Monatomic Iodine Dielectric Layer for Multimodal Optical Spectroscopy of Dye Molecules on Metal Surfaces.

Fluorescence and Raman scattering spectroscopies have been used in various research fields such as chemistry, electrochemistry, and biochemistry because they can easily obtain detailed information about molecules at interfaces with visible light. In particular, multimodal fluorescence and Raman scattering spectroscopy have recently attracted significant attention, which enables us to distinguish chemical species and their electronic states that are important for expressing various functions. However, a special strategy is required to perform simultaneous measurements because the cross sections of fluorescence and Raman scattering differ by as much as ∼1014. In this study, we propose a method for the simultaneous measurement of dye molecules on a metal surface using a monatomic layer of iodine as the dielectric layer. The method is based on adequately quenching the photoexcited state of the molecules near the metal surface to weaken the fluorescence intensity and using the resonance effect to increase the Raman signal. We have validated this concept by experiments with insulating layers of different thicknesses and dye molecules of different chemical structures. The proposed multimodal strategy paves the way for various applications such as catalytic chemistry and electrochemistry, where the adsorption structure and electronic states of molecular species near the metal surface determine functionalities.

Determination and identification of titanium dioxide nanoparticles in confectionery foods, marketed in South Korea, using inductively coupled plasma optical emission spectrometry and transmission electron microscopy.

Food-grade titanium dioxide (TiO2) is a common and widespread food additive in many processed foods, personal care products, and other industrial categories as it boosts the brightness and whiteness of colours. Although it is generally recognised as safe for humans, there is a growing interest in the health risks associated with its oral intake. This study quantified and identified TiO2 nanoparticles present in confectionery foods, which are children's favourite foods, with inductively coupled plasma optical emission spectrometry (ICP-OES) and transmission electron microscopy (TEM). A reliable digestion method using hot sulphuric acid and a digestion catalyst (K2SO4:CuSO4 = 9:1) was suggested for titanium analysis. Validations of the experimental method were quite acceptable in terms of linearity, recoveries, detection limits, and quantification limits. Of all the 88 analysed foods, TiO2 was detected in 19 products, all except three declared TiO2 in their labelling. The mean TiO2 content of candies, chewing gums, and chocolates were 0.36 mg g-1, 0.04 mg g-1, and 0.81 mg g-1, respectively. Whitish particles isolated from the confectionery foods were confirmed as TiO2 nanoparticles via TEM and energy dispersive X-ray spectroscopy (EDX), in which nanosized particles (<100 nm) were identified.

Determining the Facile Routes for Oxygen Evolution Reaction by In Situ Probing of Li-O2 Cells with Conformal Li2O2 Films.

An ongoing challenge with lithium-oxygen (Li-O2) batteries is in deciphering the oxygen evolution reaction (OER) process related to the slow decomposition of the insulating lithium peroxide (Li2O2). Herein, we shed light on the behavior of Li2O2 oxidation by exploiting various in situ imaging, gas analysis, and electrochemical methods. At the low potentials 3.2-3.7 V (vs Li/Li+), OER is exclusive to the thinner parts of the Li2O2 deposits, which leads to O2 gas evolution, followed by the concomitant release of superoxide species. At higher potentials, OER initiates at the sidewalls of the thicker Li2O2. The succeeding lateral decomposition of Li2O2 indicates the preferential Li+ and charge transport occurring at the sidewalls of Li2O2. To ameliorate the OER rate, we also investigate an alternative approach of rerouting charge carriers by using soluble redox mediators. Our in situ probes provide insights into the favorable charge-transport routes that can aid in promoting Li2O2 decomposition.

Reverse Anti-solvent Crystallization Process for the Facile Synthesis of Zinc Tetra(4-pyridyl)porphyrin Single Crystalline Cubes.

Synthesis of morphologically well-defined crystals of metalloporphyrin by direct crystallization based on conventional anti-solvent crystallization method without using any additives has been rarely reported. Herein, we demonstrate an unconventional and additive-free synthetic method named reverse anti-solvent crystallization method to achieve well-defined zinc-porphyrin cube crystals by reversing the order of the addition of solvents. The extended first solvation shell effect mechanism is therefore suggested to support the synthetic process by providing a novel kinetic route for reaching the local supersaturation environment depending on the order of addition of solvents, which turned out to be critical to achieve clean cube morphology of the crystal. We believe that our work not only extends fundamental knowledge about the kinetic process in binary solvent systems, but also enables great opportunities for shape-directing crystallization of various organic and organometallic compounds.

