Biomedical Engineering Reference
In-Depth Information
(a)
(b)
1. 11
Comparison of (a) AFM (defl ection in contact mode) and
(b) SEM (secondary electron) imaging technique on similar dry
titanium/titanium oxide surfaces (2 × 2 μm
2
). Oxide domes are visible
in both the images. (Source: Reproduced from 'Direct observation of
hydration of TiO
2
on Ti using electrochemical AFM: freely corroding
versus potentiostatically held', by J. P. Bearinger, C. A. Orme and J. L.
Gilbert,
Surface Science
(2001) 491: 370-387, © 2001 Elsevier.)
TEM yields the following structural information:
morphology,
crystallographic information,
compositional information.
The components of an SEM are shown in Fig. 1.10. Figure 1.11 compares
images using SEM imaging and AFM (see Section 1.6).
1.5.1 Image formation in the SEM
The SEM produces images by focusing an electron beam with a series of
electromagnetic lenses while under high vacuum conditions. The focused
beam forms a small electron probe which is x-y scanned across the speci-
men surface in a raster pattern; signals from the interaction volume within
the specimen produced at each point in the raster are collected in a corre-
sponding grid pattern by a detector and are assembled into an image that
exactly replicates the surface features of the specimen. A fi nal image of the
specimen is displayed on the viewing monitor of the instrument. The instru-
mental and/or experimental conditions which are employed during a par-
ticular study greatly affect the fi nal image viewed on the viewing monitor.
These conditions include accelerating voltage (KV), size of the interaction
teardrop, lens voltages, specimen tilt, specimen thickness/preparation and
measured imaging signal.
