Dissertation, RWTH Aachen University, 2017; Aachen, 1 Online-Ressource (xv, 114 Seiten) : Illustrationen, Diagramme (2018). doi:10.18154/RWTH-2018-00297 = Dissertation, RWTH Aachen University, 2017, Titanium(IV) oxide is one of the most promising materials for environmental and energy applications. Although it is already in application nowadays, still fundamental questions concerning the relation between synthesis conditions, nanostructure, defects and properties remain to be solved. This knowledge is the key to develop new Titanium(IV) oxide materials with tailored properties. This work approaches the problem by detailed investigation of hydrothermally grown rutile Titanium(IV) oxide nanowire arrays before, during and after certain post-growth treatments, namely heating and etching. The emphasis is set on the interplay between nanostructure and optical as well as electrical properties. Advanced transmission electron microscopy is used for a detailed characterization of the Titanium(IV) oxide nanowires and the properties are determined by ultra violet-visible spectroscopy and current-voltage measurements. For the post-growth heat treatment, mainly three heating conditions, which differ in temperature and environment, are conducted. Including the as-grown nanowires, which serve as a reference, four types of nanowires are investigated with respect to the influence of post-growth heat treatments: as-grown nanowires, nanowiresannealed in air at 500 °C, nanowires annealed in nitrogen at 500 °C and nanowires after a heat treatment in vacuum at 1050 °C. In addition, post-growth etching of the nanowire arrays is used, in order to obtain a variety of new one-dimensional morphologies with high surface areas. Due to the hydrothermal growth conditions, the as-grown nanowires are built by a nanofiber bundle and are full of defects, especially oxygen vacancies. Using a heat treatment at 500 °C in air leads to a transformation of the nanofiber bundle to a single crystalline nanowire. In addition, this heat treatment is capable to condense oxygen vacancies in voids, which intersperse the nanowire. The void formation can be observed in situ by transmission electron microscopy and the resulting voids are encapsulated by a Ti3+ rich material. As a result, the optical properties of nanowires after a heat treatment at 500 °C in oxygen improve as the band gap and defect related Urbach absorption are decreased. Furthermore, the removal of oxygen vacancies in the crystal structure converts the intrinsically n-type conducting nanowires to an insulator. Changing the heating environment to nitrogen does not affect the vacancy condensation. However, due to the slightly reducing atmosphere of nitrogen, the surface-near defects do not vanish and a core-shell nanowire, with a single-crystalline core that is full of voids and a Ti3+ rich shell, results. Due to the core-shell structure, the properties are completely changed and the nanowire arrays appear black instead of white and posses a metal-like conductivity. An increase of the annealing temperature to 1050 °C leads to void and defect free Titanium(IV) oxide nanowires. These nanowires show additional faceting at the tip, in order to compensate the free volume. The high temperature requires nanowire arrays grown on Silicon substrates and leads to diffusion of Silicon atoms. Consequently, this heat treatment results in the formation of a core-shell nanowire, but with an insulating, 4 nm thick Silicon(IV) oxide shell. Such a shell is promising for application as it suppresses undesired back-transfer of electrons. Thus, the last two heat treatments lead to nanowires with beneficially changed surfaces. This work is concluded with some synthesis strategies to derive new morphologies for solvothermally grown nanowires, which posses even larger surface areas. Using a combination of solvothermal growth, etching and heat treatment, the synthesis of nanostructures ranging from highly fibrous nanowires, over nanowires with tiny channels to rectangular nanotubes, is enabled., Published by Aachen