Upconversion properties of Y_2O_3:Er films prepared by sol-gel method

Y2O3：Er^3＋ films were prepared by a simple sol-gel process. The structural properties of Y2O3：Er^3＋ films were characterized with X-ray diffraction, Fourier transform infrared spectroscopy and field emission scanning electron microscopy. The results indicated that the Y2O3：Er^3＋ films might have high upconversion efficiency because of their low vibrational energy. Under 785 and 980 nm laser excitation, the samples showed green （^2H11/2→^4I15/2, ^4S3/2→^4I15/2） and red （^4F9/2→^4I15/2） upconversion emissions. The upconversion mechanisms were studied in detail through laser power dependence. Excited state absorption and energy transfer process were discussed as possible upconversion mechanisms. The cross relaxation process in Er^3＋ was also investigated.

Effects of dopant content on optical and electrical properties of In_2O_3: W transparent conductive films

The In 2 O 3 : W (IWO) films with different W content were deposited on glass substrate using direct current sputtering method. The structure, surface morphology, and optical and electrical properties were investigated. Results showed that both the carrier concentration and carrier mobility were increased with the doping of W. The IWO film with the lowest resistivity of 1.0×10 3 cm, highest carrier mobilityof 43.7 cm 2 V 1 s 1 and carrier concentration of 1.4×10 20 cm 3 was obtained at the content of 2.8 wt.%. The average optical transmittance from 300 nm to 900 nm reached 87.6%.

Preparation and Characterization of Sol-Gel Derived Au Nanoparticle Dispersed Y_2O_3∶Eu Films

Gold nanoparticles dispersed Y2O3 films were prepared through a sol-gel method by using yttrium acetate and Au nanoparticles colloid as precursors. The films were characterized by X-ray diffraction （XRD）, transmission electron microscopy （TEM） and UV-VIS absorption spectra. XRD patterns and TEM images of Y2O3 ＋ Au films give the same resuits on structure and particle size as that of pure Y2O3 films. The surface plasma resonance （SPR） of Au nanoparticles in Y2O3 ＋ Au film was observed around 550 nm in the absorption spectrum and its position shifts to red with increasing annealing temperature is caused by the increase of dielectric constant of Y2O3 matrix and the size of Au nanoparticles. The second and third order nonlinear optical effects of Y2O3 ＋ Au films were also observed. The photoluminescent properties of Y2O3 ： Eu ＋ Au films were investigated and results indicate that there exist an energy transfer from Eu^3 ＋ to Au nanoparticles and this energy transfer decreases the emission of Eu^3 ＋ in Y2O3 ： Eu ＋ Au film.

Growth of β-Ga_2O_3 Films on Sapphire by Hydride Vapor Phase Epitaxy

Two-inch Ga_2O_3 films with（ˉ201）-orientation are grown on c-sapphire at 850–1050°C by hydride vapor phase epitaxy. High-resolution x-ray diffraction shows that pure β-Ga_2O_3 with a smooth surface has a higher crystal quality, and the Raman spectra reveal a very small residual strain in β-Ga_2O_3 grown by hydride vapor phase epitaxy compared with bulk single crystal. The optical transmittance is higher than 80% in the visible and near-UV regions, and the optical bandgap energy is calculated to be 4.9 e V.

Synthesis of free-standing Ga_2O_3 films for flexible devices by water etching of Sr_3Al_2O_6 sacrificial layers

Flexible electronic devices have attracted much attention due to their practical and commercial value. Integration of thin films with soft substrate is an effective way to fabricate flexible electronic devices. Ga_2O_3 thin films deposited directly on soft substrates would be amorphous mostly. However, the thickness of the thin film obtained by mechanical exfoliation method is difficult to control and the edge of the film is fragile and easy to be damaged. In this work, we fabricated free-standing Ga_2O_3 thin films using the water-soluble perovskite Sr_3Al_2O_6 as a sacrificial buffer layer. The obtained Ga_2O_3 thin films were polycrystalline. The thickness and dimension of the films were controllable. A flexible Ga_2O_3solar-blind UV photodetector was fabricated by transferring the free-standing Ga_2O_3 film on a flexible polyethylene terephthalate substrate. The results displayed that the photoelectric performances of the flexible Ga_2O_3 photodetector were not sensitive to bending of the device. The free-standing Ga_2O_3 thin films synthesized through the method described here can be transferred to any substrates or integrated with other thin films to fabricate electronic devices.

