Dependence of NO2 gas sensitivity of WO3 sputtered films on film density Cheng-ji Jin, Toshinari Yamazaki, Yashuyoshi Shirai, Toshio Yoshizawa, Toshio Kikuta, Noriyuki Nakatani and HumioTakeda Thin Solid Films, 474(1-2), 255-260 (2005). Mar.