Ultimate TEM Observation of Tungsten Clusters on MgO(001) Surfaces

Abstract

The surface diffusion process of tungsten (W) atoms and clusters on MgO(001) surfaces was successfully studied by time-resolved high resolution electron microscopy (TRHREM) in the time resolution of 1/60 s. The observation was realized by optimizing the thickness of MgO films and by using a special imaging technique, such as the off-Bragg HREM method. During the observation, W clusters composed of four and five atoms adsorbed on MgO(001) surfaces were detected in images reproduced from the videotape images. The multislice image simulation for the interpretation of the image contrast showed a possibility of discrimination of the atomic configuration of clusters such as "bcc," "on-top" or "fcc" type clusters, from the image contrast at the center of the clusters. The reason for the discrimination was clarified through the multislice image simulation, suggesting that the lattice mismatch between the clusters and the MgO lattice was a key factor in determining the image contrast.