کد مقاله | کد نشریه | سال انتشار | مقاله انگلیسی | نسخه تمام متن |
---|---|---|---|---|
5425871 | 1395868 | 2007 | 19 صفحه PDF | دانلود رایگان |
The structural and morphological changes of a 1.1 monolayer (ML) Pt deposit on W(1Â 1Â 1) have been investigated in situ, in ultra-high vacuum, as a function of the annealing temperature from 700 to 1340Â K, by a combination of grazing incidence X-ray diffraction and grazing incidence small-angle X-ray scattering. Before annealing, the thin Pt layer is two-dimensional and lattice-matched to the W(1Â 1Â 1) surface. The faceting of Pt/W(1Â 1Â 1) towards nanoscale three-sided pyramids with {2Â 1Â 1} facets has been detected from 715Â K. At this stage, the pyramids, which have a 5-nm average lateral size, cover nearly perfectly the surface. At higher temperatures, they increase in size. The role of the edge energy in the nanofaceting process is discussed. In addition, 4Â MLs Co are deposited at room temperature on the smallest Pt/W pyramids. The obtained three-dimensional Co islands are correlated with the Pt/W nanopyramids and Co is relaxed on Pt/W. At approximately 800Â K, a CoPt alloy is formed and becomes better ordered as the annealing temperature increases. At 1100Â K, both defaceting and phase separation begin; the CoPt alloy segregates on the W(1Â 1Â 1) flat surface, while Co forms an epitaxial layer on the {2Â 1Â 1} facets. In addition, in the temperature range of 1100-1200Â K, a great majority of {2Â 1Â 1} large facets coexist with some {1Â 1Â 0} small facets. Finally, the surface becomes flat again at 1250Â K.
Journal: Surface Science - Volume 601, Issue 16, 15 August 2007, Pages 3431-3449