Thermomechanical properties of amorphous metallic tungsten-oxygen and tungsten-oxide coatings

In this work, we investigate the correlation between morphology, composition, and the mechanical properties of metallic amorphous tungsten-oxygen and amorphous tungsten-oxide films deposited by Pulsed Laser Deposition. This correlation is investigated by the combined use of Brillouin Spectroscopy and the substrate curvature method. The stiffness of the films is strongly affected by both the oxygen content and the mass density. The elastic moduli show a decreasing trend as the mass density decreases and the oxygen-tungsten ratio increases. A plateaux region is detected in correspondence of the transition between metallic and oxide films. The compressive residual stresses, moderate stiffness and high local ductility that characterize compact amorphous tungsten-oxide films make them promising for applications involving thermal or mechanical loads. The coefficient of thermal expansion is quite high (i.e. 8.9 $\cdot$ 10$^{-6}$ K$^{-1}$), being strictly correlated to the amorphous structure and stoichiometry of the films. Under thermal treatments they show a quite low relaxation temperature (i.e. 450 K). They crystallize into the $\gamma$ monoclinic phase of WO$_3$ starting from 670 K, inducing an increase by about 70\% of material stiffness.Comment: The research leading to these results has also received funding from the European Research Council Consolidator Grant ENSURE (ERC-2014-CoG No. 647554). The views and opinions expressed herein do not necessarily reflect those of the European Commissio

Low-Cost Uas Photogrammetry for Road Infrastructures' Inspection

Abstract. All over the world, road infrastructures are getting closer to their life cycle and need to be constantly inspected: a consistent number of bridges are structurally deficient, and the risk of collapse can no longer be excluded. In contrast with the past, the interest in structure durability has recently grown rapidly. In order to make bridges durable, it is necessary to carry out ordinary maintenance, preceded by inspection activities, which can be traditionally divided in two categories: destructive and non-destructive (NDT). All the NDT inspections (visual, IR thermography, GPR) can be conducted by using UAS (Unmanned Aerial Systems), a technology that makes bridges inspections quicker, cheaper, objective and repeatable. This study presents the visual inspection and survey of two bridges by using a UAS DJI Mavic 2 Pro, equipped with a 20Mpixel Hasselblad camera that records 60fps 4K video and a 10bit radiometric resolution. Starting from the acquired data, a 3D model of each structure was built by using Structure from Motion (SfM) principles and software. To validate the two models, each of them characterized by a centimetric accuracy, the UAS camera generated cloud of points and was co-registered with the point cloud of a terrestrial laser-scanner using Ground Control Points (GCPs). To make this, CloudCompare comparison software was used; the plugin M3C2 automatically calculates the distance between the points of two compared clouds. Finally, some general rules concerning the UAS main characteristics for inspection of bridges and software for data processing are proposed

Laser cleaning of diagnostic mirrors from tokamak-like carbon contaminants

This paper presents a laboratory-scale experimental investigation of laser cleaning of diagnostic First Mirrors (FMs). Redeposition of contaminants sputtered from tokamak first wall onto FMs surface could dramatically decrease their reflectivity in an unacceptable way for the functioning of the plasma diagnostic systems. Laser cleaning is a promising solution to tackle this issue. In this work, pulsed laser deposition was exploited to produce rhodium films functional as FMs and to deposit onto them carbon contaminants with tailored features, resembling those found in tokamaks. The same laser system was also used to perform laser cleaning experiments by means of a sample handling procedure that allows to clean some cm(2) in few minutes. The cleaning effectiveness was evaluated in terms of specular reflectivity recovery and mirror surface integrity. The effect of different laser wavelengths (lambda = 1064, 266 nm) on the cleaning process is also addressed

Thermal annealing and exposure to divertor-like deuterium plasma of tailored tungsten oxide coatings

