Transporte eletrônico em filmes ultrafinos nanoestruturados : o sistema SNO2:SB

Abstract

This thesis describes a study of the electronic charge transport properties in antimony-doped tin oxide (ATO) ultrathin films, prepared by two different methods: by colloidal deposition process (CDP) and by pulsed electron deposition (PED). In order to determine the ultrathin films electronic transport mechanism properties and to elaborate a model for this mechanism, microstructural analysis and electrical characterization were carried out. The samples were studied by X-ray diffraction (DRX), transmission electron microscopy operating in high resolution (HRTEM), scanning electron microscopy (FEG-SEM), atomic force microscopy (AFM), thermogravimetric analysis (TGA), ellipsometry, electrical resistivity measurements were made using the four-point probe approach from 20 to 300K and Hall effect measurements were made at room temperature. Regarding the CDP, DRX and HRTEM show nanocrystals with the cassiterite phase, highly crystalline nanoparticles and average crystal size of 6.5x4.4 nm. The FEG-SEM and AFM images indicate a crack-free deposition, constant thickness over the substrate cross-section and low roughness. Moreover, the electrical properties evaluation suggest that the experimental data fits the bi-dimensional Mott’s Law and that the electron hopping is in the order of the nanoparticles size. Concerning the PED, DRX indicates only the cassiterite phase structure and a preferential thin film growth at [110] direction, the FEG-SEM and AFM images show a homogeneous deposition and that the thickness is constant over the substrate cross-section, with low roughness. Besides, electrical characterization reveals a metal-semiconductor transition, that the experimental data fits the tridimensional Mott’s Law and that the electron hopping is in the order of the nanoparticles size. Thus, it is proposed that the charge transport mechanism obey the Mott’s Law, which occurs through the nanocrystals surfaces, i.e., the electron hooping occurs at preferential facets where there is Sb segregation.