Material scientist Yanfeng Zhang from the Department of Materials Science and Engineering and her research team have accomplished synthesis of high-quality centimeter scale uniform graphene on Pt foils. Using a traditional ambient pressure chemical vapor deposition (CVD) method, they found that Pt foils can be a perfect substitute of Cu foils for high-quality graphene growth with larger grain sizes, controllable thicknesses and wonderful in-plane continuity. Moreover, they claimed that graphene on Pt foils presents more flat surfaces than that on Cu foils. Their findings appeared in the November 11 issue of ACS Nano.

Graphene is a flat monolayer of carbon atoms that are tightly packed into a 2D honeycomb lattice. It has ideal structure and excellent elastic, electronic and thermal properties. Its 3D existence is graphite. Graphene was discovered in its full observable and testable form in 2004. Since then, there has been a long-standing interest in its research, because of both its physical properties and potential applications. In October 2010, scientists Andre Geim and Konstantin Novoselov were awarded the 2010 Nobel Prize in physics “for groundbreaking experiments regarding the two-dimensional material graphene”.

As graphene conducts electricity better than any material known to man, its potential application as transparent electrodes is a hot spot for research. For this target, preparation of high-quality graphene that is compatible with silicon-based integrated circuits is essential. Previously, a major breakthrough was made by using a simple chemical vapor deposition method (CVD) to synthesize graphene on Cu foils. However, recent reports reveal that the low carrier mobility related with the ever-present grain boundaries will strongly influence the transport property of CVD graphene on Cu foils.

In this case, Zhang’s group has been seeking other analogue systems as that of graphene on Cu. They chose Pt, a widely used hydrogen carbon catalyst, as the substrate material. Using an ambient pressure CVD method, they accomplished the synthesis of high-quality monolayer graphene on Pt foils. Then, they characterized the graphene’s single-layer nature using Raman spectroscopy in combination with scanning electron microscopy, which examined the graphene in centimeter scales. Thus the macroscopic continuity, the thickness, as well as the defect state of as-grown graphene were revealed. The perfect continuity of CVD graphene on Pt foils was then examined using atomically resolved scanning tunneling microscopy (STM).

“With atomically resolved STM, we are delighted to find that monolayer graphene grows mainly in registry with the symmetries of the underlying Pt facets,” said Zhang, senior author of the paper and member of the Center for Nanochemistry at Peking University. “The hexagonal lattices and striped superstructures were formed, and strangely, they can be connected well at the facet boundaries.”

Of particular importance is that the Pt foils after CVD growth have multifaceted texture, which allows them to explore the substrate crystallography effect on the growth rate and the continuity of graphene, and Pt(111) and Pt(100) facets are detected to be more preferred than other low index facets to serve as the growth substrates.

“We are excited about the findings with Pt foils,” said Teng Gao, a co-first author of the paper and a third-year Ph.D. student in the College of Chemistry and Molecular Engineering. “Not many researchers have done research on Pt substrates, and the findings are intriguing.”

The research findings also show that graphene on Pt foils presents more flat surfaces than that on Cu foils, which implies the formation of extra high-quality graphene even at the as-grown state.

“We believe that graphene on Pt foils provides a perfect prototype for exploring the preliminary growth dynamics of CVD processes,” Zhang said.

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Other authors who contributed to this work include ShubaoXie, Yabo Gao, Mengxi Liu, Yubin Chen and Zhongfan Liu. This work was financially supported by the National Natural Science Foundation of China and the Ministry of Science and Technology of China.

Paper cited:
TengGao, ShubaoXie, YaboGao, Mengxi Liu, Yubin Chen, Yanfeng Zhang,* and Zhongfan Liu,* Growth and Atomic-Scale Characterizations of Graphene on Multifaceted Textured Pt Foils Prepared by Chemical Vapor Deposition, ACS Nano, 5(2011)9194-9201.