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We report the pyrolysis of copper-containing metal-organic frameworks under high pressure and the effect of the applied pressure on the morphology and electrocatalytic performance toward the oxygen-related reactions of the products. The high-pressure and high-temperature (HPHT) syntheses were performed under 5, 2.5, 1, and 0.5 GPa, and the Cu@C products were obtained except for the 2.5 GPa experiment. Copper formed a shell-like nanostructure on the carbon matrices during the 0.5 GPa experiment, whereas copper formed sub-nanometer sized particles in the carbon matrices with the increasing pressure. It is considered that the transportation of copper atoms by outgassing during the pyrolysis affects the morphology. Electrochemical measurements revealed that all samples exhibited activity for the oxygen reduction reaction (ORR). The 0.5 GPa-treated product also exhibited the oxygen evolution reaction (OER). The overall ORR/OER performance of this product was excellent among Cu-based bifunctional materials even though it did not contain cocatalysts such as nitrogen-doped carbon or other metal elements. The Cu(iii) species in the nano-thick copper shell structure provided the active sites for the OER.

MoO2 nanowires (NWs), MoO2/MoS2 core-shell NWs, and MoS2 nanotubes (NTs) were synthesized by the turbulent flow chemical vapor deposition of MoO2 using MoO3, followed by sulfurization in the sulfur gas flow. The involvement of MoOx suboxide is suggested by density functional theory (DFT) calculations of the surface energies of MoO2. The thickness of the MoS2 layers can be controlled by precise tuning of sulfur vapor flow and temperatures. MoS2 had an armchair-type winding topology due to the epitaxial relation with the MoO2 NW surface. A single similar to few-layer MoO2/MoS2 core-shell structure showed photoluminescence after the treatment with a superacid. The resistivities of an individual MoO2 NW and a MoS2 NT were measured, and they showed metallic and semiconducting resistivity-temperature relationships, respectively.

Materials containing Dirac fermions (DFs) have been actively researched because they often alter electrical and magnetic properties in an unprecedented manner. Although many studies have suggested the transformation between standard fermions (SFs) and DFs, the non-availability of appropriate samples has prevented the observation of the transformation process. We observed the interconversion process of DFs and SFs using organic charge-transfer (CT) salts. The samples are unique in that the constituents (the donor D and acceptor A species) are particularly close to each other in energy, leading to the temperature- and D-A-combination-sensitive CT interactions in the solid states. The three-dimensional weak D–A CT interactions in low-symmetry crystals induced the continuous reshaping of flat-bottomed bands into Dirac cones with decreasing temperature; this is a characteristic shape of bands that converts the behavior of SFs into that of DFs. Based on the first-principles band structures supported by the observed electronic properties, round-apex-Dirac-cone-like features appear and disappear with temperature variation. These band-structure snapshots are expected to add further detailed understanding to the related research fields.

We report the crystal growth of pentacene from a solution of naphthalene. The solubility of pentacene in naphthalene was evaluated by optical absorption at elevated temperature. The crystal growth was performed in an H-shaped sealed glass tube or metal vessels sealed with ultrahigh-vacuum compatible flanges placed in heated two-zone aluminum blocks. The obtained crystals had a single-crystal-like appearance and flat surface. They were made of aligned microtwins of the "bulk type" (interlayer spacing 14.5 Å) polymorph.

The Mo6 cluster which has the great optical properties and chemical activity because of their unique electronic structure have been attracted attention in many fields such as phosphor and photocatalyst. However, the Mo6 cluster it’s hard to recycling which limited its industry application because of its such small nanoscale. Immobilizing the Mo6 cluster on 2-D material has a great value to challenge it. In this research, we study on the sulfurization process of Mo6Br12 cluster to investigate the more possibility of the immobilization of Mo6 cluster.

Single crystal diamond particles were heated with liquid phase alkali metals (Li, Na, K) in an argon atmosphere. It was found that Li reacts with the diamond above 600 degrees C, Na makes the surface rougher on a nm scale at 800 degrees C, and K did not change the surface morphology. The etching speed by the reaction with Li is the fastest on the (001) surface. Photoluminescence of the NV- (negatively charged nitrogen vacancy) center decreased only after the annealing with K. DFT calculations explained the strong chemical interaction between Li and the diamond (001) surfaces, and upward band bending at the interfaces with Na and K. The behavior of the NV-center photoluminescence is consistent with the extent of band bending. (C) 2021 Elsevier Ltd. All rights reserved.

