Archive 15 February 2024

Ten years of research & innovation in two-dimensional materials-based spintronics: highlights & future

By in Seminar

Stephan Roche

ICN2 and BIST, Barcelona, Spain

This talk will review more than a decade of intense efforts to explore the potential of graphene and two-dimensional materials for spintronic applications. Along the way, plentiful of unique properties have emerged making topological materials an enabling platform for innovation in advanced electronics, spintronics or quantum technologies. We will overview the milestones and highlight the unprecedented properties which have been revealed to date and point out current challenges and opportunities for harnessing quantum matter to design novel quantum technologies.

 

C12 Quantum Electronics: Leading the next materials leap in quantum computing

By in Seminar

Alice Castan

C12 Quantum Electronics

C12 Quantum Electronics is a spinoff of the Physics Laboratory of the Ecole Normale Supérieure (LPENS) in Paris, France. The company was founded in the beginning of 2020 with the ambitious goal to build a carbon nanotube (CNT)-based quantum processor. From a team of a few scientists at its earliest stage, C12 grew – after securing a $10M seed round in 2021 – into a multiteam organization with over 30 employees. The technology developed at C12 is based on over a decade of research led by CNRS research director Takis Kontos at the LPENS on the use of CNTs in hybrid quantum circuits.

An ultra-clean CNT is directly transferred onto a microchip, where it is suspended over a series of gate electrodes that allow the formation of a double quantum dot (DQD) in which a single electron can be trapped. The spin of the electron is then addressed through coupling to a superconducting microwave circuit. The unique possibility of selectively embedding the CNT or removing it from the microchip at the end of the chip fabrication process provides an opportunity to preselect the qubits integrated in our processor, which is absent from other spin qubit-based quantum computing technologies.

This seminar will give an overview of C12 as well as a presentation of the technology developed in its Paris-based laboratory. Focusing on the core material that makes this technology uniquely promising, we will show how the atomic structure, cleanliness, and isotopic purity of the CNTs acting as the spin qubit hosts influence the performance of the device and how measuring and controlling these parameters can help achieve record fidelity and scalability.

Segregation within bi-metallic nanoparticles at the atomic scale through a combined theoretical and experimental approach

By in Phd Defence

Abstract

The analysis of nanoparticles (NPs) on a nanometric scale for applications in real-life conditions remains a considerable challenge at the present time. In this context, the use of bi-metallic NPs is strongly envisaged in the field of catalysis, with the function of promoting and accelerating the kinetics of surface chemical reactions. It is therefore essential to describe the structure and chemical composition of the surfaces, which interact directly with the surrounding medium in which the NPs are immersed. In the context of this thesis, we have developed a combined theoretical and experimental approach at the atomic scale, with the aim of studying two types of alloy in particular: Gold-Copper (Aux-Cu1-x) and Nickel-Aluminium (Nix-Al1-x).
Using laser synthesis of 5 nm facetted octahedral Aux-Cu1-x NPs and aberration-corrected electron microscopy observations in probe mode, we developed a method for analyzing the chemical composition of each atomic plane. In this way, we have demonstrated a strong segregation effect of gold on the surface, as well as different concentration profiles within the NPs depending on the chemical order (ordered or disordered). In the case of an ordered Au0.5Cu0.5 composition of L10 phase, we have characterized a structure rarely observed until now, corresponding to the presence of the three possible variants of L10 phase within the same particle. In parallel, atomic-scale simulations have enabled more precise analyses to be carried out, considering infinite plane stacks and NPs of different sizes and compositions.
The excellent agreement between simulations and experimental analyses strengthens the relevance of our results and demonstrates the importance of this dual approach, which we subsequently applied to the study of the surface properties of Nix-Al1-x-type NPs. First, we optimized the synthesis parameters to obtain NPs with defined sizes and compositions. Experimental surface analyses coupled with atomistic simulations enabled us to observe a hitherto unseen phenomenon. Indeed, an almost complete segregation of the aluminum appears until the formation of NPs adopting a core (Nickel) – shell (Aluminum) structure, for all the concentrations studied, thus preventing any alloy formation. This is all the more surprising given that, in the bulk state and for a composition of 50% nickel and 50% aluminium, the ordered B2 phase, known for its stability and resistance to corrosion, appears. These striking structural differences between the nanometric and macroscopic scales once again demonstrate the unique physics that exist in the world of the infinitely small.

