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Herein, we report a facile approach for preparing Fe3O4@SiO2@C/Ni microtubes, which could be used as both a catalyst and adsorbent. During the synthetic process, two coating layers (SiO2 and PDA-Ni2+ layers) are polymerized on the surface of MoO3@FeOOH in turn with an extended Stober method using MoO3 microrods as sacrificing templates. Notably, the coating of inorganic SiO2 and organic PDA-Ni2+ layers and the removal of MoO3 cores are easily achieved simultaneously in ammonia solution with a one-step reaction. Interestingly, the coated silica not only protects the Fe3O4 nanoparticles, but also suppresses the reverse electron transfer from PDA to Fe3O4 in a calcination process, which leads to the in situ reduction of Ni2+ that enhances the dispersibility and density of the Ni nanoparticles. The resulting Fe3O4@SiO2@C/Ni hybrid microtubes can be used as a catalyst towards the reduction of 4-nitrophenol (4-NP) in the presence of NaBH4. Meanwhile, they also exhibit highly selective adsorption on His-rich proteins (BHb). Moreover, the hybrid microtubes can be conveniently separated with an extra magnetic field due to the presence of Ni and Fe3O4, and they show good cyclic stability, which is important for practical applications.

Molybdenum disulfide (MoS2) nanosheets have been found to exhibit intrinsic peroxidase-like activity that could be applied in colorimetric sensing platforms. However, their poor conductivity and few exposed edge sites often lead to poor catalytic activity, impeding the application of MoS2 nanosheets in enzyme-like catalysis. Here, a novel strategy was developed to selectively deposit Fe-doped MoS2 nanosheets on polypyrrole microtubes to obtain Fe-MoS2@PPy microtubes to address these issues. In the synthesized Fe-MoS2@PPy microtubes, PPy microtubes can not only be used as a conductive support to promote the electron transfer, but also greatly alleviate the aggregations of MoS2 nanosheets, and thus improve the enzyme-like activity. Meanwhile, additional active sites, formed by Fe doping, also endow the catalyst with excellent activity in enzyme-like catalysis. Notably, in the process of sulfidation, the dissolution, redistribution and diffusion result in the disappearance of MoO3@FeOOH cores and the formation of Fe doped MoS2 nanosheets, which significantly facilitate the deposition of Fe-doped MoS2 nanosheets on PPy microtubes. On the basis of the high peroxidase-like catalytic efficiency of the Fe-MoS2@PPy microtubes, a simple and convenient colorimetric strategy for the rapid and sensitive detection of L-cysteine has been developed. This strategy introduces both the PPy layer and Fe doping to increase the conductivity and the density of active sites of MoS2 nanosheets, thus enhancing the catalytic activity and stability. More importantly, Fe-MoS2@PPy microtubes could be used as a good support for loading other materials such as Au and Ag nanoparticles (NPs), forming ternary Fe-MoS2/Ag, Au@PPy nanotubes. This work offers an opportunity to develop low-cost and highly active MoS2-based nanocomposites for promising potential applications in electrochemical energy conversion and medical diagnostics.

Barium strontium titanate (Ba1−x Sr x )TiO3 (BST) thin films were deposited on Pt, Ru, RuO2, and Pt/RuO2 electrodes by radio frequency magnetron sputtering. The interfacial structure characteristic of the BST films deposited on various electrodes was investigated. X-ray photoelectron spectroscopy investigations showed that the interfacial diffusion layer in BST/Pt and BST/Ru are approximately 6 and 10 nm, respectively. The BST films are short of Ba and O elements comparing with the stoichiometry Ba0.65Sr0.35TiO3 in the interface region. Dielectric measurement of the BST films with thickness ranging from 70 to 400 nm revealed that the BST films deposited on Pt and Pt/RuO2 bottom electrodes have similar dielectric property, the BST films deposited on Ru have the highest bulk dielectric constant, and the thickness dependence of dielectric constant on the BST film deposited on RuO2 electrode can be neglected. The interfacial layer dielectric constant of BST films deposited on Pt and Ru electrodes are estimated to be about 34.5 and 157.1, respectively. The effect of interfacial dead-layer on the dielectric constant could be eliminated through selecting appropriate bottom electrodes.

