Groups for 2016 will be published soon!
Groups for 2015:
- The candidate will be part of the magnetization dynamics group and integrated into running projects led by our PhD students and postdocs. We are investigating magnetic nanostructures and patterned magnetic films. The summer student will perform experiments on the broadband ferromagnetic resonance (FMR) setup and if feasible frequency-resolved magneto-optic Kerreffect as well as the corresponding fitting and data analysis.
- In particular, it has been demonstrated that over specific bias ranges, the applied voltage induces a telegraph-noise-like behavior known as ‘back-hopping’, whose origin remains to-date under debate. This phenomenon has not been reported in fully-metallic nanopillars, and represents a considerable draw-back for spin-torque-based magnetic memory devices, as it causes the switching to be unreliable.
The focus of this study will be to carry out a systematic study aiming at identifying and separating two types of contributions to the observed telegraph-noise-like behavior: thermally activated reversal (which is known to affect various types of nanostructures) versus the dependence of the spin-torque on the applied bias voltage (which is intrinsic to MgO-based magnetic tunnel junctions).
To this end, a sub-nanosecond voltage pulse generator and a 20 GHz single-shot oscilloscope will be utilized to characterize real-time switching in Fe/MgO/Fe devices with a lateral size of the order of 100 nm. Experiments will be performed at room temperature, as well as at 4.2 K.
- Testing semiconductor-based photosensors for scintillator neutron detectors for nuclear astrophysics
Neutron detection with plastic scintillators can be achieved either by time-of-flight methods or by light pulse shape analysis discriminating neutrons from gamma rays. In both cases, a fast and efficient photosensor is needed. The classical approach is to use special photomultiplier tubes. In recent years, arrays of Geiger-mode avalanche photodiodes nicknamed "Silicon Photomultipliers (SiPMs)" have become available that show promising efficiency and time resolution. An effort is currently underway at TU Dresden and HZDR to test the suitability of analog SiPMs for neutron time of flight detection with picosecond time resolution. In the framework of the summer student project, instead the neutron/gamma pulse shape discrimination (PSD) properties of a scintillator+SiPM assembly shall be tested. The assembly shall initially be characterized using a picosecond laser and the picosecond ELBE beam. Subsequently, with a fast digital oscilloscope the PSD properties of the assemblies will be determined using neutron sources.
- The summer student shall measure and compare the complimentary effects of spin-torque driven ferromagnetic resonance (ST-FMR) and thermally-excited ferromagnetic resonance (TE-FMR). We already have magnetic tunnel junction thin films which are patterned to devices approximately 100 nanometers in diameter. The devices consist of two ferromagnetic layers, separated by an insulating MgO barrier. Transport in the device happens through quantum mechanical tunnelling. Depending on the relative alignment of the magnetic layers the electrical resistance is either low (in the parallel configuration) or high (in the antiparallel state). This phenomena is known as magnetoresistance and its discovery was the subject of the Nobel prize in Physics in 2007 which was shared between Albert Fert and Peter Grünberg.
The overall change in resistance can be of the order of 200% in state-of-the-art devices. When the devices are patterned to a few hundred nanometers in size, the effects of a highly spin-polarised current become noticeable. The highly spin-polarised current (which is responsible for the electrical conduction) can interact with the magnetisation direction of the layers, causing it to change. This is the phenomena of spin-transfer-torque. Through this technique, we can switch the device from the parallel state to the antiparallel state using only a dc current. It is the basic unit of magnetic random access memory (MRAM). By using a combination of applied field and current, neither state is preferred and the magnetisation precesses at microwave frequency. This microwave precession can be tuned using the applied dc current, and is a good candidate for nanaometer scale microwave oscillators which can be low power alternatives for communication technology. Using an ac current, we can resonantly excite one of the magnetic layers. This technique is known as ST-FMR. If we utilise the effect of magnetoresistance we can investigate the resonance of the magnetic layers which is excited by finite temperature (TE-FMR). A dc current will affect both of these phenomena. This will be the focus of the project of the summer student, to compare both techniques, with a focus on ascertaining the relative effects of the spin-transfer-torque terms. There are two torque terms, "in-plane" and "field-like" and by the end hopefully good agreement can be found between both techniques. The student will first conduct a short literature review on both effects, capture data from several devices and finally analyse the data. The data from both techniques will then be compared and commented on. The student will cover all areas related to the project, making experiments and fitting data, he/she should therefore be comfortable with hands-on experiments as well as using analysis software (for example Origin). The research group is rather small, so one can expect reasonably close supervision and one shouldn't worry about being left alone for three months. Looking forward to see you in Dresden!
