This article has been reviewed according to Science X's editorial process and policies. Editors have highlighted the following attributes while ensuring the content's credibility: Penn State researchers have refined an atom-scale model of how silicon carbide changes from a solid into vapor during crystal growth, work that could help manufacturers produce higher-quality material for advanced electronics while reducing costly trial-and-error experiments. The study, published in The Journal of Physical Chemistry C, is the first publication from Penn State's Silicon Carbide Innovation Alliance, or SCIA, an industry-university research partnership.
Silicon carbide (SiC) is a crystalline material used in high-power electronics, including electric vehicles and clean-energy systems. As opposed to other crystals, which can be grown by melting the material and then cooling it into a solid, silicon carbide is grown using physical vapor transport (PVT). In this process, solid silicon carbide is heated until it turns directly into vapor, which then settles onto a seed crystal and builds a larger crystal.
Because the process occurs at extreme temperatures inside a closed furnace, researchers cannot easily observe the early stages of sublimation, when a solid changes directly into a vapor without first becoming a liquid, or determine which molecules are present in that vapor. "Due to these extreme conditions, direct in situ experimental observation inside a closed PVT furnace is nearly impossible, leaving a critical gap in our understanding of early-stage sublimation and vapor dynamics," said Yun Kyung Shin, research professor of mechanical engineering at Penn State and lead author of the study. To investigate that hidden process, the team refined ReaxFF, short for reactive force field, a computational method co-invented and developed by Adri van Duin, Evan Pugh University professor of mechanical engineering and corresponding author of the study.
A force field is essentially a set of mathematical rules that calculates how atoms interact. ReaxFF can also simulate chemical reactions, allowing researchers to follow atoms as they move and watch chemical bonds break and form anew over time. ReaxFF itself is not new.
An earlier silicon-carbon force field had been parameterized mainly to study oxidation of SiC. Sublimation involves different chemical pathways, including breaking bonds in the solid and forming vapor species. The researchers therefore reparameterized the force field using an extensive set of quantum mechanical calculations.
The refined model let the researchers follow the different silicon- and carbon-containing molecules that form as silicon carbide heats up and turns into vapor. The results closely agreed with more detailed quantum mechanical calculations, and laboratory experiments supported the prediction that the solid material left behind becomes increasingly rich in carbon. The simulations also showed that the makeup of the vapor changes as the temperature rises.
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