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Title:Mechanics driven architectures for flexible nanomaterial-based sensors
Author(s):Yong, Keong Han
Director of Research:Nam, SungWoo
Doctoral Committee Chair(s):Nam, SungWoo
Doctoral Committee Member(s):Lee, Tonghun; Li, Xiuling; Kim, Seok
Department / Program:Mechanical Sci & Engineering
Discipline:Mechanical Engineering
Degree Granting Institution:University of Illinois at Urbana-Champaign
Subject(s):flexible sensors
graphene patterning
direct transfer
subtraction manufacturing
crumpled graphene
strain sensor
graphene electrodes
field-effect transistor
wearable technology
nanoceramic oxide
high temperature
substrate engineering
Abstract:Enhancement in desired properties of next-generation flexible sensors requires continuous development in the processing of nanomaterials as well as the integration of ultrathin or soft substrates. Notably, nanomaterials offer exciting tunable physical, chemical and electrical properties that significantly surpass their bulk counterparts. As a result, they have captivated academic and industrial interests for use as electrical and thermal conductors, transparent electrodes, semiconductors, lights absorbers, condensation channels, etc. In this dissertation, I further explore the incorporation of unique mechanics-driven architectures such as strategic folds, creases, notches, and planar placement to engineer stress-induced mechanical changes as well as complementary functionalities conducive to dynamic working environments. First study presents a polymer-free approach to patterning graphene using a stencil mask and oxygen plasma reactive-ion etching, with a subsequent polymer-free direct transfer for flexible graphene devices. In conjunction with the recent evolution of additive and subtractive manufacturing, I adopt commercial laser cutter and laminator to achieve scalable and cost-effective graphene patterning and transfer evident by micro-sized graphene features of various shapes. In addition, the rapid prototyping capability of the developed technique is showcased by the fabrication of a stretchable, crumpled graphene strain sensor and patterned graphene condensation channels for potential applications in sensing and heat transfer, respectively. This post-synthesis manufacturing scheme promotes rapid, facile fabrication of cleaner graphene devices, and can be extended to other two-dimensional materials in the future. Inspired by the ancient art of paper cutting, the second study presents kirigami integrated architectures of graphene for strain-insensitive, surface-conformal stretchable multifunctional electrodes and sensors. Specifically, I demonstrate strain-insensitive electrical properties up to 240% applied tensile strain by implementing kirigami-inspired graphene electrode. Moreover, a multitude of kirigami designs are explored computationally to predict deformation morphologies under different strain conditions and to achieve controllable stretchability. Notably, strain-insensitive graphene field-effect transistor and photodetection under 130% stretching and 360° torsion are achieved by strategically redistributing stress concentrations away from the active sensing elements. The combination of ultra-thin form factor, conformity on skin, and breathable notches suggests the applicability of kirigami-inspired platform based on atomically-thin materials in a broader set of wearable technology. In the third study, I report a nanoceramic oxide based high temperature sensor with flexible attributes via substrate engineering. Correspondingly, I adopt the sol-gel synthesis process to ensure homogeneity and controlled particle size distribution, while the dispersion and wet-casting schemes to circumvent the need for post-process machining conducive to low cost production. The fabricated temperature sensors based on nanoceramic oxide not only demonstrate exceptional sensitivity over ~6 orders of magnitude in conductivity variance between room temperature and 1000 °C, but by integration on a flexible ceramic substrate, it demonstrates the potential to be further engineered by kirigami incisions for enhanced flexibility. Such approach to flexible high temperature detection addresses the needed resolution and mechanically robustness of high temperature detection at contorted space. This dissertation represents significant advancements of mechanics-driven architectures and platform fabrication schemes in the integration of nanomaterials to a more diverse set of flexible applications. The results herein offer unique strategies toward scalable and cost-effective stretchable sensors by the adoption of novel nanomaterials and substrate engineering.
Issue Date:2019-12-19
Rights Information:Copyright 2019 Keong Han Yong
Date Available in IDEALS:2020-08-27
Date Deposited:2020-05

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