High-electric field conduction phenomena in poly-2-chloro-p-xylylene/poly-p-xylylene composite thin films

The high-field currents in poly-p-chloro-xylylene (PCPX) thin films are due to hole injection from anode metal and collision ionization. PPX thin films showed the negative temperature dependence of high-field currents. Since the chlorine atoms in PCPX thin films act as carrier scattering centers, high-field currents in PCPX thin films are suppressed in the low-temperature region. This paper discusses the high-field currents of PCPX/PPX composite thin films; these films are PCPX thin films (d < 150 nm) deposited on PPX thin films (d > 200 nm). They were strongly suppressed at room temperature, but not at low temperature. Therefore, PCPX/PPX composite thin films showed a remarkable negative temperature dependence of high-field currents. High-field currents were suppressed more in PCPX (60 nm)/PPX (230 nm) composite thin film than in PCPX (130 nm)/PPX (230 nm). This can be explained by the suppression of the hole injection from anode by homo space charge at the interface between PCPX/PPX.     

Mocvd growth and characterization of PbTiO3 thin films on Pt/Ti/SiO2/Si substrates

Abstract

PbTiO₃ thin films were grown by Metalorganic Chemical Vapor Deposition (MOCVD) on 6′′ platinized Si wafers. In a first stage of investigation, the quality of the platinum surface was correlated with the substrate temperature and the composition of the atmosphere of the warming-up procedure in the reactor. The Pt reflectivity and the surface roughness were clearly modified by higher temperatures and by oxygen environments, though no clear diffusion mechanisms could be observed with Auger. In a second stage of investigation, the growth of PbTiO₃ was studied. Using a standard PbTiO₃ growth procedure, we studied the influence of substrate temperature and gas phase composition. Below 650°C, PbO appears as the main phase; at 650°C, PbTiO₃ and PbO coexist; and at 700°C, only PbTiO₃ is detected. The morphologies were examined by SEM / AFM and the roughness at the interface was studied by ellipsometry.     

Electrical and optical properties of metal-insulator-transition VO2 thin films

Vanadium dioxide thin films were deposited using in situ pulsed laser deposition technique on a-, c-, and r-plane Al₂O_3, and MgO(100) substrates. Microstructure of the films was varied between epitaxial VO₂, polycrystalline VO₂, mixtures of VO₂ and V₆O₁₃ with VO₂ as the main phase, and mixtures of VO₂ and V₆O₁₃ with V₆O₁₃ as the main phase by controlling the deposition oxygen partial pressure. Detailed XRD, SPM, and FESEM measurements were performed in order to analyze the structure of the films. Resistivity as a function of temperature, current–voltage characteristics in electric current induced Joule heating transition process, and the optical transmittance both in insulator and metal states were measured. MIT effect led to 10³–10⁵ change in resistivity with varying transition temperature and hysteresis loop widths. The largest and the steepest transitions were found in the films with polycrystalline microstructure deposited at higher oxygen pressures. Epitaxial films had 2.5 times higher insulator state conductivity than polycrystalline films, which lead to a clearly smaller switching powers in MIT effect generated by Joule heating. However, the optical properties in both states were not considerable affected by conductivity or microstructure properties. The relationships between the microstructure, electrical and optical properties, as well as MIT switching effect together its dynamics in the films are discussed.     

Mesophase configurations and optical properties of mesoporous TiO2 thin films

Highly ordered mesoporous TiO₂ thin films have been successfully synthesized via a copolymer templating sol-gel route. A configuration transition from hexagonal, to cubic, and then to a channel-like structure was observed when the copolymer-templated thin film was thermally annealed from 110 to 450^∘C. In the mesoporous TiO₂ film annealed at 450^∘C, mesopores were merged in a preferential direction, forming a channel-like structure consisting of a semicrystalline (anatase) framework. These films exhibit excellent optical transparency with transmittance higher than 85% in the visible region. A blue shift in UV-Vis absorption onset was shown for the mesoporous TiO₂ films, indicating a size quantization effect of nanocrystalline titania.     

