxide and Fe-oxide species are presented

FABRICATION OF ZINC OXIDE MICRO-NANOSTRUCTURES AND THEIR APPLICATIONS IN GAS SENSING AND NANOCOMPOSITES

To date, one-dimensional ZnO micro/nanostructures have been attracting much attention for wide potential applications due to their unique electrical, piezoelectric, optoelectronic, and photochemical properties. The overall objective of this dissertation is to grow various ZnO micro and nanostructures using a novel microwave thermal evaporation-deposition approach, to explore the application of ZnO nanostructures in gas sensing, and to fabricate and characterize multifunctional ZnO nanowires-polyimide nanocomposite. Therefore, three parts were included in this study: (1) A novel thermal evaporation-deposition method using microwave energy was investigated. Batch of ZnO structures including microtubes, microrods, nanotubes, nanowires and nanobelts have been successfully synthesized in the microwave system with a unique source materials-substrate configuration and a desirable temperature profile. These products are pure, structurally uniform, and single crystalline. The photoluminescence (PL) exhibits strong ultraviolet emission at room temperature, indicating potential applications for short-wave light-emitting photonic devices. (2) Piezoelectric crystal langasite bulk acoustic wave (LGS) resonator based high temperature gas sensor was fabricated. Ordered ZnO nanowire arrays were grown on the langasite resonator as the sensitive layer by two-step hydrothermal method at low temperature. The gas sensor coated with ZnO nanowire arrays exhibited good sensitivity to NO2 and NH3. The response of the sensor is fast due to the large surface area of ZnO nanowires. In addition, this work demonstrates that the combination of nanowire arrays with langasite thickness shear mode resonators could provide a promising high temperature gas sensing platform with both high sensitivity and enhanced response speed. (3) The nanocomposite with controlled alignment of ZnO nanowires in the polyimide matrix was achieved using self-alignment method and external electric field assisted method. For the the self-alignment process, the morphologies of the designed nanocomposites were dramatically influenced by the viscosity of the polymer and the geometrical structure of ZnO nanowires. For the nanocomposite prepared by the electric field assisted alignment, the density and the alignment degree of ordered ZnO nanowires significantly depended on the magnitude and the frequency of the applied ac electric field. The DC offset voltage had strong effect on the deposition sites of nanowires. The resultant nanocomposite devices exhibited great dielectric constant and conductivity enhancement at room temperature due to the interfacial effect between ZnO nanowires and the polymer matrix. These nanocomposites combining the superb properties of ZnO nanowires with the polyimide matrix provide a smart material candidate for multifunctional applications that require self-sensing and self-actuation capabilities. The self-alignment method and electric field assisted alignment method also provide a bright route to combine superb properties of nanomaterials with the lightweight, flexibility, and manufacturability of dielectric polymers for future generations of multifunctional materials

Electrochemistry: A basic and powerful tool for micro- and nanomotor fabrication and characterization

Electrochemistry, although an ancient field of knowledge, has become of paramount importance in the synthesis of materials at the nanoscale, with great interest not only for fundamental research but also for practical applications. One of the promising fields in which electrochemistry meets nanoscience and nanotechnology is micro/nanoscale motors. Micro/nano motors, which are devices able to perform complex tasks at the nanoscale, are commonly multifunctional nanostructures of different materials - metals, polymers, oxides- and shapes -spheres, wires, helices- with the ability to be propelled in fluids. Here, we first introduce the topic of micro/nanomotors and make a concise review of the field up to day. We have analyzed the field from different points of view (e.g. materials science and nanotechnology, physics, chemistry, engineering, biology or environmental science) to have a broader view of how the different disciplines have contributed to such exciting and impactful topic. After that, we focus our attention on describing what electrochemical technology is and how it can be successfully used to fabricate and characterize micro/nanostructures composed of different materials and showing complex shapes. Finally, we will review the micro and nanomotors fabricated using electrochemical techniques with applications in biomedicine and environmental remediation, the two main applications investigated so far in this field. Thus, different strategies have thus been shown capable of producing core-shell nanomaterials combining the properties of different materials, multisegmented nanostructures made of, for example, alternating metal and polymer segments to confer them with flexibility or helicoidal systems to favor propulsion. Moreover, further functionalization and interaction with other materials to form hybrid and more complex objects is also shown

