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Potassium tantalate-niobate thin films were prepared from metal-organic compounds by sol-gel processing. Effects of substrates and processing parameters on K(Ta, Nb)O 3 thin film growth were studied. The results showed that perovskite phase of K(Ta, Nb)O 3 was formed through the reactions of pyrochlore phases, and K(Ta, Nb)O 3 thin films with pure perovskite phase can be obtained. The formation mechanism of the perovskite phase of K(Ta, Nb)O 3 on SrTiO 3 and MgO single crystal substrates was discussed, and the causes that K(Ta, Nb)O 3 thin films with pure perovskite structure on single crystal silicon and quartz glass substrates cannot be obtained was detailed.

Piezoelectric ignition voltage and energy formula is derived from piezoelectric equations, the correlations of energy and piezoelectric material parameters are analysed by electromechanical coupling relation, and general conclusions about comprehensive selection of piezoelectric ignition material parameters are given, also

Epitaxial and oriented K(Ta 0.65 Nb 0.35 )O 3 thin films were prepared by the sol-gel method, using metalorganic compounds. The thin films were characterized by X-ray diffraction (XRD), and reflection high energy electron diffraction (RHEED). The mechanism of orientation of the K(Ta 0.65 Nb 0.35 )O 3 films is discussed.

Expitaxial and highly oriented K(Ta0.65Nb0.35)O3 thin films were prepared on (100) SrTiO3 and (100) Mgo single crystal plates by sol-gel processing, using a multilayer sprinning method. The preparation process and the thin film characterization were studied by x-ray diffraction (XRD) and reflection high energy electron diffraction (RHEED). The mechanism of orientation of K(Ta0.65Nb0.35)O3 films was discussed in detail. The substrate strongly influenced on the film orientation, and the concentration of the precursor solution and heat-treatment conditions were also found to affect the orientation of the thin films.

Zinc oxide thin films were prepared from metallo-organic compounds through the sol-gel process. The crystal structure of ZnO films was investigated by XRD and SEM. Optical properties of the thin films were analyzed by using UV/visible spectroscopy. Strongly c-axis oriented ZnO thin films were obtained on fused quartz substrates; the surface of the thin films was smooth, homogeneous, crack-free, and dense. The growth of the thin films depends strongly on the heat-treatment conditions. The Crystal lattice constant of the thin films is a little larger than that of the ZnO crystal, the band gap is 3. 444 eV, and the absorption limit shifts to shorter wavelengths.

In this letter, the dynamic evolution of TiN/HfO2/Pt device from bipolar resistive switching (BRS) to complementary resistive switching (CRS) was reported. The device exhibits the uniform BRS with long retention, good endurance, and self-compliance characteristics after the asymmetric two-step electroforming. However, BRS of the device eventually transforms to CRS after the transitional processes through controlling the compliance current. Meanwhile, the effective barrier height rises up accordingly as the device evolves from BRS to CRS. These superior resistive switching performances of TiN/HfO2/Pt device here can be elucidated in views of evolution of asymmetric filament. This work confirms the intimate correlation and discrepancy between BRS and CRS, and also indicates the potential application of TiN/HfO2/Pt device for future ultra-dense resistive random access memory.

The opportunity of spinel ferrites in nonvolatile memory device applications has been demonstrated by the resistive switching performance characteristics of a Pt/NiFe(2)O(4)/Pt structure, such as low operating voltage, high device yield, long retention time (up to 10(5) s), and good endurance (up to 2.2 × 10(4) cycles). The dominant conduction mechanisms are Ohmic conduction in the low-resistance state and in the lower-voltage region of the high-resistance state and Schottky emission in the higher-voltage region of the high-resistance state. On the basis of measurements of the temperature dependence of the resistances and magnetic properties in different resistance states, we explain the physical mechanism of resistive switching of Pt/NiFe(2)O(4)/Pt devices using the model of formation and rupture of conducting filaments by considering the thermal effect of oxygen vacancies and changes in the valences of cations due to the redox effect.

The surface state of a topological insulator always has a weak antilocalization (WAL), and the bulk state would theoretically have a weak localization (WL). Although the WAL topological surface state has been observed, the WL bulk state has never been demonstrated by experiments. Using the Sn-doping Bi${}_{2}$Te${}_{3}$ polycrystalline topological insulator films and the magnetotransport characteristic analysis, we directly observed the WL effect from the bulk state. The experimental data suggested that an inflection from WAL to WL indeed takes place in the parallel magnetoresistance (MR) curve of the low-doped film with increasing the magnetic field, and the inversion phenomenon from a positive to a negative MR cusp at low fields driven by the temperature was observed in the parallel MR trace of the high-doped sample. Observations of the WL bulk state actually open a path toward magnetic device application of a topological insulator, and the polycrystalline topological insulator films provide an attractive material platform to explore the novel effects of topological insulators.

