ATOMIC-FORCE MICROSCOPY AND SURFACE-ENHANCED RAMAN-SPECTROSCOPY .1. AG ISLAND FILMS AND AG FILM OVER POLYMER NANOSPHERE SURFACES SUPPORTED ON GLASS

The surface roughness and nanometer scale structure of Ag films used f or surface-enhanced Raman scattering (SERS) are characterized using at omic force microscopy (AFM). Two important types of thin film based SE RS-active surface have been examined in this study: (1) Ag island film s (AgIF's) on smooth, insulating substrates and (2) thick Ag films eva porated over both preroughened and smooth substrates. AFM is demonstra ted to be capable of quantitatively defining the three-dimensional (3D ) structure of these roughened surfaces. The effects of mass thickness , d(m), and thermal annealing on the nanostructure of AgIF's are studi ed in detail. Particle size histograms are calculated from the AFM ima ges for both ''as-deposited'' and annealed IF's with d(m) = 1.8 and 3. 5 nm. Quantitative measurements of the SERS enhancement factor (EF) ar e coupled with the AFM data and interpreted within the framework of th e electromagnetic theory of SERS. AFM images for thick evaporated Ag f ilms over a monolayer of polymer nanospheres (AgFON) shows the clear p resence of ''random substructure roughness'' reducing their utility as controlled roughness surfaces. Similar roughness structures are obser ved for thick evaporated Ag films on smooth, insulating substrates. Ne vertheless, AgFON surfaces are demonstrated to be among the most stron gly enhancing thin film based surfaces ever studied with EF's comparab le to those found for electrochemically roughened surfaces. Applicatio ns of FON surfaces to ultrahigh sensitivity SERS, anti-Stokes detected SERS, and surface-enhanced hyper-Raman spectroscopy (SEHRS) are repor ted.