Very Fast Acquisition of Tilt series in Environmental TEM Tomography: Tips and Tricks

In environmental Transmission Electron Microscopy (ETEM), nanomaterials can be studied under dynamic conditions in a gaseous or liquid environment. An important challenge is to track their evolution in 3D. Intuitively, the acquisition of the tomographic tilt series must be completed in a very short time to prevent any morphological modification due to irradiation and/or dynamic change of the object during its rotation for allowing a relevant volume reconstruction. Recently we have demonstrated than Bright Field (BF) tomography can be performed in a few minutes in an environmental microscope (FEI-TITAN ETEM, 80-300 kV) [1,2]. With the help of fast recording (CMOS or direct electron) cameras capable of acquiring tens or hundreds fps in at least a (2k)² format, acquiring a tilt series during a continuous rotation of the sample without any stop can be completed in only a few seconds. Typical examples on nano-catalysts or electron beam sensitive materials will be reported of tomography acquisitions performed over a tilt amplitude of 140° in short times, down to 5-6 seconds under environmental, e.g. temperature and gas conditions (figure 1). However, several remaining problems must be addressed, like diffraction contrast, blur effects, low SNR. One of the most severe limitations is the imperfect rotation of the goniometer, which lead to systematic drifts of the sample up to the frequent exit of the projection out of the field of view. We will describe a robust solution consisting in a fast computer-routine compatible with a TITAN microscope equipped with a Gatan Oneview camera using the ‘in-situ’ option (figure 2).