Nucleation and growth of Ag on Sb-terminated Ge(100)

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• 作者：Chan ; L.H. ; Altman ; E.I.
• 关键词：Silver ; Antimony ; Germanium ; Nucleation ; Growth ; Scanning tunneling microscopy
• 刊名：Surface Science
• 出版年：2002
• 出版时间：June, 2002
• 年：2002
• 卷：511
• 期：1-3
• 页码：229-239
• 全文大小：280 K

文摘

The effect of Sb on Ag growth on Ge(100) was characterized using scanning tunneling microscopy, low energy electron diffraction, and Auger electron spectroscopy. Silver was found to immediately form three-dimensional clusters on the Sb-covered surface over the entire temperature range studied (320–570 K), thus the growth was Volmer–Weber. Regardless of the deposition conditions, there was no evidence that Sb segregated to the Ag surface, despite Sb having a lower surface tension than either Ag or Ge. The failure of Sb to segregate to the surface could be understood in terms of the much stronger interaction between Sb and Ge versus Ag and Ge creating a driving force to maintain an Sb–Ge interface. Silver nucleation on Sb/Ge(100) was characterized by measuring the Ag cluster density as a function of deposition rate. The results revealed that the cluster density was nearly independent of the deposition rate below 420 K, indicating that heterogeneous nucleation at defects in the Sb-terminated surface competed with homogeneous nucleation. At higher temperatures, the defects were less effective in trapping diffusing Ag atoms and the dependence of the cluster density on deposition rate suggested a critical size of at least two. For temperatures above 420 K, the Ag diffusion barrier plus the dissociation energy of the critical cluster was estimated by measuring the cluster density as a function of temperature; the results suggested a value of 0.84±0.1 eV which is significantly higher than values reported for Ag nucleation on Sb-free surfaces. In comparison to the bare Ge surface, Ag formed a higher density of smaller, lower clusters when Sb was present. Below 420 K the higher cluster density could be attributed to nucleation at defects in the Sb layer while at higher temperatures the high diffusion barrier restricted the cluster size and density. Although Sb does not act as a surfactant in this system since it does not continuously float to the surface and the growth is not layer-by-layer, adding Sb was found to be useful in limiting the Ag cluster size and height which led to smoother, more continuous Ag films and in preventing the formation of metastable Ag–Ge surface alloys.