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<br/>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.<br/>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.