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The experimental details of preparing the Cu2O-TiO2 samples and further characterization results of Raman spectra and XRD patterns are provided as the supplemental information to support the discussion. (DOCX 2387Â kb)

TiO

Ge-based alloys have drawn great interest as promising materials for their superior visible to infrared photoelectric performances. In this study, we report the preparation and optical properties of germanium-bismuth (Ge1-xBix) thin films by using molecular beam epitaxy (MBE). GeBi thin films belong to the n-type conductivity semiconductors, which have been rarely reported. With the increasing Bi-doping content from 2 to 22.2%, a series of Ge1-xBix thin film samples were obtained and characterized by X-ray diffraction, scanning electron microscopy, and atomic force microscopy. With the increase of Bi content, the mismatch of lattice constants increases, and the GeBi film shifts from direct energy band-gaps to indirect band-gaps. The moderate increase of Bi content reduces optical reflectance and promotes the transmittance of extinction coefficient in infrared wavelengths. The absorption and transmittance of GeBi films in THz band increase with the increase of Bi contents.

In this paper, we prepared Co2Z barium–strontium ferrite material (Ba1.5Sr1.5Co2Fe24O41) with BBSC (Bi2O3–B2O3–SiO2–CuO) glass by traditional solid state method. Using BBSC glass, the barium–strontium ferrite materials were successful synthesized in low temperature (920 °C). The effects of BBSC upon microstructure and magnetic properties of materials were systematically investigated. BBSC glass promoted the single phase formation of Co2Z ferrite and enhanced the densification of samples. With BBSC glass increased from 1 to 4 wt%, saturation magnetization (M S) increased gradually from 36.5 to 50.3 emu/g, coercivity (H C) decreased first and then increased, and magnetic permeability (μ′) increased first and then decreased. The materials with 3 wt% glass possessed excellent performances, including M S = 49.6 emu/g, H C = 164 Oe, μ′ = 7, and tan δ μ was about 0.03.

Ionic substitution is considered the most effective way to expand the operational frequency of barium hexaferrites. So far, little attention has been paid to high level substitutions and their impacts on low temperature sintering behavior. Here, co-substituted equiatomic Ni–Ti M-type barium ferrites of nominal compositions Ba(NiTi) x Fe 12−2x O 19 ( x = 0.30, 0.60, 0.90, 1.20) were prepared by a solid state reaction method and studied for their structural, and static and high frequency magnetic properties. It was found that the phase purity of M-type hexagonal barium ferrite does not depend upon the amount of Ni–Ti substitution investigated here. Concomitantly, Bi 2 O 3 additives are shown effective in lowering the sintering temperature of hexaferrite materials. For low temperature processed samples, the addition of Bi 2 O 3 enables improved densification from localized liquid phase formation and restricted grain growth from its colocation at grain boundaries. By comparing samples and process conditions, the effect of grain growth and sintering aid upon sample microstructure, bulk density ( ρ ), saturation magnetization ( M s ), coercivity ( H c ) and magnetic permeability ( μ ′ and μ ″) is made clear.

ZBS glasses (0.125–2.0 wt%) composed of ZnO–B2O3–SiO2 were added into the LiZnTi (Li0.43Zn0.27Ti0.13Fe2.17O4) ferrites to achieve low temperature sintering. Variations in microstructure, bulk density and ferromagnetic properties of the ferrites along with the changes of ZBS glasses concentration were discussed and analyzed in detail. Results suggest that LiZnTi ferrites mixed with appropriate amount of ZBS glass possess high saturation magnetization intensity, low coercivity, and low ferromagnetic resonance line width. Although this sintering process was completed at a low temperature (~900 °C), the ferrites still kept relatively good magnetic properties. Thus, the ZBS glass is a promising additive for low temperature sintering of LiZnTi ferrites.

NiZn ferrite nanoparticles (2–20 wt %) of composition Ni0.4Zn0.6Fe2O4 were introduced into LiZnTi ferrite of composition Li0.42Zn0.27Ti0.11Fe2.2O4 and sintered at a temperature of 920 °C for 2 h, well below that of the Ag melting point. Here, LiZnTi ferrites were prepared by a solid-state reaction method, and NiZn ferrite nanoparticles were fabricated by a hydrothermal chemical technique at 180 °C. A low ferromagnetic resonance (FMR) line width, low coercivity, and high magnetic moment were achieved after refinement of the heat treatment conditions of the mixture. Riveted full profile refinement of the X-ray powder diffraction patterns and analysis of Mossbauer spectra were employed to study the structure and caption distribution. The results confirm a pure spinel phase after processing. A narrow FMR line width of 152.5 Oe, a reduced coercivity of 132.9 A/m, and an improved saturation magnetization of 74.23 emu/g were obtained by way of the addition of 8 wt % NiZn ferrite nanoparticles.

