Two Pt wires with diameters of about 800 nm were successfully welded by Joule heating in a scanning electron microscope. Melting and solidification at the point contact of the thin wires occurred continuously under a constant current supply and the welding process was completed within several seconds. This rapid and self-completed welding is due to the geometrical features of the nanocontact and the heat transport properties of the thin wires. The current required for joining wires in a scanning electron microscope was much lower than that in air. This is remarkable for longer wires and was found to be due to greater insulation under high-vacuum conditions. The difference in the thermal boundary conditions, in other words the difference in the melting conditions at the nanocontact, was evaluated experimentally and a parameter, comprising the applied current, the geometrical quantities of the wires, and a function for calibrating the thermal boundary conditions, with which the conditions for welding thin wires under different vacuum levels could be determined, is presented.

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This paper demonstrates welding the tip of an ultrathin Pt wire to the side of a similar wire by Joule heating. The tip of the wire, with a diameter of 600–800 nm, is brought into contact with the side of another wire, and they are welded together into a complex form by supplying a constant direct current through the parts in contact. The conditions for tip to side welding of Pt wires are compared to those of tip to tip welding using a parameter that was proposed previously for the tip to tip welding of two wires. The parameter depends on the current, the length and cross-sectional area of the wires and comprises a function with respect to the thermal boundary conditions. Although the successful welding conditions of tip to side welding are located in the range of those for tip to tip welding, the lower limit of the conditions for tip to side welding was slightly higher than that in tip to tip welding. Finally, a three-dimensional micrometer-scale structure was created by repeating the tip to side welding process.

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