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Amorphous films of some μm in thickness, prepared by low temperature condensation in an ultra-high vacuum onto liquid helium cooled substrates, have been studied in situ by using an X-ray diffractometer operating in a symmetrical reflection mode. The structure factor of gallium has been obtained over the wavevector range 1.3 to 16.1 A − by means of two wavelengths, Cr Kα and Mo Kα , monochromatized by balanced filters. The average number of nearest neighbours deduced from the well-resolved first maximum in the radial distribution function is equal to 9.3 atoms. The results are compared to those previously found by electron diffraction measurements on thin films and also to the structure of supercooled liquid.

Les couches de gallium de plusieurs microns d’epaisseur deposees sur un support refroidi a environ 5 K ont une structure desordonnee. Nous montrons ici par ATD que la transformation de cet etat desordonne dans l'etal cristallin vers 15 K s’accompagne d’un degagement de chaleur comparable a celui libere lors de la cristallisation du liquide. Dans ces conditions, l’etat desordonne observe peut etre considere comme amorphe et non microcristallise.