Two Dimensional Materials

This module provides a detailed overview on a fascinating new class of solid state materials and 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. The following specific topics will be addressed:

• Historical and topological introduction to 2D materials;
• Overview, classification and characteristic properties of the main families of 2D materials;
• Nanofabrication and preparation methods applicable to 2D materials;
• Nanoanalytical methods specialized to 2D materials. This will include  including include visibility studies, ellispometry, atomic force, scanning tunneling, scanning electron microscopy, enhanced X-ray methods;
• Introduction of the phonon- and exciton properties on example of graphene and transition metal dichalcogenides (such as MoS₂); 
• Discussion of  potential device application for selected 2D materials in the area of electronic, sensing, opto-/electronic, photovoltaic and catalysis;
• Focus topics to introduce peculiar properties of selected materials in more detail:

1. Relativistic charge carriers, Klein Tunneling and the Quantum Hall effect in graphene and its role for the new Systems of Units;
2. Topological insulators;
3.  Exciton, spin- and valley properties and doping induced superconductivity in transition metal dichalcogenides;

Furthermore, the students will become familiar with selected recent research paper and review article in high-impact research journals such as science, nature publishing group and further literature related to 2D material. The students are being trained in how to access and extract the information from those research article articles.

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

1. understand different classes of 2D  solid state materials and to apply the classification scheme of further 2D solid state materials.
2. understand the preparation and nanofabrication methods for 2D materials and to evaluate suitable methodologies for novel materials.
3. understand optical and structural characterization methods for 2D materials, to analyze related results in recent literature and to apply suitable methodologies for given problems related to 2D material.
4. evaluate the Raman spectra from selected 2D materials.
5. remeber magnetotransport phenomena such as the quantum Hall effect in graphene and transport in topological protected surface states.
6. evaluate absorption, excitonic and spin properties of transition metal dichalcogenides;
7. understand and discuss applications of 2D materials and their heterostructures for electronic, optoelectronic, spintronics devices and solar energy conversion.
8. access and evaluate the content of topical research articles focusing on selected topics related to 2D material research in high-impact journals.

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

The module consists of a thematically structured lecture series and exercise classes. These are cross-linked and thereby the main physical concepts explained. The link to current research activities will be provided by discussing related and topical research article in high-impact journals. In the lectures and particularly, in the excercises, the students are actively involved by direct question and answer periods to better develop their individual understanding and to learn the use of up-to date’s research literature.

Power-point presentation together with handwritten lecture notes based on tablet-PC / beamer presentation (“e-chalk”); Additional literature / research articles in pdf-format;

All Materials will be available for download until the completion of the repeat exam.

• P.Y. Yu & M. Cardona: Fundamentals of Semiconductors, Springer, (2010)
• A.K. Geim & I.V. Grigorieva: Van der Waals Heterostructures, Nature 499, 419-425, (2013)

There will be a written exam of 90 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.
• Analyze the phonon fingerprint of graphene on example of selected Raman spectra.
• Discuss the impact of the layer number on the optical and mechanical properties of 2D materials.