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See ref 26 for a more detailed discussion of thisadjustment. The [Ag]/[Au]bulk values provided in the table can bedirectly compared with the ICP-AES data provided in Figure 8. (B)ICP-AES kinetics data of the reactions containing 0 μM (blacksquares), 1 μM (red triangles), and 100 μM (blue circles) AgNO3. due to the decreasing favorability of the Ag−halide interactionand an increasing favorability of the Au−halide interaction inthat same ordering.69In other words, there is a strong drivingforce for the formation of an Au−AgUPD−Cl surface structureand this driving force is much less for the formation of anAu−AgUPD−Br surface and even less still for an Au−AgUPD−Istructure.In the following experiments, we demonstrate how thepreviously described influence of halides on the underpotentialdeposition of silver can be used to direct particle growth underconditions where the halide concentration in the reaction isless than the concentration of gold ion. Growth solutions wereprepared having the appropriate concentrations of reagents toproduce rhombic dodecahedra, notably a 10 μM concentrationof Ag+in 40 mM CTA-Cl, 60 mM NaCl, 18 mM HCl, 0.5 mMHAuCl4, 1.0 mM ascorbic acid, and 0.1 μL of 7 nm diameterseeds, with the modification that each solution also containeda small amount of NaBr (0, 10, 20, or 50 μM; Chart S1). SEMimages of the products indicate that, with increasing amounts ofbromide, the yield of the {110}-faceted rhombic dodecahedraincreases compared to the yield of the {110}-facetedbipyramids until rhombic dodecahedra become the primary pro-duct at 20 μM bromide and eventually truncated ditetragonalprisms are dominant at 50 μM bromide (Figure 6A−D). This isan intriguing result, since more silver is required to stabilize the{310} facets of the truncated ditetragonal prisms than for the{110} facets of the rhombic dodecahedra, yet in this case bothgrowth solutions contain the same amount of silver ions. Inother words, by keeping the Ag+concentration in the growthsolution constant, the amount of silver on the particle surfacecan be increased by introducing bromide. XPS was used toquantify the silver/gold ratio on the surface of these particles(Figure 6E and Figure S2 (Supporting Information)). Aswould be expected on the basis of the particle shapesobserved, the amount of silver on the surface of each particleincreases as the facets become more open (i.e., higher index),andthisiscorrelatedwithincreasingconcentrationsofbromide in the growth solution. The ratios of silver to goldon the surface of the particles are also consistent with whatwould be expected for these shapes on the basis of the resultsof our previous study of silver ion as an additive (Figure S3,Supporting Information).26ICP-AES monitoring of the rate of particle formation forthese reactions suggests that, in the presence of silver ions,increasing amounts of bromide result in an acceleration of therate of particle formation (Figure 6F). This observation is instark contrast to the previously discussed experiments where,in the absence of silver, the addition of bromide resulted in adecreased rate of particle formation. To confirm the validityof these results, a second set of reactions was studied whichinvolved growth solutions containing not only the appropriateconcentrations of reagents for generating {310}-facetedtruncated ditetragonal prisms (including 40 μMAg+) but also a40 μM concentration of bromide (Chart S1). Consistent withthe above results, the addition of bromide to these reactionsresulted in the formation of concave cubes, rather than thetruncated ditetragonal prisms that would have been observed inthe absence of added bromide (Figure S4, SupportingInformation). As before, by adding bromide, we can induce theformation of a particle shape with higher-index facets than thatwhich would form at the same silver ion concentration in theabsence of bromide. XPS was used to confirm that, as would beFigure 6. (A−D) SEM images of reaction products from growth solutions containing 40 mM CTA-Cl, 10 μM AgNO3, and (A) 0.0, (B) 10, (C) 20,and (D) 50 μM NaBr. Scale bars: 200 nm. In the absence of bromide, a mixture of {110}-faceted bipyramids and {110}-faceted rhombicdodecahedra are produced. With increasing bromide, the size and yield of the bipyramids decrease while the size and yield of the rhombicdodecahedra increase. At 50 μM bromide, {310}-faceted truncated ditetragonal prisms are generated. (E) XPS data on the silver/gold ratio forparticles generated with different concentrations of bromide in the growth solution, showing that as the bromide concentration is increased the silvercontent on the surface of each particle also increases. (F) ICP-AES kinetics data of the reactions containing 0 μM (black squares), 10 μM (redtriangles), and 50 μM (blue circles) NaBr. expected from the particle shapes, the concave cubes formed inthis reaction have a higher concentration of silver on their surfacethan the truncated ditetragonal prisms (Figures S3 and S4).Shape control similar to that achieved with bromide isobserved when small amounts of iodide are introduced to thereaction in the presence of silver. This is illustrated by a setof reactions containing 10 μM silver and 0.00, 0.01, 0.05, or0.10 μM iodide. In the absence of iodide, {110}-faceted rhombicdodecahedra and bipyramids are formed.