Collecting helium diffraction patterns in microscopic regions of samples

Recent scientific advances have opened up new possibilities for the close observation of physical phenomena. Researchers from the Universities of Cambridge and Newcastle have recently introduced a new method for measuring the diffraction of helium atoms with microscopic spatial resolution.

This method, described in an article in Physical Examination Lettersallows physicists to study electron-sensitive materials and better understand their morphology using helium microdiffraction.

“The Helium Scanning Microscope has been developed by several research groups for over a decade, with a focus on improving instrument resolution and studying technological and biological samples “, Matthew Bergin, co-author of the paper, told Phys.org. “However, relatively little work has been done on using the matter wave aspect of the helium beam to study ordered surfaces with a helium scanning microscope.”

The recent study by Bergin and colleagues builds on one of their previous papers published in Scientific reports in 2020. In this previous work, the researchers observed the diffraction signature of a microscopic spot on a sample, but they could not directly measure its underlying diffraction pattern.

In their new document, they decided to continue their work in this area. The underlying goal of their study was to demonstrate that an atom-based matter wave could be used to form a diffraction pattern from spatially resolved regions of a surface.

“Because of the particle-wave duality of atoms, a helium beam directed at a lattice can behave like a wave and diffract the periodic structure,” Bergin said. “Helium atoms with thermal energy possess such a low energy (<100meV) that the resulting diffraction pattern is guaranteed to be particularly sensitive to surface structure.

“Helium atom scattering is a well-established technique that uses the position and intensity of these diffraction peaks to study the surface of a sample. However, until now, these studies have been limited to crystals homogeneous measuring at least several millimeters.”

In their experiments, Bergin and his colleagues used a helium scanning microscope that uses a pinhole to collimate a helium beam. With this microscope and a carefully designed strategy, they were able to collect diffraction patterns over a small region (~10 µm) of a sample, despite using a fixed detector.

“By carefully calibrating the instrument, we can move the sample positioning and rotation steps to vary the outgoing detection angle and sample azimuth while illuminating the same point,” explained Bergin . “The result is that we can create an exclusively surface-sensitive diffraction pattern from the small illuminated area of ​​the sample.”

This research team’s recent work demonstrates the feasibility of using atoms to collect a diffraction pattern from a microscopic region of a sample’s surface. The proposed method could be used by other physicists to study diffraction patterns and gather new information about materials that cannot be accurately examined using conventional atomic scattering techniques.

“The spatial resolution capabilities of the instrument combined with the excellent surface sensitivity now allow us to use atomic scattering to measure the material properties of small samples with interesting surface features, such as flakes of 2D materials” , added Bergin.

“At the University of Cambridge, work has already begun on applying the technique to measure diffraction from shards of 2D materials. Meanwhile, colleagues at Newcastle University are developing a new stage of measurement which can directly move the detector to collect diffraction patterns without any difficult calibration or complex sample handling.

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