Abstract: Methods used to strengthen metals generally also cause a pronounced decrease in ductility and electrical conductivity. In this work a bioinspired strategy is applied to surmount the dilemma. By assembling copper submicron flakes cladded with in-situ grown graphene, graphene/copper matrix composites with a nanolaminated architecture inspired by a natural nacre have been prepared. Owing to a combined effect-from the bioinspired nanolaminated architecture and improved interfacial bonding, a synergy has been achieved between mechanical strength and ductility as well as electrical conductivity in the graphene/copper matrix composites. With a low volume fraction of only 2.5% of graphene, the composite shows a yield strength and elastic modulus similar to 177% and similar to 25% higher than that of unreinforced copper matrix, respectively, while retains ductility and electrical conductivity comparable to that of pure copper. The bioinspired nanolaminated architecture enhances the efficiencies of two-dimensional (2D) graphene in mechanical strengthening and electrical conducting by aligning graphene to maximize performance for required loading and carrier transporting conditions, and toughens the composites by crack deflection. Meanwhile, in-situ growth of graphene is beneficial for improving interfacial bonding and structural quality of graphene. The strategy sheds light on the development of composites with good combined structural and functional properties. (C) 2017 Elsevier Ltd. All rights reserved.

Abstract: A hitherto unknown composition is highlighted in the red and black inks preserved on ancient Egyptian papyri from the Roman period (circa 100 to 200 CE). Synchrotron-based macro-X-ray fluo-rescence (XRF) mapping brings to light the presence of iron (Fe) and lead (Pb) compounds in the majority of the red inks inscribed on 12 papyrus fragments from the Tebtunis temple library. The iron-based compounds in the inks can be assigned to ocher, notably due to the colocalization of Fe with aluminum, and the detection of hematite (Fe2O3) by micro-X-ray diffraction. Using the same techniques together with micro-Fourier transform infrared spectroscopy, Pb is shown to be associated with fatty acid phosphate, sulfate, chloride, and carboxylate ions. Moreover, microXRF maps reveal a peculiar distribution and colocalization of Pb, phosphorus (P), and sulfur (S), which are present at the micrometric scale resembling diffused “coffee rings” surrounding the ocher particles imbedded in the red letters, and at the submicrometric scale concentrated in the papyrus cell walls. A similar Pb, P, and S composition was found in three black inks, suggesting that the same lead components were employed in the manufacture of carbon-based inks. Bearing in mind that pigments such as red lead (Pb3O4) and lead white (hydrocerussite [Pb-3(CO3)(2)(OH)(2)] and/or cerussite [PbCO3]) were not detected, the results presented here suggest that the lead compound in the ink was used as a drier rather than as a pigment. Accordingly, the study calls for a reassessment of the composition of lead-based components in ancient Mediterranean pigments.

Abstract: A platform for producing stabilized Pt atoms and clusters through the combination of an N-doped graphene support and atomic layer deposition (ALD) for the Pt catalysts was investigated using transmission electron microscopy (TEM) and scanning transmission electron microscopy (STEM). It was determined, using imaging and spectroscopy techniques, that a wide range of N-dopant types entered the graphene lattice through covalent bonds without largely damaging its structure. Additionally and most notably, Pt atoms and atomic clusters formed in the absence of nanoparticles. This work provides a new strategy for experimentally producing stable atomic and subnanometer cluster catalysts, which can greatly assist the proton exchange membrane fuel cell (PEMFC) development by producing the ultimate surface area to volume ratio catalyst.

Abstract: Printed chalcopyrite thin films have attracted considerable attention in recent years due to their potential in the high-throughput production of photovoltaic devices. To improve the homogeneity of printed CuInSe2 (CISe) layers, chemical additives such as binder can be added to the precursor ink. In this contribution, we investigate the influence of the dicyandiamide (DCDA) content, used as a binder in the precursor ink, on the physical and electrical properties of printed CISe solar cells. It is shown that the use of the binder leads to a dense absorber, composed of large CISe grains close to the surface, while the bulk of the layer consists of CISe crystallites embedded in a CuxS particle based matrix, resulting from the limited sintering of the precursor in this region. The expected additional carbon contamination of the CISe layer due to the addition of the binder appears to be limited, and the optical properties of the CISe layer are similar to the reference sample without additive. The electrical characterization of the corresponding CISe/CdS solar cells shows a degradation of the efficiency of the devices, due to a modification in the predominant recombination mechanisms and a limitation of the space charge region width when using the binder; both effects could be explained by the inhomogeneity of the bulk of the CISe absorber and high defect density at the CISe/CuxS-based matrix interface.

