Gold nanoclusters possess both theoretical and practical importance in the development of ultrasensitive biosensors based on surface-enhanced Raman spectroscopy (SERS). Manipulation of gold nanoclusters in a predictable and reproducible manner for the application of refined biochemical analysis still remains challenging. In this study, high-purity gold nanoclusters are isolated via a simple method based on density gradient centrifugation. Three distinct bands including monomers, small aggregates (2-4 nanospheres), and large aggregates (>5 nanospheres) can be separated via density gradient centrifugation. The isolated gold nanoclusters greatly enhance the Raman intensity of the trapped dye molecules such that single nanocluster detection is feasible. To develop a gold nanoparticle-based biosensor for influenza virus, effort was also made to modify recognition moieties such as aptamers to gold nanoparticles via distinct approaches. The increase of hydraulic diameter and the shift of optical absorbance spectrum indicate the success of surface modification to gold nanoparticles. / Master of Science

Fiber Raman amplification using the transmission line is a promising technology to increase the repeater distance as well as the capacity of the communication systems. Because of the growing importance of fiber Raman amplification, it is desired to predict the magnitude and shape of the Raman gain spectrum from the doping level and refractive index profiles of different fiber designs. This thesis develops a method to predict the Raman gain coefficients and spectra for a pure silica core fiber and two different types of GeO2-doped silica fibers given their index profiles. An essential feature of the model is the inclusion of the variation in Raman gain coefficient over the mode field due to the variation in the Ge concentration across the fiber core. The calculated Raman gain coefficients were compared with measurements of the peak Raman gain on a step-index GeO2-doped fiber and with published measurements from various sources. Agreement between the calculated and measured peak gain for the step-index fiber was excellent. There was qualitative agreement with published measurements but there were significant differences between the calculated and published gain coefficients, which are not understood. Part of the work sought a way of predicting Raman gain coefficients from a standard gain curve given only the fiber type and the effective area. This approach appears promising for moderately-doped fibers with the proper choice of effective area. / Master of Science

From the monitoring of deep ocean conditions to the imaging and exploration of the vast universe, optical sensors are playing a unique, critical role in all areas of scientific research. Optical fiber sensors, in particular, are not only widely used in daily life such as for medical inspection, structural health monitoring, and environmental surveillance, but also in high-tech, high-security applications such as missile guidance or monitoring of aircraft engines and structures. Measurements of physical parameters are required in harsh environments including high pressure, high temperature, highly electromagnetically-active and corrosive conditions. A typical example is fossil fuel-based power plants. Unfortunately, current optical fiber sensors for high-temperature monitoring can work only for single point measurement, as traditional fully-distributed temperature sensing techniques are restricted for temperatures below 800°C due to the limitation of the fragile character of silica fiber under high temperature. In this research, a first-of-its-kind technology was developed which pushed the limits of fully distributed temperature sensing (DTS) in harsh environments by exploring the feasibility of DTS in optical sapphire waveguides. An all sapphire fiber-based Raman DTS system was demonstrated in a 3-meters long sapphire fiber up to a temperature of 1400°C with a spatial resolution of 16.4cm and a standard deviation of a few degrees Celsius. In this dissertation, the design, fabrication, and testing of the sapphire fiber-based Raman DTS system are discussed in detail. The plan and direction for future work are also suggested with an aim for commercialization. / Ph. D. / This project studied the temperature dependence of Raman scattering characteristics in the single-crystal sapphire fiber. Based on these results, we designed and implemented a sapphire fiber-based fully distributed temperature sensing system using a high-power pulsed-laser. Our preliminary results show excellent and consistent temperature resolution from room temperature up to 1400 ºC. To our best knowledge, this is the first demonstration of a sapphire fiber-based distributed temperature sensing of any kind. These sensors are suitable for coal gasifiers in which the environment is corrosive, for aerospace engines and turbines requiring compact sensing elements and boilers with high-pressure environments.

