A porous carbon layer was inserted between a BiFeO3 film and a Pt catalyst for efficient solar water splitting. A photocathodic current density of −235.4 μA cm−2 at 0 V versus RHE and an onset potential of 1.19 V versus RHE were obtained under 100 mW cm−2 Xe-lamp illumination.

Si has been studied as a photocathode for water splitting; however, its commercial application is hindered by its poor stability and low solar-to-hydrogen conversion efficiency (η), where the effective loading of catalysts on the Si surface is one of the key factors. Herein, we report that uniform and small Pt nanoparticles (NPs) were successfully prepared on an n+p-Si pyramid surface by a cheap electroless deposition method using Pt salt, based on the hydrophilic character of SiO2. A high η of 10.5% was obtained under 100 mW cm−2 simulated solar illumination with a Pt loading of only 1 μg cm−2, due to the fact that the Pt NPs are small enough to avoid the optical loss of Si, are distributed uniformly on the light-trapping pyramid Si surface to ensure a large number of reaction sites for H2 production, and establish intimate contact with Si to facilitate carrier transfer. Finally, an ∼15 nm amorphous TiO2 layer covered on the Pt/n+p-Si using atomic layer deposition results in a superior stability over more than one week of continuous photoelectrochemical testing, while increasing its η to a high value of 10.8% due to the improvement of charge transfer from Pt to the electrolyte. Our findings emphasize the importance of the effective loading of the catalyst and protective layer on the Si photocathode, which subsequently makes the photoelectrochemical process both efficient and stable.

Water splitting in a photoelectrochemical cell, which converts sunlight into hydrogen energy, has recently received intense research. Silicon is suitable as a viable light-harvesting material for constructing such cell; however, there is a need to improve its stability and explore a cheap and efficient cocatalyst. Here we fabricate highly efficient and stable photocathodes by integrating crystalline MoS2 catalyst with ∼2 nm Al2O3 protected n+p-Si. Al2O3 acts as a protective and passivative layer of the Si surface, while the sputtering method using a MoS2 target along with a postannealing leads to a vertically standing, conformal, and crystalline nano-MoS2 layer on Al2O3/n+p-Si photocathode. Efficient (0.4 V vs RHE onset potential and 35.6 mA/cm2 saturated photocurrent measured under 100 mA/cm2 Xe lamp illumination) and stable (above 120 h continuous water splitting) photocathode was obtained, which opens the door for the MoS2 catalyst to be applied in photoelectrochemical hydrogen evolution in a facile and scalable way.Keywords: Al2O3 layer; MoS2 catalyst; photocathode; photoelectrochemical properties; silicon;

Carbon nanodots treated with N2-plasma are effective catalysts for solar-driven hydrogen-evolved-reaction on np+-Si photocathodes and a support for Pt allowing for the reduction in Pt loading by a factor of about 3.5 while improving the photoelectrochemical activity.

Pb(Zr0.2Ti0.8)O3 wrapped CaFe2O4 particles were constructed on ITO coated quartz as a photocathode for efficient water splitting. A photocurrent of 152 μA cm−2 was obtained under zero bias vs. Ag/AgCl and 100 mW cm−2 with the assistance of positive poling and Ag decoration.

ITO/Pb(Zr,Ti)O3 contacts and Ag nanoparticles were used to construct a novel ferroelectric film photocathode exhibiting a stable short-circuit photocurrent of 110 μA cm−2 and an open-circuit voltage of 0.76 V under 100 mW cm−2 Xe-lamp illumination and zero-bias versus SCE.

The SrTiO3 films were synthesized by a hydrothermal method using TiO2 nanotube arrays as the precursor. The photoanode of SrTiO3 film decorated by carbon quantum dots (CQDs) is capable of converting near IR photon energy to photocurrent. Efficient carrier transfer and a high electron/hole separation rate of the hetero-junction between the CQDs and SrTiO3 were achieved.

