Investigation on Laf3/Si Structure as Light-Addressable Potentiometric Fluoride (F‾) Sensor

Abstract

In this article LaF3 films in LaF3/Si structure have been investigated for the measurement of fluoride ions in aqueous solution with higher accuracy using light-addressable potentiometric sensing technique. LaF3 films were directly grown on Si by vacuum evaporation. The effects of LaF3-thickness and annealing on the fluoride-sensitivity of the LaF3/Si structures have been studied. Accordingly four different LaF3/Si structures with various thickness of LaF3 (5/50/150nm) layer were fabricated. The structures are annealed at 400ºC for 10 minutes. The un-annealed LaF3/Si structures show very poor fluoride sensitivity. As predicted in the theoretical study structures with thinner LaF3 offer better steepness of the photocurrent characteristics that indicates better accuracy in fluoride concentration measurement. Among the annealed structures, the one prepared with 150nm LaF3 layer shows the best fluoride sensitivity of ≈ 54.5mV/pF in the range of pF1-pF4. Experimental results show a good promise for LaF3/Si structure as a light-addressable potentiometric sensor that can be used for the sensing and imaging the distribution of fluoride ion in aqueous medium with higher accuracy. 
Keywords: Light-addressable potentiometric sensor (LAPS), Fluoride sensor, Capacitive EIS structure