'Wiggling' atoms for smaller electronics
Researchers at Michigan State University have figured out how to use a fast laser to wiggle atoms in a way that temporarily changes the behaviour of their host material. This approach could lead to smaller, faster and more efficient electronics — like smartphones — in the future.
Tyler Cocker, an associate professor in the College of Natural Science, and Jose L Mendoza-Cortes, an assistant professor in the colleges of Engineering and Natural Science, have combined the experimental and theoretical sides of quantum mechanics — the study of the strange ways atoms behave at a very small scale — to push the boundaries of what materials can do to improve electronic technologies.
Using a material called tungsten ditelluride, or WTe2, which is made up of a layer of tungsten, sandwiched between two layers of tellurium, Cocker’s team conducted a series of experiments where they placed this material under a specialised microscope they built. While microscopes are typically used to look at things that are hard for the human eye to see, like individual cells, Cocker’s scanning tunnelling microscope can show individual atoms on the surface of a material. It does this by moving an extremely sharp metal tip over the surface, ‘feeling’ atoms through an electrical signal, like reading braille.
While looking at the atoms on the surface of WTe2, Cocker and his team used a super-fast laser to create terahertz pulses of light that were moving at speeds of hundreds of trillions of times per second. These terahertz pulses were focused onto the tip. At the tip, the strength of the pulses was increased, allowing the researchers to wiggle the top layer of atoms directly beneath the tip and gently nudge that layer out of alignment from the remaining layers underneath it. Think of it like a stack of papers with the top sheet slightly crooked.
While the laser pulses illuminated the tip and WTe2, the top layer of the material behaved differently, exhibiting new electronic properties not observed when the laser was turned off. Cocker and his team realised the terahertz pulses together with the tip could be used like a nanoscale switch to temporarily change the electrical properties of WTe2 to upscale the next generation of devices. Cocker’s microscope could even see the atoms moving during this process and photograph the unique ‘on’ and ‘off’ states of the switch they had created.
Mendoza’s lab computationally found that the layers of WTe2 shift by 7 picometres while they are wiggling, which is hard to observe by the specialised microscope alone. They were also able to confirm that the frequencies at which the atoms wiggle match between the experiment and theory, but the quantum calculations can tell which way they wiggle and by how much.
“The movement only occurs on the topmost layer, so it is very localised,” said Daniel Maldonado-Lopez, a fourth-year graduate student in Mendoza’s lab. “This can potentially be applied in building faster and smaller electronics.”
Cocker and Mendoza-Cortes hope this research will lead to the use of new materials, faster speeds and greater energy efficiency for future phones and computer technology.
The research findings have been published in the journal Nature Photonics.
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