J. Todd Hastings
University of Kentucky
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Publication
Featured researches published by J. Todd Hastings.
Nano Letters | 2009
Eugenii U. Donev; J. Todd Hastings
We demonstrate here the first focused electron-beam-induced deposition (EBID) of nanostructures using a liquid precursor. We have deposited sub-50 nm platinum (Pt) wires and dots from a dilute, aqueous solution of chloroplatinic acid. Existing EBID processes rely on the electron-beam stimulated decomposition of gaseous precursors; as a result, the deposits are highly contaminated (up to 75 at. % carbon or 60 at. % phosphorus for Pt processes). In contrast, we show that deposition of platinum by electron-beam reduction of platinum ions from solution leads to high-purity deposits (approximately 10 at. % chlorine contamination) at rates at least ten times higher than those obtained with other platinum precursors. Liquid-phase EBID offers a new route to deterministic, three-dimensional, nanometer-scale structures composed of multiple materials without complex multistep processing. Thus, it may prove important for prototyping and low-volume production of nanoscale devices and for repair and modification of nanoscale masks and templates used in high-volume production.
Optics Express | 2011
Gazi M. Huda; Eugenii U. Donev; M. Pinar Mengüç; J. Todd Hastings
We have numerically investigated the influence of a nanoscale silicon tip in proximity to an illuminated gold nanoparticle. We describe how the position of the high-permittivity tip and the size of the nanoparticle impact the absorption, peak electric field and surface plasmon resonance wavelength under different illumination conditions. We detail the finite element method (FEM) approach we have used, whereby we specify a volume excitation field analytically and calculate the difference between this source field and the total field (i.e., scattered-field formulation). We show that a nanoscale tip can locally enhance the absorption of the particle as well as the peak electric field at length scales far smaller than the wavelength of the incident light.
IEEE Transactions on Nanotechnology | 2014
Neha Nehru; Linliang Yu; Yinan Wei; J. Todd Hastings
We report a simple label-free localized surface plasmon resonance sensor that uses the multiple resonances of a U-shaped gold nanostructure to differentiate the target interaction of interest from background refractive index interference and nonspecific binding of interfering molecules. U-shaped nanostructures were fabricated using electron-beam lithography and their sensing capabilities were tested by introducing different solutions to simulate various specific and nonspecific effects. The three resonances of the nanostructure yield distinct bulk as well as specific and nonspecific surface sensitivities that allow for the differentiation of the three effects.
Journal of Neuroscience Methods | 2011
Pooja M. Talauliker; David A. Price; Jason J. Burmeister; Silpa Nagari; Jorge E. Quintero; Francois Pomerleau; Peter Huettl; J. Todd Hastings; Greg A. Gerhardt
Amperometric measurements using microelectrode arrays (MEAs) provide spatially and temporally resolved measures of neuromolecules in the central nervous system of rats, mice and non-human primates. Multi-site MEAs can be mass fabricated on ceramic (Al₂O₃) substrate using photolithographic methods, imparting a high level of precision and reproducibility in a rigid but durable recording device. Although the functional capabilities of MEAs have been previously documented for both anesthetized and freely moving paradigms, the performance enabling intrinsic physical properties of the MEA device have not heretofore been presented. In these studies, spectral analysis confirmed that the MEA recording sites were primarily composed of elemental platinum (Pt°). In keeping with the precision of the photolithographic process, scanning electron microscopy revealed that the Pt recording sites have unique microwell geometries post-fabrication. Atomic force microscopy demonstrated that the recording surfaces have nanoscale irregularities in the form of elevations and depressions, which contribute to increased current per unit area that exceeds previously reported microelectrode designs. The ceramic substrate on the back face of the MEA was characterized by low nanoscale texture and the ceramic sides consisted of an extended network of ridges and cavities. Thus, individual recording sites have a unique Pt° composition and surface profile that has not been previously observed for Pt-based microelectrodes. These features likely impact the physical chemistry of the device, which may influence adhesion of biological molecules and tissue as well as electrochemical recording performance post-implantation. This study is a necessary step towards understanding and extending the performance abilities of MEAs in vivo.
Optics Express | 2012
Neha Nehru; Eugenii U. Donev; Gazi M. Huda; Linliang Yu; Yinan Wei; J. Todd Hastings
We demonstrate a novel localized surface-plasmon resonance sensor that can distinguish surface binding interactions from interfering bulk effects. This is accomplished by utilizing the longitudinal and transverse plasmon modes of gold nanorods. We have investigated, both numerically and experimentally, the effect of change in background refractive index and surface binding on the two resonances of a gold nanorod on an indium tin oxide coated glass substrate.
