"Identifying the forces responsible for self-organization of nanostructures at crystal surfaces" K. POHL, M. C. BARTELT, J. DE LA FIGUERA, N. C. BARTELT, J. HRBEK & R. Q. HWANG Nature 397, 238 - 241 (1999); doi:10.1038/16667

Description:

Scientists have found that nanometer-scale islands of metals and semiconductors deposited on a crystal surface self-organize into ordered arrays. When this process takes place on a single-atom-thick film of silver sprinkled with sulfur, a lacework pattern emerges with surprising precision.

The silver film is spread out on a ruthenium substrate into a layer one silver atom deep, which offers a preferred low-energy state. The added sulfur also wants to rest directly on top of the ruthenium to minimize energy. As they jostled for position during self-organization, groups of sulfur atoms displaced silver atoms and formed islands of sulfur embedded in the silver sheet. The flat ruthenium underneath started to "cup" slightly under the strain as the silver sheets between sulfur islands were distorted to accommodate the sulfur islands. These distortions caused the sulfur islands to repel each other and organize into an ordered pattern.

Patterning at such small scales is extremely difficult, so this propensity for self-organization could present an ultimate approach to making ordered arrangements.
 

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