Surface Defect Engineering of MoS₂for Atomic Layer Deposition of TiO₂Films

We studied thermal atomic layer deposition (ALD) of TiO₂ from tetrakisdimethylaminotitanium (TDMAT) and trimethylaluminum (TMA) with H₂O, combining experimental and computational approaches on MoS₂ surfaces.Depositions on as produced chemical vapor deposition MoS₂ flakes result in discontinuous films.Surface treatment with mercaptoethanol (ME) does not improve the surface coverage and DFT calculations show that ME reacts very weakly with the MoS₂ surface.However,creation of sulfur vacancies on the MoS₂ surface results in much improved surface coverage and the calculations show that TDMAT,TMA and ME react moderately with either single or extended sulfur vacancies.The computational studies however reveal that the creation of surface vacancies results in the introduction of gap states that may deteriorate the electronic properties.Treatment with ME results in the complete removal of the gap states originating from the most commonly found single vacancies and reduces substantially the density of states for double and line vacancies.As a result,we provide a pathway for the deposition of high-quality ALD dielectrics on the MoS₂ surfaces,which is required for the successful integration of these 2D materials in functional devices.