Ultrathin polycrystalline 6,13-Bis(triisopropylsilylethynyl)-pentacene films

Ultrathin (<6 nm) polycrystalline films of 6,13-bis(triisopropylsilylethynyl) pentacene (TIPS-P) are deposited with a two-step spin-coating process. The influence of spin-coating conditions on morphology of the resulting film was examined by atomic force microscopy. Film thickness and RMS surface roughness were in the range of 4.0-6.1 and 0.6-1.1 nm, respectively, except for small holes. Polycrystalline structure was confirmed by grazing incidence x-ray diffraction measurements. Near-edge x-ray absorption fine structure measurements suggested that the plane through aromatic rings of TIPS-P molecules was perpendicular to the substrate surface. (C) 2014 American Vacuum Societyclos

Enhanced selective photocatalytic oxidation of a bio-derived platform chemical with vacancy-induced core-shell anatase TiO2 nanoparticles

© 2022 Elsevier B.V. All rights reserved. 2,5-Furandicarboxylic acid (FDCA), a biodegradable alternative to fossil fuels, can be obtained via the catalytic oxidation of 2,5-hydroxymethlyfurfural (HMF), which is sourced from biomass. Anatase TiO2 nanoparticles (NPs) with oxygen vacancies (Vo) effectively promote the oxidation process under ultraviolet/visible-light illumination. The conversion process is accelerated by introducing anatase TiO2 NPs with a Vo-densified shell and stoichiometric core, which is achieved by a simple base treatment after synthesis. The defective shell acts as an electron-rich catalytic platform to facilitate HMF oxidation. Base-treated NPs measuring less than 20 nm yield ∼40% conversion to FDCA via HMF oxidation at room temperature in water. The photocatalytic activity is achieved at a 580% higher rate than with the corresponding untreated TiO2. Spectroscopic characterizations clearly visualize the densified layer of Vo enclosing the surface of the high-performance TiO2 NPs. Our results provide new insights into the optimal defect engineering of oxide-based catalysts for efficient biomass conversions.11Nsciescopu

Post-patterning of an electronic homojunction in atomically thin monoclinic MoTe2

Monoclinic group 6 transition metal dichalcogenides (TMDs) have been extensively studied for their intriguing 2D physics (e.g. spin Hall insulator) as well as for ohmic homojunction contacts in 2D device applications. A critical prerequisite for those applications is thickness control of the monoclinic 2D materials, which allows subtle engineering of the topological states or electronic bandgaps. Local thickness control enables the realization of clean homojunctions between different electronic states, and novel device operation in a single material. However, conventional fabrication processes, including chemical methods, typically produce non-homogeneous and relatively thick monoclinic TMDs, due to their distorted octahedral structures. Here, we report on a post-patterning technique using laser-irradiation to fabricate homojunctions between two different thickness areas in monoclinic MoTe2. A thickness-dependent electronic change from a metallic to semiconducting state, resulting in an electronic homojunction, was realized by the optical patterning of pristine MoTe2 flakes, and a pre-patterned device channel of monoclinic MoTe2 with a thickness-resolution of 5 nm. Our work provides insight on an optical post-process method for controlling thickness, as a promising approach for fabricating impurity-free 2D TMDs homojunction devices. © 2017 IOP Publishing Ltd3

Superconductivity in Te-deficient polymorphic MoTe2-x and its derivatives: rich structural and electronic phase transitions

The group 6 transition metal dichalcogenides (TMDs) have been received great attentions due to intriguing superconducting states correlated with structural uncertainty and electronic complexity. Here, we synthesized Te-deficient polycrystals of semimetallic MoTe2-x and its derivatives (Mo(1-y)TM(y)Te(2-x)Ch(x)(TM: Nb, Mn and V, Ch: P)), and investigated the structural and electronic phase transitions. It was found that all Te-deficient semimetallic phases (monoclinic 1T', hexagonal 2H and rhombohedral 3R) exhibited the superconducting transition, in which 2H and 3R structures were evolved in Nb-substituted Mo1-yNbyTe2-x (y = 0.4 for 2H, 0.6 for 3R), respectively. Moreover, we found that the superconducting state of 2H-and 3R-Mo1-yNbyTe2-x appears at the vicinity of the transition from insulator to semimetal regime with the increased electron concentration via TM substitution and Te-deficiency. It is revealed that all superconducting 1T'-, 2H-and 3R-Mo(1-y)TM(y)Te(2-x)Ch(x) semimetals show the half-dome shaped superconducting phase diagram with respect to the electron concentration and TM substitution © 2018 IOP Publishing Lt

