Summary: Bending Nature's rules to pattern
nanostructures on sticky surfaces
Researchers form patterned nanowires by adapting a versatile
technique used to self-assemble clusters on surfaces.
An important objective in surface science and modern technology is the development of
simple recipes for fabricating nanostructures such as quantum dots, wires, and thin films.
What makes the project challenging is that Nature places strict constraints on how atoms
and surfaces interact. In general, you want the things you build on surfaces to stick. But
you also want to move those same things into place. The first requires strong binding; the
second, weak binding.
In 1998, John Weaver (University of Illinois, Urbana-Champaign) and collaborators
resolved those conflicting requirements by developing a process that effectively replaces
one surface with another. The process, buffer-layer assisted growth (BLAG), allows one
to form assemblies of atoms on a weakly interacting buffer layer that can be evaporated
Using a buffer layer like solid xenon as a temporary proxy for the surface
effectively changes the thermodynamics of the adatom substrate system. Because atoms
are weakly bound to the Xe layer through van der Waals forces, they spontaneously
diffuse, bind to each other, and form three-dimensional clusters. Once formed at low
temperature (20 K), the self-assembled aggregates can softly land on what may be a