This paper reports an XPS surface study of pure phase BiFeO${}_3$ thin film produced and later etched by pure argon ions. Analysis of high-resolution spectra from Fe $2p$, Bi $4f$ and $5d$, O $1s$, and the valence band, exhibited mainly Fe${}^{3+}$ and Bi${}^{3+}$ components, but also reveal Fe${}^{2+}$. High-energy argon etching induces the growth of Fe${}^{\left(0\right)}$ and Bi${}^{\left(0\right)}$ and an increment of Fe${}^{2+}$, as expected. The BiFeO${}_3$ semiconductor character is preserved despite the oxygen loss, an interesting aspect for the study of the photovoltaic effect through oxygen vacancies in some ceramic films. The metal-oxygen bonds in O $1s$ spectra are related only to one binding energy contrary to the split from bismuth and iron reported in other works. All these data evidence that the low-pressure argon atmosphere is proved to be efficient to produce pure phase BiFeO${}_3$, even after argon etching.

We have investigated the structural and magnetic properties of BiFeO$_3$ (BFO) thin films grown over (100)-oriented Si substrates by rf magnetron sputtering in a new route under O$_2$ free low pressure Ar atmosphere. Single-phase BFO films were deposited in a heated substrate and post-annealed in situ. The new routed allows high deposition rate and produce polycrystalline BFO pure phase, confirmed by high resolution X-ray diffraction. Scanning electron and atomic force microscopy reveal very low surface roughness and mean particle size of 33 nm. The BFO phase and composition were confirmed by transmission electron microscopy and line scanning energy-dispersive X-ray spectroscopy in transmission electron microscopy mode. The surface chemistry of the thin film, analyzed by X-ray photoelectron spectroscopy, reveals the presence of Fe$^{3+}$ and Fe$^{2+}$ in a 2:1 ratio, a strong indication that the film contains oxygen vacancies. An hysteretic ferromagnetic behavior with room temperature high saturation magnetization $\sim 165 \times 10^3$ A/m was measured along the film perpendicular and parallel directions. Such high magnetization, deriving from this new route, is explained in the scope of oxygen vacancies, the break of the antiferromagnetic cycloidal order and the increase of spin canting by change in the surface/volume ratio. Understanding the magnetic behavior of a multiferroic thin films is a key for the development of heterogeneous layered structures and multilayered devices and the production of multiferroic materials over Si substrates opens new possibilities in the development of materials that can be directly integrated into the existent semiconductor and spintronic technologies.

P { line-height: 115%; margin-bottom: 0.25cm; background: transparent }a:link { color: #000080; text-decoration: underline }Tailoring core-shell nanostructures using iron oxide core (Fe3O4) and titanium dioxide shell (TiO2) offer a promising multifunctional platform for multimodal cancer therapies. TiO2 shell exhibits photo-responsive optical properties suitable for optical imaging and phototherapies, while Fe3O4 magnetic core enables magnetic resonance imaging (MRI) and magnetic hyperthermia therapy (MHT). This present work reports synthesis and characterization from core-shell Fe3O4@TiO2 and Fe3O4@SiO2@TiO2 nanostructures. Structural and physical properties were evaluated using X-ray Diffraction (XRD), Fourier-Transform Infrared Spectroscopy (FTIR), Transmission Electron Microscopy (TEM), High-Resolution Scanning Electron Microscopy (HRSEM), Diffuse UV-Vis Reflectance Spectroscopy (DRS) and SQUID magnetometry. This work highlights the potential use of magnetic (core) and optically activated (shell) nanostructures for multimodal therapies assisted by magnetic hyperthermia.