Study of modified photoluminescence of Graphene/1L-WS2/Graphene heterostructures

prohibitionⅠ. Introduction 1 1.1 Two-dimensional materials 1 1.1.1 Transition metal dichalcogenides 1 1.1.2 Graphene 4 1.3 Motivation 6 1.3.1 Recent reports for modified photoluminescence in TMDs 6 1.3.2 Graphene/1L-WS2/Graphene heterostructures 10 ⅠⅠ. Experimental method 11 2.1 Synthesis of monolayer WS2 11 2.1.1 Substrate preparation 11 2.1.2 WS2 growth 12 2.2 Transfer method 13 ⅠⅠⅠ. Results and discussion 15 3.1 Synthesis and characterization of WS2 monolayer 15 3.2 Fabrication of the Graphene/1L-WS2/Graphene heterostructures 18 3.3 Observation of charge carrier transfer of Graphene/1L-WS2/Graphene heterostructures 20 3.4 Investigation of photoluminescence of Graphene/1L-WS2/Graphene heterostructures 22 ⅠV. Conclusions 28MASTERdCollectio

Facet-controlled hollow Rh2S3 hexagonal nanoprisms as highly active and structurally robust catalysts toward hydrogen evolution reaction

Developing highly active and structurally robust electrocatalysts for hydrogen evolution reaction (HER) is of paramount importance for sustainable and clean production of hydrogen. Metal sulphides exposing catalytically active sites, in particular, have been actively pursued as advanced HER catalysts. Herein we report high-performance Rh2S3-based HER catalysts with excellent activity and durability. Hollow Rh2S3 hexagonal nanoprisms with controlled size and thickness could be conveniently prepared by one-step formation of core-shell nanoprisms followed by the etching of the core, and they show high surface areas and highly exposed edge sites. The hollow Rh2S3 nanoprisms exhibit very high HER activity and excellent stability under harsh acidic conditions.close

Highly Crystalline Pd13Cu3S7 Nanoplates Prepared via Partial Cation Exchange of Cu1.81S Templates as an Efficient Electrocatalyst for the Hydrogen Evolution Reaction

Chemical transformations via post-synthetic modification of colloidal nanocrystals have received great attention as a rational synthetic route to unprecedented nanostructures. In particular, cation exchange reaction is considered as an effective method to alter the composition of the starting nanostructures while maintaining the initial structural characteristics. Herein, we report the synthesis of highly crystalline Pd13Cu3S7 nanoplates (NPs) via partial cation exchange of the Cu1.81S phase by Pd cations, with Cu1.94S NPs and Pd13Cu3S7/Cu2-xS janus heterostructure as the intermediate phases. The highly crystalline Pd13Cu3S7 ternary NPs exhibit excellent electrocatalytic performance toward the hydrogen evolution reaction (HER) in acidic condition. The HER activity of Pd13Cu3S7 NPs with its overpotential as low as 64 mV at -10 mA cm-2 is superior to those of amorphous PdCuS and commercial Pd/C catalysts, demonstrating the importance of nanocrystal crystallinity in boosting the HER activity. They also exhibit excellent stability as compared to commercial Pt/C and Pd/C under strongly acidic conditions

Surface-diffusion-limited growth of atomically thin WS2 crystals from core-shell nuclei

Atomically thin transition metal dichalcogenides (TMDs) have recently attracted great attention since the unique and fascinating physical properties have been found in various TMDs, implying potential applications in next-generation devices. The progress towards developing new functional and high-performance devices based on TMDs, however, is limited by the difficulty in producing large-area monolayer TMDs due to a lack of knowledge of the growth processes of monolayer TMDs. In this work, we have investigated the growth processes of monolayer WS 2 crystals using a thermal chemical vapor deposition method, in which the growth conditions were adjusted in a systematic manner. It was found that, after forming WO 3 -WS 2 core-shell nanoparticles as nucleation sites on a substrate, the growth of three-dimensional WS 2 islands proceeds by ripening and crystallization processes. Lateral growth of monolayer WS 2 crystals subsequently occurs by the surface diffusion process of adatoms toward the step edge of the three-dimensional WS 2 islands. Our results provide understanding of the growth processes of monolayer WS 2 by using chemical vapor deposition methods. © 2019 The Royal Society of Chemistry.1

Nitrogen-Deficient ORR Active Sites Formation by Iron-Assisted Water Vapor Activation of Electrospun Carbon Nanofibers

