Fabrication of Nanoscale Oxide Textured Surfaces on Polymers

Nanoscale textured surfaces play an important role in creating antibacterial surfaces, broadband anti-reflective properties, and super-hydrophobicity in many technological systems. Creating nanoscale oxide textures on polymer substrates for applications such as ophthalmic lenses and flexible electronics imposes additional challenges over conventional nanofabrication processes since polymer substrates are typically temperature-sensitive and chemically reactive. In this study, we investigated and developed nanofabrication methodologies to create highly ordered oxide nanostructures on top of polymer substrates without any lithography process. We developed suitable block copolymer self-assembly, sequential infiltration synthesis (SIS), and reactive ion etching (RIE) for processes on polymer substrates. Importantly, to prevent damage to the temperature-sensitive polymer and polymer/oxide interface, we developed the process to be entirely performed at low temperatures, that is, below 80 °C, using a combination of UV crosslinking, solvent annealing, and modified SIS and RIE processes. In addition, we developed a substrate passivation process to overcome reactivity between the polymer substrate and the SIS precursors as well as a high precision RIE process to enable deep etching into the thermally insulated substrate. These methodologies widen the possibilities of nanofabrication on polymers.

Investigation of Microstructures and Air Permeability of Aerogel-Coated Textile Fabric Materials

This study focuses on fabrication of aerogel-coated macroporous polyester fabrics for the purposes of filtration of nanometric airborne particles and potential application in facemasks. Syndiotactic polystyrene (sPS) and polyimide (PI) gels that provide respectively majority macropores (diameter > 50 nm) and mesopores (diameter 2 to 50 nm) are coated onto woven polyester fabrics via a dip coating process. The resultant materials are supercritically dried to obtain aerogelcoated fabrics. The results show that sPS is more suitable for the dip coating process. However, evaporation of the solvent during handling of gel-coated fabrics leads to closure of the surface pores that are later recovered via solvent annealing. The resultant aerogel-coated fabrics offer high air permeability (∼10–10 m2) and high filtration efficiency (> 99.95%) of airborne sodium chloride test particles of size 25 to 150 nm.

Effect of Solvent Annealing on Optical Properties of Perovskite Dualfunctional Devices

Mixed-halide perovskite allows to realize conception of light-emitting solar cell (LESC) due to possibility to in-situ change device band structure by formation of dipole layer under applied voltage and intrinsic properties of perovskite ions. LESC has optimized perovskite-based solar cell (SC) architecture, but light-emitting diode (LED) regime performances is still low. Defect passivation can improve LED efficiencies due to reducing nonradiative recombination via defect levels. Solvent annealing allows to regulate film formation process and leads to better morphology and grain size for our application. Defect density is significantly reduced due to this passivation method. Here we demonstrate effect of annealing in vapors of dimethylformamide (DMF), dimethyl sulfoxide (DMSO) and acetonitrile (MeCN) atmosphere on LESC photovoltaic characteristic, electroluminescence (EL) peak wavelength and photoluminescence quantum yield (PLQY) of mixed-halide perovskite film.

Bending Behaviors and Directed Self-assembly of Rod-Coil Block Copolymers

The formation of zig-zags, chevrons, Y-junctions and line segments is demonstrated in thin films formed from cylindrical morphology Si-containing rod-coil diblock copolymers and triblock terpolymers under solvent annealing. Directed self-assembly of the block copolymers within trenches yields well-ordered cylindrical microdomains oriented either parallel or transverse to the sidewalls depending on the chemical functionalization of the sidewalls, and the location and structure of concentric bends in the cylinders is determined by the shape of the trenches. The innate etching contrast, the spontaneous sharp bends and junctions, and the range of demonstrated periodicity and line/space ratios make these conformationally asymmetric rod-coil polymers attractive for nanoscale pattern generation.