Tunable Properties of YBa2Cu307-x Superconducting Thin Films enabled by Varying the Energy Distribution of the Plume with Target to Substrate Distance

<p dir="ltr">Since the discovery of superconductivity, high-temperature superconductors (HTS) such as Yttrium Barium Copper Oxide (YBCO) have remained at the forefront of research due to their exceptional critical current density (���� ) and high critical temperatures. These properties make YBCO appealing for applications in Superconducting Quantum Interference Device (SQUIDS), electricity transmission lines and Magnetic Resonance Imaging magnets. Pulsed Laser Deposition (PLD) has emerged as a versatile technique for fabricating high-quality YBCO thin films, enabling enhanced flux pinning, increased critical current density, and optimized surface morphology through precise control of deposition conditions and defect engineering - both of which are pivotal areas of research. Recent research has focused on optimizing the fabrication of ultra-thin films (<100 nm) for applications in single-photon detectors and electronic devices that require high electromagnetic properties and smooth, dense surface morphologies. However, within this thickness range, significant degradation in superconducting properties and surface integrity are commonly observed, posing challenges for device fabrication. To mitigate these issues, alternative techniques, such as buffer layering, additional substrate cleaning, and superlattice formation have been employed.</p><p dir="ltr">A critical deposition parameter, the Target-to-Substrate Distance (TSD), plays a key role in determining film properties and surface morphology by influencing multiple deposition parameters, including energy distribution of the plume, flux rate, and surface diffusion rates. This work systematically investigates the structural and electromagnetic properties of YBCO thin films as a function of TSD, focusing on electromagnetic properties, film thickness, critical temperature, crystallinity, stoichiometry, surface morphology and growth modes. Reference to plume propagation models and growth processes were also used to aid this analysis. Characterization techniques including Magnetization measurements, X-ray Diffraction (XRD), Atomic Force Microscopy (AFM), and Scanning Electron Microscopy (SEM), were employed to provide a comprehensive evaluation. Notably, high crystallinity and critical current density were preserved over a large 50mm TSD range under a high laser fluence. Unexpectedly, this trend remained substantial despite a decrease in total film thickness with increasing TSD. Remarkably, while the ���� performance remained largely unchanged, surface properties and other structural features are shown to be easily tunable as a function of TSD, which would be desirable for a broad range of potential applications in electronics and energy handling.</p><p dir="ltr">Further structural analysis, including lattice parameters, oxygen content and formation mechanisms, was conducted via XRD to understand the preservation of these properties. This study presents the first report of a triple layered strain structure emerging from a monolayered deposition in YBCO thin films fabricated via PLD on single crystal substrates. This phenomenon, observed over this large 50mm TSD range, was identified by the presence of a triple peak in ��−2�� scans, despite significant variations in growth mode and thickness between layers. This multilayer strain formation is attributed to significant deviations from typical deposition conditions, particularly high laser fluence which amplifies strain throughout the film. A precise balance between the competing effects of TSD and laser fluence is required to facilitate this formation, as these parameters influence not only structural and electromagnetic properties but also the transition between monolayer and multilayered strain formation.</p><p dir="ltr">These findings demonstrate significant potential for advancing ultra-thin YBCO superconducting films, particularly in single-photon detectors and electronic applications. The results obtained in this work also suggest that a similar simplicity, which is overlooked due to space and design constraints in PLD chambers, can be adopted in other areas of science and technology, and potential applications where PLD process is the key fabrication technique.</p>