Synthesis, structural and magnetic properties of the nanocomposite Fe63B23Nd7Y3Nb3Cr1 magnets

The Fe₆₃B₂₃Nd₇Y₃Nb₃Cr₁ nanocomposite magnets in the form of sheets have been prepared by copper mold casting technique. The phase evolution, crystal structure, microstructural and magnetic properties have been investigated in the as-cast and annealed states. The as-cast sheets show magnetically soft behaviors which become magnetically hard by thermal annealing. The optimal annealed microstructure was composed of nanosize soft magnetic α-Fe (19-29 nm) and hard magnetic Nd₂Fe₁₄B (45-55 nm) grains. The best hard magnetic properties such as intrinsic coercivity, _jH_c of 1119 kA/m, remanence, B_r of 0.44 T, magnetic induction to saturation magnetization ratio, M_r/M_s=0.61 and maximum energy product, (BH)_max of 55 kJ/m³ was obtained after annealing at 680 °C for 15 min. The annealing treatment above 680 °C results in non-ideal phase grains growth, which degrade the magnetic properties.     

Development and construction of rotating polarizer analyzer ellipsometer

A detailed mathematical derivation and an experimental characterization of one to two ratio rotating polarizer analyzer ellipsometer (RPAE) are presented. The alignment, calibration, and testing of reference samples are also discussed. The optical properties of some known materials obtained by the proposed ellipsometer will be shown and compared to accepted values. Moreover, the constructed ellipsometer will be tested using two ellipsometry standards with different thicknesses.     

Conciliating surface superhydrophobicities and mechanical strength of porous silicon films

Hydrophobic surfaces on Mechanical stable macroporous silicon films were prepared by electrochemical etching with subsequent octadecyltrichlorosilane (OTS) modification. The surface morphologies were controlled by current densities and the mechanical properties were adjusted by their corresponding porosities. Contrast with the smooth macroporous silicon films with lower porosities (34.1%) and microporous silicon with higher porosities (97%), the macroporous film with a rough three-dimension (3D) surface and a moderate pore to cross-section area ratio (37.8%, PSi2′) exhibited both good mechanical strength (Yong’ modulus, shear modulus and collapse strength are 64.2, 24.1 and 0.32 GPa, respectively) and surface superhydrophobicity (water contact angle is 158.4 ± 2° and sliding angle is 2.7 ± 1°). This result revealed that the surface hydrophobicities (or the surface roughness) and mechanical strength of porous films could be conciliated by pore to cross-section area ratios control and 3D structures construction. Thus, the superhydrophobic surfaces on mechanical stable porous films could be obtained by 3D structures fabrication on porous film with proper pore to cross-section area ratios.     

Characterization of chemically deposited ZnSe/SnO2/glass films: Influence of annealing in Ar atmosphere on physical properties

The Zinc Selenide (ZnSe) thin films have been deposited on SnO₂/glass substrates by a simple and inexpensive chemical bath deposition (CBD). The structural, optical and electrical properties of ZnSe films have been characterized by X-ray diffraction (XRD), Energy Dispersive X-ray Analysis (EDAX), optical absorption spectroscopy, and four point probe techniques, respectively. The films have been subjected to different annealing temperature in Argon (Ar) atmosphere. An increase in annealing temperature does not cause a complete phase transformation whereas it affects the crystallite size, dislocation density and strain. The optical band gap (E_g) of the as-deposited film is estimated to be 3.08 eV and decreases with increasing annealing temperature down to 2.43 eV at 773 K. The as-deposited and annealed films show typical semiconducting behaviour, dρ/dT > 0. Interestingly, the films annealed at 373 K, 473 K, and 573 K show two distinct temperature dependent regions of electrical resistivity; exponential region at high temperature, linear region at low temperature. The temperature at which the transition takes place from exponential to linear region strongly depends on the annealing temperature.     

Optical and hydrophobic properties of co-sputtered chromium and titanium oxynitride films

The chromium and titanium oxynitride films on glass substrate were deposited by using reactive RF magnetron sputtering in the present work. The structural and optical properties of the chromium and titanium oxynitride films as a function of power variations are investigated. The chromium oxynitride films are crystalline even at low power of Cr target (≥60 W) but the titanium oxynitride films are amorphous at low target power of Ti target (≤90 W) as observed from glancing incidence X-ray diffraction (GIXRD) patterns. The residual stress and strain of the chromium oxynitride films are calculated by sin² ψ method, as the average crystallite size decreases with the increase in sputtering power of the Cr target, higher stress and strain values are observed. The chromium oxynitride films changes from hydrophilic to hydrophobic with the increase of contact angle value from 86.4° to 94.1°, but the deposited titanium oxynitride films are hydrophilic as observed from contact angle measurements. The changes in surface energy were calculated using contact angle measurements to substantiate the hydrophobic properties of the films. UV-vis and NIR spectrophotometer were used to obtain the transmission and absorption spectra, and the later was used for determining band gap values of the films, respectively. The refractive index of chromium and titanium oxynitride films increases with film packing density due to formation of crystalline chromium and titanium oxynitride films with the gradual rise in deposition rate as a result of increase in target powers.     

