Lidia Martínez - Academia.edu (original) (raw)
Papers by Lidia Martínez
The study of the magnetic properties of Co nanoparticles (with an average diameter of 10.3 nm) gr... more The study of the magnetic properties of Co nanoparticles (with an average diameter of 10.3 nm) grown using a gas-phase aggregation source and embedded in Au and V matrices is presented. We investigate how the matrix, the number of embedded nanoparticles (counted by coverage percentage), the interparticle interactions and the complex nanoparticles/matrix interface structure define the magnetic properties of the studied systems. A threshold coverage of 3.5% of a monolayer was found in both studied systems: below this coverage, nanoparticles behave as an assembly of independent single-domain magnetic entities with uniaxial anisotropy. Above the threshold it is found that the magnetic behavior of the systems is more matrix dependent. While magnetic relaxation and Henkel plots measurements stress the importance of the dipolar interactions and the formation of coherent clusters in the case of the Au matrix, the magnetic behavior of cobalt clusters embedded in the vanadium matrix is explained through the formation of a spin glass-like state at the V–Co interface that screens the magnetic interactions between NPs.
In this work, three rubber-like materials (NBR 7201, NBR 9003 and HNBR 8001) with applications in... more In this work, three rubber-like materials (NBR 7201, NBR 9003 and HNBR 8001) with applications in the automotive industry were studied. Different atmospheric pressure plasma treatments were used to modify the surface properties of these materials in order to improve their tribological behaviour. Surface analyses of the samples by means of X-ray photoelectron spectroscopy (XPS) were performed in order to get information about the surface chemistry and the elemental composition of the contact surfaces. In addition, wetting experiments were also carried out by measuring the contact angle of water drops on the surfaces using the sessile drop method. The XPS results showed a modification of the surface composition in both NBR rubbers, mainly due to an increase in the oxygen content, while the same treatments produced only slight modifications on the surface composition of the HNBR. The combination of N 2 and CH 3 COOH during the plasma operation produced the strongest modifications of the surface composition of the tested elastomers. All these surface modifications also produced a change in the wetting of the rubber-like materials. The results revealed that the plasma treatments modified the hydrophobicity of the rubber-like NBRs. r
Materials Research Express, 2014
We report a study of the morphological, chemical, structural and magnetic properties of FeB nanop... more We report a study of the morphological, chemical, structural and magnetic properties of FeB nanoparticles (NPs) grown using an ion cluster source. A large size distribution of NPs with the mean size of dominant population around 10-14 nm is obtained. The structural characterization confirms the spherical shape and the amorphous nature of the FeB NPs. The evolution of the chemical composition of the NPs in depth is analyzed by means of x-ray photoelectron spectroscopy. A mixture of Fe and B oxides and oxynitrides surrounds a core where metallic Fe is present. According to the magnetic measurements, this core size is close to 3 nm. The majority of NPs are superparamagnetic at room temperature and the blocking temperature was found to be 17.5 K. The outer shell thickness of more than 7 nm formed by oxides and oxynitrides inhibits the magnetic interaction between NPs resulting in an almost negligible coalescence, making these NPs suitable to be used in biomedical applications.
The Journal of Physical Chemistry C, 2013
The thermal-induced diffusion at nanoscale is investigated through the detailed study of the stru... more The thermal-induced diffusion at nanoscale is investigated through the detailed study of the structural and magnetic properties of Co@Au nanoparticles as a function of the deposition temperature. Nanoparticles of 10 nm were fabricated using an ion cluster source from a Co 95 Au 5 target. While lowtemperature deposition leads to the formation of an alloyed fcc CoAu core with an incomplete cobalt oxide shell, higher deposition temperature induces the formation of a pure hcp Co core with an intermediate Au shell and a compact outer cobalt oxide shell. The evolution of the magnetic properties of the nanoparticles is presented and discussed in light of the structural changes of the nanoparticles upon deposition temperature and nanoparticle density. It is found that thermal-induced diffusion can be successfully used to tune the structural and magnetic properties at the nanoscale in CoAu nanoparticles.
