Structural characterization of La0.9Ba0.1MnO3/Y-ZrO2 film by X-ray diffraction

Perovskite manganite La_0.9Ba_0.1MnO₃(LBMO) films were deposited on (0 0 1)-oriented single crystal yttria-stabilized zirconia (YSZ) substrate by 90° off-axis radio frequency magnetron sputtering. The film thickness ranged from 10 nm to 100 nm. Grazing incidence X-ray diffraction technique and high resolution X-ray diffraction were applied to characterize the structure of LBMO films. The LBMO film mainly consisted of (0 0 1)-orientated grain as well as weakly textured (1 1 0)-orientated grain. The results indicated that an amorphous layer with thickness of about 4 nm was formed at the LBMO/YSZ interface. The strain in LBMO film was small and averaged to be about -0.14%. The strain in the film was not lattice mismatch-induced strain but residual strain due to the difference in thermal expansion coefficient between film and substrate.     

Thickness-dependent surface morphology of La0.9Sr0.1MnO3 ultrathin films

La_0.9Sr_0.1MnO₃ (LSMO) ultrathin films with various thickness (in the range of 5-50 unit cells) are grown on (0 0 1) substrates of the single-crystal SrTi_0.99Nb_0.01O₃ by laser molecular-beam epitaxy (laser-MBE), and the surface morphology of these films were measured by scanning tunneling microscopy (STM). STM images of LSMO ultrathin film surface reveal that surface morphology becomes more flat with increasing film thickness. This study highlights the important effect of strain caused by the lattice mismatch between substrates and ultrathin films. And the results should be useful to the investigations on growing manganite perovskite materials.     

Dependence of magnetic anisotropy of the La0.67Ca0.33MnO3 films on substrate and film thickness

Strain in the La_0.67Ca_0.33MnO₃ films has been tuned by varying substrate and film thickness, and its effects on magnetic anisotropy are studied based on the measurements of isothermal magnetization. Measuring the strain in the films by the out-of-plane lattice parameter (c), we found a strong dependence of the magnetic anisotropy constant (Ku) on strain. Ku decreases linearly from ∼−1.1×10⁶ erg/cm³ for c=0.763 nm to 1.2×10⁶ erg/cm³ for c=0.776 nm, corresponding to a change from tensile strain to compressive strain. Positive Ku signifies a uniaxial anisotropy with the easy axis perpendicular to the film plane, while negative Ku demonstrates an anisotropy of the easy plane character. Smaller or larger c leads a decrease or increase in Ku, which indicates the presence of other effects in addition to those associated with strain. Three distinctive processes for the magnetization are observed along the hard magnetic axis of the films on (001)SrTiO₃, suggesting a possibility of strain relaxation even in ultra-thin films.     

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.     

Structural characterization of thermally evaporated Bi2Te3 thin films

Thermally evaporated Bi₂Te₃ thin films were deposited on glass substrates. X-ray diffraction study confirmed that the growned films are polycrystalline in nature having hexagonal structure. The film exhibits preferential orientation along the [0 1 5] direction for the films of all thickness together with other abundant planes [0 1 1 1] and [1 1 0]. Various structural parameters such as lattice constants, crystallite size, strain, and dislocation density have been calculated and they are found to be thickness dependent. The lattice parameters are found to be a=4.38 Å and c=30.40 Å. The grain size of the films increases with thickness as the dislocation density and the microstrain decreases with thickness. The mean bond energy and the average coordination number of Bi₂Te₃ thin film are found to be 1.72 eV and 2.4, respectively.     

