Effects of silver substrates on the visible light photocatalytic activities of copper-doped titanium dioxide thin films

Novel copper-doped titanium dioxide (Cu-doped TiO₂) thin films on silver (Ag) substrates with different thicknesses were prepared by sol–gel and magnetron sputtering methods. The influences of the Ag substrate thickness on the morphology and performance of the films were investigated by X-ray diffraction, scanning electron microscopy, X-ray photoelectron spectroscopy, photoluminescence spectroscopy, UV–visible spectroscopy, and photocatalytic degradation testing with methylene blue aqueous solution under visible light irradiation. The results indicated that Ag substrates with an optimal thickness of 30 nm not only maintained the tiny nanocrystals but also greatly improved dispersion of the nanoparticles on the surface of the nanofilms. Furthermore, during the calcination process, part of the Ag atoms diffused from the substrates into the Cu–TiO₂ films and substituted for the Cu ions to form Ag–TiO₂. A proper Ag substrate thickness (30 nm) greatly improved the photocatalytic properties of TiO₂ with photocatalytic efficiency, reaching approximately 86% in 300 minutes under visible light irradiation. However, an excess of Ag substrate not only led to the Cu ion separating out in the form of CuO but also resulted in the agglomeration of TiO₂ particles on the surface, which were detrimental to photocatalytic activities.     

Heat evolution and dissipation in organic light-emitting diodes on flexible polymer substrates

We investigated the effect of the heat generated in organic light-emitting diodes (OLEDs) on their performance with a focus on the thermo-physical properties of the substrates. OLEDs were fabricated on polyethylene terephthalate (PET), polyimide (PI), and glass substrates, and the instantaneous and time-resolved performances of the OLEDs were compared. The device operation temperature (T) was predicted via heat transfer analysis using the finite element method (FEM). The value of T during operation was experimentally measured using an infrared (IR) camera, and the results were compared with the numerically calculated values. The effects of T on the time-resolved electroluminescence (EL) spectra of the OLEDs on the different substrates were also investigated. The experimental results of this study agreed well with the numerical predictions that the T of the OLEDs on the polymers are higher than the T of the OLEDs on glass during operation due to the relatively low thermal diffusivity (α) of the polymer substrates used in this study. The results also showed that the performance and reliability of the flexible OLEDs (f-OLED) are highly dependent on the heat extraction capabilities of the substrates; thus, the current density (J), luminescence (L), voltage (V) characteristics, and efficiencies (η) over time of the OLEDs on PET and PI are inferior to the OLEDs on the glass substrate.     

Evaluation of PZT thin films on Ag coated Si substrates

Fabrication characteristics of hybrid thin film components are investigated. Lead zirconate titanate (PZT) films, thickness 10 μm, are fabricated by using laser ablation on the Ag electrode (about 1 μm thick) which is deposited on 200 μm Si substrates by evaporation. Composition close to the target material is obtained in PZT films even in air and without substrate heating. Low surface energy in the Ag−Si system causes spheroidization of the Ag layer on the fresh Si substrate, but the surface can be modified by grinding and oxidization. Only some cavities exist at the interface. The interface between the Ag electrode and PZT layer is physically continuous, as revealed by electron microscopy. After annealing at 750°C for 2 h, the PZT layer consists of the rhombohedral perovskite phase with a fraction of the pyrochlore phase. Detrimental interdiffusion between Pb and Si occurs during annealing if the PZT thin film is directly on the Si substrate. This is retarded by the presence of the Ag layer.     

PET柔性衬底上生长绒面ZnO-TCO薄膜及其在薄膜太阳电池中的应用

利用低压金属有机化学气相沉积(LP-MOCVD)技术在PET柔性衬底上低温生长绒面结构ZnO-TCO薄膜,DEZn和H2O作为源材料,B2H6作为掺杂剂.详细研究了薄膜掺杂流量对ZnO薄膜微观结构以及光电性能影响.优化获得的PET/ZnO:B薄膜厚约为1 500nm时,绒面结构PET/ZnO薄膜的方块电阻约为10Ω,可...     

