A recent article in Small presents a detailed investigation into the mechanisms behind the epitaxial growth of hexagonal boron nitride (hBN) on Ru(0001). Using a combination of density functional theory (DFT) and microkinetic modeling, the researchers focused on the reaction pathways that drive the growth process, paying particular attention to the critical stages leading to hBN formation and the development of nanoporous intermediates.
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Background
The growth of two-dimensional (2D) materials like hBN has received considerable attention due to their unique properties and applications in electronics, photonics, and materials science. To optimize production methods like chemical vapor deposition (CVD), it is essential to understand the chemical and physical mechanisms governing the growth process.
hBN, valued for its exceptional thermal and chemical stability, is a strong candidate for various applications. Its growth on metal substrates like ruthenium (Ru) is particularly appealing for achieving high-quality monolayers. However, this process is influenced by several factors, including substrate temperature, precursor exposure, and the underlying chemical reactions.
Borazine, a boron-nitrogen compound, is commonly used as a precursor for synthesizing hBN. Despite its frequent use, the specific mechanisms governing the adsorption, diffusion, and polymerization of borazine on metal surfaces remain unclear. This study seeks to fill that gap by providing a detailed analysis of these processes, which is essential for developing effective strategies to produce high-quality hBN layers.
The Current Study
To investigate the growth mechanism of hBN, the researchers used a combination of DFT calculations and microkinetic modeling. The DFT calculations explored how borazine interacts with the Ru(0001) surface, focusing on adsorption and reaction pathways. This involved optimizing molecular geometries, evaluating potential energy surfaces, and identifying stable configurations and transition states. Adsorption energies of borazine and its derivatives were calculated to assess their stability on the substrate.
Microkinetic modeling was utilized to simulate the reaction kinetics of the growth process, covering stages such as adsorption, diffusion, deprotonation, dimerization, and polymerization of borazine. Temperature-dependent parameters were incorporated to capture the effects of substrate temperature on reaction rates. By combining DFT results with the kinetic model, the study provides a detailed framework for understanding the epitaxial growth of hBN.
Results and Discussion
The study identifies four critical stages in the growth of hBN on Ru(0001):
- Adsorption and deprotonation of borazine
- Dimerization
- Stability of larger borazine polymers
- Formation of nanoporous intermediates
The adsorption of borazine on the Ru surface was found to be energetically favorable, with a significant energy reduction upon adsorption. Deprotonation emerged as a crucial step, enabling the formation of reactive species that can participate in polymerization reactions.
The microkinetic model showed that the stability of larger borazine polymers depends heavily on substrate temperature and precursor exposure. At higher temperatures, reaction kinetics favor the formation of stable hBN structures, whereas lower temperatures result in the accumulation of intermediate species. The formation of nanoporous intermediates plays a key role in determining the final morphology of the hBN layer.
These findings align well with experimental data, offering a robust explanation for the temperature-dependent behavior of hBN growth. The results highlight the importance of precise control over growth conditions to achieve high-quality monolayers with desired properties.
Conclusion
This study provides a detailed analysis of the epitaxial growth mechanism of hBN on Ru(0001) through DFT calculations and microkinetic modeling. The research identifies key stages in the growth process, emphasizing the significance of borazine deprotonation and the formation of nanoporous intermediates.
The findings underscore how factors like substrate temperature and precursor exposure influence the stability of intermediate species and the final structure of hBN. By advancing the understanding of the chemical pathways involved, this work contributes valuable insights for optimizing the production of high-quality hBN monolayers and supports further advancements in materials science.
Journal Reference
Payne AJR., et al. (2025). Unraveling the epitaxial growth mechanism of hexagonal and nanoporous boron nitride: A first-principles microkinetic model. Small. DOI: 10.1002/smll.202405404, https://onlinelibrary.wiley.com/doi/10.1002/smll.202405404
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