Nanophysics: The Right Turn, The stacked properties of small semiconductor materials create incredible materials that can be used for new applications. A team led by LMU scientist Alexander Högele shows the effect of slightly bending the two layers.
The new ultra-porous nanomaterials sometimes contain surprises. For example, if you gather important crystals individually, interesting physical effects can occur. For example, a double layer of graphene that is a miracle material curved at a magic angle of 1.1 degrees does a great job. Semiconductor heterostructures of two layers of transition metal dichalocogenides, which are only unbonded by van der Waals forces, have also become a research object.
Alexander Högele’s working group is studying these new heterostructures that do not exist in nature. “The combination of elements, the number of layers and their relative angular orientation determines a large number of new phenomena”, LMU physics explains. “We can match specific physical phenomena in the laboratory with various applications in electronics, photonics or quantum technologies that are unknown in natural crystals.” However, things that are visible are not always easy to explain, such as a new book published in a newspaper. Creative Nanotechnology Exhibition.
The Moiré effect depends on the orientation of the fabric
Högele’s team studied two systems composed of the semiconductors molybdenum diselenide (MoSe2) and tungsten diselenide (WSe2) held together by van der Waals forces. Depending on the orientation of the layers, moiré effect Because, as we know they exist every day life. These effects also occur in the nanoworld when two different atoms overlap or two parallel lattices twist against each other. It’s just not a visual effect. In the world of atomically thin crystalline heterostructures, the so-called Moiré interference greatly affects the properties of the composite system, including electrons and pairs of electron-hole pairs, i.e. excitons, as Högele and – explain.
“Our work shows that the complete Moiré illusion in the MoSe2-WSe2 double layer does not apply, especially for small rotation angles, and that the interpretation of the observed phenomenology so far must change to some extent,” says Högele. Instead of regular moiré patterns, there are long regions without moiré interference and regions with interesting quantum-mechanical effects that promise applications in quantum communication: one-dimensional quantum wires or quasi-quantum dots. zero-dimensional, for example in spatially localized excitons for a single photon source. In such cases, a good moire pattern can become a series of triangular or hexagonal tiles.
Collective phenomena in artificial crystals
The reason seems to be a change in the structure of the lattice that depends on the structure of the levels. In this process, the atoms are moved from their equilibrium, at the cost of increased pressure in the layers but for the benefit of better adhesion. The result is an energy landscape at these two levels that can be used in a targeted manner. Högele says, “We see different things working together in hand-made crystals, in which the modern Moiré pattern has a strong influence on the movement of electrons and their interactions with each other, ” says Högele.
The understanding of the so-called excitons, electron-hole pairs, which are characteristic of different types of crystal heterostructures and which can be used in future optoelectronic applications, is very important here. They are produced in semiconducting metal dichalcogenides change by the reception of light and can become light again. Högele explains, “Excitons thus act as mediators of thermal interactions in semiconductor crystals.” As the present work shows, different excitons are produced depending on the arrangement of two monolayers, i.e. parallel and antiparallel to each other. “We want to learn how to create Van der Waals heterostructures with structured properties.
Source: LMU Munchen
