16 research outputs found
Visible light assisted organosilane assembly on mesoporous silicon films and particles
Porous silicon (PSi) is a versatile matrix with tailorable surface reactivity, which allows the processing of a range of multifunctional films and particles. The biomedical applications of PSi often require a surface capping with organic functionalities. This work shows that visible light can be used to catalyze the assembly of organosilanes on the PSi, as demonstrated with two organosilanes: aminopropyl-triethoxy-silane and perfluorodecyl-triethoxy-silane. We studied the process related to PSi films (PSiFs), which were characterized by X-ray photoelectron spectroscopy (XPS), time of flight secondary ion mass spectroscopy (ToF-SIMS) and field emission scanning electron microscopy (FESEM) before and after a plasma patterning process. The analyses confirmed the surface oxidation and the anchorage of the organosilane backbone. We further highlighted the surface analytical potential of 13 C, 19 F and 29 Si solid-state NMR (SS-NMR) as compared to Fourier transformed infrared spectroscopy (FTIR) in the characterization of functionalized PSi particles (PSiPs). The reduced invasiveness of the organosilanization regarding the PSiPs morphology was confirmed using transmission electron microscopy (TEM) and FESEM. Relevantly, the results obtained on PSiPs complemented those obtained on PSiFs. SS-NMR suggests a number of siloxane bonds between the organosilane and the PSiPs, which does not reach levels of maximum heterogeneous condensation, while ToF-SIMS suggested a certain degree of organosilane polymerization. Additionally, differences among the carbons in the organic (non-hydrolyzable) functionalizing groups are identified, especially in the case of the perfluorodecyl group. The spectroscopic characterization was used to propose a mechanism for the visible light activation of the organosilane assembly, which is based on the initial photoactivated oxidation of the PSi matrixWe acknowledge MSC funding provided by the European Commission through FP7 grant
THINFACE (ITN GA 607232) and by Ministerio de EconomĂa y Competitividad through grant NANOPROST (RTC-2016-4776-1
Thermal route for the synthesis of maghemite/hematite core/shell nanowires
Nowadays, iron oxide-based nanostructures are key materials in many technological areas. Their physical and chemical properties can be tailored by tuning the morphology. In particular, the possibility of increasing the specific surface area has turned iron oxide nanowires (NWs) into promising functional materials in many applications. Among the different possible iron oxide NWs that can be fabricated, maghemite/hematite iron oxide core/shell structures have particular importance since they combine the magnetism of the inner maghemite core with the interesting properties of hematite in different technological fields ranging from green energy to biomedical applications. However, the study of these iron oxide structures is normally difficult due to the structural and chemical similarities between both iron oxide polymorphs. In this work, we propose a route for the synthesis of maghemite/hematite NWs based on the thermal oxidation of previously electrodeposited iron NWs. A detailed spectroscopic analysis based on Raman, Mossbauer, and X-ray absorption shows that the ratio of both oxides can be controlled during fabrication. Transmission electron microscopy has been used to check the core/shell structure of the NWs. The biocompatibility and capability of internalization of these NWs have also been proven to show the potential of these NWs in biomedical applications
Unveiling the different physical origins of magnetic anisotropy and magnetoelasticity in Ga-Rich FeGa thin films
The aim of this work is to clarify how in-plane magnetic anisotropy and magnetoelasticity depend on the thickness of Ga-rich FeGa layers. Samples with an Fe72Ga28 composition were grown by sputtering in the ballistic regime in oblique incidence. Although for these growth conditions uniaxial magnetic anisotropy could be expected, in-plane anisotropy is only present when the sample thickness is above 100 nm. By means of differential X-ray absorption spectroscopy, we have determined the influence of both Ga pairs and tetragonal cell distortion on the evolution of the magnetic anisotropy with the increase of FeGa thickness. On the other hand, we have used the cantilever beam technique with capacitive detection to also determine the evolution of the magnetoelastic parameters with the thickness increase. In this case, experimental results can be understood considering the grain distribution. Therefore, the different physical origins for anisotropy and magnetoelasticity open up the possibility to independently tune these two characteristics in Ga-rich FeGa films.This work has been financially supported through the projects MAT2015-66888-C3-3-R and MAT2015-66726-R (MINECO/FEDER) of the Spanish Ministry of Economy and Competitiveness, RTI2018-097895-B-C43 of the Spanish Ministry of Science, Innovation, and Universities, and Gobierno de AragĂłn (Grant E10-17D) and Fondo Social Europeo. A.M.-N. is thankful for the contract from Universidad Complutense and Comunidad de Madrid âAtracciĂłn de Talentoâ program 2018-T1/IND-10360, and A.B. thanks MINECO for the Ph.D. grant BES-2016-076482.Peer reviewe
Crystal defects and optical emissions of pulse electrodeposited ZnO
