Acceptor Concentration Effects on Photovoltaic Response in the La1-xSrxMnO3/SrNbyTi1-yO3 Heterojunction

Photovoltaic response in the heterojunction of La1-x SrxMnO3/SrNby Ti1-yO3 （LSMO/SNTO） is analyzed theoretically based on the drift-diffusion model. It is found that the decrease of acceptor concentration in the La1-xSrxMnO3 layer of hereto junction can increase the peak value of photovoltaic signal and the speed of photovoltaic response, whereas the changing of donor concentration in the SrNby Ti1-yO3 layer has no such evident effect. Furthermore, the result also indicates that the modulation of Sr doping in La1-xSrxMnO3 is an effective method to accommodate the sensitivity and the speed of photovoltaic response for LSMO/SNTO photoelectric devices.     

Pulsed laser deposition of perovskite La0.5Sr0.5MnO3/La0.7Sr0.3CoO3 multilayers and their magnetotransport properties

The perovskite La_0.5Sr_0.5MnO_3-'/La_0.7Sr_0.3CoO_3-' (LSMO/LSCO) bilayers and LSMO/LSCO/LSMO trilayers are fabricated by pulsed laser deposition and their magnetic and magnetoresistive properties are investigated. The "waist"-like magnetic hysteresis for both the bilayer and trilayer is explained in terms of the inter-layer exchange coupling model based on the large difference in coercivity between LSCO and LSMO layers. The shrink of hysteresis with temperature is attributed to the temperature dependence of the magnetic crystalline anisotropy and conduction band width W. We observe smoothed remnant resistance of the multilayers over a rather wide temperature range (>100 K), while the magnetoresistance (MR) is not seriously damaged.     

Structure Stability of LaAlO3 Thin Films on Si Substrates

A series of amorphous and single-crystalline LaAlO3 （LAO） thin films are fabricated by laser molecular-beam epitaxy technique on Si substrates under various conditions of deposition. The structure stability of the LAO films annealed in high temperature and various ambients is studied by x-ray diffraction as well as high-resolution transmission electron microscopy. The results show that the epitaxial LAO films have very good stability, and the structures of amorphous LAO thin films depend strongly on the conditions of deposition and post-annealing. The results reveal that the formation of LAO composition during the deposition is very important for the structure stability of LAO thin films.     

Resistance Switching Characteristic and Charge Carrier Self-Trapping in Epitaxial Pr0.7（Ca1-xSrx）0.3MnO3 Thin Films

Carrier injection performed in Pro.7 Cao.aMnOa junctions demonstrate resistance switching （RS） characteristic with dramatic changes in both resistances and interface barriers, which suggests a charge carrier self-trapping model in strongly correlated electronic framework. Un-stable RS behaviour without electric fields in epitaxial Pr0.7（Ca1-xSrx）0.3MnO3 （PCSMO） films shows dependences on insulator-metal transition temperature, which indicates that RS process is really related to the intrinsic property of carriers. The switched resistance of epitaxial PCSMO films also depends on the amount of current pulses, which shouM be another evidence of the carrier self-trapping model, similarly to the dependence on the amount of self-trapped charge carriers.     

Manganite-layer thickness-dependent photovoltaic effect of La0.9Sr0.1MnO3/SrNb0.01Ti0.99O3 p–n heterojunction

The perovskite p–n heterojunctions were fabricated by depositing La_0.9Sr_0.1MnO₃ (LSMO) layers with thicknesses ranging from 20 to 400 Å on SrNb_0.01Ti_0.99O₃ (SNTO) single-crystal substrates by laser molecular beam epitaxy (laser-MBE). The open-circuit photovoltage of the LSMO/SNTO heterojunction at room temperature increases with the increase of the thickness of LSMO layer. This result is ascribed to the increase of the carrier amount and the enhancement of the built-in electric field in the space-charge region of the LSMO/SNTO heterojunction with the increase of the thickness of LSMO layer. Furthermore, we found that the speed of photovoltaic response is almost independent of the thickness of LSMO layer in the heterojunction.     

Structural and electrical properties of La0.5Sr0.5CoO3 films on SrTiO3 and porous a-Al2O3 substrates

Films of La_0.5Sr_0.5CoO₃ (LSCO) have been deposited on specially treated TiO₂-terminated (001) SrTiO₃ substrate surfaces and on macroporous polycrystalline !-Al₂O₃ substrates, having a mean pore diameter of 80 nm, by pulsed laser deposition. The films deposited on SrTiO₃ are good conducting, (001) textured, and exceptionally smooth (1-2 Å for 100 nm thick films). LSCO films deposited on porous !-Al₂O₃ are polycrystalline and exhibit good crystallographic and electrical properties despite the large substrate roughness and the differences in lattice parameters and crystal structure between the film and the substrate. Different growth modes have been observed on the porous !-Al₂O₃ substrates depending on the oxygen pressure during film deposition. Films grown at an oxygen pressure of 10^-1 mbar are macroporous, whereas films grown at 10^-2 mbar completely cover the substrate pores. In the latter case, strain effects lead to film cracking.     

