Introduction
It is often advantageous to scan a sample in an AFM with the sample submerged in a liquid. Liquid cell offer a simple alternative for scanning under liquids with an AFM. Liquid cell, illustrated in Figure 1, is very easy to use. Figure 2 shows the light path for a liquid cell when used in a conventional light lever AFM.
 |
Figure 2: Light path in an AFM for a liquid call with the probe submerged in a liquid. The light blue lines designate the "meniscus" formed by the liquid that is trapped between the sample and chip. The probe, shown in black, is mounted on a metal spacer attached to glass chip. |
The probes were mounted directly on metal substrates and held magnetically in the Nano-RT atomic force microscope. As shown in Figure 3, a drop of liquid is placed directly on the sample being imaged. After laser alignment, it is very simple to go into tip approach and scan the sample.
 |
Figure 3: Liquid cell positioned above the liquid drop that is on the surface that will be imaged. |
In order to test the concept of using liquid cell for AFM scanning a high impact polysteryne sample was scanned. Figure 4 show the AFM image of the sample with no liquid on the surface.
Figure 4:Topography scans in air of the high impact polysteryne
After scanning the sample in air, a drop of water was placed on the sample and an AFM scan was made of the high impact polysteryne surface in liquid. The AFM scan in liquid is shown in Figure 5.
Figure 5:Topography scans in liquid of the high impact polysteryne
Initially scanning tunneling microscopes were used routinely to scan in liquids, and as Marti et. al. pointed out in their publication1; "The STMs may be operated under water and aqueous solutions, and there is no fundamental difficulty in adding the spring and tip for an AFM."
This study shows that in fact there is no fundamental difficulty in adding the spring and a tip to do AFM studies with the sample submerged in a liquid; especially with the liquid cell probes.
