Giant Faceting of Vicinal Si(001) Induced by Au Adsorption

Abstract

4° vicinal Si(001) shows perfectly ordered terraces with a width of 4 nm which are separated by double steps. Adsorption of Au at 800°C results in a dramatic change of the step morphology: the surface decomposes into areas which are perfectly flat with a (001) orientation and (119) facets, which compensate for the macroscopic miscut. Extremely straight superterraces with a length limited only by the size of the sample (here 4 mm) and a width ranging from 400 nm to 4 μm are formed by massive Si mass transport. The extreme aspect ratio of 1:10 000 of this submicron structure is attributed to a heterogeneous nucleation process. SPA-LEED reveals a new, Au-induced incommensurate 5×3.2 reconstruction above a critical coverage as the driving force for the formation of large elongated (001) terraces. LEEM shows the strongly anisotropic nucleation process in vivo. Dark field imaging and microspot LEED techniques have been used to determine the influence of the different 5×3.2 domain orientations on the growth behavior of the (001) superterraces. The majority of domain terraces grow with a speed of more than 10 μm per second. The width and area of the (001) terraces increase proportionally to the Au coverage. The steps of the vicinal surface are accumulated in irregular step bunches. With further increasing Au coverage the step bunches are transformed into well-defined facets with a (119) orientation, as determined by SPA-LEED. The kinetics of the faceting process have been studied with SPA-LEED, REM, STM, and light diffraction using a HeNe laser, because the typical size of the superterraces is of the order of the wavelength of visible light: the resulting structure is visible to the bare eye. The parallel arrangement of superterraces acts as an irregular optical phase grating: illumination with white light results in stripes of all possible diffraction colors.