Search

Cu2O-decorated TiO2 nanotube arrays (NTAs) are obtained using a two-step approach on Ti sheets. The applied voltage of Cu2O is − 0.2 V and − 0.3 V, respectively. The morphology and structure of these samples have been studied by field-emission scanning electron microscope (FESEM) and an x-ray diffractometer (XRD). FESEM analyses show that nanometre-sized Cu2O particles are attached to the TiO2 NTAs and the quantity of the Cu2O has greatly increased when the applied voltage tends to be more cathodic. The diffraction peaks for the anatase TiO2 and Cu2O are detected from XRD analysis. The bandgaps of TiO2 NTAs shift from 3.27 eV to 3.11 eV based on UV–Vis absorption spectra measurements. The photocatalytic performance of the Cu2O-TiO2 NTAs depends on the Cu2O deposition voltage. [ABSTRACT FROM AUTHOR]

A series of TiO2 nanostructures with rutile phase were synthesized on arbitrary substrates of conductive transparent fluorine-doped tin oxide (FTO), tin-doped indium oxide (ITO), and glass at the low temperature of 150 °C by the hydrothermal method. The samples were characterized by XRD, SEM, TEM, XPS, UV–Vis absorption, and micro-Raman spectroscopy. The effects of growth substrates on the morphologies and optical properties of nanostructures were investigated. TiO2 nanorods were grown on the FTO substrate, while TiO2 nanoflowers were grown on the ITO and glass substrates, and the growth mechanism for these different nanostructures is discussed in detail. The results show that the TiO2 nanorods can improve photocatalytic properties and photoelctrochemical (PEC) performance for its unique structure and optical properties. The TiO2 nanorods exhibited a maximal photocatalytic rate of 4.42 min−1 and photocurrent density of 0.049 mA/cm2, which is about 1.52 and 3.03 times higher than those of TiO2 nanoflowers grown on the ITO substrates, respectively. These findings are quite promising and encouraging for the use of TiO2 nanoarrays in photocatalysis and energy applications. [ABSTRACT FROM AUTHOR]

The novel few-layers MoS2 sensitized Ag-TiO2 were prepared through hydrothermal method, photoreduction method and spin-coating method, respectively. The microstructure, surface morphology, chemical composition and ultraviolet-visible absorbance of the samples were investigated systematically. The results indicated that the Ag nanoparticles and few-layers MoS2 were deposited successfully on the surface of TiO2 NRAs. The visible photocatalytic activity was estimated by degradation of methylene blue solution. The results indicated that the photocatalytic properties of MoS2/Ag-TiO2 was larger than pure TiO2 NRAs and Ag-TiO2. The significantly increased photocatalytic properties was attributed to the stronger visible light capture capability and the enhanced electron-hole pairs separation. [ABSTRACT FROM AUTHOR]

As p-n heterojunction photocatalysts usually possess dramatically improved photocatalytic activity than single photocatalysts, a novel ZnO/Cu2O heterojunction was designed by a facile self-templating method in this study. The crystal structure, chemical composition, surface morphology, and optical property of ZnO/Cu2O heterojunction were investigated to clarify the structure-property correlation. Scanning electron microscope and transmission electron microscope images proved the uniform core-shell submicrospheres of ZnO/Cu2O, in which a three-dimensional flower-like ZnO core was coated by a shell comprised of Cu2O nanoparticles. The photoresponse result showed that the band gap of the ZnO/Cu2O core-shell submicrospheres became narrow, and the absorption edge shifted from the ultraviolet region (380 nm) to the visible region (500 nm) compared with the pure ZnO microflowers. For the degradation of Rhodamine B under visible light, the photocatalytic efficiency of ZnO/Cu2O submicrospheres reached 96% within 40 min of reaction time, which was 3.8 times higher than that of pure ZnO microflowers and up to 4.5 times than that for pure Cu2O nanoparticles. The remarkable visible light-driven photocatalytic performance is mainly attributed to the extended photoresponse range and effective separation of the photo-generated electron-hole pairs in the unique heterojunction.ZnO/Cu2O core-shell microspheres for the degradation of RhB under visible light A novel core-shell ZnO/Cu2O heterojunction was synthesized by a facile self-templating method.Core-shell ZnO/Cu2O submicrospheres were comprised of three-dimensional flowerlike ZnO core coated by a shell of Cu2O nanoparticles.The band gap of ZnO/Cu2O submicrospheres became narrow and the absorption edge shifted to the visible region.ZnO/Cu2O submicrospheres exhibited better visible light-driven photocatalytic performance than pure ZnO or Cu2O. [ABSTRACT FROM AUTHOR]

TiO2 nanotube arrays (NTs) have been prepared by anodic oxidation and the oxidation voltages are 20, 30, 40 and 50 V, respectively. Microstructure, chemical composition and optical property of the TiO2 NTs were investigated. XRD and Raman spectra analysis show that the good crystal performance of TiO2 NTs obtained at the above voltages. The obtained samples are mainly composed of morphology nanotube arrays and TiO2 NTs are emerged at lower oxidation voltages. The Ti and O surface atom ratio for the sample prepared at 30 V is estimated about 1:2.14. UV-Visible absorption spectra analyses indicate that absorption edge appears slight blue shift phenomenon when the oxidation voltage rises and the absorption intensity decreases at the same time. The calculated optical band gaps for all samples are close to the standard value 3.2 eV of TiO2. [ABSTRACT FROM AUTHOR]

