It can be observed that both Au and Ag signals are observed on top of the same ZnO nanorod. However, whether the Au and Ag signals are from the same locations (nanodisks) is unknown due to limited resolution of EDS. In order to clarify the microstructure and Au/Ag elemental distribution, high-resolution scanning TEM TSA HDAC order with EDS mapping capability was employed for characterization. Figure 2 EDS spectrum of sample A and EDS mapping for Au and Ag elements. (a) EDS spectrum of sample A. (b) EDS mapping for Au element: the region of mapping corresponds to (a). Acquisition time 80 s. (c) EDS mapping

for Ag element. Acquisition time 80 s. Results and discussion Figure 3a shows the scanning transmission electron microscopy (STEM) image of sample A, and Figure 3b,d shows the corresponding EDS mapping for elemental signal AuM, AgL, and ZnK, respectively. It could be shown that the resolution of 0.5 nm is enough to locate the elements. Evidently, the concentration of Ag is higher at the outer ‘shell,,’ whereas Au concentrated at the inner regions. This is a clear indication of quasi core-shell structural Au/Ag nanodisk formation. In addition, the lattice spacing of 0.234 nm is determined from TEM, which is close to Ag and Au’s (111) NSC23766 concentration inter-plane distance. The (111) twin plane is observed with 72° tilted angle. This

twin planes have been widely found in the previous Au nanodisks [24]. Twinning is the typical result of coalescence of multiple nanocrystals that is driven by thermal energy. Furthermore, Apoptosis inhibitor it is also noticeable that in Figure 3b, Ag element distributes with higher density along the boundary of the twinning crystals. This is reasonable because the diffusion of Ag in Au tends to follow heptaminol the defect lines in Au crystals [25]. Nevertheless, the contrast between Au and Ag is fairly clear in the EDS mapping, suggesting the quasi core-shell formation. Since Au and Ag have very similar lattice constant, the growth of Ag shell on Au nanodisks has neglectable strain; thus, in this way, the Ag/Au heterostructural nanodisk can reasonably minimize the interface energy. Interestingly, due to the small

Ag/Au mismatch, it is observed that no singular Ag nanodisks actually formed on ZnO’s (0002) surface, and Ag atoms all lay on Au nanodisks to minimize the interface energy. Figure 4a shows low-magnification TEM image of Ag/Au nanodisks on ZnO. Nine nanodisks were identified and marked with black arrow. In the following Au and Ag elemental mapping (Figure 4b,c), it is observed that both Au and Ag disperse in or on these nine nanodisks, suggesting that no singular Ag nanodisks were formed. Figure 3 TEM image of sample A and EDS mapping for Au, Ag, and Zn elements. (a) TEM image of one nanodisk in sample A (low temperature annealing). Black arrow and white line indicate the twin boundary. Scale bar = 2 nm. EDS mapping for (b) Au, (c) Ag, and (d) Zn elements. Figure 4 TEM image of Ag/Au nanodisks and EDS mapping for Au and Ag elements.