Aiyun Liu

Electrical and optical properties of Pb(Mg1∕3Nb2∕3)O3–PbTiO3 thin films prepared by chemical solution deposition

92%Pb(Mg1∕3Nb2∕3)O3–8%PbTiO3 (PMNT) thin films have been prepared on Pt∕Ti∕SiO2∕Si substrate with a LaNiO3 (LNO) buffer layer and on sapphire substrate by a chemical solution deposition method, respectively. X-ray diffraction analysis shows that the PMNT thin films on Pt∕Ti∕SiO2∕Si substrate are polycrystalline with (110)-preferential orientation. Pt∕PMNT∕Pt capacitors have been fabricated and show a ferroelectric character with a spontaneous polarization (Ps) of 25.2μC∕cm2 and a remanent polarization (Pr) of 6.56μC∕cm2. The dielectric constant (er) and the dissipation factor (tanδ) at 1 kHz are 680 and 0.014, respectively. The band-gap energy of the PMNT thin films on the sapphire substrate was found to be about 4.03 eV by the optical transmission spectra measurement. The optical constants (n, k) of the PMNT thin films in the wavelength range of 2.5–12.6 μm were obtained by infrared spectroscopic ellipsometry measurement.

Aqueous germanate ion solution promoted synthesis of worm-like crystallized Ge nanostructures under ambient conditions

This work demonstrates that it is possible to synthesize crystallized Ge nanostructures directly in an aqueous medium under ambient conditions by using widely available GeO2 (in the form of germanate ions) as a precursor. The reaction of germanate ions with NaBH4 in an aqueous medium resulted in highly hydrogenated Ge that could be transformed into crystallized Ge after an air-drying treatment. The NaBH4/GeO2 molar ratio, reaction time and drying temperature were optimized for the synthesis of crystallized Ge products. Furthermore, the reaction time has an influence on the size and shape of the final crystallized Ge products. A reaction time of 12 h could result in crystallized Ge powder samples that contain ultra-small (5-20 nm) particles and larger (50-100 nm) particles. By controlling the reaction time to 24 h, a Ge powder product consisting of worm-like crystallized Ge nanostructures with diameters of 10-80 nm and lengths up to 1000 nm was obtained. The possible reaction and growth mechanisms involved in this method were investigated. This new synthetic route may be a good candidate for synthesizing a wide variety of crystallized Ge nanomaterials and devices due to its low cost, low safety risk, facileness, high yield (above 70% and in gram scale) and convenience for adding other chemicals (i.e. dopants or morphology modifying agents) into the reaction system.

A new method of fabricating internally sol-gel coated capillary tubes

Abstract A new method for fabricating internally sol–gel coated long capillary tubes was developed to solve the problems of the capillary vibration and the difficulty in gelation reaction inner the capillary during sol–gel processing. Firstly, a sol was coated on the inner wall of a standing long silica glass capillary filled with the sol solution by lowering the sol. Then the air was very slowly pumped into the capillary to create an air condition similar to the outside space. By this way the gelation reaction went as well as it usually goes in the dip-coating process. The multilayer or thick coating could easily be fabricated by repeating the sol up-and-down and air flowing process. Subsequently, the capillary was subjected to heat treatment in a special stove while oxygen was kept flowing through the capillary. In this way the organic groups in the gel burned as completely as possible, and the burned gases could also be easily removed out of the capillary. The equipment specially designed for the fabrication of this coating and such processing parameters as the sol-dropping speed, the fluxes of the air and oxygen and temperature programs are also discussed in the paper. The results show that this method is not only an effective method for fabricating inner sol–gel coating in a capillary but also a good supplement for the dip-coating technique under some circumstances where a dip-coating method is limited to be used.

Study of the synthesis of SiO2–TiO2–GeO2 gel glass for hollow waveguide application in CO2 laser delivery

The SiO2–TiO2–GeO2 sol–gel glass system was firstly ascertained to be the material to use in the fabrication of a hollow waveguide for application in CO2 laser delivery. SiO2–TiO2–GeO2 sols of various compositions were prepared by using Si(OC2H5)4, Ti(OC4H9)4 and Cl3GeCH2CH2COOH as the precursors. It was found by viscosity and TEM analysis that the stability of the sol was weakened greatly when the content of germanium dioxide reached 35% because of self-polycondensation of hydrolyzed Cl3GeCH2CH2COOH. The sol with a composition of 40SiO2·30TiO2·30GeO2 was chosen as the coating solution because of its relatively high content of Ti and Ge atoms and its long lifetime of 30 days. It was confirmed by XRD analysis that no crystal TiO2 and GeO2 phases separated from SiO2 and that the material remained glassy. Compared with the IR reflectivity peaks of silica glass, the IR reflectivity peaks of the SiO2–TiO2–GeO2 gel glass are greatly broadened due to the formation of various mixed bonds between Ti, Si and Ge through bridging O atoms. The wavelength of the CO2 laser is included in this peak and a refractive index below one is obtained. The use of this material in a hollow waveguide structure for the delivery CO2 laser is discussed on the basis of the calculated complex refractive index and transmission loss. The results show that a SiO2–TiO2–GeO2 sol with a composition of 40SiO2·30TiO2·30GeO2 is a good candidate material for this application.

