Electrical conductivity of carbon nanofiber reinforced resins: potentiality of Tunneling Atomic Force Microscopy (TUNA) technique

Epoxy nanocomposites able to meet pressing industrial requirements in the field of structural material have been developed and characterized. Tunneling Atomic Force Microscopy (TUNA), which is able to detect ultra-low currents ranging from 80 fA to 120 pA, was used to correlate the local topography with electrical properties of tetraglycidyl methylene dianiline (TGMDA) epoxy nanocomposites at low concentration of carbon nanofibers (CNFs) ranging from 0.05% up to 2% by wt. The results show the unique capability of TUNA technique in identifying conductive pathways in CNF/resins even without modifying the morphology with usual treatments employed to create electrical contacts to the ground

Piezo-generated charge mapping revealed through Direct Piezoelectric Force Microscopy

While piezoelectrics and ferroelectrics are playing a key role in many everyday applications, there are still a number of open questions related to the physics of those materials. In order to foster the understanding of piezoelectrics and ferroelectric and pave the way to future applications, the nanoscale characterization of these materials is essential. In this light, we have developed a novel AFM based mode that obtains a direct quantitative analysis of the piezoelectric coefficient d33. This nanoscale tool is capable of detecting and reveal piezo-charge generation through the direct piezoelectric effect at the surface of the piezoelectric and ferroelectric materials. We report the first nanoscale images of the charge generated in a thick single crystal of Periodically Poled Lithium Niobate (PPLN) and a Bismuth Ferrite (BiFO3) thin film by applying a force and recording the current produced by the materials. The quantification of both d33 coefficients for PPLN and BFO are 13 +- 2 pC/N and 46 +- 7 pC/N respectively, in agreement with the values reported in the literature. This new mode can operate simultaneously with PFM mode providing a powerful tool for the electromechanical and piezo-charge generation characterization of ferroelectric and piezoelectric materials

Imaging Ferroelectric Domains via Charge Gradient Microscopy Enhanced by Principal Component Analysis

Local domain structures of ferroelectrics have been studied extensively using various modes of scanning probes at the nanoscale, including piezoresponse force microscopy (PFM) and Kelvin probe force microscopy (KPFM), though none of these techniques measure the polarization directly, and the fast formation kinetics of domains and screening charges cannot be captured by these quasi-static measurements. In this study, we used charge gradient microscopy (CGM) to image ferroelectric domains of lithium niobate based on current measured during fast scanning, and applied principal component analysis (PCA) to enhance the signal-to-noise ratio of noisy raw data. We found that the CGM signal increases linearly with the scan speed while decreases with the temperature under power-law, consistent with proposed imaging mechanisms of scraping and refilling of surface charges within domains, and polarization change across domain wall. We then, based on CGM mappings, estimated the spontaneous polarization and the density of surface charges with order of magnitude agreement with literature data. The study demonstrates that PCA is a powerful method in imaging analysis of scanning probe microscopy (SPM), with which quantitative analysis of noisy raw data becomes possible