Papers by Author: Ao Xia

Abstract: The bamboo-like FeVO₄ nanocrystallines were synthesized by a two-step method of the microwave hydrothermal-calcination, using Fe (NO₃)₃·9H₂O and NH₄VO₃ as raw materials. The physical and photophysical properties of the as-prepared photocatalysts were fully characterized by X-ray diffraction (XRD), field emission scanning electron microscopy (FE-SEM), UV-vis diffuse reflectance spectra and photoluminescence (PL) analysis. The photocatalytic activities were evaluated by the decolorization of RhB solution under UV and visible light irradiation. The results reveal that the precursor solution concentration is 0.15 mol/L, the molar ratio n (Fe)/n (V) is 1, pH=3.0. The microwave hydrothermal reaction is at 180 °C for 120 min and then calcinated under 550 °C for 3 h so as to obtain the triclinic FeVO₄ nanocrystalline. Along [120] and [110], the fore and aft phases of the crystal orientation are bonded self-assembly to grow into the bamboo-like nanocrystalline with the energy gap of 2.42 eV. Under the UV-light irradiation for 240 min, the degradation rate of RhB is up to 91.2%. Adding 0.1 mL H₂O₂ to the solution, the out-phase photo-fenton reaction occurs and the degradation rate to RhB can reach to 98.8% after 8 h visible-light irradiation.

Abstract: Using iron nitrate, bismuth nitrate, citric acid and glacial acetic acid as the raw materials, the BiFeO₃ thin films in crystalline state were prepared on FTO substrate with the self-assembled monolayers by liquid phase deposition after graded induction and annealing at 550°C for 30min. The physical phase composition, the surface morphology and dielectric properties of the thin films were characterized respectively by XRD, SEM, and Precision LCR Meter. This paper studied that the deposition temperature and the number of film layers had the effects on the thin films. The results show that the as-prepared thin films show the random orientation and good crystalline. When the deposition temperature is 70°C, the surface of the as-prepared thin film is smooth and uniform. The size of grain is 100nm. The thin film has a dense structure without the apparent pore phase. When the test frequency is between 1kHz and 1MHz, the loss of the thin films is decreased as the increase of the number of the film layers. When the number of the layers is 15, the dielectric constant of the thin films is 44 and the loss is 0.02 when the test frequency is 10kHz.

Abstract: Yttrium hydroxide nanotubes were synthesized by hydrothermal method using Y(NO)₃•6H₂O as raw materials. X-ray powder diffraction (XRD) and scanning electron microscopy (SEM) were used to analyze the crystal phase and morphology of the as-prepared yttrium hydroxide nanotubes. In this paper, the hydrothermal temperature and the concentration of the mineralization agent were studied to have the effects on the formation of yttrium hydroxide nanotubes and their forming mechanism. The results indicate that the yttrium hydroxide nanotubes are prepared by hydrothermal method with the following optimal conditions: water as a solvent, NaOH concentration is 0.6 mol/L, the reaction temperature is 200°C, and the reaction time is 8h. In the growth process of yttrium hydroxide nanotubes, the hexagonal crystal nucleus of yttrium hydroxide is obtained first because the hexagonal crystal nucleus has the crystallization habit of growing along c axis orientationally. The yttrium hydroxide nanorods are obtained. The surface activating energy of the nanorods is stronger than that in its center. The yttrium hydroxide nanotubes are got finally.

Abstract: Patterned octadecyltrichlorosilane (OTS) self-assembled monolayers (SAMs) was fabricated on silicon substrates, utilizing short wave UV irradiation meter (λ=184.9nm) as the photolithograph apparatus under the cover of the photomask. The patterned BiFeO₃ were prepared on the functional OTS-SAMs by sol-gel method. The characterization of the samples patterns was carried out by various techniques, including X-ray diffraction (XRD), X-ray photoelectron spectroscopy (XPS), field emission scanning electron microscopy (FESEM), atomic force microscopy (AFM) and energy disperse spectroscopy (EDS). The results indicate that the pattern BiFeO₃ thin films were successfully prepared on the functional OTS-SAMs by sol-gel method and the thin films were BiFeO₃ thin films with hexagonal perovskite distorted structure which has clear boundaries and 200µm deposited lines width.

Abstract: In this paper, titanium ammonium fluoride ((NH₄)TiF₆), strontium nitrate (Sr(NO₃)₂) and boric acid (H₃BO₃) were used as raw materials, the precursor solution was prepared with molar ratio of AHFT/SN/BA=1/1/3. SrTiO₃ dielectric thin films were deposited with the self-assembled monolayers (SAMs) by the liquid-phase deposition on FTO substrate. X-ray diffraction (XRD), scanning election microscopy (SEM) and Agilent E4980A precision LCR Meter were used to characterize the SrTiO₃ films. The precursor solution concentration and the pH values of precursor solution had the effects on the dielectric properties of the as-prepared thin films. When the precursor concentration was 0.0125mol/L, the crystallization of as-prepared SrTiO₃ thin films was high and the grain sizes on the film surface were even and dense. When the frequency was 15~100KHz, the optimal dielectric constant was up to 1060, the minimal dielectric loss was 4.053. As pH=3.30, the frequency of the as-prepared SrTiO₃ thin films was 15~100KHz. The optimal dielectric constant was up to 1060, too. The minimal dielectric loss was 1.914. The optimal dielectric constants were 346.3 and 424.1 when the pH was 3.1 and below 3.5 respectively. The minimal dielectric losses were respectively 18.10 and 54.82.

