Raman spectroscopy for graphene investigation

Graphene comprises one monolayer of carbon atoms packed into a two-dimensional (2D) honeycomb lattice. Graphene has many unique properties that make it an ideal material for fundamental studies as well as for potential applications. Today graphene is being a test bed for examining core quantum mechanics principles, and the basis for development of fundamentally new functional devices, structurally smaller than those relying on conventional metals and semiconductors.

Graphene-based transistors can run at higher frequencies and more efficiently than the silicon transistors
Gas Sensors which are sensitive to a single atom or molecule
Support membranes for transmission electron microscopy
Inert coatings giving objects an atomically thin protective coating which would provide protection against many powerful acids and alkalis

Several approaches have been successfully developed to fabricate graphene. The most common one is when it is formed on a silicon substrate at random, and if the substrate has a certain amount of SiO2 film on it, graphene flakes can be detected by optical microscopy. However, it is difficult to distinguish exactly how many layers each graphene consists of.

A quick and precise method for determining the number of layers of graphene flakes is essential for speeding up the research and exploration of graphene. Although atomic force microscopy (AFM) measurement is the most direct way to identify the number of layers of graphene, the method has a very slow throughput. Raman spectroscopy proves to be the most efficient way to identify different layers of graphene without destroying the crystal lattice.

Raman Mapping of Graphene

With Raman Spectroscopy the number of graphene layers can be distinguished by examining the intensity ratio of G-band and 2D-band – the two well-characterized and understood peaks in the Raman spectra of graphene.

Mapping of a substrate with formed graphene allows visualizing the substrate’s surface according to intensities of graphene Raman lines.

In every part of the world, scientists are experimenting with new ways of fabricating graphene. In major cases, Raman spectroscopy turns to be the only reliable tool to prove the efficiency of a new method. Spectrum of graphene obtained by natural graphite exfoliation is shown in the figure.

The spectrum has explicit peaks (G and 2D bands) at 1580 cm-1 and 2680 cm-1. The spectrum obtained from a film of nanocrystalline graphite deposited by PECVD (Plasma enhanced chemical vapor deposition) method is shown in the figure.

Instrumental Specifications

The size of a typical graphene flake is about 5 microns only (if talking about graphene fabricated via mechanical exfoliation in laboratory conditions), and the easiest way to find graphene flakes and distinguish almost transparent single-layer and bilayer graphene is to do Raman mapping. The process of mapping calls for specific equipment with particular requirements which it shall meet.

Wavelength532 nm
Spectral Range120 cm-1 – 4000 cm-1
Spectral Resolution4-6 cm-1
Spatial resolution1 µm

Raman Microscope RamMics M532® by Enhanced Spectrometry is a truly indispensable tool for various applications and researches. The spatial resolution of 1 µm, spectral resolution 4-6 cm-1, and high efficiency provide precise quality of measurements at shorter acquisition time. Optionally equipped with a motorized sample stage with adjustable step (from 0.36 µm) RamMics M532® allows mapping of large surfaces at the instant quality. RamMics M532® efficiently works on low laser power (tunable) which secures avoiding damaging samples.

Benefits of RamMics M532:

  • Focusing: sample positioning and focusing can be done with a digital camera
  • Continuous performance: precise spectra measurements are achieved at a short acquisition time
  • Easy to use: simple and user-friendly interface of EnSpectr Software for 2D mapping, an automatic procession of data
  • Affordable price:  the cost of a system is remarkably lower compared to similar Raman 2D mapping solutions on the market
  • Safety: no damage to the sample due to low laser power