Francisco Yubero - Academia.edu (original) (raw)

Papers by Francisco Yubero

ACS Photonics, 2018

This work presents a simple experimental procedure to probe light confinement effects in photonic... more This work presents a simple experimental procedure to probe light confinement effects in photonic structures. Two types of porous 1D Bragg microcavities with two resonant peaks in the absorption gap were prepared by physical vapor deposition at oblique angle configurations and then infiltrated with a dye solution of increasing concentrations. The unusual position shift and intensity drop of the transmitted resonant peak observed when it was scanned through the dye absorption band have been accounted for by the effect of the light trapped at their optical defect layer. An experimentally observed giant absorption of the dye molecules and a strong anomalous dispersion in the refractive index of the solution are claimed as the reasons for the observed variations in the Bragg microcavity resonant feature. Determining the giant absorption of infiltrated dye solutions is proposed as a general and simple methodology to experimentally assess light trapping effects in porous photonic structures.

ACS applied materials & interfaces, Jan 24, 2016

This paper presents a new method for the fabrication of metal-like decorative layers on glazed ce... more This paper presents a new method for the fabrication of metal-like decorative layers on glazed ceramic tiles. It consists of the laser treatment of copper thin films prepared by electron beam evaporation at glancing angles. A thin film of discontinuous copper nanoparticles was electron beam evaporated in an oblique angle configuration onto ceramic tiles and an ample palette of colors obtained by laser treatment both in air and in vacuum. Scanning electron microscopy (SEM and FESEM) along with UV-vis-NIR spectroscopy and time of flight secondary ion mass spectrometry (TOF-SIMS) analysis were used to characterize the differently colored layers. Based on these analyses, color development has been accounted for by a simple model considering surface melting phenomena and different microstructural and chemical transformations of the outmost surface layers of samples.

minas delgadas y su utilización. El objeto de la presente invención consiste en un dispositivo qu... more minas delgadas y su utilización. El objeto de la presente invención consiste en un dispositivo que puede emplearse para determinar las isotermas de adsorción/desorción y la porosidad en láminas delgadas, membranas soportadas y materiales nanoestructurados soportados de forma directa. Para ello, en primer lugar se determinan las isotermas de adsorción y desorción de la muestra a partir de las cuales se puede obtener el tipo de porosidad de ésta, el volumen de poros y la distribución de tamaño de poros aplicando conceptos de físico-química y termodinámica de superficie de sólidos. Aviso: Se puede realizar consulta prevista por el art. 37.3.8 LP.

Industrial Plasma Technology, 2010

... Boudam, MK, Saoudi, B., Moisan, M., and Ricard, A. (2007) J. Phys. D: Appl. Phys., 40, 1694. ... more ... Boudam, MK, Saoudi, B., Moisan, M., and Ricard, A. (2007) J. Phys. D: Appl. Phys., 40, 1694. 21. Dood, JA, Lipson, SJ, Flanagan, DJ, Blumberg, WAM, Person, JC, and Green, BO (1991) J. Chem. Phys., 94, 4301. 22. Qiu, X., Zhao, Y., and Burda, C. (2007) Adv. Mater., 19, 3995. ...

Plasma Processes and Polymers, 2014

Vacuum, 2002

The structure of SiOx materials and the chemical stability of Sin+ (n&amp;amp;amp;amp;amp... more The structure of SiOx materials and the chemical stability of Sin+ (n&amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;lt;4) species have been investigated experimentally by photoemission and X-ray absorption spectroscopy. SiOx thin films and interface systems formed by small amounts of SiOx deposited on different substrates (Cu(100), TiO2(110), Al) have been studied. Theoretical analysis based on quantum mechanical calculations and cluster models have permitted to account for

$Research paper thumbnail of SiO2/TiO2 thin films with variable refractive index prepared by ion beam induced and plasma enhanced chemical vapor deposition$

