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Hydrogen-induced metal-insulator (M-I) transition in palladium (Pd) capped rare earth (RE) metals is remarkable due to continuous and reversible changes in structural, optical and electrical properties as hydrogen concentration changes between x = 2 to 3 (x= H/RE). Large changes in optical properties on hydrogenation at room temperature make these materials potentially suitable for switchable mirror devices. Pd overlayer protects the underlying RE layer from oxidation and acts like a catalytic layer during hydrogenation/dehydrogenation. The influence of Pd overlayer on switching characteristics is poorly understood due to the formation of Pd nanocrystallites of uncontrolled and varying sizes in a non-uniform and discontinuous overlayer. In the present work, Pd-Pr (Praseodymium) structures having a Pd overlayer consisting of well-defined sizes have been investigated to understand the influence of nanoparticle size on switchable mirror characteristics. Pd nanoparticles (size: 6, 12 and 15 nm)¨CPr thin film structures are formed by using a specially designed dual-deposition system. In the dual-deposition system, Pd nanoparticles are grown in a spark generator by applying high voltage between two Pd electrodes and flowing nitrogen gas at a constant rate as a process and dilution gas. Size selection is carried out by passing the polydisperse aerosol through DMA followed by sintering at 900-1200¡ãC for getting single-crystalline quasi-spherical nanoparticles. Pd nanoparticles of well-defined sizes with a geometric standard deviation ¡Ü 1.10 are deposited onto already deposited Pr thin film without any exposure to ambient. The details of the specially designed dual-deposition system will be discussed in this presentation. The dependence of the size and crystalline quality of Pd nanoparticles as a function of various deposition parameters will be discussed. The design of the dual deposition system also allows the in-situ measurement of the electrical properties of Pd nanoparticle/Pr thin film structure during hydrogenation-dehydrogenation cycles. The dependence of switching characteristics on Pd nanoparticle size will be discussed and explained in terms of larger active surface and subsurface sites and absence of interfacial (Pd-Pr) stress. |