Optical and magneto-optical properties of highly distorted Fe 100 thin films

PACS:78.20.Ls,71.15.-m,75.50.BbTiN-capped epitaxial bcc Fe films exhibit strong changes in the out-of-plane interplanar distance depending on the growth conditions. At room temperature, the increase of the volume per Fe atom appears to be as large as 5%. The observed distortions deviate substantially from elastic behavior. We explain this effect as due to the presence of nitrogen incorporated into the Fe film during the capping layer deposition. In order to elucidate the effect that these distortions might have on the optical and magneto-optical properties, we study the diagonal and off-diagonal elements of the conductivity tensor for both distorted and undistorted structures. This is done by means of spectral ellipsometry and the Kerr effect in polar and transverse configurations in the energy range from 1.5 to 4.5 eV. Theoretical calculations using ab initio techniques for the observed structures are performed and compared with experimental data. Different possible mechanisms for the experimentally observed effects such as distortion, grain size, and orbital hybridization are studied and discussed.The work was carried out with financial support from the Spanish Commission of Science and Technology (Grant Nos. MAT98-0974-C03-01 and MAT99- 0724-C03-03) and Comunidad Auto´noma de Madrid (Grant No. 07N/0056/1999).Peer reviewe

Optical and magneto-optical properties of Au:Conanoparticles and Co:Aunanoparticles doped magnetoplasmonic systems

© 2015 AIP Publishing LLC. We report a study of Au:CoNPs and Co:AuNPs doped magnetoplasmonic systems. In particular, we analyze the effect of adding different concentrations of Co (or Au) nanoparticles (NPs) in a Au (or Co) matrix on both the optical and magneto-optical constants. Through the use of a simple effective medium model, relevant changes in the optical properties of the Au NPs compared to those of bulk material have been identified. Such effects are not observed in the Co NPs system. However, in both systems, there is an increase of the effective diameter of the NPs as compared to the real diameter that can be due to interface effects surrounding the NPs. Moreover, the magneto-optical constants values of both systems are smaller (in absolute values) than expected, which could also be attributed to interface effects such as hybridization between Au and Co.This work was supported by the Spanish MINECO under Project Nos. MAT2011-29194-C02 (MAPS), CSD2007-00041 (NANOSELECT), and CSD2008-00023 (FUNCOAT). http://dx.doi.org/10.1063/1.4906946Peer Reviewe

From disk to ring: Aspect ratio control of the magnetoplasmonic response in Au/Co/Au nanostructures fabricated by hole-mask colloidal lithography

© 2015 AIP Publishing LLC. Morphology tuning of a series of Au/Co/Au nanostructures which gradually evolve from disk to ring allows controlling their optical and magneto-optical spectral responses in the visible and near infrared ranges. This is achieved by the combined use of hole mask colloidal lithography with off-normal deposition and substrate rotation. The morphological parameters responsible for this control, the disk/ring outer diameter and height, are determined by the off-normal deposition angle and the amount of deposited material, respectively. The single dipolar symmetric resonance mode in nanodisk splits into two characteristics, low (symmetric) and high energy (antisymmetric) ring modes. The ring's high energy mode, determined by the rings' section, is basically independent of the deposition angle, while the low energy symmetric mode is basically controlled by the outer diameter/height aspect ratio for both disk-like and ring structures, and therefore allowing a fine tuning of the wavelength position of this resonance.Funding from Spanish Ministry of Economy and Competitiveness through Grants “FUNCOAT” CONSOLIDER CSD2008–00023 and MAPS MAT2011–29194-C02–01are acknowledged. H. Y. Feng thanks the funding from CSC (Chinese Scholarship Council), Grant No. 201206220112. F. Luo would like to acknowledge the support of NSFC (Nos. 51002003 and 11090332) as well as Ramon y Cajal grant RYC-2012-11954.Peer Reviewe

Theoretical analysis of magnetoplasmonic interferometers for sensing

Comunicación presentada en la Conferencia Española de Nanofotónica (CEN2012), celebrada en Carmona (Sevilla) del 1 al 4 de octubre de 2012.Peer Reviewe

