SPC - Groupe Supraconductivite

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Tuning the tribological performance of plasma-treated hybrid layers of PEEK-GO-DLC

Roberto Guarino

Graphene and graphene oxide (GO)-based coatings are of great interest due to their mechanical, electrical and/or thermal performance that add functionalities to materials employed in many industrial and biomedical appli-cations. Hybrid diamond-like carbon (DLC)/GO coatings on poly ether etherketone (PEEK) devices, e.g. ortho-paedic implants, can add multiple functionalities, such as an enhanced bioactivity. In this work, we describe the mechanical stability and tribological behaviour of such coating, comparing it to a DLC-coated bare PEEK. The GO functionalisation of PEEK is realised from a water solution, whereas the DLC coatings are obtained through plasma-enhanced chemical vapour deposition, using various combinations of different precursor gases. We employ atomic force microscopy to investigate the morphology and interfacial adhesion characteristics of the materials. Then, the scratch coefficient of friction of the samples is measured under both constant-load and progressive-load conditions, also in combination with acoustic emission signals. We identify the most effective and promising plasma treatments to ensure stable coating, and discuss the effect of the presence of an inter-mediate GO layer.

ELSEVIER SCI LTD2022

A simple theoretical model for estimating the frequency characteristics of black hole mergers

Roberto Guarino

Gravitational waves, despite predicted within the Theory of General Relativity about a century ago, were observed experi-mentally only in the last few years, thanks to the recent advances of the LIGO and Virgo detectors. In this work, we introduce a simple theoretical model to study the gravitational irradiation of binary systems and derive the characteristics of the emitted gravitational waves (e.g., in terms of frequency). The simplicity of the model relies first on the consideration of the two-body problem and circular orbits. Second, we follow an energetic approach and make use of only one result of the Theory of General Relativity, to make the procedure clear and suitable for undergraduate education. The numerical solution is finally compared with the experimental data available for a few black hole mergers.

CANADIAN SCIENCE PUBLISHING2022

Modelling electronic transport in monocrystalline metal oxide gas sensors: from the surface kinetics to the experimental response

Roberto Guarino, Gianluca Piccinini

Gas sensing systems and devices based on metal oxides are widely spreading due to their high performance in terms of sensor response and relatively low costs. Despite several experimental studies, as well as molecular simulations, are available in the literature, a tool that can quickly predict the macroscopic sensor response, and potentially be used for predictive purposes, is still missing. In this work, we present a modelling approach based on finite-element simulations, using material electrical properties available in the literature. In a first approach, we derive the surface electron trap concentration from fitting the global sensor response. Then, we improve the model by eliminating this fitting and considering the actual time-dependent experimental response. We consider sensors based on single SnO2 nanowires and show how our model predicts with a good agreement the experimental response vs. NO2, as a function of the working temperature and gas concentration, and also provides many other physical quantities of interest, such as the conduction band edge bending, the space charge and the width of the depletion layer. We further discuss ideas for improving the model and thus increasing its predictive potential.

2022