Self-assembled Nanostructures and ZnO Surface Phenomena studied by Scanning Probe Microscopy and Spectroscopy

• Main Authors: Chu-HongLai, 賴柜宏
• Other Authors: Jung-Chun Huang
• Format: Others
• Language: en_US
• Published: 2010
• Online Access: http://ndltd.ncl.edu.tw/handle/86171955985843599447

博士 === 國立成功大學 === 物理學系碩博士班 === 98 === In this thesis, we have systematically investigated the surface morphological properties of self-assembled nanostructures and electronic structures on the ZnO polar surface. Chapter 1 covers the paper reviews for formation and characterization of nanostructures and surface phenomena on ZnO. The theories and principles of SPM are introduced in Chapter 2, followed by the growth and experimental procedures in chapter 3. The purpose of the first part of this research is to understand the formation self-assembled vicinal surface and morphological effects on magnetic properties of magnetic nanostructures through using the techniques of scanning probe microscopy (SPM). For the second part of this thesis, we applied the electronic probing of SPM to demonstrate the stabilization of ZnO polar planes with surface nano defects. In chapter 4, we described the self-assembly of nanostructures related to the growth process in the heteroepitaxial system. The structure and surface morphology of self-assembled vicinal surfaces (SAVS) of Mo films epitaxially grown on the Al2O3(1 02) substrates have been investigated by reflective high energy electron diffraction and scanning tunneling microscopy. The terrace edges of the Mo(001) SAVS are mainly arranged along [1-10]Mo//[11-20]Al2O3 with a narrow distribution terrace width. The structural analyses show that the formation of the SAVS is due to the tilt growth of Mo(001) plane with respect to the Al2O3(1-102) substrate. By a simple geometric model, the tilt growth and SAVS of Mo(001) can be attributed to the asymmetric lattice mismatch between Mo(001) and Al2O3(1-102) surfaces. On the other hand, we also demonstrated the nano-effects on the characters of self-assembled nanostructures, such as the magnetic properties depending on the surface morphology of ferromagnetic nanoparticles. We study the evolution of morphology and magnetization for the self-assembled Fe nanoparticles. The about 4.5 nm-Fe nanoparticles with out-of-plane magnetization have been grown on the atomically flat Pt(111) buffer layers on the Al2O3 substrate for sample grown at room temperature and annealed up to 200oC. Further annealing procedures at 400oC lead the nanoparticles coalesce into larger ones, meanwhile, the magnetization reorients from out-of-plane to in-plane direction. A theoretical model describing the nanoparticles shape and size dependence of spin-orientation transition is quantitatively in agreement with this observation. Here, we performed a sample route to engineer the spin direction for the magnetic nanoparticles by varying their diameters. In chapter 5, we have investigated the stabilization of the Zn-terminated polar plane via surface defects using the in-situ scanning probe microscopy/spectroscopy. Using middle-energy Ar+ bombardment (2.5 keV) at high temperature (850oC), the O-terminated surface defects including two different morphology of hexagonal cavities and small pits were produced on the (0001)-Zn surface The local electronic structure of O-terminated surface defect shows an upward band-bending with respect to that of the Zn-terminated surface in an agreement with the observation of Kevin probe microscopy, showing a locally reversed electrostatic field on the (0001)-Zn surface for stabilization. Moreover, the pair-distribution of O-terminated pits indicates these small defects on ZnO surface having electrostatic repulsion behavior with one electron charge.