A process for preparing a thin layer made of ferroelectric material based on alkali metal, exhibiting a determined Curie temperature, transferred from a donor substrate to a carrier substrate by using a transfer technique including implanting light species into the donor substrate in order to produce an embrittlement plane, the thin layer having a first, free face and a second face that is arranged on the carrier substrate. The process comprises a first heat treatment of the transferred thin layer at a temperature higher than the Curie temperature, the thin layer exhibiting a multi-domain character upon completion of the first heat treatment, and introducing, after the first heat treatment, protons into the thin layer, followed by applying a second heat treatment of the thin layer at a temperature lower than the Curie temperature to generate an internal electric field that results in the thin layer being made single domain.