Séminaire DMONS-DSI, axes 4 et 5 présenté par Jorge Iñiguez

Jorge Iñiguez (Materials Research and Technology Department, LIST, Department of Physics and Materials Science, University of Luxembourg)

Résumé :
Ferroelectric materials have been around for many decades, and yet they continue to challenge our imagination with unexpected behaviors. The most recent and important ferroelectric revival features nanostructures displaying exotic properties that seemed all but impossible not long ago but are now revealed by modern characterization techniques. For example, transmission electron microscopy has allowed us to visualize mesmerizing dipole vortexes and skyrmions in superlattices combining ferroelectric (PbTiO3) and dielectric (SrTiO3) layers [1], confirming the kind of electrostatic/frustration effects predicted earlier by some theory groups [2] and doubted by most.

In this talk I will review the theoretical models [3] that were used to anticipate the rich behaviors that currently generate so much excitement and describe how they allowed us to predict the occurrence of ferroelectric skyrmions [4] that were experimentally confirmed shortly after [5]. I will also discuss some of the most surprising properties of these frustrated ferroelectric states, in particular their negative capacitance behavior, which leads to a miraculous-sounding voltage amplification [6,7]. I will conclude by commenting on the most exciting opportunities in the field.

My main collaborators in these works were M.A.P. Gonçalves and Mónica Graf (formerly at LIST, now at the Czech Academy of Sciences), and Hugo Aramberri (LIST). Collaborators at the University of Cantabria (Junquera), UC Berkeley (Ramesh) and elsewhere were involved in some of the projects. Work in Luxembourg funded by the Luxembourg National Research Fund through projects FNR/C15/MS/10458889/NEWALLS, C18/MS/12705883/REFOX and INTER/RCUK/18/12601980.

[1] Observation of polar vortices in oxide superlattices, A.K. Yadav et al., Nature 530, 198 (2016).
[2] Unusual phase transitions in ferroelectric nanodisks and nanorods, I.I. Naumov, L. Bellaiche and H. Fu,
Nature 432, 737 (2004).
[3] First-principles model potentials for lattice-dynamical studies: general methodology and example of
application to ferroic perovskite oxides, J.C. Wojdel et al., J. Phys. Condens. Matt. 25, 305401 (2013).
[4] Theoretical guidelines to create and tune electric skyrmion bubbles, M.A.P. Gonçalves et al., Science
Advances 5, eaau7023 (2019).
[5] Observation of room-temperature polar skyrmions, S. Das et al., Nature 568, 368 (2019).
[6] Negative capacitance in multidomain ferroelectric superlattices, P. Zubko et al., Nature 534, 524 (2016).
[7] Giant voltage amplification from electrostatically-induced incipient ferroelectric states, M. Graf, H.
Aramberri, P. Zubko and J. Íñiguez, Nature Materials (2022) https://doi.org/10.1038/s41563-022-01332-z

contact : Riccardo HERTEL : riccardo.hertel@ipcms.unistra.fr

Séminaire présenté par Prof Dr-Ing Andrea Iris SchäferSéminaire présenté par Athanassios Boudalis

Prof Dr-Ing Andrea Iris Schäfer (membrane material and processes research for water treatment)

Abstract : Micropollutants are typically persistent organic chemicals that are toxicologically active at very low concentrations (nano- and micro grams per litre), posing a risk to both environmental and human health. Steroid hormones are endocrine disrupters and micropollutants that reach the aquatic environment mostly from wastewater discharge. Nanofiltration is known for incomplete removal (breakthrough), requires high operating pressure (thus energy) for effective removal, and retained micropollutants accumulate concentrate streams. ‘Reactive’ membranes, such as photocatalytic membranes; are an alternative that addresses such shortcomings. Photocatalyst materials can be immobilized in micro- and ultrafiltration membrane pores (1-200 nm), where reactions occur, and at the same time water permeability is high. Micropollutants are degraded in situ within the short, order of seconds, residence times.

Mechanisms of nanopores of different mechanisms, namely stericexclusion, adsorption and photocatalytic reaction are provided. Current progress of steroid hormone degradation in a flow-through photocatalytic membrane reactor is presented at one material example. The membranes used were a polyethersulfone–titanium dioxide (PES-TiO2) membrane produced by collaborators at IOM Leipzig [1, 2]. The TiO2 nanoparticles (10 nm) were immobilised in the nanopores (220 nm) of the membrane polymers (PES and PVDF). Water quality and operational parameters, including organic matter concentration, were evaluated to determine which processes limit the degradation of steroid hormones. Steroid hormone concentrations ranged from low environmentally relevant concentrations 50 ng/L to near the solubility limit of 1 mg/L. Other examples at IAMT are organic PVDF membrane with a porphyrin photosensitiser [3, 4]. These results are not presented.

