Plasmonic Effect on Photophysical and Optoelectronic Applications

等離子體對光物理和光電應用的影響

Student thesis: Doctoral Thesis

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Award date23 Feb 2023

Abstract

In recent years, Frequency Selective Surface (FSS) based two-dimensional (2D) and three-dimensional (3D) carbon materials such as carbon nanofiber, carbon nanotubes, and carbon-filled filament are essential tools to design millimeter-wave radomes, absorbers, electromagnetic interference (EMI) shielding, and antennas reflectors in Gigahertz (GHz) regimes. Terahertz (THz) technologies are also developing in applications from medical imaging to security surveillance. In this work, a 3D microstructured FSS using carbon-based material polyimide as a precursor enhances the resonant frequency at the THz range. Furthermore, gold nanoparticles (AuNPs) are embedded on 3D microstructured carbonized polyimide (3D-CPI) FSS film to improve their FSS property through plasmonic effects. From the Time Domain Spectroscopy measurements, 3D-CPI FSS film shows band-stop filter properties in the frequency range of 0.5-1.5 THz and with a maximum return loss RL of 40.5 dB (at the resonant frequency of 1 THz). The 3D-CPI/AuNPs film demonstrates the highest return loss RL of 43.7 dB at the higher excitation resonance frequency around 1.06 THz due to the interaction of plasmonic electrons with scattered delocalized electrons in carbon, which induces the mechanisms for EMI shielding. Our results will open insight into 3D plasmonic carbon microstructures as an EMI shielding material at THz frequency. Further study of the optoelectronic performance of Sb2Te3/Bi2Te3 heterojunction photodetector by enhancing plasmonic grating electrodes are carried on. The photoresponse of semiconductors in a broader spectrum is limited due to their bandgap. Integration of plasmonic metallic particles or thin films with localized surface plasmon resonances (LSPRs) into the semiconductor heterostructure is a way to overcome this problem. In this work, plasmonic grating electrodes are used to generate more charge carriers and reduce the transit time for the collection of generated charge carriers by inducing LSPR on the surface of the semiconductor heterostructure in a broadband optical absorption. To achieve our goal, we use Sb2Te3/Bi2Te3 heterojunction due to the natural p-n junction made by a separation of opposite charge carriers where BiTe antistites defects generate n-type charge carriers and SbTe antistites defects impose p-type charge carriers. Finally, we demonstrate a Sb2Te3/Bi2Te3 heterojunction photodetector with plasmonic grating electrodes that achieves a high photocurrent of 7.68 mAcm-2, higher responsivity of 42.67 mAW-1, detectivity of 1.478x109 Jones and five times faster in photoresponse time than a heterojunction without plasmonic grating electrodes. This work proposes an ideal route to improve photodetection using semiconductor heterojunction. Furthermore, we fabricate the plasmonic enhanced nanocomposite heterojunction optoelectronic devices and study the photoresponse performance. Semiconductor thin film with wide bandgap is still a demanding task for photoconversion devices in a visible range. In this regard, we study highly conducting transparent p-type copper iodide (CuI) and n-type poly(acrylic acid)-carbon nanotube (PAA-CNT) thin films as photocatalyst layers utilizing localized surface plasmon resonance (LSPRs) effect with the help of AuNPs. We decorated PAA-CNT/CuI thin film with AuNPs that is sandwiched between ITO and p-CuI thin film as a self-power photo-electrochemical (PEC) photodetector. The PEC exhibits a high photocurrent density of 12 µAcm-2 and sensitive responsivity of 0.07 mAW-1 under AM 1.5 G. LSPRs enhancement is found to be three times in PEC photodetector than those without AuNPs. This substantial enhancement of PEC performance highlights not only the importance of nanocomposite engineering but also the fundamental exploration of optoelectronic device applications.

    Research areas

  • Terahertz Spectroscopy, Frequency Selective Surface, Carbon materials, Band Stop Filter, EMI shielding, Topological insulator, Heterojunction photodetectors, Plasmonic grading electrodes, Localized surface plasmonic resonances, Photoelectrochemical photodetector, Plasmonic self-power device, Heterojunction nanocomposites