Chemist Jannika Lauth was awarded a Carl von Ossietzky Young Researchers' Fellowship this year. The researcher produces tiny semiconductor platelets that become electrically conductive when irradiated with light. She uses innovative laser processes to analyse these two-dimensional nanoparticles. Possible applications include ultra-thin solar cells, fast transistors or energy-saving LEDs.
Dr Jannika Lauth is fascinated by the peculiar laws of the nanoworld. The chemist talks quite naturally about Dirac charge carriers, quantum dots and excitons. Lauth's speciality is semiconductors in an unusual form: The researcher produces platelets from compounds such as lead sulphide, indium phosphide or indium selenide, which consist of a few or even just a single layer of atoms.
The four- or hexagonal structures that the 33-year-old researcher is working on are known as two-dimensional nanomaterials because, like a sheet of paper, they are extremely thin compared to their lateral dimensions. These are particles in the order of a few billionths of a metre (nanometres). Such tiny particles often have different physical properties than larger solids: gold nanoparticles, for example, appear red and not golden, tiny copper particles are extremely hard and not flexible. In nano-semiconductors, as Lauth is investigating, the distance between the energy levels, the so-called band gap, increases in comparison to solids. This also changes the electronic properties of a material.
Highly mobile charge carriers
Jannika Lauth is particularly interested in 2D particles that become electrically conductive when irradiated with light. "These semiconductors could be used to produce ultra-thin, flexible solar cells in the future," says the chemist. Particularly fast transistors or energy-saving LEDs are also conceivable. Depending on the dimensions of the nanoplatelets, different applications are possible: For solar cells and transistors, where fast switching processes are important, somewhat thicker nanoplatelets, in which particularly mobile charge carriers occur, are more suitable. For LEDs, on the other hand, it is advantageous if the semiconductor discs are extremely thin. In this way, chemists can customise the physical properties of a material to a certain extent.
Lauth has specialised in producing nanoparticles since her Diplom thesis at the University of Hamburg. In 2010, researchers there discovered rather by chance that tiny crystals combine to form two-dimensional structures under certain circumstances. Lauth has continued to pursue this path since her postdoctoral period. To produce disc-shaped nanoparticles, she uses dissolved salts to create so-called colloids - tiny particles encased in organic molecules. "Nanoparticles are basically between molecules and solids," explains Lauth. The organic shell stabilises the fragile state and ensures that the nanoparticles do not immediately coalesce into larger particles. Lauth can control the type of organic appendages and the temperature to ensure that the particles grow in width in particular. She is now able to produce a wide variety of nanocrystals in 2D form. She has already achieved her goal of reducing the thickness of the platelets to a single layer of atoms with some materials.
Because she not only wanted to produce such particles, but also to understand their unusual electronic properties, Lauth acquired knowledge of various laser physics characterisation methods during her postdoc at Delft University of Technology in the Netherlands. "In Delft, I completed a small degree in physics, so to speak," she says.
Testing without touching
She also developed a process there to free the nanoparticles from their organic appendages and produce thin films from them. Both in the solution and in the film, the substances can be analysed without contact using spectroscopic methods. "This allows us to find out which materials are good for something without having to produce large quantities of them," she says.
The chemist has just moved to the University of Oldenburg and now wants to set up her own junior research group at the Institute of Chemistry. She wants to further develop the 2D semiconductors and, for example, produce and spectroscopically characterise platelets that are free of heavy metals such as lead. Lauth received a Carl von Ossietzky Young Researchers' Fellowship from the university in January, which provides start-up funding for three years. Prof Dr Katharina Al-Shamery, through whose mediation Lauth came to Oldenburg, is delighted about the new addition to the Institute. "Jannika Lauth is an outstanding, determined scientist whose interdisciplinary research at the interface between materials synthesis and laser physics is attracting a great deal of international interest."