Magic Diamond: Covalent Bond Formation of Melamine and other Amines on Nanodiamond Surfaces

High-temperature high-pressure (HPHT) nanoscale diamond (ND) is a host of the nitrogen vacancy (NV) center, a quantum bit that allows for a wide range of quantum sensing capabilities including magnetometry, electrometry and thermometry using all-optical techniques at room temperature. Yet challenges remain in diversifying the chemical modalities for covalent bond formation on diamond surfaces, which is typically limited to carboxylate-based chemistry but has been recently expanded. Amine termination of diamond is attractive due to theoretical studies that described the removal of mid-gap states, which results in extended electron-spin coherence times. Chemical activation of alcohol terminated NDs into alkyl-bromides (ND-Br) using SOBr2 has been shown to be a successful strategy. The alkyl bromide is a good leaving group that forms a carbocation intermediate to generate new bonds and has previously been used to form simple amine termination. Here we test the ability of larger amine molecules to generate covalent diamond-nitrogen bonds on the sterically hindered surface. In this update, we react ND-Br with branched, linear and cyclic amines including polyethyleneimine, diethylenetriamine and melamine, a triazine derivative used in “magic eraser” products and antibacterial products. A suite of X-ray spectroscopies was employed to verify the successful amination and probe the diamond-amine electronic structure. These results expand the routes for researchers who wish to chemically tune diamond and modify the surface dipole moment and electron affinity for quantum sensing applications with atomic defects.