## 3 Results
### Formation of OTMS SAMs Verified by Water CAs and AFM Imaging
However, for SAMs with complete coverage, AFM is not capable of measuring their thickness because AFM relies on measuring the height difference between the monolayer and the substrate. It is thus necessary for both the SAMs and the substrate to be present within the scanned area, where there must be openings in the monolayer or the monolayer must be composed of islands. In order to take advantage of AFM, island-like OTMS SAMs were prepared on a UV/ozone-treated SiO\({}_{2}\) substrate via spin coating, which are shown in Figure 2c. One can clearly see the circular islands of OTMS SAMs and the underlying corrugated SiO\({}_{2}\) substrate. In order to avoid, as much as possible, the impact of the corrugated SiO\({}_{2}\) substrate on the estimation of the thickness of the OTMS SAMs, the step height differences close to the edge of the monolayer islands were measured. These islands are 2.12 \(\pm\) 0.14 nm thick and 300-600 nm across. Fiber-like features can also be observed in Figure 2c, whose height is similar to that of the islands. For comparison purposes, OTMS SAMs were also spin coated on a freshly cleaved mica substrate, which is atomically flat. As shown in Figure 2d, closely connected island-like features were detected that are 120-180 nm across. The thickness estimated from  
Figure 1: Optical images showing a static water contact angle on a bare SiO\({}_{2}\) substrate ultrasonically cleaned in methanol (**a**) and on OTMS SAMs formed on a SiO\({}_{2}\) substrate subjected to UV/ozone treatment (**b**). the AFM image is 2.01 \(\pm\) 0.06 nm. The difference in OTMS SAM thickness between the SiO\({}_{2}\) substrate and the cleaved mica substrate may be attributable to their surface roughness, i.e., corrugated vs. atomically flat. The thickness estimated from these OTMS SAMs agrees with those reported [13; 14; 15; 17]. Shown in Figure 3 are profiles isolated from each of the four AFM images in Figure 2. The surfaces of the bare SiO\({}_{2}\) substrate (Figure 3a) and the complete coverage OTMS SAMs (Figure 3b) show corrugations of 1-2 nm. Figure 3c shows a profile across islands of OTMS SAMs formed on the UV/ozone-treated SiO\({}_{2}\) substrate. The profile clearly shows that the SAM islands ride on the corrugated underlying SiO\({}_{2}\) substrate. For example, as indicated in Figure 3c, an island of OTMS SAMs has a thickness of 2.14 nm. In contrast, there is no convolution from the substrate roughness because of the atomically flat nature of the cleaved mica substrate. An island of OTMS SAMs with a thickness of 2.00 nm is indicated in Figure 3d. Figure 2: AFM topographic images for a bare SiO\({}_{2}\) substrate **(a)**; OTMS SAMs with complete coverage prepared on a UV/ozone-treated SiO\({}_{2}\) substrate **(b)**; OTMS SAMs with partial coverage formed on a UV/ozone-treated SiO\({}_{2}\) substrate **(c)**; a freshly cleaved mica substrate **(d)**. The broken line shown in each image indicates where a profile is isolated (and shown in Figure 3). The scan areas for (**a–d**) are 5 \(\upmu\)m \(\times\) 5 \(\upmu\)m and 2 \(\upmu\)m \(\times\) 2 \(\upmu\)m, respectively. The heights for (**a–d**) are 2.88, 3.02, 18.41 and 2.07 nm, respectively.