Role of substrate in melting behavior of Langmuir–Blodgett films

• The CdA LB films deposited on H and OH terminated Si surfaces have been investigated using X-ray reflectivity and in-plane EDXRD techniques.
• CdA-OH film is found to be more stable against temperature as compared to CdA-H film.
• The transition temperature from distorted hexagonal to hexatic like phase as well as melting temperature are lower in the case of CdA-H film.

Grazing incidence energy-dispersive X-ray diffraction (GID) studies of Langmuir–Blodgett (LB) films have been performed to study the role of substrate in controlling structural transformation in LB films. Thirteen monolayered LB film of cadmium arachidate (CdA) were deposited on two different chemically treated (OH and H terminated) Si(1 0 0) substrates. In both the CdA-H and CdA-OH LB multilayers, with increasing temperature the distorted hexagonal lattice structure transform to hexaticlike phase, followed by melting transition. However, there is a significant difference in the structural evolution of the two multilayers with temperature. In CdA-H multilayer the size of the coherent domains shows a continuous decrease right from the room temperature onwards while in CdA-OH multilayer it remain almost unchanged till 65 °C. In CdA-H multilayer both the transition to hexaticlike phase as well as melting transition take place at significantly lower temperatures as compared to CdA-OH multilayer. This difference can be attributed to possible higher level of defects and imperfections in the CdA-H multilayers, as a result of post-deposition configurational evolution.

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