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In this thesis we use three main approaches to enhance the performance of terahertz photoconductive switches (THz PC switches). We first propose two novel materials (GaBiAs and carbon nanotubes) for the substrate. The resulting enhancement in THz emission and reception are significant for GaBiAs. As thoroughly analyzed and addressed in Chapter 2, both the emission bandwidth and the emission amplitude of the device are improved by these materials. A systematic study of CNTs predicts 2 orders of magnitude enhancement in THz emission and one order of magnitude enhancement in THz reception. Experimental results for GaBiAs indicate 0.5 THz increase in bandwidth and 68% increase in the emitted THz wave amplitude. The bandwidth enhancement is in comparison to premium commercial devices. The optical excitation of the PC switch is studied and optimized next as the second enhancement approach (Chapter 3). The study presented in Chapter 3 provides an insight on the subwavelength dynamics of the optical excitation E-field at the edge of the electrodes. The study reveals that majority of the fast photocarriers are collected at the edge of the electrode in a subwavelength scale area. This insight leads to optimization of illumination profile and also the third enhancement approach, namely, the enhancement of electrode structure (Chapter 4). In Chapter 4 we have engineered the electrodes down to nanometer scale. This significantly enhances the optical excitation of the substrate and also overcomes the undesired properties of some substrate materials such as long carrier lifetime. Fabricated devices and fabrication processes are assessed in Chapter 5. Results (Chapter 6) highlight more than two orders of magnitude enhancement for nanostructures on GaAs. / Graduate / 0544

"There is plenty of room at the bottom." This bold and prophetic statement from Nobel laureate Richard Feynman back in 1950s at Cal Tech launched the Nano Age and predicted, quite accurately, the explosion in nanoscience and nanotechnology. Now this is a fast developing area in both science and technology. Many think this would bring the greatest technological revolution in the history of mankind. To understand electronic and optical properties of nanostructures, the following problems have been studied. In particular, intensity of mid-infrared light transmitted through a metallic diffraction grating has been theoretically studied. It has been shown that for s-polarized light the enhancement of the transmitted light is much stronger than for p-polarized light. By tuning the parameters of the diffraction grating enhancement can be increased by a few orders of magnitude. The spatial distribution of the transmitted light is highly nonuniform with very sharp peaks, which have the spatial widths about 10 nm. Furthermore, under the ultra fast response in nanostructures, the following two related goals have been proved: (a) the two-photon coherent control allows one to dynamically control electron emission from randomly rough surfaces, which is localized within a few nanometers. (b) the photoelectron emission from metal nanostructures in the strong-field (quasistationary) regime allows coherent control with extremely high contrast, suitable for nanoelectronics applications. To investigate the electron transport properties of two dimensional carbon called graphene, a localization of an electron in a graphene quantum dot with a sharp boundary has been considered. It has been found that if the parameters of the confinement potential satisfy a special condition then the electron can be strongly localized in such quantum dot. Also the energy spectra of an electron in a graphene quantum ring has been analyzed. Furthermore, it has been shown that in a double dot system some energy states becomes strongly localized with an infinite trapping time. Such states are achieved only at one value of the inter-dot separation. Also a periodic array of quantum dots in graphene have been considered. In this case the states with infinitely large trapping time are realized at all values of inter-dot separation smaller than some critical value.