Band-gap energies of sol-gel-derived SrTiO3 thin films were studied in terms of annealing temperature and film thickness. The band-gap energies of highly crystallized films were comparable to those of single crystals reported, whereas for poor-crystallized films, their band-gap energy values were much larger than those of single crystals. The larger band-gap energy shift was believed to be mainly due to both quantum size effect and existence of amorphous phase in thin films. The band-gap energies also showed a strong dependence on film thickness. There was a critical film thickness (∼200 nm), above which the films had band-gap energies close to those of crystals or bulks, but below that, the values shifted largely, which can be attributed to the influence of crystallinity of thin films. Such a thickness effect of band-gap energy should be of high interest in optical device applications.

We report abnormal ferroelectric properties of compositionally graded Pb(Zr,Ti)O3 thin films on LaNiO3-coated SiO2/Si substrates, where Pb(Zr,Ti)O3 and LaNiO3 films were prepared by a metalorganic decomposition technique and a sol–gel technique, respectively. It was found that the hysteresis loops of the Pb(Zr,Ti)O3 graded films measured by the conventional Sawyer–Tower method shifted along the polarization axis, i.e., they showed polarization offsets when applied by an alternating electric field. The polarization offsets were 82.5 μC/cm2 at 270 kV/cm and 62.5 μC/cm2 at 185 kV/cm for the up-graded film and the down-graded film, respectively. The absolute magnitude of the polarization offsets was closely related to the magnitude of the driving electric field, and the direction of the polarization offsets depended on the direction of the composition gradient with respect to the substrate. Analysis indicated that the polarization offsets did not originate from asymmetric contact effects, oxygen vacancies, al...

Homogeneous LaNiO3 thin films were grown on thermally oxidized silicon (SiO2/Si) substrates by a sol-gel technique, for the subsequent sol-gel deposition of (Pb, La)TiO3 thin films, under the assumption that the structural and compositional compatibility between ferroelectric films and bottom electrodes could lead to enhanced electrical properties of ferroelectric thin films. In this work, the LaNiO3 films served three functions: the first was used as bottom electrodes for the fabrication of integrated ferroelectric devices on Si due to their low resistivity; the second was used as a seeding layer, promoting perovskite phase formation due to their structural compatibility with ferroelectric films; and the third was to suppress the composition diffusion between ferroelectric films and bottom electrodes due to their composition compatibility. The experimental results demonstrated that (Pb, La)TiO3 films prepared on the LaNiO3/SiO2/Si substrates had excellent electrical properties. The dielectric constant an...

Compositionally graded (Pb, Ca)TiO3 thin films were prepared by a monoethanolamine-modified sol–gel technique on platinum-coated silicon substrates at the annealing temperature of 600 °C. The composition gradient of the films was greatly improved by a modified annealing method. The dielectric constants, for up-graded and down-graded films annealed at 600 °C for 60 min, were found to be 469 and 355, respectively. Both were larger than those reported for conventional (Pb, Ca)TiO3 thin films. The compositionally graded films had large polarization offsets in hysteresis loops when excited by an alternating electric field. The more smooth the composition gradient of the graded film, the larger the polarization offset. This was consistent with a theoretical model reported previously by Mantese and coworkers [Appl. Phys. Lett. 71, 2047 (1997)]. The magnitude of polarization offset displayed a power-law dependence on the electric field, and the direction of the offset depended on the direction of the composition gradient with respect to the substrate. Both up-graded and down-graded films had good leakage current characteristics.Compositionally graded (Pb, Ca)TiO3 thin films were prepared by a monoethanolamine-modified sol–gel technique on platinum-coated silicon substrates at the annealing temperature of 600 °C. The composition gradient of the films was greatly improved by a modified annealing method. The dielectric constants, for up-graded and down-graded films annealed at 600 °C for 60 min, were found to be 469 and 355, respectively. Both were larger than those reported for conventional (Pb, Ca)TiO3 thin films. The compositionally graded films had large polarization offsets in hysteresis loops when excited by an alternating electric field. The more smooth the composition gradient of the graded film, the larger the polarization offset. This was consistent with a theoretical model reported previously by Mantese and coworkers [Appl. Phys. Lett. 71, 2047 (1997)]. The magnitude of polarization offset displayed a power-law dependence on the electric field, and the direction of the offset depended on the direction of the composition ...

