Tag Archives: TU Munich

Self-assembly with porphine molecules

A Jan. 12, 2016 American Institute of Physics (AIP) news release by John Arnst (also on EurekAlert but dated Jan. 14, 2016) describes computational research into self-assembling nanodevices based on porphine molecules,

As we continue to shrink electronic components, top-down manufacturing methods begin to approach a physical limit at the nanoscale. Rather than continue to chip away at this limit, one solution of interest involves using the bottom-up self-assembly of molecular building blocks to build nanoscale devices.

Successful self-assembly is an elaborately choreographed dance, in which the attractive and repulsive forces within molecules, between each molecule and its neighbors, and between molecules and the surface that supports them, have to all be taken into account. To better understand the self-assembly process, researchers at the Technical University of Munich have characterized the contributions of all interaction components, such as covalent bonding and van der Waals interactions between molecules and between molecules and a surface.

“In an ideal case, the smallest possible device has the size of a single atom or molecule,” said Katharina Diller, who worked as a postdoctoral researcher in the group of Karsten Reuter at the Technical University of Munich. Reuter and his colleagues present their work this week in The Journal of Chemical Physics, from AIP Publishing.

One such example is a single-porphyrin switch, which occupies a surface area of only one square nanometer. [emphasis mine] The porphine molecule, which was the object of this study, is even smaller than this. Porphyrins are a group of ringed chemical compounds which notably include heme – responsible for transporting oxygen and carbon dioxide in the bloodstream – and chlorophyll. In synthetically-derived applications, porphyrins are studied for their potential uses as sensors, light-sensitive dyes in organic solar cells, and molecular magnets.

The researchers from TU Munich assessed the interactions of the porphyrin molecule 2H-porphine by using density functional theory, a quantum mechanical computational modelling method used to describe the electronic properties of molecules and materials. Their simulations were performed at the high-performance supercomputer SuperMUC at Leibniz-Rechenzentrum in Garching.

The metallic substrates the researchers chose for the porphyrin molecules to assemble on, the close packed single crystal surfaces of copper and silver, are widely used as substrates in surface science. This is due to the densely packed nature of the surfaces, which allow the molecules to exhibit a smooth adsorption environment. Additionally, copper and silver each react differently with porhyrins – the molecule adsorbs more strongly on copper, whereas silver does a better job of keeping the electronic structure of the molecule intact – allowing the researchers to monitor a variety of competing effects for future applications.

In their simulation, porphyrin molecules were placed on a copper or silver slab, which was repeated periodically to simulate an extended surface. After finding the optimal geometry in which the molecules would adsorb on the surface, the researchers altered the size of the metal slab to increase or decrease the distance between molecules, thus simulating different molecular coverages. The computational setup gave them a switch to turn the energy contributions of neighboring molecules on and off, in order to observe the interplay of the individual interactions.

Diller and Reuter, along with colleagues Reinhard Maurer and Moritz Müller, who is first author on the paper, found that the weak long-range van der Waals interactions yielded the largest contribution to the molecule-surface interaction, and showed that the often employed methods to quantify the electronic charges in the system have to be used with caution. Surprisingly, while interactions directly between molecules are negligible, the researcher found indications for surface-mediated molecule-molecule interactions at higher molecular coverages.

“The analysis of the electronic structure and the individual interaction components allows us to better understand the self-assembly of porphine adsorbed on copper and silver, and additionally enables predictions for more complex porphyrine analogues,” Diller said. “These conclusions, however, come without yet considering the effects of atomic motion at finite temperature, which we did not study in this work.”

Here’s a link to and a citation for the paper,

Interfacial charge rearrangement and intermolecular interactions: Density-functional theory study of free-base porphine adsorbed on Ag(111) and Cu(111) by Moritz Müller, Katharina Diller, Reinhard J. Maurer, and Karsten Reuter. J. Chem. Phys. 144, 024701 (2016); http://dx.doi.org/10.1063/1.4938259

This paper appears to be open access.

Finally, the researchers have made this illustrative diagram titled ‘Energy’ available,

Caption: Schematic depiction of different energy terms contributing to the adsorption energy, and charge density difference of 2H-P after adsorption onto Cu(111) at 12.8 Angstrom separation. Credit: M. Müller/TU Munich

Caption: Schematic depiction of different energy terms contributing to the adsorption energy, and charge density difference of 2H-P after adsorption onto Cu(111) at 12.8 Angstrom separation. Credit: M. Müller/TU Munich

RoboEarth (robot internet) gets examined in hospital

RoboEarth sometimes referred to as a robot internet or a robot world wide web is being tested this week by a team of researchers at Eindhoven University of Technology (Technische Universiteit Eindhoven, Netherlands) and their colleagues at Philips, ETH Zürich, TU München and the universities of Zaragoza and Stuttgart according to a Jan. 14, 2014 news item on BBC (British Broadcasting Corporation) news online,

A world wide web for robots to learn from each other and share information is being shown off for the first time.

Scientists behind RoboEarth will put it through its paces at Eindhoven University in a mocked-up hospital room.

Four robots will use the system to complete a series of tasks, including serving drinks to patients.

It is the culmination of a four-year project, funded by the European Union.

The eventual aim is that both robots and humans will be able to upload information to the cloud-based database, which would act as a kind of common brain for machines.

There’s a bit more detail in Victoria Turk’s Jan. 13 (?), 2014 article for motherboard.vice.com (Note: A link has been removed),

A hospital-like setting is an ideal test for the project, because where RoboEarth could come in handy is in helping out humans with household tasks. A big problem for robots at the moment is that human environments tend to change a lot, whereas robots are limited to the very specific movements and tasks they’ve been programmed to do.

“To enable robots to successfully lend a mechanical helping hand, they need to be able to deal flexibly with new situations and conditions,” explains a post by the University of Eindhoven. “For example you can teach a robot to bring you a cup of coffee in the living room, but if some of the chairs have been moved the robot won’t be able to find you any longer. Or it may get confused if you’ve just bought a different set of coffee cups.”

And of course, it wouldn’t just be limited to robots working explicitly together. The Wikipedia-like knowledge base is more like an internet for machines, connecting lonely robots across the globe.

A Jan. 10, 2014 Eindhoven University of Technology news release provides some insight into what the researchers want to accomplish,

“The problem right now is that robots are often developed specifically for one task”, says René van de Molengraft, TU/e  [Eindhoven University of Technology] researcher and RoboEarth project leader. “Everyday changes that happen all the time in our environment make all the programmed actions unusable. But RoboEarth simply lets robots learn new tasks and situations from each other. All their knowledge and experience are shared worldwide on a central, online database. As well as that, computing and ‘thinking’ tasks can be carried out by the system’s ‘cloud engine’, so the robot doesn’t need to have as much computing or battery power on‑board.”

It means, for example, that a robot can image a hospital room and upload the resulting map to RoboEarth. Another robot, which doesn’t know the room, can use that map on RoboEarth to locate a glass of water immediately, without having to search for it endlessly. In the same way a task like opening a box of pills can be shared on RoboEarth, so other robots can also do it without having to be programmed for that specific type of box.

There’s no word as to exactly when this test being demonstrated to a delegation from the European Commission, which financed the project, using four robots and two simulated hospital rooms is being held.

I first wrote about* RoboEarth in a Feb. 14, 2011 posting (scroll down about 1/4 of the way) and again in a March 12 2013 posting about the project’s cloud engine, Rapyuta.

* ‘abut’ corrected to ‘about’ on Sept. 2, 2014.