退火温度对Ti0.95Fe0.05O2纳米颗粒结构和磁性的影响

采用溶胶-凝胶工艺制备了磁性Fe掺杂TiO2基稀磁半导体的纳米颗粒,在空气氛围中以不同温度对样品进行退火处理.通过差热/热重综合热分析仪(TG-DTA)、X射线衍射仪(XRD)、拉曼光谱(Raman)分析了纳米颗粒的结构和相变温度.研究发现:退火温度450℃和500℃时样品为锐钛矿结构,在600℃时既有锐钛矿相,又有金...     

Structural,magnetic and XPS studies of Sn0.95Co0.05O2-0.05 and Sn0.95Fe0.05O2-0.05 nanoparticles

Structural, microstructural, X-ray photoemission spectra (XPS) and magnetic properties of transition metal ion [5 mol% of Co (SC5) and Fe (SF5)]-doped SnO₂ nanoparticles have been studied. The SC5 and SF5 nanoparticles were synthesized by a chemical route using polyvinyl alcohol as surfactant. The doped SnO₂ crystallites were found to exhibit a tetragonal rutile structure and the average grains size was measured by the Scherer relation of X-ray diffraction. Transmission electron micrographs showed that the average grain size of SC5 is smaller than SF5. SC5 nanoparticles showed strong ferromagnetic behaviour but SF5 exhibited an F-centre exchange (FCE) mechanism. Temperature-dependent magnetization showed the values of phase transition temperature. XPS confirmed the presence of Sn–O–Co and Sn–O–Fe bonds in these SC5 and SF5 nanoparticles. The oxidation states of Sn, Co and Fe were found to be +4, +2 and +2, respectively, while the core level XPS peaks of Sn 3d, O 1s, Co 2p and Fe 2p were analyzed.     

Structural and magnetic properties of bulk and thin films of Mg0.95Mn0.05Fe2O4

We present here a comparative study on structural and magnetic properties of bulk and thin films of Mg_0.95Mn_0.05Fe₂O₄ ferrite deposited on two different substrates using X-ray diffraction (XRD) and dc magnetization measurements. XRD pattern indicates that the bulk sample and their thin films exhibit a polycrystalline single phase cubic spinel structure. It is found that the film deposited on indium tin oxide coated glass (ITO) substrate has smaller grain size than the film deposited on platinum coated silicon (Pt–Si) substrate. Study of magnetization hysteresis loop measurements infer that the bulk sample of Mg_0.95Mn_0.05Fe₂O₄ and its thin film deposited on Pt–Si substrate shows a well-defined hysteresis loop at room temperature, which reflects its ferrimagnetic behavior. However, the film deposited on ITO does not show any hysteresis, which reflects its superparamagnetic behavior at room temperature.     

退火对TiO2薄膜形貌、结构及光学特性影响

利用射频磁控溅射技术在熔融石英基片上制备TiO<,2>薄膜,采用X射线衍射、扫描电子显微镜(SEM)、拉曼光谱以及透过谱研究了退火温度和退火气氛对TiO<,2>薄膜的结构、形貌和光学特性的影响.实验结果表明:在大气环境下退火,退火温度越.高,薄膜晶化越好,晶粒明显长大,温度高于700℃退火的薄膜,金红石相已明显形成.实验还发现,退火气氛对金红石相的形成是非常重要的,拉曼光谱反应出Ar气氛退火,抑制了金红石晶相的发育,薄膜仍以锐钛矿相为主.Ar气氛退火的薄膜在可见光范围内的透过率比大气退火的要低,并且由透过率曲线推知:金红石的光学带隙约为2.8 eV,比锐钛矿的光学带隙小0.2 eV.     

Growth and optical properties of Fe2O3 thin films: A study of quantum confinement effects by experiment and theory

Thin iron films in the thickness range 0.7–48 nm have been deposited on high quality Corning glass and Si(100) substrates by radio frequency magnetron sputtering. The films were then oxidized by annealing at temperatures of 400−450 °C in a furnace in air. X-ray diffraction experiments revealed the formation of single-phase α-Fe₂O₃. The films were continuous and present negligible surface roughness. Ultraviolet-visible light absorption spectroscopy has shown a blue shift of both, the indirect and direct band gaps of hematite. The experimental results are interpreted as evidences of quantum confinement effects. This is facilitated by theoretical calculations based on Hartree Fock approximation as applied for an electron-hole system, in the framework of effective mass approximation. The agreement between theory and experiment supports the quantum confinement interpretation.     