Influence of the laser wavelength on the epitaxial growth and electrical properties of La0.8Sr0.2MnO3 films grown by excimer laser-assisted MOD

Epitaxial La_1−xSr_xMnO₃ (LSMO) films were prepared by excimer laser-assisted metal organic deposition (ELAMOD) at a low temperature using ArF, KrF, and XeCl excimer lasers. Cross-section transmission electron microscopy (XTEM) observations confirmed the epitaxial growth and homogeneity of the LSMO film on a SrTiO₃ (STO) substrate, which was prepared using ArF, KrF, and XeCl excimer lasers. It was found that uniform epitaxial films could be grown at 500 °C by laser irradiation. When an XeCl laser was used, an epitaxial film was formed on the STO substrate at a fluence range from 80 to 140 mJ/cm² of the laser fluence for the epitaxial growth of LSMO film on STO substrate was changed. When the LaAlO₃ (LAO) substrate was used, an epitaxial film was only obtained by ArF laser irradiation, and no epitaxial film was obtained using the KrF and XeCl lasers. When the back of the amorphous LSMO film on an LAO substrate was irradiated using a KrF laser, no epitaxial film formed. Based on the effect of the wavelength and substrate material on the epitaxial growth, formation of the epitaxial film would be found to be photo thermal reaction and photochemical reaction. The maximum temperature coefficient of resistance (TCR) of the epitaxial La_0.8Sr_0.2MnO₃ film on an STO substrate grown using an XeCl laser is 4.0%/K at 275 K. XeCl lasers that deliver stabilized pulse energies can be used to prepare LSMO films with good a TCR.     

Thickness dependence of microstructures in La0.9Sr0.1MnO3 thin films grown on exact-cut and miscut SrTiO3 substrates

The thickness dependence of microstructures of La_0.9Sr_0.1MnO₃ (LSMO) thin films grown on exact-cut and miscut SrTiO₃ (STO) substrates, respectively, was investigated by high-angle X-ray diffraction (HXRD), X-ray small-angle reflection (XSAR), X-ray reciprocal space mapping and atomic force microscopy (AFM). Results show that the LSMO films are in pseudocubic structure and are highly epitaxial [0 0 1]-oriented growth on the (0 0 1) STO substrates. The crystalline quality of the LSMO film is improved with thickness. The epitaxial relationship between the LSMO films and the STO substrates is [0 0 1]_LSMO[0 0 1]_EXACT-STO, and the LSMO films have a slight mosaic structure along the q_x direction for the samples grown on the exact-cut STO substrates. However, an oriented angle of about 0.24° exists between [0 0 1]_LSMO and [0 0 1]_MISCUT-STO, and the LSMO films have a mosaic structure along the q_z direction for that grown on the miscut STO substrates. The mosaic structure of both groups of the samples tends to reduce with thickness. The diffraction intensity of the (0 0 4) peaks increases with thickness of the LSMO film. The XSAR and AFM observations show that for both groups, the interface is sharp and the surface is rather smooth. The mechanism was discussed briefly.     

Enhanced magnetoresistance in La0.82Sr0.18MnO3-π-conjugated semiconducting polymer heterostructure

We report a large enhancement (∼90%) in magnetoresistance in La_0.82Sr_0.18MnO₃ (LSMO) layers by incorporating a π-conjugated semiconducting polymer layer in between them. The epitaxial LSMO layers were deposited by DC magnetron sputtering on SrTiO₃ single crystal substrates and have FM transition temperature (T_C)∼310 K. A semiconducting polymer poly(3-octylthiophene) (P3OT) layer was deposited over the epitaxial LSMO layer by solution dip coating technique and with subsequent deposition of another epitaxial LSMO layer, forming a LSMO-P3OT-LSMO heterostructure. The effect of P3OT incorporation on magnetotransport properties of this heterostructure has been examined in the temperature range 77-350 K. Large MR enhancement observed near room temperature in the FM regime is explained in terms of efficient magnetic field dependent carrier injection at LSMO/P3OT interface.     

An All-Thin-Film Electrochromic Device Composed of MoO3--LiBSO--NiOx Multilayer Structure

An all-thin-tilm （ATF） electrochromic device for modulating the optical transmittance is manufactured using magnetron sputtering. The devices consists of MoO3 as the main electrochromic layer, LiBO2 ＋Li2SO4 （LiBSO） as the ion conductor layer, and NiOx as the complementary electrochromic layer. Glass covered with indium tin oxide （ITO） is used as the substrate and the ITO film is used as the bottom electrode. The ITO film deposited on the top of the devices is used as the other electrode. The structure and morphology of the films are characterized by x-ray diffraction （XRD） and scanning electron microscopy （SEM）. The devices exhibit good optical properties with low transmittance values in the coloured state, and the optical modulation is measured by spectrophotometer in the wavelength range from 400 to 800nm. The average visible light transmittance reaches 50.2% and 3.7% in bleached and coloured state, respectively. The results indicate that such a monolithic system has great potential to be applied in smart windows.     

