Rodolfo Miranda

Engineering Iron Oxide Nanoparticles for Clinical Settings

Iron oxide nanoparticles (IONPs) occupy a privileged position among magnetic nanomaterials with potential applications in medicine and biology. They have been widely used in preclinical experiments for imaging contrast enhancement, magnetic resonance, immunoassays, cell tracking, tissue repair, magnetic hyperthermia and drug delivery. Despite these promising results, their successful translation into a clinical setting is strongly dependent upon their physicochemical properties, toxicity and functionalization possibilities. Currently, IONPs-based medical applications are limited to the use of non-functionalized IONPs smaller than 100 nm, with overall narrow particle size distribution, so that the particles have uniform physical and chemical properties. However, the main entry of IONPs into the scene of medical application will surely arise from their functionalization possibilities that will provide them with the capacity to target specific cells within the body, and hence to play a role in the development of specific therapies. In this review, we offer an overview of their basic physicochemical design parameters, giving an account of the progress made in their functionalization and current clinical applications. We place special emphasis on past and present clinical trials.

Thermal stability of Cu and Fe nitrides and their applications for writing locally spin valves

We have studied the thermal stability of the Cu and Fe nitrides. These results show that a nanometer-thick Cu nitride film decomposes at the Fe4N growth temperature. Considering this, we propose for their use in spintronics, the room temperature growth of a nonmagnetic (FeN)/semiconducting (Cu3N) epitaxial nitride bilayer that transforms into a ferromagnetic (Fe4N)/metallic (Cu) one by mild thermal annealing at 700 K. This process can be employed to locally decompose by laser (or ion) irradiation FeN/Cu3N/Fe4N) trilayers, giving rise to an array of lithographically defined Fe4N/Cu/Fe4N spin valves surrounded by metal/semiconductor spacers.

High-resolution elastic and rotationally inelastic diffraction of D2 from NiAl(110)

High-resolution angular distributions of D(2) scattered from NiAl(110) have been measured at incident energies between 20 and 150 meV. The measurements were performed along the [110] azimuth using a high sensitivity time-of-flight apparatus, which allows the recording of diffraction channels not previously studied, including out-of-plane rotationally inelastic diffraction peaks. The attenuation of both elastic and rotationally inelastic diffraction intensities with surface temperature was found to follow a Debye-Waller model. The time-of-flight data analysis allowed us to assign unequivocally the different transition probabilities to each final state. In this way, 0→2, 2→0, and 1→3 transition probabilities were observed, covering relative intensities over two orders of magnitude. In the energy range investigated, the 0→2 transition was found to be a factor of 2-3 larger than the 2→0 one, which lies a factor of 10 above the 1→3 transition probability.

Role of anisotropy configuration in exchange-biased systems

We present a systematic study of the anisotropy configuration effects on the magnetic properties of exchange-biased ferromagnetic/antiferromagnetic (FM/AFM) Co/IrMn bilayers. The interfacial unidirectional anisotropy is set extrinsically via a field cooling procedure with the magnetic field misaligned by an angle bFC with respect to the intrinsic FM uniaxial anisotropy. High resolution angular dependence in-plane resolved Kerr magnetometry measurements have been performed for three different anisotropy arrangements, including collinear bFC ¼ 0 � and two opposite noncollinear cases. The symmetry breaking of the induced noncollinear configurations results in a peculiar nonsymmetric magnetic behavior of the angular dependence of magnetization reversal, coercivity, and exchange bias. The experimental results are well reproduced without any fitting parameter by using a simple model including the induced anisotropy configuration. Our finding highlights the importance of the relative angle between anisotropies in order to properly account for the magnetic properties of exchange-biased FM/AFM systems. V C 2011 American Institute of

Templated growth of an ordered array of organic bidimensional mesopores

We report on a method to fabricate a porous two dimensional (2D) array of porphyrins on c(2×2)N∕Cu(001) with pore sizes larger than 5nm, larger than the reported sizes for hydrogen-bonded or coordination porous organic networks. When deposited on the square nanopattern created by partial nitridation of the Cu(001) surface, the porphyrin molecules prefer to adsorb on clean copper instead of adsorbing on the CuN islands, forming a porous 2D array. This nanopatterning technique can be straightforwardly extended to other molecular species to form the pore walls since its working principle only depends marginally on the nature of the intermolecular interactions.

