Viable stretchable plasmonics based on unidirectional nanoprisms

Well-defined ordered arrays of plasmonic nanostructures were fabricated on stretchable substrates and tunable plasmon-coupling-based sensing properties were comprehensively demonstrated upon extension and contraction. Regular nanoprism patterns consisting of Ag, Au and Ag/Au bilayers were constructed on the stretchable polydimethylsiloxane substrate. The nanoprisms had the same orientation over the entire substrate (3 x 3 cm(2)) via metal deposition on a single-crystal microparticle monolayer assembly. The plasmonic sensor based on the Ag/Au bilayer showed a 6-fold enhanced surface enhanced Raman scattering signal under 20% uniaxial extension, whereas a 3-fold increase was observed upon 6% contraction, compared with the Au nanoprism arrays. The sensory behaviors were corroborated by finite-difference time-domain simulation, demonstrating the tunable electromagnetic field enhancement effect via the localized surface plasmon resonance coupling. The advanced flexible plasmonic-coupling-based devices with tunable and quantifiable performance herein suggested are expected to unlock promising potential in practical bio-sensing, biotechnological applications and optical devices.11Ysciescopu

Direct deposition of anatase TiO2 on thermally unstable gold nanobipyramid: Morphology-conserved plasmonic nanohybrid for combinational photothermal and photocatalytic cancer therapy

Deposition of crystalline titanium dioxide (TiO2) on gold nanostructures has been considered as a promising strategy for near-infrared (NIR) light-activated photocatalysis. A typical route comprises pre-deposition of amorphous TiO2 on the gold surface and its ensuing crystallization by high-temperature annealing. Such condition, however, is not compatible with highly plasmonic but thermally unstable sharp-tipped gold nanostructures, causing structural disruption and plasmonic decline. Herein, we report a hybridization method excluding high-temperature annealing, i.e., direct deposition of anatase TiO2 onto sharp-tipped gold nanobipyramid (Au NBP/a-TiO2) with conserving their morphology without agglomeration via low-temperature hydrothermal reaction. In addition to keeping the plasmonic photothermal performance, Au NBP/a-TiO2 exhibits enhanced photocatalytic generation of reactive oxygen species in response to the NIR excitation, evidencing the efficient injection of hot electrons from the Au NBP to the anatase shell. In vitro and in vivo studies revealed that the efficient photocatalytic/photothermal responses of Au NBP/a-TiO2, along with dispersion stability in biological media and minimal toxicity, hold potential for synergistic photothermal and photodynamic therapy. We believe that the low-temperature synthetic method introduced here might offer a general way of crystalline deposition of TiO2 on a variety of gold nanostructures, broadening the spectrum of NIR-responsive photocatalytic hybrid nanostructures for biomedical applications

KOREAN DIALECT IDENTIFICATION BASED ON INTONATION MODELING

Korean dialect identification (K-DID) is a challenging task due to its relatively unexplored field of study, mutual comprehensibility between the dialects, and lack of sufficient Korean dialect datasets available in the past. With large-scaled dialect datasets now available, this paper proposes intonational modeling of the Korean dialects by feeding frame-wise acoustic features on sequential modeling of a neural network. Compared to previous prosodic labeling with syllable-based pitch marking, our approach of intonation modeling is realized with the combination of a set of spectral features, including fundamental frequency, trained on a bidirectional LSTM network with attention mechanism. We believe the attention mechanism enables the detection of dialect-rich segments hidden among the dominant non-dialect segments within the same utterance. We test the networks on different combinations of speaker ages and speech styles. The best performance of the K-DID is achieved with 68.51% in utterance-level accuracy, which surpasses our previous work.N

Probing Multiphased Transition in Bulk MoS2 by Direct Electron Injection

© 2019 American Chemical Society.Structural phase transitions in layered two-dimensional (2D) materials are of significant interest owing to their ability to exist in multiple metastable states with distinctive properties. However, phase transition in bulk MoS2 by nondestructive electron infusion has not yet been realized. In this study, we report the 2H to 1T′ phase transition and in-between intermediates in bulk MoS2 using MoS2/[Ca2N]+·e- heterostructures, in which kinetic free electrons were directly injected into MoS2. We observed various phases in MoS2 ranging from heavily doped 2H to a distorted lattice state and then on to a complete 1T′ state. Snapshots of the multiphase transition were captured by extraordinary Raman shift and bandgap reduction and were further elucidated by theoretical calculations. We also observed a weakening in interlayer coupling in the vicinity of the metallic regime, which led to an unusually strong photoluminescence emission, suggesting light-efficient bulk MoS2. Our results thus suggest the optoelectronic applications that can fully utilize the multiphase transition of bulk 2D materials11sciescopu

