Study On A Vapor Sensitive Technic Based On Porous Silicon Photonic Crystal

Sensing technique based on porous silicon film is a new technique developed in the 1990s. Studies on sensitivity characterizations of porous silicon to volatile gases are mainly focused on its electrical aspects. However, in harsh environment, electrical contacts may cause explosion or fire. So at the time of perfecting the electrical measuring, a new sensing pattern was sought in order to settle this problem. In this way, the gas sensors basing on the porous silicon photonic crystals techniques were produced.Firstly from the physics base of the porous silicon material, Porous silicon optical constant calculation principles are set forth including the theoretical and experimental methods, the optical constant definition is given and obtains relations of those optical parameters making use of K-K relation; On the base of transfer matrix method of one-dimension photonic crystals, optical transmission properties of one dimension porous silicon photonic crystal with three typical structures have been studied. Using the way of Matlab emulation, the influences of the structure parameters the incident angles and the defective layers leading-in on the reflective characteristic of the porous silicon photonic crystals haves been discussed. So some useful conclusions are gotten which provide important theory bases in order to design porous silicon photon devices and optical sensors later.The adsorption properties of porous silicon material when exposed to the organic vapors were studied. The capillary condensation is determined as the major adsorption mechanism according to the hysterics of the adsorption isotherm. Two possible adsorption models for the porous silicon multilayers have been presented and proved the correctness of uniform adsorption model. On this, the single microcavity is considered as research object, and set up the organic vapors sensing theoretical model of the porous silicon microcavities. At the same time, results are simulated by the Matlab.Porous silicon samples with good performances are fabricated and its reflectance spectra are measured with self-constructed equipments. Thus, optical spectra are got experimentally. At the same time, effects of incident light wavelength and porosity on those parameters are studied, which makes steps to optimize optical performances and tostudy sensing techniques based on optical properties.At last, the experimental parameters have been orthogonal optimized. The porous silicon microcavity samples have been fabricated by applying the pulse electrochemical etching method. Then design porous silicon microcavity experimental sensing system, and some inflammable and explosive organic vapors are used as test gases. At the same time, the vapor species and the ethanol concentrations and response characteristics have been experimentally studied using the reflectance spectrum of porous silicon microcavity. From the view of experiment, it is proved that porous silicon microcavity is feasible new type optical sensor to detect the vapor species and concentration.Theories and experiment results indicated that applying it is a new vapor sensing method that studies on optical sensing techniques based on resonant peak shift in reflectance spectrum. It can avoid the vapor explosions and fires caused from electrical sensing measuring as well as simple. High measuring accuracy and sensitivity were achieved.