Becasue of the existence of interface Schottky barriers and depolarization electric field, ferroelectric films sandwiched between top and bottom electrodes are strongly expected to be used as a new kind of solar cells. However, the photocurrent with a typical order of μA/cm2 is too low to be practical. Here we demonstrate that the insertion of an n-type cuprous oxide (Cu2O) layer between the Pb(Zr,Ti)O3 (PZT) film and the cathode Pt contact in a ITO/PZT/Pt cell leads to the short-circuit photocurrent increasing 120-fold to 4.80 mA/cm2 and power conversion efficiency increasing of 72-fold to 0.57% under AM1.5G (100 mW/cm2) illumination. Ultraviolet photoemission spectroscopy and dark J–V characteristic show an ohmic contact on Pt/Cu2O, an n+–n heterojunction on Cu2O/PZT and a Schottky barrier on PZT/ITO, which provide a favorable energy level alignment for efficient electron-extraction on the cathode. Our work opens up a promising new method that has the potential for fulfilling cost-effective ferroelectric-film photovoltaic.

It is widely accepted that ultraviolet (UV) light illumination of ferroelectric films can result in polarization imprint because of the accumulation of photoinduced carriers on the domain walls and/or on the electrode–film interfaces, and then the decrease of the reversible remnant polarization. In this paper, however, the enhancement of remnant polarization was exhibited in Pb(Zr0.2Ti0.8)O3 (PZT) films when irradiated by UV light. The time-dependent photocurrent and hysteresis loop of PZT films indicated that the transient behavior of photocurrent and coercive voltage offset were closely related to the polarization states, moveable defect charge (mainly oxygen vacancy) density, and aging time. Based on the observation of piezoresponse force microscopy, the mechanism behind the observed photoelectric and ferroelectric phenomena was proposed.

Spintronic devices are very important for future information technology. Suitable materials for such devices should have half-metallic properties with only one spin channel conducting. Nanostructures have played an important role in this aspect. Here, we report the realization of robust half-metallic ferromagnetism via the interface electronic reconstruction in artificial LaAlO3/SrMnO3 nanosheet supperlattices. On the basis of first-principles density-functional calculations, we reveal an obvious electron transfer from the (LaO)+ layer to the adjacent (MnO2)0 layer. And the partially occupied eg orbitals at the Mn sites can mediate a half-metallic state via a Zener double-exchange mechanism. On the other hand, for the superlattices with a (SrO)0/(AlO2)− interface, hole transfer at the interface is identified. These transferred holes reside mainly at oxygen sites in SrMnO3, leading to either the preserved G-type AFM ordering in pp-type superlattices or complex magnetic ordering in np-type superlattices. Interestingly, when these systems transit to ferromagnetic ordering by an external magnetic field, an obvious change of electronic state at the Fermi level is found, suggesting a large magnetoresistive effect therein. Our studies demonstrate the unique electric and magnetic properties arising from a magnetic ordering dependent charge transfer and electronic reconstruction at perovskite heterointerfaces, and their potential applications in spintronic devices.Keywords: charge transfer; electronic reconstruction; first-principles; half-metal; nanosheet superlattice

TiO2/Pt/TiO2 (TPT) multilayered films with different thicknesses of Pt layers from about 0.75 to 12 nm were prepared by radio frequency magnetron sputtering method. The as-prepared films were characterized by X-ray diffraction, scanning electron microscopy, atomic force microscopy, UV–visible diffuse reflectance spectroscopy, and photoluminescence spectroscopy. The photocatalytic activity of the samples was evaluated by the photocatalytic decolorization of methyl blue aqueous solution under ultraviolet light irradiation. The photocatalytic activities of all TPT multilayer films were higher than that of the pure TiO2 films. When Pt thickness was increased to 3 nm, the measured photocatalytic activity of the TPT film was highest, and exceeded that of the pure TiO2 films by a factor of more than three times. Such enhancement was ascribed to the presence of Pt layer, which inhibits the recombination of the photogenerated charge and carriers, as well as modifies the crystallinity of the TiO2 top layer.Highlights► The TiO2/Pt/TiO2 multilayer films were prepared by magnetron sputtering. ► The TiO2/Pt/TiO2 multilayer films have different thicknesses of Pt layers. ► The photocatalytic properties of all films were studied upon UV irradiation. ► The TiO2/Pt/TiO2 multilayer films show enhanced photocatalytic activities.

