Researchers at the Peter Grünberg Institute (PGI) have taken an important step towards the goal of joining individual molecules together, much like Lego bricks, and building any structures from them on a nanoscale. They succeeded not only in transporting a molecule to a specific point, but also in bringing it permanently into the desired upright position. The researchers reported how they managed that in the journal “Nature”.
For some time now, researchers have been able to create structures from individual atoms. The tiny IBM logo made of xenon atoms, which scientists from the company presented in 1990 in “Nature” as well, created a stir. The lettering “Jülich” has also been “written” on a nanoscale. Such precision performances are possible with the aid of a scanning probe microscope that can deliberately move individual atoms or pick them out of a layer. A manual control system was developed at PGI for this purpose, which allows the microscope tip to be controlled by gestures.
However, producing nanostructures directly from complex molecules is still far from possible at the moment. Although molecules are much larger than atoms, they are much more difficult to control. While they, too, can be moved with the scanning probe microscope, there is more: “With atoms, orientation doesn’t matter, but molecules have a certain spatial structure. For example, it depends on the position in which they adhere to a surface or to the tip of a microscope, which exceeds the dimensions of the molecule by many orders of magnitude,” says Prof. Stefan Tautz, head of PGI, explaining the problem.
In nature, molecules are formed according to the mechanism of self-assembly, that is they arrange themselves in a certain way according to their respective properties. The goal of the researchers at the Peter Grünberg Institute in Jülich is a technology that not only enables molecules to be arranged in a few predetermined ways, but also enables structures to be produced freely on a nanoscale.
Dr. Ruslan Temirov
The group headed by Dr. Ruslan Temirov at PGI has now for the first time succeeded in orienting a platelet-shaped dye molecule called 3,4,9,10-Perylenetetracarboxylic dianhydride – PTCDA for short – as desired. The molecule consists of a layer of interconnected carbon rings, similar to the nanomaterial graphene. With the tip of a scanning probe microscope, the researchers attached two silver atoms to the edges of the PTCDA molecule. They then made it stand upright on a tiny “silver platform”. It is surprisingly stable like this. “Even if it is pushed with the tip of the microscope, it does not fall over, but simply swings back again. So far, we can only speculate about the reason,” says Dr. Taner Esat, first author of the study.
According to the authors, the work is regarded as an important step in the development of new, innovative production techniques with single molecules. They see areas of application in nanoelectronics in particular, with entirely new possibilities for building logic, memory, sensor and amplifier circuits. The researchers have already successfully used the stand-up molecule as an electron source emitting individual electrons. With such a single electron source, the electron’s wave function is precisely determined by the chemical properties of the molecule. Such sources could, for example, be used for applications in holography that use the wave character of the emitted electrons for spatial representations and recordings.
PHOTOS: Forschungszentrum Jülich/Sascha Kreklau