When smoothening makes it rough: unhindered step-edge diffusion and the meandering instability on metal surfaces

The precise microscopic origin of step meandering is not known in many real situations. A detailed study of this instability has been made for copper, and none of the microscopic mechanisms proposed until now is able to describe all of the observed characteristic features of the instability, in particular, its dependence on the crystallographic orientations of steps. We propose a novel scenario, and using kinetic Monte Carlo simulations we show that essentially all features of step meandering of copper can be explained, if atoms diffuse along step edges and freely turn around the kinks they encounter along the ledge. Then, in a rather counterintuitive way, step meandering appears due to the very mechanism--step-edge diffusion--that may be expected to oppose it.     

Oxaphosphoranylation of Methyl α-d-Glucopyranoside with Diethoxytriphenylphosphorane: Highly Stereoselective Approach to Anhydropyranosides

Diethoxytriphenylphosphorane (DTPP) efficiently oxaphosphoranylates methyl α-d -glucopyranoside to afford two unstable isomeric 1,3,2λ⁵-dioxaphospholanes. Thermolysis (60–90°C) of these 1,3,2λ⁵-dioxaphospholanes affords only two of four possible isomeric anhydropyranosides. Two distinct intermediate betaines and their unique “pre-transition state” chair or twist-boat structures are used to rationalize the regiochemistry-attending cyclodehydration. The decomposition of these rapidly interconverting 1,3,2λ⁵-dioxaphospholanes is accelerated in the presence of lithium bromide (LiBr) to afford a single anhydropyranoside.     

Vertical distribution of <Superscript>210</Superscript>Pb and <Superscript>226</Superscript>Ra and their activity ratio in marine sediment core of the East Malaysia coastal waters

Marine sediment cores were collected from two stations at East Malaysia coastal waters on June 2004. Activity concentrations of ²¹⁰Pb in sediment core were ranged from 11 Bqkg⁻¹ to 84 Bqkg⁻¹ dry wt. for SR 01 and 4 Bqkg⁻¹ to 66 Bqkg⁻¹ dry wt. for SB 03. Meanwhile, activity concentrations of ²²⁶Ra in sediment core were varied significantly depending on the sampling location of SR 01 and SB 03 with ranged 17–26 Bqkg⁻¹ dry wt. and 8–11 Bqkg⁻¹ dry wt., respectively. The activity ratios of ²¹⁰Pb/²²⁶Ra were no significantly different at all sampling stations with an average of 1.78. Refer to the entire results; the activities of ²¹⁰Pb and ²²⁶Ra were higher at station SR 01 than station SB 03, but contrast with ratio of ²¹⁰Pb/²²⁶Ra. The reasons of different ²¹⁰Pb and ²²⁶Ra activity concentration and distribution of their ratios were strictly related to their half lives, environment origin, potential sources and behavior.     

Selective single-atom electrocatalysts: a review with a focus on metal-doped covalent triazine frameworks

Single-atom electrocatalysts (SACs), which comprise singly isolated metal sites supported on heterogeneous substrates, have attracted considerable recent attention as next-generation electrocatalysts for various key reactions from the viewpoint of the environment and energy. Not only electrocatalytic activity but also selectivity can be precisely tuned via the construction of SACs with a defined coordination structure, such as homogeneous organometallics. Covalent organic frameworks (COFs) are promising supports for single-atom sites with designed coordination environments due to their unique physicochemical properties, which include porous structures, robustness, a wide range of possible designs, and abundant heteroatoms to coordinate single-metal sites. The rigid frameworks of COFs can hold unstable single-metal atoms, such as coordinatively unsaturated sites or easily aggregated Pt-group metals, which exhibit unique electrocatalytic selectivity. This minireview summarizes recent advances in the selective reactions catalysed by SACs, mainly those supported on triazine-based COFs.

Single-atom electrocatalysts (SACs) have attracted considerable attention as selective electrocatalysts. Metal-doped covalent triazine frameworks will be a novel platform for selective SACs to solve energy and environmental issues.     

Electronic stress tensor analysis of molecules in gas phase of CVD process for gesbte alloy

We analyze the electronic structure of molecules which may exist in gas phase of chemical vapor deposition process for GeSbTe alloy using the electronic stress tensor, with special focus on the chemical bonds between Ge, Sb, and Te atoms. We find that, from the viewpoint of the electronic stress tensor, they have intermediate properties between alkali metals and hydrocarbon molecules. We also study the correlation between the bond order which is defined based on the electronic stress tensor, and energy‐related quantities. We find that the correlation with the bond dissociation energy is not so strong while one with the force constant is very strong. We interpret these results in terms of the energy density on the “Lagrange surface,” which is considered to define the boundary surface of atoms in a molecule in the framework of the electronic stress tensor analysis. © 2015 Wiley Periodicals, Inc.     

Superconductivity at 15 K in NdFe0.9Rh0.1AsO without F-doping

We present results of transport and magnetic properties measurements performed on polycrystalline NdFe_0.9Rh_0.1AsO. Despite the large size difference between Fe and Rh elements, this compound undergoes a superconducting transition with T_c ～ 15 K. We have compared the transport properties of this Rh-doped oxypnictide with that of optimally doped NdFeAsO_0.88F_0.12. Contrary to this latter compound, a strong upturn of the normal-state resistivity occurs above T_c, and no peak of the thermopower has been observed.     

Copper‐Modified Covalent Triazine Frameworks as Non‐Noble‐Metal Electrocatalysts for Oxygen Reduction

The electrochemical oxygen reduction reaction (ORR) is an important cathode reaction of various types of fuel cells. The development of electrocatalysts composed only of abundant elements is a key goal because currently only platinum is a suitable catalyst for ORR. Herein, we synthesized copper‐modified covalent triazine frameworks (CTF) hybridized with carbon nanoparticles (Cu‐CTF/CPs) as efficient electrocatalysts for the ORR in neutral solutions. The ORR onset potential of the synthesized Cu‐CTF/CP was 810 mV versus the reversible hydrogen electrode (RHE; pH 7), the highest reported value at neutral pH for synthetic Cu‐based electrocatalysts. Cu‐CTF/CP also displayed higher stability than a Cu‐based molecular complex at neutral pH during the ORR, a property that was likely as a result of the covalently cross‐linked structure of CTF. This work may provide a new platform for the synthesis of durable non‐noble‐metal electrocatalysts for various target reactions.