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The antiferroelectric (Pb0.985Sm0.01) (Zr1-xTix)O3 (Ti-PSZO) thin films were synthesized on Pt(111)/Ti/SiO2/Si substrates using a chemical solution deposition method. The films were crystallized in the perovskite phase with a preferential orientation along (111) direction. With Ti doping in PSZO, a gradual transformation from antiferroelectric to ferroelectric phase transition was noticed at room temperature owing to the Ti doping induced lattice distortion. The phase transition has been confirmed through the P - E hysteresis loops, X-ray diffraction (peak shifting), capacitance-voltage measurements, and Raman scattering analysis. The thin film with Ti = 0.15 doping displayed a ferroelectric behavior with high dielectric constant and large dielectric tunability of about 62%. Also, Ti doping altered the Curie temperature (Tc) and enhanced the order of dielectric diffuseness. It is believed that Ti-doping in PSZO is an effective way to induce an antiferroelectric - ferroelectric phase transition and to tailor the electrical characteristics of PSZO thin films.

Orthorhombic Bi2SiO5 thin films were fabricated on Pt/Ti/SiO2/Si substrates by incorporating a NiO thin layer between Bi2SiO5 and bottom electrode. Compared with those bare Pt/Bi2SiO5/Pt devices, a remarkably improved uniformity of resistive switching parameters such as electroforming voltages, reset voltages, and a resistance ratio of low/high states was demonstrated in the Bi2SiO5 devices with an embedded NiO layer. This improvement was attributed to the formation of the partial conductive filaments resulted from sufficient oxygen vacancies at the interface. Our results provide a method for the optimization of the operation voltage control toward forefront applications in nonvolatile memory.

We report the coexistence of resistive switching and magnetism modulation in the Pt/Co3O4/Pt devices, where the effects of thermal annealing and film thickness on the resistive and magnetization switching were investigated. The sol-gel derived nanocrystalline Co3O4 thin films obtained crack-free surface and crystallized cubic spinel structure. The 110 nm Co3O4 film based device annealed at 600 °C exhibited optimum resistive switching parameters. From I–V curves fitting and temperature dependent resistance, the conduction mechanism in the high-voltage region of high resistance state was dominated by Schottky emission. Magnetization-magnetic field loops demonstrated the ferromagnetic behaviors of the Co3O4 thin films. Multilevel saturation magnetization of the Co3O4 thin films can be easily realized by tuning the resistance states. Physical resistive switching mechanism can be attributed to the rejuvenation and annihilation of conductive filament consisting of oxygen vacancies. Results suggest that Pt/Co3O4/Pt device shows promising applications in the multifunctional electromagnetic integrated devices.

Structure, dielectric, ferroelectric, fatigue, and photoluminescent properties of Bi3.86−kSm0.14LakTi3O12 (BSLT) thin films synthesized by sol–gel method were investigated. The XRD analysis indicated that the BSLT thin films formed single phase orthorhombic structure, and orthorhombic distortion was found to increase with increasing lanthanum doping content. Raman spectra revealed that BSLT thin films have significantly structure distorted because of La3+ doping, which is consistent with XRD results. Increasing La substitution results in improvement in dielectric and ferroelectric properties of BSLT thin films due to distorted structure and defects reduction. The films show almost fatigue-free ferroelectric polarization behavior at room temperature. Besides, the BSLT thin films show orange-red color emission at 604 nm and long florescence lifetime (about 0.75 ms). This study indicates that the thin films with an appropriate doping concentration of Sm3+, La3+ ions may have potential applications in multifunctional optoelectronic devices.

Ni-Cu ferrite (Ni1-xCuxFe2O4, x = 0, 0.05, 0.1, 0.15, 0.2, 0.25) thin films were synthesized on Pt/Ti/SiO2/Si substrates via sol-gel method. The influence of Cu2+ ions substitution on the resistive switching and magnetism of nickel ferrite thin films were investigated. The appropriate 0.2 Cu2+ ions substituted Pt/NFO/Pt device exhibited improved resistive switching parameters such as lower electroforming voltages, narrow distribution of SET/RESET voltages, good endurance (103 cycles), and long data retention upto 105 s at 25 °C and 85 °C, respectively. With increasing Cu2+ ions substitution, the saturation magnetization of Ni-Cu ferrite thin films decreased. The 0.2 Cu2+ ions substituted Pt/NFO/Pt device illustrated the controlling magnetism by accompanying with high saturation magnetization to switch into low saturation magnetization during the resistive switching process. The modulation of Cu2+ ions substitution on the magnetic properties was linked with magnetic moments and oxygen vacancies concentrations. Current transport conduction mechanisms were Ohmic behavior in low resistance state and Schottky emission in high field region of high resistance state. Moreover, temperature dependence of resistance revealed that origin of switching mechanism was related with the hybrid Cu mental and oxygen vacancies conducting filaments. Our results suggest that controlling the paths of hybrid conductive filaments is an effective strategy to modulate resistive switching performance and magnetism in ferrite based devices.

