This dissertation will demonstrate the synergy of nanoscopic materials and surface metrology methods by the fabrication and implementation of CNT atomic force microscopy (AFM) tips, CNT scanning tunneling microscopy (STM) tips, Pt spike AFM tips, and Pt spike near-field scanning optical microscopy (NSOM) tips for the methods of critical dimension metrology, STM, AFM phase imaging, scanning surface potential AFM (SSPM), NSOM, and three-dimensional AFM. Chapter 1 provides a general overview of the information that will be discussed in this dissertation. Chapter 2 describes two methods for the simultaneous fabrication of carbon nanotube atomic force microscopy and scanning tunneling microscopy probes. The fabrication of these high resolution probes, as well as their imaging characteristics, is described in detail. Resolution standards were used to characterize their behavior and resolution limits. In Chapter 3, the effect of high aspect ratio probe length on AFM phase imaging is studied by fabricating highly controllable Pt spike AFM tips. By monitoring phase shifts on homogenous surfaces as a function of Pt spike length, it is shown that attractive forces at the tip are significantly reduced when high aspect ratio structures are added to conventional AFM probes. In Chapter 4, the effect of probe geometry on scanning surface potential microscopy (SSPM) is described. By studying the effect of scan height in SSPM, it was found that large surface area probe geometries, such as conventional Pt coated AFM tips, have lower surface potential resolution because of contributions from the sides of the tip as well as the cantilever. Spatial resolution standards were probed to evaluate the effect of probe geometry on SSPM sensitivity and resolution. Chapter 5 describes the fabrication of specialized probes for three-dimensional atomic force microscopy, scanning near-field optical microscopy, and scanning electrochemical -- atomic force microscopy (SECM-AFM). Using techniques described in Chapters 2-4, high aspect ratio structures were added to conventional probes used in 3D AFM, NSOM and SECM-AFM to solve limitations inherent to current probe designs for each method. Preliminary data indicates that each probe will have a significant beneficial effect on the resolution limit of its technique.

<p>This thesis examines the bandwidth shortcomings of conventional inductive coupling biotelemetry systems for implantable devices, and presents two approaches toward an end-to-end biotelemetry system for reducing the power consumption of implanted devices at increased levels of bandwidth. By leveraging the transition zone between the near and far field, scattering in the near field at UHF frequencies for increased bandwidth at low power budgets can be employed. Additionally, taking advantage of surface wave propagation permits the use of single-wire RF transmission lines in biological tissue, offering more efficient signal routing over near field coupling resulting in controlled implant depth at low power budgets.</p><p>Due to the dielectric properties of biological tissue, and the necessity to operate in the radiating near field to communicate via scattered fields, the implant depth drives the carrier frequency. The information bandwidth supplied by each sensing electrode in conventional implants also drives the operating frequency and regime. At typical implant depths, frequencies in the UHF range permit operation in the radiating near field as well as sufficient bandwidth.</p><p>Backscatter modulation provides a low-power, high-bandwidth alternative to conventional low frequency inductive coupling. A prototype active implantable device presented in this thesis is capable of transmitting data at 30 Mbps over a 915 MHz link while immersed in saline, at a communication efficiency of 16.4 pJ/bit. A prototype passive device presented in this thesis is capable of operating battery-free, fully immersed in saline, while transmitting data at 5 Mbps and consuming 1.23 mW. This prototype accurately demodulates neural data while immersed in saline at a distance of 2 cm. This communication distance is extended at similar power budgets by exploiting surface wave propagation along a single-wire transmission line. Theoretical models of single-wire RF transmission lines embedded in high permittivity and conductivity dielectrics are validated by measurements. A single-wire transmission line of radius 152.4 um exhibits a loss of 1 dB/cm at 915 MHz in saline, and extends the implant depth to 6 cm while staying within SAR limits.</p><p>This work opens the door for implantable biotelemetry systems to handle the vast amount of data generated by modern sensing devices, potentially offering new insight into neurological diseases, and may aid in the development of BMI's.</p> / Dissertation

This thesis examines a series of near-field antenna arrays used to perform subwavelength focusing and subwavelength imaging outside the extreme near field. For this purpose, slot and dipole arrays have been designed to produce a subwavelength focal spot at a distance of a quarter wavelength from the array. The dipole arrays are then used as scanning probes to produce images with subwavelength resolution based on perturbations in the scattered field. Unlike negative-refractive-index metamaterial superlenses, the imaging resolution is not affected by losses in the array. Furthermore, the arrays are simple to fabricate and are frequency scalable up to Terahertz frequencies and beyond. A near-field analogue to classic antenna-array theory called ``shifted beam theory'' is presented as a design tool. Based on the linear independence of element field patterns in the near field, this theory is very intuitive and provides a simplified way to calculate the element current weights necessary to generate a given target near-field pattern. Two-dimensional near-field subwavelength focusing is demonstrated using a slotted transmission-screen, or ``meta-screen'', under plane-wave incidence. At a distance of a quarter wavelength, the transverse electric field was measured in experiment to have a full-width half-maximum beamwidth of 0.40 by 0.27 wavelengths. This is compared to a single slot transmission-screen which had a beamwidth of 0.60 by 0.58 wavelengths. Broadside and end-fire dipole arrays are used to perform subwavelength imaging in one and two dimensions, respectively. The experimental minimum resolvable separation between two objects at a quarter-wavelength distance was 0.26 wavelengths using the end-fire array probe, as compared to 0.43 wavelengths for a single monopole probe. For an experiment using eight objects scattered over a one-square-wavelength area, however, the array probe imaging resolution remained around 0.25 wavelengths while the baseline monopole probe was no longer able to resolve any of the objects. Experiments were also conducted using objects buried behind a dielectric barrier as well as objects immersed within a dielectric. These results were consistent with the resolution improvements observed in the free-space resolution experiments.

