Two-dimensional monolayers derived from 3D bulk structures remain a relatively unexplored class of materials because of the challenge of stabilizing nonepitaxial interfaces. Here, we report an unusual reconstruction during the deposition of precursors when targeting the synthesis of heterostructures with an odd number of PbSe monolayers. Multilayer elemental precursors of Pb|Se + V|Se were deposited to have the correct number of atoms to form [(PbSe)_1+δ]_q(VSe₂)₁ where q is the number of PbSe monolayers in the heterostructure. Structural analysis of the self-assembled precursor via X-ray reflectivity, X-ray diffraction, and HAADF-STEM suggests three different behaviors upon deposition. Precursors with q ≥ 7 and even values of q have the targeted nanoarchitectures after deposition, which are maintained as the products are self-assembled through a near diffusionless process. Significant lateral surface diffusion occurred during the deposition of precursors with q = 1, 3, and 5, resulting in the precursor to have a different nanoarchitecture than targeted. Additional perpendicular long-range diffusion occurs during self-assembly of these precursors, resulting in different final products than targeted. Density functional theory (DFT) calculations of PbSe blocks show that the odd-numbered layers are less stable than the even-numbered layers, which suggests an energetic driving force for the observed rearrangement. This work highlights the importance of understanding the reaction mechanism when attempting to prepare 2D layers of constituents with bulk 3D structures.

中文翻译：

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VSe ₂上单层厚PbSe的不稳定性

源自3D块状结构的二维单层仍然是一类相对未开发的材料，因为它具有稳定非外延界面的挑战。在这里，我们报道了针对具有奇数个PbSe单层异质结构合成的前体沉积过程中的异常重建。沉积Pb | Se + V | Se的多层元素前体，使其原子数正确，以形成[（PbSe）_{1 +δ} ] _q（VSe ₂）₁，其中q是异质结构中PbSe单层的数目。通过X射线反射率，X射线衍射和HAADF-STEM对自组装前体的结构分析表明，沉积后会出现三种不同的行为。前体与q ≥7和偶数值q具有沉积后靶向nanoarchitectures，其被保持为产品是通过近无扩散过程的自组装。在前驱体沉积q的过程中发生了明显的侧面扩散= 1、3和5，导致前驱体的纳米结构与目标结构不同。这些前体的自组装过程中会发生额外的垂直远距离扩散，从而导致最终产品与目标产品不同。PbSe块的密度泛函理论（DFT）计算表明，奇数层的稳定性低于偶数层，这表明观察到的重排具有强大的驱动力。这项工作突显了在尝试准备具有体3D结构的成分的2D层时理解反应机理的重要性。