Nano-crystalline zinc ferrite (ZnFe2O4) magnetic thin film was prepared on Pt/Ti/SiO2/Si substrate by chemical solution deposition method though spin coating technique. Reproducible nonpolar resistive switching (RS) characteristics in Pt/ZnFe2O4/Pt devices are reported. By changing the magnitude and polarity of the applied electric bias, reversible transitions among all the four nonpolar RS modes can be realized. For each switching mode, I-V characteristics were measured in the temperature range of 200 K–340 K. Temperature dependent I-V characteristics of high resistance state (HRS) have been found to support the conduction mechanism across the metal/insulator/metal (MIM) systems to be Schottky emission. Associated parameters such as activation energy and effective height of Schottky barrier at zero biasing (ϕo) have been evaluated at different temperature and electric field. In addition, the increase in resistance of low resistance state (LRS) with temperature revealed that the conduction through ZnFe2O4 in LRS is metallic. Based on the temperature-dependent characteristics, the reversible switching among the four modes of nonpolar RS via formation and rupture of the conducting filaments has been attributed to the joint effect of field-induced migration of oxygen vacancies and metallic Zn atoms.

Influence of Gd ion doping on resistive switching (RS) and magnetic properties of NiFe2O4 (NiFe2−xGdxO4, NFG-x) thin films prepared by chemical solution deposition method was investigated. The 0.075 Gd-doped NiFe2O4 based devices exhibited much reliable repeatability, endurance (>500 switching cycles), and good data retention (105 s at 25 and 100 °C) without any significant degradation in their RS performance. Dominant conduction mechanisms in devices were Ohmic conduction at low resistance state and at lower voltage region of high resistance state, while Schottky emission dominated at higher voltage region in high resistance state. The physical mechanism of resistive switching was linked with the formation and rupture of conducting filaments, and the improved stability of the switching parameters for Pt/NFG/Pt devices was attributed to appropriate concentration of oxygen vacancies which can easily minimize randomness for formation/rupture of conductive filaments. Due to variation in concentration of oxygen vacancies, saturation magnetization of the RS device at high resistance state was higher than those at virgin state and low resistance state, and changes of saturation magnetization maintained a stable value of 40% between HRS and LRS of Pt/NFG-0.075/Pt device. Our study indicates that doping rare earth element into ferrite thin films is a viable approach for enhancing resistance switching and magnetic properties.

c-Axis oriented Tm3+-Dy3+-Eu3+ tri-codoped Bi2VO5.5 ferroelectric thin films were prepared on fused silica and Pt(111)/Ti/SiO2/Si substrates by using chemical solution deposition method, and charac...

(Bi 1.90 Eu 0.10 )(V 1− z Mo z )O 5.5 ( z = 0, 0.05, 0.10, 0.15 and 0.20) thin films with c -axis oriented were prepared on Pt(111)/Ti/SiO 2 /Si substrates by using chemical solution deposition method. The effect of Mo 6+ concentration on the structure, luminescence properties and dielectric properties of the thin films were characterized systematically. X-ray diffraction data indicates that the thin films with low Mo 6+ -doping content can remain Bi 2 VO 5.5 structure. When the Mo 6+ -doping content z reaches to 0.15, the thin films are a mixture of diphase with the main phase Bi 2 VO 5.5 and secondary phase Bi 2 MoO 6 . Under UV irradiation, all the thin films emit a bright red or orange emission which origin from Eu 3+ . With increasing Mo 6+ -doping content z , the relative intensity of the Red and Orange emissions show obviously change. The value of Red/Orange ratio first decrease, and it reached minimum when z is 0.15, then it recover to the initial value. The variation trend of the Red/Orange ratio reflects the change of the lattice symmetry. Dielectric constant of the thin films increased with the increasing of the Mo 6+ concentration while dielectric loss decreased. The decrease of the quantities of oxygen vacancies and the generation of Bi 2 MoO 6 phase are responsible for the improvement of electric properties. These results explain that Eu 3+ ion can be used as an effective luminescent probe in (Bi 1.90 Eu 0.10 )(V 1− z Mo z )O 5.5 ( z = 0, 0.05, 0.10, 0.15 and 0.20) thin films, and the electric properties of the thin films can be improved by Mo 6+ doping.

