Raising the Standard of Specimen Preparation for Aberration-Corrected TEM and STEM

Introduction With the recent advances made in monochromation of electron sources and Cs-correction, the point resolution of the transmission electron microscope (TEM) has been extended into the sub-Angstrom regime. This development has led to an important consequence—that specimen preparation has become a more critical issue for the materials scientist. Nanoscale artifacts that could be tolerated a few years ago when imaging in the 0.1–0.15 nm range can no longer be allowed. An example is hydrocarbon contamination, which although only a few monolayers thick, obscures the area of interest [1]. Other examples include residual deformation and oxidation following traditional mechanical methods. Ion-based methods may induce amorphization and implantation defects, depending on the type of ion, its energy, and the particular protocol that is used. Specimen preparation begins with the application of either a conventional or focused ion beam (FIB) and ends with post-processing to optimize the results. In the FIB, a Ga liquid metal ion source is operated at accelerating voltages ranging from 30 keV to 1 keV. Depending on the beam size and current, this tool can be used to either cut or polish a cross section of the desired material. Cryogenic specimen stages have been added to allow treatment of polymers as well as metals or ceramics. Most commercial instruments have combined an electron column with the ion column, permitting high-resolution imaging with secondary or backscattered electrons during or after FIB. A variety of specimen preparation techniques and configurations are available, including exand in-situ lift-outs and the H-Bar [2].