The morphology of ABC triblock copolymers based on poly styrene-5/oc/s-polybutadiene-6/oc&polyfmethyl methacrylate) [PS-i-PB-6-PMMA] (SBM series) and their hydrogenated analogues polystyrene-6Zoc&-poly(ethylene-co-butylene)-6Zoc£-poly(methyl methacrylate) [PS-6-PEB-6-PMMA] (SEBM series) block copolymers is governed by the relatively weak incompatibility of the end blocks PS and PMMA in comparison to the strong incompatibility of the polybutadiene or poly(ethylene-co-butylene) midblock. The paper describes the morphologies of high molecular weight (Mn ~200 000) block copolymers, which are symmetrical with respect to the PS and the PMMA blocks with a varying elastomeric center block (0.06 < wei < 0.38). Besides an ABC lamellar morphology (11) (38 wt % PB or PEB), two other lamellar morphologies are observed for shorter elastomer chains: At 17 wt % of the elastomeric center block a "cylinder at the wall" morphology is observed where PB or PEB cylinders are located at the lamellar PS/PMMA interface (lc). At 6 wt % of elastomer, the polybutadiene forms spheres at the PS/PMMA interface ("ball at the wall") (Is). In this case hydrogenation of the butadiene block, which is associated with a further increase in the immiscibility to the end blocks, induces a change of the overall lamellar structure into a cylindrical morphology in which PS cylinders surrounded by PEB rings are dispersed in a PMMA matrix (cr). The transition from the lamellar (11) morphology to the (lc) and (Is) morphologies is described by a simple extension of the Meier/Alexander/de Gennes/Semenov theories of AB block copolymers in the strong segration limit to ABC block copolymers. The theoretical description predicts that morphological transitions can be achieved in ABC triblock copolymers at constant composition even in the limit of strong segregation.

Temperature-dependent Hall measurements have been performed on thin films of the ternary chalcopyrite CuGaSe 2 . Unintentionally doped samples and Na-containing samples are compared, as well as epitaxial and polycrystalline ones. Acceptor activation energies and acceptor and donor densities are extracted. Activation energies as well as defect densities vary over a wide range. We demonstrate that all samples are dominated by the same defect with an activation energy of 150 meV in the infinite-dilution limit. It is shown that the degree of compensation increases with increasing acceptor density. Thus direct evidence of self-compensation by intrinsic defects is given. CuGaSe 2 containing Na shows the same defects as CuGaSe 2 without Na: thus, it can be excluded that the dominant effect of Na is the introduction of a new acceptor. In addition, reduced compensation due to Na is not found; the net doping increases in spite of an increased compensation.

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