In the present work, the Li0.43Zn0.27Ti0.13Fe2.17O4 ferrite, a low temperature sintered gyromagnetic material, was prepared via solid-state reaction method. A pure spinel phase can be formed with a sintering temperature ranging from 880°C to 920°C, which allows them to be co-fired with silver. The addition of ZnO–Bi2O3–SiO2 (ZBS) glass in the Li0.43Zn0.27Ti0.13Fe2.17O4 ferrites contributes significantly to the grain growth and ferromagnetic properties through a low temperature (~900°C) sintering process. Results show that the addition of ZBS glass (0.125–2.00 wt%) cannot only double saturation induction (from ~150 to 300 mT) but also drastically reduce ferromagnetic resonance line width at 9.3 GHz (from 920 to 228 Oe), indicating that ZBS glass is a good candidate for lowing the sintering temperature of LiZnTi ferrites.

Inefficient gas transport in the porous cathode is disastrous for the lithium–air battery to achieve a high electrochemical performance. Previous evaluation of the cathode diffusivity relies on indirect calculations based on multiple V–I data obtained over the intact battery system, which inevitably induces evaluation uncertainty and material waste. In this report, an electrochemical device is designed for the out-of-cell diffusivity measurement in the lithium–air battery with micro/nano-sized cathodes. With the measured diffusivity, a few electrochemical parameters including the limiting current density and the concentration polarization associated with the porous cathodes can thus be directly evaluated. The work facilitates the development of highly-efficient cathode materials in the general field of metal–air battery field.

Inverted pyramid hole arrays were fabricated by photolithography and used as templates to direct the growth of colloidal nanoparticle assemblies. Cobalt ferrite nanoparticles deposit in the holes to yield high quality pyramid magnetic nanoparticle assembly arrays by carefully controlling the evaporation of the carrier fluid. Magnetic measurements indicate that the pyramid magnetic nanoparticle assembly arrays preferentially magnetize perpendicular to the substrate.

Anodic growth of TiO2 nanotube (NT) arrays has been proved to be very promising for energy conversion applications, e.g. in photovoltaic devices and fuel cells. However, disordered “nano-grass” layers were always found on the top of the anodic TiO2 NT arrays. In this paper, we demonstrate a novel and simple method using a micromechanical cleavage technique to peel off the disordered nanograss layer. Using this method, ∼1 × 1.5 cm−2 of uncapped TiO2 NT arrays with a high-aspect ratio can be easily obtained. The results further indicate that the treatment can improve the photovoltaic and photochemical performances. After the treatment, the conversion efficiency (η) of the dye sensitized solar cells (DSSCs) increased by 29.3%. This work facilitates the growth and applications of high aspect-ratio anodic TiO2 NT arrays in related devices and systems.

The effects of Li 2 O–B 2 O 3 –SiO 2 –CaO–Al 2 O 3 (LBSCA) glass on the ferromagnetic properties of low-temperature sintered LiZnTi ferrites were systematically investigated. We characterized and analyzed the variation in microstructure, bulk density, porosity and ferromagnetic properties of the samples along with the changes of LBSCA glass content. The results revealed that the densification process of the samples was sensitive to the LBSCA glass content, and low LBSCA glass content was a precondition for sufficient densification, grain growth and ferromagnetic properties. The ferromagnetic resonance (FMR) linewidth (Δ H ) was explained on the basis of spin wave theory of anisotropy and porosity broadening in polycrystalline materials. The sample sintered at 900 °C with 0.85 wt% LBSCA glass addition exhibits a saturation magnetization ( m s ) of 64.23 emu/g and a ferromagnetic resonance (FMR) linewidth (Δ H ) of 191 Oe, suggesting that it is promising for LTCC phase shifters.

Quantum dot-sensitized solar cells (QDSSCs) are one kind of promising photovoltaic devices for harvesting solar energy. Previous reports have studied various photoanode materials in order to achieve a high photoelectric performance, while little attention has been paid to the electrolyte system inside the QDSSCs. In this report, a polysulfide (S 2− /S x 2− ) electrolyte system was investigated and optimized based on a CdS quantum dot/ZnO nanowire solar cell and a CdSe/CdS co-sensitized QDSSC. Water–methanol mixed solution was taken as the solvent for this polysulfide electrolyte, considering simultaneously the penetration ability and the ion dissociation of the electrolyte. Electrochemical impedance spectra (EIS) measurement was used to investigate the impedance of the electrons recombination with the electrolyte at the photoanode/electrolyte interface. With the measured efficiency of the CdS-QDSSCs, the optimal composition of the electrolyte can be obtained. The work facilitates the development of highly-efficient electrolyte in the general field of quantum dot-sensitized solar cells.

