Theoretical model of the helium pinhole microscope

Palau, Adrià Salvador; Bracco, G.; Holst, Bodil

doi:10.1103/physreva.94.063624

Cited by 22 publications

(21 citation statements)

References 24 publications

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“…The model constructed to fit the experimental data could be used as a future tool for extracting the parameters of periodic gratings on the nanometer scale. Furthermore, the model may be used to describe the behavior of helium beams, which is important for a range of applications, including the development of an efficient neutral helium microscope [25,26].…”

Section: Discussionmentioning

confidence: 99%

Neutral-helium-atom diffraction from a micron-scale periodic structure: Photonic-crystal-membrane characterization

et al. 2017

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Surface scattering of neutral helium beams created by supersonic expansion is an established technique for measuring structural and dynamical properties of surfaces on the atomic scale. Helium beams have also been used in Fraunhofer and Fresnel diffraction experiments. Due to the short wavelength of the atom beams of typically 0.1 nm or less, Fraunhofer diffraction experiments in transmission have so far been limited to grating structures with a period (pitch) of up to 200 nm. However, larger periods are of interest for several applications, for example for the characterization of photonic crystal membrane structures, where the period is typically in the micron/high sub-micron range. Here we present helium atom diffraction measurements of a photonic crystal membrane structure with a two dimensional square lattice of 100 × 100 circular holes. The nominal period and hole radius were 490 nm and 100 nm respectively. To our knowledge this is the largest period that has ever been measured with helium diffraction. The helium diffraction measurements are interpreted using a model based on the helium beam characteristics. It is demonstrated how to successfully extract values from the experimental data for the average period of the grating, the hole diameter and the width of the virtual source used to model the helium beam.

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Section: Discussionmentioning

confidence: 99%

Neutral-helium-atom diffraction from a micron-scale periodic structure: Photonic-crystal-membrane characterization

et al. 2017

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“…a Weber window, it is possible to design an atom sieve with a resolution larger than the hole diameter. In a recent paper Palau et al 16 shows that with the velocity spread and intensity of present day beam sources and present day detector technology, the limiting factor for a realistic helium microscope design is the resolution of the optical element, determined by the width of the outermost zone. Thus our work shows that helium microscopy with a resolution better than 15 nm should be possible.…”

Section: Discussionmentioning

confidence: 99%

“…For an atom Fresnel zoneplate these numbers are further reduced due to the support rods needed to keep the zone plate ring structure together. Intensity is a big issue in helium microscopy 15,16 , so this is a major limitation.…”

Section: Introductionmentioning

confidence: 99%

Atom sieve for nanometer resolution neutral helium microscopy

Flatabø

Greve

Eder

et al. 2017

Journal of Vacuum Science &Amp; Technology B, Nanotechnology and Microelectronics: Materials, Processing, Measurement, and Phen

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Neutral helium microscopy is a new tool for imaging fragile and/or insulating structures as well as structures with large aspect ratios. In one configuration of the microscope, neutral helium atoms are focused as de Broglie matter waves using a Fresnel zone plate. The ultimate resolution is determined by the width of the outermost zone. Due to the low-energy beam (typically less than 0.1 eV), the neutral helium atoms do not penetrate solid materials and the Fresnel zone plate therefore has to be a free-standing structure. This creates particular fabrication challenges. The so-called Fresnel photon sieve structure is especially attractive in this context, as it consists merely of holes. Holes are easier to fabricate than the free-standing rings required in a standard Fresnel zone plate for helium microscopy, and the diameter of the outermost holes can be larger than the width of the zone that they cover. Recently, a photon sieve structure was used for the first time, as an atom sieve, to focus a beam of helium atoms down to a few micrometers. The holes were randomly distributed along the Fresnel zones to suppress higher order foci and side lobes. Here, the authors present a new atom sieve design with holes distributed along the Fresnel zones with a fixed gap. This design gives higher transmission and higher intensity in the first order focus. The authors present an alternative electron beam lithography fabrication procedure that can be used for making high transmission atom sieves with a very high resolution, potentially smaller than 10 nm. The atom sieves were patterned on a 35 nm or a 50 nm thick silicon nitride membrane. The smallest hole is 35 nm, and the largest hole is 376 nm. In a separate experiment, patterning micrometer-scale areas with hole sizes down to 15 nm is demonstrated. The smallest gap between neighboring holes in the atom sieves is 40 nm. They have 47011 holes each and are 23.58 μm in diameter. The opening ratio is 22.60%, and the Fresnel zone coverage of the innermost zones is as high as 0.68. This high-density pattern comes with certain fabrication challenges, which the authors discuss.

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“…We refer to varying z, while keeping the same point on the sample under the beam, as a z scan. A complication that arises when performing a z scan is that the size of the beam changes as the distance between the sample and the pinhole is varied 21,22 . The range of scattering angles that can be observed is therefore determined by both the available signal level and the largest acceptable illumination area of the helium beam, since resolution of a small feature would require a narrow helium beam.…”

Section: Contrast Formation In the Cambridge Shemmentioning

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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Theoretical model of the helium pinhole microscope

Cited by 22 publications

References 24 publications

Neutral-helium-atom diffraction from a micron-scale periodic structure: Photonic-crystal-membrane characterization

Neutral-helium-atom diffraction from a micron-scale periodic structure: Photonic-crystal-membrane characterization

Atom sieve for nanometer resolution neutral helium microscopy

Observation of diffraction contrast in scanning helium microscopy

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