Optical detection of C2 hydrocarbons ethane, ethylene, and acetylene with a photonic crystal made from carbonized porous silicon

Abstract

Carbon/porous silicon composite films are prepared by thermolysis of a poly(furfuryl alcohol) (PFA) precursor in a porous silicon photonic crystal template that results in a glassy carbon layer that coats the internal surface of the pores. The carbon/porous silicon composites are evaluated for their application as optical sensors for C2 hydrocarbon gases. The porous silicon templates are prepared by electrochemical anodization of either highly doped (p++) or moderately doped (p+) p-type silicon. The percent loading of carbon in the composites is varied and the change in reflectance spectrum and sensitivity monitored. Increased carbon loading corresponds to a decrease in the reflectance of the photonic stop band and an increase in sensitivity toward ethane. Sensitivity of the composites toward C2 hydrocarbons is also found to scale with increasing surface area, with p+ carbon/porous silicon composites having the largest surface area and being the most sensitive. The detection limit for the C2 hydrocarbons is 0.2% (v/v) in a nitrogen carrier gas, which is >10 times below the lower flammable limit.