It is anticipated that flow-through the photocatalytic membrane increases the ‘contact’, and hence the probability to react, between micropollutants and reactive oxygen species in the pores. The result is high removal (80-95%), despite very short hydraulic residence times.  Indeed, relatively simple materials can achieve a very high removal of micropollutants. Further enhancement can be achieved through potentially smaller pores (nanoconfinement), modified photocatalytic materials and longer residence times. When comparing data, reactive membranes are operated at nanofiltration range fluxes with pressures typical for micro- and ultrafiltration yield significant savings in energy. The ambitious water quality guideline (steroid hormone E2 1 ng/L for drinking water) are reachable.

Relevant publications for data in this presentation

[1] K. Fischer, R. Gläser, A. Schulze, Nanoneedle and nanotubular titanium dioxide–PES mixed matrix membrane for photocatalysis, Applied Catalysis B: Environmental, 160 (2014) 456-464.

[2] S. Lotfi, K. Fischer, A. Schulze, A.I. Schäfer, Photocatalytic degradation of steroid hormone micropollutants by TiO2-coated polyethersulfone membranes in a continuous flow-through process, Nature Nanotechnology, 17 (2022) 417–423.

[3] R. Lyubimenko, O.I.G. Cardenas, A. Turshatov, B.S. Richards, A.I. Schäfer, Photodegradation of steroid-hormone micropollutants in a flow-through membrane reactor coated with Pd (II)-porphyrin, Applied Catalysis B: Environmental, 291 (2021) 120097.

[4] R. Lyubimenko, B.S. Richards, A.I. Schäfer, A. Turshatov, Noble-metal-free photosensitizers for continuous-flow photochemical oxidation of steroid hormone micropollutants under sunlight, Journal of Membrane Science, 642 (2022) 119981.

Séminaire Axe 3 & DMO présenté par Dr. Chantal Daniel

Dr. Chantal Daniel (Laboratoire de Chimie Quantique, UMR7177 CNRS – Université de Strasbourg)

Coordination compounds, characterized by fascinating and tunable electronic properties, easily bind proteins, polymers, wires or DNA. Upon irradiation these molecular systems develop functions finding applications in solar cells, photocatalysis, luminescent and conformational probes, electron transfer triggers and diagnostic or therapeutic tools. The control of these functions is activated by the light wavelength, the metal/ligands cooperation and the environment within the first picoseconds (ps). After a brief summary of the theoretical background, this contribution reviews case studies, from 1strow to 3rd row transition metal complexes, that illustrate how spin-orbit, vibronic couplings and quantum effects drive the photophysics of this class of molecules at the early stage of the photoinduced elementary processes within the fs-ps time scale range. Besides the “routine” modeling of spectra, computational chemistry may contribute at their interpretation providing valuable information about the various chemical and optical contributions to the (chiro-)optical properties and about their correlation, not only with nuclear arrangement, but also with spin-vibronic effects which are especially relevant in transition metal complexes.

Séminaire Axe 5 et DCMI : présenté par Jean-Louis Paillaud et Taylan Ors

Orateurs : Jean-Louis Paillaud et Taylan Ors (IS2M, Mulhouse, Université de Strasbourg)

Résumé :

Lorsque la taille des cristaux est trop petite pour la diffraction des rayons X (DRX) sur monocristaux, l’analyse structurale est généralement effectuée par DRX sur poudre ou par diffraction des neutrons suivie d’un affinement par la méthode de Rietveld. Pour les structures complexes, cette analyse peut être problématique en raison d’un fort recouvrement des raies de diffraction même dans le cas d’une bonne résolution instrumentale. La diffraction électronique conventionnelle est bien adaptée pour effectuer la diffraction sur des monocristaux de taille submicrométrique mais la présence des effets dynamiques rend l’interprétation des intensités diffractées difficile pour l’affinement des structures. La diffraction électronique 3D (3D ED) est une technique émergente pour réduire la contribution des effets dynamiques en diffraction électronique par la précession du faisceau ou par la rotation continue de l’échantillon. Par conséquent, les intensités de Bragg observées deviennent traitables par des méthodes standards de la cristallographie. Lors de ce séminaire, différentes études effectuées sur zéolithes en utilisant la technique 3D ED sur microscope électronique en transmission (MET) avec la précession des électrons, d’une part, et en rotation continue de l’échantillon sur un MET de dernière génération dédié à la diffraction électronique, d’autre part, seront présentées. Dans une de ces études, la technique 3D ED a permis de situer les cations Na+ sur 3 positions cristallographiques distinctes dans une zéolithe ECR-1 pure de formule chimique Na11[(A11lSi49O120]. Lors d’un projet collaboratif, l’intensité de la diffusion diffuse obtenue sur la zéolithe ZSM-48, connue pour la présence de désordre dû au polymorphisme, a été analysée par 3D ED. Grâce à ces résultats, les défauts d’empilement se produisant suivant une direction cristalline particulière a été identifiée. De plus, l’un des polymorphes de la ZSM-48 a pu être isolé en tant que nouvelle zéolithe (RUB-58) dont la structure a été confirmée par 3D ED. Grâce à la rotation continue et une caméra à détection directe, des enregistrements rapides, à température ambiante, ont permis l’élucidation de la structure par 3D ED d’un zincophosphate lamellaire synthétisé avec l’hexaméthylènetétramine (C6H12N4 = HMT) en tant qu’agent structurant organique.

