Size determination of nanoparticles based on tapping-mode atomic force Microscopy Measurements

The determination of the size of nanoscale materials is important in understanding their physical or chemical properties. In comparison with transmission electron microscopy (TEM), which has been extensively used to determine the size of nanoparticles, Tapping-Mode atomic force microscopy (TM-AFM) provides a useful tool for size determination for samples on solid substrates, especially under in situ conditions. However, there has been limited information for the correlation between particle sizes determined by these two techniques due to the lack of nanoparticles with highly monodispersed sizes. In this paper, we report the results of an investigation of the size correlation between TEM and AFM measurements of highly-monodispersed gold nanoparticles with a range of particle sizes (2-100 nm). While the height data were shown to provide a good measure of the size in a certain size range, the lateral size of the particles is distorted due to the tip-sample convolution effect. The quantitative correlation demonstrates the ability of AFM in determining sizes of nanoparticles, which requires the understanding of the relative radius of curvature of the tip versus the particle sizes as well as the surface properties of the particles for accurate size determination. The results are discussed in terms of the particle size and the surface structure effects on the size determination.