Relationships between the electrical properties and nanostructure of soot particles in a laminar inverse diffusion flame

This paper studies the electrical properties of the soot particles generated from an n-heptane inverse diffusion flame and the relationship between the electrical properties and the nanostructure. The electrical conductivity of isolated soot particle and work function of soot particles were measured by a PeakForce tunneling atomic force microscopy and a Kelvin-probe force microscopy. The nanostructure of soot particles was evaluated using X-ray diffraction and X-ray photoelectron spectroscopy. Different electrical conductivity distributions were found as the soot particles gradually matured, and at the same time the mean electrical conductivity of soot particles exhibited a nearly exponential increase. There existed a percolation threshold at which the mean electrical conductivity sharply increased by approximately two orders of magnitude. Similarly, the work function of soot particles increased during soot maturation process, which implies that it becomes harder for the electrons to escape from the soot samples. The crystallite width had a positive correlation with the logarithm of electrical conductivity and the work function for soot particles, while the interlayer spacing presented a negative correlation with the logarithm of electrical conductivity and work function. These results suggest that the electrical conductivity and work function can serve as indicators of ordering degree of soot particles. Moreover, the dependence of electrical properties on the nanostructure demonstrates the potential of better controlled flame conditions for producing tailored soot particles for a variety of applications.