ABSTRACT
In this article, we explore methods that enable estimation of material properties with the dynamic mode atomic force microscopy suitable for soft matter investigation. The article presents the viewpoint of casting the system, comprising of a flexure probe interacting with the sample, as an equivalent cantilever system and compares a steady-state analysis based method with a recursive estimation technique for determining the parameters of the equivalent cantilever system in real time. The steady-state analysis of the equivalent cantilever model, which has been implicitly assumed in studies on material property determination, is validated analytically and experimentally. We show that the steady-state based technique yields results that quantitatively agree with the recursive method in the domain of its validity. The steady-state technique is considerably simpler to implement, however, slower compared to the recursive technique. The parameters of the equivalent system are utilized to interpret storage and dissipative properties of the sample. Finally, the article identifies key pitfalls that need to be avoided toward the quantitative estimation of material properties.
ABSTRACT
Contact Resonance Force Microscopy (CR-FM) is a leading atomic force microscopy technique for measuring viscoelastic nano-mechanical properties. Conventional piezo-excited CR-FM measurements have been limited to imaging in air, since the "forest of peaks" frequency response associated with acoustic excitation methods effectively masks the true cantilever resonance. Using photothermal excitation results in clean contact, resonance spectra that closely match the ideal frequency response of the cantilever, allowing unambiguous and simple resonance frequency and quality factor measurements in air and liquids alike. This extends the capabilities of CR-FM to biologically relevant and other soft samples in liquid environments. We demonstrate CR-FM in air and water on both stiff silicon/titanium samples and softer polystyrene-polyethylene-polypropylene polymer samples with the quantitative moduli having very good agreement between expected and measured values.
ABSTRACT
Piezoresponse force microscopy (PFM) has emerged as the tool of choice for characterizing piezoelectricity and ferroelectricity of low-dimensional nanostructures, yet quantitative analysis of such low-dimensional ferroelectrics is extremely challenging. In this communication, we report a dual frequency resonance tracking technique to probe nanocrystalline BiFeO(3) nanofibers with substantially enhanced piezoresponse sensitivity, while simultaneously determining its piezoelectric coefficient quantitatively and correlating quality factor mappings with dissipative domain switching processes. This technique can be applied to probe the piezoelectricity and ferroelectricity of a wide range of low-dimensional nanostructures or materials with extremely small piezoelectric effects.
