Improved ferroelectric,dielectric and magnetic properties with La- and Mn- doped Bi5Ti3FeO15 thin films

A series of La and Mn co-doped Bi₅Ti₃FeO₁₅ (BLTFMO) thin films were prepared by spin-coating deposition route. X-ray diffraction, atomic force microscopy and scanning electron microscopy were used to characterize the structures of these BLTFMO thin films. Ferromagnetic properties are obtained as the La-doping content is 0, 0.1, 0.2, and 0.3 with the transition temperature of 127.2 K, 65.1 K, 48.1 K, and 7.9 K, respectively. Well-defined ferroelectric loops are found in all these BLTFMO films, and a higher remnant polarization of 27.84, 24.21 and 24.02 μC/cm² is obtained in the 0.1, 0.2 and 0.3 La-doped films, respectively. A weak dielectric dispersion for the BLTFMO without La-doping, a strong one in 0.1, 0.2, 0.3 and 0.4 La doped films as indicated by the appearance of a dielectric loss peak, and a weak dispersion in 0.6, 0.8 and 1 La doped ones are demonstrated.     

Structure and electrical properties of HfO<Subscript>2</Subscript> high-<Emphasis Type="Italic">k</Emphasis> films prepared by pulsed laser deposition on Si (100)

High-k gate dielectric hafnium dioxide films were grown on Si (100) substrate by pulsed laser deposition at room temperature. The as-deposited films were amorphous and that were monoclinic and orthorhombic after annealed at 500°C in air and N₂ atmosphere, respectively. After annealed, the accumulation capacitance values increase rapidly and the flat-band voltage shifts from −1.34 V to 0.449 V due to the generation of negative charges via post-annealing. The dielectric constant is in the range of 8–40 depending on the microstructure. The I–V curve indicates that the films possess of a promising low leakage current density of 4.2×10⁻⁸ A/cm² at the applied voltage of −1.5 V.     

Microstructure and properties of manganese dioxide films prepared by electrodeposition

Nanostructured manganese dioxide films were obtained by galvanostatic, pulse and reverse pulse electrodeposition from 0.01 to 0.1 M KMnO₄ solutions. The deposition yield was investigated by in situ monitoring the deposit mass using a quartz crystal microbalance (QCM). Obtained films were studied by electron microscopy, X-ray diffraction analysis, energy dispersive spectroscopy, thermogravimetric and differential thermal analysis. The QCM and electron microscopy data were utilized for the investigation of deposition kinetics and film formation mechanism. It was shown that the deposition rate and film microstructure could be changed by variation of deposition conditions. The method allowed the fabrication of dense or porous films. The thickness of dense films was limited to ∼0.1 μm due to the insulating properties of manganese dioxide and film cracking, attributed to drying shrinkage. Porous and crack-free 1-2 μm films were obtained using galvanostatic or reverse pulse deposition from 0.02 M KMnO₄ solutions. It was shown that film porosity is beneficial for the charge transfer during deposition and crack prevention in thick films. Moreover, porous nanostructured films showed good capacitive behavior for applications in electrochemical supercapacitors. The porous nanostructured films prepared in the reverse pulse regime showed higher specific capacitance (SC) compared to the SC of the galvanostatic films. The highest SC of 279 F/g in a voltage window of 1 V was obtained in 0.1 M Na₂SO₄ solutions at a scan rate of 2 mV/s.     

Nanostructured ZnO thin films by chemical bath deposition in basic aqueous ammonia solutions for photovoltaic applications

This paper presents further insights and observations of the chemical bath deposition (CBD) of ZnS thin films using an aqueous medium involving Zn-salt, ammonium sulfate, aqueous ammonia, and thioure. Results on physical and chemical properties of the grown layers as a function of ammonia concentration are reported. Physical and chemical properties were analyzed using scanning electron microscopy (SEM), X-ray energy dispersive (EDX), and X-ray diffraction (XRD). Rapid growth of nanostructured ZnO films on fluorine-doped SnO₂ (FTO) glass substrates was developed. ZnO films crystallized in a wurtzite hexagonal structure and with a very small quantity of Zn(OH)₂ and ZnS phases were obtained for the ammonia concentration ranging from 0.75 to 2.0 M. Flower-like and columnar nanostrucured ZnO films were deposited in two ammonia concentration ranges, respectively: one between 0.75 and 1.0 M and the other between 1.4 and 2.0 M. ZnS films were formed with a high ammonia concentration of 3.0 M. The formation mechanisms of ZnO, Zn(OH)₂, and ZnS phases were discussed in the CBD process. The developed technique can be used to directly and rapidly grow nanostructured ZnO film photoanodes. Annealed ZnO nanoflower and columnar nanoparticle films on FTO substrates were used as electrodes to fabricate the dye sensitized solar cells (DSSCs). The DSSC based on ZnO-nanoflower film showed an energy conversion efficiency of 0.84%, which is higher compared to that (0.45%) of the cell being constructed using a photoanode of columnar nanoparticle ZnO film. The results have demonstrated the potential applications of CBD nanostructured ZnO films for photovoltaic cells.     