- Single atom contacts in liquid environment:
When pulling apart metal wires to atom scale dimensions, the role of single atoms in current transport can be revealed. Before losing the electrical contact, conduction takes place through a single atom, only. Therefore, metallic contacts with variable distance can be used as atomically defined contacts for nanoobjetcs, such as nanoparticles, single molecules or single semiconducting nanoclusters. In this project, we will construct a single atom contact based on commercially available electronics. The opening and closing of the contact will be performed using excitation at high frequencies, which allows the characterisation of a large number of contacts within a short time. When operating such contacts in a solvent containing organic molecules, the electronic properties of these molecules can be revealed by measuring the conductance of metal-molecule-metal junctions with comparably low effort. This will help to identify molecules, which exhibit a low resistance and are therefore suitable candidates for their use as molecular wires. Such molecular wires are needed for developing molecular electronic circuits, which are prospective candidates for replacing silicon nanoelectronics in the future.
- Particle transport simulations using Monte Carlo techniques for experimental setups at the ELBE facility. These simulations are needed to improve the understanding of experimental conditions and/or evaluate shielding requirements. During the course of the program, the student will learn how to create a geometrical model of an experiment, how to implement the primary radiation sources as well as the underlying physics processes, and how to extract and interpret the results from the simulation output.
- Fabrication and characterization of self-organized surface patterns induced by irradiation with multiple ion beams
- The student will program tools for image analysis on GPGPU clusters. This will involve implementing data caching for clusters of large data streams and asynchronous readout and/or implementing and optimizing fast convolution methods on GPGPUs. If possible, the student will also use GPUs to compute synthetic scattering images from 2D and 3D particle data.
- “Interaction of trivalent actinides with biogenic calcite produced by emiliania huxleyi”
The minor actinides Np, Pu, Am, and Cm dominate the radiotoxicity of spent nuclear fuel over hundreds of thousands of years. Once incorporated, they are associated with severe health risks, in particular cancer of the bone. Consequently, understanding their reactivity and mobility in the bio- and geosphere is of utmost importance. Biomineralization, as accomplished by many species including humans, can be an effective mechanism for the retention of contaminants, when it occurs outside of the mineralizing organism, but also increase its toxicity, when contaminants are sequestered within the body.
The student will characterize the interaction of trivalent actinides (and their lanthanide homologues) with the calcite-forming algae emiliana huxleyi by spectroscopic and microscopic techniques. Procedures for the cultivation of the algae will be developed, and monitored by biotechnical methods. The resulting coccoliths (calcite platelet exoskeleton) will be characterized by scanning electron microscopy (SEM). Once procedures are established, the impact of americium, as well as its homologue lanthanide Eu, will be quantified, and characterized by time-resolved laser fluorescence spectroscopy (TRLFS), mass-spectrometry, and biotechnical methods. Results can be compared to well-known interaction patterns in non-biogenic calcites, and bio-induced calcite. Finally, the impact on habitus and size distribution of the coccoliths will be compared using SEM
- The student should perform a task which is part of running research activities at the UPTD applying nuclear physics, radiation physics and medical physics methods and approaches.
The student can work on one or more individual tasks in one or more physics groups. A broad spectrum of individual tasks is available including both experimental work and computer based studies. Tasks are directed to the investigation of radiation detectors, signal processing techniques and data acquisition as well as data evaluation procedures for in-vivo proton range verification by prompt gamma imaging, prompt gamma timing or in-beam positron emission tomography. Further needs are the calibration of new dosimeters and the experimental determination of dose correction factors. The development of laser-based proton therapy devices requires, e.g., for testing of proton beam pulsing and the characterization of new beam transport magnets at pulsed proton beams. Contributions in design, realisation, test and optimization of proton irradiation setup components for radiobiological experiments with cells and small animals are also needed. Monte Carlo simulation of proton beam transport, secondary radiation generation and propagation as well as dose deposition by primary and secondary radiation are needed for different research topics.