ZnO nanorods have been prepared by hydrothermal method and the reaction temperatures are 120, 140, 160 and 180 °C, respectively. Microstructure, morphology, chemical composition and optical properties of the samples were investigated in detail. XRD and Raman spectrum analysis shows that the best crystal performance of ZnO obtained at 140 °C. The samples are mainly composed of morphology nanorods and abundant ZnO nanorods with hexagon-shaped crystallites structure are emerged at all reaction temperatures. XPS measurement indicates that the Zn and O surface atom ratio is estimated about 1.13:1 for the sample prepared at 140 °C. Compared with the UV-Visible absorption spectra of the samples obtained at 120, 140 and 180 °C, absorption edge appears slight blue shift phenomenon with reaction temperature increasing and the absorption intensity reduces at the same time. These analyses reveal that the optical band gap increases with increasing of reaction temperature and all the gaps are less than the standard value 3.2 eV of ZnO. [ABSTRACT FROM AUTHOR]

Firmly-structured titania nanotube arrays (TNAs) were fabricated by electrochemical anodization at high voltage in very short time. A novel approach was developed to decorate CdS nanoclusters on tube top and quantum dots on tube side walls by using the method of ultrasonically-assisted successive ionic layer adsorption and reaction (U-SILAR). This U-SILAR not only helps remove the defective structure from the top surface of TNAs but also improve the adhesion of CdS on TNAs. Moreover, the photoelectric current of U-SILAR samples shows significant enhancement as compared with the samples fabricated by traditional SILAR. As a cover layer, ZnO film was found to further improve the photoelectric performance of the sandwich nanocomposite film. The mechanism was investigated. Finally, the properties of interface in nanocomposite system were studied by electrochemical impedance spectroscopy. The processes developed in this study can be adopted to fabricate sandwich nanostructures of other materials system with desired properties for device applications. [ABSTRACT FROM AUTHOR]

Highly crystalline hydroxide MgSn(OH) (MHS) polyhedral particles were synthesized by changing reaction time (10, 15 and 20 h) in a hydrothermal process. The structural and morphological poperties of obtained samples were characterized by X-ray diffraction (XRD), scanning electron microscopy (SEM), and UV-vis diffuse reflectance spectroscopy (DRS). The photocatalytic activity of the MHS was further evaluated by the degradation of methyl orange (MO) under ultraviolet (UV) light illumination. Compared with commercial TiO (Degussa P25), the MHS prepared for 15 h showed similar degradation efficiency of methyl orange (MO), mainly due to its higher specific surface area (55 mg) and better optical properties. [ABSTRACT FROM AUTHOR]

The TiO nanotube arrays (TiO NTAs) prepared by re-oxidation were chosen as basement. The NTAs prepared through re-oxidation show smoother surface and more uniform tube mouth on large scale compared with the first as-grown one. We use successive ionic layer adsorption and reaction method to deposit quantum dots (ZnS and CdS) onto the sample successively. The findings reveal that two kinds of quantum dots (∼10 nm) distribute regularly and the nanotube mouth is open. From the UV-Vis absorption spectrum of samples, the red shift occurs after the sedimentation of the two quantum dots, which proves that the double modification can expand the absorption to 650 nm. Among all specimens, the sample produced by co-deposition has the highest speed of catalytic efficiency of 90.7% compared with bare TiO NTAs (52.9%) and just CdS QDs sensitized sample (65.8%). In the test of photocatalysis durability, the decay percentages of CdS/TiO NTAs and ZnS/CdS/TiO NTAs were 35.8 and 48.4%, respectively, which means that the ZnS passivation layer plays a crucial role in enhancing photocatalytic activities. [ABSTRACT FROM AUTHOR]

ZnO thin films were synthesized by a facile electrodeposition method in the aqueous solution. Porous ZnO thin films with wurtzite structure could be achieved by mean of annealing treatment. The growth mechanism of the porous ZnO thin film was discussed. The intensity of the E mode in the ZnO thin film, which represents crystalline quality of the thin film increases with the increasing of annealing temperature. Optical properties indicate that annealing temperature has strong effect on the optical band gap value and defect concentrations. Both the green and yellow emissions corresponding to respective oxygen vacancies and oxygen interstitials can be identified. The results show that ZnO annealed at 400 °C exhibits a significant photocurrent density enhancement which is about 18 times larger than that of the as-deposited ZnO thin films. The mechanism of the enhanced photoresponse for the ZnO thin film has been discussed in detail. [ABSTRACT FROM AUTHOR]

