Combinatorial thickness-graded film growth via substrate tilt geometry in pulsed laser deposition

Pulsed laser deposition (PLD) is a well-established method for synthesizing thin films, enabling precise control over growth parameters while maintaining stoichiometry across the specimen. Integrating PLD with combinatorial studies offers a significant advantage for conducting high-throughput experiments, thereby accelerating discovery. In this work, we introduce a reliable and reproducible approach for combinatorial thin-film synthesis that features spatially controlled thickness gradients on a substrate, achieved using a tilt-enabled stage. This technique exploits the angular distribution of the laser plume on a tilted substrate, which creates varying distances between the plume source and the substrate, resulting in a thickness gradient. While conventional PLD typically produces a plateau-shaped thickness gradient over large wafer-scale areas due to the natural profile of the ablation plume, our study aims to develop a fundamental understanding of how to create controlled thickness gradients. Using boron nitride (BN) as the model system, we investigate the effect of substrate tilt angles on the spatial distribution of thickness. Atomic force microscopy measurements show that a uniform film forms over a 10 mm × 10 mm area of the substrate at 0° tilt. In contrast, substrate tilt angles of ±20° result in a linearly graded film thickness that is asymmetric around the laser plume axis over the same area. We have extended this study to Co and NiCoCr films, which consist of elements with similar atomic numbers to minimize atomic-number-dependent variations during deposition, thereby improving the reproducibility of our approach across different material systems. Using a model having cosine-power dependency that incorporates target-substrate spacing, tilt geometry, and small-axis offsets, we simulate the ablation plasma plume profile to understand film thickness profiles for both 0° and tilted substrate geometries. The results agree with our experimental findings and provide guidance for designing combinatorial experiments that require film thickness gradients.