A facile sol–gel approach with a fixed calcination temperature is developed to prepare BiFeO3 (BFO) nanoparticles, and the gel-drying temperature is adjusted to control the appearance of a γ-Fe2O3 parasitic phase. The room temperature ferromagnetism of the samples is strongly dependent on the gel-drying temperature. When the gel-drying temperature increases from 80 to 140 °C, the saturated magnetization of the corresponding samples jumps from 0.22 emu g−1 to 1.2 emu g−1, allowing the nanoparticles to be magnetically separated in solution. From examination by transmission electron microscopy and X-ray photoelectron spectroscopy, it is confirmed that the γ-Fe2O3 parasitic phase is nucleated during the gel-drying process under high temperatures above 120 °C, and remains in the subsequent annealing process, resulting in the anomalous enhanced magnetization. Comparing with pure BFO nanoparticles prepared under low gel-drying temperature, the BFO/γ-Fe2O3 samples exhibit significantly increased visible-light photocatalytic ability towards rhodamine B. The formation of a heterojunction structure between the BFO and γ-Fe2O3 phases is proposed to be responsible for the enhanced photocatalytic activity. Further enhanced photocatalytic activity is obtained in this study when adding a small amount of H2O2 during photocatalysis, indicating the samples have photo-Fenton-like catalytic activity.

Based on the analysis of the photocurrent behavior of the Pt sandwiched (Bi3.7Nd0.3)Ti3O12 (BNT) films deposited by sol–gel method, the mechanism of the polarization effect on the photocurrent of Pt sandwiched multi-crystalline ferroelectric films was clarified that, in ferroelectric films irradiated by the extra light, the depolarization field directly gives more contribution to the photocurrent when the polarization aligned under the external poling voltage, while the variation of the top or bottom interface Schottky barriers, because of the presence of the polarization charge near the top or bottom interface, have a indirect and subordinate influence on the photocurrent.Highlights► Distinguish the two mechanisms of the polarization effect on photocurrent. ► Research the influence of the polarization charge near the interface. ► There is less study on the photovoltaic property of BNT films.

The TiO2 nanoring/nanotube (R/T) combined structure was obtained by a simple two-step anodization. The as-prepared samples were characterized by X-ray diffraction, Raman, scanning electron microscopy, photoluminescence spectra, and UV–vis absorption spectroscopy. The photoelectrochemical measurements demonstrate that the combined structure shows high photo-to-current conversion efficiency, fast charge transfer speed, and surface dominant photoelectrochemical response. The behavior of photoelctrochemical activity in TiO2 R/T combined structure and pure nanotubes (NTs) has been investigated through electrochemical impedance spectroscopy and photo-to-current conversion efficiency measurement. It is demonstrated that the formation of a heterojuction structure in R/T composite plays an important role in the kinetic behaviors (including charge separation efficiency and transport capability) of photogenerated charges. The TiO2 R/T combined structure greatly increases charge separation efficiency and photoconversion capability. We discuss the mechanism for the enhancement of TiO2 R/T combined structure photoelectrochemical activity and support our conclusions with ultraviolet photoelectron spectroscopy results.

We have investigated the effect of fluorhydric acid (HF) treatment on the photoluminescence (PL) properties of SrTiO3:Pr3+ powders prepared by sol–gel method. The red emission intensity increased significantly up to 18 times when the powders were subjected into a water-diluted 5% HF solution for 10 min. The origin of the PL enhancement was ascribed to the increase of oxygen vacancies in HF-treated SrTiO3:Pr3+ powders. This study also manifested that HF etching is more effective to improve the red PL intensity than vacuum-annealing for the sol–gel made SrTiO3:Pr3+ powders.