THE FIFTH INTERNATIONAL WORKSHOP ON THEORETICAL AND COMPUTATIONAL NANO-PHOTONICS: TaCoNa-Photonics 2012 | 2012
Gazi M. Huda; M. Pinar Mengüç; J. Todd Hastings
We numerically calculated the optical absorption of silver nanoparticles (AgNP) in the presence of metallic and dielectric AFM probes, illuminated by transverse magnetic (TM) polarized, total internal reflected waves. Nanoscale probes localize and enhance the field between the apex of the tip and the particle. However, such probes can actually suppress the optical absorption of the AgNP. To better understand this phenomenon, we fitted the numerical absorption data with the equation of a driven damped harmonic oscillator (HO), and we found that the AFM tip modifies both the driving force and increases the overall damping of the oscillator by introducing an additional radiative decay path. For a 50 nm diameter AgNP the introduction of either a metallic or dielectric AFM probe suppresses absorption.
international conference on nanotechnology | 2012
Neha Nehru; Linliang Yu; Yinan Wei; J. Todd Hastings
We demonstrate a novel localized surface plasmon resonance based sensor that can differentiate a target interaction from interfering interactions. This is accomplished by the simultaneous interrogation of the sensing medium with the multiple surface plasmon modes of the U-shaped gold nanostructure.
Proceedings of SPIE | 2013
Neha Nehru; J. Todd Hastings
Noble metal nanoparticles supporting localized surface plasmon resonances (LSPR) have been extensively investigated for label free detection of various biological and chemical interactions. When compared to traditional propagating surface plasmon based sensors, LSPR sensors offer extensive wavelength tunability, greater electric field enhancement and sensing in reduced volumes. However, these sensors also suffer from a major disadvantage – LSPR sensors remain highly susceptible to interference because they respond to both solution refractive index changes and non-specific binding as well as specific binding of the target analyte. These interactions can compromise the measurement of the target analyte in a complex unknown media and hence limit the applicability and impact of the sensor. Despite the extensive amount of work done in this field, there has been an absence of optical techniques that make these sensors immune to interfering effects. Recently, our group experimentally demonstrated a multi-mode LSPR sensor that exploits three resonances of a U-shaped gold nanostructure to differentiate the target interaction from bulk and surface interfering effects. In this paper, we provide a comprehensive description of the electric field profiles of the three resonances of the U-shaped nanostructure. We will also evaluate the sensitivities of the nanostructure to the various bulk and surface interactions using numerical simulations.
Proceedings of SPIE | 2013
Gazi M. Huda; J. Todd Hastings
This research numerically calculated the optical absorption of gold nanoparticles (AuNP) in the presence of metallic (Au) and dielectric (Si) AFM probes, illuminated by a surface plasmon polaritons on an infinite gold substrate. Nanoscale probes localize and enhance the field between the apex of the tip and the particle. However, the absorption of the nanoparticle is not always enhanced; in fact, under a gold tip, the absorption is suppressed for a 50 nm diameter AuNP. After fitting the numerical absorption data with the equation of a driven damped harmonic oscillator (HO), it was found that the AFM tip modifies both the driving force (F0), consisting of the free carrier charge (q) and the driving field (E), and the overall damping of the oscillator (β). The enhancement or suppression of absorption with different tips can be understood in terms of competition between β and F0. Introducing the metallic tip increases β and decreases F0, resulting in reduced absorption. Introducing the dielectric tip, although it increases β, it also increases F0, resulting in overall absorption enhancement. Therefore, one most consider both β and F0 to control the absorption of nanoparticles under Surface Plasmon Polaritons.
Journal of Vacuum Science & Technology. B. Nanotechnology and Microelectronics: Materials, Processing, Measurement, and Phenomena | 2013
Carlos A. Jarro; Matthew Bresin; J. Todd Hastings
Silver nanoparticles have been obtained by photoreduction from solutions during the last two decades, but the growth of differently structured silver nanoparticles directly onto transparent substrates has not been a major area of research. An analysis of silver deposition on glass substrates has shown that the density of nanoparticles deposited on glass substrates increases when a (3-aminopropyl)triethoxysilane coating is applied to the glass surface. Furthermore, the density and structure of the nanoparticles can be controlled by varying the laser illumination intensity. This fabrication method has potential applications in surface enhanced Raman spectroscopy, surface plasmon resonance sensing, and direct patterning of functional materials.