不同柔性衬底上CdS薄膜退火前后的性能比较

采用磁控溅射法分别在柔性PI衬底、柔性AZO衬底和柔性ITO衬底上制备CdS薄膜,并在干燥空气中以CdCl2为源380℃退火,分别研究了不同柔性衬底及退火工艺对CdS薄膜形貌、结构和光学性能的影响。研究结果表明:退火前在不同柔性衬底上的CdS薄膜形貌依赖于衬底类型,退火后CdS薄膜的晶粒再结晶,晶粒度增大明显,且不再依赖于衬底类型。不同柔性衬底上CdS薄膜均为立方相和六角相的混相结构,退火后,六角相比例增大,薄膜的结晶质量提高。透过率退火后改善明显,其中,在柔性AZO衬底上的CdS薄膜透过率超过80%。     

Growth and characterization of GaAs films deposited on Ge/Si composite substrates by metalorganic chemical vapor deposition

We report the results of studies which have been made on heteroepitaxial layers of GaAs and AlGaAs grown by metalorganic chemical vapor deposition on composite substrates that consist of four different types of heteroepitaxial layered structures of Ge and Ge-Si grown by molecular beam epitaxy on (100)-oriented Si substrates. It is found that of the four structures studied, the preferred composite substrate is a single layer of Ge ∼1 μm thick grown directly on a Si buffer layer. The double-crystal X-ray rocking curves of 2 μm thick GaAs films grown on such substrates have FWHM values as small as 168 arc sec. Transmission electron micrographs of these Ge/Si composite substrates has shown that the number of dislocations in the Ge heteroepitaxial layer can be greatly reduced by an anneal at about 750° C for 30 min which is simultaneously carried out during the growth of the GaAs layer. The quality of the GaAs layers grown on these composite substrates can be greatly improved by the use of a five-period GaAs-GaAsP strained-layer superlattice (SLS). Using the results of these studies, low-threshold optically pumped AlGaAs-GaAs DH laser structures have been grown by MOCVD on MBE Ge/Si composite substrates.     

ZnO films deposited on GaAs substrates with a SiO2 thin buffer layer

Sputter deposition of ZnO films on GaAs substrates has been investigated. ZnO films were radio frequency (rf)-magnetron sputter deposited on GaAs substrates with or without SiO₂ thin buffer layers. Deposition parameters such as rf power, substrate-target distance, and gas composition/pressure were optimized to obtain highly c-axis oriented and highly resistive films. Deposited films were characterized by x-ray diffraction, scanning electron microscopy (SEM), capacitance, and resistivity measurements. Thermal stability of sputter-deposited ZnO films (0.5–2.0 μm thick) was tested with a post-deposition heat treatment at 430°C for 10 min, which is similar to a standard ohmic contact alloying condition for GaAs. The ZnO/SiO₂/GaAs films tolerated the heat treatment well while the ZnO/GaAs films disintegrated. The resistivity (10¹¹ Ω-cm) of the ZnO films on SiO₂-buffered GaAs substrates remained high during the heat treatment. The post-deposition anneal treatment also enhances c-axis orientation of the ZnO films dramatically and relieves intrinsic stress almost completely. These improvements are attributed to a reduction of grain boundaries and voids with the anneal treatment as supported by SEM and x-ray diffraction measurement results.     

Microstructures and electrical properties of SrRuO3 thin films on LaAIO3 substrates

Conductive SrRuO₃ thin films have been deposited using pulsed laser deposition on LaA10₃ substrates at different substrate temperatures. Structural and microstructural properties of the SrRuO₃/LaAlO₃ system have been studied using x-ray diffraction, scanning electron microscopy, and scanning tunneling microscopy. Electrical properties of SrRuO₃ thin films have been measured. It was found that the film deposited at 250°C is amorphous, showing semiconductor-like temperature dependence of electrical conductivity. The film deposited at 425°C is crystalline with very fine grain size (100∼200?), showing both metallic and semiconductor-like temperature dependence of electrical conductivity in different temperature regions. The film deposited at 775°C shows a resistivity of 280 μΩ.cm at room temperature and a residual resistivity ratio of 8.4. Optimized deposition conditions to grow SrRuO₃ thin films on LaA10₃ substrates have been found. Possible engineering applications of SrRuO₃ thin films deposited at different temperatures are discussed. Bulk and surface electronic structures of SrRuO₃ are calculated using a semi-empirical valence electron linear combination of atomic orbitals approach. The theoretical calculation results are employed to understand the electrical properties of SrRuO₃ thin films.     