Contacts: Guillaume ROGEZ rogez@unistra.fr ; Pierre RABU rabu@unistra.fr

Séminaire AXE 1 “Sciences et Matériaux Quantiques” présenté par Eric Le Moal

Orateur : Eric Le Moal – Institut des Sciences Moléculaires d’Orsay (ISMO)

Résumé : Few-atom-thick (2D) luminescent materials, such as monolayer transition metal dichalcogenides (TMDs), are in the spotlight for their potential applications in optoelectronic nanodevices. Recently, the use of scanning tunneling microscopy (STM) to locally induce light has emerged as a unique nanoprobe of the elementary excitation and emission processes in monolayer TMDs. In this seminar, I will review five years of successful collaboration between IPCMS and ISMO in this area. Using a unique setup combining optical microscopy and tunneling microscopy in ambient air, we have demonstrated the generation of excitons by inelastic tunneling in MoSe2 and WS2 monolayers [1,2]. Moreover, this combination of techniques opens new perspectives for the study of exciton-charge carrier interactions in this class of materials [3].

[1] D. Pommier et al, Phys. Rev. Lett. 123, 027402 (2019)
[2] R. J. Peña Román et al, Phys. Rev. B 106, 085419 (2022)
[3] R. J. Peña Román et al, Nano Lett. 22, 9244 (2022)

Si vous souhaitez rencontrer Eric Le Moal, n’hésitez pas à contacter :

Stéphane BERCIAUD (berciaud@unistra.fr) et Guillaume SCHULL (schull@unistra.fr )

Séminaire DSI présenté par Benedikt LASSALLE

Benedikt LASSALLE, synchrotron-soleil

Résumé :

Controlling the composition, morphology and size of nanomaterials is key to tune their properties and function. This control requires fundamental insights into the processes that govern the synthesis of nanomaterials, but also their behaviour under functioning conditions. X-ray absorption spectroscopy is an ideal tool to observe such phenomena, since it can be used to probe reactions under in situ conditions, allowing experimental setups that are close to synthetic or operating conditions.
In this presentation, we will report our work on the structure and function of electrocatalytic materials, such as oxides and sulfides, that are active for the oxygen (OER) and hydrogen evolution reactions (HER). Using in situ X-ray absorption spectroscopy as our major tool, we will show how the local and electronic structure of the materials evolve during these catalytic reactions and influence their efficiency.
In a second part, we will present our recent work concerning the combination of microfluidic systems with X-ray techniques and their potential application to understand the synthesis of nanomaterials. This will be exemplified with an upcoming project to be carried out in collaboration with the team of Ovidiu Ersen at the IPCMS, which deals with the study of hybrid perovskites synthesis by a combination of XAS and electronic microscopy.

Pour tout contact : Ovidiu Ersen (0388107028 – ovidiu.ersen@ipcms.unistra.fr)

Séminaire DON : présenté par Daniele Brida

Daniele Brida, Department of Physics and Materials Science, University of Luxembourg

Many fundamental and ubiquitous physical phenomena have origin at the ultrafast timescale. The possibility to investigate various primary processes on their intrinsic timescales relies on the generation of ultrashort pulses with widely tunable carrier frequency, from ultraviolet to mid- and far-infrared. These optical waveforms allow the investigation of microscopic light-matter interactions in a wide variety of condensed material systems to unveil the deep origin of their optoelectronic properties. 

A novel idea consist in exploiting the optical field itself to control the properties of crystals and nanostructures. With this approach, it becomes possible to access phenomena occurring within a oscillation of light as benchmarked by three experiments: i) optical response of semiconducting nanostructures by impulsively exciting a plasma frequency in mid-infrared range that establishes a plasmonic resonance; ii) quasi-instantaneous localization of electronic wavefunctions in GaAs by non-resonant bias with intense THz radiation; iii) ultrafast electron transport driven by the peak electric field of a single-cycle optical pulses focused on nanostructured gold circuits.