Abstract
Atom-sized contacts of metals are usually characterized by their direct current (DC) conductance. However, when atom-sized contacts are used as device interconnects and transmit high frequency signals or fast pulses, the most critical parameter is not their DC conductance but their admittance , in particular its imaginary part . In this article, I will present a brief survey of theoretical and experimental results on the magnitude of for atom-sized contacts of metals. Theoretical contact models are first described and followed by numerical evaluation of based on these models. As for experiments on , previous experiments conducted under time-varying biases are surveyed, and then the results of direct signal transmission through atom-sized contacts are discussed. Both theoretical and experimental results indicate that is negligibly small for typical atom-sized contacts for signal frequencies up to 1 GHz.
Highlights
A never-ending challenge on downsizing electronic devices is nearly coming to accomplish its ultimate goal, realizing a device consisting of only one or a couple of atoms [1]
The conductance of a ballistic contact is given by the Landauer-Büttiker formula [2] which dictates G = G0 ∑i τi, where G0 ≡ 2e2/h is the quantum unit of conductance and τi stands for the electron transmission probability of the i-th conductance channel
Number of conductance channels that contribute to the conductance and their transmission differs for different elements and contact sizes
Summary
A never-ending challenge on downsizing electronic devices is nearly coming to accomplish its ultimate goal, realizing a device consisting of only one or a couple of atoms [1] In such ultrasmall devices, connections to them must be the size of atoms, and signal transmission through these atom-sized interconnects will become a vital issue for designing and operating atomic-scale devices. Discussions will be made on atom-sized contacts of metals but not on molecular junctions This is because molecules are poor conductors and unsuitable for signal transmission. Molecular junctions should be most valuable as functional elements but not as interconnects It is, noted that carbon nanotubes and graphene nanoribbons exhibit high carrier mobility and have already been enjoying various applications as high-frequency devices and components [13].
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