MgO(100) surfaces have been imaged at atomic-scale resolution by scanning force and friction microscopy (SFFM). The single crystals of MgO were cleaved and studied in dry air using a small loading force (4 * lo-'' N). Topographic and friction images reveal a square lattice of protrusions with a measured spacing of 0.274 nm. This value is close to the 2D surface lattice parameter of the MgO(100) surface (0.299nm). The largest corrugation observed in the topographic images is 0.04 nm. Large-scale images reveal nearly parallel cleavage steps, separated by an average distance of 150 nm and 0.4 nm high.

Comparison between UHV and air observations on Pd clusters deposited under UHV on a clean graphite surface is made. For the largest clusters (>10 nm), no dramatic influence of air exposure is observed. Quite surprisingly, we have been able to image in air the surface atomic arrangement of 1.5 nm Pd clusters. They have a tetrahedron shape with (111) facets and are epitaxially oriented: Pd (111)//graphite (00.1), Pd[112̄]//graphite [01.0].

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