Ferroelectric materials exhibit important multifunctional electrical properties such as ferroelectric, dielectric, piezoelectric, pyroelectric, and electrooptic properties. They can be used to fabricate various microelectronic and optoelectric devices including nonvolatile ferroelectric random access memories, microsensors and microactuators, integrated capacitors, and electrooptic modulators [1-3]. Widely studied ferroelectric materials include Pb(Zr,Ti)O3 (PZT), lanthanide doped Bi4Ti3O12 (BiT), and BaTiO3. PZT is the most important piezoelectric material which has been used in various electronic devices. BaTiO3 and its solid solution with SrTiO3 exhibit high dielectric constant and other advantageous properties. Lanthanide doped BiT gained great interest on searching new ferroelectric thin films with fatigue-free polarization properties for non-volatile random access memories. Among them, La doped bismuth titanate and Nd-doped bismuth titanate exhibit excellent electrical properties such as high fatigue resistance, good retention, fast switching speed, high Curie temperature, large spontaneous polarization, and small coercive field [2-4]. In addition, lanthanide doped BiT do not contain lead, thus, environmental pollution and harm to health of human due to lead volatility in PZT can be avoided. Studies in the past decade indicate that lanthanide doped bismuth titanate ferroelectric thin films are the most promising candidate materials for nonvolatile ferroelectric random access memory applications. Most efforts have been devoted to improving the electrical properties of Bi4Ti3O12 (BIT) thin films by rare earth ion doping for the development of non-volatile ferroelectric random access memory applications [5-7]. It is worth pointing out that besides excellent ferroelectric polarization fatigue-free characteristics, the bismuth layered perovskite structure ferroelectric thin films also exhibit good piezoelectric properties and large optical nonlinearity [8-10]. Recently, photoluminescence (PL) properties originated from defects or rare earth ions in oxide ferroelectric materials have attracted much attention for possible integrated photoluminescent ferroelectric device applications. This paper briefly reviews the status and new progress on study of photoluminescence in low-dimensional oxide ferroelectric materials including ferroelectric thin films, nanopowders, nanorods or nanowires, and nanotubes, and some of our own research work in this field with an emphasis on the photoluminescence properties of lanthanide doped bismuth titanate thin films such as (Bi,Pr)4Ti3O12, (Bi,Eu)4Ti3O12, (Bi,Er)4Ti3O12, and codoped bismuth titanate thin films will be presented in this paper, also.

Compositionally graded (Pb, Ca)TiO3 thin films were prepared on platinum-coated silicon substrates by a monoethanolamine-modified sol–gel technique. The crystalline orientation and surface morphology of the graded films were related to the deposition sequence of the film layer. The dielectric constants, for up-graded and down-graded films annealed at 600 °C for 60 min were found to be 504 and 399, respectively. Both were larger than those reported for conventional (Pb, Ca)TiO3 thin films. The compositionally graded films had large polarization offsets in hysteresis loops when driven by an alternating electric field. The magnitude of polarization offsets displayed a power-law dependence on the electric field, and the direction of the offsets depended on the direction of the composition gradient with respect to the substrate. The offset, 120 μC/cm2 at 300 kV/cm driving electric field, was obtained. These results showed that compositionally graded (Pb, Ca)TiO3 thin films had enhanced dielectric properties an...

Compositionally step-varied (Pb, Ca)TiO3 thin films were prepared on platinum-coated silicon substrates by a monoethanolamine-modified sol-gel technique. The dielectric constant and dissipation factor were found to be 342 and 0.019, respectively, for thin films of 0.6μm in thickness annealed at 550 °C for 60 min. The remanent polarization and coercive field were 37.7 μC/cm2 and 60.4 kV/cm, respectively. The leakage current was 1.31×10−7 A/cm2 at the voltage of 5 V. The compositionally step-varied (Pb, Ca)TiO3 thin films had enhanced dielectric and ferroelectric properties which were suitable for various device applications.

If we intentionally make the A-site in an ABO3 perovskite structure deficient, it is possible to tune the resistive switching effect by forming defect dipoles. In this study, an A-site-deficient calcium titanate (Ca0.95TiO3, CTO) thin film was fabricated on a Pt/Ti/SiO2/Si substrate as an active layer for resistive random-access memory. The Pt/CTO/Pt device exhibited stable bipolar resistive switching performance with good endurance and long retention. The resistive switching may be attributable to the formation and rupture of the conduction filaments due to the O vacancies and defect dipoles resulting from the interaction between the Ca and O vacancies.

c-Axis oriented zinc oxide thin films were prepared by sol-gel process on fused quartz substrates. The structure, optical and electrical properties of ZnO films were investigated. Growth of the thin films strongly depends on heat-treatment conditions. The c-axis lattice constants of the thin films and the band gap are a little bigger than that of ZnO crystal. The differences between the thin film and crystal might be attributable to the grain boundaries and imperfections in thin films.

Highly c -axis oriented Bi 4 Ti 3 O 12 thin films have successfully been prepared on fused quartz substrates by sol-gel processing. The orientation degree of the thin film was about 87%. The thin film exhibits good optical transmission. The optical-absorption properties of the thin films have been measured. The variation of bandgap with annealing temperature is studied.