Metallic attenuated total reflection infrared hollow fibers for robust optical transmission systems

A durable metallic attenuated total reflection (ATR) hollow fiber (bore size: 1.45 mm, wall thickness: 50 μm) was designed and fabricated based on a nickel capillary tube and hexagonal germanium dioxide (GeO2). The anomalous dispersion of the hexagonal GeO2 layer grown inside a nickel tube achieves low-loss light transmission at two peak-power wavelengths for CO2 laser devices (10.2 and 10.6 μm). An 11–28 W, 10.2 or 10.6 μm CO2 laser power was steadily delivered via a fiber elastically bent from 0° to 90° (radius: 45 cm) for over 40 min (transmission loss: 0.22 to 4.2 dB/m). Theoretically fitting the measured temperatures showed that front-end clipping caused greater thermal loading than the distributed mode absorption. The maximum external temperature of a nickel ATR fiber is much lower than that of a silica glass ATR fiber owing to their different heat dissipation abilities. The HE11 mode purity of the output beam profiles decreased from 90.3% to 44.7% as the bending angle increased from 0° to 90°. Large core sizes and wall roughnesses (scattering loss 0.04 dB/m) contributed to mode mixing and excess losses that were above the value predicted by the classical Marcatili and Schmeltzer equation (0.024–0.037 dB/m).

Low-temperature, low-cost growth of robust ATR GeO2 hollow fibers based on copper capillary tubes for transmission of CO2 laser light

Attenuated total reflectance (ATR) infrared hollow waveguide attracts particular interest since it has both advantages of a hollow fiber and a light guiding mechanism similar to that of solid-core fibers. Presently, ATR hollow waveguides are mainly structured with single-crystal sapphire or glassy materials. These waveguides are somewhat brittle. More robust ATR hollow fibers are required in many military and domestic applications. In this work, ATR GeO2 hollow waveguides were prepared based on a copper capillary tube for transmitting CO2 laser light. The inner wall of the copper structural tube was polished using a high-pressure pulsed nanofluid technique. A hexagonal crystalline GeO2 reflective layer with sufficient thickness (>4 μm) was grown on the inner tube wall via a simple liquid phase deposition process at room temperature. The GeO2 coated copper hollow fiber exhibits a low-loss band within 10-11.5 μm. It can still be bent since the hollow-core size (1.4 mm) and the wall thickness (50 μm) are not too large. The transmissions of CO2 laser light are 91% and 43% under a straight condition and a 90° bend with a 30-cm radius condition, respectively. The waveguide displays high heat-resisting properties due to high thermal conductivity of the copper substrate tube and a high melting point (1115°C) of the GeO2 reflective layer. This work opens a door for low-temperature, low-cost growth of long ATR GeO2 infrared hollow fibers based on various substrate tubes, even including plastic capillary tubes.

Large strain response in PZT-PZN-PAN lead-based ceramics

Solid solutions of 0.8Pb(Zr0.52Ti0.48)O3-(0.2-x)Pb(Zn1/3Nb2/3)O3-xPb(Al1/2Nb1/2)O3 (PZT-PZN-PAN, PZT-PZN-xPAN) with x from 0 to 0.1 were fabricated and the dielectric, ferroelectric, piezoelectric properties were investigated in detail. Results show the crystal structure changes from coexists of tetragonal and rhombohedral to single rhombohedral phase. At a critical composition of 0.02, a maximum quasi-static piezoelectric coefficient d33 (410 pC/N) was obtained. Furthermore, it is found that the increment of PAN content could lead to increase the strain of PZT-PZN-xPAN ceramics, and a large strain response of ~0.24% with normalized strain Smax/Emax as high as 767 pm/V was obtained for the PZT-PZN-0.1PAN under a low electric field of ~3 kV/mm, which makes it a promising material for solid-state actuator applications.

Highly (222)-oriented pyrochlore PZN-PT thin films prepared by pulsed laser deposition

Highly (222)-oriented 90%Pb(Zn1/3Nb2/3)O3-10%PbTiO3(abbreviated PZN–PT) thin films, about 550nm in thickness, have been successfully grown on (111)Pt/Ti/SiO2/Si substrate by pulsed laser deposition method. Pure pyrochlore phase with highly (222)-preferred orientation, determined by X-ray diffraction, was formed in the PZN–PT thin films when the temperature of substrates is 550°C. FE-SEM investigation shows that the surface appearance and the cross section of the films are smooth and crack-free with some dispersive spherical protrusions. The dielectric constant and loss of the thin films were measured using an impedance analyzer (HP4194A). The dielectric constant ( εr ) and the dissipation factor ( tanδ ) at 1 kHz are 205 and 0.03, respectively.

Structure and magnetic properties of Ge99.04Mn0.96 thin film prepared by thermal evaporation of Mn doped GeO2 ceramic film under hydrogen atmosphere

Ge99.04Mn0.96 thin film was fabricated by thermal evaporation of Mn doped GeO2 ceramic film under hydrogen atmosphere. Secondary phases were not detected by X-ray diffraction (XRD) and high resolution transmission electron microscopy (HRTEM) analyses. The film is p type. Room-temperature ferromagnetism was detected in the film. The ferromagnetic behavior may arise from alignment of the bound magnetic polarons (BMP) mediated by the localized holes in the system as well as ultra small secondary phases unable to be detected by XRD and HRTEM analyses.

Microstructure and electrical properties Of PMNT thin films prepared by a modified sol-gel process

0.7Pb(Mg1/3Nb2/3)O3-0.3PbTiO3 (PMNT) thin films were prepared on (111)Pt/Ti/SiO2/Si substrate by a modified sol-gel process with Nb2O5 as the niobium source. XRD analysis shows that PMNT thin films with pure perovskite were obtained by spin-coating and annealing at 700°C for 20 minutes. The remanent polarization and coercive field of the PMNT thin films are about 7.69μC/cm2 and 80.75kV/cm, respectively. The dielectric and C-V curve of PMNT thin films are also investigated. The dielectric constant ( εr ) reaches 935 and the dissipation factor (tanδ)is about 0.04 at 1kHz.