Data storage

Molecular interfaces for innovative sensors and data storage devices

20 October 2021

(Nanowerk News) The molecular interfaces formed between metals and molecular compounds have enormous potential as building blocks for future optoelectronic and electronic spin devices. The phthalocyanine and porphyrin transition metal complexes are promising components for such interfaces.

Scientists from the Forschungszentrum Jülich, together with a team of international scientists, worked on the development of a model system to design such devices with unique functions and improved performance by stabilizing and controlling spin and oxidation states. in complexes with nanoscale precision.

Among other things, they discovered a mechanism that could be used in the future to store information in porphyrins or to develop extremely sensitive sensors to detect toxic nitrogen dioxide.

Some of the most important processes in biological systems are catalyzed by enzymes containing metal ions, where unexpected reactivity corresponds to low oxidation states. For example, porphyrins, a class of coloring molecules, are involved in photosynthesis in plants and the transport of oxygen in red blood cells.

Inspired by their biological functions, scientists have attributed a wide range of technological uses to porphyrins. However, any practical application of these organometallic complexes in the field of technology requires nanoscale control of the molecular properties to be exploited.

A group of scientists from the Forschungszentrum Jülich have been working on these systems for some time with the aim of refining their electronic and magnetic properties and understanding the mechanisms that govern interactions at the interface (Small, “Switching and rotating the room temperature in a multi-functional interface based on porphyrin”).

Multifunctional porphyrin based interface template for spin switching and adjustment. (Image: FZ Jülich) (click on the image for a larger view)

“We have taken the first step in this direction by coupling nickel-porphyrin with copper, which is a highly interactive surface. This unique combination results in some really interesting properties: for example, copper promotes high charge transfer in porphyrin. In addition, it triggers the reduction of the central metal, nickel, bringing the characteristics of this system closer to the biological systems that inspired us in the first place. Suddenly, we wondered, why not go even further, using Ni (I) ‘s high reactivity? ”Explains Dr Vitaliy Feyer from the Peter Grünberg Institute in Jülich.

This is because low valence unsaturated Ni (I) metal ions at this interface are available for catalysis, and the attachment of axial ligands, such as small diatomic molecules, provides the opportunity to further control oxidation and oxidation states. spin. What appeared to be a straightforward approach resulted in some intriguing findings: For example, exposing the molecular interface to a low dose of nitrogen dioxide caused the nickel ion to switch to a higher spin state. . Even in a buried multilayer system, the chemically active low valence nickel ion can be functionalized with nitrogen dioxide, allowing selective tuning of the electronic properties of the metal center.

The axial coordinating spin switching of the ligand at the interface is a reversible process, and the pristine state can be restored by soft annealing of the interface. While nickel functions as a reversible spin switch at room temperature, the electronic structure of the backbone of the macrocycle, where boundary orbitals are primarily located, is not altered.

“The reason is that the strong contact of the porphyrin with the substrate seems to behave like an energetic counterpart, preventing other geometric modifications caused by what is called the trans surface effect”, explains Iulia Cojocariu, doctoral student at the Peter Grünberg Institute.

This method has never been observed at room temperature before and has the potential to be exploited in the future to store information in porphyrins or to build extraordinarily sensitive sensors to detect dangerous substances such as nitrogen dioxide. .

The experiments were carried out mainly at the Elettra synchrotron facility in Trieste, Italy, where the Jülich group operates its own NanoESCA beamline, and at the Swiss Light Source in Villigen, in close collaboration with Prof. Mirko Cinchetti and Dr Giovanni Zamborlini from Technical University Dortmund, Germany, and Dr Luca Floreano from the Italian National Research Council. Theoretical support was provided by Professor Peter Puschnig of the University of Graz, Austria.