Plasmonic and magnetoplasmonic interferometry for sensing

[Introduction and background] Nowadays, we are surrounded by sensors in our daily lives, in industrial processes, medical diagnosis systems, environmental monitoring, etc. The development of sensors with higher sensitivity and smaller dimensions to be integrated in miniaturized systems is then of highest importance for our society. Within all different kinds of sensors, optical sensors are advantageous because they are highly versatile, non-invasive and they can be used in aggressive conditions. In particular, sensors based on surface plasmons, known as surface plasmon resonance (SPR) sensors, have become increasingly popular in biosensing in recent decades due to their high sensitivity and ease of use. Different SPR configurations, such as modulation techniques, have been proposed and demonstrated in order to increase their sensitivity, and attempts to obtain miniaturized SPR sensors have been carried out, the development of plasmonic interferometry sensors being a promising path.[Main results] We have compared theoretically the performance of three implementations of plasmonic sensors: the standard SPR configuration, plasmonic interferometry and magnetically modulated plasmonic (magnetoplasmonic) interferometry. Our results show that the sensitivity of plasmonic interferometers surpasses that of standard SPR methods for long enough except the micrometer-sized interferometers. Moreover, when plasmonic interferometers are magnetically modulated, the direct measurement of the induced modulation in the surface plasmon wavevector allows one to further increase the system sensitivity.[Wider implications] These results show that the development of plasmonic interferometers for sensing, either plain or magnetically modulated, is an interesting route to obtain miniaturized surface plasmon based sensors with higher sensitivity. Moreover, the extended knowledge of immobilization protocols in gold already developed for standard SPR sensors will remain applicable.We acknowledge funding from the Spanish MINECO ('MAPS' MAT2011-29194-C02-01 and 'FUNCOAT' CONSOLIDER INGENIO 2010 CSD2008-00023) and the Comunidad de Madrid ('MICROSERES-CM' S2009/TIC-1476).Peer Reviewe

Capping layer effects in the structure and composition of Co nanoparticle ultrathin films

In this work, we present the correlation of the magnetic and structural properties of Co nanoparticles deposited by sputtering on Si3N4 substrates at different temperatures, and covered with different capping layers, two insulators, AlN and MgO, and a metal, Pt. High-resolution transmission electron microscopy shows the formation of CoPt3 and Co2N, for the Pt and AlN capping layers, respectively, giving to a significant change of the magnetic behavior. When using a cap of MgO, energy-filtered transmission electron microscopy shows an oxidized shell covering the Co nanoparticles with thickness decreasing as the deposition temperature increases, explaining the changes in the magnetic response induced by the MgO capping layer.This work has been funded by the Spanish Project No.MAT2002-04484-C03-02. Y.H. acknowledges the Consejo Superior de Investigaciones Científicas CSIC and Ramón y Cajal Program for financial support.Peer reviewe

Magneto-optical effects in interacting localized and propagating surface plasmon modes

We report that the effect of an external magnetic field on the propagation of surface plasmons can be effectively modified through the coupling between localized (LSP) and propagating (SPP) surface plasmons. When these plasmon modes do not interact, the main effect of the magnetic field is a modification of the wavevector of the SPP mode, leaving the LSP virtually unaffected. Once both modes start to interact, there is a strong variation of the magnetic field induced modification of the SPP dispersion curve and, simultaneously, the LSP mode becomes sensitive to the magnetic field.This work was supported by the EU (NMP3-SL- 2008-214107-Nanomagma), the Spanish MICINN (“MAGPLAS” MAT2008-06765-C02-01/NAN and “FUNCOAT” CONSOLIDER INGENIO 2010 CSD2008-00023), the Comunidad de Madrid (“NANOBIOMAGNET” S2009/MAT-1726 and “MICROSERES-CM” S2009/TIC-1476), and CSIC (“CRIMAFOT” PIF08-016-4). We thank A. Cebollada and J. M. García-Martín for growing and characterizing the Au/Co/Au trilayers and reading this manuscript, and R. Quidant and G.Badenes for fruitful discussions.Peer reviewe

Radiative corrections to the polarizability tensor of an electrically small anisotropic dielectric particle

