X-ray determination of the mean-square vibrational amplitudes of atoms in nearly perfect CdS crystals : C. Boochi and C. Ghezzi, Laboratorio MASPEC del C.N.R. Parma, Italy

Abstract

Layers of MoSe2, MoS2, MoO3 and WS2, WO3 on glass substrates have been obtained from MoTe2 and WSe2 films respectively. First, textured MoTe2 and WSe2 films were prepared by annealing under chalcogen pressure of constituents in thin film form. Then they were annealed under Se, S or O pressure in order to obtain the desired new compound. The annealing conditions were optimized for each compound by checking the texture of the films with an X-ray diffractometer.It was found that textured layers of MoSe2, MoS2, MoO3 and WS2 can be obtained while the crystallites of WO3 films were randomly oriented.A number of proposals are advanced to understand how textured films can be obtained in such a way: •— One of the elements of the compound should have a very small pressure vapour at the working temperature.•— The free enthalpy of the new compound should be more negative than that of the initial product.•— The ionic radius of the substituent should be smaller than that of the substituted atom.•— To obtain textured film, the lattice constants of the final compound should not be too different from those of the initial one.The first optical results obtained for MoSe2 layers are very promising.