Effects of thickness on superconducting properties and structures of Y_2O_3/BZO-doped MOD-YBCO films

We report the thickness dependence of critical current density （Jc） in YBa2Cu3O7-x （YBCO） films with BaZrO3 （BZO） and Y2O3 additions grown on single crystal LaAlO3 substrates by metalorganic deposition using trifluoroacetates （TFA-MOD）. Comparing with pttre YBCO films, the Jc of BZO/Y2O3-doped YBCO films was significantly enhanced. It was also found that with the increase of the thickness of YBCO film from 0.25 μm to 1.5 μm, the Ic of BZO/Y2O3-doped YBCO film increased from 130 A/cm to 250 A/cm and yet Jc of YBCO film decreased from 6.5 MA/cm2 to 2.5 M A/cm2. The thick BZO/Y2O3-doped MOD-YBCO film showed lower Jc, which is mainly attributed to the formation of a-axis grains and pores.

Amorphous Er_2O_3 films for antireflection coatings

This paper reports that stoichiometric, amorphous, and uniform Er2O3 films are deposited on Si（001） substrates by a radio frequency magnetron sputtering technique. Ellipsometry measurements show that the refractive index of the Er2O3 films is very close to that of a single layer antireflection coating for a solar cell with an air surrounding medium during its working wavelength. For the 90-nm-thick film, the reflectance has a minimum lower than 3% at the wavelength of 600 nm and the weighted average refiectances （400-1000 nm） is 11.6%. The obtained characteristics indicate that Er2O3 films could be a promising candidate for antireflection coatings in solar cells.

Structure and Waveguide Properties of Sol-Gel Derived Gd_2O_3 Films

Pure and rare earth doped gadolinium oxide (Gd 2O 3) waveguide films were prepared by a simple sol-gel process and dip-coating method. Structure of Gd 2O 3 films annealed at different temperature was investigated by X-ray diffraction and transmission electron microscopy. Oriented growth of (400) face of Gd 2O 3 has been observed when the films were deposited on amorphous substrate. The refractive index and thickness of films were determined by m-lines spectroscopy. The laser beam (λ=632.8 nm) was coupled into the film by a prism coupler and the propagation length is about 3.5 cm. Luminescence properties of europium ions doped films were measured by waveguide fluorescence spectroscopy, which shows disordered environment for Eu 3+ at 400 ℃.

Effect of Al_2O_3 Buffer Layers on the Properties of Sputtered VO_2 Thin Films

VO_2 thin films were grown on silicon substrates using Al_2O_3 thin films as the buffer layers. Compared with direct deposition on silicon, VO_2 thin films deposited on Al_2O_3 buffer layers experience a significant improvement in their microstructures and physical properties. By optimizing the growth conditions, the resistance of VO_2 thin films can change by four orders of magnitude with a reduced thermal hysteresis of 4 °C at the phase transition temperature. The electrically driven phase transformation was measured in Pt/Si/Al_2O_3/VO_2/Au heterostructures. The introduction of a buffer layer reduces the leakage current and Joule heating during electrically driven phase transitions. The C–V measurement result indicates that the phase transformation of VO_2 thin films can be induced by an electrical field.

Fabrication of GaN films through reactive reconstruction of magnetron sputtered ZnO/Ga_2O_3

A simple and easily operated technique was developed to fabricate GaN films. GaN films possessing hexagonal wurtzite structure were fabricated on Si(111) substrates with ZnO buffer layers through nitriding Ga2O3 films in the tube quartz furnace. ZnO buffer layers and Ga3O3 films were deposited on Si substrates in turn by using radio frequency magnetron sputtering system before the nitriding process. The structure and composition of GaN films were studied by X-ray diffraction, selected area electron diffraction and Fourier transform infrared spectrophotometer. The morphologies of GaN films were studied by scanning electron microscopy. The results show that ZnO buffer layer improves the crystalline quality and the surface morphology of the films relative to the films grown directly on silicon substrates. The measurement result of room-temperature photoluminescence spectrum indicates that the photoluminescence peaks locate at 365 nm and 422 nm.

Enhancing superconductivity of ultrathin YBa2Cu3O7-δ films by capping non-superconducting oxides

In this study, we have explored the ways to fabricate and optimize high-quality ultrathin YBa2 Cu3 O7-δ(YBCO) films grown on single-crystal(001) SrTiO3 substrates. Nearly atomic-flat YBCO films are obtained by pulsed laser deposition.Our result shows that the termination of SrTiO3 has only a negligible effect on the properties of YBCO. In contrast, we found that capping a non-superconducting oxide layer can generally enhance the superconductivity of YBCO. PrBa2 Cu3 O7,La2 CuO4, LaMnO3, SrTiO3, and LaAlO3 have been examined as capping layers, and the minimum thickness of superconducting YBCO with capping is ~ 2 unit cells–3 unit cells. This result might be useful in constructing good-performance YBCO-based field effect devices.

