PHYS Ashutosh Rath - Homi Bhabha National Institute

[9]. Specifically, several works have been done using the alloyed nanostructures of
Au viz Au-Si and Au-Ge as catalysts for the growth of Ge and Si nano wires [10-14].
It has been well studied that the phase stability and phase transformation of the
catalyst determine properties such as the growth rate and the structure of the nano
wire [15, 16]. It is therefore natural that the physics and chemistry of these materials
is the current research subject of great interest [17]. This thesis work focuses on the
use of bottom-up nano particle self-assembly techniques to synthesize well tuned Au,
Ge, Au-Si, and Au-Ge alloyed nano structures. Our results suggest that, by varying
the parameters such as temperature and interface conditions, we can form Au-Si and
Au-Ge nano-structures of various shapes and sizes which can be used as catalysts
for growing various crystalline nanowires. The range of the study covers thin film
thickness from as low as 2.0 nm to 50 nm of gold and germanium. The emphasis in
my thesis work is on the use of transmission electron microscopy (TEM) for carrying
out in-situ temperature dependent structural variations in Au and Ge nanostructures
and their respective alloys on silicon and germanium substrate.
The thesis is organized as follows. Chapter one is the introduction to the
thesis and gives a brief overview about the interest in assembling nano particles in
2D and 3D and several methods available in the literature for the same. It also
discusses the importance of these nanostructures with respect to their optical and
catalytic properties and different routes of synthesis of these nanostructures.
Chapter two describes the experimental characterization techniques that have
been consistently used for the depiction of the work. Transmission Electron Microscopy
(TEM), High Resolution TEM (HRTEM), Scanning TEM (STEM), Scanning
electron microscopy (SEM), Electron dispersive x-ray analysis (EDX), Electron
backscattered diffractometry (EBSD), Focused ion beam (FIB) measurement are some
of the techniques which have been extensively used to illustrate the formation of
nanostructures and their properties. Physical vapor deposition method and molecular
beam epitaxy method are used to deposit thin films. The physical principles of
different techniques and their application to understand the various aspects of formation
of the nano/micro structures have been presented. Remaining chapters of
this thesis describe the study of formation of Au and Ge nanostructures and their
respective alloys (Au-Si and Au-Ge alloy).
Various thicknesses of gold thin films were deposited using MBE as well as
thermal evaporation technique. Difference in the temperature dependent behavior of
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