Thermal expansion mismatch-driven high-pressure growth of 2D non-centrosymmetric MnTeMoO6 with giant nonlinear optical properties

Abstract

Non-centrosymmetric oxides have gained attention for their wide-ranging applications. Preparing two-dimensional (2D) non-centrosymmetric oxides is a prerequisite for on-chip integration but is challenging due to multi-element components and strong interlayer interactions. Here, we develop a thermal-expansion-difference-driven high-pressure strategy for synthesizing 2D non-centrosymmetric MnTeMoO₆ with extraordinary nonlinear optical properties. By utilizing the large thermal expansion mismatch between copper and graphite, the growth space is squeezed to a tiny slit with a high pressure of up to 20 MPa. This process reduces reaction activation energy and the precursor mean free path, yielding ultrathin flakes (down to two-unit cells) with uniform stoichiometry. The layer-parity-independent non-centrosymmetric structure of 2D MnTeMoO₆ results in one of the strongest second-harmonic generations among 2D oxides, with its second-order nonlinear susceptibility approaching the theoretical limit. This work not only offers a novel method to grow multi-element 2D oxides but also provides material platforms for miniaturized nonlinear optics.