ABSTRACT
Scanning helium microscopy is an emerging imaging technology that will be sensitive to features on the atomic scale, yet will use beam energies of no more than 50 meV. Helium atom scattering (HAS) has proved a uniquely sensitive, non-perturbing probe of surface morphology. The technique is now used routinely in the study of nucleation and growth of thin films, adsorbate diffusion, surface structure, alloying and surface phonons [1, 2, 3]. It is of particular advantage in high-precision structural studies of surfaces and in observation of delicate adsorption systems. Conventional HAS, however, is limited by a lack of spatial resolution, restricting its application to homogeneous and typically single-crystal systems. Recent advances in atom optics allow for the focusing of neutral helium atoms, producing a microprobe that can be scanned across a heterogeneous sample to create an image. Now, a scanning helium microscope (SHeM) is under construction [4]. The technique offers the prospect of a low energy, inert and charge-neutral probe that does not cause sample charging, heating or excitation and exhibits several contrast mechanisms. In this paper, we aim to give an overview of scanned helium microscopy and demonstrate potential contrast mechanisms by reference to existing HAS studies. We then conclude with a brief description of recent techological advances in the field and discuss their incorporation into a prototype SHeM.
