Énergie d'ionisation

Résumé

thumb|right|600px|Graphique des premières énergies d'ionisation en eV, en fonction du numéro atomique. L'énergie d'ionisation augmente graduellement des métaux alcalins jusqu'aux gaz nobles. Et dans une colonne donnée du tableau périodique, l'énergie d'ionisation diminue du premier rang jusqu'au dernier, à cause de la distance croissante du noyau jusqu'à la couche des électrons de valence. Le potentiel d'ionisation ou énergie d'ionisation d'un atome ou d'une molécule est l'énergie qu'il faut fournir à un atome neutre pour arracher un électron (le moins lié) à l'état gazeux et former un ion positif, le gaz étant au repos, c'est-à-dire, à 0 K. Plus généralement, la nième énergie d'ionisation est l'énergie requise pour arracher le nième électron après que les n-1 premiers électrons ont été arrachés. En chimie physique, le concept d'énergie d'ionisation est l'opposé de celui d'affinité électronique, c'est-à-dire l'énergie dégagée lorsqu'un atome neutre capte un électron et forme un anion.

Source officielle

https://fr.wikipedia.org/wiki/%C3%89nergie_d'ionisation

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Chargement

Ionization potentials of Si and GaAs from first-principles

Claudia Sgiarovello

EPFL2003

Chargement

Electron Beam Induced Copper Deposition from Carboxylate Precursors and the Study of Underlying Growth Mechanisms

Luisa Berger

The fabrication of defined and high-quality metal nanostructures is an ongoing topic of research. Direct-write deposition of copper nanostructures is of great value for many fields of research and industrial applications. Focused electron beam induced deposition (FEBID) is an additive fabrication technique with extremely high resolution and versatility. Physisorbed, gaseous precursor molecules are locally dissociated by a finely focused electron beam resulting in volatile fragments which desorb and non-volatile fragments forming the deposit. When applying suitable deposition parameters, these deposits can be as small as the beam diameter and have ideally little to no contamination. For electron beam induced metal deposition, metal-organic compounds are chosen as precursors. However, organic ligand material is often co-deposited, which is detrimental to the depositâs properties. This work addresses the study of the perfluorinated copper carboxylate [Cu2(ÎŒ-O2CC2F5)4] (Cu2(pfp)4) and its aminated derivatives Cu2(EtNH2)2(pfp)4 and Cu2(tBuNH2)2(pfp)4 as viable FEBID precursors. 25 at.% of copper was achieved with the amine free compound, and 15 at.% with each of the two aminated complexes. Based on the chemical analysis of the deposits, electron-induced dissociation paths were proposed for the adsorbed species, demonstrating the influence of the ligand chemistry and fragmentation on the deposit composition. In parallel, the perfluorinated silver carboxylate Ag2(pfp)2 was reported and compared directly to its copper equivalent. The silver complex yielded up to 74 at.% metal content and exhibited strong susceptibility to varying electron beam densities throughout the deposit. Cu2(pfp)4 did not manifest the same electron sensitivity. Theoretical models, combining analytical solutions with Monte Carlo simulations of primary and backscattered electrons were successfully fitted to the cross sections of deposits from both carboxylates, determining the growth regimes within a single spot deposit. Additionally, two previously reported Î²-diketonates, Cu(hfac)2 and Cu(tbaoac)2, were directly compared to the other Cu(II) precursors with the aim to determine any dependence of the ligand size, electron density or dwell time on the deposit purity. The investigations concluded that the metal content rather depends on the chemistry of the metal-ligand bond than on the ligand size. This applies to both, the variation of ligands and the variation of the metal center. vii Furthermore, two copper complexes, Cu(hfac)2 and Cu2(pfp)4, were investigated in situ with a dedicated, custom-made setup. The âeQCMâ combines a low energy electron source (10- 100 eV) with a quartz crystal microbalance and serves to study fundamental processes occurring during FEBI deposition. First results yielded the total dissociation cross section for each precursor at varying electron energies. Finally, alternative approaches for the electron induced copper deposition from Cu2(pfp)4 were investigated. A two-step post-purification recipe of as-deposited material was reported to yield pure copper crystals (> 97 at.%). Additionally, direct electron beam lithography in a layer of condensed precursor was explored. This room temperature deposition approach yielded in lower metal contents but could potentially produce high resolution deposition.

EPFL2020

Chargement

Energy storage is a central issue in the green economy with half the global end energy usage being heat. Latent heat thermal energy storage (LHTES) provides an energy dense heat storage solution with a well-defined discharge temperature. Utilizing low-cost, high-temperature, high-conducting metal alloys as phase change materials (PCMs) enables high energy and power density LHTES systems. Detailed characterization, reliable design tools and guidelines for modelling and building such systems are missing. This thesis presents design-related and operation-oriented innovations for such systems at different scales: (a) application-scale experimental-numerical demonstration of a LHTES test-bed, (b) non-dimensional numerical study of low and high-conducting PCMs at storage-unit scale, (c) novel power dense macro-porous PCM structures at encapsulation scale, and (d) interface scale experimental melt interface tracking by advanced tomography techniques for high-temperature PCMs.A megajoule scale high-temperature LHTES modular LHTES test-bed was built and tested, for charging-discharging at temperatures up to 950 K with aluminium alloy PCM encapsulated in stainless steel and air as the heat transfer fluid (HTF). Engineered open-cell cellular ceramic lattice were used as porous fins for enhancing the HTF-PCM heat transfer. Successful first operation was demonstrated with near-isothermal discharge for 2.7 hours in a 1.31 MJ storage. A quasi-1D lumped parameter model was developed and validated to quantify its thermal stratification, heat losses, and phase change characteristics. Heat storage characteristics of scaled configurations of the test-bed were predicted using the model.A 2D transient phase change model was used to compare a high-conducting, high melting point aluminium alloy PCM with a commercially available low-conducting, low melting point paraffin wax to quantify the effect of PCM properties, encapsulation shape, load conditions, and buoyancy driven internal convection on the power density. Parametric study and non-dimensional analysis quantified the influence of thermal and geometrical parameters on phase change and contribution of natural convection inside the encapsulations linking the melt fraction and heat transfer rates to combination of Fourier, Stefan, Rayleigh and Nusselt numbers.With high-conducting PCMs, the LHTES power density is limited by HTF-PCM convective heat transfer which can be enhanced by using novel macro-porous encapsulation designs. A comparison of several random and ordered macro-porous cells was performed with a 3D coupled CFD-phase change model. A mesh-based convolutional neural network was trained to emulate the 3D model and predict phase change time and pressure drop characteristics. Finally, a synchrotron source X-ray tomography experimental campaign to create a validation case for phase change models of high-temperature PCMs is detailed. Transient 3D melt interface tracking was conducted for aluminium alloy in cylindrical encapsulations heated using lasers. As the beamline was limited to small samples, a furnace heating setup was also built for radiography experiments of larger cubic samples at a tabletop CT facility.This thesis presents a combination of modelling frameworks and experimental setups to provide general understanding of transient heat transfer in PCMs at different scales, provide novel approaches for heat transfer enhancement, and tools for designing high-temperature LHTES systems.

EPFL2022

Chargement

Electron Beam Induced Copper Deposition from Carboxylate Precursors and the Study of Underlying Growth Mechanisms

Luisa Berger

EPFL2020

EPFL2022