Chemical vapor deposition of B12As2 thin films on 6H-SiC

Icosahedral boron arsenide (B₁₂As₂) thin films were deposited on 6H-SiC substrates by chemical vapor deposition using B₂H₆ and AsH₃ sources. X-ray diffraction analysis of the thin films showed them to have the rhombohedral crystal structure and lattice parameters of B₁₂As₂. Transmission electron microscopy showed that the films were polycrystalline with oriented crystal grains. The preferential orientation of the film with respect to the SiC substrate was determined to be: [0001]_B12_{As 2}//[0001]_6H-SiC and [ ]_B12_{As 2}//[ ]_6H-SiC to within 3°. Electron diffraction also revealed the extremely small lattice mismatch (<0.5%) between the B₁₂As₂ basal-plane lattice parameter and twice the SiC basal-plane lattice parameter.     

Deposition and characterization of indium oxide and indium tin oxide semiconducting thin films by reactive thermal deposition technique

In this paper, the deposition conditions and the characterization properties of the indium oxide (10) and indium tin oxide (ITO) thin films deposited by a reactive thermal deposition technique using the indium, indium-tin alloy sources are reported. The actively involved parameters during deposition have been identified for various substrate temperatures. The effect of oxygen partial pressure in evaporation has been identified. The indium-tin alloy source which was used in this work was prepared by hot zone diffusion technique. The structural, optical, and electrical properties have been characterized using optical microscope, x-ray diffractometer, ultraviolet spectrophotometer, and Hall effect measurement setup. The uniformity of the deposited films and the uniformity of the substrate surface effect on the deposited thin films were analyzed through sheet resistance measurements. The depositions were carried out on glass and quartz substrates. Good optical transmittance (99%) was achieved for 740 nm wavelength and above. The absorbance spectrum exhibit a value of 2% absorbance for IO/quartz structures. Large area (5.0 × 3.8 cm) film with unique optical properties is also reported here.     

Growth of polycrystalline silicon films on titanium and aluminum layers

Adherent, polycrystalline silicon films were vacuum deposited onto titanium passivated steel alloy substrates at substrate temperatures between 535 and 650°C and onto aluminum films at substrate temperatures between 480 and 520°C. Silicon films deposited onto titanium layers are characterized by a sub-micron grain size and a preferential orientation of the <110> direction perpendicular to the growth surface. Resistivities of ∿10⁴ ohm-cm are measured for the undoped films. Silicon films deposited onto aluminum layers have a larger grain size, ∿5μm, a columnar morphology and a preferential orientation of the <111> direction perpendicular to the growth surface. As-deposited resistivities of ∿10² ohm-cm are measured for these films. Boron and phosphorus doped silicon films on titanium layers were annealed. The behavior with annealing of the electrical properties of the films depended on which doping impurity was used. Silicon films on aluminum were annealed to reduce lattice damage within the silicon grains and to dope the films with aluminum from the aluminum layer. Resistivities of several ohm-cm were measured for the annealed films on aluminum.     

厚度对柔性衬底上制备的ZnO:Zr透明导电薄膜性能的影响

Transparent conducting zirconium-doped zinc oxide （ZnO：Zr） thin films with high transparency, low resistivity and good adhesion were successfully prepared on water-cooled flexible substrates （polyethylene glycol terephthalate, PET） by RF magnetron sputtering. The structural, electrical and optical properties of the films were studied for different thicknesses in detail. X-ray diffraction （XRD） and scanning electron microscopy （SEM） revealed that all the deposited films are polycrystalline with a hexagonal structure and a preferred orientation perpendicular to the substrate. The lowest resistivity achieved is 1.55 × 10-3 Ω·cm for a thickness of 189 nm with a Hall mobility of 17.6 cm2/（V·s） and a carrier concentration of 2.15×1020 cm-3. All the films present a high transmittance of above 90% in the wavelength range of the visible spectrum.     

