PhD defense
Understanding in vivo degradation of mesoporous silica therapeutic vectors through in situ ellipsometry
C2N site Marcoussis, Collège de France, ParisPhD defense
Composition du jury proposé
Prof. Mika Linden
Dr. Jacques Leng
Prof. Jean-Marc Frigerio
Prof. Clément Sanchez
Dr. Marco Faustini
Dr. Andrea Cattoni (Co-encadrant)
Dr. Cédric Boissière (Directeur de thèse)
Abstract
The last decades have seen the fast development of mesoporous silica nanoparticles as a biocompatible platform for drug delivery, thanks to their tunable porosity, high loading capacity and the possibility to be functionalized with organic molecules to control cargo release and cell surface recognition. To design efficient nanocarriers and also to assess toxicity issues on human health, a good understanding of mesoporous silica particles biodegradability is mandatory. This research work wants to determine the dissolution rate of mesoporous silica under physiological conditions and identify some of the factors affecting silica behavior in biological media. The conducted study leads to interesting results which can be used to design in vivo tests. Structure and composition of mesoporous silica nanoparticles have been reproduced on 2D thin films and studied through in situ ellipsometric analysis in phosphate buffer, concentrated protein solution and in real biological media such as serum and blood. In particular, we explored dissolution under flow conditions, reproducing the dynamic nature of bloodstream, which can affect the mechanisms of protein adsorption, particle dissolution and drug release. To do so, we developed a special ellipsometric setup which make us able to use opaque liquids (serum, blood) coupled with a microfluidic cell to control flow conditions. We monitored the influence of surface functionalization, pore size and geometry and medium flow on the interfacial behavior of mesoporous silica thin films in biological fluids.
Characterization and Modeling of Magnetoelectric Micro Sensors
C2N site Orsay, salle visio, Orsay CedexPhD defense
Magneto-electric (ME) sensors have been demonstrated as a promising alternative for the detection of weak magnetic signals with high sensitivity. To date, most applications focused on the use of bulk piezoelectric materials on which magnetostrictive thin films are deposited leading to millimeter-sized devices. The integration of such devices into micro-electro-mechanical systems (MEMS), bringing smaller size and lower power consumption, involves addressing several scientific issues ranging from the integration of active materials on silicon to the strong reduction in amplitude of generated signals related to the size reduction of the sensor.
In this context, the first goal of this thesis work was to integrate high crystalline quality piezoelectric thin films on silicon. Pb(ZrxTi1-x)O3 (PZT) with a morphotropic composition (x=0.52) having high electromechanical coupling factor was chosen. Silicon is a necessary template as it allows for the use of conventional clean room processes for the realization of the microsystem. The crystalline quality of the active films is directly linked to the buffer layers that promote the crystalline growth on silicon. For this purpose, Yttria-stabilized Zirconia (YSZ) was used in combination with CeO2 and SrTiO3 to allow further growth of epitaxial perovskites. The choice of the bottom electrode material (SrRuO3 or La0.66Sr0.33MnO3 in this work) further tunes the crystalline orientation of the PZT layer.
To probe the potential of such PZT thin films for ME devices, the first step was to characterize the electromechanical properties of this material in a free standing cantilever structure. Under an applied electric field, the measured displacement of the epitaxial PZT-based cantilevers is characterized by a coefficient d_31=-53pmV^(-1) , a reduced value with respect to the bulk material but that can be enhanced by further optimizing the film growth. The second step consists in ascertaining the ability of the cantilever to be used as resonator. For that purpose, first characterizations of oscillators have been performed to extract the resonant frequencies and the associated quality factors. Then, the resonant frequency shift with DC bias-induced stress was measured. Finally, a magnetostrictive layer of TbFeCo was added on the PZT cantilevers to sense magnetic field based on the ME effect. The resulting resonant frequency shift with external applied magnetic field was characterized with a typical sensitivity of 10’s of µT.
Keywords: Magneto-electric effect, piezoelectric, magnetostrictive materials, magnetic sensors, ME sensors.
Mots clés en anglais :
Magnetic,Sensors,Piezoelectric,magnetostriction
Edge driven magnetic switching in CoFeB-MgO Based spintronic nanodevices
C2N site Orsay, salle 44, Orsay CedexPhD defense
Jury
Gilles Gaudin
Directeur de recherche CNRS, Grenoble Rapporteur
François Montaigne
Professeur, Université de Lorraine Rapporteur
Tianxiao Nie
Professeur, Université de Beihang Examinateur
Dafiné Ravelosona
Directeur de recherche CNRS, Orsay Directeur de thèse
Weisheng Zhao
Professeur, Université de Beihang Co-Directeur de thèse
Guillaume Agnus
Maitre de conférences, Université Paris Sud Invité
This thesis focuses on the influence of edge damages introduced by the patterning process on the magnetic switching of spintronics nanodevices. Two typical magnetic switching have been investigated: (i) field-induced switching in magnetic nanodots with perpendicular magnetic anisotropy (PMA) and (ii) current-induced switching in Magnetic Tunnel Junctions (MTJ) with in-plane magnetization. Along this line, we first have developed the full nanofabrication process for both magnetic nanodots down to 400 nm and MTJ nanopillars down to 100 nm using conventional electron beam lithography, ion beam etching and lift-off approach. By studying the switching field distribution (SFD) of magnetic nanodots using Kerr image microscopy, we show that the magnetization reversal is dominated by the nucleation and pinning of Domain Walls (DWs) at the edges of the nanodots due to the damages induced by the patterning process. For MTJ nanopillars, we show that by using SiO2-based insulator material for encapsulation, unexpected resistive Si filaments are formed at the edges of the MTJ. These Si filaments exhibit resistive switching, which allows us to demonstrate for the first time a heterogeneous memristive device, namely resistively enhanced MTJ (Re-MTJ) that combines magnetic and resistive switching. We discuss the potential application for Re-MTJ as a logic-in-memory device with memory encryption function.
