Reflectivity from free surface showing

This smectic ordering is experimentally observed at the nematic-solid and nematic-air interfaces. X-ray reflectivity measurements showed the existence of the smectic order at the free surface of 80CB (l.xv) both in the nematic and the isotropic phase [14]. Other nematic compounds also exhibit smectic ordering at the free surface [15]. However, the free surface seems not to be favorable for the formation of polar layers. As usual, in polar compounds like 8CB (l.iii), bilayers are formed at the surface, probably due to the favorable orientation of the alkyl chains outward from the liquid crystal. In such a case, polar heads form dimers much easier [16]. 

Figure 2 shows the brief principle of a laser-detected FFM. A sample is put on a piezoelectrical tube (PZT), which scans X, Y plane and controls the feedback of Z axis. The laser beam from a diode is focused on the mirror of the free end of a cantilever with lens, and the reflected beam falls on the center of a position-sensitive detector (PSD), a four-quadrant photodiode. When the sample contacts with the tip and relatively moves under the control of a computer, the reflected beam deflects and changes the position on the PSD due to the twist and deflection of the cantilever caused by the changes of surface roughness, friction force, and adhesive force between the sample and the tip. The extension and re-... 

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