IN-SITU ULTRA-HIGH-VACUUM TRANSMISSION ELECTRON-MICROSCOPY STUDIES OFNANOCRYSTALLINE COPPER

We have built a particle production and transport system that allows t he characterization of nanocrystals without exposure to contaminating atmospheres such as air. Nanocrystals (formed by inert gas condensatio n 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 sys tem, we can study various nanoparticle phenomena in real time and unde r clean conditions. In this paper we discuss the experimental design a nd preliminary studies using imaging and diffraction techniques. These include, the time-evolution of copper nanoparticle morphology and sin tering behavior as a function of particle size, temperature, oxygen/at mosphere exposure and supporting substrate. In particular, we have obs erved immediate room temperature sintering of dean copper nanocrystals which does not occur with nanoparticles that have been exposed to oxy gen. Furthermore, we have seen an interaction between copper nanocryst als and amorphous carbon which produces graphite shells. This shell fo rmation process suggests a solid state analog to that seen when nanopa rticles catalyze the growth of carbon fibers through a hydrocarbon atm osphere decomposition.