Rare earth thin films

M. Gasgnier, The intricate world of rare earth thin films metals, alloys, intermetallics, chemical compounds,... 105... 

The oxidation of rare earth thin films gives large thin crystals of sesquioxides (except for Ce and Eu for which one can obtain Ce02 and EuO and for Pr and Tb which can give nonstoichiometric oxides). The diameter of these crystals is several jum, their thicknes is about 500 A. The surfaces are parallel to (00.1) for A crystals and to (201) for B crystals. Some other orientations can be observed, but only for thick crystals (more than 1000 A). This orientation cannot be related to the metal thin film made up of micro-crystals without any special orientation. This result shows that the surface energy is much lower when the surface is parallel to the (00.1) and (20T) planes than for any other orientation. They are parallel, in each case, to the (RO)J slabs, so that the observed orientation for the thin crystals reinforces the hypothesis of Caro (1968) concerning the existence of these slabs. 

There have been several papers which have appeared in the last five years concerning unusual lattice parameters and crystal structures in thin films of the rare earth metals. It is believed that these results are for highly contaminated metal which results from the high reactivity of the metallic rare earth thin films with residual gaseous impurities in the high vacuums [ 10" Torr (10 Pa)], Boulesteix et al. (1970b) and Gasgnier et al. (1974) have shown many of these structures to be impurity induced. 

THE INTRICATE WORLD OF RARE EARTH THIN FILMS Metals, Alloys, Intermetallics, Chemical compounds,... 

THE INTRICATE WORLD OF RARE EARTH THIN FILMS... 

From mass spectrometry studies Curzon (1984) reports that the reduction of CO, inside the vacuum chamber, leads to the formation of CH4 (and consequently of CH3, CH2 and CH). The results indicate that the CH4 (and also H2) arises from the reduction of the CO (and also H2O, which reacts with CO). That is another way to explain the formation of hydrides with rare earth thin films. The adsorption of CsHg, C2H2 and CH4 on clean polycrystalline Dy films at 295 K has been studied by Cemy and Smutek (1990). The experiments suggest that at low doses, the gases are completely dissociated into C and H atoms. The bonding of these atoms to Dy is assumed to be equivalent to that which... 

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