Plasmonic Hot Carriers Imaging: Promise and Outlook

Extraordinary light matter interaction on the surface of metallic nanostructures can excite surface plasmons (SPs), followed by generation of charge carriers with high energy, that is, "hot electrons and holes", via nonradiative decay. Such plasmonic hot carriers are potentially useful for photocatalysis, electrocatalysis, photovoltaics, optoelectronics, and theragnosis since hot carrier transfer to the desired substrate can accelerate specific redox reactions or facilitate electrical benefits on devices. In this regard, there is a growing interest in the detection and visualization of hot carriers at the location where plasmonic hot carriers are practically generated and transferred by means of conventional or newly developed procedures, as summarized in Table 1 of the main paper. Although direct imaging of plasmonic hot carriers or pathways are still challenging due to ultrafast dynamics of plasmonic hot carriers, state-of-the-art microscopic approaches have successfully demonstrated the mapping of the localized surface plasmons (LSPs) and plasmonic hot carriers. In addition, more accessible and facile approaches by mediation of chemical probes have also been emerged in recent years for the same purpose. The aim of this Perspective is to provide an idea of how spatial information on the generation and transfer of plasmonic hot carriers can be associated with the future design of plasmonic nanomaterials or nanocomposites to increase the output of hot carrier-driven processes. Along with a comprehensive overview of surface plasmon decay into plasmonic hot carriers and the necessity of plasmonic hot carrier imaging, we will highlight some recent advances in plasmonic hot carrier imaging techniques and provide remarks on future prospects of these technique

Enhancing Solar Light-Driven Photocatalytic Activity of Mesoporous Carbon–TiO2 Hybrid Films via Upconversion Coupling

Solar energy conversion has emerged as an attractive pathway in the decomposition of hazardous organic pollutants. Herein, tridoped β-NaYF4:Yb3+,Tm3+,Gd3+ upconversion (UC) nanorods were embedded in a carbon-doped mesostructured TiO2 hybrid film using triblock copolymer P123 acting as a mesoporous template and carbon source. The photoactivity of our novel material was reflected in the degradation of nitrobenzene, as a representative organic waste. The broad-band absorption of our rationally designed UC nanorod-embedded C-doped TiO2 in the UV to NIR range unveiled a remarkable increase in nitrobenzene degradation (83%) within 3 h compared with pristine TiO2 (50%) upon light irradiation. These results establish for the first time a synergetic bridge between the effects of a creative photon trapping TiO2 architecture, improved NIR light-harvesting efficiency upon UC nanorod incorporation, and a simultaneous decrease in the band gap energy and increased visible light absorption by C-doping of the oxide lattice. The resulting nanostructure was believed to favor efficient charge and energy transfer between the photocatalyst components and to reduce charge recombination. Our novel hybrid nanostructure and its underlined synthesis strategy reflect a promising route to improve solar energy utilization in environmental remediation and in a wide range of photocatalytic applications, e.g., water splitting, CO2 reutilization, and production of fuels

Viable stretchable plasmonics based on unidirectional nanoprisms

Well-defined ordered arrays of plasmonic nanostructures were fabricated on stretchable substrates and tunable plasmon-coupling-based sensing properties were comprehensively demonstrated upon extension and contraction. Regular nanoprism patterns consisting of Ag, Au and Ag/Au bilayers were constructed on the stretchable polydimethylsiloxane substrate. The nanoprisms had the same orientation over the entire substrate (3 × 3 cm2) via metal deposition on a single-crystal microparticle monolayer assembly. The plasmonic sensor based on the Ag/Au bilayer showed a 6-fold enhanced surface enhanced Raman scattering signal under 20% uniaxial extension, whereas a 3-fold increase was observed upon 6% contraction, compared with the Au nanoprism arrays. The sensory behaviors were corroborated by finite-difference time-domain simulation, demonstrating the tunable electromagnetic field enhancement effect via the localized surface plasmon resonance coupling. The advanced flexible plasmonic-coupling-based devices with tunable and quantifiable performance herein suggested are expected to unlock promising potential in practical bio-sensing, biotechnological applications and optical devices

