Diamond is an unconventional semiconductor with a wide bandgap and a remarkable ability to host defects and intrabandgap states, enabling applications in high-power electronics, quantum technologies — notably with NV centers — as well as (photo)catalysis using B and N doping, biology, and medicine. Unlike most semiconductors, diamond surfaces do not form a native oxide layer but are instead terminated by surface atoms and molecular groups (sp² reconstructions, –OH, =O, –H, –N, –F, etc.). These terminations introduce localized states within the bandgap, strongly modify surface electron affinity and band bending, can be photoexcited, lead to charge separation and trapping [1], and evolve depending on the environment and usage. Understanding and controlling these effects is essential for designing the diamond-based applications of tomorrow — a challenge common to all of them — yet their description often relies on fragmented models tailored to specific applications. A unified treatment that connects surface chemistry, band alignment, and charge transfer remains lacking [2].

Here I present a general framework for describing electronic coupling at diamond interfaces, grounded in Fermi-level equilibration at the interface [3] and band-diagram analysis. I derive its implications for nitrogen-vacancy (NV) center charge-state stabilization, surface conductivity, and (photo)electrochemical reactivity, unifying a broad body of previously disconnected results. Using state-of-the-art synchrotron X-ray spectroscopies [4] combined with laboratory experiments, we probe a variety of diamond interfaces, from nanodiamonds [5,6] to boron-doped nanostructured surfaces [7] to electronic-grade crystals for quantum applications [8,9].

This framework is designed as a comprehensive tool for understanding and engineering diamond-based devices, with explicit account taken of surface termination and environmental interactions. Diamond's lack of a native oxide makes its termination-controlled surface the cleanest system in which to establish such a picture; beyond diamond, the approach is sufficiently general to apply to any semiconductor interface where charge transfer and surface electrostatics are central.

References

1.   Chemin, A., et al. (2023). Surface‐Mediated Charge Transfer of Photogenerated Carriers in Diamond. Small Methods, 7(11), 2300423.

2.   Chemin, A. (2026). Evolution of Diamond Surface and Interface Research: A Bibliometric Perspective. MRS Commun., (under review).

3.   Chemin, A., et al.(2026). The role of the Helmholtz potential on electrocatalytic activity. Nat. Commun, 17, 4547.

4.   Petit, T., et al. (2023). Nanointerfaces: concepts and strategies for optical and X-ray spectroscopic characterization. ACS Physical Chemistry Au, 3(3), 263–278.

5.   Kiendl, B., et al. (2026). Intrabandgap States Engineering in Functionalized Nanodiamond to Generate Solvated Electrons for Photocatalysis Under Solar Illumination. Advanced Functional Materials, e23545.

6.   Finas, M., et al. (2026), Visible range sub band gap photoexcitation of conductivehydrogenated nanodiamonds. (2026). (Under review).

7.   Chemin, A., et al. (2025). Modulating Surface Redox Reactions and Solvated Electron Emission on Boron-Doped Diamond by (Photo)electrochemistry. PRX Energy, 4(3), 033011

8.   Chemin, A., et al. (2024). Depth profiling of microwave nitrogen-terminated polycrystalline diamond surfaces by energy-dependent X-ray photoelectron spectroscopy. Applied Surface Science, 661, 160082.

9.   Malkinson, R., et al. (2024). Enhanced quantum properties of shallow diamond atomic defects through nitrogen surface termination. Journal of Materials Chemistry C, 12(20), 7206–7213.