Low-temperature nonthermal plasma synthesis of sol-gel derived Y-stabilized ZrO₂thin films with both high hardness and UV–vis transmittance

Low temperature preparation of hard and transparent thin films is crucial for protecting flexible electronics on polymer substrates against scratches. In this work, we demonstrate the synthesis of sol-gel-derived yttria-stabilized zirconia (YSZ) thin films on polyethylene terephthalate (PET) substrates using microwave-excited oxygen nonthermal plasma (NTP), a method characterized by its low processing temperature (∼35 °C) and efficient removal of organic residues from gel films >200 nm thick. Remarkably, NTP treatment simultaneously enhanced YSZ gel film's hardness by 130 % to 11 GPa while preserving exceptional optical transparency (>89 % in visible light, >70 % in UV at 230–400 nm). This unique balance of properties stems from NTP's ability to drive film densification and precisely control grain nucleation/growth kinetics at near-room temperature, thereby bypassing the inherent constraints of conventional thermal processing.