Electrostatic field effect on molecular structures at metal surfaces

We report on the structural transitions of molecules on metal surfaces by external electrostatic field. An electrode-molecule-electrode model is considered to quantify the effect of electrostatic forces at the molecule-electrode interface. Within a quasi-parallel-plate capacitor approach, this model reveals how external electrostatic fields change the delicate balance between molecule-substrate and molecule-molecule interactions, leading to substantial changes in the molecular conformation. The predictions are validated by scanning tunneling microscopy (STM) observations of four different molecules and electrode facets. In addition, first-principles simulations verify the results of our model calculations.