ZnO has been widely studied in the last decades as an n-type semiconductor due to its wide application range, for example, in optoelectronics, solar cells, light-emitting diodes, thermoelectrics, amongst others. The material efficiency for certain applications is highly dependent on the presenting film morphology. Electrodeposition is well-known as a technique with precise control over the structural and morphological properties of the obtained materials. When the structural and morphological properties are tuned, it is possible to find a wide variety of defects in the ZnO structure. In this study, ZnO films were grown using pulsed electrodeposition with variation of the reduction potential. The crystal order, structural defects and optical emissions of the films have been analyzed by X-Ray Diffraction (XRD), X-ray Absorption Near-Edge Structure (XANES), Extended X-ray Absorption Fine Structure (EXAFS) and Photoluminescence (PL). ZnO film grown at less negative reduction potential presents a stronger texture along [0001] by XRD, higher crystalline order, and more zinc vacancies by XANES and EXAFS. The films obtained at less negative potential present less OH trapped in the ZnO structure and a relatively higher level of defects O, O, O and O than those grown at higher reduction potentials by PL. This will be related to the fact that at less negative potentials there is less concentration of OH at the film surface than at more negative potentials. The combination of X-ray absorption spectroscopy and photoluminescence reveals the complicated nature of the atomic defect in electrodeposited ZnO films. Allowing to evidence the preferential presence of atomic defect as a function of the reduction potential. In this work, we have also compared those defects with reference compounds such as a Zn foil and ZnO polycrystalline powder.The authors would like to acknowledge financial support from MAT2017-86450-C4-1-R, MAT2017-86450-C4-3-R, and RTI2018-095303-A-C52. C.V.M acknowledges financial support from Juan de la Cierva IncorporaciĂłn grants IJCI-2017-31350. A.S. and A.M.N. acknowledge the financial support from the Comunidad de Madrid for an âAtracciĂłn de Talento Investigadorâ contract No. 2017-t2/IND5395 and 2018-T1/IND-10360, respectively. We acknowledge The European Synchrotron (ESRF), MICIU, and CSIC for provision of synchrotron radiation facilities in using the BM25-SpLine beamline. We also thank the BM25-SpLine staff for the technical support beyond their duties. We acknowledge the service from the MiNa Laboratory at IMN, and funding from CM (project SpaceTec, S2013/ICE2822), MINECO (project CSIC13-4E-1794) and EU (FEDER, FSE)
LittleâParks effect governed by magnetic nanostructures with out-of-plane magnetization
LittleâParks effect names the oscillations in the superconducting critical temperature as a function of the magnetic field. This effect is related to the geometry of the sample. In this work, we show that this effect can be enhanced and manipulated by the inclusion of magnetic nanostructures with perpendicular magnetization. These magnetic nanodots generate stray fields with enough strength to produce superconducting vortexâantivortex pairs. So that, the LâP effect deviation from the usual geometrical constrictions is due to the interplay between local magnetic stray fields and superconducting vortices. Moreover, we compare our results with a low-stray field sample (i.e. with the dots in magnetic vortex state) showing how the enhancement of the LâP effect can be explained by an increment of the effective size of the nanodots.With funding from the Spanish government through the "MarĂa de Maeztu Unit of Excellence" accreditation (MDM-2017-0737
Defect chemistry, electrical properties, and evaluation of new oxides Sr2CoNb1âxTixO6âÎŽ (0â€xâ€1) as cathode materials for solid oxide fuel cells
The perovskite series Sr2CoNb1âxTixO6âÎŽ (0â€xâ€1) was investigated in the full compositional range to assess its potential as cathode material for solid oxide fuel cell (SOFC). The variation of transport properties and thus, the area specific resistances (ASR) are explained by a detailed investigation of the defect chemistry. Increasing the titanium content from x=0â1 produces both oxidation of Co3+ to Co4+ (from 0 up to 40â%) and oxygen vacancies (from 6.0 to 5.7 oxygen atom/formula unit), although each charge compensation mechanism predominates in different compositional ranges. Neutron diffraction reveals that samples with high Tiâcontents lose a significant amount of oxygen upon heating above 600â
K. Oxygen is partially recovered upon cooling as the oxygen release and uptake show noticeably different kinetics. The complex defect chemistry of these compounds, together with the compositional changes upon heating/cooling cycles and atmospheres, produce a complicated behavior of electrical conductivity. Cathodes containing Sr2CoTiO6âÎŽ display low ASR values, 0,13â
Ωâcm2 at 973â
K, comparable to those of the best compounds reported so far, being a very promising cathode material for SOFC.We thank Ministerio de EconomĂa y Competitividad and Comunidad de Madrid for funding the projects MAT2013â46452âC4â1âR, MAT2013â46452âC4â4âR, and S2013/MITâ2753, respectively. Agencia Estatal de InvestigaciĂłn and Fondo Europeo de Desarrollo Regional are also acknowledged for financing the project MAT2016â78362âC4â1âR. We acknowledge CSIC, ILL and ESRF for financial support and facilitate the access to the BM25âSpLine line at ESRF and D1B diffractometer at ILL.Peer reviewe
Realization of macroscopic ratchet effect based on nonperiodic and uneven potentials