Dielectric relaxation in LaSrCo1−x Al x O4 ceramics

Dielectric properties of LaSrCo_1−x Al _x O₄ (x=0, 0.1, 0.3, and 0.5) ceramics were investigated in a broad frequency and temperature range. The AC conductivity decreased with the increasing Al concentration. Dielectric constant increased at lower frequency and decreased at higher frequency when the Al concentration increased from 0.1 to 0.3, then it decreased at all frequencies as the x value was 0.5. While the dielectric loss decreased first and then increased with the increasing Al concentration. There was one dielectric relaxation in the curve of temperature dependence of dielectric properties of LaSrCo_0.7Al_0.3O₄ ceramics. The nonadiabatic small polaronic hopping process should contribute to the dielectric relaxation in the present ceramics. The AC conductivity increased in about one order of magnitude after annealing the sample in the oxygen atmosphere, and this should be attributed to the appearance of interstitial oxygen in the annealed sample.     

Doping effects arising from Ni for Fe in PrFeO3 ceramic thin films

Structural, morphological and transport properties of PrFe_{1? x} Ni _x O₃ (x?=?0.1, 0.2, 0.3, 0.4 and 0.5) thin films grown on LaAlO₃ substrate by pulsed laser deposition were studied experimentally. Structural analysis of the samples showed that they have in-plane compressive strain and single-phase epitaxial growth along with c-axis (001) orientation having orthorhombic structure with space group Pbnm. The observed strain is reduced with Ni substitution. The resistivity as a function of temperature follows the variable range hopping (VRH) model up to certain amount of Ni substitution (x?=?0.3) but fails for higher values of x. From the above model, parameters such as density of states at the Fermi level, N(E _F), hopping energy, E _h, and hopping distance R _h, were calculated. Ni substitution leads to an increase in conductivity and this conduction is controlled by disorder-induced localization of charge carriers. With Ni substitution the gap parameter is found to decrease. The enhancement in conductivity and the failure of VRH model for higher doped compositions at high temperature is discussed.     

Effect of Bi substitution on the magnetic and dielectric properties of epitaxially grown BaFe0.3Zr0.7O3−δ thin films on SrTiO3 substrates

The structural, dielectric and magnetic properties of single crystalline Ba_1−xBi_xFe_0.3Zr_0.7O_3−δ (x=0.0-0.29) thin films have been studied. The pseudotetragonal epitaxial thin films were obtained by pulsed laser-beam deposition (PLD) on (0 0 1) SrTiO₃ (STO) single-crystal substrates. The Bi substitution for the Ba ions up to an extent of x=0.18 caused a slight improvement in the leakage current properties, as well as an enhancement of the apparent dielectric constant. The saturation magnetization of the films was significantly decreased following Bi substitution. These changes were thought to be related to the increase in oxygen deficiencies in the films. The effect of the Bi substitution on the dielectric and magnetic properties was analyzed in conjunction with the change in valence value of the Fe ions.     

Electromechanical properties of Ba(Ti1-xZrx)O3 thin films

The electromechanical properties of thin films of barium titanate zirconate were studied with the help of a double-beam interferometer. Thin films of barium titanate zirconate (Ba(Ti_1-xZr_x)O₃) of various compositions (x=0, 0.03, 0.05, 0.07, 0.1, 0.2, 0.3 and 0.4) were deposited by chemical solution deposition on Pt/TiO₂/SiO₂/Si substrates. The thin films show a strain of around 0.05 (at 200 kV/cm) for the unsubstituted BaTiO₃ thin films. For higher Zr substitutions up to 5% the strain increases slightly and subsequently falls to 0.01 at 200 kV/cm for even higher Zr content. The d₃₃ values were found to vary between 30 pm/V and 10 pm/V for 0x0.4. PACS 77.65.-j; 77.55.+f; 77.84.Dy     