MnZn ferrite thin films were deposited on p-Si substrate and used as the dielectric layer in the graphene field effect transistor for infrared and terahertz device applications. The conditions for MnZn ferrite thin film deposition were optimized before device fabrication. The infrared properties and terahertz wave modulation were studied at different gate voltage. The resistive and magnetic MnZn ferrite thin films are highly transparent for THz wave, which make it possible to magnetically modulate the transmitted THz wave via the large magnetoresistance of graphene monolayer. Electronic supplementary material The online version of this article (doi:10.1186/s11671-017-2250-2) contains supplementary material, which is available to authorized users.

The magnetoresistance of graphene/MnZn ferrite/p-Si heterojunctions at Vsg = −15 V and room temperature. (DOCX 47 kb)

Li-Zn-Ti ferrite doped with 0.5 wt.% to 16 wt.% H3BO3-Bi2O3-SiO2-ZnO (BBSZ) glass was synthesized using a low-temperature ceramic sintering process. Selected parameters of saturation induction (BS), coercivity (HC), Curie temperature (TC), and complex permeability spectra were measured as functions of doping content, and their relationships with ferrite density and microstructure are discussed. It was found that Li-Zn-Ti ferrite can be fired at low temperature (900°C) with BBSZ glass content varying from 0.5 wt.% to 2 wt.%. The real permeability increased from 80 to 190 in the frequency range from 1 MHz to 3 MHz, the saturation induction BS increased from 105 mT to 150 mT at 1 kHz, whereas the coercivity HC decreased from 165 A/m to 65 A/m at 1 kHz and the Curie temperature TC slightly declined from 155°C to 143°C. These results confirm that this new ferrite material could be used in low-temperature cofired ceramic (LTCC) devices.

Sparse ZnO nanorod arrays (NRAs) are fabricated on transparent conducting oxide coated glass substrates by using a modified liquid phase epitaxial growth method. By adjusting the polymer concentrations and the spin-coating parameters, full infiltration of poly(3-hexylthiophene) (P3HT) into the as-prepared ZnO NRAs is achieved at 130°C in vacuum. A third component is incorporated into the P3HT/ZnO NRAs ordered bulk heterojunctions (BHJs) either through ZnO surface modification with N719 dye or CdS shell layer or by inclusion of a fullerene derivative into the P3HT matrix. Experimental results indicate that performances of the hybrid solar cells are improved greatly with the incorporation of a third component. However, the working principles of these third components differ from one another, according to morphology, structure, optical property, charge transfer and interfacial properties of the composite structures. An ideal device architecture for hybrid solar cells based on P3HT/ZnO NRAs ordered BHJs is proposed, which can be used as a guidance to further increase the power conversion efficiency of such solar cells.

The separated and ultrafine TiO2 nanotubes are fabricated by a modified rapid anodization method, which cannot be achieved through conventional anodization. Then, model dye-sensitized solar cells based on the prepared TiO2 nanotubes and commercial TiO2 nanoparticles (P25) are investigated, and a discrepancy is discovered between the light-harvesting capability and the power conversion efficiency. The charge transport and recombination are studied by the electrochemical impedance spectroscopy and the open-circuit voltage decay technique. Results show that the nanotube photoanode owns a longer electron diffusion length and a larger electron lifetime than the nanoparticle one, which can compensate for the loss of light absorption. The enhanced electron collection efficiency observed is attributed to the facilitated charge carrier pathways in the photoanode composed by the separated TiO2 nanotubes fabricated in this work. Therefore, the TiO2 nanotubes synthesized by this method are verified to have good electronic properties, which might find applications not only in photovoltaic, but also in catalysis, sensors, and other areas.

The best way to produce silicon-based Ge infrared detectors with lower dark current density is to develop high-quality buffer layers with low dislocation density and high relaxation degree. In this paper, we grew both Ge/Si and Si 1 − x Ge x /Si heterostructures and studied the effects of Ge composition, annealing-influenced dislocation density, and strain relaxation. Using high-resolution X-ray diffraction and swing curve (224) analysis, we found that the thin films after annealing exhibited strain relaxation of > 90%. Their dislocation density was lower than 8.0 × 10 5 /cm 2 , while their average roughness was 1.4–2.0 nm. These results show that such heterostructure buffer layers can be used to produce Ge-alloy infrared photodetectors with good performance.

