*3.1. Materials*

Tetraethylorthosilicate (TEOS) and Octadecyltrichlorosilane (ODS) were purchased from Sigma Aldrich (St. Louis, MO, USA). Ethanol (99.5%) and nitric acid (69%) were purchased from Wako Pure Chemical Industries Ltd. (Kanto region, Japan). PC substrates (ECK, 100UU) were bought from Sumitomo Bakelite Co. Ltd. (Akita, Japan). The commercially available TiO2 nanoparticle solution (NRC-300C) was purchased from Nippon Soda Co. Ltd. (Tokyo, Japan).
