Structural and electronic properties of atomic-size wires at low temperatures

We have studied structural and electrical behavior of gold nanowires generated by mechanical elongation at liquid nitrogen temperature. Real-time observations using a low temperature sample holder in a high resolution transmission electron microscopy and, an ultra-high-vacuum compatible mechanically controllable break junction modified to cool the sample region have been used. It has been observed that the narrowest region of gold constrictions is crystalline and defect-free at room temperature, but this pattern is quite different at 150 K. Extended defects (e.g. twins) generate defective nanometer constrictions, indicating a very different structural evolution pattern during stretching. The generation of different atomic arrangements can be also deduced from transport measurements at low temperature. Finally, one-atom-size nanowires seem to be more stable at 150 K, as revealed by very long conductance plateaus at one quantum of conductance (lasting ∼5-10 times longer than at room temperature).