The effects of zinc nitrate solution concentrations on the crystal structures, surface morphologies and optical properties of ZnO thin films were examined. X-ray diffraction patterns and scanning electron microscopy images indicated that all the samples exhibited the hexagonal structure and the morphologies of the thin films changed from 1D nanorods to 2D nanosheets with the increasing of solution concentration. The thin film grown in the 0.075 M solution presents the 3D network nanostructure, which was composed of many very thin 2D ZnO nanosheets, and possesses the largest first LO phonon mode, optical band gap, ratio for the intensity of deep level emission to that of UV emission. The results indicated that the optical properties of the ZnO thin films were affected by the solution concentration. Finally, the as-deposited ZnO thin film was used to generate a photocurrent and as a photocatalyst. Observations showed that the thin film grown in the 0.075 M solution exhibits the largest photocurrent density and degradation rate constant per unit area. The formation mechanism of the enhanced photoresponse and photocatalytic performance for the ZnO thin film has been investigated in detail. [ABSTRACT FROM AUTHOR]

NaZnO thin films were successfully synthesized on quartz glass substrates by sol-gel method. The effect of Na content on the microstructure, optical properties and UV photoresponse of the thin films was investigated using X-ray diffraction, optical absorbance, photoluminescence, and conductivity measurements. The results indicate that the NaZnO thin film exhibits the strongest preferential c-axis orientation with a polycrystalline hexagonal wurtzite structure and has the largest optical band gap. An obvious decrease in crystal size has been observed with the increasing of Na content. A weak ultraviolet emission band at about 381 nm and a strong visible emission band have been observed in the photoluminescence spectra. The NaZnO thin film has the shortest growth and decay time (45 and 18 s, respectively) and the largest photoresponse. The results indicate that the photoresponse can be effectively improved by means of moderate Na doping. [ABSTRACT FROM AUTHOR]

ZnO nanostructures were fabricated on glass substrate through a convenient deposition process. Firstly, ZnO seed layers were deposited on glass substrates through sol-gel method. Secondly, the ZnO nanostructures were then grown in a Teflon-lined stainless steel autoclave by immersing the seed layers into aqueous solution containing zinc nitrate hexahydrate and ammonia. The microstructures, morphologies, photoluminescence spectra and hydrophobicity of the nanostructures were analyzed by X-ray diffraction spectrometer, field emission scanning electron microscopy, laser micro-Raman spectrometer and contact angle apparatus, respectively. It can be seen that ZnO nanostructures display different surface morphologies such as ZnO nanorods parallel to the substrate surface, like-pencil ZnO nanorods and bending ZnO nanorods by altering the PH value. The largest intensity ratio of the UV/visible emission and the superhydrophobic surfaces (CA = 156°) with high adhesion can be achieved in the sample grown in the solutions with the PH value of 11.2. The high adhesion may be attributed to the strong capillary force and the ZnO nanostructures with petal effect can be explained by Wenzel model. [ABSTRACT FROM AUTHOR]

ZnO and NaZnO thin films were prepared by sol-gel method. NaZnO/GOQDs was prepared by spin-coating the graphene oxide quantum dots (GOQDs) on the NaZnO thin film. XRD result indicates that Na doping and modification of GOQDs does not change the crystal structure but promote the growth of ZnO crystal. The larger absorbance of the NaZnO/GOQDs in the wavelength range of 400-500 nm may be attributed to the blue absorbance of GOQDs. The orange-yellow emission of the samples may be derived from synthesis of O and V. PL result indicates that the Na doping in ZnO decreases the amount of oxygen-related O and V defects, but the GOQDs has little effect on O and V. The photocatalytic activity of NaZnO can be enhanced by Na-doping. The surface Na interstitial defects could serve as favorable trap sites of the electrons or holes to reduce their recombination and are benefit to enhance the photocatalytic activity of the NaZnO photocatalyst. In addition, the photocatalytic activity of NaZnO/GOQDs is higher than that of NaZnO. The result indicates that appropriate graphene oxide can serve as an electron trapper and retard the recombination of electron-hole pairs. [ABSTRACT FROM AUTHOR]

CuO microspheres have been prepared by means of hydrothermal method as a function of reaction temperature ranging from 70 to 130 °C. Microstructure, morphology, chemical composition, optical properties and photocatalysis performance of the as-received samples were investigated in detail. X-ray diffraction analysis shows that CuO and metal Cu content increase with increasing the reaction temperature. The samples are mainly composed of spherical particles and few CuO with octahedral structure emerges at 110 and 130 °C. X-ray photoelectron spectroscopy measurement indicates that the surface atom ratio of Cu and O is estimated about 2.3:1 for the sample prepared at 110 °C. UV-visible absorption spectra show that absorption edge appears red shift with the increase in the reaction temperature and the absorption intensity at the same time. After illuminated for 100 min, the decolorization rates of the samples obtained at 110 and 130 °C are above 80 %. [ABSTRACT FROM AUTHOR]

NaCuZnO thin films were prepared by sol-gel method on quartz glass. The effect of Na (or Cu) doping on the microstructure, surface morphology, optical properties of the thin films was investigated. The NaCuZnO thin film has the largest average grain size and the best preferential c-axis orientation, which may be attributed to the difference in ionic radius between Zn and Na (or Cu). The NaCuZnO thin film also presents denser morphology with little voids and the smallest optical band gap, which may be attributed to band edge bending and the larger grain size. The largest intensity of A(LO) modes may be due to the major structural defect concentrations. The quenching of UV and visible emissions, which may be attributed to the increase of non-radiative recombination transition, has been observed in the NaCuZnO and NaCuZnO thin films. [ABSTRACT FROM AUTHOR]

