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.