Development of advanced flexible semiconductor material and device via ultrafast light-material interaction극단초 광-물질 상호작용 기반 반도체 나노 소재 합성 및 유연 전자 소자 응용

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Ultrafast Light-Material Interaction has been explored as next generation and future-oriented technology in nanomaterial society. This powerful technology has already contributed to a tremendous breakthrough in electronic device industry since they can provide the exceptional capability of nonequilibrium reactions within an extremely short time (ns ~ ms) for the meta-phase, which cannot be obtained under conventional thermal annealing. For example, light-induced low-temperature poly-silicon (LTPS), inorganic thin film transistors (TFT), active matrix organic light-emitting diodes (AMOLEDs) and post-treatments of nanomaterial have been extensively explored as technological breakthrough of nano-technology. However, little works of direct nano-material synthesis was reported due to the difficulties of material selection, lack of basic principles and photo-synthetic mechanisms. It is essential to develop the light-induced direct material synthesis and post-treatment to overcome the thermodynamic limitation of conventional thermal techniques. Here, we introduce the novel synthesis and post-treatment techniques using ultrafast light-material interaction for demonstrating the advanced semiconductor nano-materials, such as light-emitting quantum dots (QDs), molybdenum disulfide (MoS2), graphene oxide liquid crystal fibers (GOLC fibers), graphene. In addition, we are gonna talk about the diverse high performance electronic devices using the as-demonstrated nanomaterials via light-material interaction. In chapter 1, the overall introduction of basic principles and related technologies for better understanding of this thesis. In chapter 2, we report the first novel one-step metastable QD synthesis technique enabled by ultra-fast light-material interactions. The highly intensive xenon flash lamp (wavelength of ultraviolet ~ near-infrared) was employed to facilitate the sequential self-formation of metastable In2S3 QD nucleation, chemical doping and surface passivation using single phase precursor containing four reactive species (Ag+, Zn2+, In3+ and S2-). The synthesized 2.5 nm-sized In¬2S3 QD presented thermodynamically metastable cubic crystalline α-phase in room temperature. The first synthetic mechanism of light-induced QD was successfully verified by atomic-resolution transmission electron microscopy (Titan-TEM) and scanning transmission electron microscopy (STEM) analysis. The doping process and surface passivation was also proved using spectral analysis. The maximum photoluminescence quantum yield (PLQY) of QD was ~ 42 %, which was comparable optical properties compared to the previously reported stable phase In2S3 QDs. In order to theoretically figure out the light-absorbed plasmonic stimulation and localized surface plasmon (LSP), finite-difference time-domain (FDTD) simulation was performed. Finally, meta-QD based two-channel photo-detector was demonstrated for showing versatile and practical application. In chapter 3, we report the innovative and brand-new synthesis technology of transition metal dichalcogenides (TMD) using full-wavelength ultrafast flash lamp irradiation. In order to synthesize the 10 nm-thick MoS2 using ultrafast flash irradiation, the noble metal Au heating layers with 80 nm thick was employed that could stimulate the synthesis, as well as N2/H2 (20 sccm/4 sccm) gas was continuously injected to make chemically reduction condition. The crystallinity of MoS2 was artificially controlled according to the number of flash irradiation from 1 pulse to 7 pulse during synthesis. Finally, the as-synthesized MoS2 based resistive random access memory (RRAM) with dot-patterned metal-inorganic-metal (MIM) structure was demonstrated. In chapter 4, here we report the unique post-treatment technique of graphene oxide liquid crystal fiber (GOLCF) to demonstrate the heterogeneous Janus structure via ultrafast light-material interaction. Recently, Janus heterogeneous materials presenting two chemically different phases in one single material, have been spotlighted due to their extraordinary physical properties for expansion of electronic device application. In this work, the flash-irradiated heterogeneous GOLCF presented core/shell-like structure of oxidized GO and reduced GO (rGO) phasesr. The unique physical properties were successfully verified by spectral analysis (XPS, Raman) and finite elemental method (FEM) simulation. Finally, the ultra-high performance flexible humidity sensor was demonstrated. The outstanding performance of flexible sensor was validated from the comparison between rGO fiber humidity sensor via traditional thermal annealing. The humid-sensitivities of flash-induced GOLCF-based sensor displayed 5.95 times higher than that of the thermal-annealed device. To further evaluate the mechanical reliability of flexible gas sensor, repetitive measurements were performed up to 30 cycles at humidity level of 80.8 %, which exhibit a nice long-term stability.
Lee, Keon Jaeresearcher이건재researcher
한국과학기술원 :신소재공학과,
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학위논문(박사) - 한국과학기술원 : 신소재공학과, 2021.2,[xiv, 93 p. :]


Light-material interaction▼athermodynamic nonequilibrium reaction▼aadvanced nano-materials▼aresistive random access memory▼aflexible electronics; 광-물질 상호작용▼a열적 비평형 반응▼a최신 나노물질▼a저항변화메모리▼a유연전자소자

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