Effect of the chemistry and structure of the native oxide surface film on the corrosion properties of commercial AZ31 and AZ61 alloys

The purpose of this study has been to advance in knowledge of the chemical composition, structure and thickness of the thin native oxide film formed spontaneously in contact with the laboratory atmosphere on the surface of freshly polished commercial AZ31 and AZ61 alloys with a view to furthering the understanding of protection mechanisms. For comparative purposes, and to more fully describe the behaviour of the native oxide film, the external oxide films formed as a result of the manufacturing process (as-received condition) have been characterised. The technique applied in this research to study the thin oxide films (thickness of just a few nanometres) present on the surface of the alloys has basically been XPS (X-ray photoelectron spectroscopy) in combination with ion sputtering. Corrosion properties of the alloys were studied in 0.6 M NaCl by measuring charge transfer resistance values, which are deduced from EIS (electrochemical impedance spectroscopy) measurements after 1 h of exposure. Alloy AZ61 generally showed better corrosion resistance than AZ31, and the freshly polished alloys showed better corrosion resistance than the alloys in as-received condition. This is attributed to a combination of (1) higher thickness of the native oxide film on the AZ61 alloy and (2) greater uniformity of the oxide film in the polished condition. The formation of an additional oxide layer composed by a mixture of spinel (MgAl₂O₄) and MgO seems to diminish the protective properties of the passive layer on the surface of the alloys in as-received condition.     

Preparation and characterization of bifunctional, Fe3O4/ZnO nanocomposites and their use as photocatalysts

Bifunctional magnetic-optical Fe₃O₄/ZnO nanocomposites with different molar ratio were successfully synthesized by a facile two-step strategy. Compared with the other methods, it was found to be mild, inexpensive, green, convenient and efficient. Fe₃O₄ nanocrystal was used as seed for the deposit and growth of ZnO nanoparticle. A series of the characterizations manifested that the combination of Fe₃O₄ with ZnO nanoparticles was successful. Photocatalytic activity studies confirmed that as-prepared nanocomposites had excellent photodegradating behavior to Methyl Orange (MO) compared to the pure ZnO nanoparticles. The results showed that the degradation percentage of MO was about 93.6% for 1 h when the amount of catalyst was 0.51 g L⁻¹ and initial concentration of MO was 6 × 10⁻⁵ mol L⁻¹ in the pH 7 solution. Moreover, the kinetics of photocatalytic degradation reaction could be expressed by the first-order reaction kinetic model. Furthermore, the Fe₃O₄/ZnO nanocomposites could be also served as convenient recyclable photocatalysts because of their magnetic properties.     

Studies on the structural and electrical properties of F-doped SnO2 film prepared by APCVD

Fluorine-doped tin oxide films (SnO₂:F, FTO) were deposited by atmosphere pressure chemical vapor deposition (APCVD) on Na-Ca-Si glass coated with a diffusion barrier layer of SiO_xC_y. The effects of post-heating time at 700 °C on the structural and electrical properties of SnO₂:F films were investigated. The results showed that SnO₂:F films were polycrystalline with tetragonal SnO₂ structure, SnO phase was present in SnO₂ film, and abnormal grain growth was observed. The element distribution in the film depth was measured with X-ray photoelectron spectroscopy (XPS) and revealed that when the heating time increased from 202 s to 262 s, the oxygen content in the surface increased from 78.63% to 83.38%. The resistivity increased from 3.13 × 10⁻⁴ for as-deposited films to 4.73 × 10⁻⁴ Ω cm when post-heated for 262 s. Hall mobility is limited by the ionized impurity scattering rather than the grain boundary scattering.     

可控空心光束在单轴晶体中的传输特性

基于光束在各向异性单轴介质中的傍轴矢量传输理论,对可控空心光束(CDHB)在单轴晶体中的传输特性作了研究.得出该光束在单轴晶体中传输的横向慢变振幅的表达式,并利用此表达式作数值计算,研究了CDHB在单轴晶体中的传输特性.研究表明,可控空心光束在单轴晶体中传输时,控制参数ξ和光束阶数N的取值对其光强分布有较大的影响.随着...     

Systematic study of luminescent properties of new lanthanide complexes using crown ethers as ligand

This is a report on the synthesis, characterization and spectroscopic study of 24 lanthanide-crown ether coordination compounds, where Eu(III), Tb(III) and Gd(III) were complexes to 12-crown-4 (12C4), 15-crown-5 (15C5), 1,10-phenanthroline (phen) and 2,2′-dipyridyl (dipy). The compounds were synthesized in an ethanol/acetone solution at room temperature and analyzed using CHN elemental analysis and infrared, absorption and emission spectroscopies. The polarizability that the ligand exerts on the emission process was verified and found remarkable. The Eu-15C5-phen complex showed the highest quantum efficiency (71.6%) because of its low non-radiative rate and highest polarizability with reference to the ligands system.