AVS 60th International Symposium and Exhibition
    Helium Ion Microscopy Focus Topic Thursday Sessions
       Session HI-ThP

Paper HI-ThP2
Imaging Nascent Soot Particles: Tiniest Soot Particles are Not Structurally Homogeneous

Thursday, October 31, 2013, 6:00 pm, Room Hall B

Session: Aspects of Helium Ion Microscopy Poster Session
Presenter: S. Lieb, University of Southern California
Authors: M. Schenk, Bielefeld University, Germany
S. Lieb, University of Southern California
H. Vieker, Bielefeld University, Germany
A. Beyer, Bielefeld University, Germany
A. Gölzhäuser, Bielefeld University, Germany
H. Wang, University of Southern California
K. Kohse-Höinghaus, Bielefeld University, Germany
Correspondent: Click to Email
Structural and morphological probing of nascent soot has been a challenging problem historically. Transmission electron microscopy (TEM) shows that mature soot is usually composed of stacks of polycyclic aromatic hydrocarbons arranged in a turbostratic fashion with a certain degree of microscopic crystallinity. Whether this observation can be extrapolated to nascent soot undergoing rapid mass and size growth in a flame remains an open question. In particular, recent studies show converging evidence that nascent soot may have an aromatic core-aliphatic shell structure not seen from previous TEM studies. The aliphatic component in the shell appears to be weakly bound among itself and with the aromatic core. In TEM probing, the possibility of high-energy electron beam damage or structural modification particles also remains an open question. Evidence of this possibility emerged as early as the mid 1980s when Iijima (S. Iijima, J. Electron Microsc, 34 (1985) 249-265) demonstrated the structural instability of gold nanoparticles ~3 nm in diameter under electron beam irradiation in a TEM. Sample damage can arise from electron beam induced chemical bond breaking and/or evaporation of the aliphatic component along with structural change and crystallization of the remaining particle material.

To explore the aforementioned problems and to find more suitable techniques, we report here results of two “softer” microscopic techniques: Helium Ion Microscopy (HIM) and phase imaging Atomic Force Microscope (AFM). In comparison to TEM, both techniques present far less sample damaging during imaging. The present study focuses on the HIM imaging of nanometer-sized soot particles sampled from a stagnation-point ethylene-oxygen-argon flame, under the conditions of Abid et al. (A. D. Abid, Combust.Flame 154 (2008) 775-788).