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- Hanyang University
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Metal-organic frameworks as SERS substrates with high tailorability
摘要： Surface enhanced Raman scattering (SERS) is a widely used analytical technique for detecting trace-level molecules based on an indispensable SERS substrate. SERS substrates with high tailorability are assumed to be attractive and desirable for SERS detection, because the substrates match the need for the selective detection of different species. Nevertheless, the rational design of such SERS substrates is rather challenging for both noble-metal and semiconductor substrates. Herein, expanding beyond conventional SERS substrates, we demonstrate that metal-organic framework (MOF) materials can serve as a type of SERS substrate with molecular selectivity, which are rarely realized for SERS detection without any special pretreatment. A salient structural characteristic of MOF-based SERS substrates benefiting the SERS selectivity is their high tailorability. By controlling the metal centers, organic ligands, and framework topologies of our MOF-based SERS substrates, we show that the electronic band structures of MOF-based SERS substrate can be purposively manipulated to match those of the target analytes, thus resulting in different detectable species. Going further, the SERS enhancement factors (EFs) of the MOF-based SERS substrates can be greatly enhanced to as high as 106 with a low detection limit of 10-8 M by pore-structure optimization and surface modification, which is comparable to the EFs of noble metals without “hot spots” and recently-reported semiconductors. This selective enhancement is interpreted as being due to the controllable combination of several resonances, such as the charge-transfer, interband and molecule resonances, together with the ground-state charge-transfer interactions. Our study opens a new venue for the development of SERS substrates with high-design flexibility, which is especially important for selective SERS detection towards specific analytes.
关键词： Surface enhanced Raman scattering (SERS),tailorability,charge-transfer,molecular selectivity,interband and molecule resonances,enhancement factors (EFs),metal-organic framework (MOF),ground-state charge-transfer interactions,SERS substrates
更新于2025-09-04 15:30:14
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Structural basis for a naphthyl end-capped oligothiophene with embedded metallic nanoparticles for organic field-effect transistors
摘要： We report on the apparent structure of 5,500-bis(naphth-2-yl)-2,20:50,200-terthiophene (NaT3) in organic field-effect transistors (OFETs) with and without embedded silver nanoparticles. Using regular- and microbeam grazing incidence wide- and small-angle X-ray scattering, the device structure is characterized locally in the area with the embedded particles. The NaT3 thin film order is reduced and the found unit cell (a ? 25.7 A? , b ? 5.87 A? , c ? 8.03 A? , and b ? 98.9(cid:2)) differs significantly from the one reported in the bulk, but shows no significant change, when the particles corresponding to the crystal size are incorporated into the device structure. At the same time, the apparent thin film crystal sizes in OFETs are found to be similar with and without the embedded particles. In both cases, the carrier mobilities are of the order of 10(cid:3)4 cm2/(V s).
关键词： X-ray scattering,oligothiophene,organic field-effect transistors,silver nanoparticles,crystal structure
更新于2025-09-04 15:30:14
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Quantitative mobility evaluation of organic semiconductors using quantum dynamics based on density functional theory
摘要： We present an order-N methodology to evaluate mobilities of charge carriers coupled with molecular vibrations using quantum dynamics based on first-principles calculations that can be applied to micron-scale soft materials. As a demonstration, we apply it to several organic semiconductors and show that the calculated intrinsic hole mobilities and their temperature dependences are quantitatively in good agreement with those obtained in experiments. We also clarified which vibrational modes dominate the transport properties. The methodology paves the way for quantitative prediction of the transport properties of various soft materials.
关键词： quantum dynamics,density functional theory,charge-carrier mobility,organic semiconductors,molecular vibrations
更新于2025-09-04 15:30:14
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A Two-Step Method for Stable and Impurity-Free Graphene Oxide Dispersion in Various Organic Solvents without a Stabilizer or Chemical Modification
摘要： The low stability of graphene oxide (GO) in organic solvents renders it unsuitable for several applications. Thus, an effective dispersion technique must be rapidly developed in order to allow the widespread use of GO. In this study, we successfully produced GO dispersions in various organic (including nonpolar) solvents without a stabilizer, chemical modification, or complex processing by a facile two-step method. In this technique, perfectly exfoliated single-layer GO was firstly prepared in water. Then, water was carefully replaced with each solvent. GO dispersed via this new method exhibited excellent long-term stability in organic solvents with a low impurity content. This is attributed to the release of interlayer water, which strongly links GO layers and causes aggregation in organic solvents, along with impurities trapped in interlayers during exfoliation. Additionally, a GO/polyvinyl chloride composite prepared using this new method showed better mechanical and electrical performances than prepared via the conventional method. The result obtained here will promote the widespread use of GO.
