We investigated the electronic structures of mono-and few-layered Ru nanosheets (N layers (L) with N = 1, ~6, and ~9) on Si substrate by ultraviolet and x-ray photoemission spectroscopies. The spectral density of states (DOS) near E f of ~6 L and 1 L is suppressed as it approaches E f in contrast to that of ~9 L, which is consistent with the Ru 3 d core-level shift indicating the reduction of the metallic conductivity. A power law g(ε) ∝ |ε − ε F | α well reproduces the observed spectral DOS of ~6 L and 1 L. The evolution of the power factor α suggests that the transition from the metallic state of ~9 L to the 2-dimensional insulating state with the soft Coulomb gap of 1 L through the disordered 3-dimensional metallic state of ~6 L.

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