Two-dimensional materials

WTe₂ is a promising material to study quantum effects relevant for quantum computing. In WTe₂ the surface and edge states behave differently in transport measurements from its bulk character. This difference is caused by the topological nature of WTe₂ as a type-II Weyl semimetal and a higher-order topological state, which means this transport behaviour is intrinsically embedded in the band structure of WTe₂. The surface and edge states can form an interesting platform to study Majorana-physics particularly when superconductivity is induced in these states.

We measured the electronic transport properties of thin, nanometer sized WTe₂ devices at low temperatures. Superconductivity was successfully induced into the WTe₂ flakes by using superconducting Nb-contacts. While the entire flake exhibited superconducting behavior, the topological nature of WTe₂ is expected to enhance the supercurrent at the edges. By analyzing the field dependence of the critical current, we extract the current distribution within the WTe₂ flake-based Josephson junction. Our measurements on these structures show a clear current enhancement at the edge of the flake compared to the bulk supercurrent. Interestingly, this enhancement is also observed at step edges caused by thickness variations within the flake.

Investigating topological phases and their transitions is crucial for discovering new quantum states and advancing topological device technology [1]. The transitions between distinct topological phases, especially from two-dimensional (2D) to one-dimensional (1D) systems, remain largely unexplored and poorly understood. In this study, we synthesized germanene nanoribbons, see Fig. 1a, which are 2D topological insulators [2], featuring zigzag terminations, large topological gaps (100-150 meV), and metallic edge states. These nanoribbons enable the packing of a dense array of parallel 1D topological edge states. By systematically varying the nanoribbon width, we monitored the evolution of their topological characteristics, pinpointing a transition to the novel 1D topological insulator phase below a critical width of about 2 nm, see Fig. 1b. This transition is marked by the vanishing of the 1D edge states and the emergence of distinct zero-dimensional (0D) end states. Additionally, we demonstrated a perpendicular electric field driven phase transition from a 1D topological insulator to a trivial insulator, devoid of end states, see Fig. 1c. Our study shows experimentally and theoretically that the topological phase of the germanene nanoribbons depends in a non-monotonic way on ribbon width, spin-orbit coupling, staggered mass, and termination.

Many industrial processes produce large amounts of aqueous waste streams (10 – 100 m³/h), contaminated with, e.g. micro/nanoplastics, organic solvents, and/or oxygen-containing molecules. In view of volume and contaminants, various two-dimensional-based membranes presenting high flux and high rejection have appeared as economically attractive solutions [1,2]. For example, graphene oxide (GO)-based nanosheets can be used to prepare a GO-based layer on a ceramic membrane to combine physical separation and electrochemical treatment [rGO REM]. In this last case, the membrane material acts as an active surface (anode) where organic contaminants are electrochemically converted into non-toxic compounds such as water and carbon dioxide. GO-based membranes have shown outstanding physical and electrochemical removal performance but current reported systems are limited by the mechanical stability of the GO-based layer. Several strategies to increase the surface adhesion of GO nanosheets to the surface of ceramic supports have been proposed to circumvent this issue. However, it is unknown if such systems will withstand the conditions required to make the GO electrochemically active.

In this work, several methods were compared to prepare stable and conductive GO-based membranes. First, GO-based membranes were prepared with and without covalent attachment of GO nanosheets to ceramic supports using organic linkers (molecules, or oligomers). Then two chemical reduction methods were used to produce reduced GO: solid-state, hydrothermal, and liquid-phase reductions. Relevant physico-chemical analysis methods have been used to study the surface interactions, as well as the mechanical and chemical stability of the layer via conductivity measurements.

The interactions between the GO nanosheets and ceramic support surface can be engineered using organic linkers. The chemical and mechanical stability of these interactions after chemical reduction was investigated and the hydrothermal reduction method was found to be the most suitable. Here we will present our strategy to engineer a high-flux, high-porosity stable, and conductive GO-based layer on a ceramic membrane with a large electrochemically active surface area, using two-dimensional materials and innovative synthesis approaches.

Thermal management is a critical factor in the performance and efficiency of numerous energy-intensive applications, including data centers, electronics, and electric vehicles. The increasing demand for these technologies has intensified the need for innovative materials capable of effectively dissipating heat. This presentation explores recent advancements in the development of metal-composite powder feedstocks for thermal management applications. By combining nanomaterials such as graphene and hexagonal boron nitride with metal additive manufacturing feedstock powders, we aim to create novel materials with enhanced thermal conductivity and mechanical properties. Various additive manufacturing techniques are being investigated to fabricate components from these novel materials. Initial results include cold spray deposition, laser powder bed fusion, and binder jetting, highlighting the potential of these processes for producing customized and high-performance thermal management solutions.