Epitaxial growth of borophene on substrates

Borophene, a two-dimensional (2D) planar boron sheet, has attracted dramatic attention for its unique physical properties that are theoretically predicted to be different from those of bulk boron, such as polymorphism, superconductivity, Dirac fermions, mechanical flexibility and anisotropic metallicity. Nevertheless, it has long been difficult to obtain borophene experimentally due to its susceptibility to oxidation and the strong covalent bonds in bulk forms. With the development of growth technology in ultra-high vacuum (UHV), borophene has been successfully synthesized by molecular beam epitaxy (MBE) supported by substrates in recent years. Due to the intrinsic polymorphism of borophene, the choice of substrates in the synthesis of borophene is pivotal to the atomic structure of borophene. The different interactions and commensuration of borophene on various substrates can induce various allotropes of borophene with distinct atomic structures, which suggests a potential approach to explore and manipulate the structure of borophene and benefits the realization of novel physical and chemical properties in borophene due to the structure–property correspondence. In this review, we summarize the recent research progress in the synthesis of monolayer (ML) borophene on various substrates, including Ag(1 1 1), Ag(1 1 0), Ag(1 0 0), Cu(1 1 1), Cu(1 0 0), Au(1 1 1), Al(1 1 1) and Ir(1 1 1), in which the polymorphism of borophene is present. Moreover, we introduce the realization of bilayer (BL) borophene on Ag(1 1 1), Cu(1 1 1) and Ru(0 0 0 1) surfaces, which possess richer electronic properties, including better thermal stability and oxidation resistance. Then, the stabilization mechanism of polymorphic borophene on their substrates is discussed. In addition, experimental investigations on the unique physical properties of borophene are also introduced, including metallicity, topology, superconductivity, optical and mechanical properties. Finally, we present an outlook on the challenges and prospects for the synthesis and potential applications of borophene.     

Controlled synthesis of MnSn(OH)6/graphene nanocomposites and their electrochemical properties as capacitive materials

We report the synthesis of novel MnSn(OH)₆/graphene nanocomposites produced by a co-precipitation method and their potential application for electrochemical energy storage. The hydroxide decorated graphene nanocomposites display better performance over pure MnSn(OH)₆ nanoparticles because the graphene sheets act as conductive bridges improving the ionic and electronic transport. The crystallinity of MnSn(OH)₆ nanoparticles deposited on the surface of graphene sheets also impacts the capacitive properties as electrodes. The maximum capacitance of 31.2 F/g (59.4 F/g based on the mass of MnSn(OH)₆ nanoparticles) was achieved for the sample with a low degree of crystallinity. No significant degradation of capacitance occurred after 500 cycles at a current density of 1.5 A/g in 1 M Na₂SO₄ aqueous solution, indicating an excellent electrochemical stability. The results serve as an example demonstrating the potential of integrating highly conductive graphene networks into binary metal hydroxide in improving the performance of active electrode materials for electrochemical energy storage applications.     

Flexible free-standing graphene-silicon composite film for lithium-ion batteries

Flexible, free-standing, paper-like, graphene-silicon composite materials have been synthesized by a simple, one-step, in-situ filtration method. The Si nanoparticles are highly encapsulated in a graphene nanosheet matrix. The electrochemical results show that graphene-Si composite film has much higher discharge capacity beyond 100 cycles (708 mAh g^? 1) than that of the cell with pure graphene (304 mAh g^? 1). The graphene functions as a flexible mechanical support for strain release, offering an efficient electrically conducting channel, while the nanosized silicon provides the high capacity.     

Paper-like free-standing polypyrrole and polypyrrole–LiFePO4 composite films for flexible and bendable rechargeable battery

Highly flexible, paper-like, free-standing polypyrrole and polypyrrole–LiFePO₄ composite films were prepared using the electropolymerization method. The films are soft, lightweight, mechanically robust and highly electrically conductivity. The electrochemical behavior of the free-standing films was examined against lithium counter electrode. The electrochemical performance of the free-standing pure PPy electrode was improved by incorporating the most promising cathode material, LiFePO₄, into the PPy films. The cell with PPy–LiFePO₄ composite film had a higher discharge capacity beyond 50 cycles (80 mA h/g) than that of the cell with pure PPy (60 mA h/g). The free-standing films can be used as electrode materials to satisfy the new market demand for flexible and bendable batteries that are suitable for the various types of design and power needs of soft portable electronic equipment.     

