Influence of the static atomic displacement on atomic resolution Z-contrast imaging

The influence of static atomic displacements, due to atomic size effects in alloys with atoms having different covalent or ionic radii, on high angle annular dark field image contrast is studied quantitatively by simulations and experiments. We show that the static displacements can have a large influence on the Z contrast, depending on the alloy composition and on the scanning transmission electron microscopy specimen thickness. This influence has to be taken into account for quantitative chemistry measurement based on Z-contrast imaging.

Figure 1

(Color online) Ratio of the HAADF intensities calculated with and without including the effect of the SDs, as a function of the In atomic fraction, for two specimen thicknesses of 10 and $40\mathrm{nm}$. The value $s$ of the fitting parameter with a parabola is also shown.

Figure 2

(Color online) (a) HAADF intensity for an InGaAs alloy with In concentration of 24%, with and without considering the effect of the SDs, together with the calculated intensity for GaAs, as a function of the specimen thickness. (b) Starting from the top are reported: $R_0=I_0\left(\mathrm{In}\mathrm{Ga}\mathrm{As}\right)∕I\left(\mathrm{Ga}\mathrm{As}\right)$, $R_{\mathrm{SD}}=I_{\mathrm{SD}}\left(\mathrm{In}\mathrm{Ga}\mathrm{As}\right)∕I\left(\mathrm{Ga}\mathrm{As}\right)$, $R_0-R_{\mathrm{SD}}$, and $I\left(\mathrm{In}\mathrm{Ga}\mathrm{As}\right)-I_{\mathrm{SD}}[\left(\mathrm{In}\mathrm{Ga}\mathrm{As}\right)$, respectively. (c) Derivative with respect to the specimen thickness of the HAADF intensity for the InGaAs alloy with 24% In concentration, as a function of the specimen thickness.

Figure 3

(Color online) (a) Experimental low magnification high-resolution HAADF image, in ⟨110⟩ zone axis, of three QWs of InGaAs of known composition grown on GaAs (001) substrate, and corresponding intensity line profile. (b) High magnification high-resolution HAADF image corresponding to the region marked in (a). (c) Variation of the HAADF image intensity ratios $I_{\mathrm{In}\mathrm{Ga}\mathrm{As}}∕I_{\mathrm{Ga}\mathrm{As}}$ measured on the experimental image (squared dots with experimental errors) for each of the QWs, together with the expected intensity ratios calculated with (solid line) and without (dotted line) taking into account the SDs.