Combining holographic patterning and block copolymer self-assembly to fabricate hierarchical volume gratings

Michael J. Birnkrant

doi:10.17918/etd-3134

The top-down nanomanufacturing technique is approaching its theoretic limits and processes such as e-beam lithography are extremely costly. In contrast, the bottomup method such as self-assembly can easily reach nanometer (even sub-nanometer) feature sizes. One drawback of self assembly, however, is the difficulty to achieve large scale, defect-free structures. Combining the top-down and bottom-up methods in one system can lead to novel hierarchical nanostructures with tailored properties and this approach is generally referred to as "top-down helps bottom-up." While most of the existing systems deal with (quasi) two-dimensional patterning, partly due to the demands from semiconductor industry, in this dissertation, we demonstrate that three-dimensional, dynamic tunable, optical volume gratings can be manufactured via combining holographic patterning (HP) and block copolymer (BCP) self-assembly into one system. A number of semicrystalline homopolymers and BCP have been successfully patterned into one-dimensional and two-dimensional optical structures. In the one-dimensional homopolymer case, a Bragg reflector structure with continuous alternating layers of patterned polymer and the crosslinked resin were formed. The result of combining HP and BCP was a hierarchical structure fabricated from a homogenous solution in one step. HP formed 200 nm periodic lamellar structures, confining a BCP to 100 nm domains. Subsequently, the BCP self-assembles into a lamellar structure with a period of 21 nm. This system provides an interesting basis for studying the thermo-optic behavior of the hierarchical volume grating formed by combining top-down manufacturing and bottom-up self-assembly. Upon heating and cooling a unique thermal switching occurred that can be attributed to the melting/phase separation that the BCP undergoes within the confined region of the volume grating. There are at least five advantages of this novel nanomanufacturing approach. First, two different nanomanufacturing techniques are seamlessly combined together and the resulting hierarchical structures span from a few nm to the 200 nm scale. Second, by combining these two techniques, the shortcomings of each method can be overcome. Third, this hierarchical structure can be fabricated in a few seconds. Fourth, the HP method enables the fabrication of a multiple layered structure, which is critical for three-dimensional nanodevice applications. Fifth, a variety of two-dimensional and three-dimensional nanostructures can be readily achieved by changing the HP laser set-up and BCP structures.

Combining holographic patterning and block copolymer self-assembly to fabricate hierarchical volume gratings

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Combining holographic patterning and block copolymer self-assembly to fabricate hierarchical volume gratings

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