Evolution of Glassy Carbon Microstructure: In Situ Transmission Electron Microscopy of the Pyrolysis Process

TL;DR

This study uses in situ high-resolution transmission electron microscopy to directly observe the microstructural evolution of glassy carbon during pyrolysis, revealing dynamic changes in graphene fragment geometry and atomic arrangement.

Contribution

It introduces a novel in situ HR-TEM method for real-time visualization of glassy carbon formation during pyrolysis, providing insights into its microstructural evolution.

Findings

Graphene fragments change geometry and atomic arrangement during pyrolysis.

Intermediate structures offer clues on glassy carbon evolution.

Method minimizes beam damage and sample preparation artifacts.

Abstract

Glassy carbon is a graphene-rich form of elemental carbon obtained from pyrolysis of polymers, which is composed of three-dimensionally arranged, curved graphene fragments alongside fractions of disordered carbon and voids. Pyrolysis encompasses gradual heating of polymers above 900 degree C under inert atmosphere, followed by cooling to room temperature. Here we report on an experimental method to perform in situ high-resolution transmission electron microscopy (HR-TEM) for the direct visualization of microstructural evolution in a pyrolyzing polymer in the 500-1200 degree C temperature range. The results are compared with the existing microstructural models of glassy carbon. Reported experiments are performed at 80 kV acceleration voltage using MEMS-based heating chips as sample substrates to minimize any undesired beam-damage or sample preparation induced transformations. The outcome suggests that the geometry, expansion and atomic arrangement within the resulting graphene fragments constantly change, and that the intermediate structures provide important cues on the evolution of glassy carbon. A complete understanding of the pyrolysis process will allow for a general process tuning specific to the precursor polymer for obtaining glassy carbon with pre-defined properties.