Pierre Richard Dahoo

Pressure and Temperature Sensors Using Two Spin Crossover Materials

The possibility of a new design concept for dual spin crossover based sensors for concomitant detection of both temperature and pressure is presented. It is conjectured from numerical results obtained by mean field approximation applied to a Ising-like model that using two different spin crossover compounds containing switching molecules with weak elastic interactions it is possible to simultaneously measure P and T. When the interaction parameters are optimized, the spin transition is gradual and for each spin crossover compounds, both temperature and pressure values being identified from their optical densities. This concept offers great perspectives for smart sensing devices.

Numerical simulation of a device with two spin crossover complexes: application for temperature and pressure sensors

The spin-crossover (SCO) phenomenon is related to the ability of a transition metal to change its spin state vs. a given perturbation. For an iron(II) SCO complexes the reversible changes involve the diamagnetic low-spin (S = 0) and the paramagnetic high-spin (HS S = 2) states [1,2,3]. In this contribution we simulate the HS Fraction (nHS) for different set values of temperature and pressure for a device using two SCO complexes with weak elastic interactions. We improve the calculation given by Linares et al. [4], taking also into account different volume (VHS, VLS) changes of the SCO. We perform all the calculation in the frame work of an Ising-like model solved in the mean-field approximation. The two SCO show in the case of weak elastic interactions, gradual spin transitions such that both temperature and pressure values can be obtained from the optical observation in the light of calculations discussed in this article.

2D Spin Crossover Nanoparticles described by the Ising-like model solved in Local Mean-Field Approximation

Some six-coordinate iron (II) coordination compounds exhibit thermal-, optical-, electrical-, magnetic- and pressure-induced switching between the diamagnetic low-spin (LS, S=0) and the paramagnetic high-spin (HS; S=2) states [1]. This may lead to potential application of these complexes in molecular devices such as temperature and pressure sensors [2]. An Ising-like model has been proposed to explain the occurrence of the thermal hysteresis behaviour [3,4] of this switchable solids. In this contribution, the local mean field approximation is applied to solve the Hamiltonian modelling interactions pertaining to 2D nanoparticles embedded in a magnetically-inactive matrix

Non-Destructive Characterization by Spectroscopic Ellipsometry of Interfaces in Mechatronic Devices

Abstract Failures often originate at the interfaces in the packaging of mechatronic devices because of the differences in the thermo-mechanical properties of the materials in contact. To enhance the reliability of these devices, it is necessary to have nondestructive analysis techniques such as spectroscopic ellipsometry (SE) to probe the quality of the surfaces and interfaces when the environmental constraints vary. In the field of characterization spectroscopy, SE has become indispensable in microelectronics, as well as in the study of semiconductors, protective coatings based on polymers, metals or other types of metamaterials. It is used to characterize thin films, mono- or multi-layers and bulk materials from a structural and optical point of view by probing transitions whether electronic, vibrational or rotational. In the ultraviolet (UV)- visible and near- to mid-infrared (IR) ranges, which correspond, respectively, to the electronic and vibrational absorption, SE reveals the composition, structure (amorphous or crystalline), porosity and morphology (density, roughness, etc.) of materials as a function of the light wavelength. In order to be used, SE parameters generally require an inverse method based on the simplex, the Levenberg–Marquardt or the Broyden– Fletcher–Goldfarb–Shanno algorithm to determine the dielectric function or complex optical constants. This chapter describes the SE technique and illustrates its application with two examples of characterization, that of sintered silver and polymers present in a mechatronic device. A study of the effects of temperature in dry and wet conditions is also presented and discussed in terms of optical properties.