Effect of pH variation and annealing on covalently assembled nanodiamond films

• Published in: Applied surface science 2021-11, Vol.565, p.150585, Article 150585
• Main Authors: Desai, Tithi, Patoary, Naim H., Moore, Arden L., Radadia, Adarsh D.
• Format: Article
• Language: English
• Subjects: Diamond thin films; Nano-assembly; Nanodiamond; Self-assembly; Thin film assembly
• ISSN: 0169-4332; 1873-5584
• DOI: 10.1016/j.apsusc.2021.150585

[Display omitted] •Directed covalent assembly of nanodiamonds carried out in a zwitterionic buffer pH 6-7.•SEM and AFM study show tuning of surface coverage, porosity and pore size distribution.•Thermal conductivity of nanodiamond film change with film morphology.•Thermal annealing in inert gas shows nanodiamond aggregation and reduced surface coverage. This work examines the effect of using low-ionic strength zwitterionic buffer and post-deposition thermal annealing on the microstructure and thermal conductivity of continuous nanocrystalline diamond films that are deposited via the directed covalent assembly of detonation nanodiamonds. Variation of the zwitterionic buffer pH was found to tune the surface coverage, film thickness, thermal conductivity, and film morphology as quantified by apparent porosity and pore size distribution. The sequential annealing of these films up to 400 °C, showed the anticipated severance of amide bonds holding the nanodiamonds together, followed by the detrimental aggregation of the nanodiamonds to segregated islands, losing film continuity and increasing apparent porosity. The change in thermal conductivity with annealing was subjective to buffer pH, suggesting that the morphology changes associated with annealing may have a complex relationship with thermal conductivity. The thermal conductivity data were further analyzed using a phonon hopping model to quantify the degree of phonon movement across boundaries. Overall, the results demonstrate a way to achieving porous, low-cost nanocrystalline diamond thin films with tunable film morphology and thermal conductivity.