Size Effects on Surface Chemistry and Raman Spectra of Sub-5 nm Oxidized High-Pressure High-Temperature and Detonation Nanodiamonds

Understanding materials with dimensions down to a few nanometers is of major importance for fundamental science as well prospective applications. Structural transformation and phonon-confinement effects in the nanodiamonds (NDs) have been theoretically predicted below 3 nm size. Here, we investigate effect size on surface chemistry, microscopic structure, Raman scattering high-pressure high-temperature (HPHT) detonation (DNDs) 2–3 nm. The NDs are controlled by annealing air ultracentrifugation resulting three ND fractions. Particle distribution (PSD) fractions analyzed combining dynamic light scattering, analytical ultracentrifugation, small-angle X-ray diffraction, transmission electron microscopy complementary techniques. Based obtained PSD, identify size-dependent synthesis-dependent differences properties. In particular, interpretation revisited. Comprehensive comparison pure monocrystalline HPHT reveals diamond core defects, chemical temperature (in)stability, limitations current phonon confinement models. addition, low-frequency 20–200 cm–1 range experimentally observed. dependence this signal both DNDs suggests that it may correspond confined acoustic vibrational, “breathing-like” modes NDs.