In this work, large-area ferrite thin films of ferromagnetic yttrium iron garnet (Y3Fe5O12, YIG) were synthesized on Pt/Ti/SiO2/Si (Pt) substrates by a sol-gel method to investigate the resistive and magnetization switching properties. The synthesized YIG thin films acquire a single garnet structure. The Pt/YIG/Pt stack illustrates unipolar resistive switching behavior with excellent switching uniformity, large memory window (102), stable cycle-to-cycle endurance, and good data storage retention (104 s). The ~46% saturation magnetization variation could be realized via the conversion between high and low resistance states by manipulating the electric field. Schottky emission is governed in the high-field region for the high resistance state. Temperature dependence of resistance and magnetization variation confirms that oxygen vacancies conductive filament model and valence state change (Fe2+ and Fe3+) are responsible for the resistive and magnetization switching mechanisms. These results indicate that YIG ferrite based stack is suitable to design the electro-magnetic coupling multifunctional nonvolatile memory devices.

Eu 3+ -doped Bi 2 Ti 2 O 7 pyrochlore structure thin films were prepared by a chemical solution deposition method. The red-orange photoluminescence and dielectric relaxation of Bi 2− x Eu x Ti 2 O 7 thin films have been investigated in terms of Eu 3+ doping content ( x = 0, 0.1, 0.2, 0.3, 0.4, 0.5, and 0.6) and annealing temperature. The crystallinity and surface morphology of the thin films were evaluated by X-ray diffractometer and field emission scanning electron microscopy. It was shown that the thin films annealed at 600 °C were well crystallized in pyrochlore structure without other impurity phases. Intense visible red-orange photoluminescence, originated from doubly split electric-dipole 5 D 0 → 7 F 2 and magnetic-dipole 5 D 0 → 7 F 1 transitions of Eu 3+ ions, could be observed under ultraviolet excitation. The quenching concentration for photoluminescence of Bi 2− x Eu x Ti 2 O 7 thin films is about x = 0.5. In addition, the Bi 2− x Eu x Ti 2 O 7 thin films had a relatively low dielectric loss and a high dielectric constant as well as highly stable bias electric field properties. Meanwhile, the thin films exhibited dielectric relaxation based on the temperature and frequency dependence of dielectric properties. Our study suggested that Eu 3+ -doped Bi 2 Ti 2 O 7 thin films have potential applications in new multifunctional optoelectronic thin-film devices.

Eu-doped Ba1−xSrxTiO3 (x = 0, 0.2, 0.3, and 0.4) thin films with Eu-doping content of 1 mol% have been prepared on fused silica substrates by a chemical solution deposition method and characterized by X-ray diffraction (XRD), atomic force microscopy (AFM), optical and photoluminescence measurements. XRD analysis showed that the films were well crystallized with a pure perovskite structure in the annealing temperature range from 650 to 750 °C. AFM observation indicated that the films were dense and smooth. The band-gap energies of the thin films were also investigated. The more the Sr content in the thin films, the narrower the energy gap of the thin films. Photoluminescence spectra of the thin films showed two prominent transitions of Eu3+ ions at 594 nm (5D0 → 7F1) and 618 nm (5D0 → 7F2) upon excitation at 395 nm (7F0 → 5L6). The observed changes of luminescence spectra by the decrease of the intensity ratio R, which was defined as the ratio of the integrated emission intensity of 5D0 → 7F2 transition to that of 5D0 → 7F1 transition, were associated with the increase of the inversion symmetry of Eu3+ sites when Sr content increased. Lifetime study of photoluminescence indicated that the average lifetime of the thin films was approximately 0.7 ms.

Oxygen vacancies derived resistive and magnetic switching, was demonstrated in facile solution-processed Au-Co3O4 nanocomposite thin films, in terms of optimum Au content. The metal element introduced is a unique way to create the optimum amount of oxygen vacancies in the dielectric films even in the absence of electrochemically active electrodes. Compared with pure Co3O4 based device, the RRAM device with Au additives showed bipolar switching behavior with uniform Set/Reset voltages, enhanced endurance of >103 cycles, and stable time-dependent resistances up to 104 s. The introduction of Au nanoparticles caused the oxygen vacancies based confined filament growth for optimum switching uniformity and stability. Results showed that Ohmic conduction was dominant at LRS and Schottky emission was dominated at HRS of the devices. Temperature dependence and magnetization change of various resistance states revealed that resistive and magnetic switching was due to the formation and rupture of conductive filaments of Au atoms confined oxygen vacancies with the conversion of cation valence states (Co2+ and Co3+). The present study suggests that Au-Co3O4 nanocomposite thin films have a potential for future multifunctional electromagnetic integrated device applications.

