Volume imaging of an ultrathin SBS triblock copolymer film

We use scanning force microscopy and stepwise erosion in a radio-frequency (rf) plasma to obtain a three-dimensional volume image of an ultrathin poly (styrene-b-butadiene-b-styrene) triblock copolymer film. The free surface o f the film exhibits domains of two distinctly different structures, i.e., h exagonal arrays of isolated dots and parallel stripes. A common forehand in terpretation relates these surface morphologies to a cylindrical microdomai n morphology with the cylinders oriented perpendicularly and parallel to th e plane of the film, respectively. In contrast, our experiments show that t he "dots" merge into parallel cylinders at some distance underneath the fil m surface. These results demonstrate that care has to be taken when the thi n film morphology of block copolymers is inferred from their surface struct ure.