Ziel dieser Arbeit ist es, das Verständnis der durch plasmonische und Komposit-Nanomaterialien verursachten Verstärkung der Hyper-Raman Streuung zu vertiefen. Diese Nanostrukturen werden in oberflächenverstärkten Hyper-Raman-Streuung (surface enhanced hyper Raman scattering, SEHRS) Experimenten, die durch den nichtlinearen parametrischen Prozess der Frequenzverdopplung (SHG) und der oberflächenverstärkten Raman-Streuung (SERS) ergänzt werden, zur umfassenden Untersuchung organischer Moleküle und Materialien angewendet. Die SEHRS-Verstärkung von Goldnanopartikeln unterschiedlicher Form und Größe sowie von Metallfilmen bestehend aus periodisch angeordneten Hohlräumen (Nanovoids) wurde in Experimenten mit dem Farbstoff Kristallviolett bei einer Anregungswellenlänge von 1064 nm und durch numerische Simulationen untersucht. Die Ergebnisse zeigen, dass Aggregate von großen kugelförmigen Goldnanopartikeln und Nanostäbchen in Lösung eine sehr hohe elektromagnetische SEHRS-Verstärkung bewirken. Darüber hinaus können die Homogenität des Signals, die Reproduzierbarkeit in Bezug auf die Herstellung und die Substratstabilität im Vergleich zu früheren Ansätzen durch Verwendung von Nanovoids signifikant verbessert werden. Die Weiterentwicklung von Nanostrukturen für die multimodale Mehrphotonen-Spektroskopie ist hier anhand der Synthese und der optischen Charakterisierung von plasmonischen Bariumtitanat-Nanokompositen demonstriert. Eine systematische Studie der Wechselwirkung von Aminosäuren und aromatischen Thiolen mit Gold- und Silbernanopartikeln wurde mit SEHRS bei einer Anregungswellenlänge von 1064 nm und mit SERS bei Anregungswellenlängen im sichtbaren Spektralbereich durchgeführt. Zusammenfassend wurde in dieser Arbeit gezeigt, dass ein tieferes Verständnis und ein rationales Design verbesserter plasmonischer Nanostrukturen ermöglichen, SEHRS mit anderen Mehrphotonen-angeregten Effekten zu kombinieren und diese in der analytischen Chemie und Biophysik einzusetzen. / The aim of this work is to extend the understanding of the enhancement in surface enhanced hyper Raman scattering (SEHRS) generated by plasmonic and composite nanomaterials, and to apply these nanostructures in SEHRS experiments complemented by the non-linear parametric process of second harmonic generation (SHG) and by surface enhanced Raman scattering (SERS), for the comprehensive probing of organic molecules and materials. The enhancement from gold nanoparticles with different sizes and shapes as well as from metal films comprised of periodically arranged voids was investigated in SEHRS experiments at 1064 nm excitation using the crystal violet dye and by numerical simulations. The results indicate that aggregates of large spherical gold nanoparticles and nanorods in solution provide very strong electromagnetic enhancement of HRS. Moreover, the homogeneity of the signal, reproducibility in terms of fabrication, and substrate stability can be significantly improved compared to previous approaches by using nanovoid arrays. Further developments of enhancing nanostructures towards multimodal multiphoton spectroscopic applications are demonstrated here by the synthesis and optical characterization of plasmonic-barium titanate nanocomposites. A systematic study on the interaction of amino acids and aromatic thiols with gold and silver nanoparticles was conducted with 1064 nm-excited SEHRS and SERS excited in the visible spectral range. In conclusion, this work underlines that a better understanding and a rational design of improved plasmonic nanostructures allow to combine SEHRS and other multiphoton excited effects, and to use them in analytical chemistry and biophysics.

