Electrical properties of metal nanowires (NWs) attract great attention due to their quantum conductance behavior. NWs can be generated by stretching metal contacts; during the elongation and just before rupture, the conductance shows flat plateaus and abrupt jumps of approximately a conductance quantum. As both the NW atomic arrangement and conductance change simultaneously, it is difficult to discriminate electronic and structural effects. In this work, we have determined the NW structures by dynamic atomic resolution observations in a transmission electron microscope. Independent experiments based on a UHV mechanically controllable break junction (MCBJ) were performed to measure the conductance properties. Real-time HRTEM data showed that metal (Au, Ag, Pt, Cu, etc.) junctions generated by tensile deformation are crystalline and free of defects. The correlation between the observed structural and transport properties of NW points out that the quantum conductance behavior is defined by preferred atomic arrangement at the narrowest constriction. We have also carefully analyzed the formation of one-atom thick wires.

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