High-resolution transmission electron microscopy investigation of nanostructures in SnO2 thin films prepared by pulsed laser deposition

Pulsed laser deposition (PLD) was used to grow nanocrystalline SnO2 thin films onto glass substrates. The nanocrystallites and microstructures in SnO2 thin films grown by PLD techniques have been investigated in detail by using X-ray diffraction and high-resolution transmission electron microscopy (HRTEM). The PLD process was carried out at room temperature under a working pressure of about 2x10-6mbar. Experimental results indicate that thin films are composed of a polycrystalline SnO2 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. HRTEM observations revealed that SnO2 nanocrystallites with tetragonal rutile structure embed in an amorphous SnO matrix, which are approximatively equiaxed. These approximatively equiaxed SnO2 nanocrystallites contain a high density of defects, such as twin boundaries and edge dislocations. The grain growth of SnO2 thin films may be discussed in terms of the coalescent particle growth mechanism