Speaker：Prof. WU Mingjian
Directly observe the investigated mechanisms in situ at high spatial and time resolution as they occur in the samples was the dream of materials scientists. This has become realistic in broader and more complicated and challenging materials systems in recent decades thanks to the continuous developments and breakthroughs in instruments and methods. In this presentation, I will mainly focus on the application of advanced ex situ and in situ TEM study on elucidating the formation of Bi-rich nano-clusters in annealed Ga(As,Bi) epilayers. Besides that, I will provide an overview of in situ microscopy research currently being carried out at our institute, especially our recent activity in development of novel techniques with the aim to study the electrostatic fields and potentials at nanometer scale in materials  upon external stimulus in situ in the microscope.
III-V-Bi (with Ga(As, Bi) as the prototype) is a unstable material system where many types of atomic ordering and nano-scale microstructures develop due to the inherent instability of the alloy constituents, which are of great interest and potential for semiconductor nanotechnology. Our recent findings that size-homogeneous Bi-rich nano-clusters (NCs) can form spontaneously after rapid thermal annealing (RTA) of Ga(As,Bi) epilayers, open the possibility to create Bi-rich quantum dots-like structures with potential for optoelectronic applications [2,3]. However, a clear insight into the formation mechanism and the dominating effects is still missing, which hinders the predictable optimization of the fabrication processes. We aim to gain such insight by advanced in situ and ex situ TEM observations. In this part, we will present latest results on the direct observation of the formation and growth of the NCs and analysis of the defects structures, which shed light on the mechanisms.