Transmission Electron Microscopy Sample Preparation of Tin Oxide Nanowire Sensor Using Focused Ion-Beam Milling Technique

Transmission electron microscopy (TEM) sample preparation using a focused ion-beam (FIB) milling technique, utilizing a Ga⁺ ion beam at 30 kV, is systematically demonstrated, for the first time, for a nanocrystalline, highly porous indium oxide-doped tin oxide (In-SnO₂) nanowire thin-film gas sensor. The In-SnO₂ nanowires are deposited on a sapphire (Al₂O₃) substrate by a catalyst-assisted heteroepitaxy technique. The subsequent FIB and TEM characterization of the present nanowire thin-film gas sensor show that, under the given processing conditions, an In-SnO₂ nanowire thin film with a thickness of 5-6 µm contains a highly entangled and porous network of nanowires, with a diameter of 100 nm and a nanocrystallite size less than 5 nm. These characteristics of the present In-SnO₂ nanowire thin film are highly suitable for typical gas-sensing applications.