The effect of Mg doping on the dielectric and tunable properties of Pb0.3Sr0.7TiO3 thin films prepared by sol–gel method

Mg doped Pb_0.3Sr_0.7TiO₃ (PST) thin films were fabricated by the sol–gel method on a Pt/Ti/SiO₂/Si substrate. The microstructure, surface morphology, dielectric and tunable properties of PST thin films were investigated as a function of Mg concentration. It is found that proper Mg doping dramatically improves the dielectric loss (0.0088 @ 1 MHz), furthermore, the crystallinity, dielectric constant, and tunability of films simultaneously decrease with the increase of Mg content. The 2 mol% Mg doped PST thin film shows the highest figure of merit (FOM) value of 36.8 for its the smallest dielectric loss and upper tunability. The dependence of Rayleigh coefficient on the doping concentration was examined, which indicated that the reduction of dielectric constant and tunability of films should be related to the $\mathrm{Mg}''_{\mathrm{Ti}}$ – $\mathrm{V}_{\mathrm{O}}^{\bullet\bullet}$ defect dipoles pinning the domain wall motion of residual polar clusters in PST.     

Corrosion resistant surface for vanadium nitride and hafnium nitride layers as function of grain size

In this research it was studied vanadium nitride (VN) and hafnium nitride (HfN) film, which were deposited onto silicon (Si (100)) and AISI 4140 steel substrates via r.f. magnetron sputtering technique in Ar/N₂ atmosphere with purity at 99.99% for both V and Hf metallic targets. Both films were approximately 1.2±0.1 µm thick. The crystallography structures that were evaluated via X-ray diffraction analysis (XRD) showed preferential orientations in the Bragg planes VN (200) and HfN (111). The chemical compositions for both films were characterized by EDX. Atomic Force Microscopy (AFM) was used to study the morphology; the results reveal grain sizes of 78±2 nm for VN and 58±2 nm for HfN and roughness values of 4.2±0.1 nm for VN and 1.5±0.1 nm for HfN films. The electrochemical performance in VN and HfN films deposited onto steel 4140 were studied by Tafel polarization curves and impedance spectroscopy methods (EIS) under contact with sodium chloride at 3.5 wt% solution, therefore, it was found that the corrosion rate decreased about 95% in VN and 99% for HfN films in relation to uncoated 4140 steel, thus demonstrating, the protecting effect of VN and HfN films under a corrosive environment as function of morphological characteristics (grain size).     

PLD and RF-PLD synthesis of Ba<Subscript>0.6</Subscript>Sr<Subscript>0.4</Subscript>TiO<Subscript>3</Subscript> ferroelectric thin films for electrically controlled devices

Ba_0.6Sr_0.4TiO₃ (BST) bulk ceramic synthesized by solid state reaction was used as target for thin films grown by pulsed laser deposition (PLD) and radiofrequency beam assisted PLD (RF-PLD). The X-ray diffraction patterns indicate that the films exhibit a polycrystalline cubic structure with a distorted unit cell. Scanning Electron Microscopy investigations showed a columnar microstructure with size of spherical grains up to 150 nm. The capacitance–voltage (C–V) characteristics of the BST films were performed by applying a DC voltage up to 5 V. A value of 280 for dielectric constant and 12.5% electrical tunability of the BST capacitor have been measured at room temperature.     

Synchrotron infrared reflectance microspectroscopy study of film formation and breakdown on copper

This work demonstrates the utility of synchrotron infrared reflectance microspectroscopy in the far‐ and mid‐IR for the determination of the composition of electrogenerated surface films formed during the general and localized corrosion of copper in alkaline and bicarbonate solutions. Back‐reflection geometry has been employed to identify the anodic film formed on copper in 0.1 M NaOH solution at 0.3 V (versus a Ag/AgCl reference) to be mainly CuO. In 0.01 M NaHCO₃ solution general corrosion occurs with passive film formation below 0.2 V. The surface film at 0.2 V consisted mainly of bicarbonate, copper carbonate dihydroxide or malachite [CuCO₃·Cu(OH)₂], Cu(OH)₂ and possibly some CuO. At higher potentials the passive film breaks down and localized corrosion occurs leading to the formation of pits. The composition of the surface films inside the pits formed at 0.6 V was found to be essentially the same as that outside but the relative amount of Cu(OH)₂ appears to be higher.     

