Organización espontánea de puntos cuánticos de InSb crecidos por ALMBE sobre substratos de InP

El crecimiento autoorganizado de puntos cuánticos de InSb sobre substratos de InP mediante epitaxia de haces moleculares ha sido caracterizado mediante microscopía electrónica de transmisión y microscopía de fuerzas atómicas a fin de estudiar la morfología y establecer el mecanismo de relajación de las estructuras. Medidas de difracción de electrones de alta energía durante el crecimiento de las muestras indican una transición en el modo de crecimiento de bidimensional a tridimensional a partir de un espesor total equivalente depositado de 1.1 monocapas atómicas de InSb. Los puntos cuánticos tienen en general, una buena calidad cristalina así como una distribución superficial homogénea, pero una alta anisotropía en las dimensiones entre las direcciones [110] y [110]. Así mismo, se encuentra una rugosidad superficial, también afectada de un alto grado de anisotropía, siendo las crestas y los valles paralelos a la dirección de elongación de las islas. Las imágenes de microscopía electrónica revelan un facetado de las estructuras según planos (001) que las limitan por la parte superior y planos {111}, {113} y {114}, que las limitan lateralmente. Las tensiones son eficazmente relajadas por la presencia de una red de dislocaciones situada en la interficie InSb/InP

Perpendicular magnetic anisotropy in chemically disordered FePd-FeV(100) alloy thin films

We find that the use of V(100) buffer layers on MgO(001) substrates for the epitaxy of FePd binary alloys yields to the formation at intermediate and high deposition temperatures of a FePd¿FeV mixed phase due to strong V diffusion accompanied by a loss of layer continuity and strong increase of its mosaic spread. Contrary to what is usually found in this kind of systems, these mixed phase structures exhibit perpendicular magnetic anisotropy (PMA) which is not correlated with the presence of chemical order, almost totally absent in all the fabricated structures, even at deposition temperatures where it is usually obtained with other buffer layers. Thus the observed PMA can be ascribed to the V interdiffusion and the formation of a FeV alloy, being the global sample saturation magnetization also reduced

Enhanced gas sensing performance of TiO2 functionalized magneto-optical SPR sensors

9 páginas, 7 figurasPorous TiO2 thin films deposited by glancing angle deposition are used as sensing layers to monitor their sensing capabilities towards Volatile Organic Compounds both in a standard Surface Plasmon Resonance (SPR) sensor and in Magneto-Optical Surface Plasmon Resonance (MO-SPR) configuration in order to compare their sensing performances. Here our results on the enhanced sensing capability of these TiO2 functionalized MO-SPR sensors with Au/Co/Au transducers with respect to traditional SPR gas sensors are presented.This work has been funded by the European Commission (NMP3-SL-2008-214107-Nanomagma), the Spanish MICINN (CSD 2008-00023, MAT 2008-06765-C02-01/NAN, MAT2010-21228), CSIC (JAE fellowship for E. F.-V.) and Comunidad de Madrid (S2009 / MAT – 1726, S2009/TIC – 1476).Peer reviewe

Size mediated control of the optical and magneto-optical properties of Co nanoparticles in ZrO2

We present a study of the optical and magneto-optical (MO) properties of Co nanoparticles embedded in ZrO2 in the spectral range from 1.4 to 4.3 eV. The nanostructured films were prepared by pulsed laser deposition in a wide range of Co nanoparticle concentrations varying from 20% to 80%. For Co concentration lower than x~0.45 the size of the nanoparticles was found to remain almost constant (D~2.5 nm), whereas it increases above it. Differences are found between the optical and MO constant of the Co nanoparticles and those of continuous Co films. Those differences are associated with size effects of the intraband contribution inside the nanoparticles

Surface Enhanced Infrared Characterization Using Disordered Slit-Antenna Arrays for the Detection of Electrodeposited Cytochrome C

An approach which allows both electrochemical studies and surface enhanced infrared characterization of electrodeposited Cytochrome C is presented. This approach is based on in-plane disordered arrays of resonant slits engraved in Au substrates using focused ion beam. For light-polarized perpendicular to the slit, the reflectivity spectra of the slit arrays show dips related to the excitation of the slit plasmon resonance, whose position depends on the slit length. Due to the presence of the continuous Au layer around the slits, the very same substrates can be used to perform electrochemical studies. By varying the slit length, we have tuned the plasmon resonance to match the absorption bands of electrodeposited Cytochrome C, demonstrating the detection of minute amounts of this protein, all the way down to a single monolayer.Open Access funding provided thanks to the CRUE-CSIC agreement with Springer Nature. We acknowledge financial support from MINECO through projects AMES (MAT 2014–58860-P), Quantum Spin Plasmonics (FIS2015−72035−EXP), MIRRAS (MAT2017−84009−R), and Comunidad de Madrid through project SINOXPHOS−CM (S2018/BAA-4403). We acknowledge the service from the MiNa Laboratory at IMN and funding from MINECO under project CSIC13−4E−1794 and from CM under project S2013/ICE−2822 (Space−Tec), both with support from EU (FEDER, FSE)

Interface effects, magnetic, and magneto-optical properties of Al/Co/V/MgO(100) structures