Highly c-axis oriented Bi2−xEuxVO5.5 (x = 0, 0.05, 0.10, 0.15, and 0.20) thin films were prepared on Pt(111)/Ti/SiO2/Si and fused silica substrates by using chemical solution deposition method, and characterized by X-ray diffraction, scanning electron microscopy, and optical and electrical measurements. Under 356 nm UV irradiation, a bright red photoluminescence can be observed in the thin films with x = 0.10, 0.15, and 0.20. The emission spectra included two strong peaks which originated from 5D0 → 7F1 (595 nm) and 5D0 → 7F2 (619 nm) transitions of Eu3+ ions. With increasing Eu3+-doping content x, the dielectric dispersion weakened, and dielectric loss decreased. Eu3+ doping can also decrease the leakage current of the thin films. These results demonstrate that Bi2−xEuxVO5.5 thin films are a kind of multifunctional material with potential applications in luminescent ferroelectric devices.

High-performance resistive switching Pt/TiO2/Pt memory cells were fabricated. The amorphous TiO2 active layer was prepared by using a low-temperature photochemical solution deposition method—a simple preparation process combining first chemical solution deposition of the TiO2 film layer and subsequent ultraviolet (UV) irradiation treatment. The obtained Pt/TiO2/Pt memory cells exhibited excellent resistive switching parameters, such as centralized distribution of set and reset voltages, stable current values at high and low resistance states, and long retention time. The conductive mechanisms of high resistance state and low resistance state were Schottky emission and Ohmic conduction, respectively. The X-ray photoelectron spectroscopy, Fourier transform infrared spectroscopy, and scanning electron microscopy characterization of the TiO2 thin films indicated that the UV irradiation treatment can lead to decomposition of the residual organics and the formation of enhanced metal-oxide bonds in the thin films. On the basis of the analysis of current–voltage characteristics and the temperature dependence of resistance, we explained the resistive switching phenomenon for Pt/TiO2/Pt devices by using the model of formation/rupture of conductive filaments. Our study also suggested that the simple photochemical solution deposition method can be used for preparing some other oxide thin films with good resistive switching properties at low processing temperature which is promising to be extended to flexible resistive switching devices.

Photoluminescent (PL) and dielectric properties of La 1− x Eu x AlO 3 thin films were investigated in terms of Eu doping content ( x = 0, 0.02, 0.04, 0.06, 0.08, and 0.1) and annealing temperature. The La 1− x Eu x AlO 3 thin films were prepared by a chemical solution deposition method and characterized by X-ray diffraction, field emission scanning electron microscopy, photoluminescence and dielectric measurement. The thin films were dense with a uniform thickness, and showed bright red-orange emissions, originated from the 5 D 0 → 7 F 2 and 5 D 0 → 7 F 1 transitions of Eu 3+ ions. A stronger emission of 5 D 0 → 7 F 2 than that of 5 D 0 → 7 F 1 was attributed to Eu 3+ -doping induced structural distortion. The strongest PL intensity was observed in the thin films with a Eu 3+ -doping content x of 0.06, indicating the existence of concentration quenching effect of photoluminescence. Further lifetime study of photoluminescence indicated that the concentration quenching effect was due to the lifetime decrease of 5 D 0 → 7 F 1 and 5 D 0 → 7 F 2 transitions when Eu 3+ -doping content x increased. In addition, highly stable dielectric-bias electric field properties of Eu 3+ -doped LaAlO 3 thin films have been confirmed. Our study suggests that Eu 3+ -doped LaAlO 3 thin films have potential applications in integrated thin-film optoelectronic devices.

Topological insulators with the nanoscaled metallic surface state (3-5 nm) are actually of typical functional nanostructures. Significant efforts have been devoted to study new families of topological insulators and identifications of topological surface state, as well as fundamental physics issues relating to spin-polarized surface electronic states in the past few years. However, transport investigations that can provide direct experimental evidence for potentially practical applications of topological insulators are limited, and realization of functional devices based on topological insulators is still under exploration. Here, using the Sn-doping Bi2Te3 polycrystalline topological insulator films, we fabricated high-performance current-controlled magnetic field detectors. When a parallel magnetic field is applied, the as-fabricated device exhibits a stable and reproducible magneto-resistance (MR) switching behavior, and the corresponding MR ratio can be modulated by the applied current. Even under such a low magnetic field (0.5 kG), the device still shows a distinguishable MR switching performance, suggesting that topological insulator devices are very sensitive to external stimulation and potentially applicable to weak magnetic field detection.

