Suppression of surface particle formation in YBa 2 Cu 3 O 7− δ thin films by fast post-deposition cooling

Abstract Achieving a smooth surface in YBa 2 Cu 3 O 7− δ (YBCO) films is crucial for their use in superconducting electronic devices. Despite extensive optimization of deposition parameters, how to reliably obtain such surfaces remains a long-standing challenge. Here, by studying the pulsed laser deposition of YBCO films, we show that the nucleation and growth of surface particles are strongly influenced by the post-deposition cooling stage. By decoupling deposition from cooling, we observe a strong correlation between the cooling rate and the resulting density, volume, and composition of the surface particles. Cross-sectional high-resolution transmission electron microscopy reveals a continuous YBCO layer under representative particles, providing evidence for their post-deposition formation during cooling. Faster cooling markedly suppresses particle formation, yielding nearly particle-free surfaces with a root-mean-square roughness of 0.5 nm. Crystalline structural and electrical transport measurements further confirm that particle suppression does not sacrifice film crystallinity or superconductivity. These results establish cooling-history engineering as a practical route to particle-free YBCO films, with direct implications for improved interface quality, device uniformity, and manufacturing yield in high-temperature superconducting electronics.