Electrical characteristics of high dielectric constant BCTZ thin films

Abstract

High dielectric constant Ba_0.96Ca_0.04Ti_0.84Zr_0.16O₃ (BCTZ) thin films were deposited on Pt/Ti/SiO₂/Si substrates by spin on metal-organic decomposition (MOD) technique. Undoped and 0.4% Mg-doped BCTZ thin films were annealed in the temperature range from 600 to 900 °C for 1 hour in oxygen environment. The crystal structure of BCTZ thin films was analyzed by X-ray diffraction. The electrical properties of BCTZ thin films were investigated by capacitance—voltage (C—V) characteristics. Also, the electrical properties of these films were compared in conjunction with 0.4% Mg doping effect of BCTZ thin films for possible high dielectric constant material applications.     

Nafion/SiO2/PTFE复合膜的制备及性能

采用Nafion/SiO2溶液和多孔PTFE薄膜为原料,制备了Nafion/SiO2/PTFE复合膜.SEM图片表明:复合膜具有良好的树脂填充度;FTIR测试表明:SiO2被引入到复合膜中,没有影响膜的本体结构;TG-DTA测试表明:复合膜具有良好的保水性能.充放电测试表明:由于SiO2的保水作用,复合膜在高电流密度时(＞0.4 A/cm2)具有更好的输出能力.     

The electronic structures for the optical absorption of Hf-O-N thin films

The local structures of Hf-O-N thin films were analyzed using an extended X-ray absorption fine structure (EXAFS) study on Hf L _III-edge and first-principles calculations. Depending on their composition and atomic configurations, Hf₄O₈ (CN: 7.0), Hf₄O₅N₂ (CN: 6.25) and Hf₄O₂N₄(CN: 5.5) were suggested as the local structures of Hf-O-N thin films. The optical band gaps of Hf-O-N thin films were compared with the calculated band gap. And to investigate the optical absorption, the effects of film compositions on the valence bands of Hf-O-N thin films were analyzed by comparing the experimental valence band with the valence band.     

Thermal effects in Cr/sup 2+/:ZnSe thin disk lasers

We report the modeling and experimental characterization of thermal lensing in Cr/sup 2+/:ZnSe face cooled laser disks using the phase shift interferometry technique. The thermal lens powers of the 1 mm and 0.5 mm thick disks were strong (23 and 7 diopters at 8 W pumping). The thermal lens power scaled with disk thickness and pump power, and temperatures were reached in the disks such that nonradiative relaxation was significant. Laser output greater than 4 W average power was achieved using face cooled thin disks of Cr/sup 2+/:ZnSe.     

Dielectric constant measurement of thin films using goniometricterahertz time-domain spectroscopy

Goniometric time-domain spectroscopy (GTDS), employing an ultrashort electromagnetic (EM) pulse technique, has been developed for measuring the dielectric constant of thin films in a broad band of gigahertz to terahertz. An ultrafast optoelectronic system, including an emitter and a detector unit, is constructed with a &thetas;-2&thetas; goniometer. A silicon wafer was analyzed as the reference substrate material. A sharp π phase-shift of the reflected EM wave was observed at the Brewster angle of 73.5° for a bare silicon wafer. The phase shift for a film on the Si substrate is relatively smooth due to its two surfaces' providing a complex reflectance. The dielectric constant of the film on Si, related with angular dependency of the phase shift, can be extracted by means of fitting the curve or measuring slope of the curve near the Brewster angle. The measured dielectric constants of FLARE, TiO_x, and PZT film are reported     

流延法制备的SPEEK/SiO2/SiWA复合膜

用流延法制备了磺化聚醚醚酮(SPEEK)/二氧化硅(Si O2)/硅钨酸(Si WA)复合膜,并分析了复合膜的形貌、质子传导性能、阻醇性能及溶胀性能。m(SPEEK)∶m(Si O2)∶m(Si WA)=70∶10∶20的复合膜性能良好:在90℃时的质子传导率为0.018 S/cm;在30℃和90℃时的甲醇渗透率分别为3.4×10-8cm2/s和5×10-7cm2/s;温度从30℃升高到80℃,吸水率仅增加了17.9%,溶胀率仅增加了0.9%;Si O2和Si WA在复合膜中分散均匀,颗粒细小,没有团聚。     