Fibrous biomimetic and biohybrid carbon scaffolds for 3D cell growth

The formation of three dimensional tissue (3D) in the laboratory highly depends on the biomimetic environment, the engineered extracellular matrix (scaffold), the cell type as well as the biologically active components.The primary focus of this study is to fabricate and functionalize these highly porous carbon-based scaffolds and to understand biological and cellular responses toward them. To exploit the unique spatial features of the highly porous network for bone tissue engineering, bioactive ceramic nanoparticles (hydroxyapatite (HA), bioactive glass (BG)) are successfully incorporated into CNT-based scaffolds. The methods presented in this thesis provide a novel concept to generate biocompatible and bioactive fibrous carbon scaffolds that mimic the ECM with the additional feature of conductivity. The generated scaffolds can serve as groundbreaking fiber systems for 3D cell growth, which pave the way toward further investigations of diverse tissue engineering and bioapplications.Die Entstehung eines dreidimensionalen (3D) Gewebes im Labor haängt stark von der biomimetischen Umgebung, der geformten extrazellulären Matrix (Gerüst), dem Zelltyp sowie von den biologisch aktiven Komponenten ab. Der Hauptschwerpunkt dieser Studie ist es, sowohl solche hochporösen kohlenstoffbasierten Gerüste herzustellen und zu funktionalisieren, als auch die biologischen und zellulären Reaktionen auf diese Gerüste verstehen zu lernen. Um die einzigartigen Eigenschaften dieser hochporösen Netzwerke für die Knochengewebezüchtung zu nutzen, wurden bioaktive, keramische Nanopartikel (Hydroxyapetite (HA), bioaktives Glass (BG)) erfolgreich in die CNT-basierten Gerüste eingebaut. Die hier präsentierten Methoden zeigen neue Konzepte der Herstellung von biokompatiblen und -aktiven Kohlenstoff Matrixen mit dem Vorteil der elektrischen Leitfähigkeit. Diese imitieren mit ihrer fibrösen Struktur die Extrazelluläre Matrix im Gewebe und generieren ein bahnbrechendes 3D Sytem für die Zellkultivierung. Im Bereich des Tissue Engineering und der biologischen Anwendungen können diese Strukturen somit als Grundlage zukünftiger Forschung dienen

Design and developement of energy efficient miniature devices for energy harvesting, thermal management and biomedical applications

