Diffraction Imaging in a He⁺ Ion Beam Scanning Transmission Microscope

Abstract

The scanning helium ion microscope has been used in transmission mode to investigate both the feasibility of this approach and the utility of the signal content and the image information available. Operating at 40 keV the penetration of the ion beam, and the imaging resolution achieved, in MgO crystals was found to be in good agreement with values predicted by Monte Carlo modeling. The bright-field and annular dark-field signals displayed the anticipated contrasts associated with beam absorption and scattering. In addition, the diffraction of the He ion beam within the sample gave rise to crystallographic contrast effects in the form of thickness fringes and dislocation images. Scanning transmission He ion microscopy thus achieves useful sample penetration and provides nanometer scale resolution, high contrast images of crystalline materials and crystal defects even at modest beam energies.

Helium ion microscopy

“…Both dark field and bright field images could be recorded in which thickness fringes and line defects could be identified. 52 …”

Stationary beam full-field transmission helium ion microscopy using sub-50 keV He+: Projected images and intensity patterns

“…The use of sub-50 keV transmitted He + ions for microscopy has already been reported [19–21]. As an example application, the secondary electrons produced by transmitted ions have been used to image hollow glass nanocapillaries [22].…”

“…As an example application, the secondary electrons produced by transmitted ions have been used to image hollow glass nanocapillaries [22]. Features similar to diffraction-related thickness fringes seen in transmission electron microscopy (TEM) have been observed in a HIM and have possible explanations involving diffraction [19] or inelastic scattering [23] of He + ions. This observation led to computational work investigating coherent scattering, channeling and diffraction of He + ions in crystals to explore the possibilities to obtain atomic-resolution images in a HIM [23].…”

Scanning reflection ion microscopy in a helium ion microscope

“…During the last decade the imaging capabilities of HIM were examined in the field of material science [15,[17][18][19][20][21][22][23] as well as in biology [15,16,[24][25][26]. Different techniques such as secondary electron energy filtering [27], helium ion channeling contrast [28][29][30], helium ion transmission microscopy [31], secondary ion mass spectrometry [32,33], and ionoluminescence [34,35] were developed.…”