Two Dimensional Materials

This module provides an overview on a new class of solid state materials, a fast growing research area: two-dimensional (2D) materials that are truly two-dimensional solids with a thickness of about 1 nm. Within a layer there is strong covalent bonding between atoms and weak van-der Waals coupling between adjacent layers. Nevertheless, the properties of 2D solids strongly depends on the number of layers and interaction with environment/substrate.

Subsequent to a historical and topological introduction to 2D materials, preparation and adjusted nanofabrication methods will be demonstrated. Next, the structural, optical, phonon, electronic and optoelectronic properties as well as suitable experimental methods and tools will be presented. This will include visibility studies, ellispometry, atomic force, scanning tunneling, scanning electron microscopy, enhanced X-ray methods and Raman measurements of such just 1nm thin solid state membranes. Furthermore, peculiar properties of selected materials and novel device application of 2D materials  is introduced in more detail: band-structure, Klein Tunneling and Quantum Hall effect in graphene; topological protected surface state in topological insulators; band structure, absorption, excitons and spin properties of transition metal dichalcogenides; transistor, optoelectronic devices and solar energy conversion in photovoltaic and water-splitting devices consisting of semiconducting transition metal dichalcogenides and novel heterostructures made of two-dimensional materials.

After a successful participation of the module, the student is able to:

1. specify different classes of 2D  solid state materials and their properties.
2. describe and explain  preparation and nanofabrication methods for 2D materials.
3. explain and differentiate between  suitable optical and structural characterization methods for 2D materials.
4. explain phonon properties of 2D materials.
5. explain magneto quantum transport phenomena such as the quantum Hall effect in graphene and transport in topological protected surface states.
6. explain absorption, excitonic and spin properties of transition metal dichalcogenides..
7. explain and discuss applications of 2D materials and their heterostructures for electronic, optoelectronic, spintronics devices and solar energy converstion.

There are no access requirements beyond the ones for the master study.

lecture, beamer presentation, discussion, lab visit

Class room presentation

Lecture script and references therein

There will be an oral exam of 25 minutes duration. Therein the achievement of the competencies given in section learning outcome is tested exemplarily at least to the given cognition level using comprehension questions and sample calculations.

For example an assignment in the exam might be:

• - Define fabrication methods of 2D materials.
• - Explain characterization methods of 2D materials.
• - Explain the (polarized) photoluminescence properties of semiconducting 2D materials.
• - Discuss the light scattering at 2D materials.
• - Discuss the impact of the layer number on the optical and mechanical properties of 2D materials.