(Bi,La)4Ti3O12 (BLT) thin films with various Bi2O3 template layers were prepared on Pt/Ti/SiO2/Si substrates by a chemical solution deposition method. Both of the BLT films with a thin Bi2O3 template layer and those without a Bi2O3 layer had a highly c-axis oriented growth, while both of the BLT films with a thin Bi2O3 bottom layer and those with a Bi2O3 intermediate layer were highly c-axis oriented. It was found that the use of Bi2O3 template layers improved significantly the ferroelectric properties of BLT thin films. In addition, the thin films with a thin Bi2O3 template layer showed good dielectric properties. All the capacitors with Bi2O3 template layers showed high polarization fatigue resistance and good retention properties.

Nonvolatile write-once-read-many-times (WORM) Pt/Al2O3/ITO memory devices prepared at room temperature were demonstrated. The WORM memory devices show irreversible transition from the initial low resistance (ON) state to the high resistance (OFF) state, high ON/OFF ratio, long data retention, and good reading endurance in air at room temperature. The high performances are promising for employing the Pt/Al2O3/ITO WORM memory devices in permanent storage of information. The nonvolatile memory behaviors could be attributed to the formation and permanent rupture of conductive filament consisting of positively charged oxygen vacancies.

Au-doped Bi3.6Eu0.4Ti3O12 (BET) thin films were prepared on fused silica and Pt/Ti/SiO2/Si substrates by a chemical solution deposition method. The existence of Au nanoparticles (NPs) has been confirmed by X-ray diffraction, X-ray photoelectron spectroscopy, and transmission electron microscope analysis. Enhanced photoluminescence (PL) of Eu3+ ions was obtained in a wide range of Au doping level. Role of the Au NPs in the PL enhancement was investigated by means of optical absorption, excitation, and emission spectra, as well as decay lifetime measurements. The results indicated that the intra-4f transition of Eu3+ ions can be intensively activated by the coupling of the charge transfer band of BET with the 5D0 state of Eu3+ ions. The influence of Au NPs on the PL properties of Eu3+ ions in the present thin films was attributed to the band bending at Au/BET interface and the localized surface plasma resonance absorption of Au NPs in the visible light region. The dielectric and ferroelectric properties of Au-doped BET thin films were investigated as well.

Multilevel resistive switching effect has been demonstrated in Pt/Bi12TiO20/Pt structures, in which the sillenite structure Bi12TiO20 thin films were prepared by a chemical solution deposition method. The non-volatile multilevel resistive switching can be easily realized by changing either the compliance current during set process or reset voltage during reset process. The Pt/Bi12TiO20/Pt devices show excellent switching parameters such as reproducible switching effect, low set/reset voltage, high cell yield, good endurance, and long retention time (up to 104 s). The dominated conduction mechanisms were Ohmic conduction in low resistance state (LRS) and lower voltage region of high resistance state (HRS), and Schottky emission in higher voltage region of HRS. In the reset process, the switching from LRS to HRS consists of two parts: an abrupt transition due to thermal effect and a gradual transition owing to electric field-induced migration of oxygen vacancies. On the basis of the measurements of the resistance-temperature dependence in different resistance states and analysis of current-voltage characteristics, we explained the resistive switching behavior using a conductive filament-related model.

We report reproducible resistive switching performance and relevant physical mechanism of sandwiched Pt/CoFe2O4/Pt structures in which the CoFe2O4 thin films were fabricated by a chemical solution deposition method. Uniform switching voltages, good endurance, and long retention have been demonstrated in the Pt/CoFe2O4/Pt memory cells. On the basis of the analysis of current-voltage characteristic and its temperature dependence, we suggest that the carriers transport through the conducting filaments in low resistance state with Ohmic conduction behavior, and the Schottky emission and Poole-Frenkel emission dominate the conduction mechanism in high resistance state. From resistance-temperature dependence of resistance states, we believe that the physical origin of the resistive switching refers to the formation and rupture of the oxygen vacancies related filaments. The nanostructured CoFe2O4 thin films can find applications in resistive random access memory.

We report uniform bipolar resistive switching characteristic with self-compliance effect of Pt/TiO2/p-Si devices in which TiO2 thin films were prepared directly on p-Si substrates by chemical solution deposition method. The resistive switching parameters of the Pt/TiO2/p-Si cell obtained, such as distribution of threshold voltages, retention time, as well as resistance variation of high resistance state (HRS) and low resistance state (LRS), were investigated, and the conduction mechanisms of HRS and LRS were analyzed. The conductive mechanism at LRS and low voltage region of HRS was dominated by Ohmic law. At the high voltage region of HRS, the conductive mechanism followed the space charge limited current theory. The resistive switching phenomenon can be explained by electron trapping and de-trapping process, in which the defects (most probably oxygen vacancies) act as electron traps. Our study suggests that using p-type silicon as bottom electrode can provide a simple method for fabricating a resistive random access memory with self-compliance function. In addition, the Pt/TiO2/p-Si configuration is compatible with complementary metal oxide semiconductor process.