The surface properties of photocatalysts strongly affect interfacial catalytic reaction and determine photocatalytic activity. In this work, surface-modified graphitic carbon nitride (g-C3N4) nanosheets were prepared via plasma treatment in H2, H2-CH4, and Ar atmosphere. Hydrogenated g-C3N4 nanosheets with hydrophilic group C-N-H, defect state, and exfoliated morphology were obtained via treating g-C3N4 nanosheets with H2 plasma at room temperature. The hydrogenated g-C3N4 nanosheets possessed the improved photocatalytic activity for hydrogen evolution, and the rate of hydrogen evolution exceeded that of pristine g-C3N4 by a factor of 4.8. Photocatalytic activity improvement is due to the introduction of hydrophilic group C-N-H, defect states, and exfoliated nanosheet morphology. Hydrophilic functional group of C-N-H can effectively capture water molecules. Defect states generated via plasma treatment acted as a capture center to suppress carrier recombination and transfer the trapped electrons to the adsorbed water molecules. Exfoliated nanosheet morphology provided a large number of active sites for catalytic reaction. Optical emission spectroscopy supported the introduction of hydrogen species during H2 plasma treatment of g-C3N4. First-principle density functional theory calculations confirmed the enhanced adsorption capacity of hydrogenated g-C3N4 for water molecules. The mechanism of enhanced photocatalytic H2-production activity was further proposed.

LiZnTi ferrite ceramics with high saturation flux density (Bs), large remanence ratio (Br/Bs) and high saturation magnetization (4πMs) is a vital material for high frequency devices. In the present work, we prepared uniform and compact LiZnTiBi ferrite with large average grain size (>30μm) at 900°C. Firstly, the hybrid materials, including Li2CO3, ZnO, TiO2, Bi2O3 and Fe2O3, were pre-sintered at 850°C at O2 atmosphere. Next, composite additives composited of Li2CO3 and ZnO nanoparticles were added to control grain growth. The influences of the Li2CO3 and nano-ZnO (LZ) on the microstructure and magnetic properties of LiZnTiBi ferrite, especially for grain size, have been analyzed. SEM images demonstrated that moderate LZ additives (x=0.75 wt%) can prevent abnormal grains. Also, the ferrite samples possess compact microstructures. The phenomenon indicated that the LZ additive is a good sintering aid for low-temperature sintering LiZnTiBi ferrites. XRD patterns showed that all samples have a pure spinel phase. The magnetic properties, including Bs, Br/Bs and 4πMs, have weak change when LZ additives were added. However, due to smaller average grain size, the coercivity (Hc) gradually increased. Thus, a low-temperature sintering LiZnTiBi ferrite with high saturation flux density (Bs=311.10 mT), large remanence ratio (Br/Bs=0.86), low coercivity (Hc=244.6 A/m) and high saturation magnetization (Ms=75.40) was obtained when 1.00 wt% LZ additive was added. More important, the LiZnTiBi ferrite possessed uniform average grain. Such a sintering method (i.e., adding composite additive to control abnormal grain) should also promote synthesis of other advanced ceramics for practical applications.

We proposed a new ways to control the phase shift of propagating spin waves by applying a local spin-polarized current on ferromagnetic stripe. Micromagnetic simulation showed that a phase shift of about π can be obtained by designing appropriate width and number of pinned magnetic layers. The ways can be adopted in a Mach-Zehnder-type interferometer structure to fulfill logic NOT gates based on spin waves.

The fabrication and photocatalytic properties of visible-light driven CuInSe2/TiO2 heterojunction films are reported. CuInSe2 nanoparticles (NCs) were synthesized using a solvothermal method and then decorated onto self-organized anodic TiO2 nanotube (NT) arrays through an electrophoretic deposition process, forming a CuInSe2 NC/TiO2 NT hetero-structure film. An increase in deposition time produced an increased amount of CuInSe2 NCs loaded onto the TiO2 NT arrays, expanding the light-absorption range of the CuInSe2 NCs/TiO2 NTs film from 400 nm to 700 nm. Photocatalytic degradation results show that activities of the CuInSe2 NCs/TiO2 NTs films were significantly enhanced compared to that of pure TiO2 NTs (degradation rate constant k increased from 3 × 10(-3) min(-1) to1 × 10(-2) min(-1)). Particularly, the CuInSe2 NCs/TiO2 NTs with 50 min electrophoretic deposition show the highest degradation rate, k = 1.6 × 10(-2) min(-1) (more than 5 times greater than that of the pure TiO2 NTs film), due to optimization of CuInSe2 NCs loading and a well-maintained open TiO2 tube-mouth configuration.

This study investigates the photocatalytic efficiency, type of reactive oxygen species (ROS) produced, and potential for structural and morphological modification of anodic TiO 2 nanotubes (NTs) synthesized using a novel, energy efficient, low temperature crystallization process. These TiO 2 NTs show greater photocatalytic efficiency than traditional high-temperature sintered NTs or supported Degussa P25 TiO 2 , as measured by degradation of methyl orange, a model organic dye pollutant. EPR analysis shows that low-temperature crystallized TiO 2 NTs generate both hydroxyl radicals and singlet oxygen, while high-temperature sintered TiO 2 NTs generate primarily hydroxyl radicals but no singlet oxygen. This “cocktail” of reactive oxygen species, combined with an increased surface area, contributes to the increased efficiency of this photocatalytic material. Furthermore, variation of the NT crystallization parameters enables control of structural and morphological properties so that TiO 2 -NTs can be optimized for scale-up and for specific treatment scenarios.