Review of Scientific Instruments, 2011
One of the factors that limit the spatial resolution in atomic force microscopy (AFM) is the phys... more One of the factors that limit the spatial resolution in atomic force microscopy (AFM) is the physical size of the probe. This limitation is particularly severe when the imaged structures are comparable in size to the tip's apex. The resolution in the AFM is usually enhanced by using sharp tips with high aspect ratios. In the present paper we propose an approach to modify AFM tips that consists of depositing nanoclusters on standard silicon tips. We show that the use of those tips leads to atomic force microscopy images of higher aspect ratios and spatial resolution. The present approach has two major properties. It provides higher aspect-ratio images of nanoscale objects and, at the same time, enables to functionalize the AFM tips by depositing nanoparticles with well-controlled chemical composition. to 161.111.235.130. Redistribution subject to AIP license or copyright; see http://rsi.aip.org/about/rights_and_permissions Martínez et al. Rev. Sci. Instrum. 82, 023710 (2011)
Physical Review B, 2008
Magnetic and magneto-optical properties of Co films are studied as a function of the morphology a... more Magnetic and magneto-optical properties of Co films are studied as a function of the morphology and the capping layer. We show that the nanoparticulate structure of the Co films has a clear influence on the magnetic and magneto-optical properties of the system. Kerr measurements combined with x-ray magnetic circular dichroism provide evidence of a strong correlation between the collective magnetic behavior of the system and the individual atomic magnetic response. The influence of the magnetic nature of the capping layer ͑Al, Au, and Pt͒ is also analyzed. Polarized capping layers, such as Pt, magnetically couple the nanostructures and not only increase the effective anisotropy of the system but also enhance the atomic magnetic moment of Co and the global magneto-optical activity.
Physical Chemistry Chemical Physics, 2013
The study of the magnetic properties of Co nanoparticles (with an average diameter of 10.3 nm) gr... more The study of the magnetic properties of Co nanoparticles (with an average diameter of 10.3 nm) grown using a gas-phase aggregation source and embedded in Au and V matrices is presented. We investigate how the matrix, the number of embedded nanoparticles (counted by coverage percentage), the interparticle interactions and the complex nanoparticles/matrix interface structure define the magnetic properties of the studied systems. A threshold coverage of 3.5% of a monolayer was found in both studied systems: below this coverage, nanoparticles behave as an assembly of independent singledomain magnetic entities with uniaxial anisotropy. Above the threshold it is found that the magnetic behavior of the systems is more matrix dependent. While magnetic relaxation and Henkel plots measurements stress the importance of the dipolar interactions and the formation of coherent clusters in the case of the Au matrix, the magnetic behavior of cobalt clusters embedded in the vanadium matrix is explained through the formation of a spin glass-like state at the V-Co interface that screens the magnetic interactions between NPs.
Physical Chemistry Chemical Physics, 2010
We investigate the Au-S binding properties of thiol and disulfide-modified DNA on polycrystalline... more We investigate the Au-S binding properties of thiol and disulfide-modified DNA on polycrystalline gold by means of X-ray photoelectron spectroscopy in conditions close to dynamic processes of biosensors. The dependence of the immobilisation period on the quality and density of the self-assembly process of thiol (SH-(CH 2 ) 6 -DNA), disulfide (DNA-CH 2 ) 6 -SS-(CH 2 ) 6 -DNA and DMTO-SS-(CH 2 ) 6 -DNA) sulfur-modified oligonucleotide solutions (1 mM) that are employed for bioreceptor immobilisation is analysed. Two electronic components are found in the analysis of the S 2p core levels. One of them is clearly associated to thiolate formation, while the other can be associated to different origins. In order to identify the origin of this last component, a quantification of the non-specifically adsorbed species has been performed by rinsing the self-assembled monolayers (SAMs) with a mercapto hexanol (MCH) solution. It has been found that non-specifically adsorbed species contribute only partially to the appearance of this sulfur peak component in SAMs formed from disulfides. Electron bombardment was performed to study the evolution of this component as a consequence of surface degradation due to radiation effects. The results are also correlated with the possible presence of disulfides. We found that MCH is not stable during the measurements. The evolution of this compound and the possible causes for this behaviour are discussed.
