TY - JOUR
T1 - Channelling contrast analysis of lattice images
T2 - Conditions for probe-insensitive STEM
AU - Rossouw, Chris J.
AU - Dwyer, Christian
AU - Katz-Boon, Hadas
AU - Etheridge, Joanne
N1 - Funding Information:
CD and JE acknowledge funding from the Australian Research Council (Grants DP110104734 and DP120101573 ).
Copyright:
Copyright 2014 Elsevier B.V., All rights reserved.
PY - 2014/1
Y1 - 2014/1
N2 - Quantitative analysis of lattice resolved images generated by scanning transmission electron microscopy (STEM) requires specification of probe characteristics, such as defocus, aberration and source distribution. In this paper we show that knowledge of such characteristics is unnecessary for quantitative interpretation, if the signal is integrated over a unit cell. Such a condition, whether the result of experimental setup or post-processing of lattice resolved images, reduces the intensity distribution to that of channelling contrast, where the signal for plane wave incidence is averaged over the angular range of the probe, and the result is independent of the probe characteristics. We use a Bloch wave model to show analytically how this applies to all forms of STEM imaging, such as that formed by annular dark field or backscatter detection, as well as characteristic X-ray fluorescence or electron energy loss. As a specific example, we consider how the signal from an annular dark field detector can be used to determine specimen thickness via a transfer curve for the zone axis and scattering geometries employed. This method has advantages over matching lattice images with calculations since these are sensitive to probe coherence and aberration, and saturation of the on-column intensity is approached more rapidly.
AB - Quantitative analysis of lattice resolved images generated by scanning transmission electron microscopy (STEM) requires specification of probe characteristics, such as defocus, aberration and source distribution. In this paper we show that knowledge of such characteristics is unnecessary for quantitative interpretation, if the signal is integrated over a unit cell. Such a condition, whether the result of experimental setup or post-processing of lattice resolved images, reduces the intensity distribution to that of channelling contrast, where the signal for plane wave incidence is averaged over the angular range of the probe, and the result is independent of the probe characteristics. We use a Bloch wave model to show analytically how this applies to all forms of STEM imaging, such as that formed by annular dark field or backscatter detection, as well as characteristic X-ray fluorescence or electron energy loss. As a specific example, we consider how the signal from an annular dark field detector can be used to determine specimen thickness via a transfer curve for the zone axis and scattering geometries employed. This method has advantages over matching lattice images with calculations since these are sensitive to probe coherence and aberration, and saturation of the on-column intensity is approached more rapidly.
KW - Channelling contrast
KW - Probe aberration
KW - STEM imaging
KW - Source size effects
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U2 - 10.1016/j.ultramic.2013.10.005
DO - 10.1016/j.ultramic.2013.10.005
M3 - Article
C2 - 24269638
AN - SCOPUS:84888021590
SN - 0304-3991
VL - 136
SP - 216
EP - 223
JO - Ultramicroscopy
JF - Ultramicroscopy
ER -