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

Abstract

Carbon nanotubes are potentially ideal atomic force microscopy probes because they can have diameters as small as one nanometer, have robust mechanical properties, and can be specifically functionalized with chemical and biological probes at the tip ends. This communication describes methods for the direct growth of carbon nanotube tips by chemical vapor deposition (CVD) using ethylene and iron catalysts deposited on commercial silicon-cantilever-tip assemblies. Scanning electron microscopy and transmission electron microscopy measurements demonstrate that multiwalled nanotube and single-walled nanotube tips can be grown by predictable variations in the CVD growth conditions. Force-displacement measurements made on the tips show that they buckle elastically and have very small (< 100 pN) nonspecific adhesion on mica surfaces in air. Analysis of images recorded on gold nanoparticle standards shows that these multi-and single-walled carbon nanotube tips have radii of curvature of 3-6 and 2-4 nm, respectively. Moreover, the nanotube tip radii determined from the nanoparticle images are consistent with those determined directly by transmission electron microscopy imaging of the nanotube ends. These molecular-scale CVD nanotube probes have been used to image isolated IgG and GroES proteins at highresolution.

Applications of Carbon Nanotubes in Biotechnology and Biomedicine

“…Several other properties of carbon nanotubes make them useful AFM probes: 120 they are extremely stiff (Young's modulus ~ 1 TPa), they undergo elastic deformation, and by using metal-catalyzed CVD techniques, individual SWNTs can be reliably grown on commercially available AFM tips. [121][122][123][124] Such carbon nanotube probes can provide enhanced imaging in diverse areas, but are particularly suited to the field of biology. The use of SWNT probes improved the imaging resolution of small proteins, such as antibodies, 121,123 and in DNA analysis.…”

Critical Oxide Thickness for Efficient Single‐Walled Carbon Nanotube Growth on Silicon Using Thin SiO2 Diffusion Barriers

“…[14,15,16,17,18,19,20] It is well established that the yield of single-walled nanotube growth on silicon substrates is dramatically reduced compared with growth on thick silicon dioxide layers, due to poisoning of the catalyst by the formation of a silicide. [12,21,22,23] Intriguingly, the growth of multi-walled nanotubes on silicon substrates is regularly reported and seems less susceptible to catalyst poisoning, [24,25,26,27] yet the cause of this difference has not been addressed. For device applications it is desirable to use thin oxides to increase the gate capacitance and gate efficiency, and thus it is important to understand how to minimize oxide thickness while still preventing catalyst poisoning.…”

Peer Reviewed: Atomic Force Microscopy Probes Go Electrochemical

“…Moreover, the single-walled carbon nanotube (SWNT) would provide a very powerful probe for simultaneous AFM and electrochemistry. Lieber's group at Harvard has already demonstrated the increased topographical resolution offered by SWNT-AFM tips (45). It is only a matter of time before such probes are used for simultaneous electrochemical measurement as well.…”