ELECTRICAL CHARACTERIZATION OF CARBONACEOUS PARTICLES COLLECTED FROM PREMIXED LAMINAR FLAMES

The aim of this study is the characterization of combustion-formed particulate matter for possible applications as optoelectronic organic materials. UV-visible absorption spectroscopy analysis has been used to calculate the optical band-gaps of the materials by reporting the optical spectra in the Tauc plot. The I-V characteristics, i.e. current vs. voltage plots, have been measured in order to estimate the electrical conductivity. Three different sampling procedures have been developed. A quartz substrate was rapidly inserted in flame, to collect by thermophoresis the carbon particulate matter, containing two main different classes of materials: soot and nanoparticles of organic carbon (NOC). The first class has a band-gap between 0.1 eV and 0.8 eV and a fair electrical conductivity, while the second class has a band-gap between 1.9 eV and 3 eV and a low electrical conductivity. The optical band-gap was investigated under varying flame conditions (C/O ratio and height above the burner) and residence time of substrate in flame. A probe located in flame and a particles impactor was used to sample NOC separated by total particulate matter. Soluble organic fraction (SOF) was chemically extracted from sampled particulate; electrical characterization showed an unusual presence of a hysteresis in the I quadrant of the I-V characteristic of SOF. Finally by using a theoretical model, obtained from literature, the phenomenon of electrical conduction through a soot particles layer is probably attributed to tunneling effect.