Surface anchoring of bi-functional organic linkers on piezoelectric BiFeO3 films and particles: Comparison between carboxylic and phosphonic tethering groups

The functionalization of piezoelectric/ferroelectric bismuth ferrite (BiFeO3, BFO) films and particles with bi-functional organic monolayers is reported. BFO films, grown by MOCVD adopting a bi-metallic mixed source, and BFO particles, synthetized by a sol-gel route, were functionalized either with the benzene-1,4-dicarboxylic acid (BDC) or with the phosphonobenzoic acid (PBA). The proposed functionalization route is based on an activation step of the BFO surface followed by the treatment with a BDC or PBA solution. The structural and morphological characterizations of functionalized BFO samples were carried out using X-ray diffraction (XRD) and field-emission scanning electron microscopy (FE-SEM). The chemical composition and the anchoring mode of the grafted monolayers were investigated by X-ray photoelectron spectroscopy (XPS) and FT-IR. Comparison of XPS and FT-IR results, obtained from BDC and PBA functionalized surfaces, gave indications on the role of the nature of the anchoring group in the functionalization process. Finally, piezoresponse force microscopy (PFM) and PFM spectroscopy studies demonstrated that the ferroelectric properties of the material are retained after the functionalization.