Thin Solid Films, 2006

SiO 2 /TiO 2 optical thin films with variable compositions have been prepared by ion beam induced... more SiO 2 /TiO 2 optical thin films with variable compositions have been prepared by ion beam induced and plasma enhanced chemical vapour deposition (IBICVD and PECVD). While the films obtained by IBICVD were very compact, the PECVD ones with a high content of Ti presented a columnar microstructure. The formation of Si-O-Ti bonds and a change in the environment around titanium from four-to six-coordinated has been proved by vibrational and X-ray absorption spectroscopies. The refractive index increased with the titanium content from 1.45 to 2.46 or 2.09 for, respectively, the IBICVD and PECVD films. Meanwhile, the band gap decreased, first sharply and then more smoothly up to the value of pure TiO 2. It is concluded that the optical properties of SiO 2 /TiO 2 thin films can be properly tailored by using these two procedures.

The Journal of Physical Chemistry B, 2004

Two model systems consisting of nanometric SnO and SnO 2 particles deposited by evaporation on Al... more Two model systems consisting of nanometric SnO and SnO 2 particles deposited by evaporation on Al 2 O 3 and Sb 2 O 3 or Sb 2 O x substrates (x means a mixture of Sb 3+ and Sb 5+ oxidation states) are studied by X-ray photoelectron spectroscopy to account for the interactions that develop at the interfaces. The conclusions derived from this study are relevant for the characterization by this technique of nanostructured materials formed by nanoparticles and/or very thin films of an oxide deposited on another oxide support. Electronic parameters such as the binding energy (BE) of the Sn 3d 5/2 photoemission peak and the Auger parameter (R′) of the metal cation of the deposited tin oxides shift systematically from a nanometric size of the deposited moieties to a thick layer of these materials. The changes in the electronic parameters between the thickest layers of the deposited oxides and the first deposition situations (i.e., ∆BE, ∆R′, both in eV) are as follows for the different systems: SnO/Al 2 O 3 (∆BE) 1.0, ∆R′)-1.6), SnO/Sb 2 O 3 (0.6,-0.7), SnO 2 /Al 2 O 3 (0.9,-1.2), and SnO 2 /Sb 2 O x (0.6,-0.6). These variations are stronger than those existing between Sn 2+ and Sn 4+ species in their respective bulk oxides (i.e., approximately 0.5 eV for both ∆BE and ∆R′). These changes are systematized within the concept of the "Chemical state vector" and explained on the basis of a model that considers both the development of specific interactions between the substrates and tin oxide nanoparticles and the influence of different polarizabilities by the surrounding media on the relaxation energy of the photoholes. The changes in the electronic parameters for the initial states of deposition are correlated with the size and shape of the nanoparticles deposited, as determined by XPS peak shape analysis using the Tougaard's method. The analysis of the spectra shows that the tin oxides grow on both substrates in the form of small particles that do not cover completely the substrate before ∼10 Å of material is deposited. It is found that when ∼2 Å of material is deposited, small clusters of approximately ∼8 Å (i.e., about two Sn-O monolayers) cover ∼18% of the surface. Changes in the width of the photoemission peaks are also detected. Removal of surface charging when depositing SnO is responsible for part of these changes, although very likely local inhomogeneities in coordination around the cations also contribute to broadening the peaks. This is particularly important for the smallest nanoparticles where the degree of interface interactions with the substrate is high. Finally, a shift of the valence band edge toward higher binding energies is observed at the initial stages of deposition of tin oxide nanoparticles. This shift is related with particle size effects and/or the development of specific interactions at the interface between the nanoparticles and the support.

Surface Science, 1998

The oxidation of Mo polycrystalline foils at room temperature, through O 2-ion bombardment and a ... more The oxidation of Mo polycrystalline foils at room temperature, through O 2-ion bombardment and a reactive O 2 plasma studied by XPS and AES, is reported. Samples bombarded with O 2 ions showed Mo 3d XP spectra with two broad peaks, which can be deconvoluted with standard spectra of Mo0, a small contribution of Mo6+ and a residue assigned to Mo4+ and Mon+ with n<4. Those samples treated with plasma showed three peaks resulting from signal superposition, mainly of Mo0, Mo6+, a small contribution of Mo4+ and Mon+. In the region of the Mo MNN Auger transitions (150-240 eV), three new peaks appeared upon oxidation, at~5 eV lower kinetic energy than in Mo0. The relative intensities within each pair of peaks at 160, 186, and 221 eV depend on the oxidation method, i.e. on the kind of oxide formed.