The development of state-of-the-art AlGaN/GaN high electron mobility transistors (HEMTs) has shown much promise for advancing future RF and microwave communication systems. These revolutionary devices demonstrate great potential and superior performance and many commercial companies have demonstrated excellent reliability results based on multiple temperature accelerated stress testing. However, a physical understanding of the various reliability limiting mechanisms is lacking and the role and relative contribution of the various intrinsic material factors, such as physical stress and strain has not been clearly explained in the literature. Part of issues that impact device reliability are the mechanical stresses induced in the devices as well as the self-heating that also limit device performance. Thus, quantification of stress and temperature in AlGaN/GaN HEMTs is of great importance. To address some of the needs for metrology to quantify stress in AlGaN/GaN HEMTs, micro-Raman spectroscopy and micro-photoluminescence (micro-PL) were utilized to quantify the residual stress in these devices. Through the use of micro-Raman and micro-PL optical characterization methods, mapping of the vertical and lateral stress distributions in the device channels was performed. Results show that stress can be influenced by the substrate material as well as patterned structures including metal electrodes and passivation layers. Previously developed and reported micro-Raman thermometry methods require an extensive calibration process for each device investigated. To improve the implementation of micro-Raman thermometry, a method was developed which offers both experimental simplicity and high accuracy in temperature results utilizing a universal calibration method that can be applied to a broad range of GaN based devices. This eliminates the need for performing calibration on different devices. By utilizing this technique, it was revealed that under identical power dissipation levels, the bias conditions (combination of Vgs and Vds) alter the heat generation profile across the conductive channel and thus influence the degree of device peak temperature. The role of stress in the degradation of AlGaN/GaN HEMTs was also explored. A combined analysis using micro-Raman spectroscopy, coupled electro-thermo-mechanical simulation, and electrical step stress tests was conducted to investigate the link between performance degradation and the evolution of total stress in devices. It was found that in addition to stresses arising from the inverse piezoelectric effect, the substrate induced residual stress and the operational themo-elastic stress in the AlGaN layer play a major role in determining the onset of mechanically driven device degradation. Overall, these experiments were the first to suggest that a critical level of stress may exist at which point device degradation will start to occur. The optical characterization methods developed in this study show the ability to reveal unprecedented relationships between temperature/stress and device performance/reliability. They can be used as effective tools for facilitating improvement of the reliability of future AlGaN/GaN HEMTs.

Many biological processes, pathogens, and pharmaceuticals act upon, cellular membranes. Accordingly, cell membrane mimics are attractive targets for biosensing, with research, pathology, and pharmacology applications. Lipid bilayers represent a versatile sensor functionalization platform providing antifouling properties, and many receptor integration options, uniquely including transmembrane proteins. Bilayer-coated sensors enable the kinetic characterization of membrane/analyte interactions. Addressed theoretically and experimentally is the self-assembly of model membranes on plasmonic sensors. Two categories of plasmonic sensors are studied in two parts. Part I aims to deposit raft-forming bilayers on planar nanoaperture arrays suitable for multiplexing and device integration. By vesicle fusion, planar bilayers are self-assembled on thiol-acid modified flame-annealed gold without the need for specific lipid head-group requirements. Identification of coexisting lipid phases is accomplished by AFM imaging and force spectroscopy mapping. These methods are successfully extended to metallic, plasmon-active nanohole arrays, nanoslit arrays and annular aperture arrays, with coexisting phases observed among the holes. Vis-NIR transmission spectra of the arrays are measured before and after deposition, indicating bilayer detection. Finally, the extraction of membrane proteins from cell cultures and incorporation into model supported bilayers is demonstrated. These natural membrane proteins potentially act as lipid-bound surface receptors. Part II aims to encapsulate in model lipid bilayers, metallic nanoparticles, which are used as probes in surface enhanced Raman spectroscopy. Three strategies of encapsulating particles, and incorporating Raman-active dyes are demonstrated, each using a different dye: malachite green, rhodamine-PE, and Tryptophan. Dye incorporation is verified by SERS and the bilayer is visualized and measured by TEM, with support from DLS and UV-Vis spectroscopy. In both parts, lipid-coated sensors are successfully fabricated and characterized. These results represent important and novel solutions to the functionalization of plasmonic surfaces with biologically relevant cell membrane mimics.

