The Scanning Tunnelling Microscope used to inject electrons into a silicon surface at the University of Birmingham. Credit: Michelle Tennison
The findings present a promising step forward towards being able to manipulate and control the behavior of high energy, or ‘hot’, electrons. A Scanning Tunnelling Microscope was used to inject electrons into a silicon surface, decorated with toluene molecules. As the injected charge propagated from the tip, it induced the molecules to react and ‘lift off’ from the surface. By measuring the precise atomic positions from which molecules departed on injection, the team were able to identify that electrons were governed by quantum mechanics close to the tip, and then by more classical behavior further away.
The team found the molecular lift-off was “suppressed” near the point of charge injection, because the classical behavior was inhibited. The number of reactions close to the tip increased rapidly until reaching a radius, up to 15nm away, before seeing relatively slow decay of reactions beyond that point more in keeping with classical behavior. This radius, at which the behavior changes from quantum to classical, could be altered by varying the energy of the electrons injected.
“These findings are, crucially, undertaken at room temperature. They show that the quantum behavior of electrons which is easily accessible at close to absolute zero temperature (-273°C!) persist under the more balmy conditions of room temperature and over a “large” 15 nanometre scale. These findings suggest future atomic-scale quantum devices could work without the need for a tank of liquid helium coolant.”
Dr Peter Sloan added: “Hot electrons are essential for a number of processes – certain technologies are entirely reliant on them. But they’re notoriously difficult to observe due to their short lifespan, about a millionth of a billionth of a second. This visualisation technique gives us a really new level of understanding.”
Now that the team have developed the method of visualising quantum transport, the goal is to understand how to control and manipulate the wave function of the electron. This could be by injecting electrons through a cluster of metal atoms, or by manipulating the surfaces themselves to harness the quantum effects of electrons.
Being able to manipulate hot electrons are far-reaching; from improving the efficiency of solar energy, to improving the targeting of radiotherapy for cancer treatment.
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