Several novel optical devices, which were designed to manipulate terahertz waves for broadband near-field imaging, wave-guiding (invisible space), and sensing (resonator), are presented in this thesis. We developed the original working concepts of each device, and demonstrated the prototype experimentally in our lab. The working concepts of physics were investigated in experiment, in simulation and in theoretical analysis. We exploited a tapered parallel-plate waveguide (PPWG) as a novel probe for broadband near-field imaging. This imaging probe consists of two metal plates with the plate spacing gradually tapered from one end to the other. We proved that the space tapering enables this probe to propagate the broadband THz waves efficiently (with low-loss, no cut-off and nearly no dispersion) from the input end of large spacing into the narrow end of sub-wavelength spacing. Working in a reflection mode, this imaging probe is proved to be able to differentiate the dielectric features as well as topographic information on the sample. Combined with the methodology of filtered back projection, we reconstructed a two-dimensional image of a gold pattern on a GaAs chip by using this tapered PPWG probe. The smallest feature of ~100 µm is resolved by using the waves with average wavelength of 1.5 mm. We studied the phenomenon of surface plasmon-polariton in THz range on the platform of a parallel-plate waveguide (PPWG). In this thesis, we show the characterization of the waveguide mode of a finite-width parallel plate waveguide by using an improved scattering-probe technique. An abrupt waveguide mode transition was observed at a very narrow frequency range. We demonstrated that this transition frequency is determined by the material properties of the waveguide, the frequencies of the electromagnetic waves as well as the geometry of the waveguide. This result provides a good guidance for the waveguide design for THz transmission. We also exploited the capability of using the spoof surface plasmon to enhance the reflectivity of an interface between free space and a PPWG. We demonstrated that the reflection coefficient of this interface can be enhanced up to ~100 % at a designed frequency, by cutting a designed pattern of periodic rectangular groove on the output facet of the PPWG. A lateral shift and a phase shift of the reflected beam is observed in the experiment, which is a strong reminiscent of Goos-Hanchen shift. We carried out the experimental, simulation and theoretical characterizations of the lateral and phase shift. As an application, we designed and demonstrated a prototype of a band-pass THz resonator. We introduced the concept of a waveguide-based two-dimensional inhomogeneous artificial dielectric into THz range. This artificial dielectric is the space between the two metal plates of a PPWG working in TE1 mode. We designed a THz mirage device (or an invisible space device) by using ray-tracing and full-wave simulations, which contributed to the first experimental demonstration of such a device. A metal coin of size several times larger than the working wavelength can be hidden in the device without casting any shadow. This work is in collaboration with Dr. Rajind Mendis and the author of this thesis contributed to the design and characterization of the device in simulations.

In this project a method based on surface plasmon resonance has been developed for determining the concentration of several His-tagged proteins in complex solutions. It showed large dynamic range, no measureable non-specific binding and high sensitivity (with linear range around 0.1–10 μg/ml depending on the proteins). The method showed a low variation when checked on MBP-His during an extended time period. The concentrations of the His-tagged protein in the lysate has also been determined and compared with other alternative methods. This method will later be used to analyse protein concentrations during development and optimization of chromatographic purification process.

Surface plasmon polaritons are electromagnetic surface waves coupled to electron plasma oscillation of metals at a metal-dielectric interface. At optical frequencies, these modes are of great interest because of their high confinement to a metal-dielectric interface. Due to the field enhancement at the interface, they have been used in different applications such as sensors, second harmonic generation and enhanced Raman scattering. Surface plasmon resonance based sensors are being used for detection of molecular adsorption such as DNA and proteins. These sensors are known to be highly sensitive and have successfully become commercialized. Terahertz (THz) frequency band of electromagnetic spectrum has attracted researchers in the last few years mostly because of sensing and imaging applications. Many important chemical and biological molecules have their vibrational and rotational resonance frequencies in the THz range that makes the THz sensing one of the most important applications of THz technology. Considering above mentioned facts, extending the concept of surface plasmon sensors to THz frequencies can result in sensitive sensors. In this work the possibility of this extension has been investigated. After reviewing optical surface plasmon polariton waves and a basic sensor configuration, surface plasmon polariton waves propagating on at metallic and doped semiconductor surfaces have been examined for this purpose. It has been shown that these waves on metallic surfaces are loosely confined to the metal-dielectric interface and doped semiconductors are also too lossy and cannot meet the requirements for sensing applications. Afterwards, it is shown that periodically patterned metallic surfaces can guide surface waves that resemble surface plasmon polariton waves. A periodically patterned metallic surface is used to guide THz surface plasmon polariton-like surface waves and a highly sensitive sensor is proposed based on that. The quasi-optical continuous wave (CW) THz radiation is coupled to this structure using the Otto's attenuated total reflection (ATR) configuration and the sensitivity of the device is discussed. A general scattering parameter based model for prism coupling has been proposed and verified. It is shown that a critical coupling condition can happen by changing the gap size between the prim and periodic surface. Details of fabrication of the periodic structure and experimental setup have also been presented.