Articular cartilage has been imaged using the following multi-photon modalities: Second Harmonic Generation (SHG), Two-photon Fluorescence (TPF) and Coherent Anti-Stokes Raman Scattering (CARS). A simple epi detection microscope was constructed for SHG and TPF imaging in the early stages of this research. Later the imaging was transferred to a new microscope system which allowed simultaneous forwards and epi detection and combined CARS imaging with TPF and SHG. Multiphoton spectroscopic studies were conducted on both intact tissue samples and the major components of the extracellular matrix, in order to identify sources of TPF. Fluorescence was detected from type II collagen, elastin and samples of purified collagen and elastin crosslinks. Age related glycation crosslinks of collagen may be a significant source of TPF. No fluorescence was detected from proteoglycans. In intact, unfixed healthy articular cartilage the cells were observed via CARS, surrounded in their pericellular matrix which is characterised by an increase in TPF. The collagen of the extra cellular matrix showed up clearly in the SHG images. Diseased cartilage was also imaged revealing microscopic lesion at the articular surface in early osteoarthritis and highly fibrous collagen structures and cell clusters in more advanced degeneration. In young healthy cartilage a network of elastin fibres were found lying parallel to the articular surface in the most superficial 50μm of the tissue. Regional variations in these fibres were also investigated. The fibres appeared mainly long and straight suggesting that they may be under tension, further work is needed to identify whether they have a mechanical function. The polarization sensitivity of the SHG from collagen has been investigated for both cartilage and tendon. In the most superficial tissue these measurements can be used directly to determine the collagen fibre orientation. However at increasing depths the effects of biattenuation and birefringence must be considered. Healthy cartilage has a characteristic pattern of polarization sensitivity with depth and this changes at lesions indicating a disruption of the normal collagen architecture. The methods developed in this thesis demonstrate the use of non-linear microscopy to visualise the structure of the extracellular matrix and cells in intact unstained tissue. They should also be appropriate in many areas of cell and matrix biology.

Plasmonics techniques, such as surface plasmon resonance (SPR) and surface-enhanced Raman scattering (SERS), have been widely used for chemical and biochemical sensing applications. One approach to excite surface plasmons is through the coupling of light into metallic grating nanostructures. Those grating nanostructures can be fabricated using state-of-the-art nanofabrication methods. Laser interference lithography (LIL) is one of those methods that allow the rapid fabrication of nanostructures with a high-throughput. In this thesis, LIL was combined with other microfabrication techniques, such as photolithography and template stripping, to fabricate different types of plasmonic sensors. Firstly, template stripping was applied to transfer LIL-fabricated patterns of one-dimensional nanogratings onto planar supports (e.g., glass slides and plane-cut optical fiber tips). A thin adhesive layer of epoxy resin was used to facilitate the transfer. The UV-Vis spectroscopic response of the nanogratings supported on glass slides demonstrated a strong dependency on the polarization of the incident light. The bulk refractive index sensitivities of the glass-supported nanogratings were dependent on the type of metal (Ag or Au) and the thickness of the metal film. The described methodology provided an efficient low-cost fabrication alternative to produce metallic nanostructures for plasmonic chemical sensing applications. Secondly, we demonstrated a versatile procedure (LIL either alone or combined with traditional laser photolithography) to prepare both large area (i.e. one inch2) and microarrays (μarrays) of metallic gratings structures capable of supporting SPR excitation (and SERS). The fabrication procedure was simple, high-throughput, and reproducible, with less than 5 % array-to-array variations in geometrical properties. The nanostructured gold μarrays were integrated on a chip for SERS detection of ppm-level of 8-quinolinol, an emerging water-borne pharmaceutical contaminant. Lastly, the LIL-fabricated large area nanogratings have been applied for SERS detection of the mixtures of quinolone antibiotics, enrofloxacin, an approved veterinary antibiotic, and one of its active metabolite, ciprofloxacin. The quantification of these analytes (enrofloxacin and ciprofloxacin) in aqueous mixtures were achieved by employing chemometric analysis. The limit of quantification of the method described in this work is in the ppm-level, with <10 % SERS spatial variation. Isotope-edited internal calibration method was attempted to improve the accuracy and reproducibility of the SERS methodology. / Graduate / 2018-02-17