Memory Effect of Metal--Insulator--Silicon Capacitors with SiO2/HfO2/Al2O3 Dielectrics

Charge trapping characteristics of the metal-insulator-silicon （MIS） capacitors with Si02/HfO2//A12O3 stacked dielectrics are investigated for memory applications＇. A capacitance-voltage hysteresis memory window as large as 7.3 V is achieved for the gate voltage sweeping of ±12 V, and a fiat-band voltage shift of 1.5 V is observed in terms of programming under 5 V and I ms. Furthermore, the time- and voltage-dependent charge trapping characteristics are also demonstrated, the former is related to charge trapping saturation and the latter is ascribed to variable tunnelling barriers for electron injecting and discharging under different voltages.     

Electronic Structure and Optical Properties of La-Doped SrTiO3 and Sr2TiO4 by Density Function Theory

The effect of La doping on the electronic structure and optical properties of SrTiO₃ and Sr₂TiO₄ is investigated by the first-principles calculation of plane wave ultrasoft pseudopotential based on the density function theory (DFT). The calculated results reveal that the electron doping in the case of Sr_0.875La_0.125TiO₃ and Sr_1.875La_0.125TiO₄ can be described within the rigid band model. The La³⁺ ions fully acts as electron donors in Sr_0.875La_0.125TiO₃ and Sr_1.875La_0.125TiO₄ systems and the Fermi level shifts further into the conduction bands (CBs) for Sr_1.875La_0.125TiO₄ compared to Sr_0.875La_0.125TiO₃. The two systems exhibit n-type degenerate semiconductor features. At the same time, the density of states (DOS) of the two systems shift towards low energies and the optical band gaps are broadened. The Sr_1.875La_0.125TiO₄ is highly transparent with the transmittance about 90% in the visible range, which is larger than that of Sr_0.875La_0.125TiO₃(85%). The wide band gap, small transition probability and weak absorption due to the low partial density of states (PDOS) of impurity in the Fermi level result in the optical transparency of the films...     

Preparation and Luminescence Characteristics of Ca3Y2（BO3）4：Eu^3＋ Phosphor

Ca3Y2 （BO3）4：Eu^3＋ phosphor is synthesized by high temperature solid-state reaction method, and the Iuminescence characteristics are investigated. The emission spectrum exhibits two strong red emissions at 613 and 621 nm corresponding to the electric dipole ^5 Do- ^7F2 transition of Eu^3＋ under 365 nm excitation, the reason is that Eu^3＋ substituting for Y^3＋ occupies the non-centrosymmetric position in the crystal structure of Ca3 Y2 （BO3）4. The excitation spectrum for 613 nm indicates that the phosphor can be effectively excited by ultraviolet （UV） （254 nm, 365nm and 400nm） and blue （470nm） light. The effect of Eu^3＋ concentration on the emission intensity of Ca3 Y2 （BO3）4 ：Eu^3＋ phosphor is measured, the result shows that the emission intensities increase with increasing Eu^3＋ concentration, then decrease. The CIE colour coordinates of Ca3Y2 （BO3）4：Eu^3＋ phosphor is （0.639, 0.357） at 15mol% Eu^3＋.     

Air Stability of Cs2CO3:Ag/Ag Cathode for Organic Light-Emitting Diodes

We report the superior stability of the composite Cs2CO3 ：Ag/Ag cathode structure, which can be used in efficient organic light-emitting diodes （OLEDs）. Devices with the Cs2CO3：Ag （1：10, 5nm）/Ag （95nm） cathode show a considerably improved lifetime compared with the control device with the Cs2CO3 （0.5 nm）/Ag （100 nm） cathode. The composite Cs2CO3 ：Ag/Ag film is proved to be stable in the atmosphere. X-ray diffraction （XRD） is applied to analyze the crystalline structure of the Cs2CO3：Ag film, and it is demonstrated that CsAg alloy is formed, leading to the improved stability of the thin film and the devices.     

Electroluminescence from Multilayered Diamond/CeF3/SiO2 Films

We report a thin film electroluminescent device with a three-layer structure （diamond/CeF3/SiO2 films）, which has a luminance of 1.5 cd/m^2 at dc voltage 215 V. The electroluminescence spectrum at room temperature shows that the main peaks locate at 527 and 593nm, which are attributed to isolated emission centers of Ce^3＋ ions.     