Synthesis of thick TiO2 nanotube arrays on transparent substrate by anodization technique

A vertically aligned transparent TiO₂ nanotube array (tTNA) of significantly enhanced tube-length 6.3 ± 0.3 µm was successfully synthesized on glass substrates by anodization technique with ammonium fluoride and ethylene glycol-based electrolyte. Prior to anodization, Ti metal was deposited on glass substrate by facing-target sputtering technique with various sputtering pressures at substrate temperature 420 °C to find out the relation between the structural properties of the Ti layer and the corresponding growth mechanism of the TiO₂ nanotube. The study revealed that structural properties of Ti metal layers and its adhesion to the glass substrate, which can be tuned by deposition parameters, play an important role in the process of tTNA formation.     

First-principles calculations of the structural and electronic properties of Cu3MN compounds with M = Ni,Cu, Zn,Pd, Ag,and Cd

We have performed accurate ab initio total energy calculations using the full-potential linearized augmented plane wave (FP-LAPW) method to investigate the structural and electronic properties of copper-transition metal nitrides. In its ground state, Cu₃N crystallizes in an anti-ReO₃ type cell and it is a semiconductor material with a small indirect gap. In this paper, we report a study of Cu₃MN compounds with M = Ni, Cu, Zn, Pd, Ag, and Cd. In the calculations, we have used the same anti-ReO₃ type cell of Cu₃N, but with the extra transition metal atom at the center of the cube. In particular, our calculated lattice parameters for copper nitride (a = 3.82 Å) and copper palladium nitride (a = 3.89 Å) are in excellent agreement with the experimental values of a = 3.807 Å and a = 3.86 Å, respectively. In all the cases we have studied, the addition of the transition metal atom modifies the electronic structure of Cu₃N, turning all copper-transition metal nitrides into metals.     

Structures and spectroscopic properties of meso-tetrasubstituted porphyrin complexes: Meso-substitutional and central metallic effect study based on density functional theory calculations

Effects of the meso-substituents and central metals on the molecular structures, atomic charges, molecular orbital energy gaps, electronic absorption spectra, and infrared (IR) spectra of 12 meso-tetrasubstituted porphyrin complexes including metal-free porphyrins H₂P or (Por = TPP, TFPP, TClPP, TPyP) (1–4) and their metal complexes MPor (M = Mg, Zn; Por = TPP, TFPP, TClPP, TPyP) (5–12) [TPP = meso-tetrakis(phenyl)porphyrinate; TFPP = meso-tetrakis(4-fluorophenyl)porphyrinate; TClPP = meso-tetrakis(4-chlorophenyl)porphyrinate; TPyP = meso-tetrakis(4-pyridyl) porphyrinate] are systematically studied by density functional theory calculations at the B3LYP/6-31G(d) level. Good consistency was found between the calculated molecular structures and the experimental X-ray crystallography ones for 1, 3, and 4, and between the simulated electronic absorption and IR spectra and the experimental ones for 1 and 4. The calculation results reveal that introducing substituents at the meso positions of porphyrin induces increasing change in the molecular structures, atomic charges distribution, HOMO and LUMO energy, electronic absorption spectra, and IR spectra along with the increase in the electron-withdrawing ability of substituents in the order of phenyl, 4-fluorophenyl, 4-chlorophenyl, and pyridyl group. Furthermore, the central metal in porphyrins displays much significant influence on the structure and spectroscopic properties of meso-substituted porphyrin complexes. The electronic absorption and IR spectra of 1–12 are compared and assigned in detail. The present work should be not only helpful towards understanding the meso-substitutional and central metallic effects on the structure and spectroscopic properties of meso-substituted porphyrin complexes, but also useful in correctly assigning electronic absorption and IR spectra for porphyrin complexes.     