Surface and Coatings Technology, 2011

Low density polyethylene (LDPE) films have been treated with different nitrogen containing plasma... more Low density polyethylene (LDPE) films have been treated with different nitrogen containing plasmas with the purpose of incorporating nitrogen functional groups on its surface and analyzing the changes experienced in their surface tension. Effects of a dielectric barrier discharge (DBD) at atmospheric pressure and a microwave discharge (MW) at reduced pressure are compared with those obtained by using an atom source supplied with N 2 and mixtures Ar + NH 3 as plasma gas. X-ray photoelectron spectroscopy (XPS) analysis has provided information about the chemical surface changes whereas the surface topography of the treated samples has been examined by atomic force microscopy (AFM). Non-destructive depth profiles of oxygen and carbon have been obtained for the treated and one month aged samples by means of the non-destructive Tougaard's method of XPS background analysis. Generally, an oxygen enrichment of the deeper region of treated LDPE surfaces has been observed. Chemical derivatization of the treated samples has shown that a DBD plasma with a mixture of Ar + NH 3 was the most efficient treatment for nitrogen and amine group functionalization. It is argued that the high concentration of NH* species in this plasma is the most important factor in enhancing the nitrogen functionalization of this polymer. It has been also found that the observed increase in hydrophilicity and surface tension cannot be attributed to the anchored nitrogen functional groups formed on plasma treated LDPE. Differences in the plasma activation behaviour of LDPE and that of other polymers subjected to similar treatments are stressed.

Surface and Coatings Technology, 1998

This paper reports the preparation and characterization of thin films of AI-T1 mixed oxides. Film... more This paper reports the preparation and characterization of thin films of AI-T1 mixed oxides. Films of different compositions ranging from a cationic content of Ti of 92.6% to 18.8% (i.e. AI/Ti ratios from 0.08 to 4.3) have been prepared by ion beam induced CVD (IBICVD). The films have been characterized by different methods including UV-VIS spectroscopy, XRD and X-ray absorption spectroscopy (XAS). It is found that the optical properties of the films (refraction index and band gap energy) deduced from the UV-VIS absorption spectra vary linearly with the titanium content from 1.45 (0% Ti) to 2.55 (100% Ti). The films were amorphous after preparation, but for Al/Ti ratios lower than 1.5, a partial crystallization into the anatase structure of titanium dioxide was observed after annealing at 823 K. This contrasts with the formation of the rutile structure observed when annealing thin films of TiO, or TiO,-Al,O, bilayers prepared by the same procedure. In both cases. annealing did not produce any significant change in the values of the optical parameters.

Plasma Processes and Polymers, 2009

... Additional Information. How to Cite. López-Santos, C., Yubero, F., Cotrino, J., Contreras, L.... more ... Additional Information. How to Cite. López-Santos, C., Yubero, F., Cotrino, J., Contreras, L., Barranco, A. and González-Elipe, AR (2009), Formation of Nitrogen Functional Groups on Plasma Treated DLC. Plasma Processes and Polymers, 6: 555–565. ...

Physical Review B, 2007

This work reports on x-ray absorption spectroscopy study at the Si K edge of several amorphous Si... more This work reports on x-ray absorption spectroscopy study at the Si K edge of several amorphous SiO x C y H z polymers prepared by plasma-enhanced chemical-vapor deposition with different C / O ratios. SiO 2 and SiC have been used as reference materials. The comparison of the experimental Si K-edge x-ray absorption nearedge structure spectra with theoretical computations based on multiple scattering theory has allowed us to monitor the modification of the local coordination around Si as a function of the overall C / O ratio in this kind of materials.

