Current-accelerated phase switching between semiconductor and metal in Cu nanostructures

Ling Lee^1*, Yu-Chuan Shih¹, Kuangye Wang¹, Tzu-Yi Yang¹, Ying-Chun Shen¹, Yo-Chieh Hsu¹, Chun-Shou Chiang¹, Yu-Lun Cheuh¹

¹Department of Materials Science and Engineering, National Tsing Hua University, Hsinchu, Taiwan

* Presenter:Ling Lee, email:leeling0430@gmail.com

In this work, we opened an easy possibility to manipulate the phases of Cu nanostructures between metal and semiconductor by the external bias. Once the direct-current bias applied on a Cu nanowire terminated by two Ni electrodes exceeds a threshold value of about 0.5 to 1 V in the atmosphere, the resistance increases significantly from several hundred ohms to several MΩ. On the contrary, a reverse polarity of external bias switches the resistance from high to low. According to the pseudo-operando stoichiometric images reconstructed by nano-focused x-ray absorption near-edge spectroscopy (XANES) and electron energy loss spectroscopy (EELS), it is found that 50 % of Cu is oxidized toward Cu₂O, which is generated not only at the exposed surface, but also beneath the anode. The later limits the carrier transportation and results in a high resistance. Moreover, the former perform a p-type semiconductor behavior and exhibit a sensitive response to NH₃. By combination these two spatial-separated phase change, new feasibilities of Cu nanostructures are expected, including thememristor array and the fast recovered gas sensors.

Keywords: Cu, current-accelerated redox reaction, XANES, EELS, gas sensor