Surface treatment is critical for homogeneous coating over a large area and high-resolution patterning of nanodiamond (ND) particles. To optimize the interaction between the surface of a substrate and the colloid of ND particles, it is essential to remove hydrocarbon contamination by surface treatment and to increase the surface energy of the substrate, hence improving the diamond film homogeneity upon its deposition. However, the impact of substrate surface treatment on the properties of coatings and patterns is not fully understood. This study explores the impact of UV-ozone, O₂ plasma, and CF₄ plasma treatments on the wetting properties of the fused silica glass substrate surface. We identify the optimal time interval between the treatment and subsequent ND coating/patterning processes, which were conducted using inkjet printing and ultrasonic spray coating techniques. Our results showed that UV-ozone and O₂ plasma resulted in hydrophilic surfaces, while CF₄ plasma treatment resulted in hydrophobic surfaces. We demonstrate the use of CF₄ plasma treatment before inkjet printing to generate high-resolution patterns with dots as small as 30 μm in diameter. Ultrasonic spray coating showed homogeneous coatings after using UV-ozone and O₂ plasma treatment. The findings of this study provide valuable insights into the hydrocarbon airborne contamination on cleaned surfaces over time even in clean-room environments and have a notable impact on the performance of liquid coatings and patterns. We highlight the importance of timing between the surface treatment and printing in achieving high resolution or homogeneity.

Nanocrystalline diamond (NCD) field emitters have attracted significant interest for vacuum microelectronics applications. This work presents an approach to enhance the field electron emission (FEE) properties of NCD films by co-doping phosphorus (P) and nitrogen (N) using microwave plasma-enhanced chemical vapor deposition. While the methane (CH₄) and P concentrations are kept constant, the N₂ concentration is varied from 0.2% to 2% and supplemented by H₂. The composition of the gas mixture is tracked in situ by optical emission spectroscopy. Scanning electron microscopy, atomic force microscopy (AFM), transmission electron microscopy, and Raman spectroscopy are used to provide evidence of the changes in crystal morphology, surface roughness, microstructure, and crystalline quality of the different NCD samples. The FEE results display that the 2% N₂ concentration sample had the best FEE properties, viz. the lowest turn-on field value of 14.3 V/µm and the highest current value of 2.7 µA at an applied field of 73.0 V/µm. Conductive AFM studies reveal that the 2% N₂ concentration NCD sample showed more emission sites, both from the diamond grains and the grain boundaries surrounding them. While phosphorus doping increased the electrical conductivity of the diamond grains, the incorporation of N₂ during growth facilitated the formation of nano-graphitic grain boundary phases that provide conducting pathways for the electrons, thereby improving the FEE properties for the 2% N₂ concentrated NCD films.