Sign inversion of the spontaneous polarization in ferroelectric liquid crystals: a thickness dependence study in freely suspended filmsCh. Bahr, C. J. Booth, D. Fliegner and J. W. GoodbyEurophys. Lett., 34 7 (1996) 507-512DOI: https://doi.org/10.1209/epl/i1996-00487-7