0-3 type ZnO/Bi3.6Eu0.4Ti3O12 (BEuT) nanocomposite films with ZnO nanopowders in BEuT host were prepared by chemical solution deposition. The effects of ZnO content on the structure, photoluminescence, and electrical properties of the films were investigated. The ZnO/BEuT molar ratio strongly affected the grain size and growth orientation of BEuT, dielectric and ferroelectric properties, as well as emission intensity. The nanocomposite films showed strong red emission peaks due to 5D0 → 7F1 and 5D0 → 7F2 transitions of Eu3+ ions. Good electrical properties with high dielectric constant of 480 (at 1 kHz) and large remanent polarization (2Pr) of 32 μC/cm2 were obtained for the nanocomposite films having a ZnO/BEuT molar ratio of 1:2. The mechanisms for enhanced photoluminescence and electric properties were discussed. The results suggest that the nanocomposite thin films are promising candidate materials for multifunctional optoelectronic devices.

Conducting atomic force microscopy (C-AFM) is used to observe the formation and removal of conducting filaments of Mg0.6Zn0.4O thin film at a nanoscale in order to study the mechanisms of resistive switching. C-AFM probe with Pt coating is used as a movable top electrode for measuring local I-V and for C-AFM imaging. Writing and reading of micro-bits on the resistive switching thin film are demonstrated. The local I-V behavior is similar to the macroscopic behavior of the resistive switching thin film. However, the probability for successful in situ detection of resistive switching of formation in the current experiment is only one quarter, much less than that with a macroscopic top electrode. Experimental results are explained using the filament model which illustrates the switching mechanism of the thin film. The current work would be useful for the improvement of resistive switching thin films and their applications.

High-sensitive visible-light photodetectors based on α-Fe2O3 thin films on p-Si substrates with a responsivity as high as 2 × 103 A/W have been fabricated and characterized. The solution-processed devices exhibit a rapid rise/decay time (

Bi4-xEuxTi3O12 (BEuT) ferroelectric thin films were prepared on fused silica substrates by using chemical solution deposition technique. The attained samples had a polycrystalline bismuth-layered perovskite structure, and their optical properties were composition dependent. The thin film samples had good optical transmittance above 500 nm wavelength. A blue shift of the optical absorption edge was observed in the BEuT thin films with increasing Eu3+ concentration. The optical band gaps of BEuT thin films were estimated to be about 3.57, 3.60, 3.61, 3.63, and 3.69 eV for the samples with x = 0.25, 0.40, 0.55, 0.70, and 0.85, respectively. Photoluminescence measurements showed that two emission peaks of BEuT thin films originated from two transitions of 5 D 0 → 7 F 1 (594 nm) and 5 D 0 → 7 F 2 (617 nm) had maximum intensities when Eu3+ concentration was x = 0.40. The relatively high quenching concentration of Eu3+ content was thought to be related to the layered structure of BEuT thin films. These results suggested that multifunctional BEuT thin film materials could have promising applications in optoelectronic devices.

Bi 3.95 Er 0.05 Ti 3 O 12 (BErT) thin films were prepared on flexible polyimide (PI) substrates at room temperature by pulsed laser deposition. These BErT thin films deposited under low oxygen pressures are dense, uniform, and crack-free with an amorphous structure. The highly flexible thin film with a thickness of about 160 nm deposited under 3 Pa oxygen pressure shows excellent dielectric characteristics, such as a dielectric constant of 51 and a dielectric loss of 0.025, and a maximum capacitance density of 237 nF/cm 2 at 1 kHz. When it is curved at different curvature radii (by applying external deformation), the thin film still remains superior dielectric performance. In addition, the thin film also shows good dielectric aging characteristic (or thermal stability) and high optical transparency. BErT thin films can find applications in flexible optoelectronic devices and embedded capacitors.

Highly c-axis oriented \( {\text{M}}{{\text{g}}_{\text{x}}}{\text{Z}}{{\text{n}}_{{1 - {\text{x}}}}}{\text{O}}\left( {x = 0 \sim 0.2} \right) \) thin films with pure hexagonal phase were prepared on Pt/TiO2/SiO2/Si substrates by chemical solution deposition method, and their structure, photoluminescence, and lattice vibrational properties were studied. For the thin films with Mg contents ranging 0 ≤ x ≤ 0.20, the room-temperature near-band-edge emission exhibited blueshift up to about 0.35 eV, indicating that the band-gaps of thin films could be tailored by Mg incorporation, meanwhile, the green emission of the thin films enhanced with increasing Mg content. Raman spectra analysis indicated that the decreasing high frequency E2 Raman modes showed composition-dependent asymmetrically broadening. The difference of electronegativity between Mg2+ for Zn2+ as well as the potential fluctuation were discussed. Furthermore, longtitudial optical modes exhibited one-mode behavior with observed ~25.8 cm−1 blueshift. X-ray photoelectron spectroscopy measurements clearly confirmed the Mg incorporation.

