Interface observation of heat-treated Co/Mo2C multilayers

We study the interface evolution of a series of periodic Co/Mo2C multilayers as a function of the annealing temperature up to 600 degrees C. Different complementary techniques are implemented to get information on the phenomenon taking place at the interfaces of the stack. The periodical structure of Co/Mo2C multilayer is proven by time-of-flight secondary ion mass spectrometry (ToF-SIMS) depth profiles which demonstrate the formation of an oxide layer at both air/stack and stack/substrate interfaces. From Nuclear magnetic resonance (NMR) spectra, we observed the intermixing phenomenon of Co and C atoms for the as-deposited sample, and then at annealing temperature above 300 degrees C Co and C atoms separate from their mixed regions. Comparison of NMR results between Co/Mo2C and Co/C references confirms this phenomenon. This is in agreement with X-ray emission spectroscopy (XES) measurements. Furthermore the calculation of the Co-C, Co-Mo and Mo-C mixing enthalpy using Miedema's model gives a proof of the demixing of Co and C atoms present within the stacks above 300 degrees C. From the transmission electron microscopy (TEM) analysis, we found the presence of some crystallites within the as-deposited sample as well as the mainly amorphous nature of all layers. This is confirmed using X-ray diffraction (XRD) patterns which also demonstrate the growth of crystallites induced upon annealing. (C) 2014 Elsevier B.V. All rights reserved