National Institute Of Materials Physics - Romania

The direct synthesis from elements of tungsten semicarbide, W2C, taking place in a narrow concentration range and at high temperatures, is unsuited for some applications requiring small particle sizes. We report an efficient synthesis method for obtaining pure phase W2C at low temperatures (< 1050 degrees C), through the carbothermal reduction of tungsten oxide species in the presence of metallic palladium nanoparticles obtained in situ. A 1:5 (at.) Pd:W ratio or higher yields pure phase W2C, while increasing the Pd content decreases the carburization temperature. The resulting composite materials contain Pd(0) and W2C particles well-dispersed on carbon, with sizes between 50 and 500 nm. The samples have been tested using cyclic voltammetry and chronoamperometry as potential anode materials for the electrooxidation of formic acid and show improved stability in comparison with commercial Pd and comparable current densities, up to 2 times higher than the commercial catalyst. (C) 2016 Elsevier B.V. All rights reserved.

Atomically clean lead zirco-titanate PbZr0.2Ti0.8O3 (001) layers exhibit a polarization oriented inwards P(-), visible by a band bending of all core levels towards lower binding energies, whereas as introduced layers exhibit P(+) polarization under air or in ultrahigh vacuum. The magnitude of the inwards polarization decreases when the temperature is increased at 700 K. CO adsorption on P(-) polarized surfaces saturates at about one quarter of a monolayer of carbon, and occurs in both molecular (oxidized) and dissociated (reduced) states of carbon, with a large majority of reduced state. The sticking of CO on the surface in ultrahigh vacuum is found to be directly related to the P(-) polarization state of the surface. A simple electrostatic mechanism is proposed to explain these dissociation processes and the sticking of carbon on P(-) polarized areas. Carbon desorbs also when the surface is irradiated with soft X-rays. Carbon desorption when the polarization is lost proceeds most probably in form of CO2. Upon carbon desorption cycles, the ferroelectric surface is depleted in oxygen and at some point reverses its polarization, owing to electrons provided by oxygen vacancies which are able to screen the depolarization field produced by positive fixed charges at the surface.

Hepatocellular carcinoma (HCC) is the most common primary tumor of the liver, ranking as the second most common cause of death from cancer worldwide. Magnetic nanoparticles (MNPs) have been used so far in tumor diagnosis and treatment, demonstrating great potential and promising results. In principle, three different approaches can be used in the treatment of tumors with superparamagnetic iron oxide nanoparticles: magnetically induced hyperthermia, drug targeting and selective suppression of tumor growth. This review focuses on the use of iron oxide nanoparticles for the diagnosis and treatment of liver cancer and offers a walkthrough from the MNPs imaging applicability to further therapeutic options, including their potential flaws. The MNP unique physical and biochemical properties will be mentioned in close relationship to their subsequent effects on the human body, and, also, their toxic potential will be noted. A presentation of what barriers the MNPs should overcome to be more successful will conclude this review.

The growth and thermal stability of textured iridium thin films used as bottom electrode in electronic devices based on ferroelectric materials were investigated. The thin films were grown using the dc magnetron sputtering technique. The Ir layers directly deposited on SiO2/Si substrates present a mixed (111) and (200) orientations, while the films grown on Ti seed layers exhibit a strong preferred (111) orientation favoured by good matching with the titanium lattice. The substrate temperature during the growth of iridium/titanium stack has a significant effect on the surface morphology of the iridium layer and its thermal stability. The as-grown surface of 20-nm-thick Ir films is smooth, having a root-mean-square (rms) roughness of 0.7 nm. After thermal annealing the Ir film shows an increased surface roughness due to the formation of agglomerations. The change in the surface morphology of the Ir layer is due to titanium diffusion and its oxidation. Thicker and better crystallised iridium thin films annealed in oxygen atmosphere at 700 A degrees C show a good thermal stability with only a slight modification of the surface morphology. Within the limits of experimental error, there is no change in the electrical resistivity before and after thermal annealing. The rms roughness has not varied significantly and the XPS investigation shows no traces of titanium oxide on iridium surface. Ir/Ti stack deposited under the optimum conditions could be successfully used as electrode in devices based on oxide thin films.

The adsorption of L-cysteine from ethanol solutions on GaAs(1 0 0) surfaces has been studied by XPS and density-functional theory (DFT). XPS data reveal that the formation of the adsorbate involves preferentially the As-sites for p-GaAs(1 0 0) and the Ga-sites for n-GaAs(1 0 0). The adsorbed species show different orientations of the functional groups to the surface for the different substrates. DFT calculations performed for both Ga-dimers and As-dimers terminated surfaces show that the adsorption is energetically favourable on both substrates. However, the adsorption energy is more negative on top of Ga-atoms. Here an important contribution for the stabilization of the adsorbate is the interaction of the functional groups with the surface. The parallel orientation found for the Ga-bound species by DFT calculations is in good agreement with the shift in the binding energy of the NH2/NH3+ species observed by XPS analysis.

