Cobalt induced nanocrystals on Ge(001)
- 作者：T.F. Mocking ; G. Hlawacek ; H.J.W. Zandvliet ; h.j.w.zandvliet@utwente.nl
- 关键词：Cobalt ; Nanocrystals ; Shape transition ; Germanium ; Surface stress ; STM ; Helium Ion Microscopy
- 刊名：Surface Science
- 出版年：2012
- 期刊代码：104_00396028
- 类别：ch
- 出版时间：June, 2012
- 卷：606
- 期：11-12
- 页码：924-927
- 文件大小：781 K
摘要
The deposition of several monolayers of cobalt on germanium (001) substrates results in the formation of two types of clusters: flat-topped and peaked nanocrystals. Scanning tunneling spectroscopy and helium ion microscopy measurements reveal that these nanocrystals contain cobalt. The shape evolution of the flat-topped and peaked nanocrystals as a function of their size is investigated with scanning tunneling microscopy. For small sizes the nanocrystals are compact. Beyond a critical size, however, the peaked nanocrystals exhibit an elongated shape, whilst the flat-topped nanocrystals remain compact. The shape transition of the peaked nanocrystals is driven by a competition between boundary and strain energies. For small sizes the boundary energy is the dominant term leading to a minimization of the peaked nanocrystal's perimeter, whereas at larger sizes the strain energy wins resulting in a maximization of the perimeter. On the top facet of the flat-topped nanocrystals one-dimensional structures are observed that are comprised of small square shaped units of about 1 nm2. Time-resolved scanning tunneling microscopy measurements reveal that these square shaped units are dynamic at room temperature.