In this work, amorphous MgZnO/ZnO heterostructure films were deposited on Pt/TiO2/SiO2/Si at room temperature. By programming the proper compliance current, bipolar resistive switching performances of TiN/MgZnO/ZnO/Pt devices were stabilized; the dispersion of switching voltages and resistance states of devices were suppressed simultaneously. In view of filamentary model, the elimination of secondary and multiple nanofilaments in higher compliance current was suggested to be responsible for the observed improvement. Furthermore, the good endurance and retention behaviors of the optimized TiN/MgZnO/ZnO/Pt devices were confirmed, ensuring its potential application for resistive random access memory. This simple optimizing method by programming proper compliance current is promising for resistive switching devices required avoiding damage.

We have developed a hybrid chemical solution method for preparing nanocomposite thin films composed of a ferroelectric Bi(3.6)Eu(0.4)Ti(3)O(12) (BEuT) matrix and highly c-axis-oriented ZnO nanorods on Si substrates. First, a seed-layer solution growth approach was used to prepare the highly c-axis-oriented ZnO nanorods, and then a chemical solution deposition method was employed to fabricate the BEuT matrix by coating the ZnO nanorods using a spin-coating technique. The nanocomposite thin films obtained exhibited significantly enhanced red photoluminescence (PL) properties. The PL enhancement can be attributed to very efficient radiation energy transfer from the ZnO nanorods to Eu(3+) ions in the BEuT matrix due to two spectral overlaps between the emission spectra of the ZnO nanorods and the excitation bands of Eu(3+) ions in the BEuT matrix: the spectral overlap between the sharp UV emission of ZnO centered at 380 nm and the excitation spectrum of the (7)F(0) --> (5)L(6) transition of Eu(3+) ions at 395 nm and that between the defect-related deep-level green emission band of ZnO centered at 525 nm and the excitation spectrum of the (7)F(0) --> (5)D(2) transition of Eu(3+) ions at 465 nm. Our study opens possibility of realizing highly efficient photoluminescent ferroelectric multifunctional integrated thin-film devices. In addition, the hybrid chemical solution method also provides a useful route for the synthesis of some new nanocomposite thin films consisting of other inorganic matrix and c-axis-oriented ZnO nanorods.

We report on a new route to greatly enhance the photoluminescence of Eu3+ doped ferroelectric polycrystalline oxide thin films: surface modification of grains with silver nanoclusters (NCs). The Ag doped Bi3.6Eu0.4Ti3O12 (BET) thin films were prepared by a chemical solution deposition method. According to the XRD, TEM and XPS analysis, partially oxidated Ag NCs have been formed on the surfaces of the BET grains. A greatly enhanced photoluminescence was obtained in a wide range of Ag doping level. Role of the Ag NCs in the photoluminescence enhancement was investigated by means of absorption, emission and excitation spectra, as well as decay lifetime measurement. The results indicate that the intra-4f transition of Eu3+ can be intensively activated by the coupling of the charge transfer band of BET with the 5D0 state of Eu3+ ions, and the enhancement of Eu3+ ions emission in the present thin films was attributed to the surface modification of BET crystalline grains by Ag NCs. In addition, the influences of Ag NCs on the dielectric and ferroelectric properties of these materials were discussed as well.

Demonstration of a tunable conductivity of the LaAlO3/SrTiO3 interfaces by field effect drew significant attention to the development oxide-based electronics. Increase in the gate capacitance of LaAlO3/SrTiO3-based field-effect transistor is particularly important to the conductivity modulation and the development of logic device. Here, we demonstrate that annihilation of quantum capacitance and colossal capacitance enhancement (about 1000%) in the LaAlO3/SrTiO3 heterostructures by DC gate voltage at room temperature, which we attribute to the motion of oxygen vacancies through the LaAlO3 layer thickness. The capacitor devices would provide a platform for the further development and application of metal-oxide-semiconductor transistor devices.

Photoluminescence (PL) spectra impacted by electric polarization in Pr3+ doped diphase (1-x)BaTiO3-xCaTiO3 (x = 0.4–0.7) ceramics were studied systematically. The transparent electrode of indium tin oxide was deposited on both surfaces of ceramics to reduce experimental errors and then PL properties were characterized with and without polarization. An enhancement in PL intensity of ∼100% was obtained in the Ba1−xCaxTiO3 (x = 0.7) ceramics with polarization. It was found that the PL intensity increased the same level whether the poling direction was up or down. With the x increases, the enhanced factor decreased first and then increased, which ascribed to the ratio of the tetragonal Ba0.77Ca0.23TiO3 and orthorhombic Ba0.1Ca0.9TiO3 in the diphase ceramics. The investigation of UV-Vis reflective spectrum and X-ray Photoelectron Spectroscopy spectrum demonstrated that the polarization effect on the PL was attributed to the change of band gap of host by a local electric field around Pr3+ doped in Ba0.1Ca0.9TiO3. The local electric field was supposed to be produced by the remanent polarization from ferroelectric Ba0.77Ca0.23TiO3 matrix. The band gap of the host became smaller in the polarized sample, which suggests that an increase in the band gap excitation of the host, i.e., increasing the PL intensity.

