A switch based on self-assembled thymine

The DNA base thymine is deposited at 100?K on Cu(111) and investigated and manipulated by low-temperature scanning tunneling microscopy at 5?K. At submonolayer coverage paired rows are observed. At monolayer coverage a hexagonal commensurate self-assembled layer with the methyl group pointing away from the surface forms. A reversible local manipulation of molecules within the self-assembled layer is demonstrated. This manipulation is interpreted as an out-of-plane relaxation of molecules within the layer induced by the change of the adsorption geometry of individual molecules between two meta-stable orientations. A positive field of 2-4?V leads to this local change in the molecular arrangement, while a field larger than 4?V restores the original geometry.