Structural and electronic properties of H- and O-functionalized diamond (100) with variable coverage

Diamond combines exceptional mechanical, thermal, and electronic properties, making it a prime candidate for high-power and high-frequency electronics. Its performance, however, is strongly influenced by atmospheric contaminants and the resulting surface chemistry. Using density functional theory (DFT), we investigated the (100) surface with H, OH, O e t h e r (C–O–C), and O k e t o n e (C=O) terminations, as well as mixed H/O motifs across different coverages. Oxygenated surfaces were thermodynamically favored, with O k e t o n e stabilizing at partial coverage and O e t h e r favoring full coverage. Passivation removed mid-gap states, but band gap evolution depended strongly on termination. Specifically, H and OH preserved wide gaps, while O e t h e r and O k e t o n e produced non-monotonic trends, including collapse at low and high coverages. Mixed terminations further expanded tunability, spanning semiconducting to metallic states. The electron affinities ( χ ) showed similar dependence, remaining negative for H, OH consistently near the NEA-PEA boundary, and strongly positive for O-rich surfaces. These results demonstrate that termination and coverage together dictate the stability and the electronic properties, offering a framework for the rational design of diamond (100) surfaces that will support next-generation electronic devices.