<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

When the thickness of a magnetic layer is comparable to (or smaller than) the electron mean free path, the interface between magnetic and non-magnetic layers becomes very important factor to determine magnetic properties of the ultra-thin films. The quality of interface can enhance (or reduce) the desired properties. Several interesting physical phenomena were studied using these interface effects. The magnetic anisotropy of ultra-thin Co films is studied as function of non-magnetic underlayer thickness and non-magnetic overlayer materials using ex situ Brillouin light scattering (BLS). I observed that perpendicular magnetic anisotropy (PMA) increases with underlayer thickness and saturates after 5 ML. This saturation can be understood as a relaxation of the in-plane lattice parameter of Au(111) on top of Cu(111) to its bulk value. For the overlayer study, Cu, Al, and Au are used. An Au overlayer gives the largest PMA due to the largest in-plane lattice mismatch between Co and Au. An unusual effect was found by adding an additional layer on top of the Au overlayer. An additional Al capping layer on top of the Au overlayer reduces the PMA significantly. The possible explanation is that the misfit strain at the interface between the Al and the Au can be propagated through the Au layer to affect the magnetic properties of Co even though the in-plane lattice mismatch is less than 1%. Another interesting problem in interface interdiffusion and thermal stability in magnetic tunnel junction (MTJ) structures is studied using X-ray photoelectron spectroscopy (XPS). Since XPS is a very chemically sensitive technique, it allows us to monitor interface interdiffusion of the MTJ structures as-deposited and during post-deposition processing. For the plasma-oxidized samples, Fe only participates in the oxidation reduction process. In contrast to plasma-oxidized samples, there were no noticeable chemical shifts as-deposited and during post-deposition processing in air-oxidized samples. However, peak intensity variations were observed due to interface interdiffusion.

This dissertation presents the research performed to develop an optical model, improve some design parameters, and analyze the performance of the UA modular gamma camera. Initially we provide a brief background on nuclear medical imaging with scintillation cameras. The key hardware components of a camera are introduced, and some of the fundamental physics involved in the detection of gamma rays is explained. Then we describe a stand-alone modular camera imaging system that was developed to image human breasts in the clinic. The hardware and software components, calibration procedure, and general operation of the system are detailed. We explain the concepts of position estimation and scatter rejection and note how they have been applied to imaging with the UA modular gamma camera. Position estimation uses the output signals of the camera to determine where an incident gamma ray interacted within the camera, and scatter rejection uses the signals to decide whether or not an incident gamma ray underwent scattering prior to being detected by the camera. Then we present an analytical optical model of the UA modular gamma camera. Taking into account physical and optical properties of the camera components, the model performs radiometric calculations to estimate the mean response of the camera to a scintillation event anywhere within the scintillation crystal. The results of several studies using the optical model to test and improve some camera design parameters are reported. Finally, we demonstrate how straightforward signal detection theory can be used to evaluate the performance of a modular gamma camera for the task of detecting signals in noisy backgrounds. Guided by the preliminary design of a dedicated breast imaging system, estimates of how well the UA modular gamma camera can detect lesions within human breasts were generated.

Applications of planar integrated optical waveguide (IOW) technology to problems in surface spectroscopy and optical chemical sensing have been partly limited by the difficulty of producing high quality glass IOWs is. The fabrication of IOWs by the sol-gel method from methyltriethoxysilane and titanium tetrabutoxide precursors has therefore been developed. The physical, chemical, and optical properties of the films were studied using a variety of analytical techniques. The results show that the catalyst used to accelerate the sol-gel reaction strongly influenced the optical quality of the IOW. A novel optical sensing platform was subsequently developed using a sol-gel derived, laminate planar IOW structure. The sensing element is fabricated by coating a sol-gel IOW with a second, porous sol-gel layer in which optical indicator molecules are physically entrapped, yet remain sterically accessible to analytes that diffuse into the pore network. Formation of a complex between the analyte and entrapped indicator is detected via attenuated total reflection (ATR) of light guided in the IOW. Feasibility was evaluated by constructing IOW-ATR sensors for Pb2+ and pH, based on entrapped xylenol orange and bromocresol purple respectively. The response of both sensors was sensitive and rapid. This work was further extended to the development of a new class of gaseous iodine sensors. The sensing principle is based on the detection of a charge transfer complex formed between iodine and phenyl groups that have been incorporated into a porous, methylated glass film. The sol-gel iodine sensor exhibits a linear response to gaseous I2 in the range of 100 ppb to 15 ppm with response and recovery times less than 15 sec. Langmuir-Blodgett (LB) films have also been deposited on a sol-gel IOW from zinc 1,4,8,11,15,18,22,25-octabutoxy-phthalocyanine (ZnPc). Planar waveguide linear dichroism was used to determine molecular orientation in a ZnPc LB monolayer. The IOW-supported ZnPc monolayer was found to exhibit a sensitive spectral response to gaseous I2. The overall optical sensing approach described in this dissertation is technically simple, inexpensive, and applicable to a wide variety of chemical sensing problems.

