Thickness dependence of the room-temperature ethanol sensor properties of Cu2O polycrystalline films.

Abstract

In this study, copper thin films were deposited through thermal evaporation, with film thickness controlled by modulating the Z-position. The grain size (< D >) exhibited a power law relationship (< D >∝ ωn) with n approximately 0.41 for as-fabricated copper films. Resistivity ranged from 3.3 to 4.6 µΩ·cm, aligning with expectations for crystallites sized between 20 and 26 nm. Cuprite (Cu2O) thin films were produced via thermal annealing, revealing crystallite sizes from ∼9 nm to ∼24 nm as film thickness increased. Optical bandgap varied monotonically from 2.31 to 2.17 eV with increasing film thickness, attributed to the quantum confinement effect. Refractive index and extinction coefficient also showed film-thickness dependence, with a linear relationship observed between the refractive index and charge carrier density. Electrical measurements indicated p-type semiconductors with carrier concentrations of ∼ 1014cm-3, slightly decreasing with film thickness. Thinner cuprite films exhibited enhanced sensitivity to ethanol gas at room temperature, holding promise for he development of highly responsive gas sensors&#xD;for portable devices, especially for ethanol breath testing.