Structural refinement,optical and ferroelectric properties of microcrystalline Ba(Zr0.05Ti0.95)O3 perovskite

For this study, a microcrystalline Ba(Zr_0.05Ti_0.95)O₃ (BZT) powder was prepared by a high energy ball milling method followed by calcination at 1100 °C for 4 h. The calcined powder was structurally characterized by X-ray diffraction and Rietveld refinement data, which showed that this material has a perovskite-type tetragonal structure with a space group of (P4mmm). The micro-Raman spectrum revealed local lattice distortions due to distorted octahedral [TiO₆] clusters. The temperature and frequency-dependent dielectric study of the BZT ceramic showed normal phase transition behavior. The ferroelectric property was studied by a P–E hysteresis loop. Optical band gap was investigated by ultraviolet–visible (UV–vis) absorption spectroscopy at room temperature. The UV–vis spectrum indicated that the BZT powder has an optical band gap of 3.15 eV.     

Structural,optical,and electrical properties of Cu-doped ZrO_2 films prepared by magnetron co-sputtering

Copper(Cu)-doped ZrO_2(CZO) films with different Cu content(0 at.%～ 8.07 at.%) are successfully deposited on Si(100) substrates by direct current(DC) and radio frequency(RF) magnetron co-sputtering. The influences of Cu content on structural, morphological, optical and electrical properties of CZO films are discussed in detail. The CZO films exhibit ZrO_2 monocline(ˉ111) preferred orientation, which indicates that Cu atoms are doped in ZrO_2 host lattice. The crystallite size estimated form x-ray diffraction(XRD) increases by Cu doping, which accords with the result observed from the scanning electron microscope(SEM). The electrical resistivity decreases from 2.63 ?.cm to 1.48 ?·cm with Cu doping content increasing, which indicates that the conductivity of CZO film is improved. However, the visible light transmittances decrease slightly by Cu doping and the optical band gap values decrease from 4.64 eV to 4.48 eV for CZO films.     

Influences of Al doping concentration on structural,electrical and optical properties of Zn0.95Ni0.05O powders

Nanocrystalline Zn_0.95−xNi_0.05Al_xO (x = 0.01, 0.02, 0.05 and 0.10) diluted magnetic semiconductors have been synthesized by an auto-combustion method. X-ray diffraction measurements indicate that all Al-doped Zn_0.95Ni_0.05O samples have the pure wurtzite structure. Transmission electron microscope analyses show that the as-synthesized powders are of the size 40–45 nm. High-resolution transmission electron microscope, energy dispersive spectrometer and X-ray photoemission spectroscope analyses indicate that Ni²⁺ and Al³⁺ uniformly substitute Zn²⁺ in the wurtzite structure without forming any secondary phases. The Al doping concentration dependences of cell parameters (a and c), resistance and the ratio of green emission to UV emission have the similar trends.     

Effects of high-energy ion-beam irradiation on structural and optical properties of (Mg0.95Co0.05)TiO3 thin films

We report the structural and optical properties of high-energy ion-beam irradiated Co-doped magnesium titanate thin films. (Mg_0.95Co_0.05)TiO₃ (MCT) thin films were deposited on quartz substrates using radio frequency magnetron sputtering. Subsequently, the films were annealed for crystallinity and were irradiated with 100?MeV Ag ions by varying the ion fluence. The X-ray diffraction patterns of the films before and after the irradiation were refined using the Rietveld refinement and the variations in the lattice parameters were correlated with the ion fluence. Although, annealing of thin films results in an enhancement in refractive index and optical bandgap, the ion fluence induces significant changes in the refractive index and optical bandgap. Atomic force microscopy is employed to study the surface morphology of the films. The impact of ion fluence on structural and optical properties of MCT thin films has been investigated.     