SPSU/PWA/SiO2有机-无机复合质子交换膜的研究

以磺化聚砜(SPSU)、磷钨酸(PWA)和二氧化硅(SiO2)溶胶为原料,制备了一种SPSU/PWA/SiO2有机-无机复合质子交换膜。研究了SiO2对复合膜的抗氧化性、膜内PWA的稳定性、阻醇性、电导率等性能的影响。研究表明:当SiO2掺杂质量分数为2%时,复合膜显示了最佳的性能;80℃下,质子传导率超过Nafion膜,达到0.166S/cm,而甲醇渗透系数约为Nafion117膜的1/10。     

Domains in ferroelectric VDF/TrFE copolymer thin films: Investigated by a new optical probe method

Abstract

A new optical probe method was developed by using electro-optic and piezoelectric effects and a phase sensitive detection to determine the polarization of domains in ferroelectric thin films. Ferroelectric domains within a region smaller than 1 μm were detected in annealed VDF(65)/TrFE(35) copolymer thin films. The switching dynamics of these individual domains were also investigated by using this method.     

Electrical and non-linear optical properties of Ba2NaNb5O15 thin films

Abstract

Tungsten Bronze-type Ba₂NaNb₅O₁₅ (BNN) films were deposited on the fused quartz, Si and substrates using a RF magnetron sputtering method. The sputtering conditions, such as a deposition ratio and rate of the BNN film, were optimized.     

Study of nanocrystal TiO2 thin films by thermal annealing

The amorphous films were annealed in a wide temperature range (250–1000^∘C) and film properties of TiO₂ thin films were studied. Nano-sized anatase polycrystallites had been induced by thermal annealing for the films annealed at and above 300^∘C as confirmed by X-ray diffraction. Strong LO-phonon Raman modes, especially B_1g (395 cm⁻¹) and E _g (636 cm⁻¹) in Raman spectra and the absorption peak at 436 cm⁻¹ in absorbance spectra by Fourier transform infrared spectroscopy also indicated the existence of anatase phase in crystalline thin films. In addition, with the increase of the annealing temperature, the wettability of the film surface was enhanced as shown by the decrease of water contact angle from over 90^∘ to less than 40^∘. Moreover, upon UV laser irradiation on film surface, the water contact angle saturated at 10^∘ indicative of a highly hydrophilic surface for all the films, which arose from the dissociative adsorption of water molecules on the defect sits of the surface generated by the photocatalysis reactions of TiO₂. This behavior makes the film a good potential candidate for self-clean coatings.     

Electrical and optical properties of microwave dielectric thin films prepared by pulsed laser deposition

Abstract

Bi₂(Zn_1/3Nb_2/3)₂O₇, BiZN, materials possess high dielectric constant and low loss factor in microwave frequency region. They have good potential for device application, especially in the form of thin films. However, the microwave dielectric properties of a thin film are very difficult to be accurately measured. Evaluation on the dielectric behavior of the films through the performance of the microstrip line devices made of these films involves metallic conduction and stray field losses. A novel measuring technique, which can directly evaluate the microwave dielectric properties of a thin film is thus urgently needed.

In this paper, BiZN thin films were grown on [100] MgO single crystal substrates using pulsed laser deposition process. The high-frequency dielectric properties of thus obtained thin films were determined using optical transmission spectroscopy (OTS). The [100] preferentially oriented films with pyrochlore structure can be obtained for the thin films deposited at 400–600°C substrate temperature under 0.1 mbar oxygen pressure. OTS measurements reveal that the index of refraction (n=1.95–2.35) and absorption coefficient (k=0.28x10^?4-2.25 × 10^?4 nm^?1) of the films vary insignificantly with the crystallinity of the BiZN films.     

