Van der Waals epitaxy of ultrathin α-MoO3 sheets on mica substrate with single-unit-cell thickness

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We report on van der Waals epitaxy of single-crystalline α-MoO3 sheets with single-unit-cell thickness on the mica substrate. The crystalline lattice structure, growth habits, and Raman spectra of the grown α-MoO3 sheets are analyzed. The anisotropic growth of α-MoO3 sheets can be understood by period bond chains theory. Unlike monolayer MoS2 or graphene, Raman spectra of α-MoO3 do not possess frequency shift from bulk crystal to single-unit-cell layer. The relative intensities of two Raman modes (Ag) at 159 and 818 cm−1 are sensitive to the polarization of incident light. This scenario provides a quick approach to determine the lattice orientation of α-MoO3 crystals. Our studies indicate that van der Waals epitaxial growth is a simple and effective way to fabricate high-quality ultrathin α-MoO3 sheets for physical property investigations and potential applications.