This thesis aims to make contributions to the literature in the field of energy efficient miniature devices for energy harvesting, thermal management and biomedical applications. In the first part, experimental results related to energy harvesting capability of a miniature power reclamation device based on external liquid flows are represented. The device’s reclamation principle depends on the conversion of mechanical energy into electrical energy. The mechanical energy in the device was generated by capturing vibrations caused by external liquid flows via the device’s tails, which were designed by taking inspiration from the body shape of the black ghost knife fish, apteronotus albifrons. The reclaimed power was obtained through magnetic polarization, which was generated by rotating circular waterproof magnet structures as a result of rotating movements of the mentioned tails and is transferred to 3.76 V (Ni-Mg) batteries. Power reclamation was also simulated using COMSOL 4.2 software in order to compare the maximum reclaimable theoretical energy harvesting capacity to the experimental results. Experimental tests were performed within a range of flow velocities (1.0 m/s ~ 5.0 m/s) for various fluid densities (plain water, low-salt and highsalt water) in order to obtain extensive experimental data related to the device in response to external fluid flows. According to experimental results, the device could generate powers up to 17.2W. On the other hand, the maximum reclaimable power was obtained as 25.7W from COMSOL Multiphysics 4.2 simulations. Promising energy harvesting results imply that the output from this device could be used as a power source in many applications such as in lighting and GPS (Global positioning system) devices. In the second part of the thesis, a miniature system was used for flow boiling in mini/microtubes. Flow boiling was investigated with surface enhancements provided by crosslinked polyhydroxyethylmethacrylate (pHEMA) coatings, which were used as a crosslinker coating type with different thicknesses (~50 nm, 100 nm and 150 nm) on inner microtube walls. Flow boiling heat transfer experiments were conducted on microtubes (with inner diameters of 249 μm, 507 μm and 908 μm) coated with crosslinked pHEMA coatings. pHEMA nanofilms were deposited with the initiated chemical vapor deposition (iCVD) technique. De-ionized water was utilized as the working fluid. Experimental results obtained from coated microtubes were compared to their plain surface counterparts at two different mass fluxes (5,000 kg/m2s and 20,000 kg/m2s), and significant enhancements in Critical Heat Flux (up to 29.7 %) and boiling heat transfer (up to 126.2 %) were attained. The enhancement of boiling heat transfer was attributed to the increase in nucleation site density and incidence of bubbles departing from surface due to porous structure of crosslinked pHEMA coatings. The underlying mechanism was explained with suction-evaporation mode. Moreover, thicker pHEMA coatings resulted in larger enhancements in both CHF and boiling heat transfer. In the third part, a platform for gene delivery via magnetic actuation of nanoparticles was developed. The importance of high transfection efficiency has been emphasized in many studies investigating methods to improve gene delivery. Accordingly, non-viral transfection agents are widely used as transfection vectors to condense oligonucleotides, DNA, RNA, siRNA, deliver into the cell, and release the cargo. Polyethyleneimine (PEI) is one of the most popular non-viral transfection agents. However, the challenge between high transfection efficiency and toxicity of the polymers is not totally resolved. The delivery of necessary drugs and genes for patients and their transport under safe conditions require carefully designed and controlled delivery systems and constitute a critical stage of patients’ treatment. Compact systems are considered as the strongest candidate for the preparation and delivery of drugs and genes under leak free and safe conditions because of their low energy consumption, low waste disposal, parallel and fast processing capabilities, removal of human factor, high mixing capabilities, enhanced safety, and low amount of reagents. Motivated by this need in the literature, The use of PEI-SPION (Super paramagnetic iron oxide nanoparticles) as transfection agents in in-vitro studies was investigated with the effect of varying magnetic fields provided by a special magnetic system design, which was used as a miniature magnetic actuator device offering different magnet's turn speeds in the system. Experimental results obtained from experimental magnetic actuator systems were compared to the experiments without magnetic actuation, and it was observed that significant enhancements in transfection efficiency (up to 25-30 %) in MCF-7 and PC-3 cells were attained

Nanoscale Lasers with Optical Microcavities.

