  We investigate melting and undercooling in nanoscale (radius ~100 nm) gold
particles that are levitated in a quadrupole ion (Paul) trap in a high vacuum
environment. The particle is heated via laser illumination and probed using two
main methods. Firstly, measurements of its mass are used to determine the
evaporation rate during illumination and infer the temperature of the particle.
Secondly, direct optical measurements show that the light scattered from the
particle is significantly different in its liquid and solid phases. The
particle is repeatedly heated across its melting transition, and the dependence
of heating behavior on particle size is investigated. Undercooling -- the
persistence of a liquid state below the melting temperature -- is induced via
multi-stage laser pulses. The extent of undercooling is explored and compared
to theoretical predictions.
