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Gold-snowflaked graphene makes better electronics

Posted: 04 Nov 2009     Print Version  Bookmark and Share

Keywords:gold graphene research  polymer solution  gold nanostar 

The snowflake-shaped gold nanostar, or SFGN, shows how gold formed on sheets of graphene floating in a solution.

Vikas Berry, Kansas State University's assistant professor of chemical engineering and his research team, revealed that embedding gold on graphene can functionalise it by controlling its electronics properties.

Discovered only five years ago, graphene, a carbon material and only a single atom thick, has captured the attention of a large number of researchers, who are studying its electrical, mechanical and optical properties. Berry's research group is among the few studying the material's interfacial properties and biological applications. "We're entering a new era," Berry said. "From the zero-dimensional or one-dimensional molecular or polymer solutions, we are now venturing into the two-dimensional graphene solutions, which have fascinating new properties."

Berry, along with Kabeer Jasuja, a K-State doctoral student in chemical engineering, placed the graphene oxide sheets in a gold ion solution that had a growth catalyst. Here, the atomically thick sheets swim and bathe in a pool of chemicals. The graphene derivatives act like swimming molecular carpets when in solution and exhibit fascinating physiochemical behaviour. They found that if they changed the surface functionality or the concentration, they could control their properties. They observed that rather than distributing itself evenly over graphene, the gold formed islands on the sheets' surfaces. They named these islands snowflake-shaped gold nanostars or SFGNs.

Berry: We are now venturing into the two-dimensional graphene solutions, which have fascinating new properties.

"We found out that nanostars with no surface functionality are rather challenging to produce by other chemical processes. We can control the size of these nanostars and have characterised the mechanism of nucleation and growth of these nanostructures. It's similar to the mechanism that forms real snowflakes," Berry explained. "If graphene is absent, the gold would clump together and settle down as big chunks. Its presence is critical for the formation of the gold nanostars as graphene helps in stabilising the gold and makes the nanostars more useful for electronic applications.

The discovery of these gold "snowflakes" on graphene also shows promise for biological devices. Berry is attaching DNA to these gold islands to make DNA sensors. These sensors have enhanced sensitivity. He is joined by Nihar Mohanty, a doctoral student in chemical engineering, and undergraduate researcher Ashvin Nagaraja, a senior in electrical engineering. Chemically reducing graphene oxide to obtain graphene requires harsh chemicals that destroy the DNA. Hence, they are using the harsh chemicals on the graphene oxide imbedded with gold. The isolated graphene with gold islands can then be used to functionalises DNA,

Some of the team's other research involves using graphene in conjunction with microwaves. Berry and Jasuja are "cooking" the graphene sheets as another way to produce particles on the material's surface. They are also using modified graphene sheets to compartmentalise a coagulating solution, thus stabilising it. His group has recently used hydrides to reduce graphene oxide to produce reduced graphene oxide in the matter of a few seconds. The graphene produced in this way can remain stable in the solution for several days.

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