Seaweed and Dendritic Growth in Unsaturated Fatty Acid Monolayers

The lateral movement in lipid membranes depends on their diffusion constant within the membrane. However, when the flux of the subphase is high, the convective flow beneath the membrane also influences lipid movement. Lipid monolayers of an unsaturated fatty acid at the water–air interface serve as model membranes. The formation of domains in the liquid/condensed coexistence region is investigated. The dimension of the domains is fractal, and they grow with a constant growth velocity. Increasing the compression speed of the monolayer induces a transition from seaweed growth to dendritic growth. Seaweed domains have broad tips and wide and variable side branch spacing. In contrast, dendritic domains have a higher fractal dimension, narrower tips, and small, well-defined side branch spacing. Additionally, the growth velocity is markedly larger for dendritic than seaweed growth. The domains’ growth velocity increases and the tip radius decreases with increasing supersaturation in the liquid/condensed coexistence region. Implications for membranes are discussed

Simple preparation of carbon-bimetal oxide nanospinels for high-performance bifunctional oxygen electrocatalysts

The lack of efficient cost-effective electrocatalysts for reversible oxidation of water is by far the most notorious obstacle in the development of fuel cells and electrolyzers. Here, oxygen bifunctional electrocatalysts based on C-CoFe and C-NiFe oxide nanospinels are developed by simple autocombustion between ethylene glycol/acetate and the metal nitrates. The effects of electronic modulation and the mass (or surface area) effect were examined based on the cyclic voltammograms of the unary and binary metal oxides in alkaline solution, and their high oxygen evolution and reduction activities were attributed to the synergic intermetallic interactions. The C-CoFe oxide, in particular, shows an oxygen evolution overpotential of 350 mV (without iR correction) at 10 mA cm 122 with excellent stability over 10 hours and a Tafel slope of 49 mV per decade. Furthermore, it exhibits the highest oxygen reduction activity among the synthesized electrocatalysts due the particular synergy between Co and Fe centers

Formation of palladium hydrides in low temperature Ar/H2\mathrm{Ar/H_{2}}-plasma

20 nm thick Pd coatings deposited on Si substrates with 800 nm SiO$_{2}$ and 1 nm Cr buffer layers were treated in a 2.45 GHz microwave plasma source at 700 W plasma power and 40 Pa working pressure without substrate heating. For obtaining information on the effect of energy influx due to ion energy on the palladium films the substrate potential was varied from U$_{sub}$ = 0 V to − 150 V at constant gas flow corresponding to mean ion energies E$_{i}$ from 0.22 eV ∙ cm$^{− 2}$ ∙ s$^{− 1}$ to 1.28 eV ∙ cm$^{− 2}$ ∙ s$^{− 1}$.In contrast to high pressure reactions with metallic Pd, under plasma exposure we do not observe solid solutions over a wide range of hydrogen concentration. The hydrogen incorporation in Pd films takes place discontinuously. At 0 V substrate voltage palladium hydride is formed in two steps to PdH$_{0.1}$4 and PdH$_{0.57}$. At − 50 V substrate voltage Pd$_{H0.57}$ is formed directly. However, substrate voltages of − 100 V and − 150 V cause shrinking of the unit cell. We postulate the formation of two fcc vacancy palladium hydride clusters PdH$_{Vac}$(I) and PdH$_{Vac}$(II). Under longtime plasma exposure the fcc PdHVac(II) phase forms cubic PdH$_{1.33}$.The fcc PdH$_{0.57}$ phase decomposes at temperatures > 300 °C to form metallic fcc Pd. The hydrogen removal causes a decrease of lattice defects. In situ high temperature diffractometry measurements also confirm the existence of PdHVac(II) as a palladium hydride phase. Stoichiometric relationship between cubic PdH$_{1.33}$ and fcc PdH$_{Vac}$(II) becomes evident from XR measurements and structure considerations. We assume both phases have the chemical composition Pd$_{3}$H$_{4}$. Up to 700 °C we observe phase transformation between both the fcc PdH$_{Vac}$(II) and cubic PdH$_{1.33}$ phases. These phase transformations could be explained analog to a Bain distortion by displacive solid state structural changes

Strain Effects by Surface Oxidation of Cu3N Thin Films Deposited by DC Magnetron Sputtering

We report the self-buckling (or peeling off) of cubic Cu3N films deposited by DC magnetron sputtering of a Cu target in a nitrogen environment at a gas pressure of 1 Pa. The deposited layer partially peels off as it is exposed to ambient air at atmospheric pressure, but still adheres to the substrate. The chemical composition of the thin film as investigated by means of X-ray photoelectron spectroscopy (XPS) shows a considerable surface oxidation after exposure to ambient air. Grazing incidence X-ray diffraction (GIXRD) confirms the formation of a crystalline Cu3N phase of the quenched film. Notable are the peak shifts in the deposited film to smaller angles in comparison to stress-free reference material. The X-ray pattern of Cu3N exhibits clear differences in the integral width of the line profiles. Changes in the film microstructure are revealed by X-ray diffraction, making use of X-ray line broadening (Williamson–Hall and Stokes–Fourier/Warren–Averbach method); it indicates that the crystallites are anisotropic in shape and show remarkable stress and micro-strain