酸催化溶胶凝胶法制备细菌纤维素/SiO_2复合隔膜

在细菌纤维素水凝胶中,用酸催化正硅酸乙酯水解,原位生成纳米级Si O2粒子,压缩干燥后,得到细菌纤维素(bacterial cellulose,BC)/Si O2复合隔膜,并对该复合膜的微观形貌、热稳定性以及电化学性能等进行了测试和分析。热重分析(TGA)及热收缩测试表明该BC/Si O2复合膜在200℃以下具有较好的热稳定性(零收缩);BC/Si O2复合膜的锂离子电导率在常温下(25℃)可以达到2.10×10-4 S/cm;此外,BC/Si O2复合膜在Li/Li Fe PO4半电池中表现出很好的化学和电化学稳定性。所制备的BC/Si O2复合膜有望在锂离子电池中得到应用。     

Photoluminescence and optical dispersion parameters of N-doped ZnO nano-fiber thin films

N-doped ZnO (NZO) nanocrystalline thin films were successfully synthesized via sol–gel method. The structural and optical properties of the films were characterized by various techniques including X-ray diffraction, atomic force microscopy (AFM), UV–vis absorption and photoluminescence. The UV–vis absorption edge was changed with increasing N-doping concentration. X-ray diffraction (XRD) results clearly showed that the zinc oxide doped with nitrogen (5 to 20 wt.%) were identified with phases of hexagonal ZnO and N-doped ZnO nanocrystalline thin films. The refractive index dispersion mechanism obeys the Single oscillator model. The dispersion parameters E _o and E _d of the thin films were determined. The dispersion parameters were changed by N dopant. It is evaluated that the structural, optical constants, photoluminescence properties of Zinc oxide film can be controlled by N dopants.     

Preparation and physical properties of Nano-ZnSe/SiO2 mesoporous composite for assembly system

A novel synthesis route of ZnSe/gel-glass mesoporous composite was described. $ {\text{SeO}}_{4} ^{{2 - }} $ and Zn²⁺ were loaded into the porous framework of silica gel-glasses by immersion. Followed by drying and the reductive thermal treatment, the transparent, homogeneous ZnSe/SiO₂ samples with the color of light yellow were prepared. The specific surface area, grain size, structure and phase properties of nano-sized ZnSe/SiO₂ mesoporous composites were studied by powder X-ray diffraction, nitrogen sorption, SEM. The effects of pore structure properties and loading solution concentration on the optical absorption of ZnSe/SiO₂ were investigated by UV-vis absorption. It is found that the optical absorption edges of ZnSe nanoparticles in mesoporous silica shift to the red as ZnSe loading concentration increases, which is attributed to the quantum size effect. The nonlinear optical property of these samples was presented by the open aperture z-scan technique. This method has some potential advantages in comparison to the conventional methods.     

PEMFC用Nafion1135/SiO2复合膜的性能研究

采用溶胶-凝胶法制备Nafion/SiO2复合膜,通过XRD、膜的电导率测试和单体电池测试对Nafion/SiO2复合膜的结构和性能进行研究,结果表明:采用溶胶-凝胶法可以把SiO2原位复合到Nafion膜上;80℃湿态下Nafion1135/SiO2复合膜的电导率为0.178 S/cm,Nafion1135膜的电导率为0.147 S/cm;经过失水处理后的Nafion1135/SiO2复合膜的电导率为0.024 S/cm,而Nafion1135膜的电导率仅为0.005 S/cm;在H2、O2压力为0.17 MPa,电池温度110℃、H2加湿温度70℃时,Nafion1135膜的电池性能急剧下降,Nafion1135/SiO2复合膜仍可在电压为0.6 V、电流密度为800 mA/cm2的条件下稳定运行.     

浸渍法制备色素增感太阳电池FeS2/TiO2复合薄膜

采用溶液浸渍法在ITO导电玻璃表面的多孔TiO2薄膜上沉积了FeS2薄膜.在硫气氛中热处理后,制得了FeS2/TiO2复合薄膜.采用FeS<,2./TiO2薄膜作为正电极组装成色素增感太阳电池(DSSC).应用X射线衍射仪(XRD)、扫描电镜(SEM)、数显测厚指示表、可见-紫外分光光度计、XJCM-8型太阳电池测试仪等研究了FeS2/TiO2薄膜的不同热处理条件、薄膜表面形貌、厚度、吸光度以及光电性能.结果表明:此方法制得的FeS2/TiO2复合薄膜具有良好的光电性能,适宜用于制备DSSC电池.