Langmuir, 2012
We present a bottom-up fabrication route based on the sputtering gas aggregation source that allo... more We present a bottom-up fabrication route based on the sputtering gas aggregation source that allows the generation of nanoparticles with controllable and tunable chemical composition while keeping the control of the cluster size. We demonstrate that the chemical composition of the particles can be monitored by the individual adjustment of the working parameters of the magnetrons inserted in a gas aggregation zone. Such control of the parameters leads to a fine control of the ion density of each target material and hence to the control of the chemical composition of the nanoparticles. In particular, we show through X-ray photoemission, atomic force microscopy, and high-resolution transmission electron microscopy that it is possible to generate bimetallic (AgAu) and trimetallic (AgAuPd) alloy nanoparticles with welldefined and tunable stoichiometries from three targets of pure Ag, Au, and Pd. The proposed route for the generation of nanoparticles opens new possibilities for the fabrication of nanoparticles using a physical method that, for some applications, could be complementary to the chemical methods.
Journal of Nanoparticle Research, 2011
The optical and magneto-optical properties of hybrid Co-SiO x systems are studied as a function o... more The optical and magneto-optical properties of hybrid Co-SiO x systems are studied as a function of Co concentration. The structures were prepared by alternate depositions of SiO x thin films and layers of 10-nm-diameter Co nanoparticles produced by an Ion Cluster Source. Both optical and magneto-optical constants of the system gradually increase with the amount of Co, though maintaining low optical absorption values in the visible range. The experimental results are well reproduced assuming that the nanoparticles have a cobalt core (7-8 nm in diameter) surrounded by a cobalt oxide shell (1-2 nm thick). The magneto-optical activity versus optical absorption figure of merit of this system is compared with other magneto-optical dielectric systems.
Journal of Alloys and Compounds, 2009
We present a morphological, structural, and magnetic characterization of Co nanoparticles (mean d... more We present a morphological, structural, and magnetic characterization of Co nanoparticles (mean diameter of 10.3 ± 1.8 nm) grown using a gas aggregation source and embedded in a silicon oxide matrix by sequential deposition of nanoparticles and silicon oxide. We show that the Co nanoparticles ''soft-land'' on the substrates and suffer a moderate oxidation in contact with the silicon oxide. Despite this moderate oxidation, it is found that, at room temperature, the magnetic volume of the resulting nanoparticles is below the superparamagnetic limit. The results presented in this article are compatible with the presence of an assembly of magnetically independent particles that also display a moderate exchange bias at low temperature.
European Biophysics Journal, 2010
A detailed study of the immobilization of three differently sulfur-modified DNA receptors for bio... more A detailed study of the immobilization of three differently sulfur-modified DNA receptors for biosensing applications is presented. The three receptors are DNA-(CH)n-SH-, DNA-(CH)n-SS-(CH)n-DNA, and DNA-(CH)n-SS-DMTO. Nanomechanical and surface plasmon resonance biosensors and fluorescence and radiolabelling techniques were used for the experimental evaluation. The results highlight the critical role of sulfur linker type in DNA self-assembly, affecting the kinetic adsorption and spatial distribution of DNA chains within the monolayer and the extent of chemisorption and physisorption. A spacer (mercaptohexanol, MCH) is used to evaluate the relative efficiencies of chemisorption of the three receptors by analysing the extent to which MCH can remove physisorbed molecules from each type of monolayer. It is demonstrated that -SH derivatization is the most suitable for biosensing purposes as it results in densely packed monolayers with the lowest ratio of physisorbed probes.
