In this theoretical study we analyze contrast transfer of weak-phase objectsin a transmission electron microscope, which is equipped with an aberrationcorrector (Cs-corrector) in the imaging lens system and a physical phase platein the back focal plane of the objective lens. For a phase shift of pi/2between scattered and unscattered electrons induced by a physical phase plate,the sine-type phase contrast transfer function is converted into a cosine-typefunction. Optimal imaging conditions could theoretically be achieved if thephase shifts caused by the objective lens defocus and lens aberrations would beequal zero. In reality this situation is difficult to realize because ofresidual aberrations and varying, non-zero local defocus values, which ingeneral result from an uneven sample surface topography. We explore theconditions - i.e. range of Cs-values and defocus - for most favourable contrasttransfer as a function of the information limit, which is only limited by theeffect of partial coherence of the electron wave in Cs-corrected transmissionelectron microscopes. Under high-resolution operation conditions we find that aphysical phase plate improves strongly low- and medium-resolution objectcontrast, while improving tolerance to defocus and Cs-variations, compared to amicroscope without a phase plate.
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