Band gap structure modification of amorphous anodic Al oxide film by Ti-alloying

Abstract

The band structure of pure and Ti-alloyed anodic aluminum oxide has been examined as a function of Ti concentration varying from 2 to 20 at. %. The band gap energy of Ti-alloyed anodic Al oxide decreases with increasing Ti concentration. X-ray absorption spectroscopy reveals that Ti atoms are not located in a TiO2 unit in the oxide layer, but rather in a mixed Ti-Al oxide layer. The optical band gap energy of the anodic oxide layers was determined by vacuum ultraviolet spectroscopy in the energy range from 4.1 to 9.2 eV (300–135 nm). The results indicate that amorphous anodic Al2O3 has a direct band gap of 7.3 eV, which is about ∼1.4 eV lower than its crystalline counterpart (single-crystal Al2O3). Upon Ti-alloying, extra bands appear within the band gap of amorphous Al2O3, mainly caused by Ti 3d orbitals localized at the Ti site.

New Method for the Development of Plasmonic Metal-Semiconductor Interface Layer: Polymer Composites with Reduced Energy Band Gap

“…It is clear that the sample incorporated with 5 wt.% of alumina exhibits smallest band gap of 1.4 eV. Earlier studies revealed that the wide optical band gap of materials can be significantly tuned by incorporating nanoparticles [14,19,31]. Canulescu et al successfully reduced the optical band gap of Al 2 O 3 from 7.3 eV to 6.2 eV by incorporating 20 wt.% of titanium (Ti) atoms to the structure [19].…”

“…However, this phenomenon may be beneficial for the preparation of polymer nanocomposites with small optical band gaps [14]. Alumina (Al 2 O 3 ) has recently received considerable attention in materials science because it is key material in many applications, such as metal-oxide semiconductor devices, dye-sensitized solar cells, and corrosion protection [19]. It is reported that properties of the aluminabased nanocomposites with the transition metals are shown to be improved in comparison to their bulk counterpart.…”

Band gap tuning of amorphous Al oxides by Zr alloying

“…Several studies were dedicated to understanding the electronic properties and changes in the band gap of amorphous anodic Al 2 O 3 upon alloying. [3][4][5] Theoretical studies based on density functional theory have shown that transition metal atoms, such as Zr atoms present in Al sites, introduce localized d-electron states below the conduction band (CB) of Al 2 O 3 . 6 Experimental determination of the band gap energy of Zr-alloyed Al 2 O 3 is not readily available because ultraviolet and visible measurements are limited to energies below 6 eV due to the absorption of air.…”

“…For a comprehensive electronic structure study, vacuum ultraviolet (VUV) spectroscopy is required to probe the valence-to-conduction band transitions in most high-j materials of large band gap. 3 In this letter, the band gap of anodic Al-Zr mixed oxide films was determined by vacuum ultraviolet spectroscopy (VUV), while the unoccupied conduction band states of the alloyed oxide films were investigated by X-ray absorption spectroscopy (XAS). The dependence of the energy gap of the anodic Al oxide films on the Zr alloying will be discussed.…”

High frequency anodising of aluminium–TiO2 surface composites: Anodising behaviour and optical appearance

“…Decorative anodised surfaces are commonly produced by direct current (DC) anodising of aluminium in a sulphuric acid bath [3]. The resulting anodic alumina layers are usually transparent to the visible light; however, their optical appearance depends on the anodising parameters as well as on the composition and surface morphology of the specimen being anodised [4] [5]. White appearing anodised Al surfaces have found applications in the aerospace industry for their high solar reflectance [6] [7].…”