Ratchet devices allow turning an ac input signal into a dc output signal. A ratchet device is set by moving particles driven by zero averages forces on asymmetric potentials. Hybrid nanostructures combining artificially fabricated spin ice nanomagnet arrays with superconducting films have been identified as a good choice to develop ratchet nanodevices. In the current device, the asymmetric potentials are provided by charged NĂ©el walls located in the vertices of spin ice magnetic honeycomb array, whereas the role of moving particles is played by superconducting vortices. We have experimentally obtained ratchet effect for different spin ice I configurations and for vortex lattice moving parallel or perpendicular to magnetic easy axes. Remarkably, the ratchet magnitudes are similar in all the experimental runs; i. e. different spin ice I configurations and in both relevant directions of the vortex lattice motion. We have simulated the interplay between vortex motion directions and a single asymmetric potential. It turns out vortices interact with uneven asymmetric potentials, since they move with trajectories crossing charged NĂ©el walls with different orientations. Moreover, we have found out the asymmetric pair potentials which generate the local ratchet effect. In this rocking ratchet the particles (vortices) on the move are interacting each other (vortex lattice); therefore, the ratchet local effect turns into a global macroscopic effect. In summary, this ratchet device benefits from interacting particles moving in robust and topological protected type I spin ice landscapes.This work was supported by Spanish MICINN grants FIS2016-76058 (AEI/FEDER, UE), EU COST- CA16218. IMDEA Nanociencia acknowledges support from the âSevero Ochoaâ Programme for Centres of Excellence in R&D (MICINN, Grant SEV-2016-0686). MCO and AG acknowledges financial support from Spanish MICINN Grant ESP2017-86582-C4-1-R and IJCI-2017-33991; AMN acknowledges financial support from Spanish CAM Grant 2018-T1/IND-10360. MV acknowledges financial support from Spanish MICINN Grant PID2019-104604RB/AEI/10.13039/50110001103.Peer reviewe
Functionality of Porous Silicon Particles; Surface Modification for Biomedical Applications
Porous silicon based particles (PSp) with tailored physical and biological properties have recently attracted great attention given their biomedical potential. Within this context, the objective of the present work is to optimize the experimental parameters for the formation
of biofunctional mesoporous PSps. Their functionality has been studied on the one hand by analyzing the fluorescence characteristics, such as tunable narrow band emission and fluorescence aging for PSps with different molecular capping. With regard to the biofunctional characteristics, two different molecular end-capping processes have been assayed: antifouling polyethylene glycol (PEG) and polar binding amino silanes (APTS), which were evaluated by x-ray photoelectron spectroscopy. The finding that these PSpmolecule conjugates allow the reduction of fluorescence degradation with time in solution is of interest for the development of cellular or tissue markers. From the morphological point of view, PEG termination is of special interest allowing the PSps after an abrasion ultrasonic treatment to get spherical shapes in the micron scale. The functionality as solid state dyes is preliminarily evaluated by direct fluorescence imaging.JRC.I.4-Nanobioscience
Thermal route for the synthesis of maghemite/hematite core/shell nanowires
© Amer Chemical Soc.
This work was funded by Spanish MINECO under projects MAT2013-48009-C4-1-P, MAT2014- 52477-C5-2-P and MAT2015-64110-C2-1-P. We acknowledge the European Synchrotron Radiation Facility (ESRF), MINECO and CSIC for provision of synchrotron radiation facilites and the financial support for the beam line (PIE-2010-OE-013-200014). We would like to thank the BM25-SpLine staff for the technical support beyond their duties. We also acknowledge the use of the XRD facilities of the ISOM-UPM and thank A. Prados for her help during the XRD experiments. We also thank G. Pieplow for his help with the analysis using the FSD method. BelĂ©n CortĂ©s acknowledges MINECO (FPI program) for her pre-doctoral fellowship.Nowadays, iron oxide-based nanostructures are key materials in many technological areas. Their physical and chemical properties can be tailored by tuning the morphology. In particular, the possibility of increasing the specific surface area has turned iron oxide nanowires (NWs) into promising functional materials in many applications. Among the different possible iron oxide NWs that can be fabricated, maghemite/hematite iron oxide core/shell structures have particular importance since they combine the magnetism of the inner maghemite core with the interesting properties of hematite in different technological fields ranging from green energy to biomedical applications. However, the study of these iron oxide structures is normally difficult due to the structural and chemical similarities between both iron oxide polymorphs. In this work, we propose a route for the synthesis of maghemite/hematite NWs based on the thermal oxidation of previously electrodeposited iron NWs. A detailed spectroscopic analysis based on Raman, Mossbauer, and X-ray absorption shows that the ratio of both oxides can be controlled during fabrication. Transmission electron microscopy has been used to check the core/shell structure of the NWs. The biocompatibility and capability of internalization of these NWs have also been proven to show the potential of these NWs in biomedical applications.Ministerio de EconomĂa y Competitividad (MINECO)European Synchrotron Radiation Facility (ESRF)CSICDepto. de FĂsica de MaterialesFac. de Ciencias FĂsicasTRUEpu