Z.Q. Sun

Layer-by-Layer Growth Mechanism of TiO2 Nanotube Arrays

Based on the analysis of the precise current-time data and observation of the morphology by scanning electron microscopy, a layer-by-layer growth model of anodic TiO 2 nanotube (TNT) arrays was presented. Many phenomena appeared during the anodization and can be reasonably explained by this model, such as the first sharp slope of current in initial period, current fluctuation, occurring of ridges in adjacent tubes, and the rings broken off from the tube mouths. Furthermore, key factors which determine the morphology of TNT are discussed and it would be helpful for the design of nanoarchitectures in related material systems.

Morphology and Microstructure of As-Synthesized Anodic TiO2 Nanotube Arrays

The as-grown structure of electrochemically synthesized titania nanotube arrays is investigated by scanning electron microscope (SEM) in combination with transmission electron microscope (TEM) as well as X-ray diffraction (XRD). The analysis reveals a preferred growth direction of the nanotubes relative to the substrate surface and the well control on the nanotube arrays morphology. The crystal structure of the anatase phase is detected and exists in the tube walls without any thermal treatment, which makes it possible to realize the application of as-formed TiO2 nanotubes avoiding the degradation of the nanotube structures when sintering. In addition, a new growth, layered model of the anodic TiO2 nanotubes is presented to obtain further understanding of the growth mechanism.

Influence of annealing and Ag doping on structural and optical properties of indium tin oxide thin films

Indium tin oxide (ITO) and Ag (1.2±0.1at.%)-ITO films with the thickness of 130nm were deposited on glass substrates at room temperature by dc magnetron sputtering and postannealed at the temperature range of 200–400°C. By calculating the x-ray diffraction data, the lattice constants of all samples were obtained and the results show that the annealing led to the smaller lattice constants and the Ag doping resulted in the further lattice distortion. The refractive index n and extinction coefficient k of all samples were extracted from the transmittance spectra by means of the spectroscopic ellipsometry optimization method. Ag-ITO film annealed at 400°C has the high transmittance of 80%–90% in the visible wavelength range. Ag doping dramatically increased the extinction coefficient k of ITO films in UV wavelength range but almost without change in it in visible band. Meanwhile, by contrast with ITO films, Ag-ITO films show much higher n values than that of ITO films. Finally, the optical band gaps of all sa...

Photocatalytic degradation of methyl orange by nano-TiO2 thin films prepared by RF magnetron sputtering

Nano-TiO2 thin films are deposited by radio frequency (RF) magnetron sputtering using TiO2 ceramic target and characterized by X-ray diffractometer, atomic force microscope, and ultraviolet-visible spectrophotometer. The photocatalytic activity is evaluated by light-induced degradation of methyl orange solutions (5, 10, and 20 ppm) using a high pressure mercury lamp as the light source. The film is amorphous, and its energy gap is 3.02 eV. The photocatalytic degradation of methyl orange solution is the first-order reaction and the apparent reaction rate constants are 0.00369, 0.0024, and 0.00151 for the methyl orange solution concentrations of 5, 10, and 20 ppm, respectively.

Study on optical constants of ITO:Ag nanocompsite films.

Indium tin oxide (ITO) thin films doped with a volume ratio of 0.3% Ag were prepared by sputtering and subsequently annealed in temperatures of 200, 260, 300, 360, and 400 degrees C. The annealed films show increased transmittance in the visible wavelength range. The refractive index n and extinction coefficient k were extracted from simulating the transmittance spectra by using spectroscopic ellipsometry analysis method. The n values apparently increased in the whole wavelength range, but the k values were found to have almost no change in the near ultraviolet region after Ag doping. It is, therefore, proposed that the ITO:Ag combined with an ITO multilayer structure can be applied in special optical devices.

Annealing temperature-dependent microstructure and optical and electrical properties of solution-derived Gd-doped ZrO 2 high- k gate dielectrics

In current work, the microstructure and optical and electrical properties of sol–gel-derived Gd-doped ZrO2 gate dielectric thin films as functions of annealing temperatures were systemically investigated. Analyzes by x-ray diffraction have indicated that the 240 °C-baked sample as well as those samples annealed at lower temperatures keep amorphous state. In the sample annealed at 500 °C, however, the amorphous phase disappears and tetragonal ZrO2 is formed. Measurements from ultraviolet-visible spectroscopy (UV/Vis) have demonstrated that transmittance of all samples in the visible region is approximately 80% and the increase in band gap energy has been found with increasing the annealing temperature. Electrical properties of all samples based on Al/Si/ZrGdOx/Al MOS capacitor have been investigated by using semiconductor device analyzer. Through the analysis and calculation of the electrical characteristic curves, solution-processed Al/ZrGdOx/Si/Al capacitor shows improved performances at a annealing temperature of 400 °C, such as high dielectric constant (k) of 16.56, lowest oxidation charge density (Qox) of −0.74 × 1012 cm−2, and boundary trap oxidation charge density (Nbt) of 3.17 × 1012 cm−2. In addition, the leakage current mechanism for 400 °C-annealed sample has been discussed in detail.Graphical Abstractsolution-processed Gd-doped ZrO2 gate dielectric films were realized. Al/ZrGdOx/Si/Al capacitor shows optimized and improved performances at a annealing temperature of 400 °C.

The effects of oxygen exposure on the electrical conductance characteristics of high frequency oxygen plasma anodized Al films

Abstract This paper discusses the dependence of the electrical conductance characteristic of high frequency oxygen plasma anodized Al film on the oxygen exposure during the anodization process. The results showed that under the same anodization conditions, the surface resistance of the oxide film is 6.56~ 0.11 Ω □ (where Ω/□ denotes the unit of sheet resistance) when the vacuum evaporated Al film is thick (750 ~ 800 nm) and the resistance is 1256~ 4.81 Ω □ when the Al film is thin (37~ 82 nm). The results also showed that the surface oxide layer in the aluminum oxide film is γ-Al2O3 with a lattice constant a o = 7.9124 A . At a constant temperature, the electrical conductance characteristic of the plasma anodized Al film depends on the oxygen exposure during the anodization process.

Microstructure and electrical conductance of AI oxide film anodized in an HF oxygen plasma

Abstract The microstructure and the conductance of high-frequency oxygen plasma anodized Al-films were studied and showed that: the surface oxide layer in the aluminium oxide film was γ-Al 2 O 3 with a cubic structure, the chemical shift for Al 2P was 2.91-2.96 eV or 2.94-2.98 eV, and the surface resistance of the oxide films was 0.11-6.56Ω/□ or 4.81–1256.4Ω/□. The results also showed the dependence of the film resistance on the overall film thickness, the oxide layer thickness and anodization temperature.