Fe- and N-modified carbon nanofibers (Fe–CNF) were synthesized via electrospinning and pyrolysis as electrocatalysts for oxygen reduction reaction (ORR). In order to increase the exposed surface area with the active sites buried inside Fe–CNF, we attempted water vapor activation for Fe–CNF and observed a substantial improvement of ORR activity up to the comparable level with Pt/C. Unlike what was expected, however, water vapor activation did not significantly increase the specific surface area of Fe–CNF; instead, it induced a depletion of surface N content, which makes it difficult to explain the improved ORR activity with the increase of surface area with N-based active sites. In water vapor activation, the chemical phase of embedded particles is changed from Fe₃C to Fe₃O₄ and nitrogen-free Fe- and C-based ORR active sites were exposed, which seemed to be related with hierarchical macro/mesopore structure and graphitic edge defects. This study demonstrates a facile activation method for better ORR activity of Fe-modified CNF and suggests a potential relationship of surface carbon structure with the catalytic activity toward ORR rather than the type and concentration of N in Fe–CNF, which should be investigated further

Fasting Glucose Variability as a Risk Indicator for End-Stage Kidney Disease in Patients with Diabetes: A Nationwide Population-Based Study

Given the fact that diabetes remains a leading cause of end-stage kidney disease (ESKD), multi-aspect approaches anticipating the risk for ESKD and timely correction are crucial. We investigated whether fasting glucose variability (FGV) could anticipate the development of ESKD and identify the population prone to the harmful effects of GV. We included 777,192 Koreans with diabetes who had undergone health examinations more than three times in 2005–2010. We evaluated the risk of the first diagnosis of ESKD until 2017, according to the quartile of variability independent of the mean (VIM) of FG using multivariate-adjusted Cox proportional hazards analyses. During the 8-year follow-up, a total of 7290 incidents of ESKD were found. Subjects in the FG VIM quartile 4 had a 27% higher risk for ESKD compared to quartile 1, with adjustment for cardiovascular risk factors and the characteristics of diabetes. This effect was more distinct in patients aged < 65 years; those with a long duration of diabetes; the presence of hypertension or dyslipidemia; and prescribed angiotensin-converting enzyme inhibitors, metformin, sulfonylurea, α-glucosidase inhibitors, and insulin. In contrast, the relationship between baseline FG status and ESKD risk showed a U-shaped association. FGV is an independent risk factor for kidney failure regardless of FG

2D-Material-Assisted GaN Growth on GaN Template by MOCVD and Its Exfoliation Strategy

The production of freestanding membranes using two-dimensional (2D) materials often involves techniques such as van der Waals (vdW) epitaxy, quasi-vdW epitaxy, and remote epitaxy. However, a challenge arises when attempting to manufacture freestanding GaN by using these 2D-material-assisted growth techniques. The issue lies in securing stability, as high-temperature growth conditions under metal–organic chemical vapor deposition (MOCVD) can cause damage to the 2D materials due to GaN decomposition of the substrate. Even when GaN is successfully grown using this method, damage to the 2D material leads to direct bonding with the substrate, making the exfoliation of the grown GaN nearly impossible. This study introduces an approach for GaN growth and exfoliation on 2D material/GaN templates. First, graphene and hexagonal boron nitride (h-BN) were transferred onto the GaN template, creating stable conditions under high temperatures and various gases in MOCVD. GaN was grown in a two-step process at 750 and 900 °C, ensuring exfoliation in cases where the 2D materials remained intact. Essentially, while it is challenging to grow GaN on 2D material/GaN using only MOCVD, this study demonstrates that with effective protection of the 2D material, the grown GaN can endure high temperatures and still be exfoliated. Furthermore, these results support that vdW epitaxy and remote epitaxy principle are not only possible with specific equipment but also applicable generally

Metastable hexagonal close-packed palladium hydride in liquid cell TEM

Metastable phases-kinetically favoured structures-are ubiquitous in nature1,2. Rather than forming thermodynamically stable ground-state structures, crystals grown from high-energy precursors often initially adopt metastable structures depending on the initial conditions, such as temperature, pressure or crystal size1,3,4. As the crystals grow further, they typically undergo a series of transformations from metastable phases to lower-energy and ultimately energetically stable phases1,3,4. Metastable phases sometimes exhibit superior physicochemical properties and, hence, the discovery and synthesis of new metastable phases are promising avenues for innovations in materials science1,5. However, the search for metastable materials has mainly been heuristic, performed on the basis of experiences, intuition or even speculative predictions, namely &apos;rules of thumb&apos;. This limitation necessitates the advent of a new paradigm to discover new metastable phases based on rational design. Such a design rule is embodied in the discovery of a metastable hexagonal close-packed (hcp) palladium hydride (PdHx) synthesized in a liquid cell transmission electron microscope. The metastable hcp structure is stabilized through a unique interplay between the precursor concentrations in the solution: a sufficient supply of hydrogen (H) favours the hcp structure on the subnanometre scale, and an insufficient supply of Pd inhibits further growth and subsequent transition towards the thermodynamically stable face-centred cubic structure. These findings provide thermodynamic insights into metastability engineering strategies that can be deployed to discover new metastable phases. © 2022. The Author(s), under exclusive licence to Springer Nature Limited.11Nsciescopu