Recent Advances in Unconventional Lithography for Challenging 3D Hierarchical Structures and Their Applications

Figure 4

Integrated assembly with merged top-down with bottom-up approaches. (a) Schematic illustration of procedure for template-assisted self-assembly of spherical colloids (top left). Optical images show the assembly of various PS beads in an array of cylindrical holes (3.1 μm PS beads in cylindrical holes 5 μm in diameter, top right; 2.5 μm PS beads in cylindrical holes 5 μm in diameter, top right; and 2.5 μm PS beads in cylindrical holes 6 μm in diameter, bottom right). The inset illustration indicates assembled structures (the diameter () of holes and the diameter () of spherical colloids). Reproduced with permission from [109]. Copyright 2003 WILEY-VCH Verlag GmbH & Co. KGaA. (b) Schematic illustration of procedure for fabricating free-standing three-dimensional inverse opal (3D-IO) structure of polyurethane acrylate (PUA). (c) Cross-sectional (left) and top-view (right) SEM images of well-ordered 3D-IO structure of PUA. Reproduced with permission from [112]. Copyright 2012 American Chemical Society. (d) Schematic illustration of process for Sub-10 nm pattern transfer from self-assembled PS-b-PDMS with cylindrical patterns. Thermal nanoimprint induces the alignment of cylindrical BCP domains along the length direction of mold patterns. (e) SEM images showing the PDMS cylinders show no evidence of residual layer after plasma etching. The magnified SEM image shows the PDMS cylinders aligned along the long axis of the imprint grating. Reproduced with permission from [122]. Copyright 2011 American Chemical Society. (f) Schematic illustration of procedure for the sub-10 nm transfer printing of block copolymer self-assembly patterns. The inset SEM image shows the patterns after transfer printing on a bare Si substrate and treatment with oxidative plasma. Reproduced with permission from [123]. Copyright 2012 WILEY-VCH Verlag GmbH & Co. KGaA. (g) SEM (left) image shows the tip of a glass capillary nozzle coated with Au/Pd. Thermal annealing (220°C for 5 min) results in the self-assembled PS-b-PMMA BCPs on a substrate (right). (h) SEM image shows the self-assembled PS-b-PMMA BCPs with two different morphologies (lamellae form with MWs of 37-37 K, left; cylinder form with 46–21 K, right) printed as lines. (i) Schematic illustration of process for directed self-assembly of PS-b-PMMA BCPs printed onto topographically patterned substrate. (j) SEM images show the directed self-assembly of PS-b-PMMA BCPs with MWs of 37-37 K (left) and 25-26 K (right) in adjacent trenches (depth ~70 nm, width ~260 nm). Reproduced with permission from [124]. Copyright 2013 Macmillan Publishers Ltd.

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