Raúl Gago

Raúl Gago
Spanish National Research Council | CSIC · Instituto de Ciencia de Materiales de Madrid

PhD

About

163
Publications
16,023
Reads
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4,072
Citations
Additional affiliations
August 2008 - present
Spanish National Research Council
Position
  • Tenured Scientist
September 2004 - July 2008
Universidad Autónoma de Madrid
Position
  • Ramon y Cajal Fellowship
August 2001 - August 2004
Helmholtz-Zentrum Dresden-Rossendorf
Position
  • PostDoc Position
Education
September 1996 - November 2000
Universidad Autónoma de Madrid
Field of study
  • Physics
September 1991 - July 1996
Universidad Autónoma de Madrid
Field of study
  • Physics

Publications

Publications (163)
Article
The bonding structure of tin oxide (SnOx) films grown by reactive DC magnetron sputtering has been studied by the combination of X-ray diffraction (XRD) and soft X-ray absorption near-edge structure (XANES). The oxygen incorporation in the films has been controlled by the O2 partial pressure (PO2) in the O2/Ar discharge mixture. In addition, the im...
Article
The optical and electrical properties of fluorinated tin oxide (FTO) films deposited at room temperature by sputtering have been investigated varying the fluorine content and the hydrogen atmosphere. The complex behavior of the obtained films is disclosed using a wide set of characterization techniques that reveals the combined effects of these two...
Article
The interface between pioneer sessile bacteria and a supporting substrate can be probed in situ and at the molecular scale by infrared spectroscopy in the attenuated total reflection mode (ATR‐FTIR). Here, a self‐assembled monolayer (SAM) of amino‐terminated alkanethiol is formed on the internal reflection element (IRE) composed of zinc selenide, a...
Article
We study the nanopatterning of silicon surfaces under near-normal 40-keV Ar+ sputtering with simultaneous Fe oblique codeposition. The ion-beam incidence was kept at 15°, for which no pattern is produced in the absence of metal incorporation. Morphological and compositional analyses were performed by atomic force microscopy, in its morphological an...
Article
Full-text available
Low energy (1-keV) Xe ⁺ irradiation at different incidence angles (α) has been performed on pure polycrystalline Ti pellets at room temperature. The ion current was set between 110 and 200 μA cm ⁻² (ion flux ∼ 7-12 ×10 ¹⁴ ions cm ⁻² s ⁻¹ ). Changes of the surface morphology were characterized ex-situ with scanning electron microscopy and atomic for...
Article
Full-text available
In this work, the anomalous reduction in the thermal conduction observed for nanolaminate metal-dielectric multilayers has been extended to the case of oxides. For this purpose, Ag/Al2O3 coatings were produced with different layer thicknesses (from 1 to 5 nm for Ag and 8 to 40 nm for Al2O3) and numbers of stacks. It was found that the thermal condu...
Article
The impact of Ta incorporation (up to ∼21 at.%) in titanium dioxide (TiO2) films subjected to post-deposition millisecond-range flash-lamp annealing (FLA) is addressed. Phase formation with short-range information was established by means of soft X-ray absorption near-edge structure (XANES) in combination with standard X-ray diffraction. As-grown f...
Article
Bacteria grow on surfaces and form communities called biofilms. Bacterial adhesion and properties of the derived biofilms depend, among others, on the nature of the supporting substrate. Here, we report how the surface properties of the substrate affect the biofilm growth of probiotic Lactobacillus rhamnosus GG (LGG). Hydrophilic (OH), hydrophobic...
Article
Full-text available
In this paper, we report on the phase selectivity in Cr and N co-doped TiO2 (TiO2:Cr,N) sputtered films by means of interface engineering. In particular, monolithic TiO2:Cr,N films produced by continuous growth conditions result in the formation of a mixed-phase oxide with dominant rutile character. On the contrary, modulated growth by starting wit...
Article
Scalable nanostructuring of surfaces using ion beam sputtering (IBS) is a versatile alternative to traditional lithography. Semiconductors, metals or compounds are amenable for IBS where different patterns can be obtained by tuning the experimental setup. This special issue addresses this problem in a wide range of topics, from a basic understandin...
Article
Full-text available
Multilayer nanolaminate TiAlN/Ag and Al2O3/Ag metal-insulator-metal (MIM) coatings with thicknesses of individual layers from a few to several hundreds of nanometers were fabricated by direct current magnetron sputtering. Their optical transmittance and reflectance spectra were measured for photon energies 1–5 eV (1240–248 nm). The spectra were non...
Article
Full-text available
Yb 3+ ions hold promises for high power emission in the near infrared (NIR). Yet, relevant matrices, comprising mediators to excite Yb 3+ , have to be found and the optical mechanisms to be studied in details. This is the purpose of this study that reports on the optical excitation and emission mechanisms of NIR photoluminescence (PL) of Yb-doped c...
