Monitoring Elasticity Using Tuning Fork Feedback

 AFM topography/Elasticity imaging of polymer hydrogel pattern on Silicon substrate

Height-Topographic	Amplitude-Elasticity	Phase- Error
Height-Topographic 3D	Amplitude-Elasticity 3D	Phase- Error 3D

Tuning forks have very high Q factors which correspond to a very sharp frequency spectrum allowing phase feedback to be employed to monitor topographic alterations.  Thus, the amplitude of the oscillation of the cantilever, which is not the feedback signal in this methodology as is the case in beam bounce technology, can now be used as a separate and independent channel to monitor the energy dissipation of the cantilever as a function of material elasticity.  In addition, tuning fork feedback does not exhibit jump to contact and adhesion ringing and therefore elasticity and adhesion with the tuning fork feedback is the best monitor of such material properties.

The following line profiles (correspond to marked lines above) show the polymer elasticity compared to silicon surface (Middle) where the Amplitude at the polymer area is 150 mV compared to 25 mV for the silicon area. The profile at the bottom plot shows the same value of Phase signal at both polymers and silicon regions which corresponds to the Error signal used for feedback of 250 mV. Top plot shows the correlated topographic Height profile.

WSxM software has been used for image processing of the pictures above: I. Horcas et al. Rev. Sci. Instrum. 78, 013705 (2007)