Recently developed two-dimensional colloidal semiconductor nanocrystals, or nanoplatelets (NPLs), extend the palette of solution-processable free-standing 2D nanomaterials of high performance. Growing CdSe and CdS parts subsequently in either side-by-side or stacked manner results in core–crown or core/shell structures, respectively. Both kinds of heterogeneous NPLs find efficient applications and represent interesting materials to study the electronic and lattice excitations and interaction between them under strong one-directional confinement. Here, we investigated by Raman and infrared spectroscopy the phonon spectra and electron–phonon coupling in CdSe/CdS core/shell and core–crown NPLs. A number of distinct spectral features of the two NPL morphologies are observed, which are further modified by tuning the laser excitation energy Eexc between in- and off-resonant conditions. The general difference is the larger number of phonon modes in core/shell NPLs and their spectral shifts with increasing shell thickness, as well as with Eexc. This behaviour is explained by strong mutual influence of the core and shell and formation of combined phonon modes. In the core–crown structure, the CdSe and CdS modes preserve more independent behaviour with only interface modes forming the phonon overtones with phonons of the core. / Dieser Beitrag ist aufgrund einer (DFG-geförderten) Allianz- bzw. Nationallizenz frei zugänglich.

Durante os últimos cinco anos, a nanotecnologia tem atingido avanços significativos em diversas áreas da ciência e tecnologia. Um dos assuntos que está sendo intensamente estudado pela comunidade científica é a intensificação de campo próximo (hot spot) que pode ser aplicada em dispositivos sensores com capacidade de detecção de apenas uma molécula e em nano-antenas ópticas aplicadas na fabricação de dispositivos plasmônicos. Neste sentido, as principais contribuições da presente tese são processos de fabricação de nanoestruturas metálicas e de silício e o estudo da intensificação de campo próximo denominada de pontos quentes (hot spots) nestas estruturas. As nanoestruturas metálicas de Au (ouro) foram obtidas a partir do processo de auto-organização de esferas de poliestireno. As esferas de poliestireno serviram como camada sacrificial (molde) para a obtenção de nanoestruturas metálicas organizadas. Sobre as estruturas de Au organizadas foram depositadas moléculas de cristal violeta para serem utilizadas como moléculas de prova (sondas) no monitoramento da existência dos pontos quentes com o auxílio do espalhamento Raman das moléculas. As nanoestruturas de Au possibilitaram uma intensificação do espalhamento Raman devido à intensificação do campo próximo na superfície metálica periódica de Au. As nanoestruturas e microestruturas de silício foram obtidas a partir da tecnologia de silício poroso. As propriedades do silício poroso foram moduladas através da implantação de íons de hidrogênio (H +) que possibilitou a formação de silício microporoso com forte emissão fotoluminescente (PL) e intensificação do espalhamento Raman superficial devido ao fenômeno de Raman ressonante. Sobre as estruturas macroporosas de silício foram adsorvidas moléculas de azul de metileno para serem utilizadas como moléculas de prova para monitoramento da intensificação do campo próximo e do efeito SERS no silício. A obtenção da intensificação de campo próximo em silício é uma contribuição completamente inédita, pois este fenômeno devia-se, até o momento, somente a materiais metálicos (nanoestruturas metálicas), mostrando sua existência também no silício. / During the last five years, nanotechnology has achieved significant progress in several areas of science and technology. One of the issues that are being intensively studied by the scientific community is the intensification of near-field (hot spot) that can be applied to devices with sensors capable of detecting a single molecule and nano-optical antennas used in the fabrication of plasmonic devices. In this sense, the main contributions of this thesis are processes for manufacture of metal and silicon nanostructures and the study of near-field intensification called hot spots in these structures. The metal nanostructures of Au (gold) were obtained from the process of self-assembling of polystyrene beads. The polystyrene beads were used as sacrificial layer (mold) for obtaining organized metallic nanostructures. On the structures of organized Au were deposited molecules of violet crystal to be used as proof of molecules (probes) to monitor the existence of hot spots with the help of Raman scattering of molecules. The Au nanostructures allowed an intensification of the Raman scattering due to the intensification of the near-field in the periodic Au surface. The microstructures and nanostructures of silicon were obtained using the porous silicon technology. The properties of porous silicon were modulated by the implantation of hydrogen ions (H +) that allowed the formation of microporous silicon which showed high photoluminescence emission (PL) and Raman scattering intensification of the surface due to the phenomenon of resonant Raman. Methylene blue molecules were adsorbed on the macroporous silicon structures to be used as probe molecule for the monitoring of near-field intensification and the SERS effect in silicon. The obtaining of near-field intensification in silicon is an entirely unprecedented contribution, because this phenomenon had been observed, so far, only on the metallic materials (metal nanostructures), showing its existence in the silicon too.