NANOTUBES AS NANOPROBES IN SCANNING PROBE MICROSCOPY

SINCE the invention of the scanning tunnelling microscope(1), the valu e 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 suc h devices to suh-angstrom accuracy, and in designing sensitive detecti on schemes, less has been done to improve the probe tip itself(4). Ide ally the tip should be as precisely defined as the object under invest igation, and should maintain its integrity after repeated use not only in high vacuum but also in air and water. The best tips currently use d for scanning probe microscopy do sometimes achieve sub-nanometre res olution, but they seldom survive a 'tip crash' with the surface, and i t is rarely clear what the atomic configuration of the tip is during i maging. Here we show that carbon nanotubes(11,12) might constitute wel l defined tips for scanning probe microscopy. We have attached individ ual nanotubes several micrometres in length to the silicon cantilevers of conventional atomic force microscopes. Because of their flexibilit y, the tips are resistant to damage from tip crashes, while their slen derness permits imaging of sharp recesses in surface topography. We ha ve also been able to exploit the electrical conductivity of nanotubes by using them for scanning tunnelling microscopy.