Both up and down compositionally graded Ba1−xSrxTiO3 (BST) thin films with increasing x from 0 to 0.4 were deposited on Si and Pt/Ti/SiO2/Si substrates using sol–gel technique. The microstructure of the graded BST films were characterized by X-ray diffraction (XRD), Raman spectra, scanning electron microscopy (SEM) and atomic force microscopy (AFM). The down graded BST film had a larger dielectric constant and lower dielectric loss than the up graded film. The tunability of the up and down graded BST films was 42.3 and 38.9%, respectively, at an applied field of 250 kV cm−1 and measurement frequency of 1 MHz at room temperature. Both of the graded films had low-leakage current density. While, the leakage current density of down graded film lower two orders than the up graded BST film at the applied electric field below 100 kV cm−1. This may be due to the BaTiO3 layer in the down graded BST film not only serves as a bottom layer but also as an excellent seeding layer to improve the electric properties of the film.

Compositionally graded (Ba1−xSrx)TiO3 (BST) thin films, with x decreasing from 0.3 to 0, were deposited on Pt/Ti/SiO2/Si and Ru/SiO2/Si substrates by radio frequency magnetron sputtering technology. The microstructure and dielectric properties of the graded BST thin films were investigated. It was found that the films on Ru electrode have better crystallization, and that RuO2 is present between the Ru bottom electrode and the graded BST thin films by X-ray diffraction and SEM analysis. Dielectric measurement reveals that the graded BST thin films deposited on Ru bottom electrode have higher dielectric constant and tunability. The enhanced dielectric behavior is attributed to better crystallization as well as smaller space charge capacitance width and the formation of RuO2 that is more compatible with the BST films. The graded BST films on Ru electrode show higher leakage current due to lower barrier height and rougher surface of bottom electrode.

Ba0.65Sr0.35TiO3 (BST) thin films were deposited on Pt/Ti/SiO2/Si substrates by radio frequency magnetron sputtering technique. X-ray photoelectron spectroscopy (XPS) depth profiling data show that each element component of the BST film possesses a uniform distribution from the outermost surface to subsurface, but obvious Ti-rich is present to BST/Pt interface because Ti4+ cations are partially reduced to form amorphous oxides such as TiOx (x

The influence of lattice strain on the strength of dipoles in the Ho3+-doped barium-strontium titanate (BST) thin films has been analyzed. Thin films were produced by using the sol–gel technique on Si substrate. The resulting stress due to fabrication process was quantified by analyzing the {200} planes of the cubic perovskite structure and comparing them with the data for bulk materials. The influence of strain and changes due to Ho3+-ion doping were characterized by Raman and visible photoluminescence spectroscopy, which clearly show the evidence for the increased tetragonality due to weaker dipole interaction at B-sites of cubic perovskite in the presence of Ho3+-ions at concentrations larger than 3 mol%. The film strain can therefore be controlled to enhance the intensity of emitted light at 650 nm.

Ba 0.65 Sr 0.35 TiO 3 (BST) thin films doped with Ho 3+ were prepared on silicon substrates by a modified sol–gel technique. The microstructure of the BST films was characterized by atomic force microscopy (AFM), scanning electron microscopy (SEM), X-ray diffraction (XRD) and Raman spectroscopy. The results showed that 3 mol% Ho-doped BST has the largest grain size and surface root-mean square roughness. The thickness of the film was about 1.36 μm. The Ho 3+ luminescence intensity reached a maximum value in the sample with 3 mol% Ho 3+ ions concentration sintered at 700 °C. All the results showed that the BST: Ho 3+ films may have potential use for photonic devices.

