Abstract
The interaction energy, phonon spectrum, and longitudinal and transverse sound velocity of a two-dimensional (2D) Wigner crystal are calculated within the harmonic approximation for different values of the thickness of the underlying helium film and for different types of substrates which support the He film. The phase diagram for Wigner crystallization is analyzed in terms of the Kosterlitz-Thouless-Halperin-Nelson theory of 2D melting.