Adsorption of alkali metals on Ge(0 0 1)(2 × 1) surface

Ab initio total energy calculations have been performed for Na, K and Rb adsorption on Ge(0 0 1)(2 × 1) surface. It was found that the adsorption site of AM is AM size dependent. Structural analysis showed that the Ge–Ge dimer bond becomes stronger with increasing AM size. As the coverage increases from 0.5 to 1 ML it turns out that no depolarization effect occurs upon Na adsorption, while this effect becomes more important with increasing AM size. We also found that for all adsorption systems investigated the germanium surface is metallic and semiconducting for the coverage of 0.5 and 1 ML, respectively.     

Electrochemical deposition of PbTe onto n-Si(1 0 0) wafers

Electrochemical deposition of PbTe from 50 mM Pb(NO₃)₂ + 1 mM TeO₂ + 0.1 M HNO₃ solution onto n-Si(1 0 0) wafers was studied using cyclic voltammetry (CV), chronoamperometry, ex situ SEM, XRD and EDX. Electrochemical behavior of n-Si(1 0 0) electrode in electrolytes 50 mM Pb(NO₃)₂ + 0.1 M HNO₃ and 1 mM TeO₂ + 0.1 M HNO₃ was also studied. No underpotential deposition (UPD) of Pb and Te onto n-Si was observed in the investigated systems indicating weak Pb–Si and Te–Si interactions. Deposition of Pb and Te on n-Si occurred with overvoltage via 3D island growth. Electrosynthesis of PbTe (NaCl-like structure, a = 0.650 nm) takes place due to codeposition of Pb and Te at potentials E > E_{Pb²⁺/Pb⁰} (lead UPD onto tellurium). Cathodic deposition of PbTe onto n-Si(1 0 0) is irreversible – there is no anodic current in the CV curve. Oxidation of PbTe on n-Si is observed only under illumination, when photoelectrons and photoholes are generated in silicon substrate.     

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.     

Transition metals on the (0 0 0 1) surface of graphite: Fundamental aspects of adsorption,diffusion, and morphology

In this article, we review basic information about the interaction of transition metal atoms with the (0 0 0 1) surface of graphite, especially fundamental phenomena related to growth. Those phenomena involve adatom-surface bonding, diffusion, morphology of metal clusters, interactions with steps and sputter-induced defects, condensation, and desorption. General traits emerge which have not been summarized previously. Some of these features are rather surprising when compared with metal-on-metal adsorption and growth. Opportunities for future work are pointed out.     

Desorption related to adsorption of hydrogen via detailed balance on the Si(1 0 0) surfaces

Recent progress on desorption and adsorption dynamics of hydrogen (deuterium) on monohydride and dihydride Si(1 0 0) surfaces is reviewed and discussed. The dynamics experiments reveal that the desorption dynamics of hydrogen is well related to the adsorption dynamics via detailed balance. Dependence of time-of-flight (TOF) distributions of desorbed molecules on H(D) coverage is noticed to be important in understanding the kinetics mechanism of the adsorption/desorption reactions of hydrogen on the Si(1 0 0) surface. The desorption dynamics varies from the situation of strongly translational heating to the other situation of less translational heating with D coverage. This trend seems to be consistent with the 2H/3H/4H interdimer mechanism. However, despites by far the richest 4H configuration at high H coverage, the 2H desorption prevails over the 4H desorption already at 0.8 ML. To reconcile this unexpected desorption kinetics, a diffusion-promoted desorption mechanism is proposed. Height of the adsorption barriers for the 2H and 3H pathways could be reduced by the H-atom diffusion along the Si dimer rows, but that for the 4H pathway could not be the case because of no capability of diffusion on the H saturated surface. The desorption dynamics of hydrogen from the (3 × 1) dihydride surface is also reviewed and compared with the case on the monohydride surface. The sticking coefficients of hydrogen molecules onto the monohydride surfaces are evaluated from the TOF curves and found to be strongly activated by the kinetic energy. Not only the degrees of freedom of the molecules but also the vibrational degrees of freedom of substrate Si atoms determine the barrier height for adsorption. The desorption dynamics of hydrogen from the monohydride and dihydride surfaces appears to be quite similar, but the dynamics of substrate Si atoms is expected to be quite dissimilar between the two desorption pathways.     

Electronic structure of the Au–Si(1 1 1) interface as a function of Au coverage

We have investigated the Au–Si(1 1 1) interface as a function of the Au coverage by the core-level photoemission spectroscopy. With increasing the Au coverage, the spectral features in the Si 2p core-level changed remarkably and some fine structures in both Si 2p and Au 4f spectra were observed. Based on the curve fitting analysis, the Si 2p and Au 4f spectra at more than 20 Å Au coverage were decomposed into three chemically different components, respectively. The assignments of their components were performed. In addition, we have compared these results for the Au–Si(1 1 1) interface with our previous study for the Au–Si(1 0 0) interface. It was found that the electronic structures for the Au–Si(1 1 1) interface is essentially identical to those of the Au–Si(1 0 0) interface except at the initial Au deposition.     

