Magnetic properties of strontium hexaferrite films prepared by pulsed laser deposition

The magnetic properties of strontium hexaferrite (SrFe₁₂O₁₉) films fabricated by pulsed laser deposition on the Si(100) substrate with Pt(111) underlayer have been studied as a function of film thickness (50–700 nm). X-ray diffraction patterns confirm that the films have c-axis perpendicular orientation. The coercivities in perpendicular direction are higher than those for in-plane direction which indicates the films have perpendicular magnetic anisotropy. The coercivity was found to decrease with increasing of thickness, due to the increasing of the grain size and relaxation in lattice strain. The 200 nm thick film exhibits hexagonal shape grains of 150 nm and optimum magnetic properties of M_s=298 emu/cm³ and H_c=2540 Oe.     

Composition and magnetic studies of ultrafine Al-substituted Sr hexaferrite particles prepared by citrate sol-gel method

Ultrafine aluminum-substituted strontium hexaferrite particles have been prepared via citrate sol-gel route. Gels were synthesized with molar ratios [Al³⁺]:[Fe³⁺] of 0.4:11.6, 1:11, 1.5:10.5 and 2:10 and the ferrite particles were obtained by annealing the gels at 950 °C for 2 and 24 h. Electron energy dispersive X-ray spectroscopy (EDX) verified the presence of Al in the substituted samples. X-ray diffraction (XRD) confirmed the formation of the M-type hexaferrite phase in the samples with some indication of α-Fe₂O₃. Scanning electron microscope showed that the hexaferrite powder consists hexagonal crystals with average diameter D_av (80-186 nm) that decreases with increasing Al content and increases with increasing annealing time. Magnetic properties were determined using a pulsed-field magnetometer and a vibrating sample magnetometer (VSM). The saturation magnetization at room temperature and the Curie temperature were found to decrease while the coercivity increases with increasing the Al content. The highest coercivity of 10.1 kOe was achieved for the sample with the molar ratio [Al³⁺]:[Fe³⁺]=2:10 annealed for 24 h. The influences of the particle size, composition and impurity on the magnetic properties were discussed.     

Superconducting screen printed thick films of YBa2Cu3O7 and Bi1.6Pb0.4Sr1.6Ca2.4Cu3O10 on polycrystalline substrates

Thick films of YBa₂Cu₃O₇ and Bi_1.6Pb_0.4Sr_1.6Ca_2.4Cu₂O₁₀ have been prepared using a screen printing method on polycrystalline substrates. The films have been characterized by X-ray diffraction, electrical measurements and SEM observations. YBa₂Cu₃O₇ films exhibited T_c ranging from 80 to 87 K on Y₂BaCuO₅ substrates while Bi_1.6Pb_0.5Sr_1.6Ca_2.4Cu₃O₁₀ films on polycrystalline MgO reached the zero resistance state at 104 K with critical current densities of up to 10 A/cm² at 77 K.     

丝网印刷FeS2（pyrite）薄膜的结构及光电性能

采用丝网印刷方法制备了FeS₂(pyrite)薄膜，用x射线衍射确定了样品FeS₂(pyrite)薄 膜的 晶体结构，并用Rietveld方法对样品的结构进行了精修，确定了样品的点阵常数、键长、键 角、硫原子占位等结构参数.研究了膜厚对方块电阻、载流子浓度、霍尔迁移率、光能隙等 光电参数的影响. 关键词： 丝网印刷 薄膜 结构 Rietveld方法 光电性能     

用电泳技术制备YBCO高温超导厚膜

介绍了电泳技术制备YBCO高温超导厚膜的实验方法和YBCO高温超导厚膜的电学性质测量 ,讨论了在学生小型科研实验或设计实验中开展此实验的学时安排、注意事项和实验内容的扩展 .     

Preparation of oriented thick HTSC films by cryoelectrophoretic technique

Il Nuovo Cimento D - A new technique, specifically designed for the preparation of preferentially oriented HTSC (YBCO and BSCCO) films on metallic substrates has been developed. The method, named...     

