Spectral Peak-Shift Estimation With Wavelength Dependent Sources and Detectors
J. T. Hastings
This correspondence extends Karl and Pien’s [“High-Res-
olution Biosensor Spectral Peak Shift Estimation,” IEEE TRANSACTIONS
ON SIGNAL PROCESSING, vol 53, no. 12, pp. 4631–4639, December 2005]
approach to spectral-shift estimation for optical sensors to account for
wavelength dependent illumination sources and detectors. Relaxing the
assumption of spectrally uniform source power and detector efﬁciency al-
ters the previously derived Cramér–Rao bound and maximum-likelihood
estimator. The new estimator offers signiﬁcantly reduced error compared
to the wavelength invariant estimator and common ad hoc estimators.
J. T. Hastings, "Spectral peak-shift estimation with wavelength dependent sources and detectors," IEEE Transactions on Signal Processing, vol. 56, pp. 5269-5272, (2008).
Spatially Selective Melting and Evaporation of Single and Groups of Nanosized Gold Particles
E.A. Hawes, J.T Hastings, C. Crofcheck and M.P. Mengüç
We have developed an atomic force microscope-tip-based concept to pattern metallic nanoparticles on substrates. This new process has the potential to control the assembly of nanometer sized particles by combining their unique optical and thermophysical properties and is a flexible and low energy method of patterning at the nanoscale. The proof of concept is detailed by preliminary experimental work showing selective melting and evaporation of groups of 50 and 100 nm gold spherical particles.
E.A. Hawes, J.T Hastings, C. Crofcheck and M.P. Mengüç, “Spatially Selective Melting and Evaporation of Single and Groups of Nanosized Gold Particles,” Optics Letters vol. 33, pp.1383-1385 (2008).
Accurate frequency alignment in fabrication of high-order microring-resonator filters
J. Sun, C. W. Holzwarth, M. Dahlem, J. T. Hastings, and H. I. Smith
Frequency mismatch in high-order microring-resonator filters is investigated. We demonstrate that this frequency mismatch is caused mainly by the intrafield distortion of scanning-electron-beam-lithography (SEBL) used in fabrication. The intrafield distortion of an SEBL system is measured, and a simple method is also proposed to correct this distortion. By applying this correction method, the average frequency mismatch in second-order microring-resonator filters was reduced from -8.6GHz to 0.28 GHz.
J. Sun, C. W. Holzwarth, M. Dahlem, J. T. Hastings, and H. I. Smith, "Accurate frequency alignment in fabrication of high-order microring-resonator filters," Optics Express vol. 16, pp. 15958-15963 (2008).
Mechanism for generation of the phonon-energy-coupling enhancement effect for ultrathin oxides on silicon
Large leakage-current reduction of SiO2 due to the phonon-energy-coupling enhancement effect was confirmed by measuring the oxide thickness using a cross-sectional transmission electron microscopy. There is a critical temperature Tc. Rapid thermal processing (RTP) of SiO2 at T>Tc in pure N2 leads to a destructive structure with large leakage current, while RTP at T<Tc in pure N2 does not change the oxide structure. After introducing a little amount of oxygen during RTP, the destructive structure can be converted to a constructive one by repairing the defects created during RTP at T>Tc. This leads to reduced leakage current.
Zhi Chen, "Mechanism for generation of the phonon-energy-coupling enhancement effect for ultrathin oxides on silicon" Appl. Phys. Lett. 91, 223513 (2007); DOI:10.1063/1.2820383 Published 30 November 2007
Also avaiable for thsi title is a poster of the mechanism. Please see http://www.engr.uky.edu/~cense/research/Highlight-New Effect.pdf.
Dual-mode surface-plasmon-resonance sensors using angular interrogation
Jing Guo, P. Donald Keathley, and J. T. Hastings
Surface-plasmon-resonance (SPR) sensors are widely used in biological, chemical, medical, and environmental sensing. SPR sensors supporting two surface-plasmon modes can differentiate surface binding interactions from bulk index changes at a single sensing location. We present a new approach to dual-mode SPR sensing that offers improved differentiation between surface and bulk effects. By using an angular interrogation, both long- and short-range surface plasmons are simultaneously excited at the same location and wavelength but at different angles. Initial experiments indicate that angular interrogation offers at least a factor of 3.6 improvement in surface and bulk cross-sensitivity compared to wavelength-interrogated dual-mode SPR sensors.
