Epitaxy of Semiconductors: Introduction to Physical Principles (Graduate Texts in Physics) by Pohl Udo W

Author:Pohl, Udo W. [Pohl, Udo W.]
Language: eng
Format: azw3
Publisher: Springer Berlin Heidelberg
Published: 2013-01-10T16:00:00+00:00

The in situ recorded scanning tunneling micrographs show two Si islands growing on a Si(111) substrate [17]. During growth the islands clearly show a triangular shape (Fig. 4.20a). When the growth is interrupted and the temperature is raised, the lateral form gradually turns into a hexagon-like shape (Fig. 4.20b). Here, edges perpendicular to are somewhat shorter than those perpendicular to , indicating a lower energy of the latter. When growth is resumed, the islands quickly adopt the initial triangular shape (Fig. 4.20c).

To provide some visual evidence for critical 2D nucleus formation, we consider the assembly of Co-Si clusters at 400 °C on a Si(111)-(7×7) surface. High speed scanning tunneling microscopy represents one such cluster as a single bright protrusion, though it probably contains 3 Si atoms and 6 Co atoms [18]. STM images show that the clusters are mobile on the Si surface [19]. Figure 4.21 shows a series of STM scans over 8×8 nm2 captured in 5 s frames. We note a steady change of the imaged configuration, until the cluster labeled Y occupies the vacancy visible in Fig. 4.21c. The ring composed of 6 clusters is fairly stable. Eventually a cluster detaches (arrow in Fig. 4.21f) and the ring-structure decomposes. Studies reported in Ref. [19] show that the i=6 configuration represents a critical nucleus for the studied system. Once one of the 6 clusters moves to occupy the vacant site in the center and a seventh cluster attaches to the ring, a stable nucleus with i=7 clusters is formed.

Fig. 4.21In situ recorded formation of a critical nucleus of Co-Si clusters (white protrusions) on a Si(111)-(7×7) surface. X and Y label two particular clusters. At (d) cluster Y has moved to complete a ring-like structure consisting of 6 clusters. Reproduced with permission from [19], © 2007 Royal Society of Chemistry Publishing

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