Engineering Porous Silicon-Based Microcavity for Chemical Sensing

In this article,the authors theoretically and experimentally investigatedways to improve the efficiency of porous silicon (PS)-based opticalmicrocavity sensors as a 1D/2D host matrix for electronic tongue/nosesystems. The transfer matrix method was used to compute reflectancespectra of structures with different [n (L) n (H)] sets of low n (L) and high n (H) bilayer refractiveindexes, the cavity position lambda(c), and the number ofbilayers N (bi). Sensor structures were preparedby electrochemically etching a silicon wafer. The kinetics of adsorption/desorptionprocesses of ethanol-water-based solution was monitored inreal time with a reflectivity probe-based setup. It was theoreticallyand experimentally demonstrated that the sensitivity of the microcavitysensor is higher for structures with refractive indexes in the lowerrange (and the corresponding porosity values in the upper range).The sensitivity is also improved for structures with the optical cavitymode (lambda(c)) adjusted toward longer wavelengths. Thesensitivity of a distributed Bragg reflector (DBR) with cavity increasesfor a structure with cavity position lambda(c) in the longwavelength region. The full width at half maximum (fwhm(c)) of the microcavity is smaller and the quality factor of microcavity(Q (c)) is higher for the DBR with a largernumber of structure layers N (bi). The experimentalresults are in good agreement with the simulated data. We believethat our results can help in developing rapid, sensitive, and reversibleelectronic tongue/nose sensing devices based on a PS host matrix.