Polycrystalline silicon thin film transistors fabricated in various solid phase crystallized films deposited on glass substrates

In this work, we have characterized various types of polysilicon films, crystallized upon thermal annealing from films deposited by low pressure chemical vapor deposition in the amorphous phase and a mixed phase using silane or in the amorphous phase using disilane. Polysilicon thin film transistors (TFTs) were fabricated, at low processing temperatures, in these three types of films on high strain point Corning Code 1734 and 1735 glass substrates. Double layer films, with the bottom layer deposited in a mixed phase and the top in the amorphous phase, allowed TFT fabrication at a drastically reduced thermal budget; optimum values of thicknesses and deposition rates of the layers are reported for reducing the crystallization time and improving film quality. Optimum deposition conditions for TFT fabrication were also obtained for films deposited using disilane. The grain size distribution for all types of films was shown to be wider for a larger grain size. Fabricated TFTs exhibited field effect electron mobility values in the range of 20 to 50 cm²/V·s, subthreshold swings of about 0.5–1.5 V/dec and threshold voltage values of 2–4 V.     

Thickness dependence of the properties of transparent conducting ZnO:Zr films deposited on flexible substrates by RF magnetron sputtering

Transparent conducting zirconium-doped zinc oxide(ZnO:Zr)thin films with high transparency,low resistivity and good adhesion were successfully prepared on water-cooled flexible substrates(polyethylene glycol terephthalate,PET)by RF magnetron sputtering.The structural,electrical and optical prooerties of the films were studied for different thicknesses in detail.X-ray diffraction(XRD)and scanning electron microscopy(SEM)revealed that all the deposited films are polycrystalline with a hexagonal structure and a preferred orientation perpendicular to the substrate．The lowest resistivity achieved is 1.55×10-3 Ω·cm for a thickness of 189 nm with a Hall mobility of 17.6cm2/(V·s)and a carrier concentration of 2.15×1020cm-3.All the films present a high transmittance of above 90％in the wavelength range of the visible spectrum.     

有机/无机/有机结构的封装薄膜水汽透过率研究

为了减少原子层沉积(ALD)方法在氧化物薄膜制备过程中ALD反应气对有机电致发光器件(OLED)性能的影响,利用旋涂光交联聚合物技术,直接在OLED上形成有机/无机/有机3层结构的保护薄膜。通过扫描电子显微镜(SEM)、原子力显微镜(AFM)的表面形貌分析表明,3层结构的封装薄膜表面平滑且致密,减少水(H2O)汽在氧化物表面积聚,降低H2O对氧化物薄膜的腐蚀作用,且成膜过程对OLED的各功能层没有伤害。经Ca薄膜的电学方法测量证明,这种3层结构的封装薄膜对气体有极高的阻隔作用,其H2O汽透过率(WVTR)可以达到9.0×10-5 g/(m2·day),从而实现了对OLED的有效保护。     

Study of bending reliability and electrical properties of platinum lines on flexible polyimide substrates

We have experimentally studied the variation in electrical resistance of flexible platinum lines patterned on polyimide foil when they are subjected to circular bending constraints. The lines were patterned by means of standard photolithography and sputtering deposition. Two different photolithography masks were used for comparative evaluation: an un-expensive transparency mask and a standard chromium mask. Measurements of the temperature coefficient of resistance (TCR) and time stability of the resistance have been acquired for lines bent down to 1.25 mm radius of curvature on a customized bending setup, showing good reliability results. The robustness of the lines has been also assessed by registering their change in resistance while bending at different radii of curvature. The lines showed reliability issues for radii of curvature below 1.25 mm, presenting a resistance variation of 19% for transparency mask-fabricated lines and 9% for chromium mask-fabricated lines. The worse reliability performances of transparency mask lines, compared to the chromium mask ones, was found to be due to their imperfect edges, which promoted the formation and propagation of cracks during bending. The results of the experiments in this work permitted to compare the performances of flexible conductive lines with different geometry and fabricated with two different masks, establishing quantitative and qualitative bending limits for their appropriate operation in flexible electronics systems.     

