The new finding of the restructuring process of Cu on W(110) will be shown with the dynamic observation LEEM images and selected area LEED. It is known that the growth mode of Cu on W(110) surface is layer-by-layer at around room temperature. The pseudomorphic 1st layer completes at 1 ML. The 2nd layer shows 15x1 reconstruction and a saturation coverage of the 2nd layer is 2.13 ML which was measured with Auger intensity with CMA[1], which is believed as a clear evidence of the layer-by-layer growth. The normal emission Auger signal, however, shows a plateau between 2.13 and 2.47 MLW(110) [2]. The discrepancy of such different behavior of Auger signal variation is still unclear up to now. In the present study, we observed the growth process of Cu on W(110) surface using LEEM and selected area LEED, and firstly confirmed the restructuring of the Cu double layer between 2.13 and 2.47 ML.
Dynamic images during Cu deposition onto W(110) shows the pseudomorphic 1st Cu layer, covers whole surface at 1 ML and 2nd layer starts to grow. The LEED pattern from the 2nd layer showed the 15x1 structure. The 2nd layer mostly covers the surface around 2 ML. The most remarkable change in LEEM contrast here is that area with gray contrast appears. The gray contrast area spreads over the surface with increasing coverage. At this moment, no 3rd layer forms on the 2nd layer. Most of the surface is converted to the gray contrast at around 2.47 MLW(110), and the 3rd layer finally starts to form after that. The selected area LEED pattern taken at the dark and gray areas shows the mixture of the 15x1 structure and the Cu(111) 1x1 structure. The intensity ratio of the Cu(111) 1x1 structure to the 15x1 structure, however, much larger in the gray area than that in the dark area. This indicates that the restructuring of the Cu double layer from the 15x1 structure into Cu(111) 1x1 takes place before the nucleation of the 3rd layer.
New development of highly spin-polarized and bright electron gun for spin-polarized LEEM will be also shown in order to observe the dynamic images of the magnetic domains formation process of materials.
[1] Bauer E., Poppa H., Todd G. and Bonczek F., J. Appl. Phys. 45 (1974) 5164.
[2] Lilienkamp G., Koziol C. and Bauer E., Surf. Sci. 226 (1990) 358. |