Growth and Structure of Ultrathin Iron Silicate and Iron Germanate Films

The growth and structure of two-dimensional iron silicate and iron germanate films on Ru(0001) are studied. We investigate in detail the temperature-dependent film formation of ultrathin layers of iron silicate and iron germanate. These two-dimensional films can be seen as model systems for more complex catalytically active structures, such as zeolites, which can be used as selective catalysts or molecular sieves. The experimental methods of XPS, LEED, LEEM, LEEM-IV, and XPEEM are applied for correlated chemical and physical characterization in situ and in real time, and DFT is applied for theoretical consideration. We show that both systems can be considered as two-layered systems, with a monolayer of iron oxide at the Ru interface and a monolayer of silica or germania on top, respectively. The Fe-Fe distance in the iron oxide layer is influenced by the Si-O-Si or Ge-O-Ge bond length, in agreement with those of unstrained silicates or germanates. Moreover, iron silicate can be prepared using different preparation methods. The actual loading of Fe atoms is three per unit cell for FeGeO_x and only two for FeSiO_x.