Abstract: Cyrogenic etching of silicon is envisaged to enable better control over plasma processing in the microelectronics industry, albeit little is known about the fundamental differences compared to the room temperature process. We here present molecular dynamics simulations carried out to obtain sticking probabilities, thermal desorption rates, surface diffusion speeds, and sputter yields of F, F2, Si, SiF, SiF2, SiF3, SiF4, and the corresponding ions on Si(100) and on SiF13 surfaces, both at cryogenic and near room temperature. The different surface behavior during conventional etching and cryoetching is discussed. F2 is found to be relatively reactive compared to other species like SiF03. Thermal desorption occurs at a significantly lower rate under cryogenic conditions, which results in an accumulation of physisorbed species. Moreover, ion incorporation is often observed for ions with energies of 30400 eV, which results in a relatively low net sputter yield. The obtained results suggest that the actual etching of Si, under both cryogenic and near room temperature conditions, is based on the complete conversion of the Si surface to physisorbed SiF4, followed by subsequent sputtering of these molecules, instead of direct sputtering of the SiF03 surface.

Abstract: The nonlinear absorption of Ag atomic clusters and nanoparticles dispersed in a transparent oxyfluoride glass host has been studied. The as-prepared glass, containing 0.15 atom % Ag, shows an absorption band in the UV/violet attributed to the presence of amorphous Ag atomic nanoclusters with an average size of 1.2 nm. Upon heat treatment the Ag nanoclusters coalesce into larger nanoparticles that show a surface plasmon absorption band in the visible. Open aperture z-scan experiments using 480 nm nanosecond laser pulses demonstrated nonsaturated and saturated nonlinear absorption with large nonlinear absorption indices for the Ag nanoclusters and nanoparticles, respectively. These properties are promising, e.g., for applications in optical limiting and objects contrast enhancement.

Abstract: Hydrogen-storage properties of complex hydrides depend of their form, such as a polymorphic form or an eutectic mixture. This Paper reports on an easy and reproducible way to synthesize a new stable form of magnesium borohydride by pressure-induced collapse of the porous gamma-Mg(BH4)(2). This amorphous complex hydride was investigated by temperature-programmed synchrotron X-ray diffraction (SXRD), transmission electron microscopy (TEM), thermogravimetric analysis, differential scanning calorimetry analysis, and Raman spectroscopy, and the dynamics of the BH4 reorientation was studied by spinlattice relaxation NMR spectroscopy. No long-range order is observed in the lattice region by Raman spectroscopy, while the internal vibration modes of the BH4 groups are the same as in the crystalline state. A hump at 4.9 angstrom in the SXRD pattern suggests the presence of nearly linear MgBH4 Mg fragments constituting all the known crystalline polymorphs of Mg(BH4)(2), which are essentially frameworks built of tetrahedral Mg nodes and linear BH4 linkers. TEM shows that the pressure-collapsed phase is amorphous down to the nanoscale, but surprisingly, SXRD reveals a transition at similar to 90 degrees C from the dense amorphous state (density of 0.98 g/cm(3)) back to the porous ? phase having only 0.55 g/cm(3) crystal density. The crystallization is slightly exothermic, with the enthalpy of -4.3 kJ/mol. The volumetric hydrogen density of the amorphous form is 145 g/L, one of the highest among hydrides. Remarkably, this form of Mg(BH4)2 has different reactivity compared to the crystalline forms. The parameters of the reorientational motion of BH4 groups in the amorphous Mg(BH4)(2) found from NMR measurements differ significantly from those in the known crystalline forms. The behavior of the nuclear spinlattice relaxation rates can be described in terms of a Gaussian distribution of the activation energies centered on 234 +/- 9 meV with the dispersion of 100 +/- 10 meV.

Abstract: Iron oxide nanoparticles were prepared using the simplest and most efficient chemical route, the coprecipitation, in the absence and the presence of three different and widely used surfactants. The purpose of this study is to investigate the possible influence of the different surfactants on the structure and therefore on the magnetic properties of the iron oxide nanoparticles. Thus, different techniques were employed in order to elucidate the composition and structure of the magnetic iron oxide nanoparticles. By combining transmission electron microscopy with X-ray powder diffraction and X-ray absorption fine structure measurements, we were able to determine and confirm the crystal structure of the constituent iron oxides. The magnetic properties were investigated by measuring the hysteresis loops where the surfactant influence on their collective magnetic behavior and subsequent AC magnetic hyperthermia response is apparent. The results indicate that the produced iron oxide nanoparticles may be considered as good candidates for biomedical applications in hyperthermia treatments because of their high heating capacity exhibited under an alternating magnetic field, which is sufficient to provoke damage to the cancer cells.

Abstract: We perform first-principles calculations to investigate the preferred positions of B and P dopants, both neutral and in their preferred charge state, in Si and Si/SiO2 core-shell nanowires (NWs). In order to understand the observed trends in the formation energy, we isolate the different effects that determine these formation energies. By making the distinction between the unrelaxed and the relaxed formation energy, we separate the impact of the relaxation from that of the chemical environment. The unrelaxed formation energies are determined by three effects: (i) the effect of strain caused by size mismatch between the dopant and the host atoms, (ii) the local position of the band edges, and (iii) a screening effect. In the case of the SiNW (Si/SiO2 NW), these effects result in an increase of the formation energy away from the center (interface). The effect of relaxation depends on the relative size mismatch between the dopant and host atoms. A large size mismatch causes substantial relaxation that reduces the formation energy considerably, with the relaxation being more pronounced towards the edge of the wires. These effects explain the surface segregation of the B dopants in a SiNW, since the atomic relaxation induces a continuous drop of the formation energy towards the edge. However, for the P dopants, the formation energy starts to rise when moving from the center but drops to a minimum just next to the surface, indicating a different type of behavior. It also explains that the preferential location for B dopants in Si/SiO2 core-shell NWs is inside the oxide shell just next to the interface, whereas the P dopants prefer the positions next to the interface inside the Si core, which is in agreement with recent experiments. These preferred locations have an important impact on the electronic properties of these core-shell NWs. Our simulations indicate the possibility of hole gas formation when B segregates into the oxide shell.

