Exploring neutral atom microscopy

Witham, Philip; Sánchez, Erik J.

doi:10.1002/crat.201300401

Cited by 20 publications

(23 citation statements)

References 13 publications

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“…However, by scattering from the sample multiple times, atoms can reach the detector indirectly, and thus, multiple scattering makes a further contribution to topographic contrast. We also note that multiple scattering can also provide weak diffuse illumination, a process that has been previously noted 15,17 but not examined in detail.…”

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confidence: 63%

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Multiple scattering in scanning helium microscopy

Lambrick

Vozdecky

Bergin

et al. 2020

Applied Physics Letters

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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.

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confidence: 63%

“…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

Lambrick

Vozdecky

Bergin

et al. 2020

Applied Physics Letters

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“…However the ability to image certain materials, including those sensitive to charge, or to the energy of the probe particles, remain a particular challenge. Recently, scanning helium microscopy (SHeM) has emerged as a new tool for measuring delicate materials, making use of extremely low energy neutral atoms to form images [1][2][3] . New forms of contrast are possible without any concern of beam induced damage to the sample.…”

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

confidence: 99%

“…Atoms scattered in a particular direction from the illuminated spot on the surface are counted and used to form the scattered intensity of each pixel in the image. The approach was originally demonstrated in transmission by Koch et al 1 and was later extended to reflection imaging by Witham and Sanchez 3,4 and collaborating researchers in Cambridge, UK and Newcastle, Australia who used pinhole collimation 5 .…”

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

confidence: 99%

Observation of diffraction contrast in scanning helium microscopy

Bergin

Lambrick

Sleath

et al. 2020

Sci Rep

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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.

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“…Early focussing experiments using neutral helium atoms were carried out by O.Carnal et al, Holst and Allison and Doak et al in the 1990's [5][6][7]. Since then two other research groups have managed to obtain helium microscope images in reflection with micron range resolution using pinhole microscopes [8][9][10][11]. The first reflection images were published in 2011 by Withman and Sanchez using a setup with just a pinhole and no skimmer [8].…”

Section: Introductionmentioning

confidence: 99%

Theoretical model of the helium pinhole microscope

2016

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In recent years, the development of neutral helium microscopes has gained increasing interest. The low energy, charge neutrality, and inertness of the helium atoms makes helium microscopy an attractive candidate for the imaging of a range of samples. The simplest neutral helium microscope is the so-called pinhole microscope. It consists of a supersonic expansion helium beam collimated by two consecutive apertures (skimmer and pinhole), which together determine the beam spot size and hence the resolution at a given working distance to the sample. Due to the high ionization potential of neutral helium atoms, it is difficult to build efficient helium detectors. Therefore, it is crucial to optimize the microscope design to maximize the intensity for a given resolution and working distance. Here we present an optimization model for the helium pinhole microscope system. We show that for a given resolution and working distance, there is a single intensity maximum. Further we show that with present-day state-of-the-art detector technology (ionization efficiency 1×10-3), a resolution of the order of 600 nm at a working distance of 3 mm is possible. In order to make this quantification, we have assumed a Lambertian reflecting surface and calculated the beam spot size that gives a signal 100 cts/s within a solid angle of 0.02π sr, following an existing design. Reducing the working distance to the micron range leads to an improved resolution of around 40 nm

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Exploring neutral atom microscopy

Cited by 20 publications

References 13 publications

Multiple scattering in scanning helium microscopy

Multiple scattering in scanning helium microscopy

Observation of diffraction contrast in scanning helium microscopy

Theoretical model of the helium pinhole microscope

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