Bremsstrahlung spectra produced by 89Sr beta particles in thick targets

External bremsstrahlung spectra produced by hard beta particles of ⁸⁹Sr (1.463 MeV) in thick targets of Al, Cu, Sn and Pb were studied. After making the necessary corrections, the experimental results were compared with the theoretical external bremsstrahlung distributions obtained from Elwert corrected (non‐relativistic) Bethe–Heitler theory, Tseng and Pratt theory and modified Elwert factor (relativistic) Bethe–Heitler theory. It was found that for low‐Z elements all theories are equally suitable throughout the energy region studied. For medium‐Z elements, the Tseng and Pratt and modified Elwert factor (relativistic) Bethe–Heitler theories are more accurate, particularly in medium and higher energy regions. However, for high‐Z elements, the modified Elwert factor (relativistic) Bethe–Heitler theory shows better agreement with the experiment, particularly at the higher energy end. Copyright © 2003 John Wiley & Sons, Ltd.     

Characterization of thick HVPE GaN films

The morphology of the top surface for HVPE GaN layers grown on a MOCVD GaN template with a thin LT-AlN interlayer was investigated. This surface is characterized by the formation of numerous hillocks associated with screw dislocations or nanopipes. Their size is large and may reach more than 1 mm. The rocking curves of the 002 and 102 reflections correspond to a relaxed layer. The HREM images of the as-deposited and annealed interlayers show a perfect atomic structure with a very abrupt AlN/HVPE GaN interface. Thus, the deposition of the LT-AlN layer has promoted the growth of an HVPE layer with an excellent crystalline quality.     

Rheological behavior of silver nanowire conductive inks during screen printing

The rheological behavior of silver nanowire (AgNW) suspensions adapted for screen printing inks was investigated. Aqueous silver nanowire inks consisting of AgNW (length of 30 μm, and diameter of 40 and 90 nm), dispersant and binder were formulated. The effect of AgNW content on the rheological behavior of the ink and the build-up of ink structure after screen printing were examined as they depend on applied shear and temperature. Rheological measurements under conditions that mimic the screen printing process were done to assess viscoelastic properties induced by flow alignment of the wires and the subsequent recovery of the low shear structure. The Stretched Exponential model (SEmo) was used to model the recovery process after screen printing to obtain the characteristic time of the recovery or build-up process. The characteristic time was determined at several temperatures to obtain the activation energy of recovery. The domination of Brownian motion or non-Brownian motion behavior can be characterized by a Peclet number, which is the ratio of shear rate to the rotational diffusion coefficient. The Peclet number and the dimensionless concentration of wires were used to assess the recovery mechanism. The steady viscosity at low and high shear rates was also treated by an activation energy analysis.     

Electrical and magnetic properties of variously annealed Bi(Pb)−Sr−Ca−Cu−O thick films

Superconducting thick films with the nominal composition of Bi_1.9Pb_0.4Sr_1.9Ca_2.1Cu_3.2O₁₀ were prepared by the screen-printing method, using an oxalate synthesis for making the paste, and different heat treatments for final samples. A large difference in the structural and superconducting properties between the unmelted and melted samples, and small deviations between the melted and variously annealed specimens were observed. In the first case, the structure is determined by randomly distributed small microcrystals, while in the second, by highly orientated big ones, which results in dissimilar electrical and magnetic features. Therefore the magnetic moment and superconducting material ratio are bigger in the unmelted samples, but in the melted ones, the superconductivity can be characterized by much higher electrical and magnetic parameters. In particular, the transport critical current has conspicuously greater values in the melted as compared to the unmelted samples. In some melted specimens a hyperdiamagnetic signal has been found up to 242 K, induced by the fine details of the preparation technique. The simplest possible reason for this is the diamagnetic Cu–O content in the samples.     

Use of copper ink for fabricating conductive electrodes and RFID antenna tags by screen printing

We have synthesized nano-sized copper hydroxide powder and copper (II) neodecanoate complex that can be decomposed to form copper metal films. Copper conductive ink was then prepared by mixing the powder and complex with a binder in terpineol. The lowest resistivity of 12.5 μΩ cm and 5B level of adhesion strength were obtained with 5% addition of epoxy resin as a binder. The copper ink was then applied to fabricate a loop-type RFID antenna tag and the performance of the antenna was compared with that of conventional copper-etched and silver-paste antenna. The fabricated RFID antenna showed comparable performance to the conventional RFID antenna.     

