THE EFFECT OF HYDROGEN DILUTION ON THE STRUCTURE OF A-C-H

Two a-C:H samples were prepared using a fast-atom deposition system fr om acetylene and an acetylene/hydrogen gas mixture. Their structure wa s investigated using neutron and x-ny diffraction and infrared spectro scopy measurements. Compositional analysis shows that a 1:1 C2H2:H-2 m ixture results in a change from a-C-77:H-23 to a-C-79:H-21, i.e. has a very small effect on the composition. The diffraction data also show that the addition of hydrogen to the precursor gas has no significant effect on the average bond distances and angles but shows a small chan ge in the H-C-H and C-C-H correlations between the two samples. Howeve r, the infrared data show that there are significant changes in the bo nding of hydrogen within the sample-changes which do not affect the av erage network structure. We observe a decrease in the amount of sp(3) CH2 and CH3 groups, and an increase in the fraction of sp(2) and sp(3) CH groups, with the formation of a second sp(2) CH bonding environmen t in the hydrogen-diluted sample. Therefore, in addition to providing useful structural information on these a-C:H samples, this set of expe riments illustrates very well the complementary nature of the data fro m diffraction and spectroscopic techniques.