Speaker
Description
Carbon has been well known as a compelling material to compete with silicon in the field of microchips.
One promising method to fabricate micro- or nanoscale carbon architectures is to pyrolyze a pre-
patterned polymer precursor [1]. Pyrolysis is, therefore, a crucial processing parameter. However, a
mechanistic understanding of the pyrolysis process for sub-micrometer polymer geometries is still
missing. In particular, for the temperature regime, where the highest mass loss and, in turn, the highest
shrinkage is observed, a detailed analysis of the pyrolysis-induced shrinkage kinetics, geometry
dependence shape deformation, and the roles of atmosphere and surface area is still lacking [2].
In this work, we aim to fill this knowledge gap and provide a comprehensive understanding of
morphological deformation upon pyrolysis. Here, we report a systematic study of in situ pyrolysis
process by varying environment pressure, heating temperature, and sample geometry (surface-to-
volume ratio) in an environmental SEM (ESEM). We use direct laser writing of IP-Dip photoresist to
print microstructures directly on MEMS heating chips [3]. We focus on the early stage of carbonization
from 450 to 550 °C, where polymer precursor experiences the greatest mass loss and structural
shrinkage. The structural changes are directly tracked by secondary electron imaging.
We reveal the pyrolysis kinetics illustrating the temporal and temperature dependency of the
deformation. When evaluating the data pool by generating model-free master curves, we fully
describe the dynamic process and extract the effective activation energy (Ea). After changing the
environmental conditions, the shrinkage behavior turns out to be fundamentally different, largely
kinetically hindered. A prevalence of the aspect ratio on kinetics and the final size becomes apparent,
causing a dramatically lower Ea.
To complete the picture of the structural changes during pyrolysis-induced transformation, our
ongoing experiments tackle focused ion beam (FIB) micromachined cross sections of the microstruts
after isothermal exposure using scanning transmission electron microscopy (STEM). Not only
morphological changes can be characterized but also local structural and chemical information by
electron energy loss spectroscopy in 4D-spectrum images (EELS-SI).
In conclusion, our in situ and scale-bridging study paves the way to a thorough understanding of
morphological mechanisms upon pyrolysis and correlated property strengthening. The precise tuning
of functional metamaterials by pyrolysis will facilitate the development of industrially relevant carbon
device fabrication.
| Category | Solid State (Experiment) |
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