Bi4-xPrxTi3O12 thin films were prepared by a chemical solution deposition method and their photoluminescence properties are investigated. The layered perovskite structure of the films is not destroyed by substituting Bi with Pr. The emission lines at 493, 533 and 612 nm are observed, and they can be assigned to the transitions of 3P0→3H4, 3P0→3H5 and 1D2→3H4 of Pr3+ ions. The quenching concentrations are identified to be x = 0.09 and 0.03 for the emissions at 493 and 612 nm. The crystal field plays a crucial role in the luminescence properties of Bi4-xPrxTi3O12 thin films.

Pb0.5Sr0.5TiO3 (PST50) thin films with different Cr doping amounts were prepared on LaNiO3 coated silicon substrates by a chemical solution deposition method. Their dielectric and ferroelectric properties were studied at room temperature. The dielectric constant decreased from 417 to 207 (at 1 kHz), as the Cr content increased from 0 to 8%. When the content of Cr was 3%, the tunability and the figure of merit factor reached maximal values of 61.3% and 21.4, respectively. The remnant polarization of the Cr-doped PST thin films decreased from 7.4 μC/cm2 to 2.0 μC/cm2, as the Cr content increased from 0 to 5%.

Resistive random access memory (RRAM) based on reversible bistable resistance switching effect is attracting much attention for its superior properties such as nonvolatility, long retention time, simple device structure, small size, and low operating voltage. The unique resistance switching properties have been observed in some binary transition metal oxides, perovskite oxides, and organic molecular materials. This paper briefly reviews the status and new progress on binary transition metal oxide thin film materials such as NiO, TiO 2 , Zr0 2 , ZnO, and their multilayered thin films and metal nanocomposite thin films, for resistive random access memory applications, and also presents some of our own research work in this field. There is no doubt that study on transition metal oxide thin films for RRAM application will have been a topic of great interest in the forthcoming years, and it is expected that better understanding of physical mechanisms for the bistable resistance switching of the transition metal oxide thin films sandwiched between two metal electrodes can be achieved.

Pb(Zr0.25Ti0.75)O3 (PZT25) thin films were prepared on LaNiO3-coated thermally oxidized silicon substrates by chemical solution deposition method, where LaNiO3 electrodes were also prepared by a chemical solution deposition technique. The dielectric constant and dielectric loss of the PZT25 thin films were 570 and 0.057, respectively. The remanent polarization and coercive field were 20.11 μC/cm2 and 60.7 kV/cm, respectively. The PZT25 thin films on LaNiO3-coated thermally oxidized silicon substrates showed improved fatigue characteristics compared with their counterparts on plantium-coated silicon substrates.

All-epitaxial multilayered ferroelectric thin films of (Bi,La)4Ti3O12(BLT)/ Pb(Zr,Ti)O3(PZT) were prepared on SrTiO3 substrates by pulsed laser deposition. X-ray pole-figure and electron diffraction analyses showed that the epitaxial relationships between BLT, PZT, and STO were BLT(001)//PZT (001)4//STO (001), and BLT[110]//PZT [100]//STO [100] for the multilayered thin films on (001)-oriented STO substrates, whereas for the multilayered thin films on (011)-oriented STO substrates, the epitaxial relationships between BLT, PZT, and STO were identified to be BLT(118)//PZT(011)//STO(011), and BLT[ 0]//PZT[100]//SrTiO3[100]. Clear interfaces between different film layers were confirmed by cross-sectional transmission electron microscopy observation. Tri-layered films of the same composition showed well-defined hysteresis loops as well as a high fatigue resistance up to 1 × 1010 switching cycles.

Pb(Zr,Ti)O 3 (PZT) thin films were prepared on (1 1 1) Pt-coated Si substrates by a chemical solution deposition method using zirconyl heptanoate as zirconium source instead of commonly used zirconium alkoxides. The effects of processing conditions on the microstructure and electrical properties of the PZT thin films were investigated. The texture of the PZT thin films could be changed by selecting different heat-treatment methods. Orientation-dependent electrical properties, including dielectric constant, polarization, and coercive field, were examined. The randomly oriented PZT thin films annealed at 600°C for 0.5 h showed a well-defined ferroelectric hysteresis loop with a remanent polarization of 18 μC/cm 2 and a coercive field of 74 kV/cm.