Optical and Magnetic Properties of Fe_2O_3/SiO_2 Nano-composite Films

Fe2O3/SiO2 nano-composite films were prepared by sol-gel technique combining heat treatment in the range of 100-900 ℃. The particle size was observed by FE-SEM. Optical properties of the films were investigated by UV-visible spectra. Structural and magnetic characteristics were investigated through FT-IR and VSM. The transparency of the Fe2O3/SiO2 nano-composite films decreased with the content of the Fe2O3. Water and organic solvent in the films were evaporated with heat treatment, so the transparency of the films was enhanced under high temperature. It is also found that the saturation magnetization （Ms） of the films increases with the temperature. As the content of the Fe2O3 increases, when the content of the Fe2O3 is around 30wt%, the Ms of the films has a maximum value.

Phase control of magnetron sputtering deposited Gd_2O_3 thin films as high-κ gate dielectrics

Gd2O3 thin films as high-κ gate dielectrics were deposited directly on Si（001） substrates by magnetron sputtering at a pressure of 1.3 Pa and different temperatures. X-ray diffraction results revealed that all the films grown from 450 to 570 ℃ were crystalline, and the Gd2O3 thin films consisted of a mixture of cubic and monoclinic phases. The growth temperature was a critical parameter for the phase constituents and their relative amount. Low temperature was favorable for the formation of cubic phase while higher temperature gave rise to more monoclinic phase. All the Gd2O3 thin films grown from different temperatures exhibited acceptable electrical properties, such as low leakage current density （JL） of 10-5 A/cm^2 at zero bias with capacitance equivalent SiO2 thickness in the range of 6-13 nm. Through the comparison between films grown at 450 and 570 ℃, the existence of monoclinic phase caused an increase in JL by nearly one order of magnitude and a reduction of effective dielectric constant from 17 to 9.

Strongly enhanced flux pinning in the YBa_2Cu_3O_(7-X) films with the co-doping of Ba TiO_3 nanorod and Y_2O_3 nanoparticles at 65 K

YBa2Cu3O7-x（YBCO） films with co-doping BaTiO3（BTO） and Y2O3 nanostructures were prepared by metal organic deposition using trifluoroacetates（TFA-MOD）. The properties of the BTO/Y2O3co-doped YBCO films with different excess yttrium have been systematically studied by x-ray diffraction（XRD）, Raman spectra, and scanning electron microscope（SEM）. The optimized content of yttrium excess in the BTO/Y2O3co-doped YBCO films is 10 mol.%, and the critical current density is as high as - 17 mA/cm^2（self-field, 65 K） by the magnetic signal. In addition, the Y2Cu2O5 was formed when the content of yttrium excess increases to 24 mol.%, which may result in the deterioration of the superconducting properties and the microstructure. The unique combination of the different types of nanostructures of BTO and Y2O3 in the doped YBCO films, compared with the pure YBCO films and BTO doped YBCO films, enhances the critical current density（JC） not only at the self-magnetic field, but also in the applied magnetic field.

纳米TiO_(2)对NH_(3)-H_(2)O-LiBr工质降膜吸收性能的影响

为了探讨纳米TiO_(2)对三元NH_(3)-H_(2)O-LiBr工质降膜吸收的影响,本文利用数值分析建立了三元工作流体薄膜吸收的连续方程、能量方程和组分质量平衡方程,采用Matlab软件进行编程和计算纳米流体的降膜吸收性能,将其与实验数据进行对比验证,并进一步分析了纳米TiO_(2)质量分数、初始氨浓度、初始温度、冷却水进口温度、吸收压力和下降薄膜管长度对薄膜吸收性能的影响。研究表明:添加纳米TiO_(2)可以增强降膜吸收的传质速率,主要原因为液膜中氨的扩散系数增加。当纳米TiO_(2)质量分数从0%增加到0.1%、0.3%和0.5%时,扩散系数分别增加了3.44倍、6.42倍和11.76倍。此外,增加初始氨浓度、降低初始温度、提高冷却水进口温度或降低吸收压力都可以提高最终溶液的饱和度。

