Interface observation of heat-treated Co/Mo2C multilayers

Abstract

We study the interface evolution of a series of periodic Co/Mo 2 C multilayers as a function of the annealing temperature up to 600°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/Mo 2 C 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 asdeposited sample, and then at annealing temperature above 300°C Co and C atoms separate from their mixed regions. Comparison of NMR results between Co/Mo 2 C 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°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.

X‐ray absorption spectroscopy study of buried Co layers in the Co/Mo2C multilayer mirrors

“…a, the positions of the observed features for the as‐deposited sample correspond to those of the Co foil but with different relative intensities. It is clear that for the as‐deposited sample, there is no pure Co in the stack . Compared with Co 3 Mo 3 C, the as‐deposited multilayer exhibits close EXAFS features, similar amplitudes but with different frequencies in the k 3 ‐weighted k‐space spectrum and similar low coordination numbers in the Fourier transform R‐space spectra.…”

“…There is a clear distinction between the as‐deposited and the annealed Co/Mo 2 C multilayer samples from the XAS spectra. This behavior is in agreement with the one measured through nuclear magnetic resonance experiments , where the mixing of the Co layers occurs for the as‐deposited sample, whereas pure Co is observed upon annealing from 300 °C. In addition, we show that both Mo and C atoms of the Mo 2 C layers are involved in the mixing with the Co atoms.…”

“…Those values will be used in the following sections. Different characterization methods have been carried out such as X‐ray reflectometry in the hard and soft X‐ray ranges, X‐ray emission spectroscopy, nuclear magnetic resonance spectroscopy whose results were given elsewhere .…”

“…The interfacial properties of the Co/Mo 2 C multilayer have been studied in a previously published paper . It reported that the Co and C atoms mix together during deposition and then, following annealing from 300 °C, Co and C demix from their mixed regions.…”

Evolution of interfacial structure of Co-based periodic multilayers upon annealing

“…In addition, studying the stability of the stacks under annealing is also important in order to simulate and understand the aging of such artificial structures. In this framework, the estimate of the width of interfaces and interlayers is generally provided from the fit of hard x-ray reflectivity data [8,9]. However as exemplified in this work x-ray reflectivity data cannot solely provide a complete description of such system.…”