Radiative corrections to the polarizability tensor of isotropic particles are fundamental to understand the energy balance between absorption and scattering processes. Equivalent radiative corrections for anisotropic particles are not well known. Assuming that the polarization within the particle is uniform, we derived a closed-form expression for the polarizability tensor which includes radiative corrections. In the absence of absorption, this expression of the polarizability tensor is consistent with the optical theorem. An analogous result for infinitely long cylinders was also derived. Magneto optical Kerr effects in non-absorbing nanoparticles with magneto-optical activity arise as a consequence of radiative corrections to the electrostatic polarizability tensor.This work has been supported by the EU NMP3-SL-2008-214107-Nanomagma, the Spanish MICINN Consolider NanoLight (CSD2007-00046), FIS2006-11170-C02-02 and by the Comunidad de Madrid Microseres-CM Program. R.G.-M. acknowledges support from the EU COST-MP0803. Work by R.G.-M. and L.S.F.-P. was supported by the MICINN “Juan de la Cierva” Program.Peer reviewe

Self‐assembled quantum dots of InSb grown on InP by atomic layer molecular beam epitaxy: Morphology and strain relaxation

Self-organized InSb dots grown by atomic layer molecular beam epitaxy on InP substrates have been characterized by atomic force and transmission electron microscopy. Measurement of high-energy electron diffraction during the growth indicates a Stransky–Krastanov growth mode beyond the onset of 1.4 InSb monolayer ~ML! deposition. The dots obtained after a total deposition of 5 and 7 ML of InSb present a truncated pyramidal morphology with rectangular base oriented along the ^110& directions, elongated towards the @110# direction with $111$113%/$114$111%A lateral facets in @11 ¯ 0# views, and ~001! flat top surfaces. The mismatch between the dot and the substrate has been accommodated by a network of 90° misfit dislocation at the interface. A corrugation of the InP substrate surrounding the dot has been also observedThis work has been funded by the Spanish CICYT Project MAT95-0966.Peer reviewe

High magneto-optical activity and low optical losses in metal-dielectric Au/Co/Au-SiO2 magnetoplasmonic nanodisks

Póster presentado en la Conferencia Española de Nanofotónica (CEN2012), celebrada en Carmona (Sevilla) del 1 al 4 de octubre de 2012.Magnetoplasmonics deals with the study of systems where the plasmonic and magneto-optical (MO) properties coexist and show a distinct interaction between them. In this kind of systems, the plasmonic properties can become tunable upon application of a magnetic field, or the MO effects can be largely increased by plasmon resonance excitation, as a consequence of the enhancement of the electromagnetic (EM) field in the MO component of the structure. The study of the enhanced MO activity in structures with subwavelength dimensions is especially interesting since they may be viewed as nanoantennas in the visible range with MO functionalities. The light harvesting properties of these systems upon plasmon resonance excitation brings as a consequence an enhanced EM field in its interior, and more interestingly in the region where the MO active component is present. In fact, it has been recently demonstrated that the MO enhancement can be directly linked with the amount of EM field inside the MO layer, in such a way that this layer can be used as a probe to determine the EM field distribution inside a nanostructure.Therefore, optimizing the EM field distribution within the structure by maximizing it in the MO regions while simultaneously minimizing it in all the other, non MO active, lossy components, will allow for the development of novel systems with larger MO activity and reduced optical absorption, becoming an alternative to state of the art dielectric MO materials, like garnets. Here we will present our approach to face this problem, based on the insertion of a dielectric layer in Au/Co/Au magnetoplasmonic nanodisks. The resulting nanostructure consists of two metallic nanodisks coupled through the dielectric layer, with one of the nanodisk being purely Au and the other one Au/Co (see Figure 1(a)). This kind of systems presents two hybridized localized plasmon resonance modes, showing two peaks in both the extinction and the MO spectra (see Figure 1(b)). Moreover, the EM field inside the nanostructure is strongly redistributed, being strongly concentrated in the nanodisk composed only of pure noble metal (Figure 1(c)). By optimizing the internal architecture (position of the Co layer), a configuration where the system exhibits large MO activity and low optical extinction in the same wavelength range can be obtained, as it can be seen in the right side of Figure 1(b) for the high wavelength peak.Peer Reviewe