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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

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.
what is the Synthesis, properties,and applications of carbon nano chemistry
Abhijith Reply
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
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
in general
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
what is biological synthesis of nanoparticles
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
many many of nanotubes
Porter
what is the k.e before it land
Yasmin
what is the function of carbon nanotubes?
Cesar
I'm interested in nanotube
Uday
what is nanomaterials​ and their applications of sensors.
Ramkumar Reply
what is nano technology
Sravani Reply
what is system testing?
AMJAD
preparation of nanomaterial
Victor Reply
Yes, Nanotechnology has a very fast field of applications and their is always something new to do with it...
Himanshu Reply
good afternoon madam
AMJAD
what is system testing
AMJAD
what is the application of nanotechnology?
Stotaw
In this morden time nanotechnology used in many field . 1-Electronics-manufacturad IC ,RAM,MRAM,solar panel etc 2-Helth and Medical-Nanomedicine,Drug Dilivery for cancer treatment etc 3- Atomobile -MEMS, Coating on car etc. and may other field for details you can check at Google
Azam
anybody can imagine what will be happen after 100 years from now in nano tech world
Prasenjit
after 100 year this will be not nanotechnology maybe this technology name will be change . maybe aftet 100 year . we work on electron lable practically about its properties and behaviour by the different instruments
Azam
name doesn't matter , whatever it will be change... I'm taking about effect on circumstances of the microscopic world
Prasenjit
how hard could it be to apply nanotechnology against viral infections such HIV or Ebola?
Damian
silver nanoparticles could handle the job?
Damian
not now but maybe in future only AgNP maybe any other nanomaterials
Azam
Hello
Uday
I'm interested in Nanotube
Uday
this technology will not going on for the long time , so I'm thinking about femtotechnology 10^-15
Prasenjit
can nanotechnology change the direction of the face of the world
Prasenjit Reply
At high concentrations (>0.01 M), the relation between absorptivity coefficient and absorbance is no longer linear. This is due to the electrostatic interactions between the quantum dots in close proximity. If the concentration of the solution is high, another effect that is seen is the scattering of light from the large number of quantum dots. This assumption only works at low concentrations of the analyte. Presence of stray light.
Ali Reply

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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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