We reported on W-doping induced antiferroelectric to ferroelectric phase transition in PbZrO3 (PZO) thin films prepared on Pt/Ti/SiO2/Si substrates by a chemical solution deposition method. The phase transition has been studied through polarization-electric field hysteresis loop, capacitance-voltage characteristic, and Raman scattering measurements. Suitable amount W-doping increased the saturated polarization of antiferroelectric W-doped PZO thin films, whereas the ferroelectric W-doped PZO thin films exhibited higher dielectric constant with a high dielectric-bias voltage tunability of about 70%. With increasing W-doping content, the orientation of the thin films changed from preferred (111)Cubic to complete (100)Cubic, due to W-doping-induced lattice distortion, meanwhile the Curie temperature dropped, and dielectric maximum broadened. Our study demonstrates that W-doping is an effective way to tailor the electrical properties of PZO thin films through the induced antiferroelectric-ferroelectric phase transition.

Particle separation is of great importance for a wide range of applications, such as biochemistry and biomedicine, and has been demonstrated using various techniques. Generally, these techniques necessitate carefully microfabricated devices and the assistance of microfluidics, thus making the separation difficult to accomplish. Here, we report a flexible, handy, and highly efficient optical method for particle separation using two tapered optical fibers, avoiding the use of complicated devices. By launching a laser beam with a power of 80 mW and wavelength of 1.55 μm into the first tapered fiber, particles of SiO2 with a size of 3.14 μm and poly(methyl methacrylate) (PMMA) with a size of 10 μm were trapped and collected. As the laser (330 mW) was switched to the second fiber for 29 s, SiO2 and PMMA particles were separated with separation efficiencies of 89.1% and 92.4%, respectively, because of their different photophoretic velocities. The separation performance was further demonstrated using different mixtures, with all separation efficiencies higher than 78%. The separation mechanism was explained by numerical simulations.

We report on the co-existence of bipolar and unipolar resistive switching behaviors in Ag/ZnFe2O4/Pt structures of which the ZnFe2O4 layer was fabricated by a chemical solution deposition method. The memory devices show reproducible and stable bipolar resistive switching, tri-state unipolar resistive switching under only applied negative bias voltage, and unipolar resistive switching transited from bipolar resistive switching with different electroforming conditions. Excellent switching cycling in both unipolar resistive switching and bipolar resistive switching is demonstrated. Based on the conducting filament model, electrochemical metallization effect has been proposed to explain the bipolar resistive switching behavior, whereas the unipolar resistive switching behavior is attributed to electrochemical metallization effect and thermochemical effect.

Ho3+-Yb3+ co-doped bismuth titanate ferroelectric thin films were prepared by a chemical solution deposition method on fused silica substrates and their up-conversion luminescence characteristics excited by a 980 nm diode laser were investigated. The two emission bands centered at 546 and 656 nm in the emission spectra can be assigned to 5F4 + 5S2 → 5I8 and 5F5 → 5I8 transitions of Ho3+ ions, respectively. A bright green emission was observed even when the laser pumping power was relatively low. The dependence of the emission intensity on the pumping power indicated that the up-conversion emission in the thin films was a two-photon process. The up-conversion emission mechanism is discussed in detail. This study suggests that Ho3+ and Yb3+ co-doped Bi4Ti3O12 thin films can be applied to the fabrication of new multifunctional photoluminescence ferroelectric thin-film devices.

We report on the improved red emission and ferroelectricity of three layered composite (Bi,Eu)4Ti3O12 (BEuT)/ZnO thin films prepared by chemical solution deposition. The introduction of a ZnO layer leads to the enhanced crystallization and the change in preferential orientation of the BEuT layer. All the composite films showed stronger red photoluminescence than pure BEuT thin films. The addition of a ZnO layer also greatly influenced the ferroelectricity of the composite thin films. A well-defined polarization-electric field hysteresis loop can be observed in the BEuT/ZnO composite films.

The up-conversion (UC) photoluminescence and ferroelectric properties of Bi4−xErxTi3O12 (BErT) thin films were studied in terms of annealing temperature and Er3+ doping concentration. The thin films were prepared by chemical solution deposition method. There are two green emission bands centered at 527 and 548 nm, and a red emission band centered at 663 nm in UC luminescence spectra measured under a 980 nm laser excitation at room temperature, which correspond to the radiative transitions from 2H11/2, 4S3/2, and 4F9/2 to 4I15/2, respectively. The quenching concentration of Er3+ ions for green emission was as high as 20 mol % for Bi3.2Er0.8Ti3O12 thin films. The large Er3+ quenching concentration and efficient energy transfer between two neighboring Er3+ ions result in the improved UC emission. The dependence of UC emission intensity on pumping power indicated a two-photon UC emission process in the thin films. The combination of UC emission and ferroelectricity was realized in the capacitors of Pt/Bi3.25E...

