Wang Juan = 納米金顆粒與氧化鋁複合物薄膜光學吸收譜中的尺寸和濃度效應 / 王娟. / Thesis (M.Phil.)--Chinese University of Hong Kong, 2004. / Includes bibliographical references (leaves 55-58). / Text in English; abstracts in English and Chinese. / Wang Juan = Na mi jin ke li yu yang hua lv fu he wu bo mo guang xue xi shou pu zhong de chi cun he nong du xiao ying / Wang Juan. / Abstract --- p.i / 摘要 --- p.ii / Acknowledgment --- p.iii / Table of contents --- p.iv / List of Figures --- p.vii / List of Tables --- p.ix / Chapter CHAPTER 1: --- Introduction --- p.1 / Chapter CHAPTER 2: --- Background --- p.3 / Chapter 2.1 --- Optical response of metal-particle/matrix composite system in an electronic field --- p.3 / Chapter 2.1.1 --- The concept of plasmon and the dielectric function of metal particle --- p.3 / Chapter 2.1.2 --- The concept of surface plasmon resonance --- p.4 / Chapter 2.2 --- The theories describing the optical absorption properties of metal particle/matrix composite system --- p.5 / Chapter 2.2.1 --- The Mie theory --- p.5 / Chapter 2.2.2 --- The Maxwell-Garnett (M.G.) effective medium theory --- p.6 / Chapter 2.3 --- Previous experimental works in the field --- p.7 / Chapter CHAPTER 3: --- Experimental and instrumentation --- p.8 / Chapter 3.1 --- Fabrication of the Au-nanoparticle /A12O3-matrix composite thin films --- p.11 / Chapter 3.1.1 --- Sputtering techniques and radio-frequency magnetron sputtering --- p.11 / Chapter 3.1.2 --- Experimental set up and the deposition process --- p.13 / Chapter 3.2 --- The chemical and structural characterizations of the films --- p.14 / Chapter 3.2.1 --- X-ray Photoelectron Spectroscopy (XPS) --- p.14 / Chapter 3.2.2 --- X-ray Diffraction (XRD) --- p.15 / Chapter 3.2.3 --- Transmission Electron Microscopy (TEM) --- p.17 / Chapter 3.3 --- The optical absorption measurement: UV spectrometer --- p.21 / Chapter CHAPTER 4: --- Results and discussions --- p.23 / Chapter 4.1 --- General description of the as-prepared samples --- p.23 / Chapter 4.1.1 --- Chemical composition of the films --- p.23 / Chapter 4.1.2 --- General microstructure of the films and the relationship between the deposition parameters --- p.25 / Chapter 4.2 --- The optical absorption: relationship between the SPR absorption and the microstructure --- p.27 / Chapter 4.2.1 --- The shifting of the surface plasmon resonance --- p.27 / Chapter 4.2.1.1 --- The size effect on the SPR frequency shifting --- p.27 / Chapter 4.2.1.2 --- The concentration effect on the SPR frequency shifting --- p.42 / Chapter 4.2.2 --- The broadening of the surface plasmon resonance: size dependence of the relaxation time of free electrons --- p.51 / Chapter CHAPTER 5: --- Conclusions --- p.53 / Appendix --- p.54 / Reference --- p.55

Optical properties of graphene/GaN hybrid structure were investigated by using a variety of optical spectroscopy techniques including low-temperature photoluminescence (PL) spectroscopy, time-resolved PL (TRPL) spectroscopy, confocal scanning micro-Raman spectroscopy. Single-layer graphene grown by chemical vapor deposition was transferred to GaN epilayer surface, which is verified by the Raman spectrum with a sharp characteristic peak at ~2690 cm-1and a homogeneous Raman image. Three main band-edge emissions including the free exciton A transition (denoted as FXA), the donor bound exciton transition (denoted as DX) and the third peak (denoted as Ix) were well resolved in the PL spectra of the hybrid structure as well as the as-grown GaN epilayer at low temperatures. Interestingly, the FXA transition and Ix line of the GaN epilayer were found to be dramatically altered by the top graphene layer while the DX is almost unaffected. The intensity of Ix line substantially drops after the transfer of graphene layer on GaN, indicating surface defect nature of the Ix line. More interestingly, an unpredictable dip structure develops in the FXA peak when the temperature is beyond 50 K. Similar spectral structure change also occurred in the emission of free exciton B (referred as FXB)with higher transition energy .A free exciton dissociation and electron transfer model was proposed to explain the “dip effect”. More supporting evidence to the model was found in the time-resolved PL spectra of the hybrid structure and the control sample. The results showed the significant influence of graphene monolayer on the fundamental optical properties of GaN. / published_or_final_version / Physics / Master / Master of Philosophy

published_or_final_version / abstract / toc / Physics / Doctoral / Doctor of Philosophy

