Low voltage field emission SEM (i.e., operated at several hundred volts to 5 kV), offering advantages in surface imaging due to reduced beam penetration,1 was found to be particularly useful in the investigation of uncoated, fine, geological materials down to the nano-scale. Here are four examples to highlight projects being conducted in our FESEM facility.

Kaolinite is one of the most important industrial minerals. Information about its surface properties and cation exchange capacity are important in both ore processing and applications of the clay mineral.2 Low voltage (LV) secondary electron (SE) imaging (Fig. la) reveals detailed (001) surface features of kaolinite, which are not obtainable with high voltage SEM (Fig. lb) and TEM. Kaolinite is highly sensitive to beam damage and can show obvious degradation after just a few seconds under the TEM beam. However, microtomed TEM samples maybe easily examined under LV SEM to show their thickness perpendicular to (001) and cross section features. Such information allows easy access to direct surface area determination of clay minerals.