Reflection imaging with a helium zone plate microscope

• Published in: Ultramicroscopy Vol. 261; p. 113961
• Main Authors: Flatabø, Ranveig, Eder, Sabrina D., Reisinger, Thomas, Bracco, Gianangelo, Baltzer, Peter, Samelin, Björn, Holst, Bodil
• Format: Journal Article
• Language: English
• Published: Netherlands Elsevier B.V 01-07-2024
• Subjects: Neutral helium microscopy; SHEM; Neutral helium microscopy; SHEM
• ISSN: 0304-3991; 1879-2723
• DOI: 10.1016/j.ultramic.2024.113961

Neutral helium atom microscopy is a novel microscopy technique which offers strictly surface-sensitive, non-destructive imaging. Several experiments have been published in recent years where images are obtained by scanning a helium beam spot across a surface and recording the variation in scattered intensity at a fixed total scattering angle θSD and fixed incident angle θi relative to the overall surface normal. These experiments used a spot obtained by collimating the beam (referred to as helium pinhole microscopy). Alternatively, a beam spot can be created by focusing the beam with an atom optical element. However up till now imaging with a focused helium beam has only been demonstrated in transmission (using a zone plate). Here we present the first reflection images obtained with a focused helium beam (also using a zone plate). Images are obtained with a spot size (FWHM) down to 4.7μm±0.5μm, and we demonstrate focusing down to a spot size of about 1μm. Furthermore, we present experiments measuring the scattering distribution from a focused helium beam spot. The experiments are done by varying the incoming beam angle θi while keeping the beam-detector angle θSD and the point where the beam spot hits the surface fixed - in essence, a microscopy scale realization of a standard helium atom scattering experiment. Our experiments are done using an electron bombardment detector with adjustable signal accumulation, developed particularly for helium microscopy.
•The first reflection images from a zone plate helium atom microscope.•Images with a spot size down to 4.7μm±0.5μm are presented.•Focusing down to a spot size of about 1μm is demonstrated.•Helium atom scattering on the microscopic scale is demonstrated.