Here we present design and fabrication of dielectric and plasmonic surfaces and several of their applications in biomolecular sensing. First, a metal-insulator-metal plasmonic surface is presented as a broad band absorber and field enhancer that finds application in Surface enhanced Raman Spectroscopy (SERS). Self-assembled silver nanoislands are formed on a silver reflector with a dielectric spacer in a lithography free process, and allows single molecule level SERS enhancements, resulting in observation of single molecules on a Mobile phone. Another example of plasmonic biosensing is grating coupled plasmonic surfaces for label-free biosensing. Using optical BluRay discs as a template, such plasmonic surfaces are shown to enable plasmonic imaging and multiplex sensing on a Mobile phone, using a custom designed attachment. Also, a plasmonic configuration that is inherently insensitive to the background refractive index is presented.
KEYWORDS: Near field scanning optical microscopy, 3D metrology, Plasmonics, Luminescence, Nanostructures, Optical microscopy, Nitrogen, Modulation, Absorbance, Digital recording
We present a dynamic approach to scanning near field optical microscopy that extends the measurement technique to the third dimension, by strobing the illumination in sync with the cantilever oscillation. Nitrogen vacancy (NV) centers in nanodiamonds placed on cantilever tips are used as stable emitters for emission enhancement. Local field enhancement and modulation of optical density states are mapped in three dimensions based on fluorescence intensity and spectrum changes as the tip is scanned over plasmonic nanostructures. The excitation of NV centers is done using a total internal reflection setup. Using a digital phase locked loop to pulse the excitation in various tip sample separations, 2D slices of fluorescence enhancement can be recorded. Alternatively, a conventional SNOM tip can be used to selectively couple wideband excitation to the collection path, with subdiffraction resolution of 60 nm in x and y and 10 nm in z directions. The approach solves the problem of tip-sample separation stabilization over extended periods of measurement time, required to collect data resolved in emission wavelength and three spatial dimensions. The method can provide a unique way of accessing the three dimensional field and mode profiles of nanophotonics structures.
Infrared absorption spectroscopy has greatly benefited from the electromagnetic field enhancement offered by plasmonic surfaces. However, because of the localized nature of plasmonic fields, such field enhancements are limited to nm-scale volumes. Here, we demonstrate that a relatively small, but spatially-uniform field enhancement can yield a superior infrared detection performance compared to the plasmonic field enhancement exhibited by optimized infrared nanoantennas. A specifically designed CaF2/Al thin film surface is shown to enable observation of stronger vibrational signals from the probe material, with wider bandwidth and a deeper spatial extent of the field enhancement as compared to optimized plasmonic surfaces. It is demonstrated that the surface structure presented here can enable chemically specific and label-free detection of organic monolayers using surface enhanced infrared spectroscopy. Also, a low cost hand held infrared absorption measurement setup is demonstrated using a miniature bolometric sensor and a mobile phone. A specifically designed grating in combination with an IR light source yields an IR spectrometer covering 7-12 um range, with about 100 cm-1 resolution. Combining the enhancing substrates with the spectroscopy setup, low cost, high sensitivity mobile infrared sensing is enabled. The results have implications in homeland security and environmental monitoring as well as chemical analysis.
We present polarization dependent multispectral and broadband plasmonic absorbers in the visible spectrum. The
spectral characteristics of these structures are tunable over a broad spectrum. Experimental results are verified with the
FDTD and RCWA analysis methods. These structures are used as surface enhanced raman spectroscopy(SERS)
substrates. Designed structures have resonances that span the Raman Stokes and excitation wavelength. Such structures
can be used for energy, LED and other spectroscopy applications.
We present the design, fabrication, characterization of spatially variable infrared filter and a demonstration
of the filter as a simple infrared spectrometer. A varying photonic band gap filter which consists of thermally
evaporated, high refractive index contrast amorphous chalcogenide glass multilayers, makes the structure suitable
to be used as spectrometer. Due to graded thickness structure, the filter exhibits a position dependent stop band
and a cavity mode ranging from 2 to 8 μm wavelengths. It is demonstrated that the filter can be used to detect
absorption peaks of common gases in the cavity mode range of the filter.
Conference Committee Involvement (5)
Micro- and Nanotechnology Sensors, Systems, and Applications IX
9 April 2017 | Anaheim, CA, United States
Micro- and Nanotechnology Sensors, Systems, and Applications VIII
17 April 2016 | Baltimore, MD, United States
Micro- and Nanotechnology Sensors, Systems, and Applications VII
20 April 2015 | Baltimore, MD, United States
Nanoepitaxy: Homo and Heterogeneous Synthesis, Characterization, and Device Integration of Nanomaterials
3 August 2009 | San Diego, California, United States
Nanomaterials Synthesis, Interfacing, and Integrating in Devices, Circuits, and Systems II
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