Abstract: Ando's model provides a rigorous quantum-mechanical framework for electron-surface roughness scattering, based on the detailed roughness structure. We apply this method to metallic nanowires and improve the model introducing surface roughness distribution functions on a finite domain with analytical expressions for the average surface roughness matrix elements. This approach is valid for any roughness size and extends beyond the commonly used Prange-Nee approximation. The resistivity scaling is obtained from the self-consistent relaxation time solution of the Boltzmann transport equation and is compared to Prange-Nee's approach and other known methods. The results show that a substantial drop in resistivity can be obtained for certain diameters by achieving a large momentum gap between Fermi level states with positive and negative momentum in the transport direction. (C) 2015 AIP Publishing LLC.

Abstract: We theoretically investigate the electronic transport properties of two closely spaced L-shaped semiconductor quantum wires, for different configurations of the output channel widths as well as the distance between the wires. Within the effective-mass approximation, we solve the time-dependent Schrodinger equation using the split-operator technique that allows us to calculate the transmission probability, the total probability current, the conductance, and the wave function scattering between the energy subbands. We determine the maximum distance between the quantum wires below which a relevant non-zero transmission is still found. The transmission probability and the conductance show a strong dependence on the width of the output channel for small distances between the wires. (C) 2015 AIP Publishing LLC.

Abstract: Selective etching allows for obtaining carbon nanotubes with a specific chirality. While plasma-assisted etching has already been used to separate metallic tubes from their semiconducting counterparts, little is known about the nanoscale mechanisms of the etching process. We combine (reactive) molecular dynamics (MD) and force-bias Monte Carlo (tfMC) simulations to study H-etching of CNTs. In particular, during the hydrogenation and subsequent etching of both the carbon cap and the tube, they sequentially transform to different carbon nanostructures, including carbon nanosheet, nanowall, and polyyne chains, before they are completely removed from the surface of a substrate-bound Ni-nanocluster.We also found that onset of the etching process is different in the cases of the cap and the tube, although the overall etching scenario is similar in both cases. The entire hydrogenation/etching process for both cases is analysed in detail, comparing with available theoretical and experimental evidences.

Abstract: The melting of fluorographene is very unusual and depends strongly on the degree of fluorination. For temperatures below 1000 K, fully fluorinated graphene (FFG) is thermomechanically more stable than graphene but at T-m approximate to 2800 K FFG transits to random coils which is almost 2 times lower than the melting temperature of graphene, i.e., 5300 K. For fluorinated graphene up to 30% ripples causes detachment of individual F-atoms around 2000 K, while for 40%-60% fluorination large defects are formed beyond 1500 K and beyond 60% of fluorination F-atoms remain bonded to graphene until melting. The results agree with recent experiments on the dependence of the reversibility of the fluorination process on the percentage of fluorination.

Abstract: Motivated by the recent experimental realization of a two-dimensional (2D) BeN4 monolayer, in this study we investigate the structural, dynamical, electronic, and optical properties of a monolayer and few-layer BeN4 using first-principles calculations. The calculated phonon band dispersion reveals the dynamical stability of a free-standing BeN4 layer, while the cohesive energy indicates the energetic feasibility of the material. Electronic band dispersions show that monolayer BeN4 is a semi-metal whose conduction and valence bands touch each other at the Sigma point. Our results reveal that increasing the layer number from single to six-layers tunes the electronic nature of BeN4. While monolayer and bilayer structures display a semi-metallic behavior, structures thicker than that of three-layers exhibit a metallic nature. Moreover, the optical parameters calculated for monolayer and bilayer structures reveal that the bilayer can absorb visible light in the ultraviolet and visible regions better than the monolayer structure. Our study investigates the electronic properties of Dirac-semimetal BeN4 that can be an important candidate for applications in nanoelectronic and optoelectronic. Published under an exclusive license by AIP Publishing.

Abstract: The contamination of ground samples by a commercially available Lovibond McCrone Micronizing Mill is discussed. Tracer and weighing experiments showed that abrasion of corundum grinding elements was important, introducing 620 mg of abrasion products per minute of wet grinding. Agate grinding elements were abraded at ⩽6 mg min-1. The abrasion products and grinding elements were analyzed by x-ray fluorescence, spark-source mass spectrometry and neutron activation analysis. Contamination in trace element analysis of geological materials is likely to be negligible for agate grinding elements and, except for a few transition metals, also for corundum grinding elements. Contamination of typical biological samples is significant for a few elements even when agate elements are used, and is absolutely prohibitive for trace analysis when corundum elements are used.