The optical second harmonic generation (SHG) efficiency of hexagonal boron nitride (h-BN) layered materials is profoundly influenced by the symmetry properties, which has severely limited the usefulness of their SHG for nonlinear optical applications. Herein, we report on the controlled growth of large-area and continuous ultrathin h-BN films with a high density of exposed edges that show strongly enhanced SHG, owing to the breaking of inversion symmetry occurring naturally at edge sites. The large-area growth of edge-enriched BN films was accomplished through the introduction of Turing instability into a growth process that involves the liquid–gas interface self-limiting reaction between molten boron oxide (B₂O₃) with gaseous ammonia (NH₃) at elevated temperature. Remarkably, the edge-enriched BN films give rise to a SHG response up to nearly 3 orders of magnitude higher than that of the smooth BN films prepared through the same growth approach but with different growth parameters.

中文翻译：

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具有增强的光学二次谐波产生的边缘富集大面积六方氮化硼超薄膜

六方氮化硼 (h-BN) 层状材料的光学二次谐波 (SHG) 效率受对称性的影响很大，这严重限制了它们的 SHG 在非线性光学应用中的有用性。在此，我们报告了大面积和连续超薄 h-BN 薄膜的受控生长，该薄膜具有高密度的暴露边缘，由于边缘位置自然发生的反转对称性破坏，显示出强烈增强的 SHG。通过将图灵不稳定性引入到涉及熔融氧化硼 (B ₂ O ₃ ) 与气态氨 (NH ₃) 在高温下。值得注意的是，边缘富集的 BN 薄膜产生的 SHG 响应比通过相同生长方法但具有不同生长参数的光滑 BN 薄膜高出近 3 个数量级。