Depending on the skills of the candidate, we have the following different tasks for a potential summer student:
- Implementation and evaluation of a prototype (using Shell scripts or Python) of a semi-automatic reconstruction of so-called respiratory gated studies using the vendor-based image reconstruction. In addition, the already known data formats of the existing belt-based respiratory motion devices at the PET/MR should be ported and transferred to be used by our own iterative image reconstruction to allow to reconstruct respiratory gated studies. This includes detailed analysis of the processing workflow and documentation for performing clinical respiratory motion measurements at the University Hospital.
- Evaluation of the accuracy of the standard belt-based respiratory tracking solution of the PET/MR. This task includes planning and performing of a motion tracking test measurement with simultaneous motion data acquisition using the PET/MR's own respiratory belt solution and an external marker-based optical tracking device. Based on this test measurement data analysis (using R, MATLAB, etc.) should be performed to quantify the accuracy of the belt-based motion tracking solution in comparison to optical tracking solutions. In addition, a test measurement on the influence of the patient positioning table on patient motion should be performed and included in the data analysis.
- Test and evaluation of the possibilities to use an existing optical marker-based tracking systems on the PET/MR. These tests involve running MRI phantom measurements to analyse the MR compatibility of these tracking devices. Furthermore, potential solutions (e.g. additional radio-frequency shielding) should be identified and implemented to overcome problems involved with running such tracking systems within the faraday cage of the PET/MR. Optimally, a permanent location for mounting the tracking system near the PET gantry of the PET/MR should be identified and evaluated.
All the above tasks will be performed in close collaboration with our team and involve some basic training on our PET/MR system at the University Hospital as well as on our motion tracking devices so that the candidate will learn to plan and perform own experiments. Furthermore, introduction to the existing algorithms to compensate for patient motion will be provided so that the student can perform analysis and testing of these algorithms on his own.
To fulfil these tasks the candidate should have some basic knowledge about tomographic imaging, the physics of PET and MRI and about medical physics/imaging in general. Practical experience in planning of experiments would be favourable. In addition, adequate knowledge on numerical programming languages like R or MATLAB, functional programming skills using Shell scripts, Python or C as well as, preferably, also object-oriented programming skills using C++ would be favourable. The candidate must have a strong ability in abstract and spatial thinking, should provide practical skills in handling experiments and have to be able to suggest own solutions and work on these with minor supervision.
- Title: "Xray absorption spectroscopy on laser Thomson backscattering xray beam".
1. Study Python code, study single pixel absorption event (SPAE) algorithm, make a list mode, and upgrade it for different of ROI (square, circular and ring)
2. Does Xray analysis using a reference source (Am241) and compare it with the SPAE algorithm in IGOR software
- check calibration curve
- check the energy resolution
3. Does Xray background analysis from our 2011 experiment
- Thermionic gun
- SRF gun
4. Does ICS analysis for SRF gun
5. Writing a report(25-30 pages including pictures, references,…)
Data transfer and processing
The major task of the department of research technology is to develop experiment infrastructures for the institutes of the HZDR.
Thus, data collection architectures in a scientific environment are one of our core topics – in many cases from physical input to imaging.
Analog data are read out in many cases with the use of industrial hardware in combination with own equipment, firmware and software in order to achieve top performance. These designs range from closely coupled decentralized detector subsystems to versatile control systems covering thousands of analog and digital I/O’s.
To achieve high speed data transfer and processing, standard components like Ethernet Links and GPU-Hardware are tied together on PC platforms - while our own dedicated hardware and Linux drivers often provide the glue to obtain an efficient and robust system. This approach offers the benefit to develop and pre-test your functionality in a scalable experimental setup without the use of big experimental infrastructures – and thus yields fast development cycles and early results. There is always a variety of different projects – a chance for you to join in.