Selective deuteration combined with X-ray and neutron reflectivity has been used to determine the extent of probe segregation to an interface in ultra-thin polymer films as a function of the number of thermal cycles. The extent of probe segregation to the interface was also investigated using Secondary Ion Mass Spectroscopy (SIMS). Significant probe segregation was not evident in these studies. X-ray reflectivity has also been employed to measure the coefficient of thermal expansion of ultra-thin polystyrene films supported on quartz. The glass transition temperature determined with this method is equivalent to that measured for bulk polystyrene films.