Thickness-dependent electrical and optical properties of Ge8Sb2Te11 thin films

The amorphous Ge₈Sb₂Te₁₁thin films with varying thickness are thermally deposited on well-cleaned glass substrate from its polycrystalline bulk. Absence of any sharp peak confirms the amorphous nature of deposited films. Thickness-dependent electrical and optical properties including dc-activation energy, sheet resistivity, optical band gap, band tailing parameter, etc. of Ge₈Sb₂Te₁₁thin films have been studied. The optical parameters have been calculated from transmission, reflection and absorbance data in the spectral range of 200–1100 nm. It has been found that optical band gap and band tailing parameter decreases with the increase in Ge₈Sb₂Te₁₁thin films thickness. The dc-activation energy and sheet resistivity decreases while the crystallization temperature of the amorphous Ge₈Sb₂Te₁₁ films increases with the increase in thickness of the films. The decrease of the sheet resistivity has been substantiated quantitatively using the classical size-effect theory. These results have been explained on the basis of rearrangements of defects and disorders in the amorphous chalcogenide system.     

Epitaxial MnP thin films: epitaxial growth,magnetic and electrical properties

We have grown 500 Å MnP on undoped GaAs(1 0 0) substrate using solid-source molecular beam epitaxy. In order to characterize the crystal structure of MnP, we performed in-situ reflection high energy electron diffraction and θ–2θ XRD X-ray diffraction studies. From the measurements of superconducting quantum interference device, Quantum Design, MnP thin film shows ferromagnetic ordering at around 291.5 K. It shows a metallic resistivity in MnP thin film.     

Structural and electrical properties of evaporated Fe thin films

Series of Fe thin films have been prepared by thermal evaporation onto glass and Si(1 0 0) substrates. The Rutherford backscattering (RBS), X-ray diffraction (XRD), Scanning electron microscopy (SEM) and the four point probe techniques have been used to investigate the structural and electrical properties of these Fe thin films as a function of the substrate, the Fe thickness t in the 76-431 nm range and the deposition rate. The Fe/Si samples have a 〈1 1 0〉 for all thicknesses, whereas the Fe/glass grows with a strong 〈1 0 0〉 texture; as t increases (>100 nm), the preferred orientation changes to 〈1 1 0〉. The compressive stress in Fe/Si remains constant over the whole thickness range and is greater than the one in Fe/glass which is relieved when t > 100 nm. The grain size D values are between 9.2 and 30 nm. The Fe/glass films are more electrically resistive than the Fe/Si(1 0 0) ones. Diffusion at the grain boundary seems to be the predominant factor in the electrical resistivity ρ values with the reflection coefficient R greater in Fe/glass than in Fe/Si. For the same thickness (100 nm), the decrease of the deposition rate from 4.3 to 0.3 Å/s did not affect the texture and the reflection coefficient R but led to an increase in D and a decrease in the strain and in ρ for both Fe/glass and Fe/Si systems. On the other hand, keeping the same deposition rate (0.3 Å/s) and increasing the thickness t from 76 to 100 nm induced different changes in the two systems.     

Mn-Na共掺ZnO非极性薄膜的结构及其光电磁性能研究

非极性方向生长的ZnO基多量子阱消除了量子限域Stark效应, 可以提高光电器件的发光效率. 据此我们采用脉冲激光沉积方法(PLD)在r面蓝宝石衬底上生长了高质量的a面(1120)单一取向非极性Zn(Mn,Na)O薄膜. X射线衍射(XRD)、场发射扫描电子显微镜(FE-SEM)、Hall测试、X射线光电子能谱(XPS)等测试结果表明: 衬底温度和生长气压对Zn(Mn,Na)O薄膜的非极性生长影响很大, 在600℃和0.02 Pa条件下实现了Mn-Na共掺, 得到了高结晶质量并具有良好光电性能的非极性Zn(Mn,Na)O薄膜. 此外, 我们还利用超导量子干涉仪(SQUID)研究了Zn(Mn,Na)O薄膜的生长取向对其室温铁磁性能的影响规律, 并对引起磁性变化的机理进行了讨论.     

