PFM, also called piezoelectric force microscopy, has successfully demonstrated the capability of imaging ferroelectric domains and characterizing ferroelectric surfaces on nanometer levels. In PFM measurements, the piezoelectric response, under voltage modulation, is detected as a vibration of the PFM cantilever with a conducting tip in

direct contact with the surface of the film. These vibrations arise due to the converse piezoelectric effect and hence depend on the orientation of the polarization vector. The amplitude of the acquired signal is proportional to the effective longitudinal piezoelectric coefficient. In order to optimize the electromechanical performance of ferroelectric thin films, it is very important to understand the orientation dependence of the piezoelectric constant

read more in:

Study of orientation effect on nanoscale polarization in BaTiO3thin films

using piezoresponse force microscopy

APPLIED PHYSICS LETTERS 86, 192907 (2005)

Please find link below : 

http://pubs.acs.org/doi/abs/10.1021/nn503269b

Sorry for short answer before,

I joined a conference in Penn State IEE ISF 2014. A R&D engineer of Asylum research suggested to me to use AC55TS with 194 - 2.50 frequency and 68-184 N/m stiffness. although the tip has no metal coating it is highly conductive due to high doping concentration. 

In order to eliminate electrostatic forces you need to use stiff tips. IF you you 2-3 N/m stiff tips you will measure only electrostatic effect. 

If this is expensive for you, i recommend you to make your own tip conductive. Buy a non-contact tip as i gave in the article. coat both sides with Pt and then Gold.  

Please find the link for detailed information : 

https://www.researchgate.net/publication/264865919_Spontaneous_High_Piezoelectricity_in_Poly_%28vinylidene_fluoride%29_Nanoribbons_Produced_by_Iterative_Thermal_Size_Reduction_Technique

Article Spontaneous High Piezoelectricity in Poly(vinylidene fluorid...