Site-dependent electrochemical performance of Mg doped LiFePO4

Exotic metal (EM) doping in LiFePO4 materials could mitigate their poor electronic conductivity and electrochemical performance. This effect is believed to be dependent on the EM dwelling site, which has yet been well clarified due to experimental difficulty. Herein, we report on Mg-doped LiFePO₄ samples with dopant in two distinct sites, namely the Li_1 − 2xMg_xFePO₄ and LiFe_1 − xMg_xPO₄, using a specially designed two-step reaction. The conductivity and electrochemical test results are a clear indication that the performance of the doped LiFePO₄ samples is highly Mg site dependent, consistent with theoretical analysis.     

Enhanced electrochemiluminescence based on Ru(bpy)32+-doped silica nanoparticles and graphene composite for analysis of melamine in milk

A sensitive electrochemiluminescence (ECL) sensor for melamine analysis was fabricated based on Ru(bpy)₃²⁺-doped silica (Ru(bpy)₃²⁺@SiO₂) nanoparticles and graphene composite. Spherical Ru(bpy)₃²⁺@SiO₂ nanoparticles with uniform size about 55 nm were prepared by the reverse microemulsion method. Since per Ru(bpy)₃²⁺@SiO₂ nanoparticle encapsulated a great deal of Ru(bpy)₃²⁺, the ECL intensity has been greatly enhanced, which resulted in high sensitivity. Due to its extraordinary electric conductivity, graphene improved the conductivity and accelerated the electron transfer rate. In addition, graphene could work as electronic channel improving the efficient luminophor amount participating in the ECL reaction, which further enhanced the ECL signal. This proposed sensor was used to melamine analysis and the ECL intensity was proportional to logarithmic melamine concentration range from 1 × 10⁻¹³ M to 1 × 10⁻⁸ M with the detect limit as low as 1 × 10⁻¹³ M. In application to detect melamine in milk, satisfactory recoveries could be obtained, which indicated this sensor having potential application in melamine analysis in real samples.     

Voltammetric characterization of stepped platinum single crystal surfaces vicinal to the (1 1 0) pole

Platinum stepped surfaces vicinal to the (1 1 0) crystallographic pole have been investigated voltammetrically in 0.1 M HClO₄ and 0.1 M H₂SO₄ solutions. Changes in the voltammetric profile with the step density suggest the existence of two types of surface sites, that has been ascribed to linear and bidimensional domains. This result indicates the existence of important restructuring processes that separate the real surface distribution from the nominal one. The electronic properties of the surfaces have been characterized with the CO charge displacement method and the potential of zero total charge has been calculated as a function of the step density.     

Observation of possible quantum interference effects in SrRuO3 epitaxial thin films grown by high-oxygen pressure dc sputtering

A careful study of the electronic transport and magnetotransport properties of metallic ferromagnetic SrRuO₃ (SRO) thin films is reported. Epitaxial (～150 nm) SRO films were grown on (001)-oriented SrTiO₃ (STO) substrates by dc sputtering technique at high oxygen pressure. Resistivity measurements were performed up to temperatures as low as 2 K in magnetic fields strengths of up to 9 T, applied perpendicular to the film plane. The films featured excellent metallic behavior at room temperature, with a resistivity, ρ(300 K) < 600 μΩ cm. The presence of minima in the ρ–T plots at ～4 K was clearly detected from these measurements. The 9 T magnetic field did not remove the minima signaling its nonmagnetic origin In addition, the ρ(μ₀H = 9 T,T) minima was slightly shifted to higher temperature and the ρ(μ₀H = 9 T,T ≤ 4 K) was larger when it was compared with ρ(μ₀H = 0 T,T ≤ 4 K). Increasing relevance of quantum corrections to the conductivity as the temperature is lowered has been invocated as possible cause of this anomalous electrical behavior. In this case, effects arising from quantum interference of the electronic wavelength are expected. Weak localization and renormalized electron–electron interaction have been considered as possible sources giving rise to quantum correction to the conductivity.     

