Reduction-Assisted Calcination Enhances the Photocatalytic Activity of ZnO and WO Nanoparticles in Biomass Conversion.

Rising energy needs and environmental issues have prompted the creation of effective and affordable photocatalysts for converting biomass. Utilizing abundant biomass, oxidation of 5-hydroxymethylfurfural (HMF) emerges as a method for generating high-value chemicals from biomass, offering an alternative to fossil fuels. We synthesized defect-engineered metal oxides (ZnO and WO) by calcination with NaBH as a reducing agent.

Enhancement of Sulfur Source-Dependent Zn Vacancies in Different Photocatalytic Performances of ZnInS Nanoparticles.

This study focuses on the synthesis and investigation of ZnInS nanoparticle (NP) photocatalysts treated with different sulfur sources, thioacetamide (TAA), or thiourea (TU), to explore their wavelength-dependent photocatalytic activity. The research aims to understand the impact of Zn vacancies present on the surface of ZnInS NPs. The investigation involves electron spin resonance and in situ X-ray photoelectron spectroscopy to study the photocatalytic activity of ZnInS-TU and ZnInS-TAA NPs, following the characterization of surface morphology and electronic properties using high-resolution transmission electron microscopy and X-ray diffraction.

Growth of Monolayer and Multilayer MoS Films by Selection of Growth Mode: Two Pathways via Chemisorption and Physisorption of an Inorganic Molecular Precursor.

We report facile growth methods for high-quality monolayer and multilayer MoS films using MoOCl as the vapor-phase molecular Mo precursor. Compared to the conventional covalent solid-type Mo precursors, the growth pressure of MoOCl can be precisely controlled. This enables the selection of growth mode by adjusting growth pressure, which facilitates the control of the growth behavior as the growth termination at a monolayer or as the continuous growth to a multilayer.

Tunable Optical Transition in 2H-MoS via Direct Electrochemical Engineering of Vacancy Defects and Surface S-C Bonds.

Although surface engineering has been regarded to be a great approach to modulate the optical and electrical properties of nanomaterials, the spontaneous covalent functionalization on semiconducting 2H-MoS is a notoriously difficult process, while several reactions have been performed on metallic 1T-MoS. This limitation in functionalization is attributed to the difficulty of electron transfer from 2H-TMD to the reacting molecules due to its semiconducting property and neutral charge state. Unfortunately, this is an all too important prerequisite step toward creating chemically reactive radical species for surface functionalization reactions.

AP-XPS beamline, a platform for operando science at Pohang Accelerator Laboratory.

Beamline 8A (BL 8A) is an undulator-based soft X-ray beamline at Pohang Accelerator Laboratory. This beamline is aimed at high-resolution ambient-pressure X-ray photoelectron spectroscopy (AP-XPS), soft X-ray absorption spectroscopy (soft-XAS) and scanning photoemission microscopy (SPEM) experiments. BL 8A has two branches, 8A1 SPEM and 8A2 AP-XPS, that share a plane undulator, the first mirror (M1) and the monochromator.

Long-Term Chemical Aging of Hybrid Halide Perovskites.

Because the power conversion efficiency (PCE) of hybrid halide perovskite solar cells (PSCs) could exceed 24%, extensive research has been focused on improving their long-term stability for commercialization in the near future. In a previous study, we reported that the addition of a number of ionized iodide (triiodide: I) ions during perovskite film formation significantly improved the efficiency of PSCs by reducing deep-level defects in the perovskite layer. Understanding the relationship between the concentration of these defects and the long-term chemical aging of PSCs is important not only for obtaining fundamental insight into the perovskite materials but also for studying the long-term chemical stability of PSCs.

Comparative study of catalytic activities among transition metal-doped IrO nanoparticles.

Catalytic activities of transition metal-doped IrO nanoparticles (TM-IrO NPs; TM = Cr, Mn, Fe, Co, or Ni) are compared for various oxidation reactions such as electrochemical oxygen evolution reaction (OER), gas-phase photo-oxidation of thiol function group, and CO oxidative conversion. Here, we discovered a series of TM-IrO catalysts have a common activity trend for these oxidation reactions, and their activities are closely related with modified electronic states of IrO, strongly affected by the types of the transition metal across the periodic table. For all oxidation reactions, Cr- and Mn-IrO achieved the highest oxidation catalytic activity, and sequentially decreased activities were obtained with Fe, Co, and Ni doped IrO.

