Raman Spectroscopy on Few layer graphene
Abstract
Graphene is a two-dimensional allotrope of carbon exhibiting planer honeycomb lattice
structure.1 A carbon atom in graphene makes three σ-bonds with the neighbouring atoms in the
plane and one π-bond perpendicular to the plane of these carbon atoms. The delocalized electron
due to side overlapping of π-bond in graphene gives high intrinsic carrier mobility. The
maximum carrier mobility of single layer suspended graphene is 200,000 cm2V-1s-1,2 whereas the
maximum carrier mobility of silicon is 1,400 cm2V -1s-1.
3 Hence, graphene is an excellent
substitute for high-frequency FET switch over silicon FET switch. The three σ-bonds (tight
bonds) make graphene the strongest material among all other materials. The free-standing singlelayer graphene shows Young's modulus as high as 1TPa, while that of carbon nanotube is
reported to be around 270-950 GPa.
4 This implies that graphene can be a promising material for
nanoelectromechanical systems (NEMS). The distinct electronic and mechanical properties of
graphene have attracted a lot of attention for developing alternative graphene-based alternative,
which helps address the technical limits of current technologies.
Few layers graphene (FLG) have been studied both theoretical and experimentally.6,7 These
studies show that the number of layers and staking orders of FLG has a strong influence on its
characteristic properties. Hence, identifying the structural differences in FLG is a crucial
requirement in developing FLG-based devices. The characteristic properties of monolayer and
bilayer graphene have been extensively studied. However, there are very few reports on three or
more-layers of graphene. Here, we have focused on identifying and fabricating few layers
graphene (FLG) devices and studying their electrical and optical characteristics. Different
techniques have been reported in the literature for the synthesis of graphene.
Mechanical exfoliation is the method that we have used here. The structural and electronic characteristics of
graphene are studied using Raman spectroscopy.
The thesis is arranged as follows. Chapter 2 explains the fabrication of graphene devices.
Mechanical exfoliation technique used to obtain few layers of graphene flakes and optical
microscopy used to locate graphene flakes is briefly explained. I have described the fabrication
of graphene devices for electrical measurements. The electron-beam lithography method is used
to fabricate these devices. Chapter 3 discusses Raman spectroscopy to identify the number of
layers of graphene flakes. In this section, I have compared peaks up to five layers of graphene
flakes. Also, statistical analysis is performed to obtain the number of layers in the graphene
flakes. Chapter 4 discusses electrical measurements on few layers graphene FET device.
Chapter 5 describes the exfoliation of graphene flakes on flexible substrates and Raman
spectroscopy measurements. Chapter 6 provides the summary of the results