Shift in the conduction band energy, E_CB, as a function of radius for nanodiamonds, calculated using Eq. (C.2). The thick, solid portion of the curve indicates the behaviour supported by the experimental results of Chang et al. (1999) and the dashed portion is the extrapolation to smaller sizes using Eq. (C.2). For reference, the vertical solid line marks the mean radius of the meteoritic pre-solar nanodiamonds (~1.4 nm). The vertical dashed line marks the radius of the smallest diamond-type entity, the molecule adamantane, C₁₀H₁₆.