Enhanced Performance of Field-Effect Transistors Based on Black Phosphorus Channels Reduced by Galvanic Corrosion of Al Overlayers.

Two-dimensional (2D)-layered semiconducting materials with considerable band gaps are emerging as a new class of materials applicable to next-generation devices. Particularly, black phosphorus (BP) is considered to be very promising for next-generation 2D electrical and optical devices because of its high carrier mobility of 200-1000 cm V s and large on/off ratio of 10 to 10 in field-effect transistors (FETs). However, its environmental instability in air requires fabrication processes in a glovebox filled with nitrogen or argon gas followed by encapsulation, passivation, and chemical functionalization of BP.

Carbon-Heteroatom Bond Formation by an Ultrasonic Chemical Reaction for Energy Storage Systems.

The direct formation of CN and CO bonds from inert gases is essential for chemical/biological processes and energy storage systems. However, its application to carbon nanomaterials for improved energy storage remains technologically challenging. A simple and very fast method to form CN and CO bonds in reduced graphene oxide (RGO) and carbon nanotubes (CNTs) by an ultrasonic chemical reaction is described.

Long-Range Lattice Engineering of MoTe by a 2D Electride.

Doping two-dimensional (2D) semiconductors beyond their degenerate levels provides the opportunity to investigate extreme carrier density-driven superconductivity and phase transition in 2D systems. Chemical functionalization and the ionic gating have achieved the high doping density, but their effective ranges have been limited to ∼1 nm, which restricts the use of highly doped 2D semiconductors. Here, we report on electron diffusion from the 2D electride [CaN]·e to MoTe over a distance of 100 nm from the contact interface, generating an electron doping density higher than 1.

Heterogeneous Defect Domains in Single-Crystalline Hexagonal WS.

Single-crystalline monolayer hexagonal WS is segmented into alternating triangular domains: sulfur-vacancy (SV)-rich and tungsten-vacancy (WV)-rich domains. The WV-rich domain with deep-trap states reveals an electron-dedoping effect, and the electron mobility and photoluminescence are lower than those of the SV-rich domain with shallow-donor states by one order of magnitude. The vacancy-induced strain and doping effects are investigated via Raman and scanning photoelectron microscopy.

Efficient CO Oxidation by 50-Facet CuO Nanocrystals Coated with CuO Nanoparticles.

As carbon monoxide oxidation is widely used for various chemical processes (such as methanol synthesis and water-gas shift reactions HO + CO ⇄ CO + H) as well as in industry, it is essential to develop highly energy efficient, inexpensive, and eco-friendly catalysts for CO oxidation. Here we report green synthesis of ∼10 nm sized CuO nanoparticles (NPs) aggregated on ∼400 nm sized 50-facet CuO polyhedral nanocrystals. This CuO-NPs/50-facet CuO shows remarkable CO oxidation reactivity with very high specific CO oxidation activity (4.

Charge transport-driven selective oxidation of graphene.

Due to the tunability of the physical, electrical, and optical characteristics of graphene, precisely controlling graphene oxidation is of great importance for potential applications of graphene-based electronics. Here, we demonstrate a facile and precise way for graphene oxidation controlled by photoexcited charge transfer depending on the substrate and bias voltage. It is observed that graphene on TiO2 is easily oxidized under UV-ozone treatment, while graphene on SiO2 remains unchanged.

Enhancement of Photo-Oxidation Activities Depending on Structural Distortion of Fe-Doped TiO2 Nanoparticles.

To design a high-performance photocatalytic system with TiO2, it is necessary to reduce the bandgap and enhance the absorption efficiency. The reduction of the bandgap to the visible range was investigated with reference to the surface distortion of anatase TiO2 nanoparticles induced by varying Fe doping concentrations. Fe-doped TiO2 nanoparticles (Fe@TiO2) were synthesized by a hydrothermal method and analyzed by various surface analysis techniques such as transmission electron microscopy, Raman spectroscopy, X-ray diffraction, scanning transmission X-ray microscopy, and high-resolution photoemission spectroscopy.

