Angew. Chem. Int. Ed. 49, 4669–4673 (2010)

Injecting electrons into a material can be used both to make and break chemical bonds. Electrons from the tip of a scanning tunnelling microscope have, for example, been used to manipulate individual bonds, and electron beams in electron microscopes have been employed to create intricate nanostructures. Of particular technological interest is the approach known as electron-beam-induced deposition, in which an electron beam decomposes adsorbed precursor molecules, leaving non-volatile fragments behind on the surface. By using an organometallic precursor and a focused electron beam, the technique can create arbitrary metallic structures with high resolution. Hubertus Marbach and colleagues at the University of Erlangen-Nürnberg have now developed an alternative, two-step version of the approach that uses the electrons as 'invisible ink'.

The researchers first activated a silicon oxide surface with a 3-nm-wide electron beam, a procedure that creates oxygen vacancies in the substrate through an electron-induced oxygen-desorption mechanism. The pattern written by the electron beam was then revealed by exposing the surface to iron pentacarbonyl, Fe(CO)5, precursor molecules. The organometallic molecules catalytically decompose at the irradiated regions on the surface and grow autocatalytically to form pure iron nanocrystals. The growth of the iron nanostructures can continue until the supply of precursor molecules is turned off.