Thickness dependence of the room-temperature ethanol sensor properties of Cu 2 O polycrystalline films.

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 >∝ ω n ) 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 (Cu 2 O) 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 ∼ 10 14 cm -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.