  Twist grain boundary (TGB) phases represent liquid crystalline systems with a
regular array of defects. In our research, we studied a compound with a stable
TGBC phase and established its structure by various experimental techniques. We
observed the surface of the smectic film by AFM microscope and detected a
periodic relief. We found that the displacement amplitude is few nanometers
with the periodicity about 500 nm. Such periodicity is in accordance with the
periodicity of the TGBC blocks rotation estimated by polarizing microscopy. The
surface modulation is explained by the deformation of TGBC structure, which is
created on TGBC films. A simplified model interpreting the observed smectic
surface displacement to occur as a consequence of rotating TGBC blocks inside
the sample is proposed. TGBC blocks deform differently depending on their
orientation with respect to the force acting by the tip of AFM microscope
cantilever probing the smectic surface.
