4.2. Probe Surface Modifications and Contact Angle Measurements

The hydrophilic probe was prepared by washing a new probe with plasma for 3 min. The medium hydrophobic probe was prepared by first cleaning a new probe with plasma and then modifying it using the OTS agent in the gaseous phase. After more than 12 h, the probe was taken out and dried in a vacuum drying oven at 120 °C for 5 min to obtain a medium hydrophobic probe. The strong hydrophobic probe was obtained by first cleaning a new probe in plasma and then immersing it in 1 vol % OTS toluene solution for approximately 5 min. It was then cleaned with acetone, ethanol, and ultrapure water, purged using nitrogen after being removed from the modified solution, and then dried in a vacuum drying oven at 120 °C for 5 min.²⁷

While the probes were being modified, new silicon wafers were cleaned by plasma and modified with OTS surfaces by the corresponding methods, and the modification effect was characterized via contact angle measurements to represent the hydrophobicity of the probes. A drop of ultrapure water (approximately 8 μL) was deposited on the wafer surface using the drop method. The surface contact angle was measured using a contact angle measuring instrument (DSA100, A.Krüss, Germany).