Investigating the Selectivity of Porous Silicon Based Optical Vapour Sensors

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dc.contributor.advisor Miskelly, G en Chun, Soo en 2015-07-26T21:17:45Z en 2015 en
dc.identifier.citation 2015 en
dc.identifier.uri en
dc.description Full text is available to authenticated members of The University of Auckland only. en
dc.description.abstract This study was conducted to investigate the sensitivity and selectivity of porous silicon based optical sensors, using different fabrication, imaging and statistical methods. As the reflectance of the porous silicon samples were intended to be measured using a digital camera, a rugate filter structure was fabricated. The effect of pore sizes on vapour sensing was also investigated, by fabricating the porous silicon samples with an approximately radial pore size gradient across the surface. Porous silicon samples were fabricated with two surface chemistries, one side being more hydrophilic than the other side. This was achieved by using a masking solution of 13% (w/w) polystyrene dissolved in toluene. Three combinations of two surface chemistries were made; samples OH, OM and DM. One side of the OH sample was thermally oxidised while the other side was thermally hydrosilylated. One side of the OM sample was also thermally oxidised while the other side was electrochemically methylated. One side of the DM sample was modified with pentyl acetate which was then deacetylated while the other side was electrochemically methylated. The samples were characterised using SEM, ATR‐FTIR, water contact angle, UV‐Vis reflectance, and hyperspectral imaging with a Varispec Liquid Crystal Tunable Filter (LCTF). The sensitivity and selectivity of the vapour sensing of each porous silicon sample was investigated using an in‐house custom built Vapour Dosing System with imaging equipment. Each sample was exposed sequentially to separate doses of acetone, ethanol, heptane, proan‐2‐ol and toluene at concentration ranging from 100 mg m‐3 to 3000 mg m‐3. The optical responses of the porous silicon samples OM and DM were imaged using three different camera modes; hyperspectral imaging, RGB colour imaging and Mode 0 imaging (raw unprocessed Bayer pattern). Selected parameters derived from the images during vapour dosing were investigated using the multivariate analysis techniques Principal Component Analysis (PCA) and Linear Discriminant Analysis (LDA). The results showed that the shifts in the wavelengths of the rugate peak at each pixel derived from the hyperspectral image data could discriminate between the different solvents and the different concentrations of each solvent, while the change in hue at each pixel position derived from the data for RGB and Mode 0 image modes did not provide as good discrimination. The shift in rugate peak wavelength from the hyperspectral images of the OM sample, which had greater difference in hydrophilicity/hydrophobicity between its two surfaces, enabled discrimination of all the vapours, while measurements with sample DM, which had surfaces with a lesser difference in hydrophilicity/hydrophobicity, could only discriminate between general classes of hydrophobic (heptane and toluene) and hydrophilic (acetone, ethanol, and propan‐2‐ol) vapours. The results showed that the discrimination between solvents was mainly due to the two different surface chemistries and that pore size gradients did not enhance selectivity significantly. en
dc.publisher ResearchSpace@Auckland en
dc.relation.ispartof Masters Thesis - University of Auckland en
dc.relation.isreferencedby UoA99264819112702091 en
dc.rights Items in ResearchSpace are protected by copyright, with all rights reserved, unless otherwise indicated. Previously published items are made available in accordance with the copyright policy of the publisher. en
dc.rights Restricted Item. Available to authenticated members of The University of Auckland. en
dc.rights.uri en
dc.rights.uri en
dc.title Investigating the Selectivity of Porous Silicon Based Optical Vapour Sensors en
dc.type Thesis en Chemistry en The University of Auckland en Masters en
dc.rights.holder Copyright: The Author en
pubs.elements-id 492265 en
pubs.record-created-at-source-date 2015-07-27 en

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