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Papers by diego martinez

Research paper thumbnail of Mechanical properties of TiC/a-C(:H) nanocomposite coatings

Nanocomposite structures formed by a hard phase embedded in a soft lubricious matrix exhibit a co... more Nanocomposite structures formed by a hard phase embedded in a soft lubricious matrix exhibit a combination of properties that make them very attractive for protective purposes. Among others, they show fracture toughness, high hardness, low coefficient of friction and high wear resistance. However, while their tribological performance can be explained in terms of phase ratio and surface interactions, their behavior under stress is still not well understood. For instance, coatings with similar chemical compositions may show very different mechanical properties depending on the preparation conditions. The reason for that is the complexity of the deformation process itself and the high number of sample characteristics that influence the final result (grain size, porosity, growth type, etc.). The aim of this work is to explore the mechanical behavior of nanocomposite structures. In order to do that, TiC/a-C(:H) has been selected as a model due to its relative chemical simplicity, ease of...

Research paper thumbnail of Metal carbide/amorphous C-based nanocomposite coatings for tribological applications

Surface and Coatings Technology, 2009

This paper tries to assess the factors governing the tribological behaviour of different nanocomp... more This paper tries to assess the factors governing the tribological behaviour of different nanocomposites films composed by metallic carbides (MeC) mixed with amorphous carbon (a-C). Different series of MeC/a-C coatings (with Me: Ti(B) and W) were prepared by magnetron sputtering technique varying the power applied to the graphite target in order to tailor the carbon content into the films. A deep investigation of the chemical and structural features at the nano-scale is carried out by X-ray diffraction (XRD), X-ray photoelectron spectroscopy (XPS), electron energy-loss spectroscopy (EELS) and Raman spectroscopy techniques in order to establish correlations with the tribological properties measured by a pin-on-disk tribometer in ambient air. The analysis of the counterfaces by Raman confocal microscopy after the friction tests is used to follow the chemical phenomena occurring at the contact area responsible of the observed friction behaviour. The importance of determining the nanocrystalline/amorphous ratio is highlighted as a key-parameter to control the tribological properties. A comparative analysis of the mechanical and tribological performance of the three systems (TiC/a-C, WC/a-C, TiBC/a-C) is done and conclusions are obtained concerning the friction and wear mechanism involved.

Research paper thumbnail of Anti-adhesion and antibacterial activity of silver nanoparticles supported on graphene oxide sheets

Colloids and Surfaces B: Biointerfaces, 2014

This work reports the preparation, characterization and evaluation of antibacterial activity of n... more This work reports the preparation, characterization and evaluation of antibacterial activity of nanocomposite formed by graphene oxide (GO) sheets decorated with silver nanoparticles (GO-Ag). The GO-Ag nanocomposite was prepared in the presence of AgNO 3 and sodium citrate. The physicochemical characterization was performed by UV-Vis spectroscopy, X-ray diffraction (XRD), thermogravimetric analysis (TGA), Raman spectroscopy and transmission electron microscopy (TEM) techniques. Silver nanoparticles anchored on GO surface presented an average size of 7.5 nm and oxidation debris fragments (a byproduct adsorbed on GO surface) were found to be a crucial entity for nucleation and growth of silver nanoparticles in these nanocomposites. The antibacterial activity of GO and GO-Ag nanocomposite was investigated against the microorganism Pseudomonas aeruginosa by using the standard counting plate methodology. The GO dispersion showed no antibacterial activity against P. aeruginosa strain for the overall concentration range investigated here. In other hand, GO-Ag composites presented high biocide property with minimum inhibitory concentration ranging from 2.5 to 5.0 µg/mL. The anti-biofilm property was also investigated toward adhered cells of P. aeruginosa in stainless steel surfaces. The results showed an inhibition rate of 100% of the adhered cells after one hour of their exposition to GO-Ag nanocomposite. To the best of our knowledge, this work provides the first direct evidence that GO-Ag nanocomposite can inhibit the growth of microbial adhered cells, thus preventing the process of biofilm formation. This promising results support the idea that GO-Ag nanocomposite may be applied as an antibacterial coating material in order to prevent the development of biofilms in food packing and medical devices.

Research paper thumbnail of Determination of the thickness of the embedding phase in 0D nanocomposites

Applied Surface Science, 2017

0D nanocomposites formed by small nanoparticles embedded in a second phase are very interesting s... more 0D nanocomposites formed by small nanoparticles embedded in a second phase are very interesting systems which may show properties that are beyond the ones observed in the original constituents alone. One of the main parameters to understand the behavior of such nanocomposites is the determination of the separation between two adjacent nanoparticles, in other words, the thickness of the embedding phase. However, its experimental measurement is extremely complicated. Therefore, its evaluation is performed by an indirect approach using geometrical models. The ones typically used represent the nanoparticles by cubes or spheres. In this paper the used geometrical models are revised, and additional geometrical models based in other parallelohedra (hexagonal prism, rhombic and elongated dodecahedron and truncated octahedron) are presented. Additionally, a hybrid model that shows a transition between the spherical and tessellated models is proposed. Finally, the different approaches are tested on a set of titanium carbide/amorphous carbon (TiC/a-C) nanocomposite films to estimate the thickness of the a-C phase and explain the observed hardness properties.

