[Summary]

 A research group led by Associate Professor Hironori Tohmyoh at Graduate School of Engineering, Tohoku University has succeeded in developing a new technology of self-completed Joule heat welding. The new technology helps ultrathin metallic wires less than 1 micron in diameter to weld by using Joule heat. Electrical current applied to the point contact of the wires generates Joule heat and the metal at contact area melts and solidifies. The research group has also expanded the applicable range of the new technology significantly by verifying a newly proposed parameter that provides welding condition on which self-welding occurs under constant current. The research has been conducted with a Grant-in-Aid for Scientific Research from Japan Society for the Promotion of Science (JSPS.) The research results have been published in Physical Review B on the Web on October 2, 2009. The paper’s title is “Self-completed Joule heat welding of ultrathin Pt wires.”

[Details]

 To fully use properties of metals and semiconductor nanomaterials needs thedevelopment of the technology of cutting and welding the produced nanomaterials. The researches on welding process by heating, applying electric current, and irradiating dense electron beams have been conducted globally. However, it is difficult to control the process of welding, and the new method has been empirically developed.

 The research group led by Associate Professor Tohmyoh has been conducted a study on the above technology, and succeeded in welding micromaterials in air environment. An experiment with a close observation of the process of welding has been successful in a scanning electron microscope (SEM.) A point contact of ultrathin wires is a collective entity of nano-projections. The high thermal field is locally generated when electrical current is applied to the point contact. The metal at the point contact melts when its temperature exceeds the melting point and the nano-projections are disappeared. The melted material at the contact of wires is solidified under electrical current after the temperature drops. The mechanism of self-completed welding has been explained by the in-situ observation of the process of welding and the change of circuit voltage applied to the point of contact. The research group has already presented the parameter that dominates the melting phenomenon at the nanocontact, and showed its effectiveness in SEM under high vacuum. The current range that can be used for high precision weld of ultrathin wires has been verified.

 The new technology will help to produce the next-generation electric circuit and multi-functional micro-devices including superfine micro thermoelectric conversion elements and electromagnetic elements. The technology is also expected to be helpful in developing a manipulation technique for nanoscale objects.

[Contact]

Associate Professor Hironori Tohmyoh

Graduate School of Engineering, Tohoku University

Tel: 022-795-4026

E-mail: tohmyoh@ism.mech.tohoku.ac.jp