PbTiO3 (PT) thin films were prepared on ZrO2, SrTiO3, thermally oxidized silicon, and fused silica substrates by a simple sol–gel technique. The crystallization and optical properties of the thin films were investigated. The PT films on ZrO2 and SrTiO3 substrates have a c-axis preferential orientation, whereas the films on thermally oxidized silicon and fused silica substrates are slightly a-axis oriented. The thin films exhibited good optical transmittivity, and had optical direct transitions. The band gap energy of the film annealed at 650°C was 3.60 eV, which is comparable to those of PT polycrystalline ceramic bulk and films. The thin films on Pt/Ti/SiO2/Si substrates exhibited a ferroelectric hysteresis loop with a remanent polarization of 17.1 μC cm−2 and a coercive field of 132.1 kV cm−1.

Well-crystallized LaNiO3 (LNO) thin films were grown on thermally oxidized silicon (SiO2/Si) and SrTiO3 substrates by a simple chemical solution deposition (CSD) technique. The LNO thin films obtained had pseudocubic phase without the existence of impurity phase. The LNO films on SiO2/Si substrates were polycrystalline, dense, and randomly oriented with a uniform surface and cross-section, whereas those on SrTiO3 substrates were (100) highly oriented with uniform grain size. The room temperature resistivity of the films on SiO2/Si substrates annealed at 750°C was about 0.54 mΩ cm, which is much lower than that of the films derived by the water-based solution technique. The subsequent deposition and electrical measurements of PbTiO3, (Pb,La)TiO3, Pb(Zr,Ti)O3 thin films on the CSD derived LNO/SiO2/Si confirmed the LNO films to be promising electrode materials for ferroelectric thin films.

PbTiO3 (PT) thin films were prepared on various substrates by a simple sol–gel technique. The surface morphology and crystal structure, dielectric, and ferroelectric properties of the thin films were investigated. The orientation of PT thin films on Pt/Ti/Si substrates can gradually change with the annealing temperature from a-axis preferential orientation to c-axis preferential orientation. The PT films on Pt/Ti/SiO2/Si substrates have a bi-axis preferential orientation, whereas the films on LaNiO3/SiO2/Si substrates are randomly oriented due to the random orientation of LaNiO3 (LNO) electrode. The dielectric constant, dissipation factor, remanent polarization, coercive field are found to be 143, 0.032, 21.45 μC cm−2, and 115.3 kV cm−1, respectively, for the thin films on Pt/Ti/Si, and 115, 0.022, 17.1 μC cm−2, and 132.1 kV cm−1, respectively, for the thin films on Pt/Ti/SiO2/Si substrates annealed at 600 °C, whereas the remanent polarization and coercive field of PT films on LNO/SiO2/Si substrates annealed at 650 °C are 27.345 μC cm−2 and 71.1 kV cm−1, respectively.

Sandwich structured (Bi, La)4Ti3O12/Pb(Zr, Ti)O3/(Bi, La)4Ti3O12 thin films were fabricated on Pt/Ti/SiO2/Si substrates, with the intention of simultaneously utilizing the advantages of both (Bi, La)4Ti3O12 (BLT) and Pb(Zr, Ti)O3 (PZT) thin films such as non-fatigue behaviours of BLT and good ferroelectric properties of PZT. Both BLT and PZT layers were prepared by a chemical solution deposition technique. The experiments demonstrated that the sandwich structure showed fatigue-free characteristics at least up to 1010 switching bipolar pulse cycles under 8 V and excellent retention properties. The sandwich structured thin films also exhibited well-defined hysteresis loops with a remanent polarization (2Pr) of 8.8 µC cm-2 and a coercive field (Ec) of 47 kV cm-1. The room-temperature dielectric constant and dissipation factor were 210 and 0.031, respectively, at a frequency of 100 kHz. These results suggest that this sandwich structure is a promising material combination for ferroelectric memory applications.

Several (Bi, La) 4 Ti 3 O 12 /Pb (Zr, Ti)O 3 composite thin films, including a sandwich structure (Bi, La) 4 Ti 3 O 12 / Pb (Zr, Ti)O 3 / (Bi, La) 4 Ti 3 O 12 , a multilayer structure (Bi, La) 4 Ti 3 O 12 /Pb (Zr, Ti)O 3 /LaNiO 3 , and two bilayer structures of (Bi, La) 4 Ti 3 O 12 /Pb(Zr, Ti)O 3 and Pb(Zr,Ti)O 3 /(Bi,La) 4 Ti 3 O 12 , were fabricated on Pt/Ti/ SiO 2 /Si substrates. Both (Bi, La) 4 Ti 3 O 12 and Pb (Zr, Ti)O 3 layers were prepared by a chemical solution deposition technique. The electrical properties of the composite films are affected not only by the stacking configuration of the composite films but also by the electrical properties of individual layer in the composite films. The experiments demonstrated that the (Bi, La) 4 Ti 3 O 12 /Pb(Zr, Ti)O 3 / (Bi, La) 4 Ti 3 O 12 sandwich structure and the (Bi, La) 4 Ti 3 O 12 /Pb(Zr, Ti)O 3 /LaNiO 3 multilayer structure showed fatigue-free characteristics at least up to 10 10 switching bipolar pulse cycles and excellent retention properties. The room-temperature dielectric constants of all composite thin films ranged between 200 and 300, at a frequency of 100 kHz.

