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Steel Surface Preparation for SPM


Figure 2 : Topographic AFM map showing a steel surface with a good coarse polish, but the overall result was marred by insuffi cient diamond polishing (which should have removed the ~ 2 nm deep scratches) and salt crystals formed during the drying of tap water.


polishing pad is recommended to maintain reproducibility in applied pressure compared to manual polishing. Polishing steps . T e following steps are recommended for AISI 300 series and SAF 2205 stainless steels: 1. 60 s at 300 rpm, and 30 N, on 320-Grit SiC paper with water lubricant. T is step is necessary to remove excess resin from the face of the sample.


2. 60 s at 300 rpm, and 30 N, on 800-Grit SiC paper with water lubricant.


3. 3 minutes at 300 rpm, and 30 N, on 1200-Grit SiC paper with water lubricant.


4. 5 minutes at 300 rpm and 30 N on 2400-Grit SiC paper with water lubricant.


5. 10 minutes at 150 rpm and 30 N on 4000-Grit SiC paper with water lubricant.


6. 5 minutes at 150 rpm and 15 N on 4000-Grit SiC paper with water lubricant.


7. 10 minutes polishing by hand, using 1 μ m diamond paste on a nylon cloth and aerosol lubricant (for example, Hyprez fl uids, Engis Ltd., Maidstone, UK). T e direction of polishing should be varied throughout the process.


8. 10 minutes polishing by hand, using 1/4 μ m diamond paste on a nylon cloth and aerosol lubricant (for example, Hyprez fl uids, Engis Ltd., Maidstone, UK). T e direction of polishing should be varied throughout the process.


9. 24 hours on a Vibro-polisher (Buehler Vibromet 2 Buehler/Illinois Tool Works Inc., Lake Bluff , Illinois), at a rotational speed of 3 rpm with an oxide polishing suspension (OPS).


Each time the grinding pad is changed, both the sample and sample holder should be removed from the grinder and given a thorough wash with dionized (DI) water and detergent, followed by rinsing with methanol and blow-drying using N 2 . If samples are particularly delicate, it is suggested that steps I and II be skipped and step III repeated until the polishing breaks through the resin.


Between each of the last 3 polishing steps, the specimen should be washed twice with DI water and detergent using a lint-free cloth before being rinsed with isopropanol and


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Figure 4 : Shows sequential frames from a high-speed AFM of a steel sample that has been incorrectly prepared for AFM imaging. Scratch marks due to partial polishing running vertically are clearly visible, as is surface contamination. Organic material, present as a fi lm in (a) is collected up by the tip as it passes over the surface and is redistributed, infi lling sample topography and presenting itself as positive topological features. Frames (a)–(d) are taken at 0 s, 0.5 s, 1 s, and 5 s after moving to a new location on the sample at 2 frames per second. Organic material can be hard to spot in a single image, but when frames are combined to form a video or time lapse, the motion of the organic material due to contact with the probe is obvious. The organic material also adheres itself to the tip thus reducing the resolution of the image.


www.microscopy-today.com • 2016 May


Figure 3 : Topographic AFM map showing a well-polished sample. The streaking is generated by the movement of loose particles/resin-debris, resulting from ineffective specimen cleaning following the removal of the resin mount.


blow-dried using dry N 2 . T ese washes are important to avoid cross-contamination of the polishing pastes. Figure 1 shows a specimen with a poor initial polish (leaving large scratches), but more eff ective polishing at later stages revealed grain boundary precipitation.


Cleaning steps . Aſt er the fi nal step in the procedure, it is necessary to rinse the specimen thoroughly with de-ionised (DI) water and detergent. Many SPM applications require a small specimen size, and as such it may be necessary to remove


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