TiO2 films consisting of single-crystal anatase nanoparticles with exposed {001} facets were fabricated from anodized TiO2 nanotube arrays. The films' photocatalytic activities were further activated and then enhanced (∼2.5 times) by removing F(-) from the {001} facets. This study indicates that fluorine-free crystal surfaces are of great importance for the application of such kinds of single-crystal TiO2 nanoparticle films with exposed {001} facets in related areas.

One-dimensional ZnO nanorods arrays were self-assembly grown on a ZnO thin film, and then CdS quantum dots were deposited on the ZnO nanorods arrays by a successive ionic layer adsorption and reaction process. Scanning electron microscopy and transmission electron microscopy results indicate that the CdS quantum dots can be uniformly deposited on the ZnO nanorods arrays and the thickness of the CdS shell can be controlled through varying the number of the adsorption and reaction cycle. For a typical sample prepared by the adsorption and reaction cycles of 10 times, the thickness of the CdS is about 4.0 nm. Monodispersed CulnS2 quantum dots with a size of 3.5 nm were synthesized by a solvothermal route and then deposited on the ZnO nanorods arrays coated with the CdS quantum dots by using an electrophoretic deposition technique. Optical and electrical properties indicate that the as-fabricated ZnO/CdS/CulnS2 heterojunction structure not only exhibits a high absorption of the incident light in visible region but also can reduce a leakage current as compared to the ZnO/CdS heterojunction structure. Electrical impedance spectroscopy is used to analyze the electrochemical reaction of the interfaces.

A novel photocatalyst, which is composed of the Sb2S3/TiO2 nanotube coaxial heterogeneous structure arrays, was synthesized by combining an anodization method with an ion exchange adsorption method. Resultant products were characterized by X-ray diffraction analysis, scanning electron microscopy and UV–vis absorption spectroscopy. Results indicate that the Sb2S3 thin film layer can be well deposited on inside surface of the TiO2 nanotubes to form the coaxial heterogeneous structure arrays and there is an obvious absorption band peaked at 650 nm with a deposition of the Sb2S3 film layer. Furthermore, the photocatalytic activities of the Sb2S3/TiO2 nanotube coaxial heterogeneous structure arrays were also evaluated to exhibit a photodegradation for the methyl orange aqueous solution under UV–visible irradiation, which is mainly attributed to a formation of the Sb2S3/TiO2 nanotube coaxial heterogeneous structure arrays.

Germanium Tin (GeSn) films have drawn great interest for their visible and near-infrared optoelectronics properties. Here, we demonstrate large area Germanium Tin nanometer thin films grown on highly flexible aluminum foil substrates using low-temperature molecular beam epitaxy (MBE). Ultra-thin (10–180 nm) GeSn film-coated aluminum foils display a wide color spectra with an absorption wavelength ranging from 400–1800 nm due to its strong optical interference effect. The light absorption ratio for nanometer GeSn/Al foil heterostructures can be enhanced up to 85%. Moreover, the structure exhibits excellent mechanical flexibility and can be cut or bent into many shapes, which facilitates a wide range of flexible photonics. Micro-Raman studies reveal a large tensile strain change with GeSn thickness, which arises from lattice deformations. In particular, nano-sized Sn-enriched GeSn dots appeared in the GeSn coatings that had a thickness greater than 50 nm, which induced an additional light absorption depression around 13.89 μm wavelength. These findings are promising for practical flexible photovoltaic and photodetector applications ranging from the visible to near-infrared wavelengths.

In order to reduce dark current density for the silicon-based Ge infrared detector, the best way is to develop high quality buffer layers with low dislocation density as well as high relaxation degree. In this paper, Si 1−x Ge x /Si heterostrutures have been grown to study the Ge composition, roughness influenced dislocation density and strain relaxation. High resolution XRD results and swing curve (224) analysis indicate that the strain relaxation of thin film after annealing is larger than 90%. The film dislocation density is lower than 8.0×105/cm2, while the average roughness changes between 1.4 nm and 2.0 nm. Such buffer layer can be applied to grow high quality Ge alloy infrared detector.