Seamless lamination of a concave-convex architecture with single-layer graphene.

Graphene has been used as an electrode and channel material in electronic devices because of its superior physical properties. Recently, electronic devices have changed from a planar to a complicated three-dimensional (3D) geometry to overcome the limitations of planar devices. The evolution of electronic devices requires that graphene be adaptable to a 3D substrate.

Comparative study of photocatalytic activities of hydrothermally grown ZnO nanorod on Si(001) wafer and FTO glass substrates.

ZnO nanorods have been grown on Si(001) wafer and fluorine-doped tin oxide (FTO) glass substrates for 1 and 4 h with the hydrothermal methods. The morphologies and photocatalytic activities of the ZnO nanorods were found to depend on the substrates. We investigated their properties by using spectroscopic analysis and demonstrated that the shape of nanorod and the ratios of external defects can be controlled by varying the substrates.

DEVICE TECHNOLOGY. Phase patterning for ohmic homojunction contact in MoTe₂.

Artificial van der Waals heterostructures with two-dimensional (2D) atomic crystals are promising as an active channel or as a buffer contact layer for next-generation devices. However, genuine 2D heterostructure devices remain limited because of impurity-involved transfer process and metastable and inhomogeneous heterostructure formation. We used laser-induced phase patterning, a polymorph engineering, to fabricate an ohmic heterophase homojunction between semiconducting hexagonal (2H) and metallic monoclinic (1T') molybdenum ditelluride (MoTe2) that is stable up to 300°C and increases the carrier mobility of the MoTe2 transistor by a factor of about 50, while retaining a high on/off current ratio of 10(6).

Photoelectron spectroscopic imaging and device applications of large-area patternable single-layer MoS2 synthesized by chemical vapor deposition.

Molybdenum disulfide (MoS2) films, which are only a single atomic layer thick, have been synthesized by chemical vapor deposition (CVD) and have gained significant attention due to their band-gap semiconducting properties. However, in order for them to be useful for the fabrication of practical devices, patterning processes that can be used to form specific MoS2 structures must be integrated with the existing synthetic approaches. Here, we report a method for the synthesis of centimeter-scale, high-quality single-layer MoS2 that can be directly patterned during CVD, so that postpatterning processes can be avoided and device fabrication can be streamlined.

Excavated Fe-N-C sites for enhanced electrocatalytic activity in the oxygen reduction reaction.

Platinum (Pt) is the best electrocatalyst for the oxygen reduction reaction (ORR) in hydrogen fuel cells, but it is an extremely expensive resource. The successful development of a cost-effective non-Pt ORR electrocatalyst will be a breakthrough for the commercialization of hydrogen-air fuel cells. Ball milling has been used to incorporate metal and nitrogen precursors into micropores of carbon more effectively and in the direct nitrogen-doping of carbon under highly pressurized nitrogen gas in the process of the preparation of non-noble ORR catalysts.

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.

Selective catalytic burning of graphene by SiOx layer depletion.

We report catalytic decomposition of few-layer graphene on an Au/SiOx/Si surface wherein oxygen is supplied by dissociation of the native SiOx layer at a relatively low temperature of 400 °C. The detailed chemical evolution of the graphene covered SiOx/Si surface with and without gold during the catalytic process is investigated using a spatially resolved photoelectron emission method. The oxygen atoms from the native SiOx layer activate the gold-mediated catalytic decomposition of the entire graphene layer, resulting in the formation of direct contact between the Au and the Si substrate.

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.

Cycloaddition reaction of 1,3-butadiene with a symmetric Si adatom pair on the Si(111)7x7 surface.

We first found experimentally a cycloaddition reaction of a molecule on a symmetry Si pair, 1,3-butadiene on the Si adatom pair of Si(111)7x7, while up to now only asymmetric Si pairs were reported to be involved in cycloaddition reactions on Si surfaces. As the symmetry of a Si pair is expected to influence significantly a cycloaddition product and a reaction pathway, the [4+2]-like cycloaddition product of 1,3-butadiene on the Si adatom pair is suggested to form through a concerted reaction pathway in comparison to a stepwise reaction pathway, which is favorable in the formation of the [4+2]-like cycloaddition product on the asymmetric Si pair (the Si adatom-restatom pair).