Matching Items (43)
Description
A proposed visible spectrum nanoscale imaging method requires material with permittivity values much larger than those available in real world materials to shrink the visible wavelength to attain the desired resolution. It has been proposed that the extraordinarily slow propagation experienced by light guided along plasmon resonant structures is a viable approach to obtaining these short wavelengths. To assess the feasibility of such a system, an effective medium model of a chain of Noble metal plasmonic nanospheres is developed, leading to a straightforward calculation of the waveguiding properties. Evaluation of other models for such structures that have appeared in the literature, including an eigenvalue problem nearest neighbor approximation, a multi- neighbor approximation with retardation, and a method-of-moments method for a finite chain, show conflicting expectations of such a structure. In particular, recent publications suggest the possibility of regions of invalidity for eigenvalue problem solutions that are considered far below the onset of guidance, and for solutions that assume the loss is low enough to justify perturbation approximations. Even the published method-of-moments approach suffers from an unjustified assumption in the original interpretation, leading to overly optimistic estimations of the attenuation of the plasmon guided wave. In this work it is shown that the method of moments approach solution was dominated by the radiation from the source dipole, and not the waveguiding behavior claimed. If this dipolar radiation is removed the remaining fields ought to contain the desired guided wave information. Using a Prony's-method-based algorithm the dispersion properties of the chain of spheres are assessed at two frequencies, and shown to be dramatically different from the optimistic expectations in much of the literature. A reliable alternative to these models is to replace the chain of spheres with an effective medium model, thus mapping the chain problem into the well-known problem of the dielectric rod. The solution of the Green function problem for excitation of the symmetric longitudinal mode (TM01) is performed by numerical integration. Using this method the frequency ranges over which the rod guides and the associated attenuation are clearly seen. The effective medium model readily allows for variation of the sphere size and separation, and can be taken to the limit where instead of a chain of spheres we have a solid Noble metal rod. This latter case turns out to be the optimal for minimizing the attenuation of the guided wave. Future work is proposed to simulate the chain of photonic nanospheres and the nanowire using finite-difference time-domain to verify observed guided behavior in the Green's function method devised in this thesis and to simulate the proposed nanosensing devices.
ContributorsHale, Paul (Author) / Diaz, Rodolfo E (Thesis advisor) / Goodnick, Stephen (Committee member) / Aberle, James T., 1961- (Committee member) / Palais, Joseph (Committee member) / Arizona State University (Publisher)
Created2013
Description
Integrated photonics requires high gain optical materials in the telecom wavelength range for optical amplifiers and coherent light sources. Erbium (Er) containing materials are ideal candidates due to the 1.5 μm emission from Er3+ ions. However, the Er density in typical Er-doped materials is less than 1 x 1020 cm-3, thus limiting the maximum optical gain to a few dB/cm, too small to be useful for integrated photonics applications. Er compounds could potentially solve this problem since they contain much higher Er density. So far the existing Er compounds suffer from short lifetime and strong upconversion effects, mainly due to poor quality of crystals produced by various methods of thin film growth and deposition. This dissertation explores a new Er compound: erbium chloride silicate (ECS, Er3(SiO4)2Cl ) in the nanowire form, which facilitates the growth of high quality single crystals. Growth methods for such single crystal ECS nanowires have been established. Various structural and optical characterizations have been carried out. The high crystal quality of ECS material leads to a long lifetime of the first excited state of Er3+ ions up to 1 ms at Er density higher than 1022 cm-3. This Er lifetime-density product was found to be the largest among all Er containing materials. A unique integrating sphere method was developed to measure the absorption cross section of ECS nanowires from 440 to 1580 nm. Pump-probe experiments demonstrated a 644 dB/cm signal enhancement from a single ECS wire. It was estimated that such large signal enhancement can overcome the absorption to result in a net material gain, but not sufficient to compensate waveguide propagation loss. In order to suppress the upconversion process in ECS, Ytterbium (Yb) and Yttrium (Y) ions are introduced as substituent ions of Er in the ECS crystal structure to reduce Er density. While the addition of Yb ions only partially succeeded, erbium yttrium chloride silicate (EYCS) with controllable Er density was synthesized successfully. EYCS with 30 at. % Er was found to be the best. It shows the strongest PL emission at 1.5 μm, and thus can be potentially used as a high gain material.
