Papers by miguel crespillo
Journal of Nuclear Materials, Apr 1, 2016
Knowledge of radiation-induced helium bubble nucleation and growth in SiC is essential for applic... more Knowledge of radiation-induced helium bubble nucleation and growth in SiC is essential for applications in fusion and fission environments. Here we report the evolution of microstructure in nanoengineered (NE) 3C SiC, pre-implanted with helium, under heavy ion irradiation at 700 °C up to doses of 30 displacements per atom (dpa). Elastic recoil detection analysis confirms that the as-implanted helium depth profile does not change under irradiation to 30 dpa at 700 °C. While the helium bubble size distribution becomes narrower with increasing dose, the average size of bubbles remains unchanged and the density of bubbles increases somewhat with dose. These results are consistent with a long helium bubble incubation process under continued irradiation at 700 °C up to 30 dpa, similar to that reported under dual and triple beam irradiation at much higher temperatures. The formation of bubbles at this low temperature is enhanced by the nano-layered stacking fault structure in the NE SiC, which enhances point defect mobility parallel to the stacking faults. This stacking fault structure is stable at 700 °C up to 30 dpa and suppresses the formation of dislocation loops normally observed under these irradiation conditions.
Unveiling the Effects of the Surface and In-Depth Nanostructure on the Far-Uv Optical Reflectance of Thin Fluoride Multilayer Coatings
Defect generation mechanisms in silica under intense electronic excitation by ion beams below 100 K: Interplay between radiative emissions
Acta Materialia, Aug 1, 2023
European Physical Journal D, Dec 1, 2021
Results recently reported on the effect of thermochemical treatments on the (He-Cd) laserexcited ... more Results recently reported on the effect of thermochemical treatments on the (He-Cd) laserexcited emission spectra of strontium titanate (STO) are re-analyzed here and compared with results obtained under ion-beam irradiation. Contributing bands centered at 2.4 eV and 2.8 eV, which appear under laser excitation, present intensities dependent upon previous thermal treatments in oxidizing (O2) or reducing atmosphere (H2). As a key result, the emission band centered at 2.8 eV is clearly enhanced in samples exposed to a reducing atmosphere. From a comparison with the ionoluminescence data, it is concluded that the laser-excited experiments can be rationalized within a framework developed from ion-beam excitation studies. In particular, the band at 2.8 eV, sometimes attributed to oxygen vacancies, behaves as expected for optical transitions from conduction-band (CB) states to the ground state level of the self-trapped exciton center. The band at 2.0 eV reported in ion-beam irradiated STO, and attributed to oxygen vacancies, is not observed in laser-excited crystals. As a consequence of our analysis, a consistent scheme of electronic energy levels and optical transitions can now be reliably offered for strontium titanate.
Correlation between Cr<sup>3+</sup> Luminescence and Oxygen Vacancy Disorder in Strontium Titanate under MeV Ion Irradiation
Journal of Physical Chemistry C, Sep 1, 2017
Strontium titanate (SrTiO3), a model system with a strongly correlated electronic structure, has ... more Strontium titanate (SrTiO3), a model system with a strongly correlated electronic structure, has attracted much attention recently because of its outstanding physicochemical properties and considerable potentials for technological applications. The capability to control oxygen vacancy profiles and their effect on valence states of cations will increase significantly the functionality of devices based on transition metal oxides. This work presents new insights into the near-infrared luminescence emission of Cr3+ centers in stoichiometric SrTiO3 induced using 3 MeV protons at temperatures of 100 K, 170 K, and room temperature. The study covers a wide spectral range, including near-infrared, visible, and near-UV regions. Our main purpose is to investigate the role of the oxygen vacancies introduced by energetic charged particles on the shape and yield of induced luminescence spectra, in particular to explore the interplay between the Cr3+ luminescence at 1.55 eV and oxygen disorder. A clear correlation is fo...
Reinforcement of the plasmon–phonon coupling in α-quartz via deposition of gold nanoparticles in etched ion tracks
European Physical Journal Plus, Oct 26, 2022
The European Physical Journal Plus
This paper describes in detail a novel manufacturing process for optical gratings suitable for us... more This paper describes in detail a novel manufacturing process for optical gratings suitable for use in the UV and soft X-ray regimes in a single-crystal diamond substrate based on highly focused swift heavy-ion irradiation. This type of grating is extensively used in light source facilities such as synchrotrons or free electron lasers, with ever-increasing demands in terms of thermal loads, depending on beamline operational parameters and architecture. The process proposed in this paper may be a future alternative to current manufacturing techniques, providing the advantage of being applicable to single-crystal diamond substrates, with their unique properties in terms of heat conductivity and radiation hardness. The paper summarizes the physical principle used for the grating patterns produced by swift heavy-ion irradiation and provides full details for the manufacturing process for a specific grating configuration, inspired in one of the beamlines at the ALBA synchrotron light sourc...
