|Title:||High impermeability and layer-dependent electronic properties of two-dimensional layered materials|
|Advisors:||Chai, Yang (AP)|
Lau, Shu Ping (AP)
|Subject:||Layer structure (Solids)|
Hong Kong Polytechnic University -- Dissertations
|Department:||Department of Applied Physics|
|Pages:||xxviii, 182 pages : color illustrations|
|Abstract:||Two-dimensional (2D) materials provide an ideal platform for studying the fundamental properties of atomic-level thickness system, and motivate a large number of engineering applications in various fields. As the thinnest membrane, graphene has been demonstrated with high impermeability even to the smallest molecule. Another catalog of 2D materials are transition metal dichalocogenides (TMDs) with sizable band gap, which are promising materials for future logical electronic component. Although the properties of group-6 TMDs have been investigated thoroughly, the group-10 TMDs with the richest d electrons remain relatively unexplored. In this thesis, firstly, we show that monolayer graphene can be ultra-thin protection barrier for Ag thin film due to its high impermeability and transparency. We demonstrate high corrosion-resistance of monolayer graphene to gas and liquid. The Tafel analysis illustrates the declined corrosion rate of Ag thin film with the use of graphene protection barrier by about 66 times. Furthermore, monolayer graphene is used to enhance the stability and reproducibility of surface enhanced Raman spectroscopy (SERS). Graphene on top of the Rhodamine 6G (R6G) molecules isolates them from ambient oxygen. Graphene encapsulation greatly enhances the photostability of organic molecules and prevent the photobleaching. Secondly, graphene is inserted between Cu and SiO₂ as a barrier layer. The mass transport mechanism of Cu species through the graphene barrier is systematically investigated by density functional theory (DFT) calculations, second-ion mass spectroscopy (SIMS), capacitance-voltage measurement and cyclic voltammetry. These studies shed the light on controlling the mass transport in solid-state electrolyte devices with graphene layers. Thirdly, a new member of group-10 TMD - platinum disulfide (PtS₂) is studied experimentally and theoretically. The indirect bandgap of PtS₂ dramatically shifts from 1.6 eV (monolayer) to 0.25 eV (bulk samples). The mechanical coupling at the interlayer is almost isotropic. In our studies, we not only study the effect of d-electron number on the interlayer interaction in TMDs, but also demonstrate the exceptionally electronic and vibrational properties of PtS₂. Last, the electronic transport properties of PtSe2 was studied and the layer-dependent semimetal-semiconductor transition is observed with high electron mobility. In conclusion, the mass transport of gas and solid species through graphene has been investigated and it shows great potential for graphene as the impermeable membrane. The group-10 TMDs exhibits unique electronic and vibrational properties and are promising nanomaterials for next generation electronic applications.|
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