Morphology and Electronic Properties of Incipient Soot by Scanning Tunneling Microscopy and Spectroscopy

TL;DR

This study uses scanning tunneling microscopy and spectroscopy to analyze the morphology and electronic properties of very early-stage soot particles formed in combustion, revealing their semiconductor nature and nanoscale structure.

Contribution

First high-resolution imaging and spectroscopic analysis of incipient soot particles, providing new insights into their morphology and electronic behavior.

Findings

Incipient soot particles are sub-5 nm in size.

They exhibit semiconductor behavior with a band gap of 1.5 to 2 eV.

Morphology and electronic properties are characterized at atomic resolution.

Abstract

Soot nucleation is one of the most complex and debated steps of the soot formation process in combustion. In this work, we used scanning tunneling microscopy (STM) and spectroscopy (STS) to probe morphological and electronic properties of incipient soot particles formed right behind the flame front of a lightly sooting laminar premixed flame of ethylene and air. Particles were thermophoretically sampled on an atomically flat gold film on a mica substrate. High-resolution STM images of incipient soot particles were obtained for the first time showing the morphology of sub-5 nm incipient soot particles. High-resolution single-particle spectroscopic properties were measured confirming the semiconductor behavior of incipient soot particles with an electronic band gap ranging from 1.5 to 2 eV, consistent with earlier optical and spectroscopic observations.