  Surface termination and interfacial interactions are critical for advanced
solid-state quantum applications. In this paper, we demonstrate that atomic
layer deposition (ALD) can both provide valuable insight on the chemical
environment of the surface, having sufficient sensitivity to distinguish
between the common diamond (001) surface termination types and passivate these
interfaces as desired. We selected diamond substrates exhibiting both smooth
and anomalously rough surfaces to probe the effect of morphology on ALD
nucleation. We use high resolution in situ spectroscopic ellipsometry to
monitor the surface reaction with sub-angstrom resolution, to evaluate the
nucleation of an ALD Al2O3 process as a function of different ex and in situ
treatments to the diamond surface. In situ water dosing and high vacuum
annealing provided the most favorable environment for nucleation of
dimethylaluminum isopropoxide and water ALD. Hydrogen termination passivated
both smooth and rough surfaces while triacid cleaning passivated the smooth
surface only, with striking effectiveness.
