Directional Discovery: Circular Polarized Light Produces Oriented Currents in Nanocrystals

Nanocrystals that have been produced wet-chemically, that is, in a solution, are already present in the latest TV screens or are used in imaging diagnostic procedures in medicine. A research group around CUI researchers PD Dr. Christian Klinke from the Institute for Physical Chemistry at the University of Hamburg has now demonstrated a special property in such nanostructures. Circular-polarized light, as is also used in 3D cinemas, can be used to align electrons in lead sulfide nanocats and generate an oriented current. As a result, more economical and high-performance transistors and computer chips are possible in the future, with lower power consumption. The research results have now been published in the journal Nature Communications.

Left: Color-coded electron microscope image of a two-dimensional lead sulfide nanoplate (green), which is contacted with two gold electrodes. Fig. Right: Scheme of the phenomenon: Circular polarized light that strikes the nanoplate, directs the electrons in their spin, drives them to the contacts and thus generates electricity. Photo: UHH / Klinke

Nanomaterials are only a millionths of a millimeter in size and have special properties. The group around Christian Klinke specializes in the production and characterization of two-dimensional nanocrystals. The platelet-shaped structures are adjustable in their geometrical, optical and electrical properties. This makes them particularly interesting for application in solar cells or computer circuits.

When light is passed through optical filters, it can be circularly polarized, ie the light particles are given a torque, the so-called spin. By the illumination with circular-polarized light, it is possible to align electric charges in semiconductor materials and convert them into electric current without applying a voltage. These researchers have now been able to detect this so-called Rashba effect in two-dimensional lead sulfide nanoplates. Because of the crystal symmetry of the nanoplates, this effect is normally not observed there. It occurred only through the influence of an external electric field that breaks the symmetry. By varying the layer thickness of the nanoplates, the character of the light used and the intensity of the electric fields, the effect could be controlled and adapted specifically to the targeted applications. The experimental observations were carried out by the group of Prof. Dr. Carmen Herrmann of the Institute for Inorganic and Angewandte Chemie of the University of Hamburg with simulations of the electronic structure of the materials.

“The findings are particularly valuable as it was demonstrated for the first time that basic effects of electric spin transport are also possible in wet-chemically generated nanomaterials,” says Klinke. “We were also able to show that the two-dimensional materials in the chemical laboratory can be produced cheaply and on a large scale and still are of the highest quality.”

Original publications:
Moayed MMR, Bielewicz Th., Zöllner MS, Herrmann C. & Klinke Ch.
“Towards colloidal spintronics through Rashba spin-orbit interaction in lead sulphide nanosheets”
Nature Communications 8, 15721 (2017)
DOI: 10.1038 / ncomms15721

Source : University of Hamburg