The electrical, optical and magnetic properties of Si-doped ZnO films

In this paper, the influences of Si-doping on electrical, optical and magnetic properties of ZnO films have been systematically investigated. It is found that the resistivity of the films decreases from 3.0 × 10³ to 6.2 × 10^-2 Ωcm with Si-doping due to the increase of carrier concentration. The bandgap of ZnO films increases from 3.28 to 3.52 eV with increasing of Si concentration, which is found to be due to the collective effects of bandgap narrowing and Burstein-Moss effect induced by high carrier concentration. With increase of Si concentration, the near band edge (NBE) emission decreases due to the deterioration of crystal quality, while the yellow emission enhances due to the increase of extrinsic impurity or defects. The additional Si-doping has a profound influence on the enhancement of magnetic property and the maximum magnetic moment of 2.6 μ_B/Si is obtained. The ferromagnetic ordering is seen to be correlated with carrier concentration and structural defects.     

Dielectric and piezoelectric properties of the Ba0.92Ca0.08Ti0.95Zr0.05O3 thin films grown on different substrate

Lead free Ba_0.92Ca_0.08Ti_0.95Zr_0.05O₃ (BCZT) thin films were deposited on Pt/Ti/SiO₂/Si and LaNiO₃(LNO)/Pt/Ti/SiO₂/Si substrates by a sol–gel processing technique, respectively. The effects of substrate on structure, dielectric and piezoelectric properties were investigated in detail. The BCZT thin films deposited on LNO/Pt/Ti/SiO₂/Si substrates exhibit (100) orientation, larger grain size and higher dielectric tunability (64%). The BCZT thin films deposited on Pt/Ti/SiO₂/Si exhibit (110) orientation, higher Curie temperature (75 °C), better piezoelectric property (d₃₃ of 50 pm/V) and lower dielectric loss (0.02). The differences in dielectric and piezoelectric properties in the two kinds of oriented BCZT films should be attributed to the difference of structure, in-plane stress and polarization rotation in orientation engineered BCZT films.     

Effect of substrate temperature on electrical and magnetic properties of epitaxial La1−x Pb x MnO3 films

Epitaxial La_1−x Pb _x MnO₃ (LPMO) thin films, grown on (100) SrTiO₃ substrates by laser ablation technique at different temperatures between 600 and 850°C, have been characterized for electrical and magnetic properties. The temperature dependence of resistivity showed that the metal-insulator transition temperature (T _MI) decreases with increasing substrate temperature, which has been attributed to decrease in Pb content in the filsm. The YBa₂Cu₃O _x /La_1−x MnO₃ heterostructures, exhibiting both superconductivity and ferromagnetism, have been fabricated.     

Morphology, magnetic, magnetoresistance and optical properties of Co-Ni-Mo alloys thin films

We present in this paper several results concerning the preparation by means of electrolysis and characterization of Co-Ni-Mo thin films. Co-Ni-Mo thin films with different molybdenum content in the range 0-25 at% Mo were prepared from a complex solution containing ions of Co, Ni and Mo, using galvanostatic control, on aluminum substrates. The effects of applied current density on the morphology, magnetic, magnetoresistance, and optical properties of the electrodeposited Co-Ni-Mo films were investigated. The applied current density significantly influenced the film composition and their magnetic properties. The increase of molybdenum content in Co-Ni films (up to 25 at% Mo) enhances the resistivity, but it reduces the magnetoresistance effect. We report the first observation of magnetoresistance as high as 8% in Co-Ni-Mo thin films.     

Synthesis and characterization of arc deposited magnetic (Cr,Mn)2AlC MAX phase films

(Cr_1–xMn_x)₂AlC MAX phase thin films were synthesized by cathodic arc deposition. Scanning transmission electron microscopy including local energy dispersive X‐ray spectroscopy analysis of the as‐deposited films reveals a Mn incorporation of as much as 10 at% in the structure, corresponding to x = 0.2. Magnetic properties were characterized with vibrating sample magnetometry, revealing a magnetic response up to at least room temperature. We thus verify previous theoretical predictions of an antiferromagnetic or ferromagnetic ground state for Cr₂AlC upon alloying with Mn. (© 2014 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)