An ultrastable platform for the study of single-atom chains

We describe a surface probe instrument capable of sustaining single atomic bond junctions in the electronic quantum conduction regime for tens of minutes, and present results for Au junctions that can be locked stably in n=1 and n=2 quantum conduction states with electrical conductivity nG(0) (G(0) = 2e(2)/h) and switched in a controlled way. The instrument measures and controls the gap formed between a probe and a flat surface with better than 5 pm long-term stability in a high-vacuum chamber at 4 K using a high-sensitivity fiber-optic interferometer that forms a Fabry-Perot cavity immediately adjacent and parallel to the probe. We also report the experimental observation of stable noninteger conduction states, along with preliminary density functional theory-based calculations of one-dimensional (1D) and two-dimensional Au bridges that produce comparable noninteger conduction states. Finally, we report the observation of novel stochastic processes related to nonballistic electron transport through strained single atomic bond junctions. The instrument permits detailed study of electron transport in 1D systems, and the long-term picometer stability of the junction holds great promise for application to single-molecule spectroscopy. (C) 2010 American Institute of Physics. [doi:10.1063/1.3369584]