Study on Dual RF Plasma-Enhanced Pulsed Laser Deposition of TiO₂ Thin Films

Efficient and cost-effective routes to engineer photovoltaic materials are essential, with metal oxides such as TiO₂ playing a key role. Precise control of phase composition and defects in metal-oxide thin films is crucial for improving performance in energy conversion and photocatalysis.

Pulsed laser deposition (PLD) is widely used for metal-oxide thin films due to its stoichiometric transfer and versatility. Dual-frequency RF plasma-enhanced PLD (PE-PLD) further improves the process by independently controlling ion flux through the high-frequency (HF) power and ion energy through the low-frequency (LF) power, enabling more precise thin-film growth. In this study, TiO₂ thin films were grown on glass substrates using dual RF PE-PLD, and their properties were evaluated as a function of HF and LF powers.

XRD and Raman analyses show that LF power strongly affects phase evolution, driving TiO₂ from a mixed anatase/rutile composition to an almost pure rutile phase due to increased LF-driven ion energy, which enhances ion bombardment and phase transformation. This control enables rutile formation below 400 °C, suitable for heat-sensitive substrates.

AFM reveals that increasing HF power raises the density of anatase-like nanostructures and surface roughness, while higher LF power reduces these features and keeps roughness nearly constant.

XPS shows that dual-RF PE-PLD significantly modifies TiO₂ surface chemistry. HF power increases oxygen desorption and vacancy concentration, reflected in higher Ov/O-M ratios, whereas LF power yields denser and more stoichiometric films with fewer vacancies.

Optical measurements show that both HF and LF powers reduce the indirect bandgap, with HF producing the strongest shift due to vacancy-related states, consistent with XPS.

The results presented here are based on our recently published study and highlight the potential of dual RF PE-PLD TiO₂ films for photocatalysis and photoelectrochemical hydrogen evolution.