Browsing by Subject "Near-field"
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Item Atomic Force Microscope Based Near-field Imaging for Probing Cell Surface Interactions(2013-03-26) Amini, SinaNear-membrane and trans-membrane proteins and their interactions with the extracellular matrix (ECM) can yield valuable information about cell dynamics. However, advances in the field of nanoscale cellular processes have been hindered, in part, due to limits imposed by current technology. In this work, a novel evanescent field (EF) imaging technique is designed, modeled, created and tested for near-field imaging in the apical surface of cells. This technique and F?rster resonance energy transfer (FRET) were used to investigate interactions between integrins on the cell surface and the ECM protein, fibronectin. The goal was to monitor changes in the integrin density at the cell surface as a function of clustering after binding to fibronectin on the microsphere surface. For the EF technique, quantum dot (QD)-embedded polystyrene microspheres were used to couple light into whispering gallery modes (WGMs) inside the microspheres; the resulting EF at the surface of the microsphere was used as a near-field excitation source with ~50 nm axial resolution for exciting fluorescently-labeled integrins. For FRET measurements (~10 nm axial resolution), QDs (donors) were coated on the surface of microspheres and energy transfer to red fluorescent protein (RFP)-integrin constructs (acceptors) studied. In both techniques, the QD-modified microspheres were mounted on atomic force microscope (AFM) cantilevers, functionalized with fibronectin, and brought into contact with fluorescently-labeled HeLa or vascular smooth muscle (VSM) cells. The results obtained from both methods show the clustering and activity of the integrins and are in good agreement with each other. Amsterdam discrete dipole approximation (ADDA) was used to study the effects of inhomogeneous surrounding refractive index on the quality factor and position of the WGMs due to the attachment of a microsphere to an AFM cantilever. WGMs of various QD-embedded microspheres mounted on AFM cantilevers were experimentally measured and shown to be consistent with the model.Item Embedded metallic grating and photonic crystal based scanning probes for subwavelength near-field light confinement(2012-12) Wang, Lingyun, Ph. D.; Neikirk, Dean P., 1957-; Zhang, Xiaojing, Ph. D.; Shi, Li; Yeh, Hsin-Chih; Yu, Edward T.; Alὺ, AndreaNear-field light confinement on scanning probe is the backbone technology for near-field imaging with subwavelength resolution that overcomes the diffraction limit by exploiting the properties of evanescent waves. The fusion of the photonics and the latest nanofabrication technology creates emerging frontier for near-field light confinement research with new design approach. The propagation of light can now be controlled by periodical structure at subwavelength scale with low loss in the artificially synthesized dielectric material. New light propagation patterns can now be implemented in subwavelength structure, such as directional free space light focus grating coupler, photonic bandgap material like photonic crystal by permitting light propagation at certain wavelength while prohibiting light outside of bandgap, and nano-slot light resonator for increased light-matter interaction at nanometer scale. Advances in this research area will have tremendous impact on electromagnetic modeling and biomedical technology for probe based subwavelength optical detection. My doctoral research focused on investigating highly efficient, nanofabrication compatible directional light coupling structure and near-field subwavelength light focus through photonic crystal material. The distinct significance of this research was placed on exploitation of the embedded metallic grating coupler of high free space directivity and subwavelength light processing circuit of enhanced near-field transmission rate, the two most dominating basic elements of the scanning optical imaging system. First, I designed a compact elliptical grating coupler based on embedded noble metal such as gold or silver that efficiently interconnects free space with dielectric rectangular waveguide. The dense system integration capability shows the application potential for on-chip interfacing subwavelength light processing circuits and near-field fluorescent biosensors with far-field detection of superb radiation directivity and coupling efficiency. Second, a novel all-dielectric light confinement probe designed by slotted photonic crystal waveguide provides a light confinement mechanism on the lateral plane. The resonating nano-cavities and the λ/4 nano-slot are used to enlarge the light throughput while as the nano-slot waveguide provides single subwavelength center lobe. The impetus of this