If you decide to work in liquid environment with your atomic force microscope, you will need some adjustment. First, you will change the position of your camera to see your cantilever in liquid since you know Snell's Law. It is like nightmare! It's too hard to adjust it to find a hundred micrometer cantilever. Second, in liquid environment, the resonance frequency of your cantilever will decrease and some of them will not work such as your favourite cantilever you use in air. Third, if you use diether piezo excitation, maybe your piezo will be small to work in liquid. Or if you use photothermal excitation, maybe the power of your laser will not be enough. You will try to find solutions however %95 will not work. You will feel your stress in your blood in this time interval. However, trust me, when you see a peak in liquid environment for the first time, you will feel like you have won the war!
The most important problem in this stage was my PS3 lasers. Although there is no excessive amount of heat and output voltage is not high and also I wear anti static grounding strap, PS3 excitation laser broke down itself every day. Since it is happening every day, we thought that the problem could be the driver circuit. By using oscilloscope we monitored output voltage and saw that output is changing continuously. The problem was excessive amount of heat on op-amp. We need to spread out heat and by adding suitable cooler we did it.
Since focusing your lasers in liquid is a bit harder, you need find a solution. Actually, focusing the detection laser is easy, its focus is changing a little since the angle between incidence laser and interface is 90 degree. However, focusing excitation laser is not due to its angle. In the picture, you see our flipped AFM head to focusing it easily by reflecting lasers on papers.
We tried long cantilevers however we could not see any reasonable oscillation peak and also nice graph due to their low resonance frequency. Secondly, by using short cantilever, since their resonance frequency is about 4 times higher than longer one, we caught nice graph in liquid environment.
In graph, oscillation amplitude is 0.11V and center frequency is about 163 kHz while Ft=2.314V, Fn=-0.023V and Fl=-0.005V. We have roughly 32.5 kHz FWHM value.