It is well known that nanotechnology is too small to see with the naked eye and yet chemists have found a way to make it even less perceptible by creating a nanoscopic form of invisible ink.

The technique was published in „Angewandte Chemie International” and offers a way of growing nanocrystals of a much higher purity than achieved to date.

Hubertus Marbach at the University of Erlangen-Nuremberg in Germany and his colleagues removed oxygen ions from a silicon oxide wafer by using an electron beam, leaving nanoscopic dents in the surface. Virtually there is no visible trace, but a hidden message written onto the wafer with the electron beam is revealed later by flowing iron pentacarbonyl gas across the surface. The iron pentacarbonyl gas reacts at the indentations and forms carbon monoxide while leaving solid and reflective iron nanocrystals fixed to the surface.

According to Hubertus Marbach the electron beams are used commercially to deposit nanocrystals like in semiconductor industry which uses the technology to repair defects in the lithographic masks used to create integrated circuits. But this involves targeting electron beams directly at molecules like iron pentacarbonyl, forcing them to decompose into iron nanocrystals. The harsh process leads to carbon and oxygen impurity levels as high as 60 % within the crystals. With the new technique the crystals are over 95 % iron.

„Instead of using a sledgehammer approach to destroy the iron pentacarbonyl molecules, ours is gentler”, because the decomposition of the molecules is purely chemical, said Hubertus Marbach.

„It’s a nice technique. The problem with existing electron-beam deposition is that the quality is not great”, which affects the properties of the nanocrystals, said Russell Cowburn at Imperial College London.