BiFeO3 (BFO) is of considerable interest because of its potential applications in the design of devices combining magnetic, electronic, and optical functionalities. Effects of the Gd dopant on the structural, photocatalytic activity, and ferromagnetic properties of BFO nanoparticles have been studied. X-ray diffraction and Raman spectra results of Bi1−xGdxFeO3 (BGFOx, x = 0, 0.05, 0.1, and 0.15) reflect that the crystal structure of the samples remain stable for x < 0.1, while compositional-driven phase transition from rhombohedral to orthorhombic is observed at x = 0.1. The photocatalytic activity to decompose Rhodamine-B under visible-light illumination increases in BGFOx as x increases from zero to 0.1 and then decreases for x = 0.15. The maximum in photocatalytic activity near the phase boundary of x = 0.1 is associated with the changing of the polar behavior of the nanoparticles. Comparing with the linear magnetization−magnetic field (M−H) relation in pure BFO nanoparticles, obvious M−H loops can be observed in the doped samples, which are ascribed to the distorted spin cycloid and magnetically active characteristic of Gd3+ ions.

The effect of different Ca deficiencies on structural and luminescent properties of the Ca1−x−yPrxTiO3 powders was investigated in this study. Ca deficiencies affect both the fluorescence intensity at 613 nm and afterglow properties of the phosphors. An increase in the fluorescence intensity at 613 nm was observed when x = 0.25 mol% and y increases from 0 to 1.5x. Similar result was found for x = 0.15 and 0.35 mol%. Increased afterglow was observed for samples having low y values after irradiated by 375 nm light. To explain the experimental results, the formation of trapping centers related to Pr3+ defects when they are not compensated by Ca vacancies was proposed based on the research works of [P. Boutinaud, E. Pinel, M. Dubois, A.P. Vink, R. Mahiou, J. Lumin. 111 (2005) 69] and [W. Jia, D. Jia, T. Rodriguez, D.R. Evans, R.S. Meltzer, W.M. Yen, J. Lumin. 119/120 (2006) 13].

Ca1−x + yPrxTiO3 (CPTO) films with x = 0.25 mol% and different y values were prepared by the sol–gel method. Both Ca excess and deficiency were found to be effective to improve the red emission brightness of the CPTO films, while they have small effect on the surface roughness and grain sizes of the films. The highest red emission at 612 nm for the case of Ca2+ deficiency happened on y = −x/2, and the one for the case of Ca2+ ions excess was on y = 3x. Charge compensation and substitution of Pr3+ for Ti4+ when Ca2+ ions was excessive in the CPTO films were proposed to explain the experimental results. These results indicate that the traditionally adopted Ca deficiencies may not be the best one for the efficient red emission of CPTO films, instead, a proper Ca excess is more effective.

The structural, electrical, luminescent, and magnetic properties of Eu3+-doped Ba0.77Ca0.23TiO3 (BCT23:Eu) ceramics were investigated in this paper. Three different incorporation mechanisms of Eu3+ were realized in BCT23 by considering different charge compensation mechanisms: (i) Ca site substitution with Ca vacancy compensation; (ii) Ti site substitution with O vacancy compensation; (iii) simultaneous substitution at both Ca and Ti sites with self-compensation. Besides the evident ferroelectric properties, the BCT23:Eu ceramics showed the photoluminescence and paramagnetic properties, implying that they can be considered as the multifunctional materials. Both the electric and luminescent properties were sensitive to the Eu doping concentrations and positions, due to the variations of the microstructures and different charge compensation mechanisms.

CaTiO3:Pr3+ films have been prepared by pulsed-laser deposition method on SiO2-buffered Si substrates, and their microstructure and photoluminescence properties have been compared with those of the films deposited directly on bare Si substrates. The SiO2 buffer layers were prepared using thermal oxidization and HF-etching. Photoluminescence intensities of CaTiO3:Pr3+ films on the SiO2-buffered Si substrates are significantly higher (up to 800%) than those of the films on bare Si substrates, which is attributed to the low refractive index and low light absorption of the SiO2 buffer layer. This study reveals that the presence of the buffer layer is effective in improving the red emission brightness of CaTiO3:Pr3+ films without sacrificing the surface roughness.

