Dr. Christine Zimmermann

Communications & Media Relations
Phone: +49 351 260 2450

Scientific Highlights

Online Annual Report 2018

Electronic skin compass for artificial magnetoreception and interactive electronics

Illustration Magnetsensor Panda ©Copyright: HZDR / G.S. Cañón Bermúdez

The magnetic skin sensor enables navigation of a panda in a virtual environment.

Source: HZDR / G.S. Cañón Bermúdez

Researchers at HZDR’s Institute of Ion Beam Physics and Materials Research have developed a new kind of magnetic field sensor that embeds the functionality of an electronic compass into a skin-like ultrathin patch. The micrometer-thick sensor is fabricated on a highly flexible substrate, and is capable of perceiving the direction of motion in the open by readily interacting with the earth’s magnetic field. Such magnetic field sensors can be used as lightweight and imperceptible add-ons for real-time tracking a person’s position and motion in outdoor environments.

In addition, the HZDR researchers have demonstrated, by interfacing their sensors with a game engine, that they can navigate virtual objects in virtual reality (VR) and augmented reality (AR) scenarios, relying only on the earth’s magnetic field vector. In contrast to available human-machine interfaces, this new approach provides a seamless interactive experience for the user without the need for bulky equipment or motion restricting gadgets.

This innovative sensor technology has potential well beyond the computer and gaming industries. For instance, such an “e-skin compass“, combined with targeted neurostimulation, may in future enable humans to imitate the magnetoreception sense that some animals naturally possess. Furthermore, this approach could be used as a therapeutic aid for patients suffering of sensory processing disorder or as a tool for cognitive research and sensory substitution experiments.  

Graphene efficiently enables clock rates in the terahertz range

Graphen ermöglicht Taktraten im Terahertz-Bereich ©Copyright: Juniks/HZDR

Graphene enables clock rates in the terahertz range.

Source: Juniks/HZDR

The logical next step in the development of innovative, ever-faster (opto-)electronic components is to access the terahertz frequency range. Until now, however, the materials and technologies required for the simple, efficient generation and conversion of spectral tunable terahertz radiation were lacking. Graphene – an ultrathin material consisting of a single layer of interlinked carbon atoms – has long been discussed as a potential material to achieve this. In a groundbreaking experiment, a team of HZDR researchers led by Dr. Sergey Kovalev and Prof. Michael Gensch (previously at HZDR, now at TU Berlin and Deutsches Zentrum für Luft- und Raumfahrt (DLR, German Aerospace Center) in collaboration with the Max Planck Institute for Polymer Research and the University of Duisburg-Essen (UDE), has managed for the first time to experimentally prove the theoretically predicted, strongly nonlinear properties of graphene in the terahertz range for the first time. With the aid of the unique experimental possibilities available at the TELBE – the terahertz user facility at the ELBE Center for High-Power Radiation Sources of the HZDR – the scientists involved have succeeded in providing the first direct proof of frequency multiplication from gigahertz to terahertz in a graphene monolayer.

The resulting nonlinear coefficients of graphene – a measure of process efficiency – were extremely high, exceeding values for other nonlinear materials by 7 to 18 orders of magnitude. Using a comparatively simple thermodynamic model, developed by the group led by Professor Dmitry Turchinovich (previously at UDE, now at Bielefeld University), the scientists were also able to interpret the experimental results quantitatively well. The model describes the effect of the excited field in the high gigahertz range as an ultrafast, collective heating and cooling process of the free charge carriers available in graphene. This results in the strong modulation of the opto-electronic properties of graphene, and especially electrical conductivity. If a sufficiently large number of free charge carriers are available, such as through doping, the excited field results in the emission of higher harmonic oscillations with three, five and seven times the initial frequency.

The study shows that graphene-based components may be a highly efficient way of creating a bridge from the gigahertz to the terahertz range. This finding paves the way for the realization of completely new ultrafast technologies.

Proton beams and magnetic resonance imaging: A promising combination in the fight against cancer

Dr. Aswin Hoffmann ©Copyright: HZDR / R. Weisflog

Dr. Aswin Hoffmann with the setup for the combination of proton beam and magnetic resonance imaging systems in the experimental room at the National Center for Radiation Research in Oncology – OncoRay.

Source: HZDR / R. Weisflog

One advantage that proton beam therapy has over conventional radiation therapy with X-rays in cancer treatment is its better ability to spare healthy tissues surrounding the tumor. However, a safety margin around the tumor is required, because, until now, it has been difficult to predict exactly where in the tumor the protons will have their full effect. Scientists at the HZDR are investigating methods to improve the targeting precision of proton therapy, such that the full clinical benefit can be exploited. In a proof-of-concept study, the researchers for the first time investigated simultaneous proton beam irradiation and magnetic resonance imaging (MRI). Compared to X-ray-based computed tomography, MRI provides unparalleled soft-tissue contrast and avoids exposure to ionizing radiation. It therefore has the potential to provide continuous real-time imaging during proton irradiation.

