Probing surface lattice dynamics with hyperthermal ion scattering

In recent experiments, we have succeeded in measuring thermal momentum fluctuations of surface atoms using hyperthermal (E<500 eV) energy ions. These fluctuations lead to a broadening of the energy loss peaks observed in ion surface scattering experiments. Specifically, we have measured the temperature-dependent energy broadening (ΔE)2 of the quasisingle scattering peak for Na+ ions scattering from a Cu(001) surface, and found it to agree with a parameter-free theoretical prediction to within 10%. We point out that at lower temperatures than those of the present experiment, and with no detailed knowledge of the ion surface potential, this peak should yield quantitative information about the surface lattice dynamics.