Bismuth ferric oxide (BiFeO3) films grown on quartz substrate were prepared by a simple chemical solution deposition. Phase constitution characterization of the films were obtained by X-ray diffraction, surface morphology and transmittance of the films were studied by atomic force microscopy and ultraviolet–visible–infrared light spectrophotometer. The optical constants (refractive index n, extinction coefficient k) were calculated by straightforward method proposed by Swanepoel [Swanepoel R, J. Phys., E J. Sci. Instrum. 1983; 16: 1214–1222. [1]]. The influence of the processing parameters on microstructure and optical properties, especially band gap, were studied.

A thin TiO2 buffer layer was used to control the microstructure and electrical properties of the polycrystalline (Pb,Sr)TiO3 (PST) films produced by a Sol–Gel method on Pt(111)/Ti/SiO2/Si(100) substrates. The PST films included (Pb0.6Sr0.4)TiO3 (PST40) and (Pb0.4Sr0.6)TiO3 (PST60). It was found that a crystallized TiO2 buffer layer with a thickness of nearly 5 nm was critical for improving the crystallinity and surface morphology of both the thinner (about 40 nm) and thicker (about 330 nm) PST films, which exhibited a (l00) preferred orientation and much smoother surface comparing with those without the buffer layer. The electrical properties of the PST films having TiO2 buffer layer were also improved. For 330-nm-thick PST40 films, the dielectric constant and its tunability by dc voltage were increased from 482 and 26.8% at 10 kHz to 590 and 51.2%, while the loss and leakage current density were reduced from 0.04 and 4.26 × 10−4 A/cm2 at 100 kV/cm to 0.034 and 7.63 × 10−6 A/cm2, respectively. Similar results were also found in the PST60 films.

The dielectric and ferroelectric properties of (BaxSr1−x)0.77Ca0.23TiO3 ceramics with x=1x=1 to 0.7 were studied and compared with those of BaxSr1−xTiO3 and Ba0.77Ca0.23TiO3 ceramics. It has been found that Sr doping of the Ba0.77Ca0.23TiO3 ceramics causes a drastic decrease of the Curie temperature, just like Sr doping of pure BaTiO3 ceramics, demonstrating a cell volume effect. However, the (BaxSr1−x)0.77Ca0.23TiO3 ceramics with x=0.9x=0.9 and 0.8 have larger spontaneous polarization than those of the corresponding BaxSr1−xTiO3 and Ba0.77Ca0.23TiO3 ceramics, along with sufficient insulating properties. The enhancement of their polarization was explained by the increase of the lattice parameter c/ac/a ratio due to the lattice distortion and strain developed in the ceramics.

A TiO2 thin buffer layer was introduced between the (Pb0.4Sr0.6)TiO3 (PST) film and the Pt/Ti/SiO2/Si substrate in an attempt to improve their electrical properties. Both TiO2 and PST layers were prepared by a chemical solution deposition method. It was found that the TiO2 buffer layer increased the (100)/(001) preferred orientation of PST and decreased the surface roughness of the films, leading to an enhancement in electrical properties including an increase in dielectric constant and in its tunability by DC voltage, as well as a decrease in dielectric loss and leakage current density. At an optimized thickness of the TiO2 buffer layer deposited using 0.02 mol/l TiO2 sol, the 330-nm-thick PST films had a dielectric constant, loss and tunability of 1126, 0.044 and 60.7% at 10 kHz, respectively, while the leakage current density was 1.95 × 10−6 A/cm2 at 100 kV/cm.

Alternating rhombohedral/tetragonal Pb(ZrxTi1−x)O3 (Px) multilayered films were prepared via a chemical solution method. It has been found that the P45/P55 multilayers show significant dielectric enhancement comparing with the uniform P45 and P55 films, and this dielectric enhancement increases as the decrease of the layer periodicity. However, the dielectric constant of the Pb(Zr,Ti)O3 rhombohedral/tetragonal multilayered films decreases when the layer compositions are away from morphotropic phase boundary (MPB), and no remnant polarization enhancement was observed in all the multilayered films. After comparing the dielectric and ferroelectric properties of the multilayers with the corresponding single-phase films, the dielectric enhancement in P45/P55 multilayers was ascribed to the formation of the MPB region around the interfaces between the P45 and P55 layers.