Cuprous oxide thin films were successfully synthesized on FTO substrates via the electrochemical method by changing the deposition potential. The effects of deposition potential on the microstructure, morphology, optical band gap and photoresponse of the thin films were investigated. The results revealed that intensity of (111) diffraction peak and preferential orientation along (111) plane increase with increasing the absolute value of deposition potential. The thin film with the more negative deposition potential has an increased average particle size and compact degree. The optical band gap of the sample deposited at −0.5 eV presents the largest value of 1.82 eV. Upon sunlight illumination, the photocurrent of thin film rises quickly at first and then gets slower. The slow photoresponse may be attributed to the capture of carriers by deep level traps in our case. [ABSTRACT FROM AUTHOR]

TiO nanorods (NRs) and nanoflowers (NFs) were synthesized on conductive and nonconductive sides of fluorine doped tin oxide (FTO-glass) substrate using a facile hydrothermal method. The effects of growth substrates on the various TiO morphologies and the optical performance of the different morphologies were also investigated. The average length of the TiO NRs was approximately 4.5 µm with a diameter of 175-215 nm. The average diameter of the TiO NFs was ca. 7.2 µm. The band gap values of the NRs and NFs were calculated to be 2.86 and 2.93 eV, respectively. Under illumination of UV-light, the prepared TiO NRs photocatalyzed the degradation of methyl orange at a higher rate than that of the TiO NFs, which can be attributed to the larger specific surface area of the TiO NRs. [ABSTRACT FROM AUTHOR]

Single-crystalline TiO nanosheet array films with tunable percentage of exposed {001} facets were synthesized on FTO by a simple hydrothermal method. The effects of the hydrochloric acid concentration on morphology, crystal structure, and optical property have been investigated by scanning electron microscopy, high-resolution transmission electron microscopy, X-ray diffraction, micro-Raman spectroscope system, and UV-Vis spectrophotometer. When the hydrochloric acid concentration increases from 4.8 to 5.2 mol/L, dense regular nanosheets tend to grow perpendicular to the substrate surface, and the percentage of exposed {001} facets is increasing from 76 to 84 %. Evolution of these nanosheet array films has accompanied by significant variations of photoelectronic and photocatalytic properties. The intensity of Raman peak E at 144 cm decreases, and the photocurrent increases when more proportion areas of {001} facets are exposed. The sample prepared at hydrochloric acid concentration of 4.8 mol/L shows the highest photocatalytic activity. This can be explained by the preferential carrier transport to different facets of the TiO crystal with tradeoff relation between the {101} and {001} facets, and a increasing of total catalytic sites. [ABSTRACT FROM AUTHOR]

In this paper, anatase TiO films have been prepared by hydrothermal method with different NaOH concentrations. The microstructures, optical and photoelectron-chemical properties of the as-deposited films were studied. SEM micrographs show the obtained films change from wave-like structure to one dimensional wire structure then to network structure. The average grain size of TiO thin films first increases and then decreases with increasing NaOH concentration. XPS measurement results exhibited the atomic ratio of Ti:O is estimated to be 1:2.21 for the sample deposited at 1 M. Band gaps obtained from UV-Vis absorption spectra shift from 3.29 to 2.23 eV with increasing reaction concentration. The photocurrent of TiO film deposited for 0.5 M reaction concentration is 3.8 µA, which is higher than other samples. [ABSTRACT FROM AUTHOR]

ZnO thin films were prepared by hydrothermal method in mixed solvent with different reaction temperatures. Microstructure, surface morphology, optical properties and UV photoresponse of the thin films have been investigated by means of X-ray diffractometer, scanning electron microscopy, laser micro-Raman spectrometer, UV-Vis spectrophotometer and interactive source meter instrument. The results indicated that ZnO thin films consist of ZnO nanoparticles with hexagonal wurzite structure. A small quantity of Zn(OH) appear as reaction temperature increase to 125 °C. ZnO thin film grown at 175 °C consists of many densely vertically aligned ZnO nano rods on the substrate and has the best preferential c-axis orientation. Three peaks centered at about 446, 568 and 1150 cm have been attributed to E(high), A( LO) and 2 A( LO) phonon mode. Broadening of the visible emission band may be attributed to abundant surface defects and surface states of the thin films. Variation of the E may be attributed to the synergy of surface morphology and oxygen-vacancy (V) density. The fast and slow UV photo response may be attributed to the adsorption and photo desorption of oxygen molecules on the surface of ZnO thin films and exchange process between oxygen gas and native deep defect level, respectively. [ABSTRACT FROM AUTHOR]

ZnO/ZnO-SL/CuO heterojunction was successfully fabricated on Cu foil by hydrothermal and sol-gel method. Crystalline phase, surface morphology and photoluminescence spectrum of the heterojunction were measured by X-ray diffraction, scanning electronic microscopy and fluorescence spectrometer, respectively. Contact angles of ZnO thin films were measured using a contact angle apparatus. The current-voltage characteristics of heterojunction in dark were investigated at room temperature. The results indicated that the heterojunction was composed of CuO phase and ZnO phase. The post-heat temperature of 250 °C was beneficial to preferred growth of ZnO thin film along the c-axis direction. The Sample 2 was composed of the uniform, compact and vertically aligned ZnO nanorods and has the most obvious hydrophobic-to-hydrophilic transition. The transport characteristics of the Sample 2 may be related to the space-charge-limited current in region II and a trapped-charge-limited current in region III. [ABSTRACT FROM AUTHOR]

