Comment on ``Diamond (111) surface reconstruction and epitaxial graphene interface''

In a recent paper by Reed et al. [Phys. Rev. B 105, 205304 (2022)10.1103/PhysRevB.105.205304], angle resolved photoemission spectroscopy (ARPES) experimental results as well as density functional theory (DFT) calculations performed on the diamond C(111)-(2×1) surface, both clean and graphene covered, are presented. We only address the first part of the paper (clean surface). On the basis of their photoemission data, the authors claim that the C(111)-(2×1) surface is metallic, adding that "our ARPES measurements do not compare well"with previous experimental results. Indeed, in the literature one can find a number of results obtained with different techniques, including ARPES, proving the semiconducting character of this surface. In this Comment we disagree with the interpretation of the experimental data given in the paper and conclude that the surface is semiconducting and any disagreement with published results is almost completely eliminated. We also discuss the theoretical approach used, placing it in a wider framework. When well founded, also the theoretical simulation shows the semiconducting character of the C(111)-(2×1) surface.