Ab Initio Calculation of Matter Wave Interactions with Strained Surfaces

Helium atom scattering (HAS) is a powerful tool for investigating a wide range of systems with a previously inaccessible surface sensitivity. In the context of scanning helium microscopy (SHeM), the use of a low energy, neutral probe particle results in a variety of new image contrasts like chemical or Debye-Waller contrast. The work presented explores the possibility of using contrast imaging to study mechanical properties like strain. In particular, a first-principles calculation of
scattering from the (001) α quartz surface is done using a combination of density functional theory (DFT) and close-coupled scattering simulations. The approach outlined utilises the structure and potential determined using DFT to simulate the final diffraction pattern. The induced strain in α quartz due to an external electric field is then studied in the framework of perturbative DFT.
The resultant estimates of the lattice and response parameters were found to be in good agreement with experimentally measured values. In a static electric field of 1.1 kV mm⁻¹, the surface lattice parameter varied by about 0.004 Å. The consequent changes in diffraction peak positions and intensities indicate the feasibility of such a contrast mechanism.