Unexpected Li2O2 Film Growth on Carbon Nanotube Electrodes with CeO2 Nanoparticles in Li-O2 Batteries.

In lithium-oxygen (Li-O2) batteries, it is believed that lithium peroxide (Li2O2) electrochemically forms thin films with thicknesses less than 10 nm resulting in capacity restrictions due to limitations in charge transport. Here we show unexpected Li2O2 film growth with thicknesses of ∼60 nm on a three-dimensional carbon nanotube (CNT) electrode incorporated with cerium dioxide (ceria) nanoparticles (CeO2 NPs). The CeO2 NPs favor Li2O2 surface nucleation owing to their strong binding toward reactive oxygen species (e.g., O2 and LiO2). The subsequent film growth results in thicknesses of ∼40 nm (at cutoff potential of 2.2 V vs Li/Li(+)), which further increases up to ∼60 nm with the addition of trace amounts of H2O that enhances the solution free energy. This suggests the involvement of solvated superoxide species (LiO2(sol)) that precipitates on the existing Li2O2 films to form thicker films via disproportionation. By comparing toroidal Li2O2 formed solely from LiO2(sol), the thick Li2O2 films formed from surface-mediated nucleation/thin-film growth following by LiO2(sol) deposition provides the benefits of higher reversibility and rapid surface decomposition during recharge.

Germanium Silicon Alloy Anode Material Capable of Tunable Overpotential by Nanoscale Si Segregation.

We developed the novel electrode that enables fine control of overpotential by exploiting surface segregation that is the enrichment of one component at the surface of binary alloy. To realize this approach, we controlled the proportion of Si with low Li diffusivity at the surface by annealing the SiGe nanowire in H2 environment at various temperatures. The resulting SiGe nanowires annealed at 850 °C exhibited high reversible capacity (>1031 mA·h·g(-1)), and long cycle life (400 cycles) with high capacity retention (89.0%) at 0.2 C. This superior battery performance is attributed to the remaining unlithiated part acting as support frame to prevent pulverization of anode material, which results from the fine-tuning of overpotential by controlling the degree of Si segregation.

A 3.5 V lithium-iodine hybrid redox battery with vertically aligned carbon nanotube current collector.

A lithium-iodine (Li-I2) cell using the triiodide/iodide (I3(-)/I(-)) redox couple in an aqueous cathode has superior gravimetric and volumetric energy densities (∼ 330 W h kg(-1) and ∼ 650 W h L(-1), respectively, from saturated I2 in an aqueous cathode) to the reported aqueous Li-ion batteries and aqueous cathode-type batteries, which provides an opportunity to construct cost-effective and high-performance energy storage. To apply this I3(-)/I(-) aqueous cathode for a portable and compact 3.5 V battery, unlike for grid-scale storage as general target of redox flow batteries, we use a three-dimensional and millimeter thick carbon nanotube current collector for the I3(-)/I(-) redox reaction, which can shorten the diffusion length of the redox couple and provide rapid electron transport. These endeavors allow the Li-I2 battery to enlarge its specific capacity, cycling retention, and maintain a stable potential, thereby demonstrating a promising candidate for an environmentally benign and reusable portable battery.

Patternable large-scale molybdenium disulfide atomic layers grown by gold-assisted chemical vapor deposition.

A novel way to grow MoS2 on a large scale with uniformity and in desired patterns is developed. We use Au film as a catalyst on which [Mo(CO)6 ] vapor decomposes to form a Mo-Au surface alloy that is an ideal Mo reservoir for the growth of atomic layers of MoS2 . Upon exposure to H2 S, this surface alloy transforms into a few layers of MoS2 , which can be isolated and transferred on an arbitrary substrate. By simply patterning Au catalyst film by conventional lithographic techniques, MoS2 atomic layers in desired patterns can be fabricated.

In situ AFM imaging of Li-O2 electrochemical reaction on highly oriented pyrolytic graphite with ether-based electrolyte.

