Growth and Characterization of AlScN: A New Promising Material for Piezoelectric and Ferroelectric Devices
III-nitride semiconductors — GaN, AlN, and InN — have revolutionized the lighting market and are rapidly entering the power electronics sector. Currently, new nitride compounds are being explored in the search for novel functionalities. In this context, aluminum scandium nitride (AlScN) has emerged as a particularly promising new member of the nitride family. Incorporating scandium into AlN leads to:
* Enhanced Piezoelectric Constants: Making AlScN highly attractive for the fabrication of piezoelectric generators and high-frequency SAW/BAW filters.
* Increased Spontaneous Polarization: The enhanced polarization can be exploited in designing high-electron-mobility transistors (HEMTs) with very high channel charge densities.
* Ferroelectricity: The recently discovered (2019) emergence of ferroelectric properties opens up possibilities for developing new non-volatile memory devices.
Over the past five years, AlScN has become a major focus of research, presenting numerous open questions and exciting opportunities to explore.
This PhD thesis will focus on the study of the growth and properties of AlScN and GaScN synthesized by molecular beam epitaxy (MBE). The student will receive training in the use of an MBE system for the synthesis of III-nitride semiconductors and in the structural characterization of materials using atomic force microscopy (AFM) and X-ray diffraction (XRD). The variation of the polarization properties of the materials will be investigated by analyzing the photoluminescence of quantum well structures. Finally, the student will be trained in the use of simulation software to model the electronic structure of the samples, aiding in the interpretation of the optical results.
Development of photo-printed interferometric biosensors on multi-core optical fibers for molecular diagnostics
Optical fibers are minimally invasive devices commonly used in medicine for in vivo tissue imaging by endoscopy. However, at present, they only provide images and no molecular information about the tissues observed. The proposed thesis is part of a project aimed at giving optical fibers the ability to perform molecular recognition in order to develop innovative biosensors capable of performing real-time, remote, in situ, and multiplexed molecular analysis. Such a tool could lead to significant advances in the medical field, particularly in the study of brain pathologies, where knowledge of the tumor environment, which is difficult to access using conventional biopsies, is essential.
The proposed approach is based on 2-photon polymerization printing of interferometric structures at the end of each core of a multifiber assembly. The detection principle is based on the interference occurring in these structures and their modification by the adsorption of biological molecules. Each fiber in the assembly will act as an individual sensor, and measuring the intensity of the light reflected at the functionalized end will provide information about the biological interactions occurring on that surface. By modeling the interference phenomenon, we determined parameters to optimize the shape and sensitivity of interferometric structures (PTC InSiBio 2024-2025). These results enabled the printing and characterization of the sensitivity of interferometric structures on single-core fibers. The objectives of the thesis are to continue this optical characterization on new samples and to develop original photochemical functionalization methods in order to graft several biological probes onto the surface of the fiber assemblies. This multi-functionalization will enable multiplexed detection, which is essential for future medical applications. Depending on the progress of the thesis, the biosensors will be validated through the detection of biological targets in increasingly complex environments, up to and including a brain tissue model.
Modeling of a magnonic diode based on spin-wave non-reciprocity in nanowires and nanotubes
This PhD project focuses on the emerging phenomenon of spin wave non-reciprocity in cylindrical magnetic wires, from their fundamental properties, to their exploitation towards realizing magnonic diode based devices. Preliminary experiments conducted in our laboratory SPINTEC on cylindrical wires, with axial magnetization in the core and azimuthal magnetization on the wire surface, revealed a giant non-symmetrical effect (non-symmetrical dispersion curves with different speeds and periods for left- and right-propagating waves), up to an extent of creating a band gap for a given direction of motion, related to the circulation of magnetization (right or left). This particular situation has not been yet described theoretically or modeled, which sets an unexplored and promising ground for this PhD project. To model spin-wave propagation and derive dispersion curves for a given material we plan to use different numerical tools: our in-home 3D finite element micromagnetic software feeLLGood and open source 2D TetraX package dedicated to eigen modes spectra calculations. This work will be conducted in tight collaboration with experimentalists, with a view both to explain experimental results and to guide further experiments and research directions.
Mapping surface potentials of catalytically activated metal oxide photoanodes
During photoelectrolysis (or solar water splitting), charge transfer at the photoanode / electrolyte interface is determined by the alignment between energy bands, both at the electrode and electrolyte side. Surface potential of the electrode plays a major role on the final band bending and thus charge separation at the interface. Also called electrochemical surface potential, it varies as a function of material environment (vacuum, air, water, etc.). The objective of this thesis is to address the OER (Oxygen Evolution Reaction) at the photoanode / electrolyte interface in terms of energy bands and in particular from the electrochemical surface potential perspective. Thus, during this thesis the student will characterize surface potentials of a series of catalytically activated metal oxide photoanodes in contact with different environments (vacuum, variable humidity air, water) and correlate it to photoelectrochemical activity. PhD student’s activity will be structured around fours axes: i) synthesis of photoanodes; ii) photoelectrochemical activity characterization; iii) characterization by atomic force microscopy (AFM) correlated with Kelvin force microscopy (KPFM); iv) synchrotron X-ray spectromicroscopies (STXM, XPEEM) and near ambient pressure photoemission (NAP-XPS). The student will be hosted at the SPEC laboratory at CEA-Saclay for the duration of the thesis. HisHer work is part of a long-standing collaboration between SPEC and SOLEIL.
ULTRAFAST SENSING BY ELECTRON AND MAJORANA FLYING QUBITS
An emerging pathway for quantum information is the use of flying electronic charges, such as single-electron excitations, as qubits.
These flying qubits present a key advantage: their intrinsic Coulomb interaction, which enables deterministic two-qubit gates and applications in quantum sensing.
Compared to photonic qubits, they therefore provide a natural means to overcome certain fundamental limitations.
Their main drawback lies in rapid decoherence, but this challenge can be mitigated by operating at ultrafast timescales, on the order of a picosecond.
An additional strategy involves exploiting the topological protection provided by Majorana modes, non-Abelian quasiparticles that are insensitive to local perturbations.
So far, most research has focused on localized 0D modes (at the ends of superconducting nanowires), with no conclusive experimental demonstrations.
This project proposes a new approach based on 1D chiral Majorana modes, offering a pathway toward topologically protected flying qubits.
The ambition is to establish a novel platform for quantum computing and quantum sensing.
This platform will exploit engineered multilayer graphene, combining the quantum anomalous Hall effect, superconductivity, and chiral Majorana modes.