Imaging nanocarbon materials: soot particles in flames are not structurally homogeneous

Area of Science:

• Materials Science
• Nanotechnology
• Chemical Engineering

Background:

• Soot particle formation is a critical process in combustion and atmospheric chemistry.
• Previous studies using transmission electron microscopy (TEM) had limitations in resolving nascent soot morphology.
• Understanding soot nanostructure is vital for controlling emissions and improving combustion efficiency.

Purpose of the Study:

• To introduce and evaluate helium-ion microscopy (HIM) for imaging nascent soot particles.
• To compare the capabilities of HIM with existing microscopy techniques for soot analysis.
• To investigate the morphology and structural inhomogeneity of the smallest soot particles.

Main Methods:

• Application of helium-ion microscopy (HIM) to probe nascent soot particles.
• High-contrast imaging to achieve improved surface sensitivity.
• Analysis of particle size, shape, and surface details down to nanometer scales.

Main Results:

• HIM provides significantly higher contrast and surface sensitivity for carbonaceous materials compared to SEM and TEM.
• Nascent soot particles as small as 2 nm were clearly detected, with surface details visible down to 5 nm.
• The study revealed that nascent soot is structurally and chemically inhomogeneous.
• Even the smallest soot particles exhibited non-spherical shapes, deviating from ideal spheres.

Conclusions:

• Helium-ion microscopy (HIM) is an ideal technique for rapid and reliable characterization of nascent soot morphology.
• HIM enables the unambiguous recognition of smaller nascent soot particles than previously possible.
• The findings highlight the complex nanostructure of nascent soot, with implications for combustion and aerosol science.