Understanding the lithium-oxygen (Li-O2) electrochemical reaction is of importance to improve reaction kinetics, efficiency, and mitigate parasitic reactions, which links to the strategy of enhanced Li-O2 battery performance. Many in situ and ex situ analyses have been reported to address chemical species of reduction intermediate and products, whereas details of the dynamic Li-O2 reaction have not as yet been fully unraveled. For this purpose, visual imaging can provide straightforward evidence, formation and decomposition of products, during the Li-O2 electrochemical reaction. Here, we present real-time and in situ views of the Li-O2 reaction using electrochemical atomic force microscopy (EC-AFM). Details of the reaction process can be observed at nano-/micrometer scale on a highly oriented pyrolytic graphite (HOPG) electrode with lithium ion-containing tetraglyme, representative of the carbon cathode and ether-based electrolyte extensively employed in the Li-O2 battery. Upon oxygen reduction reaction (ORR), rapid growth of nanoplates, having axial diameter of hundreds of nanometers, length of micrometers, and ~5 nm thickness, at a step edge of HOPG can be observed, which eventually forms a lithium peroxide (Li2O2) film. This Li2O2 film is decomposed during the oxygen evolution reaction (OER), for which the decomposition potential is related to a thickness. There is no evidence of byproduct analyzed by X-ray photoelectron spectroscopy (XPS) after first reduction and oxidation reaction. However, further cycles provide unintended products such as lithium carbonate (Li2CO3), lithium acetate, and fluorine-related species with irregular morphology due to the degradation of HOPG electrode, tetraglyme, and lithium salt. These observations provide the first visualization of Li-O2 reaction process and morphological information of Li2O2, which can allow one to build strategies to prepare the optimum conditions for the Li-O2 battery.

Copper-vapor-assisted chemical vapor deposition for high-quality and metal-free single-layer graphene on amorphous SiO2 substrate.

We report that high-quality single-layer graphene (SLG) has been successfully synthesized directly on various dielectric substrates including amorphous SiO2/Si by a Cu-vapor-assisted chemical vapor deposition (CVD) process. The Cu vapors produced by the sublimation of Cu foil that is suspended above target substrates without physical contact catalyze the pyrolysis of methane gas and assist nucleation of graphene on the substrates. Raman spectra and mapping images reveal that the graphene formed on a SiO2/Si substrate is almost defect-free and homogeneous single layer. The overall quality of graphene grown by Cu-vapor-assisted CVD is comparable to that of the graphene grown by regular metal-catalyzed CVD on a Cu foil. While Cu vapor induces the nucleation and growth of SLG on an amorphous substrate, the resulting SLG is confirmed to be Cu-free by synchrotron X-ray photoelectron spectroscopy. The SLG grown by Cu-vapor-assisted CVD is fabricated into field effect transistor devices without transfer steps that are generally required when SLG is grown by regular CVD process on metal catalyst substrates. This method has overcome two important hurdles previously present when the catalyst-free CVD process is used for the growth of SLG on fused quartz and hexagonal boron nitride substrates, that is, high degree of structural defects and limited size of resulting graphene, respectively.

Crystal-plane-dependent photoluminescence of pentacene 1D†wire and 2D†disk crystals.

Down to the wire: Pentacene exhibits crystal-plane-dependent photoluminescence (PL) activity, as demonstrated in highly crystalline 1D wires and 2D disks, which were selectively synthesized using the vaporization-condensation-recrystallization (VCR) process. Although pentacene 1D wires and 2D disks have identical triclinic crystal structures, PL activity is observed only from pentacene 1D wires owing to the presence of "PL-active" (010) planes.

Role of NF-κB-p53 crosstalk in ultraviolet A-induced cell death and G1 arrest in human dermal fibroblasts.

Photoaging is the premature aging of the skin caused by repeated exposure to sunlight and is characterized by a depletion of the dermal extracellular matrix. This depletion is due to the loss of fibroblast cells and their multiple functions. UVA was revealed as a major inducer of photoaging in various clinical studies. As UVA photons have long wavelength spectra, UVA penetrates deeper into the dermis than UVB and UVC, leading to the induction of cell death, the destruction of the dermal extracellular matrix through the induction of matrix metalloproteinase expression, and the repression of collagen expression. However, the exact effects of UVA on the skin remain a matter of debate. Here, we assess cell cycle stage to demonstrate that NF-κB-p53 crosstalk induces apoptosis and growth arrest in UVA-irradiated human dermal fibroblasts. In addition, UVA irradiation led to an increase of NF-κB-HDAC1 complexes, which in turn repressed cyclin D1 expression in UVA-irradiated human dermal fibroblasts. We provide direct evidence that UVA irradiation induces changes in the p53-dependent NF-κB complex that lead to growth arrest and apoptosis through the repression of cyclin D1. These studies uncovered that NF-κB-p53 crosstalk is a key regulator of UVA-dependent growth arrest and apoptosis.

Direct growth of graphene pad on exfoliated hexagonal boron nitride surface.

A direct and metal layer-free growth of flat graphene pads on exfoliated hexagonal boron nitride substrate (h-BN) are demonstrated by atmospheric chemical vapour deposition (CVD) process. Round shape with high flatness graphene pads are grown in high yield (∼95%) with a pad thickness of ∼0.5 nm and homogenous diameter.