RG

R. Gremaud

17 records found

Enthalpy-entropy compensation (EEC) is very often encountered in chemistry, biology and physics. Its origin is widely discussed since it would allow, for example, a very accurate tuning of the thermodynamic properties as a function of the reactants. However, EEC is often discarde ...

Optical response of the sodium alanate system

GW0-BSE calculations and thin film measurements

We calculate from first principles the optical spectra of the hydrides in the sodium alanate hydrogen storage system: NaH, NaAlH4, and Na 3AlH6. In particular we study the effects of systematic improvements of the theoretical description. To benchmark the calculations we also mea ...
We investigated the influence of the substrate on the thermodynamic properties of metal hydride thin films by hydrogenography, using PdHx as a model system. After appropriate hydrogen cycling, reproducible hydrogenation properties are found at the same equilibrium pres ...
A detailed structural analysis of Mg-Ti-H thin films reveals the presence of a chemically partially segregated but structurally coherent metastable phase. By combining X-Ray Diffraction and Extended X-ray Absorption Fine Structure (EXAFS) spectroscopy on MgyTi1-y< ...

Hydrogenography of PdHx thin films

Influence of H-induced stress relaxation processes

Hydrogenography is a new optical thin film combinatorial method that follows hydrogenation and determines its associated thermodynamic properties. Due to clamping to the substrate, stresses generated in thin films are larger than in bulk. This must be taken into account for a com ...
A multisite lattice gas approach is used to model pressure-optical- transmission isotherms (PTIs) recorded by hydrogenography on Mgy Ti1-y Hx sputtered thin films. The model reproduces the measured PTIs well and allows us to determine the chemical short-range order parameter s. T ...
MgHx thin films are grown by activated reactive evaporation in a Molecular Beam Epitaxy system fitted with an atomic hydrogen source. During deposition the electrical and optical properties are measured in-situ. The structural properties are determined ex-situ by Atomic Force Mic ...
Using hydrogenography, we recently mapped the thermodynamic properties of a large range of compositions in the quaternary Mg-Ti-Ni-H system. The enthalpy of hydride formation of Mg-Ni alloys is significantly altered upon Ti doping. For a small range of compositions, we find a hyd ...
The structural, optical, and electrical transformations induced by hydrogen absorption and/or desorption in Mg-Ti thin films prepared by co-sputtering of Mg and Ti are investigated. Highly reflective in the metallic state, the films become highly absorbing upon H absorption. The ...
The search for new lightweight metal hydride storage materials is essentially like looking for a needle in a haystack. Over the years, a number of combinatorial methods have been developed to scan the properties of materials in an efficient way. We demonstrate that combinatorial ...

Hydrogenography

An optical combinatorial method to find new light-weight hydrogen-storage materials

Hydrogenography is an advanced combinatorial and standard method used for the search of new hydrogen-storage materials to synthesize bulk samples and to use volumetric or gravimetric techniques to follow their hydrogenation reaction. Hydrogenography, with a straightforward optica ...
The hydrogenation of metallic Mg2 Ni films was shown to proceed via a self-organized double layering of transparent Mg2 NiH4 and metallic Mg2 NiH0.3. For stoichiometries departing from Mg2 Ni we conclude from optical reflection, transmission and electrical measurements that the h ...
Thin film composition spreads of Mg-Ni were deposited by co-sputtering on micromachined Si-cantilevers. The investigated compositions range from about Mg 60 Ni ...
Hydrogenography, an optical high-throughput combinatorial technique to find hydrogen storage materials, has so far been applied only to materials undergoing a metal-to-semiconductor transition during hydrogenation. We show here that this technique works equally well for metallic ...
The optical properties, the switching kinetics and the lifetime of hydrogen switchable mirrors based on Mg-Ni alloys are determined with particular regard to the composition of the optically active metal-hydride layer in combination with the thickness ...
The structural, optical and dc electrical properties of Mg xAl1-x (0.2 ≤ x ≤ 0.9) gradient thin films covered with Pd/Mg are investigated before and after exposure to hydrogen. We use hydrogenography, a novel high-throughput optical technique, to map simulta ...

Ti-catalyzed Mg(AlH4)2

A reversible hydrogen storage material

Mg-Al thin films with a compositional gradient are co-sputtered from off-centered magnetron sources and capped with a thin Pd layer. We study their hydride formation by monitoring their optical transmission during hydrogenation under defined pressure and temperature conditions. W ...