The study focused on the electromagnetic interactions arising when systems for proton therapy and MRI were integrated. Since protons are positively charged particles, the beam is deflected by the magnetic fields of the MRI scanner, hence affecting the beam quality and dose distribution. Conversely, the magnetic fields produced by the proton therapy system influence the magnetic field of the MRI scanner, which latter must be homogenous to ensure a high geometric image quality. The HZDR researchers have managed to prove that it is possible to integrate the two systems without introducing degradations to the proton beam or MR image quality.

To conduct their investigations, the researchers placed a low-field open MRI scanner in the path of a proton beam in the experimental area of the National Center for Radiation Research in Oncology – OncoRay. A standardized MRI knee phantom and tissue-mimicking samples were used as test objects. Based on their results and accompanying calculations, the researchers were able to prove that, although the magnetic fields originating from the proton therapy system produced small geometrical shifts in the MR images, these shifts were easy to predict and eliminate. Furthermore, they demonstrated that it is also possible to accurately calculate the deflection of the beam while the protons slow down in the test objects in the presence of the MR magnetic field, and thus can be corrected for during treatment planning and dose delivery.
The importance of this work is underlined by the awarding of the 2019 Roberts’ Prize by the Institute of Physics in Medicine (IPEM), Great Britain, for the best paper published in the scientific journal Physics in Medicine and Biology in 2018.

Biomineralization of uranium in rock salt deposits

Mikroorganismen im Salzgestein (ref.) ©Copyright: HZDR / Juniks

Haloarchaea (pink) in rock salt are able to convert solved Uranium into a non-soluble mineral form (green needles).

Source: HZDR / Juniks

Salt domes are among the geological formations being investigated as potential sites for the final disposal of high-level radioactive waste in Germany. The ability to store the material safely over a period of one million years is relevant for assessment purposes. In this context, HZDR researchers investigated geobiological processes that could occur under the expected environmental conditions. Haloarchaea – primeval microorganisms – are the dominant life form in rock salt. Until now, little was known about how these organisms interact with radionuclides. A team of researchers from the HZDR has discovered that dissolved uranium is converted by means of biomineralization into U(VI) phosphate by the haloarchaea present in the rock salt.

To conduct their investigations, the scientists used two microbial strains (Halobacterium noricense DSM 15987T and Halobacterium sp. putative noricense) that were originally found in a salt mine in Altaussee, Austria, and in a US-American Waste Isolation Pilot Plant (WIPP). During the experiment, haloarchaea that had been cultivated in a concentrated saline solution were exposed to different uranium concentrations for a longer period. The experimental conditions corresponded to a simulated worst-case scenario, such as that associated with water ingress in a salt dome repository.

Both Halobacterium strains exhibited unexpected multistage interaction with uranium: After an initial phase of sorption of the radionuclides, a period of release was observed, followed by renewed bioassociation. Using special spectroscopic methods, the scientists managed to unravel the structure of the uranium complexes that had formed over time. Finally, mineral U(VI) phosphate was formed. The dominant microorganisms in rock salt are therefore capable of converting uranium into a non-soluble form in the event of its release, effectively preventing further distribution in the environment. 

Circular use of critical raw materials: Efficient recovery of gallium

Complexation of siderophores DFOB (a) and DFOE (b) with gallium(III) ©Copyright: Dr. Jain, Rohan

Complexation of siderophores DFOB (a) and DFOE (b) with gallium(III)

Source: HZDR / Rohan Jain

Gallium is a critical raw material in developing renewable energy sources and energy-efficient systems. Since there are risks associated with gallium supplies on the world market, efficient recycling technologies are required, which may continue to ensure the availability of this rare metal for advanced technologies. HZDR researchers have developed a technology to recover gallium (III) ions from their low-concentrated industrial wastewaters generated during GaAs wafer fabrication. To this end, they used two different siderophores: desferrioxamine B (DFOB) and desferrioxamine E (DFOE) for the recovery of gallium.

Siderophores (the Greek term for “iron carriers“) are a group of around 500 low-molecular weight compounds (500 -1500 Dalton), characterized by the formation of stable complexes with iron ions. In nature, they are formed by a wide range of bacteria, fungi and plant roots following iron deficiency, enabling this essential mineral to be taken up from the surrounding area. 

According to the investigations undertaken by the HZDR researchers, both DEOB and DEOE form highly stable gallium-siderophore complexes. This finding correlates with the observed high selectivity of both siderophores towards gallium. Indeed, the siderophores were able to successfully complex 100% gallium in two different process wastewaters stemming from wafer production. The researchers used different spectrometric methods (infrared and nuclear magnetic resonance) as well as density functional theory calculations to identify how gallium (III) ions are complexed. They found that the siderophores fix the metal to special functional groups containing not only carbon, oxygen and hydrogen, but also a nitrogen atom. 

The scientists used chromatographic method – C18 reversed-phase column chromatography – to separate the gallium complex from the process wastewater. This enabled the researchers to complex almost 100% of the gallium and to recover more than 95% as a siderophore complex. The gallium was then released from the complex following the addition of a 6-fold excess of the complexing agent ethylenediaminetetraacetic acid (EDTA) to an acidic solution (pH value of 3.5), achieving a regeneration of > 90% of the siderophores without any loss of function. It was proven that the siderophores could be applied for at least ten cycles without any loss of function.