2.6. Surface Roughness, Morphology, and Pencil Hardness of Thin-Film Electrodes

The roughness and surface three-dimensional (3D) views of F_Titania and F_COMP were obtained by atomic force microscopy (AFM) (OLS–4500, Olympus, Tokyo, Japan) by scanning each 2 × 2 µm² area. The surface morphologies of F_Titania, F_COMP, F_CNT, F′_CNT, and F″_CNT were observed by field-emission scanning electron microscopy (FE-SEM) using a JSM-6701F microscope (JEOL Ltd., Tokyo, Japan) at an accelerating voltage of 5 kV. The average thickness of the SWCNT bundles of each thin film was calculated from ten randomly selected bundles.

The pencil hardness of F_Titania and F_COMP was evaluated according to the Japanese Industrial Standard (JIS) K5400 by a pencil scratch test using an MJ-PHT pencil hardness meter (Sato Shouji Inc., Kanagawa, Japan) with a 0.75 kg load. The surfaces of the thin-film electrodes were scratched using a pencil (UNI, Mitsubishi Pencil Co., Ltd., Tokyo, Japan) with various hardness values standardized in the hardening order from 6B to 9H.