Anatase TiO microspheres have been prepared by hydrothermal method and the reaction concentrations of mix solution containing hydrofluoric acid (HF) and ammonium fluoride (NHF) are 0.1, 0.2, and 0.4 M, respectively. Microstructure, morphology, chemical composition, optical and photoelectron-chemical properties of the as-deposited thin films were investigated in detail. XRD analysis shows that the grain size of the microspheres increases with increasing the reaction concentration. The films deposited at 0.1 and 0.2 M are formed by wellfaceted, regular microspheres with the size of 2-3 μm. XPS measurement indicates that the atomic ratio of Ti:O is estimated to be 1:2.05 for the sample deposited at 0.2 M. The band gap is close to the standard values of anatase TiO 3.2 eV as the reaction concentration increases. The photocurrent of TiO film deposited for 0.1 M reaction concentration is around three times as strong as those for 0.2 and 0.4 M under the same illumination. Current results will help to synthesise desired TiO films and expand its applications. [ABSTRACT FROM AUTHOR]

CuO/CuO composite thin films were synthesized by a facile hydrothermal method on Cu foils. Surface morphology, chemical composition, microstructure and wettability were investigated by scanning electron microscope, X-ray photoelectron spectroscopy, X-ray diffractometer and water contact angle apparatus. The results indicate that the Sample 2 is composed of many regular CuO octahedrons, tiny nanovillus and a small amount of spheric particles. The other samples were composed mainly of flower-like microparticles and regular CuO octahedrons. The content of copper (II) increases firstly and then decreases and the maximal value of content of copper (II) has been observed in the Sample 2. The Sample 2 displayed superhydrophobic property owing to its hierarchical porous micro/nanostructured surface. [ABSTRACT FROM AUTHOR]

Cuprous oxide (CuO) thin films were prepared by using electrodeposition technique at different applied potentials (−0.1, −0.3, −0.5, −0.7, and −0.9 V) and were annealed in vacuum at a temperature of 100°C for 1 h. Microstructure and optical properties of these films have been investigated by X-ray diffractometer (XRD), field-emission scanning electron microscope (SEM), UV-visible (vis) spectrophotometer, and fluorescence spectrophotometer. The morphology of these films varies obviously at different applied potentials. Analyses from these characterizations have confirmed that these films are composed of regular, well-faceted, polyhedral crystallites. UV-vis absorption spectra measurements have shown apparent shift in optical band gap from 1.69 to 2.03 eV as the applied potential becomes more cathodic. The emission of FL spectra at 603 nm may be assigned as the near band-edge emission. [ABSTRACT FROM AUTHOR]

ZnO thin films have been synthesized by means of a simple hydrothermal method with different solvents. The effect of deionized water content in the mixed solvents on the surface morphology, crystal structure, and optical property has been investigated by scanning electron microscopy, X-ray diffraction, and UV-Vis spectrophotometer. A large number of compact and well-aligned hexagonal ZnO nanorods and the maximal texture coefficient have been observed in the thin film, which is grown in the mixed solvent with x = 40%. A lot of sparse, diagonal, and pointed nanorods can be seen in the ZnO thin film, which is grown in the 40-mL DI water solution. The optical band gap decreases firstly and then increases with the increase of x. Reversible wettability of ZnO thin films were studied by home-made water contact angle apparatus. Reversible transition between hydrophobicity and hydrophilicity may be attributed to the change of surface chemical composition, surface roughness and the proportion of nonpolar planes on the surface of ZnO thin films. Photocurrent response of ZnO thin films grown at different solvents were measured in air. The response duration of the thin film, which is grown in the solvent with x = 40%, exhibits a fast growth in the beginning but cannot approach the saturate current value within 100 s. The theoretical mechanism for the slower growth or decay duration of the photocurrent has been discussed in detail. [ABSTRACT FROM AUTHOR]

Highly ordered TiO nanotube array (TN) films were prepared by anodization of titanium foil in a mixed electrolyte solution of glycerin and NHF and then annealed at 200°C, 400°C, 600°C, and 800°C, respectively. The samples were characterized by X-ray diffraction (XRD), scanning electron microscopy (SEM), water contact angle (WCA), and photoluminescence (PL). It was found that low temperature (below 600°C) has no significant influence on surface morphology, but the diameter of the nanotube increases from 40 to 50 nm with increasing temperature. At 800°C, the nanotube arrays are completely destroyed and only dense rutile film is observed. Samples unannealed and annealed at 200°C are amorphous. At 400°C, anatase phase appears. At 600°C, rutile phase appears. At 800°C, anatase phase changes into rutile phase completely. The wettability of the TN films shows that the WCAs for all samples freshly annealed at different temperatures are about 0°. After the annealed samples have been stored in air for 1 month, the WCAs increase to 130°, 133°, 135°, 141°, and 77°, respectively. Upon ultraviolet (UV) irradiation, they exhibit a significant transition from hydrophobicity to hydrophilicity. Especially, samples unannealed and annealed at 400°C show high photoinduced hydrophilicity. [ABSTRACT FROM AUTHOR]