Adsorption of hydrogen on Pt(1 1 1) and Pt(1 0 0) surfaces and its role in the HOR

Hydrogen adsorption isotherms, evaluated by combination of cyclic voltammetry and chronoamperometry, are reported on Pt(1 1 1) and Pt(1 0 0) surfaces in 0.1 M HClO₄. We found that at E > 0.05 V Pt(1 1 1) and Pt(1 0 0) are only partially covered by the adsorbed hydrogen (H_ad). On both surfaces, a full monolayer of the adsorbed hydrogen is completed at −0.1 V, i.e. the adsorption of atomic hydrogen is observed in the hydrogen evolution potential region. We also found, that the activity of the hydrogen oxidation reaction is mirrored by the shape of the hydrogen adsorption isotherms, implying that H_ad is in fact a spectator in the HOR.     

Computational simulations of pore nucleation in silicon(1 1 1)

Float zone n-Si(1 1 1) was electrochemically etched in diluted NH₄F to form porous nuclei. The experimental results were compared with computational simulations of pore nucleation and growth. Electrochemical etching of silicon(1 1 1) results in pore nucleation preferentially localized on the edges of atomic terraces. The initial pore nuclei have diameter and depth of 17 nm and 0.3 nm, respectively. We find a correlation between H-terminated Si(1 1 1) atomic surface morphology and electric field distribution on pore nucleation and growth mechanism. The H-terminated surface is composed from wide (100–200 nm) atomic terraces with steps of 0.3 nm height. Electric field enhancement occurs at the terrace edges leading to focusing the holes trajectories. This leads to weakening of the Si–Si backbonds resulting in easy atom removing. The maximum electric field was observed at terrace edges and at the semispherical pore bottom.     

Angle-resolved soft X-ray magnetic circular dichroism in a monatomic Fe layer facing an MgO(0 0 1) tunnel barrier

The electronic and magnetic states of a monatomic Fe(0 0 1) layer directly facing an MgO(0 0 1) tunnel barrier were studied by angle-resolved X-ray magnetic circular dichroism (XMCD) at the Fe L_2,3 edges in the longitudinal (L) and transverse (T) arrangements. A strong XMCD reveals no oxidation of the 1-ML Fe, showing its crucial role in giant tunnel magnetoresistance effects in Fe/MgO/Fe magnetic tunnel junctions. Sum-rule analyses of the angle-resolved XMCD give values of a spin moment, in-plane and out-of-plane orbital and magnetic dipole moments. Argument is given on their physical implication.     

Preparation and electrocatalytic activity of Rh adlayers on Pt(1 0 0) electrodes: reduction of nitrous oxide

Rhodium adlayers (submonolayer range) have been prepared on Pt(1 0 0) electrodes by electrodeposition from acidic solutions containing an excess of chloride. These Rh/Pt(1 0 0) electrodes give a well-defined voltammetric signal in the hydrogen adsorption region, which gives evidence of a high level of order in the Rh adlayer and allow a reliable estimation of the coverage. The voltammetric behavior of the Rh/Pt(1 0 0) electrodes points to an epitaxial growth with formation of rhodium islands. The well-ordered bimetallic surfaces freshly prepared were tested as electrocatalysts for nitrous oxide reduction and the responses were compared with those of the bulk Pt(1 0 0) and Rh(1 0 0) electrodes. The voltammogram for the bimetallic surface showed well separated N₂O reduction signals for Rh and Pt surface zones. An exceptionally high electrocatalytic activity for the Rh adlayer was found for low coverages. This behavior is explained on the basis of a high activity of the rhodium adatoms in the periphery of the islands.     

Formation of Pd dimers at regular and defect sites of the MgO(1 0 0) surface: cluster model calculations

The formation of Pd dimers on the surface of MgO has been studied by means of density functional theory (DFT) cluster model calculations. The following surface sites have been considered: regular five-coordinated anions at the (1 0 0) terraces, monoatomic steps, OH groups, and neutral vacancies (F centers). We discuss the energy balance of forming a dimer at a given site with respect to two isolated Pd atoms, one adsorbed at the defect and one on a regular terrace site. We found that all the defects considered lead to an energy gain when the dimer is formed, suggesting that they can be involved in nucleation and growth processes of metal clusters on the MgO surface. The dimerization energy is moderate for steps (≈0.8 eV), large for OH groups (≈1.3 eV) and rather small (<0.5 eV) for F centers.     

Calorimetric investigation of mixing enthalpy of liquid (Co + Cu + Zr) alloys at T = 1873 K

The enthalpies of mixing of liquid (Co + Cu + Zr) alloys have been determined using the high-temperature isoperibolic calorimeter. The measurements have been performed along three sections (x_Co/x_Cu = 3/1, 1/1, 1/3) with x_Zr = 0 to 0.55 at T = 1873 K. Over the investigated composition range, the partial mixing enthalpies of zirconium are negative. The limiting partial enthalpies of mixing of undercooled liquid zirconium in liquid (Co + Cu) alloys are (−138 ± 18) kJ · mol⁻¹ (the section x_Co/x_Cu = 3/1), (−155 ± 10) kJ · mol⁻¹ (the section x_Co/x_Cu = 1/1), and (−130 ± 22) kJ · mol⁻¹ (the section x_Co/x_Cu = 1/3). The integral mixing enthalpies are sign-changing. The isenthalpic curves have been plotted on the Gibbs triangle. The main features of the composition dependence of the integral mixing enthalpy of liquid ternary alloys are defined by the pair (Co + Zr) and (Cu + Zr) interactions.     

