Date of Award
August 2021
Document Type
Dissertation
Degree Name
Doctor of Philosophy (PhD)
Department
Electrical Engineering
Committee Member
Goutam Koley
Committee Member
William H. Harrell
Committee Member
Apparao M. Rao
Committee Member
Judson D. Ryckman
Abstract
This dissertation aims to repot the demonstration of strong enhancement in photoacoustic signal due to plasmonic absorption and highly sensitive detection of trace level analytes utilizing the plasmonic enhancement of photoacoustic signal using piezotransistive GaN microcantilevers. A pulsed 790 nm laser focused on the Au metallization of the piezotransistor resulted in a high amplification of photoacoustic signal compared to the non-metallized areas. Upon deposition of 5 nm Au layer, the photoacoustic signal increased significantly for both previously metallized and non-metallized areas, while 2 nm Ni deposition decreased the photoacoustic signal, confirming the role of Au nanostructures in facilitating plasmonic absorption. Infrared microscopy images covering the boundary of Au metallized and non-metallized surface indicated a much larger rise in temperature of the former region with laser exposure, explaining the generation of photoacoustic signals through plasmonic absorption. Photoacoustic detection of H2 and NH3 using plasmonic excitation in Pt and Pd decorated GaN piezotransistive microcantilevers has been investigated using pulsed 520 nm laser illumination. The sensing performances of 1 nm Pt and Pd nanoparticle (NPs) deposited cantilever devices have been compared, of which the Pd coated sensor devices exhibited consistently better sensing performance, with lower limit of detection and superior SNR values, compared to the Pt coated devices. Among the two functionalization layers, Pd coated devices were found to respond only to H2 exposure and not to NH3, while Pt coated devices exhibited repeatable response to both H2 and NH3 exposures, highlighting the potential of the former in performing selective detection between these reducing gases. Optimization of the device biasing conditions were found to enhance the detection sensitivity of the sensors. Detection of H2 using plasmonic amplification of photoacoustic waves generated in Pd nanoparticle deposited GaN piezotransistive microcantilevers has been investigated in detail using a pulsed 520 nm laser. Using 1.5 nm thickness of Pd functionalization layer, H2 detection down to 1.5 ppm was demonstrated with a high signal-to-noise ratio, underscoring the feasibility of sub-ppm level detection using this novel sensing method. Adsorption of H2 in Pd nanoparticles (NPs) changes their plasmonic absorption spectra due to Pd lattice expansion, in addition to changing their work function. The high sensitivity exhibited by the photoacoustic based H2 detection method is attributed to a combination of changes in plasmonic spectrum and work function of Pd NPs, and was observed to be a strong function of Pd thickness, biasing conditions and probe laser power. A comparison of the photoacoustic based detection technique with traditional chemi-diode and chemi-resistor sensors, integrated in the functionalized piezotransistor, indicated a superior detection performance of the former.
Recommended Citation
Khan, Digangana, "Plasmon Enhanced GaN MEMS Photoacoustic Sensors" (2021). All Dissertations. 2870.
https://tigerprints.clemson.edu/all_dissertations/2870