The research deals with a two-dimensional material, a single atom thick layer of boron and nitrogen atoms arranged in a cyclic hexagonal structure. During the experiment, the researchers managed to break the symmetry of this crystal by artificially assembling two such layers
Scientific breakthrough: researchers at Tel Aviv University managed to engineer the tiniest technology in the world, only two atoms thick. According to the researchers, the new technology offers a way to encode electrical information into the thinnest unit known to science today, in a crystal that is one of the strongest and most stable in nature.
The research was conducted at the School of Physics and Astronomy and the School of Chemistry at the Raymond and Berly Sackler Faculty of Exact Sciences at Tel Aviv University by a team of researchers that includes Ma'ayan Wisner Stern, Yuval Vashits, Dr. Vai Khao, Dr. Yiftach Nebo, Prof. Eran Sela, Prof. Michael Orbach, Prof. Oded Hod and Dr. Moshe Ben Shalom. The study was published in the prestigious journal Science.
The background for our research is curiosity about the behavior of atoms and electrons in matter, which throughout history has given birth to many of the technologies that surround our modern lives, says Dr. Ben Shalom. We (and many other scientists) are trying to understand, predict, and even control the fascinating properties of these particles when they solidify into an ordered periodic structure called a crystal. At the heart of the computer, for example, sits a tiny crystal device whose purpose is to control some kind of response that has at least two states (switching) - "yes" or "no". Without this dichotomous ability - it is not possible to encode and process information. The practical challenge is to find a mechanism that will allow switching in a small, fast and cheap device.
As of today, the most advanced devices are made of tiny crystals containing only about a million atoms (about a hundred atoms in height, width, and thickness), so that it is possible to place a million like them about a million times in the area of one coin and switch each of the devices at a speed of about a million times per second.
Significant miniaturization of the thickness of the crystalline devices
Now, as mentioned, following the technological breakthrough, the researchers succeeded for the first time in significantly reducing the thickness of the crystalline devices down to only two atoms. Dr. Ben Shalom emphasizes that the new structure allows memory devices based on the quantum ability of electrons to efficiently and quickly jump through barriers with a thickness of a small number of atoms, and therefore may enable significant optimization of electronic devices in terms of density, speed and energy consumption.
As part of the research, the researchers dealt with a two-dimensional material, a single-atom-thick layer of boron and nitrogen atoms arranged in a cyclic hexagonal structure. During the experiment, the researchers managed to break the symmetry of this crystal by artificially assembling two such layers. "In its natural and three-dimensional form, this material is built from a large number of such layers placed one on top of the other, with each layer rotated 180 degrees relative to the layer below it (anti-parallel configuration)" - According to Dr. Ben Shalom. ” In the laboratory, we were able to artificially stack the layers in a parallel configuration, which apparently places atoms of the same type in full overlap despite the strong repulsion between them (as a result of their identical charge). In practice, the crystal prefers to slide one of the layers slightly in relation to the other so that only half of the atoms of each layer overlap, but those that overlap are of different types (that is, with a charge of opposite sign), while the rest of the atoms stand above (or below) an empty space - the center of the hexagon. Although this state is a little less stable than the natural arrangement (called a metastable state), the new arrangement distinguishes well between the layers. For example, if in the upper layer the overlapping atoms are only hole type, then in the lower layer the situation is reversed.
Dr. Ben Shalom adds that the discovery was made possible thanks to a joint and particularly fruitful effort with their theoretician colleagues who performed months of computer simulations to analyze in depth why the electrons in the system line up exactly as we measured.
Wisner Stern spring, the doctoral student who led the research, explains: "The breaking of the symmetry that we were able to create in the laboratory, and does not exist in the natural crystal, forces the electric charge to reorganize between the layers and create a tiny electric polarization perpendicular to the plane of the layers. The resulting opposite polarization remained stable even when we stopped the external field, similar to three-dimensional "proelectric" systems that are widely used in contemporary technology."
"The possibility of forcing a crystalline and electronic arrangement in such a thin system, with unique polarization and inversion characteristics resulting from the weak Huan-der-Waals bonds between the layers, is not limited only to the boron and nitrogen crystal" - Dr. Ben Shalom adds. "In fact, we predict that the phenomenon can be extended to many layered crystals with suitable symmetry characteristics and use interlayer sliding as an original and efficient way to realize advanced electronic devices."
Wiesner Stern summarizes: "We are excited to find out what will happen in other situations imposed on nature, and predict that it will be possible to create new couplings between different degrees of freedom. We hope that the minimization and inversion by sliding will improve the electronic devices of today, and in particular, will allow other original ways of controlling information in the devices of tomorrow. In addition to computing devices, it is possible to foresee a contribution to devices for detection, storage and conversion of energy, reaction with light rays and more. Our challenge, as we see it, is to find additional crystals with new and sliding degrees of freedom."
It should be noted that research was funded with the assistance of the European Research Council ERC, the Israel Science Foundation ISF, and the Ministry of Science.
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