Role of crystal orientation on the magnetic properties of CoFe2O4 thin films grown on Si (1 0 0) and Al2O3 (0 0 0 1) substrates using pulsed laser deposition

We report the influence of crystal orientation on the magnetic properties of CoFe₂O₄ (CFO) thin films grown on single crystal Si (1 0 0) and c-cut sapphire (Al₂O₃) (0 0 0 1) substrates using pulsed laser deposition technique. The thickness was varied from 200 to 50 nm for CFO films grown on Si substrates, while it was fixed at 200 nm for CFO films grown on Al₂O₃ substrates. We observed that the 200 and 100 nm thick CFO-Si films grew in both (1 1 1) and (3 1 1) directions and displayed out-of-plane anisotropy, whereas the 50 nm thick CFO-Si film showed only an (1 1 1) orientation and an in-plane anisotropy. The 200 nm thick CFO film grown on an Al₂O₃ substrate was also found to show a complete (1 1 1) orientation and a strong in-plane anisotropy. These observations pointed to a definite relation between the crystalline orientation and the observed magnetic anisotropy in the CFO thin films.     

La0.8Ca0.2MnO3/SrTiO3薄膜厚度对其结构及磁学性能的影响

采用多种X射线衍射技术和磁电阻测量技术研究了不同厚度的La_0.8Ca_0.2MnO₃/SrTiO₃ (LCMO/STO)薄膜的应变状态及其对磁电阻性能的影响.结果表明，在STO(001)单晶衬底上生长的LCMO薄膜沿［00l］取向生长.LCMO薄膜具有伪立方钙钛矿结构，随着薄膜厚度的增加，面内晶格参数增加，垂直于面内的晶格参数减小,晶格参数a和b相近，略小于c.LC 关键词： X射线衍射 微结构 应变 物理性能     

Microstructure and dielectric properties of La2O3 doped amorphous SiO2 films as gate dielectric material

As a potential gate dielectric material, the La₂O₃ doped SiO₂ (LSO, the mole ratio is about 1:5) films were fabricated on n-Si (0 0 1) substrates by using pulsed laser deposition technique. By virtue of several measurements, the microstructure and electrical properties of the LSO films were characterized. The LSO films keep the amorphous state up to a high annealing temperature of 800 °C. From HRTEM and XPS results, these La atoms of the LSO films do not react with silicon substrate to form any La-compound at interfacial layer. However, these O atoms of the LSO films diffuse from the film toward the silicon substrate so as to form a SiO₂ interfacial layer. The thickness of SiO₂ layer is only about two atomic layers. A possible explanation for interfacial reaction has been proposed. The scanning electron microscope image shows the surface of the amorphous LSO film very flat. The LSO film shows a dielectric constant of 12.8 at 1 MHz. For the LSO film with thickness of 3 nm, a small equivalent oxide thickness of 1.2 nm is obtained. The leakage current density of the LSO film is 1.54 × 10⁻⁴ A/cm² at a gate bias voltage of 1 V.     

Low-temperature deposition of L10 FePt films for ultra-high density magnetic recording

A method based on strain-induced phase transformation was used to lower the ordering temperature of FePt films. The strain resulted from the lattice mismatch between the FePt film and the substrate or underlayer favored the ordering. The relationships between the lattice mismatch, the ordering of FePt film, and the corresponding magnetic anisotropic constant were investigated. A critical lattice mismatch near 6.33% was believed to be most suitable for improving the chemical ordering of the FePt films. CrX (X=Ru, Mo, W, Ti) alloys with (2 0 0) texture was used to control the easy axis and ordering temperature of FePt films on glass substrate. Large uniaxial anisotropy constant K_u?1×10⁷ erg/cm³, good magnetic squareness (∼1) and FePt(0 0 1) texture (rocking curve −5°) were obtained at the temperature T_s?250 °C when using CrRu underlayer. The diffusion from overlying layers of Ag and Cu and an inserted Ag pinning layer were effective in reducing the exchange decoupling and changing the magnetization reversal. The media noise was effectively reduced and the SNR was remarkably enhanced when a 2 nm Ag was inserted.     