The improvement of pyroelectric properties of PZT thick films on Si substrate by TiOx barrier layer

The effects of TiO_x diffusion barrier layer thickness on the microstructure and pyroelectric characteristics of PZT thick films were studied in this paper. The TiO_x layer was prepared by thermal oxidation of Ti thin film in air and the PZT thick films were fabricated by electrophoresis deposition method (EPD). To demonstrate the barrier effect of TiO_x layer, the electrode/substrate interface and Si content in PZT thick films were characterized by scanning electron microscope (SEM) and X-ray energy dispersive spectroscopy (EDS), respectively. The TiO_x barrier thickness shows significant influence on the bottom electrode and the pyroelectric performance of the PZT thick films. The average pyroelectric coefficient of PZT films deposited on 400 nm TiO_x layer was about 8.94 × 10⁻⁹ C/(cm² K), which was improved by 70% than those without diffusion barrier layer. The results showed in this study indicate that TiO_x barrier layer has great potential in fabrication of PZT pyroelectric device.     

The correlation between strain and electronic structure in monolayer thick films

We explote and empirical relationship between strain (and lattice constant) and the valence electronic structure for mercury, bromine and iron overlayers. These overlayers have a range of lattice constants. For the Hg overlayers, all share a common cubic crystallography. We generally observe that the smaller the overlayer lattice constant, the greater the energy separation betweend-bands (Hg and Fe) orp-bands (Br). These results have important implications in relating electronic structure to fundamental properties such as magnetism. In addition, the film thickness limits for pseudomorphic growth calculated from the bulk properties are consistent with the experimental studies of Hg pseudomorphic growth on Ag (100) at 90 K.     

Landau theory of phase transitions in thick films

A simple expression is used for the free energy density with a one-component order parameter, and the boundary conditions at the surfaces of a film of thickness L are given by means of an extrapolation length δ. Exact expressions are given for the critical temperature and the order parameter profile in terms of elliptic functions, and the nature of the phase transition is discussed.     

Preparation of Bi-Sr-Ca-Cu-O bulk superconductor and thick films

The preparation of ceramic superconductors based on the Bi-Sr-Ca-Cu-O system in a reproducible manner with zero-resistance transition temperatures (T _c) tailored between 65 and 85 K is described. Partial melting of the sample pellet during preparation helps in raising itsT _c. Thick crystallographically oriented films of the material withT _c=77 K have been prepared on sintered SrTiO₃ substrates.     

Enhanced luminescence related to transparent conductive oxide in ZnS-based EL device fabricated by screen printing method

This experiment is focused to characterize electroluminescence (EL) properties related to transparent conductive oxide (TCO) like In₂O₃ or SnO₂ being dispersedly inserted into the two different layered structures fabricated by screen printing method. X-ray diffraction and FE-SEM measurement were carried out to characterize the material properties of the ZnS-based EL devices depending on the layered structures and the material constitutions. The results show that the enhanced EL intensity with the TCO insertion is approximately 1.2 times greater than TCO-free sample under the 1-layered structure while in no significant improvement of EL intensity is observed under the 2-layered EL structure. But for the EL intensity comparison under the device structure, 2-layered EL structure having a separate dielectric layer is 1.4 times brighter than the 1-layered structure.     

Investigation of low-temperature cathodoluminescence mechanism of Er-doped Ga N thick films by ion implantation

Er ions are implanted into the Ga N thick films grown by hydride vapor phase epitaxy. The implantation energy is 200 ke V and the implantation doses are 1×10~(13),1 × 10~(14),1 × 10~(15),and 5×10~(15) atom∕cm~2,respectively. The effects of the implantation dose and annealing temperature on the Ga N band-edge luminescence are investigated. The cathodoluminescence spectra from 82 to 323 K are measured for 1×10~(15) atom∕cm~2-implanted Ga N annealed at 1100°C. Luminescence peaks at 356,362,376,390,and 414 nm are observed on the 82 K cathodoluminescence spectrum. When the temperature is increased to 150 K,the intensities of the 356 and 414 nm peaks are nearly unchanged and the 362,376,and 390 nm peaks disappear. The intensity ratio of 538 nm(~2H_(11∕2)→ ~4I/_(15∕2)) and 559 nm(~4S_(3∕2)→ ~4I_(15∕2)) is increased with the increase in temperature. We try to shed light on the above interesting phenomena.     

Preparation and characterization of thick cubic boron nitride films

Cubic boron nitride （c-BN） films are prepared by the radio frequency magnetron sputtering technique. The stresses and crystallinities of the films are estimated by the Fourier transform infrared spectroscopy of c-BN samples, including the peak shifts and varieties of full widths at half maximum. The effects of the B-C-N interlayer and the two-stage deposition method on the c-BN films are investigated. Then the thick and stable c-BN films are prepared by a combination of the two methods. The properties of the interlayer and film are also characterized.