Physics of Block Copolymers in Thin Films

A block copolymer in a confined environment exhibits certain properties that can be characterized as thin film behavior. This behavior is primarily dictated by the enhanced role of surface/interfacial energetics, as well as by the interplay between the characteristic block copolymer spacings and the film thickness. 

Preferential attraction of one of the blocks to the surface brakes the symmetry of the structure and results in layering of microdomains parallel to the surface plane through the entire film thickness. The energetically favored film thicknesses are then quantinized with the characteristic structure period in the bulk through the formation of surface relief structures, also called terrace formation. These structures were established initially for lamella systems [37-39] and later for cylinder- [40-43] and sphere-forming block copolymers. 

Experimentally, nucleation and subsequent growth of surface relief structures have been investigated as a function of surface fields [44 16], molecular architecture [37], film thickness [39, 47, 48], and annealing conditions [37 10, 49], A more detailed summary of the experimental studies can be found in recent reviews [15, 19, 50, 51] theoretical work on this issue is summarized in [41,42], 

The spontaneous development of the macroscopic topographic features in spin-coated samples, or in samples prepared by a gradient combinatorial approach [52,53], has been fruitfully used for the analysis of thickness-dependent morphological behavior by constructing phase diagrams of surface structures [43,49, 53, 54], 

An interesting, but little-exploited, strategy is to use a regular thickness gradient created by patterned substrates in order to achieve complex sequenced microphase-separated structures within macroscopic topographic patterns [55, 56], 

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