Molecular Transformations for Direct Synthesis of Thorium Dioxide Films

Abstract

New Th(IV) complexes with high volatility were synthesized and applied as molecular single‐source precursors for chemical vapor deposition (CVD) of ThO2 thin films. The change in the steric profile of alkoxide ligands and concomitant reduction in the molecular weight of [Th(L)2(OR)2] (1‐OR, R = iso‐propyl (1‐OiPr) or tert‐butyl (1‐OtBu), L = N‐(4,4,4‐trifluorobut‐1‐ene‐3‐one)‐methoxyethylamide)) had a profound effect on the vapor pressure (at 10‐5 mbar) evident in the drop in sublimation temperature to 100 °C for the iso‐propoxide derivative against 130 °C observed for the tert‐(1‐OtBu). Hirshfeld surface analysis of both complexes showed different degrees of intermolecular H⋅⋅⋅F interactions responsible for the observed differences in the volatilities of the two complexes. Both mixed‐ligand compounds (1‐OiPr, 1‐OtBu) were applied in the CVD process to deposit thorium oxide thin films without any carrier or reactive gas that verified their suitability as single‐source precursors to ThO2 coatings. Thin films of ThO2 were grown at 500 °C and 600 °C on Si/SiO2 substrates, which showed presence of C, N, and F presumably originating from the incorporation of ligand fragments in the growing CVD deposits. Subsequent calcination of CVD‐grown ThO2 films at 800 °C in air led to phase pure ThO2 coatings with uniform morphology.