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7LS-P-6
LASER SYSTEMS AND MATERIALS
Sensitivity limit of a chemical sensor based on porous silicon microresonator
V.I. Krasovskii, L.A. Apresyan, T.V. Vlasova, S.I. Rasmagin
Prokhorov General Physics Institute of the Russian Academy of Sciences, 38 Vavilova str., Moscow 119991, Russia E-mail: krasovskii@inbox.ru
The use of porous silicon as an inorganic matrix for embedding organic materials combines the potential of organic and nanoelectronic devices with traditional silicon technology. Porous silicon is produced by electrochemical etching. The electrolyte composition and etching current determine the average pore size and morphology, degree of porosity, and pore surface condition.
Porous silicon has high specific surface area (~ 200 m2/cm3 or 500-800 m2/g) and can be used for chemical and biochemical sensors. A promising direction to create sensors of nitroaromatic compounds, acting on the principle of quenching the fluorescence of certain polymers embedded in a multilayered structure with a microcavity should be highlighted. These sensors use sorption of the analyte in the pores and have been shown to have a high sensitivity of 10-15 [1].
In this work, a microcavity structure similar to [1] was used, the starting material for the microresonators were p-type boron-doped silicon wafers with an orientation (100) with a conductivity of 0.01 Ohm cm in a 15% HF solution in ethanol. Low and high porosity layers were formed at current densities of 6 and 50 mA/cm2 , respectively. The structure contained a layer of porous silicon with high porosity of optical thickness X/2, located between two Bragg mirrors formed by a sequence of alternating layers of high and low porosity. The first Bragg mirror consisted of 5 periods, and the second one consisted of 20 periods; each period contained two layers of optical thickness A,/4, with high and low porosity. By selecting the appropriate layer thicknesses, the resonance in the reflection spectrum was tuned to the desired wavelength.
The transfer matrix formalism was used to calculate the structure [2]. The wavelength was varied between 300 and 900 nm. The parameter values were obtained from the results of electron microscopic studies and were close to the real
The signal of the chemical sensor was determined in two ways: as a diffrent reflectance spectrum or as a ratio of the reflectance spectra before or after exposure to the analyte. The sensitivity of the chemical sensor was calculated numerically and analytically using the effective medium approximation [3] to account for the volume fraction of the sensitive component in the microcavity structure, taking into account technological limitations. Calculations were performed using phthalocyanine and phthalocyanine-gold complexes as an sensitive media [4]. It was shown that the sensitivity growth can reach several orders of magnitude compared to film-based sensors.
[1]. I.Levitsky, Fluorescent polymer-porous silicon microcavity devices for explosive detection Appl. Phys. Lett. 90, 041904, (2007);
[2]. McLeod, Thin film optical filters, Adam Hilger Ltd., Bristol.
[3].L.Apresyan, T.V. Vlasova., V.I. Krasovskii et al., Effective medium approximations for the description of multicomponent composites, Technical Physics. 65 (7), 1130-1138, (2020).
[4].D.MKrichevsky, A.Tolbin, T.Dubinina et al., Resonant plasmon-enhanced absorption of charge transfer complexes in a metal-organic monolayer, Advanced Optical Materials, 9 (1), 2100065, (2021).
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