A possible approach towards spin-polarized transport through single molecule magnets: Mn12 on Au(1 0 0)/Fe(1 0 0)/MgO(1 0 0)

The possibility to use the Au(1 0 0)/Fe(1 0 0)/MgO(1 0 0) system as a substrate for future spin-polarized transport measurements on Mn₁₂ single molecule magnets has been investigated by means of scanning tunneling microscopy and X-ray photoelectron spectroscopy at room temperature. In particular, the stability of the iron layer during a wet chemical preparation of Mn₁₂ monolayers was studied. The results demonstrate that Mn₁₂ can be deposited on Au(1 0 0)/Fe(1 0 0)/MgO(1 0 0) while preserving the metallic nature of the ferromagnetic iron layer which is required as a possible source of spin-polarized electrons in future studies.     

Fast formation of thick and transparent titania nanotubular films from sputtered Ti

Ti films sputtered on transparent fluorine-doped tin oxide glass substrates were anodized in fluoride-containing organic electrolyte in the presence of H₂O. In this work, anodic TiO₂ nanotubes (ATNs) as long as 9.2 ± 0.3 μm were obtained with high growth rate of 0.64 ± 0.3 μm min^?1. We demonstrated the optimum anodization conditions for ATN growth on foreign substrates, were within the range of 0.3–0.5% (wt) NH₄F, with 3–5% (vol) H₂O at 60 V. XPS and ICP-MS were utilized to elucidate the increase of thickness and volume expansion obtained from the sputtered Ti film to their ATN forms. The ATN films exhibited excellent uniformity and adhesion to the substrates.     

In situ growth of polymer electrolytes on lithium ion electrode surfaces

Polyacrylonitrile (PAN) films were grown on glassy carbon, nickel foam and MnO₂ substrates by cathodic electropolymerisation of acrylonitrile in acetonitrile with tetrabutylammonium perchlorate (TBAP) as the supporting electrolyte. The electronic barrier properties of the films were confirmed by impedance spectroscopy of carbon |PAN| Hg cells while the ionic resistance of the films varied from 200 kΩ cm² in the dry state to 1.4 Ω cm² when plasticised with 1 M LiPF₆ in propylene carbonate. A galvanic cell was prepared by successive electrodepositions of MnO₂ and PAN on a carbon substrate, using liquid lithium amalgam as the top contact. The cell showed a stable open circuit potential and behaved normally under the galvanostatic intermittent titration technique (GITT).     

A DFT study on group III and V combined hexagonal clusters as potential building motifs for inorganic nanomaterials

A detail theoretical investigation on the structure and electronic properties of inorganic hexagonal units and their higher order derivatives comprising group III (B, Al and Ga) and V (N, P and As) elements is performed. A series of 45 clusters, formed by a linear combination of hydrogen saturated hexagonal motifs up to five units, (MY)_2n+1H_2n+4 (M = B, Al, Ga; Y = N, P, As; n = 1–5) are considered to look into their metal–insulator–semiconductor (MIS) behavior. It is evident from the present study that the arsenic doped group III hexagonal units clearly have a decisive role in forming semiconductor materials.     

Electrochemistry of Actinides and Selected Fission Products in the Head End of Spent Nuclear Fuel Reprocessing

The data on the uranium metal corrosion rate in the solutions of nitric acid (0,1 – 4 M) and effect of complex forming agents on uranium corrosion properties are presented. The increase of HNO₃ concentration caused the shift of corrosion potential from 38 mV to 446 mV and the increase of the corrosion rate from 0,02 to 0,62 mg.cm^-2h^-1. Transpassivation potential of U metal was found weakly effected by HNO₃ concentration varying from 448 to 470 mV/Ag/AgCl. The addition of HCOOH to the electrolytes containing less than 3 M HNO₃ found to shift the values of corrosion potentials about 500 mV towards negative direction reducing the passivation of U metal. The data on the kinetics of oxidative dissolution of PuO₂ using Ag(II) and Am(VI,V) as mediators and the effect of the mediator generation techniques are discussed. The electrochemical properties of UC in the solutions 2 – 4 M HNO₃, results of the quantitative determination of “oxidizable carbon” in dissolver solutions are presented. The results of corrosion and dissolution studies of Tc metal and Tc - Ru alloys containing from 19 to 70 at.% Ru in 0.5 0– 6 M HNO3 indicate the formation of passive films of Tc(IV) – Ru(III,IV) hydroxides at the electrode surface in the solutions containing less than 2 M HNO₃ at the potentials less than 650 mV/Ag/AgCl. The increase of HNO3 concentration to values exceeding 3 M and the shift of the electrode potential towards positive direction causes the transition of the Tc and Tc-Ru alloys to transpassive state. The values of transpassivation potentials increase with the increasing with HNO₃ concentration. Quantitative dissolution of Tc metal without application of oxidation potential becomes possible in the electrolytes, containing more than 4 M HNO₃. The rate of Tc – Ru alloys dissolution is noticed to slow down with the increase of Ru content in the alloy.     

