Atomic configuration and mechanical and electrical properties of stable gold wires of single-atom width

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The formation dynamics of stable gold (Au) wires of single-atom width during tensile deformation of the nanometer-sized Au contacts was observed in situ at room temperature by transmission electron microscopy. Simultaneously, force and conductance were measured using functions of scanning probe microscopy. The wires were extended to $2.7\ifmmode\pm\else\textpm\fi{}0.1\phantom{\rule{0.3em}{0ex}}\mathrm{nm}$ and the number of atoms was increased to 10; the average interatomic distance was $0.30\ifmmode\pm\else\textpm\fi{}0.02\phantom{\rule{0.3em}{0ex}}\mathrm{nm}$. The duration of the observation of the wires exceeded $10\phantom{\rule{0.3em}{0ex}}\mathrm{s}$. The results of the simultaneous observation of the atomic configuration, force, and conductance led to the conclusion that the stable Au wires observed in this study are complexed with light-element atoms. The constants of the mechanical properties of the individual wires, i.e., elastic limit, Young's modulus, and strength, were analyzed on the basis of stress-strain curves experimentally measured on an atomic scale. During elastic elongation, a force of $1.6\ifmmode\pm\else\textpm\fi{}0.7\phantom{\rule{0.3em}{0ex}}\mathrm{nN}$ acted on the Au wires with an elastic limit of 0.15--0.20. Young's modulus of single-atom-width Au wires was $47--116\phantom{\rule{0.3em}{0ex}}\mathrm{GPa}$ and strength was $8--17\phantom{\rule{0.3em}{0ex}}\mathrm{GPa}$, estimated using a cross-sectional area of $0.118\phantom{\rule{0.3em}{0ex}}{\mathrm{nm}}^{2}$, which is that of a single atom in bulk along ⟨110⟩. Using these mechanical constants, the average interatomic distance in stress-free wires was estimated to be $0.26\ifmmode\pm\else\textpm\fi{}0.02\phantom{\rule{0.3em}{0ex}}\mathrm{nm}$. The histogram of conductances for the single-atom-width Au wires showed a peak at approximately $1{G}_{0}$ (where ${G}_{0}=2{e}^{2}∕h$, $e$ being the charge of an electron and $h$ Planck's constant) until the total number of atoms exceeds 5. For longer wires constructed of more than six atoms, the conductance decreased to less than $0.1{G}_{0}$.