2007 Volume 93 Issue 2 Pages 169-175
In this paper we will demonstrate how the use of low-voltage scanning electron microscopy (SEM) improves surface sensitivity and effective spatial resolution. The separation of chemical and morphological information can be possible when an SEM has two or more secondary electron (SE) detectors. A strong chemical contrast from a thin oxide layer on a steel sheet was obtained using a LEO 1530 with an on-axis annular in-lens SE detector by reducing the accelerating voltage down to 500 V. However, in using the E-T detector at the same accelerating voltage, the chemical contrast was weak and only the morphological information was visible. Secondary electron images obtained at various working distances confirmed that “separation” of secondary electrons occurred between the two SE detectors. Secondary electrons whose yield is sensitive to surface structure seem to be selectively detected by the in-lens detector. Consequently, surface sensitivity and a high resolution can be retained even at high accelerating voltages for secondary electron images obtained using the in-lens detector. Bulk contrast becomes dominant for secondary electron images obtained using the E-T detector, resulting in the degradation of spatial resolution at high voltages. The improvement in spatial resolution of backscattered electron images due to low electron penetration is clearly demonstrated for a complex oxide-sulfide inclusion.
