Preparation of TiO2 Nanotube Array on the Pure Titanium Surface by Anodization Method and Its Hydrophilicity

In this work, a highly ordered TiO2 nanotube array on pure titanium (Ti) was prepared by anodization. The effects of the applied voltage and anodization time on the microstructure of the TiO2 nanotube arrays were investigated, and their hydrophilicity was evaluated by the water contact angle measurement. It was found that a highly ordered array of TiO2 nanotubes can be formed on the surface of pure Ti by anodized under the applied voltage of 20 V and the anodization time in the range of 6-12 h, and the nanotube diameter and length can be regulated by anodization time. The as-prepared TiO2 nanotubes were in an amorphous structure. After annealing at 550°C for 3 h, the amorphous TiO2 can be transformed to the anatase TiO2 through crystallization. The anatase TiO2 array exhibited a greatly improved hydrophilicity, depending on the order degree of the array and the diameter of the nanotubes. The sample anodized at 20 V for 12 h and then annealed at 550°C for 3 h exhibited a superhydrophilicity due to its highly ordered anatase TiO2 nanotube array with a tube diameter of 103.5 nm.

Porous Si (111) Fabrication Using Electrochemical Anodization: Effects of Electrode Distance and Current Density

Porous silicon (PSi) has developed for many applications such as gas and humidity sensors. Various methods are available to fabricate PSi, and electrochemical anodization is common due to low cost and easy use. Current density, etching/anodization time, type of etching solution, and electrode distance are the parameters determining resulting pores. The substrate used n-type silicon wafer with (111)-orientation and resistivity of 1.5-4.5 Ω.cm with a size of 1.5×1 cm2. The cleaning process of the samples employed the RCA cleaning procedure. Conductive contacts required for the electrochemical anodization were aluminum on the samples. The electrodes were the Si sample acting as anode and platinum (Pt) electrode as a cathode. The etching solution using a mixture of HF (40%) and ethanol (99%) with a 1:1 ratio. The electrode distance was 1.5, 2.0, and 2.5 cm. The current density for each electrode distance was 10, 30, and 50 mA/cm2 with an anodization time of 30 min. SEM and UV-Vis characterizations were applied to obtain surface morphology and reflectance, respectively. For all samples, the reflectance of PSi was lower than the reflectance of the original silicon surface (no pores). This condition indicates that the PSi is suitable as an anti-reflective layer in a solar cell. However, the PSi of reflectance curves has irregular shapes as a function of wavelength for different electrode distance and the current density. The SEM images confirmed that the pores formed on the silicon surface were inhomogeneous. The pore size decreased with the increase of the electrode distance while it increased as the increase of the current density. There was a correlation between pores size and reflectance at specific wavelength numbers.

Спектры электролюминесценции и структура анодного оксида алюминия при его формировании в химически чистой воде и спиртах

For a film of aluminum oxide (Al2O3) formed in distilled water (H2O), a linear growth was revealed during the high-voltage anodization time of 2000 s, and it was found that its electroluminescence (EL) is reliably recorded at an Al2O3 thickness of about 120 nm. It is shown that in DV and its deuterium-containing analogue, deuterium water (D2O), the electrolysis formation of Al2O3 is possible. cellular-nanoporous structure, identical to that formed in aqueous solutions of electrolytes. It was found that the presence of such a structure in the oxide is not a prerequisite for the generation of its EL. The EL spectrum of Al2O3 in H2O and D2O, as well as in “water-like” electrolytes: ethylene glycol, N, N-dimethylethanolamine, and isopentanol, was recorded for the first time. In the investigated range of 400–700 nm, significant differences in the luminescence in water and the above alcohols are revealed. For EL, the short-wavelength component with a wavelength of the order of 440 nm dominates in water, and in alcohols, the long-wavelength component with a maximum at 625 nm. In this case, nonstationarity of luminescence is observed both in the spectral composition and in the intensity of individual parts of the spectrum for the entire time of aluminum anodization.

The Effect of Crystal Structure on the Growth of Nanotubular Oxide Layers Formed on Ti–Ni Alloys

Electrochemical anodization of Ti–Ni alloys with different Ni composition was carried out in an ethylene glycol base electrolyte under the various conditions to investigate the effect of crystal structure and chemical composition of the Ti–Ni alloy. X-ray diffraction patterns indicated that Ti-48.0 Ni and Ti-49.0Ni alloys were the martensitic phase at room temperature, while Ti 50.6Ni and 51.0Ni were the austenitic phase. Self-organized nanotubular oxide layers were formed on four Ti–Ni alloys. The thickness of oxide layers increased with increasing anodization time and applied voltages. Energy-dispersive X-ray analysis indicated that the nanotubular oxide layers consist of two kinds of oxides, one of which is Titanium oxide and the other is Nickel oxide. These results indicate that the growth of nanotubular oxide layer formed Ti–Ni alloys are not affected by crystal structure, but by applied voltage and anodization time.