The formed ZnO nanorods are with length of 1 ~ 3 μm and diameter of 100 ~ 400 nm, and for absorption measurement, aligned ZnO nanorod sample should be used. From the previous experience,
BMS-907351 the formation of single-element nanodisk is fairly reproducible and controllable; thus, the design of hybrid nanodisks is viable in a two-step strategy: to deposit and anneal Au and Ag separately on top of the ZnO (0002) surface and then anneal them to form different structures. In the experiment, 1-nm (this Selleck PR 171 thickness is given by the quartz crystal of the evaporator, not the real ‘film thickness’) Au was firstly deposited by e-beam evaporation and subsequently annealed at 700°C for 60 s to enable the formation of a first layer of shape well-defined Au nanodisks. In general, as summarized in previous report , the growth mechanism of such hexagonal nanodisks can be briefly described: Au undergoes Volmer-Weber (VW) mode growth on ZnO. The formation
process is therefore dominated by minimizing the total energy, which is dominated by the interface strain. For relatively small strain <20%, elements such as Au (111) plane will match on sixfold ZnO (0002) plane and form hexagonal nanodisks. In later experiment, this Au nanodisks layer acted as the scaffold for Au/Ag core-shell and intermixing alloy nanodisks.The sample was then put into e-beam evaporation again for 1-nm Ag capping. Since the rapid annealing is very important for the hexagonal SB431542 metal nanodisks’ growth, hence here we also
focus Cediranib (AZD2171) on studying the annealing temperatures’ effect on Ag/Au hybrid structures. Annealing was then performed on the Ag on Au/ZnO samples under different temperatures (sample A: 500°C, sample B: 550°C, and sample C: 600°C). Figure 1a,b,c shows the SEM images for samples A, B, and C, respectively. It is clearly shown that samples A and B preserve the well-defined hexagonal/triangular shapes of those single elemental nanodisks. It is found that sample C lost a noticeable degree of those defined shapes and exhibits round-shaped corners due to possible severe diffusion of Au and Ag. Figure 1 SEM images of samples A, B, and C. (a) Sample A: Au/Ag nanodisk annealed at 500°C, (b) sample B: Au/Ag nanodisk annealed at 550°C, and (c) sample C: Au/Ag nanodisk annealed at 600°C. Scale bar = 100 nm. Two possible cases may happen and should be clarified in the formation of these hybrid nanodisks: (1) Ag resides on top of the surface of Au nanodisks; (2) Ag forms independent hexagonal nanodisks. Since Au and Ag’s lattice constants (a) are 4.08 and 4.09 Å, the lattice mismatch of Ag on Au is (a Ag − a Au)/a Au = 0.25%. Therefore, Ag residing on Au lattice will have a significantly smaller strain. However, it is still important to clarify the material distribution of Ag. X-ray EDS spectra for sample A was performed and shown in Figure 2a. It clearly resolves the signal from AuM and AgL.