Bachelor/Master-Thesis or Hiwi-jobs

We are constantly looking for motivated students who are interested in doing their Bachelor/Master thesis or help us with our research projects in terms of a student job (Hiwi). Please send your enquiries in this respect directly by email to: wolfgang.wenzel∂kit.edu. Apart from this, there are specific topics which we propose right now as follows.

1) Master thesis: Predictive design of doped organic semiconductors

Motivation. Organic electronics is a new fast developing area of the materials science and technology, which allows for low-cost and flexible applications. Organic-light emitting diodes utilized in the displays of the modern smartphones are a good example of its recent success. Organic photovoltaic (OPV) and organic field-effect transistors (OFETs) are the other promising areas where organic materials may replace traditional technologies. There exist many interesting scientific problems in the field of organic materials, which would enable new applications of OLEDs (e.g. in general lighting and organic displays) and commercializing OPV and OFET technologies.

The search for new materials, principles of operations and device architectures, which satisfy some set of requirements, is a very important research goal in this field. Today, new materials are being searched by the trial-and-error method experimentally, which requires a lot of time and resources, but the outcome (i.e. number of new materials, which are better than the reference one) is low.

Predictive in silico design of advanced organic materials has been a long-standing activity of Wenzel’s research group. In this field we have advanced in many areas such as: (1) multiscale simulation of organic semiconductors [1]; (2) in-silico design of the advanced molecules [2].


About the Master Project. One of the directions of materials predictive design in our group is the simulation of charge and exciton dynamics in organic semiconductors with the aid of the kinetic Monte-Carlo (KMC) method [3]. Today, our group is focused on the understanding of fundamental processes related to the conductivity doping of electron and hole-transport layers (ETLs and HTLs, respectively) in organic light-emitting diodes (see Fig.).

 
 Fig. Typical structure of the mono-color OLED

ETLs and HTLs serve to deliver electrons and holes to the active region of an OLED, and the doping is a way to increase their electron and hole conductivity. In spite of the recent progress in the KMC implementations for organic materials, full OLED stack simulations are now impossible due to the enormous computational time required to treat doped transport layers. Our group has several promising ideas how to accelerate the simulations of doped layers. As a result, we expect that the simulation of the full OLED stack including doped layers will be possible for the first time. This can be extremely useful for industrial applications. The scope of works on implementing this method suits perfectly the time scale required to accomplish a Master’s thesis.


Tasks. Your work will cover both investigating interesting physical phenomena and computational solutions, including object-oriented programming together with the use of the state-of-the-art high-performance computational facilities. Your end goal will be to implement the method, which would accelerate simulations of doped layers within the KMC method.

By implementing this advanced KMC method and by applying it to various OLED stacks, you will make your own small but important contribution into the further progress of the field of organic electronics.

Having accomplished this project, you will acquire the following competences:
  • Science: You will become an expert in a hot and demanded research field, the multiscale simulation of organic semiconductors and devices.
  • Programming: You will acquire advanced skills in scientific programming (mainly Python) including the HPC.
  • Practical outcome: You will make fundamental research, which will be used to design real organic electronic devices.

Contact
If you are interested, please, contact us:
Prof. Wolfgang Wenzel wolfgang.wenzel∂kit.edu
Dr. Artem Fediai artem.fediai∂kit.edu

References:
[1] P. Friederich, F. Symalla, V. Meded, T. Neumann, and W. Wenzel, “Ab Initio Treatment of Disorder Effects in Amorphous Organic Materials: Toward Parameter Free Materials Simulation,” J. Chem. Theory Comput., vol. 10, no. 9, pp. 3720–3725, Sep. 2014.
[2] P. Friederich et al., “Rational in Silico Design of an Organic Semiconductor with Improved Electron Mobility”, Adv. Mat. vol. 29, no. 43, 2017.
[3] F. Symalla et al., “Charge Transport by Superexchange in Molecular Host-Guest Systems,” Phys. Rev. Lett., vol. 117, no. 27, Dec. 2016.

 

2) Bachelor/Master thesis in the area of quantum transport in carbon nanotube/metal contacts


   
Atomistic structure of the carbon nanotube contacted to the metallic electrodes as it is simulated The object of research as it looks in reality (SEM picture)

Motivation. Nanocarbons (carbon nanotubes (CNT), carbon nanoribbons (CNR) and graphene) are unique materials for the future electronics in that they have electron mobility as high as 105 m2/Vs compared to 1.4x103 m2/Vs of that of Si (among other attractive features). Carbon-based electronics is a possible contender of the silicon-based electronics, which has almost reached its technological limit. Regardless of the specific electronic device where nanocarbons are utilized, they have to be connected to an external circuit, which, in practice, means that the contact between the carbon nanotube and metallic electrodes is unavoidable (in what follows, we are talking about a CNT as an example). Experimental studies showed that these are not internal properties of CNTs, which limit the current in a junction, but the contact resistance [1]. This yields the necessity to understand CNT-metal contacts theoretically to decide, what has to be done in practice to diminish their parasitic effect.

Your tasks. Your goal will be to predict theoretically quantum transport properties of carbon nanotube/metal contacts, which real-world counterparts will be fabricated by our experimental partner. More specifically, you will have to explain observed dependence of the carbon-nanotube’s contact resistance on the specific metal, chirality of the carbon nanotube, purity of the nanotubes, and the contact geometry.

Approach. Due to the nanoscale size and the perfection of the system in hand, an electron can be considered as a wave, whose motion is coherent. The electronic structure of the medium where an electron moves is treated at a level of atomic/molecular orbitals, which are described with the density functional theory. The nonequilibrium Green’s functions method is used as a convenient tool to solve the Schrödinger-like (Kohn-Sham) equation in the basis of these orbitals. You will use and further develop the method and simulation framework developed by one of the Wenzel group’s member in 2014-2016 [2], [3].

Knowledge and skills you will acquire:
  • You will understand, what governs nanoscale devices properties at the atomistic level
  • You will acquire skills of a scientific programming in Python/Fortran/Matlab including HPC
  • You are expected to write and publish at least one research paper in a scientific journal

Research group of Prof. Wenzel:
  • International, friendly and professional
  • Efficient management
  • Supported by our spin-off company Nanomatch (http://www.nanomatch.com) in scientific programming issues

Cooperation with experimental groups:
  • The leading experimental group in the area of carbon nanotube/graphene (research group of Prof. Krupke (INT KIT) https://www.int.kit.edu/krupke.php) will fabricate real devices that you are simulating

Contact
If you are interested, please contact us:
Prof. Wolfgang Wenzel wolfgang.wenzel∂kit.edu
Dr. Artem Fediai artem.fediai∂kit.edu

References:
[1] A. D. Franklin, D. B. Farmer, and W. Haensch, “Defining and Overcoming the Contact Resistance Challenge in Scaled
Carbon Nanotube Transistors,” ACS Nano, vol. 8, no. 7, pp. 7333–7339, Jul. 2014.
[2] A. Fediai, D. A. Ryndyk, and G. Cuniberti, “Electron transport in extended carbon-nanotube/metal contacts: Ab initio based
Green function method,” Phys. Rev. B, vol. 91, no. 16, Apr. 2015.
[3] A. Fediai et al., “Towards an optimal contact metal for CNTFETs,” Nanoscale, vol. 8, no. 19, pp. 10240–10251, 2016.