关键词： Organic solvent,polymer composite,Graphene oxide
更新于2025-09-04 15:30:14
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Synthesis, Growth and Characterization of Nonlinear Optical Ce-Doped L-Prolinium Picrate Single Crystals
摘要： A non-linear optical material L-prolinium picrate and cerium doped L-prolinium picrate were synthesized and grown as single crystals by slow evaporation method. The grown crystals were subjected to structural, elemental, thermal, optical and dielectric studies. The structural analysis reveals that pure L-prolinium picrate and Ce doped L-prolinium picrate belongs to the monoclinic crystallographic system with space group P21. Optical transparency of the grown crystals was investigated by UV-visible-NIR spectrum. The thermal analyses reveal that Ce doped L-prolinium picrate is thermally stable up to 162 °C. The dielectric constant and dielectric loss of the crystals were studied as a function of frequency. The non-linear optical property of the doped crystal was confirmed by the Kurtz-powder second harmonic generation test and the result is compared with pure L-prolinium picrate. Mechanical strength of the crystals was also carried out by Vicker's micro hardness test.
关键词： X-ray diffraction,Micro hardness,Growth from solution,Semi organic compound,Non-linear optical crystal
更新于2025-09-04 15:30:14
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Synthesis and Characterization of novel Thiophene and Carbazole-based Polymers – Optical and Electrochemical Characterization
摘要： A donor/acceptor series of carbazole copolymers, composed of alternating 2,7-linked 3,6-difluoro-9-(1-octyl-nonyl)-carbazole units and bithiophene repeated units [P1], 5,7-bis(5-bromothiophen-2-yl)-2,3-bis(4-(2-ethylhexyloxy) phenyl) thieno[3,4-b]pyrazine repeated units [P2] and bithiophene mixed with thieno[3,4-b]pyrazine repeated units [P3] have been prepared following Suzuki polymerisation procedures. The route of synthesis and characterisation techniques of this novel class of materials, together with their photo-physical and electrochemical properties are presented in this study. The polymers were characterised by 1H NMR, 13C NMR and Elemental Analysis. Molecular weights were estimated using gel permeation chromatography (GPC). The thermal stability behaviour for polymers was investigated using thermogravimetric analysis (TGA) and differential scanning calorimetry (DSC). The electronic and photo-physical properties were investigated by use of cyclic voltammetry (CV) and UV-Vis spectroscopy, respectively.
关键词： Conjugated polymer,Organic solar cell,Band gap
更新于2025-09-04 15:30:14
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[IEEE 2017 IEEE Nuclear Science Symposium and Medical Imaging Conference (NSS/MIC) - Atlanta, GA, USA (2017.10.21-2017.10.28)] 2017 IEEE Nuclear Science Symposium and Medical Imaging Conference (NSS/MIC) - Characterization of Stilbene Scintillation Detectors with Light Guide Coupling and Silicon Photomultiplier Readout
摘要： We experimentally investigated the low energy pulse shape discrimination (PSD) capabilities of four cubic stilbene crystals with 6 mm, 10 mm, 15 mm, and 20 mm sides. We used a 6 × 6 mm2 silicon photomultiplier (SiPM) for readout, and coupled the crystals both with and without light guides, optimizing light guide wrapping for PSD. We compared the crystals’s figure of merit (FOM) dependence on light output. For the smaller three crystals, direct coupling provided better PSD (roughly 116% FOM of the guided at 100 ? 150 keVee). For the 10 mm sided crystal the trend was reversed and the light guide became advantageous (105% FOM of the direct at 100 ? 150 keVee).