Several different glass materials were investigated for waveguide amplifier and laser applications, and the potential to realize practical devices with these materials were examined using waveguides fabricated by ion exchange processes. Channel waveguides in an erbium doped phosphate laser glass were fabricated by a dry silver-film ion exchange technique, and the effects of high Er³⁺ concentration were investigated in terms of Er³⁺ ion interactions and energy transfer from Yb³⁺ to Er³⁺. Cooperative upconversion coefficients of the ⁴I₁₃/₂ level,7.7±0.7x 10⁻¹⁹ cm³/sec and 9.3±0.7x10⁻¹⁹ cm³/sec, were obtained experimentally for Er³⁺ concentration of 1x10²⁰ cm³ in the bulk and waveguide samples, respectively. These values are one order of magnitude smaller than the ones reported for silica glass. The increase in the cooperative upconversion coefficient with the increase in Er³⁺ concentration was found to be small. The effects of cooperative upconversion on the gain performance were analyzed for different Er³⁺ concentrations using a theoretical model which adopted experimentally obtained parameters. Given the small cooperative upconversion coefficients in this glass, Er³⁺ concentrations potentially as high as 3.7x10²⁰ cm⁻³ were shown to be feasible by the modeling. This would result in a 12 dB gain with a 4 cm long waveguide for 150 mW pump power at 1.48 μm. The transfer efficiency from Yb3+ to Er³⁺ was found to be 95% or higher for samples with Er³⁺ concentrations of 1.9x10²⁰ cm⁻³, and 24x10²⁰ cm⁻³, even when the ratio of the concentrations, Yb/Er, is only about 1.2 and 2. Planar channel waveguides of rare-earth doped fluoride glass were demonstrated with single mode excitation and propagation loss below 3 dB/cm. The waveguide core was fabricated by Ag⁺-Na⁺ molten salt ion exchange process in a borosilicate glass (BGG31), and a Nd³⁺-doped ZBLAN glass was used as a cladding. A 0.45 dB signal amplification at 1.064 μm was observed in the fabricated 1cm long waveguide, and a 0.9 dB amplification is expected at the emission peak (1.049 μm). Modeling results suggest that 2.5 dB/cm is possible by improving surface flatness of the ZBLAN glass.

Iridium silicides are of current interest as candidate detector materials for silicon based, Schottky-barrier infrared focal plane arrays. In this work, the growth and structure of codeposited IrSi₃ and Ir₃Si₄ films is discussed as well as the effect of annealing and deposition temperature on pure Ir film depositions. Nearly single-phase polycrystalline IrSi₃ films were formed by codeposition of Ir and Si in a 1:3 ratio at temperatures as low as 450°C. Localized epitaxial crystallite growth, identified by x-ray and electron diffraction, is found for IrSi₃ films formed at temperatures >600 °C, with a previously unreported c-axis epitaxial crystallite growth on Si(111) dominating at ∼700 °C. Single-phase polycrystalline Ir₃Si₄ films were formed by annealing room temperature 3:4 codeposited films, whereas localized epitaxial Ir₃Si₄ crystallite growth occurred for codeposition at temperatures of ∼500 °C. Annealed Ir films initially form IrSi crystallites at temperatures of ∼350 °C and further react with the substrate to form polycrystalline Ir₃Si5 at temperatures ≥ 550 °C. The Ir₃Si₄ phase, not found in annealed reactions, dominated the growth of silicide films formed by hot Ir depositions at 500 °C. A previously unreported Ir₃Si₄ epitaxial growth was identified for Ir depositions on Si(111)substrates. Resistivity measurements indicate that IrSi₃, IrSi, and Ir₃Si₄ films are metallic, where Ir₃Si₄ had the lowest resistivity of ∼60 μΩ-cm. Optical photoresponse and I-V measurements performed on diode structures indicate the barrier height of IrSi₃ on p-type Si(111) (∼0.33 eV) to be higher than that on p-type Si(100) (∼0.22-0.25 eV), limiting infrared imaging capability to the SWIR (1-3 μm) and MWIR (3-5 μm) atmospheric transmission windows, respectfully. Codeposited Ir₃Si₄ films display optical barrier heights between 0.125 to 0.175 eV on p-type Si(100), providing possible imaging capability in the LWIR (8-12 μm) spectral region. Ir₃Si₄ devices, displaying localized epitaxial crystallite growth, yield higher emission efficiency than polycrystalline Ir₃Si₄ films. Optical photoresponse measurements on a IrSi device also indicate a low optical barrier height (∼0.12 eV) providing access to the LWIR spectral region. Optical measurements on Ir₃Si5 films are also presented.

