Spin driven emergent antiferromagnetism and metal insulator transition in nanoscale p-Si

The entanglement of the charge, spin and orbital degrees of freedom can give rise to emergent behavior especially in thin films, surfaces and interfaces. Often, materials that exhibit those properties require large spin orbit coupling. We hypothesize that the emergent behavior can also occur due to spin, electron and phonon interactions in widely studied simple materials such as Si. That is, large intrinsic spin-orbit coupling is not an essential requirement for emergent behavior. The central hypothesis is that when one of the specimen dimensions is of the same order (or smaller) as the spin diffusion length, then non-equilibrium spin accumulation due to spin injection or spin-Hall effect (SHE) will lead to emergent phase transformations in the non-ferromagnetic semiconductors. In this experimental work, we report spin mediated emergent antiferromagnetism and metal insulator transition in a Pd (1 nm)/Ni81Fe19 (25 nm)/MgO (1 nm)/p-Si (~400 nm) thin film specimen. The spin-Hall effect in p-Si, observed through Rashba spin-orbit coupling mediated spin-Hall magnetoresistance behavior, is proposed to cause the spin accumulation and resulting emergent behavior. The phase transition is discovered from the diverging behavior in longitudinal third harmonic voltage, which is related to the thermal conductivity and heat capacity.Comment: 34 pages, Physica Status Solidi B- Physics, 201

Rapid, room-temperature, solvent-free mechanochemical oxidation of elemental gold into organosoluble gold salts

Gold is highly valued for a wide range of commercial and technological applications but is processed exclusively through highly aggressive and toxic solvents and/or reagents, ultimately yielding water-soluble salts that are difficult to separate from inorganic reaction byproducts. As a result, development of safer, cleaner processes that would enable gold processing in non-aqueous, organic solvent is an attractive technological goal. Here, we describe a methodology that simultaneously avoids aggressive reagents and enables gold extraction into a safe organic solvent. The methodology is based on solventless, mechanochemical oxidation of metallic gold with Oxone® in the presence of tetraalkylammonium halide salts, to directly, rapidly (within 30–60 minutes) and at room temperature convert gold metal into solid salts that are immediately soluble in pure organic solvents and aqueous alcoholic media. The organosoluble gold salts are easily separated from sulfate byproducts by direct extraction into the benign solvent ethyl acetate, which is also easily recycled for re-use, providing a strategy for gold activation and dissolution without any additional reagents for purification, such as cation exchange resins, salts, or chelating agents. Besides enabling direct extraction of gold into an organic solvent, the mechanochemically obtained organosoluble gold salts can also be readily used for further syntheses, as shown here by a two-step one-pot route to prepare air- and moisture-resistant Au(i) salts, and an improved synthesis of gold nanoparticles from bulk gold

Synthetic approaches for accessing rare-earth analogues of UiO-66

Rare-earth (RE) analogues of UiO-66 with non-functionalised 1,4-benzenedicarboxylate linkers are synthesised for the first time, and a series of synthetic approaches is provided to troubleshoot the synthesis. RE-UiO-66 analogues are fully characterised, and demonstrate a high degree of crystallinity, high surface area and thermal stability, consistent with the UiO-66 archetype

Building a Shp: A New Rare-Earth Metal-Organic Framework and Its Application in a Catalytic Photo-Oxidation Reaction

The design and synthesis of new metal–organic frameworks (MOFs) is important from both a fundamental and application standpoint. In this work, a novel, highly‐connected rare‐earth (RE) MOF with shp topology is reported, named RE‐CU‐10 (RE = rare‐earth, CU = Concordia University), comprised of nonanuclear RE(III)‐cluster nodes and tetratopic pyrene‐based linkers. This represents the first time that the 1,3,6,8‐tetrakis(p‐benzoic acid)pyrene (H4TBAPy) linker is integrated in the shp topology. Y‐CU‐10 was explored as a heterogeneous photocatalyst for the selective oxidation and detoxification of a sulfur mustard simulant, 2‐chloroethyl ethyl sulfide (2‐CEES), showing a halflife for conversion to the less toxic 2‐chloroethyl ethyl sulfoxide (2‐CEESO) of 6.0 min.<br /

Crystal Engineering of Molecular Networks: Tailoring Hydrogen-Bonding Self-Assembly of Tin-Tetrapyridylporphyrins with Multidentate Carboxylic Acids As Axial Ligands

This study reveals the self-assembly patterns of six-coordinate complexes of the tetra­(4-pyridyl)- and tetra­(3-pyriyl)-tin-porphyrin moieties (SnT⁴PyP and SnT³PyP, respectively) with multidentate carboxylic acids as axial ligands. Detailed structural characterization of the supramolecular organization in the resulting ordered solids by X-ray diffraction is reported. Crystals of the five new Sn­(acid)₂-TPyP complexes consist of multiporphyrin polymeric chains and networks that are sustained by extensive hydrogen bonding, involving the functional substituents on the axial ligands as proton donors and the peripheral N-sites of the porphyrin as proton acceptors. The use of different ligands leads to different connectivity features of the supramolecular assemblies that form. Structures with the 5-hydroxy-isophthalic acid and trimesic acid ligands (1 and 2) reveal the formation of one-dimensional hydrogen-bonded chains only, as solvation effects prevent interporphyrin interaction in other directions. Reaction of the tin-porphyrin with 5-amino-isophthalic acid yielded a two-dimensional hydrogen-bonding network (3), while the reaction products with <i>cis</i>-1,3,5-cyclohexane-tricarboxylic acid (4) and 5-bromo-isophthalic acid (5) are characterized by three-dimensionally interlinked assemblies. The above examples highlight the pronounced effect of the axial ligands (A) on the hydrogen-bonding-driven supramolecular aggregation of the Sn­(A)₂-TPyP building blocks in crystals

Computational insight into the halogen bonded self-assembly of hexa-coordinated metalloporphyrins

We demonstrate herein a computational study probing the influence of metalloporphyrin ring current directionality on intermolecular halogen bonding (XB) during supramolecular self-assembly. The results demonstrate that porphyrin ring current can activate or deactivate halogen bonding interactions, an essential superamolecular driving force.</p