A scientific breakthrough: Researchers at Tel Aviv University have developed the world’s smallest technology, only two atoms thick. According to the researchers, the new technology provides a way to store electrical information in the finest unit known to science, in one of nature’s most stable and inert materials. The quantum mechanical electron tunneling allowed through the atomically thin film can stimulate the process of reading information far beyond current technologies.
The research was carried out by scientists from the Raymond and Beverly Sackler School of Physics and Astronomy and the Raymond and Beverly Sackler School of Chemistry. The group includes Maayan Vizner Stern, Yuval Waschitz, Dr Wei Cao, Dr Iftach Nevo, Prof. Eran Sela, Prof. Michael Urbakh, Prof. Oded Hod and Dr. Moshe Ben Shalom. The work is now published in Science magazine.
“Our research stems from the curiosity for the behavior of atoms and electrons in solid materials, which has generated many technologies supporting our modern way of life,” says Dr. Ben Shalom. “We (and many other scientists) try to understand, predict, and even control the fascinating properties of these particles as they condense into an ordered structure that we call a crystal. At the heart of the computer, for example, is a tiny crystalline device designed to switch between two states indicating different answers – “yes” or “no”, “high” or “low” and so on. Without this dichotomy – it is not possible to encode and process information. The practical challenge is to find a mechanism that would allow switching in a small, fast, and inexpensive device.
Today’s advanced devices consist of tiny crystals that contain only about a million atoms (about a hundred atoms in height, width and thickness) so that a million of these devices can be squeezed about a million times. in the zone. of a room, each device switching at a speed of about a million times per second.
Following the technological breakthrough, researchers were able, for the first time, to reduce the thickness of crystalline devices to just two atoms. Dr Ben Shalom points out that such a thin structure allows memories based on the quantum capacity of electrons to jump quickly and efficiently through barriers that are only a few atoms thick. So, it can greatly improve electronic devices in terms of speed, density and power consumption.
In the study, the researchers used a two-dimensional material: layers of boron and nitrogen one atom thick, arranged in a repeating hexagonal structure. In their experiment, they managed to break the symmetry of this crystal by artificially assembling two of these layers. “In its natural three-dimensional state, this material is composed of a large number of superimposed layers, each layer being rotated 180 degrees with respect to its neighbors (antiparallel configuration)”, explains Dr Ben Shalom.
“In the laboratory, we were able to artificially stack the layers in a parallel configuration without rotation, which hypothetically places atoms of the same nature in perfect overlap despite the strong repulsive force between them (resulting from their identical charges). In reality, however, the crystal prefers to glide slightly from one layer to the next, so that only half of the atoms in each layer overlap perfectly and the overlapping ones are of opposite charges – while all others are located above or below an empty space – the center of the hexagon. In this artificial stacking configuration, the layers are quite distinct from each other. For example, if in the upper layer only the boron atoms overlap, in the lower layer, it is the reverse.
Dr Ben Shalom also highlights the work of the theoretical team, which has carried out numerous computer simulations. “Together, we established a deep understanding of why the electrons in the system organize themselves as we had measured in the lab. With this fundamental understanding, we also expect fascinating responses in other symmetrically broken layer systems, ”he says.
Maayan Wizner Stern, the doctoral student who led the study, explains: “The symmetry breaking that we created in the lab, which does not exist in the natural crystal, forces the electric charge to rearrange itself between the layers and generate a tiny internal electrical polarization. perpendicular to the plane of the layer. When we apply an external electric field in the opposite direction, the system slides sideways to change the orientation of the polarization. The switched polarization remains stable even when the external field is cut. In this, the system is similar to thick three-dimensional ferroelectric systems, which are widely used in technology today.
“The ability to force a crystalline and electronic arrangement in such a thin system, with unique polarization and inversion properties resulting from the weak Van der Waals forces between layers, is not limited to the crystal of boron and nitrogen. “, adds Dr Ben Shalom. . “We would expect the same behaviors in many layered crystals with the right symmetry properties. The concept of midslip as an original and efficient way to control advanced electronic devices shows great promise, and we named it Slide-Tronics ”.
Maayan Vizner Stern concludes, “We are excited to find out what can happen in other states that we impose on nature and predict that other structures that couple additional degrees of freedom are possible. We hope that miniaturization and slip-flipping will improve today’s electronic devices, and furthermore, enable other original ways of controlling information in future devices. In addition to computing devices, we expect this technology to contribute to sensors, energy storage and conversion, interaction with light, etc. Our challenge, in our opinion, is to discover more crystals with new sliding degrees of freedom.
Reference: “Interfacial ferroelectricity by van der Waals glissement” by M. Vizner Stern, Y. Waschitz, W. Cao, I. Nevo, K. Watanabe, T. Taniguchi, E. Sela, M. Urbakh, O. Hod and M Ben Shalom, June 25, 2021, Science.
DOI: 10.1126 / science.abe8177
The study was funded with support from the European Research Council (ERC Seed Grant), the Israel Science Foundation (ISF) and the Ministry of Science and Technology (MOST).