Magnetization reversal in half metallic La0.7Sr0.3MnO3 films grown onto vicinal surfaces

We present the study of the magnetic properties of well-characterized epitaxial half metallic La0.7 Sr0.3 MnO3 films grown onto vicinal SrTiO3(001) substrates with different miscut angles. Room temperature high resolution vectorial Kerr magnetometry measurements have been performed at different applied magnetic field directions in the whole angular range. The films present a substrate-induced uniaxial (twofold) magnetic anisotropy originated from in-plane [110]-oriented elongated structures, whereas the strength of this anisotropy increases with the miscut angle of the substrate surfaces. Our results demonstrate that we can artificially control the magnetic anisotropy of epitaxial films, up to 120 nm thick, by exploiting the substrate-induced anisotropy. We also determine in this case the minimum vicinal angle required to get well-defined uniaxial magnetic anisotropy.

Imaging and quantifying perpendicular exchange biased systems by soft x-ray holography and spectroscopy

The magnetic properties of perpendicular exchange biased ferromagnetic (FM)/antiferromagnetic (AFM) [Pt/Co]n/IrMn systems were investigated by a new set-up combining element-selective soft x-ray holography and spectroscopy measurements. The holography experiments allow imaging the magnetization reversal of an exchange biased FM layer with an equivalent Co thickness below 5 nm in real space and in external magnetic fields, and provide direct evidence of its asymmetric nature. From the spectroscopy analysis, we have quantified the unpinned (pinned) uncompensated AFM moments, providing direct evidence of its parallel (antiparallel) alignment with respect to the FM moments.

Exploring the limits of soft x-ray magnetic holography: Imaging magnetization reversal of buried interfaces (invited)

Only a very few experimental techniques can address the microscopic magnetization reversal behavior of the different magnetic layers in a multilayered system with element selectivity. We present an element-selective study of ferromagnetic (FM) [Co/Pt]n multilayers with perpendicular anisotropy exchange-coupled to antiferromagnetic (AFM) FeMn and IrMn films performed with a new experimental set-up developed for both soft x-ray spectroscopy and holography imaging purposes. The spectroscopy analysis allows the quantification of the unpinned (pinned) uncompensated AFM moments, providing direct evidence of its parallel (antiparallel) alignment with respect to the FM moments. The holography experiments give a direct view of both FM and uncompensated AFM magnetic structures, showing that they replicate to each other during magnetization reversal. Remarkably, we show magnetic images for effective thicknesses as small as one monolayer. Our results provide new microscopic insights into the exchange coupling phenomena and explore the sensitivity limits of these techniques. Future trends are also discussed.

Cu diffusion as an alternative method for nanopatterned CuTCNQ film growth

In this paper we show by means of in situ x-ray diffraction studies that CuTCNQ formation from Cu(solid)-TCNQ(solid tetracyanoquinodimethane) goes through Cu diffusion at room temperature. The film quality depends on the TCNQ evaporation rate. At low evaporation rate we get a single phase-I CuTCNQ film very well crystallized and well oriented. The film has a CuTCNQ(0u20092u20090) orientation. The film is formed by CuTCNQ nanorods of a very homogeneous size. The film homogeneity has also been seen by atomic force microscopy (AFM). The electronic properties of the film have been measured by x-ray photoelectron spectroscopy (XPS) and ultra-violet photoelectron spectroscopy (UPS). Thus, the Cu-diffusion method has arisen as a very simple, clean and efficient method to grow localized CuTCNQ nanorods on Cu, opening up new insights for technological applications.

Electronic Properties of Sulfur Covered Ru(0001) Surfaces

The structural properties of sulfur superstructures adsorbed on Ru(0001) have been widely studied in the past. However, much less effort has been devoted to determine their electronic properties. To understand the connection between structural and electronic properties, we have carried out density functional theory periodic boundary calculations mimicking the four long-range ordered sulfur superstructures identified experimentally by means of scanning tunneling microscopy (STM) techniques. Our simulations allow us to characterize the nature of the sulfur-Ru bond, the charge transfer between the Ru substrate and the sulfur adlayers, the interface states, and a parabolic state recently identified in STM experiments. A simple analysis, based on a one-dimensional model, reveals that this parabolic state is related to a potential well state, formed in the surface when the concentration of sulfur atoms is large enough to generate a new minimum in the surface potential.