Growth of highly-oriented CaCu3Ti4O12 thin films on SrTiO3 (1 0 0) substrates by a chemical solution route

Highly-oriented CaCu₃Ti₄O₁₂ (CCTO) thin films deposited directly on SrTiO₃ (1 0 0) substrates have been developed successfully using a chemical solution coating method. X-ray diffraction (XRD), scanning electron microscopy (SEM), and atomic force microscopy (AFM) were employed to characterize the structure and the morphology. It was observed that the CCTO thin films had the 1 μm × 1 μm domain-like microstructure that consists of compact grains of about 0.1 μm in size. The cross sectional SEM image shows that the CCTO grains grow regularly close to the clear interface between the CCTO film and the SrTiO₃ substrate. The result was discussed in terms of lattice mismatch between CCTO and SrTiO₃.     

Effect of crystallinity of Co layer on perpendicular exchange bias in Au-capped ultrathin Co film on Cr2O3(0 0 0 1) thin film

The effect of the crystalline quality of ultrathin Co films on perpendicular exchange bias (PEB) has been investigated using a Au/Co/Au/α-Cr₂O₃ thin film grown on a Ag-buffered Si(1 1 1) substrate. Our investigation is based on the effect of the Au spacer layer on the crystalline quality of the Co layer and the resultant changes in PEB. An α-Cr₂O₃(0 0 0 1)layer is fabricated by the thermal oxidization of a Cr(1 1 0) thin film. The structural properties of the α-Cr₂O₃(0 0 0 1) layer including the cross-sectional structure, lattice parameters, and valence state have been investigated. The fabricated α-Cr₂O₃(0 0 0 1) layer contains twin domains and has slightly smaller lattice parametersthan those of bulk-Cr₂O₃. The valence state of the Cr₂O₃(0 0 0 1) layer is similar to that of bulk Cr₂O₃. The ultrathin Co film directly grown on the α-Cr₂O₃(0 0 0 1) deposited by an e-beam evaporator is polycrystalline. The insertion of a Au spacer layer with a thickness below 0.5 nm improves the crystalline quality of Co, probably resulting in hcp-Co(0 0 0 1). Perpendicular magnetic anisotropy (PMA) appears below the Néel temperature of Cr₂O₃ for all the investigated films. Although the PMA appears independently of the crystallinequality of Co, PEB is affected by the crystalline quality of Co. For the polycrystalline Co film, PEB is low, however, a high PEB is observed for the Co films whose in-plane atom arrangement is identical to that of Cr³⁺ in Cr₂O₃(0 0 0 1). The results are qualitatively discussed on the basis of the direct exchange coupling between Cr and Co at the interface as the dominant coupling mechanism.     

Mg diffusion in K(Ta0.65Nb0.35)O3 thin films grown on MgO evidenced by Auger electron spectroscopy investigation

The diffusion of Mg in pulsed laser deposited K(Ta_0.65Nb_0.35)O₃ thin films epitaxially grown on (1 0 0) MgO single crystal substrate were investigated by Auger electron spectroscopy (AES). A diffusion of Mg from the substrate into the whole thickness (400 nm) of the as-deposited K(Ta_0.65Nb_0.35)O₃ films was observed with an accumulation of Mg at the surface. Ex situ post-annealing (750 °C/2 h) has led to a homogeneous distribution of Mg in all the ferroelectric coating. This strong reaction between film and substrate promotes a doping effect, responsible for the reduction of K(Ta_0.65Nb_0.35)O₃ dielectric losses in comparison with films grown on other substrates.     

Fabrication and magnetic properties of Ce1Y2Fe5O12 thin films on GGG and SiO2/Si substrates

Microstructure and magnetic properties of crystalline Ce₁Y₂Fe₅O₁₂ thin films prepared on GGG and on SiO₂/Si substrates by pulsed laser deposition were studied. The results show that highly textured Ce₁Y₂Fe₅O₁₂ film with (4 4 4) preferred orientation prepared on GGG (1 1 1) shows strong paramagnetism superimposed by a weak ferromagnetism. However, polycrystalline Ce₁Y₂Fe₅O₁₂ thin films on SiO₂/Si, which can only be obtained after post-annealing, show strong ferromagnetism with easy axis of magnetization lying in the plane of the film. With post-annealing temperature increasing, CeO₂ segregates from Ce₁Y₂Fe₅O₁₂; then YIG continues to be decomposed, forming Fe₂O₃. Consequently, the saturation magnetization of Ce₁Y₂Fe₅O₁₂ films decreases first and then increases correspondingly, which indicates that the magnetic properties of Ce₁Y₂Fe₅O₁₂ films are mainly related to the microstructure.     

