arXiv subjects

Andrew Jardine

Publications and source records attributed to Andrew Jardine.

4 recordsLinked to original sources

arXiv2025

Heliometric stereo: a new frontier in surface profilometry

Accurate and reliable measurements of three-dimensional surface structures are important for a broad range of technological and research applications, including materials science, nanotechnology, and biomedical research. Scanning helium microscopy (SHeM) uses low-energy (64 meV) neutral helium atoms as the imaging probe particles, providing a highly sensitive and delicate approach to measuring surface topography. To date, topographic SHeM measurements have been largely qualitative, but with the advent of the heliometric stereo method - a technique that combines multiple images to create a 3D representation of a surface - quantitative maps of surface topography may now be acquired with SHeM. Here, we present and discuss two different implementations of heliometric stereo on two separate instruments, a single detector SHeM and a multiple-detector SHeM. Both implementations show good accuracy (5% and 10% respectively) for recovering the shape of a surface. Additionally, we discuss where heliometric stereo is most applicable, identify contrast features that can limit its accuracy, and discuss how to mitigate these limitations with careful design and sample choices that be readily implemented on current instruments.

physics.ins-det↗

arXiv2024

Helium atom micro-diffraction as a characterisation tool for 2D materials

We present helium atom micro-diffraction as an ideal technique for characterization of 2D materials due to its ultimate surface sensitivity combined with sub-micron spatial resolution. Thermal energy neutral helium scatters from the valence electron density, 2-3A above the ionic cores of a surface, making the technique ideal for studying 2D materials, where other approaches can struggle due to small interaction cross-sections with few-layer samples. Sub-micron spatial resolution is key development in neutral atom scattering to allow measurements from device-scale samples. We present measurements of monolayer-substrate interactions, thermal expansion coefficients, the electron-phonon coupling constant and vacancy-type defect density on monolayer-MoS2. We also discuss extensions to the presented methods which can be immediately implemented on existing instruments to perform spatial mapping of these material properties.

physics.app-ph↗

arXiv2024

Measuring vacancy-type defect density in monolayer semiconductors

Two-dimensional (2D) materials have attracted wide-spread interest due to their unique and tunable properties. Their optoelectronic, mechanical, and thermal properties are greatly influenced by crystal defects, which are, in turn, used to control these properties. However, experimental quantification of the density of defects, whether deliberately introduced or inherent, is very difficult in these atomically thin materials. Here we show that helium atom micro-diffraction can be used to measure the defect density in 15x20um monolayer MoS2, a prototypical 2D semiconductor, quickly and easily compared to standard methods. We present a simple analytic model, the lattice gas equation, that fully captures the relationship between atomic Bragg diffraction intensity and defect density. The model, combined with ab initio scattering calculations, shows that our technique can immediately be applied to a wide range of 2D materials, independent of sample chemistry or structure. Additionally, wafer-scale characterization is immediately possible.

physics.app-ph↗

arXiv2024

Minimising Interference in Low-Pressure Supersonic Beam Sources

Free-jet atomic, cluster and molecular sources are typically used to produce beams of low-energy, neutral particles and find application in a wide array of technologies, from neutral atom microscopes to instruments for surface processing. We present a simple analytical theory that is applicable to many of these sources, when (i) the nozzle-skimmer distance is such that free molecular flow is achieved and (ii) there is negligible interference within the skimmer itself. The utility of the model is demonstrated by comparing experimental data with calculations performed using the theory. In particular, we show that skimmer interference is negligible compared to attenuation by 'background' gas for room-temperature beams. Our treatment does not depend on any free parameters and obviates the complexity of previous theories. As a result, we are able to devise a number of design recommendations to minimize interference in sources operating with cryogenic-temperature beams.

physics.atom-ph↗