Abstract: Fe(NO₃)₃•9H₂O and Bi(NO₃)₃•5H₂O were used as raw materials. BiFeO₃ thin films were prepared by sol-gel method. The effects of annealing temperatures on the morphology and dielectric property of the thin films were studied. XRD results show that the multi-crystal thin films with pure phase are obtained when annealed at 500°C and 550°C. But annealing at 580°C will lead to the appearance of Bi_2.46Fe₅O₁₂ phase.AFM images show that as the increase of annealing temperatures the surface toughness of the thin film is decreased, but the surface undulation of the thin films is decreased gradually. Within the frequency range of 1KHz~1MHz, the dielectric constant of BiFeO₃ thin films is kept over 125 and it does not change very much from 500°C to 580°C. Annealed at 550°C, the BiFeO₃ thin films with the lower loss are obtained. At 1MHz, the dielectric loss is 0.12.

Abstract: Octadecyltrichlorosilane (OTS) was prepared on glass substrate to form self-assembled monolayer (OTS-SAM). The OTS-SAM was then UV-irradiated to endow the film with good chemisorption ability. Zirconia films were formed on silanol SAM by the LPD method. The phase structure and surface configuration of the zirconia films were studied by XRD and SEM respectively. The XRD results indicate that the as-deposited ZrO2 thin films are pure tetragonal phase after being annealed at 500°C for 1 h. SEM images show the zirconia film is uniform, but not very compacted.

Abstract: This article used PTCS to dispose the self-assembled substrate, and prepared the precursor by the ratio of AHFT / SN / BA = 1:1:3 and then immersed the functionalized substrate into the precursor supersaturated solution. With the colloidal particles absorption induced by SAMs, SrTiO3 thin film was prepared by the self-assembled monolayers with liquid phase deposition method. The effects of the time of UV radiation and the time of PTCS immersion on the substrate contact angle were studied and the time of UV radiation had an effect on the substrate functionalization after PTCS immersion. The results showed that the first UV radiation for 25 min, PTCS immersion for 7 min and the second UV radiation for 30 min were beneficial to the crystallization of SrTiO3. XRD and AFM were used to characterize the thin film physical phase and surface morphology at 600oCwith annealing and heat retaining for 2 hours. The results also showed that under the same condition, the SrTiO3 crystals on the thin film surface had the clear outline and the spherical crystals were distributed regularly and evenly.

Abstract: Polycrystalline BiFeO3 (BFO) thin films were grown via metal organic deposition method on OH-functionalized organic self-assembled monolayers (SAMs) on glass. The stable BiFeO3 precursor solutions were obtained by using iron nitrate and bismuth nitrate as raw materials, acetic acid and glycol as solvent and citric acid as chelating agent. Firstly, the preparation and functionalization of octadecyltrichlorosilane (OTS) self-assembled monolayers on the hydroxylated glass substrates was investigated. Water contact angle measurement and atomic force microscopy (AFM) confirmed the presence of a uniform, complete monolayer. After BiFeO3 was prepared on glass substrates, the film- forming and heat treatment processing of BiFeO3 films were studied. The BFO film was characterized with X-ray diffraction (XRD), scanning electron microscopy (SEM) and energy dispersion spectrograph (EDS). XRD pattern indicated that the grains of sample began to grow at 450 °C, and which was made up of BiFeO3 and some impure phase. With the increase of temperature, impure phase were disappeared and the intensity of diffraction peaks strengthened. Pure BiFeO3 phase were obtained at 500 °C ~ 600 °C. When the heat treatment temperature increased above 650 °C, the impure phase appeared. SEM showed that the BFO thin film possessed a dense microstructure on OH-functionalized SAMs.

Abstract: Bismuth ferrite powders were synthesized by a simple citric acid complexing co-precipitation method at much lower temperature of 600°C. The work studies the calcination temperature and molar ratio of Fe and Bi on the structure and morphology. The as-prepared BiFeO3 powder was characterized by X-ray diffraction, field emission scanning electron microscopy, transmission electron microscope and Fourier transform infrared spectrophotometer. The result shows that the phase pure BiFeO3 powders with cubic morphology were prepared as the calcination temperature was 600°C and molar ratio of Fe and Bi was 1:1. The nanoparticles was uniform with the size of about 200nm.