Nanosphere lithography (NSL) is an inexpensive, inherently parallel, high-throughput, and materials-general nanofabrication technique capable of producing well-ordered 2D periodic particle arrays of nanoparticles. This paper focuses on the synthesis of size-tunable silver nanoparticle arrays by nanosphere lithography and their structural characterization by atomic force microscopy (AFM). The in-plane diameter, a, of Ag nanoparticles was tuned from 21 to 126 nm by systematic variation of the nanosphere diameter, D. Similarly, the out-of-plane height, b, was tuned from 4 to 47 nm by varying the mass thickness, d m, of the Ag overlayer. Experimental measurements of a, b, and interparticle spacing d ip of many individual nanoparticles as a function of D and d m were carried out using AFM. These studies show (i) b = d m, (ii) d ip accurately corresponds to predictions based on the nanosphere mask geometry, (iii) a, after correction for AFM tip convolution, is governed only by the mask geometry and the standard deviation, σD, of the nanosphere diameter, and (iv) line-of-sight deposition is strictly operative. Furthermore, we have established that nanosphere lithography can fabricate nanoparticles that contain only ca. 4 × 104 atoms and are in the size range of a surface-confined cluster.

The surface roughness and nanometer scale structure of Ag films used for surface-enhanced Raman scattering (SERS) are characterized using atomic force microscopy (AFM). Two important types of thin film based SERS-active surface have been examined in this study: (1) Ag island films (AgIF's) on smooth, insulating substrates and (2) thick Ag films evaporated over both preroughened and smooth substrates. AFM is demonstrated to be capable of quantitatively defining the three-dimensional (3D) structure of these roughened surfaces. The effects of mass thickness, d, , and thermal annealing on the nanostructure of AgIF's are studied in detail. Particle size histograms are calculated from the AFM images for both "as-deposited" and annealed IF's with d,,,= 1.8 and 3.5 nm. Quantitative measurements of the SERS enhancement factor (EF) are coupled with the AFM data and interpreted within the framework of the electromagnetic theory of SERS. AFM images for thick evaporated Ag films over a monolayer of polymer nanospheres (AgFON) shows the clear presence of "random substructure roughness" reducing their utility as controlled roughness surfaces. Similar roughness structures are observed for thick evaporated Ag films on smooth, insulating substrates. Nevertheless, AgFON surfaces are demonstrated to be among the most strongly enhancing thin film based surfaces ever studied with EF's comparable to those found for electrochemically roughened surfaces. Applications of FON surfaces to ultrahigh sensitivity SERS, anti-Stokes detected SERS, and surfaceenhanced hyper-Raman spectroscopy (SEHRS) are reported.

The basic principles of scanning electrochemical microscopy are discussed. Recent applications of this technique to studies of fast heterogeneous and homogeneous reactions and processes occurring in thin films (AgBr, polymers) are described. The use of novel scanning probes, e.g., ionselective electrodes and enzyme electrodes, is also discussed.

No abstract