Manipulation of Dirac Cones and Edge states in Polariton Honeycomb Lattices
C2N site Marcoussis, Salle R. Planel, NozayPhD defense
Composition du jury proposé
Rapporteur M. Dimitrii Krizhanovskii, University of Sheffield, Royaume-Uni
Rapporteur M. Mark Oliver Goerbig, LPS, Université Paris-Sud
Examinatrice Mme. Hannah Price, University of Birmingham, Royaume-Uni
Examinateur M. Jean Dalibard, Collège de France
Examinateur M. Mathieu Bellec, LPMC, Université de Nice-Sophia Antipolis
Directrice de thèse Mme. Jacqueline Bloch, C2N
Encadrant de thèse M. Alberto Amo, PhLAM, Lille
Abstract
The engineering of Dirac matter using photonic materials opens unhindered opportunities to explore unconventional transport and novel topological phases. Thanks to the direct optical access to the spatial and momentum wavefunctions and spectrum exciton polaritons in semiconductor microcavities appear as an extraordinary platform to emulate 1D and 2D Hamiltonians, including Dirac Hamiltonians.
By etching a GaAs-based microcavity, a honeycomb lattice for polaritons has been fabricated. The lowest two bands of this structure emulate for photons the π and π* bands of graphene. Remarkably, the system also permits exploring orbital degrees of freedom, inaccessible in actual graphene.
In the first part of this thesis a polariton emulator is used to address the physics of edge states in a honeycomb lattice. New edge states, with flat and dispersive bands, have been discovered and visualised in orbital graphene.
In the second part of the thesis we demonstrate experimentally a method to tailor the Dirac dispersion for photons. By implementing uni-axial strain in the honeycomb lattice, Dirac photons that combine zero, finite and infinite effective masses are created.
The experimental and theoretical results here presented open new perspectives for the engineering of interfaces between photonic lattices with different types of Dirac dispersions. Furthermore, the excitonic component of polaritons assures sensitivity to external magnetic fields, providing the possibility to break the time reversal symmetry of the system and to study photonic topological edge states in exotic Dirac cones. Finally, nonlinear Dirac physics can be probed in this system owing to polariton-polariton interactions
(in french)
C2N site Orsay, , Orsay CedexPhD defense
(in french)
Thales Research & Technology, Palaiseau, PalaiseauPhD defense
(in french)
C2N site Orsay, salle 44, Orsay CedexPhD defense
(in french)
C2N -Site Orsay, Salle 044 (P. Grivet), Orsay CedexPhD defense
(in french)
C2N -Site Orsay, Salle Visioconférences, Orsay CedexPhD defense
Single photon generation and manipulation with semiconductor quantum dot devices
C2N - Site de Marcoussis, , MarcoussisPhD defense
Composition du jury :
Rapporteur : Fabio Sciarrino - La Sapienza University, Rome
Rapporteur : Julien Claudon - CEA, Institut Nanosciences et Cryogenie
Examinateur : Antoine Browaeys - Laboratoire Charles Fabry
Examinateur : Wolfgang Löffler - Leiden University
Examinatrice : Eleni Diamanti - Université Pierre et Marie Curie
Directrice de thèse : Pascale Senellart - CNRS-C2N
Abstract:
Single photons play a central role as quantum information carriers in quantum networks to connect distant nodes. A promising approach is the realization of efficient atom-cavity interfaces, which allows the deterministic and reversible transfer of information between the flying photons and the stationary atomic quantum bit. In this work, we use light-matter interfaces based on a single semiconductor quantum dot, acting as an artificial atom, deterministically coupled to a micropillar cavity. We show that such a device is both an efficient emitter and receiver of single photons, and can be used to implement basic quantum functionalities.
First, the device is shown to act as a source of single photons, which allows the generation of highly indistinguishable photons with a record brightness. These single-photon sources are then used to investigate path-entangled N00N states and propose a new tomographical method. And finally, we observe optical nonlinearities at the single photon level, and we demonstrate the filtering of single photon Fock states from classical incident light pulses.