Effects of the self-assembled layers of biphenyl 4,4'-dithiol (BPDT) and 1,8-octanedithiol (ODT) on the chemical and electronic properties of p-doped GaAs (111)-As terminated substrate, (p-GaAs(111)B), were investigated in order to evidence whether the hydrocarbon moiety plays a role in tailoring the semiconductor surface properties. The electrochemical properties of the BPDT and ODT coated p-GaAs(111)B substrates were studied by Electrochemical Impedance Spectroscopy (EIS). The structural and chemical changes caused by the dithiolate layers formed on p-GaAs(111)B substrates were monitored by Atomic Force Microscopy (AFM) and X-ray Photoelectron Spectroscopy (XPS) investigations, respectively. The XPS data showed that BPDT and ODT bind to pGaAs(111)B via the thiol group. The ODT layer provides better protection against the further oxidation in air of p-GaAs(111)B substrate compared to the BPDT layer. The EIS investigations are in good agreement with XPS results, pointing to better insulating properties of the ODT layer compared to the BPDT layer in the electron transfer at the electrode/solution interface. The results evidenced that backbone plays an important role in tailoring the properties of p-GaAs(111)B substrate. (C) 2016 Elsevier B.V. All rights reserved.

By means of a combination of surface-science spectroscopies and theory, we investigate the mechanisms ruling the catalytic role of epitaxial graphene (Gr) grown on transition-metal substrates for the production of hydrogen from water. Water decomposition at the Gr/metal interface at room temperature provides a hydrogenated Gr sheet, which is buckled and decoupled from the metal substrate. We evaluate the performance of Gr/metal interface as a hydrogen storage medium, with a storage density in the Gr sheet comparable with state-of-the-art materials (1.42 wt %). Moreover, thermal programmed reaction experiments show that molecular hydrogen can be released upon heating the water-exposed Gr/metal interface above 400 K. The Gr hydro/dehydrogenation process might be exploited for an effective and eco-friendly device to produce (and store) hydrogen from water, i.e., starting from an almost unlimited source.

A new synthesis method based on the electrochemical reduction of alpha,alpha,alpha',alpha'-tetrabromo-p-xylene in the presence of single-walled carbon nanotubes (SWNTs) is used to obtain composites of carbon nanotubes (CNTs) functionalized with poly(para-phenyl-enevinylene) (PPV). To separate the effects of metallic and semiconducting CNTs on their interaction with PPV, the experiments are carried out with SWNTs enriched in semiconducting (S, 99%) and metallic (M, 98%) tubes. Significant changes in the relative intensity and shift of the radial breathing vibrational mode are reported in the Raman spectra of the as-prepared SWNTs samples, i.e., as mixtures of metallic (33%) and semiconducting (66%) entities and SWNTs enriched in M tubes (98%) that result from the electrofunctionalization with PPV. This different behavior originates in the noncovalent and covalent functionalization of SWNTs enriched in M and S SWNTs tubes with PPV, respectively. A gradual decrease in the absorption of the infrared (IR) bands of PPV situated in the spectral range of 750-1000 cm(-1) as a result of the increase of the polymer weight on the blank Au support is reported. The electrofunctionalization of the as-prepared SWNTs induces position changes of the PPV IR absorption bands. In the presence of S-enriched SWNTs, a significant increase in the absorbance of the two IR bands peaked at 1452 and 1471 cm(-1), which are assigned to the vibrational modes of the phenyl ring stretching and the quinoid structure of the PPV, respectively, is reported. This results from the covalent bonding of the PPV macromolecular chains onto the surface of the SWNTs enriched in S tubes. Our results also demonstrate that the photoluminescence quenching effect reported for the PPV/SWNTs composites is due to the metallic nanotubes.

The possibility to intercalate noble gas atoms below epitaxial graphene monolayers coupled with the instability at high temperature of graphene on the surface of certain metals has been exploited to produce Ar-filled graphene nanosized blisters evenly distributed on the bare Ni(111) surface. We have followed in real time the self-assembling of the nanoblisters during the thermal annealing of the Gr/Ni(111) interface loaded with Ar and characterized their morphology and structure at the atomic scale. The nanoblisters contain Ar aggregates compressed at high pressure arranged below the graphene monolayer skin that is decoupled from the Ni substrate and sealed only at the periphery through stable C-Ni bonds. Their in-plane truncated triangular shapes are driven by the crystallographic directions of the Ni surface. The nonuniform strain revealed along the blister profile is explained by the inhomogeneous expansion of the flexible graphene lattice that adjusts to envelop the Ar atom stacks.

The Peierls transition of polycrystalline CuGeO3 samples was investigated by thermal and magnetic investigations. We find that spin disorder induced by chain breaking and grain boundaries has similar effects to doping but without suppressing the spin-Peierls transition temperature or the spin-Peierls gap.