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\subsection{Background}  The polyol synthesis is the most popular solution-phase synthesis of Ag nanocrystals.   Slight modification of the protocol, such as introducing foreign species, enables different nanocrystal shapes to be produced. nanocrystals \cite{Skrabalak_2007}.  In the polyol synthesis, ethylene glycol acts as both the solvent and the reducing agent.  The source of Ag is from AgNO_3 that is dissolved in ethylene glycol.  Structure-directing agents, typically polyvinylpyrrolidone (PVP), are added to prevent aggregation of nanocrystals and direct their shape.  The ratio of PVP to AgNO_3 is critical to the formation of different nanocrystal shapes.  The  typical reaction temperature is $150^{\circ} C$, $150^{\circ}$ C,  although it can vary for different nanocrystal shapes with different protocols. Slight modifications of the polyol synthesis protocol, such as introducing foreign species, enable different nanocrystal shapes to be produced.  In the synthesis of Ag nanocubes, trace amount of Na_2S can be added to increase the selectivity towards nanocubes \cite{Skrabalak_2007}.  The addition of Na_2S allows the formation of Ag_2S nanocrystals, which catalyzes the reduction of AgNO_3.  It is proposed that the faster reduction process can limit formation of twinned Ag seeds \cite{Wiley_2006}, thus favoring nanocube formations.  Comparatively, Ag nanowires can be promoted by adding H_2PtCl_6  \subsection{Goal and Objectives} 
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