ZnO-based nanostructures by PLD: growth mechanism, doping and geometry

The present work covers investigation of the growth mechanism and growth kinetics of the ZnO nanowires and nanoneedles fabricated by using high-pressure pulsed laser deposition. The growth model based on the combination of four different flows of the interfacial particles is introduced. A variation of the free energy is given as a major reason of the change of the growth mechanism which appears by using different doped seed layers, growth temperature and the doping of the deposited material. A fabrication of the ultrathin nanowires with a diameter of d < 10 nm at CMOS compatible growth temperature of T = 400°C is demonstrated. The diameter of these nanowires is comparable with the Bohr radius. The growth of the Al and Ga doped and undoped ZnO nanoneedles with a sharp tip was shown. The doping of the nanowires and nanoneedles can be promising for their applications. By using a patterned sapphire substrate, an unidirectional growth of the nanowires and nanoneedles was achieved. These nanostructures are tilted by 58°ZnO with respect to the surface normal.:Bibliographic Record Contents 1 Introduction I Basics and Methods 2 Basic properties and growth concept 2.1 ZnO nanowires and nanoneedles 2.1.1 Applications 2.2 Nanowire and nanoneedle fabrication 2.2.1 Growth mechanisms which require a catalyst 2.2.2 Catalyst-free epitaxial growth mechanism 2.3 Free energy and the growth mechanism 2.4 NW growth techniques 2.5 Aligned tilted growth 3 Growth and characterization 3.1 Preparation of the seed layers by CVD 3.2 Preparation of the seed layers by low pressure PLD 3.3 HP PLD for the NW and NN growth 3.4 Characterization techniques 3.4.1 X-ray Diffraction 3.4.2 Atomic Force Microscopy 3.4.3 Scanning electron microscopy 3.4.4 Energy Dispersive X-ray Spectroscopy 3.4.5 Spectroscopic Ellipsometry 3.4.6 Cathodoluminescence 3.4.7 Angle-varied X-ray photoelectron spectroscopy 3.4.8 Etching of the seed layers 4 Seed layer characterization 4.1 Doping concentration 4.2 Surface morphology 4.3 Crystalline quality 4.4 Surface polarity 4.5 Summary of the Chapter II NW growth: results 5 NW growth characteristics 5.1 Material free energy and the deposited material parameters 5.2 Growth kinetics 5.3 Summary of the Chapter 6 NW growth on doped seed layers 6.1 Al doped seed layers 6.2 NW growth on Ga doped seed layers 6.3 Optical characteristics of the ZnO NWs 6.4 Summary of the Chapter 7 Growth of ZnO(Al) and ZnO(Ga) NWs 7.1 Al-doped ZnO NWs grown on ZnO(Al) seed layers 7.2 Ga-doped ZnO NWs grown on ZnO(Ga) seed layers 7.3 Summary of the Chapter 8 Growth of tilted ZnO NWs and NNs 8.1 Patterning of the substrates . 8.2 Growth of tilted NNs 8.3 Growth of tilted NWs 8.4 Optical properties of the tilted nanostructures 8.5 Summary of the Chapter 9 Summary and outloock 9.1 Summary 9.2 Outlook Acknowledgements Curriculum Vitae List of own Articles List of own Conference Talks and Posters Reference