In this work, Germanium-Tin (Ge 1−x Sn x , x=0.01−0.08) have been grown on p-Si (100) substrate using low temperature molecular beam epitaxy technique. 50 nm n-type GeSn layers were realized using a rapid thermal phosphorus diffusion with a doping concentration of 2.6×1016/cm3 to form p-Si/i-GeSn/n-GeSn p-i-n photodiodes. The results of I-V characteristic measurements show the p-Si/i-GeSn/n-GeSn structure has a typical diode rectifying effect. Near infrared range reflection spectra and terahertz transmittance spectra reveal that the optoelectronic properties of GeSn film in both infrared and terahertz wave range are closely related to the Sn concentration, the oxidation level of Sn and Ge as well as the microstructure of Ge 1−x Sn x films.

Highly active noble metal-free hydrogen evolution catalysts are critical for the development of more energy and cost-efficient hydrogen production. We report for the first time a novel nanosheet-assembled tube-like hierarchical MoSe2/CoSe2 microcage synthesized via a very simple and facile one-pot hydrothermal method for the electrocatalytic hydrogen evolution reaction (HER). The hierarchical structure of the MoSe2/CoSe2 microcage can be easily tuned by merely varying the Mo/Co ratio. Compared against pure MoSe2 and CoSe2 nano compounds synthesized by following the same procedure, the MoSe2/CoSe2 with an optimized composition shows a significantly enhanced HER activity, with a much lower onset of overpotential, larger cathodic current, and a smaller Tafel slope. The HER improvement is attributed to the increase in conductivity originating from the hierarchical tube-like structure, as well as by the nano defects induced by the Mo/Co synergic effect. This work opens a new class of nanomaterials for the development of an efficient hybrid HER catalyst.

In this paper, highly ordered TiO 2 nanotube arrays with the tube length in a very wide range between 10 and 100 μm are quickly fabricated on Ti sheets by using a modified electrochemical anodization process, and incorporated into dye-sensitized solar cells having the back-illuminated device architecture. Results indicate that the as-prepared TiO 2 nanotube arrays have well-defined tube geometry, with a diameter around 100 nm at present conditions, and the nanotubes are in fact comprised by TiO 2 nanoparticles other than single crystals. A maximum power conversion efficiency of 4.25% for the assembled DSSC can be achieved at an optimized nanotube length of 34 μm, which is consistent with the simulated results reported previously. By using the techniques of electrochemical impedance microscopy and open-circuit voltage decay, it has been further demonstrated that the vertically oriented TiO 2 nanotube arrays work as direct electron transport paths, reduce the electron recombination, and thus enhance the electron collection efficiency, as compared to the mesoporous film based on TiO 2 nanoparticles.

TiO 2 nanotube–nanoparticle mixture was prepared by a rapid anodization process in a perchlorate containing electrolyte followed by an ultrasonic process. Ag–TiO 2 nanocomposites were prepared at low temperature in polyethylene glycol (PEG600) solution, in which PEG600 was employed as the stabilizing agent as well as the reducer which can reduce Ag + on the surface of prepared TiO 2 nanocrystals. The synthesized samples were characterized by X-ray diffraction, transmission electron microscopy, energy dispersive X-ray detector, X-ray photoelectron spectroscopy and UV–vis absorption spectroscopy. Results showed that well dispersed Ag nanoparticles with a typical size of 5–10 nm can be synthesized on the surface of TiO 2 nanocrystals assisted by the PEG600. To investigate the photocatalytic activity of the samples, TiO 2 powders with different Ag contents were prepared and employed to decompound methyl orange under UV-light irradiation. Compared with pure TiO 2 nanocrystals and commercial P25, a great improvement of photocatalytic performance was found for the Ag–TiO 2 nanocomposites. It is believed that the excellent photocatalytic properties of the samples prepared in our experiment mainly result from promoted separation of photogenerated electron-hole pairs and higher reductive power due to the formed heterostructure between TiO 2 and Ag as well as the advanced absorption of light due to surface plasmon effect of Ag nanoparticles.

A low-cost and novel nanostructure heterojunction, which consists of the CuInSe 2 nanocrystals (NCs)/CdS quantum dots (QDs)/ZnO nanowire (NW) arrays, is fabricated for photovoltaic applications. The ZnO NW arrays with high transmittance are used as a highly efficient channel for rapid collection of the carriers to reduce the charge recombination, as well as to increase the contact area of the heterojunction. The p-type CuInSe 2 NCs are synthesized by a solvothermal method and then deposited on the CdS QDs coated ZnO NW arrays by an electrophoretic deposition technique. Results indicate that such a heterojunction configuration not only has high absorption for the incident light in the visible region but also can reduce the leakage current. A photovoltaic efficiency of the heterojunction is doubled as compared with that of the CuInSe 2 NCs/CdS QDs/ZnO thin film photovoltaic devices.

