PhD, Hong Kong University of Science and Technology
The property of some layered materials such as graphene are thickness dependent. For example, the reduction in thickness of MoS2 from bulk to single layer will lead to a change from indirect semiconductor to direct semiconductor. This will generate a great deal of possibilities in improving applications such as ultra thin field effect transistor, high efficiency water splitting for hydrogen, etc. It is also believed that these two dimensional (2D) materials may be alternative option of Silicon in our future life.
Although the novel properties of 2D materials have been widely proven or confirmed in lab, the realization of 2D materials industrialization just starts. One essential challenge is to fabricate large area and high quality materials. My research topic is aimed to grow high quality monolayer MoS2 with controllable size, morphology by chemical vapor deposition (CVD). This method allows the direct growth of centimeter scale single layer MoS2 and possibilities of tuning the size and morphology to fit a certain application.
Abstract: Hexagonal boron nitride (h-BN), an atomically thin insulating material, shows a large band gap, mechanical flexibility, and optical transparency. It can be stacked with other two-dimensional (2D) materials through van der Waals interactions to form layered heterostructures. These properties promise its application as an insulating layer of novel 2D electronic devices due to its atomically smooth surface with a large band gap. Herein, we demonstrated the ambient-pressure chemical vapour deposition (CVD) growth of high-quality, large-area monolayer h-BN on a Cu(111) thin film deposited on a c-plane sapphire using ammonia borane (BH3NH3) as the feedstock. Highly oriented triangular h-BN grains grow on Cu(111), which finally coalescence to cover the entire Cu surface. Low-energy electron diffraction (LEED) measurements indicated that the hexagonal lattice of the monolayer h-BN is well-oriented along the underlying Cu(111) lattice, thus implying the epitaxial growth of h-BN, which can be applied in various 2D electronic devices.
Pub.: 09 Mar '17, Pinned: 27 Jul '17
Abstract: Non-neutral layered crystals, another group of two-dimensional (2D) materials that lack a well-defined van der Waals (vdWs) gap, are those that form strong chemical bonds in-plane but display weak out-of-plane electrostatic interactions, exhibiting intriguing properties for the bulk counterpart. However, investigation of the properties of their atomically thin counterpart are very rare presumably due to the absence of efficient ways to achieve large-area high-quality 2D crystals. Here, high-mobility atomically thin Bi2O2Se, a typical non-neutral layered crystal without a standard vdWs gap, was synthesized via a facial chemical vapor deposition (CVD) method, showing excellent controllability for thickness, domain size, nucleation site, and crystal-phase evolution. Atomically thin, large single crystals of Bi2O2Se with lateral size up to ∼200 μm and thickness down to a bilayer were obtained. Moreover, optical and electrical properties of the CVD-grown 2D Bi2O2Se crystals were investigated, displaying a size-tunable band gap upon thinning and an ultrahigh Hall mobility of >20000 cm(2) V(-1) s(-1) at 2 K. Our results on the high-mobility 2D Bi2O2Se semiconductor may activate the synthesis and related fundamental research of other non-neutral 2D materials.
Pub.: 12 Apr '17, Pinned: 27 Jul '17
Abstract: Recently there have been many research breakthroughs in two-dimensional (2D) materials including graphene, boron nitride (h-BN), black phosphors (BPs), and transition-metal dichalcogenides (TMDCs). The unique electrical, optical, and thermal properties in 2D materials are associated with their strictly defined low dimensionalities. These materials provide a wide range of basic building blocks for next-generation electronics. The chemical vapor deposition (CVD) technique has shown great promise to generate high-quality TMDC layers with scalable size, controllable thickness, and excellent electronic properties suitable for both technological applications and fundamental sciences. The capability to precisely engineer 2D materials by chemical approaches has also given rise to fascinating new physics, which could lead to exciting new applications. In this Review, we introduce the latest development of TMDC synthesis by CVD approaches and provide further insight for the controllable and reliable synthesis of atomically thin TMDCs. Understanding of the vapor-phase growth mechanism of 2D TMDCs could benefit the formation of complicated heterostructures and novel artificial 2D lattices.
Pub.: 07 Jul '17, Pinned: 27 Jul '17