Image formation in the scanning helium microscope

Sleath

et al. 2020

Sci Rep

Scanning helium microscopy is an emerging form of microscopy using thermal energy neutral helium atoms as the probe particle. The very low energy combined with lack of charge gives the technique great potential for studying delicate systems, and the possibility of several new forms of contrast. To date, neutral helium images have been dominated by topographic contrast, relating to the height and angle of the surface. Here we present data showing contrast resulting from specular reflection and diffraction of helium atoms from an atomic lattice of lithium fluoride. The signature for diffraction is evident by varying the scattering angle and observing sharp features in the scattered distribution. The data indicates the viability of the approach for imaging with diffraction contrast and suggests application to a wide variety of other locally crystalline materials.

Section: Contrast Formation In the Cambridge Shemsupporting

confidence: 56%

Section: Sample Preparation and Image Acquisition A Sample Of Lif Wamentioning

confidence: 53%

Section: Bergin * S M Lambrick H Sleath D J Ward J Ellimentioning

confidence: 99%

See 1 more Smart Citation

Observation of diffraction contrast in scanning helium microscopy

Sleath

et al. 2020

Sci Rep

“…First, height contrast arises primarily from a change in the proportion of the scattered signal that is detected using a fixed position detector; 14,15 however, such contrast is weak and only appears over large changes in the height. [14][15][16] Second, angular orientation contrast 14,16 occurs when the local orientation of the sample changes the portion of the scattering distribution that enters the detector aperture. For the largely diffuse scattering that occurs from unprepared surfaces, higher intensity is expected when the local surface is orientated toward the detector.…”

mentioning

confidence: 99%

“…Finally, masking, due to the detector being occluded from the illuminated spot on the sample, gives very strong contrast as primary scattered atoms cannot be detected. Masking is independent of the atom-surface interaction [14][15][16][17] but is related to the underlying surface topography, thus enabling quantitative topographic information to be extracted.…”

mentioning

confidence: 99%

Multiple scattering in scanning helium microscopy

Vozdecky

Applied Physics Letters

et al. 2020

Self Cite

Using atom beams to image the surface of samples in real space is an emerging technique that delivers unique contrast from delicate samples. Here, we explore the contrast that arises from multiple scattering of helium atoms, a specific process that plays an important role in forming topographic contrast in scanning helium microscopy (SHeM) images. A test sample consisting of a series of trenches of varying depths was prepared by ion beam milling. SHeM images of shallow trenches (depth/width < 1) exhibited the established contrast associated with masking of the illuminating atom beam. The size of the masks was used to estimate the trench depths and showed good agreement with the known values. In contrast, deep trenches (depth/width > 1) exhibited an enhanced intensity. The scattered helium signal was modeled analytically and simulated numerically using Monte Carlo ray tracing. Both approaches gave excellent agreement with the experimental data and confirmed that the enhancement was due to localization of scattered helium atoms due to multiple scattering. The results were used to interpret SHeM images of a bio-technologically relevant sample with a deep porous structure, highlighting the relevance of multiple scattering in SHeM image interpretation.

A ray tracing method for predicting contrast in neutral atom beam imaging

Jardine

et al. 2018

Micron

A ray tracing method for predicting contrast in atom beam imaging is presented. Bespoke computational tools have been developed to simulate the classical trajectories of atoms through the key elements of an atom beam microscope, as described using a triangulated surface mesh, using a combination of MATLAB and C code. These tools enable simulated images to be constructed that are directly analogous to the experimental images formed in a real microscope. It is then possible to understand which mechanisms contribute to contrast in images, with only a small number of base assumptions about the physics of the instrument. In particular, a key benefit of ray tracing is that multiple scattering effects can be included, which cannot be incorporated easily in analytic integral models. The approach has been applied to model the sample environment of the Cambridge scanning helium microscope (SHeM), a recently developed neutral atom pinhole microscope. We describe two applications; (i) understanding contrast and shadowing in images; and (ii) investigation of changes in image formation with pinhole-to-sample working distance. More generally the method has a broad range of potential applications with similar instruments, including understanding imaging from different sample topographies, refinement of a particular microscope geometry to enhance specific forms of contrast, and relating scattered intensity distributions to experimental measurements.