Melting and supercooling of gold nanoparticles in an electric field trap in high vacuum prior to deposition on a substrate*

A nanoparticle levitated in an electric field trap in high vacuum has minimal thermal contact with its surroundings. It can be heated efficiently with a laser beam, allowing thermodynamic measurements as well as precise control of its temperature. While the method is generalizable to many nanoscale materials, we use 200 nm gold nanoparticles to establish the technique. We discuss improvements to our method of injecting charged particles into the trap via electrospraying of a liquid nanoparticle suspension. We present measurements of the temperature of a trapped gold nanoparticle across the melting transition and show that it can be supercooled below its melting temperature. We repeat these measurements with 532 nm (green) and 660 nm (red) laser light. To facilitate further examination of trapped particles, we have developed a method of expelling the particle from the trap and depositing it on a removable substrate with high positional accuracy using an electrostatic lens. We discuss plans to improve adhesion by raising the temperature of particles to soften or melt them at the time of deposition.