In Situ Investigation of the Silver-CTAB System
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In Situ Investigation of the Silver-CTAB System Jeremy Gray1, Christine Orme2, Danxu Du3, and David Srolovitz4 1 CMLS, Lawrence Livermore National Laboratory, 7000 East Ave, Livermore, CA, 95550 2 LLNL, Livermore, CA, 94550 3 Princeton, Princeton, NJ, 08540 4 Yeshiva University, New York, NY, 10033 ABSTRACT Recent research has shown that biologically inspired approaches to materials synthesis and self-assembly, hold promise of unprecedented atomic level control of structure and interfaces. In particular, the use of organic molecules to control the production of inorganic technological materials has the potential for controlling grain structure to enhance material strength; controlling facet expression for enhanced catalytic activity; and controlling the shape of nanostructured materials to optimize optical, electrical and magnetic properties. In this work, we use organic molecules to modify silver crystal shapes towards understanding the metal-organic interactions that lead to nanoparticle shape control. Using in situ electrochemical AFM (EC-AFM) as an in situ probe, we study the influence of a cationic surfactant cetyltrimethylamminobromide (CTAB) on Ag growth during electrochemical deposition on Ag(100). The results show that the organic surfactant promotes the growth of steps on the (100) surface and changes the surface evolution from island nucleation to step flow growth. Overall, this leads to a smoother, faster growing (100) surface, which may promote plate-formation. INTRODUCTION Recently, the metal-organic modulation of nanocrystals composed of metals and metaloxides have garnered much interest. Because of their size, surface area, and unique properties, there is great interest in the use of metal and metal-oxide nanoparticles for a wide range of technological applications. Tight control of shape and size are very important for these applications. For example, the optical properties of gold and silver depend sensitively on their shape and size. The plasmon resonance can be tuned from red to blue by adjusting size, and the aspect ratio of the nanoparticles determines the coupling with longitudinal and transverse light waves. In a similar manner the magnetic properties of nickel and iron particles can be tailored by changing the shape from a sphere to a rod. Nanocrystals are also being utilized in catalysis and remediation due to their high surface area. In these applications, the facet expression and the step structure determines the overall chemical activity and, therefore, shape is crucial to function. Several studies have shown that CTAB can be used to create silver nanorods and nanoplates[1-3]. These include several studies at room temperature where the mechanisms for shape change appear to depend upon CTAB concentration. At high concentrations of CTAB (~0.1M) it is suggested that shape control is due to the structure of the surfactant gel and promotes nanorod formation. At lower concentrations of CTAB (.006M) growth lead to {111} dominated plates with a truncated triangular morphology. By c
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