Heterogeneous Defect Domains in Single-Crystalline Hexagonal WS2

Although intricate defects are inevitably generated during the synthesis of transition metal dichalcogenides (TMdCs) by chemical vapor deposition (CVD), the related discussions are mostly limited to chalcogen vacancies.[1–3] Here, we report the prevailing role of metal vacancies determining macroscopic material properties using a single-crystalline monolayer 2H-WS2 grown by CVD. The hexagonal shape of the WS2 flake is segmented into alternating triangular domains without forming explicit defective grain boundaries: sulfur-vacancy (SV)-rich and tungsten-vacancy (WV)-rich domains. The WV-rich domain with deep-trap states[4–6] revealed an electron-dedoping effect, and its electron mobility and photoluminescence were lower by one order of magnitude than those of the SV-rich domain with shallow-donor states.[7] The vacancy-induced strain and doping effects in such domains were investigated by analyzing spectral changes via Raman spectroscopy and the core-level shift via scanning photoelectron microscopy. Our work sheds light on tailoring macroscopic physical properties of 2D materials via native defect engineering. 2D layered materials such as monolayer graphene and TMdCs can be obtained on a wafer scale by CVD,[8] which could be a direct route for realizing various heterostructures for practical applications.[9] The electrical and optical properties of TMdCs are generally determined by crystal imperfections such as grain boundaries (GBs),[10–12] vacancies,[1,13] and impurities.[14,15] Intrinsic defects are likely more abundant in CVD-grown samples than mechanically exfoliated (ME) ones. In polycrystalline CVD-grown films, GBs are inevitably generated via the coalescence of individual grains and have been well characterized because of their critical influence on electrical transport.[10,11] Vacancies are unavoidably formed inside grains and can also be a key factor in determining the carrier. © 2017 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim114131sciescopu

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 degrees 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. The notably low contact resistivity found in this system suggests that the catalytic depletion of a SiOx layer could realize a new way to micromanufacture high-quality electrical contact

Efficient CO Oxidation by 50-Facet Cu2O 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 H2O + CO reversible arrow CO2 + H-2) 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 similar to 10 nm sized CuO nanoparticles (NPs) aggregated on similar to 400 nm sized 50-facet Cu2O polyhedral nanocrystals. This CuO-NPs/50-facet Cu2O shows remarkable CO oxidation reactivity with very high specific CO oxidation activity (4.5 mu mol(CO) m(-2) s(-1) at 130 degrees C) and near-complete 99.5% CO conversion efficiency at similar to 175 degrees C. This outstanding catalytic performance by CuO NPs over the pristine multifaceted Cu2O nanocrystals is attributed to the surface oxygen defects present in CuO NPs which facilitate binding of CO and O-2 on their surfaces. This new material opens up new possibilities of replacing the usage of expensive CO oxidation materials.clos

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. Here, we demonstrate that chemical-vapor-deposited single-layer graphene can be transferred onto a silicon dioxide substrate with a 3D geometry, such as a concave-convex architecture. A variety of silicon dioxide concave-convex architectures were uniformly and seamlessly laminated with graphene using a thermal treatment. The planar graphene was stretched to cover the concave-convex architecture, and the resulting strain on the curved graphene was spatially resolved by confocal Raman spectroscopy; molecular dynamic simulations were also conducted and supported the observations. Changes in electrical resistivity caused by the spatially varying strain induced as the graphene-silicon dioxide laminate varies dimensionally from 2D to 3D were measured by using a four-point probe. The resistivity measurements suggest that the electrical resistivity can be systematically controlled by the 3D geometry of the graphene-silicon dioxide laminate. This 3D graphene-insulator laminate will broaden the range of graphene applications beyond planar structures to 3D materials.close0