Analysis of Order Formation in Block Copolymer Thin Films Using Resonant Soft X-ray Scattering

Abstract The lateral order of poly(styrene-block-isoprene) copolymer (PS-b-PI) thin films is characterized by the emerging technique of resonant soft X-ray scattering (RSOXS) at the carbon K edge and compared to ordering in bulk samples of the same materials measured using hard Xray small-angle scattering. We show using theory and experiment that the loss of scattering intensity expected with a decrease in sample volume can be overcome by tuning X-rays to the π* resonance of PS or PI. Using RSOXS, we study the microphase ordering of cylinder and sphere forming PS-b-PI thin films and compare these results to position space data obtained by atomic force microscopy. Our ability to examine large sample areas (~9000 µm 2 ) by RSOXS enables unambiguous identification of the lateral lattice structure in the thin films. In the case of the sphere forming copolymer thin film, where the spheres are hexagonally arranged, the average sphere-to-sphere spacing is between the bulk (body centered cubic) nearest neighbor and bulk unit cell spacings. In the case of the cylinder forming copolymer thin film, the cylinder-tocylinder spacing is within experimental error of that obtained in the bulk.