Flame synthesis of soot/TiO2 nanoparticle composite films with improved electrical properties characterized by Scanning Probe Microscopy

This paper presents a multiple-mode Scanning Probe Microscopy (SPM) analysis applied for the first time to characterize the electrical and electronic behaviors in flame-synthesized composite films of soot carbon nanoparticles (CNPs) and TiO2 nanoparticles (TNPs). Nanostructured composite films are produced by the combination of flame synthesis and thermophoretic deposition through a two-step procedure. Two flame reactor conditions are selected to synthesize 16 nm CNPs characterized by high graphitization degree, low band gap and high electrical conductivity, and smaller pure anatase TNPs of 3 nm particle size. Porous nanostructured layers of CNPs are then realized on whose surface the smaller TNPs are deposited to form the nanocomposite films. The physicochemical analysis of nanomaterials is performed by Raman spectroscopy, showing interaction phenomena between TNPs and CNPs in the composite films. Two experimental techniques on SPM are used to analyze the electrical and electronic properties of nanostructured composite films. Scanning tunneling spectroscopy (STS) measures a reduction in band gap for the composite nanomaterial compared to pure TNP films. A resistive switching behavior of the composite CNP/TNP films, an increased electrical conductivity and lower power consumptions compared to the pure TNPs during the entire resistive switching are observed by conductive atomic force microscopy (c-AFM) measurements. The c-AFM experimental setup can effectively measure the resistive switching at the nanoscale. It is based on a tip/sample/electrode circuit, which suggests a similarity to modern highly technological devices, such as resistive random-access memory. Those features make this technique suitable to properly characterize the resistive switching performance in films of nanomaterials produced via flame-synthesis for the next-generation of miniaturized memory device systems.