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Effect of Ag Templates on the Formation of Au-Ag Hollow/Core-Shell Nanostructures.

Tsai CH, Chen SY, Song JM, Haruta M, Kurata H - Nanoscale Res Lett (2015)

Bottom Line: Au-Ag alloy nanostructures with various shapes were synthesized using a successive reduction method in this study.High angle annular dark field-scanning TEM (HAADF-STEM) images observed from different rotation angles confirm that Ag NPs turned into AuAg alloy rings with an Au/Ag ratio of 1.It is proposed that in addition to the ratio of Ag templates and Au ion additives, the twin boundaries of the Ag templates were the dominating factor causing hollow alloy nanostructures.

View Article: PubMed Central - PubMed

Affiliation: Graduate Institute of Applied Science and Technology, National Taiwan University of Science and Technology, Taipei, 106, Taiwan.

ABSTRACT
Au-Ag alloy nanostructures with various shapes were synthesized using a successive reduction method in this study. By means of galvanic replacement, twined Ag nanoparticles (NPs) and single-crystalline Ag nanowires (NWs) were adopted as templates, respectively, and alloyed with the same amount of Au(+) ions. High angle annular dark field-scanning TEM (HAADF-STEM) images observed from different rotation angles confirm that Ag NPs turned into AuAg alloy rings with an Au/Ag ratio of 1. The shifts of surface plasmon resonance and chemical composition reveal the evolution of the alloy ring formation. On the other hand, single-crystalline Ag NWs became Ag@AuAg core-shell wires instead of hollow nanostructure through a process of galvanic replacement. It is proposed that in addition to the ratio of Ag templates and Au ion additives, the twin boundaries of the Ag templates were the dominating factor causing hollow alloy nanostructures.

No MeSH data available.


Mechanism for the formation of Ag@AuAg core-shell NWs
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Fig10: Mechanism for the formation of Ag@AuAg core-shell NWs

Mentions: With respect to 1-D Au-Ag nanostructure, AuAg alloy nanocrystals were deposited on the surface of Ag wires as a compact layer of nanocrystals. We suggest that there may have been two interfaces, the inner surface of the nanocrystalline deposit between Ag and reduced Au (interface I in Fig. 10) and the other one, the outer surface between reduced Au and solution (interface II in Fig. 10). Dissociation of Ag (Eq. 2) can be considered to have occurred at interface I, while the reduction of Au took place at interface II (Eq. 3). There is no evidence so far showing the orientation relationship between single-crystalline Ag and nanocrystalline deposits. However, it can be inferred that boundaries in between nanocrystals provided large quantities of microchannels for the transportation of Ag ions, and thus Ag ions generated at interface I could transfer rapidly through the Au deposit. On the other hand, the electrons could travel through highly conductive deposits easily to support the reduction of Au ions at interface II. Meanwhile, it can be deduced that not only the galvanic reaction but also the interdiffusion of Au and Ag proceeded to turn Au deposits into AuAg alloy shell. The chemical composition shown in Table 2 led us to believe that the Au/Ag ratio of 1 is the stablest composition for interdiffusion products. This may be due to the isomorphous feature of this binary system (Au and Ag are mutual soluble at any composition) and the minimum free energy caused by the high entropy of mixing [40].Fig. 10


Effect of Ag Templates on the Formation of Au-Ag Hollow/Core-Shell Nanostructures.

Tsai CH, Chen SY, Song JM, Haruta M, Kurata H - Nanoscale Res Lett (2015)

Mechanism for the formation of Ag@AuAg core-shell NWs
© Copyright Policy - OpenAccess
Related In: Results  -  Collection

License
Show All Figures
getmorefigures.php?uid=PMC4644130&req=5

Fig10: Mechanism for the formation of Ag@AuAg core-shell NWs
Mentions: With respect to 1-D Au-Ag nanostructure, AuAg alloy nanocrystals were deposited on the surface of Ag wires as a compact layer of nanocrystals. We suggest that there may have been two interfaces, the inner surface of the nanocrystalline deposit between Ag and reduced Au (interface I in Fig. 10) and the other one, the outer surface between reduced Au and solution (interface II in Fig. 10). Dissociation of Ag (Eq. 2) can be considered to have occurred at interface I, while the reduction of Au took place at interface II (Eq. 3). There is no evidence so far showing the orientation relationship between single-crystalline Ag and nanocrystalline deposits. However, it can be inferred that boundaries in between nanocrystals provided large quantities of microchannels for the transportation of Ag ions, and thus Ag ions generated at interface I could transfer rapidly through the Au deposit. On the other hand, the electrons could travel through highly conductive deposits easily to support the reduction of Au ions at interface II. Meanwhile, it can be deduced that not only the galvanic reaction but also the interdiffusion of Au and Ag proceeded to turn Au deposits into AuAg alloy shell. The chemical composition shown in Table 2 led us to believe that the Au/Ag ratio of 1 is the stablest composition for interdiffusion products. This may be due to the isomorphous feature of this binary system (Au and Ag are mutual soluble at any composition) and the minimum free energy caused by the high entropy of mixing [40].Fig. 10

Bottom Line: Au-Ag alloy nanostructures with various shapes were synthesized using a successive reduction method in this study.High angle annular dark field-scanning TEM (HAADF-STEM) images observed from different rotation angles confirm that Ag NPs turned into AuAg alloy rings with an Au/Ag ratio of 1.It is proposed that in addition to the ratio of Ag templates and Au ion additives, the twin boundaries of the Ag templates were the dominating factor causing hollow alloy nanostructures.

View Article: PubMed Central - PubMed

Affiliation: Graduate Institute of Applied Science and Technology, National Taiwan University of Science and Technology, Taipei, 106, Taiwan.

ABSTRACT
Au-Ag alloy nanostructures with various shapes were synthesized using a successive reduction method in this study. By means of galvanic replacement, twined Ag nanoparticles (NPs) and single-crystalline Ag nanowires (NWs) were adopted as templates, respectively, and alloyed with the same amount of Au(+) ions. High angle annular dark field-scanning TEM (HAADF-STEM) images observed from different rotation angles confirm that Ag NPs turned into AuAg alloy rings with an Au/Ag ratio of 1. The shifts of surface plasmon resonance and chemical composition reveal the evolution of the alloy ring formation. On the other hand, single-crystalline Ag NWs became Ag@AuAg core-shell wires instead of hollow nanostructure through a process of galvanic replacement. It is proposed that in addition to the ratio of Ag templates and Au ion additives, the twin boundaries of the Ag templates were the dominating factor causing hollow alloy nanostructures.

No MeSH data available.