The aim of this paper is to present a process of making ultra thin quasicrystalline coatings with free surfaces of the AlCuFe ternary alloy. These deposits, whose thickness ranges from 100 to 150 nm, were formed under ultra high vacuum by evaporation of the three metals heated by electron bombardment. We show the harmful influence of oxidising gases, mainly water vapour. whose oxygen could be trapped in the film during deposition and annealing. A process is proposed that guarantees the alloy's stoichiometry, without contamination in the deposit. in particular by oxygen, and thus achieves the quasicrystalline phase.