<p>Expanding the role of plasmonics in tomorrow's technology requires a broader knowledge base from which to develop such applications today. Several limitations to the current plasmonics field limit progress to incremental advances within a narrow set of materials and techniques rather than developing non-traditional metals and flexible growth and characterization methods. The work described herein will provide an introduction to the burgeoning field of spectroscopic ellipsometry for plasmonic characterization; in particular, the power of its real-time monitoring capabilities and flexibility will be demonstrated. More importantly, a novel plasmonic metal, gallium, is investigated in detail. Critical characteristics of gallium for an array of applications include its tunability over a wide spectral range, phase stability across a wide temperature range, plasmon stability even after air exposure, and an ultra high vacuum evaporation growth process enabling simple, alloyed nanostructure development. Deeper scientific investigation of the underlying ripening mechanisms driving gallium nanoparticle formation and in concert with in situ alloying paves the way for future work contributing to the development of advanced nanostructured alloys. Finally, this work demonstrates the first example of gallium nanoparticle-enhanced Raman spectroscopy - an area craving materials innovation. While the specific application of gallium for SERS detection is interesting, the far-reaching implication lies in the demonstrated potential for plasmonic gallium nanoparticles' ultimate use in a wider variety of applications enhanced by nanoscale materials.</p> / Dissertation

<p>The refractive index sensitivity of plasmonic nanoparticles is utilized in the development of real-time, label-free biodetection. Analyte molecules that bind to receptor-conjugated nanoparticles cause an increase in local refractive index that in turn induces an energy shift in the optical resonance of the particle. Biomolecular binding is quantified by quantitatively measuring these resonance shifts. This work describes the application and optimization of a biomolecular detection system based on gold nanorods as an optical transducer.</p> <p>A microspectroscopy system was developed to collect scattering spectra of single nanoparticles, and measure shifts of the spectra as a function of biomolecular binding. The measurement uncertainty of LSPR peak shifts of the system was demonstrated to be 0.3 nm. An analytical model was also developed that provides the optimal gold nanorod geometry for detection with specified receptor-analyte pair. The model was applied to the model biotin-streptavidin system, which resulted in sensing system with a detection limit of 130 pM - an improvement by four orders of magnitude over any other single-particle biodetection previously presented in the literature.</p> <p>Alternative optical detection schemes were also investigated that could facilitate mulitplexed biosensing. A theoretical model was built to investigate the efficacy of using a multi-channel detector analogous to a conventional RGB camera. The results of the model indicated that even in the best case, the detection capabilities of such a system did not provide advantages over the microspectroscopic approach.</p> <p>We presented a novel hyperspectral detection scheme we term Dual-Order Spectral Imaging (DOSI) which is capable of simultaneously measuring spectra of up to 160 individual regions within a microscope's field of view. This technique was applied to measuring shifts of individual nanoparticles and was found to have a peak measurement uncertainty of 1.29 nm, at a measurement rate of 2-5 Hz.</p> / Dissertation

Electron-excited surface plasmon resonance (eSPR) is investigated for potential use in biosensors. Optical SPR sensors are commercially available at present and these sensors are extremely sensitive, but have the tendency to be relatively large, expensive, and ignore the potentials of microelectronic technology. By employing the use of various microelectronic and nanotechnology principles, the goal is to eventually design a device that exploits the eSPR phenomenon in order to make a sensor which is siginificantly smaller in size, more robust, and cheaper in cost.

