Conversion of ZnS into Cu2-xS superlattice nanobelts through cation exchange reactions

(1)

Conversion of ZnS into Cu

2-x

S superlattice nanobelts through cation exchange

reactions

1_{Chi-Lin Tsai,}1_{Chuan-Pu Liu*}

1_{Department of Materials Science and Engineering, National Cheng Kung University} 1_{No.1 Daxue RD., East Dist., Tainan City 70, Taiwan (R.O.C.)}

e-mail: cpliu@mail.ncku.edu.tw Abstract

Copper sulfide is known to be an important p-type semiconductor. It exists in different phases ranging from copper-rich (Cu2S) to sulfur-rich (CuS). Owing to the wide variation in their optical as well as electrical properties, copper sulfides find promising applications in various fields.

In this study, a two-step synthesis with chemical vapor deposition is employed. ZnS nanobelts were first synthesized using ZnS powders as the source, followed by the growth of Cu2-xS nanobelts through cation exchange reactions using CuCl2 as the source [1]. The purpose of this study is to investigate the mechanism of cation exchange reactions through microstucture characterization of copper sulfide under different conditions in the second step. Fig.1 shows transmission electron microscopy (TEM) analysis of a typical porous Cu1.8S nanobelt after cation exchange reactions at 300℃ for 15 minutes, where superlattices and twins can be found.

Fig.1 A Cu1.8S nanobelt by cation exchange reactions at 300℃ for 15 min. (a) TEM image (b) HRTEM from the red square region in (a) (c) diffraction pattern of (b)

The morphology evolution of the resulting nanotructures after cation exchange reactions for various durations is showed in the scanning electron microscopy (SEM) images (Fig.2). With prolonging reaction times, the copper content deposited on the nanobelts increase. Some copper

atoms would diffuse into ZnS nanobelts through interstitial sites and “kick out” zinc atoms [2]. Fig.3 are X-ray diffraction patterns (XRD) showing the presence of Cu1.8S and Cu2S under different conditions.

Fig.2 SEM images of (a) as-grown ZnS; and resulting nanostructures after cation exchange reactions at 300℃ for (b) 5 min. (c) 15 min. (d) 25 min.

Fig. 3 XRD patterns of the various resulting Cu2-xS nanobelts from ZnS (a) at 300℃ for different reaction time (b) at different temperature (300℃~600℃) for 15 min.

Acknowledgments

This work is supported by MOST 104-2221-E-006-078-MY3 and MOST 104-2221-E-006-079-104-2221-E-006-078-MY3

References

[1] Kim, Han Sung; Sung, Tae Kwang; Jang, So Young; Myung, Yoon; Cho, Yong Jae; Lee, Chi-Woo; Park, Jeunghee; Ahn, Jae-Pyoung; Kim, Jin-Gyu; Kim, Youn-joong: CrystEngComm, 13, 6 (2011)

[2] Fan, Z.; Lin, L. C.; Buijs, W.; Vlugt, T. J.; van Huis, M. A.: Nat Commun, 7 (2016)