General PurposeThe resolution in AFM depends on the shape of surface features, the mechanical properties of the sample, and its interaction with the tip. There are many of AFM applications where the size of the surface features to resolve is in the 10 - 150 nm range, thus not requiring tips with a radius smaller than 10 nm. Fig. 1 demonstrates clear resolution of large macromolecules along with submolecular features such as branches.
High resolution may not be attainable when imaging real-time processes such as molecular diffusion, crystallization, and wetting. This depends on the characteristic process rates in relation to the scanning rate and the distance between the scan sampling points. Moreover, sharp probes needed for high resolution imaging require special care in use, which leads to further reduction of the scanning speed. The 5 nm resolution offered by General Purpose tips may be a compromise in this case.
General Purpose probes are uncoated silicon tips that can be usually used in Contact, Noncontact or Tapping mode for imaging topography and mapping mechanical properties without significant limitations. Imaging of DNA is one of the examples of such applications (see Fig. 2).
General Purpose probes having tips with a radius of below 10 nm provide good-quality images for a broad variety of samples. The best resolution is achieved when scanning spherical particles that are hard and exhibit weak attraction to the tip. Note that the resolution of AFM images larger than 1µm by 1µm may be more determined by the density of sampling points ratio than the General Purpose tip radius.
General recommendations apply to the cantilever choice. Contact mode needs probes with small spring constant below 1 N/m, Non-contact mode requires high-frequency probes, while cantilevers with intermediate spring constant and resonance frequency are optimal for most samples in Tapping mode.
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HQ:CSC probes for contact mode
HQ:NSC probes with high resonance frequency and large spring constant
High contrast on hard samples
HQ:NSC probes with large spring constant
True topography imaging
HQ:NSC probes with medium spring constant
Samples of medium hardness
HQ:NSC probes with low spring constant