This thesis examines a series of near-field antenna arrays used to perform subwavelength focusing and subwavelength imaging outside the extreme near field. For this purpose, slot and dipole arrays have been designed to produce a subwavelength focal spot at a distance of a quarter wavelength from the array. The dipole arrays are then used as scanning probes to produce images with subwavelength resolution based on perturbations in the scattered field. Unlike negative-refractive-index metamaterial superlenses, the imaging resolution is not affected by losses in the array. Furthermore, the arrays are simple to fabricate and are frequency scalable up to Terahertz frequencies and beyond. A near-field analogue to classic antenna-array theory called ``shifted beam theory'' is presented as a design tool. Based on the linear independence of element field patterns in the near field, this theory is very intuitive and provides a simplified way to calculate the element current weights necessary to generate a given target near-field pattern. Two-dimensional near-field subwavelength focusing is demonstrated using a slotted transmission-screen, or ``meta-screen'', under plane-wave incidence. At a distance of a quarter wavelength, the transverse electric field was measured in experiment to have a full-width half-maximum beamwidth of 0.40 by 0.27 wavelengths. This is compared to a single slot transmission-screen which had a beamwidth of 0.60 by 0.58 wavelengths. Broadside and end-fire dipole arrays are used to perform subwavelength imaging in one and two dimensions, respectively. The experimental minimum resolvable separation between two objects at a quarter-wavelength distance was 0.26 wavelengths using the end-fire array probe, as compared to 0.43 wavelengths for a single monopole probe. For an experiment using eight objects scattered over a one-square-wavelength area, however, the array probe imaging resolution remained around 0.25 wavelengths while the baseline monopole probe was no longer able to resolve any of the objects. Experiments were also conducted using objects buried behind a dielectric barrier as well as objects immersed within a dielectric. These results were consistent with the resolution improvements observed in the free-space resolution experiments.

Apertureless near-field scanning infrared microscopy is a technique in which an impinging infrared beam is scattered by a sharp atomic force microscopy (AFM) tip oscillating at the resonant frequency of the cantilever in close proximity to a sample. Several advantages offered by near-field imaging include nanoscale imaging with high spatial resolution (near-field imaging is not restricted by the diffraction limit of light) and the ability to differentiate between chemical properties of distinct compounds present in the sample under study due to differences in the scattered field. An overview of the assembly, tuning, and implementation of the near-field instrumentation is provided, as well as detailed descriptions about the samples probed and other instrumentation used. A description of the near-field phenomena, a comparison between aperture and apertureless-type near-field microscopy, and the coupled dipoles model explaining the origin of the chemical contrast present in near-field infrared imaging was discussed. Simultaneous topographic and chemical contrast images were collected at different wavelengths for the block copolymer thin film, polystyrene-b-poly(methyl ethacrylate) (PS-b-PMMA) and for amyloid fibrils synthesized from the #21-31 peptide of β2-microglobulin. In both cases it was observed that the experimental scattered field spectrum correlates strongly with that calculated using the far-field absorption spectrum, and using near-field microscopy, nanoscale structural and/or compositional variations were observed, which would not have been possible using ensemble FTIR measurements. Lastly, tip-enhanced Raman spectra of the #21-31 and #16-22 peptide fragments from the β2-microglobulin and Aβ(1-40) peptide were collected, examined, and an outline of the optimization conditions described.

Thesis (Ph. D.)--University of Texas at Austin, 2007. / Vita. Includes bibliographical references.

Thesis (Ph. D.)--Duke University, 2007. / Includes bibliographical references.

Thesis (M.S. in Combat Systems Science and Technology)--Naval Postgraduate School, December 2008. / Thesis Advisor(s): Haegel, Nancy M. ; Luscombe, James. "December 2008." Description based on title screen as viewed on January 29, 2009. Sponsoring/Monitoring Agency Report Number: "DMR-0526330." Includes bibliographical references (p. 59-61). Also available in print.

Thesis (Ph. D.)--University of Texas at Austin, 2000. / Vita. Includes bibliographical references (leaves 177-184). Available also in a digital version from Dissertation Abstracts.

abstract: 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. / Dissertation/Thesis / Ph.D. Physics 2012