Graphene has been considered for a variety of applications including novel nanoelectronic device concepts. However, the deposition of ultra-thin high-k dielectrics on top of graphene has still been challenging due to graphene's lack of dangling bonds. The formation of large islands and leaky films has been observed resulting from a much delayed growth initiation. In order to address this issue, we tested a pre-treatment with NF<sub>3</sub> instead of XeF<sub>2</sub> on CVD graphene as well as epitaxial graphene monolayers prior to the Atomic Layer Deposition (ALD) of Al<sub>2</sub>O<sub>3</sub>. All experiments were conducted in vacuo; i. e. the pristine graphene samples were exposed to NF<sub>3</sub> in the same reactor immediately before applying 30 (TMA-H<sub>2</sub>O) ALD cycles and the samples were transferred between the ALD reactor and a surface analysis unit under high vacuum conditions. The ALD growth initiation was observed by in-situ real-time Spectroscopic Ellipsometry (irtSE) with a sampling rate above 1 Hz. The total amount of Al<sub>2</sub>O<sub>3</sub> material deposited by the applied 30 ALD cycles was cross-checked by in-vacuo X-ray Photoelectron Spectroscopy (XPS). The Al<sub>2</sub>O<sub>3</sub> morphology was determined by Atomic Force Microscopy (AFM). The presence of graphene and its defect status was examined by in-vacuo XPS and Raman Spectroscopy before and after the coating procedure, respectively.