The semiconductor nanowires, especially III-V nanowires have attracted a lot of research attentions in the last decade due to their fascinating properties. They have emerged as building blocks for state-of-art electronic and optoelectronic devices, as well as chemical and biological sensors. Among the various approaches of synthesising nanowires, Au-assisted vapour-liquid-solid (VLS) growth, which was first revealed by Wagner and Ellis in 1964, has become the most prominent one because of its advantages in fabricating epitaxial free-standing nanowires, as well as its versatilities in the control of nanowire dimensions and morphologies. However, there are some longstanding issues that remain challenging in the community, which include understanding the fundamentals of VLS growth mechanism itself.
One of the confronting issues is the controlled VLS growth of ternary III-V nanowires. Many previous studies have shown some structural and compositional complexities within ternary nanowires. In this thesis, cross-sectional transmission electron microscopy (TEM) investigations are involved, in order to understand the growth of ternary InGaAs nanowires. This study reveals a novel phenomenon of phase separation, where binary GaAs nanowire cores may be formed inside InGaAs ternary shells. A comprehensive theory is developed to explain the growth mechanism of the core-shell InGaAs nanowires. Additionally, by taking advantage of the ternary system (where two group-III elements competitively alloying with the Au catalysts), some fresh insights into the fundamentals of VLS mechanism are provided through this unique perspective provided by ternary nanowires. Another key issue that is addressed in this thesis is the zinc blende/wurtzite polymorphism in III-V nanowires. A new theory that can explain wide range of experimental observations is developed in this work. Some insights into the fundamentals of the VLS mechanism are gained with this new theory. Last but not the least, some trivia aspects of III-V nanowires are also addressed through this thesis, which include the last chapter, the study of strains in lattice-mismatched core-shell nanowires.