# Wettability of CNW/ITO Micro Structure for Modification of Surface Hydrophilicity
## 3 Results and Discussion  
Figure 2 shows the surface of pristine-CNW (starting material) and CNW/ITO micro-structure (modified CNW). As shown in Figure 2a, typical pristine-CNW was freely grown with graphene layers-based nanosheets on the substrate, which has a thickness of 5-10 nm and height of 1.0-1.3 \(\upmu\)m. These nanosheets show a curve and wrinkle-shaped morphology entangled in multiple directions. It is a phenomenon owing to the field-effect induced by plasma and it is one of the representative characteristics. The surfaces of the CNW/ITO micro-structure modified by ITO nano-particles sputtered onto pristine-CNW were observed, corresponding to Figure 2b-d. The wall thickness in the CNW/ITO micro-structure with ITO sputtered for 15 min is 60-80 nm, which shows that it is thicker compared with the pristine-CNW (Figure 2b). In increasing the sputtering time, the wall thickness of CNW/ITO micro-structure became thicker (30 min, 105-120 nm; 45 min, 160-173 nm), respectively (Figure 2c,d). The nano-porous area (yellow circle) reduced as the thickness increased of the CNW/ITO micro-structure. After examining the surface of the pristine-CNW and CNW/ITO micro-structure through FE-SEM, we can suppose that the boundary surface between the water droplet and ITO widens depending on the surface thickness of ITO, which may affect wettability with variations of nano-porous areas. For wettability on the side of ITO synthesized on pristine-CNW, we conducted a cross-sectional FE-SEM measurement as shown in Figure 3. In the case of pristine-CNW, pillar-shaped carbon nanowalls perpendicularly aligned on Si substrate were identified. Interestingly, innumerable protrusions (yellow quadrangle) were observed by gathering carbon-riched agglomerates on the sides of the carbon nanowalls (right in Figure 3a), and lateral morphological features were examined only in pristine-CNW. When this phenomenon is compared to micro-structures induced by ITO nano-particle sputtered onto pristine-CNW from Figure 3b up to Figure 3d, the distribution area of protrusion on the side of carbon nanowalls significantly reduced, which is indicated by yellow quadrangles in Figure 3b,c. The reduced yellow quadrangles signify that the visually identifiable height of the protrusion area decreased more than on pristine-CNW, since carbon-based protrusions were partially covered with ITO sputtered onto pristine-CNW. Figure 2: Surface FE-SEM image of pristine-CNW and CNW/ITO micro-structure: (**a**) pristine-CNW; CNW/ITO micro-structure by ITO nano-particles sputtered for (**b**) 15 min; (**c**) 30 min; (**d**) 45 min. In addition, we must investigate the formation of ITO on the top of pristine-CNW. The specimens, ITO sputtered onto pristine-CNW, appeared to have a thickness of around 1.1-1.5 \(\upmu\)m. It can be assumed that indium tin oxide was deposited at nano-scale thickness compared to pristine-CNW (1.0-1.3 \(\upmu\)m). For precise thickness analysis, we deposited indium tin oxide on the Si substrate, and its thickness was within 150 nm as shown in Figure 3e, which means ITO sputtered onto pristine-CNW and Si substrate/ITO have a similar thickness. Additionally, we noticed that columnar-shaped grain boundaries (blue quadrangles) were distinctly generated at indium tin oxide on top of CNW. It suggests that as the similar grain boundaries were examined in the reference indium tin oxide deposited under the same conditions by sputtering, it was thoroughly deposited on pristine-CNW. To figure out the crystallization of ITO and defects of CNW based on carbon disorder with alignment, XRD (X-ray diffraction) and Raman spectra were employed. Figure 4a shows the crystallization peaks of ITO by different sputtering times. The polycrystalline with various peaks corresponding to the planes (222), (400), (440), (622) observed in bixbyite-structure were commonly identified [17]. When sputtering time increases up to 30 min, a sharp (222) peak showed extraordinary crystallization.