Joule heat welding of thin wires to thin films

To effectively use micro or nano materials and create advanced materials systems from them, welding techniques for such small scale materials are vital. For this purpose, the tips of two thin wires were welded together with Joule heat and the conditions required to achieve it was discovered experimentally. In this paper, the Joule heat welding of thin wires to thin films deposited on substrates is described. To derive the conditions required to achieve this, a heat conduction model for a cylindrical element in the film located at the contact between the wire and the film is considered and the critical thickness of the film above which the welding conditions are independent of film thickness is derived analytically. The validity of the heat conduction model was experimentally verified by welding 0.8 nm diameter Pt wires onto thin Pt films on electrically-insulated substrates. The experiments are performed for various combinations of the length of the wire and the thickness of the films. The current required for welding the wires onto the films having the thickness over the critical thickness are investigated and the conditions required for the welding are found to be coincident with those for welding the tips of two wires with Joule heat.