Developing a technology to terminate chalcogen vacancies for transition-metal dichalcogenides is a crucial task for applications, such as transistors, diodes, and sensors, because chalcogen vacanci...

A simple co-grinding treatment with fructose is introduced for the efficient and scalable preparation of g-C3N4 nanoplates. The results revealed that these g-C3N4 nanoplates still preserved the basic framework of carbon nitride and even displayed superior morphological properties and electronic structures. With respect to the pristine carbon nitride, the few-layered g-C3N4 impressively demonstrated an enhanced photocatalytic activity towards hydrogen generation and the degradation of Rhodamine B (RhB) under visible light illumination, emphasizing the vital roles of the morphology and electronic structures on the photocatalytic performance. This study provided sustainable and cost-effective tactics for the delamination of g-C3N4 for efficient energy conversion. (C) 2020 Hydrogen Energy Publications LLC. Published by Elsevier Ltd. All rights reserved.

Single-crystal Fe nanowires (NWs) were synthesized on SiO2/Si substrates by chemical vapor deposition (CVD) using a two-flow system in the presence of FeO nanoparticles as catalysts. Transmission electron microscopy observations and an electron diffraction analysis revealed that the NW was defect-free α-Fe (bcc structure) oriented in the ⟨100⟩ direction. A plausible mechanism of the Fe NW growth is suggested based on the observations of the morphology and characteristic diameter of the Fe NW. We found that the NWs became polycrystalline when their diameter was approximately 100 nm. The excellent crystal quality of the single-crystal NW was confirmed by electron diffraction and the residual resistance ratio. Magnetic uniformity and a strong shape-anisotropic behavior of magnetization were observed by measuring the hysteresis loop and the angle dependence of the magneto-optical Kerr effect, respectively.

Introducing ferromagnetism in light-element materials that contain only s and p electrons has captured much attention for their possible application in spintronic devices. In this study, we explored the ferromagnetic properties of carbon-doped boron nitride (B C N) nanosheets obtained by high-temperature annealing of a stacked mixture of boron nitride nanosheets (BNNSs) and graphene prepared by urea-assisted aqueous exfoliation. Three types of BCN nanosheets, referred to as BCN (1:1), BCN (1:2) and BCN (1:3), were successfully synthesized through multistep processes. Strong ferromagnetic responses were observed in the BCN nanosheets with a saturation magnetization of 0.142 emu/g at room temperature. It was found that the thickness of the precursors plays a critical role in the determination of the ferromagnetic properties of the BCN nanosheets. Our results provide a new possibility for the manipulation of ferromagnetism in light-element systems.

Spinel-type magnetite ${\mathrm{Fe}}_{3}{\mathrm{O}}_{4}$ is predicted to be a half-metal material with negative spin polarization. However, magnetic tunnel junctions (MTJs) using an ${\mathrm{Fe}}_{3}{\mathrm{O}}_{4}$ electrode exhibit a small tunnel magnetoresistance (TMR) effect, the sign of which has not been established experimentally. The development of ${\mathrm{Fe}}_{3}{\mathrm{O}}_{4}$ as an excellent TMR material requires a better understanding of the characteristics of the interface and the phase transition of ${\mathrm{Fe}}_{3}{\mathrm{O}}_{4}$ called the Verwey transition. We fabricate MTJs using epitaxial ${\mathrm{Fe}}_{3}{\mathrm{O}}_{4}$-based stacks on $\mathrm{Mg}\mathrm{O}(001)$ substrates and find a large inverse TMR ratio of \ensuremath{-}55.8% at 80 K, which corresponds to 126% by the optimistic definition of the TMR ratio. The temperature dependence of the TMR ratio is significantly affected by the Verwey transition. Moreover, we investigate the dependence of TMR on oxygen partial pressure during ${\mathrm{Fe}}_{3}{\mathrm{O}}_{4}$ deposition. It is found that the magneto-transport properties of the MTJs show different behaviors depending on the oxygen partial pressure because the Verwey transition is sensitive to the oxygen concentration. Furthermore, the electronic and magnetic properties at the interfacial regions are investigated by x-ray magnetic spectroscopy and first-principles calculation. These findings greatly support the use of ${\mathrm{Fe}}_{3}{\mathrm{O}}_{4}$ in spintronic devices and should lead to further developments in oxide spintronics.

