Room Temperature Ammonia and Humidity Sensing Using Highly Ordered Nanoporous Alumina Films

Elizabeth Dickey,Maggie Paulose,Keat Ong,Dawei Gong,Oomman Varghese,Craig Grimes

doi:10.3390/s20300091

Elizabeth Dickey, Maggie Paulose + Show 4 more

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https://doi.org/10.3390/s20300091

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Journal: Sensors	Publication Date: Mar 18, 2002
Citations: 167	License type: CC BY 4.0

Affiliation: Pennsylvania State University

Abstract

The effect of pore size and uniformity on the response of nanoporous alumina, formed on aluminum thick films through an anodization process, to ammonia and humidity at room temperature is reported. Pore sizes examined range from 13 nm to 48 nm, with pore size standard deviations ranging from 2.6 nm to 7.8 nm. The response of the material to ammonia and humidity is a strong function of pore size and operating frequency. At 5 kHz an alumina sensor with an average pore size of 13.6 nm, standard deviation 2.6 nm, exhibits a factor of two change in impedance magnitude as it is cycled between an ammonia and argon environment. At 5 kHz the same sensor exhibits a well-behaved change in impedance magnitude of 103 over 20% to 90% relative humidity. Cole-Cole plots of the 5 Hz to 13 MHz measured impedance spectra, modeled using equivalent circuits, are used to resolve the effects of adsorption and ion migration.

Highlights

Both humidity and ammonia sensors have attracted considerable attention over many years due to their great importance in applications ranging from monitoring food quality to meteorological studies [1,2,3,4]
Sensor DS15 is sensitive to a wide range of humidity levels, approximately 20% to 90% relative humidity (RH), with an impedance variation of approximately three orders of magnitude
Sensors SO30 and SO50 become sensitive to humidity at relatively high humidity levels, approximately 65 % and 75% RH respectively

Summary

Introduction

Both humidity and ammonia sensors have attracted considerable attention over many years due to their great importance in applications ranging from monitoring food quality to meteorological studies [1,2,3,4]. The ability of alumina to sense humidity is based upon ionic conduction; the presence of an adsorbed layer of water at the surface reduces the total sensor impedance due to the increase in the ionic conductivity, as well as capacitance due to the high dielectric constant of water. The results of our study on uniform nanoporous alumina films made through anodization show that an built and highly reproducible wide range humidity, and ammonia, sensor can be achieved using nano-dimensional pores of a narrow size distribution.

Results

Conclusion