(a) Horizontal and (b) vertical line scans over the focus grid bar edges.
Grey scale representation of secondary electron image [(a), (c), (e)] and corresponding 2D ACF [(b), (d), (f)] for different focus conditions [(a) and (b)] optimal focus, [(c) and (d)] vertical focus—12 steps from optimal, [(e) and (f)] horizontal and vertical—24 and—12 steps from optimal.
Area-normalized horizontal (a) and vertical (b) cuts through the ACF in the region of the central peak as the vertical lens excitation was stepped through the focus while the horizontal maintained a constant for the sample shown in Fig. 2.
Comparison as the lens excitation currents are scanned through focus of nonlinear fitting widths [(a), (c)] with figures of merit [(b), (d)] and . In (a) and (b) both the horizontal and vertical excitations are varied. In (c) and (d) the vertical excitation is stepped through the focus while the horizontal excitation maintained at focus. The triangles and dashed lines refer to the horizontal parameters while the circles and full line denotes the parameters in the vertical direction. The error bars represent the statistical uncertainty in calculating the fitted width and and .
Direct STIM images (Ref. 21) of a human breast cancer cell and corresponding ACF. (a) and (b) are off-focus measured under low-fluence conditions ( ions corresponding to ). (c) and (d) correspond to in-focus under low-fluence conditions and (e) corresponds to in-focus under high-fluence conditions ( corresponding to ). In (b) and (d) the gray scale has been optimized to show the central peak region only.
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