Metallic nanostructures supporting surface plasmon modes can concentrate optical fields, and enhance luminescence processes from the metal surface at plasmonic hotspots. Such nanoplasmonic metal luminescence contributes to the spectral background in surface-enhanced Raman spectroscopy (SERS) measurements and is helpful in bioimaging, nano-thermometry, and chemical reaction monitoring applications. Despite increasing interest in nanoplasmonic metal luminescence, little attention has been paid to investigating its dependence on voltage modulation. Also, the hyphenated electrochemical surface-enhanced Raman spectroscopy (EC-SERS) technique typically ignores voltage-dependent spectral background information associated with nanoplasmonic metal luminescence due to limited mechanistic understanding and poor measurement reproducibility. In this thesis, we combine the experimental observations and theoretical study on dynamic Faradaic & non-Faradaic modulated nanoplasmonic metallic luminescence and molecular vibrational Raman from hotspots at the electrode-electrolyte interfaces using multiple novel nano-optoelectrodes. Our work represents a critical step toward the general application of nanoplasmonic metal luminescence signals in optical voltage biosensing, hybrid optical-electrical signal transduction, and interfacial electrochemical monitoring. / Master of Science / Understanding the non-Faradaic and Faradaic process pathway is crucial for unraveling reaction mechanisms, developing efficient catalysts, designing bionsensing methodology, energy conversion and cellular stimulator (1-7). Advances in spectroscopic techniques( 8, 9) and computational models (3, 10) have facilitated the investigation of the non-Faradic and Faradaic processes. Unlike bulk reactions, interfacial electrochemical reactions occur in nanometer-thin layers (3, 11), necessitating highly sensitive detection methods. A significant challenge is background interference from bulk electrolytes and electrodes, often obscuring weak signals from the interfacial region – traditional spectroelectrochemistry struggles to match the high temporal resolution requirement due to noise (12, 13). Surface plasmons have become a promising solution for enhancing the sensitivity of spectroelectrochemical techniques (14, 15). Surface plasmons are collective oscillations of electrons at the metal-dielectric interface, which can focus and intensify optical fields at the nanoscale (16), boosting diverse nonlinear emission signals, including fluorescence, Raman scattering, and harmonic generation (17-23). By utilizing surface plasmons, spectroelectrochemistry techniques have shown promise in detecting interfacial activities with high sensitivity. In this thesis, we introduce a pioneering dual-channel in situ EC-SERS methodology, which harnesses the synergy between plasmon-enhanced vibrational Raman scattering (PE-VRS) and plasmon-enhanced electronic Raman scattering (PE-ERS) interfacial signals to monitor and analyze the Faradaic and non-Faradaic process at the electrode-electrolyte interfaces.

Monoklonala antikroppsbaserade läkemedel (mAb) är ett av de snabbast växande segmenten på läkemedelsmarknaden, främst på grund av deras tillämpning inom onkologi, immunologi och hematologi. Traditionellt sker den industriella produktionen av mAb med fed-batch-odling. Detta är en relativt lätthanterlig process med mAb-utbyten på 5-10 g/L, men dess brist på kontroll över kritiska processparametrar (CPP) orsakar höga mAb-förluster på grund av att kvalitetsspecifikationer inte uppfylls. Ökande marknadskrav och regulatoriska förändringar pådriver läkemedelsindustrin iinnovation inom mAb-tillverkningsprocessen, för att nå kontinuerlig tillverkning. För närvarande, som ett övergångssteg till kontinuerlig tillverkning, sker investeringar i intensifierade fed-batch-odlingar. Dessa uppnår högre celldensiteter på cirka 25-30 g/L, men detta är fortfarande mycket lägre än motsvarande mAb-koncentrationer på 130 g/L som kan uppnås med perfusionsprocesser. Andra fördelar med perfusionsprocesser är att de tillåter flexibla produktionsanläggningar och möjliggör en nivå av processkontroll som skulle tillåta realtidstestning av release. För att upprätthålla en perfusionsprocess under de specificerade förhållandena som garanterar den önskade mAb-kvaliteten, måste CPP kontrolleras noggrant. Process Analytical Technologies (PAT) kan mäta CPP i realtid på ett icke-destruktivt sätt. Denna studie undersökte tillämpningen av två PAT, ArgusEye®-sensorerna och Time-gated Raman-spektroskopi, på perfusionsprocesser. Vi visade att ArgusEye®-sensorerna kan användas för att mäta IgG i perfusionsprover med ganska bra korrelation med referensmetoden. Vi har också visat att multivariata Raman-baserade modeller kan konstrueras för att förutsäga flera CPP, baserat på samma spektra. Framförallt belyser denna studie komplexiteten i tillämpningen av dessa PAT för att kontrollera perfusionsprocesser. För ArgusEye® drar vi slutsatsen att för att få exakta mätningar måste vi ta hänsyn till förändringarna i koncentrationen av värdcellsprotein under en perfusionsprocess, eftersom deras ospecifika