Properties of cobalt-doped zinc oxide thin films grown by pulsed laser deposition on glass substrates

Undoped and cobalt-doped zinc oxide (CZO) polycrystalline piezoelectric thin films (Co: 3, 5 at.%) using a series of high quality ceramic targets have been deposited at 450 °C onto glass substrates using a pulsed laser deposition method. The used source was a KrF excimer laser (248 nm, 25 ns, 2 J∕cm²). X-ray diffraction patterns showed that the Co-doped ZnO films crystallize in a hexagonal wurtzite type structure with a strong (0 orientation, and the grain sizes calculated from these patterns decrease from 37 to 31 nm by increasing Co doping. The optical waveguiding properties of the films were characterized by using a prism-coupling method. The distinct M-lines of the guided transverse magnetic (TM) and transverse electric (TE) modes of the ZnO films waveguide have been observed. With the aim of study the optical properties of the ZnO films, an accurate refractive index and thickness measurement apparatus was set up, which is called M-lines device. An evaluation of experimental uncertainty and calculation of the precision of the refractive index and thickness were developed on ZnO films. The optical transmittance spectra showed a good transparency in the visible region. Calculated optical band gap varying from 3.23 to 3.37 eV when the content of Co doping increases from 0 to 5 at.%.     

Synthesis method and substrate influence on TiO2 films doped with low vanadium content

Titania films doped with low amount of vanadium were deposited on different substrates (microscope glass, microscope glass covered with SiO₂ barrier layer, and silicon wafer with a thermally grown layer of SiO₂) by dip coating from solutions prepared by sol-gel and microwave (MW) assisted sol-gel syntheses. The selected molar composition was 99.95:0.05 which corresponds to 0.03 at% of V. The films were characterized by Scanning Electron Microscopy (SEM), Atomic Force Microscopy (AFM), X-ray diffraction (XRD) and Spectroscopic Ellipsometry (SE). The deposited films thermally treated at 450 °C, presented homogeneous and continuous nanostructured surfaces and good adherence to the substrates used. All samples crystallized in anatase phase and have good optical properties. The highest transmission value was obtained for the V-doped TiO₂ films (T > 90%) deposited from solutions prepared by microwaves assisted sol-gel method. Based on the obtained results it was concluded that the method of preparation has higher influence on the properties of the resulted films than the substrates used.     

A comparative study on the growth of InAlN films on different substrates

This work investigates the growth of InAlN films on Si (111), sapphire (001), GaAs (100) and glass substrates and compares the structural, morphological, electrical and optical properties of these films. One micron thick InAlN films were synthesized on these substrates at 300 °C by using reactive magnetron co-sputtering system. The structural analysis showed the formation of polycrystalline InAlN films on all the substrates having preferred orientation along (101) plane. The films grown on sapphire and silicon displayed better structural quality than the films grown on GaAs and glass. The morphological results revealed identical granular features on all the substrates with small variation in the grain size. The electrical resistivity of InAlN film on sapphire was the lowest one (8×10⁻³ Ω-cm) whereas the highest carrier concentration (8×10²⁰ cm⁻³) was obtained for the film deposited on glass. The energy band gap of InAlN films was determined through UV–vis absorption and reflectance spectroscopy. The band gap value obtained on the glass was slightly higher as compared to its value on the other substrates. The changes in InAlN properties on different substrates were explained on the basis of lattice mismatch, crystallite size, residual strain and orientation of the substrates.     

Fabrication and characterization of Ti-Ba-Ca-Cu-O superconducting films on LaAlO3 substrates

A multi-step process is used to fabricate Tl₂Ba₂Ca₁Cu₂O₈ films on (100) LaA10₃ substrates. Submicron thick precursor films of Ba-Ca-Cu-O are rf magnetron sputter deposited from a single target. Film stoichiometry is measured by ion beam backscattering spectroscopy. Deficiencies of the alkaline earths that are found in the precursor films are then compensated for by the addition of appropriate CaF₂ and/or BaF₂ films onto the surface of the precursor film. Post deposition annealing of the films is then done in an atmosphere of thallium oxide and oxygen in order to form the superconducting phases. The annealed films are examined using x-ray diffraction (XRD), an ac inductance technique, and critical current in an external magnetic field. XRD shows the c-axis length of the superconducting phase to increase as the overall film stoichiometry approaches 2212. The transition widths measured by inductive coupling weakly correlate with 77 K critical current measurements. Our best critical current results are 1.5*10⁶ amps/ cm² for a film measured at 4 K in an 8 T magnetic field (parallel to the films' c-axis).