FLAME SYNTHESIS AND CHARACTERIZATION OF SELF-ASSEMBLED NANOSTRUCTURED FILMS OF TIO2-CARBON NANOPARTICLES

In this work, nanostructured films of flame-formed carbon (CNPs) and TiO2 (TNPs) nanoparticles are produced through a simple procedure based on the flame synthesis of nanoparticles and their deposition by thermophoresis into films. A two-step procedure is used to produce composite TNP-CNP films. First, carbonaceous granular film is produced by thermophoresis-driven self-assembling of CNPs with diameters of about 20 nm. The flame reactor used for the synthesis of CNPs is a laminar premixed flame of ethylene and air operated in fuel-rich conditions. Then, the composite film is produced by the subsequent thermophoretic deposition of anatase TNPs with a mean diameter of 3.5 nm produced in a flame-synthesis system. The electronic properties of TNP-CNP films are characterized by measuring the electronic band gap using the scanning tunneling spectroscopy (STS) technique and comparing these results to UV-vis absorption optical band gaps. Composite of TNPs with CNPs resulted in a decrease of measured band gap of the film (both optical and electronic) and so in an improvement of the electrical conductivity with respect to pure TNPs films. The STS measurements allow also to quantify the band edge energy distribution of the nanomaterials from the distribution of the positions of conduction band and valence band edges.