Investigation into the viability of N,N-disubstituted-N′-acylthiourea copper(ii) precursors for thermal deposition without the use of solvents and the affect precursor geometry has on the deposited composites

Abstract

Molecular engineering of nine closely related copper(II) N,N-disubstituted-N′-acylthiourea complexes (single source precursors containing pre-organised Cu–S bonding motifs) has enabled systematic optimisation of their volatilisation behaviour and thermal stability. The influence of ligand substituents, steric branching, and solid-state geometry on precursor performance was examined. All complexes are monomeric and exhibit high thermal stability, with tuneable volatility arising from structural modifications to the acylthiourea backbone. Based on thermal and vapour pressure analysis, the most promising candidates were selected for proof-of-concept solvent free Chemical Vapour Deposition (CVD), representing the first use of this ligand class in a purely thermal deposition process; previous reports employed only aerosol-assisted CVD. Under these conditions the precursors yielded a copper rich digenite (Cu_1.8S) nanocrystalline material; with a minor covellite (CuS) contribution observed, likely arising from an incompletely converted surface layer. Vapour pressure measurements demonstrate that, through appropriate ligand design, an equilibrium vapour pressure of ≈0.1 Torr can be achieved without compromising precursor stability. These results highlight N,N-disubstituted-N′-acylthiourea complexes as a versatile and tuneable platform for single-source precursor development.