Cornell Researchers Link Quality of Graphene to Size and Boundary of “Patches”

By Will SoutterJun 2 2012

Researchers at the Cornell Center for Materials Research claim that the electrical properties of graphene depend on how well the crystals of graphene are sewn together. Cornell researchers led by Assistant Professor Jiwoong Park at Cornell for Nanoscale science made use of advanced imaging and measurement techniques to validate their claim.

Graphene consists of a layer of carbon atoms. It is polycrystalline in structure and is grown through chemical vapor deposition process in which small crystals of carbon are deposited at random orientations and allowed to grow on their own and they eventually unite in carbon-carbon bonds. Scientists have always considered the size of these crystals to be the determining factor of graphene’s electrical properties. Material scientists have worked extensively to optimize the properties on the basis of this consideration. Even the earlier work done at Cornell attempted to improve the properties by growing larger crystals of graphene. It was during this study that Cornell group related graphene sheets to quilts with the patches being represented by the orientation of each set of grains. The group used an electron microscope to study the image.

The recent study questions the basis of the previous considerations by comparing the electrical properties of graphene crystals grown at different rates. The observation was that the crystals that grew faster were knitted tightly together and crystals that grew slowly resulted in bigger patches that were loosely bound. The tightly bound grains showed improved performance. Another important aspect of the study is the technique the team used to study the graphene. They used fellow researcher Adam Tsen’s four-step lithography process to measure the electrical properties of graphene by placing an electrode on a 10 nm membrane substrate. This paves the way for measurement of atomically thin materials.