Sputter Coaters
Sputter Coaters: Carbon (C) and Platinum (Pt)
In scanning electron microscopy, analysis of the surface is performed on the signals generated from the material after interaction with the primary electron beam. If the impacting electrons cannot be conducted away from the point of impact at a fast enough rate, the surface builds up a net negative charge. This interferes with the primary electron beams’ interaction with the surface, compromising the analysis. This is typically seen in the sample “charging” and becoming very bright when imaging in secondary electron mode, or by the sample image moving/”drifting” when the sample is stationary when imaging in backscattered electron mode.
The principal method for overcoming charging issues, particularly for poorly electrically conducting materials or cross-sectional samples mounted in nonconducting polymers, is to apply a thin film of a conducting material via sputter coating. This thin film provides a path for the impacting electrons to be conducted away to the sample holder, while being thin enough to not negatively impact SE or BSE imaging at all but the highest magnifications.
The thin films are typically comprised of inert, high electrical conductivity metals such as gold, silver or platinum, or alternatively carbon.
CEMMS offers the option of either platinum (Pt) coating or carbon (C) coating.
Pt coating is suitable for general imaging purposes. It offers advantages in imaging low atomic mass biological samples because the high atomic mass Pt sputter coating generates a greater number of secondary electrons for imaging. However, it can be observed that high magnification using SE imaging and will be detected in the spectrum of EDS analysis samples. In addition, Pt coatings prevent the analysis of surfaces by EBSD due to the surface sensitivity of the technique.
Carbon sputter coating generates a thin, dense film of amorphous carbon. This is beneficial when EDS analysis is required since the carbon peak does not overlap those of higher atomic mass elements of interest. The thin, amorphous nature of the carbon sputter coating means that EBSD analysis can be performed on carbon coated surfaces.