Two-dimensional (2D) graphitic carbon nitride (g-C3N4) nanoplates (CNNP) have become a hot research topic in photocatalysis due to their small thickness and large specific surface area that favors charge transport and catalytic surface reactions. However, the wide application of 2D g-C3N4 nanoplates prepared by ordinary methods suffers from increased band gaps with a poor solar harvesting capability caused by the strong quantum confinement effect and reduced conjugation distance. In this paper, a facile approach of exfoliation and the following fast thermal treatment of the bulk g-C3N4 is proposed to obtain a porous few-layered g-C3N4 with nitrogen defects. Due to the preferable crystal, textural, optical and electronic structures, the as-obtained porous CNNP demonstrated a significantly improved photocatalytic activity towards water splitting than the bulk g-C3N4 and even the 3 nm-thick CNNP obtained by sugarassisted exfoliation of the bulk g-C3N4. The difference in the enhancement factors between the H2O splitting and organic decomposition has revealed the effect of N defects. This study offers insightful outlooks on the scalable fabrication of a porous few-layered structure with a promoted photocatalytic performance. (C) 2020 Elsevier Inc. All rights reserved.

The doping of element (Nb, Ta, etc.) into MoS2, one of the layered transition metal dichalcogenides, is a key technology for electronic devices because the lack of the p-type MoS2 has limited the range of applications. We report that the Mo1−xNbxS2 thin films were synthesized on SiO2/Si substrates by chemical vapor deposition (CVD). It was critical to use chloride sources (MoCl5 and NbCl5) for the synthesis of Mo1−xNbxS2. The Nb concentration can be increased to 10% by controlling the supplied amount of Nb using a separate-flow CVD apparatus. The Raman spectra changed as the Nb concentration increased, appearing E2(Nb S) vibrational mode. The photoluminescence (PL) at 655 nm, attributed to emission from excitons, disappeared, when Nb was incorporated into the MoS2. PL due to trions at 680 nm was observed for the Mo1−xNbxS2 thin films.

Morphology of diamond films has been controlled via intermediate frequency induction heated microwave plasma chemical vapor deposition (IH-MPCVD), which was transformed with various substrate temperatures (Tsub = 923–1123 K) and CH4/H2 ratios (ηc = 0.5–2 vol%). The coupling effects of Tsub and ηc on the structure of diamond films have been studied. At ηc = 0.5 vol%, the sp3/sp2 ratio of diamond films reached 98% at 1073 K, surface roughness (Rms) increased from 50 to 85 nm with increasing Tsub, the maximum hardness (Ha) reached 84 GPa at 973 K, and the maximum Young's modulus (E) reached 642 GPa at 1023 K. The residual stress (σ) was calculated as a function of Tsub and ηc. The quality factor (Q), combining microstructure and mechanical behavior, has been creatively defined to evaluate the quality of diamond films.

Photocatalytic generation of hydrogen peroxide (H2O2) is a sustainable technique to realize the solar-energy conversion. Here, ultrathin graphitic carbon nitride (g-C3N4) nanoplates with thickness of 1–3 nm was introduced for the efficient H2O2 production. The as-obtained nanoplates demonstrated the H2O2 production rate of 43.07 μmol g−1 h−1 and about 4 times as high as the pristine g-C3N4. Experimental results reflected that the ultrathin morphology offered an increased surface area, more active sites, smaller charge transfer length and stronger redox ability than that of the bulk counterparts. Moreover, the introduction of ultrathin structure switched the H2O2 production pathway from a two-step single-electron reduction to a one-step two-electron reduction route. This study offered the deep elucidation of the influence of ultrathin structure on the photoactivity of semiconductor photocatalysts.

This paper present computational study on molybdenum disulfide (MoS2 ) nanotubes with square cross sections in order to elucidate the growth mechanism and properties of experimentally synthesized nanotubes. The results show that these square nanotubes have strain energies lower than the traditional cylinder ones in the small-diameter region. They also show a much smaller band gap and higher surface energies compared with the cylindrical ones. Zigzag and armchair chirality shows qualitatively different electronic structures about the localization of the edge states.

