Formation and stability of small well-defined Cu- and Ni oxide particles

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• 作者：Ramona Thalinger ; Marc Heggen ; Daniel G. Stroppa ; Michael St枚ger-Pollach ; Bernhard Kl枚tzer ; Simon Penner
• 关键词：Oxides ; Epitaxial growth ; Electron microscopy ; Electron energy loss spectroscopy ; Metals
• 刊名：Materials Chemistry and Physics
• 出版年：16 December, 2013
• 年：2013
• 卷：143
• 期：1
• 页码：184-194
• 全文大小：3765 K

文摘

Well-defined and -structured Cu/Cu₂O and Ni/NiO composite nanoparticles have been prepared by physical-vapor deposition on vacuum-cleaved NaCl(001) single crystal facets. Epitaxial growth has been observed due to the close crystallographic matching of the respective cubic crystal lattices. Distinct particle morphologies have only been obtained for the Ni/NiO particles, comprising truncated half-octahedral, rhombohedral- and pentagonal-shaped outlines. Oxidation of the particles in the temperature range 473-673聽K in both cases led to the formation of well-defined CuO and NiO particles with distinct morphologies. Whereas CuO possibly adopts its thermodynamical equilibrium shape, NiO formation is accompanied by entering a Kirkendall-like state, that is, a hollow core-shell structure is obtained. The difference in the formation of the oxides is also reflected by their stability under reducing conditions. CuO transforms back to a polycrystalline mixture of Cu metal, Cu₂O and CuO after reduction in hydrogen at 673聽K. In contrast, as expected from theoretical stability considerations, the formation of the hollow NiO structure is reversed upon annealing in hydrogen at 673聽K and moreover results in the formation of a Ni-rich silicide structure Ni₃Si₂. The discussed systems present a convenient way to tackle and investigate various problems in nanotechnology or catalysis, including phase transformations, establishing structure/activity relationships or monitoring intermetallic particles, starting from well-defined and simple models.