Impacts of compressive strain on phase diagram of epitaxial Pr0.5Sr0.5MnO3 films grown on LaAlO3 (0 0 1)

Series Pr_0.5Sr_0.5MnO₃ (PSMO) films of thickness ranging from 20 to 400 nm were epitaxially grown on (0 0 1)-oriented LaAlO₃ using pulsed laser deposition method. The biaxial compressive strain effect on phase transition of the films was systematically investigated by both electrical and magnetic measurements. The 60 nm film shows a ferromagnetic metal to antiferromagnetic insulator (FMM-AFI) transition at a temperature of ∼190 K. Such a FMM-AFI transition is depressed as the films become thicker, and finally disappears in the strain-relaxed situation. On the other hand, the Curie temperature is remarkably enhanced (∼50 °C) when the film thickness increases from 60 to 400 nm. These results may yield the possibility to modulate the phase transitions by varying the structural strain.     

Multilayer Bi1.5Zn1.0Nb1.5O7/Ba0.6Sr0.4TiO3/Bi1.5Zn1.0Nb1.5O7 thin films for tunable microwave applications

Bi_1.5Zn_1.0Nb_1.5O₇/Ba_0.6Sr_0.4TiO₃/Bi_1.5Zn_1.0Nb_1.5O₇ tunable multilayer thin film has been fabricated by pulsed laser ablation and characterized. Phase composition and microstructure of multilayer films were characterized by X-ray diffraction, scanning electron microscopy (SEM) and atomic force microscopy (AFM). The film has very smooth surface with RMS roughness of 1.5-2 nm and grain size of 100-150 nm. Total film thickness has been measure to be 375 nm. The BZN thin films at 300 K, on Pt(1 1 1)/SiO₂/Si substrate showed zero-field dielectric constant of 105 and dielectric loss tangent of 0.002 at frequency of 0.1 MHz. Thin films annealed at 700 °C shows the dielectric tunability of 18% with biasing field 500 kV/cm at 0.1 MHz. The multilayer thin film shows nonferroelectric behavior at room temperature. The good physical and electrical properties of multilayer thin films make them promising candidate for tunable microwave device applications.     

Structure and electronic properties calculation of ultrathin α-Al2O3 films on (0 0 0 1) α-Cr2O3 templates

Ab initio total energy Hartree-Fock calculations of ultrathin films of α-Al₂O₃ on (0 0 0 1) α-Cr₂O₃ templates are presented. The surface relaxation, the in-plane reconstruction and the surface and strain energies of the slabs are studied as a function of alumina film thickness. The surface Al layer is found to relax inwards considerably, with the magnitude of the inwards relaxation depending on the thickness of the ultrathin alumina film in a non-linear manner. The calculations also reveal that ultrathin films of alumina lower the surface energy of (0 0 0 1) α-chromia substrates. This indicates that the (0 0 0 1) α-chromia surface provides favourable conditions for the templated growth of α-alumina. However, increasing the alumina film thickness is found to give rise to a significant increase in strain energy. Finally, the electronic properties at the surface of the (0 0 0 1) α-Al₂O₃/α-Cr₂O₃ slabs are investigated. Here it is found that the alumina coating gives rise to an increase in the covalency of the bonds at the surface of the slabs. In contrast, the influence of an alumina layer on the electrostatic potential at the surface of the chromia slab is relatively minor, which should also be beneficial for the templated growth of α-alumina on (0 0 0 1) α-chromia substrates.     

