Optical,electrical and magnetic properties of nanostructured Mn3O4 synthesized through a facile chemical route

Nanostructured Mn₃O₄ sample with an average crystallite size of ∼15 nm is synthesized via the reduction of potassium permanganate using hydrazine. The average particle size obtained from the Transmission Electron Microscopy analysis is in good agreement with the average crystallite size estimated from X-ray diffraction analysis. The presence of Mn⁴⁺ ions at the octahedral sites is inferred from the results of Raman, UV–visible absorption and X-ray photoelectron spectroscopy analyzes. DC electrical conductivity of the sample in the temperature range 313–423 K, is about five orders of magnitude larger than that reported for single crystalline Mn₃O₄ sample. The dominant conduction mechanism is identified to be of the polaronic hopping of holes between cations in the octahedral sites. The zero field cooled and field cooled magnetization of the sample is studied in the range 20–300 K. The Curie temperature for the sample is about 45 K, below which the sample is ferrimagnetic. A blocking temperature of 35 K is observed in the field cooled curve. It is observed that the sample shows hysteresis at temperatures below the Curie temperature with no saturation, even at an applied field (20 kOe). The presence of an ordered core and disordered surface of spin arrangements is observed from the magnetization studies. Above the Curie temperature, the sample shows linear dependence of magnetization on applied field with no hysteresis characteristic of paramagnetic phase.     

Modulating microstructure and optical properties of hydrogenated nanocrystalline silicon photovoltaic materials prepared under hydrogen diluted silane PECVD by various DC bias

Hydrogenated nanocrystalline silicon (nc-Si:H) thin films were fabricated by plasma enhanced chemical vapor deposition under the various negative substrate bias voltages with hydrogen as a diluent of silane. The microstructure and optical properties of nc-Si:H thin films were studied by Raman scattering spectroscopy, X-ray diffraction (XRD), transmission electron microscopy, and optical transmission spectroscopy. Raman spectra and XRD pattern reveal that applying negative bias voltages at the moderate level favors the enhancement of crystalline volume fraction, increase of crystallite sizes and decrease of residual stress. We also demonstrated that the negative direct current bias can be used to modulate the volume fraction of voids, refractive index, absorption coefficient, compactness and ordered degree of nc-Si:H films. It is found that the film deposited at −80 V shows not only high crystallinity, size of crystallite, and static index n₀ but also low residual stress and volume fraction of voids. Furthermore, the microstructural evolution mechanism of nc-Si:H thin films prepared at different bias voltages is tentatively explored.     

Surface characteristics and electrochemical behaviour of sputter-deposited NiTi thin film

Thin nanocrystalline amorphous NiTi film was deposited on Si substrate using DC magnetron sputtering. The as-deposited NiTi thin film was crystallized by heat treatment at 500 °C for 1 h. The crystal structure, surface morphology, microstructure and surface chemistry of the deposited films were studied using X-ray diffraction, atomic force microscopy, scanning electron microscopy and X-ray photoelectron spectroscopy (XPS), respectively. Corrosion behaviour was assessed in Ringer’s solution at 37 °C by open circuit potential (OCP), potentiodynamic polarization and electrochemical impedance spectroscopy as a function of exposure time. OCP values indicate that the tendency for the formation of a spontaneous oxide film is greater for the NiTi thin films than the bulk NiTi. Long time exposure to Ringer’s solution was found to have a great effect on the corrosion behaviour of the samples. Significantly low corrosion current density was obtained for the annealed NiTi film from the potentiodynamic polarization curves indicating a typical passive behaviour, but as-deposited film and bulk NiTi alloy exhibited breakdown of passivity at potentials approximately +1.4 V (vs. SCE). XPS showed that the oxide film formed on the annealed NiTi thin film mainly composed of Ti oxides, and no evidence of Ni was found up to 8.2 nm beneath the top surface, suggesting the excellent corrosion resistance of this sample in Ringer’s solution.     

Thickness dependent magnetic and ferroelectric properties of LaNiO3 buffered BiFeO3 thin films

BiFeO₃ (BFO) thin films with thickness increasing from 40 to 480 nm were successfully grown on LaNiO₃ (LNO) buffered Pt/Ti/SiO₂/Si(100) substrate and the effects of thickness evolution on magnetic and ferroelectric properties are investigated. The LNO buffer layer promotes the growth and crystallization of BFO thin films. Highly (100) orientation is induced for all BFO films regardless of the film thickness together with the dense microstructure. All BFO films exhibited weak ferromagnetic response at room temperature and saturation magnetization is found to decrease with increase in film thickness. Well saturated ferroelectric hysteresis loops were obtained for thicker films; however, the leakage current dominated the ferroelectric properties in thinner films. The leakage current density decreased by three orders of magnitude for 335 nm film compared to 40 nm film, giving rise to enhanced ferroelectric properties for thicker films. The mechanisms for the evolution of ferromagnetic and ferroelectric characteristics are discussed.     

Fabrication of Cu2ZnSn(SxSe1−x)4 thin film solar cell by single step sulfo-selenization of stacked metallic precursors

We have synthesized an efficient Cu₂ZnSn(S_xSe_1−x)₄ (CZTSSe) absorbers by using single-step rapid thermal sulfo-selenization process of sputtered stack metallic precursor (Zn/Sn/Cu) films. The structural and morphological studies confirm that the suitability of the rapid thermal sulfo-selenization process for the synthesis of a CZTSSe absorber without any secondary phases with large grains. The annealing atmosphere with a mixed-chalcogen source enhances the grain growth of the CZTSSe absorber as compared with pure Cu₂ZnSnS₄ (CZTS) and Cu₂ZnSnSe₄ (CZTSe) absorbers. The CZTSSe thin film solar cell shows the best conversion efficiency of ∼7%.     