Nanoscale lasers on silicon, defined by a confined modal volume less than a cubic wavelength in free space, have been attracting interest due to their possible application in on- and off-chip optical interconnects. This thesis is devoted to exploring different nanoscale coherent light sources with low threshold, which can be integrated with silicon technology. Silicon-based coherent light sources using colloidal PbSe quantum dots (QDs) embedded in photonic crystal (PC) microcavities were investigated. The room temperature photo- and electro-luminescence were enhanced by the PC microcavity at a wavelength of ~1.5μm accompanied by a linewidth reduction to ~4nm. The PbSe QDs were also sandwiched between metallic and distributed Bragg reflector (DBR) mirrors. Measured electroluminescence at room temperature showed coherent and directional emission at a wavelength of ~1.5μm with a linewidth of ~3nm. Optically pumped lasing from a monolithically integrated single GaN nanowire embedded in a PC microcavity on silicon was demonstrated. A single GaN nanowire is a favorable material to achieve nanoscale lasing due to its defect free nature and nanoscale dimensions. The PC microcavity device exhibited a lasing transition at λ=371.3 nm with a linewidth of 0.55nm and a modal volume of 0.003223μm3 (0.92(λ/n)3). A single GaN nanowire was also embedded in a dielectric microcavity with DBR mirrors to investigate optically pumped polariton lasing. Extremely low threshold polariton lasing, almost two orders of magnitude lower than previously reported values, was measured. Finally, a strain-driven rolled up microtube cavity with InAs QDs was studied. Rolled up microtubes provide a high quality factor due to their atomically smooth surface and near perfect overlap between the maximum optical field intensity and the QD layers. Optically pumped lasing from a free-standing microtube was demonstrated with multiple resonance peaks spaced apart by ~12meV with a pump threshold of ~700kW/cm2. Theoretical studies of the modal gain in a microtube were carried out to understand the effects of key design parameters, such as the tube diameter and wall thickness. The analysis reveals that the modal gain of this type of laser is inversely proportional to the radius of the microtube.Ph.D.Electrical EngineeringUniversity of Michigan, Horace H. Rackham School of Graduate Studieshttp://deepblue.lib.umich.edu/bitstream/2027.42/89735/1/jsheo_1.pd

Synthesis of peptide microstructures for nanogenerators

University of Minnesota Ph.D. dissertation. May 2017. Major: Mechanical Engineering. Advisors: Rusen Yang, Xiaojia Wang. 1 computer file (PDF); viii, 88 pages.Electromechanical energy conversion at the small scale utilizing micro/nanomaterials can have significant technological impacts in various areas such as mechanical energy harvesting, tissue engineering, and sensing/actuation. The breakthrough discoveries over the last decade in piezoelectric micro/nanostructures, which converts minute material deformation directly into electrical signal, has spurred intense research in micro/nano scale mechanical energy harvester, also called nanogenerator. Although a variety of advanced inorganic piezoelectric micro/nanostructures have been fabricated, little progress has been made for bioinspired piezoelectric materials, which can enable biocompatible and biodegradable energy harvesting. Meanwhile, piezoelectricity has been widely observed in biological materials such as bone, collagen, viruses and other protein-based materials. Diphenylalanine (FF) peptide, which consists of two naturally occurring phenylalanine amino acids, has attracted significant research interest due to its exceptional mechanical and piezoelectric properties as well as rich biological properties. Thus FF is promising to become one of the most technologically important bioinspired materials for piezoelectric devices, such as mechanical energy harvester. However, many challenges exist in realizing the potential of piezoelectric FF peptide, such as the lack of scalable structural alignment, lack of controllability of polarizations and lack of prototyped device. This thesis aims to address those challenges to advance the applications of FF peptide towards piezoelectric nanogenerator (PENG) and beyond. As an alternative to PENG, which converts minute material deformation into electricity, triboelectric nanogenerator (TENG) has also been proposed recently to harvest energy from large motion through a combination of triboelectric effect and electrostatic induction. Since tiny material deformation and large motion are usually available together, advances in nanogenerator are needed to harvest them effectively. Due to the apparent complementary energy conversion mechanisms of piezoelectric and triboelectric effects, performance of TENG in various environmental conditions will be studied, and hybridization of PENG and TENG into one device will also be explored as an approach to enhance the outputs of the mechanical energy harvester. In overview, first this thesis will develop a novel low-temperature epitaxial growth process to address the challenge of synthesizing aligned piezoelectric FF peptide structures in a scalable and controllable manner. Second, the random orientation and unswitchability of its polarization will be addressed by modifying the growth parameters and including an applied external electric field during the growth. The improved FF microstructures will be used to demonstrate the first peptide PENG. Third, a standalone TENG will be studied for its operation in various environmental conditions, verifying its wide applicability. Finally, a hybrid nanogenerator structure will be proposed to constructively combine the outputs of FF peptide PENG with a TENG, and the hybrid energy conversion process will be experimentally verified

Strong optical coupling between 3D confined resonant modes in microtube cavities

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