First-order wetting transition in CF4 solid films adsorbed on the (0001) graphite surface

2014 The configuration of CF4 films condensed on a graphite single crystal (0001) surface has been observed by reflection high energy electrons diffraction (RHEED) and by low energy electron diffraction (LEED). The films exhibit a first order incomplete to complete wetting transition at 37 K, a temperature far below the CF4 bulk triple point (89. 5 K). The structure of the film has been studied around the wetting temperature. The double layer structure is unstable against deposition of a third layer and loses its long range order. Upon further condensation the structure of the film is reorganized and gives well defined RHEED diffraction patterns featuring layer by layer condensation above 37 K and clustering below. LEED adsorption isotherms measured on graphite spots are used to characterize the secondand third-layer condensation between 51 and 58 K. The equilibrium vapour pressure vs. inverse temperature phase diagram is constructed from data obtained in this work and in the literature for 50 T 110 K and 5 10-8 p 50 torr. Finally, LEED kinetics adsorption measurements are also carried out between 15 and 45 K. The shapes of the recorded curves are discussed. J. Physique 45 (1984) 1497-1504 SEPTEMBRE 1984,