Scanning tunneling microscopy (STM) has been used to image gold and palladium clusters deposited under ultrahigh vacuum (UHV) conditions on clean cleaved surfaces of natural graphite single crystals. Extensive transmission electron microscopy (TEM) studies were performed to determine the growth conditions. Moreover each sample was checked by ex situ TEM after each in situ STM study. The overall shape of the largest isolated clusters imaged by STM (100–200 Å) is consistent with TEM observations: triangular or hexagonal outlines and clusters sitting along surface steps are elongated by coalescence. STM also reveals that they have a height versus diameter ratio about 0.1. Smallest clusters (10–20 Å) are imaged with atomic resolution simultaneously with the graphite lattice. They are close packed and 2–3 atomic layers high. On occasion, two-dimensional Pd islands are observed. They have an hexagonal non-close-packed arrangement.
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Humbert et al. (1990) studied this question.