CrystEngComm, 2011
ABSTRACT The extended use of self-assembling approaches for the generation of oxidenanostructures... more ABSTRACT The extended use of self-assembling approaches for the generation of oxidenanostructures with engineered functional properties firstly relies on the ability to control their growth processes. In this paper, we focus on the growth of Ce1−xGdxO2−y (CGO) nanoislands on ABO3 substrates (i.e. LaAlO3 (LAO)) as a model system to investigate the nucleation and kinetic evolution of epitaxial nanostructures grown by high-throughput ex situ methods based on chemical solution deposition. Fine-tuning of growth conditions enables us to select the crystallographic orientation of CGO leading to two systems with different equilibrium shapes and kinetics. Self-assembled (001)CGO‖(001)LAOnanostructures grow with stable uniform square-based nanopyramid shape, whereas the nucleation of (011)CGO‖(001)LAO leads to highly elongated nanowires with enhanced diffusive mobility. At high temperatures, shape selection is merely achieved through a modified growth atmosphere (oxidizing or reducing). However, a temperature-induced nucleation orientation crossover occurs under the reducing growth atmosphere, allowing the tuning of a nanodot-to-nanowire ratio through kinetic control. We prove by XPS that an enhanced concentration of oxygen vacancies in the nanowires is linked to their ultrafast coarsening. The nucleation processes are scrutinized through thermodynamic analysis, and it is concluded that the supersaturation degree controls the nanoislands' orientation.
Applied Surface Science, 2010
Fluorination plasma treatments at atmospheric pressure were used to modify the surface compositio... more Fluorination plasma treatments at atmospheric pressure were used to modify the surface composition of EPDM elastomer. In this study, two different precursors (CF 4 and SF 6 ) and two carrier gases (He and Ar) were used for the surface modification of EPDM elastomer. The surface modifications were studied by means of X-ray photoelectron spectroscopy. We have observed a strong influence of the gas selection on the extent of the surface modification induced with these treatments. In general terms, the use of CF 4 generates a higher concentration of fluorine in the elastomer surface. On the other hand, the use of He as carrier gas also increases the effectiveness of the modification process. The fluorine uptake varies between 2 and 13%, although the formation of fluorine-containing functional groups was detected when the amount of fluorine on the surface exceeded 7%. After all treatments, an important oxygen uptake was observed, with amounts three or four times higher than the untreated elastomer.
![Research paper thumbnail of X-ray absorption and magnetic circular dichroism characterization of a novel ferromagnetic MnN[sub x] phase in Mn/Si[sub 3]N[sub 4] multilayers](https://attachments.academia-assets.com/43352509/thumbnails/1.jpg)
](Applied Physics Letters, 2008
Ferromagnetism above room temperature has been observed in Mn/ Si 3 N 4 multilayered films for th... more Ferromagnetism above room temperature has been observed in Mn/ Si 3 N 4 multilayered films for the first time. Characterization of the structural and electronic properties was performed to study the ferromagnetic behavior of this system. X-ray absorption spectroscopy at the Mn K and L edges, as well as x-ray magnetic circular dichroism, evidences the presence of divalent Mn in the films. X-ray absorption near edge structure measurements, which are compared to calculations, confirms the presence of a slightly distorted Mn 3 N 2 phase that is proposed to be the origin of the ferromagnetism in this system.
Nitrile-butyl rubber-like materials were coated with amorphous hydrogenated diamond-like carbon (... more Nitrile-butyl rubber-like materials were coated with amorphous hydrogenated diamond-like carbon (DLC) coatings in order to modify their surface and tribological properties. Measurements of water contact angle were performed by the sessile drop method and showed that the coated samples are more hydrophobic with water contact angles up to 116°. The surface free energy of the elastomers was calculated by the acid–base regression method considering polar and dispersive contributions and the results were correlated with changes in the surface chemistry measured by X-ray photoelectron spectroscopy. It has been found that the lower presence of oxygen functional groups on the elastomer surfaces led to lower surface free energies, even though the polar contribution was not predominant. We also found that the DLC coatings led to a significant decrease of the surface free energy (up to 16%) and that there is a good correlation between the surface free energy values and the corresponding water contact angle values. The coefficient of friction was also measured and presented a significant decrease after coating with DLC.
