Tip Characterization from AFM Images of Nanometric Spherical Particles

Abstract

Since atomic force microscopy (AFM) images are a composite of probe and sample geometry, accurate size determinations are problematic. A relatively straightforward mathematical procedure for determining tip radius of curvature (RT) for an asymmetrical tip was recently developed by Garcia et al. (Probe Microsc. 1997, 1, 107). This study represents an experimental test of that procedure for both silica (∼150 nm) and polystyrene (∼50 nm) nanospheres. The procedure can be summarized by two steps: (1) tip characterization assuming that the observed AFM height is a true measure of a spherical particle's diameter and (2) use of the tip shape to extract a calculated width. To ensure that AFM heights were equivalent to the true width, a direct comparison of individual particle sizes determined by transmission electron microscopy (TEM) and AFM was conducted. Heights measured from AFM images of polystyrene nanospheres differed, on average, less than 5% from widths measured by TEM. The quality of RT values was there...