Electrodeposition from supercritical fluids

Recent studies have shown that it is possible to electrodeposit a range of materials, such as Cu, Ag and Ge, from various supercritical fluids, including hydrofluorocarbons and mixtures of CO2 with suitable co-solvents. In this perspective we discuss the relatively new field of electrodeposition from supercritical fluids. The perspective focuses on some of the underlying physical chemistry and covers both practical and scientific aspects of electrodeposition from supercritical fluids. We also discuss possible applications for supercritical fluid electrodeposition and suggest some key developments that are required to take the field to the next stage

Nanoscale arrays of antimony telluride single crystals by selective chemical vapor deposition

Arrays of individual single nanocrystals of Sb2Te3 have been formed using selective chemical vapor deposition (CVD) from a single source precursor. Crystals are self-assembled reproducibly in confined spaces of 100 nm diameter with pitch down to 500 nm. The distribution of crystallite sizes across the arrays is very narrow (standard deviation of 15%) and is affected by both the hole diameter and the array pitch. The preferred growth of the crystals in the orientation along the diagonal of the square holes strongly indicates that the diffusion of adatoms results in a near thermodynamic equilibrium growth mechanism of the nuclei. A clear relationship between electrical resistivity and selectivity is established across a range of metal selenides and tellurides, showing that conductive materials result in more selective growth and suggesting that electron donation is of critical importance for selective deposition

The reactivity of lattice nitrogen within the Ni2Mo3N and NiCoMo3N phases

In this study, the reactivity of bulk lattice nitrogen within the filled β-Mn structured Ni2Mo3N phase has been investigated by application of powder neutron diffraction and heterolytic nitrogen isotopic exchange measurements. In contrast to Co3Mo3N, despite the similarity in the N immediate local environment comprising NMo6 octahedra, its reactivity is found to be limited and this lower reactivity was maintained upon the introduction of a significant proportion of cobalt to yield its filled β-Mn structured CoNiMo3N quaternary nitride counterpart

Компьютерное моделирование удара упругой сферы с упругим полупространством

В последнее время физика взаимодействия твердых частиц представляет интерес для большинства технологических процессов, связанных с динамикой сыпучих сред. Однако до сих пор не было разработано единой теории взаимодействия частиц при их соударении из-за сложности описания контакта взаимодействующих частиц. Аналитическое решение существует только для простейшего случая, когда при ударе наблюдается полное скольжение без трения

Anodic Sb2S3 Electrodeposition from a Single Source Precursor for Resistive Random-Access Memory Devices

In this paper we report the use of Na3[SbS4].9H2O as a single source precursor for the electrodeposition of Sb2S3 from aqueous electrolyte at pH 9.1. We present the electrochemistry of the [SbS4]3− anion and the redox processes observed for the deposited Sb2S3 film. We show that an amorphous Sb2S3 film can be deposited by anodic electrodeposition onto glassy carbon and that the by-product that accompanies this deposition can be avoided by using a suitable pulse plating approach. Raman spectroscopy and grazing incidence X-ray diffraction were used to characterise the deposits and to show that good quality crystalline films of Sb2S3 are produced on annealing. The crystalline Sb2S3 films were screened for application in Resistive Random-Access Memory, and it was demonstrated that crystalline Sb2S3 films display typical bipolar resistive switching behaviour, and that the resistance ratio between the high resistance state and the low resistance state is approximately one order of magnitude at 1.5 V, which is sufficient for memory applications. A mechanism for the resistive switching is also proposed

X-ray absorption spectroscopy systematics at the tungsten L-edge

A series of mononuclear six-coordinate tungsten compounds spanning formal oxidation states from 0 to +VI, largely in a ligand environment of inert chloride and/or phosphine, has been interrogated by tungsten L-edge X-ray absorption spectroscopy. The L-edge spectra of this compound set, comprised of [W<sup>0</sup>(PMe<sub>3</sub>)<sub>6</sub>], [W<sup>II</sup>Cl<sub>2</sub>(PMePh<sub>2</sub>)<sub>4</sub>], [W<sup>III</sup>Cl<sub>2</sub>(dppe)<sub>2</sub>][PF<sub>6</sub>] (dppe = 1,2-bis(diphenylphosphino)ethane), [W<sup>IV</sup>Cl<sub>4</sub>(PMePh<sub>2</sub>)<sub>2</sub>], [W<sup>V</sup>(NPh)Cl<sub>3</sub>(PMe<sub>3</sub>)<sub>2</sub>], and [W<sup>VI</sup>Cl<sub>6</sub>] correlate with formal oxidation state and have usefulness as references for the interpretation of the L-edge spectra of tungsten compounds with redox-active ligands and ambiguous electronic structure descriptions. The utility of these spectra arises from the combined correlation of the estimated branching ratio (EBR) of the L<sub>3,2</sub>-edges and the L<sub>1</sub> rising-edge energy with metal Z<sub>eff</sub>, thereby permitting an assessment of effective metal oxidation state. An application of these reference spectra is illustrated by their use as backdrop for the L-edge X-ray absorption spectra of [W<sup>IV</sup>(mdt)<sub>2</sub>(CO)<sub>2</sub>] and [W<sup>IV</sup>(mdt)<sub>2</sub>(CN)<sub>2</sub>]<sup>2–</sup> (mdt<sup>2–</sup> = 1,2-dimethylethene-1,2-dithiolate), which shows that both compounds are effectively W<sup>IV</sup> species. Use of metal L-edge XAS to assess a compound of uncertain formulation requires: 1) Placement of that data within the context of spectra offered by unambiguous calibrant compounds, preferably with the same coordination number and similar metal ligand distances. Such spectra assist in defining upper and/or lower limits for metal Z<sub>eff</sub> in the species of interest; 2) Evaluation of that data in conjunction with information from other physical methods, especially ligand K-edge XAS; 3) Increased care in interpretation if strong π-acceptor ligands, particularly CO, or π-donor ligands are present. The electron-withdrawing/donating nature of these ligand types, combined with relatively short metal-ligand distances, exaggerate the difference between formal oxidation state and metal Z<sub>eff</sub> or, as in the case of [W<sup>IV</sup>(mdt)<sub>2</sub>(CO)<sub>2</sub>], add other subtlety by modulating the redox level of other ligands in the coordination sphere

