High-resolution transmission electron microscopy investigation of the nanostructure of nanocrystalline pulsed laser deposition SnO₂ thin films

Pulsed laser deposition (PLD) was used to grow nanocrystalline SnO₂ thin films into glass substrates. The nanocrystallines and microstructure performances of SnO₂ thin films grown by PLD techniques have been shown to be highly sensitive to the deposition conditions. The reactive PLD process was carried out at room temperature under the working pressure of about 2 × 10^-6 mbar. Experimental results indicate the PLD deposition under vacuum is found to produce thin films that are composed of both a polycrystalline SnO₂ phase and an amorphous SnO phase. In particular, the presence of such an amorphous SnO phase in the thin films greatly limits their practical use as gas-sensing devices. High-resolution transmission electron microscopy (HRTEM) observations revealed that the SnO₂ nanocrystallines with tetragonal rutile structure embed in an amorphous SnO matrix, and tend to be in quasi-spherical shape. This quasi-spherical SnO₂ nanocrystalline contains a high density of defects, such as twin boundaries and edge dislocations. The microstructure of the thin films is highly sensitive to their PLD conditions.