Thin copper oxide films prepared by ion beam sputtering with subsequent thermal oxidation: Application in chemiresistors
Abstrakt
Copper oxide films were prepared by thermal oxidation of thin Cu films deposited on substrates by ion beam sputtering. The subsequent oxidation was achieved in the temperature range of 200 degrees C-600 degrees C with time of treatment from 1 to 7 h (with a 1-h step) in a furnace open to air.
At temperatures 250 degrees C-600 degrees C, the dominant phase formed was CuO, while at 200 degrees C mainly the Cu2O phase was identified. However, the oxidation at 200 degrees C led to a more complicated composition - in the depth Cu2O phase was observed, though in the near-surface layer the CuO dominant phase was found with a significant presence of Cu(OH)(2).
A limited amount of Cu2O was also found in samples annealed at 600 degrees C. The sheet resistance R-S of the as-deposited Cu sample was 2.22 Omega/square, after gradual annealing R-S was measured in the range 2.64 MS Omega/square-2.45G Omega/square.
The highest Rs values were obtained after annealing at 300 degrees C and 350 degrees C, respectively. Oxygen depth distribution was studied using the O-16(alpha,alpha) nuclear reaction with the resonance at energy 3032 keV.
It was confirmed that the higher oxidation degree of copper is located in the near-surface region. Preliminary tests of the copper oxide films as an active layer of a chemiresistor were also performed.
Hydrogen and methanol vapours, with a concentration of 1000 ppm, were detected by the sensor at an operating temperature of 300 degrees C and 350 degrees C, respectively. The response of the sensors, pointed at the p-type conductivity, was improved by the addition of thin Pd or Au catalytic films to the oxidic film surface.
Pd-covered films showed an increased response to hydrogen at 300 degrees C, while Au-covered films were more sensitive to methanol vapours at 350 degrees C.