Growth of Nanocrystalline Diamond Thin Films from Detonation and HPHT Nanodiamonds: Correlative Microscopy Study

The nucleation layer formed by diamond nanoparticles (nanodiamonds, NDs) is nowadays probably the most common approach how to facilitate polycrystalline diamond growth on diverse substrates by chemical vapor deposition (CVD). Yet the formation of thin and ultrathin functional diamond films [Stehlik et al., doi 10.1021/acsami.7b14436] gives rise to numerous challenges in terms of adhesion, surface uniformity, layer density, sp2/sp3 carbon phases, grain sizes, grain boundaries, etc. A recent study with oxidized nanodiamonds showed that the nanodiamond material quality (determined by origin and surface modifications) has a pronounced effect on the diamond CVD growth and resulting properties, including the brightness of SiV color centers [Zhang et al., doi 10.1039/d2tc01090a].<br/> Thus, in this work we compare the effect of several types of hydrogenated nanodiamonds (being principally more suitable) for nucleation and growth of nanocrystalline diamond thin films with SiV centers. We employ detonation nanodiamond (DND) solutions from standard 4 nm DNDs and novel size-reduced 2 nm DNDs and 4 nm DNDs with reduced nitrogen content (&lt; 0.05 at.%), all obtained from pre-production stock (OZM Research). We also employ HPHT NDs of 0-30 nm size (MSY30, Pureon) purified by annealing in air (450°C, 5h). All NDs were hydrogenated by annealing in a hydrogen atmosphere, providing them positive zeta potential and stability in a colloidal solution [Kolarova et al., doi 10.1016/j.diamond.2023.109754]. The nucleation solutions were prepared by sonication of 100 mg NDs in 20 mL water and subsequent centrifugation to remove larger aggregates. Nucleation layers were formed on Si substrates and Si self-sensing AFM probes which were immersed in the nucleation solution and sonicated for 10 min. We applied CVD diamond growth for 5-30 min (10 - 80 nm thickness) using microwave plasma SEKI SDS6K reactor with standard growth conditions (hydrogen 300 sccm, methane 15 sccm, 60 mbar, 3 kW, 800 °C).<br/> We characterize the morphology, material, and functional properties of the nucleation layers and resulting CVD diamond thin films by correlative microscopy combining SEM, AFM, Raman, and photoluminescence measurements. We show the dependence of these features on the specific properties of the 4 types of employed nanodiamonds. The work has been supported by the Technology Agency of the Czech Republic (TACOM project) and the Czech Science Foundation.