Research paper thumbnail of Mechanical properties of TiC/a-C(:H) nanocomposite coatings

Nanocomposite structures formed by a hard phase embedded in a soft lubricious matrix exhibit a co... more Nanocomposite structures formed by a hard phase embedded in a soft lubricious matrix exhibit a combination of properties that make them very attractive for protective purposes. Among others, they show fracture toughness, high hardness, low coefficient of friction and high wear resistance. However, while their tribological performance can be explained in terms of phase ratio and surface interactions, their behavior under stress is still not well understood. For instance, coatings with similar chemical compositions may show very different mechanical properties depending on the preparation conditions. The reason for that is the complexity of the deformation process itself and the high number of sample characteristics that influence the final result (grain size, porosity, growth type, etc.). The aim of this work is to explore the mechanical behavior of nanocomposite structures. In order to do that, TiC/a-C(:H) has been selected as a model due to its relative chemical simplicity, ease of...

Research paper thumbnail of Metal carbide/amorphous C-based nanocomposite coatings for tribological applications

Surface and Coatings Technology, 2009

This paper tries to assess the factors governing the tribological behaviour of different nanocomp... more This paper tries to assess the factors governing the tribological behaviour of different nanocomposites films composed by metallic carbides (MeC) mixed with amorphous carbon (a-C). Different series of MeC/a-C coatings (with Me: Ti(B) and W) were prepared by magnetron sputtering technique varying the power applied to the graphite target in order to tailor the carbon content into the films. A deep investigation of the chemical and structural features at the nano-scale is carried out by X-ray diffraction (XRD), X-ray photoelectron spectroscopy (XPS), electron energy-loss spectroscopy (EELS) and Raman spectroscopy techniques in order to establish correlations with the tribological properties measured by a pin-on-disk tribometer in ambient air. The analysis of the counterfaces by Raman confocal microscopy after the friction tests is used to follow the chemical phenomena occurring at the contact area responsible of the observed friction behaviour. The importance of determining the nanocrystalline/amorphous ratio is highlighted as a key-parameter to control the tribological properties. A comparative analysis of the mechanical and tribological performance of the three systems (TiC/a-C, WC/a-C, TiBC/a-C) is done and conclusions are obtained concerning the friction and wear mechanism involved.

Research paper thumbnail of Anti-adhesion and antibacterial activity of silver nanoparticles supported on graphene oxide sheets

Colloids and Surfaces B: Biointerfaces, 2014

This work reports the preparation, characterization and evaluation of antibacterial activity of n... more This work reports the preparation, characterization and evaluation of antibacterial activity of nanocomposite formed by graphene oxide (GO) sheets decorated with silver nanoparticles (GO-Ag). The GO-Ag nanocomposite was prepared in the presence of AgNO 3 and sodium citrate. The physicochemical characterization was performed by UV-Vis spectroscopy, X-ray diffraction (XRD), thermogravimetric analysis (TGA), Raman spectroscopy and transmission electron microscopy (TEM) techniques. Silver nanoparticles anchored on GO surface presented an average size of 7.5 nm and oxidation debris fragments (a byproduct adsorbed on GO surface) were found to be a crucial entity for nucleation and growth of silver nanoparticles in these nanocomposites. The antibacterial activity of GO and GO-Ag nanocomposite was investigated against the microorganism Pseudomonas aeruginosa by using the standard counting plate methodology. The GO dispersion showed no antibacterial activity against P. aeruginosa strain for the overall concentration range investigated here. In other hand, GO-Ag composites presented high biocide property with minimum inhibitory concentration ranging from 2.5 to 5.0 µg/mL. The anti-biofilm property was also investigated toward adhered cells of P. aeruginosa in stainless steel surfaces. The results showed an inhibition rate of 100% of the adhered cells after one hour of their exposition to GO-Ag nanocomposite. To the best of our knowledge, this work provides the first direct evidence that GO-Ag nanocomposite can inhibit the growth of microbial adhered cells, thus preventing the process of biofilm formation. This promising results support the idea that GO-Ag nanocomposite may be applied as an antibacterial coating material in order to prevent the development of biofilms in food packing and medical devices.

Research paper thumbnail of Determination of the thickness of the embedding phase in 0D nanocomposites

Applied Surface Science, 2017

0D nanocomposites formed by small nanoparticles embedded in a second phase are very interesting s... more 0D nanocomposites formed by small nanoparticles embedded in a second phase are very interesting systems which may show properties that are beyond the ones observed in the original constituents alone. One of the main parameters to understand the behavior of such nanocomposites is the determination of the separation between two adjacent nanoparticles, in other words, the thickness of the embedding phase. However, its experimental measurement is extremely complicated. Therefore, its evaluation is performed by an indirect approach using geometrical models. The ones typically used represent the nanoparticles by cubes or spheres. In this paper the used geometrical models are revised, and additional geometrical models based in other parallelohedra (hexagonal prism, rhombic and elongated dodecahedron and truncated octahedron) are presented. Additionally, a hybrid model that shows a transition between the spherical and tessellated models is proposed. Finally, the different approaches are tested on a set of titanium carbide/amorphous carbon (TiC/a-C) nanocomposite films to estimate the thickness of the a-C phase and explain the observed hardness properties.