In this paper, the contact effects at the electrode/sample interfaces on the dielectric properties of the CaCu3Ti4O12 (CCTO) ceramic were studied. The experimental results provide clear evidence that the colossal dielectric constant in CCTO is related to the ceramic itself; however, it may also partly originated from the electrode/sample contact effects which depends on the surface resistivity of the sample. When the surface resistivity of the ceramic is as high as 1.2 × 108 Ω cm, no obvious mobile space charges can be observed, and the dielectric properties of the sample is inert to the different metal electrodes and various sample thicknesses, indicating the colossal dielectric constant (near 2000 at 10 kHz) at room temperature is due to the true properties of the ceramic itself. However, after the surface resistivity is lowered to 3.1 × 107 Ω cm through post-annealing the sample in N2 atmosphere at 750 °C, obvious mobile space charges can be observed, and the dielectric properties of the sample become sensitive to the different types of contacts. The dielectric constant of the sample with Pt electrode shows a significant enhancement (up to 5000 at 10 kHz), comparing with that of the sample with Ag electrode. Clearly, in this case, the extrinsic contact contributes partly to the colossal dielectric constant of CCTO ceramic.

Pb0.92La0.08Ti0.96O3 films with thickness between 580 nm and 1830 nm were deposited on ITO-coated glass substrates using a sol–gel process under a relative low temperature of 580 °C. The films are crystallized well and of pure perovskite polycrystalline structure, and the surface of the films was smooth and condense. With the increase of the film thickness, the grain size and dielectric constants of the films increase. The dielectric constant-voltage curves are symmetric about a zero-bias axis and showed the hysteresis for all the films. In addition, the coercive field Ec decreases with the film thickness. All the films are transparent and the absorption edges were found to shift to longer wavelength with increasing thickness of the films. The refractive index (n) and extinction coefficient (k) of 1830 nm thick film are 2.39 and 0.009, respectively, at 633 nm wavelength.

We report the presence of a field-induced intermediate ferroelectric phase in pre-poled [111] oriented 0.955Pb(Zn1 / 3Nb2 / 3)O3–0.045PbTiO3 (PZN–4.5%PT) single crystals, based on the dielectric, differential scanning calorimetry and pyroelectric measurements. It was found that this phase exists in a very narrow interval of 4.3 °C between the ferroelectric rhombohedral and tetragonal phases. This may be explained as an electric-field-induced orthorhombic phase based on previous investigations on the PZN–8%PT single crystals. An electric-field-induced phase diagram of <111> oriented PZN–PT has been redrawn based on this study.

A high dielectric constant of 2500 at 10 kHz near room temperature was observed in (Ba0.5Sr0.5)TiO3 (BST) films prepared by pulsed-laser deposition (PLD) at 550 °C in N2 atmosphere. The dielectric constant is weakly temperature-dependent above 200 K. However, there is about one hundred fold drop below 200 K, which can be characterized by a thermally excited relaxation process. The temperature and frequency-dependent dielectric response of the film is very similar to that reported for the so-called ‘colossal’ dielectric constant material, such as CaCu3Ti4O12. The dielectric properties are sensitive to the metal contacts with different work functions, however insensitive to the film thicknesses. Such an anomalous dielectric response for the BST films is ascribed to the formation of the Schottky barrier between the metallic electrode and the film surface, and the existence of the mobile charges in the film as indicated by the frequency characteristics of dielectric constant changing as the applied dc bias.

