Nanotubes as nanoprobes in scanning probe microscopy

SINCE the invention of the scanning tunnelling microscope(1), the value of establishing a physical connection between the macroscopic world and individual nanometre-scale objects has become increasingly evident, both for probing these objects(2-4) and for direct manipulation(5-7) and fabrication(8,10) at the nanometre scale. While good progress has been made in controlling the position of the macroscopic probe of such devices to suh-angstrom accuracy, and in designing sensitive detection schemes, less has been done to improve the probe tip itself(4). Ideally the tip should be as precisely defined as the object under investigation, and should maintain its integrity after repeated use not only in high vacuum but also in air and water. The best tips currently used for scanning probe microscopy do sometimes achieve sub-nanometre resolution, but they seldom survive a 'tip crash' with the surface, and it is rarely clear what the atomic configuration of the tip is during imaging. Here we show that carbon nanotubes(11,12) might constitute well defined tips for scanning probe microscopy. We have attached individual nanotubes several micrometres in length to the silicon cantilevers of conventional atomic force microscopes. Because of their flexibility, the tips are resistant to damage from tip crashes, while their slenderness permits imaging of sharp recesses in surface topography. We have also been able to exploit the electrical conductivity of nanotubes by using them for scanning tunnelling microscopy.