In recent years, the development of graphene and other two-dimensional (2D) materials, e.g. transition metal dichalcogenides (TMDs), have been experiencing a renaissance since the discovery of graphene. These layered materials play increasingly important roles as building blocks for functional devices, due to their versatile physical and chemical properties that can behave as semimetal, semiconductors, metals or superconductors, according to various band gap. In this thesis, firstly, we demonstrate the successful achievement in controlling synthesis of these 2D materials by chemical vapor deposition (CVD) method and reveal the different physical and chemical properties of them with changeable physical structures. By means of tuning the band gap through different strategies, we...[ Read more ]

In recent years, the development of graphene and other two-dimensional (2D) materials, e.g. transition metal dichalcogenides (TMDs), have been experiencing a renaissance since the discovery of graphene. These layered materials play increasingly important roles as building blocks for functional devices, due to their versatile physical and chemical properties that can behave as semimetal, semiconductors, metals or superconductors, according to various band gap. In this thesis, firstly, we demonstrate the successful achievement in controlling synthesis of these 2D materials by chemical vapor deposition (CVD) method and reveal the different physical and chemical properties of them with changeable physical structures. By means of tuning the band gap through different strategies, we can expand the applications of them to many promising research fields, e.g. electronics, optoelectronics and energy storage. Specifically, the physical and chemical properties of these 2D materials have been effectively tuned through two approached, including chemical functionalization and heterostructures. In the first part, we have systematically researched the chemical activity differences of few layer graphene (including bilayers and trilayers) through a kinetic dominated chemical functionalization with diazounium salts. Along with the experiment, the intrinsic energy band distribution for few layer graphene with varies stacking modes can contribute to the chemical reaction activity differences is proof-of-principle. Outlined by computational calculations with density functional theory (DFT) as roadmaps, according to the amount of electron in graphene valence band (VB) which can be excited to the conduction band (CB) during chemical reaction for graphene with different stacking modes, their chemical reactivity can be sequenced. In addition, in the second part, the band structure of two different TMDs as semiconductors (n-type MoS₂ and p-type MoTe₂) has been rearranged by forming a vertical heterostructure, resulting in the new optoelectronic property different from either of them. The reshaped band structure for the heterostructures provides a different path for the transfer of photo-excited electrons and resulted in a broadband photo-responsive property which is in stark contrast to the optoelectronic properties of these two TMDs. The approaches demonstrated in this thesis can make the 2D materials become attractive candidates for the fabrication of ultrathin technological devices in next generation of functional materials.