Nano News: 12/19/14

Nanosensoren für Herz und Hirn

16 Arbeitsgruppen der Christian-Albrechts-Universität zu Kiel (CAU), des Universitätsklinikums Schleswig-Holstein (UKSH) und des Fraunhofer Instituts für Siliziumtechnik (ISIT) erforschen zukünftig gemeinsam neuartige Sensoren für die medizinische Diagnostik. Damit sollen über winzigste Magnetfelder Gehirn- und Herzfunktionen aufgezeichnet werden. Die Geräte sollen es auch möglich machen, Prothesen mit Gedanken zu steuern und das Lernen zu optimieren. Mehr als 2 Millionen Euro für zunächst zwei Jahre gibt die Deutsche Forschungsgemeinschaft (DFG) für die zehn Teilprojekte.

Im Reinraum des Kieler Nanolabors. Sensoren, die ohne Kühlung und Abschirmung auskommen und kaum detektierbare Magnetfelder aufspüren können, sind das ehrgeizige Ziel der Forschenden. Das würde die Magnetoenzephalographie (MEG) und die Magnetokardiographie (MKG) weiterentwickeln. "Neue visionäre medizinische Anwendungen sind denkbar, die mit bisherigen Sensoren nicht zu verwirklichen sind, zum Beispiel neue Körperüberwachungssysteme“, erklärt Professor Eckhard Quandt vom Kieler Institut für Materialwissenschaft, der die Projektanträge federführend begleitete. "Meine herzlichsten Glückwünsche gehen an alle beteiligten Kolleginnen und Kollegen“, freute sich CAU-Präsident Professor Lutz Kipp über den Förderbescheid. "Die DFG hat die Innovationskraft und grosse gesellschaftliche Bedeutung der Nano- und Oberflächenforschung an der Universität Kiel erkannt. Wir hoffen sehr, dass auch das Land durch Erfolge wie diese anerkennt, welche Bedeutung die Spitzenforschung für die Reputation Schleswig-Holsteins und die Versorgung der Bevölkerung mit Zukunftstherapien hat.“ Vielversprechende Vorarbeiten haben die Wissenschaftlerinnen und Wissenschaftler bereits im Sonderforschungsbereich "Magnetoelektrische Verbundwerkstoffe – biomagnetische Schnittstelle der Zukunft“ geleistet. Ergebnis dieses Projektes waren Werkstoffe, die aus sogenannten magnetostriktiven und piezoelektrischen Materialien bestehen. Werden diese verformt, entsteht eine elektrische Spannung. Umgekehrt verformen sie sich, wenn eine Spannung angelegt wird. Damit war es den Kieler Forschenden bereits gelungen, kaum vorhandene Magnetfelder zu messen. In den kommenden zwei Jahren wollen sie die Messgrenze weiter nach unten verschieben, aus den Sensoren Systeme entwickeln und diese in der Kardiologie und Enzelphalographie einsetzen. Optimistisch stimmt Quandt dabei die etablierte und enge Zusammenarbeit in Kiel zwischen Materialwissenschaft, Physik, Elektrotechnik und Medizin.

Quantum world without queues could lead to better solar cells

In a recent study ("Coherent two-dimensional photocurrent spectroscopy in a PbS quantum dot photocell") from Lund University in Sweden, researchers have used new technology to study extremely fast processes in solar cells. The research results form a concrete step towards more efficient solar cells. The upper limit for the efficiency of normal solar cells is around 33 per cent. However, researchers now see a possibility to raise that limit to over 40 per cent, thereby significantly improving the potential of this energy source. The experiments in the present study involved ‘juggling’ on quantum level with photons, i.e. light particles, and electrons. Quantum level refers to the microcosm of the world formed by individual atoms and their building blocks. In juggling the particles, the researchers took advantage of the fact that the laws of nature work slightly differently on quantum level than what we are used to in our world. “We were actually a bit surprised that it worked”, said Tönu Pullerits, Professor of Chemical Physics at Lund University. In the study, Tönu Pullerits and his colleagues studied solar cells containing nanometre-sized balls of material known as quantum dots. These quantum dots can be likened to individual artificial atoms of semiconductor materials. When sunlight hits the quantum dots, two electrons can be extracted from one photon, which can increase the efficiency of the solar cells. “This would mean a radical improvement to solar cells”, said Professor Pullerits. The explanation for this effect lies in the laws of quantum mechanics that control particles on the quantum scale. The phenomenon is called quantum coherence and can lead to a type of energy transfer that produces an almost perfect flow of energy without any obstacles. Coherence opens up a possibility that the flow of energy can find the shortest route by taking all the possible routes at the same time and then selecting the best. To stretch a metaphor, you could compare it to avoiding choosing a queue in the supermarket – instead you can stand in all the queues and see which moves the fastest. Although in reality, the process is extremely fast: it takes a matter of billionths of a second in the quantum world. There are ongoing discussions between researchers on whether the phenomenon might be used by certain photosynthetic organisms to capture sunlight. Over recent years, Tönu Pullerits and his colleagues have conducted research to try to understand and control the coherence phenomenon in order to make use of it in more efficient solar cells, but the results can also be used in other contexts where the transport and interaction of electrons and photons is decisive, such as in future high-speed quantum electronics.

Skyrmions like it hot

A simulation study by researchers from the RIKEN Center for Emergent Matter Science has demonstrated the feasibility of using lasers to create and manipulate nanoscale magnetic vortices ("Creation of skyrmions and antiskyrmions by local heating"). The ability to create and control these ‘skyrmions’ could lead to the development of skyrmion-based information storage devices. The information we consume and work with is encoded in binary form (as ‘1’s or ‘0’s) by switching the characteristics of memory media between two states. As we approach the performance and capacity limits of conventional memory media, researchers are looking toward exotic physics to develop the next generation of magnetic memories.

Schematic representation of skyrmion creation by local heating using a laser. (Image: Mari Ishida, RIKEN Center for Emergent Matter Science) One such exotic phenomenon is the skyrmion—a stable, nanoscale whirlpool-like magnetic feature characterized by a constantly rotating magnetic moment. Theoretically, the presence or absence of a skyrmion at any location in a magnetic medium could be used to represent the binary states needed for information storage. However, researchers have found it challenging to reliably create and annihilate skyrmions experimentally due to the difficulty in probing the mechanics of these processes in any detail. The challenge lies in the incredibly short timescale of these processes, which at just a tenth of a nanosecond is up to billion times shorter than the timescale observable under the Lorentz microscope used to measure magnetic properties. The study authors, Wataru Koshibae and Naoto Nagaosa, sought a solution to this problem by constructing a computational model that simulates the heating of a ferromagnetic material with pinpoint lasers (Fig. 1). This localized heating creates both skyrmions and ‘antiskyrmions’. The simulations, based on known physics for these systems, showed that the characteristics of skyrmions are heavily dependent on the intensity and spot size of the laser. Further, by manipulating these two parameters, it is possible to control skyrmion characteristics such as creation time and size. “Heat leads to random motion of magnetic spins,” explains Nagaosa. “We therefore found it surprising that local heating created a topologically nontrivial ordered object, let alone composite structures of skyrmions and antiskyrmions” The issue of control is what differentiates these structures. Nagaosa believes that as skyrmions are quite stable, these nanoscale features could conceivably be used as an information carrier if a reliable means of creating them at will can be achieved. Koshibae and Nagaosa’s work could therefore form the basis of the development of state-of-the-art memory devices. The work also provides valuable information on the creation of topological particles, which is crucial for advancing knowledge in many other areas of physics.