bindning till sensorerna är den troliga orsaken till variationen i IgG-mätningarna. För de Raman-baserade modellerna, visar denna studie att en stor mängd data krävs för att bygga korrekta prediktionsmodeller, något som rapprterats om i litteraturen. Sammantaget visar denna rapport att dessa PAT har en stor tillämpningspotential, men de måste förbättras ytterligare innan de kan användas som automatiska återkopplingskontrollverktyg. / Monoclonal antibody-based therapeutics (mAb) are one of the fastest-growing segments in the pharmaceutical market, mainly due to their application in oncology, immunology, and hematology. Traditionally, the industrial production of mAb is done with fed-batch cultivation. This is a relatively easy to operate process with mAb yields of 5-10 g/L, but its lack of control over critical process parameters (CPP) causes high mAb losses due to unmet quality specifications. Driven by increasing market demands and regulatory changes, the pharmaceutical industry is innovating in the mAb manufacturing process to reach continuous manufacturing. Currently, as a transition step to continuous manufacturing, the pharmaceutical industry is investing in intensified fed-batch cultivations. They achieve higher cells densities and present yields around 25-30 g/L, but this is still much lower than the equivalent mAb titers of 130 g/L that can be achieved with perfusion processes. Other advantages of perfusion processes are that they allow the existence of flexible production facilities and enable a level of process control that would permit Real-Time Release Testing. To maintain a perfusion process under the specified conditions to guarantee the desired mAb quality, the CPP need to be closely controlled. Process Analytical Technologies (PAT) can measure CPP in real-time and non-destructively. This study evaluated the application of two PAT, the ArgusEye® sensors and Time-gated Raman spectroscopy, on perfusion processes. We showed that the ArgusEye® sensors can be used to measure IgG in perfusion samples with quite good correlation to the reference method. We have also shown that multivariate Raman-based models can be constructed to predict several CPP based on the same spectra. Most importantly, this study highlights the complexity of the application of these PAT to control perfusion processes. For the ArgusEye®, we conclude that to obtain accurate measurements, we need to account for the changes in the concentration of host cell protein during a perfusion process, as their unspecific binding to the sensors is the probable cause for the variation in the IgG measurements. For the Raman-based models, as previously reported in the literature, this study shows that a high volume of data is require to build accurate prediction models. Overall, this report shows that these PAT have a great potential of application, but they need to be further improved prior to their use as automatic feedback control tools.

To increase the survival rate from infectious- and noncommunicable diseases, reliable diagnostic during the preliminary stages of a disease onset is of vital importance. This is not trivial to achieve, a highly sensitive and selective detection system is needed for measuring the low concentrations of biomarkers available. One possible route to achieve this is through biosensing based on plasmonic nanostructures, which during the last decade have demonstrated impressive diagnostic capabilities. These nanoplasmonic surfaces have the ability to significantly enhance fluorescence- and Raman signals through localized hotspots, where a stronger then normal electric field is present. By further utilizing a periodic sub-wavelength nanohole array the extraordinary optical transmission phenomena is supported, which open up new ways for miniaturization. In this study a nanoplasmonic chip (NPC) composed of a nanohole array —with lateral size on the order of hundreds of nanometer— covered in a thin layer of gold is created. The nanohole array is fabricated using soft nanoimprint lithography on two resists, hydroxypropyl cellulose (HPC) and polymethyl methacrylate (PMMA). An in depth analysis of the effect of thickness is done, where the transmittance and Raman scattering (using rhodamine 6G) are measured for varying gold layers from 5 to 21 nm. The thickness was proved to be of great importance for optimizing the Raman enhancement, where a maximum was found at 13 nm. The nanohole array were also in general found beneficial for additionally enhancing the Raman signal. A transmittance minima and maxima were found in the region 200-1000 nm for the NPCs, where the minima redshifted as the thickness increased. The extraordinary transmission phenomena was however not observed at these thin gold layers. Oxygen plasma treatment further proved an effective treatment method to reduce the hydrophobic properties of the NPCs. Care needs be taken when using thin layers of gold with a PMMA base, as the PMMA structure could get severely damaged by the plasma. HPC also proved inadequate for this projects purpose, as water-based fluids easily damaged the surface despite a deposited gold layer on top.