Preparation, characterization and electrical properties of fluorine-doped tin dioxide nanocrystals

Fluorine-doped tin dioxide (FTO) nanocrystals were prepared with a sol-gel process followed by a hydrothermal treatment using SnCl(4) and NH(4)F as SnO(2) and fluorine dopant, respectively. The nanostructure and composition were characterized by X-ray diffraction (XRD), transmission electron microscopy (TEM), high-resolution transmission electron microscopy (HRTEM), zeta potential analysis, electrochemical measurement technology and X-ray photoelectron spectroscopy (XPS) respectively. The diameter of the fluorine doped SnO(2) nanocrystal in rutile-type structure is about 10nm. Compared to the pure SnO(2) nanocrystals, the fluorine doped SnO(2) nanocrystals can be dispersed homogeneously in H(2)O, forming transparent sol with high stability. The powder of fluorine doped SnO(2) nanocrystals could be obtained by removing the solvent, and the electrical resistivity properties were measured by a four-point probe measurement. The results show that sheet resistances (Rs) of fluorine doped SnO(2) decrease with the increasing NH(4)F/Sn molar ratio in the range from 0 to 2. However, further increase of NH(4)F/Sn molar ratio from 2 to 5 leads to higher sheet resistance. The F/Sn molar ratio of fluorine doped SnO(2) measured by XPS is about 0.18 when NH(4)F/Sn molar ratio is equal to 2, and the sheet resistance of fluorine doped SnO(2) powder is 110Ω/□.