[Thesis]. Manchester, UK: The University of Manchester; 2012.
Graphene and monoatomic boron nitride as members of the new class of two dimensional
materials are discussed in this thesis. Since the discovery of graphene in 2004, various
aspects of this one atom thick material have been studied with previously unexpected
results. Out of many outstanding amazing properties of graphene, its elastic properties
are remarkable as graphene can bear strain up to 20% of its actual size without breaking.
This is the record value amongst all known materials. In this work experiments were
conducted to study the mechanical behaviour of graphene under compression and tension.
For this purpose graphene monolayers were prepared on top of polymer (PMMA) substrates.
They were then successfully subjected to uniaxial deformation (tension- compression)
using a micromechanical technique known as cantilever beam analysis. The mechanical
response of graphene was monitored by Raman spectroscopy. A nonlinear behaviour of
the graphene G and 2D Raman bands was observed under uniaxial deformation of the graphene
monolayers. Furthermore the buckling strength of graphene monolayers embedded in the
Polymer was determined. The critical buckling strain as the moment of the final failure
of the graphene was found to be dependent on the size and the geometry of the graphene
monolayer flakes. Classical Euler analysis show that graphene monolayers embedded
in the polymer provide higher values of the critical buckling strain as compared to
the suspended graphene monolayers. From these studies we find that the lateral support
provided by the polymer substrate enhances the buckling strain more than 6 orders
of magnitude as compared to the suspended graphene. This property of bearing stress
more than any other material can be utilized in different applications including graphene
polymer nanocomposites and strain engineering on graphene based devices. The second
part of the thesis focuses on a two dimensional insulator, single layer boron nitride.
These novel two dimensional crystals have been successfully isolated and thoroughly
characterized. Large area boron nitride layers were prepared by mechanical exfoliation
from bulk boron nitride onto an oxidized silicon wafer. For their detection, it is
described that how varying the thickness of SiO2 and using optical filters improves
the low optical contrast of ultrathin boron nitride layers. Raman spectroscopy studies
are presented showing how this technique allows to identify the number of boron nitride
layers. The Raman frequency shift and intensity of the characteristic Raman peak of
boron nitride layers of different thickness was analyzed for this purpose. Monolayer
boron nitride shows an upward shift as compared to the other thicknesses up to bulk
boron nitride. The Raman intensity decreases as the number of boron nitride layers
decreases. Complementary studies have been carried out using atomic force microscopy.
With the achieved results it is now possible to successfully employ ultrathin boron
nitride crystals for precise fabrication of artificial heterostrutures such as graphene-boron