Highly ordered TiO nanotube arrays (TiO-NTAs), with a uniform tube size on titanium substrate, were obtained by means of reoxidation and annealing. A composite structure, CdSe quantum dots@TiO nanotube arrays (CdSe QDs@TiO-NTAs), was fabricated by assembling CdSe quantum dots into TiO-NTAs via cyclic voltammetry electrochemical deposition. The X-ray diffractometer (XRD), field-emission scanning electron microscope (SEM), and transmission electron microscope (TEM) were carried out for the determination of the composition and structure of the tubular layers. Optical properties were investigated by ultraviolet-visible spectrophotometer (UV-Vis). Photocurrent response under visible light illumination and photocatalytic activity of samples by degradation of methyl orange were measured. The results demonstrated that the photo absorption of the composite film shifted to the visible region, and the photocurrent intensity was greatly enhanced due to the assembly of CdSe QDs. Especially, photocurrent achieved a maximum of 1.853 μA/cm after five voltammetry cycles of all samples. After irradiation under ultra violet-visible light for 2 h, the degradation rate of composition to methyl orange (MO) reached 88.20%, demonstrating that the CdSe QDs@TiO-NTAs exhibited higher photocatalytic activity. [ABSTRACT FROM AUTHOR]

Crystal structure, surface morphology, surface chemical composition and photocurrent response curves of the thin films were investigated by X-ray diffraction, scanning electron microscopy, X-ray photoelectron spectroscopy and electrochemical workstation. The results show that the composite thin films are composed of CuO and CuO phase. The relative content of copper (I) oxide on the composite thin films increases with the increase of solution concentration. Leaf-like CuO particles have been observed on the thin film grown in the 0.5 mol/L solution. Some regular octahedral and truncated octahedral CuO particles have been observed on the surface of thin films grown in the 0.6 and 0.8 mol/L solution, respectively. The best photocurrent response and the fastest growth and decay have been observed in the thin film grown in 0.6 mol/L solution. [ABSTRACT FROM AUTHOR]

A visible-blind ultraviolet GaN back-illuminated avalanche photodiode with separate absorption and multiplication regions (SAM APDs) are simulated based on drift-diffusion equation. The current-voltage characteristics of the device have been numerically obtained. The result is in good agreement with the experimental data. It was found that the thickness of the multiplication layer is important to improve the electrical field profiles and spectral response characteristics. A peak responsivity of 106.5 mA/W is achieved at 364 nm corresponding to the cutoff wavelength of GaN. [ABSTRACT FROM AUTHOR]

The dependence of laser beam induced current (LBIC) on the junction structure of $$\text {n}^{+}$$ -on-p HgCdTe photodiode has been numerically investigated. The calculated LBIC profiles varying with the junction depth are in good agreement with the experimental results (Musca et al. in J Electron Mater 28:603-610, ). It is found that there is a linear relationship between the magnitude of LBIC peak and the size of junction, such as depth and length. In addition, the LBIC shape between two peaks becomes more flat with increasing the junction depth. A competition mechanism of lateral and vertical current flow is proposed to explain the junction size dependence of the LBIC signal. The results help us to better understand the induced current flowing in photodiodes with different junction structures. [ABSTRACT FROM AUTHOR]

Zinc oxide (ZnO) thin films with different ethylene glycol monomethyl ether (EGME) ratio were prepared on Si substrates using a two-step process. The results show that they possess a polycrystalline hexagonal wurtzite crystal structure. The topography of the ZnO thin films evolves from nanoparticles to hexagonal nanorods with the decrease of EGME content. The photoluminescence spectra consist of a near-band-edge emission and two visible emissions. The optical band gap energy decreases first and then increases with the increase of EGME ratio in mixed solvent, the broadening of the optical band gap can be explained by Moss-Burstein effect. The wetting behavior of all the samples can switch from hydrophobicity to hydrophilicity through UV illumination. The degradation efficiency of the thin films increases with decreasing EGME content, photocatalytic reaction mechanism of the ZnO thin films is discussed in detail. [ABSTRACT FROM AUTHOR]

MgZnO thin films were prepared on silicon substrates by a sol-gel dip-coating technique. Microstructure, surface topography and optical properties of the thin films were characterized by X-ray diffraction, atom force microscopy, Fourier transform infrared spectrophotometer and fluorescence spectrometer. The results show that the thin film annealed at 700 °C has the largest average grain size and exhibits the best c-axis preferred orientation. As annealing temperature increases to 800 °C, the grain along c-axis has been suppressed. Roughness factor and average particle size increase with the increase of annealing temperature. The IR absorption peak appearing at about 416 cm is assigned to hexagonal wurtzite ZnO. The thin film annealed at 700 °C has the maximum oxygen vacancy, which can be inferred from the green emission intensity. Photocatalytic results show that the thin film annealed at 700 °C exhibits remarkable photocatalytic activity, which may be attributed to the larger grain size, roughness factor and concentration of oxygen vacancy. Enhanced photocatalytic activity of MgZnO thin films after a cycle may be attributed to the increase of surface oxygen vacancy and photocorrosion of amorphous MgO on the surface of thin film under UV irradiation. [ABSTRACT FROM AUTHOR]

