Saturday, June 4, 2011

Introduction to Graphene and Graphene Nanoribbons-Part2

Graphene Production

Graphene was first produced by mechanical exfoliation of graphite. This method provided a small number of high-quality samples for fundamental studies. Later on, several methods have been utilized to synthesize graphene sheets which might be categorized into bottom-up and top-down approaches with carbon-containing molecules and graphite as initial materials, respectively. Cost, throughput, size of sheets, quality of sheets, chemical modification, and compatibility with the commercial chip fabrication process are among the most notable considerations in selecting a method for synthesizing graphene. Some of the groundbreaking efforts in synthesizing graphene are Mechanical exfoliation, Supported growth (thermal decomposition of carbides or epitaxial growth by CVD and wet chemical routes)

· Mechanical exfoliation: (top-down approach)

· Supported growth:

It has been known since the early 1970s that graphene could be grown directly on solid substrates and two different mechanisms can be exploited: the thermal decomposition of carbides or the epitaxial growth of graphene on metallic or metal carbide substrates by chemical vapor deposition of hydrocarbons.

Graphene Nanoribbons (GNRs)

Graphene is a zero-gap semiconductor, so a field effect transistor (FET) will not have an ‘‘off’’ state unless a forbidden gap is created. Such a gap can be produced by confining the electronic wave functions by etching narrow graphene nanoribbons (GNRs) typically of a few nanometers in width and with well-defined crystallographic orientation.

So GNRs are 1D while the Graphene layer is a 2D allotrope of carbon.