The role of carbon monomers and dimers in graphene growth

We show that the growth kinetics are controlled by a complex interplay between the diffusion of the carbon precursors on the growing graphene islands and their desorption. 
SELECTED FOR THE COVER ISSUE 10 (2018)


F. Presel et al., Nanoscale 10, 7396 (2018)
MBE of graphene
The growth of graphene by molecular beam epitaxy from an elemental carbon precursor is a very promising technique to overcome some of the main limitations of the chemical vapour deposition approach, such as the possibility to synthesize graphene directly on a wide variety of surfaces including semiconductors and insulators. However, while the individual steps of the chemical vapour deposition growth process have been extensively studied for several surfaces, such knowledge is still missing for the case of molecular beam epitaxy, even though it is a key ingredient to optimise its performance and effectiveness. In this work, we have performed a combined experimental and theoretical study comparing the growth rate of the molecular beam epitaxy and chemical vapour deposition processes on the prototypical Ir (111) surface.
The measurements were carried out at the Surface Science Laboratory (Physics Department of the University of Trieste and Elettra) and at the SuperESCA beam line of Elettra. By employing high-resolution fast X-ray photoelectron spectroscopy, we were able to follow the growth of both single- and multi-layer graphene in real time, and to identify the spectroscopic fingerprints of the different C layers.
In addition, by comparing the growth rate of graphene using different growth techniques based on different precursors (chemical vapour deposition and molecular beam epitaxy), we show that in the latter technique there is a tight competition between the diffusion and desorption of the C feedstock on the growing graphene flakes, which is controlled both by the size of the flakes and composition of the feedstock.




 


Our experiments, supported by density functional theory calculations, highlight the role of the interaction between different C precursor species and the growing graphene flakes on the growth rate of graphene. These results provide an overview of the main differences between chemical vapour deposition and molecular beam epitaxy growth and thus on the main parameters which can be tuned to optimise growth conditions, not only on metal surfaces but also on substrates of wider interest for nanoelectronic applications such as semiconductors and insulators.


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Graphene growth by molecular beam epitaxy: an interplay between desorption, diffusion and intercalation of elemental C species on the islands
Francesco Presel, Holly Tetlow, Luca Bignardi, Paolo Lacovig, Cristian Tache, Silvano Lizzit, Lev Kantorovich and Alessandro Baraldi
Nanoscale 10, 7396 (2018)


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