Fig. 3From: Preparation and Application of TiO2 Nanotube Array Gas Sensor for SF6-Insulated Equipment Detection: a ReviewFour kinds of surfaces. a–c The views of (1 0 1) perfect surface. d (1 0 1) defect surface. e–g The views of (0 0 1) perfect surface. h (0 0 1) defect surface. Ti and O atoms are shown in gray and red, respectively. Ti6c, Ti5c, and O2c are marked by arrows, and oxygen vacancy sites are marked by ellipse Back to article page