Project

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Achieving High-performance Light-Induced Magnetic Properties of Surface-Adsorbed Molecular Switches

Applicant Daffé Niéli
Number 193293
Funding scheme Ambizione
Research institution Paul Scherrer Institut
Institution of higher education Paul Scherrer Institute - PSI
Main discipline Condensed Matter Physics
Start/End 01.09.2021 - 31.08.2025
Approved amount 591'200.00
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All Disciplines (2)

Discipline
Condensed Matter Physics
Inorganic Chemistry

Keywords (7)

Electrospray; Surface; Cyanometallates; XMCD; XAS; Photomagnetism; Ultrafast

Lay Summary (French)

Lead
Les molécules dites commutables dont la structure électronique, les propriétés optiques et magnétiques peuvent être contrôlées par un stimulus extérieur (irradiation lumineuse, pression, température, champ électrique) sont des candidates à fort potentiel pour la construction de dispositifs. Nos travaux se focalisent sur des complexes polymétalliques moléculaires à base de fer et de cobalt présentant des ponts cyanures et aux propriétés photomagnétiques pouvant être modulées par irradiation lumineuse ou changement de température. Notre objectif est d'étudier ce phénomène physique lorsque ces molécules sont déposées sur des surfaces à l’échelle de la monocouche. Ce dernier point constitue un aspect crucial lors de leur intégration dans des dispositifs pour des applications et parfois, peut même en devenir l’aspect limitant.
Lay summary

Avec ce projet de recherche, notre but est de contribuer à une meilleure compréhension des propriétés commutables de molécules photomagnétiques à base de fer et de cobalt lorsque celles-ci sont déposées sur surface. Outre leurs propriétés de commutation, ces molécules offrent divers avantages (solubilité, possibilité de fonctionnalisation de ligands…) qui en font des candidates idéales pour l’étude des états transitoires dût à la commutation ainsi que leur design sur surface.

Afin de réaliser cet objectif, nous souhaitons développer sur la ligne de lumière X-treme (Swiss Light Source) une installation permettant de déposer les molécules par électrospray, couplant ainsi directement la préparation des échantillons avec les mesures physiques de leurs propriétés. Les propriétés électroniques et magnétiques des matériaux obtenus seront évaluées par spectroscopie magnétique d’absorption des rayons X en synchrotron. Par la mise en place de ces nouvelles conditions expérimentales nous souhaitons identifier les relations entre substrat (surface) et molécules permettant de préserver ou au contraire d’annihiler les propriétés photomagnétiques. Nous chercherons également à explorer les modifications résultant du dépôt des molécules sur surface et de leur environnement proche par comparaison avec les propriétés de ces mêmes molécules en solution par exemple.

Ce travail permettra de générer des résultats inédits et essentiels sur ces systèmes à fort potentiel technologique. S’ils sont concluants, ces résultats ouvriront la voie vers l’utilisation de ces systèmes sur des surfaces et bénéficiera à des applications potentielles en nanoélectronique par exemple.

Direct link to Lay Summary Last update: 22.08.2021

Lay Summary (English)

Lead
Molecular switches-based materials can be regarded as a valuable alternative to the demand of new technologies for their exciting and novel features, able to overcome the capacity of existing materials. Recent investigations have established the great potential of cyanide-bridged iron-cobalt polymetallic complexes showing a concomitant change in their optical and magnetic properties upon light irradiation. However, research to date has not yet determined if the bistable properties of these systems can be properly addressed in electronic circuit or another relevant interface. This step often constitutes the main challenge of the device fabrication and even sometimes is the limiting factor.
Lay summary

With this project of research our goal is to address the photoswitchable properties of monolayers charge-transfer molecules adsorbed onto different substrates. Besides the photo-induced magnetic properties, the Fe/Co based molecular switchable units present considerable advantages making them preferred candidates for the study of the transient absorption states and the design of surface molecules. 

To achieve this goal set, an electrospray deposition setup will be implemented at the X-treme beamline (Swiss Light Source) in a first step to allow solution depositions of molecules onto surfaces in high vacuum. Using the newly developed experimental setup, the photomagnetic molecules will be deposited onto surfaces in high vacuum and their electronic and magnetic properties will be explored using x-ray magnetic spectroscopy performed at synchrotron. Our efforts will be devoted to understand how the influence of the interface substrate-molecule affect the physical properties of complexes. To obtain answers to the question, different substrates will be investigated, and the nature of the coordinating ligands of the molecules in contact with the substrate will be varied.

Our work intends to take a step forward in the manipulation of electronic states of cyanide-bridge molecular compounds with light and temperature. An implication of this is the identification of the experimental conditions (interface surface-molecule, structural properties of the molecules, technique of deposition…) allowing down-scaling the switchable properties in these systems. These findings will open room to the use of electron-transfer switchable systems in surface science, Hence, such research will benefit to potential applications as otherways of addressing bits are demanding, in memories based on thermal assisted switching or spin transfer switching for instance.

 

Direct link to Lay Summary Last update: 22.08.2021

Responsible applicant and co-applicants

Employees

Abstract

Molecular switches-based materials can be regarded as a valuable alternative to the demand of new technologies for their exciting and novel features, able to overcome the capacity of existing materials. Recent investigations have established the great potential of cyanide-bridged iron-cobalt polymetallic complexes showing a concomitant change in their optical and magnetic properties upon light irradiation. However, research to date has not yet determined if the bistable properties of these systems can be properly addressed in electronic circuit or other relevant interface. This step often constitutes the main challenge of the device fabrication and even sometimes is the limiting factor. The main objective of this project is the controlled manipulation of the electronic states of surface deposited cyanide-bridged Fe/Co molecular cubes using temperature and light. We will focus on A-Fe4Co4 (with A, an alkali ion) heterocubane complexes, which demonstrate outstanding photomagnetic properties combined with unique redox-flexibility features. The optical switching phenomena in these molecules results from an electron transfer between the metallic centers coupled to a spin transition of the Co ions. The specific goal of this work is to identify the conditions allowing to transfer the switching properties to the nanoscale in the form of monolayers on surfaces or even beyond, to the limit of single molecules. To achieve this goal, an electrospray deposition (ESD) setup shall be implemented to allow solution depositions of Fe4Co4 molecules onto surfaces in high-vacuum. The topography of the surface adsorbed Fe4Co4 molecules shall be observed with low-temperature scanning tunneling microscopy (STM) to study pattern formations. Transition metals L-edge X-ray absorption spectroscopy and X-ray magnetic circular dichroism (XMCD) in external magnetic fields and at low temperatures shall be performed to explore the electronic and magnetic states in the presence of suitable laser excitations. In parallel to the main research project, Fe2Co2 square molecules with even further reduced dimensionality are available. Therefore, the above-mentioned surface deposition studies can also be performed on these molecules whose photo-reversal effect can be obtained using a laser wavelength different from the one used to reach the excited state of the molecules.For these systems to be useful and to control their light-induced properties, it is an open, important and timely question: What are the transient intermediate states involved in the optical switching phenomena? Therefore, the second and equally important focus of this project is to understand the intimate mechanism of the electron-transfer and spin transition on the femtosecond time-scale. For that purpose, element-specific transient X-ray absorption and emission spectroscopy (XAS and XES) shall be used to track the ultrafast out-of-equilibrium dynamics of the Fe4Co4 molecular cages in solution. All together, the proposed research will be of immense benefits for the thermal and optical writing of these systems and its further optimization in return.
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