Article
Surface pattern formation on amorphous SiO2 substrates by implantation of 1.0 MeV Si+ ions at a current of 1.3 µA at 70° angle is reported. Surface micrometer sized ripples perpendicular to the ion beam direction are formed, observed by scanning electron microscopy and atomic force microscopy. The morphological features are more or less similar for...
Article
The surface morphology of molybdenum silicide (Mo<sub>x</sub>Si<sub>1-x </sub>) films has been studied after low-energy Ar<sup>+</sup> ion-beam sputtering (IBS) to explore eventual pattern formation on compound targets and, simultaneously, gather information about the mechanisms behind silicide-assisted nanopatterning of silicon surfaces by IBS. Fo...
Article
Full-text available
Plasmon resonance heterogeneities were identified and studied along Ag and TiAlN layers within a multilayer stack in nanolaminate TiAlN/Ag coatings. For this purpose, a high-resolution plasmon microscopy was used. The plasmons intensity, energy, and depth of interface plasmon-polariton penetration were studied by scanning reflected electron energy...
Article
We address the impact of chromium (Cr) incorporation (<15 at.%) in the structure of titanium dioxide (TiO2:Cr) films for as-grown and after flash-lamp-annealing (FLA) states. Samples were produced by DC magnetron sputtering on either unheated or heated (400 °C) substrates. Complementary medium- and local-order information was extracted by X-ray dif...
Article
Cerium-doped aluminum nitride (Ce-AlN) thin films were prepared at room temperature (RT) using radio frequency (RF) reactive sputtering. As-grown samples were then subjected to rapid thermal annealing (RTA). X-ray diffraction and high resolution transmission electron microscopy (HRTEM) revealed a well crystalline textured microstructure with single...
Article
In this study, tantalum nitride (TaN) thin films were deposited on Si(100) and 316L stainless steel (SS) substrates by reactive DC magnetron sputtering. The effect of the nitrogen fraction ([N2]) in the gas mixture on the composition, phase formation, roughness and corrosion resistance was investigated. The films were characterized by Rutherford ba...
Article
Insufficient corrosion resistance and surface conductivity are two main issues that plague large-scale application of stainless steel (SS) bipolar plates in proton exchange membrane fuel cells (PEMFCs). This study explores the use of nanocrystalline Ta/TaN multilayer coatings to improve the electrical and electrochemical performance of polished 316...
Article
Full-text available
TiAlN/Ag multilayer coatings with a different number of bilayers and thicknesses of individual layers were fabricated by DC magnetron co-sputtering. Thermal conductivity was measured in dependence of Ag layer thickness. It was found anomalous low thermal conductivity of silver comparing to TiAlN and Ag bulk standards and TiAlN/TiN multilayers. The...
Article
TiAlN/Ag multilayer coatings with different number of bilayers and thicknesses of individual layer were fabricated by DC magnetron sputtering. Thermal conductivity and electronic structure features were measured on a set of samples with different number of bilayers and individual layer thickness from a 5 to 150 nm for total coating thickness of ∼ 0...
Article
Chromium oxide (CrOx) thin films were grown by pulsed-DC reactive magnetron sputter deposition in an Ar/O2 discharge as a function of the O2 fraction in the gas mixture (ƒ) and for substrate temperatures, Ts, up to 450ºC. The samples were analysed by Rutherford backscattering spectrometry (RBS), spectroscopic ellipsometry (SE), atomic force microsc...
Article
Full-text available
A lack of universality with respect to ion species has been recently established in nanostructuring of semiconductor surfaces by low-energy ion-beam bombardment. This variability affects basic properties of the pattern formation process, like the critical incidence angle for pattern formation, and has remained unaccounted for. Here, we show that no...
Article
Full-text available
Transformations of the electronic structure in thin silver layers in metal-dielectric (TiAlN/Ag) multilayer nanocomposite were investigated by a set of electron spectroscopy techniques. Localization of the electronic states in the valence band and reduction of electron concentration in the conduction band was observed. This led to decreasing metall...
Article
Full-text available
We investigate the role of the initial structural condition in silicon surface nanopatterning by low-energy ion beam sputtering. Specifically, we address the influence of the target atomic structure in ripple formation under oblique irradiation by 500 eV &$\text{Ar}^+$ ; ions. To this end, we compare results obtained on single-crystal, amorphous, a...
Article
We address the impact of metal co-deposition in the nanodot patterning dynamics of Si(100) surfaces under normal-incidence 1 keV Ar(+) ion-beam sputtering (IBS). In particular, the effect of both the metal nature (Fe or Mo) and flux has been studied. Morphological and compositional evolution were followed by atomic force microscopy (AFM) and Ruther...
