| Summary: | 博士 === 國立臺灣大學 === 材料科學與工程學研究所 === 101 === With the rapid advances in nanotechnology, the demand for spatially-resolved nano-characterizations is greatly increasing. Recently, scanning transmission electron microscope (STEM) has gained growing attentions in the investigations of nano-materials owing to its atomic-number sensitivity in the incoherent imaging regime. Most importantly, the capability to combine STEM with various spectroscopies further allows a direct unveiling of the structural and chemical information of a local area without ambiguity.
This Ph. D. thesis has been dedicated to the developments and applications of the advanced STEM spectrum imaging techniques, STEM-EDS (EDS, energy dispersive spectroscopy) and STEM-EELS (EELS, electron energy-loss spectroscopy), and the three-dimensional (3D) STEM tomography.
A general introduction of STEM is presented in Chapter 1 and an overall experimental elucidation is documented in Chapter 2. In Chapters 3 and 4, we show the STEM-EDS and STEM-EELS investigations of the oxide-heterostructure interfaces, (Nd0.35Sr0.65)MnO3/SrTiO3, at atomic resolution. In (Nd0.35Sr0.65)MnO3/SrTiO3, the interface can have two different morphologies, coherent (defect free) and incoherent (misfit dislocations), which were dependent on lattice mismatch of NSMO thin film to STO substrate and the film thickness. In the atomically abrupt NSMO(20 nm)/STO interface, the interdiffusion across the interface was demonstrated by atomic resolved chemical mapping. Further EELS quantification revealed the graded polar discontinuity and a localized two-dimensional electron density at interface. In thicker (40 nm) NSOM film, the edge misfit dislocations with the [100] Burgers vector and A-site deficiency accordingly existed at interface. The dislocation behaves as the charge segregation center, totally undocumented atomic resolution before, and the associated implications were also discussed.
In Chapter 5, we demonstrate the 3D visualizations of silica-supported gold nanocatalyst and the TiO2-nanowires/polymer hybird solar cells using STEM tomography. The size, sharp, and spatial distribution of all these nano-materials can be nicely revealed in the corresponding tomography results with an estimated spatial resolution of slightly better than ~2 nm. Chapter 6 represents the general conclusion of this thesis with a particular focus on the future opportunities of the STEM spectrum imaging and electron tomography.
|
|---|