Electrical and optical properties of Si-doped indium tin oxides as transparent electrode and anti-reflection coating for solar cells

We have studied the electrical and optical properties of Si-doped indium tin oxides (ITSOs) as transparent electrodes and anti-reflection coatings for Si-based solar cells. The ITSO thin films were obtained by co-sputtering of ITO and SiO₂ targets under target power control. The resistivity of the ITSO thin films deposited at 0.625 in terms of power ratio (ITO/SiO₂) were 391 Ωcm. In this condition, the ITSO thin films showed very high resistivity compared to sputted pure ITO thin films (1.08 × 10⁻³ Ωcm). However, refractive index of ITSO thin films deposited at the same condition at 500 nm is somewhat lowered to 1.97 compared to ITO thin films (2.06). The fabricated graded refractive index AR coatings using ITO, ITSO, and SiO₂ thin films kept over 80% of transmittance regardless of their thickness varing from 97 nm to 1196 nm because of their low extinction coefficient. As the AR coating with graded refractive indices using ITO, ITSO, and SiO₂ layers was applied to general silicon-based solar cell, the current level increased nearly twice more than that of bare silicon solar cell without AR coating.     

Thin-film multi-layer capacitors using Bi2Mg2/3Nb4/3O7 (BMNO) pyrochlore thin films via radio-frequency sputtering

Thin-film multi-layer ceramic capacitors (MLCCs) were prepared using high-dielectric constant Bi₂Mg_2/3Nb_4/3O₇ thin-films deposited at room temperature via radio-frequency magnetron sputtering. The multi-layer capacitors, in sizes 0402, 0603 and 1005, were well equipped with both inner and outer Cu electrodes. The capacitances of the bi-layer capacitors were twice that of the single-layer version in sizes 0402, 0603, and 1005. The 200 nm-thick Bi₂Mg_2/3Nb_4/3O₇ thin-films would be suitable for thin-film multi-layer capacitor applications.     

Effects of acid etching on the structure of PtNi catalyst and total exposed active sites

The integration technology of hydrogen preparation–hydrogen storage not only can utilize hydrogen energy efficiently but also can improve the selectivity of the electrode maximally. In the present work, the structure and composition of the PtNi catalyst was characterized by X-ray diffraction (XRD); and its electrochemical properties, morphology, and surface binding energy were analyzed by cyclic voltammetry (CV) and linear scanning voltammetry (LSV), scanning electron microscopy equipped with energy-dispersive spectrometry (SEM-EDS), and X-ray photoelectron spectroscopy (XPS), respectively. The effects of different acid etching treatments (e.g., etching time, etchant concentration, and etching temperature) on the structure and surface active sites were investigated by the orthogonal experiment. The experimental results reveal that after etching with 0.5 mol/L of perchloric acid for 0.5 h at 60°C, the electrode weight loss of the PtNi catalyst is mainly attributed to the large loss of Ni atoms in film layer. This results in the reduced alloy phase in film layer and the appearance of Pt characteristic diffraction peak. The relative content of Pt on the surface of the film electrode increases significantly, and the total number of active sites also increases correspondingly. The binding energy of Pt4f_7/2 decreases by 0.19 eV, and the number of active sites involved in hydrogen release decreases, indicative of the reduced promotion effect of the PtNi catalyst on hydrogen release.     

Anti-glycating and anti-oxidant compounds from traditionally used anti-diabetic plant Geigeria alata(DC) Oliv. & Hiern.

Abstract

A new sesquiterpene lactone geigerianoloide (1) and four known flavonoids axillarin (2), quercetin (3), 3-methoxy-5,7,3',4'-tetrahydroxy-flavone (4) and hispidulin (5) were isolated from Geigeria alata (DC) Oliv. & Hiern. (Asteraceae). Structures were deduced using ¹H- and ¹³C- NMR spectroscopy, mass spectrometry, while the structure of compound 1 was also deduced using X-ray crystallography technique.

Geigeria alata is traditionally used for diabetes, therefore compounds were tested for anti-glycation activity, in which compounds 2 and 3 showed potent activities (IC₅₀ values of 246.97?±?0.83 and 262.37?±?0.22 µM, respectively) compared to IC₅₀ value 294.50?±?1.5 µM of rutin. Moreover, compound 4 exhibited a comparable activity to rutin (IC₅₀?=?293.28?±?1.34 µM). Compound 5 showed a weak activity.

Compounds 2, 3, and 4 exhibited potent DPPH radical scavenging activity (IC₅₀?=?0.1?±?0.00, 0.13?±?0.00 and 0.15?±?0.01 µM, respectively). Compounds 2, 3, and 4 demonstrated significant superoxide anion scavenging activity with IC₅₀ values of 0.14?±?0.001, 0.17?±?0.00, and 0.11?±?0.006 µM, respectively.     

氧分压对IWO薄膜表面形貌及光电性能的影响

掺钨氧化铟(In2O3:W,IWO)薄膜是一种新型的透明导电氧化物(TCO)薄膜,其中W与In之间存在着较高的价态差,使得IWO薄膜与其他TCO薄膜相比,在相同的电阻率条件下具有载流子浓度低、迁移率高和近红外区透射率高的特点.利用直流磁控溅射法制备了IWO薄膜,利用X射线衍射、扫描电子显微镜、霍尔效应及分光光度计表征了薄膜的表面形貌及光电性能.在工作压力1 Pa、氧分压为2.4×10-1Pa的条件下,实验中制备的IWO薄膜最佳电阻率为6.3×10-4Ω.cm,最高载流子迁移率为34 cm2V-1s-1,载流子浓度达到2.9×1020cm-3,可见光平均透射率约为85%,近红外平均透射率大于80%.