Thermal Faceting of Clean and Oxygen-Covered Ir Nanocrystals

Thermal faceting of a clean and oxygen-covered iridium nanosized crystal was studied by field ion microscopy for oxygen exposures up to 6 langmuirs (1 langmuir = 1.3 x 10(-4) Pa.s) and annealing temperatures of 300-1100 K. The dean Ir specimen (the "tip"), originally hemispherically shaped, started to facet upon annealing to at least 850 K, exposing only {111} and {001} facets in the final cuboctahedral form. Even small amounts of adsorbed oxygen caused changes in the Ir tip morphology. An oxygen exposure of 0.3 langmuir caused {113} facets to develop at 700 K For larger (1 to 6 langmuirs) exposures, well characterized {111}, {001}, {113}, and {011} facets were observed to develop when annealing to at least 650 K The recorded micrographs suggest (1 x 3) or, to a lesser extent, (1 x 4) missing row reconstructions of the {011} facets, while other facets do not exhibit any clear evidence of reconstruction.