Pen plotter printing of Co3O4 thin films: features of the microstructure, optical, electrophysical and gas-sensing properties

Сombining the sol–gel method and pen plotter printing, using the hydrolytically active heteroligand complex [Co(C5H7O2)2-x(C4H9O)x] as a component of a new functional ink, Co3O4 thin films were produced on the surface of substrates of various types. The influence of synthesis conditions and print modes on the microstructure, optical, electrophysical and sensor properties of planar nanomaterials was comprehensively studied. The optical band gap energies associated with charge transfer for transitions O2-→Co3+ and O2-→Co2+ of the obtained thin films were evaluated. Using Kelvin probe force microscopy and impedance spectroscopy, the electrophysical characteristics (the electronic work function of the film surface, the temperature dependence of electrical conductivity, and the activation energy of electrical conductivity) of the obtained Co3O4 films were determined. The sensitivity of printed cobalt(II, III) oxide thin films with respect to various gases (Н2, СН4, СО and NO2) was studied. It was established that the obtained samples demonstrated the highest sensor response when detecting CO and NO2 in the operating temperature range of 150–200°С. The prospects of the proposed synthesis method and printing technology when forming Co3O4 thin-film nanostructures to create electrodes of supercapacitors and receptor components of resistive CO and NO2 gas sensors were shown.