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Vapor Deposition Strategies for Tuning Surface and Interface Chemistry for Optoelectronics and Biosensors

Ordered assemblies of molecular semiconductors have been of particular interest for their integral role in organic optoelectronics, originating from interesting optical and charge transport properties. Compared with disordered films, organized nanostructured organic semiconductors display enhanced optoelectronic characteristics. However, past studies using template layer and self-assembly strategies are not applicable to molecular heterointerfaces and cannot be practically integrated into existing device fabrication routines to achieve large-area optoelectronic devices. This dissertation demonstrates unprecedented strategies to create one-dimensional (1D) nanostructures of molecular semiconductors using vapor deposition techniques. We begin this work by investigating how the interplay between dipole-dipole and van der Waals interactions competes to direct the assembly of molecular semiconductors in Chapter 2. Four small molecules consist of anisotropic, non-planar structures with large dipole moments are examined, and we establish robust algorithms to control their molecular self-assembly via physical vapor deposition (PVD). We study the kinetics of self-assembly for these molecules and create diverse 1D morphologies by varying PVD growth parameters. In Chapter 3, an ultrathin seed layer of the compound coronene is incorporated to create 1D nanostructures of an electron-transporting molecule (Dp-IFD), which has a strong propensity to form disordered films in the absence of the seed layer. This seed layer strategy can generate uniform nanostructures over large areas at low processing temperatures. Notably, the coronene seed layer creates Dp-IFD nanostructures when applied over either oxide or organic layers, meaning that this approach can be inserted into existing diode manufacturing algorithm to realize large-area flexible optoelectronic devices. In Chapter 4, we further show that nanostructured Dp-IFD films exhibit enhanced optical and photonic properties, including photoluminescence quantum yield and decay lifetimes. It is revealed that these enhanced optical properties are attributed to aggregation-induced delayed fluorescence process, which is beneficial for solid-state light emitting device applications. Lastly, we present a widely applicable strategy to develop robust solid-state biosensors using emergent nanobody recognition elements coupled with a vapor-deposited polymer encapsulation layer in Chapter 5. Photoinitiated chemical vapor deposition (piCVD) affords thin, protective polymer barrier layers over immobilized nanobody arrays that allow for retention of nanobody activity and specificity after storage under harsh conditions.
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