It was found that Langmuir-Blodgett (LB) deposition process led to the direct formation of ferroelectric 13 phase in poly(vinylidene fluoride) (PVDF) homopolymer ultra-thin films, in which the molecular chains were parallel to the substrates and the dipoles were aligned perpendicular to the substrates. Theoretical analysis and experimental results further showed that the mechanism of forming the beta phase and the dipole orientation were attributed to the hydrogen bonds formed between the PVDF molecules and water through the LB deposition. A large local effective piezoelectric coefficient (d(zz)) of -49.4 pm/V was observed in the self-polarized PVDF LB film. (C) 2012 Elsevier Ltd. All rights reserved.