TlBiSe2 epitaxial thin films were grown on NaCl substrates by electron beam evaporation under different growth conditions. The as-grown films were characterised by infrared reflectance measurements and transmission electron microscopy observations. It is determined that the interfacial region of such films under certain supersaturation conditions presents a new fee cubic phase sub-layer which grows with the substrate lattice parameter to a considerable thickness. The occurrence of this phase has a dependence on the deposition rate which is evident particularly when low substrate temperatures are employed in the growth process. A plausible explanation is offered for the observed cubic phase in terms of a pressure induced structural modification. Finally, it is shown that the complimentary nature of the two methods allows a complete structural and electrical characterisation of thin film structures.