Enhancing Chemical Stability of Pt Ultrathin Films on Substrates by Controlled Intermixing of Pt-Zn at Interface

Abstract

Platinum (Pt) ultrathin films supported on substrates can enable reduced metal loading, but their long-term stability in harsh environments remains a challenge. This work establishes that an optimal thickness of the intermediate adhesion layer can provide this stability. Pt ultrathin films (20 nm) are deposited on Silicon substrates using a Zinc (Zn:4, 6 nm) adhesion layer in a DC magnetron sputtering system. Results show that the addition of the Zn layer nearly doubled the adhesion strength of Pt films, from 420 to 780 μN. A maximum of 4 nm Zn leads to longevity of Pt films in 1 m H₂SO₄ environments with negligible variation in sheet resistance (15–20 Ω sq⁻¹) for over 4 months. Films with 6 nm Zn deteriorated within 2 weeks. Observed adhesion and stability are due to limited (for 4 nm) and complete intermixing (for 6 nm) of Zn and Pt, resulting in the formation of Pt-Zn solid solution. Solid solution formation is validated by X-ray photoemission spectroscopy, X-ray diffraction, and density functional theory. This study opens up the possibility of using engineered adhesion layers to enhance the durability of ultrathin metal films for a wide range of industrial applications.