Novel Oxygen–Boron-Terminated Diamond (111) Surface with Negative Electron Affinity: Theoretical Simulations

Negative electron affinity (NEA) properties make diamond promising for various electron emission and field-effect tube applications. However, the NEA property of conventional H-terminated diamond suffers from a stability issue, particularly with the development of power electronics. This prompts exploration of alternative NEA structures. Herein, this work explores oxygen–boron-terminated diamond (111) surfaces via density functional theory calculations. Employing the particle swarm optimization method, one monolayer (1 ML), 0.5 ML, and 0.25 ML of the O–B-terminated diamond (111) surfaces are predicted. The stability of predicted O–B-terminated surfaces is verified through adsorption energy, phonon spectrum, and thermal stability calculations. The 1 ML surface shows the most negative adsorption energy of −7.78 eV/atom, indicating superior stability and exceeding that of hydrogen-terminated diamonds. Moreover, all coverage diamond surfaces exhibit NEA properties regardless of coverage. Notably, the most negative NEA value of −1.49 eV is shown at type I coverage of 1 ML. Also, there are no defect states within the band gap of the 1 ML structure, indicating perfect surface arrangement and minimal leakage current. These results predict that O–B-terminated diamond (111) surfaces, with impressive thermal stability, strong NEA, and outstanding band structure, represent a promising candidate for electron emission and FET applications.