关键词： organic scintillator,stilbene,Pulse shape discrimination,light guide
更新于2025-09-04 15:30:14
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[IEEE 2018 IEEE International Conference on Semiconductor Electronics (ICSE) - Kuala Lumpur (2018.8.15-2018.8.17)] 2018 IEEE International Conference on Semiconductor Electronics (ICSE) - Detecting Hydrogen Using TiO<inf>2</inf>-B<inf>2</inf>O<inf>3</inf> at Different Operating Temperature
摘要： Performance of TiO2-B2O3 gas sensor that annealed using nitrogen at 650°C for 30 minutes was observed and analyzed. The sensing film of the gas sensor was prepared by mixing TiO2-B2O3 with an organic binder. The sensing film was characterized by field emission scanning electron microscopy (FESEM) and X-ray diffraction (XRD). The gas sensor was exposed to hydrogen at a concentration of 100 - 1000 ppm with operating temperatures of 100°C and 200°C. However, no response was detected for 100 ppm at 100°C. But, as the operating temperature was increased to 200°C, the gas sensor indicated a good response for 100 ppm of hydrogen. The gas sensor exhibited p-type response based on decreased current when exposed to hydrogen. The sensitivity of gas sensor was calculated at 1.00, 2.18 and 3.58 for 100 ppm, 500 ppm and 1000 ppm respectively, at an operating temperature of 200°C.
关键词： TiO2-B2O3,hydrogen,organic binder,nitrogen,gas sensor
更新于2025-09-04 15:30:14
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Confinement of Perovskite‐QDs within a Single MOF Crystal for Significantly Enhanced Multiphoton Excited Luminescence
摘要： The development of the photostable higher-order multiphoton-excited (MPE) upconversion single microcrystalline material is fundamentally and technologically important, but very challenging. Here, up to five-photon excited luminescence in a host–guest metal–organic framework (MOF) and perovskite quantum dot (QD) hybrid single crystal ZJU-28?MAPbBr3 is shown via an in situ growth approach. Such a MOF strategy not only results in a high QD loading concentration, but also significantly diminishes the aggregation-caused quenching (ACQ) effect, provides effective surface passivation, and greatly reduces the contact of the QDs with the external bad atmosphere due to the confinement effect and protection of the framework. These advantages make the resulting ZJU-28?MAPbBr3 single crystals possess high PLQY of ≈51.1%, a high multiphoton action cross-sections that can rival the current highest record (measured in toluene solution), and excellent photostability. These findings liberate the excellent luminescence and nonlinear optical properties of perovskite QDs from the solution system to the solid single-crystal system, which provide a new avenue for the exploitation of high-performance multiphoton excited hybrid single microcrystal for future optoelectronic and micro–nano photonic integration applications.
关键词： single crystals,multiphoton excited luminescence,metal–organic frameworks,perovskite-QDs
更新于2025-09-04 15:30:14
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Experimental Evidence for “Hot Exciton” Thermally Activated Delayed Fluorescence Emitters
摘要： Contradiction between no effective photophysical experiments and high device results causes the “hot exciton” thermally activated delayed fluorescence (TADF) mechanism to be still a controversial question. Here, the steady and transient photophysical characterization combined with theoretical calculation based on 4,7-bis(9,9-dimethyl-9H-fluoren-2-yl)-5,6-difluorobenzo[c][1,2,5]thiadiazole (2F-BTH-DMF), 4,7-bis(9,9-dimethyl-9H-fluoren-2-yl)benzo[c][1,2,5]thiadiazole (BTH-DMF), and 5,6-bis(9,9-dimethyl-9H-fluoren-2-yl)benzo[c][1,2,5] thiadiazole (o-BTH-DMF) demonstrate that all the emitters exhibit TADF via reverse intersystem crossing (RISC) from “hot exciton” triplet excited state. The fast RISC process “hot exciton” mechanism affords a very short delayed lifetime (1 μs). Organic light-emitting diodes (OLEDs) based on these emitters exhibit high exciton utilization over 25% and the best device shows a maximum current efficiency of 31.02 cd A?1, maximum power efficiency of 27.85 lm W?1, and external quantum efficiency of 9.13%, which are the highest performances for reported OLEDs with “hot exciton” mechanism. The experimental evidence for fast RISC process via “hot exciton” triplet state and short delayed lifetime highlights the TADF emitters with “hot exciton” mechanism for high-performance OLEDs with very low efficiency roll-off.
关键词： hot excitons,reverse intersystem crossing,thermally activated delayed fluorescence,organic light-emitting devices
更新于2025-09-04 15:30:14