In Situ Observation of Gold Chloride Decomposition in a Confined Nanospace by Transmission Electron Microscopy

The behavior of gold chloride (AuClx) encapsulated within the inner space of a single-wall carbon nanotube (SWCNT) was investigated under electron beam (e-beam) irradiation and high temperatures. Analysis of the pristine specimen by transmission electron microscopy (TEM), energy-dispersive X-ray spectroscopy (EDX), and Raman spectroscopy show that AuClx is encapsulated within the SWCNTs as a dilute disordered structure. In situ TEM observation of the specimen under e-beam irradiation shows that, within the SWCNTs, AuClx is reduced to a crystalline Au nanowire (AuNW). The AuNW drifts significantly within the SWCNT during the reduction. At high temperatures (>673 K), in situ TEM shows that the AuNW oscillates intermittently at a frequency of similar to 1.1 s(-1) and amplitude of similar to 60 nm. Raman spectroscopy and EDX suggest that these phenomena are caused by an increase in the internal gas pressure in the SWCNTs because the decomposition of AuClx by e-beam irradiation or heat treatment produced chlorine (Cl-2) gas.