Directed covalent assembly of nanodiamonds into thin films

Abstract

The wide-spread use of polycrystalline diamond thin films is limited by the costs associated with chemical vapor deposition, high growth temperature, and poor substrate adhesion. Here, a solution-phase method to grow nanocrystalline diamond films is demonstrated through carbodiimide-mediated cyclic attachment of carboxylated nanodiamonds and a diamine linker on amine-functionalized substrates. XPS and Raman spectroscopy confirm formation of the desired amide bonds and incorporation of the linker to form the covalently-bonded nanoparticle network. The assembly process was demonstrated in solution phase as well as via spin coating with both methods resulting in similar film morphology as observed using SEM and AFM. The assembly process leaves the films amine-terminated, which is convenient for application-specific surface modifications. The thermal conductivity of the covalently assembled NDs as measured via the 3ω method ranged between 2 and 20 W m−1 K−1, which is comparable to those of CVD nanocrystalline diamond films of similar grain size. Future strategies to reduce porosity during the directed covalent assembly strategy hold strong potential for applications requiring thermal dissipation or mechanical and chemical stability.