Radiological TEM (ARM)

Located in RadEMSL (Radiochemistry Annex), the JEM-ARM200CF transmission electron microscope (TEM) enables atomic resolution of biogeochemical spatial associations, mineral identification and oxidation state determination of radiological samples. The JEM-ARM200CF TEM enables structure analysis with atomic resolution in TEM and scanning transmission electron microscope (STEM) modes. Furthermore, it allows elemental and chemical bonding analysis of single atomic columns via energy-dispersive x-ray spectroscopy (EDS), and electron energy-loss spectroscopy (EELS) from Gatan and the Gatan digital imaging system. The resolution limit for TEM and STEM imaging with Z-contrast is 80pm.

The JEM-ARM200CF has a cold-field emission gun (CFEG) electron source, and an integrated probe aberration (Cs) corrector, resulting in smaller probes with higher currents. The JEM-ARM200CF is capable of probe sizes from <0.1 nm to >0.3 nm with large beam currents for better energy-dispersive X-ray (EDX) efficiency. The probe current for a 0.16nm probe is on the order of 1500 pA, allowing a large number of EDX counts to be collected quickly. The small probes are important for atomic resolution chemical mapping while the higher probe currents allow this mapping to be done quickly and efficiently. To take full advantage of the aberration correction, the ARM200CF has enhanced mechanical, electrical, and thermal stability, and includes thermal and magnetic shielding to minimize environmental effects. The ARM includes a dedicated piezoelectric goniometer for sub-Angstrom positioning accuracy of the specimen and minimized drift. The microscope is capable of acquiring four different scanned signals simultaneously: high angle annular dark field (HAADF) STEM, mid-or-low angle annular dark field (MAADF) STEM, bright field STEM and secondary electron (SE). The bright field STEM image can be acquired as either a standard bright field or annular bright field (ABF) image. These ABF images have enhanced sensitivity for light elements.