A strong blue up-conversion photoluminescence and a greatly enhanced ferroelectric polarization were observed in Tm 3+ -Yb 3+ -W 6+ -triply-doped bismuth titanate thin films. The thin films were prepared on fused silica and Pt/Ti/SiO 2 /Si (111) substrates by chemical solution deposition and annealed at 700°C. The strong blue up-conversion emission centered at 478 nm, corresponding to 1 G 4 → 3H6 transitions of Tm 3+ ions, was confirmed to be a three-photon energy-transfer process by pumping laser power dependence of emission intensity. The enhanced ferroelectricity with a high remnant polarization (Pr) value of about 32 μC/cm 2 is attributed to the weakened domain pinning due to the reduced oxygen vacancies by W 6+ substitution for Ti 4+ ions. The thin films combining the strong blue up-conversion photoluminescence with the good ferroelectric properties would provide possibility of realizing novel multifunctional optoelectronic integration device applications.

The magnetic anisotropy of epitaxial spinel ferrite CoFe2O4 films grown on SrTiO3 substrates by pulsed laser deposition can be reoriented by inserting a thin SrRuO3 buffer layer. Without SrRuO3, the CoFe2O4 films show a uniaxial anisotropy with the easy axis perpendicular to the film plane, while inserting a SrRuO3 buffer layer results in the switching of the easy axis into the in-plane orientation. This is associated with a tensile and a compressive strain for the films without and with buffer layer, respectively, which is also correlated with the different density of interfacial misfit dislocations. As a result, the ferrite films can be effectively tailored by using SrRuO3.

We reported the discovery of colossal resistance switching effect in polycrystalline spinel-like structure MgZnO thin films with high Mg contents sandwiched by Pt electrodes. The ultrahigh resistance ratio of high resistance state to low resistance state of about seven to nine orders of magnitude with a low reset voltage of less than 1 V was obtained in this thin film system. The resistance ratio shows an increase of several orders of magnitude compared with those of previously reported resistance switching material systems including metal oxides, semiconductors, and organic molecules. This colossal resistance switching effect will greatly improve the signal-to-noise ratio and simplify the process of reading memory state for nonvolatile memory applications. Our study also provides a material base for studying the origin of resistance switching phenomenon.

Transparent p-n heterojunctions composed of p-type NiO and n-type MgZnO thin films were fabricated on indium-tin-oxide-coated glass substrates by sol-gel spin coating technique. The p-n junctions exhibit typical current-voltage behaviors with good rectifying characteristics, and their electrical properties can be effectively tuned by band gap engineering of n-MgZnO. With increment of Mg content in n-MgZnO layer, enlarging band gap can lead to the higher forward threshold voltage, higher breakdown voltage, and lower reverse saturation current. The electrical behaviors of the p-n junctions can be further improved by using compositionally graded n-MgZnO layer instead of single n-MgZnO layer. These results suggest that the transparent all-oxide p-NiO/n-MgZnO heterojunctions can find applications in transparent electronic devices.

Highly c-axis oriented Mg0.2Zn0.8O thin films with hexagonal structure were prepared on Pt/TiO2/SiO2/Si substrates by sol-gel spin coating technique. The Pt/Mg0.2Zn0.8O/Pt devices showed a reversible and steady resistance switching characteristic. The resistance switching from low resistance state (LRS) to high resistance state (HRS) with a resistance ratio of HRS to LRS of about 25 was achieved at a voltage of as low as 0.65 V. The dominant conduction mechanisms of LRS and HRS were explained by Ohmic behavior and trap-controlled space charge limited current, respectively. Furthermore, formation of conducting filaments in LRS was suggested. This study indicates that the Pt/Mg0.2Zn0.8O/Pt device may be a promising candidate for memristor applications.

Eu- and Gd-codoped bismuth titanate [Bi3.15Eu0.425Gd0.425Ti3O12], thin films as well as Bi3.15Eu0.85Ti3O12 (BEuT) and Bi3.15Gd0.85Ti3O12 (BGdT) thin films were prepared on indium-tin-oxide-coated glass substrates by chemical solution deposition and the photoluminescence, ferroelectric, and dielectric properties of the thin films were investigated. All the thin films exhibited a polycrystalline bismuth-layered perovskite structure. Photoluminescence studies showed that the enhancement of emission intensities for two Eu3+ emission transitions of D05→F17 (594nm) and D05→F27 (617nm) was observed for the BEGT thin films as compared to BEuT thin films. This photoluminescence improvement can be attributed to Eu content of BEGT thin films close to quenching concentration of BEuT thin films and local distortion of crystal field surrounding the Eu3+ activator induced by different ionic radii of Eu3+ and Gd3+ ions. Electrical measurements indicated that BEGT thin films had larger remanent polarization and higher die...