Ba 0.65 Sr 0.35 TiO 3 thin films have been prepared by radio frequency (RF) magnetron sputtering on fused quartz at different substrate temperatures. Optical constants (refractive index n , extinction coefficient k ) were determined from the optical transmittance spectra using the envelope method. The dispersion relationship of the refractive index versus substrate temperature was also investigated. The refractive index of BST thin films increased from 1.778 to 1.961 (at λ = 650 nm) as deposited temperature increases from 560 to 650 °C. The extinction coefficient of as-deposited BST thin films increased with the increase of the oxygen to argon ratio, which was due to the change of the film stoichiometry, structure and texture of BST thin films. The oxygen to argon ratio also affected the fluorescence spectra. The fluorescence peaks intensity was greatly increased, apparent frequency shift was detected and the linewidth became narrow as the ratio of oxygen to argon increased from 1:4 to 1:1. The fluorescence spectra also indicated the band transition of BST thin films was an indirect gap transition.

Complex impedance spectra of BST ceramics were measured at different temperatures, and the results reveal that all the centers of the semicircles lie below the real axis, and the area of the semicircles decreases with the increasing temperature. Activation energy of grains and grain boundaries was obtained from a classical Arrhenius relation. The results show that the activation energy of grains and grain boundaries of undoped BST ceramics is 0.98 and 0.97 eV, respectively. After doping B2O3–SiO2, the activation energy of grain increased to 1.12 eV, which was due to B2O3–SiO2 redistribution to the grain boundary during the cooling process. The activation energy of grains increased to 1.16 eV after 1 mol% MgO doping, which was caused by the decrease of the oxygen vacancy concentration and the increase of the potential barrier of the grain boundary.

Ba0.65Sr0.35TiO3 (BST) thin films on p-silicon substrates were deposited by radio frequency magnetron sputtering. The effects of the deposition parameters on the crystallization and microstructure of BST thin films were investigated by X-ray diffraction and filed emission electron microscopy, respectively. The crystallization behavior of these films was apparently affected by the substrate temperature, annealing temperature and sputtering pressure. The improved crystallization can be observed for BST thin films that deposited at higher temperature. The dominant X-ray diffraction peaks became sharper and more intense as the annealing temperature increased. BST thin films deposited at high sputtering pressure of 3.9 Pa exhibited the (110) + (200) preferred orientation. Possible correlations of the crystallization with the sputtering pressure were discussed. The SEM morphology indicated the film was small grains and smooth.

BaxSr1−xTiO3 (BST) thin films were grown on different substrates with or without LaNiO3 (LNO) layer by a modified sol–gel process. The BST thin films obtained have full perovskite phase with dense and crack-free surface. BST thin films on different substrates with LNO layer show (100) preferential orientation, the texture coefficient (TC) value is calculated to be about 42.7%, whereas those without LNO layer show a fairly reduced preferential orientation, the TC value is just about 24.8%. It is considered that the preferential orientation is induced by the interface stress between LNO and BST. Electrical property measurements showed that BST thin film with a LNO interlayer has lower capacitance and larger dielectric loss, which is due to smaller grains of the thin film.

Ba0.65Sr0.35TiO3 (BST) thin films have been prepared by radio frequency magnetron sputtering on fused quartz at different substrate temperatures. Optical constants (refractive index n, extinction coefficient k) were determined from the optical transmittance spectra using the envelope method. The dispersion relationship of the refractive index vs. substrate temperature was also investigated. The refractive index of BST thin films increased from 1.778 to 1.961 (at λ = 650 nm) as deposited temperature increases from 560°C to 650°C. The extinction coefficient of as-deposited BST thin films increased with the increase of the oxygen-to-argon ratio, which was due to the change of the film stoichiometry, structure, and texture of BST thin films. The oxygen-to-argon ratio also affected the fluorescence spectra. The fluorescence peaks intensity was greatly increased, apparent frequency shift was detected, and the linewidth became narrow as the ratio of oxygen to argon increased from 1:4 to 1:1. The fluorescence spectra also indicated the band transition of BST thin films was an indirect gap transition.

