1 research outputs found
Interface-Confined Doubly Anisotropic Oxidation of Two-Dimensional MoS<sub>2</sub>
Despite
their importance, chemical reactions confined in a low
dimensional space are elusive and experimentally intractable. In this
work, we report doubly anisotropic, in-plane and out-of-plane, oxidation
reactions of two-dimensional crystals, by resolving interface-confined
thermal oxidation of a single and multilayer MoS<sub>2</sub> supported
on silica substrates from their conventional surface reaction. Using
optical second-harmonic generation spectroscopy of artificially stacked
multilayers, we directly proved that crystallographically oriented
triangular oxides (TOs) were formed in the bottommost layer while
triangular etch pits (TEs) were generated in the topmost layer and
that both structures were terminated with zigzag edges. The formation
of the Mo oxide layer at the interface demonstrates that O<sub>2</sub> diffuses efficiently through the van der Waals (vdW) gap but not
MoO<sub>3</sub>, which would otherwise sublime. The fact that TOs
are several times larger than TEs indicates that oxidation is greatly
enhanced when MoS<sub>2</sub> is in direct contact with silica substrates,
which suggests a catalytic effect. This study indicates that the vdW-bonded
interfaces are essentially open to mass transport and can serve as
a model system for investigating chemistry in low dimensional spaces