Arthur Yelon

Bio: Arthur Yelon is an academic researcher from École Polytechnique de Montréal. The author has contributed to research in topics: X-ray photoelectron spectroscopy & Giant magnetoimpedance. The author has an hindex of 34, co-authored 269 publications receiving 4793 citations. Previous affiliations of Arthur Yelon include National Renewable Energy Laboratory & École Normale Supérieure.

Origin and consequences of the compensation (Meyer-Neldel) law.

Abstract: We have recently demonstrated that the Meyer-Neldel (MN) rule (compensation law) may be understood as arising naturally when the activation energy for a process is significantly larger than both the typical excitations available and kT. This conclusion was supported by the results of two microscopic models, related to special cases. In the present paper we present arguments, based on general results from statistical physics, which lead to the same conclusion. We show that this simple explanation also leads to the solution of a number of puzzles which have been associated with Meyer-Neldel behavior. We show that phenomena in groups of similar materials yield similar MN slopes. Finally, we show that the values of the slope for semiconductors with gaps in the 1--2-eV range are consistent with the suggestion that optical phonons are the source of the excitation energy in such processes.

Multi-excitation entropy: its role in thermodynamics and kinetics

Abstract: This review concerns the concept of multi-excitation entropy (MEE) and its consequences When a fluctuation involving a large number of excitations occurs, for example, when a large activation barrier is overcome, there must be a large entropy associated with this fluctuation First, the concepts of free energy and entropy, of activated processes and the Arrhenius and Eyring equations are reviewed The tendency to neglect entropy, whose value is difficult to determine, in modelling kinetic processes, is briefly discussed We then present a review of the experimental observations of the phenomenon which is variously known as the Compensation Law, the Isokinetic Rule and the Meyer–Neldel Rule (MNR) These observations include examples from chemistry, condensed matter physics, biology and geology Arguments are then presented for the importance of entropy and particularly of MEE in both kinetics and thermodynamics, when activation energies are large After a discussion of non-entropic models of compensation, we present results which support the MEE model as an explanation of MNR The behaviour of systems with low activation energies, or at high temperatures, to which the MEE model does not apply, is then discussedSeveral consequences of MEE, including applications to the interpretation of experimental data, particularly the unification of models of dc and ac electrical properties of materials are considered The high temperature behaviour of systems which obey the MNR at low temperature is then explained, and the idea of a total entropy, of which the MEE is a part, is introduced, as is the correlation between the two empirical parameters encountered in MNR Finally, these ideas lead to verified predictions of reasonable values of attempt frequencies and cross sections in kinetic processes, which initially appear unreasonable

Giant magnetoimpedance in a cylindrical magnetic conductor

Abstract: A rigorous treatment of the giant magnetoimpedance (GMI) in soft magnetic wires is presented. A small-signal approximation is used for a cylindrical magnetic conductor which is saturated along its axis by a static magnetic field. The general analysis of GMI includes a discussion of the influence of different parameters on the GMI and of how the calculation can be extended to nonsaturating fields. The comparison with high frequency impedance spectra of CoFeSiB wires measured with a network analyzer, including the observation of the ferromagnetic resonance peaks, confirms that the proposed model gives a satisfactory explanation for the linear GMI effect over a broad frequency range and opens the way to more refined calculations.

A New Property of Ferromagnetic‐Antiferromagnetic Coupling

Abstract: Three systems exhibiting ferromagnetic-antiferromagnetic coupling, CoCoO, NiFeNiFeMn, NiFeCr2O3, are studied using uniaxial thin films. A new property of such systems is found, i.e., a concentration of the hysteresis loops as a function of the number of cycles traced (n). This contraction follows a 1/n law for the first 50 cycles and is related to the rotational hysteresis. This phenomenon is attributed to fluctuations in the ferromagnetic-antiferromagnetic coupling, which modify the magnetic interactions between differently coupled regions with each reversal.

Calculations of giant magnetoimpedance and of ferromagnetic resonance response are rigorously equivalent

Abstract: It is simply demonstrated that the giant magnetoimpedance (GMI) response of a plate or ribbon is rigorously equivalent to the response of the same sample in ferromagnetic resonance (FMR) experiment. Thus, all of the solutions for FMR response behavior of metals may be applied to the description of GMI. For situations which have not been studied before, the methods which have been developed over the past 40 years for theoretical description of FMR in metals may be applied to predict the GMI behavior.

I and i

Abstract: There is, I think, something ethereal about i —the square root of minus one. I remember first hearing about it at school. It seemed an odd beast at that time—an intruder hovering on the edge of reality. Usually familiarity dulls this sense of the bizarre, but in the case of i it was the reverse: over the years the sense of its surreal nature intensified. It seemed that it was impossible to write mathematics that described the real world in …

Na-ion batteries, recent advances and present challenges to become low cost energy storage systems

Abstract: Energy production and storage have become key issues concerning our welfare in daily life. Present challenges for batteries are twofold. In the first place, the increasing demand for powering systems of portable electronic devices and zero-emission vehicles stimulates research towards high energy and high voltage systems. In the second place, low cost batteries are required in order to advance towards smart electric grids that integrate discontinuous energy flow from renewable sources, optimizing the performance of clean energy sources. Na-ion batteries can be the key for the second point, because of the huge availability of sodium, its low price and the similarity of both Li and Na insertion chemistries. In spite of the lower energy density and voltage of Na-ion based technologies, they can be focused on applications where the weight and footprint requirement is less drastic, such as electrical grid storage. Much work has to be done in the field of Na-ion in order to catch up with Li-ion technology. Cathodic and anodic materials must be optimized, and new electrolytes will be the key point for Na-ion success. This review will gather the up-to-date knowledge about Na-ion battery materials, with the aim of providing a wide view of the systems that have already been explored and a starting point for the new research on this battery technology.

The structural and luminescence properties of porous silicon

Abstract: A large amount of work world-wide has been directed towards obtaining an understanding of the fundamental characteristics of porous Si. Much progress has been made following the demonstration in 1990 that highly porous material could emit very efficient visible photoluminescence at room temperature. Since that time, all features of the structural, optical and electronic properties of the material have been subjected to in-depth scrutiny. It is the purpose of the present review to survey the work which has been carried out and to detail the level of understanding which has been attained. The key importance of crystalline Si nanostructures in determining the behaviour of porous Si is highlighted. The fabrication of solid-state electroluminescent devices is a prominent goal of many studies and the impressive progress in this area is described.