Characterization and electrical properties of high-<Emphasis Type="Italic">k</Emphasis> GdScO<Subscript>3</Subscript> thin films grown by atomic layer deposition

Gadolinium scandium oxide (Gd-scandate, GdScO₃) thin films were grown by atomic layer deposition (ALD) from β-diketonate precursors M(thd)₃ (M=Gd, Sc; thd=2,2,6,6-tetramethyl-3,5-heptanedionato) and ozone. The deposition parameters were optimized to produce films with the stoichiometric 1:1 metal ratio and a series of samples with nominal thicknesses of 5, 10, 15, and 20 nm were prepared. At 300 °C the metal precursor pulsing ratio Gd:Sc=5:6 yielded amorphous stoichiometric films and a growth rate of 0.21 Å/cycle. The films stayed amorphous up to 900 °C. The surface was probed with an AFM and the rms roughness was found to be 0.3 nm for the 5–20 nm thick films. The electrical properties of the as-deposited films proved to be very promising, with a dielectric constant of ～22 and leakage current density of 340 μA/cm², measured at -2 V.     

Al3+掺杂的CuZn铁氧体的结构，电学和磁学特性

采用固相合成反应技术制备纳米Cu_0.5Zn_0.5Fe_2-xAl_xO₂(x=0.0,0.1,0.2,0.3,0.4和0.5)铁氧体材料,研究Al³⁺含量对结构,电学和磁学性质的影响. 采用X射线衍射研究单相立方尖晶石结构. 利用Scherrer公式估算晶粒尺寸. 测定了温度依赖的直流电阻率.结果表明随Al³⁺含量的增加,晶格常数减小,孔隙度增加,饱和磁化强度值降低,Al³⁺对铁氧体的介电常数、介电损耗角的正切值和介质损耗因子等介电性能有明显影响,这可能与空间电荷极化有关.     

Optical parameters of In–Se and In–Se–Te thin amorphous films prepared by pulsed laser deposition

The thin films of materials based on In–Se are under study for their applicability in photovoltaic devices, solid-state batteries and phase-change memories.The amorphous thin films of In₂Se_3−xTe_x (x=0–1.5) and InSe were prepared by pulsed laser deposition method (PLD) using a KrF excimer laser beam (λ=248 nm, 0.5 J cm⁻²) from polycrystalline bulk targets. The compositions of films verified by energy-dispersive X-ray analysis (EDX) were close to the compositions of targets. The surfaces of PLD films containing small amount of droplets were viewed by optical and scanning electron microscopy (SEM).The optical properties (transmittance and reflectance spectra, spectral dependence of index of refraction, optical gap, single-oscillator energy, dispersion energy, dielectric constant) of the films were determined.The values of index of refraction increased with increasing substitution of Te for Se in In₂Se₃ films, the values of the optical gap decreased with increasing substitution of Te for Se in In₂Se₃ films.     

Tb0.3Dy0.7－xPrx(Fe0.9Al0.1)1.95合金的磁致伸缩、自旋重取向和穆斯堡尔谱研究

系统研究了室温下Tb_0.3Dy_0.7-xPr_x(Fe_0.9Al_0.1)_1.95 (x=0，0.1，0.2，0.25，0.3，0.35)合金中稀土元素Pr替代Dy对晶体结构、磁致伸缩、各向异性和自旋重取向的影响. 结果发现，x≤0.1时，Tb_0.3Dy_0.7-xPr_x(Fe_0.9Al_0.1)_1.95完全保持MgCl₂立方Laves相结构，0.1<x≤0.3，有杂相出现并且随Pr替代量逐渐增多；晶格常数a随Pr含量x的增加缓慢增大. 磁致伸缩测量发现，随着替代量x的增多磁致伸缩减小；x>0.2时超磁致伸缩效应消失. 然而，x=0.1时合金的磁致伸缩略大于没有替代的，而且磁致伸缩随磁场更易趋于饱和，说明Pr替代有助于降低磁晶各向异性. 内禀磁致伸缩λ₁₁₁随Pr替代量x的增加接近线性增加. 由相对磁化率随温度的变化关系可以看出，自旋重取向温度随Pr替代量的增多呈先增后降趋势，在x=0.1处出现极大值. 穆斯堡尔效应表明，随Pr含量的增加Tb_0.3Dy_0.7-xPr_x(Fe_0.9Al_0.1)_1.95合金中易磁化轴可能在{110}面上绕主对称轴作微小转动，发生自旋重取向. 与Al元素替代效应相比，Pr替代Dy对自旋重取向的影响相对较小.     

