A direct comparison of the structures of 2D and 3D types of capped stacked submonolayer (SML) InAs nanostructures is evaluated by transmission electron microscopy (TEM). Results of the TEM observation of SML samples with three stacks of InAs unambiguously show a stark contrast between the structures of 2D and 3D SML nanostructures, where the 2D SML nanostructures exhibit a planar structure with thickness that is consistent with the deposited stack height, whereas the 3D SML nanostructures exhibit several-nm-high structures that exceed the height of the deposited stack. In addition, structural evolution at the 2D to 3D transition in uncapped SML nanostructures is investigated by atomic force microscopy (AFM). The AFM results clearly reveal that the 2D to 3D transition occurred during the deposition of the third (and last) InAs SML stack in the present samples, where the density of 3D structures increases in orders of magnitude with the deposited amount of InAs on the order of a tenth of a monolayer at the onset. This effectively bridges the gap between the 2D and 3D nanostructures elucidating the abrupt nature of the transition.

中文翻译：

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堆叠亚单层 InAs 纳米结构中 2D 到 3D 转变的结构研究

通过透射电子显微镜 (TEM) 对 2D 和 3D 类型的加帽堆叠亚单层 (SML) InAs 纳米结构的结构进行了直接比较。具有三个 InAs 堆叠的 SML 样品的 TEM 观察结果明确显示 2D 和 3D SML 纳米结构的结构之间形成鲜明对比，其中 2D SML 纳米结构表现出厚度与沉积堆叠高度一致的平面结构，而3D SML 纳米结构表现出超过沉积堆叠高度的几纳米高结构。此外，通过原子力显微镜 (AFM) 研究了无帽 SML 纳米结构中 2D 到 3D 转变的结构演变。AFM 结果清楚地表明，2D 到 3D 的转变发生在本样品中第三个（也是最后一个）InAs SML 堆栈的沉积过程中，其中 3D 结构的密度随着 InAs 沉积量的数量级增加而增加开始时为单层的十分之一。这有效地弥合了 2D 和 3D 纳米结构之间的差距，阐明了过渡的突然性质。