||Pilkyu Kim et al., Efficient electrochemical etching method to fabricate sharp metallic tips for scanning probe microscopes. Rev. Sci. Instrum. 77, 103706 (2006) link p.103706-4 right column
||AFM=atomic force microscopy
||p.103706-4 left column bottom paragraph:"To test functionality of the fabricated tips as a probe, the topography of a standard AFM test sample (TGX 01, Micromasch) is measured using a tuning-fork-type SFM [scanning shear-force microscope] that was built at the Advanced Photonics Research Institute. The tungsten tip utilized for this measurement had a minimum diameter below 50nm at its apex (see Fig. 5)."