ZnO thin films were synthesized via hydrothermal method on silicon substrate at various solution concentrations. The thin films were characterized by X-ray diffraction, field-emission scanning electron microscope and UV-Vis spectrophotometer. The results show that the thin films are polycrystalline with wurtzite hexagonal structure. The T values of (101) surface of the thin film increase from 0.929 to 1.840 at first, and then decrease to 0.779 with increasing solution concentration. The preferential orientation along the (101) crystal surface can be controlled by changing the solution concentration. Solution concentration has a significant effect on surface morphology of the thin films. The optical band gap of the thin films decreases, when the solution concentration of zinc nitrate hexahydrate increases from 0.01 to 0.06 mol/L and then increases when the solution concentration of zinc nitrate hexahydrate further increases to 0.08 mol/L. Photocatalytic activity of the thin films on degradation of methyl orange under UV light irradiation was studied in detail. The ZnO thin film with many cracks prepared from 0.01 mol/L shows the higher photocatalytic activity but the tower-like ZnO thin film prepared from 0.08 mol/L reveals the lower photocatalytic activity. Therefore, the photocatalytic activity of the thin films are mainly relate to surface morphology and crystallographic orientation. [ABSTRACT FROM AUTHOR]

Transflective and highly conductive Ag/ITO/Ag multilayer films were prepared by magnetron sputtering on glass substrates. The microstructure and optical properties of Ag/ITO/Ag multilayer films were systematically investigated by X-ray diffraction, scanning electron microscopy, and ultraviolet-visible spectroscopy. The optical properties of the multilayer films were significantly influenced by the thickness of the Ag surface layer from 3.0 to 12.6 nm. The multilayer film of Ag9.3nm/ITO142nm/Ag9.3nm shows the best comprehensive property. It could satisfy the requirement for transflective LCD. [ABSTRACT FROM AUTHOR]

Lead-free piezoelectric ceramics (1 − x)KNaNbO- xSrTiO with 6 mol% LiSbO doping have been prepared by conventional solid state sintering technique at 1,125 °C for 3 h in air. The effects of the SrTiO and LiSbO on the phase structure and electrical properties of the ceramics were systematically investigated. All ceramic samples show a single phase perovskite structure with tetragonal symmetry when LiSbO content was 6 mol% and SrTiO content was 2-10 mol% by X-ray diffraction analysis and highly dense structure by SEM patterns. The ceramic with x = 0.04 exhibits optimum electrical properties at room temperature ( d = 267 pC/N, k = 46 %, ε = 1,168, tan δ = 0.021, P = 30.3 μC/cm, E = 1.98 kV/mm), which suggests that the ceramic is a promising candidate material for lead-free piezoelectric ceramics. [ABSTRACT FROM AUTHOR]

ZnO, ZnCuO, ZnCuO and ZnCuO nanorod arrays are produced via a two-step process including an initial sol-gel method followed by hydrothermal growth. Effects of the Cu on microstructure, surface topography and optical properties of the nanorod arrays were studied and discussed. The results indicate that the nanorod arrays with a highly preferred orientation along the c axis were obtained on glass substrate. The ZnCuO possesses the maximum density of nanorod arrays of 6.0 × 10 cm. The optical band-gap energy E decreases first and then increases with Cu additions increase. The broadening of the optical band-gap can be explained by Moss-Burstein effect. The Cu additions will effective enhance the violet emission and suppress the green emission. The violet and green emissions are likely due to the electron transition from the localized level below conduction band and oxygen vacancy to the valance band. [ABSTRACT FROM AUTHOR]

ZnO micro/nanostructures with various morphologies were grown via hydrothermal etching of Zn foil. Controlling the reaction temperature and time, rod-like, pencil-like, tube-like and flowerlike ZnO micro/nanostructures could be prepared directly on the Zn foil surface at temperatures 100-180 °C with excellent reproducibility. X-ray diffraction patterns indicated that these ZnO micro/nanostructures were hexagonal. Possible mechanisms for the variation of morphology are discussed. Moreover, photoluminescence spectra of the as-grown samples revealed that all of them consist of UV emission band at around 392 nm. [ABSTRACT FROM AUTHOR]

Na-doped ZnO thin films were deposited on the glass substrates using sol-gel method. The effect of Na concentrations on the structural and optical properties of ZnO films was studied. As Na concentration increases from 0.0 at% to 16.0 at%, preferential c-axis orientation becomes more and more obvious, and the intensity of the diffraction peaks from (103) increases. The optical band gap E value increases from 3.261 to 3.286 eV first and then decreases as Na concentration increases from 0.0 to 2.0 at% and then beyond 2.0 at%. The intensity of all the emissions increases with increasing Na concentration and the origins of the violet emission (wavelength in the 400-407 nm) and the blue emission (wavelength at 473 nm) were discussed in detail. [ABSTRACT FROM AUTHOR]

