Quantitatively in Situ Imaging Silver Nanowire Hollowing Kinetics

Abstract

We report the in situ investigation of the morphological evolution of silver nanowires to hollow silver oxide nanotubes using transmission X-ray microscopy (TXM). Complex silver diffusion kinetics and hollowing process via the Kirkendall effect have been captured in real time. Further quantitative X-ray absorption analysis reveals the difference between the longitudinal and radial diffusions. The diffusion coefficient of silver in its oxide nanoshell is, for the first time, calculated to be 1.2 × 10 cm/s from the geometrical parameters extracted from the TXM images.

In Situ Techniques for Probing Kinetics and Mechanism of Hollowing Nanostructures through Direct Chemical Transformations

“…The hollowing process is driven by the nanoscale Kirkendall effect that originates from the outward diffusion of Ag atoms through the Ag 2 O layer to react oxygen, followed by thickening of the Ag 2 O layer. The typical snapshots of the in situ TXM study shown in Figure a highlight the corresponding geometrical evolution of the Ag nanowire during oxidation, which is similar to the typical hollowing process highlighted in Figure e . The intensity contrast in the TXM images originates from the spatially nonuniform distribution of Ag and Ag 2 O.…”

“…At t < 14 min, F(t) exhibits a good proportionality to G(t), providing the diffusion coefficient of Ag atoms in the thin Ag 2 O sheath being 1.2 × 10 −13 cm 2 s −1 . [130] The deviation from the proportionality at t > 14 min is ascribed to the complete separation of the Ag core and the Ag 2 O sheath, which significantly lowers the diffusion of Ag atoms into the Ag 2 O sheath. Instead, the surface-mediated diffusion mechanism shown in Figure 2 takes over to continuously consume the Ag core and grow the Ag 2 O shell.…”

“…The time‐dependent F ( t ) and G ( t ) are calculated from the results presented in Figure b by following and , which are shown in Figure c. At t < 14 min, F ( t ) exhibits a good proportionality to G ( t ), providing the diffusion coefficient of Ag atoms in the thin Ag 2 O sheath being 1.2 × 10 −13 cm 2 s −1 . The deviation from the proportionality at t > 14 min is ascribed to the complete separation of the Ag core and the Ag 2 O sheath, which significantly lowers the diffusion of Ag atoms into the Ag 2 O sheath.…”

“…The typical snapshots of the in situ TXM study shown in Figure 8a highlight the corresponding geometrical evolution of the Ag nanowire during oxidation, which is similar to the typical hollowing process highlighted in Figure 1e. [130] The intensity contrast in the TXM images originates from the spatially nonuniform distribution of Ag and Ag 2 O. The time-dependent TXM images provide the shrinkage of core radius (r c ), the growth of the shell thickness (d), and the expansion of the outer radius of the shell (r o ) as a function of reaction time using in situ TXM imaging (Figure 8b).…”

In Situ Transmission Electron Microscopy Study of Nanocrystal Formation for Electrocatalysis

“…To explore the detailed formation pathway of 1D nanowire and then guide the rational design of 1D nanowire, most observations and analyses have been carried out. In‐situ dark‐field optical microscopy has been used to reveal the rate‐limiting step during the nanowire formation, and in‐situ transmission X‐ray microscopy was used for relatively thick metal nanowires . In addition, electrochemical method was utilized to explore the actual role of capping agent during the formation of nanowire .…”