UV-activated ZnO films on a flexible substrate for room temperature O2 and H2O sensing

Abstract

We demonstrate that UV-light activation of polycrystalline ZnO films on flexible polyimide (Kapton) substrates can be used to detect and differentiate between environmental changes in oxygen and water vapor. The in-plane resistive and impedance properties of ZnO films, fabricated from bacteria-derived ZnS nanoparticles, exhibit unique resistive and capacitive responses to changes in O2 and H2O. We propose that the distinctive responses to O2 and H2O adsorption on ZnO could be utilized to statistically discriminate between the two analytes. Molecular dynamic simulations (MD) of O2 and H2O adsorption energy on ZnO surfaces were performed using the large-scale Atomic/Molecular Massively Parallel Simulator (LAMMPS) with a reactive force-field (ReaxFF). These simulations suggest that the adsorption mechanisms differ for O2 and H2O adsorption on ZnO, and are governed by the surface termination and the extent of surface hydroxylation. Electrical response measurements, using DC resistance, AC impedance spectroscopy, and Kelvin Probe Force Microscopy (KPFM), demonstrate differences in response to O2 and H2O, confirming that different adsorption mechanisms are involved. Statistical and machine learning approaches were applied to demonstrate that by integrating the electrical and kinetic responses the flexible ZnO sensor can be used for detection and discrimination between O2 and H2O at low temperature.

Magnetron Sputtering for ZnO:Ga Scintillation Film Production and Its Application Research Status in Nuclear Detection

“…When the substrate temperature is low, which means that the particles sputtered onto the substrate have less kinetic energy and the mobility of surface atoms is low, low-density film, rough surface, and porous amorphous structure are easily formed [75]. However, higher substrate temperature will reduce the amount of oxygen adsorbed near substrate and the particles sputtered onto substrate do not react completely due to the oxygen deficiency, resulting in many defects in the formed films [83]. Therefore, when ZnO:Ga films are produced by magnetron sputtering, the optimized substrate temperature can reduce the various defects in film and improve the film's crystalline quality and photoelectric properties [84].…”

Sensing of Oxygen Partial Pressure in Air with ZnO Nanoparticles

“…It is evident that the Nyquist plot consists of two semicircles, which indicates two RC parallel circuits in series (inset of Figure 5c). Two RC parallel circuits correspond to the grain and boundary of ZnO NP [27,32]. Resistance R 0 stands for electrode and cable resistance.…”

“…It has been widely accepted that ZnO interacts with oxygen in air through the adsorption and desorption processes [21][22][23][24][25][26] (shown in Figure 1). Oxygen molecules adsorb to the surface of ZnO NP by capturing free electrons [27], which forms a highly resistive depletion layer. Oxygen desorption can be achieved by light or heat with sufficient energy such that free electron-hole pairs are generated, releasing adsorbed oxygen molecules.…”

ZnO Nanowire Application in Chemoresistive Sensing: A Review

“…The high operating temperatures (typically about 350 °C) are essential for gas detection and sensing, which is a major technical limitation in applicability. Moreover, adsorption of water on the ZnO surface leads to a decrease in surface potential, at relative humidity higher than 14% due to adsorbed water molecules increasing the surface electron density [ 59 ]. Irradiation of ZnO by photons with an energy greater than the band gap (3.37 eV) changes adsorbed oxygen species on the surface, which is a practical alternative for achieving chemical reactions without the necessary heating.…”