(Ba1 − x Sr x )TiO3 (BST) thin films were deposited on Pt/Ti/SiO2/Si and YSZ/Pt/Ti/SiO2/Si substrates by radio frequency (RF) magnetron sputtering. The influence of YSZ interlayer on microstructures and dielectric properties of BST thin films were investigated by X-ray diffraction, atomic force microscopy, scanning electron microscopy and dielectric frequency spectra. It was found that the preferred orientation of BST thin films could be tailored by insertion of YSZ interlayer and adjusting the thickness of YSZ interlayer. The BST thin films deposited on YSZ interlayer exhibited a more compact and uniform grain structure than that deposited directly on Pt electrode. Dielectric measurement revealed that the BST thin films deposited on 10 nm YSZ interlayer have the largest dielectric constant and a low dielectric loss tangent. The enhanced dielectric behavior is mainly attributed to the YSZ interlayer which serves as an excellent seeding layer to enhance the crystallization of subsequent BST films layer, and a smaller thermal stress field built up at the interface between YSZ interlayer and BST film layer.

Ba"0"."6"5Sr"0"."3"5TiO"3 (BST) thin films doped with holmium were prepared on silicon and fused quartz substrates by a modified sol-gel technique. The microstructures of BST films were characterized by atomic force microscopy (AFM) and X-ray diffraction (XRD). The results showed that 3mol% Ho-doped BST has the largest grain size and surface root-mean square roughness. The transmission spectra of Ho-doped BST films were measured by spectrophotometer. The refractive index and thickness of 1mol% Ho-doped BST film was calculated using envelope method from the transmission spectra. It showed that the refractive index increased from 1.94 to 2.09 as wavelength decreased from 700nm to 400nm, which was smaller than pure BST thin films we have reported. The average oscillator strength and wavelength were estimated using a Sellmeir-type dispersion equation. These results show the potential of using Ho-doped BST thin films as an electro-optical novel material.

Compositional graded Ba x Sr 1- x TiO 3 ( x =0.6, 0.7, 0.8, 0.9, 1.0) (BST) thin films (less than 400 nm) were fabricated on Si and Pt/Ti/SiO 2 Si substrates by sol-gel technique. A special heating treatment was employed to form the uniform composition gradients at 700 °C. The microstructures of the films were studied by means of X-ray diffraction, atomic force microscope and field emission scanning electron microscopy. The results show that the films have uniform and crack-free surface morphology with perovskite structure phase. The small signal dielectric constant (ɛ r ) and dielectric loss (tanδ) are found to be 335 and 0.045 at room temperature and 200 kHz. The dielectric properties change significantly with applied dc bias, and the graded thin film show high tunability of 42.3% at an applied field of 250 kV/cm. All the results indicate that the graded BST thin films prepared by sol-gel technique have a promising candidate for microelectronic device.

Ba0.65Sr0.35TiO3 thin films have been prepared by RF magnetron sputtering. The crystallization and microstructure of the films were characterized by X-ray diffraction (XRD), scan electronic microstructure (SEM) and atom force microstructure (AFM). As-deposited thin films were found to be amorphous. The more intense characteristic diffraction peaks and improved crystallization can be observed in (Ba,Sr)TiO3 (BST) thin films deposited at high temperatures and annealed at higher than 650°C. Optical constants were determined from transmittance spectra by using the envelope method. The refractive index increased from 1.778 to 1.961 as the substrate temperature increased from 560 to 650°C. Both the refractive index and extinction coefficient increased with annealing temperature. The refractive index and extinction coefficient increased when the oxygen-to-argon ratio increased from 1:4 to 1:1. The dispersion of relation of the extinction coefficient vs wavelength was also investigated. The optical band gap of BST thin films was found to be about 3.56 eV, which decreased apparently with increasing annealing temperature.