Nanofabrication Etching Techniques for Advanced Energy Transport Materials

Abstract

Recent years have witnessed catastrophic environmental disasters and extreme global temperatures resulting from climate change. Greenhouse gas emissions are directly linked to such environmental impacts. Two of the largest sectors contributing to greenhouse gas emissions and energy use in the United States are the transportation and commercial & residential divisions. Therefore, the elimination of combustion engine vehicles as well as decreasing the use of building heating, ventilation, and air conditioning (HVAC) systems is essential for reducing carbon dioxide emissions and mitigating the impacts of climate change.Batteries for electric vehicles (EVs) currently lack fast charging capabilities comparable to fueling rates of combustion engine vehicles. Conventional battery electrodes are limited by a highly tortuous framework reducing Li ion diffusion preventing higher capacities. Low-temperature environments resulting in sluggish kinetics further reduces capacity. Hence, an investigation and adoption of optimized pore configurations are needed to advance energy density in EV batteries. Inspired by the natural vascular transport system, a microfabrication etching technique is developed to fabricate an optimized hierarchical channel configuration in porous electrodes to create fast-charging batteries with improved specific energy density, cell-life, safety, and performance in low-temperature environments. Machine learning and an artificial neural network are used to predict the optimal vascular structure of electrode porosities by inverse design. Personal thermoregulatory textiles reduce energy use of building HVAC systems by lowering the emissivity of personal fabrics thereby retaining human body heat. Metal nanowires are commonly used to reflect human body thermal radiation, yet their optical properties are limited by the geometrical dimensions of the nanowire and wire-mesh network. Guided by two established optical theorems, a flexible visibly transparent radiative shield is synthesized by a solution processing method achieving >75 % visible transmittance (wavelength, λ = 500 nm) and a low emissivity of 0.35 in the mid-infrared regime (λ = 8 – 13 μm). Furthermore, synthesis of long (<500 μm) and very thin (<30 nm) metal nanowires is challenging. Additionally, uniformly distributed nanowire spacings is difficult to achieve along with a single-layer mesh grid restricting visible transparency. To advance the optical properties of a silver nanowire (AgNW) network, a nanoimprinting fabrication technique is developed via sidewall lithography on a master mold. The new method produces a single-layer wire-mesh screen with AgNWs consisting of widths <50 nm and lengths >500 μm. Guided by the optical theoretical approach once again, a flexible visibly transparent radiative shield is synthesized. A polarizer is manufactured to demonstrate the value of nanoimprinting AgNWs for various applications. The extinction coefficient of the polarizer achieves a value of approximately 14 dB when λ = 25 μm.