The deposition of functional coatings on open-cell foam substrates using magnetron sputtering is gaining popularity, particularly for applications like oxygen evolution reaction/hydrogen evolution reaction catalysis, batteries, and supercapacitors. While most research focuses on performance, little attention has been paid to the coating growth mechanisms or properties within the foam, which could significantly impact device performance. This work investigates the properties and growth mechanisms of TiO 2 coatings inside porous foams, using experimental and modeling techniques. The structure, composition and thickness of the coating on the outermost surface of the foam are studied using focused ion beam (FIB), scanning transmission electron microscopy (STEM), energy-dispersive x-ray spectroscopy (EDS), selected area electron diffraction (SAED) and high-resolution transmission electron microscopy (HRTEM). The experimental results reveal the formation of a dense, (quasi-)stoichiometric and crystalline coating. Numerical simulations and experiments highlight the transport of plasma particles in the foam. Interestingly, direct simulation Monte Carlo (DSMC)/particle-in-cell Monte Carlo (PICMC) models, coupled with mass-energy analyzer (MEA) experiments, demonstrate that the particle flux is reduced, but the particle energy distribution is not affected while traveling inside the foam. Using kinetic Monte Carlo thin film growth models provided by Virtual Coater TM , the physical properties of the coating inside the foam have been modeled, and the drop in coating thickness as well as the impact of bias voltage on densification, resistivity, and optical absorption are confirmed. synchrotron x-ray diffraction (SXRD) analyses of the foam demonstrate that the same crystalline phase is obtained along the foam thickness, but it can be tailored with bias voltages. The decrease in the recorded SXRD signal with increasing depth inside the foam also suggests a drop in coating thickness. The new insights on the properties of coatings inside open-cell foams presented in this study can be used to improve future foam-based devices.

The synthesis of functional material (e.g. TiO2) on foams is a becoming an important research area, particularly in photocatalysis. However, photocatalytic coatings on foams are most of the time synthesised using the sol-gel and soft template methods. PVD-based methods are rarely used to deposit photocatalytic coatings on such substrates and when they are, the growth mechanisms are never mentioned. However, PVD deposition can bring significant breakthroughs when using such 3D substrates, like accurate control and tuning of film morphology, composition, and/or synthesis of metastable phases.This work is a comprehensive study of the film growth on complex 3D substrates. TiO2 films have been deposited on Ni and C foams by magnetron sputtering in different discharge modes (DC transition regime, DC fully reactive, and HiPIMS) to understand the correlation between discharge parameters, covering of the foam, and photocatalytic performance of coated substrate. Depending on the choice of deposition parameters, the structure is tuned between anatase, or a mix of rutile and anatase, with the possibility to synthesise highly unstable {001} crystal facets. SEM cross-sections of the TiO2@C foam assemblies allow to observe the change in coating morphology with increasing depth inside the foam. The photoelectrochemical measurements, combined with the XRD results, highlight the superior photocurrent generation provided by the coatings deposited using DC magnetron sputtering in the transition regime, as they display a well-crystallised anatase structure with a large amount of highly photocatalytically active {001} facets.

The development of environment-friendly, low-cost and efficient catalyst preparation processes has always been a major issue in the field of catalysis. Wet chemistry methods are often used but these techniques are not sustainable, as post waste solution treatment remains an important drawback. Here an innovative dry low-pressure plasma process for metal nanoparticles supported nanocatalysts preparation is reported. The solid metal and oxide support precursors are physically mixed and then exposed to a radiofrequency Ar/N-2 plasma discharge, leading to the precursor degradation and the subsequent nanoparticles generation, without pre- or post- preparation steps. The metal nanoparticle loading and the particle size of metal and oxide support can be easily tuned by changing the ratio of the precursor materials, making the process simple, versatile, highly efficient, and scalable. As a proof of concept, gold nanoparticles (Au NPs) supported on titanium dioxide (TiO2) were prepared and tested as nanocatalysts for toluene (C7H8) degradation at temperatures ranging from 25 to 450 degrees C. Up to 100% of C7H8 conversion into CO2 was achieved over the Au-TiO2 nanocatalysts, demonstrating that this dry method is a very efficient way to prepare highly active nanocatalysts.

Although TixAl1-xN has been thoroughly studied, it is still unclear how TixAl1-xN coatings annealed for extended duration behave from a structural point of view, and if these structural changes are linked with oxidation mechanisms. This work aims to fill this gap by studying the chemical, structural and mechanical behaviour of TixAl1-xN coatings (0.38 <= x <= 0.58) deposited by dual bipolar magnetron sputtering, annealed in air and vacuum for an extended duration (up to 16 h) at temperatures ranging from 600 & DEG;C to 800 & DEG;C. X-ray photoelectron spectroscopy confirms previously reported results, with the formation of an Al2O3/TiO2 bilayer during oxidation, that is shifted to higher temperatures when increasing Al-content. X-ray diffraction demonstrates that Al-rich coatings undergo spinodal decomposition at lower annealing temperature/duration, but with the stabilisation of fcc-TiN and fcc-AlN. For Ti-rich films, the spinodal decomposition occurs at higher annealing temperature/duration, but the rapid transformation of fcc-AlN into w-AlN occurs, which is detrimental for the mechanical properties and the thermal stability. This study demonstrates that the oxidation mechanisms of TixAl1-xN are process-and time-independent, and occur independently from the structural changes. Two behavioural maps summarising the oxidation mechanisms combined with the structural behaviour of TixAl1-xN at 600 & DEG;C and 800 & DEG;C are proposed.

A new and original method is presented to synthesize Pt, Cu, and PtxCuy nanoparticles (NPs) anchored onto an inorganic nanopowder substrate (TiO2), based on the plasma degradation, within an Ar/NH3 radiofrequency plasma discharge, of solid organometallics (Cu and Pt acetylacetonate), mixed with TiO2. Both chemical and crystallographic characterizations confirm the formation of metastable alloyed Pt-Cu nanoparticles. The difference of Pt and Cu concentrations in NPs measured with a volume technique (X-ray diffraction) and a surface technique (X-ray photoelectron spectroscopy) suggests a Pt concentration gradient within NPs attributed to a difference in organometallics degradation kinetics. (C) 2021 Elsevier B.V. All rights reserved.

The use of efficient, durable and low-impact processes for the environment is highly desirable to synthesize nanomaterials for various applications. A new approach is presented to synthesize nanoparticles on different powder substrates. The process is based on the plasma degradation of solid organometallic precursors mixed with the powder substrate in order to generate e.g. new catalytic systems. Compared to conventional wet chemistry, plasma processing offers the advantage of reducing the environmental impact of the synthesis by reducing the energy consumption and relying on a solvent-free and waste-free scalable process. The novelty and high versatility of the process is demonstrated in this work. Choosing the right discharge parameters (pressure, reactive gas , plasma power,…), amorphous or crystalline monometallic, bimetallic, oxide or nitride nanoparticles can be produced, onto inorganic (such as TiO2) or carbon-based substrates like graphene, carbon xerogel or carbon nanotubes. Results have been obtained for various nanoparticles, including transition (Mn, Fe, Ni), post transition (Zn, Al), and noble metals (Cu, Pt, Pd, Rh). Moreover, the organometallic precursor(s) decomposition and the subsequent nanoparticles synthesis can be monitored in situ using optical emission spectroscopy of the plasma discharge. Applications in photocatalysis, magnetic materials, or catalysts for fuel cells are demonstrated.