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Raman spectroscopy is a powerful and easy tool, and can be used to identify the number of layers and structure of graphene.

Introduction

Graphene is a quasi-two-dimensional material, which comprises layers of carbon atoms arranged in six-member rings ( [link] ). Since being discovered by Andre Geim and co-wokers at the University of Manchester, graphene has become one of the most exciting topics of research because of its distinctive band structure and physical properties, such as the observation of a quantum hall effect at room temperature, a tunable band gap, and a high carrier mobility.

Idealized structure of a single graphene sheet. Copyright: Chris Ewels ( (External Link) ).

Graphene can be characterized by many techniques including atomic force microscopy (AFM), transmission electron microscopy (TEM) and Raman spectroscopy. AFM can be used to determine the number of the layers of the graphene, and TEM images can show the structure and morphology of the graphene sheets. In many ways, however, Raman spectroscopy is a much more important tool for the characterization of graphene. First of all, Raman spectroscopy is a simple tool and requires little sample preparation. What’s more, Raman spectroscopy can not only be used to determine the number of layers, but also can identify if the structure of graphene is perfect, and if nitrogen, hydrogen or other fuctionalization is successful.

Raman spectrum of graphene

While Raman spectroscopy is a useful technique for characterizing sp 2 and sp 3 hybridized carbon atoms, including those in graphite, fullerenes, carbon nanotubes, and graphene. Single, double, and multi-layer graphenes have also been differentiated by their Raman fingerprints.

[link] shows a typical Raman spectrum of N-doped single-layer graphene. The D-mode, appears at approximately 1350 cm-1, and the G-mode appears at approximately 1583 cm -1 . The other Raman modes are at 1620 cm -1 (D’- mode), 2680 cm -1 (2D-mode), and 2947 cm -1 (D+G-mode).

Raman spectrum with a 514.5 nm excitation laser wavelength of N-doped single-layer graphene.

The g-band

The G-mode is at about 1583 cm -1 , and is due to E2g mode at the Γ-point. G-band arises from the stretching of the C-C bond in graphitic materials, and is common to all sp 2 carbon systems. The G-band is highly sensitive to strain effects in sp 2 system, and thus can be used to probe modification on the flat surface of graphene.

Disorder-induced d- band and d’- band

The D-mode is caused by disordered structure of graphene. The presence of disorder in sp 2 -hybridized carbon systems results in resonance Raman spectra, and thus makes Raman spectroscopy one of the most sensitive techniques to characterize disorder in sp 2 carbon materials. As is shown by a comparison of [link] and [link] , there is no D peak in the Raman spectra of graphene with a perfect structure.

Raman spectrum with a 514.5 nm excitation laser wavelengthof pristine single-layer graphene.

If there are some randomly distributed impurities or surface charges in the graphene, the G-peak can split into two peaks, G-peak (1583 cm -1 ) and D’-peak (1620 cm -1 ). The main reason is that the localized vibrational modes of the impurities can interact with the extended phonon modes of graphene resulting in the observed splitting.

The 2d-band

All kinds of sp 2 carbon materials exhibit a strong peak in the range 2500 - 2800 cm -1 in the Raman spectra. Combined with the G-band, this spectrum is a Raman signature of graphitic sp 2 materials and is called 2D-band. 2D-band is a second-order two-phonon process and exhibits a strong frequency dependence on the excitation laser energy.

What’s more, the 2D band can be used to determine the number of layer of graphene. This is mainly because in the multi-layer graphene, the shape of 2D band is pretty much different from that in the single-layer graphene. As shown in [link] , the 2D band in the single-layer graphene is much more intense and sharper as compared to the 2D band in multi-layer graphene.

Raman spectrum with a 514.5 nm excitation laser wavelength of pristine single-layer and multi-layer graphene.

Bibliography

  • G. G. Chen, P. Joshi, S. Tadigadapa, and P. C. Eklund, Nano Lett. , 2006, 6 , 2667.
  • C. Ferrari, J. C. Meyer, V. Scardaci, C. Casiraghi, M. Lazzeri, F. Mauri, S. Piscanec, D. Jiang, K. S. Novoselov, and S. Roth, A. K. Geim, Phys. Rev. Lett. , 2006, 97 , 187401.
  • M. A. Pimenta, G. Dresselhaus, M. S. Dresselhaus, L. A.Cancado, A. Jorio, and R. Sato, Phys. Chem. Chem. Phys. , 2007, 9 , 1276.

Questions & Answers

what does nano mean?
Anassong Reply
nano basically means 10^(-9). nanometer is a unit to measure length.
Bharti
do you think it's worthwhile in the long term to study the effects and possibilities of nanotechnology on viral treatment?
Damian Reply
absolutely yes
Daniel
how to know photocatalytic properties of tio2 nanoparticles...what to do now
Akash Reply
it is a goid question and i want to know the answer as well
Maciej
characteristics of micro business
Abigail
for teaching engĺish at school how nano technology help us
Anassong
Do somebody tell me a best nano engineering book for beginners?
s. Reply
what is fullerene does it is used to make bukky balls
Devang Reply
are you nano engineer ?
s.
fullerene is a bucky ball aka Carbon 60 molecule. It was name by the architect Fuller. He design the geodesic dome. it resembles a soccer ball.
Tarell
what is the actual application of fullerenes nowadays?
Damian
That is a great question Damian. best way to answer that question is to Google it. there are hundreds of applications for buck minister fullerenes, from medical to aerospace. you can also find plenty of research papers that will give you great detail on the potential applications of fullerenes.
Tarell
what is the Synthesis, properties,and applications of carbon nano chemistry
Abhijith Reply
Mostly, they use nano carbon for electronics and for materials to be strengthened.
Virgil
is Bucky paper clear?
CYNTHIA
so some one know about replacing silicon atom with phosphorous in semiconductors device?
s. Reply
Yeah, it is a pain to say the least. You basically have to heat the substarte up to around 1000 degrees celcius then pass phosphene gas over top of it, which is explosive and toxic by the way, under very low pressure.
Harper
Do you know which machine is used to that process?
s.
how to fabricate graphene ink ?
SUYASH Reply
for screen printed electrodes ?
SUYASH
What is lattice structure?
s. Reply
of graphene you mean?
Ebrahim
or in general
Ebrahim
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s.
Graphene has a hexagonal structure
tahir
On having this app for quite a bit time, Haven't realised there's a chat room in it.
Cied
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Sanket Reply
what's the easiest and fastest way to the synthesize AgNP?
Damian Reply
China
Cied
types of nano material
abeetha Reply
I start with an easy one. carbon nanotubes woven into a long filament like a string
Porter
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Porter
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Yasmin
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Cesar
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Uday
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Ramkumar Reply
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AMJAD
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how to synthesize TiO2 nanoparticles by chemical methods
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Source:  OpenStax, Nanomaterials and nanotechnology. OpenStax CNX. May 07, 2014 Download for free at http://legacy.cnx.org/content/col10700/1.13
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