In this work we produced tungsten (W) and W oxide (WOx) films by pulsed laser deposition (PLD) with the aim of the addressing modifications of structure and morphology that occur after annealing treatments and high-flux deuterium plasma. Thanks to the high flexibility of PLD we produced nanostructured W containing non-bounded oxygen, different types of WOx and multilayered films. W coatings are dense, non-porous and exhibit a nanocrystalline structure, resembling the coatings used as first wall in tokamaks. The oxide films are nearly stoichiometric amorphous WOx (x = 3) with different morphology from compact to porous. Depending on annealing temperature, nucleation of different crystalline phases (e.g. WO3, W18O49) occurs. Exposure of films to high-flux (similar to 10(24) m(-2) s(-1)) deuterium plasmas in Magnum-PSI at different surface temperatures (T-max = 580 K) determines material modifications at the nanoscale (e.g. nanometric defects) but no delamination. In addition preliminary deuterium retention results are reported

Tungsten oxide nanowires grown on amorphous-like tungsten films

Tungsten oxide nanowires have been synthesized by vacuum annealing in the range 500-710 °C from amorphous-like tungsten films, deposited on a Si(100) substrate by pulsed laser deposition (PLD) in the presence of a He background pressure. The oxygen required for the nanowires formation is already adsorbed in the W matrix before annealing, its amount depending on deposition parameters. Nanowire crystalline phase and stoichiometry depend on annealing temperature, ranging from W18O49-Magneli phase to monoclinic WO3. Sufficiently long annealing induces the formation of micrometer-long nanowires, up to 3.6 μm with an aspect ratio up to 90. Oxide nanowire growth appears to be triggered by the crystallization of the underlying amorphous W film, promoting their synthesis at low temperatures

Target normal sheath acceleration: theory, comparison with experiments and future perspectives

Ions can be effectively accelerated during the interaction of an ultra-intense ultra-short laser pulse irradiating a thin solid target via the so-called target normal sheath acceleration (TNSA) mechanism. One of the pivotal questions at this stage of the research is how to predict the properties of the accelerated ions, both from a fundamental point of view and in the light of foreseen applications. In this context, it is desirable to have a simple but reliable description to be used to extrapolate current results to future regimes, which will be made available in the near future, thanks to developments in laser technology. In this paper, the possible approaches for an analytical description of TNSA are discussed, and a theoretical TNSA model is developed. This model is then used to investigate the maximum ion energy as a function of laser parameters. Detailed comparisons with available experimental data and scaling laws are presented. In particular, the relative role played by both the laser pulse energy and irradiance in determining the ion features is investigated

Evidence of resonant surface wave excitation in the relativistic regime through measurements of proton acceleration from grating targets

The interaction of laser pulses with thin grating targets, having a periodic groove at the irradiated surface, has been experimentally investigated. Ultrahigh contrast ($\sim 10^{12}$) pulses allowed to demonstrate an enhanced laser-target coupling for the first time in the relativistic regime of ultra-high intensity >10^{19} \mbox{W/cm}^{2}. A maximum increase by a factor of 2.5 of the cut-off energy of protons produced by Target Normal Sheath Acceleration has been observed with respect to plane targets, around the incidence angle expected for resonant excitation of surface waves. A significant enhancement is also observed for small angles of incidence, out of resonance.Comment: 5 pages, 5 figures, 2nd version implements final correction

Thermomechanical properties of amorphous metallic tungsten-oxygen and tungsten-oxide coatings

Metallic amorphous tungsten-oxygen and amorphous tungsten-oxide films, deposited by Pulsed Laser Deposition, are characterized. The correlation is investigated between morphology, composition, and structure, measured by various techniques, and the mechanical properties, characterized by Brillouin Spectroscopy and the substrate curvature method. The stiffness of the films is correlated to the oxygen content and the mass density. The elastic moduli decrease as the mass density decreases and the oxygen-tungsten ratio increases. A plateau region is observed around the transition between the metal-like (conductive and opaque) films and the oxide ones (non-conductive and transparent). The compressive residual stresses, moderate stiffness and high local ductility of compact amorphous tungsten-oxide films are interesting for applications involving thermal or mechanical loads. The coefficient of thermal expansion is quite high (8.9 ⋅ 10 −6 K −1 ), being strictly correlated to the amorphous structure and stoichiometry of the films. Upon thermal treatments the coatings show a quite low relaxation temperature of 450 K. Starting from 670 K, they crystallize into the γ monoclinic phase of WO 3 , the stiffness increasing by about 70%. The measured thermomechanical properties provide a guidance for the design of devices which include a tungsten based layer, in order to assure their mechanical integrity