The as-grown structure of electrochemically synthesized titania nanotube arrays is investigated by scanning electron microscope (SEM) in combination with transmission electron microscope (TEM) as well as X-ray diffraction (XRD). The analysis reveals a preferred growth direction of the nanotubes relative to the substrate surface and the well control on the nanotube arrays morphology. The crystal structure of the anatase phase is detected and exists in the tube walls without any thermal treatment, which makes it possible to realize the application of as-formed TiO nanotubes avoiding the degradation of the nanotube structures when sintering. In addition, a new growth, layered model of the anodic TiO nanotubes is presented to obtain further understanding of the growth mechanism. [ABSTRACT FROM AUTHOR]

Ag-TiO nanostructured thin films with silver volume fraction of 0-20% were deposited on silicon and quartz substrates by RF magnetron sputtering and annealed in ambient air at 950°C for 1 h. The phase structure and surface topography of the films were characterized by X-ray diffractometer and transmission electron microscope. Photocatalytic activity of the films was evaluated by light induced degradation of methyl orange (CHNNaOS) solution using a high pressure mercury lamp as lamp-house. The relation of photocatalytic activity and silver content was studied in detail. It was found that silver content influences phase structure of TiO thin films, and silver in the films is metallic Ag (Ag). With increasing silver content from 0 to 20 vol%, photocatalytic activity of the films increases first and then decreases. A suitable amount (2.5-5 vol%) silver addition can significantly enhance the photocatalytic activity of TiO films. The enhanced photocatalytic activity was mainly attributed to the extension of visible light absorption region of the films, the presence of anatase phase, the increase of oxygen anion radicals O and reactive center of surface Ti, and the better separation between electrons and holes on the films surface. [ABSTRACT FROM AUTHOR]

ITO films with thicknesses (134±8) nm, grown on glass substrates by sputtering method, were post-annealed at the temperatures of 100, 200, 300 and 400°C for 1 h, respectively. The as-deposited ITO film was amorphous, but crystallized with annealing at elevated temperatures, as demonstrated by X-ray diffraction. The transmittance spectra of all samples were obtained and subsequently simulated by means of spectroscopic ellipsometry. The optical constants n and k of the films were extracted. With the annealing temperature increasing, the optical constants n and k of the films firstly decreased then increased in the whole investigated wavelength range. The optical band gaps of all films were evaluated and they varied between 3.74 and 3.93 eV. [ABSTRACT FROM AUTHOR]

Nano Ag-ITO films with Ag volume fraction of 0.3%-1.0% were prepared by radio-frequency magnetron co-sputtering and analyzed by X-ray diffraction, scanning electron microscopy and ultraviolet-visible spectroscopy. Microstructure analysis shows that the films are composed of polycrystalline ITO matrix embedded with Ag nanoparticles with a mean size of 60-100 nm. Transmissivity spectra of Ag-ITO films indicate that the visible light transmissivity of the films decreases with increasing the Ag fraction. The transmissivity of the annealed films is higher than that of the as-deposited films. The volume 0.3% Ag-ITO films have the highest light reflectance. The annealed films exhibit lower light absorptance than as-deposited films. A surface plasmon resonance (SPR) peak of volume 0.3% Ag-ITO films is located around 510 nm. Compared with the annealed ITO film, the annealed volume 0.3% Ag-ITO film shows 10% higher reflectivity, while its transmittance is almost the same as that of the annealed ITO film, indicating its potential application in new-type transflective displays. [ABSTRACT FROM AUTHOR]

Al-doped ZnO nanospears were prepared by a hydrothermal method. The crystalline structure and photoluminescence properties of ZnO nanospears were characterized for investigating the effect of Al doping on the properties of ZnO nanospears. ZnO nanospears grow preferentially along the c-axis and have a fine tip. Al doping reduces the length of ZnO nanospears. In room temperature, photoluminescence spectra of Al-doped ZnO nanospears, a near band edge emission (~3.16 eV), and a violet emission (~2.91 eV) exhibit a strong doping-dependent characteristic and a temperature-independent characteristic, while deep level emission peak shows a temperature-dependent characteristic. In variable temperature, photoluminescence spectra near band edge emission (~3.31 eV) and its fine structures were observed when the measurement temperature is less than 57 K, and it shows an obvious temperature-dependent characteristic. The thermal quenching of this near band edge emission should be attributed to exciton scattering by defects and the presence of a high concentration of defects in Al-doped ZnO nanospears. [ABSTRACT FROM AUTHOR]

Iron oxides/reduced graphene oxide composites were synthesized by facile thermochemical reactions of graphite oxide and FeSO4·7H2O. By adjusting reaction temperature, α-Fe2O3/reduced graphene oxide and Fe3O4/reduced graphene oxide composites can be obtained conveniently. Graphene oxide and reduced graphene oxide sheets were demonstrated to regulate the phase transition from α-Fe2O3 to Fe3O4 via γ-Fe2O3, which was reported for the first time. The hydroxyl groups attached on the graphene oxide sheets and H2 gas generated during the annealing of graphene oxide are believed to play an important role during these phase transformations. These samples showed good electromagnetic wave absorption performance due to their electromagnetic complementary effect. These samples possess much better electromagnetic wave absorption properties than the mixture of separately prepared Fe3O4 with rGO, suggesting the crucial role of synthetic method in determining the product properties. Also, these samples perform much better than commercial absorbers. Most importantly, the great stability of these composites is highly advantageous for applications as electromagnetic wave absorption materials at high temperatures. [ABSTRACT FROM AUTHOR]