Difluorinated polycyclic aromatic hydrocarbons (PAHs) containing three to five benzene rings were systematically synthesized by the Pd(II)-catalyzed Friedel–Crafts-type cyclization of 1,1,2-trifluoro- and 1,1-difluoro-1-alkenes and the In(III)-catalyzed tandem cyclization of bis(1,1-difluoroallene)s. Using an array of the difluorinated PAHs that were obtained and previously reported monofluorinated PAHs, the physical properties of the pinpoint-fluorinated PAHs were investigated. (i) The 19F NMR signals of the bay-region fluorine atoms were shifted downfield by ca. 8–14 ppm for vic-difluorinated PAHs and ca. 11–19 ppm for non-vic-difluorinated and monofluorinated PAHs. (ii) The introduction of fluorine into PAH molecules increased their solubilities in organic solvents, which was best exemplified by the high solubilities of 6,7-difluoropicene (5.4 wt%) and 6-fluoropicene (5.3 wt%) in THF. (iii) The HOMO–LUMO energy gaps of the pinpoint-fluorinated PAHs were smaller than that of the corresponding fluorine-free PAH (i.e., picene) by 0.02–0.26 eV, and the HOMO and LUMO energy levels were lowered by 0.10–0.22 eV and 0.12–0.41 eV, respectively.

The application of magnetic oxides in spintronics has recently attracted much attention. The epitaxial growth of magnetic oxide on Si could be the first step of new functional spintronics devices with semiconductors. However, epitaxial spinel ferrite films are generally grown on oxide substrates, not on semiconductors. To combine oxide spintronics and semiconductor technology, we fabricated Fe3O4 films through epitaxial growth on a Si(111) substrate by inserting a γ-Al2O3 buffer layer. Both of γ-Al2O3 and Fe3O4 layer grew epitaxially on Si and the films exhibited the magnetic and electronic properties as same as bulk. Furthermore, we also found the buffer layer dependence of crystal structure of Fe3O4 by X-ray diffraction and high-resolution transmission electron microscope. The Fe3O4 films on an amorphous-Al2O3 buffer layer grown at room temperature grew uniaxially in the (111) orientation and had a textured structure in the plane. When Fe3O4 was deposited on Si(111) directly, the poly-crystal Fe3O4 films were obtained due to SiOx on Si substrate. The epitaxial Fe3O4 layer on Si substrates enable us the integration of highly functional spintoronic devices with Si technology.

Magnetocapacitance (MC) effect, observed in a wide range of materials and devices, such as multiferroic materials and spintronic devices, has received considerable attention due to its interesting physical properties and practical applications. A normal MC effect exhibits a higher capacitance when spins in the electrodes are parallel to each other and a lower capacitance when spins are antiparallel. Here we report an inverse tunnel magnetocapacitance (TMC) effect for the first time in Fe/AlOx/Fe3O4 magnetic tunnel junctions (MTJs). The inverse TMC reaches up to 11.4% at room temperature and the robustness of spin polarization is revealed in the bias dependence of the inverse TMC. Excellent agreement between theory and experiment is achieved for the entire applied frequency range and the wide bipolar bias regions using Debye-Fröhlich model (combined with the Zhang formula and parabolic barrier approximation) and spin-dependent drift-diffusion model. Furthermore, our theoretical calculations predict that the inverse TMC effect could potentially reach 150% in MTJs with a positive and negative spin polarization of 65% and −42%, respectively. These theoretical and experimental findings provide a new insight into both static and dynamic spin-dependent transports. They will open up broader opportunities for device applications, such as magnetic logic circuits and multi-valued memory devices.

Nanowires of layered materials are important because they exhibit the highest sensitivity as electrically-detecting chemical sensors. MoS2 nanowires have been synthesized by a catalytic chemical vapor deposition method on silicon substrates drop-coated with FeO nanoparticles of different shapes. Switching of the products (MoS2 nanowires to SiO2 nanowires) has been observed when the shapes and sizes of the FeO nanoparticles changed. MoS2 nanowires were grown in the presence of six-horned octahedral nanoparticles, whereas SiO2 nanowires were formed in the presence of spherical nanoparticles. Their morphology, crystal structure and elemental composition have been fully investigated to elucidate the growth mechanism of the nanowires. The kinetics of the grown SiO2 and MoS2 nanowires are competing, giving rise to the observed switching.

We found that oxidized Cu nanoparticles can catalyze the growth of boron nitride nanotubes from borazine via plasma-assisted chemical vapor deposition. The Raman spectra suggest that the formation of thin-walled nanotubes show a radial breathing mode vibration. The presence of oxygen in the plasma environment was necessary for the growth of the nanotubes, and a part of the nanotubes had a core shell structure with a cupper species inside it. In atomic resolution transmission electron microscope (TEM) images, Cu2O was found at the interface between the Cu-core and turbostratic BN-shell. The growth mechanism seemed different from that of carbon nanotube core-shell structures. Therefore, we pointed out the important role of the dynamic morphological change in the Cu2O-Cu system.

