To begin exploration of molecular-sized nanodiamonds we introduce a high-yield technique based on controllable size reduction of conventional 4-6 nm DNDs via oxidative etching in air, which provides DNDs with the volumetric mean size around 2 nm (S. Stehlik et al., Sci.
Rep. 6 (2016) 38419). Analytical ultracentrifuge serves here as in particular useful and accurate tool for analyses and adjustment of size distribution of DNDs in colloidal dispersions on nanometer scale in contrast to conventional dynamic light scattering (DLS) method. We show that molecular-sized DNDs keep the specific DND structure and variable surface chemistry (e.g. hydrogenated to oxidized) and corresponding zeta potentials (positive to negative) down to 2 nm or below. This, among others, provides numerous opportunities to achieve a desired electrostatic interaction between 2 nm DND and a substrate. In particular, we show how to apply these novel 2 nm H-DNDs to form homogeneous, ultra-thin (2 nm), extremely dense (1.3 × 1013 cm-2) and smooth (RMS < 1 nm) nucleation layers for growing as thin as 5.5 nm continuous NCD films with distinct photoluminescence from SiV centers (S. Stehlik et al., ACS Appl. Mater. Interfaces 9 (2017) 38842–38853).