The study of the magnetic properties of Co nanoparticles (with an average diameter of 10.3 nm) gr... more The study of the magnetic properties of Co nanoparticles (with an average diameter of 10.3 nm) grown using a gas-phase aggregation source and embedded in Au and V matrices is presented. We investigate how the matrix, the number of embedded nanoparticles (counted by coverage percentage), the interparticle interactions and the complex nanoparticles/matrix interface structure define the magnetic properties of the studied systems. A threshold coverage of 3.5% of a monolayer was found in both studied systems: below this coverage, nanoparticles behave as an assembly of independent single-domain magnetic entities with uniaxial anisotropy. Above the threshold it is found that the magnetic behavior of the systems is more matrix dependent. While magnetic relaxation and Henkel plots measurements stress the importance of the dipolar interactions and the formation of coherent clusters in the case of the Au matrix, the magnetic behavior of cobalt clusters embedded in the vanadium matrix is explained through the formation of a spin glass-like state at the V–Co interface that screens the magnetic interactions between NPs.
In this work, three rubber-like materials (NBR 7201, NBR 9003 and HNBR 8001) with applications in... more In this work, three rubber-like materials (NBR 7201, NBR 9003 and HNBR 8001) with applications in the automotive industry were studied. Different atmospheric pressure plasma treatments were used to modify the surface properties of these materials in order to improve their tribological behaviour. Surface analyses of the samples by means of X-ray photoelectron spectroscopy (XPS) were performed in order to get information about the surface chemistry and the elemental composition of the contact surfaces. In addition, wetting experiments were also carried out by measuring the contact angle of water drops on the surfaces using the sessile drop method. The XPS results showed a modification of the surface composition in both NBR rubbers, mainly due to an increase in the oxygen content, while the same treatments produced only slight modifications on the surface composition of the HNBR. The combination of N 2 and CH 3 COOH during the plasma operation produced the strongest modifications of the surface composition of the tested elastomers. All these surface modifications also produced a change in the wetting of the rubber-like materials. The results revealed that the plasma treatments modified the hydrophobicity of the rubber-like NBRs. r
Materials Research Express, 2014
We report a study of the morphological, chemical, structural and magnetic properties of FeB nanop... more We report a study of the morphological, chemical, structural and magnetic properties of FeB nanoparticles (NPs) grown using an ion cluster source. A large size distribution of NPs with the mean size of dominant population around 10-14 nm is obtained. The structural characterization confirms the spherical shape and the amorphous nature of the FeB NPs. The evolution of the chemical composition of the NPs in depth is analyzed by means of x-ray photoelectron spectroscopy. A mixture of Fe and B oxides and oxynitrides surrounds a core where metallic Fe is present. According to the magnetic measurements, this core size is close to 3 nm. The majority of NPs are superparamagnetic at room temperature and the blocking temperature was found to be 17.5 K. The outer shell thickness of more than 7 nm formed by oxides and oxynitrides inhibits the magnetic interaction between NPs resulting in an almost negligible coalescence, making these NPs suitable to be used in biomedical applications.
The Journal of Physical Chemistry C, 2013
The thermal-induced diffusion at nanoscale is investigated through the detailed study of the stru... more The thermal-induced diffusion at nanoscale is investigated through the detailed study of the structural and magnetic properties of Co@Au nanoparticles as a function of the deposition temperature. Nanoparticles of 10 nm were fabricated using an ion cluster source from a Co 95 Au 5 target. While lowtemperature deposition leads to the formation of an alloyed fcc CoAu core with an incomplete cobalt oxide shell, higher deposition temperature induces the formation of a pure hcp Co core with an intermediate Au shell and a compact outer cobalt oxide shell. The evolution of the magnetic properties of the nanoparticles is presented and discussed in light of the structural changes of the nanoparticles upon deposition temperature and nanoparticle density. It is found that thermal-induced diffusion can be successfully used to tune the structural and magnetic properties at the nanoscale in CoAu nanoparticles.
