Nanosphere lithography: Size-tunable silver nanoparticle and surface cluster arrays

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, σ_D, 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.