research is the growing interests by near-field imaging researchers to obtain a low loss visible light confinement probe designs through mass production.Item Morphological effects of organic and inorganic semiconducting materials by scanning probe microscopy(2012-12) Glaz, Micah Sivan; Vanden Bout, David A.; Webb, Lauren J.; Zhu, Xiaoyang; Holliday, Bradley J.; Korgel, Brian A.Solution deposition of thin film photovoltaic materials leads to large variations in the morphological and chemical compositions of the film. In order to improve device functionality, it is important to understand how morphology and chemical composition affects charge generation, separation, and collection. This PhD work will first study bulk methods in order to characterize materials in solution and films. The results are then correlated with microscopy studies examining morphology. Other methods used in this PhD work will directly couple spectra and microscopy. Microscopic regions of such films and devices can be illuminated using scanning confocal microscopy or near-field scanning optical microscopy (NSOM), which allows for one to directly probe regions of the film at or below the optical diffraction limit. By scanning the sample over a fixed laser spot we can simultaneously create image maps of the topographical, electrical and optical properties. This technique, known as laser beam induced current (LBIC) allows one to directly probe a local area of a device with 100-300nm resolution. Along with bulk device efficiency studies, near field and confocal data of inorganic and organic materials are investigated. These include devices fabricated with a blend of P3HT (poly[3-hexylthiophene]) and perylene diimide derivatives, and Cu(InxGa1-x)Se2 [CIGS] nanoparticle devices. Finally, we use a new device architecture, a lateral organic photovoltaic (LOPV) in order to spatially resolve transport in functional organic devices.Item Realizing efficient wireless power transfer in the near-field region using electrically small antennas(2012-08) Yoon, Ick-Jae; Ling, Hao; Alù, Andrea; Baldick, Ross; Foltz, Heinrich; Yilmaz, Ali E.Non-radiative wireless power transfer using the coupled mode resonance phenomenon has been widely reported in the literature. However, the distance over which such phenomenon exists is very short when measured in terms of wavelength. In this dissertation, how efficient wireless power transfer can be realized in the radiating near-field region beyond the coupled mode resonance region is investigated. First, electrically small folded cylindrical helix (FCH) dipole antennas are designed to achieve efficient near-field power transfer. Measurements show that a 40% power transfer efficiency (PTE) can be realized at the distance of 0.25λ between two antennas in the co-linear configuration. These values come very close to the theoretical upper bound derived based on the spherical mode theory. The results also highlight the importance of antenna radiation efficiency and impedance matching in achieving efficient wireless power transfer. Second, antenna diversity is explored to further extend the range or efficiency of the power transfer. For transmitter diversity, it is found that a stable PTE region can be created when multiple transmitters are employed at sufficiently close spacing. For receiver diversity, it is found that the overall PTE can be improved as the number of the receivers is increased. Third, small directive antennas are investigated as a means of enhancing near-field wireless power transfer. Small directive antennas based on the FCH design are also implemented to enhance the PTE. It is shown that the far-field realized gain is a good surrogate for designing small directive antennas for near-field power transfer. Fourth, to examine the effects of surrounding environments on near-field coupling, an upper bound for near-field wireless power transfer is derived when a transmitter and a received are separated by a spherical material shell. The derived PTE bounds are verified using full-wave electromagnetic simulation and show good agreement for both TM mode and TE mode radiators. Using the derived theory, lossy dielectric material effects on wireless power transfer are studied. Power transfer measurements through walls are also reported and compared with the theory. Lastly, electrically small circularly polarized antennas are investigated as a means of alleviating orientation dependence in near-field wireless power transfer. An electrically small turnstile dipole antenna is designed by utilizing top loading and multiple folding. The circularly polarization characteristic of the design is first tested in the far field, before the antennas are placed in the radiating near-field region for wireless power transfer. It is shown that such circularly polarized antennas can lessen orientation dependence in near-field coupling.