Immobilization, Trapping, and Anion Exchange of Perrhenate Ion Using Copper-Based Tripodal Complexes

We describe a multidentate tripodal ligand in which three pendant arms carrying di(2-picolyl)amine units are linked to the ortho positions of a tris(o-xylyl) scaffold, providing N(CH[subscript 2]-o-C[subscript 6]H[subscript 4]CH[subscript 2]N(CH2py)[subscript 2])[subscript 3] (L). Reaction of L with CuCl[subscript 2] in the presence of hexafluorophosphate anion afforded blue cubes of [(CuCl)[subscript 3]L](PF[subscript 6])[subscript 3]·5H[subscript 2]O (1). Crystallographic studies of 1 revealed that the three symmetry-related arms each coordinate a {Cu[superscript II]Cl} unit, and two molecules of 1 are connected to one another through a Cu(μ-Cl)[subscript 2]Cu bridge, extending the molecular structure to form a two-dimensional (2-D) layer. These 2-D layers pack in an ABCABC... fashion with PF[subscript 6]– anions located in between. Reaction of 1 with a stoichiometric amount of perrhenate ion afforded blue plates of [(CuCl)[subscript 3]L](PF[subscript 6])(ReO[subscript 4])[subscript 2]·3H[subscript 2]O (2). Compound 2 has the same lattice structure as 1, but the tricopper unit backbone now traps one ReO[subscript 4]– anion through Coulombic interactions. In addition, three molecules of 2 are bridged by a perrhenate ion, forming a Cu[subscript 3](μ[superscript 3]-ReO[subscript 4]) cluster, to give a different 2-D structure displaying a rare tridentate bridging ReO[subscript 4]– mode. Thus, in addition to classic perrhenate trapping through weak Coulombic interactions, 2 represents an exceptional example in which the ReO[subscript 4]– anion is immobilized in an extended framework through tight covalent interactions. The interlamellar PF[subscript 6]– anions in 1 can be exchanged with other anions including perrhenate, perchlorate, or periodate. The structural similarity between perrhenate and pertechnetate makes these materials of potential interest for pertechnetate trapping

Luminescent Tris(8-hydroxyquinolates) of Bismuth(III)

Luminescent homoleptic bismuth(III) complexes have been synthesized by adding several functionalized 8-hydroxyquinolate ligands to bismuth(III) chloride in a 3:1 mole ratio in either ethanol or tetrahydrofuran (THF) solvent. These complexes have been characterized by single-crystal X-ray diffraction (XRD) analysis, UV-vis spectroscopy, fluorescence spectroscopy, and density functional theory (DFT) calculations to determine their structures and photophysical properties. Reversible dimerization of the mononuclear tris(hydroxyquinolate) complexes was observed in solution and quantified using UV-vis spectroscopy. The fluorescence spectra show a blue shift for the monomer compared with homoleptic aluminum(III) hydroxyquinolate compounds. Four dimeric compounds and one monomeric isomer were characterized structurally. The bismuth(III) centers in the dimers are bridged by two oxygen atoms from the substituted hydroxyquinolate ligands. The more sterically hindered quinolate complex, tris(2-(diethoxymethyl)-8-quinolinato)bismuth, crystallizes as a monomer. The complexes all exhibit low-lying absorption and emission spectral features attributable to transitions between the HOMO (π orbital localized on the quinolate phenoxide ring) and LUMO (π* orbital localized on the quinolate pyridyl ring). Excitation and emission spectra show a concentration dependence in solution that suggests that a monomer-dimer equilibrium occurs. Electronic structure DFT calculations support trends seen in the experimental results with a HOMO-LUMO gap of 2.156 eV calculated for the monomer that is significantly larger than those for the dimers (1.772 and 1.915 eV). The close face to face approach of two quinolate rings in the dimer destabilizes the uppermost occupied quinolate π orbitals, which reduces the HOMO-LUMO gap and results in longer wavelength absorption and emission spectral features than in the monomer form