This book is based upon work from COST Action TUMIEE (CA17126), supported by COST (European Coope... more This book is based upon work from COST Action TUMIEE (CA17126), supported by COST (European Cooperation in Science and Technology). COST (European Cooperation in Science and Technology) is a funding agency for research and innovation networks. Our Actions help connect research initiatives across Europe and enable scientists to grow their ideas by sharing them with their peers. This boosts their research, career and innovation. www.cost.eu
Crystals
Nd3+-doped LaNbO phosphor thin films were prepared by radio-frequency magnetron sputtering on Si ... more Nd3+-doped LaNbO phosphor thin films were prepared by radio-frequency magnetron sputtering on Si substrates. The effects of a 1% Nd-doping concentration, after annealing at 1200 °C for 12 h, on the light-emitting properties of the sputtered thin films were characterized via several experimental techniques and deeply discussed. Photoluminescence characterization showed strong emission peaks typical of Nd3+ centers at 880 nm and 1060 nm when a 325 nm wavelength laser source was applied. Similar responses were detected in Nd3+-doped La3NbO7 powder samples fabricated by the solid-state reaction method. The coexistence of two phases (LaNbO4 and La3NbO7) in the thin films with higher nominal thickness was clearly identified based on different structural analyses. The promising results open the possibility for developing phosphor substrates as a preliminary step for the improvement of solar cells based on photon recycling mechanisms.
Acta Materialia, 2018
The irradiation tolerance of SiC/SiC composites was studied using 10 MeV Au ion irradiations at 3... more The irradiation tolerance of SiC/SiC composites was studied using 10 MeV Au ion irradiations at 350 C, for surface doses between 1 and 50 displacements per atom (dpa). Atomic force microscopy and optical profilometry revealed irradiation-induced axial and radial shrinkage of SiC-fibers. At 50 dpa, net fiber shrinkage reached 2.8 ± 0.3%. We conclude that the primary cause of SiC-fiber shrinkage in SiC/SiC composites is the irradiation-induced loss of pre-existing carbon packets, which had occupied 2e3% fiber volume in unirradiated state. A compelling evidence of the carbon packet loss was revealed using a combination of state-of-art conventional transmission electron microscopy (TEM), high resolution TEM, energy-filtered TEM and electron energy loss spectroscopy. The carbon packet volume fraction decreased with increasing dose, reaching near-complete loss after 50 dpa. Carbon packet loss was further confirmed using Raman spectroscopy where the carbon D and G peaks disappeared after irradiation. In contrast, irradiation-induced swelling of 1 ± 0.5% was observed in the matrix after 50 dpa. The study also shows that up to 50 dpa, the multilayer pyrolytic-carbon (PyC) interface in the composite is highly irradiation tolerant as it maintained its morphology, graphitic nature and showed no signs of amorphization. Additionally, Raman spectroscopy revealed a saturation of TEM invisible disorder at 1 dpa for both ultrafine grains of the fiber and the larger SiC-matrix grains. However, TEM visible extended defect formation such as dislocation loops were only detected in the larger matrix grains, thereby revealing a potential role of grain size on defect accumulation in SiC.
Non-radiative luminescence decay with self-trapped hole migration in strontium titanate: Interplay between optical and transport properties
Applied Materials Today, 2021
Abstract A novel model for the non-radiative decay of self-trapped excitons (STEs) in the advance... more Abstract A novel model for the non-radiative decay of self-trapped excitons (STEs) in the advanced functional oxide SrTiO3 is proposed and supported by experimental observations. The study is based on the initial ionoluminescence stage for STE emission at 2.5 eV, and its dependence on temperature and electronic excitation rate under energetic heavy-ion irradiation. For all temperatures, this initial stage reaches rapidly a quasi-steady level, and then decreases as induced-structural damage increases. The quasi-steady luminescence exhibits a linear dependence on the excitation rate, suggesting a constant efficiency for STEs formation. An activation energy of 55 meV, essentially independent of the incident ion mass and energy of projectile-ion, is deduced from an Arrhenius-type relationship with irradiation temperature. This energy is in good agreement with experimental values, measured for non-radiative STE decay under ns-laser pulse excitation, and reasonably consistent with density functional theory calculations for migration of self-trapped holes (STHs) described by a small-polaron adiabatic hopping model. A new mechanism dealing with a non-radiative contribution to the STE transition is discussed, consisting of STH migration through thermally-activated hopping and annihilation with the STE-electron. Luminescence kinetics from the chromium intrinsic impurity strongly supports this model, being consistent with the annihilation of Cr3+ centers through recombination with migrating STHs.
