Carbon-nanotube tip for highly-reproducible imaging of deoxyribonucleic acid helical turns by noncontact atomic force microscopy

A carbon nanotube (CNT) was used as a tip for a noncontact-mode atomic forc e microscope (NC-AFM). A CNT tip was attached to an Au/Si tip by a well-con trolled procedure in a scanning-electron-microscope (SEM) chamber. The NC-A FM with the CNT tip produced highly reproducible images of right-handed hel ical turns of linear droxyribonucleic acid (DNA) with a spacing of 3.5 +/- 1.0 nm. The full-width at half-maximum (FWHM) of the cross section of DNA m easured was 3.1 +/- 0.6 nm.