A significant aspect of ALD research involves developing new precursor molecules, primarily metal precursors, that possess favourable physical and chemical properties. These advancements aim to enable material deposition at lower temperatures and produce films with reduced impurity levels. An ALD precursor must be sufficiently volatile to be transported to the reaction chamber and growth surface. It should not decompose in the gas phase in a way that leads to continuous CVD growth. At the surface, the precursor should react in a self-limiting manner to form a stable monolayer and volatile, unreactive by-products that can be easily removed by purging. After purging, the monolayer should react with the second precursor (eg. H2O, H2S, NH3) in another self-limiting reaction. Additionally, using precursors with the same oxidation state as the target material eliminates the need for redox chemistry during the process, reducing the risk of forming undesired mixed-phase materials. This consideration is not applicable to the deposition of most metallic films, such as Cu films for interconnects, where reduction to the ground state is required. Although the surface chemistry requirements of precursors are well understood, creating a metal precursor with all these desired properties has been challenging to date.