ABSTRACT

Ultrathin Bi films have attracted substantial attention as promising candidates for two-dimensional topological insulators. The nucleation and growth of ultrathin Bi films on various substrates are reviewed, while the focus is on the Si(111) substrates in this article. During film growth, the Si substrate becomes covered by a one-monolayer-thick wetting layer, upon which Bi(110) islands composed of an even number of layers with the black phosphorus (BP) allotrope structure preferentially nucleate. However, a small number of Bi(110) islands containing an odd number of layers also coexist during the nucleation stage. In these islands, the top and bottom layers have the BP structure, whereas the inner layers have a bulk-like rhombohedral structure. Upon increasing the deposited amount of Bi atoms beyond a certain critical thickness, the Bi(110) islands transform into Bi(111) islands. These structural changes and the transformation occurring in the ultrathin films are driven by competition between the surface and bulk cohesive energies.

摘要

超薄Bi薄膜作为二维拓扑绝缘体的有希望的候选者已引起了广泛的关注。本文回顾了超薄Bi膜在各种衬底上的成核和生长，而本文重点是Si（111）衬底。在膜生长过程中，Si衬底被一层单层的润湿层覆盖，在该层上，由偶数层具有黑磷（BP）同素异形体结构的Bi（110）岛优先成核。但是，在成核阶段，也同时存在少量包含奇数层的Bi（110）岛。在这些岛中，顶层和底层具有BP结构，而内层则具有块状菱形结构。当Bi原子的沉积量增加到超过某个临界厚度时，Bi（110）岛变成Bi（111）岛。这些结构变化和超薄膜中发生的转变是由表面和整体内聚能之间的竞争驱动的。