Article
Cadmium telluride (CT) and Zn-doped (∼4 at%) CT (CZT) crystals grown by the Bridgman method were mechanically polished to achieve mirror-like surfaces and subsequently irradiated with medium-energy (30–200 keV) Ar + ions under oblique incidence (60° with respect to the target normal). Atomic force microscopy shows that ion sputtering induces the fo...
Article
The growth of ultra-smooth amorphous thin films induced by low-energy (below 1 keV) ion-assistance processes is studied. The relative contribution of ion-induced smoothening effects is analysed by means of a Monte Carlo model and experimental data. In general, highly rough granular or ultra-smooth (with roughness below one monolayer) films are prod...
Article
Full-text available
In spite of the efforts devoted for the last 20 years to elucidating ion-beam sputtering (IBS) as an instance of surface self-organization, the classic view on the main mechanism inducing the morphological instability has been recently challenged. We report on the verification of a recent theoretical description of this nanopattern formation proc...
Article
Full-text available
Ion-beam sputtering (IBS) is known to produce surface nanopatterns over macroscopic areas on a wide range of materials. However, in spite of the technological potential of this route to nanostructuring, the physical process by which these surfaces self-organize remains poorly understood. We have performed detailed experiments of IBS on Si substrate...
Chapter
Full-text available
Normally, self-organized surface nanopatterns produced by ion beam sputtering (IBS) result in nanodot or nanoripplemorphologies depending on geometrical considerations. However, recent studies show that additional contributions should be considered when multielemental targets are involved due to the eventual development of a modulation between the...
Article
Full-text available
Hydrogen (H) stability in hydrogenated amorphous carbon (a-C:H) films with different structures grown by (biased) electron-cyclotron-resonance chemical vapor deposition has been studied against thermal annealing and swift-ion impact (2 MeV He+). For this purpose, a-C:H films with either polymer-like (PLCH) or diamond-like (DLCH) character grown on...
Article
N-containing TiO2 (TiO2:N) films have been grown by reactive pulsed magnetron sputtering (RPMS) with different N2/O2 mixtures and substrate temperatures (Ts) up to 450 °C. In this way, highly-doped films (N between 5 and 8 at.%) have been produced, as derived by elastic recoil detection analysis. The structural properties have been studied by grazi...
Article
Protective nanocomposite coatings based on hard ceramic phases (TiC, TiB2) combined with amorphous carbon (a-C) are of interest because of their adequate balance between mechanical and tribological performances. In this work, Ti–B–C nanocomposite coatings were prepared by co-sputtering of graphite and TiB2 targets. Varying the discharge power ratio...
Article
Full-text available
Interrupted coarsening (IC) has recently been identified as an important feature for the dynamics of the typical length-scale in pattern-forming systems on surfaces. In practice, it can be beneficial to improve pattern ordering since it combines a certain degree of defect suppression with a limited increase in the typical pattern wavelength. Howeve...
Article
Full-text available
The formation and dynamics of nanopatterns produced on Si(100) surfaces by 40-keV Ar+ oblique (α = 60°) bombardment with concurrent Fe codeposition have been studied. Morphological and chemical analysis has been performed by ex situ atomic force microscopy, Rutherford backscattering spectrometry, x-ray photoelectron spectroscopy, and scanning and t...
Article
Full-text available
Ion Beam Sputtering (IBS) is known to produce surface nanopatterns over macroscopic areas on a wide range of materials. However, in spite of the technological potential of this route to nanostructuring, the physical process by which these surfaces self-organize remains poorly under- stood. We have performed detailed experiments of IBS on Si substra...
Article
Full-text available
A review is given on the use of ion-beam-assisted deposition (IBAD) to the growth of films within the B-C-N system, both as monolithic and multilayer coatings. The films considered include elemental, binary, and ternary materials like pure carbon (diamond-like carbon), pure boron (B), boron nitrides (c-BN, h-BN, and BNx), boron carbides (B4C and Bx...
Article
Full-text available
The effect of the substrate temperature on the sublattice ordering in ZnO layers grown by reactive pulsed magnetron sputtering on sapphire has been investigated by different techniques. The improvement of the crystal quality and heteroepitaxial growth at relatively low temperatures (550 °C) is verified by x-ray diffraction, high-resolution transmis...
Article
Thermal treatment of supersaturated Ti1−xAlxN films (x≈0.67) with a dominant ternary cubic-phase were performed in the 700–1000°C range. Grazing incidence X-ray diffraction (GIXRD) shows that, for annealing temperatures up to 800°C, the film structure undergoes the formation of coherent cubic AlN (c-AlN) and TiN (c-TiN) nanocrystallites via spinoda...
Article
Heterogeneous TiO2 films with nanocrystalline (nc-) rutile and amorphous (a-) phases were annealed in vacuum up to 450 °C. The structural and morphological changes were studied by in situ X-ray absorption and ex-situ X-ray diffraction and atomic force microscopy. The annealing process leads to phase and morphological changes depending on the initia...
