sealing the phosphorus atoms with protective layers of silicon and then making electrical contact with the embedded atoms - appear to have been essential to reliably fabricate many copies of atomically precise devices, say the researchers. Their method of applying the layers, they believe, provides more stable and precise atomic-scale devices.
The researchers also developed a novel technique for the crucial step of making electrical contact with the buried atoms so that they can operate as part of a circuit. The researchers gently heated a layer of palladium metal applied to specific regions on the silicon surface that resided directly above selected components of the silicon-embedded device.
The heated palladium reacted with the silicon to form an electrically conducting alloy called palladium silicide, which naturally penetrated through the silicon and made contact with the phosphorus atoms. Their contact method, say the researchers, has a nearly 100% success rate - a key achievement.
Fabricating single-atom transistors, say the researchers, "is a difficult and complicated process that maybe everyone has to cut their teeth on, but we’ve laid out the steps so that other teams don't have to proceed by trial and error."
For more, see " Atom-by-Atom Fabrication of Single and Few Dopant Quantum Devices ."
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