Theoretical understanding on the formation mechanism of two dimensional materials

Abstract

Since the discovery of graphene, within only one decade, great achievements have been made in the field of two dimensional (2D) materials and the researches on it is still very extensive because of its potential applications in electronic devices, energy harvesting, micro sensors, catalysis and so on. To realize these potential applications in real life and industrial scale, the synthesis of high quality 2D materials in large area at a reasonable cost is a critical step and therefore has attracted great attention. With more than 10 years' efforts, wafer-scale single-crystal monolayer graphene films have been fabricated on metal substrates with the so-called chemical vapor deposition (CVD) method as well as its large scale roll-to-roll production. In contrast to graphene, the techniques of synthesizing other 2D materials is far immature and many great challenges remain.In this thesis, I report my recent studies of two important 2D materials, graphene and phosphorene, focusing on their structural stability and mechanisms regarding their synthesis. Three relative independent studies included in this thesis are: i) the mechanism of the ultrafast CVD growth of large area single crystal graphene on the copper foils with the continuous supply of oxygen. In this study, together with our experimental collaborators, we have revealed a key role of oxygen in graphene CVD growth on Cu surface, that it facilitates the catalytic decomposition of carbon feedstock and therefore enables the ultrafast growth of graphene with the growth rate of ~3 mm/min, which is about two orders magnitude faster than previous record. ii) a global searching to find out the possible phosphorene isomers. In this study, we systematically explored more than 10 phosphorene isomers and have found a few ultra-stable isomers. iii) the potential of growing monolayer phosphorene films with CVD method on metal substrates. In this study, we have carefully explored the stability of four most important phosphorene isomers and studied the possibility of synthesizing them via a CVD method. In contrast to the intuition, we have found that blue phosphorene (BLP), instead of the black one, should be synthesized on most metal surfaces. The black one can be synthesized on Sn surface and the gamma one can be synthesized on Ru(0001) surface. The above studies advance our knowledge of 2D materials' stability and the mechanism of their synthesis greatly and are very helpful for leading the large-scale synthesis of 2D materials in general. The conclusion that the growth of phosphorene is highly substrate dependent can be extended to nearly all 2D materials.