So far, little has been understood about the underlying atomic-scale principles. In cooperation with researchers at the universities of Münster and Gießen as well as the Fraunhofer Institute for Mechanics of Materials IWM in Freiburg, scientists at the INM – Leibniz Institute for New Materials were able to show that on atomic scale gold surfaces smoothen out by themselves at room temperature. In their publication in Physical Review Letters, they reveal that this effect disappears at low temperatures.
So far, it has been assumed that perfect sliding works the better the more rigid the surface is. On the atomic scale this could mean freezing lattice vibrations in the crystal at low temperatures below -100°C; where the atoms hardly move. Against expectation, smooth sliding on gold surfaces is not quite possible at these temperatures, but, however, at room temperature. The scientists explain this phenomenon with the diffusion of the gold atoms: If they are able to move freely on the surface, the gold atoms migrate into defects on the surfaces and remove holes and bumps. The diffusion effectively stops below -100°C.
"Imagine a record player whose needle made from rubber moves over a wax plate. If the wax is hard, wax pieces will be scratched out and, after a while, the needle pushes a pile of wax, which can only be surmounted by the needle after it bends strongly", explains Roland Bennewitz, Head of the Program Division "Nanotribology". If the temperature rises, the wax melts and the needle leaves no more traces in the wax. In fact, the liquid wax removes holes and bumps at once, and the needle slides uniformly through the wax.
A similar process occurs on the gold surfaces. Although they do not melt at room temperature, the diffusion of the gold atoms is so strong that smallest asperities on the nanoscale are removed at once. The regular structure of the surface is preserved.
Experiments were performed by atomic force microscopy (AFM). A thin needle slides forth and back on the gold surface. The measured signal shows how strong the needle bends in contact. On a crystalline surface, the needle "jumps" regularly from atom group to atom group – the scientists measure a stable so-called stick-slip pattern. In the event of defects, such as the accumulated gold atoms, the needle bends stronger and the stick-slip pattern will be broken.
In their research, the scientists also employed atomistic modelling on the computer. Here, they were able to reproduce the stick-slip pattern for the scanning of the gold surface with gold and nickel needles. With a 3D simulation, they were also able to show how gold atoms accumulate at low temperatures. The accumulated gold atoms are attracted by the needle like a liquid into a capillary.
INM – Leibniz Institute for New Materials, situated in Saarbrücken/Germany, is an internationally leading centre for materials research. It is a scientific partner to national and international institutes and a provider of research and development for companies throughout the world. INM is an institute of the Scientific Association Gottfried Wilhelm Leibniz and employs around 190 collaborators. Its main research fields are Chemical Nanotechnology, Interface Materials, and Materials in Biology.
Let the good tubes roll
19.01.2018 | DOE/Pacific Northwest National Laboratory
Method uses DNA, nanoparticles and lithography to make optically active structures
19.01.2018 | Northwestern University
On the way to an intelligent laboratory, physicists from Innsbruck and Vienna present an artificial agent that autonomously designs quantum experiments. In initial experiments, the system has independently (re)discovered experimental techniques that are nowadays standard in modern quantum optical laboratories. This shows how machines could play a more creative role in research in the future.
We carry smartphones in our pockets, the streets are dotted with semi-autonomous cars, but in the research laboratory experiments are still being designed by...
What enables electrons to be transferred swiftly, for example during photosynthesis? An interdisciplinary team of researchers has worked out the details of how...
For the first time, scientists have precisely measured the effective electrical charge of a single molecule in solution. This fundamental insight of an SNSF Professor could also pave the way for future medical diagnostics.
Electrical charge is one of the key properties that allows molecules to interact. Life itself depends on this phenomenon: many biological processes involve...
At the JEC World Composite Show in Paris in March 2018, the Fraunhofer Institute for Laser Technology ILT will be focusing on the latest trends and innovations in laser machining of composites. Among other things, researchers at the booth shared with the Aachen Center for Integrative Lightweight Production (AZL) will demonstrate how lasers can be used for joining, structuring, cutting and drilling composite materials.
No other industry has attracted as much public attention to composite materials as the automotive industry, which along with the aerospace industry is a driver...
Scientists at Tokyo Institute of Technology (Tokyo Tech) and Tohoku University have developed high-quality GFO epitaxial films and systematically investigated their ferroelectric and ferromagnetic properties. They also demonstrated the room-temperature magnetocapacitance effects of these GFO thin films.
Multiferroic materials show magnetically driven ferroelectricity. They are attracting increasing attention because of their fascinating properties such as...
08.01.2018 | Event News
11.12.2017 | Event News
08.12.2017 | Event News
19.01.2018 | Materials Sciences
19.01.2018 | Health and Medicine
19.01.2018 | Physics and Astronomy