In order to enable the application of atomic probe tomography combinatorial processing platforms for atomic-scale investigations of phase evolution at elevated temperatures, the pre-sharpened Si tip of 10–20 nm in diameter must be protected against interdiffusion and reaction of the reactive Si with a film of interest by a conformal coating on the Si tip. It is shown that unwanted reactions can be suppressed by introducing a 20-nm-thick intermediate Al₂O₃ layer grown by atomic layer deposition (ALD). As a representative case, Pt is chosen as a film of interest, as it easily forms silicides. Whereas without the ALD coating diffusion/reactions occur, with the protective film, this is prevented for temperatures up to at least 600°C. The effectiveness of the Al₂O₃ layer serving as a diffusion barrier is not limited to a sharpened Si tip but works generally for all cases where a Si substrate is used.