Fabrication of Zinc Oxide Film Grown by Successive Ionic Layer Adhesion and Reaction for Hydrocarbon Gas Sensing
EMMANUEL A. FLORIDO1*, Sarah Allyssa S. Solidum2
1Institute of Mathematical Sciences and Physics, University of the Philippines Los Banos, Los Banos, Laguna, Philippines
2Institute of Electrical and Electronic Engineering, University of the Philippines Diliman, Quezon City, Philippines
* presenting author:EMMANUEL FLORIDO, email:eaf_physics@yahoo.com
Zinc oxide (ZnO) film fabricated by successive ionic layer adsorption and reaction (SILAR) to detect hydrocarbon including as butane, propane and methane gas. The film was fabricated by alternate dipping of pre-cleaned glass substrates in a sodium zincate bath and in a 950C hot water bath using an automated dipping machine to control the sequence and dipping time. The sodium zincate solution was prepared by mixing zinc sulfate (ZnSO4 7H2O) in excess sodium hydroxide in aqueous solution. When the glass substrate was dipped in the zincate bath, Na2ZnO2 was deposited on the glass surface. When the glass substrate was next dipped in hot water bath, ZnO was subsequently produced. The process was then repeated several times.

Uniform films consisting of wurtzite ZnO nanorods were observed using scanning electron microscopy (SEM) for the sample grown using 0.1M concentration of sodium zincate and 200 dippings. Current-voltage characterization of the samples showed an average resistivity of 1.343 -m. The sensing circuit for the zinc oxide film consisted of a wheatstone bridge and instrumentation amplifier. The ZnO film was then exposed to the gas in an air tight chamber at 1 atm pressure to determine the gas response. This is the ratio of the change in voltage upon exposure to gas to the voltage output when the target gas is not present. EDS analysis of the film confirmed the existence of zinc oxide with 65.9% zinc and and 34.1% oxygen.

The ZnO film was able to detect the gas with an average gas response of 0.44, average response time of 14 seconds and average recovery time of 25 seconds using a gas concentration in air of 1.5 % by volume. Response time is the time for the sensor to reach the peak voltage output from the start of gas exposure while recovery time is the time for the voltage output to return to the initial value without gas when the gas is removed from the chamber.

The sensor sensitivity was found to be equal to 32 (mV)/(%conc). The zinc oxide film showed a voltage output of 100, 109.31, 118.92, 123.61, 133.5, and 149.52 mV when exposed to percent volume gas concentrations of 0, 0.5, 0.75, 1.0, 1.25, and 1.5, respectively with a correlation coefficient of 0.97.

Keywords: zinc oxide, gas sensing, sensitivity, successive ionic layer adhesion and reaction