Review of Scientific Instruments, 2016
A systematic study of the ion beam heating effect was performed in a temperature range of −170 to... more A systematic study of the ion beam heating effect was performed in a temperature range of −170 to 900 • C using a 10 MeV Au 3+ ion beam and a Yttria stabilized Zirconia (YSZ) sample at a flux of 5.5 × 10 12 cm −2 s −1. Different geometric configurations of beam, sample, thermocouple positioning, and sample holder were compared to understand the heat/charge transport mechanisms responsible for the observed temperature increase. The beam heating exhibited a strong dependence on the background (initial) sample temperature with the largest temperature increases occurring at cryogenic temperatures and decreasing with increasing temperature. Comparison with numerical calculations suggests that the observed heating effect is, in reality, a predominantly electronic effect and the true temperature rise is small. A simple model was developed to explain this electronic effect in terms of an electrostatic potential that forms during ion irradiation. Such an artificial beam heating effect is potentially problematic in thermostated ion irradiation and ion beam analysis apparatus, as the operation of temperature feedback systems can be significantly distorted by this effect.
Anisotropic nanostructure formation by vapor etching of ion tracks in α-quartz
Nuclear Instruments and Methods in Physics Research Section B: Beam Interactions with Materials and Atoms, 2021
Abstract In this study, latent and etched ion tracks generated by high electronic excitation in a... more Abstract In this study, latent and etched ion tracks generated by high electronic excitation in alpha quartz (α-SiO2) were characterized. Single crystals of Y- and Z-cut α-SiO2 were irradiated at room temperature with 20 MeV Ni6+ ions and 40 MeV I7+ ions. The track morphology depends on the energy of the incident ion and the stopping power on the target material. Subsequent chemical vapor-etching with hydrofluoric acid solutions was conducted with varying etching times and acid concentrations. The vapor etching process produced nanostructures whose dimensions increased with etching time and etchant concentrations. Y-cut samples etched more slowly than Z-cut samples and exhibited anisotropic track etching behavior. Production of nanowells with different aspect ratios was accomplished by altering the etching time and etchant concentration. The nanowells were characterized by Atomic Force Microscopy. The etched nanostructure templates could be used in the fabrication of novel nanodevices with unique optical, thermal, and electronic properties.
Structural damage response of lanthanum and yttrium aluminate crystals to nuclear collisions and electronic excitation: Threshold assessment of irradiation damage
Journal of Materials Science & Technology
Crystals
Oxygen vacancies are known to play a central role in the optoelectronic properties of oxide perov... more Oxygen vacancies are known to play a central role in the optoelectronic properties of oxide perovskites. A detailed description of the exact mechanisms by which oxygen vacancies govern such properties, however, is still quite incomplete. The unambiguous identification of oxygen vacancies has been a subject of intense discussion. Interest in oxygen vacancies is not purely academic. Precise control of oxygen vacancies has potential technological benefits in optoelectronic devices. In this review paper, we focus our attention on the generation of oxygen vacancies by irradiation with high energy particles. Irradiation constitutes an efficient and reliable strategy to introduce, monitor, and characterize oxygen vacancies. Unfortunately, this technique has been underexploited despite its demonstrated advantages. This review revisits the main experimental results that have been obtained for oxygen vacancy centers (a) under high energy electron irradiation (100 keV–1 MeV) in LiNbO3, and (b)...
Sequential Ion-Electron Irradiation of Zirconium Carbide Ceramics: Microstructural Analysis
Journal of the European Ceramic Society
Raman characterization of phonon confinement and strain effects from latent ion tracks in α‐quartz
Journal of Raman Spectroscopy
High‐Entropy Alloys: Irradiation‐Induced Extremes Create Hierarchical Face‐/Body‐Centered‐Cubic Phases in Nanostructured High Entropy Alloys (Adv. Mater. 39/2020)
Advanced Materials
Irradiation‐Induced Extremes Create Hierarchical Face‐/Body‐Centered‐Cubic Phases in Nanostructured High Entropy Alloys
Advanced Materials
Coupled effects of electronic and nuclear energy deposition on damage accumulation in ion-irradiated SiC
Acta Materialia
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Papers by miguel crespillo