For a decade high-resolution imaging techniques, such as Scanning Tunneling Microscopy (STM) and Atomic Force Microscopy (AFM), have spurred intense studies of nanoscopic activities on solid surfaces.  It is found that atoms may self-assemble into a periodic structure, such as an array of stripes or dots.  The feature size may be of nanoscale, small compared to bulk structures, but large compared to individual atoms.  The following are some examples of observed patterns.  

    Kern et al. (1991) deposited a submonolayer of oxygen on a copper (110) surface.  On annealing, the oxygen atoms arranged into stripes that alternate with bare copper stripes.  The width of the stripes was on the order of 10 nm.

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    The figure on the left is another example.  Pohl et al. (1999) deposited a monolayer of silver on a ruthenium (0001) surface, and then exposed the silver-covered ruthenium to sulfur.  The epilayer became a composite of sulfur disks in a silver matrix.  The sulfur disks were of diameter about 3.4 nm, and formed a triangular lattice.

    The observations common to both systems are phase separation, size selection, and spatial ordering within monolayers on solid surfaces.  Similar observations have been made in other material systems (e.g., Parker et al., 1997; Brune, et al. 1998).

    Why do atoms self-assemble?  What sets the feature size and the spatial ordering?  We developed a thermodynamic framework to study the remarkable phenomena.

Brune, H., M. Giovannin, K. Bromann, and K. Kern, 1998.  Self-organized growth of nanostructure arrays on strain-relief patterns.  Nature 394, 451-453.

Kern, K., H. Niebus, A. Schatz, P. Zeppenfeld, J. George, G. Comsa, 1991. Long-range spatial self-organization in the adsorbate-induced restructuring of surfaces: Cu{110}-(2x1) O.  Phys. Rev. Lett.  67, 855-858.                                      

Park, M., C. Harrison, P.M. Chaikin, R.A. Register, and D.H. Adamson, 1997.  Block copolymer lithography:  periodic arrays of ~10¹¹ holes in 1 square centimeter.  Science 276, 1401-1404.

Pohl, K., M.C. Bartelt, J. de la Figuera, N.C. Bartelt, J. Hrbek, R.Q. Hwang, 1999.  Identifying the forces responsible for self-organization of nanostructures at crystal surfaces.  Nature 397, 238-241.