Research

Text Box: Stoykovich Research Group:  Self-assembly and nanofabrication laboratory

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Block copolymer self-assembly and directed self-assembly

Diblock copolymers (A-block-B or AB) spontaneously microphase separate and self-assemble into ordered lamellar, cylindrical, spherical, or network nanostructures with tunable dimensions from 5 to 50 nm.  Such self-assembling materials are attractive for nanofabrication because the nanostructures 1) are spontaneously assembled in dense, periodic arrangements with length scales below those accessible to conventional top-down fabrication processes, 2) have molecular-level control over the interfaces and surfaces, and 3) can be simultaneously generated over large areas.  Nanostructures of diblock copolymers in thin films have therefore attracted significant attention as a next generation lithographic technique, and have been demonstrated to be suitable masks for pattern transfer by etching or deposition and as templates for the synthesis of inorganic structures.  We are currently exploring:

Topology of two-dimensional block copolymer networks:  The lamellar morphology in thin films looks like a ’fingerprint’, as shown in the SEM image at the left.    The topology (i.e., connectivity and continuity) of the lamellar network is a function of the types of defects and defect density formed during self-assembly, and thus, as we have recently discovered, is a function of the composition of the copolymer system and the processing conditions.  Our current research considers how the topology of these two-dimensional networks in thin films impacts in-plane transport in devices fabricated with such patterns and the effects of structural confinement on the transport pathways. 

Selected Publications: 

1.  ACS Macro Letters, 2013, 2, 918-923 (PDF).

2. Macromolecules, 2012, 45(3), 1587-1594 (PDF).

Interfaces:  Polymer-polymer interfaces are often generated spontaneously through phase separation processes in copolymers or polymer blends, and dominate the structural, mechanical, optical, and transport properties of such systems.  These interfaces are relatively soft/flexible and therefore their shape is influenced by the interface bending rigidity, capillary waves, and thermal fluctuations.  We study the interfaces between lamellar block copolymer domains focusing upon their impact as line edge roughness (LER) in the resulting nanopatterns.

Selected Publications: 

1.  Macromolecules, 2010, 43, 2334-2342 (PDF).

3D structures through multilayer assembly:  We are developing systems for the ‘layer-by-layer’ self-assembly of block copolymers, where each ‘layer’ is 25~100 nm thick, to achieve nanostructured multilayer films.  The process involves initially self-assembling the block copolymer nanostructures in an individual layer and then locking-in the nanostructured morphology by cross-linking the polymer domains in response to thermal- or UV-stimuli to become more chemically, thermally, and mechanically robust.

Selected Publications: 

1.  Adv. Func. Mater., 2014, in press (PDF).

 

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