Iron Silicides Nanostructures Grown on Si (111) by Reactive Deposition Epitaxy

EXPERIMENT The samples were grown in an ultra high vacuum chamber at 1027 K and annealed during two hours at the same temper- ature. High purity iron (99,999 %) was evaporated on the sur- face of Si (111) substrates using an electron beam evaporator. The deposition rate and iron coverage were measured using a quartz balance. The crystallographic structure, mean height and strain of the nanostructures were characterized by X-ray diffraction (XRD) in the co-planar geometry as a function of the deposited nominal iron coverage. The XRD experiments were carried out using the 3-circle Huber diffractometer of the XRD1 beam line of the Brazilian Light Synchrotron Labora- tory. RESULTS AND DISCUSSION Figure 1 shows the evolution of the morphology of the sam- ples as the iron coverage increases. The iron silicide nanos- tructures exhibit the typical evolution of self-assembled is- land. Theses islands appear when approximately 1 nm of iron is deposited and grow in number and size almost linearly with the iron coverage until their agglomeration at approxi- mately 5 nm of deposited iron. The analysis of the evolution of the area density of islands and the XRD data as a func- tion of the iron coverage indicates that the system grows in a Stranskii-Krastanow fashion, with an initial wetting layer 1.5- 1.8 nm thick of ε¡ FeSi. The relative amount of each iron sili- cide phase in the samples and the respective out-of-the-plane strains as measured by XRD are summarized in figures 2 and 3, respectively. For samples with iron coverage lower than 5 nm there is a predominance of the ε¡ FeSi phase. However, a clear phase transition happens for iron coverage larger than 5 nm, were the β¡ FeSi2 phase turns into the dominant one. A relaxation of the out-of-the-plane strain can be also observed, for both phases, as the iron coverage increases and reaches 5 nm. This behavior indicates that for low iron coverage, and