Growth of 1D TiO₂ nanostructures on Ti substrates incorporated with residual stress through humid oxidation and their characterizations

Abstract

Different Ti substrates, such as particles (as-received and ball milled), plate and TEM grid were oxidized for the growth of 1D TiO 2 nanostructures. The Ti substrates were oxidized for 4 h at temperatures of 700-750 °C in humid and dry Ar containing 5 ppm of O 2 . The effects of residual stress on the growth of 1D TiO 2 nanostructures were investigated. The residual stress inside the Ti particles was measured by XRD-sin 2 ψ technique. The oxidized Ti substrates were characterized using field emission scanning electron microscope (FESEM) equipped with energy dispersive X-ray (EDX) spectroscope, transmission electron microscope (TEM), X-ray diffractometer (XRD) and Xray photoelectron spectroscope (XPS). Results revealed that humid environment enhances the growth of 1D TiO 2 nanostructures. Four different types of 1D morphologies obtained during humid oxidation, e.g., stacked, ribbon, plateau and lamp-post shaped nanostructures. The presence of residual stress significantly enhances the density and coverage of 1D nanostructures. The as-grown TiO 2 nanostructures possess tetragonal rutile structure having length up to 10 µm along the <1 0 1> directions. During initial stage of oxidation, a TiO 2 layer is first formed on Ti substrate. Lower valence oxides (Ti 3 O 5 , Ti 2 O 3 and TiO) then form underneath the TiO 2 layer and induce stress at the interface of oxide layers. The induced stress plays significant role on the growth of 1D TiO 2 nanostructures. The induced stress is relaxed by creating new surfaces in the form of 1D TiO 2 nanostructures. A diffusion based model is proposed to explain the mechanism of 1D TiO 2 growth during humid oxidation of Ti. The 1D TiO 2 nanostructures and TiO 2 layer is formed by the interstitial diffusion of Ti 4+ ions to the surface and reacts with the surface adsorbed hydroxide ions (OH -). Lower valence oxides are formed at the metal-oxide interface by the reaction between diffused oxygen ions and Ti ions.

Synthesis of ZnO and CuO Nanowires by Thermal Oxidation on Metallic Substrates

“…However, these methods often have associated problems including removal of catalyst and template, multi-steps and complex synthesis procedure, poor adhesion with underlying substrate, less scalability and expensive equipment [38]. Alternatively, thermal oxidation is a simple, single-step and inexpensive route for the formation of metal oxide nanostructures directly on metal substrates [38][39][40][41][42], which is desirable for many in-situ device fabrication processes [40]. In principle, nanowires of metal oxide based arrays synthesized by thermal oxidation can be electrically addressed by the supporting interdigitated electrodes for some applications, such as gas sensor and field emitter [40,43,44].…”

“…In principle, nanowires of metal oxide based arrays synthesized by thermal oxidation can be electrically addressed by the supporting interdigitated electrodes for some applications, such as gas sensor and field emitter [40,43,44]. The resultant nanostructures obtained by thermal oxidation are highly crystalline and pure, which do not require any further treatment [38][39][40][41][42].…”