Stability of Nanodiamond Surfaces Exposed to N, NH, and NH2

Knowledge about the surface functionalization of nanodiamonds is of great importance for nanomedical and nanobiological applications. In this paper, we explore the relative stability of the nanodiamond passivated by amidogen (NH2), imidogen (NH), and nitrogen (N) in N-2 + H-2 and ammonia environments, using density functional tight binding simulations over a range of temperatures. The N-adsorption is found to be energetically unfavorable on the nanodiamond surfaces up to 1500 K. In contrast, adsorption of NH and NH2 is found to be thermodynamically stable at least around room temperature. We also compare the possibility of anisotropic (facet-dependent) adsorption and find that {100} facets of the nanodiamond are more preferred for the NH adsorption in the entire temperature range considered but are only favored at high temperature for the NH2 adsorption. We also show that this chemical functionalization is more stable in the N-2 + H-2 environment than in the ammonia environment, but its stability depends on the size, shape, and morphology of the nanodiamond.