α-RuCl ₃ is a candidate material for the realization of a Kitaev spin liquid with envisioned applications for quantum computing. It is a van-der-Waals material with in-plane honeycomb lattice equivalent to the CrX ₃ (X= Cl, Br, I) type 2D magnets. Here, possibilities of defect engineering and surface modification of thin crystals are explored by Ar ⁺ dosing and vacuum annealing. Chlorine is easily removed from the surface, which reduces the Ru valence and eventually leaves a Ru rich surface layer behind. A peculiar thickness dependence of the work function emerges after Ar ⁺ sputtering, which is ascribed to the remaining chlorine concentration. This work elucidates material properties of thin α-RuCl ₃ and introduces concepts of property engineering to create homojunctions and control level alignment by standard in situ methods.