Various ptychographic methods provide super resolution, but the inverse multislice method has recently set the record with a spatial resolution on par with that of lattice vibrations [1]. However, the limiting factor for many materials investigations is not the optical resolution of a modern aberration corrected microscope, but the signal one can obtain before damaging the material being studied. Dose efficiency is a prominent feature of ptychography, but the different algorithms work best under different conditions at low doses. Direct methods such as single side band (SSB) ptychography [2] work well in a focused probe configuration, whereas iterative methods such as ePIE [3] generally require a significantly defocused probe to converge at low doses. As sample thickness increases contrast reversals can also occur with both direct and iterative ptychography methods which do not explicitly consider the thickness. Recent investigations have found it is possible to overcome such contrast reversals in direct ptychography by application of small amounts of defocus, including after taking the data, allowing one to maintain optimal focus for the ADF signal [4]. The multislice method takes thickness into account explicitly by dividing the sample into thin slices and iteratively solving for the phase of each. We will investigate the low dose performance of the multislice method and evaluate the advantages and disadvantages compared to direct methods. We will also examine the sensitivity of the multislice method for samples containing features such as defects.

References

[1] C. Zhen. et al. Science, 2021, 372, 826-831.

[2] T. J. Pennycook. et al. Ultramicroscopy, 2019, 196, 131-135.

[3] M. Andrew. et al. Ultramicroscopy, 2009, 109, No. 10.

[4] C. Gao. et al. Applied Physics Letters, 2022, 121, 081906.