# Wettability of CNW/ITO Micro Structure for Modification of Surface Hydrophilicity
## 1 Introduction  
Carbon nanomaterials such as graphene, carbon nanotube (CNT), carbon nanosheet (CNS), and carbon nanowall (CNW) have a nano-micro thin scale and structure, causing flexibility as well as remarkable electric, mechanic, and thermal properties. Hence, carbon nanomaterials have been spotlighted as an advanced crucial material on application devices [1; 2; 3; 4].  
As time passes, the application fields of carbon nanomaterials are being expanded and widened. Recently, it is attracting attention for its utilization on filter devices for desalination, medical devices in blood, and sensor devices for the detection of liquids. Furthermore, it is expected that carbon nanomaterials-based devices will be utilized in water, ocean, and oil to detect variations of them [5; 6; 7]. For the application of carbon nanomaterials on advanced devices related to liquids, it is crucial to interact between carbon nanomaterials and liquids, and thus the surface wettability of the carbon material is the key point. The wettability is one of the surface properties which is settled by molecules and the area distributed at the boundary surface of carbon nanomaterials and liquids with a range from nm to um, and alteration of the molecules-area with a surface structure of carbon nanomaterials is efficiently able to affect wettability. As methods for change of wettability, various techniques modifying the surface structure and components have been employed [8; 9; 10; 11]. In this regard, and compared with the surface structure of carbon nanomaterials mentioned above, graphene and CNT are horizontal against the substrate. It is difficult to modify surface structure due to a thin carbon layer less than 2 nm. Hence, surface componential modification techniques are suitable for graphene and CNT [12]. The typical method employed for modification of the surface component is chemical processing, which enables indisputable surface modification, however, it induces a non-eco-friendly environmental impact [13]. Additonally, the CNW stands perpendicular to the substrates with a nano-micro structure.  
The CNW named as vertical graphene, free-standing graphene, and graphene nanowall includes a lot of graphene layer-based walls capable of growing up to 2.33 \(\upmu\)m (from the last experiment), which affects the laplace pressure (P\({}_{\text{L}}\)) and enables it to change the wettability [14; 15; 16]. Moreover, the CNW, which is outstanding on binding capacity, stable chemistry, and reactivity with various materials, is simple to surface structure change through evaporation or sputtering.  
The CVD-based carbon nanowalls are mainly non-polar and are near hydrophobicity due to the absence of oxygen functional groups on the surface. The surface modification is essential because these surface properties are difficult to apply to devices that require contact with liquids. The hummer's method and oxygen plasma are mainly used to modify the surface, both of which destroy the natural properties of the carbon materials. Therefore, we report research and results on surface structure modification-based manipulation of wettability using ITO (indium tin oxide). ITO, one of the TCO (transparent conductive oxide), was utilized to vary the surface structure and area of pristine-CNW as a starting material. Then, we investigated wettability change based on the influence from the ITO-structure deposited on pristine-CNW and the O-H group included in In\({}_{2}\)O\({}_{3}\) and SnO\({}_{2}\) on wettability.