Search Results (5)

Thin films of lithium spinel ferrite, LiFe₅O₈, have attracted much scientific attention because of their potential for efficient excitation, the manipulation and propagation of spin currents due to their insulating character, high-saturation magnetization, and Curie temperature, as well as their ultra-low damping value. In addition, LiFe₅O₈ is currently one of the most interesting materials in terms of developing spintronic devices based on the ionic control of magnetism, for which it is crucial to control the lithium’s atomic content. In this work, we demonstrate that dual ion beam sputtering is a suitable technique to tailor the lithium content of thin films of lithium ferrite (LFO) by using the different energies of the assisting ion beam formed by Ar⁺ and O₂⁺ ions during the growth process. Without assistance, a disordered rock-salt LFO phase (i.e., LiFeO₂) can be identified as the principal phase. Under beam assistance, highly out-of-plane-oriented (111) thin LFO films have been obtained on (0001) Al₂O₃ substrates with a disordered spinel structure as the main phase and with lithium concentrations higher and lower than the stoichiometric spinel phase, i.e., LiFe₅O₈. After post-annealing of the films at 1025 K, a highly ordered ferromagnetic spinel LFO phase was found when the lithium concentration was higher than the stoichiometric value. With lower lithium contents, the antiferromagnetic hematite (α-Fe₂O₃) phase emerged and coexisted in films with the ferromagnetic Li_xFe_6-xO₈. These results open up the possibility of controlling the properties of thin lithium ferrite-based films to enable their use in advanced spintronic devices. Full article

A quantitative X-ray Photoelectron Spectroscopy (XPS) study has been undertaken on different experimental data sets of ZrN thin films deposited using reactive Bipolar Pulsed Dual-Magnetron Sputtering (BPDMS) on silicon/stainless steel substates, to obtain dense, pure and homogeneous coatings, free from morphological defects. Zirconium nitride (ZrN) occupies a central role within the class of transition metal nitrides (TMN) for its excellent properties, such as high hardness, low resistivity and chemical/thermal stability when its stoichiometric ratio is 1:1. Many deposition techniques, reported in the literature, tried to obtain oxygen-free and defect-free structures, but they proved a hard task. In this paper it has been demonstrated, using quantitative XPS, that stoichiometric, pure and homogeneous ZrN films have been grown at certain deposition conditions, optimized also via optional accessories mounted on the deposition apparatus. Almost all the films considered for microanalytical characterization resulted as completely oxygen-free, pure (with a lowest-detection limit of 1%) and homogeneous. Apart from these features, a stoichiometric ratio (N/Zr) close to one was calculated for six samples of the ten investigated, with a precision of ± 0.01. In this frame XPS, widely known for being a highly surface-sensitive technique (average depth resolution of 20–30 Å), and powerful for characterizing the chemical composition of materials, has been extensively employed to extract information both in the surface regions and in depth. A cluster ion beam Ar+ ₂₅₀₀ facility on our main XPS chamber has not proved adequate for depth-profiling acquisitions. Therefore, Ar+ ion sputtering was performed instead. To the best of our best knowledge, the results achieved in the present paper possess a level of accuracy never reached before. Rigorous calibration procedures before and during experimental spectrum acquisitions and a careful and scrupulous data processing using software CasaXps v.2.3.24PR1 were carried out to ensure a low percentage error. Progress has also been made for shake-up satellite extraction and interpretation from Zr 3d high-resolution spectra with the help of the literature milestones reported in the text. The total absence of oxygen inside most of the films prevented the formation of zirconium oxide compounds during deposition, which are generally resonant with the binding energy of the shake-up satellite peaks and hide them. A little summary about the experimental shake-up satellite peaks revealed and extracted from the Zr 3d region, after Shirley background subtraction and data processing, will be presented in the last subparagraph of the “Results” section for the ZrN samples analyzed. Figures of Zr 3d deconvoluted spectra for in-depth area analysis have been reported. The quantitative satellite contribution to the Zr 3d total area would not be included in stoichiometric calculations. Full article

Ion beam sputtered hafnia is a preferred high index coating material for laser applications. It exhibits a mostly amorphous structure and an adequate laser-induced damage (LIDT) threshold. In this work, we investigated the influence of an assisting ion source on the film stress as well as the LIDT of the sputtered hafnia layers. The stress increases with an increasing ion energy of the assisting ion beam. We identified a maximum compressive stress of 3–3.5 GPa before the film cracks, blisters, and delaminates. Different states of stress lead to different laser-induced damage thresholds and damage morphologies. Full article

To meet the requirements for lightweight, miniaturized dispersive optical systems for space applications, linear variable filters with a high transmittance and spatial dispersion coefficient are proposed. The filters were produced with dual ion beam sputtering, where a single layer thickness variation was achieved with a deposition rate adjustment based on a linear variable correction formula. A linear variable trend matching method was used to correct the film thickness based on the reduction of the mismatch error between two materials: Ta₂O₅ and SiO₂. The influence of the spectral and spatial measuring average effects was addressed by sampling the spot size optimization. This paper presents an all-dielectric linear variable filter that operates between 520 and 1000 nm, with an excellent linear dependence of 40 nm/mm over 12 mm. The linear variable filter possessed a 2.5% bandwidth, and its transmittance was found to be >80% at the central wavelength of the band, with a 0.1% transmittance in the cut-off region. These results indicate great potential for optical devices for space applications, and the developed process has good reproducibility and stability. Full article

Optical coatings deposited by the dual ion beam sputtering (DIBS) method usually show high compressive stress, which results in severe wavefront deformation of optical elements. Annealing post-treatment has been widely used to control the residual stress of optical coatings. However, the effect of annealing on the stress of Ta₂O₅ films deposited by the IBS method has not been reported in detail. In this study, different thicknesses of Ta₂O₅ films were deposited by IBS and annealed at different temperatures from 473 to 973 K in air, and the effect of annealing on the stress of Ta₂O₅ films was investigated. The as-deposited Ta₂O₅ films deposited by IBS show high compressive stress, which are about 160 MPa. The compressive stress decreases linearly with the increasing temperature, and the wavefront deformation of Ta₂O₅ films increases linearly with film thickness (within 20 μm) at the same annealing temperature. When the temperature rises to 591 K, Ta₂O₅ films with zero-stress can be obtained. Ta₂O₅ films show tensile stress instead of compressive stress with further increasing annealing temperature, and the tensile stress increases with increasing temperature. Meanwhile, with the increasing annealing temperature, the refractive index of Ta₂O₅ film decreases, indicating the decreasing packing density. The atomic force microscope (AFM) test results show that surface roughness of Ta₂O₅ films slowly increases with the increasing of annealing temperature. Moreover, X-ray photoelectron spectroscopy (XPS) analysis shows that the Ta in Ta₂O₅ films can be further oxidized with increasing annealing temperature, namely, the absorption of Ta₂O₅ film can be reduced. X-ray diffraction (XRD) analysis shows that the annealing temperature should be below 923 K to maintain the amorphous structure of the Ta₂O₅ film. Full article