W. Richard Bowen and Nidal Hilal 4

4.8 CHARACTERIsATION OF METAL sURFACEs 131
of surfaces at fine levels of detail is easily accomplished by AFM imaging,
the monitoring of the polishing of surfaces is an obvious application.
Abbot and co-workers used AFM both in air and in situ in liquid to
monitor the changes in morphology over time of a stainless steel surface
during electropolishing with an ionic liquid [17]. Roughness values,
described by maximum z-height, were 597 and 88 nm for the unpolished
and polished surfaces respectively. As the z-max figures for the unpolished
surface were likely to be greater than would be expected owing to the surface
not being flat, the authors also calculated roughness as a percentage
difference in the flat scanning area versus the actual surface area of the
sample. This yielded roughness values of 7.9% for the unpolished surface
and 0.2% for the polished surface. It was also noted that a trough was seen
to have been etched out at the boundary between the polished and unpolished
areas, varying in depth from 1–2 �m, Figure 4.26.
y / µm
A
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(x = 35.6µm)
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FIgURE 4.26 AFM images obtained at the transition between polished and non-
polished areas of a stainless steel surface. (a) and (b) show the same areas in 2D and 3D
modes. Unpolished surface is flat but has high roughness, whereas the polished surface
is relatively smooth, but still shows large height variations. At the interface is an etched
trench. (c) shows a line profile from the image, with the unpolished section on the left and
polished on the right. Reproduced from [17].
x / µm