Until recently, two positions were advertised in our group that have not yet been fully filled.
Both positions will focus on the investigation and control of charge carrier dynamics in nanostructures on the low femtosecond time scale. This is a highly topical research field combining a number of techniques. Accordingly, a high level of motivation to get involved in new topics is expected, but not extensive prior knowledge in these specific fields. Rather, creativity and a quick grasp of the subject are helpful in finding one's way in this field of research. Intensive supervision is ensured by the size of the group and the nature of the project.
The aim is to develop and test two new methods to investigate charge carrier dynamics at nanoscale interfaces on the atomic to femtosecond time scale. A laser pulse in the visible or near-infrared spectral range optically excites the dynamics to be investigated in a nanostructure (see image). These charge carrier dynamics now evolve in time and we interrogate their state after a variable waiting time with an even shorter pulse. This pulse is so short that it freezes the dynamics, as in a camera with a flash light. Moreover, its photon energy is so high that electrons are emitted close to the surface (e.g. in the picture in the top left). These electrons carry valuable information about which dynamic fields are present at the nanostructure surface. We want to elicit this information from the electrons for the first time with the help of an electron microscope (PhD project 1).
But exciting charge carrier dynamics also take place in the nanostructure (and not only at the surface), which so far cannot be studied with sufficient spatial and temporal resolution. PhD project 2 aims to investigate how attosecond pulses (see above) have changed after transmission through and interaction with the nanostructure. These now carry the valuable information about the dynamics in the nanostructure, which we also want to investigate with an electron microscope with high spatial resolution. This is shown in the lower and right part of the figure. Parts of the optical spectrum were absorbed in the nanostructure, depending on the energetic charge carrier distribution in the material. In short, we would like to convert the optical spectrum into an electron spectrum so that we can apply our spatially high-resolution electron microscopic methods. Corresponding preliminary work already exists, which promises exciting results in both PhD projects.
Students who would like to write their thesis with us are of course very welcome.
In general, there are many smaller and larger projects that can be worked on within the framework of the construction of the new attosecond laboratory and the time-resolved photoemission electron microscope. Previous experience is not necessary; however, an interest in learning new things and actively tackling challenges is certainly advantageous. From femtosecond laser systems to vacuum systems, from attosecond pulses in the ultraviolet to electron microscopy, a wide variety of techniques can be tried out and used to investigate charge transfer processes in nanostructures. We work closely with other physics groups and use the attosecond laboratory of the UNO and ULTRA groups until our own laboratory is fully functional.
Currently, there is an opportunity for a Master's student (or a particularly ambitious Bachelor's student) to get directly involved in cutting-edge research on the control of attosecond pulses. These are (among) the shortest light flashes ever produced and the aim is to better understand their generation. For this purpose, light pulses in the visible spectral range are manipulated with only a few oscillations of the electric field, so that the attosecond pulses thus generated acquire desired properties. Adjusting screws here are, for example, the polarisation of the light and the oscillation amplitude in time. Control of these attosecond flashes is relevant in order to better understand electronic processes on the shortest time scales.
This Bachelor's or Master's project is about putting a recently procured electron microscope into operation and initially characterising it with regard to its specified parameters. In the second step, it is planned to carry out the first time-resolved experiment on such a microscope in Oldenburg, whereby the exact research question and sample to be investigated will be determined during the first part of the project in consultation with the candidate.
Photoemission electron microscopy is somewhat different from conventional microscopy techniques. In this case, the sample is also the electron source, in that electrons are triggered from it - by illumination with light. These trigger sites are imaged in the microscope with high spatial resolution. At the same time, the time of flight of the electrons is recorded so that their kinetic energy spectrum can also be measured. This allows detailed insights into the charge carrier dynamics near the surface of a nanostructure.
A variety of techniques will be introduced to you in this project, including sample preparation, nanopositioning systems, ultra-high vacuum, electron microscopy, time-of-flight electron spectroscopy and excitation-interrogation experiments with short laser pulses. This project, like many in this group, is rather challenging but offers the opportunity to learn a lot through close collaboration with group members.
This project forms part of the basis for the future work of the junior research group Attosecond Microscopy. We are currently building a laser system that uses nonlinear processes to generate ultrashort laser pulses in the infrared spectral range. However, these pulses are not (quite) short enough for the planned experiments. There are several approaches to shorten light pulses by spectral broadening and subsequent temporal compression to such an extent that they last only a few oscillations of the electric field. The aim of this project is to further compress laser pulses at a central wavelength of 2 µm and a pulse duration of about 30 fs by focusing them into thin glass plates and to characterize them with respect to their pulse duration, beam quality and power stability. Intensive on-site supervision is ensured (don't worry!), and an exchange with colleagues in Lund (Sweden) is possible at the same time.
Feel free to contact us if there is something for you in the proposed projects. And feel free to contact us even if no project appeals to you directly. Sometimes we come up with spontaneous project ideas or a project seems different after we've done a little lab tour.
We are generally happy if you bring this with you:
- A solid physics background
- An interest in learning new things
- Fun in working in the laser lab
In return, you will receive, among other things:
- Intensive supervision, support for the whole group
- the opportunity to try out many new devices and techniques
- first own research results
- an exciting final project
Please contact us briefly. :)