The demonstration of controlled surface modification achievable with a scanning tunnelling microscope on graphite, metallic films, organic molecules and polymeric biomolecules

The structural alteration of surfaces which can be initiated by the probe of a scanning tunnelling microscope during the imaging process represents an important effect to account for when recording or interpreting scan data. With this in mind, the authors have attempted to demonstrate, and quantify for various surfaces, two specific types of controlled damage that can be caused with a scanning tunnelling microscope. Firstly, areas of surface damage caused by scanning with a low tunnelling gap resistance, and hence with the tip 'close' to the sample, are demonstrated for gold films, platinum-carbon films, an organic molecule, and a polymeric biomolecule, both naked and coated in gold. The use of the smaller and less mobile grains of a platinum-carbon film to coat biomolecules also was shown to effectively eliminate this effect in the case of xanthan gum. Secondly, damage which occurs at a high tunnelling gap voltages has been used to produce sharply defined depressed features in both gold and platinum-carbon films and highly oriented pyrolytic graphite. In addition raised features on the platinum-carbon films have been produced using this technique.