Effect of oxygen pressure on microstructure and magnetic properties of strontium hexaferrite (SrFe12O19) film prepared by pulsed laser deposition

The effects of oxygen pressure during deposition on microstructure and magnetic properties of strontium hexaferrite (SrFe₁₂O₁₉) films grown on Si (100) substrate with Pt (111) underlayer by pulsed laser deposition have been investigated. X-ray diffraction pattern confirms that the films have c-axis perpendicular orientation. The c-axis dispersion (Δθ₅₀) increases and c-axis lattice parameter decreases with increasing oxygen pressure. The films have hexagonal shape grains with diameter of 150-250 nm as determined by atomic force microscopy. The coercivities in perpendicular direction are higher than those in in-plane direction, which shows the films have perpendicular magnetic anisotropy. The saturation magnetization and anisotropy field for the film deposited in oxygen pressure of 0.13 mbar are comparable to those of the bulk strontium hexaferrite. Higher oxygen pressure leads to the films having higher coercivity and squareness. The coercivity in perpendicular and in-plane directions of the film deposited in oxygen pressure of 0.13 mbar are 2520 Oe and 870 Oe, respectively.     

Growth and characterization of Y2O3 thin films

Y₂O₃ thin films were grown on silicon (1 0 0) substrates by pulsed-laser deposition at different substrate temperatures and O₂ pressures. The structure and composition of films are studied by using X-ray diffraction (XRD) and X-ray photoelectron spectroscopy (XPS). The Y₂O₃ thin films deposited in vacuum strongly oriented their [1 1 1] axis of the cubic structure and the film quality depended on the substrate temperature. The magnitude of O₂ pressure obviously influences the film structure and quality. Due to the silicon diffusion and interface reaction during the deposition, yttrium silicate and SiO₂ were formed. The strong relationship between composition and growth condition was discussed.     

Dielectric properties of continuous composition spreaded MgO-Ta2O5 thin films

The dielectric properties of MgO-Ta₂O₅ continuous composition spread (CCS) thin films were investigated. The MgO-Ta₂O₅ CCS thin films were deposited on Pt/Ti/SiO₂/Si substrates by off-Axis RF magnetron sputtering system, and then the films were annealed at 350 °C with rapid thermal annealing system in vacuum. The dielectric constant and loss of MgO-Ta₂O₅ CCS thin films were plotted via 1500 micron-step measuring. The specific point of Ta₂O₅-MgO CCS thin film (post annealed at 350 °C) showing superior dielectric properties of high dielectric constant (k ∼ 28) and low dielectric loss (tan δ < 0⋅004) at 1 MHz were found in the area of 3-5 mm apart from Ta₂O₅ side on the substrate. The cation's composition of thin film was Mg:Ta = 0.4:2 at%.     

Fabrication and characterization of epitaxial Sr0.6Ba0.4Nb2O6/La0.7Sr0.3CoO3 heterostructures

Epitaxial Sr_0.6Ba_0.4Nb₂O₆(SBN60)/La_0.7Sr_0.3CoO₃ heterostructures were fabricated on LAO(0 0 1) substrates using pulsed laser deposition (PLD). Their structural properties were investigated by X-ray diffraction. The θ-2θ scans showed single crystalline Sr_1−xBa_xNb₂O₆ (SBN) and La_xSr_1−xCoO₃ (LSCO) layers with a 〈0 0 1〉 orientations perpendicular to the substrate plane. Phi scans on the (2 2 1) plane of SBN layer indicated that the films have two in-plane orientations with respect to the substrate. The SBN unit cells were rotated in the plane of the film by ±18.4° as well as ±45° with respect to the LAO substrate. This rotation was explained by considering the lattice matching between films and substrate, and minimization of electrostatic energy. Spectroellipsometry (SE) was used to characterize the depth profile, the microstructural inhomogeneities, including voids and surface roughness, refractive indices and extinction coefficients of the films.