Ag–ZnO composite nanocrystals were prepared by a simple hydrolysis process of zinc acetate dihydrate together with a reduction of the Ag ions in diethylene glycol. Different contents of sodium hydroxide were added into the initial reaction mixture so as to form an effective contact between Ag and ZnO. X-ray diffraction analysis, ultraviolet–visible spectroscopy, X-ray photoelectron spectroscopy, energy dispersive X-ray spectroscopy, scanning electron microscopy and transmission electron microscopy were used to characterise the structural and morphological properties of the derived nanoparticles. The effects of the content of sodium hydroxide on the structural and morphological properties of the derived nanoparticles were discussed in detail. Photocatalytic measurement was also conducted, and the results indicate that the sample derived from 0·2M NaOH has the best ultraviolet photocatalytic activity for the degradation of the methyl orange aqueous solution among all the samples, which should be asc...

In this paper, p-type CuInS2 quantum dots are synthesized by a solvothermal route and incorporated with n-type TiO2 nanoparticles by a thermal treatment process. Transmission electron microscopy (TEM) results indicate that the CuInS2 quantum dots distribute uniformly and the size is ∼3.4 nm. Photocatalytic activities of the TiO2 nanoparticles sensitized with the CuInS2 quantum dots are evaluated by the degradation of the methyl orange aqueous solution under ultraviolet (UV) and visible (vis) light irradiation and show an enhanced performance, compared with the pure TiO2 nanoparticles and the pure CuInS2 quantum dots. Microstructural, morphological, and optical properties of the TiO2 nanoparticles sensitized with the CuInS2 quantum dots are characterized by X-ray diffraction (XRD) analysis, TEM, and UV–vis absorption spectroscopy. Results indicate that the CuInS2 quantum dots greatly enhance the absorption of UV and visible light due to the p–n heterojunction being constructed between p-type CuInS2 quantum...

In this paper, anodic TiO2 nanotubes are blended into the TiO2 mesoporous films based on P25 nanoparticles to assemble a list of dye-sensitized solar cells (DSSCs) with different nanotube concentrations. The electron properties of transport and recombination in the fabricated DSSCs are studied by using electrochemical impedance spectroscopy and the open-circuit voltage decay technique under AM 1.5 illumination. Results indicate that the electron lifetime increases with increasing the concentration of the anodic TiO2 nanotubes, the electron transport time at a blending level of 10 wt% TiO2 nanotubes is short as compared to that at 0 wt%, and above 10 wt%, the electron transport time has a trend of becoming large. Due to the combining effects of the electron transport and recombination, the electron collecting efficiency and the electron diffusion length obtain maxima at a blending level of 10 wt% nanotubes, which results in a highest short circuit current and a maximum energy conversion efficiency at this point in the DSSCs. This study gives a clear explanation for the performance enhancement of TiO2 particle-based DSSCs at a blending level of 10 wt% anodic TiO2 nanotubes and for the performance decrease at a blending level over 10 wt% anodic TiO2 nanotubes from the angle of the electron transport and recombination. This study also supplies a feasible and easy way to improve the performance of particle-based DSSCs by restraining electron recombination and accelerating electron transportation.

ZnO film with a novel bilayer structure, which consists of ZnO nanowire (ZnO NW) arrays as underlayer and polydisperse ZnO nanocrystallite aggregates (ZnO NCAs) as overlayer, is fabricated and studied as dye-sensitized solar-cell (DSSC) photoanode. Results indicate that such a configuration of the ZnO nanocrystallite aggregates on the ZnO nanowire arrays (ZnO-(NCAs/NWs)) can significantly improve the efficiency of the DSSC due to its fast electron transport, relatively high surface area and enhanced light-scattering capability. The short-circuit current density (Jsc) and the energy-conversion efficiency (η) of the DSSC based on the ZnO-(NCAs/NWs) photoanode are estimated and the values are 9.19 mA cm−2 and 3.02%, respectively, which are much better than those of the cells formed only by the ZnO NWs (Jsc = 4.02 mA cm−2, η = 1.04%) or the ZnO NCAs (Jsc = 7.14 mA cm−2, η = 2.56%) photoanode. Moreover, the electron transport properties of the DSSC based on the ZnO-(NCAs/NWs) photoanode are also discussed.

Anodic growth of TiO2 nanotubes has attracted intensive interests recently. However, the as-prepared TiO2 nanotubes are usually amorphous and they generally need to be crystallized by sintering above 450 °C. Here, we report on a facile method to crystallize amorphous anodized TiO2 nanotubes at a low temperature. We find that, simply by immersing them into hot water, the anodized TiO2 nanotubes can be transformed from amorphous to crystalline state at a temperature as low as 92 °C. Results indicate that the hot water treatment might be a versatile strategy to crystallize amorphous anodized TiO2 nanotubes at low temperature. Field-emission scanning electron microscopy, transmission electron microscopy, X-ray diffraction analysis, UV–vis spectroscopy, and Brunauer–Emmett–Teller (BET) analysis via N2 adsorption are used to characterize the resulting samples. In addition, the TiO2 nanotubes in powder form are taken as photocatalysts to explore their potential applications. Results indicate that the sample afte...

