The Structure and Orientation of Supported Nanometer-size Clusters Using Field-Ion Microscopy, D. Lovall, R.P. Andres*, and R. Reifenberger, Department of Physics, Purdue University, West Lafayette, IN 47907, *School of Chemical Engineering, Purdue University, West Lafayette, IN 47907
Recent work using field-ion microscopy (FIM) to investigate the atomic structure and preferred orientation of supported nanometer size Au clusters on a W substrate will be presented. Field-ion microscopy not only possesses the large magnification and high resolution necessary to image atoms on the surface of nanometersize metal clusters, but also allows the atomic structure of the cluster to be determined in a non-intrusive way.
The techniques developed to produce and anneal Au clusters in the gas phase and deposit these clusters on the apex of a sharp tungsten tip will be described as well as the conditions under which field-ion images are obtained. Methods to simulate the FIM micrographs of individual clusters will also be reviewed.
Preliminary results demonstrate a promising future for this approach. Simulations of FIM micrographs from unannealed Au clusters have been completed and clearly show 2-fold, 3-fold and 5-fold symmetry, depending on the cluster orientation. Comparisons of simulated FIM images from a 309 atom icosahedral Au cluster to experimental FIM images from a ~2 nm diameter unannealed Au cluster show striking similarities and permit a determination of the orientation and structure of individual supported clusters.
This work was partially supported by the Army Research Office URI Program under contract #DAAL03-G-0144.