Cu2O island shape transition during Cu-Au alloy oxidation.

In situ transmission electron microscopy observations of the oxidation of (001) Cu-Au alloys indicate that the Cu2O islands that form undergo a remarkable transformation from an initially compact morphology to a dendritic structure as growth proceeds. Correspondingly, the surface composition becomes nonuniform and the fractal dimension associated with the islands evolves from 2.0 to a stable value of 1.87, indicating a transition in the rate-limiting mechanism of oxidation from oxygen surface diffusion to diffusion of copper through the increasingly gold-rich regions adjacent to the islands.

Structure of nanometre-sized Xe particles embedded in Al crystals.

The structure and lattice parameters of Xe particles about 1 nm to about 6 nm in size embedded in Al were investigated with off-Bragg condition high-resolution transmission electron microscopy. An Xe particle about 1 nm in size had different structural properties from those 2-6 nm in sizes. Some 1-nm Xe particles had an face-centred cubic (f.c.c.) structure with the same orientation as the Al matrix, whereas others of the same size had a non-f.c.c. structure. The lattice parameters of a 1-nm f.c.c. Xe particle were about 20% smaller than the average value obtained from electron diffraction, i.e. the particle was compressed by about 80%. The lattice parameters of Xe crystals about 2 nm to about 6 nm in size were almost the same as those obtained from diffraction results. One of the reasons for the extra compression seen with a 1-nm Xe particle is the increase in pressure inside an Xe particle with decreasing particle size.

Origin of atomic clusters during ion sputtering.

Previous studies have shown that the size distributions of small clusters ( n < or = 40; n = number of atoms/cluster) generated by sputtering obey an inverse power law with an exponent between -8 and -4. Here we report electron microscopy studies of the size distributions of larger clusters ( n > or = 500) sputtered by high-energy ion impacts. These new measurements also yield an inverse power law, but one with an exponent of -2 and one independent of sputtering yield, indicating that the large clusters are produced when shock waves, generated by subsurface displacement cascades, ablate the surface.