Growth and structure of Pd films on ZnO(0001)

The growth and structure of Pd films on ZnO(0001) were investigated using high resolution electron energy loss spectroscopy, x-ray photoelectron spectroscopy, and low energy electron diffraction. Vapor deposited Pd films at 300 K were found to follow a two-dimensional (2D) island growth mode, in which 2D metal islands are formed up to a critical coverage at which point growth occurs primarily in a layer-by-layer fashion on top of the islands. Heating to only 350 K was found to be sufficient to induce partial agglomeration of Pd films into three-dimensional particles. In addition to causing further agglomeration into particles, heating to 700 K resulted in partial reduction of the ZnO surface and the formation of a PdZn alloy

Characterization and microhardness of electrodeposited Ni-W-P coatings obtained from gluconate bath

Electrodeposited Ni-W-P alloy coatings are considered as one of the potential replacements for conventional hard chromium. In this work, Ni-W-P coatings with different phosphorous concentrations have been prepared by direct current (DC) and pulse current (PC) electrodeposition methods using gluconate bath for the first time. These coatings were characterized by XRD, FESEM, AFM, DSC and XPS techniques. Thicknesses and current efficiencies are found to be more in DC plated coatings compared to PC plated coatings. EDX analysis confirms the presence of nickel, tungsten and phosphorous in the deposits and amount of P is observed to be more in PC coatings compared to DC coatings. XRD studies demonstrate that the coatings are nanocrystalline in nature which on heat treatment show the formation of Ni3P phase. FESEM demonstrates that DC Ni-W-P alloy deposits show fine nodules, whereas all PC Ni-W-P coatings have fine grains with smooth morphology. Increase in roughness with time and increase in P content is observed in AFM roughness measurement. DSC of DC coatings are characterized by two peaks (250 and 360 oC) while pulse plated exhibits only the high temperature peak. Ni is in both +2 and metallic states in all coatings, whereas Wo and W6+ species are observed in all coatings. Amount of oxidized Ni is more in PC coatings in comparison with DC coatings. On the other hand, P is in Pd- and P5+ states in these coatings. PC coatings show higher microhardness and it increases with heat treatment

XPS Characterization and Microhardness of Heat treated Co-W Coatings Electrodeposited with Gluconate Bath

Thermal stability and effect of heat treatment on electronic structure and microhardness of electrodeposited CoW alloy coatings using gluconate bath was characterized by DSC and XPS. XPS studies demonstrate that as-deposited alloy coating has significant amount of Co and W metals as well as Co2+ and W6+ species. There is a decrease in Co metal concentration in the alloy heated at 600 C and Co is in fully oxidized form when it is heat treated at 800 C. Marginal decrease in W metal concentration and presence of both W6+ and W5+ species are observed when the coating is heated at 600 C, whereas mostly W6+ species along with a little amount of W5+ could be seen in the coating heated at 800 C. Microhardness values of 1017 and 1336 HK are observed when Co−W coatings are heated at 500 and 600 C, respectively and they are comparable with as-deposited hard ch

Stable superhydrophobic coatings Using PVDF/MWCNT nanocomposite

Thermally stable superhydrophobic coatings have been prepared using Polyvinylidene fluoride (PVDF)Multiwalled carbon nanotubes (MWCNTs) by spray coating method. The effects of MWCNT (0 – 66 wt%) and temperature (300 to 623 K) on wettability have been studied. A transformation from hydrophobic to superhydrophoic state was achieved with increase of CNT content. X-ray diffraction (XRD) and Fourier transform infrared spectroscopy (FTIR) studies reveal that with increase in CNT content, -phase of PVDF decreases suggesting that MWCNT has strong effect on the phase separation of PVDF. Field emission scanning electron microscopy (FESEM) studies show that the coatings have rough surface with porous structure. With increase in CNT content the protrusion like structures decreased reaching micro/nano scales. The coatings were thermally stable upto 573 K exhibiting superhydrophobicity and thereafter transformed to superhydrophilic state at 623 K. Energy dispersive X-ray spectroscopy (EDXS) analysis show the absence of fluorine after annealing at 623 K suggesting decomposition of PVDF. X-ray photoelectron spectroscopy (XPS) of C1s and F1s core levels in as-deposited PVDFMWCNT coating show the presence of CF2 related species. Concentration of fluorine drastically decreases after heat treatment of the coating at 350 C. The main advantage of the present method is feasibility for application over large area and the coatings are stable upto 573 K

