Volume 225, Issue 3 - Functional Nanocoatings

The new features in the electroless (autocatalytic) deposition, structure and properties of Ni-Cu-P, Ni-Sn-P, Ni-Zn-P, Ni-W-P, Co-W-P, and Co-Re-P as well as the quaternary coatings Ni-Sn-Cu-P, Ni-W-Re-P, and Co-Re-Ni-P established in the Institute of Physical Chemistry of the Bulgarian Academy of Sciences (IPC BAS) are reviewed. The role of disproportionation reactions of Cu(I), Sn(II) and Re(VI) during electroless deposition of Ni-Cu-P, Ni-Sn-P and Co-Re-P is considered. The data about the localization and chemical state of Zn, W and Re are presented. The influence of Cu and Sn added to high P (> 10 wt. %) Ni-P coatings on the thermal stability of their amorphous state is illustrated. A comparison of the corrosion resistance of Ni-Cu-P and Ni-Sn-P with that of Ni-P with the same quantity of phosphorus is given. The application of Ni-Cu-P in a hybrid multilayer with TiN is demonstrated.

ZnO nanoparticles surface functionalized with α -oxo-carboxylic acids have been used as photo-initiators for the curing of UV off-set printing inks. Other than commercial molecular photo-initiators ZnO nanoparticles do not migrate in the cured resins, they do not leach out and therefore, even if in contact with food, there is no danger of contamination. ESR and in-situ Raman-spectroscopy have been applied to analyze the kinetics of this free radical bulk photo-polymerization process. Upon UV irradiation the Photo-Kolbe-reaction (decarboxylation of carbonic acids by the photo generated electron hole) takes place as could be confirmed by ESR and GC-MS measurements.

Nanocomposite coatings were obtained by electrochemical codeposition of TiO 2 nano-particles (mean diameter 21 nm, Degussa P 25 ) with nickel, from an additive-free Watts type bath. Pure Ni and composite Ni-TiO 2 coatings were electrolytically deposited under both direct and pulse current conditions and an extended region of electrolysis conditions (pH, current density, TiO 2 loading in the bath). Pure Ni deposits were produced under the same experimental conditions for comparison. The aim of this study was to correlate the observed structural characteristics of the coatings (crystallographic orientation and grain size of nickel matrix,) and incorporation percentage with the resulting microhardness values and tribological behavior. Overall, the data have demonstrated that when attributing the observed strengthening effect of composites, not only grain refinement and dispersion strengthening mechanisms, but also preferred crystalline orientation should be taken into consideration. The variation of the wear rate is directly associated with the microhardness variations and consequently, governed by the same parameters that determine the synergistic strengthening mechanism proposed. Pure and composite coatings with [110] crystalline orientation exhibited the highest microhardness values and wear resistance.

The electrodeposition process of Eosin Y/ZnO: Mn as films and nanowires performed using a solution containing zinc and manganese nitrates + lactic acid mixture was studied by linear voltammetry. The films and wires grown by polarization at −1.1 V/SCE electrode potential were characterized using X-ray diffraction (XRD), scanning electron microscopy (SEM), energy-dispersive X-ray analysis (EDX), and X-ray photoelectron spectroscopy (XPS). Additionally, the Eosin Y presence was evidenced by optical measurements as absorption and photoluminescence spectroscopy. The manganese content in films depends on the nature of support electrode used. On the other hand, the presence of Eosin Y species in the deposition bath increased significantly the manganese concentration in the ZnO: Mn nanowires electrodeposited at −1.1 V/SCE.

Controlling the growth of ZnO nanostructures for photovoltaic applications will ensure greater device efficiency and parameter control. This paper reports on methods to engineer the morphology and tailor the nanostructure growth direction through the hydrothermal synthesis method. Effective control is achieved through the use of a sputtered zinc layer together with modifications of the growth solution. These nanostructures have been developed with a view to incorporation into excitonic solar cells, and methods to improve surface stability using a fully aqueous synthesis method will be discussed.

NiCo films with incorporated ferrite (BaFe 12 O 19 ) nano-particles were studied with the motivation of future MEMS application. The microstructure was characterized by SEM, TEM, EBSD and XRD. Magnetic properties were derived from SQUID magnetometry. Two types of layers were electrodeposited distinguished by their microstructure. One type is a pure NiCo nano-grained matrix without particle incorporation; the other is a composite of the nano-grained NiCo matrix with co-deposited nano-sized ferrite particles with a content of about 0.2 wt. %. The soft magnetic matrix dominates the global magnetization behavior expected for NiCo alloys. Despite the low incorpotation rate, the influence of the BaFe 12 O 19 particles in the matrix is apparent in the in-plane measurement.

In this work we present a simple method to obtain silver sols stabilized by tetrazole derivatives. The well established metal precursor silver nitrate and the reductant sodium borohydride have been combined with 5-R-tetrazoles (R = CH 3 , NH 2 ) acting as stabilizing ligands. Depending on the utilized tetrazole, different agglomeration kinetics could be observed. Long term stability and agglomeration processes have been in situ investigated by the use of UV/Vis- and Raman-spectroscopy.

A facile method of patterning of various dielectric substrates (glass, quartz, and polyimide) with thin films of conducting polyaniline with at least 10 μm resolution is demonstrated. This method can be applied for the fabrication of functional conducting polymer interconnections between microelectrode arrays separated by dielectric gaps. Such interconnections may find applications in microelectrochemical sensors and electrocatalytic systems.

Nanocoatings have the potential to improve the surface properties of various materials. They are of extreme importance for surfaces in sliding contact such as highly stressed engine parts. Here, nanocoatings have to be optimized with respect to low friction properties and a high wear resistance to enhance the energetic and environmental efficiency. An important example are diamond-like carbon (DLC) films, which exhibit high mechanical stability depending on their deposition process. We present an introduction to this field of tribology by giving a short overview on DLC films, on the influence of lubricants from a theoretical point of view and in a broader sense, on basic principles of modeling tribological processes with molecular dynamic methods.