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Exploring magnetism in 2-D materials

Since the discovery of graphene, atomically thin materials such as transition metal dichalcogenides and/or trichalcogenides (MPX3) have sparked a lot of attention due to their  honeycomb morphology and variable electronic properties(superconductors, metals, semiconductors). While the electronic and optical properties of these 2-D layered materials have been explored, the 2-D magnetism of these materials remain unexplored. A selection of physical phenomena has not been explored as a result such as protected long-range magnetic order, local spin textures or topological Hall effect,  subjected to a manipulation by external stimuli (e.g. electric field, doping, strain, light). These properties change when observing isolated monolayers as opposed to bulk layered materials, as suddenly only one layer is being observed. Furthermore, exploring the correlation between these magnetic properties and unique optical properties of these materials.

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Transitional Metal Thiophosphates

One of our scientific interests is to  concentrate on synthesis, exfoliation (mechanical or liquid) and investigation of vast family of layered semiconductors – transition metal thiophosphates (MPS3 and MPS4). We synthesize chromium phosphorous tetrasulfide (CrPS4) and many transmission metal phosphorous trisulfides (MPS3), that are MnPS3, FePS3, CoPS3, NiPS3 and ZnPS3, also alloyed (Mn0,5Fe0,5PS3), mixed oxidation state (Cr0,5Cu0,5PS3) and doped ones (Mn:ZnPS3). Main focus is put on electron microscopy investigations, that are (HR-)SEM, (HR-)cTEM and (HR-)STEM coupled also with EDS. Our latest work presented application of liquid exfoliated CrPS4 in all-printed photodetector.

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Single-Crystal Measurements

Magneto-optical measurements of MAPbBr3 single crystal show strong evidence of the coupling between a photo-generated carrier and nuclei in the lattice. The counter balance between the Rashba, Overhauser and Zeeman fields in this case is exploited. This new observation further supports the correlation between the formation of the Rashba effect with the breaking of inversion of symmetry.


Doping with Lanthanides

My research involves development of the synthesis procedure of doping with lanthanide ions in material platform composed of II-VI semiconductors materials (i.e. CdSe, CdS) with different morphologies like quantum dots (QDs), nanorods (NRs) or nanoplatelets (NPLs), as well as investigating the composition of obtained materials. The general procedure can be seen in the Figure below.

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Magneto-optical properties of 2D Organic-inorganic halide perovskite materials.

Metal halide Perovskites (MHP) and hybrid organic-inorganic MHPs have captivated Researcher's attention in the recent years for their physical properties such as superconductivity, ferroelectricity, piezoelectricity, ferromagnetism and so on. This properties rely on the electronic and spin interactions which are still poorly understood in theses materials.

This project includes the investigation of magneto-optical properties utilizing the following methods: Circularly and linearly polarized photoluminescence in the presence of external magnetic field and optically detected magnetic resonance spectroscopy. Those methodologies, should reveal information about selective electronic states with their spin-orientation, exposing internal magnetism (e.g., nuclear spins effective fields), g-factor of carriers, spin-spin.


Magnetically doped colloidal semiconductor nanocrystals

Colloidal nanocrystals (NCs) are known for their tunable photo-physical properties by variation of size, shape and composition. Magnetically doped NCs endow them with additional degree of freedom. The confined structures enhance the spin-spin interaction between photo-generated carriers (electron and hole) and spins of the magnetic impurities. The degree of magnetization depends on the quantum confinement, the type of impurity, and its position with respect to the host-carrier distribution function. In this study we describe the synthesis and characterization ofthe generated magnetism in Mn2+ doped colloidal nanocrystals of different morphologies, the quantum dots (QDs), seeded nanorods (NRs) and nanoplatelets (NPLs), all with core/shell configuration based on CdSe/CdS composition with a quasi-type-II core-shell band alignment.


Colloidal Synthesis of PbS Nanocrystals

lead sulfide (PbS) nanocrystals are of a great interest due to their tunable-optical activity in the near infrared (IR) spectral regime. In the present study, we introduce a feasible approach towards the formation of different PbS nanocrystals using colloidal chemistry. The size and shape of the nanocrystals were controlled by adjusting the ratio of amphiphilic ligands and synthesis temperature. This eventually altered the absorption band gab in the Visible –IR. The mechanism of formation of the nanocrystals, final shape and crystal structure is investigated using electron microscopy imaging, x-ray diffraction technique and FTIR spectroscopy. Which can provide an insight for engineering the desired nanocrystals that may serve as an active layer material in opto-electronics devices.


2D halide perovskites

The project primarily focuses on the two-dimensional halide perovskites, determining the effect of magnetic doping to explore the spintronic properties. Magneto-optical studies of these hybrid 2D materials are studied to reflect on their polaronic properties. A part of my research work also focuses on the colloidal synthesis of III-V semiconductor nanocrystals with varying morphology as a function of synthesis conditions.


Doping of CsPbX3 Nanocrystals

In our lab, a novel dynamic cation exchange driven by an anion exchange procedure isused for incorporating Ni dopants into the Pb-site of CsPbBr3 and CsPb(BrCl)3 perovskite nanocrystals under ambient conditions. Ni doping has significant merits in tuning the optical properties and introducing magnetic functionality. Moreover, Ni doping provides chemical and photochemical stability to a host phase with consequent importance for solar cell applications.


Effective Reduction of Oxygen Debris in Graphene Oxide

The present work deals with open questions related to a derivative of graphene including oxygen species, named graphene oxide (GO). This derivative raised a substantial interest in the last two decades thanks to its unique properties beyond those of pristine graphene, including electronic energy bandgap, hydrophilic behavior and numerous anchoring sites required for functionalization, including oxygen groups (clustering of which are named debris). However, the presence of numerous oxygen debris on the GO surface hinders the integration of GO in electronic devices.Therefore, the present work focuses on the investigation of the position and clustering of oxygen centers on top of a graphene surface and their linking nature to a substrate.


Optically Detected Mangetic Resonance Spectroscopy

Optically Detected Magnetic Resonance (ODMR) is a spectroscopic method used to revel semiconductors' excited infrastructure.  We excite the nanocrystals semiconductors (NCs) with laser and split the exciton level with a magnetic field due to the Zeeman effect. We implement microwave radiation in the NCs, in resonance condition, when the energy of the microwave fit to the Zeeman sliting, spin-flip can occur and change the population of the dark and bright energy levels.  The change in the population effect of the integrated photoluminesce. Interaction with magnetic doped revealed by extra splitting in the ODMR spectrum.

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