A scanning tunneling microscopy study of electrostatic and proximity effects in tip-assisted migration and desorption of a DNA base molecule on SrTiO3

Manipulation of DNA base molecules has been achieved using the tip of a scanning tunneling microscope (STM). The authors have identified three distinct manipulation modes, namely, lateral sliding by proximity effect and migration and extraction by electrostatic forces for adenine (one of the DNA base molecules) on the SrTiO3(100)-root 5 x root 5 surface. The mechanisms of these modes have been revealed by measuring the absolute separation between the tip and the surface (or the adsorbate) from the current versus tip displacement relationship, and the surface dipole moment using tunneling barrier height measurement. Controlling the tip-surface separation has revealed that the proximity effect can be attributed to the chemical forces acting with a critical tip-surface internuclear separation of 4.4 Angstrom. Conversely, the extraction and sliding induced by electrostatic interaction show striking bias polarity dependence. This behavior is determined by the electrostatic stability of the surface dipole under the tip field.