Journal of Vacuum Science & Technology A: Vacuum, Surfaces, and Films, 2006

Cadmium sulfide has been deposited by evaporation on five different substrates: CdTe, ZnO, Ag, Ti... more Cadmium sulfide has been deposited by evaporation on five different substrates: CdTe, ZnO, Ag, TiO2, and partially reduced titanium oxide (i.e., TiO1.73). The deposition rate and the evolution of the Cd∕S ratio on the different substrates have been determined by x-ray photoelectron spectroscopy. The growth mode of the films has been also studied by analyzing the shape of the backgrounds behind the photoemission peaks (peak shape analysis). It has been found that, under completely equivalent conditions, the deposition efficiency (i.e., sticking coefficient) is large on CdTe and TiO1.73, but very small on ZnO and TiO2. Silver constitutes an intermediate situation characterized by a long induction period where the deposition rate is small and a later increase in deposition efficiency comparable to that on CdTe. For the initial stages of deposition, below an equivalent monolayer, it has been also found that the Cd∕S ratio is smaller than unity on TiO1.73 and ZnO but larger than unity on...

Journal of Vacuum Science & Technology A: Vacuum, Surfaces, and Films, 1998

Al x Ti y O z thin films (i.e., mixture of Al2O3 and TiO2) with different Al/Ti ratios have been ... more Al x Ti y O z thin films (i.e., mixture of Al2O3 and TiO2) with different Al/Ti ratios have been characterized by several electron spectroscopies. The Auger parameter of Ti, determined by x-ray photoelectron spectroscopy, increases with the percentage of Ti in the films. The same trend is found for the evolution of the refractive index in the visible region n0, that, as measured by UV-Vis absorption spectroscopy, varies from 1.5 to 2.5 as a function of the percentage of Ti. Within the same range of compositions, the Auger parameter of Ti changes by 1.2 eV. Such behavior permits an empirical use of the Auger parameter to assess optical parameters of this type of films. On the other hand, reflection electron energy loss spectroscopy has provided information on the optical properties of the films in the far-ultraviolet region (5<ℏω<80 eV). From the analysis of the loss spectra, the refractive index n(ℏω), the extinction coefficient k(ℏω), and the absorption coefficient α(ℏω) have...

Journal of Colloid and Interface Science, 2012

The wetting behavior of fluorocarbon materials has been studied with the aim of assessing the inf... more The wetting behavior of fluorocarbon materials has been studied with the aim of assessing the influence of the surface chemical composition and surface roughness on the water advancing and receding contact angles. Diamond like carbon and two fluorocarbon materials with different fluorine content have been prepared by plasma enhanced chemical vapor deposition and characterized by X-ray photoemission, Raman and FT-IR spectroscopies. Very rough surfaces have been obtained by deposition of thin films of these materials on polymer substrates previously subjected to plasma etching to increase their roughness. A direct correlation has been found between roughness and water contact angles while a superhydrophobic behavior (i.e., water contact angles higher than 150° and relatively low adhesion energy) was found for the films with the highest fluorine content deposited on very rough substrates. A critical evaluation of the methods currently used to assess the roughness of these surfaces by atomic force microscopy (AFM) has evidenced that calculated RMS roughness values and actual surface areas are quite dependent on both the scale of observation and image resolution. A critical discussion is carried out about the application of the Wenzel model to account for the wetting behavior of this type of surfaces.

Diamond and Related Materials, 2011

ABSTRACT A diamond like carbon material has been exposed to a low pressure microwave and atmosphe... more ABSTRACT A diamond like carbon material has been exposed to a low pressure microwave and atmospheric pressure plasma of oxygen to enhance its hydrophilicity and surface energy. For comparison, data are also reported after activation with a beam of neutral atoms of oxygen. The surface incorporation of oxygenated functional groups and the determination of the in-depth distribution of this element have been analysed by means of the X ray photoemission spectroscopy (XPS). Atomic force microscopy (AFM) has been used to get information of the surface topography and, by recording friction maps of the surface, the lateral distribution of oxygenated functional groups formed after the different activation treatments. Differences in surface composition, topography and in-depth and lateral distribution of oxygen have been correlated with the intrinsic characteristics of the activation plasma processes.