This electron density is one to two orders higher in magnitude than could be achieved in 3D bulk materials, the researchers said. The layer of ionic liquid allowed the researchers to inject the semiconductor with electrons at a density of a hundred trillion to a quadrillion per square centimeter. The researchers used molybdenum ditelluride (MoTe 2), a typical 2D semiconductor, and coated it with an ionic liquid (DEME-TFSI) with an ultra-high capacitance, or ability to store electric charges. It has greater potential for integration into the manufacturing of cell phones, computers and other electronic devices."
LEAD ATOMIC STRUCTURE FREE
"Compared to the use of chemicals, our method is reversible and free of impurities. "Here we use electrostatic doping to control the atomic configuration of a 2D material," said study co-lead author Ying Wang, another graduate student in Zhang's lab. A number of research groups have also investigated using chemicals to alter the configuration of atoms in semiconductor materials, but that process is still difficult to control and has not been widely adopted by industry. Such methods are energy-intensive and not feasible for practical applications, while the excess heat can significantly reduce the life span of components in integrated circuits. The classic approach to driving the structural transition of materials involves heating them to above 500☌. "The idea of electron doping to alter a material's atomic structure is unique to 2D materials, which are much more electrically tunable compared with 3D bulk materials," said study co-lead author Jun Xiao, a graduate student in Zhang's lab. By comparison, 2D monolayer materials are composed of a single layer of atoms or molecules whose thickness is 100,000 times smaller than a human hair. Electronic components capable of this phase transition have been shrunk down to paper-thin sizes, but they are still considered to be bulk, three-dimensional (3D) layers by scientists. Switching a material's structural configuration from one phase to another is the fundamental, binary characteristic that underlies today's digital circuitry. Such electron doping-driven structural phase transitions at the 2D limit is not only important in fundamental physics it also opens the door for new electronic memory and low-power switching in the next generation of ultra-thin devices." "By adding electrons into a material, the overall energy goes up and will tip off the balance, resulting in the atomic structure re-arranging to a new pattern that is more stable. "We show, for the first time, that it is possible to inject electrons to drive structural phase changes in materials," said study principal investigator Xiang Zhang, senior faculty scientist at Berkeley Lab's Materials Sciences Division and a professor at the University of California, Berkeley. The process uses far less energy than current methods for changing the configuration of a material's structure. In a study published in Nature, the researchers have found a way to reversibly change the atomic structure of a two-dimensional (2D) material by injecting, or ‘doping’, it with electrons. That is according to a new study led by researchers at the US Department of Energy's Lawrence Berkeley National Laboratory (Berkeley Lab).
The same electrostatic charge that can make hair stand on end and attach balloons to clothing could offer an efficient way to drive atomically thin electronic memory devices of the future. The ionic liquid covering the monolayer and electrodes allows a high density of electrons to populate the monolayer, leading to a structural change in the lattice from a hexagonal (2H) to monoclinic (1T') pattern. This schematic shows the configuration for structural phase transition on a monolayer of molybdenum ditelluride (shown as yellow and blue spheres), which is anchored by metal electrodes (top gate and ground).
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