An international team of scientists working with the
Nanoscale Science and Engineering Center
has built new nanoscale structures from a self-assembling material, with potential applications ranging from catalysis and chemical separation to semiconductor manufacturing.
The team has discovered that materials known as block copolymers will spontaneously assemble into intricate 3-D shapes when deposited onto 2-D surface patterns created with photolithography. The result demonstrates that complex, 3-D nanostructures can be built by using existing semiconductor industry tools.
Lithography is already used to make devices with dimensions substantially smaller than 100 nanometres, but photolithography is currently only applied as a two-dimensional process. The new process allows photolithography to be used in three dimensions, creating structures completely different from the original block copolymer materials.
The team has produced structures consisting of tightly interwoven, yet completely independent, networks of channels and passages on an atomic scale. The networks register with the photolithographic pattern underneath, letting scientists know exactly where each channel ends and giving them access to channel openings.
An example application might be to introduce a gas through the openings to react with a catalyst deposited on the walls of the network, taking advantage of the fact that nanoscale materials have massive surface areas compared to their volumes, making catalysis very efficient. The process could also be used to create a membrane to filter chemicals at a molecular level.
The research examines specific block copolymers consisting of long chains of two different types of molecules, which alternate with each other in blocks. At high temperatures, block copolymers are molten and randomly mixed. But when cooled down, the material spontaneously assembles into alternating layers of molecules. The advantage of using self-assembling materials to create structures rather than traditional semiconductor technology is that they provide much more precise control over the dimensions and shapes of features as small as 10 nanometres.
The team employed a lithographic surface with a square array of dots on which to deposit the block copolymer film, rather than the naturally layered or striped structure of bulk block copolymers.