Determination of the Glass Transition in Polymer Thin Films via Neutron Reflectometry


Darrin Pochan, Eric Lin, Wen-li Wu
Polymers Division
Materials Science and Engineering Laboratory Bldg. 224, Rm. B320
National Institute of Standards and Technology Gaithersburg, MD 20899

Measurements of the physical properties of materials at interfaces are very important in microelectronics packaging and interconnection, especially as electronics devices decrease in size and interfaces become a larger proportion of the device. In particular, polymers have recently been found to have different thermal expansion and glass transition properties when in the confined geometry of a thin film as opposed to the bulk state. These properties are further perturbed from the bulk values when adhesive interactions are present between the polymer film and the substrate. To deconvolute the effects of wall adhesion and chain confinement on the thermal properties of polymeric thin films, we have used neutron reflectometry to non-invasively probe the thermal expansion of polymer thin films between two non-attractive polymer confinement layers. The temperature dependence of the thickness of a deuterated polystyrene (d-PS) layer, which is confined between two polycarbonate layers, was measured to specifically examine the effect of confinement on the thermal expansion and glass transition of the d-PS. The initial thickness of the d-PS layer range from 30 nm - 900 nm. The results are compared to polystyrene bulk behavior and previous thin film experiments which included free surfaces as well as adhesive interactions between the layer of interest and substrate.