The adsorption stage of the Eu-Si(1 1 1) interface formation has been studied within a broad temperature range by thermal desorption spectroscopy (TDS), isothermal desorption spectroscopy (ITDS), low-energy electron diffraction (LEED), Auger electron spectroscopy (AES), and the contact potential difference (CPD) method. The adsorption and desorption kinetics of Eu atoms is investigated for the first time by the two former methods. It is established that the adsorbed layer consists of the single atoms (2D gas) at very low coverages (0 < 0.06). At higher coverages, the islands of the two-dimensional (2D) reconstructions form. Their structure depends on the amount of the metal deposited onto the surface. These islands are found to be very stable. The diffraction patterns corresponding to them are directly observed even at the temperatures at which the Eu atom evaporation occurs from a surface (1100 K and higher). The energies required to remove the isolated atoms of the 2D gas as well as the edge atoms of the islands into the vacuum have been measured. The latter quantity is shown to decrease in going to the high coverages, i.e. in the following sequence of 2D reconstructions: 3 x 2, 3 x 1, 5 x 1, 7 x 1, and 2 x 1. The dependencies of the work function on an adsorbate concentration are for the first time obtained. It is found that the heating of the Si crystal together with the Eu film adsorbed on its surface results in increasing the work function by the considerable value (in some cases, 0.85 eV).