TY - JOUR
T1 - Z dependence of electron scattering by single atoms into annular dark-field detectors
AU - Treacy, Michael
PY - 2011/12/1
Y1 - 2011/12/1
N2 - A simple parameterization is presented for the elastic electron scattering cross sections from single atoms into the annular dark-field (ADF) detector of a scanning transmission electron microscope (STEM). The dependence on atomic number, Z, and inner reciprocal radius of the annular detector, q0, of the cross section σ(Z,q 0) is expressed by the empirical relation σ(Z,q 0) = A(q 0)Z n(Z,q0), where A(q 0) is the cross section for hydrogen (Z = 1), and the detector is assumed to have a large outer reciprocal radius. Using electron elastic scattering factors determined from relativistic Hartree-Fock simulations of the atomic electron charge density, values of the exponent n(Z,q 0) are tabulated as a function of Z and q 0, for STEM probe sizes of 1.0 and 2.0 Å. Comparison with recently published experimental data for single-atom scattering [Krivanek et al. (2010). Nature 464, 571-574] suggests that experimentally measured exponent values are systematically lower than the values predicted for elastic scattering from low-Z atoms. It is proposed that this discrepancy arises from the inelastic scattering contribution to the ADF signal. A simple expression is proposed that corrects the exponent n(Z,q 0) for inelastic scattering into the annular detector.
AB - A simple parameterization is presented for the elastic electron scattering cross sections from single atoms into the annular dark-field (ADF) detector of a scanning transmission electron microscope (STEM). The dependence on atomic number, Z, and inner reciprocal radius of the annular detector, q0, of the cross section σ(Z,q 0) is expressed by the empirical relation σ(Z,q 0) = A(q 0)Z n(Z,q0), where A(q 0) is the cross section for hydrogen (Z = 1), and the detector is assumed to have a large outer reciprocal radius. Using electron elastic scattering factors determined from relativistic Hartree-Fock simulations of the atomic electron charge density, values of the exponent n(Z,q 0) are tabulated as a function of Z and q 0, for STEM probe sizes of 1.0 and 2.0 Å. Comparison with recently published experimental data for single-atom scattering [Krivanek et al. (2010). Nature 464, 571-574] suggests that experimentally measured exponent values are systematically lower than the values predicted for elastic scattering from low-Z atoms. It is proposed that this discrepancy arises from the inelastic scattering contribution to the ADF signal. A simple expression is proposed that corrects the exponent n(Z,q 0) for inelastic scattering into the annular detector.
KW - HAADF
KW - Z contrast
KW - annular dark field (ADF)
KW - annular detector
KW - scattering cross sections
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U2 - 10.1017/S1431927611012074
DO - 10.1017/S1431927611012074
M3 - Article
C2 - 22051035
AN - SCOPUS:82055172681
SN - 1431-9276
VL - 17
SP - 847
EP - 858
JO - Microscopy and Microanalysis
JF - Microscopy and Microanalysis
IS - 6
ER -