Review of Scientific Instruments, 2011
One of the factors that limit the spatial resolution in atomic force microscopy (AFM) is the phys... more One of the factors that limit the spatial resolution in atomic force microscopy (AFM) is the physical size of the probe. This limitation is particularly severe when the imaged structures are comparable in size to the tip's apex. The resolution in the AFM is usually enhanced by using sharp tips with high aspect ratios. In the present paper we propose an approach to modify AFM tips that consists of depositing nanoclusters on standard silicon tips. We show that the use of those tips leads to atomic force microscopy images of higher aspect ratios and spatial resolution. The present approach has two major properties. It provides higher aspect-ratio images of nanoscale objects and, at the same time, enables to functionalize the AFM tips by depositing nanoparticles with well-controlled chemical composition. to 161.111.235.130. Redistribution subject to AIP license or copyright; see http://rsi.aip.org/about/rights_and_permissions Martínez et al. Rev. Sci. Instrum. 82, 023710 (2011)
Physical Review B, 2008
Magnetic and magneto-optical properties of Co films are studied as a function of the morphology a... more Magnetic and magneto-optical properties of Co films are studied as a function of the morphology and the capping layer. We show that the nanoparticulate structure of the Co films has a clear influence on the magnetic and magneto-optical properties of the system. Kerr measurements combined with x-ray magnetic circular dichroism provide evidence of a strong correlation between the collective magnetic behavior of the system and the individual atomic magnetic response. The influence of the magnetic nature of the capping layer ͑Al, Au, and Pt͒ is also analyzed. Polarized capping layers, such as Pt, magnetically couple the nanostructures and not only increase the effective anisotropy of the system but also enhance the atomic magnetic moment of Co and the global magneto-optical activity.
Physical Chemistry Chemical Physics, 2013
The study of the magnetic properties of Co nanoparticles (with an average diameter of 10.3 nm) gr... more The study of the magnetic properties of Co nanoparticles (with an average diameter of 10.3 nm) grown using a gas-phase aggregation source and embedded in Au and V matrices is presented. We investigate how the matrix, the number of embedded nanoparticles (counted by coverage percentage), the interparticle interactions and the complex nanoparticles/matrix interface structure define the magnetic properties of the studied systems. A threshold coverage of 3.5% of a monolayer was found in both studied systems: below this coverage, nanoparticles behave as an assembly of independent singledomain magnetic entities with uniaxial anisotropy. Above the threshold it is found that the magnetic behavior of the systems is more matrix dependent. While magnetic relaxation and Henkel plots measurements stress the importance of the dipolar interactions and the formation of coherent clusters in the case of the Au matrix, the magnetic behavior of cobalt clusters embedded in the vanadium matrix is explained through the formation of a spin glass-like state at the V-Co interface that screens the magnetic interactions between NPs.
Physical Chemistry Chemical Physics, 2010
We investigate the Au-S binding properties of thiol and disulfide-modified DNA on polycrystalline... more We investigate the Au-S binding properties of thiol and disulfide-modified DNA on polycrystalline gold by means of X-ray photoelectron spectroscopy in conditions close to dynamic processes of biosensors. The dependence of the immobilisation period on the quality and density of the self-assembly process of thiol (SH-(CH 2 ) 6 -DNA), disulfide (DNA-CH 2 ) 6 -SS-(CH 2 ) 6 -DNA and DMTO-SS-(CH 2 ) 6 -DNA) sulfur-modified oligonucleotide solutions (1 mM) that are employed for bioreceptor immobilisation is analysed. Two electronic components are found in the analysis of the S 2p core levels. One of them is clearly associated to thiolate formation, while the other can be associated to different origins. In order to identify the origin of this last component, a quantification of the non-specifically adsorbed species has been performed by rinsing the self-assembled monolayers (SAMs) with a mercapto hexanol (MCH) solution. It has been found that non-specifically adsorbed species contribute only partially to the appearance of this sulfur peak component in SAMs formed from disulfides. Electron bombardment was performed to study the evolution of this component as a consequence of surface degradation due to radiation effects. The results are also correlated with the possible presence of disulfides. We found that MCH is not stable during the measurements. The evolution of this compound and the possible causes for this behaviour are discussed.