Preparation and characterization of electrodeposited Sb2Se3 thin films from non-aqueous media

Semiconducting Sb₂Se₃ thin films have been prepared onto the stainless steel and fluorine doped tin oxide coated glass substrates from non-aqueous media using an electrodeposition technique. The electrodeposition potentials for different bath compositions and concentrations of solution have been estimated from the polarization curves. SbCl₃ and SeO₂ in the volumetric proportion as 1:1 with their equimolar solution concentration of 0.05 M form good quality films. The films are characterized by scanning electron microscopy (SEM), X-ray diffraction (XRD) and optical absorption techniques. The SEM studies show that the film covers the total substrate surface with uneven surface morphology. The XRD patterns of the films obtained by varying compositions and concentrations show that the as-deposited films are polycrystalline with relatively higher grain size for 1:1 composition and 0.05 M concentration. The optical band gap energy for indirect transition in Sb₂Se₃ thin films is found to be 1.195 eV.     

Metallo-organic decomposition derived (Ca, Sr)ZrO3 dielectric thin films on Pt coated Si substrate

Metallo-organic decomposition derived dielectric thin films of calcium zirconate doped with various concentrations of strontium ((Ca, Sr)ZrO₃) were prepared on Pt coated silicon substrate. Mainly in this paper, we present the investigations of their structural developments and present their electric and dielectric properties as well. The structural developments show that the CaZrO₃ film has amorphous structure with carbonate existing when annealed at 600 °C, while annealed at 650 °C and above, the carbonate is decomposed and those films crystallize into perovskite phase without preferred orientation. In addition, the prepared (Ca, Sr)ZrO₃ films with their Zr-O bonds affected by strontium doping are homogenous and stable as solid solutions in any concentration of strontium and all Bragg diffraction characteristics for the films shift downward with the increase in the concentration of strontium. Moreover, the electric properties show that the (Ca, Sr)ZrO₃ films have very low leakage current density and high breakdown strength; typically, the CaZrO₃ film annealed at 650 °C has the leakage current density approximately 9.5 × 10⁻⁸ A cm⁻² in the field strength of 2.6 MV cm⁻¹. Furthermore, the dielectric properties show that their dielectric constants are higher than 12.8 with very little dispersion in the frequency range from 100 Hz to 1 MHz and are independent of applied dc bias as well. The dielectric properties, in combination with the electric properties, make the materials promising candidates for high-voltage and high-reliability capacitor applications.     

Investigation of the low-and infralow-frequency dielectric response of Ba0.7Sr0.3TiO3 thin films

The low-and infralow-frequency dielectric properties of Ba_0.7Sr_0.3TiO₃ thin films annealed at temperatures of 750 and 900°C are investigated over wide ranges of temperatures (from ?180 to +100°C), frequencies (from 0.1 Hz to 10.0 kHz), and amplitudes of the measuring electric field (from 15 to 255 kV/cm). The samples are found to undergo giant relaxation characteristic of layered heterogeneous structures. It is noted that, at a higher annealing temperature (900°C), the relaxation region is shifted toward lower temperatures (higher frequencies).     

Optical and thermoelectric characterizations of electroplated n-Bi2(Te0.9Se0.1)3

Bismuth selenotelluride (Bi₂(Te_0.9Se_0.1)₃) films were electrodeposited at constant current density from acidic aqueous solutions with Arabic gum in order to produce thin films for miniaturized thermoelectric devices. X-ray fluorescence spectroscopy determined film compositions. X-ray diffraction pattern shows that the films as deposited are polycrystalline, isostructural to Bi₂Te₃ and covered by crystallites. Mueller-matrix analysis reveals that the electroplated layers are optically like an isotropic medium. Their pseudo-dielectric functions were determined using mid-infrared spectroscopic ellipsometry. Tauc-Lorentz combined with Drude dispersion relations were successfully used. The energy band gap E_g was found to be about 0.15 eV. Moreover, the fundamental absorption edge was described by an indirect optical band-to-band transition. From Seebeck coefficient measurement, films exhibit n-type charge carrier and the value of thermoelectric power is about −40 μV/K.