Deposition and Chemical Preparation Techniques

The preparation of rough silver films by vapor deposition results in reproducible and stable surfaces for SERS. For example, deposition of 20-nm Ag films onto Teflon, polystyrene, or latex spheres [29,30] has been performed. These substrates produced strong SERS intensities for various organic adsorbates and good reproducibility between multiple rims. However, vapor deposition can be slow and needs access to a vacuum system. There are also some variables that need to be controlled, such as the film thickness, deposition temperature, and use of annealing procedures. Moreover, unless the experiment is performed under vacuum, the film is exposed to the atmosphere after deposition. Even a brief exposure to the atmosphere results in contamination of the surface and the formation of an inactive oxide layer. 

Chemically deposited films on frosted glass slides provide a more facile and reproducible approach to SERS substrates. One such approach [31], which has proven to be very successful, involves the initial preparation of Tollen s reagent. The reagent is prepared by adding about 10 drops of fresh 5% sodium hydroxide solution to 10 mL of 2 to 3% silver nitrate solution, whereupon a dark-brown AgOH precipitate is formed. This step is followed by the dropwise addition of concentrated NH4OH, at which point the 

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