Saturday, September 13, 2014

Scientists Come up with ALD Technique to Repair Atom-sized Graphene Defects

As reported by The Korea Bizwire: Ulsan National Institute of Science and Technology said on September 10 that its College of Natural Sciences professor Kim Kwanpyo, jointly with Lee Han-Bo-Ram (Incheon National University), and Zhenan Bao and Stacey F. Bent (Stanford University), succeeded in developing a technique to repair graphene’s line defects by selectively depositing metal.

Graphene is pure carbon in the form of a very thin, nearly transparent sheet, one atom thick, with excellent mechanical, electrical properties. In order to apply graphene to photovoltaic cells, displays, or sensors, it must be made in large scale.

But graphene tended to crack and produce boundary lines, making it difficult to maintain excellent material properties. To address this problem, there have been attempts to deposit metal on graphene surface, which was not effective as the metal deposition was not selective enough to defective parts.

By using platinum, the research team successfully demonstrated the selective deposition of metal at chemical vapor deposited graphene’s line defects, notably grain boundaries, by atomic layer deposition. As a result, the team proved three times improved electrode and hydrogen gas sensors at room temperature. The research outcome was reported on the September 2 issue of Nature Communications (see abstract below).

Kim Kwanpyo, the principal author, said, “We used platinum in the latest experiment. But other metals such as gold and silver may be used in subsequent experiments to repair graphene defects and the applications may be expanded to other areas.”

Kwanpyo Kim, Han-Bo-Ram Lee, Richard W. Johnson, Jukka T. Tanskanen, Nan Liu, Myung-Gil Kim, Changhyun Pang, Chiyui Ahn, Stacey F. Bent, & Zhenan Bao
One-dimensional defects in graphene have a strong influence on its physical properties, such as electrical charge transport and mechanical strength. With enhanced chemical reactivity, such defects may also allow us to selectively functionalize the material and systematically tune the properties of graphene. Here we demonstrate the selective deposition of metal at chemical vapour deposited graphene’s line defects, notably grain boundaries, by atomic layer deposition. Atomic layer deposition allows us to deposit ​Pt predominantly on graphene’s grain boundaries, folds and cracks due to the enhanced chemical reactivity of these line defects, which is directly confirmed by transmission electron microscopy imaging. The selective functionalization of graphene defect sites, together with the nanowire morphology of deposited ​Pt, yields a superior platform for sensing applications. Using ​Pt–graphene hybrid structures, we demonstrate high-performance hydrogen gas sensors at room temperature and show its advantages over other evaporative ​Pt deposition methods, in which ​Pt decorates the graphene surface non-selectively.
Selective ​Pt growth by ALD on one-dimensional defect sites of polycrystalline CVD graphene.

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