College of Science, China Jiliang University, 310018 Hangzhou, China.
Nanoscale. 2018 Jul 5;10(25):12133-12140. doi: 10.1039/c8nr03433h.
Group-III metal monochalcogenides have emerged as a new class of two-dimensional (2D) semiconductor materials. For the integration of 2D materials for various potential device applications, there is an inevitable need to reduce their dimensionality into specific sized nanostructures with edges. Owing to the properties of finite-sized 2D nanostructures strongly related to the edge configurations, the precise understanding of the edge geometric structures at an atomic level is of particular importance. By means of first-principles calculations, the geometric structures and electronic properties of stable zigzag and armchair edges in a prototype example GaSe monolayer have been identified. Our results demonstrate that both Ga- and Se-terminated zigzag edges prefer to the (3 × 1) reconstructions, and the armchair edges with the perfect flat configuration are energetically favorable. It is unexpectedly found that both zigzag and armchair GaSe nanoribbons with reconstructed edges are semiconductors, which is different from previous recognition where the zigzag edges are metallic. Moreover, the edge-dependent flake shape in GaSe has been plotted using the Wulff construction theory, and the shape evolution with chemical potentials can be applied to explain broad experimental observations on the morphologies of GaSe flakes. Importantly, similar reconstructions and electronic properties also appeared at InSe edges, suggesting that the reconstruction induced semiconducting edges are a fundamental phenomenon for 2D group-III metal monochalcogenides.
III 族金属单硫属化物已成为一类新的二维（2D）半导体材料。为了将 2D 材料集成到各种潜在的器件应用中，不可避免地需要将其维度降低到具有边缘的特定尺寸的纳米结构。由于有限尺寸的 2D 纳米结构的性质与边缘构型密切相关，因此在原子水平上精确理解边缘几何结构尤为重要。通过第一性原理计算，确定了原型 GaSe 单层中稳定的锯齿形和扶手椅边缘的几何结构和电子特性。我们的结果表明，Ga 和 Se 终止的锯齿形边缘都倾向于（3×1）重构，而具有完美平坦构型的扶手椅边缘在能量上是有利的。出人意料的是，具有重构边缘的锯齿形和扶手椅 GaSe 纳米带都是半导体，这与之前认为锯齿形边缘是金属的认识不同。此外，还使用 Wulff 构造理论绘制了 GaSe 中依赖于边缘的薄片形状，并且可以应用化学势的形状演化来解释 GaSe 薄片形貌的广泛实验观察。重要的是，在 InSe 边缘也出现了类似的重构和电子特性，这表明重构诱导的半导体边缘是二维 III 族金属单硫属化物的一个基本现象。
