Ligand effect on In–Ti-oxo nanoclusters for nanolithography

Metal-oxo clusters have emerged as promising candidates for nanolithography technology. However, achieving precise control over their structures and compositions to enhance solution processability and film properties remains a significant challenge. This study introduces a novel ligand-regulation strategy for modularly assembling In-Ti-oxo clusters and represents the pioneering application of In-Ti-oxo clusters in nanolithography. Specifically, we explore the indium-based flexible trifurcate InL₃ as a metalloligand (L = salicylate derivatives) to stabilize isomeric In₄Ti₁₂-cores with varying spherical shells: InOC-20V, InOC-21V, InOC-22V and InOC-23H. These isomers, in turn, induce markedly distinct solution processabilities. InOC-20V to InOC-22V feature vertically connected Ti₆In₂-SBUs, resulting in superior solubility compared to InOC-23H, which has parallel-connected Ti₆In₂-SBUs. In addition, the organic periphery is critical for film formation, and only InOC-20V, decorated with salicylate groups, produces high-quality films via spin-coating with 50 nm resolution patterns for lithography. To gain insight into the exposure mechanisms, a combination of DFT calculations, TGA-MS, XPS, and AFM-IR was used, indicating that the decarboxylation of the ligands significantly contributes to the solubility-switching behaviors necessary for lithography. These findings offer generalizable synthetic methods to expand the In-Ti-oxo cluster structural chemistry and highlight the efficacy of tailored structural modulation of cluster materials in enhancing solution processability and lithography performance, providing valuable insights for future material design and applications.