A combined XPS-UPS-EELS study of nitrogen adsorbed on clean and barium-promoted iron surfaces: The nature of the precursor to dissociation

For N2 on a clean Fe surface, the adsorbed precursor in a parallel orientation becomes predominant around 110 K, while at lower temperatures it coexists with a weakly adsorbed species. On a Ba-promoted Fe surface, however, N2 is present exclusively in the precursor state in the temperature range 80–150 K following moderate exposure. Besides exhibiting a low N-N stretching frequency of 1530 cm−1, the precursor shows a clear separation between the 5σ and 1π levels in the UPS; the precursor dissociates to give a nitridic species around 160 K.

Direct electrochemical formation of nanostructured amorphous Co(OH)2 on gold electrodes with enhanced activity for the oxygen evolution reaction.

The oxides of cobalt have recently been shown to be highly effective electrocatalysts for the oxygen evolution reaction (OER) under alkaline conditions. In general species such as Co3O4 and CoOOH have been investigated that often require an elevated temperature step during their synthesis to create crystalline materials. In this work we investigate the rapid and direct electrochemical formation of amorphous nanostructured Co(OH)2 on gold electrodes under room temperture conditions which is a highly active precursor for the OER. During the OER some conversion to crystalline Co3O4 occurs at the surface, but the bulk of the material remains amorphous. It is found that the underlying gold electrode is crucial to the materials enhanced performance and provides higher current density than can be achieved using carbon, palladium or copper support electrodes. This catalyst exhibits excellent activity with a current density of 10 mA cm-2 at an overpotential of 360 mV with a high turnover frequency of 2.1 s-1 in 1 M NaOH. A Tafel slope of 56 mV dec-1 at low overpotentials and a slope of 122 mV dec-1 at high overpotentials is consistent with the dual barrier model for the electrocatalytic evolution of oxygen. Significantly, the catalyst maintains excellent activity for up to 24 hr of continuous operation and this approach offers a facile way to create a highly effective and stable material.

Low temperature electrical transport properties of carbon matrix containing iron nanoparticles

We present a comparative study of the low temperature electrical transport properties of the carbon matrix containing iron nanoparticles and the films. The conductivity of the nanoparticles located just below the metal-insulator transition exhibits metallic behavior with a logarithmic temperature dependence over a large temperature interval. The zero-field conductivity and the negative magnetoresistance, showing a characteristic upturn at liquid helium temperature, are consistently explained by incorporating the Kondo relation and the two dimensional electron-electron interaction. The films, in contrast, exhibit a crossover of the conductivity from power-law dependence at high temperatures to an activated hopping law dependence in the low temperature region. The transition is attributed to changes in the energy dependence of the density of states near the Fermi level. The observed magnetoresistance is discussed in terms of quantum interference effect on a three-dimensional variable range hopping mechanism.

Origin of anomalous photoinduced transformations in amorphous Ge-based chalcogenide thin films

Anomalous photoinduced transformations in amorphous Ge-based chalcogenide thin films are established as being due to photochemical modification of the surfaces, by photoemission studies. Mass measurements indicate that the giant thickness reduction on irradiation is predominantly due to the loss of material as a result of photogenerated volatile high vapor pressure oxide fractions on the surface. This extrinsic contribution contradicts the models of the phenomenon proposed so far, which are based purely on intrinsic structural transformations.

Metallization and crystallization of semiconducting amorphous Ga20Te80 alloy under high pressure

Pressure and temperature dependence of the electrical resistivity of amorphous Ga20Te80 alloy is reported for the first time. The alloy undergoes a pressure induced amorphous semiconductor-to-crystalline metal phase transition at 6.5 ± 0.5 GPa. The high pressure crystalline phase is a mixture of Te and GaTe3 phases.

The effect of rapid solidification on the order-disorder transformation in iron-based alloys

The effect of rapid solidification on the ordering reaction in Fe---Si and Fe---Al alloys has been reported. It is shown that rapid solidification can influence the ordering reaction in alloys with higher critical ordering temperatures. For ordering reactions at lower temperatures, the effect is similar to that of solid-state quenching. Different factors influencing the ordering reactions and domain structures during rapid solidification of iron-based alloys are discussed.

Pressure induced effects in bulk amorphous n-type semiconductors(GeSe3.5)100âxBix

The effect of pressure on the electrical resistivity of amorphous n-type (GeSe3.5)100�xBix been studied in a Bridgeman anvil system up to a pressure of 90 kbar down to liquid nitrogen temperature. A continuous amorphous semiconductor to metal-like solid transition in the undoped GeSe3.5 is observed at room temperature. Incorporation of Bi in the GeSe3.5 network is found to significantly disturb the behaviour of the resistivity with pressure. With increasing Bi concentration a much broader variation in resistivity with pressure is observed. The temperature dependence of the resistivity and activation energy at different pressures is also measured and they are found to be composition dependent. Results are discussed in the light of the Phillips Model of ordered clusters in chalcogenide semiconductors.

