A governing parameter for the melting phenomenon at nanocontacts by Joule heating and its application to joining together two thin metallic wires

Abstract

For cutting and joining extremely thin metallic wires, the issue of Joule heating in the wires is considered. The middle of a section of a thin Pt wire with a diameter of about 800 nm was melted locally by a direct current supply, and the wire was cut at a predetermined point by applying a force to shear the molten part of the wire. Furthermore, a constant current was applied to a system in which the free ends of two Pt wires were contacted, and the wires were joined together. A parameter, which governs the melting phenomenon at the point of contact of very thin wires, is proposed. It was verified that the conditions required for joining thin wires were able to be determined by the parameter that depends on the applied current, the length and cross sectional area of the wires, and a function of the geometrical quantities for calibrating the thermal conditions.

Joining of Individual Silver Nanowires via Electrical Current

“…With a sufficiently high constant current, the resistance reduces once a good contact has been formed, and thus the power and the heat are autonomously reduced. Using a constant current is the tactic used in other nanowire Joule heat welding experiments, where thanks to the use of vacuum or a different set of nanowires, no significant intermediate layer hinders the welding process [13][14][15]25]. However, due to the very high initial resistance of the junctions in our work, even the lowest setting of a practical current source generates too much power such that nanowires get damaged before welding is complete.…”

“…This means that a process can be designed whereby as the welding completes, the heat automatically subsides, leading to a selfexecuting welding process. As Tohmyoh showed [14], there is a threshold of power at which the heat applied is enough for welding yet low enough not to cause to damage to the nanowires. Current ramps serve as a method of finding the appropriate current quickly, without having to incrementally adjust a constant current measurement.…”

“…This procedure requires two steps, which is contrary to Joule heating recipes presented previously. Due to a lack of significant intermediate layers, other researchers were able to weld nano-objects together using constant current [13,14] or constant voltage [15]. This method of welding is insufficient with this type of nanowire due to large initial resistances and breakdown behavior.…”

“…Connecting nanowires with electrodes and the formation of nanowire interconnects also require ohmic welding. Methods used to weld nanowires include electron beam bombardment [7], ion beam bombardment [8], plasmonic welding [9], soldering [10], cold fusion [11], pulsed laser [12], and Joule heating [13][14][15]. Of these, Joule heat welding has several advantages.…”

“…Procedures such as e-beam lithography [17], focused ion beam chemical vapor deposition [18], and micro-actuators [14] have previously been used to contact nanowires. However, these techniques require costly equipment, can induce damage in the nanowires, are slow, and can be difficult to execute.…”