Question

1. Influence of Working Distance (WD) (2 marks) Fig 1 (a) and (b) are SEM secondary electron (SE) images for a composite material with carbon fibres taken with different WD. Interpret the images and explain the influence of WD. a) c-fiber composite, WD-8mm, x500 50 Hm c-fiber composite, WD-24mm, x500 50 um Figure 1 a) WD- 8mm. b) WD 24mm.

Answer 1

Working distance is defined as the distance between the lower lower pole piece and the specimen. Scanning Electron Microscopy is generally used to inspect the topography of the given specimen.

Now consider the following diagrams below,

a) ELECTRON CII LENS SPECIMEN c-fiber composite, WD-8mm, x500 a) WD- 8mm. WORKIN c-fiber composite, WD#24min, x500 b) WD- 24mm.

The higher the working distance is, magnification is less and thus the resolution of the image is more and on the other hand, the lower the working distance, magnification is more and thus the resolution of the image is less.