Examples of AFM applications in liquid environment

Important advantage of atomic force microscopy (also tunneling microscopy) is the ability to work in different environments (vacuum, controlled atmosphere, liquid environment). The last one, open interesting possibilities, such as imaging of delicate biological materials in their natural state. The use of electrochemical mode allows for the modification of surface properties in situ by changing the electrode potential. According to literature [1] about 40 % of current atomic force microscopy (AFM) research is performed in liquids, making liquid-based AFM a rapidly growing and branch of modern probe microscopy. However, measurement using AFM in a liquids involves several problems specific to the working environment. The presence of an additional liquid/air surface significantly changes the path of the laser beam. This introduces the need to calibrate the position of the laser spot after immersing the probe in the solution. Moreover, the solution of the lever movement equation suggests the existence of several modes of oscillations and different resonant frequencies. In the case of oscillations in liquids, their amplitude is smaller, additionally the frequencies are shifted. The worst, however, is the fact that there are a lot of new resonance peaks, resulting for example from the excitation of acoustic waves by the vibrating lever. The peaks on the frequency response do not have to correspond to the lever oscillations. Above mentioned issues are the reason for need for careful preparation of AFM experiment in liquid. The results contained in this set presents images of steel surface scanned at different frequencies and probes along with respective resonance curves. Collection contains 6 images and 4 resonance curves.
[1]       B.W. Hoogenboom, AFM in Liquids BT  - Encyclopedia of Nanotechnology, in: B. Bhushan (Ed.), Springer Netherlands, Dordrecht, 2012: pp. 83–89. doi:10.1007/978-90-481-9751-4_108.