## 2 Materials and Methods  
OTMS (90%) was purchased from Fisher Scientific Company (Fair Lawn, NJ, USA) and used as received. The chemical (liquid) was used to prepare a 3 mM OTMS solution in trichloroethylene. A Si wafer with a 300 \(\upmu\)m thermally grown SiO\({}_{2}\) was used as the substrate for the preparation of OTMS SAMs. The Si wafer is referred to as a SiO\({}_{2}\) substrate in this article. The SiO\({}_{2}\) substrates were cleaned ultrasonically with acetone for 15 min, followed by UV/ozone treatment for 40 min. The cleaned SiO\({}_{2}\) substrates were immediately immersed in the OTMS solution for 1 h. The SiO\({}_{2}\) substrates were dry when they were removed from the solution, which was a sign of the formation of OTMS SAMs. These OTMS SAM-covered SiO\({}_{2}\) substrates were NH\({}_{4}\)OH vapor annealed for \(\sim\)10 h, followed by a deionized water rinse for 30 s and cleaning ultrasonically in acetone for 15 min [13]. In order to achieve partial coverage OTMS SAMs for AFM imaging to measure the thickness of the SAMs, a diluted OTMS solution was spin coated at 3000 rpm onto a UV/ozone-treated SiO\({}_{2}\) substrate and a freshly cleaved mica substrate. Static water CAs on the OTMS SAMs formed on SiO\({}_{2}\) substrates were measured using a Drop Shape Analyzer (DSA30E, KRUSS GmbH, Hamburg, Germany). For comparison purposes, CAs were also measured on a SiO\({}_{2}\) substrate cleaned ultrasonically in methanolfor 15 min. CAs were measured using 2 \(\mu\)L deionized water droplets as the probing liquid over 5-10 areas for each sample. The dynamic force mode of an AFM (XE-100, Park Systems, Suwon, South Korea) was used to image the surface morphology of OTMS SAMs. The AFM sensing system contained a silicon cantilever (NSC15, MikroMasch, Sofia, Bulgaria) with a tip attached to one side of its free end, while the other side was irradiated by a laser beam, which was reflected to a position-sensitive photodetector to measure the interaction between the tip and the sample surface. The cantilever used in this study had a nominal spring constant of 40 N/m, resonant frequency of 325 kHz and tip radius of 10 nm. In the dynamic force mode, the cantilever is vibrated via a piezoelectric device driven by a sinewave voltage at a frequency slightly lower than its resonant frequency. The amplitude of the cantilever in free space was \(\sim\)25 nm [38], which decreased when the tip approached the sample surface due to the interactive force between the tip and the sample surface. A reduced amplitude was used as the feedback parameter to allow the tip to trace the contour of the sample surface, thus constructing the surface morphology. AFM images were collected at 256 \(\times\) 256 pixels in air (relative humidity \(\sim\)50%) at room temperature. Pure OTMS molecules, a UV/ozone-treated SiO\({}_{2}\) substrate and the OTMS SAMs were investigated using ToF-SIMS (TOF SIMS IV, ION-TOF GmbH, Munster, Germany), in which a pulsed (\(\sim\)1 ns) 25 keV Bi\({}_{3}\)\({}^{+}\) primary ion beam was used to bombard the sample surface to generate (secondary) ions from the surface. The secondary ions were extracted by an electric field and they arrived at the detector with different flight times that are a function of mass to charge ratio (\(m/z\)) after they flew through a reflectron-type tube. The intensities of ions against their flight time make up a secondary ion mass spectrum, where the \(m/z\) was calibrated using carbon, hydrocarbons and other known species. A low-energy electron beam was then flooded over the sample surface for charge compensation, which completes the 100 \(\mu\)s cycle for bombarding the sample surface with one shot of the primary ion beam. The pressure of the analysis chamber of the ToF-SIMS instrument was approximately 10\({}^{-7}\) mbar. Secondary ion mass spectra were collected at 128 \(\times\) 128 pixels over a rastered area of 500 \(\mu\)m \(\times\) 500 \(\mu\)m with one shot of the pulsed primary ion beam per pixel, which was repeated 25 times for data collection.