Influence of Surface Chemistry on the Optical Properties of IV Group Color Centers in Diamond

The diamond surface plays a crucial role in defining its electronic, chemical, and optical properties, particularly in applications involving near-surface defects and interfaces1. Surface chemical termination directly affects charge stability, band bending, and carrier dynamics, which are critical for the performance of color centers2. Moreover, surface functionalization improves compatibility with external environments, including biological media and device integration, making precise control of surface chemistry essential for achieving stable and reproducible optical responses. In this work, we developed a fluorine termination procedure for the diamond surface aimed at enhancing the photoluminescence emission of color centers. The approach is based on the deposition of a thin SiO₂ film by atomic layer deposition (ALD), which provided uniform and conformal surface coverage, followed by SiO₂ selective wet etching by buffered hydrofluoric acid. Wet chemical etching enabled the exposure of the underlying diamond surface and induced fluorine termination, as confirmed by X-ray photoelectron spectroscopy (XPS) analysis. Prior to the fluorination process, germanium ions were implanted into electronic-grade diamond by Focused Ion Beam (FIB) at a kinetic energy of 70 keV, over raster-scanned areas of 10 × 10 μm² using three different ion fluences (1x1014, 3x1014, and 5x1015 ions/cm²). The optical properties of the implanted regions were investigated by photoluminescence spectroscopy before and after fluorine termination. The results show a clear enhancement of the photoluminescence intensity of germanium-vacancy (GeV) centers for all the investigated fluences, with a maximum increase of up to three times.