ContributorsYin, Leijun (Author) / Ning, Cun-Zheng (Thesis advisor) / Chamberlin, Ralph (Committee member) / Yu, Hongbin (Committee member) / Menéndez, Jose (Committee member) / Ponce, Fernando (Committee member) / Arizona State University (Publisher)
Created2013
Description
Dual-wavelength laser sources have various existing and potential applications in wavelength division multiplexing, differential techniques in spectroscopy for chemical sensing, multiple-wavelength interferometry, terahertz-wave generation, microelectromechanical systems, and microfluidic lab-on-chip systems. In the drive for ever smaller and increasingly mobile electronic devices, dual-wavelength coherent light output from a single semiconductor laser diode would enable further advances and deployment of these technologies. The output of conventional laser diodes is however limited to a single wavelength band with a few subsequent lasing modes depending on the device design. This thesis investigates a novel semiconductor laser device design with a single cavity waveguide capable of dual-wavelength laser output with large spectral separation. The novel dual-wavelength semiconductor laser diode uses two shorter- and longer-wavelength active regions that have separate electron and hole quasi-Fermi energy levels and carrier distributions. The shorter-wavelength active region is based on electrical injection as in conventional laser diodes, and the longer-wavelength active region is then pumped optically by the internal optical field of the shorter-wavelength laser mode, resulting in stable dual-wavelength laser emission at two different wavelengths quite far apart. Different designs of the device are studied using a theoretical model developed in this work to describe the internal optical pumping scheme. The carrier transport and separation of the quasi-Fermi distributions are then modeled using a software package that solves Poisson's equation and the continuity equations to simulate semiconductor devices. Three different designs are grown using molecular beam epitaxy, and broad-area-contact laser diodes are processed using conventional methods. The modeling and experimental results of the first generation design indicate that the optical confinement factor of the longer-wavelength active region is a critical element in realizing dual-wavelength laser output. The modeling predicts lower laser thresholds for the second and third generation designs; however, the experimental results of the second and third generation devices confirm challenges related to the epitaxial growth of the structures in eventually demonstrating dual-wavelength laser output.
ContributorsGreen, Benjamin C (Author) / Zhang, Yong-Hang (Thesis advisor) / Ning, Cun-Zheng (Committee member) / Tao, Nongjian (Committee member) / Roedel, Ronald J (Committee member) / Arizona State University (Publisher)
Created2011
Description
In this work, atomic force microscopy (AFM) and time resolved confocal fluorescence microscopy are combined to create a microscopy technique which allows for nanometer resolution topographic and fluorescence imaging. This technique can be applied to any sample which can be immobilized on a surface and which can be observed by fluorescence microscopy. Biological problems include small molecular systems, such as membrane receptor clusters, where very high optical resolutions need to be achieved. In materials science, fluorescent nanoparticles or other optically active nanostructures can be investigated using this technique. In the past decades, multiple techniques have been developed that yield high resolution optical images. Multiple far-field techniques have overcome the diffraction limit and allow fluorescence imaging with resolutions of few tens of nanometers. On the other hand, near-field microscopy, that makes use of optically active structures much smaller than the diffraction limit can give resolutions around ten nanometers with the possibility to collect topographic information from flat samples. The technique presented in this work reaches resolutions in the nanometer range along with topographic information from the sample. DNA origami with fluorophores attached to it was used to show this high resolution. The fluorophores with 21 nm distance could be resolved and their position on the origami determined within 10 nm. Not only did this work reach a new record in optical resolution in near-field microscopy (5 nm resolution in air and in water), it also gave an insight into the physics that happens between a fluorescent molecule and a dielectric nanostructure, which the AFM tip is. The experiments with silicon tips made a detailed comparison with models possible on the single molecule level, highly resolved in space and time. On the other hand, using silicon nitride and quartz as tip materials showed that effects beyond the established models play a role when the molecule is directly under the AFM tip, where quenching of up to 5 times more efficient than predicted by the model was found.
