Investigation of Germanene, Stanene and Blue Phosphorene-Au Network

Two-dimensional (2D) materials have evoked tremendous attention in fundamental studies and technological applications, inspired by their unique properties ascribed to the symmetry-broken as the thickness decreases down to the single-unit-cell-layer limit. In this thesis, there are four experimental sections of germanene (germanium analogue of graphene), stanene (tin analogue of graphene), blue phosphorene (blueP) (phosphorus analogue of graphene)-Au network, and potassium (K) intercalation in blueP-Au network. The 2D materials formed by adjacent elements are expected to have common and specific natures. Unlike graphene, silicene, formed by group IV element Si, has been extensively investigated with buckled/puckered hexagonal structures due to its varied interatomic distances and sp2/sp3 hybridized states, showing multi-phases and attractive properties like superior compatibility with silicon-based nanotechnology. Germanene, stanene (formed by the heavier group IV elements), and blueP (formed by the adjacent group V element) are also predicted with a variety of exotic properties and potential applications different from graphene and silicene, which is worth planned and in-depth research. Therefore, this thesis aims to achieve systematic studies including the synthesis, characterization, analysis, possible application, and functionalization/intercalation of these materials, in which we gain more insight into 2D materials. It is an important discovery that the Dirac fermions exist in the elemental 2D materials which sit on the semiconducting or conducting substrate. Remarkably, linear Dirac state and semiconducting state lead to distinct optical response as revealed by transient reflection spectroscopy. By using few-layer germanene nanosheets on the Ag(111) substrate as saturable absorber, stable soliton state mode-locking at 1550 nm in a fiber laser cavity is observed. However, as a group VI elemental 2D material similar to germanene, stanene on the Au(111) substrate has no feature of Dirac fermions. Its interesting part is the surface reconstruction with a coverage-dependent structural evolution and the tensile strain evoked by the singular buckled structure. As a group V 2D material, P growing on the Au(111) substrate proved to be blueP-Au network which is expected to be a single atomic layer like germanene and stanene. While, the unique structure of blueP-Au network provides large space in its hollow sites for the K intercalation and deintercalation process induced by an external electric field. And the crystalline structure and electronic properties of BlueP-Au network have been altered to those of free-standing BlueP after K intercalation, by altering the buckled structure and increasing the bandgap.