STABILITY OF CADMIUM ARACHIDATE LANGMUIR-BLODGETT MULTILAYERS AS DETERMINED BY NEUTRON AND X-RAY REFLECTIVITY

The thermal stability of Langmuir-Blodgett multilayers of cadmium arac hidate and perdeuterated cadmium arachidate layers deposited on hydrop hobic silicon is investigated by neutron and X-ray reflectometry. Usin g this pair of techniques allows one to depth resolve changes induced by annealing and also to discriminate between the behavior of the Cd h ead lattice and that of the aliphatic tails. All samples initially hav e ill-defined interfaces between the tails of adjoining protonated and deuterated layers, and some interchange of chains among layers occurs during the deposition process itself. The form of the multilayer stru cture is thermally stable at 70 and 84 degrees C, even though aliphati c tails are lost gradually due to ablation, leading to noticeable loss es when annealing for 1 week at 84 degrees C, These losses occur almos t exclusively from the layers closest to air, suggesting that the rate of ablation is considerably higher than that of interdiffusion. There appears to be little interlayer interdiffusion of chains when anneali ng for several hours at 84 degrees C. We conjecture that the type of i nteraction anchoring the two layers adjoining an interface may influen ce the stability of that interface to molecular exchange across it.