Langmuir, 2012
We present a bottom-up fabrication route based on the sputtering gas aggregation source that allo... more We present a bottom-up fabrication route based on the sputtering gas aggregation source that allows the generation of nanoparticles with controllable and tunable chemical composition while keeping the control of the cluster size. We demonstrate that the chemical composition of the particles can be monitored by the individual adjustment of the working parameters of the magnetrons inserted in a gas aggregation zone. Such control of the parameters leads to a fine control of the ion density of each target material and hence to the control of the chemical composition of the nanoparticles. In particular, we show through X-ray photoemission, atomic force microscopy, and high-resolution transmission electron microscopy that it is possible to generate bimetallic (AgAu) and trimetallic (AgAuPd) alloy nanoparticles with welldefined and tunable stoichiometries from three targets of pure Ag, Au, and Pd. The proposed route for the generation of nanoparticles opens new possibilities for the fabrication of nanoparticles using a physical method that, for some applications, could be complementary to the chemical methods.
Journal of Nanoparticle Research, 2011
The optical and magneto-optical properties of hybrid Co-SiO x systems are studied as a function o... more The optical and magneto-optical properties of hybrid Co-SiO x systems are studied as a function of Co concentration. The structures were prepared by alternate depositions of SiO x thin films and layers of 10-nm-diameter Co nanoparticles produced by an Ion Cluster Source. Both optical and magneto-optical constants of the system gradually increase with the amount of Co, though maintaining low optical absorption values in the visible range. The experimental results are well reproduced assuming that the nanoparticles have a cobalt core (7-8 nm in diameter) surrounded by a cobalt oxide shell (1-2 nm thick). The magneto-optical activity versus optical absorption figure of merit of this system is compared with other magneto-optical dielectric systems.
Journal of Alloys and Compounds, 2009
We present a morphological, structural, and magnetic characterization of Co nanoparticles (mean d... more We present a morphological, structural, and magnetic characterization of Co nanoparticles (mean diameter of 10.3 ± 1.8 nm) grown using a gas aggregation source and embedded in a silicon oxide matrix by sequential deposition of nanoparticles and silicon oxide. We show that the Co nanoparticles ''soft-land'' on the substrates and suffer a moderate oxidation in contact with the silicon oxide. Despite this moderate oxidation, it is found that, at room temperature, the magnetic volume of the resulting nanoparticles is below the superparamagnetic limit. The results presented in this article are compatible with the presence of an assembly of magnetically independent particles that also display a moderate exchange bias at low temperature.
European Biophysics Journal, 2010
A detailed study of the immobilization of three differently sulfur-modified DNA receptors for bio... more A detailed study of the immobilization of three differently sulfur-modified DNA receptors for biosensing applications is presented. The three receptors are DNA-(CH)n-SH-, DNA-(CH)n-SS-(CH)n-DNA, and DNA-(CH)n-SS-DMTO. Nanomechanical and surface plasmon resonance biosensors and fluorescence and radiolabelling techniques were used for the experimental evaluation. The results highlight the critical role of sulfur linker type in DNA self-assembly, affecting the kinetic adsorption and spatial distribution of DNA chains within the monolayer and the extent of chemisorption and physisorption. A spacer (mercaptohexanol, MCH) is used to evaluate the relative efficiencies of chemisorption of the three receptors by analysing the extent to which MCH can remove physisorbed molecules from each type of monolayer. It is demonstrated that -SH derivatization is the most suitable for biosensing purposes as it results in densely packed monolayers with the lowest ratio of physisorbed probes.