Transparent graphene/PEDOT–PSS composite films as counter electrodes of dye-sensitized solar cells

Composite films of graphene and polystyreneslufonate doped poly(3,4-ethylenedioxythiophene) (graphene/PEDOT–PSS) were deposited on indium tin oxide (ITO) substrates by spin coating at room temperature and applied as counter electrodes of dye-sensitized solar cells (DSSCs). A 60 nm thick composite film (contained 1 wt% graphene) coated ITO electrode exhibited high transmittance (>80%) at visible wavelengths and high electrocatalytic activity. The energy conversion efficiency of the cell with this film as counter electrode reached 4.5%, which is comparable to 6.3% of the cell with platinum counter electrode under the same experimental condition.     

A new π-acidity scale for several N-donor heterocycles as ligands in neutral gold(III) complexes

A computational DFT approach for the comparison of the π-acceptor character of some N-donor heterocycles L {L = pyridines (py), pyrimidines (pm), imidazoles (im), pyrazoles (pz) and isoxazoles (io)} in neutral AuCl₃L complexes is reported. The electronic properties of these ligands have been tuned by adding methyl and/or trifluoromethyl groups in various positions. Linear relationships between the Mulliken charge of the AuCl₃ fragment in AuCl₃L and the computed proton affinity (PA) of the heterocycle were obtained for all the considered ligands. The different slopes found on changing the N-donor type represent a measure of the π-acidity of these nitrogen ligands once coordinated to AuCl₃, and as a consequence the π-acceptor ability scale pyridines ≈ pyrimidines < imidazoles < pyrazoles ≈ isoxazoles has been derived. Moreover, on the basis of the metal fragment charge variation, a minimum proton affinity value for a meaningful interaction between the ligands and the AuCl₃ fragment has been estimated.     

Steric and electronic effects in the bonding of N-heterocyclic ligands to transition metals

N-heterocyclic (NHC) ligands constitute a new class of ligands that is going to commonly be used in organometallic chemistry. Nevertheless, detailed understanding of the bonding properties of these ligands to transition metals is scarce. In particular, a clear separation between steric and electronic effects is missing. Only in recent years combined experimental and computational studies on this topic have been performed. Here we review some advances in the field. We thus present a quantification of steric effects on the bond dissociation energy of various NHC-ligands from transition metals in complexes as Cp*Ru(NHC)Cl and Ni(CO)₃(NHC). We further compare the steric requirements of various NHC ligands with the steric requirements of some phosphines. In the second part, we examine the different bonding modes that can contribute to the NHC–metal bond. We will review examples of metal-to-NHC back-donation (σ → d*) as well as of ligand-to-metal-to-NHC back-donation (π → d).     

Synthesis,characterization and spectroscopic studies of pyrazinamide metal complexes

The present paper deals with the synthesis and characterization of Schiff base complexes of pyrazinamide an antitubercular drug. Metals selected for complexation are copper, silver, gold, zinc, mercury, iron and cobalt. The complexes have been suitably synthesized and isolated in pure powdered form. Analytical data agrees with the compositions M(L), M′(L)₂ and M″(L)₂·2H₂O, respectively where M = Ag, M′ = Cu, Au, Zn and Hg and M″ = Fe and Co, ligand metal ratios were also confirmed by monovariation method and Job’s method of continuous variation. Molar conductance values suggest the non ionic nature of the complexes. The tentative structure assigned to the complexes on the basis of stoichiometry and analytical data were further supported by spectral studies viz; IR, NMR, magnetic susceptibility and electronic spectra. A preliminary attempt has also been made to compare the potencies of metal complexes with parent drug. The Cu and Ag complexes are giving encouraging results. Particle size studies further suggest that the drug molecule undergoes reduction in size on complexation.