The Opticam spherical surface generator is developed at the Center for Optics Manufacturing (COM). It combines computer-numerical-control (CNC) technology with bound abrasive ring grinding geometry to create advantages over the conventional loose abrasive grinding systems in flexibility, productivity and accuracy. The Opticam SX utilizes a ring grinding geometry to generate spherical surfaces. By adjusting the tilt angle and the diameter of the ring cutter, the Opticam is capable of generating spherical surfaces with an essentially unlimited range of radius of curvature. This ring grinding geometry, however, requires a precise alignment between the cutter and the generated part. Residual cutter misalignments in the machine setup cause the finished surface to deviate from the design shape. Current tool misalignment detection techniques seriously limit the productivity of the Opticam system, and a new metrology system is introduced in this dissertation. The new system is geometrical ray trace based, and has some similarities to the moire deflectometry techniques. It uses a non-contact method to measure surface slope errors from images reflected off Opticam generated surfaces. The detected slope errors are used to determine the corresponding tool misalignments in the Opticam generator. The system setup is simple and not sensitive to vibrations. This system is compatible with the wet grinding environment. Furthermore, this new metrology system is capable of measuring surfaces with a wide range of radius of curvature from convex to concave. A prototype system was built based on this technique. It has been evaluated on-line in the Opticam SX. A surface wetting technique is used to allow detection on Opticam generated surfaces independent of the actual surface finish. The experimental results suggested that the on-line detection system is capable of detecting tool misalignment corresponding to a peak-to-valley surface figure error that is 1 mum or greater on ground surfaces. Better than 0.5 μm peak-to-valley surface error detection was achieved on specular surfaces. It was also found that machine dwell produces surface figure errors that are opposite to the errors produced by y-direction tool misalignment. Best surface figures are achieved when machine dwell errors are balance by residual tool misalignments in the Opticam machine.

This dissertation describes the development of ultra-short pulse solid-state lasers and the investigation of ultra-short pulse propagation in a nonlinear waveguide. We present laser design considerations involving astigmatism compensation, spot-size estimation, stability, and dispersion compensation, and their application to chromium doped forsterite lasers. Making use of the Kerr nonlinearity of the Cr:forsterite crystal we demonstrate self-mode-locking in Cr:forsterite lasers, both in the hard-aperture and soft-aperture Kerr-lens mode-locking regimes. Sub-200-fs pulses tunable between 1240 and 1285 nm were obtained, with the shortest transform-limited pulses having 45 fs duration at 90 MHz repetition rate with 100 mW output power at 1265 nm. Using a semiconductor quantum-well saturable absorber integrated with a Bragg reflector we demonstrated self-starting passive continuous-wave mode-locked operation of a Cr:forsterite laser. Self-starting mode-locking was the only operational mode of the laser and could be achieved with and without intracavity dispersion compensation. We obtained 70 fs transformed-limited pulses using a prism pair for dispersion compensation, 4 ps pulses without prisms, and pulse energies of up to 2.3 nJ at 90 MHz repetition rate at 1260 nm. Using quantum-confined nanocrystals of lead sulfide in glass as intracavity saturable absorbers we obtained self-starting passive continuous-wave mode-locking in a Cr:forsterite laser. We obtained near transform-limited 4.6 ps laser pulses at 100 MHz repetition rate, and a wide tunability range of 1207 to 1307 nm. We studied femtosecond pulse propagation near a two-photon transition in CdS quantum-dot-doped waveguides produced by the solgel and ion-exchange methods. The observed two-photon absorption and asymmetric spectral modulation of the transmitted pulses were explained by the theoretical model, which incorporated a near-resonant two-photon transition.