PhD Candidate :
Grégoire Breyton

Jury :

Dr. Christine Goyhenex – IPCMS – Referee
Pr. Claude Henry – CINaM – Referee
Dr. Pascale Bayle – CEA/Grenoble – Reviewer
Dr. Geoffroy Prévot – INSP – Reviewer
Dr. Hakim Amara – LEM – PhD co-supervisor
Pr. Christian Ricolleau – MPQ – PhD supervisor

Friday 15th December 2023 at 14h00
Pierre-Gilles de Genes Amphitheater, Paris Cité University, Paris

Impact of Mechanical Loading on Deformation and Electronic Properties of Metallic Nanoparticles

By in Phd Defence

Abstract

Metallic nanoparticles (NP) possess unique properties, distinct from bulk materials, offering potential application in mechanics, catalysis and optics. This thesis examines how NPs’ mechanical properties, influenced by shape, size, and composition, affect their electronic properties. Using Molecular Dynamics and Finite Element simulations, we demonstrate shape’s significant effect on the effective elastic response. Our findings highlight that plasticity is controlled by both shape and size with a universal size effect for face-centered-cubic crystalline NPs. In alloyed structures, both strengthening and softening mechanisms are observed, indicating local order’s influence on elasticity and plasticity. Finally, through tight-binding and ab initio calculations, we reveal that plastic deformation creates new reactive NP surface sites.

PhD candidate:
Matteo Erbi’

Jury:

Pr. Riccardo Ferrando – University of Genoa (Italy)- Referee
Dr. Julien Godet – University of Poitiers – Referee
Pr. Francesco Montalenti – University of Milan-Bicocca (Italy) – Reviewer
Dr. Christine Mottet – CINaM – Reviewer
Dr. Fabio Pietrucci – Sorbonne University – Reviewer
Dr. Barbaru Putz- Empa (Suisse) – Reviewer
Dr. Riccardo Gatti – LEM – PhD co-supervisor
Dr. Hakim Amara – LEM – PhD supervisor

Friday 24th November 2023 at 2 pm
Contensou Room, ONERA, 29 Avenue de la Division Leclerc,92320, Chatillôn

 

Impact of nanostructuration on thermal conductivity in amorphous crystalline nanocomposites

By in Seminar

Paul Desmarchelier

Johns Hopkins University, Baltimore, USA

Engineering the thermal properties of semiconductors can benefit a wide range of applications. In particular, the performance of thermal management and thermoelectric generators could be enhanced by greater control over the thermal conductivity of materials. Such a control is possible via the nanostructure, which influences phononic properties. In this context, this seminar will present several studies of amorphous/crystalline silicon nanostructures. In amorphous materials, due to disorder, the vibrational contribution to thermal conductivity is different from that of crystals, and it is possible to distinguish the propagative or ballistic contribution from the diffusive contribution. These different contributions can be studied individually, in particular using a wave-packet approach on molecular dynamics models. In a first study, this categorization is applied to nanocomposites composed of crystalline nanoinclusions in an amorphous matrix. In particular, it is shown that while it is possible to manipulate the propagative contribution via the shape and interconnection of the inclusions, the diffusive contribution is more difficult to control. In a second step, the influence of an amorphous outer layer on a crystalline nanowire is studied by combining a molecular dynamics approach and a continuous media approach. It appears that the addition of the outer layer has little effect on the flux at the amorphous-crystalline interface, but does influence the heat flux at the center of the nanowire.

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