How will it benefit my AFM imaging capability?
Our tests have shown considerable imaging improvement when tried on a number of different systems. In each case, we have optimised the imaging conditions as far as possible without ActivResonance Control, before turning on the ActivResonance Control to improve the imaging further.

Here are a few examples:

Gel samples are particularly difficult to image when swollen. To prevent the surface from drying out they need to be imaged under the swelling solvent. Due to their extreme softness they can easily be deformed even when imaging in dynamic mode.

In the following example a 30% isotactic polystyrene gel in dekalin has been imaged under dekalin with the quality factor of the cantilever enhanced by the ActivResonance Controller. The same area is then imaged without the ActivResonance Controller. From the comparison it is clear that the increase in the quality factor of the cantilever produces much better resolution in the image.

Image on the left, taken with an effective quality factor of 70, shows much finer details than the corresponding image using conventional dynamic mode on the right. The image on the right was fully optimised to enable a fair comparison (scale bar 1 micron).
Images courtesy of Jamie Hobbs and Andy Humphris, University of Bristol.

DNA is an extremely popular specimen for imaging by AFM. Operating in dynamic mode in fluid is often the best technique for studying biomolecules as it minimises lateral forces on the specimen.

The image on the left shows a typical image of entangled DNA molecules deposited on a mica surface. The image was taken using dynamic mode of operation in butanol, and is displayed with a colour table z-range of 3 nm. (Image size is 3 microns x 3 microns.)

By switching on the ActivResonance Controller and imaging the same area, the image on the right was obtained. Shown using exactly the same colour table and z-range, the DNA molecules (and the smaller contamination features) are lighter in colour, and therefore higher. Imaging using the ActivResonance Controller requires operation with far less force exterted on the sample - ideal for delicate or weakly adsorbed biological molecules such as DNA.
Images courtesy of Andy Round, University of Bristol.

Cells are considered to be very difficult to image by AFM - they are large, soft and difficult to keep alive. Using the ActivResonance Controller, the imaging force can be made as low as possible, enabling high quality imaging and helping to keep the cells happy!

The left image is an AFM topographic image of a living rat kidney cell, taken with an effective quality factor of 300. Image is 32 x 32 microns, with a z-range of 2.5 microns.

Right hand image is a simultaneous phase image, z-range 60 degrees.
Images courtesy Rachel Owen, University of Bristol

The quality factor controls the settle time of the probe, and therefore how long the probe takes to react to a change in interaction, for instance when moving over the surface. Thus a high quality factor gives improved force sensitivity but reduced scan speeds.

If the quality factor is very high it can be reduced, allowing faster scans, without having an adverse impact on force sensitivity. In SNOM, or NSOM, where shear-force feedback is used, this is a common problem, especially as scanning too fast, without good height control, can lead to topographic artefacts ruining the optical information, or even damaging the delicate probe.

Two shear force images of double-stranded DNA taken at the same scan speed. On the left, where the Q is 404, the true Q of the SNOM probe. On the right, the Q was reduced to 134. the reduced Q allows the surface to be tracked much more successfully - a similar image with the high Q took three times as long to collect. The inserts show the change in probe amplitude with time after the drive force has been switched off at the red arrow, i.e. the settle time of the probe.

Infinitesima's ActivResonance Controller now provides Q-control from 1 to 400 kHz, allowing the quality factor of cantilevers typically used for tapping in air to be modified. It is now possible to modify the Q of your probe to give consistent imaging, regardless of the individual probe or imaging conditions.

The figures below show the crystallisation of polymer spherulites at room temperature, in which the effective quality factor has been reduced from 270 to 90 (resonant frequency 272 kHz). This enables faster imaging of the sample but maintains good force sensitivity, particularly important when following a process such as crystallisation from the molten phase.

The topography image (unhovered) and corresponding phase image (hovered) of a 50 micron scan, tip velocity 403 microns/second.

The 1 micron phase image above, taken at a scan rate of 22 Hz, shows lamellar resolution of the growing spherulite.

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