The development of advanced technological methods for growth of semiconductors, such as molecular beam epitaxy, have allowed growth of layered semiconductor structures with precision to a single atomic layer. One important structure is the semiconductor quantum well, consisting of a thin layer of a smaller bandgap semiconductor grown between layers of thicker, larger bandgap semiconductor. Quantum wells are, for example, largely responsible for making the semiconductor laser a practical device. By increasing the binding energy of excitons (hydrogen-like, bound electron-hole pairs in semiconductors), and allowing them to couple to the continuum of vacuum photon modes, semiconductor quantum wells have made excitons the focus of numerous fundamental optical studies. Stacks of periodically grown quantum wells, grown far enough apart such that electronic tunneling between quantum wells is unimportant, can still be coupled by light. N light-coupled quantum wells have N exciton-light, or exciton-polariton, eigenmodes, each characterized by a distinct energy and radiative lifetime dependent on the periodicity of the quantum wells. By adjusting the periodicity of the quantum wells and the material parameters, engineering of the light-matter interaction of these one-dimensional mesoscopic crystals is possible. The interesting new properties of these structures open the possibility for new devices. Periodic multiple quantum wells with a period in the vicinity of half the exciton resonance wavelength are studied in linear measurements of reflection, transmission and absorption. The optical properties are dominated by the eigenmodes of the light-coupled quantum wells. At Bragg periodicity, where the oscillator strengths of all quantum well excitons are concentrated into one superradiant mode, a photonic band gap grows in amplitude and linearly in energy width with increasing number of quantum wells N. A corresponding N times increased radiative damping rate compared to a single quantum well is observed, originating from expulsion of the light character of the superradiant mode from the photonic bandgap structure. The slope of linewidth versus N gives the radiative linewidth of the exciton. For periods away from Bragg condition, all normal modes become optically active, and are observed in reflection and absorption experiments. Because light-coupling alters the photon density of states, formation of the N exciton-polariton eigenmodes is also evidenced in photoluminescence after nonresonant excitation into the free carrier continuum. The strongly modified light-matter interaction for photons in the photonic gap at Bragg periodicity is also manifest in the inhibited emission from the superradiant mode, a surprising result explained by a consideration of the linear properties. The temporal dynamics of Rayleigh scattering of a resonant excitation pulse from disordered semiconductor multiple quantum wells has many interesting aspects, and has recently been the subject of much debate. The effect of light-coupling on resonant Rayleigh scattering from periodic semiconductor multiple quantum well structures is investigated both experimentally and theoretically. Polaritonic effects are found to dominate the Rayleigh scattered light temporal dynamics due to the simultaneous coexistence of several eigenmodes with different energy and radiative decay times for a given periodicity. They give rise to polarization beating between modes and determine rise and decay times of the resonance Rayleigh scattered signals.

The present dissertation compiles three aspects of my Ph.D. work on OLED device design, fabrication and characterization. The first chapter is a review of the concepts and theories describing the mechanisms of organic electroluminescence. The second chapter makes use of these concepts to articulate some basic principles for the design of efficient and stable OLEDs. The third chapter describes the main characterization and sample preparation techniques used along this dissertation. Chapter IV describes the processing of efficient organic electroluminescent EL devices with ITO\TPD\AIQ₃\Mg:Ag structures. The screen printing technique of a hole transport polymeric blend was used in an unusual mode to render thin films in the order of 60-80 nm. EL devices were then fabricated on top of these sp films to provide ∼0.9% quantum efficiencies, comparable to spin coating with the same structures. Various polymer:TPD and solvent combinations were studied to find the paste with the best rheological properties. The same technique was also used to deposit a patterned MEH-PPV film. Chapter V describes my research work on the wetting of TPD on ITO substrates. The wetting was monitored by following its surface morphology evolution as a function of temperature. The effect of these surface changes was then correlated to the I-V-L characteristics of devices made with these TPD films. The surface roughness was measured with tapping AFM showed island formation at temperatures as low as 50-60°C. I Also investigated the effect of the purity of materials like AlQ3 on the device EL performance, as described in Chapter VI. In order to improve the purity of these environmentally degradable complexes a new in situ purification technique was developed with excellent enhancement of the EL cell properties. The in situ purification process was then used to purify/deposit organic dyes with improved film formation and EL characteristics.