ContributorsSchulz, Olaf (Author) / Ros, Robert (Thesis advisor) / Levitus, Marcia (Committee member) / Liu, Yan (Committee member) / Lindsay, Stuart (Committee member) / Shumway, John (Committee member) / Arizona State University (Publisher)
Created2012
Description
Microfluidics is the study of fluid flow at very small scales (micro -- one millionth of a meter) and is prevalent in many areas of science and engineering. Typical applications include lab-on-a-chip devices, microfluidic fuel cells, and DNA separation technologies. Many of these microfluidic devices rely on micron-resolution velocimetry measurements to improve microchannel design and characterize existing devices. Methods such as micro particle imaging velocimetry (microPIV) and micro particle tracking velocimetry (microPTV) are mature and established methods for characterization of steady 2D flow fields. Increasingly complex microdevices require techniques that measure unsteady and/or three dimensional velocity fields. This dissertation presents a method for three-dimensional velocimetry of unsteady microflows based on spinning disk confocal microscopy and depth scanning of a microvolume. High-speed 2D unsteady velocity fields are resolved by acquiring images of particle motion using a high-speed CMOS camera and confocal microscope. The confocal microscope spatially filters out of focus light using a rotating disk of pinholes placed in the imaging path, improving the ability of the system to resolve unsteady microPIV measurements by improving the image and correlation signal to noise ratio. For 3D3C measurements, a piezo-actuated objective positioner quickly scans the depth of the microvolume and collects 2D image slices, which are stacked into 3D images. Super resolution microPIV interrogates these 3D images using microPIV as a predictor field for tracking individual particles with microPTV. The 3D3C diagnostic is demonstrated by measuring a pressure driven flow in a three-dimensional expanding microchannel. The experimental velocimetry data acquired at 30 Hz with instantaneous spatial resolution of 4.5 by 4.5 by 4.5 microns agrees well with a computational model of the flow field. The technique allows for isosurface visualization of time resolved 3D3C particle motion and high spatial resolution velocity measurements without requiring a calibration step or reconstruction algorithms. Several applications are investigated, including 3D quantitative fluorescence imaging of isotachophoresis plugs advecting through a microchannel and the dynamics of reaction induced colloidal crystal deposition.
ContributorsKlein, Steven Adam (Author) / Posner, Jonathan D (Thesis advisor) / Adrian, Ronald (Committee member) / Chen, Kangping (Committee member) / Devasenathipathy, Shankar (Committee member) / Frakes, David (Committee member) / Arizona State University (Publisher)
Created2011
Description
A system for illuminating a sample in situ with visible and UV light inside a transmission electron microscope was devised to study photocatalysts. There are many factors which must be considered when designing and building such a system. These include both mechanical, optical, and electron optical considerations. Some of the restrictions posed by the electron microscope column are significant, and care must be taken not to degrade the microscope's electron optical performance, or to unduly restrict the other current capabilities of the microscope. The nature of these various design considerations is discussed in detail. A description of the system that has been added to the microscope at ASU, an FEI Tecnai F20 environmental transmission electron microscope is also given. The system includes a high brightness broadband light source with optical filters, a fiber to guide the light to the sample, and a system for precisely aligning the fiber tip. The spatial distribution and spectrum of the light reaching the sample has been characterized, and is described in detail.
ContributorsMiller, Benjamin (Author) / Crozier, Peter A. (Thesis advisor) / McCartney, Martha (Committee member) / Rez, Peter (Committee member) / Arizona State University (Publisher)
Created2012
Description
Two-dimensional vision-based measurement is an ideal choice for measuring small or fragile parts that could be damaged using conventional contact measurement methods. Two-dimensional vision-based measurement systems can be quite expensive putting the technology out of reach of inventors and others. The vision-based measurement tool design developed in this thesis is a low cost alternative that can be made for less than $500US from off-the-shelf parts and free software. The design is based on the USB microscope. The USB microscope was once considered a toy, similar to the telescopes and microscopes of the 17th century, but has recently started finding applications in industry, laboratories, and schools. In order to convert the USB microscope into a measurement tool, research in the following areas was necessary: currently available vision-based measurement systems, machine vision technologies, microscope design, photographic methods, digital imaging, illumination, edge detection, and computer aided drafting applications. The result of the research was a two-dimensional vision-based measurement system that is extremely versatile, easy to use, and, best of all, inexpensive.
ContributorsGraham, Linda L. (Author) / Biekert, Russell (Thesis advisor) / Macia, Narciso (Committee member) / Meitz, Robert (Committee member) / Arizona State University (Publisher)
Created2011
Description
This dissertation presents research findings regarding the exploitation of localized surface plasmon (LSP) of epitaxial Ag islands as a means to enhance the photoluminescence (PL) of Germanium (Ge) quantum dots (QDs). The first step of this project was to investigate the growth of Ag islands on Si(100). Two distinct families of Ag islands have been observed. “Big islands” are clearly faceted and have basal dimensions in the few hundred nm to μm range with a variety of basal shapes. “Small islands” are not clearly faceted and have basal diameters in the 10s of nm range. Big islands form via a nucleation and growth mechanism, and small islands form via precipitation of Ag contained in a planar layer between the big islands that is thicker than the Stranski-Krastanov layer existing at room-temperature.
