Chengbin Jing

Optical second-order nonlinearity of the infrared transmitting 82GeS2∙18CdGa2S4 nanocrystallized chalcogenide glass

The infrared (IR) transmitting nanocrystallized chalcogenide glass only containing α-CdGa2S4 IR nonlinear optical crystallites, which were confirmed by x-ray diffraction and Raman scattering measurements, was fabricated through the controllable nucleation and crystallization of the glass with the composition 82GeS2∙18CdGa2S4 at a temperature of 325°C far below the glass transition temperature (Tg:415°C) for a long duration. A clear second harmonic generation (green light, 532nm) could be observed in the transparent 82GeS2∙18CdGa2S4 nanocrystallized chalcogenide glass, demonstrating the IR frequency-doubling function of the prepared nanocrystallized composite material.

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.

In situ synthesis and third-order nonlinear optical properties of CdS/PVP nanocomposite films

Cadmium sulfide (CdS) nanocrystals were in situ grown in a polyvinylpyrrolidone (PVP) matrix at room temperature using cadmium nitrate and thioacetamide as the cadmium and sulfur sources, respectively. It was found that the growth of CdS nanocrystals in the PVP matrix was well controlled and the mass concentration of CdS could be up to 18.2 wt% without the formation of large precipitates. The third-order nonlinear optical properties of the composite films were studied at 532 nm in the nanosecond regime by using the Z-scan technique. The results showed that the CdS/PVP nanocomposite film has a promising optical property exhibited by a nonlinear optical refractive index and an absorption coefficient of −1.65 × 10−11 cm2 W−1 and −4.25 × 10−7 cm W−1, respectively. The flexible processing technique allows the production of optical devices with various shapes.

Effect of Fe-doping concentration on microstructure, electrical, and magnetic properties of Pb(Zr0.5Ti0.5)O3 thin films prepared by chemical solution deposition

The highly (l00) oriented Pb(Zr0.5Ti0.5)O3 thin films with different Fe3+ doping concentrations were fabricated on LaNiO3-coated silicon substrates by chemical solution deposition. And the microstructure, ferroelectric, leakage, and magnetic properties were investigated. The results indicate that incorporation of Fe3+ into PZT thin films can promote the degree of the lattice distortion and greatly improve the surface roughness. In comparison with the pure PZT sample, the ferroelectric hysteresis loops of Fe-doped PZT samples demonstrate larger and larger polarizations and coercive fields with the increase in Fe3+ doping amount. Moreover, leakage mechanism of present films evolves from the space charge limited conduction to the “modified” space charge limited conduction, and then returns to the space charge limited conduction with increasing Fe3+ doping concentration. The occurrence of exchange bias in these Fe-doped PZT samples implies that the magnetic exchange interaction can be explained by the bound m...

Fabrication and characteristics of porous germanium films

Abstract Porous germanium films with good adhesion to the substrate were produced by annealing GeO2 ceramic films in H2 atmosphere. The reduction of GeO2 started at the top of a film and resulted in a Ge layer with a highly porous surface. TEM and Raman measurements reveal small Ge crystallites at the top layer and a higher degree of crystallinity at the bottom part of the Ge film; visible photoluminescence was detected from the small crystallites. Porous Ge films exhibit high density of holes (1020 cm−3) and a maximum of Hall mobility at ∼225 K. Their p-type conductivity is dominated by the defect scattering mechanism.

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.

Fabrication of sol–gel 70GeO2–30SiO2 thick films from TEOG and DEOS and investigation of the 5 eV band

Crack-free germanosilicate films, 3.6 µm-thick and containing up to 70 mol% germanium dioxide, which are inaccessible through the conventional sol–gel process, were fabricated using tetraethyl orthogermanate (TEOG) and diethylorthosilicate (DEOS) as precursors for germania and silica, respectively. The studies using viscosity, TEM and SEM revealed that DEOS contributed largely to stabilizing the GeO2–SiO2 sol and suppressing crack formation in thick films. XRD study showed that the films remained amorphous after being sintered at 600 °C in air for 60 min and annealed at 550 °C under a flowing H2/N2 atmosphere for 120 min. An intense absorption band at around 241 nm was distinctly observed in the films. The intensity of this absorption band was found to be effectively bleached by UV illumination. Weak photoluminescence emission bands which originated from the neutral oxygen di-vacancy were detected near 375 and 275 nm. Therefore, the 5 eV absorption band observed in this work was mainly caused by the neutral oxygen monovacancy. A saturated absorptivity change of the UV-bleachable band after prolonged illumination was found to be 389 cm−1 for 70GeO2–30SiO2 films.

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.

Attenuated total reflection GeO2 hollow waveguide for 9.6–11.7 μm infrared light transmission

We report the preparation and characterization of an attenuated total reflection (ATR) GeO2 hollow waveguide. An internally GeO2-coated silica glass tube (bore size 1.0–1.2 mm, length 1.2 m) was prepared using a homogeneous liquid phase deposition method. Kramers-Kronig analysis reveals that the GeO2 cladding material qualifies as a reflective layer (nr < 1) for the ATR hollow waveguide structure. ATR-transmission of 9.6–11.7 μm light through HE11 mode is confirmed by loss spectrum analysis of the sample. The straight and bending (30°) transmission losses for delivery of a ∼40 W CO2 laser beam (10.6 μm) are 0.56 dB/m and 1.64 dB/m, respectively.

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).