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

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 C-2 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 C-2 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 C-2 hydrocarbons is 0.2% (v/v) in a nitrogen carrier gas, which is >10 times below the lower flammable limit. (C) 2014 Elsevier B. V. All rights reserved.