CrystEngComm, 2011
ABSTRACT The extended use of self-assembling approaches for the generation of oxidenanostructures... more ABSTRACT The extended use of self-assembling approaches for the generation of oxidenanostructures with engineered functional properties firstly relies on the ability to control their growth processes. In this paper, we focus on the growth of Ce1−xGdxO2−y (CGO) nanoislands on ABO3 substrates (i.e. LaAlO3 (LAO)) as a model system to investigate the nucleation and kinetic evolution of epitaxial nanostructures grown by high-throughput ex situ methods based on chemical solution deposition. Fine-tuning of growth conditions enables us to select the crystallographic orientation of CGO leading to two systems with different equilibrium shapes and kinetics. Self-assembled (001)CGO‖(001)LAOnanostructures grow with stable uniform square-based nanopyramid shape, whereas the nucleation of (011)CGO‖(001)LAO leads to highly elongated nanowires with enhanced diffusive mobility. At high temperatures, shape selection is merely achieved through a modified growth atmosphere (oxidizing or reducing). However, a temperature-induced nucleation orientation crossover occurs under the reducing growth atmosphere, allowing the tuning of a nanodot-to-nanowire ratio through kinetic control. We prove by XPS that an enhanced concentration of oxygen vacancies in the nanowires is linked to their ultrafast coarsening. The nucleation processes are scrutinized through thermodynamic analysis, and it is concluded that the supersaturation degree controls the nanoislands' orientation.
Applied Surface Science, 2010
Fluorination plasma treatments at atmospheric pressure were used to modify the surface compositio... more Fluorination plasma treatments at atmospheric pressure were used to modify the surface composition of EPDM elastomer. In this study, two different precursors (CF 4 and SF 6 ) and two carrier gases (He and Ar) were used for the surface modification of EPDM elastomer. The surface modifications were studied by means of X-ray photoelectron spectroscopy. We have observed a strong influence of the gas selection on the extent of the surface modification induced with these treatments. In general terms, the use of CF 4 generates a higher concentration of fluorine in the elastomer surface. On the other hand, the use of He as carrier gas also increases the effectiveness of the modification process. The fluorine uptake varies between 2 and 13%, although the formation of fluorine-containing functional groups was detected when the amount of fluorine on the surface exceeded 7%. After all treatments, an important oxygen uptake was observed, with amounts three or four times higher than the untreated elastomer.
Applied Physics Letters, 2008
Ferromagnetism above room temperature has been observed in Mn/ Si 3 N 4 multilayered films for th... more Ferromagnetism above room temperature has been observed in Mn/ Si 3 N 4 multilayered films for the first time. Characterization of the structural and electronic properties was performed to study the ferromagnetic behavior of this system. X-ray absorption spectroscopy at the Mn K and L edges, as well as x-ray magnetic circular dichroism, evidences the presence of divalent Mn in the films. X-ray absorption near edge structure measurements, which are compared to calculations, confirms the presence of a slightly distorted Mn 3 N 2 phase that is proposed to be the origin of the ferromagnetism in this system.
Nitrile-butyl rubber-like materials were coated with amorphous hydrogenated diamond-like carbon (... more Nitrile-butyl rubber-like materials were coated with amorphous hydrogenated diamond-like carbon (DLC) coatings in order to modify their surface and tribological properties. Measurements of water contact angle were performed by the sessile drop method and showed that the coated samples are more hydrophobic with water contact angles up to 116°. The surface free energy of the elastomers was calculated by the acid–base regression method considering polar and dispersive contributions and the results were correlated with changes in the surface chemistry measured by X-ray photoelectron spectroscopy. It has been found that the lower presence of oxygen functional groups on the elastomer surfaces led to lower surface free energies, even though the polar contribution was not predominant. We also found that the DLC coatings led to a significant decrease of the surface free energy (up to 16%) and that there is a good correlation between the surface free energy values and the corresponding water contact angle values. The coefficient of friction was also measured and presented a significant decrease after coating with DLC.