Highlight Lecture (Symp. D01)
Graphene and other two dimensional (2D) materials show great potential for future applications thanks to their extraordinary structural, electronic and optical properties. Recently various methods of graphene synthesis have been developed. In particular, chemical vapor deposition (CVD) and related technologies have given insights to the possibility of large scale application. However, functional devices are still far from realization because of the lack of precise control on all necessary fabrication steps, such as growth, transfer and doping. The final properties of functional materials are strongly influenced by each step of fabrication, therefore controlling and understanding of the atomic arrangement of 2D layers through-out the different processes is crucial. Following the invention of the aberration corrector (AC), transmission electron microscopy (TEM) has become one of the most powerful characterization techniques for atomically thin 2D materials, by providing atomic-scale information at low acceleration voltage. In this work, graphene and related materials for large scale application are studied using AC-TEM based techniques. The evolution of crystallinity during growth was initially probed by Raman spectroscopy in graphene synthesized by a modified CVD growth process. Atomic structure analysis revealed that a peculiar recrystallization of the graphene monolayer was induced, which suggests a new route to achieve high quality graphene for large scale production. Additionally, chemical doping of graphene was also studied for transparent electrode applications. Dopant distribution and atomic arrangement were characterized as a function of doping process, which are then correlated to the electrical properties of graphene measured on large surface. Agglomeration of metal particles and formation of 2D network of dopant on graphene monolayer probed by AC-TEM analysis explained the performance and stability of different doping system. Furthermore, the use of graphene as a substrate for the growth of other 2D materials, in particular transition metal dichalcogenides (TMDs), will be also demonstrated to explore new 2D systems. Finally, our study will underline the interest of atomic scale observation to control large scale 2D materials.