Colorimetric analysis of optical reflection from thin porous silicon for detection of organic liquids

Abstract

A single porous silicon (PS) layer sensor structure was applied to analyze the kinetics of adsorption/desorption processes of water, ethanol and ethanol-water solution using CIE1931 chromaticity coordinates based parameters such as dominant wavelength λdom, complementary wavelength λcom and excitation purity (EP). Matrix method was used to obtain reflectance spectra dependences on porosity (P), PS layer thickness (LPS), refractive index of analyte (nanalyte). Dependences of λdom, λcom, EP on P, LPS, nanalyte were computed on the base of computed reflectance spectra, and optimal parameters were determined for distinction of model analytes such as water and ethanol. Time dependences of λdom, λcom were experimentally obtained using CCD-based spectrometer for water, ethanol and ethanol-water solution. Advantage of characterisation of whole complex multiple peaks spectra using chromaticity parameters as opposed to sensor characterization with parameters of individual interference peaks as peak position was demonstrated.