Self-limiting Optical Welding of Nanowires
When trying to weld together pieces of metal, most people look to a torch or electric-arc welder, and some look to a friction welder (NASA used this for welding together sections of a capsule because it does not add weight but still creates a high quality weld). None of these methods work when dealing with nanowires though. Heating them risks destroying the sample, and pressure can also ruin the delicate structures. Fortunately, at such a small scale there are certain phenomena that can be used.
Researchers have been looking to plasmons for a variety of reasons. These quasi-particles, which are a photon and electron coupled together, have some interesting properties and can be directed along the metals they are formed. Researchers at the Stanford School of Engineering have realized that shining light onto nanowires will cause hotspots where two wires cross because of plasmonic effects.
The top wire collects plasmons, like an antenna, and focuses them at the junction between the two wires. This creates a hotspot as the energy transfers from one wire to the other, and the heat is enough to fuse them together. Once the weld is made though, the effect stops, because it is the transfer from one wire to the other that generates the heat.
To test the potential and quality of this welding technique, the researchers sprayed silver nanowires onto a piece of Saran wrap, which has a considerably lower melting point than the metal. An advantage to testing with Saran wrap is the nanowire mesh should be transparent, like the plastic. The plastic was completely unharmed by the welding process, unlike if this were done on a hot plate. The researchers then balled up the plastic and nanowire mesh, to check if the welds would withstand such treatment, and they did. This means nanowire meshes, which could be used in solar panels, LEDs, touch and non-touch screen displays, could be sprayed onto most any surface, and welded on the spot. In the future this could allow a ‘solar panel’ to be sprayed onto you window.