Bactericidal surfaces are in high demand for biomedical as well as industrial applications. In this paper, we have investigated if black diamond is useful for this application. Black diamond is derived from black silicon, a silicon surface structured into nano-sized needles. These needles can pierce through bacteria on contact. Black diamond is obtained by coating black silicon with a thin diamond film rendering the nanostructures more robust. We compared the bactericidal and anti-bacterial properties of fluorine-terminated and hydrogen-terminated black diamonds with those for black silicon and for flat surfaces of diamond (on silicon) with the same terminations. In this study we evaluated the ability to repel and kill Gram-positive S. aureus and S epidermidis, which have a thicker cell wall and are more mechanically robust than the bacteria that have been studied before. We evaluated the short-term 1 h initial adhesion as well as long-term 24 h biofilm formation. We found that the number of bacteria that initially adhered to the fluorine-terminated black diamond surface was significantly reduced and had the highest dead bacterial ratio compared to fluorine-terminated flat diamond, black silicon surfaces and hydrogen-terminated diamond surfaces, respectively. Biofilm formation after 24 h showed that while all surfaces outperform glass over the long-term (24 h), diamond-coated surfaces with both fluorine and hydrogen termination have a significant inhibiting biofilm formation effect. In conclusion, fluorinated and hydrogenated diamond-coated surfaces with and without nano-needles have repelling, bactericidal and biofilm-inhibiting effects on Gram-positive bacterial strains and are promising antimicrobial surfaces.