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Ultra high molecular weight polyethylene has been commonly used as a biomaterial for hip and knee implants. This thesis concerns optical and three phase morphology of nano composites of ultra high molecular weight polyethylene (UHMWPE) with Mg0.15Ni0.15Zn0.70Fe2O3 using analytical techniques such as UV-visible spectroscopy and Raman spectroscopy. Muller matrix spectro-polarimeter has been used to study the absorption behavior over the visible spectral range i.e. 400-800 nm. The results show significant changes in the absorption behavior of UHMWPE/Zn nano ferrite samples. To analyze these changes in pure and UHMWPE/Zn-nano ferrite composites, the Urbach edge method was used for the calculation of optical activation energy. Moreover, direct and indirect energy band gaps, and the number of carbon atoms in C=C unsaturation have been evaluated by using the modified Urbach formula and Tauc’s equation, respectively. The results show that the optical activation energy decreases more with the addition of 2wt% Mg0.15Ni0.15Zn0.70Fe2O3 than 1wt% of Mg0.15Ni0.15Zn0.70Fe2O3. The values of direct and indirect energy band gaps are also found to decrease more with 2wt% of Mg0.15Ni0.15Zn0.70Fe2O3. Furthermore, indirect energy gaps are found to have lower values as compared to direct energy gaps. The numbers of carbon atoms in clusters determined from modified Tauc’s equation were approximately the same for 1wt% and 2 wt% of Mg0.15Ni0.15Zn0.70Fe2O3 but differ for pure UHMWPE. The degree of crystallinity obtained from Raman spectroscopy was 42%, 43%, and 42% for UHMWPE, UHMWPE+1% of Mg0.15Ni0.15Zn0.70Fe2O3, and UHMWPE+2% of Mg0.15Ni0.15Zn0.70Fe2O3, respectively, i.e. about the same, but the relative amount of interphase and amorphous regions varied. Optical activation and sub band gap energies can be estimated for utilization of this composite in applications such as optical sensors, solar cells etc.

published_or_final_version / abstract / Physics / Master / Master of Philosophy

Optical and electrical properties of solids have a close relationship with their dimensionalities. In this thesis, optical properties of several direct bandgap materials with different dimensionalities were investigated in detail. In three dimensional bulk zinc oxide (ZnO) single crystal, two electron satellite transition (TES) was examined in terms of a radiative Auger effect. On the basis of experimental spectral data, a model was proposed to interpret temperature dependence of its integrated intensity. Meanwhile, the phonon coupling with various excitonic transitions were discussed as a function of temperature in bulk ZnO single crystals. Being as a new family of two dimensional materials, monolayers of transition metal dichalcogenides (TMDCs) have received an increasing research interest in the past few years because they have been proved to be direct bandgap semiconductors. Light emission properties of tungsten sulfide (WS2) monolayers were characterized by using excitation power dependent photoluminescence (PL) technique. Two kinds of emission mechanisms, namely band-edge free excitonic transition and localized-states ensemble emission, were revealed in WS2 monolayers. Meanwhile, PL and Raman mapping for WS2 monolayers were conducted. It was found the relative intensity of inter-plane vibration mode with respect to in-plane mode is critical for monolayer identification with Raman spectroscopic technique and PL mapping can yield more information on the uniformity and quality of the samples. In the third part of this degree research, various low dimensional nanostructures of WS2, ZnO and GaN were studied. WS2 nanotubes were found to show interesting Raman light scattering features, while ZnO nanorods prepared by vapor phase transport method were revealed to have distinctive light emission properties. Finally, by focused ion beam milling, GaN and ZnO nano-array were fabricated. Surface vibration mode was firmly demonstrated to exist in these nanostructures with optical studies and theoretical analysis. / published_or_final_version / Physics / Doctoral / Doctor of Philosophy