Photoluminescence And Surfaceenhanced Spectroscopy Of Surface-modified ZnO Nanorods

Surface-enhanced spectroscopy is a cutting-edge bio-detection technology integrated nanoscience and advanced optical technology. Noble metal nanoparticles, such as silver(Ag) and golden(Au) nanoparticle, have been widely employed in surface-enhanced fluorescence platform and stimulated intense interest. In the past decade, zinc oxide(Zn O) nanorod(NR) arrays have attracted tremendous attention in the field of bio-detection due to their welldefined alignment, high surface to volume ratio, excellent optical and electrical properties, and good biocompatibility. It has been reported that Zn O nanorod array could also be an excellent surface-enhanced fluorescence(SEF) or surface enhanced Raman spectroscopy(SERS) platform, however, the related mechanisms are still unclear. In particular, by combining with the advantages of different kinds of nanomaterials, surface-modified Zn O nanorods could have much improved performance on surface-enhanced fluorescence, although no such report has been published to date. In addition, SERS of surface-modified Zn O nanorods is also of interest for its considerable scientific value and application potential. In this dissertation, controllable growth of Zn O nanorod arrays and various Zn O-Si O2, Ag-Zn O and Au-Zn O heterostructured Zn O nanorods were realized through various strategies. Photoluminescence(PL) and, especially, SEF and SERS properties of these nanorod arrays were extensively explored. The related mechanisms were proposed and discussed accordingly. The main contents of this thesis are summarized as follows:Controllable growth and PL properties of Zn O NR arrays produced by a seed layer-assisted hydrothermal method have been studied. It has been revealed that the growth conditions have remarkable influence on morphologies, crystalline defects, and the induced PL properties of the Zn O NRs. In particular, annealing or plasma pre-treating influences the density, size and surface defects of particles within the nucleating seed layer, which impacts on the subse quent nanorod growth via sequential reaction with OH- and Zn2+ species. More importantly, oxygen-rich defects at the seed layer surface are deduced to have particular impact–affecting both the c-axis growth rate and the PL properties of the as-grown nanorods; Growth, PL and SEF properties of Zn O-Si O2 heterostructured nanorods have been studied. It has been revealed that the effect of identical silica-coating procedure on the two types of Zn O nanorods(distinct in diameters) are totally dissimilar: transition from nanorods to nanoparticles as well as enhanced near-UV band emission for the thinner samples, while unchanged morphology and significantly enhanced visible-band emission for the thicker type. To explore the underlying mechanisms, PL of bare and Si O2 coated Zn O NRs have been studied extensively. In addition, a new well-defined Zn OSi O2 NR structure, in which the Zn O nanodots(NDs) are neatly packaged inside a Si O2 NR matrix has been proposed, and this novel structure exhibits much enhanced UV emission efficiency and greatly improved stability in solution in comparison with the bare Zn O NR. Furthermore, Zn O-Si O2 core-shell structured NRs have been confirmed to have enhanced SEF properties compared to the as-grown Zn O NRs, and the related underlying mechanism has been discussed.Several metal-Zn O heterostructured NRs have been employed for SEF studies:(1) Zn O NRs/Ag thin film heterostructures have been confirmed to be a new SEF platform with extraordinary capability on SEF, with an enhancement factor as high as 86 times that of Zn O NR arrays on bare Si. The optical properties studies show that the coupling of optical waveguiding properties of Zn O NRs and the mirror reflection of Ag films plays a crucial role in enhanced fluorescence;(2) Au and Ag nanoparticles decorated Zn O nanorods have been proposed as new SEF platforms. By using these platforms, picomolar detection sensitivity of fluorophore molecules has been achieved;(3) Si O2 coating has been demonstrated to further enhance SEF performance of Ag NPs-Zn O NRs. Additionally, Au NPs-Zn O NRs have been revealed not only to serve as SEF platform but also to be an ultra-efficient quencher of fluorophores. The simulation on electric field enhancement factor exhibites that the fluorescence quenching and enhancing depend on the size and distribution of Au particles.Au(Ag) NPs-Zn O NRs have also been investigated on their performance as SERS-active platform to realize high sensitive bio-detection. After systematical studies on SERS properties of the heterostructured NRs by detecting flourescent dye molecules, SERS detection of an individual cell, e.g. human red blood cell, gram positive bacteria staphylococcus aureus and gram negative bacteria escherichia coli has been realized. What’s more, rapid recognization of biological specimens, such as Glucose, Human serum albumin and 3Glypican, has been implemented by using Ag NPs-Zn O NRs as SERS platforms without pre-labeling. Based on the experimental results, finite-difference time-domain method has employed to explore the corresponding SERS mechanisms.