The electro-optical properties of the ZnO thin film are affected by the deposition parameters. In this study, we find the optimum growth parameters to grow high quality ZnO film. We change the RF power to adjust the surface roughness. The higher RF power will result in a higher deposition rate and rough surface roughness. We obtained an optimum surface roughness of 1.811nm at 50W RF power. The ZnO films have more than 80% transmittance in visible range, and obvious absorption in UV range. A significant peak in the wavelength of 385nm is observed in PL measurement. For the electric characteristics, the resistivity of as-grown ZnO films is high and decreases with post annealing treatment. We have obtained a minimum resistivity of 2.764¡Ñ10-2(£[-cm) at 700oC annealing treatment. Under the fixed 50RF power and 5sccm Ar flux, the optical characteristics and the crystal qualities are worse in the lower pressure (below 5mTorr). The ZnO films have lowest resistivity of 1.826¡Ñ10-2(£[-cm) in the 15mTorr and, strongest PL intensities in 25mTorr after 700oC annealing treatment. After the optimum growth condition, we enhance the optical characteristics through the surface Plasmon effect of the metal nanoparticles. The nano gold particles in the diameter of 50nm and 200-250nm can be obtained under the 5nm and 10nm Au film deposition and annealing at 700oC, respectively. For the optical characteristics, the PL intensity and optical transmittance are enhanced dependent on the size and position of the gold nanoparticles. For the electric characteristics, the n-ZnO/p-Si shows a good rectification effect. The mechanisms of current conduction are space charge current limit, and tunnel current. Sample with 50nm diameter has a significant space charge current limit mechanism. In the C-V measurement, we observed the hysteresis curve in the sample with gold nanoparticles. The sample with larger gold particles have larger memory window of ¡µVFB=0.23.

Surface-enhanced Raman scattering (SERS) effect on Ag films with different morphology is studied. We varied the deposition rates and also proposed a new method to control the nano-gaps on the silver island film. By bending the glass substrates during film deposition, we can control the gap width on the fractal Ag film. The measured SERS intensity is related to the metal film morphology and we found that the gap width is the dominant factor to analyze the SERS signal. The 3-layer metal-insulator-metal structure is simulated and the E-field intensity with different gaps fits to our measurement results.

This dissertation focused on the applications of self-assembled monolayers (SAMs) technique for the investigation of molecule based electronics, plasmon coupling between CdSe quantum dots and metal nanoparticles (MNPs), and copper ion detection using enhanced emission of CdSe quantum dots (QDs). The SAMs technique provides an approach to establish a robust, two-dimensional and densely packed structure which can be formed on metal or semiconductor surfaces. This allows for the design of molecular assemblies that can be used to understand the details of molecular conduction by employing various electrical testbeds. In this work, the strategy of molecular assemblies was used to pattern metal nanoparticles on GaAs surfaces, thereby furnishing a platform to explore the interactions between QDs and MNPs. The enhanced emission of CdSe QDs by MNPs was then used as a probe for ultrasensitive, cheap, and rapid copper(II) detection. The study is divided into three main facets. The first one aimed at controlling electron transport behavior through porphyrins on surfaces with an eye toward optoelectronic and light harvesting applications. The binding of the porphyrin molecules to Au surfaces, pre-covered with a dodecanethiol matrix, was characterized by FTIR, XPS, AFM, STM, of. This study has shown that the perfluoro coupling group between the porphyrin macrocycle and the thiol tether may provide a means of controlling the tunneling behavior. The second area of this study focused on the design of a simple platform to examine the coupling between metal nanostructures and quantum dot assemblies. Here we demonstrate that by using a patterned array of Au or Ag nanoparticles on GaAs, plasmon enhanced photoluminescence (PL) can be directly measured and quantified by direct scaling of regions with and without metal nanostructures. The third field presented a simple manner for using the enhanced PL of CdSe QDs as a probe for ultrasensitive Cu2+ ion detection and quantitative analysis. The PL of QDs was enhanced by two processes: first, photobrightening of the material, and second, plasmonic enhancement by coupling with Ag nanoprisms. This strong PL leads to a high sensitivity of the QDs over a wide dynamic range for Cu2+ detection, as Cu2+ efficiently quenches the QD emission.

The purpose of this thesis is to find out carrier concentration in nitride semiconductors by micro Raman measurements. We focus on the Raman measurements of two different III-nitride semiconductors doped with Si. First series is narrow band gap InN films with varying carrier concentration (ne). The highest (ne) in this series is 1.9 X 1019 cm-3. The second series is wide band gap GaN films, with highest (ne) of 8.0 X 1019 cm-3.From the room temperature Ramam measurements ,it is observed that the L- LOPCM (lower branch of longitudinal-optical phonon-plasmon coupled modes) depends on the carrier concentration. We focus the further analysis of this result and try to extract the carrier concentration and compare with electrical measurements.