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Title: Optical properties of WS₂ decorated with gold nanoparticles
Authors: Choi, Sin Yuk
Degree: M.Phil.
Issue Date: 2016
Abstract: Since the discovery of graphene, two-dimensional (2D) materials have been extensively studied and shown potential applications in electronic, optical and optoelectronic devices. Atomically thin layers of transition metal dichalcogenides (TMDs) have drawn much attention due to their superb properties compared to graphene. Among TMDs, tungsten disulfide (WS₂) is one of the mostly studied 2D materials due to its fascinating properties. In this project, gold nanoparticles (AuNPs) were used to decorate 2D WS₂ crystals to tune their optical properties. 2D WS₂ was prepared by sulfurization of thin tungsten film which was deposited through the magnetron sputtering system. The surface functionality of atomically-thin WS2 was decorated by various AuNPs. The optical properties of the decorated WS₂ layers were investigated by Raman, photoluminescence (PL) and absorption spectra. Besides, Finite Difference Time-Domain (FDTD)Solutions 8.9 from Lumerical Solutions was adapted to perform the simulated calculation in order to address the enhancement in the AuNPs/WS₂ hybrid system. After decoration, the enhancement of PL was exhibited by increasing the peak intensity and narrowing the peak width. Furthermore, the immersion of HAuCl4-could generate 8-folded PL enhancement comparing to the other two methods. In the comparison of the FDTD calculation, the PL enhancement arises from the arrangement of AuNPs pair. This is due to exciton-plasmon interaction which is highly related to spatial distribution of AuNPs, while the nucleations of Au atoms tend to form into the defective sites on the surface of WS₂. In addition, laser irradiation was employed to increase the number of defects in 2D materials in order to achieve the further enhancement of PL in the AuNPs/WS₂ hybrid system.The decoration of AuNPs makes a change in surface functionality of 2D WS₂ such that it enhances the full width at half maximum (FWHM) of the absorption peaks and gives a slight shift to higher energy regions. These features might provide the possibility to develop potential photonic and energy harvesting applications in 2D materials. In addition, the special design of AuNPs on 2D WS₂ with different sizes, morphologies and spatial distribution would also give an effect, resulting in localized surface plasmon resonance (LSPR) interpreted in terms of surface plasmon enhanced optical properties. It can help to achieve the development for optoelectronic devices on account of the light-to-current conversion.
Subjects: Nanoparticles.
Nanostructured materials.
Hong Kong Polytechnic University -- Dissertations
Pages: 115 pages : color illustrations
Appears in Collections:Thesis

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