Phase equilibria for ternary liquid systems of (water + tetrahydrofuran + nonprotic aromatic solvent) at T = 298.2 K

(Liquid + liquid) equilibrium (LLE) data of the solubility curves and tie-line end compositions are presented for mixtures of {water (1) + tetrahydrofuran (2) + xylene or chlorobenzene or benzyl ether (3)} at T = 298.2 K and P = (101.3 ± 0.7) kPa. Among the studied C6 ring-containing aromatic solvents, xylene gives the largest distribution ratio and separation factors for extraction of tetrahydrofuran. A solvation energy relation (SERLAS) has been used to estimate the (liquid + liquid) equilibria of associated systems containing a nonprotic solvent. The tie-lines were also predicted using the UNIFAC-original model. The reliability of both models has been analyzed against the LLE data with respect to the distribution ratio and separation factor. SERLAS matches LLE data accurately, yielding a mean error of 9.9% for all the systems considered.     

Liquid density of biofuel mixtures: 1-Heptanol + heptane system at pressures up to 140 MPa and temperatures from 298.15 K to 393.15 K

This work reports new experimental density data (954 points) for binary mixtures of 1-heptanol + heptane over the composition range (seven compositions; 0 ⩽ 1-heptanol mole fraction x ⩽ 1), between 298.15 and 393.15 K, and for 23 pressures from 0.1 MPa up to 140 MPa. An Anton Paar vibrating tube densimeter, calibrated with an uncertainty of ±0.7 kg · m⁻³ was used to perform these measurements. The experimental density data were fitted with a Tait-like equation with low standard deviations. Excess volumes have been calculated from the experimental data. In addition, the isobaric thermal expansivity and the isothermal compressibility have been derived from the Tait-like equation, provided as supplementary material.     

(Solid + liquid) isothermal evaporation phase equilibria in the aqueous ternary system (Li2SO4 + MgSO4 + H2O) at T = 308.15 K

The solubility and the density in the aqueous ternary system (Li₂SO₄ + MgSO₄ + H₂O) at T = 308.15 K were determined by the isothermal evaporation. Our experimental results permitted the construction of the phase diagram and the plot of density against composition. It was found that there is one eutectic point for (Li₂SO₄ · H₂O + MgSO₄ · 7H₂O), two univariant curves, and two crystallization regions corresponding to lithium sulphate monohydrate (Li₂SO₄ · H₂O) and epsomite (MgSO₄ · 7H₂O). The system belongs to a simple co-saturated type, and neither double salts nor solid solution was found. Based on the Pitzer ion-interaction model and its extended HW models of aqueous electrolyte solution, the solubility of the ternary system at T = 308.15 K has been calculated. The predicted solubility agrees well with the experimental values.     

Study on the enhanced fluorescent spectrum of ciprofloxacin + Al(III) + La(III) + cetyltrimethylammonium bromide system and its application

The fluorescence of ciprofloxacin (CIP) in HAc–NaAc buffer solution and the presence of cetyltrimethylammonium bromide (CTMAB) enhanced visibly with adding Al(III) and La(III). This enhanced fluorescence spectra were studied, and a new co-luminescence system of CIP + Al(III) + La(III) + CTMAB was discovered. There was a linear relationship between the enhanced fluorescence intensity and the concentration of CIP in the range of 0.50–80.2 μg l^?1 under the optimized condition. A novel enhanced fluorescence method for the determination of trace CIP was established by using this co-luminescence system. The detection limit of the proposed method was 0.17 μg l^?1 for CIP. This method is simple, rapid and sensitive. The CIP in milk samples were analyzed by the proposed method with satisfactory results. The relative standard deviation and the recovery were in ranges of 3.21–4.34% and 97.1–100.1%, respectively. The mechanism of the co-luminescence reaction and the reasons for fluorescence enhancement has been discussed.     

Excess molar enthalpies for (benzonitrile + an aromatic hydrocarbon) atT = 298.15 K

The excess molar enthalpies of (benzonitrile  +  benzene, or methylbenzene, or 1,2-dimethylbenzene, or 1,3-dimethylbenzene, or 1,4-dimethylbenzene, or 1,3,5-trimethylbenzene, or ethylbenzene) have been determined at T =  298.15 K. The excess molar enthalpies range from  − 10 J · mol ^− 1for methylbenzene to 130 J · mol ^− 1for 1,3,5-trimethylbenzene. The Redlich–Kister equation, the NRTL, and UNIQUAC models were used to correlate the data. The results indicate a relatively strong association between benzonitrile and each of the aromatic compounds, decreasing with increasing methyl substitution on the benzene moiety.