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Bottom-up meets top-down

Electron micrograph of spherical block copolymer nanodomain arrays

Electron micrograph of spherical block copolymer nanodomain arrays self- assembled on a silicon substrate that was patterned with sub-micron sized grooves by conventional top-down lithography. Each dot is about 25 nm in diameter.

Self-assembling materials are the basic building blocks for bottom-up nano fabrication processes, but many self-assembled nanostructures contain defects and lack sufficient long-range order for certain nanotechnology applications. For example, to create ultra-high density magnetic storage devices, a “perfect” array of nanostructures must be created to ensure that each individual domain can be addressed reliably. While a number of researchers have attempted to use block
copolymers as nanolithographic templates for high-density magnetic storage media, the inability to achieve perfect ordered arrays has hindered progress. Professors Mayes and Ross of the MIT MRSEC have developed a technique to create perfect arrays of block copolymer nanospheres that could be useful for fabricating addressable magnetic nanodot arrays, by marrying this bottom-up technique with more conventional top-down lithography approaches (Cheng et al., Nature Materials 3, 823-828, 2004). Block copolymer films were cast onto silicon substrates in which sub-micron sized grooves were created using top-down lithographic methods. Perfect ordered sphere arrays were formed in the grooves up to a critical groove width. Perfect ordering of the spheres was possible even in grooves created with periodic width undulations, demonstrating that defect-free bottom-up assembly could be achieved with a high tolerance for lithographical imperfections from the top-down steps.

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