TEM and X-ray diffraction investigation of the structural characteristics of the microporous oxide film formed on polycrystalline Ti

A New Electrochemical Lithography

“…The fabrication of self-organized anodic titania nanostructures with three-dimensional controllable morphology similar to anodic alumina films [1][2][3] is attracting ever-increasing interest because of the broad applications for nanostructured titania materials in electronic, optoelectronic, photovoltaic, photocatalytic, and biomaterial purposes. So far, the anodization of titanium sheets has been investigated in many studies for electrochemical investigations [4][5][6][7][8][9] and for electrical or dielectric, 10 optoelectronic, 11 and biomaterial applications. [12][13][14] Anodizing titanium in ordinary electrolytes ͑e.g., sulfuric acid͒ at low potentials (Ͻ20 V 4 ) usually produces a thin, compact ͑or a barrier-type͒ titania film several nanometers thick, due to its high insulative and anticorrosive natures.…”

Anodically synthesized titania films for lithium batteries: Effect of titanium substrate and surface treatment

“…Based on data from previous studies [38,40] the thickness of such films is expected to be around 1.0 m. Based on the mass changes and assumptions stated in Sections 3.1 and 3.4 the suggested thickness in the range 1.33-1.89 m is not unrealistic. Equating the mass changes to a mass of titania suggested discharge capacities at the 50th cycle in the range of 35-77 mAh g −1 .…”

“…If the films are hydrated this could result in the formation of HF through reaction with the battery electrolyte and lead to the separation of the large columnar grained upper layer of the film [38]. A general weakness due to the structure of the films [40] is expected with the large columnar grains in the upper layer of the film having a much lower strength than the finer grained underlying layer [40]. This could result in the separation of the upper layer as a result of the stresses generated from continuous volume changes experienced during electrochemical cycling.…”

“…The critical potential at which this occurs does vary with the anodising conditions. Gueneau de Mussy et al [40] reported its occurrence at voltages greater than 80 V during galvanostatic anodising in [41]. The sparking phenomenon is believed to be related to dielectric breakdown of the film [42] and can be accompanied by the forceful expulsion of oxygen from the surface of the electrode.…”

“…The sparking phenomenon is believed to be related to dielectric breakdown of the film [42] and can be accompanied by the forceful expulsion of oxygen from the surface of the electrode. The structure of films anodised under such conditions to 120 V (in sulphuric acid) have been examined via TEM and found to be mainly composed of two different regions parallel to the substrate [40]. A polycrystalline anatase region (300 ± 100 nm) nearest the Ti/TiO 2 interface, composed of 20-80 nm crystals, and a second region composed of columnar grains (80-600 nm crystals) extending to the film surface, of mostly anatase but also some rutile.…”