Control and characterization of a piezo TEM stage for automated atomic-resolution and atomic-precision image mapping

Abstract text (incl. figure legends and references)

The information gained from a native specimen is limited by the introduced dosage. One way to reduce dose, is to distribute it across an area, which is typically larger than the field of view of the detector, when acquiring atomically resolved TEM images. Therefore, in low dose experiments, a region of interest in the specimen can be mapped, by iterative displacements of the specimen, thus always exposing a fresh region of the sample. The stability and resolution of the TEM stage limits the quality of the final image map. This motivated the use of a piezo TEM stage for image mapping. The characterization of the lateral stepsize, the stage and imaging system control, as well as the automated low dose image acquisition was the objective of this work. The mapping system was implemented on an image corrected JEOL JEM-ARM200F microscope, equipped with a Gatan OneView. These systems were controlled via the backend of the Gatan and JEOL user interfaces (DigitalMicrograph, Temcenter), using custom python servers on each control computer. These servers were controlled simultaneously on a third computer, serving as a host. The stage was characterized by using a freestanding 2D material, and visible features served as a reference in the observed area, as illustrated in Figure 1. The reference was periodically displaced for 10,5 nm within the image and the stage start and end positions were recorded from the temcenter UI. The standard deviation from the start and end positions were smaller than 0,5 Å as well as the calculated step size at the lowest speed setting in the temcenter UI. The standard deviation of the start and end positions indicate that the stage is atomically precise, when conducting a unidirectional displacement. The step size was used in the mapping, to displace the specimen to a set of coordinates and to acquire a stack of images at each position, as illustrated in Figure 2. The electron beam was blanked during each displacement, reducing the dosage during mapping. In conclusion, the accuracy and precision of the piezo stage allows a mapping with non overlapping (or minimally overlapping) field of view in each exposure, which are closer packed together than for standard non piezo driven TEM stages. This enables the collection of low dose images from a smaller sample area, which might be especially helpful for 2D specimen with smaller patches of non-contaminated area or specimen with small regions of interest. Also, it enables the acquisition of an atomic resolution image from a large area (up to 380x380 nm) by stitching together a large number of exposures with a smaller field of view.

Figure 1: Characterization for the X direction of a piezo super fine stage of an JEOL ARM200F. The intended periodic forth and back displacement is indicated with arrows and the step size is illustrated as dimensioning arrows. The Precision is indicated along the edge of the reference structure (highlighted in red) with two barred lines.

Figure 2: Illustration of an atlas acquisition using the piezo stage of a JEOL JEM-ARM200F TEM. The field of view was 21,5x21,5 nm and the spacing along the stage x and y-axis were 18 nm. Videos for each spot were acquired with a Gatan OneView with 14fps.