Enhancing the nucleation in atomic layer deposition: A study on vanadium sulfide and oxide layers

The nucleation and growth of atomic layer deposited (ALD) vanadium oxide and sulfide layers were examined on the surface of sapphire and silicon. The growth of vanadium oxide was layer by layer on sapphire, but islandlike on silicon. The stable growth rates could be derived from the steric hindrance of the precursor molecules. The nucleation of vanadium sulfide was always islandlike. The merging of the islands, and, thus, continuous film growth, could be achieved by enhancing the surface active sites by chemical pretreatments, as well as by starting the ALD growth by longer cycles. With the combination of these approaches, ultrathin continuous VO2 and VS layers could be grown. The nucleation was also modeled mathematically, and the unknown starting boundary conditions could be derived from the model fitting.