制备方法对Ni-Al2O3催化剂在CO2-CH4重整反应中催化性能的影响

为提高镍基催化剂的干法重整活性,采用溶液燃烧法、等体积浸渍法、胶体磨循环浸渍法和水热-沉积法制备了SCM、IM P、T310和HTP四种催化剂,在800℃考察了其在CO2-CH4重整反应中的催化性能,并结合ICP-AES、N2吸附-脱附、XRD、H2-TPR和TEM等表征手段对催化剂进行分析。结果表明,水热-沉积法和胶体磨循环浸渍法制备的催化剂比表面积较大,分别为190.83和182.21 m2/g,可为反应提供较多的接触面积,进而提高催化剂的初始活性(HTP试样CH4和CO2初始转化率相对较高,分别达85.15%和90.84%);而溶液燃烧法和等体积浸渍法制备的催化剂具有较多的Ni Al2O4尖晶石,其还原峰面积占总还原峰面积90%以上,还原后可获得更多晶粒粒径更小的稳定活性组分Ni(SCM和IMP试样稳定性更好,反应50 h后活性超过HTP和T310试样,100 h后CH4转化率方降至50%以下)。因此,决定催化剂稳定活性的更重要的因素应该是活性组分Ni晶粒粒径的大小及其抗烧结能力的强弱。

溶液燃烧法制备Ni-Al_2O_3催化剂用于CO_2-CH_4重整研究

采用溶液燃烧法制备了Ni含量为2wt%、4wt%、6wt%、8wt%和10wt%系列催化剂,并对反应前后催化剂进行N_2吸附–脱附、XRD、H_2-TPR、TPH、Raman、TEM和TG-DTG等表征。与等体积浸渍法（以溶液燃烧法制备的Al_2O_3为载体）制备的催化剂相比,溶液燃烧法制备的催化剂具有较大的比表面积,孔径分布可分为2~4.5 nm和4.5~10 nm两段,属典型的多级孔结构;NiO高度分散在载体上,与载体具有较强的相互作用,这种相互作用有利于提高催化剂的稳定性。催化剂210 h稳定性试验表明,溶液燃烧法制备的Ni含量为8wt%试样的CH_4转化率维持在90%左右,失活速率仅为0.035%/h,优于浸渍法制备的相同Ni含量催化剂。

氨基磺酸盐复合镀Ni-Al_2O_3

为了探讨镍基亚微米Al2O3复合共沉积过程中镀液中Al2O3分散量和电流密度对镀层中Al2O3复合量的影响,以及加入Al2O3颗粒和阳离子表面活性剂对阴极极化的影响,研究了氨基磺酸镍溶液中添加亚微米级Al2O3颗粒形成Ni-Al2O3复合镀层的共沉积过程,并分析了各参量之间的相互关系.结果表明:镍基亚微米Al2O3的共沉积符合两步吸附机理,且强吸附步骤为控制步骤;提高电沉积的阴极极化对亚微米在镀层中的复合有促进作用.

纳米Ni-Al_2O_3复合层的超声电沉积制备

采用超声 电沉积方法在常用金属表面制备纳米Ni Al2O3复合层。在试验的基础上,研究了超声波机械扰动效应对电解液传质过程的作用,超声波空化效应对纳米粒子团聚的抑制作用,脉冲电参数对控制晶粒成核及生长的作用。获得了由镍晶(20～60nm)和纳米Al2O3粒子构成的纳米级复合层。

温度和空速对CO甲烷化Ni-Al_2O_3催化剂性能影响

采用低温固相法制备Ni-Al_2O_3催化剂,考察反应温度和空速对Ni-Al_2O_3催化剂浆态床CO甲烷化性能的影响,并对反应后的催化剂进行XRD,BET,TPH,TG-DTG和TEM等进行表征。评价结果表明,反应温度增加,CO转化率先增大后趋于不变,较适宜的反应温度为290—305℃。反应空速增大,催化剂活性先增大后减小,空速为1 200 mL/(g·h)时,活性最好,其CO转化率、CH4选择性和收率分别为98.3%、95.8%和94.2%。寿命实验表明,该催化剂在经过10 h的诱导期后,活性趋于稳定,超过25 h后,活性开始下降。表征发现,温度升高和空速增大,均导致Al O(OH)增多,不利于反应进行;积炭反应伴随着消炭反应,温度越高,越有利于消炭反应发生。因此,反应温度和空速的选择需要综合考虑各方面的影响因素。