The pseudodielectric functions of epitaxial Ag islands on Si(100) substrates were investigated with spectroscopic ellipsometry. Comparing the experimental pseudodielectric functions obtained for Si with and without Ag islands clearly identifies a plasmon mode with its dipole moment perpendicular to the surface. This observation is confirmed using a simulation based on the thin island film (TIF) theory. Another mode parallel to the surface may be identified by comparing the experimental pseudodielectric functions with the simulated ones from TIF theory. Additional results suggest that the LSP energy of Ag islands can be tuned from the ultra-violet to the infrared range by an amorphous Si (α-Si) cap layer.
Heterostructures were grown that incorporated Ge QDs, an epitaxial Si cap layer and Ag islands grown atop the Si cap layer. Optimum growth conditions for distinct Ge dot ensembles and Si cap layers were obtained. The density of Ag islands grown on the Si cap layer depends on its thickness. Factors contributing to this effect may include the average strain and Ge concentration on the surface of the Si cap layer.
The effects of the Ag LSP on the PL of Ge coherent domes were investigated for both α-Si capped and bare Ag islands. For samples with low-doped substrates, the LSPs reduce the Ge dot-related PL when the Si cap layer is below some critical thickness and have no effect on the PL when the Si cap layer is above the critical thickness. For samples grown on highly-doped wafers, the LSP of bare Ag islands enhanced the PL of Ge QDs by ~ 40%.
The pseudodielectric functions of epitaxial Ag islands on Si(100) substrates were investigated with spectroscopic ellipsometry. Comparing the experimental pseudodielectric functions obtained for Si with and without Ag islands clearly identifies a plasmon mode with its dipole moment perpendicular to the surface. This observation is confirmed using a simulation based on the thin island film (TIF) theory. Another mode parallel to the surface may be identified by comparing the experimental pseudodielectric functions with the simulated ones from TIF theory. Additional results suggest that the LSP energy of Ag islands can be tuned from the ultra-violet to the infrared range by an amorphous Si (α-Si) cap layer.
Heterostructures were grown that incorporated Ge QDs, an epitaxial Si cap layer and Ag islands grown atop the Si cap layer. Optimum growth conditions for distinct Ge dot ensembles and Si cap layers were obtained. The density of Ag islands grown on the Si cap layer depends on its thickness. Factors contributing to this effect may include the average strain and Ge concentration on the surface of the Si cap layer.
The effects of the Ag LSP on the PL of Ge coherent domes were investigated for both α-Si capped and bare Ag islands. For samples with low-doped substrates, the LSPs reduce the Ge dot-related PL when the Si cap layer is below some critical thickness and have no effect on the PL when the Si cap layer is above the critical thickness. For samples grown on highly-doped wafers, the LSP of bare Ag islands enhanced the PL of Ge QDs by ~ 40%.
ContributorsKong, Dexin (Author) / Drucker, Jeffery (Thesis advisor) / Chen, Tingyong (Committee member) / Ros, Robert (Committee member) / Smith, David (Committee member) / Arizona State University (Publisher)
Created2015
Description
Due to the ever increasing relevance of finer machining control as well as necessary reduction in material waste by large area semiconductor device manufacturers, a novel bulk laser machining method was investigated. Because the cost of silicon and sapphire substrates are limiting to the reduction in cost of devices in both the light emitting diode (LED) and solar industries, and the present substrate wafering process results in >50% waste, the need for an improved ingot wafering technique exists.
The focus of this work is the design and understanding of a novel semiconductor wafering technique that utilizes the nonlinear absorption properties of band-gapped materials to achieve bulk (subsurface) morphological changes in matter using highly focused laser light. A method and tool was designed and developed to form controlled damage regions in the bulk of a crystalline sapphire wafer leaving the surfaces unaltered. The controllability of the subsurface damage geometry was investigated, and the effect of numerical aperture of the focusing optic, energy per pulse, wavelength, and number of pulses was characterized for a nanosecond pulse length variable wavelength Nd:YAG OPO laser.
A novel model was developed to describe the geometry of laser induced morphological changes in the bulk of semiconducting materials for nanosecond pulse lengths. The beam propagation aspect of the model was based on ray-optics, and the full Keldysh multiphoton photoionization theory in conjuncture with Thornber's and Drude's models for impact ionization were used to describe high fluence laser light absorption and carrier generation ultimately resulting in permanent material modification though strong electron-plasma absorption and plasma melting. Although the electron-plasma description of laser damage formation is usually reserved for extremely short laser pulses (<20 ps), this work shows that it can be adapted for longer pulses of up to tens of nanoseconds.
In addition to a model describing damage formation of sub-band gap energy laser light in semiconducting and transparent crystalline dielectrics, a novel nanosecond laser process was successfully realized to generate a thin plane of damage in the bulk of sapphire wafers. This was accomplished using high numerical aperture optics, a variable wavelength nanosecond laser source, and three-dimensional motorized precision stage control.
