Origin of the isotope effect on solid friction

Friction of hydrogen-passivated surfaces can be reduced by replacing terminating hydrogen atoms with heavier deuteriums. Using molecular-dynamics simulations, we show that this experimentally observed isotope effect can be explained quantitatively by small differences in surface coverage, which are due to isotope-dependent bond stabilities. We also demonstrate that a change in vibrational frequencies alone does not account for an isotope-dependent solid friction in our model system.