RobustWhen the sample is relatively robust, i.e. hard and strongly adhering, this allows imaging without tip-induced deformation in a broad range of tip-sample interaction forces. One may choose using both soft cantilevers to obtain true surface topography and stiff cantilevers to ensure high topographic and phase contrast.
The harder the surface, the wider the choice of AFM techniques that can be used for its investigation. The contact mode technique is still the speediest and roughest among them.
When in tapping mode, "hard" tapping conditions are usually used to obtain good material sensitive contrast in phase imaging, while "light" tapping keeps the maximum of the topography data (see Fig. 1). "Light" tapping conditions imply lower free amplitudes and higher setpoint values.
When in liquid, one can use AFM cantilevers without back side coating or AFM probes with chemically inert Cr-Au coating.
The tip-sample interaction force depends on the adhesive properties of material, the sharpness of the AFM probe tip and the scanning mode. If the experimental conditions permit, one should avoid using stiff AFM cantilevers that may cause severe deformation and even damaging of the sample. Softer AFM cantilevers usually show better and more reproducible results. However, in some experiments, e.g. very hard and/or sticky samples, stiff AFM cantilevers are required. For unknown physical properties of the domains it is recommended using AFM probes of the HQ:NSC14 series that feature an intermediate spring constant of ~ 5 N/m.
Sharper AFM tips provide higher lateral resolution. This advantage should be balanced against the scanning speed.
For imaging in liquids, the choice of the AFM probe is usually limited to those having resonance frequency of 50 - 70 kHz in air (HQ:NSC18). It is generally recommended to use uncoated AFM cantilevers in liquids or AFM probes with l chemically stable Cr-Au coating.
Non-contact modeAFM cantilevers having high spring constant of 20 - 100 N/m and the highest possible resonance frequency are usually used in non-contact mode.
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AFM probes with stable reflective coating
In aggressive liquid media
AFM probes with chemically stable coating
Hard or sticky samples
HQ:NSC AFM probes with high spring constant
True topography, soft samples
HQ:NSC AFM probes with medium spring constant
Hi'Res-C AFM probes with medium spring constant