Material properties particularly suited to be measured with helium scattering: selected examples from 2D materials, van der Waals heterostructures, glassy materials, catalytic substrates, topological insulators and superconducting radio frequency materials

Holst, Bodil; Alexandrowicz, Gil; Avidor, Nadav; Benedek, G.; Bracco, G.; Ernst, Wolfgang; Farı́as, Daniel; Jardine, A. P.; Lefmann, Kim; Manson, J. R.; Marquardt, Roberto; Artés, Salvador Miret; Sibener, S. J.; Wells, Justin W.; Tamtögl, Anton; Allison, W.

doi:10.1039/d0cp05833e

Cited by 35 publications

(28 citation statements)

References 201 publications

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“…Compared with other techniques, He atom scattering has the advantage of being the most delicate surface-probing technique and is sensitive to H atoms in the top layer 63 – 66 . All measurements have therefore been performed using the Cambridge helium-3 spin-echo facility (HeSE) 27 , 67 , 68 . The schematic principle of He spin-echo is illustrated in Fig.…”

Section: Methodsmentioning

confidence: 99%

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Motion of water monomers reveals a kinetic barrier to ice nucleation on graphene

et al. 2021

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The interfacial behaviour of water remains a central question to fields as diverse as protein folding, friction and ice formation. While the properties of water at interfaces differ from those in the bulk, major gaps in our knowledge limit our understanding at the molecular level. Information concerning the microscopic motion of water comes mostly from computation and, on an atomic scale, is largely unexplored by experiment. Here, we provide a detailed insight into the behaviour of water monomers on a graphene surface. The motion displays remarkably strong signatures of cooperative behaviour due to repulsive forces between the monomers, enhancing the monomer lifetime ( ≈ 3 s at 125 K) in a free-gas phase that precedes the nucleation of ice islands and, in turn, provides the opportunity for our experiments to be performed. Our results give a molecular perspective on a kinetic barrier to ice nucleation, providing routes to understand and control the processes involved in ice formation.

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Section: Methodsmentioning

confidence: 99%

“…If the surface changes between scattering of the two parts of the wavepacket, a loss of polarisation is observed in the detected beam, which is directly related to the change in surface correlation and in the case of surface diffusion, usually follows an exponentially decaying form (see refs. 27 , 67 , 68 for more information).…”

Section: Methodsmentioning

confidence: 99%

Motion of water monomers reveals a kinetic barrier to ice nucleation on graphene

et al. 2021

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“…For recent reviews of helium scattering see Refs. [22,23]. Al Taleb et al obtained the first experimental measurement of κ for monolayer graphene, which shows good agreement with theory.…”

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confidence: 67%

Temperature-Dependent Bending Rigidity of AB -Stacked Bilayer Graphene

et al. 2021

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The change in bending rigidity with temperature κðTÞ for 2D materials is highly debated: theoretical works predict both increase and decrease. Here we present measurements of κðTÞ, for a 2D material: AB-stacked bilayer graphene. We obtain κðTÞ from phonon dispersion curves measured with helium atom scattering in the temperature range 320-400 K. We find that the bending rigidity increases with temperature. Assuming a linear dependence over the measured temperature region we obtain κðTÞ ¼ ½ð1.3 AE 0.1Þ þ ð0.006 AE 0.001ÞT=K eV by fitting the data. We discuss this result in the context of existing predictions and room temperature measurements.

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“…In order to understand what forms the contrast in SHeM images, we first need to discuss the different processes that can occur when a thermal helium atom scatters off a surface. The general theory of helium scattering has been treated in a range of books and review articles, see for example [82,83,71,84]. Unlike electrons, X-rays and neutrons which all interact with the core electronic cloud and atomic nuclei in the sample, thermal helium atoms scatter off the outermost electron density distribution at the sample surface.…”

Section: Contrast Propertiesmentioning

confidence: 99%

“…Here λ i and λ f denote the wavelength of the incident and scattered helium atoms, respectively. Inelastic scattering leads to a wavelength change, figure reproduced from[82].…”

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Neutral Helium Microscopy (SHeM): A Review

Palau¹,

Eder²,

Bracco³

et al. 2021

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Neutral helium microscopy, also referred to as scanning helium atom microscopy and commonly abbreviated SHeM, is a novel imaging technique that uses a beam of neutral helium atoms as an imaging probe. The technique offers a number of advantages such as the very low energy of the incident probing atoms (less than 0.1 eV), unsurpassed surface sensitivity (no penetration into the sample bulk), a charge neutral, inert probe and a high depth of field. This means that fragile and/or non-conducting samples can be imaged as well as samples with high aspect ratio, with the potential to obtain true to scale height information of 3D surface topography with nanometer resolution. However, for a full exploitation of the technique, a range of experimental and theoretical issues still needs to be resolved. In this paper we review the current state of research in the field. We do this by following the trajectory of the helium atoms step by step through the microscope. From the initial acceleration in the supersonic expansion used to generate the probing beam over the interaction of the helium atoms with the sample (contrast properties) to the final detection and post-processing. We also review recent advances in scanning helium microscope design and we present an overview of the samples that have been investigated with SHeM up till now.

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Material properties particularly suited to be measured with helium scattering: selected examples from 2D materials, van der Waals heterostructures, glassy materials, catalytic substrates, topological insulators and superconducting radio frequency materials

Abstract: Helium Atom Scattering (HAS) and Helium Spin Echo scattering (HeSE), together Helium Scattering, are well established, but non-commercial surface science techniques. They are characterised by the beam inertness and very...

Cited by 35 publications

References 201 publications

Motion of water monomers reveals a kinetic barrier to ice nucleation on graphene

Motion of water monomers reveals a kinetic barrier to ice nucleation on graphene

Temperature-Dependent Bending Rigidity of AB -Stacked Bilayer Graphene

Neutral Helium Microscopy (SHeM): A Review

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