Enhancing Solar Light-Driven Photocatalytic Activity of Mesoporous Carbon-TiO2 Hybrid Films via Upconversion Coupling

Solar energy conversion has emerged as an attractive pathway in the decomposition of hazardous organic pollutants. Herein, tridoped ??-NaYF4:Yb3+,Tm3+,Gd3+ upconversion (UC) nanorods were embedded in a carbon-doped mesostructured TiO2 hybrid film using triblock copolymer P123 acting as a mesoporous template and carbon source. The photoactivity of our novel material was reflected in the degradation of nitrobenzene, as a representative organic waste. The broad-band absorption of our rationally designed UC nanorod-embedded C-doped TiO2 in the UV to NIR range unveiled a remarkable increase in nitrobenzene degradation (83%) within 3 h compared with pristine TiO2 (50%) upon light irradiation. These results establish for the first time a synergetic bridge between the effects of a creative photon trapping TiO2 architecture, improved NIR light-harvesting efficiency upon UC nanorod incorporation, and a simultaneous decrease in the band gap energy and increased visible light absorption by C-doping of the oxide lattice. The resulting nanostructure was believed to favor efficient charge and energy transfer between the photocatalyst components and to reduce charge recombination. Our novel hybrid nanostructure and its underlined synthesis strategy reflect a promising route to improve solar energy utilization in environmental remediation and in a wide range of photocatalytic applications, e.g., water splitting, CO2 reutilization, and production of fuels

Sophisticated plasmon-enhanced photo-nanozyme for anti-angiogenic and tumor-microenvironment-responsive combinatorial photodynamic and photothermal cancer therapy

In the exploitation of nanozymes possessing intrinsic enzyme-like activities for cancer therapy, minor focus has been devoted to plasmonic nanostructures with localized surface plasmon resonance (LSPR)-driven properties. Here, we report the application of unique peroxidase-mimicking plasmonic photo-nanozymes coupling tumor-microenvironment-responsive reactive oxygen species generation with photothermal effect for effective combinatorial therapy. The well-defined anisotropic photo-nanozyme is synthesized by selectively depositing Pd nanoparticles on the tips of gold nanobypyramids. Intrinsic peroxidase-like properties with 1.5-fold-activity enhancement under photoexcitation are ascribed to a Pd-induced hot electrons/holes separation with efficient H2O2 decomposition. The LSPR-induced photocatalytic/photothermal combinatorial effects are remarkably enhanced upon H2O2 addition, critically suppressing the cell survival rate under near-infrared light. An effective decomposition of cell-signaling H2O2 additionally reveals prominent expression hindrance of vascular endothelial growth factor and hypoxia-inducible factor 1α. Our seminal findings uncover an interrelation between LSPR-induced phenomena and biomimetic fingerprints, valuable to overcome the shortcomings of conventional photodynamic therapy

Upconversion-Triggered Charge Separation in Polymer Semiconductors

Upconversion is a unique optical property which is driven by a sequential photon pumping and generation of higher energy photons in a consecutive manner. The efficiency improvement in photovoltaic devices can be achieved when upconverters are integrated since upconverters contribute to the generation of extra photons. Despite numerous experimental studies confirming the relationship, fundamental explanations for a real contribution of upconversion to photovoltaic efficiency are still in demand. In this respect, we suggest a new approach to visualize the upconversion event in terms of surface photovoltage (SPV) by virtue of Kelvin probe force microscopy (KPFM). One of the most conventional polymer semiconductors, poly(3-hexyl thiophene) (P3HT), is employed as a sensitizer to generate charge carriers by upconverted light. KPFM measurements reveal that the light upconversion enabled the formation of charge carriers in P3HT, resulting in large SPV of -54.9 mV. It confirms that the energy transfer from upconverters to P3HT can positively impact on the device performance in organic solar cells (OSCs).clos