The Effect of Ethanol on Abnormal Grain Growth in Copper Foils

Abstract

Single-crystal Cu not only has high electrical and thermal conductivity, but can also be used as a promising platform for the epitaxial growth of two-dimensional materials. Preparing large-area single-crystal Cu foils from polycrystalline foils has emerged as the most promising technique in terms of its simplicity and effectiveness. However, the studies on transforming polycrystalline foil into large-area single-crystal foil mainly focus on the influence of annealing temperature and strain energy on the recrystallization process of copper foil, while studies on the effect of annealing atmosphere on abnormal grain growth behavior are relatively rare. It is necessary to carry out more studies on the effect of annealing atmosphere on grain growth behavior to understand the recrystallization mechanism of metal. Here, we found that introduction of ethanol in pure argon annealing atmosphere will cause the abnormal grain growth of copper foil. Moreover, the number of abnormally grown grains can be controlled by the concentration of ethanol in the annealing atmosphere. Using this technology, the number of abnormally grown grains on the copper foil can be controlled to single one. This abnormally grown grain will grow rapidly to decimeter-size by consuming the surrounding small grains. This work provides a new perspective for the understanding of the recrystallization of metals, and a new method for the preparation of large-area single-crystal copper foils.

Keywords: abnormal grain grown; contact-free annealing; decimeter-size grains; ethanol annealing atmosphere; recrystallization of copper foils.

Figure 1

(a) Schematic diagram of contact-free annealing configuration, from which the copper foil is suspended in the middle of furnace. (b,c) are the photographs of Cu foil annealed in argon atmosphere without and with 150 μL ethanol, respectively. The black dashed line in (c) corresponds to the grain boundaries between large grains and polygranular regions.

Figure 2

(a–f) and (g–l) are the photographs of copper foils annealed under different amounts of introduced ethanol, and their corresponding false-color images, respectively. (m) Statistics chart of the number of millimeter-sized grains and above on the copper foils, annealed under different amounts of ethanol introduced. (n) Statistics chart of number of grains on copper foils obtained in different annealing batches after different amounts of ethanol were introduced.

Figure 3

(a,b) are the photographs of the annealed copper foil with a decimeter-sized abnormally grown grain, respectively. (c) The XRD 2θ scan spectrum of the large grain. EBSD IPF maps in the normal direction (d); (001) pole figures (e); and KAM maps (f) of the single large grain of copper foil collected at the corresponding positions marked in (a). (ND, normal direction).

Figure 4

(a) Annealing sequence of copper foils. (b) EBSD IPF maps in the normal direction of copper foils at the different annealing temperatures shown in (a).

Figure 5

(a) Photographs of eight representative annealed copper foils with a decimeter-sized, abnormally grown grain. (b) The corresponding EBSD IPF maps in the normal direction of these large grains, collected at the corresponding positions marked with white dotted box in (a). Black dash line in (a) corresponds to grain boundaries between large grain and polygranular regions. ND, normal direction).