MICROROUGHNESS OF POLYMER THIN-FILMS STUDIED BY TOTAL-REFLECTION X-RAY-FLUORESCENCE AND ATOMIC-FORCE MICROSCOPY

The surface roughness of polymer thin films supported on nickel-coated silicon substrates was analyzed by angle-dependent total-reflection x -ray fluorescence (TXRF) in conjunction with atomic force microscopy ( AFM). For highly rubbed polystyrene (PS) surfaces (500 cm rubbing leng th at a load of 2 g/cm(2) over a velour cloth) displaying sharp groove s and ridges, the TXRF showed no significant change while the AFM resu lts revealed an anisotropic 6.08 nm root-mean-square roughness with an average peak-to-peak distance of 170 nm. These results were compared to the isotropic, gradually varying sinusoidal surface roughness of ph ase-separated polystyrene/poly(vinyl methyl ether) blend thin films. T he AFM results were very similar to the results from the rubbed PS in terms of root-mean-square roughness and average peak-to-peak distance; however, the TXRF results revealed enhanced nickel fluorescence at in cident angles smaller than the polymer critical angle for reflection. This discrepancy highlights some of the qualitative differences in sur face topography between rubbed and phase-separated polymer thin films, and demonstrates the utility-of angle-dependent TXRF to study thin fi lm roughness and planarity.