Present study reports a facile method for preparing individual TiO 2 nanotube (NT) powders by a two-step process, which includes that TiO 2 NT bundles are rapidly synthesized by an electro-chemical process in perchlorate-containing electrolyte and then they are disaggregated into individual TiO 2 NT powders under an assistance of ultrasonic oscillation treatment. Morphological and microstructural properties of the individual TiO 2 NT powders are characterized by field emission scanning electron microscopy and transmission electron microscopy. Results indicate that the individual TiO 2 NT powders, which have an outer diameter of about 20 nm and an inner diameter of 10 nm, can be easily obtained from the disaggregation of the TiO 2 NT-bundles by combining the electrochemical process with the physical processing. Furthermore, the individual TiO 2 NT powders exhibit higher photocatalytic activity than the TiO 2 NT-bundle powders.

TiO 2 nanotubes (NTs) in powder form were synthesized by a facile electrochemical process in a perchlorate-containing electrolyte. Transmission electron microscopy results indicate that the TiO 2 NT-powder is in an amorphous structure and has outer diameter of 20 nm and tube-wall thickness of 5 nm. X-ray diffraction analysis reveals that phase composition of the annealed TiO 2 NT-powders is related to the heat treatment scheme. Methyl orange was employed as a representative dye pollutant to evaluate the ultraviolet photocatalytic activity of the TiO 2 NT-powders. It was found that different post heat treatment schemes affect greatly the photocatalytic activities of the TiO 2 NT-powders, which should be ascribed to the changes in phase structural and morphological properties of the TiO 2 NT-powders. These results indicate that there should be a balance between crystal phase and nanotubular configuration for achieving the best photocatalytic activity of the TiO 2 nanotube powders.

TiO 2 nanotube powders as a photocatalyst for water processing were prepared by a rapid anodization process in a perchlorate containing electrolyte. Morphological and micro-structural properties of the TiO 2 nanotube powders were carefully characterized. Results indicate that the TiO 2 nanotubes with high aspect ratio, perfect tubular architecture, and smooth surface were successfully synthesized by a one-step electrochemical process. It is also noted that the nanotubes grow rather rapidly and well ordered in bundles with about 3 μm in length, 15 nm in outer diameter, and 10 nm in inner diameter. Effects of synthesis temperature of water bath on the morphological properties of the TiO 2 nanotubes were also studied, and a crystalline transformation process from amorphous to anatase then to rutile was revealed as the annealing temperature rises. Methyl orange was taken as a model compound to confirm the photocatalytic activities of the as-synthesized TiO 2 nanotube powders with different crystal structures. It is found that when annealed at 550 °C, the TiO 2 nanotube powders with a mixing phase structure of anatase and rutile have the best photocatalytic degradation activity for the methyl orange aqueous solution.

We propose to use a soft/hard exchange-spring coupling bilayer magnetic structure to introduce a narrow channel for spin-wave propagation. We show by micromagnetic simulations that broad-band Damon-Eshbach geometry spin waves can be strongly localized into the channel and propagate effectively with a proper high group velocity. The beamwidth of the bound mode spin waves is almost independent from the frequency and is smaller than 24nm. For a low-frequency excitation, we further investigate the appearance of two other spin beams in the lateral of the channel. In contrast to a domain wall, the channel formed by exchange-spring coupling can be easier to realize in experimental scenarios and holds stronger immunity to surroundings. This work is expected to open new possibilities for energy-efficient spin-wave guiding as well as to help shape the field of beam magnonics., Comment: 13 pages, 11 figures, letter

B2O3–Bi2O3–SiO2–ZnO (BBSZ) glass-modified Li2(Mn[Formula: see text]Ti[Formula: see text])O3 ceramics were fabricated via a solid-state reaction route. Pure phase and dense crystal morphology were obtained at 900[Formula: see text]C. Suitable amount of Mn[Formula: see text]-ion substitution could adjust the [Formula: see text] value of the Li2(Mn[Formula: see text]Ti[Formula: see text])O3 system to near zero. Among all of the Li2(Mn[Formula: see text]Ti[Formula: see text])O3 samples, the sample with x = 0.9 (marked as BL9 in this paper) possessed good microwave dielectric properties: [Formula: see text] = 18, Q × f = 14,056 GHz (9.58 GHz) and [Formula: see text] = (+)2.43 ppm/[Formula: see text]C. It is suggested that the Li2(Mn[Formula: see text]Ti[Formula: see text])O3 ceramic with BBSZ glass is a suitable low-temperature co-fired ceramic (LTCC) candidate for microwave applications.