Article
The local structure of TiBC and amorphous carbon (a-C) nanocomposite films (TiBC/a-C) was correlated with their optical and electrical properties. TiBC/a-C films with increasing C content were deposited by magnetron co-sputtering from TiC:TiB2 (60: 40) and graphite targets. Chemical composition is determined by electron energy-loss spectroscopy. Gr...
Article
Cover: Nanocomposite coatings mixing hard nanocrystalline phases of TiBC in a soft amorphous carbon matrix are prepared by magnetron sputtering of a composite TiC:TiB2 target and graphite. The electrical resistivity and crystalline structure of the coatings can be varied depending on the carbon content. The formation of two types of boron bonding i...
Article
Although reports on surface nanostructuring of solid targets by low to medium energy ion irradiation date back to the 1960s, only with the advent of high resolution tools for surface/interface characterization has the high potential of this procedure been recognized as a method for efficient production of surface patterns. Such morphologies are mad...
Article
Full-text available
Ultrasmooth amorphous silicon films with a constant roughness below 0.2 nm were produced for film thickness up to ∼ 1 μm by magnetron sputtering under negative voltage substrate biasing (100–400 V). In contrast, under unbiased conditions the roughness of the resulting mounded films increased linearly with growth time due to shadowing effects. A det...
Article
Titanium dioxide films were grown on unheated substrates by mid-frequency (100 kHz) reactive pulsed magnetron sputtering at different O-2 partial pressures in an Ar/O-2 atmosphere. X-ray diffraction and absorption measurements reveal a transition from amorphous anatase to nanocrystalline rutile with [O-2], with a mixture of both phases at intermedi...
Article
Back Cover: TiO2 films grown by reactive pulsed magnetron sputtering exhibit a heterogeneous mixture of nanocrystalline rutile and amorphous anatase-like phases. The structural evolution also reflects on the surface topography, where hollow (flat) structures are related to the underlying nanocrystalline rutile (amorphous anatase) phase. Further det...
Article
Full-text available
This work reports on the fabrication of Schottky barrier based Mg-doped (In,Ga)N layers for fluorescence applications. Mg acceptors are used in order to compensate surface and bulk donors that prevent the fabrication of Schottky contacts on unintentionally doped (In,Ga)N layers grown by plasma-assisted molecular beam epitaxy (PA-MBE). Rectifying pr...
Article
We investigated the mechanical and tribological properties of hydrogenated amorphous carbon (a-C:H) films on silicon substrates by nanoindentation, ball-on-disc tribotesting and scratch testing. The a-C:H films were deposited from an argon/methane gas mixture by bias-enhanced electron cyclotron resonance chemical vapour deposition (ECR-CVD). We fou...
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Full-text available
In this study, we have successfully used the extended X-ray absorption fine structure (EXAFS) technique at the Ti-K edge to extract the local structure in a set of nanocomposite TiBC/a-C coatings deposited by a combined d.c.-pulsed and r.f.-magnetron sputtering deposition process. The sequence of Fourier transform spectra in the deposited films sho...
Article
Full-text available
X-ray absorption near edge structure and x-ray diffraction studies with synchrotron radiation have been used to relate the electrical properties of ZnO:Al films to their bonding structure and phase composition. It is found that Al-sites in an insulating metastable homologous (ZnO)3Al2O3 phase are favored above a certain substrate temperature (TS) l...
Article
Full-text available
An increasing amount of effort is currently being directed towards the development of new functionalized nanostructured materials (i.e., multilayers and nanocomposites). Using an appropriate combination of composition and microstructure, it is possible to optimize and tailor the final properties of the material to its final application. The analyti...
Article
TEM (transmission electron microscopy) and EELS (electron energy loss spectroscopy) study of the atomic structure of BCxN (ternary boron carbonitride) coatings grown on silicon wafers by ion beam assisted deposition (IBAD) at room temperature was investigated. The bonding structure of BCN and BC4N compounds was investigated by EELS. No oxygen inten...
Article
Full-text available
We report the detection of phase separation of an Al1-xIn xN/GaN heterojunction grown close to lattice-matched conditions (x ∼ 0.18) by means of Rutherford backscattering spectrometry in channelling geometry and high-resolution x-ray diffraction. An initial pseudomorphic growth of the film was found, with good single crystalline quality, the nomina...
Article
Full-text available
We report the experimental observation of interrupted coarsening for surface self-organized nanostructuring by ion erosion. Analysis of the target surface by atomic force microscopy allows us to describe quantitatively this intriguing type of pattern dynamics through a continuum equation put forward in different contexts across a wide range of leng...
Thesis
Tesis doctoral inédita. Universidad Autónoma de Madrid, Facultad de Ciencias, Departamento de Física Aplicada . Fecha de lectura: 09-06-2010 Bibliografía