Two-Dimensional Covalent Organic Framework Solid Solutions.

Covalent organic frameworks (COFs) generally leverage one or two monomers with specific sizes and shapes to access highly symmetric and periodic polymer networks. Almost all reported COFs employ the minimum sets of monomers needed for the polymerization (usually two, sometimes one) and crystallize in high-symmetry topologies. COFs synthesized from more than two monomers usually employ mixtures with different pendant functionalities to distribute these groups statistically throughout the structure, or monomers with different sizes in ratios targeting lower symmetry topologies.

Synthesis and High-Pressure Mechanical Properties of Superhard Rhenium/Tungsten Diboride Nanocrystals.

Rhenium diboride is an established superhard compound that can scratch diamond and can be readily synthesized under ambient pressure. Here, we demonstrate two synergistic ways to further enhance the already high yield strength of ReB. The first approach builds on previous reports where tungsten is doped into ReB at concentrations up to 48 at.

Investigation of ternary metal dodecaborides (MMM)B (M, M and M = Zr, Y, Hf and Gd).

Samples of metal borides with a nominal composition of ((M1)(1-x-z)(M2)(x)(M3)(z)) : 20B (M1, M2 and M3 = Zr, Y, Hf and Gd) were prepared by arc-melting and studied for phase composition (using powder X-ray diffraction (PXRD) and energy dispersive X-ray spectroscopy (EDS)) and mechanical properties (Vickers hardness). Ternary metal dodecaboride phases were successfully synthesized for the majority of compositions, including stabilization of two high-pressure (6.5 GPa) phases (cubic-UB12 structure), HfB12 and GdB12, in (Zr1-x-zHfxGdz) : 20B and (Y1-x-zHfxGdz) : 20B nominal alloy compositions.

Effects of Variable Boron Concentration on the Properties of Superhard Tungsten Tetraboride.

Tungsten tetraboride is an inexpensive, superhard material easily prepared at ambient pressure. Unfortunately, there are relatively few compounds in existence that crystallize in the same structure as tungsten tetraboride. Furthermore, the lack of data in the tetraboride phase space limits the discovery of any new superhard compounds that also possess high incompressibility and a three-dimensional boron network that withstands shear.

Lithium-Ion Insertion Properties of Solution-Exfoliated Germanane.

The high theoretical energy density of alloyed lithium and germanium (LiGe), 1384 mAh/g, makes germanium a promising anode material for lithium-ion batteries. However, common alloy anode architectures suffer from long-term instability upon repetitive charge-discharge cycles that arise from stress-induced degradation upon lithiation (volume expansion >300%). Here, we explore the use of the two-dimensional nanosheet structure of germanane to mitigate stress from high volume expansion and present a facile method for producing stable single-to-multisheet dispersions of pure germanane.

Rediscovering the Crystal Chemistry of Borides.

For decades, borides have been primarily studied as crystallographic oddities. With such a wide variety of structures (a quick survey of the Inorganic Crystal Structure Database counts 1253 entries for binary boron compounds!), it is surprising that the applications of borides have been quite limited despite a great deal of fundamental research. If anything, the rich crystal chemistry found in borides could well provide the right tool for almost any application.

Stabilization of LnB (Ln = Gd, Sm, Nd, and Pr) in ZrLnB under Ambient Pressure.

We report ambient pressure stabilization of a previously synthesized high-pressure (6.5 GPa) phase, GdB, in a ZrGdB solid solution (with ∼54 at. % Gd solubility, as determined by both powder X-ray diffraction and energy-dispersive spectroscopy).

Characterization of Aniline Tetramer by MALDI TOF Mass Spectrometry upon Oxidative and Reductive Cycling.

By combining electrochemical experiments with mass spectrometric analysis, it is found that using short chain oligomers to improve the cycling stability of conducting polymers in supercapacitors is still problematic. Cycling tests via cyclic voltammetry over a potential window of 0 to 1.0 V or 0 to 1.

Superhard Monoborides: Hardness Enhancement through Alloying in W1- x Tax B.

In tungsten monoboride (WB), the boron atoms are linked in parallel serpentine arrays, with tungsten atoms in between. This lattice is metallic, unlike conventional covalent superhard materials such as diamond or cubic boron nitride. By selectively substituting tungsten atoms with tantalum, the Vickers hardness can be increased to 42.

Stabilization of HfB12 in Y1-xHfxB12 under Ambient Pressure.

Alloys of metal dodecaborides-YB12 with HfB12-were prepared via arc-melting in order to stabilize the metastable HfB12 high-pressure phase under ambient pressure. Previously, HfB12 had been synthesized only under high-pressure (6.5 GPa).

Extrinsic Hardening of Superhard Tungsten Tetraboride Alloys with Group 4 Transition Metals.

Alloys of tungsten tetraboride (WB4) with the group 4 transition metals, titanium (Ti), zirconium (Zr), and hafnium (Hf), of different concentrations (0-50 at. % on a metals basis) were synthesized by arc-melting in order to study their mechanical properties. The phase composition and purity of the as-synthesized samples were confirmed using powder X-ray diffraction (PXRD) and energy dispersive X-ray spectroscopy (EDS).

Graphene-Assisted Solution Growth of Vertically Oriented Organic Semiconducting Single Crystals.

Vertically oriented structures of single crystalline conductors and semiconductors are of great technological importance due to their directional charge carrier transport, high device density, and interesting optical properties. However, creating such architectures for organic electronic materials remains challenging. Here, we report a facile, controllable route for producing oriented vertical arrays of single crystalline conjugated molecules using graphene as the guiding substrate.

High Surface Area Tunnels in Hexagonal WO₃.

High surface area in h-WO3 has been verified from the intracrystalline tunnels. This bottom-up approach differs from conventional templating-type methods. The 3.

Vapor-phase polymerization of nanofibrillar poly(3,4-ethylenedioxythiophene) for supercapacitors.

Nanostructures of the conducting polymer poly(3,4-ethylenedioxythiophene) with large surface areas enhance the performance of energy storage devices such as electrochemical supercapacitors. However, until now, high aspect ratio nanofibers of this polymer could only be deposited from the vapor-phase, utilizing extrinsic hard templates such as electrospun nanofibers and anodized aluminum oxide. These routes result in low conductivity and require postsynthetic template removal, conditions that stifle the development of conducting polymer electronics.

Tungsten tetraboride, an inexpensive superhard material.

Tungsten tetraboride (WB(4)) is an interesting candidate as a less expensive member of the growing group of superhard transition metal borides. WB(4) was successfully synthesized by arc melting from the elements. Characterization using powder X-ray diffraction (XRD) and energy-dispersive X-ray spectroscopy (EDX) indicates that the as-synthesized material is phase pure.