Influences of Bi2O3/V2O5 Additives on the Microstructure and Magnetic Properties of Lithium Ferrite

Lithium ferrite materials with different concentrations of Bi2O3 and V2O5 additives are prepared by the conventional ceramic technique. The x-ray diffraction analysis proves that the additives do not affect the final crystal phase of the lithium ferrite in our testing range. Both Bi2O3 and V2O5 additives could promote densification and lower sintering temperature of the lithium ferrite. The average grain size first increases, and then gradually decreases with the Bi2O3 content. The maximal grain size appears with 0.25 wt% Bi2O3. The average grain size first increases, and then is kept almost unchanged with the V2O5 content. The maximal average grain size of the samples with V2O5 additive is much smaller than that of the samples with Bi2O3 additive. Furthermore, the V2O5 additive more easily enters the crystal lattice of the lithium ferrite than the Bi2O3 additive. These characteristics evidently affect the magnetic properties, such as saturation flux density, ratio of remanence Br to saturation flux density Bs, and coercive force of the lithium ferrite. The mechanisms involved are discussed.     

LaNiO3 under-electrode layers for the growth of textured (Pb0.4Zr0.6)TiO3 thin films using pulsed laser deposition

We investigated the structural properties of LaNiO₃ thin films of three different thicknesses deposited by pulsed laser deposition on Si(001) mainly by using a synchrotron X-ray scattering measurement. The LaNiO₃ thin films were grown with the (00l) preferred growth direction, showing completely random distribution in the in-plane direction. In the early stage of the growth, the film was almost unstrained. However, as the film grew further, tensile strain was markedly involved. Also its surface became rougher but its crystalline quality improved significantly with increasing film thickness. A completely (00l)-oriented (Pb_0.4Zr_0.6)TiO₃ thin film was successfully grown on such a LaNiO₃/Si(001) substrate at a substrate temperature of 350 °C by using the same pulsed laser deposition. Our results show that the LaNiO₃ film can serve effectively as a bottom electrode layer for the preparation of a well-oriented (Pb_0.4Zr_0.6)TiO₃ thin film on Si substrates.     

Raman and X-Ray Investigation of Pyrope Garnet （Mg0.76Fe0.14Ca0.10）3Al2Si3O12 under High Pressure

The compressional behavlour of natural pyrope garnet is investigated by using angle-dlspersive synchrotron radiation x-ray diffraction and Raman spectroscopy in a diamond anvil cell at room temperature. The pressureinduced phase transition does not occur under given pressure. The equation of state of pyrope garnet is determined under pressure up to 25.3 GPa. The bulk modulus KTO is 199 GPa, with its first pressure derivative K′TO fixed to 4. The Raman spectra of pyrope garnet are studied. A new Raman peak nearly at 743 cm^-1 is observed in a bending vibration of the SiO4 tetrahedra frequency range at pressure of about 28 GPa. We suggest that the new Raman peak results from the lattice distortion of the SiO4 tetrahedra. All the Raman frequencies continuously increase with the increasing pressure. The average pressure derivative of the high frequency modes （650-1000 cm^-1） is larger than that of the low frequency （smaller than 650 cm^-1）. Based on these data, the mode Grǖneisen parameters for pyrope are obtained.     

Enhanced Magnetoresistance of （La0.67Ca0.33MnO3） Composites Coated by Zn0.95Co0.05O

La0.7Ca0.3MnO3：xZn0.95Co0.05O （x=0.0,0.05, 0.1, 0.15mol） composites are prepared by a sol-gel process. X- ray diffraction and energy diffraction spectroscopy reveal that there is no evidence of a reaction between the La0.7 Ca0.3 MnO3 （LCMO） and Zn0.95Co0.05 O （ZCO）. Magnetization M, Curie temperature Tc and metal-insulator transition temperatures Tp are observed to decrease with increasing ZCO content. Compared with x = 0.0, a great enhancement in the magnetoresistance （MR） is observed at around Tc for x = 0.05, 0.10, 0.15. Based on the tunneling MR and percolation models, this great change of MR is well explained.     

Optical Properties of Co-BaTiO3/Mg（100） Nano-Composite Films Grown by Pulsed Laser Deposition Method

Co nanoparticles embedded in a BaTiO3 matrix, namely Co-BaTiO3 nano-composite films are grown on Mg（100） single crystal substrates by the pulsed laser deposition （PLD） method at 650℃. Optical properties of the CoBaTiO3 nano-composite films are examined by absorption spectra （AS） and photoluminescence （PL） spectra. The results indicate that the concentration of Co nano-particles strongly influences the electron transition of the Co BaTiO3 nano-composite films. The PL emission band ranging from 1.9 to 2.2eV is reported. The AS and PL spectra suggest that the band gap is in the range of 3.28-3.7eV.