Porous silicon optical cavity structure applied to high sensitivity organic solvent sensor

Optical characteristics and environmental pollutants detection of porous silicon microcavities

“…In addition, higher indices do not promise more prominent shifts: toluene, chloroform and cyclohexane are of relatively higher refractive indices than acetonitrile, acetone and ethanol, but they turn out to show smaller shifts. These results are very different from those reported in some papers [10,22,34], where red shift shows a positively linear dependence on refractive index. The discrepancy can be explained by the fact that the change of the resonant peak position is dominated by not only the refractive index of an organic species, but also the filling fraction due to capillary condensation of the organic liquid into the stratified silicon pores.…”

“…Compared with the optical absorption spectrum of the freshly etched chip (solid line, Figure 7(a)), the spectrum of the oxidized PSM chip (dash line, Figure 7(a)) displays not only a substantial blue shift of 53.1 nm but also a decreased width of the photonic band-gap indicating a reduced quality of the edges features. These results can be attributed to a partial conversion of crystalline Si into SiO 2 that reduces the refractive indices of layers [10] and also the existence of expansion and contraction effects respectively on the low and high refractive index layers [28]. The oxidation process was further investigated by the FTIR spectra (Figure 7(b)).…”

“…For example, due to capillary condensation aliphatic hydrocarbons were detected in either the gaseous or the liquid state [2], different flammable substances were rapidly identified within 10 seconds [8], and low-dielectric-constant hydrocarbons exhibited much higher sensitivity compared to that measured via electrical sensors [9]. When the PSM was thermally annealed, the sensitivity for organic solvent detection could be further promoted [10]. In order to enhance the sensor selectivity through specific interactions, some researchers have proposed to modify the PSi surface: the common approach is to create a covalent bond between the porous silicon surface and the biomolecules which specifically recognize the unknown analytes [11][12][13].…”

Sensing characteristics of the organic vapors according to the reflectance spectrum in the porous silicon multilayer structure

“…During exposure of the porous silicon multilayer to the various organic vapors, the peak of the reflectance spectrum promptly shifted to a longer wavelength. This experimental result is in agreement with previous results [6,[18][19][20]. This phenomenon can be ascribed to capillary condensation of the organic vapor in pores of the porous silicon multilayer [19,20].…”

Conductometric Gas Nanosensors

“…• C. Good sensitivity for organic solvent detection was observed after thermal annealing of microcavity devices based on this technology [87].…”