The focus of this work is the design and understanding of a novel semiconductor wafering technique that utilizes the nonlinear absorption properties of band-gapped materials to achieve bulk (subsurface) morphological changes in matter using highly focused laser light. A method and tool was designed and developed to form controlled damage regions in the bulk of a crystalline sapphire wafer leaving the surfaces unaltered. The controllability of the subsurface damage geometry was investigated, and the effect of numerical aperture of the focusing optic, energy per pulse, wavelength, and number of pulses was characterized for a nanosecond pulse length variable wavelength Nd:YAG OPO laser.
A novel model was developed to describe the geometry of laser induced morphological changes in the bulk of semiconducting materials for nanosecond pulse lengths. The beam propagation aspect of the model was based on ray-optics, and the full Keldysh multiphoton photoionization theory in conjuncture with Thornber's and Drude's models for impact ionization were used to describe high fluence laser light absorption and carrier generation ultimately resulting in permanent material modification though strong electron-plasma absorption and plasma melting. Although the electron-plasma description of laser damage formation is usually reserved for extremely short laser pulses (<20 ps), this work shows that it can be adapted for longer pulses of up to tens of nanoseconds.
In addition to a model describing damage formation of sub-band gap energy laser light in semiconducting and transparent crystalline dielectrics, a novel nanosecond laser process was successfully realized to generate a thin plane of damage in the bulk of sapphire wafers. This was accomplished using high numerical aperture optics, a variable wavelength nanosecond laser source, and three-dimensional motorized precision stage control.
ContributorsLeBeau, James (Author) / Bowden, Stuart (Thesis advisor) / Honsberg, Christiana (Committee member) / Bertoni, Mariana (Committee member) / Cotter, Jeffrey (Committee member) / Arizona State University (Publisher)
Created2015
Description
The Milky Way galaxy is a powerful dynamic system that is highly efficient at recycling material. Stars are born out of intergalactic gas and dust, fuse light elements into heavier elements in their cores, then upon stellar death spread material throughout the galaxy, either by diffusion of planetary nebula or by explosive events for high mass stars, and that gas must cool and condense to form stellar nurseries. Though the stellar lifecycle has been studied in detail, relatively little is known about the processes by which hot, diffuse gas ejected by dying stars cools and conglomerates in the interstellar medium (ISM). Much of this mystery arises because only recently have instruments with sufficient spatial and spectral resolution, sensitivity, and bandwidth become available in the terahertz (THz) frequency spectrum where these clouds peak in either thermal or line emission. In this dissertation, I will demonstrate technology advancement of instruments in this frequency regime with new characterization techniques, machining strategies, and scientific models of the spectral behavior of gas species targeted by these instruments.
I begin this work with a description of radiation pattern measurements and their use in astronomical instrument characterization. I will introduce a novel technique to measure complex (phase-sensitive) field patterns using direct detectors. I successfully demonstrate the technique with a single pixel microwave inductance detectors (MKID) experiment. I expand that work by measuring the APEX MKID (A-MKID) focal plane array of 880 pixel detectors centered at 350 GHz. In both chapters I discuss the development of an analysis pipeline to take advantage of all information provided by complex field mapping. I then discuss the design, simulation, fabrication processes, and characterization of a circular-to-rectangular waveguide transformer module integrated into a circularly symmetric feedhorn block. I conclude with a summary of this work and how to advance these technologies for future ISM studies.
I begin this work with a description of radiation pattern measurements and their use in astronomical instrument characterization. I will introduce a novel technique to measure complex (phase-sensitive) field patterns using direct detectors. I successfully demonstrate the technique with a single pixel microwave inductance detectors (MKID) experiment. I expand that work by measuring the APEX MKID (A-MKID) focal plane array of 880 pixel detectors centered at 350 GHz. In both chapters I discuss the development of an analysis pipeline to take advantage of all information provided by complex field mapping. I then discuss the design, simulation, fabrication processes, and characterization of a circular-to-rectangular waveguide transformer module integrated into a circularly symmetric feedhorn block. I conclude with a summary of this work and how to advance these technologies for future ISM studies.
ContributorsDavis, Kristina (Author) / Groppi, Christopher E (Thesis advisor) / Bowman, Judd (Committee member) / Mauskopf, Philip (Committee member) / Jellema, Willem (Committee member) / Pan, George (Committee member) / Trichopoulos, Georgios (Committee member) / Arizona State University (Publisher)
Created2018