Fig. 1. (a) Schematic illustration of the synthetic process of alloyed Au-Ag NRs. HAADF-STEM images of as-prepared. (b) Au@Ag core-shell NRs and (c) alloyed NRs with in situ STEM heating up to 350°C (scale bars: 100 nm).

Fig. 2. UV-vis-NIR absorption spectra of (a) Au@Ag core-shell NRs and (b) alloyed Au-Ag NRs under annealing at 400°C in N2 flow. (c) SPRL and SPRT wavelength versus the volume of the AgNO3 precursor. (d)–(i) TEM images of alloyed Au-Ag NRs with increasing aspect ratios (n=L/W, the ratio between length and width of NRs, i.e., 3, 4, 5, 6, 8, 9). The insets of (d)–(i) are corresponding TEM images of Au@Ag core-shell NRs capsuled within mesoporous silica. (j),(k) HAADF-STEM images and element mapping of alloyed Au-Ag NRs (aspect ratio n=3 and 6, respectively) (scale bars: 200 nm).

Fig. 3. Annealing temperature effects on alloying of Au and Ag. (a) UV-vis-NIR absorption spectra and (b)–(d) corresponding TEM images of alloyed Au-Ag NRs obtained at annealing temperatures of 450°C, 500°C, and 600°C. The inset of (a) is the evolution schematics of partially and fully alloyed Au-Ag NRs. (e) The elemental distribution of fully alloyed Au-Ag NRs obtained at 450°C (scale bars: 200 nm).

Fig. 4. UV-vis-NIR absorption spectra and corresponding TEM images of (a) Au@Ag core-shell NRs and (b) alloyed Au-Ag NRs before and after incubated in NH4OH and H2O2 solution. The insets in (a),(b) are corresponding colloidal products. The following samples were etched and further observed. (c) HAADF-STEM images and corresponding elemental distribution of fully/partially alloyed Au-Ag NRs. (d)–(g) TEM images of alloyed Au-Ag NRs with increasing Au composition under annealing at 400°C. The bottom insets in (d)–(g) are TEM images of Au NBPs, and the top inset in (d) is the TEM image of alloyed Au-Ag NRs by annealing at 450°C.

Fig. 5. UV-vis-NIR absorption spectra and corresponding TEM images of as-prepared alloyed NRs after re-annealing at higher temperatures in an N2 or air atmosphere.

Fig. 6. (a) UV-vis-NIR absorption spectra of core-shell and alloyed NRs with the same resonance intensity. (b), (c) SERS spectra of R6G absorbed on alloyed and core-shell NRs-loaded substrates before and after etching in NH4OH and H2O2.

Fig. 7. (a) Schematic of DOX release under 980 nm laser irradiation. (b) TEM images of alloyed Au-Ag NRs with full and hollow silica capping by annealing in N2 flow and air, respectively. (c) UV-vis-NIR absorption spectra of free DOX molecules before and after being loaded on alloyed Au-Ag NRs. The inset in (c) is the absorption spectra of alloyed Au-Ag NRs coated by full/hollow mesoporous silica. (d) DOX release profiles with and without laser irradiation. The inset in (d) is the absorption spectra of released DOX after 1 h. (e) The photo-thermal conversion and (f) corresponding UV-vis-NIR spectra of alloyed Au-Ag NRs (1 mL) under irradiation of a 980 nm laser with different powers (laser spot: 2  mm×2  mm).

Table 1. Morphology Evolution of As-Prepared Alloyed NRs after Re-Annealing at Higher Temperatures in an N2 or Air Atmosphere^a