The Influence of UV-Ozone, O2 Plasma, and CF4 Plasma Treatment on the Droplet-Based Deposition of Diamond Nanoparticles.

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.

Velocity and size measurement of droplets from an ultrasonic spray coater using photon correlation spectroscopy and turbidimetry.

We have developed a combination of light scattering techniques to study and characterize droplets of an ultrasonic spray coater in flight. For this economically relevant spray coater, there is so far no reliable technique to systematically adjust the experimental parameters. We have combined photon correlation spectroscopy and turbidimetry to determine the size and speed of the droplets depending on parameters of the printing process as shroud gas pressure, flow rate, and atomizing power. Our method will allow us to predetermine these parameters to control the properties of the coated films as, e.g., thickness from tens of nanometers to micrometers.