The magnetic and magneto-optical properties of Al/Co/V/MgO(100) structures and the influence of the Co/V interface for different thicknesses of the Co and V layers have been studied experimentally. From the element-specific hysteresis loops obtained by x-ray magnetic circular dichroism (XMCD) at the Co and V L3 edges we find that the V layers are magnetically polarized antiparallel to the Co layers and that magnetization reversal occurs at the same magnetic field in both layers. The effect of the V atomic volume and the relative thicknesses of V and Co layers on the magnetic moments of the V and Co atoms are also studied. Contrary to what might be expected, the atomic magnetic moments of the V and Co atoms do not depend on the V atomic volume, however they depend strongly on the thicknesses of the V and Co layers. From the trend in the Co and V atomic magnetic moments as a function of Co and V thicknesses and the absence of any spectroscopic evidence for the formation of a VCo alloy, a long-range spin polarization of the V atoms is proposed. The extracted magneto-optical (MO) constants of V and Co as a function of photon energy clearly evidence a large amount of polarization in the V films in agreement with the XMCD results, which is indicative of the magnetic coupling between Co and V. The experimental MO results and simulations also show the strong influence of these polarized V layers in the MO properties of the complete system. These results, given the absence of spectroscopic evidence for the formation of a VCo alloy, support a long-range magnetization of the V atoms and a reduction of the Co atomic magnetic moments.This research was carried out with the financial support of the Spanish Ministry of Science and Education (NAN2004-09195-C04 and MAT2005-05524-C02-01), Comunidad de Madrid (S-0505/MAT/0194 NANOMAGNET) and the European Commission through the NoE PHOREMOST (FP6/2003/IST/2-511616). M. U. G. thanks the Spanish Ministry of Education for funding through the “Ramón y Cajal” program.Peer reviewe

Enhanced gas sensing performance of TiO2 functionalized magneto-optical SPR sensors

9 páginas, 7 figurasPorous TiO2 thin films deposited by glancing angle deposition are used as sensing layers to monitor their sensing capabilities towards Volatile Organic Compounds both in a standard Surface Plasmon Resonance (SPR) sensor and in Magneto-Optical Surface Plasmon Resonance (MO-SPR) configuration in order to compare their sensing performances. Here our results on the enhanced sensing capability of these TiO2 functionalized MO-SPR sensors with Au/Co/Au transducers with respect to traditional SPR gas sensors are presented.This work has been funded by the European Commission (NMP3-SL-2008-214107-Nanomagma), the Spanish MICINN (CSD 2008-00023, MAT 2008-06765-C02-01/NAN, MAT2010-21228), CSIC (JAE fellowship for E. F.-V.) and Comunidad de Madrid (S2009 / MAT – 1726, S2009/TIC – 1476).Peer reviewe

Organización espontánea de puntos cuánticos de InSb crecidos por ALMBE sobre substratos de InP

El crecimiento autoorganizado de puntos cuánticos de InSb sobre substratos de InP mediante epitaxia de haces moleculares ha sido caracterizado mediante microscopía electrónica de transmisión y microscopía de fuerzas atómicas a fin de estudiar la morfología y establecer el mecanismo de relajación de las estructuras. Medidas de difracción de electrones de alta energía durante el crecimiento de las muestras indican una transición en el modo de crecimiento de bidimensional a tridimensional a partir de un espesor total equivalente depositado de 1.1 monocapas atómicas de InSb. Los puntos cuánticos tienen en general, una buena calidad cristalina así como una distribución superficial homogénea, pero una alta anisotropía en las dimensiones entre las direcciones [110] y [110]. Así mismo, se encuentra una rugosidad superficial, también afectada de un alto grado de anisotropía, siendo las crestas y los valles paralelos a la dirección de elongación de las islas. Las imágenes de microscopía electrónica revelan un facetado de las estructuras según planos (001) que las limitan por la parte superior y planos {111}, {113} y {114}, que las limitan lateralmente. Las tensiones son eficazmente relajadas por la presencia de una red de dislocaciones situada en la interficie InSb/InP

Size effects in the magneto-optical response of Co nanoparticles

A study of the magneto-optical (MO) spectral response of Co nanoparticles embedded in MgO as a function of their size and concentration in the spectral range from 1.4 to 4.3 eV is presented. The nanoparticle layers were obtained by sputtering at different deposition temperatures. Transmission electron microscopy measurements show that the nanoparticles have a complex structure which consists of a crystalline core having a hexagonal close-packed structure and an amorphous crust. Using an effective-medium approximation we have obtained the MO constants of the Co nanoparticles. These MO constants are different from those of continuous Co layers and depend on the size of the crystalline core. We associate these changes with the size effect of the intraband contribution to the MO constants, related to a reduction of the relaxation time of the electrons into the nanoparticles

Coverage effects on the magnetism of Fe/MgO(001) ultrathin films

Different aspects of the structure-magnetism and morphology-magnetism correlation in the ultrathin limit are studied in epitaxial Fe films grown on MgO(001). In the initial stages of growth the presence of substrate steps, intrinsically higher than an Fe atomic layer, prevent the connection between Fe islands and hence the formation of large volume magnetic regions. This is proposed as an explanation to the superparamagnetic nature of ultrathin Fe films grown on MgO in addition to the usually considered islanded, or Vollmer-Weber, growth. Using this model, we explain the observed transition from superparamagnetism to ferromagnetism for Fe coverages above 3 monolayers (ML). However, even though ferromagnetism and magnetocrystalline anisotropy are observed for 4 ML, complete coverage of the MgO substrate by the Fe ultrathin films only occurs around 6 ML as determined by polar Kerr spectra and simulations that consider different coverage situations. In annealed 3.5 ML Fe films, shape or configurational anisotropy dominates the intrinsic magnetocrystalline anisotropy, due to an annealing induced continuous to islanded morphological transition. A small interface anisotropy in thicker films is observed, probably due to dislocations observed at the Fe¿MgO(001) interface