RESUMO
We have demonstrated a direct metallic conversion from nickel hydroxide nanosheets to nickel metal nanostructures by thermal annealing in vacuum. The metal transition of the single-layer nanosheets deposited on a Si substrate was revealed by x-ray absorption near edge structure (XANES) measurements. The XANES signal significantly changed at annealing temperatures above 250 °C. The metal transition temperature coincides with the reported temperatures at which layered nickel hydroxide nanosheets are converted to nickel oxide nanosheets by calcination in air. Auger measurements confirmed that a dissociation of oxygen from the hydroxide nanosheet induces the metallic conversion. The converted nickel metallic structures exhibit ferromagnetic behavior revealed by x-ray magnetic circular dichroism (XMCD) measurement. Atomic force microscopy measurements indicate that diffusions of nickel atoms on the substrates leads to a structural change from a 2D-like structure to a particle-like structure.