Common variants in TMPRSS6 are associated with iron status and erythrocyte volume

We report a genome-wide association study to iron status. We identify an association of SNPs in TPMRSS6 to serum iron (rs855791, combined P = 1.5 x 10(-20)), transferrin saturation (combined P = 2.2 x 10(-23)) and erythrocyte mean cell volume (MCV, combined P = 1.1 x 10(-10)). We also find suggestive evidence of association with blood hemoglobin levels (combined P = 5.3 x 10(-7)). These findings demonstrate the involvement of TMPRSS6 in control of iron homeostasis and in normal erythropoiesis.

Ultrasonic velocities and thermal expansion coefficients of amorphous Se80Te20 and Se90Te10 alloys near glass transitions

Precise measurements of the ultrasonic velocities and thermal expansivities of amorphous Se80Te20 and Se90Te10 alloys are reported near the glass transition. The samples are produced by liquid quenching. The longitudinal and transverse velocities are measured at 10 MHz frequency using the McSkimin pulse superposition technique. The thermal expansivities,agr, are measured using a three-terminal capacitance bridge. Theagr-values show a sharp maximum near the glass transition temperature,T g. The ultrasonic velocities also show a large temperature derivative, dV/dT nearT g. The data are discussed in terms of existing theories of the glass transition. The continuous change inagr shows that the glass transition is not a first-order transition, as suggested by some theories. The samples are found to be deformed by small loads nearT g. The ultrasonic velocities and dV/dT have contributions arising from this deformation.

Iron(II) and iron(III) complexes of 2,4-dithiobiuret

Ferrous and ferric complexes of 2,4-dithiobiuret (Dtb) of the type Fe(Dtb)m Xn where m, n = 1-3, and X = CI–, Br–, I– and SO 4 2– , and a neutral Fe(Dtb-H)2 complex have been synthesized and characterised by elemental analyses, magnetic susceptibility, i.r., electronic and Mössbauer spectroscopic studies. From its i.r. spectrum Dtb was found to act as a S,S-coordinating bidentate chelate. The magnetic moment, electronic and Massbauer spectra are consistent with a low spin distorted octahedral structure for the ferric complexes and a high spin form for ferrous complexes.

Investigation of surface activity and photoinduced diffusion of metals in solution deposited amorphous films of As2S3

Surface activity of solution deposited (SD) amorphous films of As2S3 has been investigated. Silver and copper are readily deposited on such films from appropriate aqueous ionic solutions. The metals diffuse into the films upon irradiation with energetic photons. Structure and properties of SD films have been investigated using electron microscopy, optical spectroscopy and differential scanning calorimetry. The amorphous films tend to crystallize upon metal diffusion. The stability of amorphous films, the deposition of metals on their active surfaces and the photo-induced diffusion may all be attributed to the presence or production of charged defects in amorphous chalcogenide films.

Iron(II, III) complexes with N, N'-DI(2-)Pyridyl Thiourea. Moumlssbauer and other spectroscopic studies

Several iron(II, III) complexes of N, N'-di(2-)pyridyl thiourea have been synthesized. The preparation of the complexes from iron(III) salts proceeds through a reduction of iron(III) to iron(II) followed by a subsequent reoxidation. The Moumlssbauer, electronic and infrared spectra of these complexes have been measured. The results are concordant with the coordination of pyridine nitrogens and thiocarbonyl sulfur yielding polymeric complexes. A variable temperature NMR study of the free ligand shows that two conformation are accessible for it in solution at subambient temperatures.

Magnetic Properties of Iron Particles Embedded in Multiwall Carbon Nanotubes

Iron nanoparticles are embedded in multiwall carbon nanotubes by the chemical vapor deposition, where benzene and ferrocene are taken as precursor materials. Varying quantity of iron particles are embedded in these tubes by taking different amount of ferrocene. These particles exhibit a magnetic moment up to 98 emu/g and an enhanced coercivity in the range of 500-2000 Oe. Negative magnetoresistance similar to 10% is observed in the presence of magnetic field up to 11 T applied at various temperatures in the range of 1.3 K-300 K. It is argued that the enhanced coercivity is due to the shape anisotropy. The negative magnetoresistance is believed to be due to the weak localization and spin dependent scattering of electrons by the ferromagnetic particles. In addition we also observe a dependence of the magnetoresistance on the direction of applied field and this is correlated with the shape anisotropy of the Fe particles.