Pt/CexPr1−xO2 (x = 1 or 0.9) NOx storage–reduction (NSR) catalysts

Model Pt/Ce0.9Pr0.1O2 and Pt/CeO2 NOx storage–reduction catalysts were prepared via nitrate calcination, co-precipitation and carbon-templating routes. Raman spectroscopic data obtained on the catalysts indicated that the introduction of praseodymium into the ceria lattice increased the concentration of defect sites (vacancies), arising from the higher reducibility of the Pr4+ cation compared to Ce4+. For the Pr-promoted samples, H2-TPR profiles contained high temperature bulk reduction peaks which were less pronounced compared with their ceria analogs, indicating that the presence of praseodymium enhances oxygen mobility due to the creation of lattice defects. Under lean-rich cycling conditions, the cycle-averaged NOx conversion of the Pt/Ce0.9Pr0.1O2 samples was in each case substantially higher than that of the Pt/CeO2 analog, amounting to a difference of 10–15% in the absolute NOx conversion in some cases. According to DRIFTS data, a double role can be assigned to Pr doping; on the one hand, Pr accelerates the oxidation of adsorbed NOx species during the lean periods. On the other hand, Pr doping destabilizes the adsorbed NOx species during the rich periods, and the kinetics of nitrate decomposition are faster on Pt/Ce0.9Pr0.1O2, leading to improved catalyst regeneration. These results suggest that ceria-based mixed oxides incorporating Pr are promising materials for NOx storage–reduction catalysts intended for low temperature operation.The financial support of Generalitat Valenciana (predoctoral stay BEFPI/2012), the Spanish Ministry of Economy and Competitiveness (Project CTQ2012-30703), and co-financing by FEDER resources is acknowledged. Partial financial support was also provided by the National Science Foundation and the U.S. Department of Energy (DOE) under award no. CBET-1258742

Nanocolumnar Crystalline Vanadium Oxide-Molybdenum Oxide Antireflective Smart Thin Films with Superior Nanomechanical Properties

Vanadium oxide-molybdenum oxide (VO-MO) thin (21-475 nm) films were grown on quartz and silicon substrates by pulsed RF magnetron sputtering technique by altering the RF power from 100 to 600 W. Crystalline VO-MO thin films showed the mixed phases of vanadium oxides e.g., V2O5, V2O3 and VO2 along with MoO3. Reversible or smart transition was found to occur just above the room temperature i.e., at similar to 45-50 degrees C. The VO-MO films deposited on quartz showed a gradual decrease in transmittance with increase in film thickness. But, the VO-MO films on silicon exhibited reflectance that was significantly lower than that of the substrate. Further, the effect of low temperature (i.e., 100 degrees C) vacuum (10(-5) mbar) annealing on optical properties e.g., solar absorptance, transmittance and reflectance as well as the optical constants e.g., optical band gap, refractive index and extinction coefficient were studied. Sheet resistance, oxidation state and nanomechanical properties e.g., nanohardness and elastic modulus of the VO-MO thin films were also investigated in as-deposited condition as well as after the vacuum annealing treatment. Finally, the combination of the nanoindentation technique and the finite element modeling (FEM) was employed to investigate yield stress and von Mises stress distribution of the VO-MO thin films

Effect of codeposition of P on characterization and microhardness of electrodeposited Co-W coatings obtained from gluconate bath

Electrodeposited Co-W alloy coatings are considered as one of the potential replacements for conventional hard chromium. However, it has been observed that addition of small amount of P in Co–W matrix greatly influences its properties. Therefore, it is envisaged that with appropriate composition, Co–W–P films may exhibit superior and unique properties which can be utilized in sophisticated electronic and automobile industries and space technology. In this work, Co-W-P coatings with different phosphorous concentrations have been prepared by direct current (DC) and pulse current (PC) electrodeposition methods using gluconate bath for the first time. The coatings were characterized by XRD, FESEM, AFM, DSC and XPS techniques. The current efficiency reduction decreases with the addition of phosphorous to the deposit. EDX analysis confirms the presence of cobalt, tungsten and phosphorous in the deposit and amount of P is observed to be more in PC coatings compared to DC coatings. XRD studies demonstrate that the coatings are nanocrystalline which on heat treatment show the formation of Co3W phase. Phase transformation behavior from DSC studies exhibits the reduction in thermal stability with the addition of phosphorous. FESEM reveals the presence of spherical nodular morphology of the coatings, whereas increase in roughness with time and increase in P content is seen in AFM roughness measurement. It has also been observed that the PC coatings are smoother and have less number of nodules compared to that of DC coatings. Co is in both +2 and metallic states in all coatings, whereas W0 and W6+ species are observed in all coatings. On the other hand, P is in

Growth, characterization and interfacial reaction of magnetron sputtered Pt/CeO2 thin films on Si and Si3N4 substrates

Pt/CeO2 thin films were deposited on Si and Si3N4 substrates by magnetron sputtering at room temperature. Growth of the films on Si and Si3N4 were characterized by XRD, FESEM and AFM. Interaction of Pt/CeO2 films with Si in Si and Si3N4 substrates was extensively investigated by XPS. XRD studies show that films are oriented preferentially to (200) direction of CeO2. XPS results show that Pt is mainly present in +2 oxidation state in Pt/CeO2/Si film, whereas Pt4+ predominates in Pt/CeO2/Si3N4 film. Ce is present as both +4 and +3 oxidation states in Pt/CeO2 films deposited on both Si and Si3N4 substrates, but concentration of Ce3+ species is observed to be more in Pt/CeO2/Si film. Interfacial reaction between CeO2 and Si substrate is controlled in presence of Pt. Pt/Ce concentration ratio decreases in Pt/CeO2/Si3N4 film upon successive sputtering, whereas this ratio decreases initially and then increases in Pt/CeO2/Si film. Pt is segregated at the interface in Pt/CeO2/Si film, whereas Pt is diffused outwards in Pt/CeO2/Si3N4 film as observed from depth profiling studies