| Resumo: | This dissertation reports on the integration of cellulose nanocrystals (CNCs) as photonic films into optoelectronic devices, where the films’ inherent left-handed mesoporous chiral nematic structure acts as a circular polarized light (CPL) filter in the visible light range. The outcome demonstrates for the first time micro- scopic semiconducting devices based on cellulose, capable of producing specific electronic outputs when irradiated with either left- or right- handed CPL (LCPL and RCPL, respectively). For this proof-of-concept two distinct optoelectronic devices are targeted: a thin-film field-effect transistor and a thin-film photodiode, spanning the whole visible electromagnetic spectrum. The devices are jointly developed each one with a specific type of CNC, presenting photonic bandgaps that are tuned for the active layer of the devices. On the one hand, lab-produced (home-made CNCs – HM-CNCs) are synthesized through sulfuric acid hydrol- ysis, yielding HM-CNC films with a photonic bandgap in the blue/UV region. On the other hand, industrially produced Na neutralized spray-dried CNCs by CelluForce (C-CNCs) are studied on behalf of their redispersion in water to yield C-CNC films with a photonic bandgap in the green/red region. The work is essentially divided into three main parts: • Study of liquid crystalline and photonic properties of HM-CNCs and C- CNCs in aqueous suspensions (Chapter 3) • Implementation of HM-CNCs into field-effect transistors (Chapter 5) • Implementation of C-CNCs into thin-film photodiodes (Chapter 6) The main objective of Chapter 5 deals with the implementation of HM-CNCs films, optimized through the first Objective in Chapter 3, into field-effect tran- sistors based on amorphous indium-gallium-zinc-oxide (a-IGZO) as the semicon- ductor. In the resulting devices the HM-CNC films take simultaneously the role of the devices’ dielectric as a solid-state electrolyte and as a photonic filter for CPL. Consequently, this study encompasses two sub-objectives, connected firstly to the study of the electrochemical properties of these films and their success- ful integration into field-effect transistors without compromising self-assembly behavior. And secondly, successful proof of CPL sensing capabilities of these devices. The final study shows the incorporation of C-CNC films, into amorphous silicon-based thin-film photodiodes, achieving a light sensor capable of discrimi- nating between RCPL and LCPL. The spectral response of the fabricated photo- diodes is maximum for specific wavelengths in the green/red region. Irradiating the devices in these wavelengths they produce photocurrents that are over 50% distinct between RCPL and LCPL. Fast transient responses (on the order of ms) of CPL are shown with possible logic operations, as well as humidity sensing. Films produced through the methods described in Chapter 3 show promis- ing properties for their application in sensing, co-templating, enantioselectivity, photonic pigments or anti-counterfeiting. The insights presented in Section 5.1 contribute to applications in solid-state ionics of mesoporous structures or the combination of optically active electrolytes capable of providing unique func- tionalities in ion-gated transistors and circuitry. Finally, the types of devices pro- duced in Section 5.2 and Chapter 6 may find applications in photonics, emission, conversion, or sensing with CPL but also imaging, spintronics, optoelectronic counterfeiting or information processing with logic states that depend solely on the handedness of the incident light.
|
|---|