The thermal stability and degradation mechanism of Cu/Mo nanomultilayers

Abstract

The microstructural evolution of Cu/Mo nanomultilayers upon annealing was investigated by X-ray diffraction and transmission electron microscopy. The isothermal annealing process in the temperature ranges of 300-850°C was conducted to understand the thermal behavior of the sample and follow the transformation into a nanocomposite. Annealing at 600°C led to the initiation of grain grooving in the investigated nanomultilayer, and it degraded into a spheroidized nanocomposite structure at 800°C. The sample kept the as-deposited Cu {111}//Mo{110} fiber texture up to 850°C. The residual stress was investigated to explain microstructure changes. The activation energy of degradation kinetics of Cu/Mo nanomultilayers was determined to understand the rate-determining mechanism for the degradation of nanolaminate structures.

Keywords: Cu/Mo nanomultilayers; X-ray diffraction; annealing; fiber texture; magnetron sputtering.

Graphical abstract

Figure 1.

As-prepared sample: (a) illustration, (b) SEM surface image, (c) BF-STEM cross-sectional image with overlaid EDX image; the colors of the elements are indicated on the right-hand side, (d) pole figures of Cu {111} and Mo {110}.

Figure 2.

XRD θ-2θ scans of NMLs as-prepared and annealed at 300°C, 600°C, 800°C, and 850°C. The intensities were plotted on a logarithmic scale. Asterisks in the figure indicate the peaks from non-monochromatic Cu radiation.

Figure 3.

Microstructure and texture evolution of Cu/Nb NML: (a), (c), (e), (g) SEM surface images of Cu/Mo after annealing; (b), (d),(f), (g) BF-STEM cross-sectional images of with overlaid EDX images (the color of elements was kept as Figure 1); i) pole figures of Cu {111} and Mo {110} after annealing at 850°C. The dotted lines in (d) indicate aligned grain boundaries.

Figure 4.

Residual stress evolution of Cu/Mo NML as-prepared and annealed at 300°C, 600°C, 800°C, and 850°C. (a) residual stress of Cu. (b) residual stress of Mo.

Figure 5.

(a) HR-TEM cross-sectional image of Cu/Mo NML annealed at 600°C, (b) illustration of degradation mechanism of Cu/Mo NML.

Figure 6.

In-situ HT-XRD results. (a) θ-2θ scans as a function of isothermal holding time exemplarily shown for an annealing temperature fixed at 700°C (only scans after every 5 min are shown for clarity). The intensity is plotted on a logarithmic scale. A multi-peak fit procedure was applied to deconvolute the integrated intensity of the different satellite peaks. (b) Normalized intensity of satellite (I/I₀) as a function of annealing time for the different holding temperatures investigated (650 ~ 725 °C). The intensity is plotted on a linear scale. (c) it shows an Arrhenius plot deduced from stage II. The activation energy was evaluated using the slope.