Prof. Michael S. Strano, Charles and Hilda Roddey Associate
Professor of Chemical Engineering, MIT.
Dr. Qing Hua Wang (primary author), Postdoctoral Associate, Department
of Chemical Engineering, MIT.
Corresponding author: firstname.lastname@example.org
In this Thought Leader interview with Will Soutter, Prof. Michael Strano and Dr. Qing Hua Wang talk about their work on graphene, and explain how the properties of the atomically thin layers of carbon depend on what type of material they are placed on.
What made you decide to study graphene?
Graphene has so many interesting and unusual physical properties in
terms of its electronic transport properties, mechanical strength,
thermal conductivity, etc. It's also a purely two-dimensional substance
that makes it unique and different from conventional materials that
have an exterior and a bulk. Because it's only one atomic layer thick,
but can be made into rather large areas, it provides really interesting
opportunities from a materials perspective and from a chemistry
Can you outline the findings of your current research for us?
In our current work, we have found that the chemical properties of
graphene are strongly affected by the substrate on which it rests. That
is, depending on what material the underlying substrate is, the
chemical reactivity on the top side of graphene can change quite
drastically. The reason is that graphene is so thin it is readily
affected by its surroundings. In particular, if there are charged
impurities in the underlying substrate – which we can control by
changing the surface chemistry of the substrate – they can cause
electrons and holes in the graphene to cluster together in the
graphene, forming what are known as electron–hole puddles. Within these
puddles, which can be as small as a few nanometers across or as large
as several hundred nanometers, graphene's local chemical reactivity can
be very high if there a lot of electrons, or very low if there is a
lack of electrons. Once we know this, we can actually make patterns on
the substrate over many square centimeters before graphene is placed
onto it, in order to control the level of electron–hole puddles, and
thus achieve precise spatial control of chemical reactions in graphene.
Figure 1. (A) Large-area
single-layer graphene is transferred onto a substrate that is patterned
in alternating regions of bare SiO2 (pale blue) and
octadecyltrichlorosilane (OTS) (orange), which shields the graphene
from charged impurities in the SiO2 that induced
electron–hole puddles in graphene. (B) After reaction with a diazonium
salt, which forms covalently attached groups on the graphene, the
reaction is strongest in regions where graphene is resting on SiO2.
The reactivity pattern reflects the initial substrate pattern. (C)
Raman spectroscopy is used to map the degree of reaction, which varies
spatially, by tracking the intensity ratio of the D peak and G peak.
The stripes in blue are the low reactivity regions where graphene was
resting on OTS, and the stripes in red are the high reactivity regions
What implications will this have for future graphene research?
Our work and the work of other groups has shown that we must pay
close attention to graphene's surroundings, because materials on top of
and underneath graphene can significantly affect its electronic and
chemical properties. Graphene is not just a single uniform layer; it
can interact in complex ways with its environment. We think this opens
up new areas of research to really take advantage of graphene's
sensitivity towards its surrounding environment.
Are there any applications for graphene in commercial devices
which are made possible by these new findings?
This research is currently aimed at getting a better fundamental
understanding of the chemical properties of graphene, but there are
likely implications for graphene-based biosensing because we can
spatially pattern biomolecules without resorting to harsh methods
involving etching or photolithography. There are also implications for
adding graphene-based coatings to a variety of materials that can be
then chemically functionalized, for instance to make materials
biocompatible or to protect metals from corrosion.
What areas will your research be moving into next?
We have several members of the our group studying graphene, and
we're looking at how different chemical treatments affect the
electronic transport in graphene devices, how the behaviour of bilayer
graphene differs from monolayer graphene under different chemical
treatments, and how graphene and carbon nanotubes interact when brought
into contact with each other. A lot of what we are doing is exploring
the fundamental properties of graphene and other nanomaterials because
there are so many fascinating things to study, but at the same time we
are still engineers and want to find interesting new applications.
Where can people find out more about your work?
Our current results are published in Nature Chemistry, volume 4, pp. 724-732. Our
other publications can be found listed on the Strano group