Pb0.5Sr0.5TiO3 (PST) ferroelectric films were deposited onto Pt/Ti/SiO2/Si substrates by pulsed laser deposition. The state of the films can be described as a mixed state, with both ferroelectric and relaxor-like features. The films exhibited high dielectric constant and tunability at room temperature. At 10 kHz, the dielectric constants of the 200-nm- and 400-nm-thick films are 771 and 971, with the tunability of 60.2% and 70.9%, respectively. The temperature-dependent dielectric properties were studied and the relaxor-like behavior was observed in both the thinner and thicker PST films, which can be established in terms of diffuse phase transition characteristics and Vögel–Fulcher relationship. In addition, the contribution of the film–electrode interface layer to the dielectric properties was evaluated and the true dielectric properties of the films were reconstructed. Consequently, the relaxor-like character of the PST films was mainly ascribed to the effect of the film-electrode interfaces.

Neodymium (Nd)-doped Bi4Ti3O12 (Bi3.15Nd0.85Ti3O12, BNT) ferroelectric films have been deposited on Pt/Ti/SiO2/Si substrates by a sol–gel process and crystallized in nitrogen, air and oxygen environments, respectively. The crystallization environment was found to be important in determining the crystallization and ferroelectric properties of the BNT films. The film crystallized in nitrogen at a relatively low temperature of 650 °C, and exhibits excellent crystallinity and ferroelectricity with a remanent polarization of 2Pr=63.6 μC/cm2, a coercive field of 130 kV/cm and a fatigue-free characteristic. While the films annealed in air and oxygen, they did not show good crystallinity and ferroelectricity until they were annealed at 710 and 730 °C, respectively. A correlation between the remanent polarization and dielectric constants of the BNT films has been observed.

We report a theoretical investigation on the band structures of electrons in both infinite and finite semiconductor quantum well/barrier superlattices with each unit cell containing alternately two types of materials. When the unit cell of a superlattice, made of GaAs and AlxGa1−xAs, is further divided into four and six sublayers of these two materials, narrower passbands and/or broad stopbands can be obtained for electrons with energy slightly larger than the potential barrier. When a finite superlattice has two different periods and each unit cell contains six sublayers of alternating GaAs and AlxGa1−xAs, very sharp passbands can be obtained for electron energy right below and above the potential barrier. The results may be used to build a high-Q electron energy filter.

Polycrystalline BaTiO3/SrTiO3 multilayered thin films have been prepared on Pt/Ti/SiO2/Si substrates by a sol–gel processing. The X-ray diffraction (XRD) patterns and Auger electron spectroscopy (AES) indicate that the multilayered thin films were formed. The dielectric constant of the multilayered films was significantly enhanced and the dielectric loss was almost the same as that of the uniform BaTiO3 and SrTiO3 thin films. A dielectric constant of 660 at 1 kHz was observed for a stacking periodicity of 66 nm at room temperature and the corresponding dielectric loss was maintained below 0.05. The study indicates that there are some differences between the multilayered films and the uniform films in the dielectric constant–frequency relation and capacitance–voltage characteristics. The report also analyzes the mechanism of dielectric enhancement of the multilayered thin films prepared by the sol–gel process.

•An accurate theoretical model for thermophotovoltaic system is constructed.•Parallel connected module is superior if radiator temperature is uneven.•Series connected module is superior if cell temperature is uneven.•Short circuit current of series module rises when the shunt resistance decreases.•Fill factor is not always accurate to evaluate the module performance.An experimental thermophotovoltaic (TPV) system with a cylindrical-geometry radiator was established to test the output performances of modules under different conditions. The results demonstrate that the output performance of a cell module decreases when the combustion power increases because of the uneven temperature of the radiator or cells. On this basis, a theoretical model for a TPV system was constructed to compare the performance under different conditions of the series-connected (SC) module and the parallel-connected (PC) module, and was verified by the experimental results. The influences of the temperature gradient of the radiator or the cell module, and the series and shunt resistance of the TPV cell on the module performance were analyzed in detail. The results demonstrate that the PC module can effectively reduce the mismatch loss of output power caused by the uneven radiator temperature. The PC module, for instance, has a maximum output power of 2.54 times higher than that of the SC module when the radiator temperature difference is 500 K. However, the output performance of the module connected in series is superior to the PC module while the cell temperature is non-uniform. The output power of the SC module is 9.93% higher than that of the PC module at the cell temperature difference of 125 K. The short circuit current of the SC module is sensitive to the series and shunt resistance if the radiator temperature distribution is non-uniform. As the shunt resistance falls from ∞ to 0.5 Ω, the current varies from 1.757 A to 4.488 A when the radiator temperature difference is 500 K. As the series resistance rises from 6.6 mΩ to 0.5 Ω, this current falls from 2.132 A to 1.654 A under the same condition. This research also shows that the fill factor is not appropriate to evaluate the output performance of a TPV system. Furthermore, the theoretical model developed in this study is used to analyze and optimize the experimental TPV system, and consequently the output powers under two different conditions are enhanced by 20.24% and 33.99% respectively when a module is connected in parallel.

