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May 11 (UPI) -- Scientists have developed a new method for constructing single-atom transistors, an essential component of the next generation of super-fast, ultra-powerful computers. Using the new step-by-step guide, the research team -- led by scientists at the National Institute of Standards and Technology and the University of Maryland -- became just the second group to construct a single-atom transistor, according to research published Monday.
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The novel construction technique allowed the team of scientists to build single-atom transistors with atom-scale control over the geometry of the supercomputer component, a first. This kind of unprecedented precision helped scientists successfully alter the rate at which individual electrons flowed across the transistor's physical gap or electrical barrier, a feat that classical physics suggests should be impossible.
The phenomenon, known as quantum tunneling, and its manipulation can allow for the entanglement of a transistor. Quantum entanglement describes an inextricable link between two particles, whereby the measure or manipulation of one particle is observed in the other, regardless of time or location.
Entangled transistors can be used to create quantum quantum bits, or qubits, the information that powers quantum computers.
To build the new transistor, researchers covered a silicon chip with a layer of hydrogen atoms. Scientists then used a scanning tunneling microscope to precisely remove individual hydrogen atoms. Next, researchers replaced the missing hydrogen atoms with phosphine gas molecules.
When scientists heated the silicon chip, the phosphine molecules ejected their hydrogen atoms and the remaining phosphorus atom embedded itself on the surface of the chip. With a few additional processing steps, scientists were able to use the sites featuring a single phosphorus atom as transistors.
After the phosphorus atoms were embedded on the surface the chip, scientists sealed the layer of silicon, while ensuring electrical contact with the individual phosphorus atoms. In the past, scientists have used heat to remove defects as they apply protective silicon layers, but the process threatened to dislodge the phosphorus atoms. Instead, scientists applied the first few layers of silicon at room temperature, applying heat only later, after the phosphorus atoms were well-insulated.
"We believe our method of applying the layers provides more stable and precise atomic-scale devices," NIST researcher Richard Silver said in a news release.
Researchers were able to forge electrical contact with the phosphorus atoms by precisely applying palladium metal to the silicon layers above the target atoms. The two materials reacted to form a conducting alloy called palladium silicide. As it forms, the allow naturally penetrates through the silicon layers and makes contact with the phosphorus atom on the chip surface.
"You can have the best single-atom-transistor device in the world, but if you can't make contact with it, it's useless," NIST researcher Jonathan Wyrick said.
Silver, Wyrick and their colleagues described their new single-atom transistor and its ability to control electron flow rates in the journal Communications Physics.
In the lab, the research team produced a series of seemingly identical single-atom transistors. However, each one featured different-sized tunneling gaps. By augmenting the size of the tunneling gap by distances less than a nanometer, scientists were able to precisely control the flow of single electrons through the transistor.
"Because quantum tunneling is so fundamental to any quantum device, including the construction of qubits, the ability to control the flow of one electron at a time is a significant achievement," Wyrick said.