A forming-free resistive switching effect was obtained in Pt/Eu2O3/Pt devices in which the Eu2O3 thin films were fabricated by a chemical solution deposition method. The devices show unipolar resistive switching with excellent switching parameters, such as high resistance ratio (107), stable resistance values (read at 0.2 V), low reset voltage, good endurance, and long retention time (up to 104 s). On the basis of the analysis of the current–voltage (I–V) curves and the resistance-temperature dependence, it can be concluded that the dominant conducting mechanisms were ohmic behavior and Schottky emission at low resistance state and high resistance state, respectively. The resistive switching behavior could be explained by the formation and rupture of conductive filament, which is related to the abundant oxygen vacancies generated in the deposition process. This work demonstrates the great potential opportunities of Eu2O3 thin film in resistive switching memory applications, which might possess distinguished properties.

A topological insulator represents a new state of quantum matter that possesses an insulating bulk band gap as well as a spin-momentum-locked Dirac cone on the surface that is protected by time-reversal symmetry. Photon-dressed surface states and light-induced surface photocurrents have been observed in topological insulators. Here, we report experimental observations of an anomalous photoelectric effect in thin films of Bi2Te3, a polycrystalline topological insulator. Under illumination with non-polarised light, transport measurements reveal that the resistance of the topological surface states suddenly increases when the polycrystalline film is illuminated. The resistance variation is positively dependent on the light intensity but has no relation to the applied electric field; this finding can be attributed to the gap opening of the surface Dirac cone. This observation of an anomalous photoelectric effect in polycrystalline topological insulators offers exciting opportunities for the creation of photodetectors with an unusually broad spectral range. Moreover, polycrystalline topological insulator films provide an attractive material platform for exploring the nature and practical application of topological insulators.

Transparent and crack-free SrTiO 3 thin films were prepared on fused silica substrates by a sol-gel technique. Strontium acetate and titanium tetra-n-butoxide were used as starting materials. The structural properties of the thin films were studied by X-ray diffraction. The films annealed at 700 °C have good crystallinity. The optical transmission properties of the thin films were measured in the wavelength range 200 to 1100 nm. The thin films possess high optical transmission. By using an approximate formula, the refractive index and the band gap were evaluated. The dispersion relation follows the single electron oscillation model. The band gap of well-crystallized film is comparable to that of single crystal reported. However, for poor-crystallized films, their band gap values are much larger than of single crystal. The larger gap shift is believed to be mainly due to both quantum size effect and amorphous phase effect.

Growth of well(111)-oriented Pt and Pt/Ti films on SiO2/Si(111) substrates and crystallinity of PZT films grown on the Pt(111)/SiO2/Si(111) and Pt(111)/Ti/SiO2Si(111) substrates have been investigated. It was found by X-ray diffraction analysis that well (111)-oriented Pt film with a best full-width at half maximum (FWHM) of 0.28° was grown by the DC sputtering method. PZT films were prepared by metallo-organic decomposition (MOD) on Pt(111)-coated SiO2Si(111) substrates. The crystallinity of the PZT films improved as the FWHM of the Pt(111) diffraction peak decreased. The best FWHM obtained for a PZT film grown on a Pt(111)/Ti/SiO2/Si(111) substrate was 0.33°.

Ferroelectric Bi 4 Ti 3 O 12 thin films were prepared on SrTiO 3 crystal substrates by a sol–gel process. A homogeneous and stable precursor solution was obtained from Bi(NO 3 ) 3 and Ti(OC 4 H 9 ) 4 . Stability of solution was determined by its pH value, which directly affects the growth behaviour and orientation of the thin films. The single-phase Bi 4 Ti 3 O 12 polycrystalline thin films were grown at 500°C by using a pH 2.5 solution, which turns into highly c -axis orientation at 550°C. Completely c -axis oriented thin film was prepared by using a solution of pH 3.5.

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.

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.

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.

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.