Carbon nanotube atomic force microscopy tips: Direct growth by chemical vapor deposition and application to high-resolution imaging

Carbon nanotubes are potentially ideal atomic force microscopy probes becau se they can have diameters as small as one nanometer, have robust mechanica l properties, and can be specifically functionalized with chemical and biol ogical probes at the tip ends. This communication describes methods for the direct growth of carbon nanotube tips by chemical vapor deposition (CVD) u sing ethylene and iron catalysts deposited on commercial silicon-cantilever -tip assemblies. Scanning electron microscopy and transmission electron mic roscopy measurements demonstrate that multiwalled nanotube and single-walle d nanotube tips can be grown by predictable variations in the CVD growth co nditions. Force-displacement measurements made on the tips show that they b uckle elastically and have very small (less than or equal to 100 pN) nonspe cific adhesion on mica surfaces in air. Analysis of images recorded on gold nanoparticle standards shows that these multi- and single-walled carbon na notube tips have radii of curvature of 3-6 and 2-4 nm, respectively. Moreov er, the nanotube tip radii determined from the nanoparticle images are cons istent with those determined directly by transmission electron microscopy i maging of the nanotube ends. These molecular-scale CVD nanotube probes have been used to image isolated IgG and GroES proteins at high-resolution.