Mapping Surface Potentials using Helium-3 Spin-Echo
The Helium-3 Spin-Echo technique represents a unique and powerful approach to surface dynamics measurements. The technique opens up a wide range of exciting new experimental opportunities, measuring new and otherwise totally inaccessible physics (either experimentally or theoretically) on the sub-nanometre length and nanosecond timescales.
Although the spin-echo spectrometer is primarily aimed at dynamical measurements, it is also uniquely suited to the measurement of helium-surface potentials, through the selective adsorption resonance phenomena. Selective adsorption resonances are where instead of diffracting into a real, observable beam, a helium atom can become transiently trapped in one of the energy levels of the helium-surface potential.Single coil spin-echo measurements, made as a function of azimuthal orientation of the sample, reveal the 2D band structure for helium atoms moving in the potential energy well at a lithium fluoride surface. The sharp variations in reflectivity are due to the bound state resonance phenomena.