Electrofabrication of multilayer Fe–Ni alloy coatings for better corrosion protection

Electrofabrication of multilayer Fe–Ni alloy coatings were accomplished successfully on mild steel and their corrosion behaviors were studied. Multilayer comprised of alternatively formed ‘nano-size’ layers of Fe–Ni alloy of different composition have been produced from a single bath having Fe²⁺and Ni²⁺ ions using modulated (i.e. periodic pulse control) current density (cd). The deposition conditions were optimized for both composition and thickness of individual layers for best performance of the coatings against corrosion. The deposits were analyzed using scanning electron microscopy (SEM), powder X-ray diffraction (PXRD), Hardness Tester, electrochemical AC and DC methods respectively. The multi layered deposits showed better corrosion resistances compared to the monolayer Fe–Ni (CR = 3.77 mm year^?1) coating deposited using DC from the same bath; the maximum corrosion resistance being shown by the coating having 300 layers, deposited at cyclic cathodic current densities of 2.0 and 4.0 A dm^?2 (CR = 0.03 mm year^?1). Drastic improvement in the corrosion performance of multilayer coatings were explained in the light of changed kinetics of mass transfer at cathode and increased surface area due to modulation and layering.     

Hypersonic phononic crystals

In this Letter we propose the use of hypersonic phononic crystals to control the emission and propagation of high frequency phonons. We report the fabrication of high quality, single crystalline hypersonic crystals using interference lithography and show that direct measurement of their phononic band structure is possible with Brillouin light scattering. Numerical calculations are employed to explain the nature of the observed propagation modes. This work lays the foundation for experimental studies of hypersonic crystals and, more generally, phonon-dependent processes in nanostructures.     

Dielectric omnidirectional visible reflector

We demonstrate the fabrication of an all-dielectric omnidirectional mirror for visible frequencies. The dielectric reflector consists of a stack of 19 alternating layers of tin (IV) sulfide and silica. Using a combination of thermal evaporation (for tin sulfide) and thick electron-beam evaporation (for silica), we have achieved a refractive-index contrast of 2.6/1.46 , one of the highest refractive-index contrasts demonstrated in one-dimensional photonic bandgap systems designed for the visible frequency range. The tin sulfide-silica material system developed allowed the formation of a broadband visible reflector with an omnidirectional range greater than 10%. Possible applications of the system include efficient reflectors, high-frequency waveguides for communications and power delivery, and high- Q cavities.