In situ ultra-high vacuum transmission electron microscopy studies of nanocrystalline copper

We have built a particle production and transport system that allows the characterization of nanocrystals without exposure to contaminating atmospheres such as air. Nanocrystals (formed by inert gas condensation of a sputtered atom population) are transported in situ via the gas phase to an ultra-high vacuum transmission electron microscope (UHVTEM) equipped with a heating stage and gas exposure system. With this system, we can study various nanoparticle phenomena in real time and under clean conditions. In this paper we discuss the experimental design and preliminary studies using imaging and diffraction techniques. These include, the time-evolution of copper nanoparticle morphology and sintering behavior as a function of particle size, temperature, oxygen/atmosphere exposure and supporting substrate. In particular, we have observed immediate room temperature sintering of clean copper nanocrystals which does not occur with nanoparticles that have been exposed to oxygen. Furthermore, we have seen an interaction between copper nanocrystals and amorphous carbon which produces graphite shells. This shell formation process suggests a solid state analog to that seen when nanoparticles catalyze the growth of carbon fibers through a hydrocarbon atmosphere decomposition.