2D-TOP – ‘2D crystalline thin films with non-trivial topology’

Principal Investigator: Dr. Evangelia Xenogiannopoulou

Active since 5/9/18; Duration: 36 months

Funding: GSRT-HFRI / 1st call for Post-Doctoral Researchers

Τhe advent of graphene has generated an enormous interest in a number of other 2D crystals (silicene, germanene, transition metal dichalcogenides MX2), creating the prospect for exciting new versatile applications. In the ‘2D-TOP’ Project we attempt the “fusion” between 2D materials and topological quantum matter worlds with the aim to unveil new electronic states with unique properties. Τhe Project focuses on the experimental realization and physical characterization of two different classes of 2D crystals with a non-trivial topological order, namely the topological insulators (TI) and the topological Weyl semimetals (WSM). It is predicted, that stanene, a 2D layer of Sn atoms, is a TI with an energy band gap of approximately 0.1 eV, that conducts electricity only in 1D edge channels with virtually no heat dissipation and remarkable spin coherence over macroscale distances. In addition, the recent discovery of topological Weyl (WSM) opens new opportunities to store and/or process information by taking benefits from the selected chirality of Weyl Fermion bands. The 2D topological materials investigated in this Project could ultimately establish topology as paradigm shift for nanoelectronics and spintronics enabling a whole new line of technology for low power electronics. Taking into account that the continued scaling of CMOS becomes limited due to power dissipation, the topological materials could have a remarkable impact in the semiconductor market in the next years.

To achieve the objectives, crystalline 2D TI (stanene/bismuthene) and WSM (MTe2, M=Mo, W, Hf, Zr) will be grown by molecular beam epitaxy (MBE). Various Surface Science techniques will be employed in order to investigate the crystallinity, the topology-related valence band features and the electrical response of the topological materials, such as Reflection High Energy Electron Diffraction (RHEED),  X-Ray Diffraction (XRD), Raman spectroscopy, Scanning Tunneling Microscopy (STM), X-ray Photoelectron Spectroscopy (XPS) and Angle Resolved Photo-Electron Spectroscopy (ARPES).

Graphene-based hybrid composites for technology applications

Scientific Director: Dr. George Nounesis (Post doc Fellow: Dr. Stefanos Chaitoglou)

Active since 1/6/17; Duration: 36 months

Funding: Stavros Niarchos Foundation/Industrial Post-Doc Fellowship

The present project is developed in the framework of an industrial Post-Doc fellowship, awarded by Stavros Niarchos Foundation in collaboration with Adamant Composites Ltd. The objective of the project is the preparation of hybrid graphene-based materials for cross-disciplinary technological applications. Emphasis is given in the 3 following applications.

1. Graphene hybrid structures as anode electrodes in energy storage and energy production applications.

We proceed with the preparation of graphene/transition metal carbide (TMC) heterostructures for application in electrocatalysis. TMC are efficient catalysts towards the hydrogen evolution reaction and can potentially replace the expensive and scarce Noble metals that are used in this application. The capacity to prepare heterostructures of graphene and 2-dimensional TMCs in one-step synthesis process open a novel route towards the development of more efficient electrocatalysts. Graphene can enhance the electrocatalytic activity of the TMCs by accelerating charge transfer kinetics from the catalytic surface towards the electrode.

2. Graphene films in gas barriers applications.

High quality graphene is an impermeable material to most gases, including He. Partial permeability can occur due to defects that are usually present in the crystal lattice of single layer graphene films. Here, we prepare stacks of multilayer graphene films. A key feature of the technology is the random stack of various single layers, avoiding defect matching between the layers. The graphene stack is applied as a coating in Thermoplastic polyurethane (TPU) films to reduce their permeability to gases.

3. Graphene based materials for mechanical reinforcement.

Graphene is applied as a coating on carbon fibers to reinforce their mechanical behaviour and conductivity.