Highly transparent (Bi,Eu)4Ti3O12 (BEuT) ferroelectric thin films were prepared on indium-tin-oxide (ITO)-coated glass substrates by using chemical solution deposition technique, and the photoluminescence and electrical properties of the thin films were investigated in terms of annealing temperature and concentration of europium ions. The BEuT thin films had a polycrystalline bismuth-layered perovskite structure and exhibited excellent optical transmittance. Photoluminescence spectra of the thin films included two strong peaks which originated from two transitions of D05→F17 (594nm) and D05→F27 (617nm). The emission intensity of two peaks increases with increasing annealing temperature due to improved crystallinity of the thin films. An unusual composition quenching effect of photoluminescence was found in the rare earth doped bismuth titanate thin films. In addition, the BEuT thin films also showed ferroelectric properties comparable to those of BEuT thin films deposited on Pt∕Ti∕SiO2∕Si substrates. Thes...

Epitaxial antiferroelectric PbZrO3 (PZO) thin films of two different crystallographic orientations were grown by pulsed laser deposition on (100)-oriented SrTiO3 single crystal substrates. The latter were covered either with SrRuO3 epitaxial bottom electrodes, or with an epitaxial BaZrO3 buffer layer and an epitaxial BaPbO3 bottom electrode, respectively. Their crystal orientation and microstructure were characterized by x-ray diffraction, transmission electron microscopy, and electron diffraction. The orthorhombic (index O) PZO films on SrRuO3∕SrTiO3 were predominantly (120)O oriented and consisted of four azimuthal domains forming 90° and 60° boundaries, whereas those grown on BaPbO3∕BaZrO3∕SrTiO3 were (001)O oriented. All films showed well-defined double P-E hysteresis loops, four distinct switching peaks in the current-voltage characteristics, and piezoelectric double loops recorded by piezoresponse scanning force microscopy. The values of the saturation polarization PS and the critical field EC of th...

Artificially designed Pb(Zr,Ti)O3 (PZT)∕PbZrO3 (PZ) superlattices were grown on (100)-oriented SrTiO3 (STO) substrates with and without SrRuO3 bottom electrodes by pulsed laser deposition. Their microstructure was characterized using x-ray diffraction and transmission electron microscopy. Different from single PZT films having a c-axis orientation on STO (100) substrates, during growth the PZT and PZ layers in the superlattices turn to an a-axis orientation from the c-axis orientation of the first PZT layer. This growth behavior is explained by minimization of the respective interfacial lattice mismatch. The superlattices have a rather smooth morphology and sharp PZT/PZ interfaces. At the latter, misfit dislocations have been found occasionally. There are indications for the absence of the orthorhombic, antiferroelectric phase in part of the PZ layers, possibly due to strain hindering the phase transition. An elongated, “linearized” shape of the ferroelectric hysteresis loop has been found, with a remanen...

Trilayered ferroelectric (Bi,La)4Ti3O12(BLT)/Pb(Zr,Ti)O3(PZT)/(Bi,La)4Ti3O12thin films were grown epitaxially on SrTiO3(STO) substrates by pulsed laser deposition. The epitaxial relationships between BLT, PZT and STO were identified to be BLT(001)∥PZT(001)∥STO(001) and BLT[110]∥PZT[100]∥STO[100] for the trilayered thin films on (001)-oriented STO substrates, whereas for the trilayered thin films on (011)-oriented STO substrates, the epitaxial relationships were BLT(118)∥PZT(011)∥STO(011) and BLT[110]∥PZT[100]∥STO[100]. The morphology of the BLT/PZT interfaces and of the surface of the trilayered thin films depended largely on the orientation of the film layers. A rather large remanent polarization as well as a high fatigue resistance of up to 1010switching pulse cycles was obtained for the trilayered thin films deposited on SrRuO3-coated STO substrates.

(Bi,La)4Ti3O12(BLT)∕Pb(Zr,Ti)O3(PZT)∕(Bi,La)4Ti3O12 trilayered ferroelectric thin films were epitaxially grown by pulsed laser deposition onto (001) SrTiO3 (STO) substrates with and without SrRuO3 (SRO) bottom electrodes. From x-ray pole figures and electron-diffraction patterns, the epitaxial relationships between BLT, PZT, SRO, and STO were identified to be BLT(001)‖PZT(001)‖SRO(001)‖SrTiO3(001); BLT[110]‖PZT[100]‖SRO[100]‖SrTiO3[100]. Cross-sectional transmission electron microscopy investigations revealed that 90° ferroelectric domain boundaries lying on {110} planes are present in the PZT layer, with an average domain width of 20nm and an average spacing of 120nm. These long 90° ferroelectric domains, as a rule having nucleated at the bottom of the PZT layer, extend to the top of the latter. The thin films have sharp BLT/PZT interfaces and a very flat surface. The remanent polarization and coercive field were determined as 13.9μC∕cm2 and 72.9kV∕cm, respectively, indicating that the epitaxial, all (00...