DEVELOPMENT OF THERMALLY CONTROLLED LANGMUIR–SCHAEFER CONVERSION TECHNIQUES FOR SUB-10-NM HIERARCHICAL PATTERNING ACROSS MACROSCOPIC SURFACE AREAS
Creators: name: Hayes, Tyler R
Publisher: name: Purdue University Graduate School
Year: 2020
Subjects: Analytical chemistry not elsewhere classified

description: As hybrid 2D materials are incorporated into next-generation device designs, it becomes more and more pertinent that methods are being developed which can facilitate large-area structural control of noncovalent monolayers assembled at 2D material interfaces. Noncovalent functionalization is often leveraged to modulate the physical properties of the underlying 2D material without disrupting the extended electronic delocalization networks intrinsic to its basal plane. The bottom-up nanofabrication technique of self-assembly permits sub-10-nm chemical patterning with low operational costs and relatively simple experimental designs. The Claridge Group is interested in leveraging the unique chemical orthogonality intrinsic to the cellular membrane as a means of creating sub-10-nm hydrophilic-hydrophobic striped patterns across 2D material interfaces for applications ranging from interfacial wetting to large-area molecular templates to guide heterogeneous nanoparticle assembly. Using Langmuir–Schaefer conversion, standing phases of polymerizable amphiphiles at the air-water interfaces of a Langmuir trough are converted (through rotation) to lying-down phases on 2D material substrates. Using room temperature substrates, transfer of amphiphiles to a lowered substrate results in small domains and incomplete surface coverage. Recognizing that heating the substrate during the LS conversion process may lower the energy barriers to molecular reorientation, and promote better molecular domain assembly, we developed a thermally controlled heated transfer stage that can maintain the surface temperature of the substrate throughout the deposition process. We found that heating during transfer results in the assembly of domains with edge lengths routinely an order of magnitude larger than transfer using room temperature substrates that are more stable towards rigorous repeat washing cycles with both polar and nonpolar solvents. To promote the effectiveness of the LS conversion technique beyond academic environments for the noncovalent functionalization 2D material substrates for next-generation device designs, we designed and built a thermally controlled rotary stage to address the longstanding scaling demerit of LS conversion. First, we report the development of a flexible HOPG substrate film that can wrap around the perimeter of the heated disk and can be continuously cycled through the Langmuir film. We found that thermally controlled rotary (TCR) LS conversion can achieve nearly complete surface coverage at the slowest translation speed tested (0.14 mm/s). TCR–LS facilitates the assembly of domains nearly 10,000 μm<sup>2</sup> which were subsequently used as molecular templates to guide the assembly of ultranarrow AuNWs from solution in a non-heated rotary transfer step. Together, these findings provide the foundation for the use of roll-to-roll protocols to leverage LS conversion for noncovalent functionalization of 2D materials. A true roll-to-roll thermally controlled LS conversion system may prove to be advantageous and a cost-efficient process in applications that require large areas of functional surface, or benefit from long-range ordering within the functional film.