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Deviation of the Fast Faraday Cup signal from the longitudinal shape of the measured bunch is estimated, and a simple formula for the increase of the signal rms width is suggested.
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The use of nanoporous metals as catalysts has attracted significant interest in recent years. Their high-curvature, nanoscale ligaments provide not only high surface area but also a high density of undercoordinated step edge and kink sites. However, their long-term stability, especially at higher temperatures, is often limited by thermal coarsening and the associated loss of surface area. Herein, it is demonstrated that the nanoscale morphology of nanoporous Cu can be regenerated by applying oxidation/reduction cycles at 250 °C. Specifically, the morphological evolution and H 2 dissociation activity of hierarchical nanoporous Cu catalysts doped with Ti during structural rearrangement triggered by oxidative and reductive atmospheres at elevated temperatures are studied. In addition to coarsening of the structure at elevated temperatures, oxidation at 400 °C causes an expansion of the ligaments. Further, subsequent reduction at 400 °C leads to the formation of particles and a drop in the H 2 dissociation activity compared the fresh catalyst. However, performing the redox cycle at 250 °C reverses coarsening and boosts the H 2 dissociation activity for the hydrogen–deuterium (H 2 –D 2 ) reaction. Herein, the possibility to reverse coarsening is demonstrated, thereby mitigating the loss of activity frequently observed in nanoporous catalysts.
Defects are ubiquitous in 2D materials and can affect the structure and properties of the materials and also introduce new functionalities. Methods to adjust the structure and density of defects during bottom-up synthesis are required to control the growth of 2D materials with tailored optical and electronic properties. In this study, the authors present an Au-assisted chemical vapor deposition approach to selectively form S W and S2 W antisite defects, whereby one or two sulfur atoms substitute for a tungsten atom in WS 2 monolayers. Guided by first-principles calculations, they describe a new method that can maintain tungsten-poor growth conditions relative to sulfur via the low solubility of W atoms in a gold/W alloy, thereby significantly reducing the formation energy of the antisite defects during the growth of WS 2 . The atomic structure and composition of the antisite defects are unambiguously identified by Z-contrast scanning transmission electron microscopy and electron energy-loss spectroscopy, and their total concentration is statistically determined, with levels up to ≈5.0%. Furthermore, scanning tunneling microscopy/spectroscopy measurements and first-principles calculations also verified these antisite defects and revealed the localized defect states in the bandgap of WS 2 monolayers. This bottom-up synthesis method to form antisite defects should apply in the synthesis of other 2D materials.
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In this work, we report on the disparity in the assembly behavior of four types of nano-sized macroions induced by isotopic substitution of protium (H) to deuterium (D) in solvents. Additionally, macroions with modest charge density can self-assemble into single-layer, hollow, spherical “blackberry”-type structures, with larger assembly sizes representing stronger attractions among the macroions. Kinetically, all assembly processes become slower in D 2 O than in H 2 O. Thermodynamically, the polyoxometalate {SrPd 12 }, the uranium cage {U 60 } with alkali metal counterions, and the metal–organic cationic cage {Pd 12 L 24 } demonstrate similar assembly sizes in both H 2 O and D 2 O, whereas the metal oxide cluster {Mo 72 Fe 30 } as a weak acid shows an unusually large assembly size in H 2 O—suggesting a stronger contribution from the hydrogen bonding in the last case.
Molten salts are crucial materials with exceptional properties that make them suitable for applications such as heat transfer media, coolants, and liquid fuels in molten salt nuclear reactors and the concentrated solar power industry. Understanding their properties requires unraveling the intricate mysteries of their structure. To achieve this, advanced characterization tools are essential. Among various techniques, X‐ray absorption fine structure (XAFS) stands out as a versatile method capable of studying the structure of molten salts under in situ conditions. This review highlights recent advancements in the application of XAFS for investigating the local structure of molten salts, discusses its limitations and potential improvements, and explores complementary approaches such as simulations, machine learning, and correlative experimental methods.
ABSTRACT The supported aqueous‐phase catalysis (SAPC) using hydrated interface has been used to synthesize branched polymers (star and graft) of benzyl methacrylate (BnMA) via atom‐transfer radical polymerization (ATRP) in the presence of Na‐clay supported catalyst in anisole at ambient temperature. The propagation of star poly(BnMA)s using diPENDTA‐Br 6 , as hexa ‐functional initiator is confined at the hydrated interface between the support and the liquid medium as evident from the obtained polymers that are catalyst contamination‐free, and exhibited moderately narrow molecular weight distributions ( M w / M n ≤ 1.33). The hexa ‐functionality of synthesized stars is verified by 1 H NMR, the measurement of their intrinsic viscosity ([ η ]), and radius of gyration ( R g ). The polymerization was also recycled up to 5 times to produce star PBnMAs with high initiator efficiency. The star polymers prepared using hydrated Na‐clay supported is compared with star prepared using covalent silica supported catalyst system. The star polymer obtained from covalently supported catalyst gave broad M w / M n and poor initiator efficiency. The polystyrene‐ graft ‐PBnMA (PS‐ g ‐PBnMA) copolymer is also prepared using hydrated Na‐clay supported catalyst system in anisole at ambient temperature. The graft ‐copolymer had narrow M w / M n and was confirmed using 1 H NMR and atomic force microscopy. © 2018 Wiley Periodicals, Inc. J. Polym. Sci., Part A: Polym. Chem. 2018 , 56 , 2225–2237
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Theoretical investigations on rutile SnO{sub 2} doped with V and Cr were performed by using recently implemented Tran and Blaha’s modified Becke-Johnson exchange potential model (TB-mBJ) based on density functional theory. The electronic, magnetic, dielectric and optical properties of V and Cr-doped tin oxide have been calculated by full-potential linearized augmented plane wave method (FP-LAPW) by WIEN2k code. The present works demonstrate accurate prediction of band structures and properties using the TB-mBJ model. The calculated values of magnetic moment, dielectric constant and refractive index of doped and undoped compounds agree well with the experimental results. The TB-mBJ model is a direct method without using empirical corrections and hence, the furnished data are useful in material modelling for spintronics applications.
Monte Carlo (MC) simulation method with the Metropolis algorithm is used to study the magnetic and thermal phase transition properties of a spherical nanoparticle. The system consists of two concentric spheres of rays R{sub C} and R{sub S}, respectively (R{sub c} < R{sub s}). For r < R{sub c}, the spin is σ = ±3 /2 and ±1 /2, and for R{sub C} < r ≤ R{sub S}, the spin is S = ±7 /2, + 5/2, ±3 /2, and ±1 /2 with antiferromagnetic interface coupling. Between R{sub C} and R{sub S}, the sites are populated with the probability (p). We present a detailed discussion on the magnetic and thermal phase transition characteristics of the system under consideration. Our investigations show that this system can be used as a magnetic nanostructure possessing potential applications in magnetism.