ELECTRONIC STRUCTURE, MAGNETISM AND DYNAMICS
OXYGEN CONTENT: A KEY PARAMETER TO TUNE THE MEMRISTIVITY IN LANTHANUM NICKELATE-BASED MEMORY DEVICES
X-ray absorption near-edge structure (XANES) experiments are an effective means of relating the redox state of Ni in La2NiO4+δ (L2NO4) thin films to changes in its structure, oxygen over-stoichiometry (δ) and electrical properties. This work is an incremental step towards the understanding of the microscopic origins behind the Valence-Change Memory (VCM) mechanism in lanthanum-nickelate thin films.
VCMs are a promising technology for the hardware implementation of neuromorphic computing as they can combine a large number of desired properties, including switching speed, multilevel memory storage, scalability, low power consumption and CMOS compatibility . The resistance-change mechanism in these bipolar memristive devices is governed by internal redox reactions , and thus the control over the oxygen drift and diffusion kinetics is key in obtaining a gradual change in resistance required for analog-type artificial synapse applications.
Surprisingly, few devices have been designed with this in mind, as they are commonly built around ionic insulating active materials. Here, this shortcoming is addressed by using a Mixed Ionic- Electronic Conducting (MIEC) oxide. This work demonstrates how the oxygen content in L2NO4, tuned through post-annealing treatments, has a critical influence on the memory characteristics of these VCM devices.
Highly oriented L2NO4 thin films were prepared by pulsed injection metal-organic vapour deposition
Atomic scale insight into the formation, size and location of platinum nanoparticles supported on γ-alumina, A.T. Batista (a), W. Baaziz (b), A.-L. Taleb (a), J. Chaniot (a,c), M. Moreaud (a,d), C. Legens (a), A. Aguilar-Tapia (e), O. Proux (f), J.-L. Hazemann (e), F. Diehl (a), C. Chizallet (a), A.-S. Gay (a), O. Ersen (b)
and P. Raybaud (a), ACS Catal. 10, 4193- 4204 (2020); https://doi.org/10.1021/ acscatal.0c00042/. (a) IFP Energies nouvelles, Solaize (France) (b) Institut de Physique et Chimie des Matériaux de Strasbourg, CNRS-Université de Strasbourg (France) (c) Laboratoire Hubert Curien, CNRS-
Université Jean Monnet de Saint-Etienne (France) (d) Centre for Mathematical Morphology, MINES ParisTech, Fontainebleau (France) (e) Institut Néel, CNRS-Université Grenoble Alpes, Grenoble (France) (f) OSUG, CNRS-Université Grenoble Alpes, Grenoble (France)
 O. Proux et al., J. Environ. Qual. 46, 1146-1157 (2017).  A. Aguilar-Tapia et al., Rev. Sci. Instrum. 89, 35109_1-35109_8 (2018).  A.T. Batiste et al., J. Catal. 378, 140-143 (2019).  J. Chaniot et al., Image Anal. Stereol. 38, 25-41 (2019).
PRINCIPAL PUBLICATION AND AUTHORS
Fig. 97: a) 3D tomographic reconstruction volume and DFT model of the Pt13 cluster anchored at the chlorinated edge of alumina. b) High-resolution HAADF-STEM image. c) Wavelet transform analysis of Pt L3-edge k2 weighted
EXAFS data, for the reduced 0.3%Pt/γ-Al2O3-Cl catalyst.
edges, as suggested by DFT models, can be at the origin of the catalytic performance observed for these catalytic systems. The EXAFS analysis was a key step to assess the general characteristics of the catalyst at the macroscopic scale and to
validate the chemical descriptors determined from the localised electron microscopy observations and DFT simulations. Future work could investigate, for instance, the genesis of the Pt NPs during the activation step under H2.