Conditions required for detection of specimen-specific SE-I secondary electrons in an analytical SEM

An analytical SEM equipped with an above-the-lens detector, an in-the-lens specimen stage and a high brightness LaB6 emitter was used to produce a specimen-specific, secondary electron-I (SE-I) signal for recording edge brightness contrast with high intensity on small particles at high magnification (200,000). The SE-I edge brightness contrast produced from 20-40 nm colloidal gold on silicon wafers was useful for estimating instrument resolution since the edge brightness is the sum of the SE-I signal range (approximately equal to 1 nm) and the beam diameter. LaB6 crystal saturation and gun conditions were determined in order to minimize the probe diameter at the first cross-over position. Ferritin particles also on the silicon wafers were imaged by adjustments of the gun bias voltage conditions. Establishment of these conditions was useful for high resolution SEM studies of appropriately coated bulk biological specimens.