The growth behavior of interlayers deposited at the interfaces of multilayers was investigated using x-ray photoemission spectroscopy, x-ray reflectivity, and x-ray diffraction measurements. We report an asymmetry in the formation of at the -on-Mo interface compared to the -on-Si interface. X-ray photoelectron spectroscopy (XPS) depth profiling shows that for -on-Mo the formed stoichiometry is close to expectation ( ratio), while for -on-Si it is observed that carbon diffuses from the interfaces into the multilayer, resulting in nonstochiometric growth (). As a result, there is a discrepancy in the optical response near wavelength, where -on-Mo behaves according to model simulations, while -on-Si does not. The as-deposited off-stoichiometric -on-Si interface also explains why these interfaces show poor barrier properties against temperature induced interdiffusion. We show that the stoichiometry of at the Mo-Si interfaces is connected to the structure of the layers onto which is grown. Because of enhanced diffusion into the amorphous Si surface, we suggest that deposited boron and carbon atoms form and compounds. The low formation enthalpy of ensures C depletion of any interlayer. Only after a saturated interfacial layer is formed, does further deposition of boron and carbon atoms result in actual formation. In contrast to the off-stoichiometric growth on top of Si, grown on top of Mo retains the correct stoichiometry because of the higher formation enthalpies for and formation and the limited diffusion depth into the (poly)-crystalline Mo surface.
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