Multilateral and Bilateral Projects

Title: "Exploring spectroscopic fingerprints of defects and dopants in two dimensional magnetic insulators"

Program: Bilateral collaboration
Project duration: 2024. - 2026.
Project number: 337-00-140/2023-05/12

PI: Andrijana Šolajić

Abstract:

The air-stable two-dimensional magnetic insulators with long-range magnetic ordering at room temperature are a “game-changer” in the field of 2D materials and 2D magnetism. These could be used in the next generation magnetoresistive tunnelling junctions, lifting the constrain of using hard/soft magnetic electrode materials in magnetoresistive random-access memories. The project is focused on ion implanted talc, a layered magnetic 2D insulator. We intend to combine first principle calculations with state of the art ion beam implantation of magnetic ions into phyllosilicate single crystals. Our combined theoretical and experimental study will focus on pinpointing the spectroscopic fingerprints of specific defects in 2D phyllosilicates. Using the first principle calculations, we will model various types of defects in phyllosilicates, and predict their characteristic vibrational modes. This will be an essential information to the Raman spectroscopy experiments, in order to fully understand and determine specific types of defects in 2D magnetic phyllosilicates.

Title: "Synthesis and characterization of ternary Van der Waals Mo_xW_x-1S₂ nanotubes for advanced field emission application"

Program: Bilateral project between Serbia and Slovenia
Project duration: 2023. - 2025.

PI: Bojana Višić

Inorganic layered materials, where atomic or molecular layers are formed by atoms held together in-plane by covalent or ionic bonds, and out-of-plane via weak van der Waals interactions, are abundant in nature. While readily found in a three-dimensional (3D) structure, these inorganic materials regained popularity when, after isolation of graphene in 2004, it was shown that they can be exfoliated as well in a 2D form (Novoselov et al., PNAS 102 (2005)). Furthermore, these materials have been synthesized in a nanotube (NT) or fullerene-like morphologies back in 1992, making them available in 3D, 2D and quasi-1D form (Tenne et al., Nature 360, 6403 (1992)). This family of materials is extremely versatile, as they can range from being paramagnetic, diamagnetic, ferro- or antiferromagnetic depending on the phase. Furthermore, their bandgaps can range from IR to UV throughout the visible range, making them  metallic to semiconducting or insulating in nature. These properties make them interesting candidates for assembling into stacked heterostructures or alloys, combining the properties of individual material into a hybrid structure.

In this project, we will attempt a one-pot synthesis of ternary transitional metal dichalcogenides, with main focus on Mo_xW_1-xS₂ and Nb_xTa_1-xS_2. The chemical transport reaction inside quartz ampules has been used at Institute Jozef Stefan (IJS) for pioneering syntheses of various inorganic nanotubes and nanowires. This approach will be modified in order to obtain hybrid materials in form of nanotubes or ribbons. The motivation behind this synthesis route is the simplicity behind the one-pot growth and the resulting highly crystalline structures. Here, by growing the material inside a closed quartz ampule at nearly equilibrium conditions and with very slow growth rate, one can minimize the density of inbuilt structural defects and simultaneously obtain different morphologies of the material: flakes, nanotubes, nanoribbons, and scrolls.  Mo_xW_1-xS₂ hybrid material is chosen as the starting material since the properties of both constituents (MoS₂ and WS₂) are well known, with the rising interest in their heterostructures in recent years.

Temperature-dependent Raman spectroscopy will be used to study the changes in phonon behaviour in such  hybrid materials.   Using density functional theory (DFT) calculations, the lattice dynamic will be studied. Their electrical properties will  be determined  and a single-nanotube transistor will be made. With field-effect transistors already prepared from both MoS2 and WS2 (Levi et al, Nano Lett 13 (2013);  Fathipour, APL 106 (2015)), it can be expected that their hybrid has a potential as a component for optoelectronic devices. In the case of Nb_xTa_1-xS₂, since both NbS₂ and TaS₂ are materials that sustain charge density waves (CDW), their hybrid can be interesting to study with respect to modification of CDWs with composition change.