J. Guo, P. D. Keathley, J.T. Hastings, "Dual-mode surface-plasmon resonance sensors using angular interrogation," Optics Letters, vol. 33, pp. 512-514, 2008.
Optimizing Surface-Plasmon Resonance Sensors for Limit of Detection Based on a Cramer Rao Bound
J. T. Hastings
This paper addresses the optimization of prism-coupled, wavelength-interrogated surface-plasmon resonance (SPR) sensors. Limit of detection (LOD), rather than sensitivity, is chosen as a figure of merit. The Cramer–Rao bound (CRB) for spectral shift estimation allows lower bounds to b placed on LOD independent of interrogation system and estimation algorithm. Analytic evaluation of the CRB for a Lorentzian spectral feature justifies common observations about the relationship between resonance line shape and sensor performance. Numerical evaluation of standard SPR sensor configurations shows that maximizing sensitivity is an insufficient criterion for minimizing limit of detection. Designs optimized for LOD are presented for common SPR sensor materials and geometries.
J. T. Hastings, "Optimizing Surface-Plasmon Resonance Sensors for Limit of Detection Based on a Cramer Rao Bound," IEEE Sensors Journal, vol. 8, pp. 170-175, 2008.
Optimal self-referenced sensing using long- and short- range surface plasmons
J. T. Hastings,1 J. Guo,1 P. D. Keathley,1 P. B. Kumaresh,1
Y. Wei,2 S. Law,2 and L. G. Bachas2
Dual-mode surface-plasmon resonance (SPR) sensors use both long- and short- range surface plasmon waves to differentiate surface binding interactions from interfering bulk effects. We have optimized the design of these sensors for minimum surface limit of detection (LOD) using a Cramer-Rao lower bound for spectral shift estimation. Despite trade-offs between resonance width, minimum reflectivity, and sensitivity for the two modes, a range of reasonable design parameters provides nearly optimal performance. Experimental verification using biotin-streptavidin binding as a model system reveals that sensitivity and LOD for dual-mode sensors remains competitive with single-mode sensors while compensating for bulk effects.
J. T. Hastings, J. Guo, P. D. Keathley, P. B. Kumaresh, Y. Wei, S. Law, and L. G. Bachas, "Optimal self-referenced sensing using long- and short- range surface plasmons," Optics Express, vol. 15, pp. 17661-17672, 2007.
Spectrally selective heating of nanosized particles by surface plasmon resonance
E.A. Hawes, J.T. Hastings, C. Crofcheck and M.P. Mengüç
We present a series of computer simulations of 10 nm particles optically excited at their surface plasmon resonance. These simulations are focused on gold and silver nanocylinders, resting on either on a thin metallic film or on a glass surface. The results indicate that excitation is highly dependent on both the material and the proximity of other particles. These findings suggest that manipulation and assembly of nanoparticles is feasible. This study also underlines the importance of computational radiation transfer research for the successful implementation of novel nanomachining processes.
E.A. Hawes, J.T. Hastings, C. Crofcheck and M.P. Mengüç, “Spectrally selective heating of nanosized particles by surface plasmon resonance,” Journal of Quantitative Spectroscopy and Radiative Transfer, v. 104(2): 199-207, 2007.
Real-time Spatial Phase Locking for Vector-Scan Electron Beam Lithography
Y. Yang and J. T. Hastings
Spatial-phase locked electron beam lithography (SPLEBL) provides feedback control of electron beam position by monitoring the signal from a fiducial grid on the substrate. Continuous, or “real-time,” spatial-phase locking has been investigated for raster-scan Gaussian beam and for shaped-beam systems. Discontinuous feedback, or “look-then-write,” techniques have been implemented for vector-scan systems. However, it would be advantageous to provide real-time spatial-phase locking for vector-scan systems because of their wide adoption for research,prototyping, and specialty device production. Here, the authors present a phase locking algorithm, performance simulations, and initial experimental results for real-time, vector-scan SPLEBL. The authors demonstrate that real-time, vector-scan SPLEBL can provide subnanometer precision phase locking for different feature filling strategies, exposure parameters, and pattern geometries using reasonable data lengths and practical grid signal-to-noise ratios.
Y. Yang and J. T. Hastings, "Real-time Spatial Phase Locking for Vector-Scan Electron Beam Lithography," Journal of Vacuum Science & Technology B., vol. 25, pp. 2072-2076, 2007.