Pb(Zr0.2Ti0.8)O3 wrapped CaFe2O4 particles were constructed on ITO coated quartz as a photocathode for efficient water splitting. A photocurrent of 152 μA cm−2 was obtained under zero bias vs. Ag/AgCl and 100 mW cm−2 with the assistance of positive poling and Ag decoration.

It is widely accepted that ultraviolet (UV) light illumination of ferroelectric films can result in polarization imprint because of the accumulation of photoinduced carriers on the domain walls and/or on the electrode–film interfaces, and then the decrease of the reversible remnant polarization. In this paper, however, the enhancement of remnant polarization was exhibited in Pb(Zr0.2Ti0.8)O3 (PZT) films when irradiated by UV light. The time-dependent photocurrent and hysteresis loop of PZT films indicated that the transient behavior of photocurrent and coercive voltage offset were closely related to the polarization states, moveable defect charge (mainly oxygen vacancy) density, and aging time. Based on the observation of piezoresponse force microscopy, the mechanism behind the observed photoelectric and ferroelectric phenomena was proposed.

A porous carbon layer was inserted between a BiFeO3 film and a Pt catalyst for efficient solar water splitting. A photocathodic current density of −235.4 μA cm−2 at 0 V versus RHE and an onset potential of 1.19 V versus RHE were obtained under 100 mW cm−2 Xe-lamp illumination.

A facile sol–gel approach with a fixed calcination temperature is developed to prepare BiFeO3 (BFO) nanoparticles, and the gel-drying temperature is adjusted to control the appearance of a γ-Fe2O3 parasitic phase. The room temperature ferromagnetism of the samples is strongly dependent on the gel-drying temperature. When the gel-drying temperature increases from 80 to 140 °C, the saturated magnetization of the corresponding samples jumps from 0.22 emu g−1 to 1.2 emu g−1, allowing the nanoparticles to be magnetically separated in solution. From examination by transmission electron microscopy and X-ray photoelectron spectroscopy, it is confirmed that the γ-Fe2O3 parasitic phase is nucleated during the gel-drying process under high temperatures above 120 °C, and remains in the subsequent annealing process, resulting in the anomalous enhanced magnetization. Comparing with pure BFO nanoparticles prepared under low gel-drying temperature, the BFO/γ-Fe2O3 samples exhibit significantly increased visible-light photocatalytic ability towards rhodamine B. The formation of a heterojunction structure between the BFO and γ-Fe2O3 phases is proposed to be responsible for the enhanced photocatalytic activity. Further enhanced photocatalytic activity is obtained in this study when adding a small amount of H2O2 during photocatalysis, indicating the samples have photo-Fenton-like catalytic activity.

Carbon nanodots treated with N2-plasma are effective catalysts for solar-driven hydrogen-evolved-reaction on np+-Si photocathodes and a support for Pt allowing for the reduction in Pt loading by a factor of about 3.5 while improving the photoelectrochemical activity.

ITO/Pb(Zr,Ti)O3 contacts and Ag nanoparticles were used to construct a novel ferroelectric film photocathode exhibiting a stable short-circuit photocurrent of 110 μA cm−2 and an open-circuit voltage of 0.76 V under 100 mW cm−2 Xe-lamp illumination and zero-bias versus SCE.