Structural Study of Acetylene Thin Films Absorbed on Exfoliated Graphite (0001)

The structures of deuterated acetylene [C2D2] thin films adsorbed on the (0001) surfaces of exfoliated graphite have been investigated by elastic neutron diffusion. The aim of this study was to assess the structures of the condensed phases. Neutron diffraction spectra have been recorded at temperature ranging from 10K to 141K and for coverages corresponding to the monolayer completion 0.7 layer ? ? ? 1.23 layers. Two bidimensional solid phases S1 and S2 have been identified. Their structures present commensurability with the (0001) graphite surface. At an intermediate coverage (? = 1.0 layer) there is coexistence of the two solid phases. The evolution of the recorded spectra with the temperature suggests the fusion of the S1 solid to occur at Tm(S1) = 135 ?1K. The fusion of S2 solid happened at higher temperature: Tm(S2) greater than Tm(S1).