IRG-II Nugget
Bottom-up meets top-down
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.
