ELECTRON HOLOGRAPHY REVEALS THE INTERNAL STRUCTURE OF PALLADIUM NANO-PARTICLES

Phase images of palladium particles 5-15 nm in diameter were reconstru cted from electron holograms acquired using the coherent beam of a fie ld emission transmission electron microscope. The Pd particles were su pported on amorphous silica microspheres, 0.2 mu m in diameter. A cent ral contrast feature, suggestive of an internal void, was visible on m ost of the Pd particles. The phase profiles obtained from the hologram s matched computed phase profiles confirming the existence of an inter nal void in these nano-particles. This is the first observation where internal morphology at the nano-scale has been unambiguously determine d. While the observed voids are similar in scale to those occurring in recently reported hollow nanometre-sized particles, such as graphite polyhedra [9, 10], this represents the first report of such voids in m etallic particles that are single crystals.