Energy dispersive X-ray reflectivity applied to the study of thermal stability of self-assembled organic multilayers: Results on phosphonic acids

The temperature evolution of self-assembled phosphonic acid multilayers was investigated by energy dispersive X-ray reflectivity and angular-resolved reflectivity. Energy dispersive measurements were performed in an experimental setup specially designed for the X-ray fluorescence beamline of the Brazilian Synchrotron Light Laboratory. It allows the precise monitoring of phase transitions observed in organic thin film and multilayer systems. The studied multilayers – obtained from dip coating of a solution of octadecylphosphonic acid – present different bilayer periodicities of 50 Å (straight bilayer) and 34 Å (tilted bilayer). Energy dispersive and angular-resolved data evidence re-organization of the lamellar ordering of octadecylphosphonic acid multilayers as a function of temperature. The energy dispersive technique presents many advantages over conventional methods such as short acquisition time, possibility to vary external parameters and high flux, making it suitable for light scatterers as polymers and other organic molecules.