Measuring the top–bottom effect of a tilted thick specimen in an ultrahigh-voltage electron microscope.

From the 40 nm gold particles on the surface of a 5 μm thick amorphous specimen tilted by a 360° tilt holder, we have observed the top–bottom effect (TBE) in a 3 MV ultrahigh-voltage electron microscope. Because of the TBE, object points located on the top surface of the specimen have poorer image quality than those on the bottom. Measurements of the diameter and contrast of gold-particle images show that the TBE becomes strong when increasing the effective thickness of the specimen by tilting the specimen. The TBE can produce additional image blurring of about 10, 27, and 74 nm in the gold-particle diameter for the effective thickness of 5.0, 10.0, and 14.6 μm, respectively. The need for further investigations is thus suggested to understand and determine the TBE limitation on the resolution or fidelity of electron tomography for thick specimens. [ABSTRACT FROM AUTHOR]