This paper describes an attempt to synthesize bismuth-doped diamond by plasma CVD. Solid bismuth was inserted into the reaction plasma of CH4 and H2. Examination by TEM showed that most of the bismuth was included as Bi nanoparticles in the carbon nanospheres, which segregated at the grain boundary of the diamond polycrystals. Diffraction peaks corresponding to the carbon allotrope Chaoite were observed at the grain boundaries. The Raman spectra showed very complex features between 100–1600 cm− 1, suggesting the existance of molecule-like species.

This article reports the growth and characterization of c-axis-oriented NbS2 thin films on SiO2/Si substrate by ambient pressure chemical vapor deposition (CVD) using a generic metal chloride source. We found that NbS2 nanosheets can be grown directly on the SiO2/Si substrate with the aid of hydrogen gas mixed in the carrier gas. Detailed examination of the growth parameters was made possible using a separate-flow CVD apparatus. It appears that the major cause of the misorientation is the off-stoichiometry with surplus Nb. The quality of the films was evaluated by X-ray diffraction and Raman spectroscopy as well as resistivity measurements at low temperatures. They showed a resistivity minimum at the same temperature of the charge density wave (CDW) transition for a bulk single crystal of 3R-NbS2.

High-crystalline diamond films were prepared by laser (wavelength: 532 nm) microwave plasma chemical vapor deposition (Laser MPCVD). The effects of laser power density (E) on the microstructure and properties of diamond films were investigated. The laser enhanced the precursor reaction process which reduces the non-diamond components such as graphite and amorphous carbon. At E = 40 W/cm2, more methyl radicals and atomic hydrogen were generated with coupling of laser and plasma, which promoted crystal growth until the grain size reaches the maximum value of 0.72 μm. The phase purity of film reached the highest as the full width at half maximum (FWHM) of Raman peak reached the minimum of FWHMmin = 4.2 cm−1. And hardness (H) and Young's modulus (M) values reached the maximum of Hmax = 91 GPa and Mmax = 721 GPa, respectively. The discovery of the advantages of laser in diamond growth is of great significance for improving the synthesis of many technically crucial materials.

Nickel cobalt spinel oxide, NiCo2O4, is an important material for spintronics because it exhibits both ferrimagnetic characteristics and electrical conductivity. Because high oxygen pressure during deposition is necessary to obtain useful properties, pulsed laser deposition has been used to fabricate NiCo2O4 films. In this study, we investigated the physical properties of NiCo2O4 films synthesized by reactive molecular beam epitaxy and annealing in a high-pressure oxygen atmosphere. The characteristics of the films strongly depended on the oxygen pressure, and a larger pressure tended to give larger magnetization and higher conductivity. Crystal structure analysis by x-ray diffraction and transmission electron microscopy revealed that the films consisted of a rock salt (Ni,Co)O phase and a spinel NiCo2O4 phase. This phase separation caused the small magnetization and large electric resistance because the rock salt phase was an antiferromagnetic insulator.

Magnetic spinel oxides, including CoFe2O4 (CFO), have crucial applications in spintronics. They have excellent magnetic properties, such as high spin polarization and high Curie temperature, which enables the operation of spintronic devices at room temperature. Some interesting phenomena have also been discovered for interfaces consisting of spinel oxides and heavy metals. However, the magnetic properties of ultrathin CFO films have not been investigated sufficiently. In this report, a characterization of the magnetic properties of an ultrathin CFO film was performed by using the magnetic proximity effect (MPE) to observe the anomalous Hall effect (AHE) in Pt. The result was consistent with the measurement performed with magneto-optical effects. By fitting AHE with the Langevin function, it was concluded that these ultrathin films (tCFO

The facile exfoliation of graphitic carbon nitride (g-C3N4) into single- or few-layered nanoplates remains a grand challenge for the fundamental studies and applications of g-C3N4. Herein, we present an efficient tactic for the facile fabrication of few-layered porous g-C3N4 nanoplates using a novel combination of thermal etching and gas-driven exfoliation of bulk g-C3N4. In comparison with the pristine g-C3N4, the few-layered porous g-C3N4 nanoplates displayed modified electronic structures and large specific surface area. Consequently, the obtained g-C3N4 nanoplates after the several exfoliation cycles showed greatly enhanced photocatalytic activities. The average hydrogen (H2) evolution rate of g-C3N4 nanoplates exceeds that of the bulk counterpart by almost 9 times and the photodegradation efficiency of rhodamine B (RhB) increased by about 6-fold under visible light irradiation. Our work provides an efficient method towards the fabrication of porous g-C3N4 nanoplates with impressive photocatalytic performance.